Effect of disorder on self-collimated beam in photonic crystal

We report a numerical analysis of various types of disorder effects on self-collimated beam in two-dimensional photonic crystal. Finite-difference time-domain (FDTD) method is used to simulate the process by using a pulse propagation technique. The position disorders along the directions parallel and perpendicular to the incidence are considered. We show that random disorder along the perpendicular direction will have a lesser effect on the performance of the dispersion waveguides than those along the parallel direction. Furthermore, the self-collimation waveguide (SCW) has new characteristics when compared with the photonic crystal line defect waveguide. (c) 2006 Elsevier B.V. All rights reserved.

Light-propagation characteristics of photonic crystal waveguide based on SOI materials at different polarized states

Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator (SOI) wafer by 248-nm deep UV lithography. We present an efficient way to measure the light transmission spectrum of the photonic crystal waveguide (PhC WG) at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.

AlGaInAs narrow stripe selective growth on substrates patterned with different mask designs

We have performed a narrow stripe selective growth of oxide-free A1GaInAs waveguides on InP substrates patterned with pairs of SiO2 mask stripes under optimized growth conditions. The mask stripe width varied from 0 to 40 mu m, while the window region width between a pair of mask stripes was fixed at 1.5, 2.5 or 3.5 mu m. Flat and smooth A1GaInAs waveguides covered by specific InP layers are successfully grown on substrates patterned with different mask designs. The thickness enhancement ratio and the photoluminescence (PL) spectrum of the A1GaInAs narrow stripe waveguides are strongly dependent on the mask stripe width and the window region width. In particular, a large PL wavelength shift of 79 nm and a PL FWHM of less than 64 meV are obtained simultaneously with a small mask stripe width varying from 0 to 40 mu m when the window region width is 1.5 mu m. We present some possible interpretations of the experimental observations in considering both the migration effect from a masked region and the lateral vapour diffusion effect.

Signal bandwidth of general N x N multimode interference couplers

Analytical expression of signal bandwidth of general straight and tapered N x N multimode interference (MMI) couplers is presented. The signal bandwidth is characterized as a function of mode relative energy, mode propagation delay time, and mode pulse broadening in the multimode section of MMI coupler. The model is used to evaluate the signal bandwidth of specific couplers. Results indicate that the signal bandwidth decreases seriously with the increase of channel number and channel guide space. Compared with the straight MMI coupler, the tapered MMI coupler has an improved signal bandwidth.

Thick SiO2 layer produced by anodisation

A method for oxidising porous silicon to obtain thick SiO2 as the cladding layer of silicon-based silica waveguides is presented. The experimental results of oxidation are given. The following conclusions are drawn: the oxidation rate of porous silicon is several orders higher than that of bulk silicon, the appropriate temperature variation rate during oxidation combined with proper porosity can prevent SiO2 on silicon substrates from cracking. and a 25 mu M thick silicon dioxide layer has been obtained.

Realization of SOI submicrometer optical waveguide components - art. no. 68380L

Submicrometer channel and rib waveguides based on SOI (Silicon-On-Insulator) have been designed and fabricated with electron-beam lithography and inductively coupled plasma dry etching. Propagation loss of 8.39dB/mm was measured using the cut-back method. Based on these so-called nanowire waveguides, we have also demonstrated some functional components with small dimensions, including sharp 90 degrees bends with radius of a few micrometers, T-branches, directional couplers and multimode interferometer couplers.

Design considerations for a silicon-based p-i-n phase modulator in a double ridge waveguide with side isolating grooves

We present detail design considerations and simulation results of a forward biased carrier injection p-i-n modulator integrated on SOI rib waveguides. To minimize the free carrier absorption loss while keeping the comparatively small lateral dimensions of the modulator as required for high speed operation, we proposed two structural improvements, namely the double ridge (terrace ridge) structure and the isolating grooves at both sides of the double ridge. With improved carrier injection and optical confinement structure, the simulated modulator response time is in sub-ns range and absorption loss is minimized.

High speed silicon optical switches based on carrier depletion - art. no. 67812D

The novel design of a silicon optical switch on the mechanism of a reverse p-n junction is proposed. The figuration of contact regions at slab waveguides and the ion implantation technology for creation of junctions are employed in the new design. The two-layer rib structure is helpful for reduction of optical absorption losses induced by metal and heavily-doped contact. And more, simulation results show that the index modulation efficiency of Mach-Zehnder interferometer enhances as the concentrations of dopants in junctions increase, while the trade-off of absorption loss is less than 3 dB/mu m. The phase shift reaches about 5 x 10(-4) pi/mu m at a reverse bias of 10V with the response time of about 0.2ns. The preliminary experimental results are presented. The frequency bandwidth of modulation operation can arrive in the range of GHz. However, heavily-doped contacts have an important effect on pulse response of these switches. While the contact region is not heavily-doped, that means metal electrodes have schottky contacts with p-n junctions, the operation bandwidth of the switch is limited to about 1GHz. For faster response, the heavily-doped contacts must be considered in the design.

