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International School of Liquid Crystals
22nd Course
1st International school of the IEEE Photonics Society - Italy Chapter
“Photonic Integration: advanced materials,
new technologies and applications”
E. Majorana Centre for Scientific Culture, Erice (Italy)
25th September - 1st October 2016
Directors of the Course:
A. d’Alessandro, P. Pasini,
S. Selleri, C. Zannoni
Director of the School:
C. Zannoni
COST Action IC1208 “Integrating
devices and materials: a challenge for
new instrumentation in ICT”
Scientific Program
Please find below the updated program. Click on the title of each lecture to download the
corresponding abstract.
25th September
Afternoon: Arrival
21.15: Welcome Reception at the Marsala Lecture Hall (S. Rocco)
26th September
9.00-9.20 Welcome by C. Zannoni – Director of the ISLC and S. Selleri (IEEE PS President)
9.20 – 10.20
Meint Smit)
Lecture 1 “Photonic Integration: what, where, why, when, how?” (Lecturer:
10.20 – 11.20
Romagnoli)
Lecture 2 The food chain for photonics integration (Lecturer: Marco
11.20 – 11.50
11.50 – 12.50
12.50 – 15.00
Coffee Break
Lecture 3 “Fundamentals on integrated optics” (Lecturer: Gabriella Cincotti)
Lunch break
15.00 – 16.00
Lecture 4 “Advances on integrated optics” (Lecturer: Andrea Melloni)
16.00 – 17.00
Lecture 5 “Materials and technologies: Si” (Lecturer: Bertrand Szelag)
17.00 – 17.30
17.30 – 18.30
Meint Smit)
Coffee Break
Lecture 6 “Materials, technologies and devices: InP and III-V” (Lecturer:
27th September
9.00 – 10.00
Lecture 7 “Si3N4 waveguide technology for broadband and ultra-low-loss
photonic integrated circuits” (Lecturer: Martijn Heck)
10.00 – 11.00
Lecture 8 “Glass and Glass-Ceramic Photonic Systems: advances and
perspectives” (Lecturer: Maurizio Ferrari)
11.00 – 11.30
Coffee Break
11.30 – 12.30
Lecture 9 “InP-on-Silicon Integration Through Waferbonding and
Epitaxy” (Lecturer: Dries Van Thourhout)
12.30 – 13.30
Lecture 10 “Integration of Si and SiN PICs with New Active
Materials” (Lecturer: Dries Van Thourhout)
Lunch break
13.30 – 15.00
15.00 – 16.00
Lecture 11 “Materials and technologies: electro-optic dielectrics” (Lecturer:
Alessandro Busacca)
16.00 – 17.00
Lecture 12 “Liquid crystals and photonic integration: materials, properties,
technologies, devices” (Lecturer: Antonio d’Alessandro)
17.00 – 17.30
Coffee Break
17.30- 19.00
Poster Session
28th September
9.00 – 10.00
Lecture 13 “Control layer: Electronics at service of photonics” (Lecturer:
Francesco Morichetti)
10.00 – 11.00
Lecture 14 “Optical Interconnections: photonics at service of
electronics” (Lecturer: Antonio La Porta)
11.00 – 11.30
11.30 – 12.30
Coffee Break
Lecture 15 “Photonic packaging at glance” (Lecturer: Antonello Vannucci)
12.30 – 13.30
Lecture 16 “Design tools and design flows for integrated
photonics” (Lecturer: Twan Korthorst)
13.30 – 15.30
Lunch break
15.30 – 16.30 Lecture 17 “Optical spatial solitons and nonlinear guided waves: the legacy of
Prof. George Stegeman and some recent developments” (Lecturer: Gaetano Assanto)
16:30 -17:30 Lecture 18 “From nonlinear integrated optics to microresonator frequency combs”
(Lecturer: Stefan Wabnitz)
17.30 – 18.00
18.00 – 19.00
Coffee Break
POSTER SESSION and e-COST ACTION IC 1208 Meeting
29th September
8.00 – 20.00
30th September
Social Program: Visit to the archeological sites of Selinunte and Segesta.
9.00 – 10.00
Rendina)
Lecture 19 “Applications: biosensing in integrated optics” (Lecturer: Ivo
10.00 – 11.00
Lecture 20 “Photonics technologies for future 5G mobile networks” (Lecturer:
Roberto Sabella)
Coffee Break
11.00 – 11.30
11.30 – 12.30
Lecture 21 “Applications: Imaging microscopy for biomicrofluidic
platform” (Lecturer: Pietro Ferraro)
12.30- 13.30
Lecture 22 “Integrated Microwave Photonics” (Lecturer: José Capmany)
Lunch break
13.30 – 15.00
15.00 – 16.00
Lecture 23 “Quantum integrated photonics” (Lecturer: Fabio Sciarrino)
16.00 – 17.00
Lecture 24 “The generic photonic foundry perspective: existing foundries,
manufacturing, access, expectations, philosophy” (Lecturer: Meint Smit)
17.00 –
20.30 Social dinner
1st October
Departures
Concluding remarks
LECTURES
Photonic Integration: what, where, why, when, how?
Meint K. Smit
Institute for Photonic Integration, TU Eindhoven, The Netherlands
e-mail: [email protected]
The twentieth century is sometimes referred to as the century of electronics. The twenty-first
century could well be the century of photonics. In other words the century of light but then light
used in technical applications such as screens, solar cells, LED lighting, optical communication, 3D
printers, medical diagnostics, metrology and sensors. The market for photonic technology is
currently about one fifth of the global market for electronics but it is growing faster and Europe has
a strong position in this market. Electronics and photonics can be found almost everywhere but
electronics is currently further developed and relatively cheaper, especially due to the emergence of
microelectronic and nanoelectronic integration technology. In photonics, integration technology is
still in its infancy but it is developing rapidly.
Integrated optical chips are the optical counterparts of microelectronic integrated circuits. Electronic
equipment used to consist of a box or a cabinet full of electronic components such as vacuum tubes,
resistors, capacitors and coils. After the invention of the transistor, electronics became more
compact and circuits that were not too big could be integrated on a single print plate. However the
real breakthrough came in the 1960s and 1970s when a growing volume of electronics could be
integrated in a piece of silicon with dimensions of just a few millimetres. In photonics we are now
in the same situation as the initial years of microelectronics. Most optical systems still consist of
separate components such as lasers, modulators, detectors and filters, which are connected to each
other with lenses or glass fibres or plastic fibres. However the technology to integrate tens to
hundreds of optical components on a small piece of semiconductor material, an optical chip, has
made considerable progress in the past twenty years. In the lecture an overview will be given of
where we are presently.
The food chain for photonics integration
Marco Romagnoli
CNIT (National Interuniversity Consortium for Telecommunications)
TeCIP (Institute of Communication, Information and Perception Technologies) - Scuola Superiore Sant'Anna
via Moruzzi, 1 - 56124 Pisa, Italy
As digital applications, services, communications are dramatically increasing with super-linear
growth rate the need of bandwidth is increasing as well and the exploitation of photonics is
becoming always more pervasive.
The lecture will illustrate the present and perspective situation starting from the vision of the
applications, in general, and the communication infrastructure for ubiquitous connections. Given the
present situation and the perspectives, an analysis of the requirements enabling scaling will be
presented.
Technologies enabling scalable bandwidth will be indicated and discussed in general with a focus
on the key/critical building blocks that still require improvements..
Fundamentals on Integrated Optics
Gabriella Cincotti
Engineering Department, University Roma Tre, via Vito Volterra 62, 00143 Rome, Italy
The lecture provides students with the basic knowledge of photonic passive devices for optical
communications. The topics include fundamentals of optical waveguides, fibers, filters,
multiplexers, couplers splitters, evidencing for each device the design guidelines and performance.
The optical modes and dispersion equations of planar waveguides and fibers are described, as well
as the effects of intermodal and chromatic dispersion. The main features of power splitters,
directional couplers, MMI couplers, optical filters, Mach Zehnder interferometers, Bragg gratings
and arrayed waveguide gratings (AWG) are analyzed in details.
Advances on Integrated Optics
Andrea Melloni
DEIB – Politecnico di Milano, Piazza Leonardo da Vinci, 32 - 20131 Milano, Italy
http://photonics.deib.polimi.it
http://www.polifab.polimi.it
The analysis and design of advance and complex photonic integrated circuit is an art that have to
take into account subtle aspects, technological details, tricks and skills that expert in the filed
accumulate in years of activity. Well aware that in a short time it is impossible to cover
exhaustively the various aspects related to technologies, passive and active devices, linear and non
linear, and so on, the aim of this lecture is to consider with some detail aspects apparently trivial or
negligible that can have a large impact on the overall performance of the entire circuits.
The topics include aspects related to the index contrast and effective and group index with a
comparison between technologies, the surface of the waveguide, backscatter, crosstalk and
attenuation. Rings resonators will be treated in detail, starting from an historical survey and going
through the theory and applications with potentials and limits. The combination of basic building
blocks towards the design of complex circuit will be considered with an introduction towards circuit
analysis and synthesis. The effect of tolerances will be introduced and simple consideration on
robust design, statistical analysis and yield estimation mentioned.
Several arguments have the scope and are essential to introduce the other lectures.
