1084 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 42, NO. 10, OCTOBER 2006
Nematic Liquid Crystal OpticalChannel Waveguides on Silicon
Antonio d’Alessandro, Senior Member, IEEE, Bob Bellini, Domenico Donisi, Student Member, IEEE,Romeo Beccherelli, and Rita Asquini
Abstract—We demonstrate the first channel waveguides made ofE7 nematic liquid crystal (LC) in SiO2–Si V-grooves. The grooveshave been obtained by wet etching n-Si substrates first and thenby thermally growing an approximately 2- m-thick SiO2 claddinglayer. Propagation of infrared light at a wavelength of 1550 nmshows a good optical confinement in 10- m-wide LC waveguides.Modal analysis and beam propagation simulations predict singlemode propagation. This is experimentally confirmed by the ac-quired near field images. The optical waveguide acts as an inte-grated optic polarizer, since only vertical polarization can prop-agate due to the orientation of the LC molecules. The horizontalpolarization state is suppressed by more than 25 dB.
Index Terms—Integrated optic polarizers, liquid crystal (LC),optical waveguides, silicon photonics.
I. INTRODUCTION
THE impressive success of liquid crystal (LC) flat paneldisplay technology in the recent years clearly shows the
advances in handling LCs. High specification robust functionaldevices can be made with these materials, by confining thembetween two surface-aligning substrates separated by just afew micrometers. LCs are anisotropic uniaxial materials, withbirefringence exceeding 0.2 or even higher. This may resultin large phase shifts within very short optical paths. Further-more, various powerful electrooptical field effects designed forLCs enable low power consumption applications by voltagecontrolling the direction of the LC optic axis. Power dissi-pation for a 1 mm active area nematic LC (NLC) device isin the microwatt range. The combination of device-specificLC-molecular properties and electrooptical effects renders LCsattractive as materials for many optoelectronic applications, notjust displays [1].
Manuscript received April 6, 2006; revised June 26, 2006. This work wassupported in part by the European Training and Mobility Research NetworkSynclinic and Anticlinic Mesophases for Photonic Applications (SAMPA).
A. d’Alessandro is with the Department of Electronic Engineering, Univer-sity of Rome “La Sapienza,” Rome00184 , Italy and also with the ConsiglioNazionale delle Ricerche, Istituto Nazionale per la Fisica della Materia (CNR-INFM), Rome 00184, Italy (e-mail: [email protected]).
B. Bellini was with University of Rome “La Sapienza,” 00184 Rome, Italyand with Consiglio Nazionale delle Ricerche, Istituto Nazionale per la Fisicadella Materia (CNR-INFM) 00184 Rome, Italy. He is now with the ConsiglioNazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi (CNR-IMM), Rome 100-00133, Italy (e-mail: [email protected]).
D. Donisi and R. Asquini are with Department of Electronic Engi-neering, University of Rome “La Sapienza,” Rome 00184, Italy e-mail:[email protected]; [email protected]).
R. Beccherelli is with Consiglio Nazionale delle Ricerche, Istituto per la Mi-croelettronica e Microsistemi, (CNR-IMM), Rome 100-00133, Italy (e-mail:[email protected]).
Digital Object Identifier 10.1109/JQE.2006.881827
In free-space propagation, different functions have beendemonstrated and some devices are commercially availablefrom a few companies both in Europe and in the US.1 Signalprocessing devices based on free-space spatial light modulatorshave been demonstrated to perform optical functions such asbeam steering and optical switching among optical fibres fortelecommunications [2]. Optical filters using fiber Fabry–PerotLC cavities have also been demonstrated [3]. Polarizationconversion of near-infrared light, based on nonlinear effectshas been shown in a simple standard NLC cell [4]. While suchfree space components have good performance for opticalcommunication systems their insertion losses were foundabove 16 dB with a predicted value between 8.6 and 9.4 dB[2]. The larger losses measured experimentally were partlydue to misalignment and light passing repeatedly through ITO(indium tin oxide) electrodes, therefore such losses representan intrinsic limitation.
