Fiber to chip coupler and method of making the same

A coupling system comprising:

• an optical fiber configured to carry an optical signal;
• a substrate;
• a waveguide layer on a first side of the substrate;
• a grating optically connected to the waveguide layer, wherein the grating is configured to receive the optical signal;
• an interconnect structure on the first side of the substrate, wherein the waveguide layer is between the interconnect structure and the substrate, and the interconnect structure defines a cavity aligned with the grating;
• a first polysilicon layer over the grating on the first side of the substrate;
• and
• a second polysilicon layer on a second side of the substrate, wherein a maximum thickness of the first polysilicon layer is equal to a maximum thickness of the second polysilicon layer.

A coupling system comprising:

• an optical fiber configured to carry an optical signal;
• and
• a chip in optical communication with the optical fiber, wherein the chip comprises:
• a substrate;
• a grating on a first side of the substrate, wherein the grating is configured to receive the optical signal;
• an interconnect structure over the grating on the first side of the substrate, wherein the interconnect structure defines a cavity aligned with the grating;
• and
• 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;
• and
• a second polysilicon layer on the first side of the substrate, wherein a maximum thickness of the first polysilicon layer is equal to a maximum thickness of the second polysilicon layer.