Some References
D. Melati, A. Melloni, and F. Morichetti, “Real photonic waveguides: guiding light through imperfections,” Adv. Opt.
Photon. 6, 156-224 (2014)
S. Grillanda, F. Morichetti, “Light-induced metal-like surface of silicon photonic waveguides”, Nature Communications
6, Article number: 8182, 2015.
D. Melati, F. Morichetti, G.G. Gentili, and A. Melloni, “Optical radiative crosstalk in integrated photonic waveguides”,
Optics Letters Vol. 39, Iss. 13, pp. 3982–3985 (2014).
D. Melati, F. Morichetti, and A. Melloni, “A unified approach for radiative losses and backscattering in optical
waveguides”, J. Opt. 16 055502 (2014), (Featured Article)
A. Melloni, P. Monguzzi, R. Costa, and M. Martinelli, “Design of curved waveguides: the matched bend,” J. Opt. Soc.
Am. A 20, 130-137 (2003)
D. Jalas, A. Petrov, M. Eich, W. Freude, S.H. Fan, Z.F. Yu, R. Baets, M. Popovic, A. Melloni, J.D. Joannopoulos, M.
Vanwolleghem, C.R. Doerr and H. Renner, “What is: and what is not an optical isolator” Nature Photonics 7(8), 2013
Lecture 5: Materials and technologies
Silicon photonic process integration
Bertrand SZELAG
LETI, MINATEC campus, CEA-Grenoble, Grenoble, France, F38054
After more than a decade of exploratory research, silicon photonics has now become a business
segment coveted by various industrials. The rationale behind the emergence of silicon photonics is
to take advantage of the production capacities of CMOS foundries, that is, big volume and low cost
manufacturability. The semiconductor industry benefits from a long experience in silicon
processing take advantage of process maturity of this non-zero impulse to launch silicon photonics
and ensure a quick qualification of technology nodes with respect to targeted photonic device
performances. We learn from recent publications that most of the processes associated to the current
silicon photonic production can be imported with minimum implementation from CMOS fab
processes. Nevertheless, a few exceptions still exist to fulfill completely the needs of a totally
integrated photonic circuit.
In this lecture, we will review the motivations for photonic integration using silicon technology and
more precisely cmos fabrication capabilities. Typical silicon photonic fabrication flow will be
detailed, highlighting the specific needs versus cmos process. The major particularities of silicon
photonics are mainly related to the silicon patterning. For example, in silicon photonics the
integrated devices are optically interconnected at silicon level. Thus, silicon patterning must be
done at one step to guarantee the auto-alignment of structures. Another issue is the sidewall
waveguide roughness which directly impacts the optical performances of the devices. A specificity
of silicon photonic technology is the use of pure germanium epitaxy as an absorbing material for
photo detection function. Figure 2 presents a tilted SEM pictures of an integrated Butt-coupled
lateral Germanium photodiode. Doped silicon junctions required also some specific controls and
integration strategies to address the needs of active photonic device, mainly modulator. Process
robustness and impact on variability on silicon photonics device will be also discussed in this
lecture.
Fig.1: Array Wave Guide
Fig.2: Integrated
photodiode
Butt-coupled
lateral
Germanium
Materials, technologies and devices: InP and III-V
Meint K. Smit
III-V materials have the advantage over silicon of a direct bandgap which allows for optical
amplification and short detectors. Further they have a higher electron-mobility as silicon, which
gives them better rf-properties. The most widely used III-V semiconductors are based on InP, GaAs
and GaN. InP is particularly suited for telecommunication purposes because it can generate and
detect light in a wide wavelength range from 1.2 to 1.6 mm. Also for non-telecom application it is
an interesting platform, however, because of the unprecedented functionality that it offers. In the
lecture we will discuss the most important components available in InP-based integration platforms.
The most important one is the optical amplifier. It is at the heart of a number of different lasers:
tunable lasers, pulsed lasers and multi-wavelength lasers. Further InP supports a number of
modulators: low-loss phase modulators, which are usually applied in a Mach-Zehnder structure to
provide high-speed amplitude modulation, up to 50 Gb/s. Mach-Zehnder modulators are fairly long,
in the order of 1 mm or longer. They have excellent chirp and loss properties. Much shorter highspeed modulators can be created by using the electro-absorption effect. Electro-absorption
modulators have higher losses and more chirp, however. InP detectors are very compact and can
have bandwidths well beyond 50 GHz. Propagation losses in passive waveguides are typically in
the order of 2 dB/cm. In undoped waveguides they can be lower than 1 dB/cm. The most important
passive components used in InP-based Photonic ICs are MMI-couplers and AWG demultiplexers.
In the lecture the most important properties of the InP-based integration platform and its most
frequently used components will be discussed.
Si3N4 waveguide technology for broadband and ultra-low-loss
photonic integrated circuits
Martijn J. R. Heck
Department of Engineering, Aarhus University, Finlandsgade 22, 8200 Aarhus, Denmark
Traditionally, routing, switching and filtering functions for communications are performed by
photonic integrated circuits (PICs) fabricated on a silica or silicon nitride based platform [1]. In
such a platform, doped silica, silicon oxynitride (SiON), or stoichiometric silicon nitride (Si3N4) is
used for the light guiding core, embedded in a silicon oxide upper and lower cladding. Only passive
components and thermo-optic tuners are available.
The reason for the widespread use is the low intrinsic material loss over a wide wavelength range,
from the ultra-violet to the mid-infrared. Traditionally, doped silica and SiON were the preferred
solutions, as the waveguide core index can be tuned by material composition. This allows for lowindex contrast waveguides, e.g., 0.3% - 3% [2], thereby minimizing scatter losses.
The interest in silicon nitride waveguide technology has significantly increased recently, due to its
potential compatibility with CMOS fabrication technology. Si3N4 has a relatively large index
contrast with the oxide cladding. This allows for small waveguide cores and tight bending radii,
with a potential for large-scale photonic integration. Another benefit of this tight confinement is the
optimization of nonlinearities. Silicon nitride resonators have been used for comb generation [3]
and frequency doubling [4]. At first sight, silicon nitride might not seem like a good approach for
low-loss waveguide design. This is due to the high index contrast with silicon dioxide and, hence,
the large scattering. However, it has been shown that the lowest loss waveguides can be made using
very thin silicon nitride waveguides of only 30 nm – 40 nm thin [5] (Figure 1). The CMOScompatibility of the process also allows for further integration with silicon photonics, leading to
highly functional and high-end PICs [6].
Figure 1. (left) Silicon nitride waveguide in a spiral layout, showing red light propagation. (right) Overview of waveguide
propagation loss as a function of bend radius. Data for silica and silicon nitride before 2008 (red, open), recent silicon nitride (red,
solid), silicon (blue), indium phosphide (green squares), and gallium arsenide (green triangles) are given [7].
References
[1] C. R. Doerr, and K. Okamoto, Journ. of Lightw. Technol. vol. 24, pp. 4763-4789, 2006.
[2] M. Kawachi, IEE Proceedings-Optoelectronics vol. 143, pp. 257-62, 1996.
[3] Y. Okawachi et al., Optics Letters vol. 36, pp. 3398-400, 2011.
[4] J. S. Levy et al., Optics Express vol. 19, pp. 11415-21, 2011.
[5] J. F. Bauters et al., Optics Express vol. 19, pp. 24090-24101, 2011.
[6] J. F. Bauters et al., Optics Express vol. 21, pp. 544-555, 2013.
[7] M. J. R. Heck et al., Laser & Photonics Reviews vol. 8, pp. 667-686, 2014.
Acknowledgment: supported by the Aarhus University Research Foundation AUFF with a Lektor Starting Grant
Glass and Glass-Ceramic Photonic Systems:
advances and perspectives
Lidia Zur1,2, Thi Ngoc Lam Tran3,2,4, Marcello Meneghetti5,2, Stefano Varas2, Cristina
Armellini2, Alessandro Chiasera2, Francesco Scotognella6,7, Daniele Zonta3,2,8, Dominik Dorosz9,
Anna Lukowiak10, Giancarlo C. Righini1,11, Roberta Ramponi15, Maurizio Ferrari2,1,*
1. Centro di Studi e Ricerche “Enrico Fermi”, Piazza del Viminale 1, 00184 Roma, Italy
2. IFN-CNR CSMFO Lab. and FBK Photonics Unit via alla Cascata 56/C Povo, 38123 Trento, Italy
3. Department of Civil, Environmental and Mechanical Engineering, Trento Univ. Via Mesiano, 77, 38123 Trento, Italy
4. Ho Chi Minh City University of Technical Education, Thu Duc District, Ho Chi Minh City, Viet Nam
5. Dipartimento di Fisica, Università di Trento, via Sommarive 14, Povo, 38123 Trento, Italy
6. Center for Nano Science and Technology@PoliMi, IIT, via Giovanni Pascoli, 70/3, 20133, Milano, Italy 7. Politecnico di Milano, Dip. Fisica and IFN-CNR, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
8. Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow, G11XJ, UK
9. Bialystok University of Technology, Dep. of Power Eng., Photonics and Lighting Technology, Bialystok, Poland.
10. Institute of Low Temperature and Structure Research PAS, Okolna St. 2, 50-422 Wroclaw, Poland
11. MDF Lab. IFAC - CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
12. IFN-CNR and Department of Physics, Politecnico di Milano, p.zza Leonardo da Vinci 32, 20133 Milano, Italy.
*e-mail: [email protected]
The development of optically confined structure is a major topic in both basic and applied physics
not solely ICT oriented but also concerning lighting, laser, sensing, energy, environment, biological
and medical sciences, and quantum optics. Glasses and glass-ceramics activated by rare earth ions
are the bricks of such structures. Glass-ceramics are nanocomposite systems that exhibit specific
morphologic, structural and spectroscopic properties allowing to develop new physical concepts, for
instance the mechanism related to the transparency, as well as novel photonic devices based on the
enhancement of the luminescence. The dependence of the final product on the specific parent glass
and on the fabrication protocol still remain an important task of the research in material science.
Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to
those of the amorphous structures constitute an important point for the development of integrated
optics devices, including optical amplifiers, monolithic waveguide laser, novel sensors, coating of
spherical microresonators, and up and down converters. This lecture presents some results obtained
by our consortium regarding glass-based photonics systems. After a short history of research in
glass ceramics we will comment the energy transfer mechanism in transparent glass ceramics taking
as examples the up and down conversion systems and the role of SnO2 nanocrystals as sensitizers.
Coating of
spherical resonators by glass ceramics, 1D-Photonic Crystals for luminescence
enhancement, laser action and disordered 1-D photonic structures, polymeric-based structures for
integrated optics, will be discussed. Finally, RF-Sputtered rare earth doped P2O5-SiO2-Al2O3-Na2OEr2O3 planar waveguides, will be presented.
Acknowledgment: Effort sponsored by the projects COST MP1401 “Advanced Fibre Laser and Coherent Source as
tools for Society, Manufacturing and Lifescience” (2014 - 2018), PAS-CNR (2014-2016), PLANS - Centro Fermi,
“Plasmonics for a better efficiency of solar cells”bilateral project between South Africa and Italy (contributo del
Ministero degli Affari Esteri e della Cooperazione Internazionale, Direzione Generale per la Promozione del Sistema
Paese), “Grandi progetti 2012” PAT: “Developing and Studying novel intelligent nano Materials and Devices towards
Adaptive Electronics and Neuroscience Applications” - MaDEleNA Project.
InP-on-Silicon Integration Through Waferbonding and Epitaxy
Dries Van Thourhout
1. Photonics Research Group, Ghent University – imec, Technologiepark 15, 9052 Gent
Silicon Photonics is rapidly evolving to a mature platform for realizing complex Photonic ICs and
several companies are currently introducing first commercial products based on this platform.
However the platform is missing a natural light source. In this talk I will discuss two approaches
for overcoming this issue. Using wafer bonding high quality epitaxial layers can be directly
integrated on the silicon circuits. Following a decade of research this technology now allows to
realize device that can compete and in some cases even outperform standard InP-based telecom
devices. I will introduce the basics of this III-V on silicon platform and present some new
developments. A second and much more exploratory approach is the direct epitaxial growth of IIIV materials on silicon substrates. We recently demonstrated InP and InP/InGaAs DFB lasers
directly grown on silicon. I will present these results together with other recent results from
literature.
References:
[1] M. Paladugu, C. Merckling, R. Loo, O. Richard, H. Bender, J. Dekoster, W. Vandervorst, M. Caymax, and M.
Heyns, “Site selective integration of III-V materials on Si for nanoscale logic and photonic devices,” Cryst. Growth
Des., vol. 12, no. 10, pp. 4696–4702, 2012. [2] C. Merckling, N. Waldron, S. Jiang, W. Guo, N. Collaert, M. Caymax, E. Vancoille, K. Barla, A. Thean, M. Heyns,
and W. Vandervorst, “Heteroepitaxy of InP on Si (001) by selective-area metal organic vapor-phase epitaxy in sub-50
nm width trenches : The role of the nucleation layer and the recess engineering,” J. Appl. Phys., vol. 115, p. 023710,
2014. [3] Z. Wang, B. Tian, M. Paladugu, M. Pantouvaki, N. Le Thomas, C. Merckling, W. Guo, J. Dekoster, J. Van
Campenhout, P. Absil, and D. Van Thourhout, “Polytypic InP nanolaser monolithically integrated on (001) silicon.,”
Nano Lett., vol. 13, no. 11, pp. 5063–9, Nov. 2013. [4] B. Tian, Z. Wang, M. Pantouvaki, W. Guo, M. Clement, and J. Van Campenhout, “InP Nanowire lasers Epitaxially
Grown on (001) Silicon ‘V-groove’ templates,” in IPRM 2014, paper Thu–B1–4. [5] Z. Wang, B. Tian, M. Pantouvaki, W. Guo, P. Absil, J. Van Campenhout, C. Merckling, and D. Van Thourhout,
“Room Temperature InP DFB Laser Array Directly Grown on (001) Silicon,” http://arxiv.org/abs/1501.03025, Jan.
2015.
Integration of Si and SiN PICs with New Active Materials
Dries Van Thourhout
1. Photonics Research Group, Ghent University – imec, Technologiepark 15, 9052 Gent
In this presentation we will report on our recent work on new materials that can be monolithically integrated on highindex contrast silicon or silicon nitride photonic ICs to enhance their functionality. This includes graphene and other
2D-materials for realizing compact electro-absorption modulators and non-linear devices, ferroelectric materials for
realizing phase modulators and colloidal quantumdots for lasers and integrated quantum optics devices.
[1] Y. Hu, M. Pantouvaki, J. Van Campenhout, S. Brems, I. Asselberghs, C. Huyghebaert, P. Absil, D. Van
Thourhout, Broadband 10 Gb/s operation of graphene electro-absorption modulator on silicon, Laser & Photonics
Reviews, 10(2), p.307-316 (2016). [2] K. Alexander, Y. Hu, M. Pantouvaki, S. Brems, I. Asselberghs, S.-P. Gorza, C. Huyghebaert, J. Van Campenhout,
B. Kuyken, D. Van Thourhout, “Electrically Controllable Saturable Absorption in Hybrid Graphene-Silicon
Waveguides”, accepted for publication in Conference on Lasers and Electro-Optics (CLEO), United States, 2015 [3] J. George, J. Beeckman, W. Woestenborghs, P.F. Smet, W. Bogaerts, “Preferentially oriented BaTiO3 thin films
deposited on silicon with thin intermediate buffer layers”, Nanoscale Research Letters, 8, p.1-7 (2013) Materials and technologies: electro-optic dielectrics
Prof. Alessandro Busacca
When an electric field is applied across an optical medium, the distribution of electrons within is
distorted, so that the polarizability and hence the refractive index of the medium changes
anisotropically. The result of this electro-optic effect may be to introduce new optic axes into
naturally doubly refracting crystals.
In solids, the linear variation in the refractive index associated with the applied field is known as
the Pockels effect while the variation arising from the quadratic term is called the Kerr effect.
During the lecture, we will investigate the two phenomena also giving some examples of practical
interest. In particular, we will discuss with regard to light-wave modulation using electro-optic
materials.
Liquid crystals and photonic integration: materials, properties,
technologies, devices
Antonio d’Alessandro
Department of Information Engineering, Electronics and Telecommunications, Sapienza University, Rome, Italy
Liquid crystals (LC) are materials with good electro-optic and nonlinear optical properties suitable
to make switchable and reconfigurable devices using low driving power.
These materials have been mainly developed for flat panel displays but their mature technology can
be effectively used to make integrated optic devices for other applications such telecom, sensors,
datacom and so on.
In the first part of this lecture molecular orientation of LC mesophases and the corresponding
dielectric, elastic, thermal and optical properties will be presented. In particular the relationship
between molecular orientation and optical anisotropy of LC will be shown. Linear and nonlinear
propagation of light will be discussed. The basic fabrication technologies of LC electrooptic devices
and the most used design techniques will be illustrated.
In the second part the state of art of the most recent techniques will be presented in which liquid
crystals are combined with other materials to make active integrated optic devices such as tuneable
lasers, photonic switches, optical tunable filters based on Bragg gratings and so on.
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Design tools and design flows for integrated photonics
Twan Korthorst
PhoeniX Software, Hengelosestraat 705, 7521PA Enschede, the Netherlands
The lecture will discuss the available design tools and some example design flows for integrated
photonic circuits (PICs). It will show the special requirements for photonics and will compare this,
so called, Photonic Design Automation (PDA) with Electronic Design Automation (EDA). The
w will be shown in detail. The current situation will be
discussed showing the various available tools and improvement points will be addressed. One of the
main improvements for PDA is the use of a mature and complete Process Design Kit (PDK) as
widely being used in the electronics semiconductor industry and has been introduced for photonics
by European collaborations over the last few years. The PDK will be discussed in more detail.
Another improvement that can be controlled from the PDK are automated Design Rule Checks
(DRC). A couple of examples of Design Rule Checks will be given, showing the huge benefits
when this can be performed automatically.
References
[1] Korthorst, Twan, Stoffer, Remco, Bakker, Arjen Photonic IC design software and process design kits Advanced
Optical Technologies, Volume 4, Issue 2, pp.147-155, 04/2015.
[2]
Chapter 4, 2016.
Optical spatial solitons and nonlinear guided waves: the legacy of Prof.
