Architecture of crosstalk-reduced digital optical 2×2 switch(CRDOS)

Coherent crosstalk of optical space switch matrices is a key problem of optical transparent networks. An analysis of the crosstalk sources of electrooptical digital switches (DOS) is given and a new crosstalk compensating technique based on the integration of a general mode converter as correcting device into a 3×2 DOS is proposed and theoretically investigated. It can be shown, that a -20 dB crosstalk 2×2 DOS device can be enhanced to -40 dB. This architecture leads to an increase of the device length by only a few percent. It opens up the possibility to realize short optical switches for larger matrices     

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     

Multichannel frequency-selective switch employing anarrayed-waveguide grating multiplexer with fold-back optical paths

The optimized configuration of an N-channel frequency-selective 2×2 switch based on an arrayed-waveguide grating (AWG) (2N+1)×(2N+1) multiplexer is proposed that offers significant crosstalk reduction and loss-imbalance equalization. The optimization is achieved by employing fold-back optical paths instead of loop-back paths. A switch constructed with a silica-based AWG 16×16 multiplexer demonstrates coherent crosstalk of less than -30 dB in the transmitting frequency-division-multiplexed (FDM) channels; the gain in optimization is more than 15 dB. The largest loss-difference among the seven FDM channels is simultaneously reduced from 4.5 dB to 1.6 dB. These improvements will extend the cascadable number of nodes in all-optical FDM networks     

4×4 digital optical matrix switch using polymeric oversizedrib waveguides

For the first time the concept of oversized rib waveguides has been employed in a complex integrated optical device. Using commercially available polymers, a strictly nonblocking 4×4 digital optical matrix switch with full functionality has been realized. The matrix consists of 24 1×2 switching elements and showed a polarization independent average crosstalk of -28.8 dB     

Client-configurable eight-channel optical add/drop multiplexerusing micromachining technology

A client-configurable optical add/drop multiplexer (OADM) is demonstrated using a micromachined 8×6 matrix switch. The matrix switch can be configured to add/drop any of the eight input channels from/to any of the six add/drop ports. For the switching fabric, the insertion loss is 2~3 dB for the dropped channels and 8~9 dB for the added channels by using the backsides of the micromirror switches. The switching extinction ratio is over 40 dB, the crosstalk between channels is less than -40 dB, and they are equipment-limited in this experiment     

Theoretical design of a novel N×N two-dimensional integratedoptical crosspoint switch architecture

A novel two-dimensional integrated optical (2-DIO) crosspoint switch architecture is proposed for InGaAsP-InP, which is achieved by the use of novel 2-DIO beam splitters. A modal propagation model (MPM) is used to optimize device size, loss and crosstalk and study beam propagation in a 2-DIO slab waveguide. Theoretical results show that a lossless 4×4 2-DIO crosspoint device less than 2×2 mm² in size is predicted to exhibit less than -40 dB crosstalk     

Arrayed-waveguide grating multiplexer with loop-back optical pathsand its applications

We present a basic configuration of an unique integrated-optic arrayed-waveguide grating (AWG) multiplexer with loop-back optical paths and demonstrate an add-drop multiplexer (ADM), a network access terminal, and a wavelength channel selector for dense-WDM ring or bus networks, as three useful examples of its attractive applications. A key device in these components is a silica-glass based 1.55 μm polarization-insensitive 32×32 AWG multiplexer chip with 0.8 nm channel spacing which is fabricated using planar lightwave circuit (PLC) technologies. Fine operation in their new functional components is achieved by using the AWG multiplexer module having low insertion loss of 3.9 dB and low interchannel crosstalk of less than -28 dB     

A rearrangeable multichannel free-space optical switch based onmultistage network configuration

A rearrangeable 128×128-channel optical switch based on a multistage network configuration is demonstrated. The properties of optical components required for achieving up to 1000×1000-channel switches are discussed, taking into account the diffraction limit and liquid crystal light modulator (LCLM) crosstalk. An examination of the insertion loss and crosstalk properties of the switch reveals an average loss and crosstalk of 7.9 and -21.2 dB, respectively, and worst-case loss and crosstalk of 11.0 and -12.8 dB, respectively. Such low-loss and low-crosstalk properties indicate that the proposed switch structure is suitable for a large-scale rearrangeable switch     

A low crosstalk microoptic liquid crystal switch

A total internal reflection liquid crystal optical switch has been developed which gives crosstalk levels of -33 dB and switching speeds of 4 ms, with low operating voltage. A novel architecture for larger switch arrays is also proposed and prototype device constructed and tested. The effects of modulation on the optical carrier by the electrical drive signal, and methods of minimizing its effect are reported. Finally, a novel space-saving architecture is proposed and demonstrated for 4×4 switch arrays and its performance reported     

Low crosstalk 4 × 4 TiLiNbO3optical switch with permanently attached polarization maintaining fiber array

Several low crosstalk 4 × 4 crossbar optical switch arrays have been fabricated for use atlambda = 1.3 mum. Each array consists of 16 independently functioning directional coupler switches. We describe the typical device performance characteristics. The average insertion loss is 5.2 dB. Crosstalk levels routinely measured < -35 dB. The voltage required to operate the device is ≈ 13 V. The inputs to one of the device arrays were permanently attached to four laser transmitters using lensed polarization maintaining fiber at the laser end and an array of polarization maintaining fibers at the device end.     

