System degradation due to phase error induced crosstalk in WDM optical networks employing arrayed waveguide grating multi/demultiplexer

The phase error induced crosstalk within arrayed waveguide gratings (AWG) have been investigated theoretically as well as simulation. For WDM system, a crosstalk level of −21.9 dB causes a power penalty of 1 dB for 64 channels and less than 0.5 dB for 16 channels and 32 channels, respectively. For crosstalk level of −30 dB and below, the power penalty is negligible. Crosstalk due to phase error also causes higher power penalty at higher bit rate. Bit rate of 10, 20 and 40 Gbits/s causes power penalty of 1 dB with crosstalk level of −41.5, −46.25 and −49 dB, respectively.     

Crosstalk improvement of a thermo-optic polymer waveguide MZI-MMI switch

A 2 × 2 MZI-MMI switch based on thermo-optic effect with a ridge in the silicon substrate was proposed and the performance of switch was simulated. The main purpose behind this change in substrate layer is to localize the heating at a heated arm single mode waveguide and limit the increasing temperature at a second one. The switch performance of the device should be improved, compare to the usual one. Using finite difference beam propagation method (FD-BPM) and thermal computing simulation based on finite element method (FEM), the results clearly indicate that the MZI-MMI switch can satisfy −31 dB crosstalk at two states.     

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.     

Systematic investigation of silicon digital 1×2 electro-optic switch based on a microdisk resonator through carrier injection

We perform a systematic investigation on the silicon digital 1×2 electro-optic switch based on a microdisk resonator with the refractive index tuned by carrier injection and extraction. Analytical expressions are proposed to quantify the crosstalk, insertion loss and switching time, and then they are used to analyze the effect of the coupling-in/out coefficient, internal loss, and quality factor. Both electron beam lithography and photolithography were employed to construct the asymmetrically coupled microdisk resonator integrated with a p-i-n diode. A high-performance switch has been demonstrated with a crosstalk of less than −20 dB, a switching time of ∼2 ns, as well as a power consumption of 0.46 mW. Moreover, the switching of optical signals with high data rates has been characterized and analyzed under different working conditions.     

A terabit capacity passive polymer optical backplane based on a novel meshed waveguide architecture

An optical backplane based on a meshed polymer waveguide architecture enabling high-speed board-to-board optical interconnection is presented. This planar array of multimode polymer waveguides can provide passive strictly non-blocking links between server line cards fitted with optical transmitter and receiver arrays. This architecture offers a scalable and low-cost solution to the bandwidth limitations faced by electrical backplanes and is suitable for PCB integration. The reported backplane demonstrator uses a matrix of 100 waveguides each capable of 10 Gb/s operation to interconnect 10 cards for a total capacity of a terabit per second aggregate data rate in multicast mode. Characterisation of the backplane demonstrator reveals low link losses of 2 to 8 dB for a multimode fibre input and crosstalk values below −35 dB. Error free data transmission at 10 Gb/s is achieved with a power penalty of only 0.2 dB at a bit-error-rate of 10⁻⁹. Additionally, lossless operation of a Gigabit Ethernet link over the backplane is achieved even when using the worst-case highest loss links.     

Design of a polymer directional coupler electro-optic switch using two-section reversed electrodes

By using the coupled mode theory, electro-optic modulation theory, conformal transforming method and image method, the structure is designed, the parameters are optimized, and the characteristics are analyzed for a polymer directional coupler electro-optic switch with two-section reversed electrodes. Simulation shows that the designed device exhibits excellent switching functions. Under the operation wavelength of 1550 nm, the electro-optic coupling region length is 4751 μm, the cross-state and bar-state voltages are about 1.22 and 2.65 V, and the insertion loss and crosstalk are less than 2.21 and −30 dB, respectively. By slightly adjusting the state voltages, the blight of the fabrication errors on the switching characteristics can be easily eliminated. The calculation results of the presented technique are in good agreement with those of the beam propagation method (BPM).     

Simulation and optimization of a polymer directional coupler electro-optic switch with push-pull electrodes

Structural model and design technique are proposed for a polymer directional coupler electro-optic switch with rib waveguides and push-pull electrodes, of which the electric field distribution is analyzed by the conformal transforming method and image method. In order to get the minimum mode loss and the minimum switching voltage, the parameters of the waveguide and electrode are optimized, such as the core with, core thickness, buffer layer between the core and the electrode, coupling gap between the waveguides, electrode thickness, electrode width and electrode gap. Switching Characteristics are analyzed, which include the output power, insertion loss, and crosstalk. To realize normal switching function, the fabrication error, spectrum shift, and coupling loss between a single mode fiber (SMF) and the waveguide are discussed. Simulation results show that the coupling length is 3082 μm, push-pull switching voltage is 2.14 V, insertion loss is less than 1.17 dB, and crosstalk is less than −30 dB for the designed device.     

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.     