In integrated optics, the use of NLC as a propagation mediumwas originally discarded. Propagation losses of the order of18 dB/cm have thus far prevented development and commer-cialisation of waveguide devices based on NLC as a core [5].This was because large light scattering losses were found inNLCs made of rod-like molecules. Reduced scattering losseswere found in smectic LCs [6]. However following improvedalignment of the LCs, propagation losses can be greatly reducedand integrated optics using LCs is worth being reconsidered,enabling competitive integrated optical devices based on LCs.
Another competitive feature of using LCs for photonicintegrated circuits is associated with the LC light absorbance.Like virtually all organic materials, LCs absorb light in theUV region. However, depending on molecular design, in thevisible and near-infrared regime (i.e., from 350 to 5000 nm),LCs are highly transparent [7]. Furthermore, the values oftheir ordinary refractive indexes range from 1.45–1.6 whichperfectly match the refractive indexes of silica optical fibersand low loss silica on silicon optical waveguides. Mechanicalstability and the possibility to photo-pattern the alignmentof LCs [8], [9] on a nano/micro scale are other interestingfeatures of LCs compared with state-of-the-art optomechanicalmicro switches [10].
Ultrashort vertical directional couplers made of passivewaveguides separated by a gap filled with refractive indexcontrollable LC material have been predicted by exploiting LCsexhibiting large birefringence, which allows coupling lengthsshorter than 100 micrometers. These vertical couplers were
D’ALESSANDRO et al.: NEMATIC LIQUID CRYSTAL OPTICAL CHANNEL WAVEGUIDES ON SILICON 1085
shown to be applicable in novel compact guided wave opticalswitches [11]. Furthermore, guided wave tuneable filters com-bining polymeric and monomeric LCs have been demonstrated[12], [13].
Since many interesting demonstrations have shown all thepotentialities of LC for both linear and nonlinear optical effectbased devices, the pending question is whether LC can be em-bedded in materials for more effective optical and electronicintegration.
In this paper, we report the fabrication and the optical char-acterization of the first LC channel waveguide in silica-coatedsilicon grooves. The goal is to make low cost, active integratedoptic devices feasible in a material traditionally used to makeexcellent low loss but only passive photonic devices, suchas those ones made of SiO –Si or silicon-on-insulator (SOI)technology [14].
Photonics on silicon is partly motivated by the fact that sil-icon is the dominant material for electronics, therefore opticalfunctions could be efficiently coupled to electronic functions[15], [16]. On the technological side, it is well-known thatsilicon is an excellent material for micromachining and mi-crofluidic structures: the technology leads to very reproducible,precise grooves. Such V-grooves are already used for accuratefiber ribbon positioning. Single crystal silicon wafers are alsoeasy to cleave or saw, furthermore the silicon native oxide isa good electrical insulator and makes an excellent low-lossoptical buffer layer.
Moreover silicon micromachining shows additional meritsfor LC technology. On one hand, it can provide well-definedand smooth cells and reservoirs and avoids the use of spacers,as usually employed in standard LC glass plate cells. On theother hand, by using a conductive silicon wafer as one of thetwo facing electrodes, a control electric field waveform can beapplied to the LC. This allows to exploit the rich variety of elec-trooptical effects of LC. Thus, functionalities such as phase andpolarization control, switching, beam steering, etc., can be im-plemented in integrated planar optics.
This paper focuses on the basic fabrication steps of silicagrooves filled with a standard NLC and on the first demonstra-tion of light confinement in such novel structures. The measuredpolarization properties of guided light have been simulated bymeans of a three-dimensional (3-D) beam propagation method(BPM). The simulations helped to formulate some realistic hy-pothesis on the most likely orientation of LC molecules in suchconfined novel geometries never demonstrated and never inves-tigated up to now.
