Compact polarization transformation-enabled on-chip delay line for frequency-swept laser nonlinearity calibration

Area of Science:

• Photonics
• Integrated Optics
• Optical Engineering

Background:

• On-chip optical delay lines are essential for advanced photonic integrated circuits.
• Applications include optical coherence tomography, optical gyroscopes, and frequency-modulated continuous-wave (FMCW) LiDAR.
• Existing designs often face challenges with loss and compactness.

Purpose of the Study:

• To propose and demonstrate a novel low-loss and compact on-chip optical delay line.
• To integrate a polarization transformation-enabled 2-pass architecture for enhanced performance.
• To validate the delay line's utility in nonlinearity calibration for FMCW LiDAR systems.

Main Methods:

• Designed a compact on-chip delay line using a silicon nitride waveguide spiral.
• Implemented a polarization transformation-enabled 2-pass architecture.
• Achieved a total delay of 10.46 ns with a 0.8-m waveguide length.
• Measured propagation losses for TE and TM modes (0.083 dB/cm and 0.213 dB/cm, respectively).

Main Results:

• Demonstrated a low-loss (0.083 dB/cm for TE, 0.213 dB/cm for TM) and compact optical delay line.
• Achieved a significant total delay of 10.46 ns.
• Successfully utilized the delay line for nonlinearity calibration of a frequency-swept laser.
• Validated the calibration method in an FMCW LiDAR system, showing enhanced signal-to-noise ratio.

Conclusions:

• The proposed on-chip optical delay line offers a practical solution for high-performance photonic integrated circuits.
• This technology significantly improves the linearity and signal-to-noise ratio in FMCW LiDAR systems.
• The work provides valuable insights for developing highly integrated FMCW LiDAR systems.