Narrow linewidth ytterbium-doped fiber laser with external distributed feedback

Area of Science:

• Photonics and Laser Technology
• Fiber Optics
• Materials Science

Background:

• Narrow linewidth lasers are crucial for applications requiring high spectral resolution.
• Traditional methods for linewidth reduction often involve complex setups or introduce frequency shifts.
• Fiber lasers offer advantages in robustness and compactness but achieving ultra-narrow linewidths remains challenging.

Purpose of the Study:

• To demonstrate a sub-kilohertz linewidth ytterbium-doped fiber laser operating at 1064 nm.
• To investigate the effectiveness of Rayleigh scattering-based external distributed feedback for linewidth narrowing and noise reduction.
• To analyze the impact of this technique on laser stability and its immunity to external disturbances.

Main Methods:

• Utilized a linear lasing cavity incorporating two fiber Bragg gratings (0.16 nm FWHM).
• Inserted a bandpass filter (84.21 MHz FWHM) for stable single longitudinal mode operation.
• Imported external distributed feedback using Rayleigh scattering from a high numerical aperture fiber.

Main Results:

• Achieved a Lorentzian linewidth narrowing from 3.36 kHz to 232 Hz.
• Reduced frequency and relative intensity noise to 10.84 Hz²/Hz @1MHz and -140.62 dB/Hz @1MHz, respectively.
• Suppressed the relaxation oscillation peak from -100.68 dB/Hz to -126.03 dB/Hz without frequency shift.

Conclusions:

• Rayleigh scattering-based external distributed feedback is an effective method for achieving sub-kilohertz linewidths in ytterbium-doped fiber lasers.
• This technique significantly reduces laser noise and enhances stability, particularly against low-frequency disturbances like vibration and acoustic noise.
• The absence of frequency shift in noise reduction is critical for applications sensitive to spectral position, offering an advantage over self-injection locking methods.