Beat note stabilization in dual-polarization DFB fiber lasers by an optical phase-locked loop

Area of Science:

• Physics
• Optical Engineering
• Photonics

Background:

• Microwave-optical sources are crucial for radio frequency (RF) and microwave photonics.
• Stabilizing the frequency and phase of these sources is essential for high-performance applications.
• Existing methods often involve bulky or complex setups.

Purpose of the Study:

• To experimentally investigate a fully fibered microwave-optical source at 1.5 µm.
• To demonstrate efficient stabilization of the beat note between two orthogonally polarized modes of a distributed-feedback fiber laser.
• To assess the feasibility of using pump-power-induced birefringence as an actuator for stabilization.

Main Methods:

• Utilized a distributed-feedback fiber laser operating at 1.5 µm.
• Employed an optical phase-locked loop (OPLL) for frequency stabilization.
• Used pump-power-induced birefringence as the tuning mechanism within the OPLL.
• Stabilized beat notes at 1 GHz and 10 GHz to a reference synthesizer.

Main Results:

• Achieved efficient stabilization of the beat note between orthogonally polarized laser modes.
• Reduced the free-running linewidth from 3 kHz to sub-Hertz.
• Demonstrated low phase noise of -75 dBc/Hz at 100 Hz offset from the carrier.
• Successfully stabilized beat notes at both 1 GHz and 10 GHz.

Conclusions:

• The OPLL technique effectively stabilizes the microwave-optical source.
• Pump-power-induced birefringence is a viable actuator for precise frequency control.
• The stabilized dual-frequency lasers offer a pathway to compact, integrated RF and microwave photonics components.