Zhiqi Wang

A Compact and Low-Loss MMI Coupler Fabricated With CMOS Technology

We present the design, fabrication, and measurement of a compact and low-loss multimode interference (MMI) coupler based on the silicon nanowire waveguide. The device is carefully designed to achieve both a good performance and a compact size by using the mode matching method. The device is fabricated on silicon-on-insulator (SOI) with 0.13-μm CMOS technology. By measuring the MMI coupler with a cascaded configuration, a very low excess loss of 0.06 dB at the wavelength of 1550 nm is obtained. The device can also work well for a wide wavelength band. The present MMI coupler is very compact with a footprint of ~ 3.6 × 11.5 μm2 for the multimode region.

Poly-Silicon Grating Couplers for Efficient Coupling With Optical Fibers

Waveguide grating couplers based on complementary metal-oxide-semiconductor (CMOS) poly-silicon gate layers are designed and fabricated. Sharing the same etching profile as that of the CMOS poly-silicon gate layer, the fabrication of the grating couplers is fully embedded in the CMOS process without adding any additional masks or process steps. Peak coupling efficiency of 40% and 3 dB bandwidth of ~60 nm, as well as a low reflection, are experimentally achieved. The coupling efficiency can be further improved to ~70% by using silicon-on-insulator wafers with optimal parameters.

InGaAs PIN photodetectors integrated and vertically coupled with silicon-on-insulator waveguides

Abstract. Heterogeneous integration of III–V materials with silicon-on-insulator (SOI) waveguide circuitry by an adhesive die-to-wafer bonding process has been proposed as a solution to Si-based lasers and photodetectors. Here, we present the design and optimization of an InGaAs PIN photodetector vertically coupled with the underlying SOI waveguide, which could be readily fabricated using this bonding process. With the help of grating couplers, a thick bonding layer of 2.5 μm is applied, which inherently avoids the risk of low-bonding yield suffering in the evanescent coupling counterpart. An anti-reflection layer is also introduced between the bonding layer and the III–V layer stack to relieve the accuracy requirement for the bonding layer thickness. Besides, by optimizing the structure parameters, a high-absorption efficiency of 82% and a wide optical 1dB-bandwidth of 220nm are obtained. The analysis shows that the detection bandwidth of the present surface-illuminated photodetector is generally limited by transit-time in the i-InGaAs layer. The relationship of the detection bandwidth and the absorption efficiency versus the i-InGaAs layer thickness is presented for the ease of choosing proper structure parameters for specific applications. With the results presented here, the device can be readily fabricated.