Simulation and optimization of a polymer 2×2 multimode interference-Mach Zehnder interferometer electro-optic switch with push-pull electrodes

Structural model and design technique are proposed for a polymer 2×2 multimode interference-Mach Zehnder interferometer electro-optic (MMI-MZI EO) switch with push-pull electrodes. The electric field distribution is analyzed by the conformal transforming method and image method. To get the minimum mode loss and half-wave voltage, the parameters of the waveguide and electrodes are optimized, such as the core width, core thickness, buffer layer thickness, size of the MMI couplers and the modulating region, electrode thickness, electrode width, and electrode gap. Switching characteristics are analyzed, including the output power, crosstalk, and wavelength shift. Simulation results show that the half-wave voltage is 0.74 V, the optical 3 dB bandwidth is 12.66 GHz, and the crosstalk is less than −30 dB for the designed device.     

Optical waveguide fabrication and integration with a micro-mirror inside photosensitive glass by femtosecond laser direct writing

Photosensitive glass is a potentially important material for micro-fluidic devices that can be integrated with micro-optical components for biochemical analysis. Here, we demonstrate the fabrication of optical waveguides inside glass by femtosecond laser direct writing. The influence of the laser parameters on the waveguide properties is investigated, and it is revealed that the waveguide mode can be well controlled. The single mode is achieved at a low writing energy, while the multimode is achieved with increasing energy. In spite of a longitudinally elongated elliptical shape of the cross-sectional profile, the far-field pattern of the single-mode waveguide shows an almost symmetric profile. The measured propagation loss and the coupling loss are evaluated to be ∼0.6 dB/cm and ∼1.6 dB at a wavelength of 632.8 nm, respectively, under the conditions of 1.0–2.0 μJ pulse energy and 200–500 μm/s scan speed. The increased optical loss is associated with a higher waveguide mode at higher writing energy. Furthermore, the integration of waveguides and a micromirror made of a hollow microplate inside the glass is demonstrated to bend the laser beam at an angle of 90° in a small chip. The bending loss is estimated to be smaller than 0.3 dB. PACS 42.62.-b; 42.82.Cr; 82.50.Pt; 42.79.Gn; 42.81.Qb     

An Easily Operating Polymer 1×4 Optical Waveguide Switch Matrix Based on Vertical Couplers

A three-dimensional （3D） polymer thermo-optic （TO） 1 × 4 waveguide switch matrix based on vertical couplers is demonstrated. It consists of four basic 3D switch units and because of its 3D structure, its construction is compact, only 9 mm in length; moreover, the control logic of the entire switch is very simple, the light signal can be easily switched to any output port by operating only a single switch unit. The finished devices exhibit a switching extinction ratio greater than 21 dB for all of four output ports and the crosstalk between two adjacent output ports is lower than -19 dB. The rise time and the fall time of the switch matrix are 0.8ms and 1.4ms, respectively. The required electrical power to initiate the switching function for M1 switching units is about 50mW.     

Robust 2 × 2 Multimode Interference Optical Switch

A robust 2 × 2 photonic switch based on multimode interference (MMI) effects is proposed. We demonstrate that the device is very tolerant to material modifications and typical fabrication errors. This is a result of the MMI design and the high symmetry of the switch. The key parameter for the operation of the device is that the input light forms a pair of well defined self-images exactly in the middle of the switch. The index modulated regions precisely overlap the positions where these two self-images are formed. By creating identical contact features at these locations, any refractive index change induced in the material as a result of electrical isolation will be replicated in both self-images, and therefore the off-state output will not be altered. In the same way, offset and dimension errors are reflected symmetrically on both self-images and do not seriously affect the imaging. The characteristics of the switch under different scenarios are investigated using the finite difference beam propagation method. By employing this configuration, crosstalk levels better than −20 dB are achievable over a wavelength range of 100 nm while maintaining polarization independence.     

Etched-Diffraction-Grating-Based Planar Waveguide Demultiplexer on Silicon-on-Insulator

An optical wavelength demultiplexer with the etched diffraction grating (EDG) on the silicon-on-insulator (SOI) material is demonstrated. Fabricated by the wet-anisotropic-etching method, 90° turning mirrors are used to bend waveguides, and the size of the EDG-based demultiplexer is minimized to only 16×2.5 mm². The crosstalk is below −16 dB. The on-chip loss is about 9.97 dB, which is composed of about 8.72 dB excess loss and 1.25 dB diffraction loss. The polarization-dependent central wavelength shift is below 0.13 nm, and the polarization-dependent loss is about 0.35 dB. The sources of the crosstalk and loss are discussed in details, and the related measures to improve the performance are also presented.     

Short-length and broadband mismatched optical couplers with tapered Hamming function for C- and L-band

Mismatched optical couplers with variable widths of waveguide tapered by Hamming function are numerically investigated in the demand of short-length, broadband, and low crosstalk. We used global search algorithm and beam propagation method to seek optimal structure parameters of coupling waveguide. The coupler length is 3.6 mm within the C+L-band (1.53-1.61 μm) for variable widths of waveguide at crosstalk level of −35 dB. Comparison with constant width of waveguide, the constant width of waveguide has a coupler length of 4.4 mm and can only achieve −20 dB of crosstalk within the C-band (1.53-1.565 μm). Obviously, the waveguide with variable widths has the advantage over constant width for the demand of short-length, bandwidth, and low-crosstalk.     

