Electro-optic Switch Research Articles

High-speed electro-optic switch based on nonlinear polymer-clad waveguide incorporated with quasi-in-plane coplanar waveguide electrodes

Nonlinear optical (NLO) polymer is a promising material for active waveguide devices that can provide large bandwidth and high-speed response time. However, the performance of the active devices is not only related to the waveguide materials, but also related to the waveguide and electrode structures. In this paper, a high-speed Mach–Zehnder interferometer (MZI) type of electro-optic (EO) switch based on NLO polymer-clad waveguide was fabricated. The quasi-in-plane coplanar waveguide electrodes were also introduced to enhance the poling and modulating efficiency. The characteristic parameters of the waveguide and electrode were carefully designed and simulated. The switches were fabricated by the conventional micro-fabrication process. Under 1550-nm operating wavelength, a typical fabricated switch showed a low insertion loss of 10.2 dB, and the switching rise time and fall time were 55.58 and 57.98 ns, respectively. The proposed waveguide and electrode structures could be developed into other active EO devices and also used as the component in the polymer-based large-scale photonic integrated circuit.

Optically-Enabled Bloom Filter Label Forwarding Using a Silicon Photonic Switching Matrix

Simplified forwarding schemes relying on Bloom filter (BF)-based labels emerge as a promising approach for coping with the substantial increase in lookup table memory requirements associated with the growing number of end-hosts in DataCenters. In this paper, we present for the first time the successful implementation of a BF-label forwarding scheme over a silicon photonic switch fabric and we demonstrate its functionality with 10 Gb/s data packets that carry BF-encoded labels. The optically enabled BF-label forwarding setup utilizes a Si-based 4 × 4 electro-optic switch directly controlled by an amplifier-less and digital-to-analog-converter-less high speed Field Programmable Gate Array board. The FPGA is responsible for extracting the BF-label from the incoming packets and for carrying out the BF-based forwarding function, determining the appropriate switching state towards conveying incoming packets to the desired output. The use of BF-label forwarding allows for rapid switch reconfiguration avoiding the need for large look-up table updates as the network topology changes and devices are added, removed or simply change physical location. Successful operation for 10 Gb/s data packets has been obtained for a 1 × 4 routing layout.

Fabrication of new photoreactive vertical alignment thin layers for fast switching liquid crystal display

New photoreactive vertical alignment layers have been fabricated by spin coating the mixtures of polyimide (PI) and bi-functional monomers on the indium tin oxide substrate. Post ultraviolet (UV) surface treatment under electric field induced fast electro-optical switching of liquid crystal (LC) through formation of pre-tilted alignment layer. To investigate the effect of reactive monomers on the electro-optical properties of LC device, newly designed four types of monomers with different aromatic cores and photoreactive groups were applied to PI mixtures. Stable homeotropic alignment and fast response time in the LC device were achieved with a simple coating and subsequent UV process of monomer with both a phenyl core and methacrylic groups in the PI layer and it yields electro-optical performance superior to that achieved with the conventional PI alignment layer. This elegant approach provides a stable and fast switching LC alignment layer for high performance LC displays.

Designing ultra-compact high efficiency electro-optical plasmonic switches by using of nanocavity reflectors

An ultra-compact plasmonic electro-optical (EO) switch based on a silver-insulator-silver bus waveguide coupled to two nanocavity reflectors and two drop cavities is introduced. All cavities are filled with 4-dimethylamino-N-methyl-4-stilbazolium tosylate as an EO material. Finite difference time domain (FDTD) method and coupled-mode-theory (CMT) approaches are used to numerically and theoretically investigate the properties of the device. Results reveal that the proposed device can work properly as 1×1 and 1×2 switches. By inserting nanocavity reflectors, one can improve the performance of the switches. Results are shown for switches with single and double nanocavity reflectors operating at 984 nm and 1560 nm, respectively. A transmission of 0.83 (0.77) and modulation depth of 31.41 dB (17.72 dB) at the wavelength of 1560 nm (984 nm) could be obtained. The proposed device has potential nanophotonic applications due to simple geometry and compactness.

