Liquid crystal-based optical time delay units for phased arrayantennas

Novel two-dimensional (2-D) spatial light modulator (SLM)-based optical time delay units (OTDU's) using freespace/solid optics and fiber delays are introduced for phased array antenna and wideband signal processing applications. In particular, the mature nematic liquid crystal (NLC) SLM technology is considered for the proposed architectures. A 1×2 optical switch is demonstrated using a parallel-rub birefringent-mode NLC cell, a bulk optics cube polarizing beamsplitter, and a sheet polarizer. Switch measurements taken at 633 nm show a >3400:1 or >35 dB output port optical isolation. The 1×2 NLC switch is used to build a 1-bit, 3.33-ns-duration, free-space OTDU using mirrors and total internal reflection corner prisms. The unit demonstrated a >30 dB optical (or >60 dB electrical) signal-to-noise ratio for both delay and no-delay positions. A 1500 pixel NLC SLM is built, and a 128:1 or 21 dB on/off isolation is demonstrated limited by the digital drive electronics of thin-film transistor (TFT)-based pixel control     

Two-dimensional GaAs photonic switch array with direct gain andhigh contrast

The fabrication and design of a 4×4 surface-normal reflection photonic switch array, with an operating principle based on the change of the gain coefficient in GaAs, is described. A 3-μm-thick GaAs active layer and carrier confinement layers are sandwiched between a semiconductor multilayer reflector and an antireflection window. The beryllium ion implantation technique is used to make a narrow current path to reduce the operation current. Each photonic switch independently realizes direct amplification and absorption of the optical signal. It features an optical gain of 4 dB and a contrast of 9.6 dB, for an applied voltage of 2.2 V. The array has a simple planar structure     

A silicon-based moving-mirror optical switch

A multimode 2×2 optical switch made from chemically micro-machined silicon piece parts is described. This switch uses microlenses, aligned to fibers by a silicon base, to expand the optical beam and relax alignment tolerances and a pivoting silicon mirrors as the switching mechanism. The moving mirror switch meets or exceeds all the requirements for FDDI applications. The switch loss is typically 0.7 dB and operates at 5 V and 30 mA. The switch insertion/deinsertion time is less than 10 ms, and the optical interruption time is less than 1 ms. The switch design, which minimizes alignments in fabrication and provides for z-axis assembly and the low cost of the high precision piece parts contribute to making this a low-cost switch to manufacture     

Lossless 1×4 laser diode optical gate switch

The fabrication of a compact 1×4 laser diode (LD) optical gate switch for the 1.3 μm band, comprising five LD optical gate submodules and a 1×4 planar lightwave circuit, is described. The switch exhibited a lossless switching function and polarization sensitivities of 0.5-1.1 dB, with operation currents of 45 to 55 mA. At operation currents of 120 mA, the switch exhibited positive gains of 9.0 to 10.2 dB. No power penalty was detected for nonreturn-to-zero (NRZ) transmissions of up to 2 Gb/s at -10 dBm input levels, when a narrowband optical filter for spontaneous emission reduction was used     

Crosstalk measurements of integrated high-speedTi:LiNbO3 Δβ-reversal switching circuits

Directional coupler crosstalk was measured at multigigahertz frequencies using an optical sampling method for improved sensitivity. At both 2- and 4-GHz switching frequency, the crosstalk in both switch states of the coupler was ⩽-19 dB for an element of a 1×4 switch array intended for time-division-multiplexing applications. The authors also report measurements of intercoupler crosstalk for this switch array     

An 8 mm length nonblocking 4×4 optical switch array

A novel single-mode-single-slip-structure S³ optical switch using carrier-induced refractive index change is proposed as a unit cell for a small polarization-independent nonblocking N×N optical switch array. Sixteen S³ optical switches have been integrated into a nonblocking 4×4 optical switch array on an InP substrate. The 8-mm-length InGaAsP/InP 4×4 optical array has shown satisfactory switching characteristics and is suitable for larger scale integration of optical switch arrays and also for integration with other active optical devices such as laser diodes     

Multiple-chip precise self-aligned assembly for hybrid integratedoptical modules using Au-Sn solder bumps

We have developed a novel three-dimensional high precision self-aligned assembly using stripe-type Au-Sn solder bumps and a micro-press solder bump formation method. This produces a high bonding precision of 1 μm for optical device assembly in both lateral and vertical directions without the need for time-consuming optical axes alignment. Furthermore, we tested a hybrid integrated 4×4 optical matrix switch, in which multiple SSC-SOAG arrays were simultaneously positioned and optical fibers were passively positioned on a silica based PLC platform using this technology. Four optical chips and seven wiring chips are assembled on a planar lightwave circuit (PLC) platform. The insertion loss for each of these paths at an injection current of 40 mA was within a range of 9±4 dB. The average extinction ratio was 40 dB. This self-aligned assembly technology was shown to be useful for building hybrid-integrated multichannel optical network components     

Dynamic range and switching speed limitations of an N×Noptical packet switch based on low-gain semiconductor optical amplifiers

