Compact single-etched sub-wavelength grating couplers for O-band application

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nanophotonics

Background:

• Sub-wavelength grating couplers (SWGCs) are crucial for interfacing optical fibers with integrated photonic circuits.
• Optimizing SWGCs for specific applications like high efficiency or broad bandwidth remains an active research area.
• Miniaturization of photonic components is essential for dense integration and advanced optical systems.

Purpose of the Study:

• To design and demonstrate two novel single-etched SWGCs for O-band applications.
• To achieve high coupling efficiency in one design and a broad operating bandwidth in another.
• To minimize the footprint of SWGCs while maintaining excellent optical performance.

Main Methods:

• Fabrication of single-etched SWGCs using standard nanofabrication techniques.
• Characterization of coupling efficiency and 3-dB bandwidth across the O-band.
• Utilizing focusing grating designs to reduce device dimensions.
• Measurement of back reflections to ensure signal integrity.

Main Results:

• A high-efficiency SWGC achieved a peak coupling efficiency of -3.8 dB with a 40 nm 3-dB bandwidth.
• A broadband SWGC demonstrated a peak coupling efficiency of -4.3 dB and a 71 nm 3-dB bandwidth.
• Both SWGC designs feature footprints smaller than 45 μm × 24 μm.
• Back reflections were suppressed below -15 dB from 1260 nm to 1360 nm.

Conclusions:

• The demonstrated SWGC designs offer effective solutions for O-band photonic integration.
• The trade-off between coupling efficiency and bandwidth is clearly shown in the two designs.
• The compact size and low back reflection make these SWGCs suitable for various integrated photonic applications.