II. WAVEGUIDE FABRICATION AND STRUCTURE
A. Sample Preparation
In a (100) silicon wafer the anisotropy of the etching rate inKOH solution leads to the formation of grooves, whose crosssection is inscribed in a triangle of base and depth , where
(1)
The width of the groove is provided by the mask aper-ture in the photolithographic process. Partial etching eventu-ally produces trapezoidal grooves and careful process control
Fig. 1. Cross section of a LC waveguide in a silicon V-groove.
results in a smooth flat bottom. By varying the groove widthand depth, different devices can be fabricated such as straightwaveguides, spot-size converters and other passive components[17], by filling the grooves either with polymers, LCs, or moregenerally fluid or soft matter that can take the shape of thegroove [18]. The molecules of LC placed therein take the shapeof the groove, which is V-type in the case of complete etchingas shown in Fig. 1. In order to form an optical waveguide, theoptical confinement is provided by embedding the LC betweentwo different claddings.
The bottom cladding consists of silicon dioxide, the nativeelectrical and optical buffer of silicon, which has an adequaterefractive index for LC. The silicon is n-doped so that it may beused as electrode.
In the first step of the groove fabrication, a thin layer of silicondioxide was grown by means of a thermal oxidation. This layerhad a typical thickness of about 300 nm and acted as a physicalmask for Si-etching. In order to define patterns in silica, a post-exposure cured photoresist was used. Then silica was etched inan aqueous solution of buffered HF (BHF). After resist removal,silicon was etched in KOH solution at 80 C.
Once Si etching had been completed, the substrate wascleaned in BHF. Afterwards a silicon dioxide cladding layerwas thermally grown up to a thickness of 1.5 m along the[1 0 0] direction and 2 m along [1 1 1]. The growth process issuch that 44% of SiO thickness results by consumption of thesilicon wafer, while the remaining 56% grows above the siliconlevel [19].
The top cladding consists of a coated glass plate, like in reg-ular LC cells where a cover glass is always required. On thiscover glass a thin layer of nylon 6 was deposited. Typically, a50-nm-thick layer of nylon 6 is obtained by spinning a solutionof 0.5% wt./vol in trichlorethanol at 4000 r/min for 40 s.
Nylon 6 was then crystallized by thermal treatment in air at atemperature of 160 C for 4 h. Afterwards a mechanical rubbingof nylon 6 was made by using a velvet cloth to promote planarhomogeneous alignment of the LC. We emphasize that this layeris present only on the glass plate.
Then the silicon wafer and the glass cover were assembled tomake a cell to be filled with LC. The glass cover was placed ontop of the silicon substrate by orienting it such that the rubbingdirection and the consequent LC molecule orientation resultedalong the grooves.
The glass cover was glued by using a UV-curable adhesive.Two opposite sides along the rubbing direction were left open
1086 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 42, NO. 10, OCTOBER 2006
Fig. 2. Picture of three LC channel waveguides taken under a polarized micro-scope. The waveguide width is 10 �m.
to allow a better and complete filling of the LC. The filling pro-cedure is quite simple and is based on capillary forces actingon the LC inside the cell. A small drop of the NLC E7, a well-known commercial mixture supplied by Merck, was placed atthe border of the glass, such that the LC fills the cell followingthe rubbing direction. The filling was accomplished in vacuumat the temperature of 70 C, at which the NLC E7 is in itsisotropic phase. After filling the cell was cooled down to roomtemperature and completely sealed with the same UV-curableadhesive.
The alignment was observed under a polarized microscopein reflection mode. This revealed that the LC molecules areoriented along the rubbing direction. Fig. 2 shows the top viewof LC channels, whose maximum width is 10 m approxi-mately. Angled sidewalls form a shallow greyshaded contourof the LC waveguide, since they correspond to the (111) slantedplanes, for which light cannot be reflected back into the mi-croscope objective. In the picture of Fig. 2, a small leakage ofLC occurred between the silicon substrate and the glass cover.This inconvenience can be avoided by optimized processingconditions.
