Tunable narrowband cascaded random Raman fiber laser

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Optics

Background:

• Random Raman fiber lasers (RRFLs) offer wavelength agility but typically produce broad spectral outputs.
• Cascaded RRFLs often use broadband reflectors, leading to wide spectral widths for high-order lasing.
• Narrowband emission is desirable for advanced laser applications.

Purpose of the Study:

• To demonstrate a tunable narrowband cascaded RRFL with improved spectral resolution.
• To achieve single- or dual-wavelength emission for each order of random lasing.
• To investigate the performance of an etalon-assisted point reflector in RRFLs.

Main Methods:

• Experimental demonstration of a cascaded RRFL incorporating an air-spaced etalon as a point reflector.
• Design of an etalon with a broad operating wavelength range, narrowband transmission, and large free spectral range (FSR).
• Characterization of laser output power, spectral width (-3 dB bandwidth), and tunability by adjusting pump wavelength or etalon tilt.

Main Results:

• Achieved 1st- to 3rd-order random Raman lasing with single-wavelength emission between 1.1-1.27 μm.
• Generated narrowband emission with -3 dB bandwidths below 0.4 nm in a 15 km single mode fiber (SMF), approximately four times narrower than conventional RRFLs.
• Demonstrated tunable single- and dual-wavelength emission, with maximum output power of 615 mW and 10% optical conversion efficiency.
• Verified potential for >1.5 W output power with <0.6 nm bandwidth using a shorter 10 km fiber.

Conclusions:

• The etalon-assisted point reflector effectively enables tunable narrowband emission in cascaded RRFLs.
• This approach significantly reduces spectral width compared to traditional broadband reflectors.
• Represents the first demonstration of tunable sub-1 nm narrowband cascaded RRFLs with single- or dual-wavelength emission per order.