George Stegeman and some recent developments
Gaetano Assanto
NooEL, Nonlinear Optics and Optoelectronics Lab
CNISM, INFN, CNR-ISC, Department of Engineering
University of Rome "Roma Tre" - Italy
Optics Lab, Department of Physics
Tampere University of Technology - Finland
Abstract
After a brief and incomplete summary of the professional career and achievements of Prof. George
I. Stegeman, passed away last year, I will pinpoint a few of his scientific results on optical
bistability and spatial optical solitons, linking them to some recent achievements in the area of
liquid crystal photonics.
In particular, the extension of optical bistability and spontaneous symmetry breaking to nonlinear
propagating beams in reorientational anisotropic media will be discussed with reference to
nematicons, spatial optical solitons in nematic liquid crystals.
From Nonlinear Integrated Optics
to Microresonator Frequency Combs
S. Wabnitz1, T. Hansson2, F. Leo3, I. Ricciardi4, M. De Rosa4, J. Anthony5, S. Coen5,
and M. Erkintalo5
1.
Dipartimento di Ingegneria dell’Informazione, Università di Brescia, via Branze 38, 25123 Brescia, Italy
2. INRS-EMT, 1650 Blvd. Lionel-Boulet, Varennes, Quebec J3X 1S2, Canada
3. OPERA-photonics, ULB, 50 Avenue F. D. Roosevelt, CP 194/5, B-1050 Bruxelles, Belgium
4. CNR-INO, Istituto Nazionale di Ottica, Via Campi Flegrei 34, 80078 Pozzuoli (NA), Italy
5. Dodd-Walls Centre, Department of Physics, The University of Auckland, Auckland 1142, New Zealandemail: [email protected]
Perhaps one of the most spectacular current applications of nonlinear integrated optics, a field
which was pioneered by George Stegeman more than thirty years ago [1], is that of nonlinear
microresonator based optical frequency comb light sources. Optical frequency comb sources are
characterized by a spectrum comprising many equally spaced components [2], and have a wide
range of scientific and technological applications. Although commercial comb generators are based
on mode-locked lasers and fiber supercontinuum generation, nonlinear integrated optics provides a
low-cost and chip-scale alternative, based on a low-power cw laser coupled into a high-Q
microresonator [3]. So far microresonator frequency combs have exploited the third order “Kerr”
nonlinearity, which permits to generate successive comb lines with a spacing equal to the resonator
free-spectral range via cascaded four-wave mixing [4-5]. Modeling of microresonator frequency
combs can be greatly simplified by a single partial differential equation approach [4-6], analogous
to the case of other coherently driven Kerr spatially diffractive [7] or temporally dispersive [8-9]
nonlinear cavities. In order to lower the threshold power and extend the spectral range of frequency
comb generation, for example into the visible or mid-infrared, while still using near-infrared cw
laser pumps, quadratic nonlinear cavities can be exploited [10]. These quadratic microresonator
frequency comb sources operate close to the phase-matching condition for the underlying quadratic
processes, and not in the cascading regime that reduces the dynamics to the Kerr case [11]. Quite
remarkably, a single time domain partial differential equation with an effective delayed third-order
nonlinearity was derived to describe with excellent accuracy the dynamics of quadratic frequency
comb generation [12-13]. In situations where multiple processes are present, and the frequency
combs generated around the interacting waves over multiple octaves overlap, we carried out
numerical modeling based on a single envelope equation approach [14].
References
[1] G.I. Stegeman, E.M. Wright, N. Finlayson, R. Zanoni, and C.T. Seaton, J. Lightwave Technology 6, 953 (1988).
[2] T. Udem, R. Holzwarth, and T. W. Hänsch, Nature 416, 233 (2002).
[3] P. Del’Haye, A. Schliesser, O. Arcizet, T. Wilken, R. Holzwarth, and T. J. Kippenberg, Nature 450, 1214 (2007).
[4] S. Coen, H. G. Randle, T. Sylvestre, and M. Erkintalo, Opt. Lett. 38, 37 (2013).
[5] T. Hansson, D. Modotto, and S. Wabnitz, Phys. Rev. A 88, 023819 (2013).
[6] T. Hansson, D. Modotto, and S.Wabnitz, Opt. Comm. 312, 134 (2014).
[7] L. A. Lugiato and R. Lefever, Phys. Rev. Lett. 58, 2209 (1987).
[8] M. Haelterman, S. Trillo, and S. Wabnitz, Opt. Commun. 91, 401 (1992).
[9] F. Leo, S. Coen, P. Kockaert, S.-P. Gorza, P. Emplit, and M. Haelterman, Nature Photon. 4, 471 (2010).
[10] I. Ricciardi, S. Mosca, M. Parisi, P. Maddaloni, L. Santamaria, P. De Natale, and M. De Rosa, Phys. Rev. A 91,
063839 (2015).
[11] G. I. Stegeman, D. J. Hagan, and L. Torner, Optical and Quantum Electronics 28, 1691 (1996).
[12] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. Lett. 116, 033901
(2016).
[13] F. Leo, T. Hansson, I. Ricciardi, M. De Rosa, S. Coen, S. Wabnitz, and M. Erkintalo, Phys. Rev. A 93 (2016).
[14] T. Hansson, F. Leo, M. Erkintalo, J. Anthony, S. Coen, I. Ricciardi, M. De Rosa, and S. Wabnitz, J. Opt. Soc. Am.
B 33, 1207 (2016).
Applications: Biosensing in integrated optics
Ivo Rendina
National Research Council, Institute for Microelectronics and Microsystems
Area della Ricerca CNR, Via P. Castellino 111, 80131 Napoli, Italy
In the last years, an increasing interest has been devoted to the exploitation of integrated optics to
biosensing for biomedicine, food analysis, environmental monitoring and security applications. The
lecture provides students with a survey starting from the basic concepts applied to biosensing up to
the most advanced lab-on-chip technologies. A particular emphasis will be given to new ideas
emerging in label-free biosensing, exploiting strong light confinement and resonance in micro and
nanostructures.
Photonics technologies for future 5G mobile networks
Roberto Sabella
ERICSSSON, Research Corporate Center, Pisa , Italy, Italy
The evolution of mobile networks towards 5G will really enable the networked society and create
significant opportunities for Industry and Society.
Huge traffic growth as well as a significant reduction of latency dictated by time-sensitive MTC
services will require a substantial transformation of the radio access networks (RAN) and,
consequently, imposes a rethinking of the underlying transport network.
The conventional point-to-point fronthaul concept is evolving towards a geographical network
connecting a pool of DUs with a plurality of RRUs using the CPRI protocol. Centralization of radio
baseband processing functions is gaining great interest for its potential to allow a consolidation of
nodes and network elements, so as to lower CapEx and OpEx (e.g. fewer nodes to install, to
maintain, to upgrade, and to power supply), while at the same time increase radio coordination
functions.
Optical technologies with their conventional benefits of high bandwidth, protocol transparency,
scalability, low latency, high resiliency and network re-configurability, are today perceived as a
promising key piece of the radio access network puzzle, in both front haul and back haul transport
areas. But previous generation of optical networking technologies (e.g. SDH/SONET, WDM, OTN
etc.), based on discrete components and modules, that played a relevant role to realize an affordable
transport medium in metro and core networks are not adequate for the needs of the emerging RAN
transport segments requiring low cost, lower power consumption and a level of miniaturization.
Re-configurability features, provided by WDM technologies, can further increase CPRI transport
efficiency.
Photonic Integration and in particular silicon photonics with its recent advances in integrating many
optical circuits and functions (for instance multiplexer, attenuator, switches, couplers) in a single
chip using the well-developed CMOS production infrastructure, is the ideal technology to fit the
RAN needs.
In addition to this, the exponential growth of traffic is driving important evolutions in the
development of HW platforms of next generation telecom and data-com equipments. Future
hardware platforms will have to be much more efficient with regard to energy consumption,
footprint and cost. Hence, the critical challenges for telecom/data-com vendors will be to
continuously increase bandwidth density at every point in the communication infrastructure. This
leads to put more and more features onto the same hardware unit (e.g. a chip, a module, or even a
board); and integrate as much as possible multiple functions in a single chip and also integration of
many chips in the same module. This is crucial.
Photonics has become the key technology for board to board and chip to chip interconnects for its
characteristics of large bandwidth, nearly reach and data rate agnostic characteristics and reduced
energy consumption. Similarly to RAN transport application, also in the new HW platform
evolution, the traditional optical devices based on discrete components cannot be used for cost and
footprint reasons. Whole new optical devices based on photonic integration have to be envisaged. In
particular, rapidly maturing CMOS compatible photonics which is mass-producible at low cost and
high level of integration is a proven candidate to ensure effective integration with the control and
host electronics.
Applications: Imaging microscopy for biomicrofluidic platform
Pietro Ferraro
National Research Council, Institute of Applied Sciences & Intelligent Systems
www.isasi.cnr.it
Via Campi Flegrei 34, 800078 Pozzuoli (Napoli) Italy
Lab-on-a-chip(LoC)devicesareextremelypromisingtobringclinicaldiagnosticfunctionsatthe
point-of-care. At this scope, an important goal is to design imaging schemes integrated with
microfludic platforms. In fact, imaging in microscopy modality is one of most powerful tool for
clinic diagnostic. An ideal microscopy system for LoC systems should satisfy three main
requirements, i.e. high-throughput data collection, label-free imaging, and quantitative
measurements. Recent advancements in the field will be reviewed and illustrated. In particular
latest evolutions of imaging systems based on Quantitative Phase Imaging (QPI) developed by
leadingresearchgroupsworldwideforin–flowcytometryandwillbeconsidered.
