Fully integrated 45-GHz harmonically mode-locked ring laser with an intra-cavity Mach-Zehnder filter

Area of Science:

• Photonics and Optical Communications
• Integrated Optics
• Laser Technology

Background:

• Datacenters require higher bandwidths, driving demand for advanced optical communication systems.
• Wavelength division multiplexing (WDM) leverages optical fiber capacity but faces challenges with large channel spacing.
• Harmonic mode-locking offers a solution to increase channel spacing while maintaining a fixed laser cavity size.

Purpose of the Study:

• To demonstrate the feasibility of a monolithically integrated 45-GHz harmonically mode-locked ring laser.
• To investigate the performance of such a laser on a generic integration platform for WDM applications.
• To overcome limitations in achieving large channel spacing in traditional mode-locked lasers.

Main Methods:

• Design and fabrication of a monolithically integrated ring laser.
• Implementation of an intra-cavity Mach-Zehnder filter for harmonic mode-locking.
• Characterization of the laser's output, including pulse train, RF spectrum, and comb bandwidth.

Main Results:

• Achieved true harmonic mode-locking at 45 GHz with no measurable RF peak at the fundamental frequency.
• Demonstrated a pulse train with an autocorrelation trace width of approximately 2.5 ps FWHM.
• Obtained a radio frequency (RF) linewidth of approximately 0.44 MHz and a 3-dB comb bandwidth of approximately 240 GHz.

Conclusions:

• A monolithically integrated 45-GHz harmonically mode-locked ring laser is feasible on a generic integration platform.
• This laser architecture effectively increases channel spacing for WDM systems.
• The demonstrated performance metrics are promising for future high-bandwidth datacenter interconnects.