The waveguide maximum depth is precisely defined by sil-icon etching, which is 7 m in this case. This simultaneously de-fines three boundary conditions, top and two sidewalls, withoutany need for spacers, which are required in standard LC cellsinstead.
A pretilt angle of the molecules with respect to the glasscover was expected as sketched in Fig. 3. Such an angle is de-termined by the anchoring surface energy at LC-alignment layersurface. The pretilt angle is an important parameter for deter-mining the waveguiding behavior.
The most common method for the determination of pretilt inLC devices works better for a sufficiently extended layer of LC[20]. Here the LC material is confined in the groove making thedirect determination of the pretilt far from being a straightfor-ward task.
Fig. 3. Schematic illustration of a V-groove filled with LC molecules alignedalong the direction of propagation z. Inset shows the pretilt angle of the LCmolecules with respect to the surface of the alignment layer. This and the SiObuffer are not shown for sake of figure clarity.
Fig. 4. Modal analysis (m = mode order) of the 10-�m-wide LC waveguideversus LC pretilt angle.
B. Modal Analysis and Pretilt Angle
The pretilt angle induces a refractive index step betweenthe waveguide core and the surrounding hybrid cladding for aquasi-TM mode. To have a better insight into the influence ofthe pretilt, a modal analysis of the LC channel both by a finiteelement method [21], [22] and by a 3-D semi-vectorial BPMwas computed. The analysis was carried out at the wavelengthof 1550 nm for a waveguide width m. Both methodsgive similar results.
In the modal analysis the refractive index of the LC isthe one seen by a TM polarized input light and varies with thepretilt angle according to the following formula:
(2)
where and are, respectively, the extraordinary and theordinary refractive indexes of the LC. Equation (2) takes intoaccount that the optical axis of the LC is along the long axis ofthe rod-like shape geometry of the molecules.
In Fig. 4, the effective refractive indexes of the first five modessupported by a LC channel waveguide versus the pretilt angleare plotted. Measured extraordinary and ordinary refractive in-dexes of the NLC E7 were used in the calculations:and [23], [24]. The plots of Fig. 4 indicate that thewaveguide is cut-off for a pre-tilt angle below about 15 and
D’ALESSANDRO et al.: NEMATIC LIQUID CRYSTAL OPTICAL CHANNEL WAVEGUIDES ON SILICON 1087
Fig. 5. Contour maps of the first five modes propagating in the triangular LCwaveguide.
becomes multimode if the pre-tilt is larger than 24 . In the caseof nylon 6 as alignment layer, pretilt angles below 3 is gen-erally obtained. The tilt angle can be controlled by applying anelectric field along the vertical direction and exploiting the elec-trooptic effect in the LC. In this case, in absence of an electricfield, an effective average pretilt angle higher than 10 can bedue to some unevenness resulting from compressive stress ofthermally grown silicon oxide in the bottom of the V-groove, asobserved at the microscope before filling.
However, the rubbing only on the coated glass plate, differ-ences in the materials surrounding the LC (thermally grownSiO and nylon) and the very confining unconventional geom-etry may play some role as well.
Fig. 5 shows the contour maps of the first five modes, whichcan be supported by the waveguide when the LC tilt angle isabout 37 . It is rather evident how the modes follow the trian-gular shape of the cross section of the waveguide.
III. EXPERIMENTAL
A. Setup
Fig. 6 shows the optical setup used to investigate the opticalpropagation through the LC waveguides and in particular toquantify their capability of polarized light propagation. Inputand output facets of the waveguides were cut in order to couplelight by butt-coupling technique. The laser source is an external-cavity tunable laser emitting wavelengths ranging from 1510 to1590 nm.