Two important system performance limitations-dynamic range and switching speed-of an integrated packet switch fabric based on low-gain semiconductor optical amplifiers (SOA's) have been examined by using cascaded blocks of an SOA model, which includes transient effect, nonlinear pulse distortion effect, and amplified spontaneous emission (ASE) noise. Low-gain SOA's were used to minimize ASE noise considering that no optical filters can be integrated in an SOA-based switch fabric. The system performance with and without a narrowband optical filter at the receiver were both studied. By assuming fixed-wavelength transmitters and no optical filter can be used at the receiving end owing to the unpredictability of arriving packet wavelengths, our simulation results indicate that the dynamic ranges of 4×4 and 8×8 SOA-based packet switches at 2.5 Gb/s can only be about 3.2 and 0.8 dB, respectively. However, at 155 Mb/s, even without a receiving-end optical filter, the dynamic range of each switch size can be increased by more than 17 dB as compared to the cases of 2.5 Gb/s. Note that the dynamic ranges were estimated under the conditions of a bit error rate (BER) ⩽10^-9 and a pulse distortion ratio ⩽30%. We have also shown that, when an optical filter with a 1 nm bandwidth was used at the receiving end to simulate (1) a circuit-switched condition where the center wavelength of the filter can be adjusted according to the established circuit, or (2) a packet-switched condition where each receiver has a wavelength demultiplexer and a detector array, the dynamic range of 4×4 and 8×8 switches can be increased to 16.3 and 14 dB, respectively, at 2.5 Gb/s     

Linear crosstalk in 4×4 semiconductor optical amplifier gateswitch matrix

We report a comprehensive crosstalk investigation of a packaged InGaAsP/InP 4×4 semiconductor optical amplifier gate switch matrix, experimentally as well as theoretically. For a fully loaded switch with the same wavelength on all four inputs, all possible switching combinations are analyzed, thus yielding realistic crosstalk figures. Coherent and incoherent crosstalk phenomena are identified, and a switch crosstalk less than -40 dB has been measured     

1/spl times/4 optical switch based on transversal filter configuration with constant power consumption

An optical switch based on a transversal filter configuration is demonstrated. The switch consists of cascaded 3 dB optical power splitters and a phase shifter array. By using a silica-based planar lightwave circuit, a 1/spl times/4 optical switch was realised. A characteristic of the switch is that its power consumption is constant regardless of the output selection.     

Four-channel integrated-optic wavelength demultiplexer with weakpolarization dependence

A planar four-channel wavelength demultiplexer with weak polarization dependence is proposed and demonstrated. This demultiplexer is based on an optical-phased array. An experimental device with dimensions 4.5×3.2 mm² was designed and fabricated, using conventional (high-quality) optical lithography. The demultiplexer operates in the wavelength range 776.5-781.2 nm, with a channel spacing of 1.55 nm. Insertion loss was 0.6 dB for the central channels and 1.2 dB for the outer channels for transverse-electric (TE) polarization, excluding 1.3-dB waveguide propagation loss. Crosstalk values measured 15.4-29.7 dB for the TE and 13.4-22.2 dB for the transverse-magnetic (TM) polarization     

Fully packaged polymeric four arrayed 2×2 digital opticalswitch

A fully packaged polymeric four arrayed 2×2 digital optical switch is fabricated. Crosslinkable fluorinated polymers with a large thermooptic coefficient and a low loss are used for a low electrical power consumption and a low insertion loss. We improve the uniformity, crosstalk, and insertion loss with introducing a rib waveguide, a channel waveguide, and a tapered waveguide in the polymeric four arrayed 2×2 digital optical switch. The deviation of crosstalks is ±2 dB at 250 mW. The crosstalks are less than -30 dB for all four 2×2 digital optical switch elements with each total electrical power of 250 mW. The fall and rise times are less than 5 ms. The polarization-dependent losses are in the range of 0.2-0.7 dB. The total insertion losses range from 3.5 to 4.0 dB     

Free-space fiber-optic switches based on MEMS vertical torsionmirrors

This paper reports on the design, fabrication, and performance of a novel MEMS (micro-electro-mechanical-system) fiber-optic switch based on surface-micromachined vertical torsion mirrors. The vertical torsion mirror itself can be used as a 1×2 or an ON-OFF switch. A 2×2 MEMS fiber-optic switch with four vertical torsion mirrors has also been fabricated. The switching voltage is measured to be 80 V for switching angles of 45°. We have achieved a switching time of less than 400 μs (fall time) and an optical insertion loss of 1.25 dB for single-mode fibers. In addition, a bulk-micromachined silicon submount has been developed to package the switch with microball lenses and multimode fibers with passive alignment. With the micromachined switch chip and the hybrid-packaging scheme, the size, weight, and potentially the cost of the fiber-optic switches can be dramatically reduced     