Integrated Microwave Photonics
José Capmany
Universidad Politecnica de Valencia, Spain
Integrated microwave photonics (IMWP) deals with the application of integrated photonics
technologies to microwave photonics (MWP) systems. The lecture will cover this topic from a
multi-facet point of view. After briefly introducing the basic concept behind MWP and IMWP and
their application to emerging ICT system, it will briefly outline the salient characteristics of
available material platforms that can be employed for the implementation of IMWP chips. I will
cover basic features of mature material platforms such as InP, SOI and Si3N4. The second part of
the lecture will be devoted to describe the two salient approaches that are available for the
implementation of IMWP chips from a functional point of view. On one hand, we will review the
recent progress in Application-Specific Photonic Integrated Circuits (ASPICs), where a particular
circuit and chip configuration is designed to optimally perform a particular MWP functionality. On
another hand, recent progress will be reported on a radically different approach, the universal MWP
signal processor architecture that can be integrated on a chip and is capable of performing all the
main functionalities by suitable software programming of its control signals.
Quantum integrated photonics
Fabio Sciarrino
Dipartimento di Fisica, Sapienza Università di Roma
P.le Aldo Moro 2, 00185 Roma, Italy
Integrated photonic circuits have a strong potential to perform quantum information processing [1,
2]. Indeed, the ability to manipulate quantum states of light by integrated devices may open new
perspectives both for fundamental tests of quantum mechanics and for novel technological
applications. By exploiting waveguides fabricated by femtosecond laser waveguide, integrated
circuits with three dimensional geometry can be designed to carry out several quantum information
processing tasks. Our aim has been to develop and implement quantum simulation by exploiting 3dimensional integrated photonic circuits. As first we implemented an integrated beam splitter able
to support polarization-encoded qubits. As following step we addressed the implementation of
discrete quantum walk: we investigated how the particle statistics, either bosonic or fermionic,
influences a two-particle discrete quantum walk both in ordered and disordered systems [3]. We
will discuss the perspectives of optical quantum simulation: the implementation of the boson
sampling to demonstrate the computational capability of quantum systems [4,5,6] and the
development of integrated architecture with three-dimensional geometries [7].
References
[1] T. D. Ladd, et al, “Quantum computers”, Nature 464, 45 (2010).
[2] J. L. O’Brien, A. Furusawa, and J. Vuckovic,
“Photonic quantum technologies”, Nature Photonics 3, 687
(2009).
[3] L. Sansoni, F. Sciarrino, G. Vallone, P. Mataloni, A. Crespi, R. Ramponi, R. Osellame, “Two-particle bosonicfermionic quantum walk via 3D integrated photonics”, Phys. Rev. Lett. 108, 010502 (2012); A. Crespi, R. Osellame, R.
Ramponi, V. Giovannetti, R. Fazio, L. Sansoni, F. De Nicola, F. Sciarrino, and P. Mataloni, “Anderson localization of
entangled photons in an integrated quantum walk”, Nature Photonics 7, 322 (2013).
[4] A. Crespi, R. Osellame, R. Ramponi, D. J. Brod, E. F. Galvao, N. Spagnolo, C. Vitelli, E. Maiorino, P. Mataloni,
and F. Sciarrino, “Experimental boson sampling in arbitrary integrated photonic circuits”, Nature Photonics 7, 545
(2013).
[5] N. Spagnolo, C. Vitelli, M. Bentivegna, D. J. Brod, A. Crespi, F. Flamini, S. Giacomini, G. Milani, R. Ramponi, P.
Mataloni, R. Osellame, E. F. Galvao, F. Sciarrino, “Efficient experimental validation of photonic boson sampling”,
Nature Photonics 8, 615 (2014).
[6] M. Bentivegna, N. Spagnolo, C. Vitelli, F. Flamini, N. Viggianiello, L. Latmiral, P. Mataloni, D. J. Brod, E. F.
Galvao, A. Crespi, R. Ramponi, R. Osellame, F. Sciarrino, Experimental scattershot boson sampling, Science
Advances 1, e1400255 (2015).
[7] N. Spagnolo, C. Vitelli, L. Aparo, P. Mataloni, F. Sciarrino, A. Crespi, R. Ramponi, and R. Osellame, “Threephoton bosonic coalescence in an integrated tritter”, Nature Communications 4, 1606 (2013).
The generic photonic foundry perspective: existing foundries,
manufacturing, access, expectations, philosophy
Meint K. Smit
The development of the manufacturing technology for complex optical chips is very expensive. The
costs of a well-equipped chip factory add up to several hundred million euros and then you only
have the equipment and the building. Also the development of the integration processes that involve
a large number of lithography, deposition and etching steps costs seceral millions of euros. There
are few markets large enough to justify such huge investments. In microelectronics this problem has
been solved by the development of standardised technology in which a number of building blocks,
such as transistors, resistors and capacitors, can be integrated in large numbers – billions of
transistors per chip – in a single standardized manufacturing process. As a result of this the high
investment costs can be earned back across a combined market that is much larger than the markets
for the individual applications. To drastically reduce the high costs for the use of optical chips a
similar development is underway in photonics. If you have a technology with which components for
manipulating the amplitude, phase and polarisation of light can be integrated as basic building
blocks, then you can realise chips with different functionalities in a single integration process. Such
a technology is called a generic integration technology.
By providing open access to such a technology through generic foundries, the entry costs for
developing PICs for a variety of applications are dramatically reduced: You do not need to build an
expensive cleanroom, and you also do not have to develop an expensive integration process: both
the cleanroom and the standardized process are available and their costs can be shared by many
users. In the lecture the philosophy of the generic foundry approach will be explained and the
capabilities of the existing InP-foundry platforms will be discussed.
POSTERS
Optimal conditions for amplified spontaneous emission collection with
the aid of a nematicon
Serena Bolis 1,2, Jeroen Beeckman2 and Pascal Kockaert 1
1. OPERA-Photonics Group, Université libre de Bruxelles, CP 194/5, 50 Av. F.D. Roosevelt, 1050 Bruxelles, Belgium
2. ELIS Department, Ghent University, Technologiepark-Zwijnaarde 15, 9052 Gent,
The huge Kerr-like nonlinearity of liquid crystals (LC) allows the formation of solitons (nematicons
in nematic LC) with a low power threshold (~mW) [1]. Recently we have shown that a nematicon
generated in a dye-doped LC cell can efficiently collect and inject amplified spontaneous emission
(ASE) into an optical fiber [2].
A 75 µm thick planar antiparallel cell (rubbing direction at 45° with respect to the edges) is filled
with 1 wt.% PM597 in E7 LC. A CW infrared (1064 nm) laser beam is injected into the cell through
a non-standard optical fiber (core diameter 2.9 µm) slid inside the cell. When a pump beam (532
nm, 400 ps, 2.0 µJ/pulse at 10 Hz) is focused onto the sample with cylindrical lenses, ASE is
emitted along the excited stripe axis. If the stripe is oriented towards the fiber, a small part of the
ASE is coupled into the fiber even in the absence of the soliton (Fig.1a-b). However, when the
nematicon is present, the soliton-induced waveguide increases the collected ASE by one order of
magnitude (Fig.1c-d). The guiding efficiency of the soliton increases with the soliton power (i.e. the
molecular reorientation). However at high IR powers the local LC director fluctuations cause the
deviation of the nematicon from its path (Fig.1e), with the spatial oscillations of the soliton that
increase with the soliton power (Fig.1f). An optimum power of 2 mW for the soliton is found. A
numerical modeling of the thermal noise impact on the nematicon propagation is still ongoing.
(a)
(c)
(b)
(d)
(b)
(d)
(e)
(f)
Figure 1. (a)-(d) Intensity profile of the ASE at the fiber output without (a)-(b), and with (c)-(d) the nematicon, for
polarizations parallel (a)-(c) or orthogonal (b)-(d) to the substrate. (e) Example of nematicon profiles for high (3.7mW) IR
powers (the pump is not present). The dotted black line is a straight line. (f) Soliton position after 3.6 mm of propagation for
three different powers and 100 acquisitions.
References
[1] A. Piccardi, A. Alberucci, U. Bortolozzo, S. Residori and G. Assanto, “Soliton gating and switching in liquid crystal
light valve”, Appl. Phys. Lett., vol. 96, 071104, 2010.
[2] S. Bolis, T. Virgili, S.K. Rajendran, J. Beeckman and P. Kockaert, “Nematicon-driven injection of amplified
spontaneous emission into an optical fiber”, Opt. Lett., vol. 41, 2245–2248, 2016.