A pigtailed polarization controller was connected to a singlemode fiber (SMF), terminated with a cleaved face to couple
Fig. 6. Measurement set-up to visualize and acquire the modal profile of theLC optical waveguide output. TL: tunable laser; SMF: single mode fiber; LCW:liquid crystal waveguide; OB: microscope objective; FG: frame grabber.
light to the LC optical channel waveguides. The polarizationcontroller consists in a sequence of three miniature waveplates
placed between two aligned fiber collima-tors. Each waveplate is mounted on a graduated goniometer,which allows rotation angles with a resolution of 5 of the inputlight without power variation. After calibrating the input lightby means of a polarizer before coupling the cleaved fiber withthe waveguides, it was possible to measure the state of polariza-tion of light injected into the waveguides. The optical waveguideoutput was collected by a 10X microscope objective (with nu-merical aperture equal to 0.2) and focussed on an IR vidiconcamera. The optical field image was acquired by using a framegrabber and then processed. In order to measure the output in-tensity and the optical loss, the objective was replaced by asecond cleaved SMF aligned to the waveguide output facet. Theoutcoming light was then measured by an optical power meter.
B. Measurements
We have characterized 10- m-wide 2-cm-long waveguides.Insertion loss, coupling and propagation losses were estimatedby following a procedure similar to the one described by Zouet al. [25]. The insertion loss measured by collecting the lightwith an SMF at the waveguide output resulted 30 dB approxi-mately. In order to measure the coupling loss, the output SMFwas replaced by the microscope objective using the same inputSMF. The coupling loss, calculated as difference between theoutput power collected by the objective and output power cou-pled to the SMF, resulted about 10 dB/facet. By subtracting thetotal coupling loss of 20 dB for both facets from the insertionloss, a propagation loss of 5 dB/cm was estimated.
Fig. 7(a) represents the image of the output near-field formaximum optical transmission. A good confinement can be ob-served from the slightly saturated image given by the IR camera.Nevertheless, some light external to the LC channel, inside thesilicon, can be observed as a consequence of the scattering fromthe irregular input and output faces of the waveguide.
This explains most of the observed large insertion loss. Infact it is not trivial to obtain sharp facets from a sandwich madeof silicon and common glass. An optical inspection of the end-faces of the sample revealed many chips on the Si edge. In factfacets were not lapped, nor polished, nor matching fluid wasused. Further sources of loss are the irregular input and outputedges of the waveguide made of the UV curable adhesive em-ployed to seal the edges of the sample. Several tens of microm-eters at the beginning and end of the waveguide consist of LCdroplets in the glue, which scatter light as visible in Fig. 7(a).
1088 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 42, NO. 10, OCTOBER 2006
Fig. 7. Output beam from an LC channel waveguide. (a) Snapshot of opticalnear-field captured by the IR-vidicon camera. (b) Digitalized image of the outputbeam by using a frame grabber and a laptop PC.
Better adhesive-LC input and output interfaces can be defi-nitely obtained by controlling the profile of the adhesive edges.Some preliminary tests have been resulted successful in thissense [26] so coupling losses can be reduced.
The propagation losses are due to two main reasons. The firstone is related to the poor alignment in the groove which inducesvisible defects and the second reason is related to some defectsin the grooves. Both loss sources can be greatly attenuated byan improved fabrication process. Therefore, much lower totallosses can be reasonably expected in a next generation of LC onSi waveguides.
The intensity profile of the light spot is reported in Fig. 7(b).The spot profile was obtained after converting the snapshot fromthe IR camera in numerical format. The field profile given byFig. 7(b) shows a sharp peak in the region of the LC wave-guide, consistent with single-mode propagation. The beam-sizeis slightly larger than 10 m, the maximum width of the LCwaveguide. Single-mode propagation was experimentally ob-served over the entire tuning range of the laser source. This sug-gests an effective average pretilt angle between 15 and 23 , asindicated by Fig. 4.
Fig. 8. BPM simulation of the optical electric field, for y = �1:5 �m, propa-gating along the LC waveguide for (a) vertical and (b) horizontal polarization.
C. Polarization Dependency
Dependency of propagation on input light polarization wasalso evaluated. By varying the input polarization it was evidentthat maximum transmission was obtained for vertical polariza-tion. It was also observed that light intensity gradually decreasedas input polarization became horizontal.
