Microcomb-referenced photonic stabilization of resonant tunneling diode terahertz oscillators

TL;DR

This paper presents a compact method for stabilizing terahertz sources by using microresonator-based optical frequency combs to lock resonant tunneling diode oscillators, significantly improving their spectral purity and stability.

Contribution

It introduces a novel microcomb-assisted injection locking technique for RTDs, achieving high spectral purity without complex frequency multiplication.

Findings

RTD linewidth reduced from 50 MHz to 165 Hz

Phase noise at 10 kHz offset reached -80 dBc/Hz

Locking range of 80 MHz demonstrated

Abstract

We demonstrate a compact stabilization scheme for terahertz (THz) sources by exploiting the complementary advantages of microresonator-based optical frequency combs (microcombs) and resonant tunneling diodes (RTDs). A microcomb-driven photomixing THz signal is employed as the master for injection locking of an RTD, enabling faithful transfer of the microcomb stability into the RTD. Using this approach, the free-running RTD linewidth of 50 MHz was narrowed to 165 Hz, while the single-sideband phase noise reached -80 dBc/Hz at a 10 kHz offset with a locking range of 80 MHz. Compared with conventional electronic frequency multiplier or fiber-comb-based schemes, this method avoids high-order frequency multiplication and associated noise penalties, offering a compact and practical alternative. The dual functionality of linewidth narrowing and power scalability highlights the potential of microcomb-assisted injection locking as a route toward chip-scale, spectrally pure THz sources for beyond-5G/6G wireless communication and radar, with prospects for future extension to time-frequency metrology and precision sensing.