Low-repetition-rate all-fiber integrated optical parametric oscillator for coherent anti-Stokes Raman spectroscopy

Area of Science:

• Fiber optics
• Nonlinear optics
• Spectroscopy

Background:

• All-fiber optical parametric oscillators (OPOs) are valuable for spectroscopy due to their robustness and compactness.
• Conventional fiber-based OPOs suffer from nonlinear effects that degrade performance, especially at low repetition rates.
• Intense pump fields in fiber coupling devices can negatively impact spectral purity and conversion efficiency.

Purpose of the Study:

• To demonstrate a new all-fiber OPO design with an integrated amplifier.
• To improve OPO performance, including lower threshold, higher output power, and narrower spectrum.
• To suppress spectral noise for enhanced Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy and biomedical imaging.

Main Methods:

• A modified all-fiber OPO configuration was developed with the main amplifier placed inside the cavity.
• Amplified pump pulses were directly coupled into the nonlinear fiber.
• The performance of the new OPO design was compared to a conventional OPO at repetition rates of 1, 2, and 3 MHz.
• The generated synchronized two-color laser sources were used to detect CH vibrational bands in ethanol.

Main Results:

• The new OPO design achieved a lower threshold, higher output power, and a narrower spectrum.
• Significant suppression of spectral noise was observed.
• Threshold reductions of 37.5%, 17.2%, and 5.2% were achieved at 1, 2, and 3 MHz repetition rates, respectively, compared to a conventional OPO.
• Successful detection of CH vibrational bands in ethanol using the synchronized two-color laser sources.

Conclusions:

• The integrated amplifier design effectively mitigates nonlinear effects in all-fiber OPOs.
• This spectral-tailored cavity design offers improved performance for low repetition rate operation.
• The enhanced all-fiber OPO is suitable for Coherent Anti-Stokes Raman Scattering (CARS) spectroscopy and has potential for nonlinear biomedical imaging.