OFDR analysis of Si photonics FMCW LiDAR chip

Area of Science:

• Integrated Optics
• Silicon Photonics
• Optical Metrology

Background:

• Silicon photonics is crucial for advanced optical systems like frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR).
• Understanding internal reflections and losses within these integrated circuits is essential for optimizing performance and minimizing noise.
• Optical frequency domain reflectometry (OFDR) offers high spatial resolution for analyzing optical components.

Purpose of the Study:

• To experimentally analyze the internal reflection and loss of individual components in a silicon photonics FMCW LiDAR device.
• To demonstrate the utility of OFDR as a precise diagnostic tool for silicon photonic integrated circuits.

Main Methods:

• Utilized optical frequency domain reflectometry (OFDR) with a spatial resolution better than 2.5 µm.
• Swept the incident laser wavelength over 120 nm to individually assess reflections and losses of various components, including wire waveguides, widened waveguides, and optical switches.
• Evaluated the slow-light grating (SLG) beam scanner by narrowing the wavelength sweep range, achieving a spatial resolution greater than 10 µm.

Main Results:

• Successfully revealed and quantified reflections and losses for wire waveguides, widened waveguides, and optical switches.
• Identified a significant reflection at the interface between the wire waveguide and the SLG beam scanner.
• Demonstrated that OFDR is a powerful tool for characterizing silicon photonic integrated circuits with high spatial resolution.

Conclusions:

• The strong reflection at the wire waveguide-SLG transition is a critical noise source in FMCW LiDAR systems.
• OFDR is an indispensable analysis tool for the detailed characterization and optimization of silicon photonic integrated circuits.
• This study represents the first demonstration of OFDR's capability as a key diagnostic method for silicon photonics.