Broadband 2 × 2 lithium niobate electro-optic switch based on a Mach-Zehnder interferometer with counter-tapered directional couplers.

We demonstrate a broadband 2×2 electro-optic switch based on a Mach-Zehnder interferometer with counter-tapered directional couplers (DCs). The counter-tapered DC is introduced here to replace the conventional one formed with uniform waveguides so that a splitting ratio of 50%∶50% is much easier to be realized over a wide wavelength range and, hence, increase bandwidth of the switch. The proposed switch is fabricated with x-cut lithium niobate by the annealed proton exchange process. A comparison of several experimental devices, fabricated on the same chip with the conventional and different counter-tapered DCs, respectively, confirms the increase of the bandwidth and the improvement of the fabrication tolerance by using the counter-tapered DC. Our fabricated best device, which has a length of ∼22 mm, exhibits an ∼85 nm bandwidth for an extinction ratio (ER) higher than 15dB and a maximum ER of ∼35 dB at 1563nm at a driving voltage of 6.0V. The insertion losses are less than 8.5dB for all channels. Our proposed optical switch could find applications in wavelength-division-multiplexing optical communication systems.

Command Electro-Optical Switching of Photoaligned Liquid Crystal on Photopatterned Graphene

We report command electro-optical switching on photolithographically-patterned graphene into a high-density electrode pattern for a high-transmission in-plane-switching (IPS) liquid crystal device. A highly-effective liquid crystal photoalignment method is used to maximize the field-driven optical contrast of a prototyped device. A non-contact and low-temperature photoalignment allows delicate surface treatment required for successful processing of graphene layer into an IPS electrode structure. Electro-optic performance of the graphene-based single pixel laboratory IPS prototype demonstrates the application potential of graphene for liquid crystal electro-optic devices with complex and high-definition electrode patterns.

16 × 16 Silicon Optical Switch Based on Dual-Ring-Assisted Mach–Zehnder Interferometers

In this paper, we report a nanosecond 16 × 16 silicon electro-optic switch chip based on a Benes architecture. The switch adopts dual-ring-assisted Mach–Zehnder interferometers as the basic building blocks. In each switch element, both TiN microheaters and PIN diodes are integrated for ring resonance alignment and high-speed switching, respectively. A transfer-matrix-based theoretical model is established to analyze the switch performances. The 16 × 16 switch is characterized by measuring the optical transmission spectra and quadrature phase-shift keying (QPSK) data transmission through 16 representative optical paths. The insertion loss of the entire switch chip is 10.6 ± 1.7 dB and the crosstalk is less than −20.5 dB. The 32-Gb/s QPSK signal is successfully switched to different destination ports by reconfiguring the optical paths, verifying the signal integrity after switching.

Room temperature operation of electro-optical bistability in the edge-emitting tunneling-collector transistor laser

Optical bistable devices are fundamental to digital photonics as building blocks of switches, logic gates, and memories in future computer systems. Here, we demonstrate both optical and electrical bistability and capability for switching in a single transistor operated at room temperature. The electro-optical hysteresis is explained by the interaction of electron-hole (e-h) generation and recombination dynamics with the cavity photon modulation in different switching paths. The switch-UP and switch-DOWN threshold voltages are determined by the rate difference of photon generation at the base quantum-well and the photon absorption via intra-cavity photon-assisted tunneling controlled by the collector voltage. Thus, the transistor laser electro-optical bistable switching is programmable with base current and collector voltage, and the basis for high speed optical logic processors.

Enhancement of polar anchoring strength in a graphene-nematic suspension and its effect on nematic electro-optic switching.