Acknowledgment: Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA); Belgian
Science Policy Office (BELSPO) (IAP7-35)
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Ultrafast Optical Kerr Effect method
indicates negative nonlinear refractive index for graphene
Evdokia Dremetsika*,1, Bruno Dlubak2, Simon-Pierre Gorza1, Charles Ciret1,
Marie-Blandine Martin3, Stephan Hofmann3, Pierre Seneor2, Daniel Dolfi2, Serge
Massar1, Philippe Emplit1, and Pascal Kockaert1
1.OPÉRA-photonique, Université libre de Bruxelles, Brussels, Belgium
2.Unité Mixte de Physique CNRS/Thales (UMR137), Palaiseau Cedex, France
3.Department of Engineering, University of Cambridge, Cambridge, United Kingdom
Recent advances in integrated photonics lead to a growing demand for ultrathin materials
compatible with CMOS technology. Graphene appears to be a promising candidate for all-optical
signal processing in photonic integrated applications, as it presents broadband optical properties and
a high and broadband optical nonlinearity [1-4]. However, researchers do not agree on the value of
its nonlinear refractive index [2-4]. In this work, we report on the use of the ultrafast optical Kerr
effect method with optical heterodyne detection (OHD-OKE) [5] for the characterization of the
nonlinear refractive index of monolayer CVD graphene on quartz [6] at telecom wavelength. This
method is advantageous over the previously used Z-scan, as it is neither sensitive to the
inhomogeneities of the sample, nor to thermal nonlinearities. Our measurements in Fig. 1(a) and (b)
indicate a negative nonlinear refractive index for monolayer CVD graphene. We confirmed this
negative sign by Z-scan measurements on the same samples [Fig. 1(c)]. We discuss the different
parameters that could affect the sign of the nonlinearity.
Figure 1. (a), (b) OHD-OKE signals for silicon and graphene respectively. Graphene presents a response with opposite sign and
slower relaxation time than silicon. (c) Z-scan trace resulting from division of closed-aperture by open-aperture data. Savitzky-Golay
filtering has been used for data smoothing before fitting. The peak-valley trace is typical of a self-defocusing material [M.SheikBahae et al, IEEE J. Quant. Elect. 1990, 26 760].
References
[1] S. A. Mikhailov and K. Ziegler, J. Phys.-Condens. Mat. 2008, 20, 384204.
[2] H. Zhang, S. Virally, Q. Bao, L. Kian Ping, S. Massar, N. Godbout, and P. Kockaert, Opt. Let. 2012, 37, 1856.
[3] W. Chen, G. Wang, S. Qin, C. Wang, J. Fang, J. Qi, X. Zhang, L. Wang, H. Jia, and S. Chang, AIP Adv. 2013, 3,
042123.
[4] D. Chatzidimitriou, A. Pitilakis, and E. E. Kriezis, J. App. Phys. 2015, 118, 023105.
[5] N. A. Smith and S. R. Meech, Int. Rev. Phys. Chem. 2002, 21, 75.
[6] P. R. Kidambi, C. Ducati, B. Dlubak, D. Gardiner, R. S. Weatherup, M.-B.Martin, P. Seneor, H. Coles, and S.
Hofmann, J. Phys. Chem. C 2012, 116, 22492.
Acknowledgment: Effort sponsored by the Belgian Science Policy Office (BELSPO) (IAP7- 35), the EU FP7 Work
Program (Graphene Flagship) (604391). E. Dremetsika is funded by the Fund for Research Training in Industry and
Agriculture (FRIA), Belgium.
Infrared detection in multifunctional graphene-based transistors
M. A. Giambra1,2, A. Benfante1, R. Pernice1, S. Stivala1, E. Calandra1, A. C. Busacca1
W. H. P. Pernice2, R. Danneau2
1. DEIM – University of Palermo, Viale delle Scienze, Bldg. 9, 90128, Palermo, Italy
2. Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), 76344 Egg.-Leopoldshafen, Germany
In the last years great attention has been paid to graphene-based devices for optoelectronic
applications such as photodetection [1, 2]. In this work, we report on Graphene Field Effect
Transistors (GFETs) photoelectrical response due to the photo-transistor effect [3]. The devices
fabrication steps and their electro-optic characterization are herein presented. The transistors, whose
cross section is shown in Fig. 1 (a), were built on a sapphire substrate. First, the dual-finger backgate was patterned on a sapphire substrate by e-beam lithography followed by the evaporation of a
thin Ti/Au bilayer (∼ 5/40 nm). A ~ 10 nm thick Al2O3 film was directly grown via atomic layer
deposition at 90° as dielectric layer. A CVD-grown graphene film was directly transferred onto the
oxide layer and etched in a meandered pattern by Reactive Ion Etching (RIE) to minimize the
contact resistance. Subsequently, source/drain electrodes were patterned onto the graphene sheet
using E-beam lithography followed by a Ti / Au (~ 5 / 100 nm) deposition. Finally, a ~ 300 nm Au
was directly grown by PVD as contact pads. Photoelectrical measurements were performed using a
1.55 μm erbium fiber laser with the output output beam, chopped at 667 Hz and coupled into a
single mode optical fiber through a microscope objective. The output of the fiber was placed above
the sample at a distance of 1.55 mm from the photoactive area (i.e., the 20 μm × 1 μm graphene
area above the gates) that was illuminated by an IR beam with a spot radius (1/e2) of 144 μm. An
auxiliary visible laser was employed for alignment purpose. The GFETs electrical drain-source
voltages (VDS) were measured using a lock-in amplifier synchronized to the chopper frequency. A
sketch of the set-up is depicted in Fig. 1 (b). Optical measurements as a function of both the
incident laser power and the DC bias of the devices have been carried out. As it can be easily
noticed, the photocurrent (Iph, in Fig. 1 (c)) increases with the power of the IR beam illuminating the
sample and a maximum responsivity of 0.34 A/W has been obtained.
(a)
(b)
(c)
Figure 1. (a) GFET cross-section, (b) measurement setup, (c) GFET photo-response at different values of IR power (V DS = 0.4 V).
References
[1]
[2]
[3]
Z. Sun et al., “Graphene and Graphene-like Two-Dimensional Materials in Photodetection: Mechanisms and
Methodology”, ACS Nano, vol. 8, n. 5, 2014, pp. 4133–56.
A. C. Ferrari et al., “Science and technology roadmap for graphene, related two-dimensional crystals, and
hybrid systems,” Nanoscale, vol. 7, 2014, pp. 4598–4810.
B. K. Sarker et al., “Gate-tunable and high responsivity graphene phototransistors on undoped semiconductor
substrates”, arXiv preprint arXiv:1409.5725, 2014.
Acknowledgment: This activity was supported by PON03PE_00214_1 "Nanotecnologie e nanomateriali per i beni
culturali" (TECLA) Research Program.
Light coupling in microscale polymer photonic circuits
Manuel Gil-Valverde 1, Manuel Caño-García1, David Poudereux1, Morten A. Geday1,
José M. Otón1, Xabier Quintana1
1. CEMDATIC, Universidad Politécnica de Madrid, Av. Complutense, 30, 28040 Madrid, Spain
Photonic integrated circuits (PICs) are devices that integrate multiple photonic functions. The
visible light is guided between components by light waveguides of the same order as light
wavelength, i.e. 1-5μm or even less [1]. Because of the size of connections, coupling light into PICs
is a challenging task previous to characterizing them. The aim of our group is to turn a passive PIC
into an active one by adding layers of electro-optics materials, either as a component within the
light path, or deposited onto the waveguide affecting the evanescent field of the guided light.
Testing the light behavior inside the PICs may be hampered by the arduous light coupling from
external sources. This problem may be faced up from several points of view.
Figure 1. Different views of the X-Y-Z nanopositioner setup for coupling light to PICs.
We are developing improved versions of classical coupling setups. It is possible to appreciate in the
figure 1 one of our latest realizations to couple light into the PICs. It consists of an X-Y-Z
electrically-manual controlled nanopositioned microscope objective, two microscopes and green/red
He-Ne lasers. The nanopositioner let us focus the laser beam into the small cross section of the
waveguide, where the first microscope is placed. The second microscope is used to analyze the
output signal in the opposite end of the waveguide, which can be eventually brought to another
detection system. Moreover, others alternative mechanisms are being developed now in the group
for light coupling, being the most promising solutions those in which light is coupled by difractive
elements [2] or generating it internally.
References
[1] D. Geuzebroek, R. Dekker, E. Klein, J. van Kerkhof , “Photonic Integrated Circuits for visible light and near
infrared: Controlling transport and properties of light”, Sensors and Actuators B: Chemical, vol. 223,p.952956, 2015.
[2] J. Zhang, J. Yang, H. Lu, W. Wu, J. Huang, S. Chang, “Subwavelength TE/TM grating coupler based on silicon-oninsulator”, Infrared Physics & Technology, vol. 71, p. 542546, 2015.
Acknowledgment: This work has been supported by Spanish Government RETOS Program grant no. TEC2013-47342C2-R, the R&D Program SINFOTON S2013/MIT-2790 of the Comunidad de Madrid, and the Euopean COST Action
IC1208.
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Fabrication of high quality alignment layer for nematic liquid crystal
cell with variable orientations
B. W. Klus, M. Kwaśny and U. A. Laudyn
Faculty of Physics, Warsaw University of Technology
Koszykowa 75, 00-662 Warsaw, Poland
e-mail:[email protected]
Concerning the control of the liquid crystal alignment by means of substrate surface treatment there
are different treatment methods for achieving such a control, among others directional rubbing,
photoalignment, ion-beam exposure on polymer substrates, irradiation by plasma beam, etc. Any
one of these methods has its advantages and disadvantages and what is suitable for some materials
or applications may not be suitable for another. In this work we present an alignment method for the
near-zero pretilt angle of NLCs using electron beam lithography. Much attention will be paid to the
uniformity of the obtained orientation and the anchoring strength. We highlight that proposed
method allows to obtain high quality alignment layer that is not worse than that achieved by other
commonly used methods, and in many ways much better, allowing to obtain molecules orientation
difficult or impossible to achieve by other methods.
