A coupling system includes an optical fiber configured to carry an optical signal. The coupling system further includes a chip in optical communication with the optical fiber. The chip includes a substrate. The chip further includes a grating on a first side of the substrate, wherein the grating is configured to receive the optical signal. The chip further includes an interconnect structure over the grating on the first side of the substrate, wherein the interconnect structure defines a cavity aligned with the grating. The chip further includes a first polysilicon layer on a second side of the substrate, wherein the second side of the substrate is opposite to the first side of the substrate.