Wide-bandwidth phase lock between a CW laser and a frequency comb based on a feed-forward configuration

Area of Science:

• Optical Physics
• Laser Spectroscopy
• Frequency Metrology

Background:

• Continuous-wave (CW) lasers are crucial for various applications but often suffer from broad linewidths.
• Frequency combs provide a highly stable and precise optical frequency reference.
• Phase-locking a CW laser to a frequency comb can transfer the comb's narrow linewidth and stability.

Purpose of the Study:

• To achieve wide-bandwidth phase lock between a frequency comb tooth and a CW extended-cavity diode laser (ECDL).
• To transfer the coherence properties of the frequency comb to the ECDL.
• To narrow the linewidth of the ECDL using the frequency comb reference.

Main Methods:

• Utilized an acousto-optical frequency shifter (AOFS) in a feed-forward configuration.
• Implemented phase-locking electronics to control the AOFS based on the beat note between the comb and the ECDL.
• Operated at a wavelength of 1.55 μm, a key telecommunication band.

Main Results:

• Successfully achieved wide-bandwidth phase lock between the frequency comb and the CW ECDL.
• Transferred the coherence of the frequency comb to the ECDL, narrowing its linewidth to approximately 10 kHz.
• Demonstrated a maximum control bandwidth of approximately 0.6 MHz.

Conclusions:

• The feed-forward AOFS configuration is an effective method for phase-locking ECDLs to frequency combs.
• This technique significantly enhances the spectral purity and stability of CW lasers.
• The achieved control bandwidth is currently limited by the AOFS acoustic transit time, suggesting avenues for future improvement.