Our work relates generally to nematic liquid crystal cell, particularly, it relates to fabrication of
micro structure waveguides in NLC cell for light beam guiding and switching. The huge advantage
of the proposed method is the ability to obtain variable direction of orientation of the long axes of
NLC molecules along light beam propagation with the nanoscale resolution. This allows for
designing precise paths for light beam, in general with curved trajectory. Such fabricated liquid
crystal waveguide supports a full control on the direction of propagation of the light beam both in
linear as well as in nonlinear regime. It operates due to the high quality alignment layer with
adequate anchoring energy and variable alignment conditions along propagation distances.
References
[1] I. Ostromęcka, M. Kwasny, P. Jung, B. W. Klus, U. A. Laudyn, “Measurements of the quality of nematic liquid
crystal alignment”, Phot. Lett. Poland, vol. 8, No 1 (2016).
[2] K. Takatoh, M. Hasegawa, M. Koden, N. Itoh, R. Hasegawa, and M. Sakamoto, “Alignment Technologies and
Applications of Liquid Crystal Devices”, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim (2006).
Acknowledgment: Effort sponsored by the National Centre for Research and Development by the grant agreement
LIDER/018/309/L-5/13/NCBR/2014.
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Longitudinal writing of vertical waveguides in fused silica
D. P. Lopes*1,2, R. Martinez Vazquez2, R. Osellame1,2
1.
Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133, Milano
2. IFN-CNR, Politecnico di Milano, Piazza L. da Vinci, 32, 20133, Milano.
*e-mail: [email protected]
The past decade has seen femtosecond direct writing fully developing into a solid tool that provides
fabrication of optofluidic devices with great flexibility of geometry with its truly 3D direct writing
[1]. Longitudinal writing is less commonly used due to its limitations: writing depth limited by the
working distance of the objective used and the modification profile being highly dependent on the
writing depth due to spherical aberrations [2]. Still, it provides naturally a symmetrical
modification, and for writing vertical waveguides it enables writing in any position on the sample.
The main objective of this research is to fabricate 1 mm length vertical waveguides in fused silica
that must be compatible with telecom photonic circuits.
We first explored to fabricate waveguides with a dry low numerical aperture objective (20x, 0.35
NA), in order to reduce aberrations during longitudinal writing. The modification profile was too
small (~1 um) for single mode waveguiding (SMW) at 1550 nm. In order to enlarge the index
modification region, two approaches were followed: 1-multiscanning across the waveguiding area,
enlarging the waveguide by building up the positive modification; 2- write a helix shape by direct
writing pilled circles in order to have waveguiding in the highly stressed central area.
In figure 1a we report the microscope images from the edge of three multiscan waveguides, varying
the scan distances. It is possible to build up the modification by separating the scans by less than 1
µm. Each scan was made with 10 µm/s scan speed, repetition rate of 1 MHz and pulse energy of
0.15 µJ. After enlarging the modified region with three layers, with 0.75 µm separation, SMW was
observed on these waveguides but with very high insertion losses (>10 dB).
In the cladding writing, SMW at 1550 nm was achieved by writing with 1 MHz repetition rate, 0.16
µJ pulse energy, ring diameter of 16 µm and 1 µm pitch, obtaining an insertion loss of 1.7 dB.
However, the waveguide was not uniform since the guided modes observed coupling from the two
edges were much different (12 µm vs 11 µm).
In alternative to the above mentioned objective we tried a water immersion objective (20x, 0.5 NA).
With these updates we should avoid the presence of ablation at both surfaces of the glass, and
reduce the spherical aberrations by making a better phase matching with water instead of air. We
obtained homogeneous modification with the single scan modification too small for SMW at 1550
nm. Using the cladding geometry, we observed again SMW at 1550 nm and the modes on both
sides are roughly symmetric and close to the fiber (figure 1b), which shows improvements in
uniformity with depth.
a
b
i
ii
iii
Figure 1a: Merging of the modification observed by making 6 equidistant scans with different distances (r[µm]) from the
central line. 1b: cladding waveguides characterization: i- microscope image, ii-imaged waveguiding mode, iii- fiber mode.
References
[1] R. Osellame, et al. Femtosecond Laser Micromachining: Photonic and Microfluidic Devices in Transparent
Materials. Vol. 123. Springer Science & Business Media, 2012.
[2] C. Mauclair, et al., Optics express 16.8: 5481-5492, (2008).
Acknowledgment: This research was supported by the European project TERABOARD
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Gain-ratio Brillouin Optical Correlation Domain Analysis for
distributed strain and temperature monitoring
Jacopo Morosi
Politecnico di Milano - Dipartimento di Elettronica, Informazione e Bioingegneria (DEIB)
Fiber-optic Brillouin sensors for temperature and strain distributed monitoring offer unique
performance in terms of distance, high spatial resolution and accuracy. Most of the available
systems rely on Brillouin Optical Time-Domain Analysis (BOTDA) techniques, which employ
pulsed pump signals guaranteeing a spatial resolution fundamentally limited to 1 meter [1]. An
attractive alternative approach is the so-called Brillouin Optical Correlation-Domain Analysis
(BOCDA), based on the simultaneous phase modulation of both pump and probe waves [2]. This
way, efficient amplification is confined only in a narrow fiber section, called correlation peak,
where the Brillouin phase-matching condition in satisfied. Correlation peak width can be made
arbitrarily narrow and its position along the sensing fiber can be moved by properly tuning phase
modulation rate. Phase-BOCDA sensors can thus guarantee high flexibility in measurement
configuration, with spatial resolution enhanced to centimetric or even sub-centimetric scale, at the
expense of longer acquisition times and lower number of monitored points. In this work, a method
similar to that described in [3] has been applied for the first time to a traditional phase-BOCDA
scheme, without any modification of the experimental setup shown in Fig. 1(a), leading to a tentimes reduction in measurement time while retaining high resolution and measurement accuracy.
Instead of performing a reconstruction of the full Brillouin Gain Spectrum (BGS) thickly scanning
pump-probe frequency difference (ΔυB) in a ~200 MHz span for each monitored point, it is
sufficient to measure gain in two fixed positions corresponding to positive and negative slopes of
the unstrained BGS at room temperature. The ratio of these two values gives information on the
direction and amount of shift induced by temperature or strain variations. A calibration procedure is
required to convert measured RB values into correspondent Brillouin Frequency Shift (BFS) values,
from which the actual strain/temperature distribution over the entire FUT can be estimated. Fig.
1(b) shows preliminary results for an 8cm strained fiber section near the end of a 10m SSMF FUT,
confirming 2 cm spatial resolution and dynamic range of more than 600 µε.
Figure 1 – (a) Experimental phase-BOCDA setup and (b) Measured strain distributions on a 8 cm section near the end of the FUT
References
[1] A. Motil, A. Bergman, M. Tur, “State of the art of Brillouin fiber-optic distributed sensing”, in Optics & Laser
Technology, vol. 78, pp. 81-103, 2016..
[2] A. Zadok, Y. Antman, N. Primerov, A. Denisov, J. Sancho, and L. Thevenaz, “Random-access distributed fiber sensing”,
in Laser & Photon. Rev., 6: L1-L5, 2012.
[3] A. Motil, O. Danon, Y. Peled and M. Tur, "Pump-Power-Independent Double Slope-Assisted Distributed and Fast
Brillouin Fiber-Optic Sensor," in IEEE Photonics Technology Letters, vol. 26, no. 8, pp. 797-800, 2014.
Spatial and temporal imaging of polymeric integrated circuits
Dmitry Nuzhdin1,2, Sara Nocentini1, Lorenzo Pattelli1, Simone Zanotto1,3
and Diederik S. Wiersma1
European Laboratory for Nonlinear Spectroscopy (LENS), University of Florence, Via Nello Carrara 1, 50019
Sesto Fiorentino (FI), Italy
2. Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
3. CNR-INO, U.O.S. Sesto Fiorentino, University of Florence, Via Nello Carrara 1, 50019 Sesto Fiorentino (FI), Italy
1.
[email protected]
Integrated photonic circuits, realized with many different materials and advanced technologies, are
nowadays applied to many fields, including telecommunication, optical sensors and healthcare
diagnostics. The functional characterization of such structures is extremely important to highlight
differences between the intended design and the fabricated device, allowing to identify the possible
presence of defects. Quite often, though current state-of-the-art techniques in CW can be applied
only to simple optical devices, time or frequency resolved domains provide only limited
information. We propose a wide-field, single-shot characterization technique combining ultrafast
temporal and spatial imaging, and use it to investigate the propagation of light inside waveguides
coupled to whispering gallery mode resonators. The sample under analysis is a three-dimensional
polymeric circuit made of a commercial polymer (Nanoscribe GmbH) using the Direct Laser
Writing lithographic technique (DLW). The light is coupled into the waveguide through a grating
coupler designed for telecom wavelengths. A whispering gallery mode resonator is therefore
vertically coupled to the waveguide and images of the transmitted light from the output coupler are
recorded with sub-ps resolution with a CCD and a PMT for comparison, exploiting sum-frequency
optical gating on a non-linear crystal [1]. From these data, we can reconstruct the evolution in time
of the pulse through the photonic structure and highlight the different characteristics of the circuits
and their defects using both a spatial and temporal imaging. The final aim of this experiment is to
visualize the light inside the photonic circuits in time domain and perform a direct imaging of the
propagating modes.