A small quantity of monolayer graphene flakes is doped in a nematic liquid crystal (LC), and the effective polar anchoring strength coefficient between the LC and the alignment substrate is found to increase by an order of magnitude. The hexagonal pattern of graphene can interact with the LC's benzene rings via π-π electron stacking, enabling the LC to anchor to the graphene surface homogeneously (i.e., planar anchoring). When the LC cell is filled with the graphene-doped LC, some graphene flakes are preferentially attached to the alignment layer and modify the substrate's anchoring property. These spontaneously deposited graphene flakes promote planar anchoring at the substrate and the polar anchoring energy at alignment layer is enhanced significantly. The enhanced anchoring energy is found to impact favorably on the electro-optic response of the LC. Additional studies reveal that the nematic electro-optic switching is significantly faster in the LC-graphene hybrid than that of the pure LC.

Carbon Nanotube Reinforced Polymer-Stabilized Liquid Crystal Device: Lowered and Thermally Invariant Threshold with Accelerated Dynamics.

Polymer-stabilized liquid crystal (PSLC) devices comprise a polymer matrix in an otherwise continuous phase of liquid crystal. The fibrils of the polymer provide, even in the bulk, virtual surfaces with finite anchoring energy resulting in attractive electro-optic properties. Here, we describe a novel variation of the PSLC device fabricated by reinforcing the polymer matrix with polymer-capped single-walled carbon nanotubes (CNTs). The most important outcome of this strengthening of the polymer strands is that the threshold voltage associated with the electro-optic switching becomes essentially temperature independent in marked contrast to the significant thermal variation seen in the absence of the nanotubes. The reinforcement reduces the magnitude of the threshold voltage, and notably accelerates the switching dynamics and the effective splay elasticity. Each of these attributes is quite attractive from the device operation point of view, especially the circuit design of the required drivers. The amelioration is caused by the polymer decorating CNTs being structurally identical to that of the matrix. The resulting good compatibility between CNTs and the matrix prevents the CNTs from drifting away from the matrix polymer, a lacuna in previous attempts to have CNTs in PSLC systems. The difference in the morphology, perhaps the primary cause for the effects seen, is noted in the electron microscopy images of the films.

Unusual electro-optical behaviour of the nematic polyacrylate

ABSTRACTHigh sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties.The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated.

Graphene as transmissive electrodes and aligning layers for liquid-crystal-based electro-optic devices.

In a conventional liquid crystal (LC) cell, polyimide layers are used to align the LC homogeneously in the cell, and transmissive indium tin oxide (ITO) electrodes are used to apply the electric field to reorient the LC along the field. It is experimentally presented here that monolayer graphene films on the two glass substrates can function concurrently as the LC aligning layers and the transparent electrodes to fabricate an LC cell, without using the conventional polyimide and ITO substrates. This replacement can effectively decrease the thickness of all the alignment layers and electrodes from about 100 nm to less than 1 nm. The interaction between LC and graphene through π-π electron stacking imposes a planar alignment on the LC in the graphene-based cell-which is verified using a crossed polarized microscope. The graphene-based LC cell exhibits an excellent nematic director reorientation process from planar to homeotropic configuration through the application of an electric field-which is probed by dielectric and electro-optic measurements. Finally, it is shown that the electro-optic switching is significantly faster in the graphene-based LC cell than in a conventional ITO-polyimide LC cell.

Three-Dimensional Analysis of an Ultrashort Optical Cross-Bar Switch Based on a Graphene Plasmonic Coupler

A high-performance electro-optical cross-bar switch based on a vertical graphene plasmonic directional coupler is proposed. The structure consists of two pattern-free graphene plasmonic waveguides which have major advantages over their previous counterparts. An ultrashort switching length of just 223 nm is obtained at the frequency of 37.5 THz. To the best of our knowledge, this switching length is remarkably shorter than those in the recently reported structures. Our designed structure is simulated using a three-dimensional finite-difference time-domain method. According to the illustrated results, extinction ratios of 10.5 and 9.52 dB are obtained at the cross and bar ports, respectively, and a wide spectral width of more than 1 μ m is presented. The required switching voltage is also calculated as 6 V and a very high 3 dB bandwidth of more than 60 GHz is obtained. An extremely low switching energy of 3.8 fJ/bit is also estimated.