Design and Fabrication of a Photonic Crystal Channel Drop Filter Based on an Asymmetric Silicon-on-Insulator Slab

We report on the design and fabrication of a photonic crystal (PC) channel drop filter based on an asymmetric silicon-on-insulator (SOI) slab. The filter is composed of two symmetric stick-shape micro-cavities between two single-line-defect (W1) waveguides in a triangular lattice, and the phase matching condition for the filter to improve the drop efficiency is satisfied by modifying the positions and radii of the air holes around the micro-cavities. A sample is then fabricated by using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching processes. The measured 0 factor of the filter is about 1140, and the drop efficiency is estimated to be 73% +/- 5% by fitting the transmission spectrum.

Experimental Demonstration on Structure-Parameter Dependence of Photonic Crystal Optical Spectrum

We present fabrication and experimental measurement of a series of photonic crystal waveguides and coupled structure of PC waveguide and PC micro-cavity. The complete devices consist of an injector taper down from 3 mu m into a triangular-lattice air-holes single-line-defect waveguide. We fabricated these devices on a silicon-on-insulator substrate and characterized them using tunable laser source. We've obtained high-efficiency light propagation and broad flat spectrum response of photonic-crystal waveguides. A sharp attenuation at photonic crystal waveguide mode edge was observed for most structures. The edge of guided band is shifted about 31 nm with the 10 nm increase of lattice constant. Mode resonance was observed in coupled structure. Our experimental results indicate that the optical spectra of photonic crystal are very sensitive to structure parameters.

Characteristics of SOI rib waveguide microring and racetrack resonators

Characteristics of microring/racetrack resonators, in submicron SOI rib waveguides, have been investigated. The effects of waveguide dimensions, coupler design, roughness, and oxide cladding are considered. Moreover, guided mode, loss and dispersion of such waveguides are analyzed.

SOI optical switch matrix integrated with spot size converter (SSC) and total internal reflection (TIR) mirrors

SOI (Silicon on Insulator) based photonic devices has attracted more and more attention in the recent years. Integration of SOI optical switch matrix with isolating grooves, total internal reflection (TIR) mirrors and spot size converter (SSC) was studied. A folding re-arrangeable non-blocking 4x4 optical switch matrix and a blocking 16x16 matrix with TIR mirrors and SSC were fabricated on SOI wafer. The performaces, including extinction ratio and the crosstalk, are better than before. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length, more bend and intersecting waveguides. The insertion losses decrease 2 similar to 3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

Mode analysis of the UV-written channel waveguide - art. no. 60340J

The effective index method (EIM) was adopted to model the channel waveguide patterned by the UV in photosensitive silica film. The effective indexes of the different dimension symmetrical and asymmetrical channel waveguides were calculated, and the resource of the error of the method was pointed out. At last, the dimension rang to propagate single mode was presented.

Recent progresses of SOI-based photonic devices - art. no. 60201R

SOI (Silicon on Insulator) based photonic devices, including stimulated emission from Si diode, RCE (Resonant Cavity Enhanced) photodiode with quantum structure, MOS (Metal Oxide Semiconductor) optical modulator with high frequency, SOI optical matrix switch and wavelength tunable filter are reviewed in the paper. The emphasis will be played on our recent results of SOI-based thermo-optic waveguide matrix switch with low insertion loss and fast response. A folding re-arrangeable non-blocking 4x4 matrix switch with total internal reflection (TIR) mirrors and a first blocking 16 x 16 matrix were fabricated on SOI wafer. The extinction ratio and the crosstalk are better. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length and more bend and intersecting waveguides. The insertion losses are expected to decrease 2-3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

Novel compact SOI-based reconfigurable optical add/drop multiplexer using microring resonators - art. no. 60190L

Novel compact design for 4-channel SOI-based reconfigurable optical add/drop multiplexer using microring resonators is presented and analyzed. Microring resonators have two important attributes as a key new technology for future optical communications, namely functionality and compactness. Functionality refers to the fact that a wide range of desirable filter characteristics can be synthesized by coupling multiple rings. Compactness refers the fact that ring resonators with radii about 30 mu m can lead to large scale integration of devices with densities on the order of 10(4) similar to 10(5) devices per square centimeter. A 4-channel reconfigurable optical add/drop multiplexer comprises a grid-like array of ridge waveguides which perpendicularly cross through each other. SOI-based resonators consisted of multiple rings at each of the cross-grid nodes serve as the wavelength selective switch, and they can switch an optical signal between two ports by means of tuning refractive index of one of the rings. The thermo-optic coefficient of silicon is 1.86x 10(-4) /K. Thus a temperature rise of 27K will increase the refractive index by 5 x 10(-3), which is enough to cause the switching of our designed microring resonators. The thermo-optic effect is used to suppress the resonator power transfer, rather than to promote loss. Thus, the input signal only suffers small attenuation and simultaneously low crosstalk can be achieved by using multiple rings.