Fast Electro-optic Modulation Research Articles

Experimental study on polarization evolution locking in a stretched-pulse fiber laser.

Polarization evolution locking (PEL) of a stretched-pulse fiber laser is experimentally investigated with a simple pulse selection method based on a fast electrooptic modulator, capable of revealing the temporal and spectrum evolution of the PEL pulses. Moreover, the wavelength dependence of PEL is observed by spectrally filtering the pulses and is further investigated for individual fiber laser comb lines through beat note measurements with narrow-linewidth cw lasers.

Active modulation of visible light with graphene-loaded ultrathin metal plasmonic antennas.

Electro-optical modulation of visible and near-infrared light is important for a wide variety of applications, ranging from communications to sensing and smart windows. However, currently available approaches result in rather bulky devices, suffer from low integrability, and can hardly operate at the low power consumption levels and fast switching rates required by microelectronic drivers. Here we show that planar nanostructures patterned in ultrathin metal-graphene hybrid films sustain highly tunable plasmons in the visible and near-infrared spectral regions. Strong variations in the reflection and absorption of incident light take place when the plasmons are tuned on- and off-resonance with respect to externally incident light. As a result, a remarkable modulation depth (i.e., the maximum relative variation with/without graphene doping) exceeding 90% in transmission and even more dramatic in reflection (>600%) is predicted for graphene-loaded silver films of 1–5 nm thickness and currently attainable lateral dimensions. These new structures hold great potential for fast low-power electro-optical modulation.

Second-Order Nonlinear Optical Susceptibilities of Nonelectrically Poled DR1–PMMA Guest–Host Polymers

Guest-host nonlinear optical polymers have attracted considerable interest due to their applications in fast electro-optical modulators and wavelength converters. In general, the electrical poling procedures, for which high DC external fields are applied, are necessary for aligning guest chromophores in polar order and activating the second-order nonlinearity. We present the nonelectrical poling behaviors for guest-host polymers: DR1 (4-[ethyl (2-hydroxyethyl) amino]-4'-nitroazobenzene) is the guest, and PMMA (poly (methyl methacrylate)) is the host. Second-order nonlinear optical susceptibility was induced in the conventional guest-host polymers after annealing at temperatures above the glass transition points of the host polymer even without applying the external fields. This phenomenon did not occur in the side-chain polymers, where the guests were directly bonded to the host chains. The guest polar alignments were most likely generated from the guest hydroxyl groups chemisorbing on the substrates. The polar alignments of the guest formed not only near the surface of the substrate, but also inside the host polymers. The optimized conditions for the SHG conversion were examined in the context of the polymer film thickness and guest concentration. The nonelectrical poling techniques described in this study are useful for enhancing the surface nonlinearity in the several materials, and they will be useful for further developments in nanophotonics and plasmonics.

Highly promising electrooptic material: Distorted helix ferroelectric liquid crystal with a specific tilt angle

Short pitch deformable helix ferroelectric liquid crystals are shown to become optically isotropic at certain critical tilt angle with an average dielectric constant (ε1+ε2+ε3)/3. For uniaxial medium, this angle equals θd=cos−1(1/3), and it depends weakly on the local biaxial anisotropy. The degeneracy is removed upon the application of a small electric field and the medium becomes optically biaxial. A high contrast fast electrooptic modulation and display devices can be built using such materials even when aligned in a multi-domain. For tilt angles very near the degeneracy angle, ultrasensitivity of the eigenaxes rotation to the applied field is found.

A 25 ns switching time Mach­Zehnder modulator in as-deposited a-Si:H

A very simple and fast Mach-Zehnder electro-optic modulator based on a p-i-n configuration, operating at λ = 1.55 μm, has been fabricated at 170 °C using the low cost technology of hydrogenated amorphous silicon (a-Si:H). In spite of the device simplicity, refractive index modulation was achieved through the free carrier dispersion effect resulting in characteristic rise and fall times of ~2.5 ns. By reverse biasing the p-i-n device, the voltage-length product was estimated to be V(π)∙L(π) = 40 V∙cm both from static and dynamic measurements. Such bandwidth performance in as-deposited a-Si:H demonstrates the potential of this material for the fabrication of fast active photonic devices integrated on standard microelectronic substrates.