Intrinsic reduction the depolarization loss in electro-optical Q-switched laser using a rectangular KD*P crystal

We presented the first demonstration of a new structure KD*P crystal as electro-optic switch, in which the thermal depolarization loss was intrinsically reduced. The thermally induced birefringence and depolarization of both cylindrical and rectangular crystalline structure were simulated. The higher pulse energy or average power output was achieved in the diode pumped E-O Q-switched laser using a rectangular KD*P crystal. At the repetition rate of 100Hz, the maximum average output power was 27.2W at 145A pump current, corresponding to the pulse energy was 272mJ with pulse width of 65ns and the beam quality of M2=20.4. Comparing the highest average power or corresponding single pulse energy, the laser with the rectangular KD*P crystal was two times of the laser with the traditional cylindrical KD*P crystal.

Ferroelectric Liquid Crystals in Microcapillaries: Observation of Different Electro-optic Switching Mechanisms.

Ferroelectric liquid crystals (FLCs) can provide fast electro-optic switching effects in photonic crystal fibers, which are promising for developing integrated optical modulators to be used for optical telecommunication. The present study describes experiments on capillaries filled with FLCs, which pave the way toward application of FLCs in state-of-the-art solid core microstructured optical fibers. A method to achieve uniform alignment of the helix axis and the appearance of two different switching modes with switching times in the submillisecond range are found. An additional slow relaxation that was reported recently can be attributed to space charge fields, which may appear due to the migration of ions.

Efficient modulation of orthogonally polarized infrared light using graphene metamaterials

We propose an efficient modulation of linearly polarized infrared light using graphene metamaterials (GMMs) by exploiting the phase-coupled plasmon-induced transparency (PIT) mechanism. Because of the phase-coupling effect in GMMs, pronounced PIT peaks can be simultaneously obtained for the orthogonally polarized light through tuning of the Fermi level in graphene. Taking advantage of such polarization-selective PIT spectral responses and precise phase management, a dual-polarization GMM modulator is successfully achieved with ultra-high modulation depths of ∼32 dB at 10 μm and ∼28 dB at 12.45 μm for the x- and y-polarized light beams, respectively. The underlying principle of the proposal is well explained and verified by using transfer matrix method. The proposed scheme provides new opportunities for developing graphene-integrated high-performance electro-optical modulation, switching, and other optoelectronics applications.

Ultra-High-Capacity Optical Packet Switching Networks with Coherent Polarization Division Multiplexing QPSK/16QAM Modulation Formats

Optical packet switching (OPS) networks and its subsystems, like the burst-mode receiver, are an essential technology currently used in passive optical networks (PONs). Moreover, OPS may play a fundamental role on future hybrid optical circuit switching (OCS)/OPS networks and datacenter networks. This paper focuses on two fundamental subsystems of packetized optical networks: the digital coherent burst-mode receiver and the electro-optical switch. We describe and experimentally characterize a novel digital coherent burst-mode receiver that makes uses of the Stokes parametrization to rapidly estimate the state of polarization (SOP) and optimize the equalizer convergence time. This burst-mode receiver is suitable for optical packetized networks that make use of advanced modulation formats such as quadrature amplitude modulation (QAM). We study the suitability of (Pb,La)(Zr,La)O3 (PLZT) optical switches for amplitude-variable coherent polarization division multiplexing (PDM) 16QAM modulation format and demonstrate a switching capacity of 10.24 Tb/s/port. We demonstrate a full 2 × 2 OPS node with a control plane capable of solving packet contention by means of packet dropping or buffering with a switching capacity of 10.24 Tb/s/port. Finally, we demonstrate the operation of the 2 × 2 OPS node with a record capacity of 12.8 Tb/s/port plus 100 km of dispersion-compensated fiber transmission.