Figure 1. a) Scanning Electron Microscope image of a integrated polymeric circuit. b) Time resolved setup scheme.
References
[1] L. Pattelli, R. Savo, M. Burresi, and D. S. Wiersma, “Spatio-temporal visualization of light transport in complex
photonic structures.” Light: Science & Applications, 5(5), e16090, (2016).
Acknowledgment: Effort sponsored by the funding from the European Research Council under the European Union's
Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° [291349] on photonic micro-robotics and
by the Erasmus Mundus Doctorate Program Europhotonics (Grant No. 159224-1-2009-1-FR-ERA MUNDUS-EMJD).
Fabrication and Characterization of PDMS Optical Waveguides
structured by means of Two-Photon Polymerization Effect
Giulia Panusa1,2, Antonio d'Alessandro1,2, Ye Pu3, Demetri Psaltis3.
1. Informatics, Electronics and Telecommunication Engineering Department, Sapienza Unversity of Rome, Via
Eudossiana 18, 00184, Roma.
2. Nanotechnology Enginnering, Sapienza Unversity of Rome, Via Eudossiana 18, 00184, Roma.
3. Optics Laboratory, School of Engingeering, École Polytechnique Fédérale de Lausanne, BM 4101, Station 17, CH1015, Lausanne.
email: [email protected]
Sensorineural hearing loss (SNHL) is the most common type of hearing loss that affects more than
10% of the population worldwide [1]. Cochlear implants (CIs) are devices that generate hearing
sensation through electrical stimulation of the auditory sensory neurons using an array of electrodes
in patiens with partial or complete hearing loss. Significant damage to the inner ear often occurs due
to the misplacement of the CI electrode array, resulting in the loss of residual hearing ability.
Therefore, visualization within the cochlea would help diagnosing the status of the important
intracochlear hearing structures.
In this work, polidimethylsiloxane (PDMS) optical waveguides made by using Two-Photon
Polymerization (2PP) for cochlear implants applications are presented. The waveguides will be used
to make a CI guiding endoscope: an "auxiliary" optical microendoscope to be incorporated into
cochlear implants. 2PP is based on a nonlinear absorption effect that occurs when very high intense
laser pulses are focused inside a material [2],[3]. By direct femtosecond laser writing, it is possible
to polymerize a PDMS matrix material, that contains a suitable photoinitiator and an appropriate
monomer mixture.
In this work, many commercially available photoinitiators and monomers have been investigated:
depending on the molecular structure of the used photoinitiators, the source wavelength has to
change in order to trigger the photo-polymerization. Photo-polymerization occurs only where the
laser beam is focused. The unreacted monomers can be removed by heating the sample. We
obtained optical waveguides with a diameter of 1-1.5 µm and we characterized the optical
waveguides in terms of refractive index change through holographic phase change recording
(Digital Holographic Interferometry). We measured a refractive index change of about 0.06, which
allows light confinement in the waveguides.
References
[1] Ye Pu, Demetri Psaltis, Christophe Moser, Integration of Optical Guidance Mechanism in Cochlear Implants, CTI
Proposal, EPFL.
[2] R. Inführ, N. Pucher, C. Heller, H.Lichtenegger, R. Liska, V. Schmidt , L. Kuna, A. Haase, J. Stampfl, Functional
Polymers by Two Photon 3D Lithography, Applied Surface Science 254 (2007) 836-840.
[3] J. Stampfl, R. Inführ, K. Standlmann, N. Pucher, V. Schmidt, R. Liska, Materials for the Fabrication of Optical
Waveguides with Two Photon Photopolymerization, Proceedings of the Fifth International WLT-Conference on Laser
Manufacturing 2009.
Acknowledgment: Effort sponsored by the Optics Laboratory of École Polytechnique Fédérale de Lausanne.
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Reconfigurable Fabry-Perot Cavity Leaky-Wave Antennas Based on
Nematic Liquid Crystals for THz Applications
Silvia Tofani 1,2, Walter Fuscaldo1,3, Romeo Beccherelli2, Alessandro Galli1
1. Dipartimento di Ingegneria dell’Informazione, Elettronica e delle Telecomunicazioni (DIET),
“Sapienza” Università di Roma, Via Eudossiana 18, 00184, Roma, Italia.
2. Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche (CNR-IMM),
via del Fosso del Cavaliere 100, 00133, Roma, Italia.
3. Institut d’Électronique et de Télécommunications de Rennes, UMR CNRS 6164,
Université de Rennes 1, 35700, Rennes, France.
Reconfigurable antennas are usually designed by means of metamaterials in both the microwave
and optical range. In the THz range, graphene has been recently as a tuning element, but
preliminary results revealed the low efficiency of graphene-based antennas [1]. Here, we propose
the use of nematic liquid crystals (NLCs) as tuning elements for the design of a THz Fabry-Perot
cavity leaky-wave antenna (FPC-LWA). Such an antenna allows for achieving the beamscanning
property at fixed-frequency through the simple application of a bias to the NLC layers. A theoretical
model is first investigated as a proof concept . Then, two more practical designs are considered to
estimate the technological implementation of such device.
The structure consists of a multilayered stack of alternating dielectric layers, placed above a
grounded dielectric slab. The alternation of tunable low-permittivity layers (NLC layers) and highpermittivity layers (Al2O3), with thicknesses fixed at odd multiples of a quarter wavelength in their
respective media, produces a resonance condition, which makes possible to obtain a narrow radiated
beam at broadside [2]. The application of a common bias voltage to the NLC layer allows for
changing the resonance condition and, thus, the propagation constant of the fundamental leaky
modes with consequent beam steering capability. A suitable circuit model for the dispersive
analysis of planar structures in the presence of anisotropic layers is developed [3].
Dispersion curves of the fundamental TM leaky mode of three different layouts [4] are shown in
Figure 1: a theoretical design (a) is compared with two realistic implementations (b, c) with the aim
to design an antenna suitable for fabrication. In the next months, prototyping and measurements of
the structures are expected as well as further theoretical investigations.
Figure 1. Normalized complex propagation constant of the TM leaky mode for applied voltages starting from 0 V (red lines) to
high-voltage limit V∞ (blue lines) for ideal 1 THz (a), realistic 0.59 THz (b), more realistic 0.56 THz (c) FPC-LWAs.
References
[1] W. Fuscaldo, P. Burghignoli, P. Baccarelli, A. Galli, “Reconfigurable Substrate–Superstrate Graphene-Based
Leaky-Wave THz Antenna”, IEEE Antenna Wireless Propag. Lett. 15 (2016).
[2] D. R. Jackson, A. A. Oliner, A. Ip, “Leaky-wave propagation and radiation for a narrow-beam multiple-layer
structure”, IEEE Trans. Antennas Propagat. 41, pp. 344-348 (1993).
[3] G. Valerio, D. R. Jackson, A. Galli, “Fundamental properties of surface waves in lossless stratified structures”, Proc.
R. Soc. A, 466, pp. 2447-2469 (2010).
[4] W. Fuscaldo, S.Tofani, D. C. Zografopoulos, P. Burghignoli, P. Baccarelli, R. Beccherelli, A. Galli, “Tunable
Fabry-Perot cavity THz antenna based on leaky-wave propagation in nematic liquid crystals”, submitted to Opt. Lett.
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Ferroelectric liquid crystals with short helical pitch
Dorota Węgłowska and Michał Czerwiński
Faculty of Advanced Technologies and Chemistry, Military University of Technology
2 Kaliskiego Str., 00-908 Warsaw 49, Poland
The deformed helix ferroelectric liquid crystal effect (DHF) [1] exhibits short switching times
(<100 ms) at a very low applied voltage (1 V/mm) and hysteresis-free V-shape switching curve,
nearly independent of the frequency of the applied voltage in a broad frequency range (10 Hz-4
kHz). The above features make ferroelectric liquid crystals (FLCs) working in the DHF mode very
useful for photonic applications.
For the DHF mode FLCs having a low melting point, a broad temperature range of SmC*
phase, a short helical pitch, a high tilt angle and a high spontaneous polarization are especially
promising. Several chiral compounds with a benzoate rigid core with the general structure:
X
O
O
C3F7CH2O(CH 2)mO
C6H13
O
H3C
wherein: m=2-7 and X=H or F
have been synthesized, and their mesomorphic properties have been studied [2]. The tilt angle, the
spontaneous polarisation as well as the helical pitch of the compounds have been evaluated in the
full temperature domain. New mesogenic compounds exhibit short helical pitch (< 0.8m) and
unique, so called orthoconic, behavior at the synclinic smectic SmC* phase: the tilt angles measured
in the SmC* phase reveal extremely high values at saturation approaching 45. The values of the
spontaneous polarization for all investigated compounds are between 80 and 100 nC/cm2.
References
[1] L. A. Baresnev, V. Chigrinov, D. I. Dergachev, E. P. Poshidaev, J.
M. Schadt, Liq. Cryst., 1989, 5, 1171.
[2] D. Węgłowska, P. Perkowski, W. Piecek, M. Mrukiewicz, R. Dąbrowski, RSC Adv., 2015, 5, 81003.
Funfshilling,
Acknowledgements: This work has been supported by the Polish Ministry of Science and Higher Education, grant RMN
No. 08-796/2016.
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