High-purity microwave generation using a dual-frequency hybrid integrated semiconductor-dielectric waveguide laser

TL;DR

This paper demonstrates a hybrid integrated laser that produces dual-frequency emission with ultra-narrow linewidth and tunable microwave/THz beat frequencies, advancing integrated microwave and THz source technology.

Contribution

It introduces a novel hybrid semiconductor-dielectric laser with record-narrow linewidth and tunable dual-frequency operation for microwave and THz generation.

Findings

Achieved a linewidth as low as 2 kHz.

Generated a stable 11 GHz microwave beat frequency.

Enabled broad wavelength tuning of about 80 nm.

Abstract

We present an integrated semiconductor-dielectric hybrid dual-frequency laser operating in the 1.5 $\mu$m wavelength range for microwave and terahertz (THz) generation. Generating a microwave beat frequency near 11 GHz, we observe a record-narrow intrinsic linewidth as low as about 2 kHz. This is realized by hybrid integration of a single diode amplifier based on indium phosphide (InP) with a long, low-loss silicon nitride (Si$_3$N$_4$) feedback circuit to extend the cavity photon lifetime, resulting in a cavity optical roundtrip length of about 30 cm on a chip. Simultaneous lasing at two frequencies is enabled by introducing an external control parameter for balancing the feedback from two tunable, frequency-selective Vernier mirrors on the Si$_3$N$_4$ chip. Each frequency can be tuned with a wavelength coverage of about 80 nm, potentially allowing for the generation of a broad range of frequencies in the microwave range up to the THz range.