Electrical Design of High-Speed Electro-Optically Modulated Coupled-Cavity VCSELs

We present an equivalent circuit cut-off frequency analysis of a Coupled-Cavity Vertical-Cavity Surface-Emitting Laser with one cavity used as a fast electro-optic modulator with lumped electrodes. We find that the mesa capacitance and the polyimide capacitance and series resistance are the most influencing parameters. In order to enhance the -3 dB bandwidth the design steps should be: reduction of the contact pad area and modulator mesa radius together with increasing the modulator cavity length, as well as implementing a pnp structure. Based on the model, we suggest a realistic structure that is theoretically able to achieve about 100 GHz modulation speed.

Design study of integrated photonic transmitters for application in Fiber-to-the-Home networks

Different solutions of photonic transmitters based on arrayed waveguide gratings are demonstrated. The basic concepts of realizing integrated multiwavelength lasers with optical modulators are presented and discussed in detail. Full Text: PDF References M. K. Smit, "New focusing and dispersive planar component based on an optical phased array", Electron. Lett. 24(7), 385 (1988). [CrossRef] M.K. Smit, 3rd Int. conference on Optics-photonics Design and Fabrication, 51-52, Tokyo 1, 30 Oct. - 1 Nov. 2002, Optical Society of Japan, 2002. J.H. den Besten, Integration of Multiwavelength Lasers with Fast Electro-Optical Modulators, PhD Thesis, 2004. B.Docter, Deeply-Etched DBR Mirrors for Photonic Integrated Circuits and Tunable Lasers, PhD Thesis, 2009. S. C. Nicholes, M. L. Masanovic, B. Jevremovic, E. Lively, L. A. Coldren, and D. J. Blumenthal, "An 8$,times,$ 8 InP Monolithic Tunable Optical Router (MOTOR) Packet Forwarding Chip", J. Lightwave Techn. 28(4) Feb. (2010). [CrossRef] R.Broeke, A Wavelength Converter Integrated with a Discretely Tunable Laser for Wavelength Division Multiplexing Networks, PhD Thesis, 2003. F.M. Soares, J.H. Baek, N.K. Fontaine, C. Junesand, S. Lourdudoss, K.Y. Liou, R.A. Hamm, W. Wang, B. Patel, W.S. Hobson, J.R. Lothian, S. Vatanapradit, L.A. Gruezke, W.T. Tsang, and S.J.B. Yoo, Optical Fiber Communications Conference, Paper OThS1, 2010. H. Yang, M. Chin, J. Zhou, S. Lee, W. Chen, and H. Zhu, "A traveling-wave electroabsorption modulator with a large optical cavity and intrastep quantum wells", Semicond. Sci. Technol. 23, 105011 (2008). [CrossRef] J.H. den Besten, D. Caprioli, W. Pascher, R. van Dijk, X.J.M. Leijtens, M.K. Smit, "Simulation and design of a 40 GHz Mach?Zehnder modulator on InP", Proceedings of the Symposium on IEEE/LEOS Benelux Chapter, Amsterdam, 2002, pp. 123?126 H.N. Klein, H. Chen, D. Hoffmann, S. Staroske, A.G. Steffan, K.-O. Velthaus, "1.55?m Mach- Zehnder Modulators on InP for Optical 40/80 Gbit/s Transmission Networks", International Conference on Indium Phosphide and Related Materials Conference Proceedings, 171?173, 2006 [CrossRef]

Electro-optical modulator in a polymerinfiltrated silicon slotted photonic crystal waveguide heterostructure resonator

We present a novel concept of a compact, ultra fast electro-optic modulator, based on photonic crystal resonator structures that can be realized in two dimensional photonic crystal slabs of silicon as core material employing a nonlinear optical polymer as infiltration and cladding material. The novel concept is to combine a photonic crystal heterostructure cavity with a slotted defect waveguide. The photonic crystal lattice can be used as a distributed electrode for the application of a modulation signal. An electrical contact is hence provided while the optical wave is kept isolated from the lossy metal electrodes. Thereby, well known disadvantages of segmented electrode designs such as excessive scattering are avoided. The optical field enhancement in the slotted region increases the nonlinear interaction with an external electric field resulting in an envisaged switching voltage of approximately 1 V at modulation speeds up to 100 GHz.

