Large group delay and low loss optical delay line based on chirped waveguide Bragg gratings

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Waveguide Devices

Background:

• On-chip optical delay lines (ODLs) are crucial components in modern optical systems.
• Chirped waveguide Bragg gratings (CWBGs) offer a promising platform for ODLs, but achieving large group delay (GD) and delay-bandwidth product simultaneously with low loss and without a circulator remains challenging.

Purpose of the Study:

• To propose and experimentally demonstrate a novel CWBG-based ODL.
• To achieve a circulator-free ODL with large GD, large delay-bandwidth product, and low loss on a silicon nitride platform.

Main Methods:

• Fabrication of an ODL using a low-loss 800-nm-height silicon nitride platform.
• Integration of a 20.11-cm long index-chirped multi-mode spiral waveguide antisymmetric Bragg grating with a directional coupler.
• Characterization of the device's bandwidth, group delay, delay-bandwidth product, and insertion loss.

Main Results:

• Demonstration of a circulator-free ODL with a bandwidth of 23 nm.
• Achieved a total group delay (GD) of 2864 ps and a delay-bandwidth product of 65.87 ns·nm, the largest reported for on-chip CWBG.
• Measured a loss of 1.57 dB/ns and a total insertion loss of 6 dB at 1550 nm.

Conclusions:

• The proposed CWBG-based ODL represents a significant advancement in integrated photonic delay lines.
• The device's superior performance metrics make it suitable for practical applications in microwave photonics, temporal optics, and optical communications.