All-fiber-referenced ultra-narrow-linewidth laser with broad wavelength agility

Area of Science:

• Optics and Photonics
• Laser Physics
• Precision Measurement

Background:

• External-cavity diode lasers (ECDLs) typically have broad linewidths (>100 kHz).
• Achieving ultra-narrow linewidths is crucial for high-precision scientific applications.
• Locking broad-linewidth lasers to high-finesse references presents significant technical challenges.

Purpose of the Study:

• To demonstrate an ultra-narrow-linewidth laser by locking a commercial ECDL to a cascaded, all-fiber reference.
• To overcome the difficulty of directly locking broad-linewidth lasers to high-finesse fiber references.
• To achieve significant frequency noise suppression and broad wavelength tunability.

Main Methods:

• Employed a two-stage locking scheme involving a fiber ring resonator for pre-stabilization.
• Utilized a fiber delay line interferometer for subsequent spectral purification.
• Locked a commercial external-cavity diode laser (ECDL) to the cascaded fiber reference.

Main Results:

• Achieved a 100-ms 1/f integrated linewidth of 28 Hz.
• Demonstrated a fundamental linewidth of 0.1 Hz.
• Attained frequency-noise suppression exceeding 80 dB between 30 Hz and 1 kHz offset frequencies.
• Validated the scheme's effectiveness across the ECDL tuning range of 1520-1580 nm.

Conclusions:

• The developed two-stage fiber locking scheme successfully produces an ultra-narrow-linewidth laser.
• The technique offers both ultra-low phase noise and broad wavelength agility.
• This laser system is suitable for demanding precision metrology applications.