A novel 1×4 coupler-multiplexer permutation switch for WDMapplications

A novel 1×4 coupler multiplexer permutation switch (CMPS) is proposed for applications in wavelength-division-multiplexing (WDM) optical networks. The structure of the CMPS integrates the multiplexing and switching functions into a single compact device. It consists of a single-mode/multimode-waveguide grating-assisted, backward-coupler multiplexer followed by a 1×4 digital optical switch (DOS). The specific design uses an InP-based 1×4 CMPS with InGaAsP-InP multiple-quantum-well (MQW) DOS. The calculated values of crosstalk for the coupler multiplexer and the DOS are <-25 dB and -23 dB, respectively, giving an overall crosstalk <-21 dB for channel bandwidths of 10-13 GHz. The device channels are unequally spaced, which reduces unwanted four-wave mixing (FWM), but are fitted to the ITU standard wavelength grid     

Design and performance of an optical path cross-connect systembased on wavelength path concept

This paper describes the system design and performance of an optical path cross-connect (OPXC) system based on wavelength path concept. The (OPXC) is designed to offer 16 sets of input and output fiber ports with each fiber transporting eight multiwavelength signals for optical paths. Each optical path has a capacity of 2.5 Gb/s. Consequently, the total system throughput is 8×16×2.5=320 Gb/s and the OPXC features high modularity and expandability for switch components. By exploiting planar lightwave circuit (PLC) technologies, four sets of (8×16) delivery-and-coupling-type optical switches (DC-switches) are developed for the 320 Gb/s throughput OPXC system. The DC-switch offers the average insertion-loss of 12.6 dB and ON/OFF ratio of 42.1 dB. The PLC arrayed-waveguide gratings are confirmed to successfully demultiplex the eight directly modulated signals, multiplexed at a spacing of 1 nm, with a crosstalk of under -25 dB. Eight wavelength-division multiplexing signals, directly modulated at 2.5 Gb/s, are confirmed to be transported over 330 km via a cross-connection node in the test-bed system that simulates five-node network. The experimental performances demonstrated In this paper ensures full scale implementation of the proposed optical path cross-connect system with 320 Gb/s throughput and high integrity     

2×2 buffered switch fabrics for traffic routing, merging, andshaping in photonic cell networks

An approach to optical packet switching is discussed, which uses small, simplified optical elements for traffic routing, merging, and shaping. The elements are constructed from 2×2 switches and optical delay lines, and may be implemented in a variety of technologies. They are designed for use with deflection routing, and even when using only six switches in a module, a deflection probability of 2.8×10^-7 is possible with a load of 0.8. The modules may also be used as 2×1 mergers where a deflection probability of 10^-12 is possible with six switches and a total load of 0.8. The BER performance of the modules is simulated with respect to crosstalk, with even relatively poor switch devices of -18.5 dB isolation yielding a power penalty of less than 1 dB. A networking strategy radically different from today's is discussed, driven by the need to reduce hardware, software and operating costs     

Hybrid-integrated 4×4 optical gate matrix switch usingsilica-based optical waveguides and LD array chips

The fabrication and characteristics of a hybrid-integrated optical gate matrix switch were studied. The switch was composed of a silica-based single-mode guided-wave circuit and two InGaAsP gate array chips, each of which comprised eight laser diode optical gates. The gate array chips were assembled on the guided-wave circuit using a hybrid integration technique. The insertion loss of the fabricated 4×4 matrix switch was scattered among switching paths and ranged from 26 to 33 dB. The switch was applicable to a 400 Mb/s signal system with a bit error rate of 10^-9. The numerical analysis shows that the residual reflectivity at the LD gate and waveguide facets caused the loss scattering among the paths and that reduction of the residual reflectivity is essential for improving the switch characteristics     

4×4 OEIC switch module using GaAs substrate

A compact 4×4 optical switch module consisting of a monolithic 4-channel OEIC receiver chip, a 4×4 GaAs IC chip, and a 4-channel OEIC transmitter chip has been developed for the first time. The module offers good performance, without an optical loss, a bandwidth of more than 600 MHz, and a crosstalk between neighboring channels of less than -20 dB. It has a good switching and distributive performance for high speed optical input signals of 560 Mbit/s. The switch module is attractive for use in high data-rate optical communication systems, particularly in local area networks, CATV systems, and intra-office links     

Low-power consumption silica-based 2×2 thermooptic switchusing trenched silicon substrate

We propose a silica-based 2×2 thermooptic switch using heat insulating grooves and trenches on a Si substrate to reduce electric power consumption. The switching power of a fabricated switch was successfully reduced to 135 mW, less than 1/3 that of a conventional switch. No detrimental effect on optical characteristics was observed: we obtained the insertion loss of 1 dB, the extinction ratio of better than 30 dB and no polarization dependency     

A high-speed 4×4 Ti:LiNbO3 integrated optic switchat 1.5 μm

The operation of a fully packaged and pigtailed polarization dependent Ti:LiNbO₃ 4×4 integrated optic switch with an operating wavelength of 1.5 μm is demonstrated. The switching matrix is fast, with a measured 3-dB small-signal bandwidth greater than 1 GHz. Unwanted cross modulation between channels due to coupling between switching elements was measured and found to be less than -20 dB of the signal strength. The switch is composed of balanced bridge switching elements having a 17-V switching voltage, an 18 dB extinction ratio, and an excess optical loss of 0.6 dB