Yang Jianyi

Experimental demonstration of two-dimensional multimode-interference optical power splitter

A two-dimensional multimode-interference optical power splitter is designed and demonstrated. The new device can be used for the optical power splitting in two transverse directions. Silicon-on-insulator technology is utilized to fabricate the device. The performance of the device is tested.

Compact and economical MMI optical power splitter for optical communication

We present 1/spl times/8 and 1/spl times/16 optical power splitters based on MMI coupler in GaAs-GaAlAs. The input and output single mode waveguides are optimized by the discrete spectral index method (DSIM) and we obtain moderate square spot on the output in deep-etched rib waveguides. These splitters have good optical performance. They are suitable and important components in modern-day optical communication networks.

Photocurrent Effect in Reverse-Biased p-n Silicon Waveguides in Communication Bands

The photocurrent effect in reverse biased p-n silicon waveguides at wavelength 1550 nm is experimentally investigated. The photocurrent, which is mainly related to surface-state absorption, defect-state absorption and/or two-photon absorption, is more than 0.08 μA/mm under 8 V reverse biasing and 0.75 mW irradiation. The responsivity of a silicon waveguide with length of 4500 μm achieves 0.5 mA/W. Moreover, the enhancement of the photocurrent effect under the electric field is discussed.

Multimode-waveguide-based optical power splitters in glass

Low-loss glass-based buried multimode waveguides are fabricated by using the field-assisted Ag+-Na+ ion-exchange technique, and multimode optical power splitters are investigated. The measured loss of the multimode waveguides is lower than 0.1dB/cm, and the additional loss of the multimode optical power splitters is lower than 1.3 dB under the uniform splitting condition.

Optical Ring-Resonator Modulator Based on 0.8 μm CMOS Technology

Optical ring-resonator-based modulators are fabricated on the silicon-on-insulator material through the mature commercial 0.8 μm complementary metal oxide semiconductor foundry. The device configuration is based on a single ring resonator coupled to one bus waveguide. The waveguide widths are about 1 μm. The p-i-n junctions are employed to inject currents. The experimental result shows that the ring resonators with the quality factor of above 40000 are obtained. The maximum extinction ratio of the modulators is larger than 10dB. The speed is tens of nanoseconds, and the corresponding injected current is smaller than 10mA.

Ultracompact, Reflection-Free and High-Efficiency Channel Drop Filters Based on Photonic Crystal Nanobeam Cavities

We propose an ultracompact channel drop filter (CDF) based on photonic crystal nanobeam cavities. The conditions for implementing such an ideal CDF are derived from the temporal coupled-mode equations governing the operation of the CDF. By considering the intercoupling of the two involved nanobeam cavities, some ambiguities of the previous equivalent circuit model analysis are cleared up. Practical configurations on silicon-on-insulator (SOI) for the proposed CDF are suggested with a typical length less than 15 μm. Finite difference time domain (FDTD) method calculations show that the proposed filter can achieve drop efficiency higher than 99% without any reflection. Compared to the λ/4-shifted Bragg grating resonators based CDF, the proposed CDF is more compact, high-efficient and reflection-free. It is also easy to implement a low-power tunable filter due to the ultrahigh quality factor Q and ultrasmall modal volume V of the involved photonic crystal nanobeam cavities.

Analysis of the thermo-optic effect in lateral-carrier-injection SOI ridge waveguide devices

The thermo-optic effect in the lateral-carrier-injection pin junction SOI ridge waveguide is analyzed according to the thermal field equation. Numerical analysis and experimental results show that the thermo-optic effect caused by carrier injection is significant in such devices, especially for small structure ones. For a device with a 1000 μm modulation length, the refractive index rise introduced by heat accounts for 1/8 of the total effect under normal working conditions. A proposal of adjusting the electrode position to cool the devices to diminish the thermal-optic effect is put forward.

A Novel Coupled Quantum Well Structure with Low-Driving Voltage, Low Absorption Loss and Large Field-Induced Refractive Index Change

Based on a two-energy-level system, we analyse the changing ground eigenenergies of symmetric GaAs/AlxGa1−x As coupled quantum wells in the presence of an applied electric field. From the theoretical analysis for symmetric coupled quantum well, we find the advantages and disadvantages when it is applied to travelling wave modulator. Hence the conception of quasi-symmetric coupled quantum wells is put forward. Based on the demands of travelling wave modulator for quantum well materials, the configuration of quasi-symmetric coupled quantum well is further optimized. Consequently, in the case of low applied electric field (F = 20 kV/cm) and low absorption loss (α≤100 cm−1), a large field-induced refractive change Δn (for TE mode, Δn = 0.021; for TM mode, Δn = 0.0121) is attained in the optimized coupled quantum well.

Silica-based arrayed waveguide grating with flattened spectral response using a multimode interference coupler

We designed and fabricated an arrayed waveguide grating based on silica-on-silicon materials with flattened spectral response by adding a multimode interference coupler in the input region. The theoretical analysis and calculation are given. The device has worked effectively and has been tested with the passband 0.43 nm at 1 dB, 0.72 nm at 3 dB and 1.56 nm at 20 dB respectively, at a cost of power penalty of about 1.5 dB. The crosstalk is less than -30 dB, owing to the high-resolution photomask and well-controlled fabrication processes.

Properties of metal-clad dielectric waveguides in near cutoff

The mode propagation characteristics of metal-clad dielectric waveguides are investigated in near cutoff by using an approximate analytical method. The effects of the metal-cladding thickness on the mode cutoff conditions are considered. The modulation characteristic of the cutoff intensity modulator is equivalently described by the power ratios. The computed results are in good agreement with the exact numerical solutions in near cutoff.