Heng Zhou, Junqiang Sun,* Jianfeng Gao, Jialin Jiang, and Yang Zhou

In photonic integrated circuits (PICs), taper coupler is an important approach to achieve efficient vertical coupling between layers. Recently, there have been extensive progresses in the integrated SiGe active optical devices such as modulators and photodetectors within the communication wavelength. It is necessary to study the compact taper coupler for efficient optical power transfer between SiGe active device and passive waveguides.

In this paper, we propose a polarization-insensitive laterally tapered coupler for the integration of the active Ge/SiGe multi-quantum-well device with a passive SiGe waveguide. A 45-μm-long taper is designed to achieve more than 90% coupling efficiency for both TE- and TM-polarized modes. The mode interference is utilized to obtain a compact taper coupler with high coupling efficiency. Fabrication tolerances are analyzed in terms of taper width, thickness, material refractive and operation wavelength. The results indicate that a width variation of ±200 nm and a thickness variation of ±100 nm are allowed. The designed taper coupler can provide efficient coupling under normal operating conditions in the wavelength range of 1460-1625nm. The designed taper coupler has broad applications in polarization-insensitive modulators, detectors, switches as well as fiber communication systems.

The paper is published on Optical Express (Vol. 24, Issue 21, 2016.doi: 10.1364/OE.24.023784). This work is supported by the National Natural Science Foundation of China (Grant No. 61435004).

Fig. 1. Schematic diagram of the designed taper coupler. The input optical mode is from the passive Si0.16Ge0.84 waveguide at the left, and the tapered SiGe active waveguide allows the optical power to be transferred from lower passive waveguide to upper active device.