Continuous-wave single-sampling-point characterisation of optoelectronic on-chip terahertz transceiver

Fast electro-optic modulation of the terahertz phase, single-sampling-point lock-in detection and the use of interdigitated-finger photomixers improve the dynamic range of the transceiver by several orders of magnitude compared with standard chopping techniques. This allowed the frequency range of the continuous-wave on-chip terahertz transceiver to be extended beyond 1THz, which is roughly a factor of five improvement compared to previous reports.

Intercalated Smectic A Phases in Banana‐Shaped Liquid Crystals with Carbonate End Groups

Novel, symmetrical, bent-core mesogens, namely substituted 1,3-phenylenebis{4'-[(ethoxycarbonyl)oxy]-1,1'-biphenyl}-4-carboxylates, are prepared with carbonate groups at both ends of the molecules. The mesophase properties are investigated for different electron-donating and -withdrawing substituents connected to the central ring at different positions. These compounds exhibit nematic and/or smectic A intercalated (SmA(int)) mesophases. Electro-optical studies show a very significant electric-field-induced biaxiality that is fast (<1 ms) and large (0.03) associated with a high birefringence (0.33 at 500 nm, 10 V mum(-1) field) for the unsubstituted analogue. For one substance this effect is observable from above 100 degrees C down to room temperature. Such electric-field-induced biaxiality may find practical applications in fast electro-optic modulation devices.

Polymers for Electro‐Optical Modulation

Second‐order nonlinear optical (NLO) properties of polymeric materials have been attracting a lot of attention, especially for such potential applications as fast waveguides electrooptic (EO) modulation and frequency‐doubling devices. For these photonic applications, the performance of the NLO materials has to be optimized. This requires not only a fundamental knowledge of inter‐relationship between their chemical and NLO properties, but new technologies competitive or superior to existing ones as well. This review focuses on the synthesis of NLO polymers including chromophore design, and the comparison among comprehensive EO polymer systems. Moreover, characterization and device fabrication of electro‐optical polymer planar waveguides are also reported in this review.

In-fiber nematic liquid crystal optical modulator based on in-plane switching with microsecond response time

We describe a simple method and device design that enables fast in-plane electro-optic modulation in conventional nematic liquid crystal (NLC) devices. When combined with optimized NLC materials, this approach yields rotational speeds of 1°/μs (independent of rotation angle, over a wide range) at a moderately low voltage. The observed rotational dynamics indicate that even these high speeds may not represent fundamental physical limits. We demonstrate these ideas in a compact tunable NLC waveplate that uses microelectrodes patterned directly on the tips of optical fibers. These devices offer fast, continuously tunable optic axis with low insertion loss and good performance in the near infrared. Modulators that use this design have promising potential applications for polarization control and analysis in optical communication systems.

Investigation of the electro-optic properties of electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer

The electro-optic property of electron-irradiated poly- (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymer is presented. It is found that this special treated polymer not only has a giant electrostriction and relaxor ferroelectric behavior but also has a relatively good electro-optic effect. Thus, this copolymer may be a good candidate for making fast speed electro-optic modulators and switches, which are critical components for information optics.

Hot-carrier-transport-governed nonresonant optical nonlinearity: transient Gunn-domain grating

We review recent investigations of nonlinear carrier transport and related optical nonlinearities in GaAs and InP crystals for the case in which photoexcited carriers are nonuniformly heated by a strong external electric field and are redistributed in a spatially nonuniform internal electric field. We simulated the nonequilibrium carrier and internal field spatial evolution in picosecond and nanosecond time domains and estimated criteria for bipolar high-field Gunn-domain grating formation in dc and ac fields. The coexisting refractive-index modulation mechanisms for free-carrier and electro-optic nonlinearities are analyzed for various external field strengths, grating periods, and excitation levels, thus providing conditions for an efficient and fast electro-optic refractive-index modulation by the transient Gunn-domain grating. Comparison of the experimentally observed enhancement of light’s self-diffraction efficiency with numerical calculations has confirmed that the nonresonant electro-optic Gunn-domain-based nonlinearity may exceed the free-carrier nonlinearity.

