Mid-infrared polarization-insensitive grating coupler | JoVE Visualize

Area of Science:

Photonics and Optical Engineering
Materials Science
Integrated Optics

Background:

Mid-infrared (Mid-IR) silicon photonics (2-20 µm) is crucial for applications including free-space optical communications, light detection and ranging, and molecular analysis.
Grating couplers are essential for interfacing optical fibers with waveguides, but face challenges in the Mid-IR spectrum due to polarization-dependent losses from available fiber types.
Existing polarization-insensitive grating coupling techniques for Mid-IR wavelengths are underdeveloped, hindering the progress of Mid-IR photonic integrated circuits.

Purpose of the Study:

To address the significant insertion losses in Mid-IR grating couplers caused by arbitrary polarization states.
To develop and demonstrate an ultra-thin, polarization-insensitive grating coupler for Mid-IR silicon photonics.
To improve the polarization-dependent loss compared to conventional subwavelength grating couplers.

Main Methods:

Design and fabrication of an ultra-thin grating coupler optimized for Mid-IR wavelengths.
Characterization of coupling efficiency and bandwidth at specific Mid-IR wavelengths (e.g., ~2200 nm and 2700 nm).
Comparative analysis of polarization-dependent loss against conventional subwavelength grating couplers.

Main Results:

Demonstrated an ultra-thin Mid-IR polarization-insensitive grating coupler with a maximum coupling efficiency of -11.5 dB at ~2200 nm and a 1-dB bandwidth of ~148 nm.
Achieved a significant improvement in polarization-dependent loss, reducing it from 9.6 dB to 2.1 dB compared to conventional couplers.
Successfully demonstrated a polarization-insensitive grating coupler at 2700 nm with a maximum coupling efficiency of -12.0 dB.

Conclusions:

The developed ultra-thin grating coupler effectively mitigates polarization-dependent losses in Mid-IR silicon photonics.
This advancement is critical for overcoming limitations in current Mid-IR fiber-to-chip coupling.
The findings provide a pathway for the realization of advanced Mid-IR photonic integrated circuits and their applications.