A simulation of the LC waveguide behavior with respect toinput light polarization was carried out by means of BPM to re-produce the experimental results on the polarization dependenceof light propagation.
Fig. 8 shows the propagation of the optical electric field am-plitude launching as input field a fiber mode, whose profile isthe one of a standard SMF with a core diameter of 8 m.
A pretilt angle of 15 , for which the vertical polarization“sees” the maximum LC refractive index equal to 1.5107,was considered. The graphs of Fig. 8 refer to a depth of about1.5 m from the LC-glass interface where the electric fieldintensity is maximum. The behavior of the electric field inFig. 8(a) shows that propagation is allowed when polarizationof input light is vertical as found experimentally. Horizontallypolarized light does not propagate along the LC waveguide,as shown in Fig. 8(b), since it “sees” the minimum LC refrac-tive index for which the waveguide is in cut-offcondition.
Fig. 9 reports the plot of the polarization extinction ratio,both measured (circles) and numerically calculated (squares) byusing the 3-D BPM, versus input light polarization angle. The
D’ALESSANDRO et al.: NEMATIC LIQUID CRYSTAL OPTICAL CHANNEL WAVEGUIDES ON SILICON 1089
Fig. 9. Calculated (squares) and measured (circles) output power normalizedwith respect to horizontally polarized output light versus polarization orientationfrom horizontal or quasi-TE (0 ) to vertical or quasi-TM (90 ).
polarization extinction ratio is defined as the output power nor-malized with respect to horizontally polarized output light.
The orientation of the polarization axis is measured with re-spect to horizontal axis. The plot of Fig. 9 shows that the trans-mitted power increases as polarization is rotated from horizontalto vertical. Such behavior is easily explained by the fact that aspolarization becomes vertical the refractive index of the LC inthe channel waveguide becomes closer to the extraordinary re-fractive index of the LC according to (1). Vertically or quasi-TMoutput light is more than 25 dB higher than horizontally orquasi-TE polarized light.
IV. CONCLUSION
This work has shown a novel waveguiding structure made ofa NLC core filling oxidised silicon grooves. Single mode prop-agation has been designed and experimentally demonstratedfor near infrared light at wavelengths of standard optical fibers.Propagation loss of 5 dB/cm and 10 dB/facet coupling losscan be drastically reduced by improving the overall fabricationprocess. In fact, further improvements are possible since nobasic limitation seems to exist. Although losses are still sig-nificant, this first prototype shows the lowest propagation lossreported so far for an optical waveguide using an NLC as acore.
Such NLC waveguides behave as high extinction ratio inte-grated optics polarizers by exploiting LC optical anisotropy.Only TM-like propagation was supported by 10- m-widewaveguides, since the NLC are oriented along the propagationdirection, with a small pretilt angle. The orthogonal polarizationresulted to be suppressed by more than 25 dB.
The experimental behaviour and orientation of LC in theseunconventional channel waveguides are well fitted by standardBPM simulations.
As a perspective of this work, the control of the molecularpretilt angle of LC by applying an external electric field willlead to a new generation of active integrated optic devices onsilicon.
ACKNOWLEDGMENT
The authors wish to thank Dr. I. G. Manolis for enlighteningdiscussions.
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Antonio d’Alessandro (M’97–SM’06) was born inFoggia, Italy, in 1963. He received the Laurea (cumlaude) and Ph.D. degrees in electronic engineering atPolitecnico of Bari, Bari, Italy.
