Ultra-thin mid-infrared silicon grating coupler.

Area of Science:

• Photonics
• Integrated Optics
• Materials Science

Background:

• Mid-infrared (mid-IR) silicon photonics is crucial for nonlinear optics, ranging, sensing, and spectroscopy.
• Existing mid-IR silicon devices use thick silicon layers (hundreds of nanometers).
• Ultra-thin silicon devices offer enhanced evanescent fields and optical mode areas, vital for biochemical sensing and nonlinear optics, but face light coupling challenges.

Purpose of the Study:

• To address the difficulty of light coupling in ultra-thin mid-infrared silicon devices.
• To demonstrate an effective coupling method for ultra-thin suspended subwavelength-grating-cladding waveguides.
• To enable the development of mid-infrared ultra-thin photonic integrated circuits.

Main Methods:

• Demonstration of an ultra-thin focusing subwavelength-grating coupler.
• Fabrication of mid-IR ultra-thin suspended subwavelength-grating-cladding waveguides.
• Characterization of coupling efficiency, bandwidth, back reflection, fiber alignment tolerance, and bending loss.

Main Results:

• Achieved a maximum coupling efficiency of -7.1 dB at 2200 nm.
• Obtained a 1-dB bandwidth of approximately 115 nm.
• Measured a back reflection of -19.9 dB, fiber alignment tolerance of 12 µm, and bending loss of 0.25 dB/90°.

Conclusions:

• The developed focusing grating coupler effectively enables light coupling for mid-IR ultra-thin silicon devices.
• This technology overcomes previous limitations, paving the way for advanced mid-IR photonic integrated circuits.
• The findings are significant for biochemical sensing, nonlinear optics, and other mid-IR applications.