Robust self-injection locking to a non-confocal monolithic Fabry-Perot cavity

Area of Science:

• * Physics
• * Optical Engineering
• * Electrical Engineering

Background:

• * Generating low-noise microwave signals is crucial for advanced communication and sensing systems.
• * Semiconductor lasers offer compact and cost-effective solutions but often suffer from phase noise.
• * Fabry-Perot cavities can enhance laser spectral purity through optical feedback.

Purpose of the Study:

• * To demonstrate efficient simultaneous self-injection locking of two semiconductor lasers to a monolithic Fabry-Perot cavity.
• * To generate a low-noise microwave signal using the locked lasers and a fast photodiode.
• * To evaluate the spectral purity improvement and phase noise performance.

Main Methods:

• * Utilized a standalone monolithic non-confocal Fabry-Perot cavity.
• * Implemented simultaneous self-injection locking of two semiconductor lasers to high-order cavity modes.
• * Employed a fast photodiode for microwave signal generation and phase noise measurement.

Main Results:

• * Achieved an overall improvement in laser spectral purity exceeding 80 dB.
• * Measured single-sideband phase noise of -110 dBc/Hz for X- to W-band signals.
• * Identified thermorefractive noise of the cavity as the primary limiting factor for phase noise.

Conclusions:

• * The demonstrated cavity-laser configuration enables efficient generation of spectrally pure microwave signals.
• * The system exhibits excellent phase noise performance, suitable for demanding RF applications.
• * The compact and robust design is promising for high-frequency RF signal generation and optical frequency comb referencing.