Polymer selective laser curing for integrated optical switches

A simple in-layer electro optical switch has been prepared by selectively curing a photocurable optical polymer with a UV laser. The core of the device is a NOA-81 multimode waveguide grown by selective laser curing. The cladding is a positive calamitic liquid crystal, which allows tunability and switching of the waveguide by external driving electric signals. The effective refractive index in the guide changes upon switching the liquid crystal. Depending on the geometry, this setup leads to an electrooptical modulator or a switch between two levels of transmitted light. Full Text: PDF ReferencesT. Ako, A. Hope, T. Nguyen, A. Mitchell, W. Bogaerts, K. Neyts, and J. Beeckman, "Electrically tuneable lateral leakage loss in liquid crystal clad shallow-etched silicon waveguides", Opt. Express 23, 2846 (2015). CrossRef K. Kruse, C. Middlebrook, "Laser-direct writing of single mode and multi-mode polymer step index waveguide structures for optical backplanes and interconnection assemblies", Photon. Nanostruct. - Fundamentals and Appl. 13, 66 (2015). CrossRef A. Günther, A.B. Petermann, M. Rezem, M. Rahlves, M. Wollweber, and B. Roth, European Conf. Lasers and Electro-Optics - European Quantum Electronics Conference, Munich, Germany (2015).C. Florian, S. Piazza, A. Diaspro, P. Serra, M. Duocastella, "Direct Laser Printing of Tailored Polymeric Microlenses", ACS Appl. Mater. Interfaces, 8(27), 17028 (2016). CrossRef F. Costache, M. Blasl, "Optical switching with isotropic liquid crystals", Opt. Photonik 6, 29 (2011). CrossRef M. Cano-Garcia, R. Delgado, T. Zuo, M.A. Geday, X. Quintana, Jose M. Otón, 16th OLC Topical Meeting on the Optics of Liquid Crystals, Sopot, Poland (2015).S. Ishihara, H. Wakemoto, K. Nakazima, Y. Matsuo, "The effect of rubbed polymer films on the liquid crystal alignment", Liq. Cryst. 4(6), 669 (1989). DirectLink

Evaluation of Versatile CdS Nanomaterials Based Liquid Crystals Switchable Device.

Novel synthesis and properties of versatile CdS nanostructures (e.g., Nano-brush, nano-cube, nanosphere) dispersed liquid crystals application in chemical friendly medium exploring this article. Most recent studies, CdS nano-wire brush with the stacking fault structures were hydrothermally synthesized through a dissolution-recrystallization approach in concentrated ammonia solvent in one step solution, for the first time. Those structures-property relations with respect to ferroelectric hydrogen-bonded liquid-crystalline complex (HBLC; AC + 5BAO) controlled and efficient formation of surface relief nanostructures. A successful attempt has been made to form hydrogen bonding between CdS nanostructures and supramolecular LC with p–n-alkyloxy benzoic acids (n-OBA). The formation of an inter-H-bond is evinced through FTIR study, as well as Gaussian simulation also ensures complete formation of intermolecular hydrogen bond optimized geometry. In contrast, a new sensitive response of smectic G ordering observed in this series is investigated by constructing a phase diagram obtained from two binary mixtures of CdS nanostructures influenced by homogeneous liquid crystals. Temperature-dependent dielectric relaxation, tilt angle, electro-optical switching measurements allow for monitoring very unique and useful behavior in that the polarization of the emission from the semiconductor nanostructures can be controlled by an external bias. It reveals electrically tunable interaction of the composites may allow for engineering of practical electro-optic switchable device.

Effect of thermally induced birefringence on performance of KD*P electro-optics crystal with rectangular shape.

In this paper, we present what we believe is the first demonstration of a new rectangular KD*P crystal as an electro-optic switch and calculations of the stress-induced birefringence and depolarization loss in the crystal. We simulated and experimentally demonstrate the thermal depolarization loss of crystal in both cylindrical and rectangular shape. The results show that by using a rectangular KD*P crystal, the effects of the thermally induced birefringence and depolarization can be lessened.