Minghua Wang

Imaging properties and phase relations in MMI devices with two-dimensional confinement

The imaging properties and phase relations of MMI devices with two-dimensional (2-D) confinement have been discussed in this paper. The self-imaging effect in 2-D MMI can be regarded as the superposition coupling of two orthogonal and independent one dimension self-imaging effect. Because of the coupling of two orthogonal and independent self-imaging effects and asymmetry structure in three-dimensional waveguide, it is obvious that the imaging characteristic of 2-D confinement MMI devices is provided with asymmetry characteristic. The formalism of 2-D confinement MMI phase relation is presented. The law of the imaging and phase relations depends on the waveguide structure and the propagation distances.

Design and fabrication of GaAs-integrated optical chip used in a fiber optic gyroscope

In this paper, we present the design, fabrication and measurement of the GaAs integrated optic chip which is used in fiber optic gyroscope system. The integrated optic chip consists of the single mode waveguide, Y-branch power divider, polarizer and phase modulators. According to the design results, we succeed in fabricating the chip on GaAs/GaAlAs single-heterostructure epitaxial materials which are grown by MBE. The total size of the chip is as small as 10 X 0.5 mm2. The device has been being measured. We have got two light spots outputting from the device by the measuring system. And the half wave voltage of its phase modulator is about 10 V.

New compact design of planar 1×N branching splitter

We proposed a compact design of cascade Y-branch splitter devices. The new device consists of a 1×N branching region and a fan-out region. The length requirement of this new design is analyzed, the results show that the device length can be sharply cut, when N is larger than 8. As an example of this new structure, we designed an 1×16 branching splitter by K+/Na+ ion-exchange in BK7 glass, the smallest S-bend radius is 30mm, and the total bends length is about 20mm, it is 69% length of ordinary splitter.

Different effects on bandwidth for traveling-wave quantum well electro-absorption modulator and bulk Mach-Zehnder electric-opto modulator

For high-speed traveling-wave modulator, impedance match, velocity match and low microwave attenuation are important. But they have different effects on bandwidth for different structure and scheme for quantum well electroabsorption modulator and bulk Mach-Zehnder electrooptic modulator. For bulk Mach-Zehnder electrooptic modulator, the longer active waveguide is needed, and at such situation, according to the normalized gain (or modulation reduction factor) the velocity match and impedance match and low microwave attenuation should be well satisfied to achieve good performance. While for the quantum well electroabsorption modulator, limited by the optical loss, short active waveguide must be used. When the device length is largely reduced match requirement is not so strict and it is also difficult to achieve good match. Low terminator electroabsorption modulator is reported recently. Its concept could be inferred from the normalized gain formula. And some technology tendency in traveling-wave electroabsorption and Mach-Zehnder modulator could be also obtained and could explain series of experiment. From calculation and experiment the low impedance and low terminator could expand the bandwidth by slight mismatch. The relation of modulator characteristic impedance, microwave phase velocity and microwave attenuation is not much considered for simplification. The results are useful to design and optimize modulator.

Novel design of Y-branch in LiNbO3 by proton exchange

We design and analyze a novel low-loss symmetric Y-branch in Lithium Niobate by heavily annealed proton exchange (APE). In this design, a wide transitional waveguide is used between the input and two S-shape output waveguides, making the field match with the mode in the two output waveguides by intentionally generating second-order mode and radiation. By this method, optical power can be coupled into the two output waveguides with high efficiency. simultaneously , the minimum gap between the two output waveguides is 2.7 microns, thus the stem region of this Y-branch has no sharp taper and the fabrication of the device is easy. The Y-branch is optimized by the method of three-dimensional FD-BPM, after optimization, losses can be less than 0.05dB.

Analysis and optimization of the arrayed-waveguide grating device with total internal reflection mirrors based on silicon-on-insulator material

In the AWG device, a total internal reflection(TIR) mirror is fabricated at the middle ofeach arrayed waveguide based on silicon-on-insulator material. We simulate the field distribution of the output lightwave before and after a few TIR mirrors are damaged due to fabrication process and find that there is almost no any change of the output lightwave and the insertion loss ofthe AWG device, which indicates that fabrication ofthis type ofAWG device with TIR mirrors has high tolerance. Simulation results indicate that usage of tapered waveguides can reduce the insertion loss but affect the spectral response of the device. We design a rectangular groove in the middle of each output waveguide near the junction, of the output waveguide and the slab waveguide. Simulation results indicate that this type of structure can broaden the passband and improve the spectral response, while increase the insertion loss of the device a little in the same time.

Microwave properties of coplanar strips of MQW Mach-Zehnder modulator with finite metallization thickness and conductivity

A novel structure ofGaAs/GaAIAs multi-quantum well (MQW) traveling wave (TW) Mach-Zehnder modulator (MZM) with coplanar strips is proposed. This device uses n+ heavy doped layer to obtain velocity match. Then the Method of Lines is applied to characterize the influence ofmetallization thickness and conductivity loss on the velocity match and impedance match. With optimum parameters ofthe structure, the bandwidth over 80GHz is obtained.

GaAs 1x4 optical power splitter

In this paper, an optical power splitter based on MMI coupler in GaAs/GaAlAs heterostructure materials is fabricated. The epitaxial materials are grown by MBE. The dry etching process is applied to fabricate the ribs in this device. The measuring results are presented.

Design of 4x4 GaAs-GaAlAs carrier-injected total internal reflect optical switch array

A new scheme of GaAs-GaAlAs total-internal-reflect (TIR) optical switch unit based on bandfilling effect is presented in this paper. Asymmetric Y-branch, which is the essential part of switch structure, is analyzed using beam propagate method (BPM) on three different conditions: index change due to injection, width of injection region and position of injection edge. Unit with two perpendicular output ports is designed according to the numerical results to realized small sized 4 X 4 array which can easily couple with fibers and quickly give off heat.

Effects of metal-cladding on the cutoff condition of optical waveguides

The effects of metal-cladding on the cutoff condition of step and graded index optical waveguides are analyzed by the perturbation method in this paper. The cutoff thickness of metal-cladding waveguide is thicker than the waveguide with the dielectric (air) cladding. For step index profiles optical waveguides, the cutoff thickness of TE0 mode is more 7% than the case with air cladding, and TM0 mode is 26%.