Optimized design of a new three branch optical waveguide

A new type of 1 × 3 Y-branch optical waveguide structure with a cone transitional section is introduced in this paper. The symmetrical branch ratio of the 1 × 3 Y branch optical waveguide is obtained by changing the width of this waveguide. The loss and the uniformity are obtained by using the finite difference beam propagation methods, and their values are 0.2 dB and 0.05 dB, respectively. Therefore, it provides some experimental basis for production of three branch optical waveguide.     

Broadband 2 × 2 free-space optical switch using electronically controlled liquid lenses

To the best of our knowledge, proposed is the first liquid lens technology-based 2 × 2 free-space optical switch using a pair of Electronically Controlled Variable Focus Lenses (ECVFLs). By independently controlling the focal lengths of two cascaded liquid ECVFLs, the two input optical beams are spatially adjusted to couple to their respective output beam ports. At 633-nm, the experimental switch demonstrates 26.3 dB crosstalk, 23.0 dB within-channel isolation, 1.1 dB optical loss, and 0.2 dB Polarization Dependent Loss (PDL). A 0.2 dB Wavelength Dependent Loss (WDL) is measured over 633-nm and 514-nm wavelengths. A 1 × 2 optical-fiber coupled switch version is also tested. The proposed switch can be useful in free-space laser systems as well as fiber-based modules.     

High-speed compact silicon digital optical switch with slot structure

A high-speed compact silicon digital optical switch (DOS) is proposed in this paper. The direct electro-optic effect is applied by filling electro-optic polymer in the void slot of the branches, which compensates the limitation of silicon itself. The crosstalk of about 35 dB and the insertion loss of 0.7 dB is obtained, the switching speed is less than 1 ps, and the whole device length can be shortened to 616 μm even using the basic mode-evolving principle and a simple Y-type structure. Analysis also shows that the device has good fabrication tolerance and wavelength independence over the C-band.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

1 × N add-drop filter structures using one dense wavelength division multiplexing thin-film filter

This paper proposes 1 × N add-drop filter structures in which only one thin-film filter (TF) is used. Our key idea is based on a combination of an angle-multiplexing concept and the flexibility of the optical fiber to allow a multiwavelength optical beam hit the TF several times, each time at a different angle but same position. Due to the TF angle sensitivity, the desired wavelength optical beam corresponding to the incident angle is therefore spatially isolated from the main optical beam. Our first TF-based 1 × N add-drop filter structure is arranged in a reflective design in which N wavelength optical beams can be dropped out from the main channel. For our transmissive architecture, N − 2 channels are directed to their associated output terminals while the remaining λ_N−1 and λ_N wavelength optical beams are sent out at the same port. Experimental proof of concept for our reflective TF-based 1 × 3 add-drop filter using one off-the-shelf TF, a triple fiber-optic collimator, and an optical circulator separates two wavelength optical beams with their channel spacing of 0.8 nm from the main channel. In this case, measured optical losses of 0.67 dB, 1.66 dB, and 2.59 dB are obtained for the first, the second, and the remaining dropped wavelength optical beams, respectively. Optical crosstalk and polarization dependent loss of <−18 dB and <0.08 dB are also investigated, respectively.     

GaAs1×4Mach－Zehnder型光开关列阵研究

采用非对称Ｘ结耦合器设计并研制了ＧａＡｓ１×４Ｍａｃｈ－Ｚｅｈｎｄｅｒ型光开关列阵。简述了非对称Ｘ结和相应的光开关列阵的工作原理及器件的设计和制作过程。在波长为１．１５μｍ的光波下测量单元器件，得到了小于－２０ｄＢ的串音和小于１２Ｖ的开关电压，器件的光波导传输损耗约为７ｄＢ／ｃｍ。文中最后分析了导致器件中串音和损耗的各因素，并提出了可能的改进方法     

Design and simulation of a novel 32 × 32 photonic bandgap power switch based on SOI waveguide

In this paper, we propose a novel 32 × 32 photonic bandgap (PBG) power switch based on silicon-on-insulator (SOI) substrate. The 32 × 32 PBG power switch merges the design concept of PBG structure and multimode interference (MMI) structure. With controlling the voltages of 256 blocks for changing the refractive index, we can demonstrate that the light propagation direction can be switched to the assigned output port as a 32 × 32 power switch. According to the simulations, the power switching control tables are searched and selected for successful switching. The size of our designed 32 × 32 PBG switch can be reduced to 252 × 6040 μm which is much smaller than the conventional opto-electronic switches.     