He joined Bell Communication Research asVisiting Scientist in 1992 and was PostdoctoralMember of the Technical Staff until 1994, makingsignificant scientific contribution to the developmentof integrated acoustooptic filters/switches for wave-length division multiplexing optical communicationsystems. Since 1994, he has been with the Depart-
ment of Electronic Engineering of University of Rome “La Sapienza,” Rome,Italy, as an Assistant Professor and became Associate Professor from 2002. Hehas been teaching the courses of photonics, optoelectronics and optoelectronicsystems. He is responsible for research projects funded by the EuropeanCommunity and by the Italian Government. His background and his researchactivity is related to lightwave electrooptic switching devices and systems, inparticular integrated optic switches for fiber optic communication systems, andelectrooptic sensor systems. Recently, he has been pioneering liquid crystaland composite materials based photonic devices on glass and on silicon.
Dr. d’Alessandro is a member of Optical Society of America, the OpticalSociety of Optical Engineering, and the Steering Committee of the Italian LiquidCrystal Society.
Bob Bellini was born in Middelburg, South Africa,in 1972. He graduated from the Ecole Polytechnique,Palaiseau, France, in 1996 and from Supélec, Gif-sur-Yvette, France, in 1998. He received the Ph.D. degreein 2000 from the University of Lille, Lille, France, onthe modeling and technology of optical switching inpolymer waveguides.
From 2001 to 2003, he was a Research Fellowat the Technological Center of the European SpaceAgency (ESTEC—ESA), The Netherlands. Since2003, he has been working as a Young Researcher
with the European Training and Mobility Research Network “SAMPA,” Uni-versity of Rome “La Sapienza,” Rome, Italy, and at the Polytechnic Universityof Madrid, Spain. He is now working at the University of Rome “La Sapienza”and the National Research Council (CNR), Rome, Italy. His research focuseson the technology of liquid crystals on silicon substrate.
Domenico Donisi (S’06) was born in Rome, Italy, in1980. He received the diploma degree in electronicengineering in 2004 and is currently working towardthe Ph.D. degree at the University of Rome “LaSapienza,” Rome, Italy.
His main research interests include design and re-alization of integrated optic devices based on liquidcrystals for optical communication systems as well asfiber sensors for environmental monitoring.
Romeo Beccherelli was born in Plovdiv, Bulgaria,in 1969. He received the Laurea degree (cum laude)in electronic engineering in 1994 and the Ph.D.degree in 1998, both from University of Rome “LaSapienza,” Rome, Italy. The doctoral thesis focusedon analog grayscale ferroelectric liquid crystaldisplays and its driving circuitry.
In 1995, he served in the Technical Corps ofthe Italian Army as a Second Lieutenant. In 1997and 2001, he was Visiting Research Fellow at theDepartment of Physics, Division of Microelectronics
and Nanoscience, Chalmers University of Technology , Gothemburg, Sweden.In 1997, he joined the Department of Engineering Science, University ofOxford, Oxford, U.K., as a Postdoctoral Research Assistant and in 2000, hejoined the Department of Electronic Engineering, University of Rome “LaSapienza,” Rome, Italy, as a Research Fellow. In 2001, he was appointedResearcher at the Institute for Microelectronics and Microsystems of the ItalianNational Research Council in Rome. His initial research interests in liquidcrystal display technology have evolved into photonics based on liquid crystaland silicon.
Dr Beccherelli’s doctoral thesis was awarded the International Otto LehmanPrize 1999 in liquid crystal technology by the University of Karlsruhe, Karl-sruhe, Germany, and the Otto Lehmann Foundation.
Rita Asquini received te M.Sc. degree in electronicengineering (cum laude) in 1998 from University ofRome “Roma Tre,” Rome, Italy, and the Ph.D. degreein electronic engineering in 2002 from University ofRome “La Sapienza”, Rome, Italy.
From 1998 to 2000, she worked for Telecom Italiaon Service Assurance of Communication Networksand since 2002, she has been a Research Fellowwith the Department of Electronic Engineering,University of Rome “La Sapienza.” She is also anAdjunct Professor of electronics with the Faculty of
Engineering. Her main research interests include modeling, fabrication, andcharacterization of guided-wave as well as free-space optoelectronic deviceswith liquid crystals and polymers. For these activities, she was recently awardeda prize from the Italian Liquid Crystal Society.