Carrier-injected GaInAsP/InP directional coupler optical switchwith both tapered velocity and tapered coupling

For most applications, a quasi-digital switching response is desired. The authors report on the design and fabrication of a 2×2 `digital' optical switch in GaInAsP/InP based on a directional coupler with both tapered velocity and tapered coupling and designed to be in the cross state at the zero bias condition. Complete power transfer to the cross output port for both TE and TM polarizations has been realized in the passive couplers for a wide range of device lengths proving the theoretically predicted fabrication tolerances. In the very first controllable device, switching operation with a crosstalk of -7 dB has been achieved using carrier injection     

Y-cut LiNbO3 directional coupler with a self-alignedelectrode

A 2×2 Y-cut LiNbO₃ directional coupler switch using a self-aligned uniform Δβ electrode is fabricated by the proton diffusion method. Our design method makes it possible to form the electrode without the delicate alignment of the electrode pattern mask and optical waveguide. The switching voltage is also reduced due to the enhanced electro-optic efficiency by using the self-aligned electrode. To achieve the initial cross state of the uniform Δβ switch that is essential for low crosstalk, we control the proton diffusion time successively after the proton exchange. The measured crosstalk level of the directional coupler switch is -23 dB~-29 dB and its voltage-length product is as small as 9.6 Vmm     

Multimode interference photonic switches (MIPS)

The switching characteristics of multimode interference photonic switches (MIPS) are analyzed by wide-angle finite difference beam propagation method (FD-BPM). As a result, it is found that the MIPS with a multimode interference (MMI) length of 599 μm can switch the output light polarization insensitively with a crosstalk of less than -20 dB for a wavelength range of 70 nm. These analyses show that the MIPS can also have a 3-dB coupler function. Experimentally, an InGaAsP/InP 1×2 MIPS with a thicker InP cladding layer was fabricated and exhibited switching operation with crosstalks of -8 dB and -10 dB at 0 and 20 mA current injections, respectively. For a 2×2 MIPS with a thinner InP cladding layer, better switching characteristics with a crosstalk of -13 dB and an extinction ratio of 17 dB were realized     

Fabrication of 2×2 tapered multimode interference coupler

The authors demonstrate a 3 dB 2×2 parabolically tapered multimode interference (MMI) coupler with a large cross-section and space between the different ports using silicon-on-insulator technology. The device exhibits a uniformity of <0.8 dB and can be used in the realisation of an MMI-based optical switch with a high extinction ratio     

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     

FDM-channel selection filter employing an arrayed-waveguide gratingmultiplexer

A novel channel selection filter based on an arrayed-waveguide grating multiplexer is reported for optical frequency-division-multiplexer (FDM) networks. The filter employs fold-back optical paths and optical switches, and can be operated digitally with multiple switches. A 16 channel selection filter employing a silica-based 16×16 multiplexer achieves a 20 GHz bandwidth and a crosstalk of less than 27 dB     

Impact of crosstalk in an arrayed-waveguide multiplexer onN×N optical interconnection

The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10^-9     

低串扰载流子注入型光开关的设计

针对载流子注入马赫-曾德尔干涉型光开关,提出使用输出比可调的3dB耦合器,补偿相移臂上通过载流子注入实现π相位调制所产生的吸收损耗,从而降低光开关的串扰。使用传输矩阵方法计算分析了载流子注入所伴随的吸收损耗对光开关串扰的影响,同时计算了可调3dB耦合器对光开关串扰性能的改进。计算结果表明,可调3dB耦合器的引入可以有效补偿相移臂的吸收损耗,对改善光开关的串扰性能有着明显的作用。     

2×2多模干涉光开关的设计与制作

以多模干涉耦合器为主体,通过载流子注入效应所引起的折射率改变来调整二重像之间的相位差,当折射率下降所引起的相位改变达到π相位时完成开关功能。在AlGaAs/GaAs/AlGaAs外延材料上,利用两步湿法腐蚀工艺,实际制作了2×2光开关并进行了测试。测试结果表明,工作在1.55μm波段,当注入电流达到160mA时,完成了开关功能。     

Surface-normal 4×4 nonblocking wavelength-selective opticalcrossbar interconnect using polymer-based volume holograms andsubstrate-guided waves

We present a 4×4 surface-normal wavelength-selective nonblocking crossbar using polymer-based volume holograms and substrate-guided waves. A prototype device is demonstrated using the center wavelengths of 750, 780, 810, and 840 nm. The employment of wavelength-division multiplexer and of address coding reduce the required 16 wavelengths to four while maintaining the 4×4 interconnects. Diffraction efficiencies of 85%, 83%, 79%, and 82% are experimentally confirmed for randomly polarized light at 750, 780, 810, and 840 mm, respectively. The measured crosstalk is less than -24 dB