An integrated reconfigurable optical add-drop multiplexer based on using an opto-VLSI processor and a 4-f imaging system

A novel integrated reconfigurable optical add-drop multiplexer (ROADM) structure is proposed and demonstrated experimentally. The ROADM employs an interface substrate that enables the integration of a fiber-lens collimator array and an Opto-VLSI processor to realise a 4-f imaging system through optical beam steering. Phase hologram optimization of the Opto-VLSI processor is investigated, for maximizing the number of wavelength channels while keeping adequate insertion loss and crosstalk levels. Experimental results are shown, which demonstrate a broadband operation and the principle of the ROADM with crosstalk of less than −30.5 dB and insertion loss of less than 6 dB for the drop and through operation modes.     

Beam Steering Type of 1 : 4 Optical Switch Using Thermo-Optic Effect

We propose a beam steering type optical switch employing a phase shifter. It consists of collimating waveguide mirrors, an arrayed-waveguide which has deep trenches incorporating polymer materials, and input/output waveguides. The incident light is guided to the front mirror, where it is then collimated, and input to the arrayed waveguide. The number of trenches filled with polymer linearly increases in order. The refractive index of the polymer can be controlled with temperature, and the propagation direction of the output light from the arrayed waveguide can also be controlled. A switch with 15 waveguides in the array has been fabricated. The chip size is about 2:5 × 9:0 mm², the insertion loss is 10 dB, and the extinction ratio is about 10–13 dB.     

Design of a spectrum-expanded polymer Mach�CZehnder interferometer electro-optic switch using two-phase generating couplers

A novel structure, thorough analysis and design technique are presented for a kind of polymer Mach?CZehnder Interferometer (MZI) electro-optic (EO) switch consisting of two-phase generating couplers (PGCs). By optimizing the PGCs structure, the output spectrum of the two PGCs based MZI EO switch is greatly expanded to almost six times of that of the traditional MZI EO switch with two 3?dB directional couplers. Under a central wavelength of 1550 nm, the driving voltages of the designed switch are as low as about 0 (ON state) and ±0.925?V (OFF state) with an EO region length of 5000???m. A wide spectrum more than 350 nm (1380??1730?nm) is achieved, and within this wavelength range, the crosstalk is less than ?30?dB, and the insertion loss is less than 5.91?dB which is larger than that of the traditional MZI EO switch due to the longer waveguide length by introducing two PGCs. The design technique on the two PGCs based MZI EO switch is supported to be reasonable compared with the beam propagation method (BPM). The proposed structure shows potential wide applications especially in optical cross-connect (OXC) and optical add-drop multiplexing (OADM) systems.     

Analysis of optical crosstalk within optoelectronic integrated circuits including lasers and photodetectors

Optical crosstalk from a 1.3 μm laser to a 1.55 μm photodiode on a single InP substrate, and its suppression within 1.3 μm/1.5 μm Y-junction transceiver OEICs, has been analyzed experimentally. The results indicate that the optical crosstalk suppression is limited by the accumulated light in the OEIC substrate coming mainly from the spontaneous emission of the integrated laser and from stray light at the laser–waveguide butt joint interface. For OEICs, integrating lasers and photodetectors, the achievable optical intra-chip crosstalk at present will be in the range of 30–40 dB at the required small die dimensions. Received: 16 May 2001 / / Published online: 23 October 2001     

A 1 × 2 optical switch using one multimode interference region

A 1 × 2 optical switch using only one multimode interference (MMI) region is designed and demonstrated in GaAs/AlGaAs. This design makes a single MMI region works as MMI coupler using paired interference at “off” state and symmetric interference at “on” state. By injecting a current of 110 mA, the measured on/off ratio and crosstalk are 23 dB and 33 dB, respectively in the demonstrated device with GaAs/GaAlAs.     

Plasmonic Metasurfaces Enabled Ultra‐Compact Broadband Waveguide TM‐Pass Polarizer

Silicon waveguide polarizers offer a simple yet robust approach to address the polarization‐dependent issue of silicon‐based optical components, and hence have found numerous applications in silicon photonics. However, the available silicon waveguide polarizers suffer from the issue of large device footprint, high insertion loss (IL), and/or fabrication complexities. Here, a silicon waveguide transverse magnetic (TM)‐pass polarizer is constructed by coating a silicon waveguide with an ultra‐thin plasmonic metasurface structure that is capable of guiding slow surface wave (SW) mode. The transverse electric (TE) waveguide mode can be converted into SW mode with the involvement of metasurfaces, and hence is intrinsically absorbed and forbidden to pass, while the TM waveguide mode can be well guided due to little influence. A typical metasurface polarizer with an ultra‐short length of 2.4 µm enables the IL of 28.16 dB for the TE mode, and that of 0.53 dB for the TM mode at 1550 nm. Multiple‐band TM‐pass polarizers can be obtained by cascading two or more different metasurface‐coated silicon waveguides along the propagation direction, and a dual‐band TM‐pass polarizer is demonstrated with the IL being of 19.21 and 29.09 dB for the TE mode at 1310 and 1550 nm, respectively.