Measurement and compensation of frequency chirping in pulsed dye laser amplifiers

Rapid changes of the refractive index in the active medium of a pulsed, excimer laser pumped dye laser amplifier were investigated with an optical heterodyne technique. Time-dependent shifts in the phase of optical light waves could be observed which for Coumarin 102, 153 and 307 dyes at wavelengths of 488 and 550 nm depend predominantly on the thermal properties, in particular, on the expansitivity of the dye solutions. A fast Electro-Optic Modulator (EOM) using LiTaO3 crystals has been designed for compensating these phase perturbations. With appropriately shaped voltage pulses applied to the EOM the resulting changes in the instantaneous frequency of the pulsed laser output could be lowered by a factor of 4 with respect to the values measured in the uncompensated light.

A Novel and Perfectly Aligned Highly Electro−Optic Organic Cocrystal of a Merocyanine Dye and 2,4-Dihydroxybenzaldehyde

A Novel and Perfectly Aligned Highly Electro−Optic Organic Cocrystal of a Merocyanine Dye and 2,4-Dihydroxybenzaldehyde

Design and synthesis of ferroelectric liquid crystals. 24. Incorporation of the disperse red 1 chromophqre into side-by-side dimers for nonlinear optics

ABSTRACTWith excellent processibility on silicon integrated circuits and thermodynamically stable polar order, ferroelectric liquid crystals (FLCs) show great potential as components of fast integrated electro-optic modulators. In order to realize this potential, however, an increase in the magnitude of the electronic secona order nonlinear susceptibility χ(2) is required. This has been problematical since functional arrays with large molecular second order susceptibility β orient with improper supermolecular stereocontrol (i.e. with the charge transfer axis normal to the polar axis) when incorporated into traditional FLC structures. Herein we present examples of a new LC structural class designed to achieve the proper supermolecular structure for large χ(2) in FLCs. The observed sign and magnitude of the ferroelectric polarization of the new mesogens extrapolated from smectic C* mixtures is fully consistent with the desired supermolecular structure.

Linear optical switching in a FLC/waveguide composite device

Abstract A fast electrooptic modulation in a polymer waveguide using a ferroelectric liquid crystal has been proposed. In this device, the surface stabilized ferroelectric liquid crystal and the soft mode ferroelectric liquid crystal are used as an active material on the passive polymer waveguide, and electrooptic switching is realized by controlling the total reflection at the polymer waveguide-liquid crystal interface. The response time is of the order of several microseconds. The analogue electrooptic modulation in the waveguide is realized using the field induced linear molecular tilt of the electroclinic effect in the soft mode ferroelectric liquid crystal.

Electrooptic Modulation in the Optical Waveguide Using Ferroelectric Liquid Crystal

A fast electrooptic modulation in the polymer waveguide using ferroelectric liquid crystal has been proposed. In this device, the soft mode ferroelectric liquid crystal (SMFLC) is used as an active material on the passive polymer waveguide, and electrooptic switching is realized by controlling the total reflection at the polymer waveguide-liquid crystal interface. The response time is of the order of several microseconds. An analogue electrooptic modulation in the waveguide is realized using the field-induced linear molecular tilt of the electroclinic effect in SMFLC.

Candidate materials and technologies for integrated optics: fast and efficient electro-optic modulation

This review discusses the linear electro-optic effect and how it is used in the fabrication of light modulators in a variety of different material systems. Lithium niobate is chosen as the foremost example of a suitable material since it currently forms the base for the most mature technology, although newer research on semiconductors and electro-optic polymers is also addressed. The fundamentals of modulator design which lead to the possibility of fast and efficient modulation are covered, as are some of the problems that are typically encountered during the realization of working devices.