Optical switch with low-phase transition temperature based on thin nanocrystalline VOx film

An optical switch is fabricated by using micromachining technology, which is based on thin nanocrystalline vanadium oxide (VO_x) film, and it consists of four layers: a silicon (Si) substrate layer, a VO_x layer, a Si₃N₄ buffer layer, and an aurum (Au) electrode layer. By applying a switching power supply to a pair of the Au electrodes, the optical switch is controlled to exhibit from an “on” state with semi-conducting phase to an “off” state with metallic phase. The optical switch performance is investigated, and testing results show that its extinction ratio is about 14 dB, its switching response time can achieve about 1.5 ms, and the power dissipation required for stimulating switching to work can be below about 15 mW at least, which is lower than the power dissipation of conventional optical switches based on microstructure thin vanadium dioxide (VO₂) films. This kind of optical switch is potential to be applied as optical switch for optical communication.     

Polymer waveguide thermo-optic switches with −70 dB optical crosstalk

To reduce the crosstalk of the polymer waveguide optical switches, waveguide attenuators are integrated with the switch on the same substrate. The switch and attenuator shares a single connected electrode which is controlled by a single current source. Due to the simple structure of the integrated attenuator, the device length is reduced to 10 mm so as to provide low insertion loss of 0.8 and 1.1 dB for 1300 and 1550 nm, respectively. Further radiation of the remained optical signal on the switch-off branch is induced by the integrated attenuator so that the switching crosstalk is reduced to −70 dB with an applied electrical power of 200 mW. The low crosstalk is maintained for the environmental temperature range of −10 to 55 °C.     

Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

Improvement of switching properties and cascadability of an ultra-fast reconfigurable optical crosspoint switch matrix using DPSK payloads

In this paper, we demonstrate mitigation of pattern-induced degradation in an optical crosspoint switch (OXS) matrix by utilizing differential phase shift keying (DPSK) modulation format. We experimentally demonstrate 4 × 4 unicast optical packet switching and dynamic reconfiguration for 4-channel, 200 GHz spacing of RZ-DPSK payloads. Reconfigurable time as fast as 2 ns is achieved owing to the optimized control circuit and device fabrication. The power and wavelength dependence are obtained for the RZ-DPSK payload. We also investigate the cascadability of the OXS based on re-circulating loops. Due to the great suppression of the pattern effect in OXS, DPSK has shown dramatical improvement of switching properties compared to conventional ON-OFF keying (OOK) signal. The DPSK payload can outperform OOK for 3.2 dB after 9 hops optical switching.     

Optimal design and analysis of a high-speed, low-voltage polymer Mach-Zehnder interferometer electro-optic switch

Detailed model, analysis and design technique are presented for simulating a high-speed polymer Mach-Zehnder interferometer (MZI) electro-optic switch with push-pull dual driving electrodes and rib waveguides. The novel formulas of the time-domain response are derived. Thorough optimization and simulation for the designed device are performed. The total length of the basic function unit of the switch is about 5049 μm, the push-pull switching voltage is 2.23 V, the switching time is 18.1 ps, and the insertion loss and crosstalk are less than 2.64 and −30 dB, respectively, within the range of the operation wavelength from 1534 to 1566 nm. These results are in good agreement with those obtained from the beam propagation method (BPM).     

A novel method of developing all-optical frequency encoded memory unit exploiting nonlinear switching character of semiconductor optical amplifier

The very fast running optical memory and optical logic gates are the basic building blocks for any optical computing data processing system. Realization of a very fast memory-cell in the optical domain is very challenging. In the last two decades many methods of implementing all-optical flip-flops have been proposed. Most of these suffer from speed limitation because of low switching response of the active devices. In our present communication the authors propose a method of developing a frequency encoded memory unit based on the switching action of semiconductor optical amplifier (SOA). Nonlinear polarization rotation characters of SOA and ‘SOA based Mach-Zehnder Interferometer’ switch, i.e. ‘SOA-MZI’ switch, are exploited for the purpose of some switching action with least switching power (<−3 dB_m) and high switching contrast ratio (20 dB). Here two logic states (‘0’ state and ‘1’ state) of the memory is encoded by two different frequencies, which will remain unchanged throughout the data communication irrespective of loss of light energy due to reflection, refraction, attenuation, etc. Though the SOA based switch runs with the operational speed 100 Gb/s, still due to the presence of the other optical components in the memory unit, the overall speed of the proposed system will come down to 10 Gb/s.     

Analysis of polymer electro-optic microring resonator switches

The structure and the principle for the polymer electro-optic microring resonator (MRR) switch are proposed as well as the transfer functions. The structural parameters are optimized; the transmission characteristics are analyzed including the output power, switching time, switching voltage, insertion loss, and crosstalk. When the operation voltage is 0 V, the insertion loss and crosstalk are ∼1.2 and −20.2 dB, respectively; when the operation voltage is 10.0 V, those are ∼0.35 and −20.0 dB, respectively. Furthermore, a novel method is presented for analyzing time-domain response of the device and the switching time is determined to be ∼10.71 ps. These results indicate the favorable switching functions of the designed device.     

