Efficient and fabrication error tolerant grating couplers on the InP membrane on silicon platform

In order to couple light between photonic integrated circuits and optical fibers, grating couplers are commonly employed. This paper describes the design and fabrication of deep and shallow-etched grating couplers with a metal back-reflector with record low insertion losses in InP-based platforms. The measured insertion losses for deep and shallow-etched gratings are 2.4 and 2.6 dB, respectively. Additionally, fabrication error tolerances in shallow etched grating couplers have been examined experimentally, which showed high tolerance of this structure toward the grating period and fill factor.