Focusing subwavelength grating coupler for mid-infrared suspended membrane waveguide

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Integrated Optics

Background:

• Mid-infrared (mid-IR) photonics is crucial for sensing and communication.
• Subwavelength grating (SWG) couplers offer precise light manipulation.
• Silicon-on-insulator (SOI) platforms are versatile for integrated photonic devices.

Purpose of the Study:

• To design and fabricate a focusing SWG coupler for mid-IR applications.
• To characterize the performance of the SWG coupler and suspended membrane waveguide (SMW).
• To evaluate the coupling efficiency and bandwidth of the mid-IR photonic device.

Main Methods:

• Finite-difference time-domain (FDTD) simulations for initial design.
• Phase-matching formulas for transforming uniform SWGs into focusing SWGs.
• Finite element method (FEM) analysis for SMW characterization.
• Fabrication of SWG couplers and SMWs on SOI wafers.
• Experimental characterization using an Er3+-Pr3+ co-doped mid-IR fiber laser.

Main Results:

• FDTD simulations predicted 44.2% coupling efficiency for a uniform SWG.
• Simulated device exhibited a 1 dB bandwidth of ~220 nm and 0.78% backreflection at 2.75 μm.
• The fabricated mid-IR SWG coupler achieved a coupling efficiency of 24.7%.

Conclusions:

• The study demonstrates the feasibility of focusing SWG couplers for mid-IR integrated photonics.
• Fabricated devices show promising performance for on-chip light coupling in the mid-IR spectrum.
• Further optimization could enhance coupling efficiency and broaden applications in mid-IR sensing and communication.