Demonstration of biaxially tensile-strained Ge/SiGe multiple quantum well (MQW) electroabsorption modulators with low polarization dependence

We demonstrate a novel biaxially tensile-strained Ge/SiGe multiple quantum well (MQW) electroabsorption modulator with low polarization dependence. The device is waveguide integrated and has a length of 900 mu m. Suspended microbridge structure is utilized to introduce biaxial tensile strain to the Ge/Si0.19Ge0.81 MQWs. Light is coupled into and out of the waveguide through deeply etched facets at the ends of the waveguide. Both TE and TM polarized electroabsorption contrast ratios are tested by the use of polarization maintaining focusing lensed fiber and a linear polarizer. A polarization irrelevant contrast ratio of 4.3 dB is achieved under 0 V/2 V operation. Both simulations and experiments indicate that the demonstrated device has potential in waveguide integrated utilizations that have high requirements on polarization uniformity.