Plasmonic modulator utilizing three parallel metal-dielectric-metal waveguide directional coupler and elasto-optic effects

We report, for the first time, on the design of a plasmonic modulator working on the principle of the elasto-optic effects in a directional coupling structure, utilizing three parallel metal-dielectric-metal waveguides. We propose to achieve the active switching of the power propagation using the elasto-optic effect and optimize the extinction ratio of the optical modulation. The device is characterized and numerically analyzed using the finite-element-method at the wavelengths of 1.55 μm. For the modulator length of 2.33 μm, the extinction ratio of the modulation is nearly 14 dB, and the calculated attenuation loss is 4.5 dB. The calculated driving voltage is 4.8 V for the given modulator. The effect of the applied voltage on the modulation is also analyzed.     

Crosstalk reduced and low power consumption polymeric thermo-optic switch

A new polymeric 1 × 2 thermo-optic switch with significantly low crosstalk and low power consumption is presented. The thermo-optic coefficients of the core layer and the cladding layer are obviously different to each other. The refractive index of the core changes so that it would be less than that of the top cladding when the temperature is sufficiently high. Using this phenomenon, low crosstalk performance is achieved. The result indicated that the crosstalk of the proposed device could be improved from −20 to −60 dB. The switching insertion loss is 1.71 dB and the total heating power is no more than 16 mW.     

Synthesis of azo benzothiazole polymer and its application of 1 × 2 Y-branched and 2 × 2 Mach–Zehnder interferometer switch

The azo benzothiazole polyurethane–urea (ABPUU) was synthesized from chromophore molecule 4-[(6-nitrobenzothiazole-2-yl)diazenyl]phenyl-1,3-diamine NBDPD, polyether polyol (NJ-210) and isophorone diisocyanate (IPDI). The structure, thermal property, mechanical property and physical property were characterized and investigated. The refractive index (n) and thermo-optic coefficient (dn/dT) of ABPUU was determined at different temperature and wavelength (532 nm, 650 nm and 850 nm) using attenuated total reflection (ATR) technique. Using the CCD digital imaging devices, transmission loss of ABPUU was measured. A 1 × 2 Y-branched and 2 × 2 Mach–Zehnder interferometer (MZI) switch with two rib waveguides, dual driving electrodes and two critical 3-dB couplers polymeric thermo-optic switches based on thermo-optic effect of prepared ABPUU were designed and simulation. The power consumption of the Y-branched switch is less than 0.84 mW. The Y-branched and MZI switching rising and falling times obtained are 0.8 ms and 0.2 ms, respectively.     

Analysis and optimization of an InGaAsP/InP waveguide variable optical attenuator

An InGaAsP/InP waveguide variable optical attenuator (VOA) is proposed in this paper. The device consists of straight input and output waveguides and an S-bend waveguide. An electrode is deposited on a portion of the waveguide to form an active region so that its refractive index can be modified by a current injection, resulting in the variation of the transmitted optical power. The beam propagation method is employed in the numerical simulation and the device structure is optimized using a genetic algorithm. The optimized VOA has a low excess loss (<1 dB) and a large dynamic range of about 40 dB.     

A liquid lens-based broadband variable fiber optical attenuator

To the best of our knowledge, proposed is the first variable fiber optical attenuator (VFOA) using an electronically controlled variable focus liquid lens. The approach uses the changes in the radius of curvature of the liquid lens edge to enable an electronically controlled optical wedge that produces a varying beam tilt angle. In effect, changing beam tilt within a single mode fiber (SMF) lens free space coupling assembly leads to a polarization independent broadband VFOA design. The demonstrated VFOA experiment shows broadband operation over the 1530-1560 nm C-Band with a 40 dB dynamic range, <0.5 dB resolution, 0.3 dB polarization dependant loss, 4.3 dB fiber-to-fiber optical loss, 3 dB optical bandwidth from 1510 nm to 1700 nm, and switching time of <100 ms. Applications for this VFOA include use in hand held test and measurement equipment.     

Polymer-silica hybrid 1 × 2 thermooptic switch with low crosstalk

A new polymer-silica hybrid 1 × 2 thermooptic switch with significantly low crosstalk is demonstrated. The top cladding and the core layers are composed of polymer, while the bottom cladding layer is made of silica. Since polymer and silica have algebraic signs of their thermooptic coefficients that are opposite to each other, the refractive index of the core changes in the opposite direction to that of the bottom cladding as the temperature is increased. Thus, switching operation is initially done through adiabatic mode evolution in the Y-branch, and then a heated waveguide arm in the Y-branch can enter into the optical cut-off region if the temperature is sufficiently high. Using this phenomenon, low crosstalk performance is achieved. The proposed device has a crosstalk of −35 dB, while most integrated-optic switches with a single stage have a relatively high crosstalk in the region of −20 dB. The switching power of the proposed device is about 70 mW.