Sub-kilohertz linewidth fiber laser by using Bragg grating filters.

Area of Science:

• Photonics and Optical Engineering
• Laser Physics
• Materials Science

Background:

• Single-frequency (SF) fiber lasers are crucial components in various scientific and industrial applications.
• Existing fiber Bragg grating (FBG) filters often have limitations in achieving ultra-narrow bandwidths required for advanced laser systems.
• The development of narrower bandwidth filters is essential for improving the performance of SF fiber lasers.

Purpose of the Study:

• To present a novel ultra-narrow bandwidth fiber filter design.
• To demonstrate the effectiveness of cascaded FBGs for bandwidth reduction.
• To implement and characterize an SF fiber laser utilizing the developed filter.

Main Methods:

• Constructing an in-series fiber filter using commercial FBGs with partially overlapping reflection spectra.
• Cascading multiple FBG filters to progressively narrow the bandwidth.
• Integrating the developed filter into a long linear cavity SF fiber laser setup.
• Measuring the filter and laser linewidth using optical spectrum analyzers.

Main Results:

• Achieved a filter bandwidth of 0.024 nm at 3 dB reflection, a 300% reduction compared to single FBG filters.
• Demonstrated further bandwidth narrowing to 0.0025 nm by increasing the number of cascaded FBGs.
• Implemented a 30 cm linear cavity SF fiber laser with a 941 Hz linewidth at 3 dB.
• The laser linewidth is approximately 210% narrower than previous records for FBG-based SF fiber lasers.

Conclusions:

• The cascaded FBG filter offers a superior method for achieving ultra-narrow bandwidths.
• This approach significantly enhances the performance of single-frequency fiber lasers.
• The developed technique opens new avenues for ultra-narrow bandwidth filters and SF fiber lasers.