Flexible spectral manipulation property of a high power linearly polarized random fiber laser

Multi-color switchable visible light source generated via nonlinear frequency conversion of a random fiber laser

Nonlinear frequency conversion of random fiber lasers could provide new possibilities to realize visible and mid-infrared light with flexible wavelength and low temporal/spatial coherence. Frequency doubling of random fiber laser is reported to generate visible light with single-color output. Here, we propose a new way to generate multi-color switchable visible light source from a dual-wavelength switchable 1^st-order random Raman fiber laser (RRFL) with phosphosilicate fiber. Taking advantage of the existence of the two Raman gain peaks with significant different Raman gain bandwidth at the frequency shifts of 13.2 THz (silica-related one with broad Raman gain bandwidth) and 39.9 THz (phosphorus-related one with narrow Raman gain bandwidth) in phosphosilicate fiber, a dual-wavelength switchable RRFL is developed which can emit 1120 and 1238 nm random Raman lasing individually or simultaneously with 3-watt level output power and sub-1 nm bandwidth by precisely tuning the pump wavelength to manipulate the Raman gain at two fixed Raman Stokes wavelengths. It is expected that the output power can be further increased with a shorter fiber length and more powerful pump, and the spectral bandwidth can be much narrower by adopting a narrowband point reflector in 1^st-order RRFL. Based on the dual-wavelength RRFL with a flexible power ratio and a periodically poled lithium niobate (PPLN) crystal array containing three separate poled gratings with different periods, the second-harmonic generation of 1120 nm or 1238 nm random lasing and sum-frequency generation of 1120 nm and 1238 nm random lasing can be performed. As a result, the switchable output of green light at 560 nm, yellow light at 588 nm and red light at 619 nm can be realized with optical power of 22.2 mW, 16.9 mW and 18.5 mW, respectively. Our work demonstrates dual-wavelength RRFL could act as a new platform for generating visible light source with flexible color output which has potential applications in imaging, sensing and visible temporal ghost imaging.

Self-gain-modulation random distributed feedback Raman fiber laser with switchable repetition rate

We experimentally demonstrate a pulsed operation in a random fiber laser operation via self-gain-switching. The pulses have low timing jitter and high average output power. We show that repetition rate switches abruptly while varying the pump power, and introduce a simple formula for oscillation frequencies.

Tunable narrowband cascaded random Raman fiber laser

Random Raman fiber lasers (RRFLs) with half-opened cavity have been used as a new platform for designing high performance, wavelength-agile laser sources in the infrared region due to their intrinsic modeless property and structural simplicity. To provide the point feedbacks for cascaded random Raman lasing at different wavelengths, wavelength-insensitive broadband reflectors are commonly used in cascaded RRFLs, resulting in the rather broad high-order random Raman lasing with several nanometers of typical spectral width. Here, we experimentally demonstrate a tunable narrowband cascaded RRFL with an air-spaced etalon assisted point reflector. To realize narrowband, single- or dual-wavelength emission for each order of random lasing, the etalon is specially designed to have broad operation wavelength range, narrowband transmission lines and large free spectral range (FSR) associated with the Raman frequency shift. As a result, 1st- to 3rd-order random Raman lasing with single-wavelength emission in 1.1-1.27 μm region are generated in a 15 km single mode fiber (SMF) with -3 dB bandwidths below 0.4 nm, which are approximately four times less than those of cascaded RRFL without etalon. The maximum output power of the 3rd-order random Raman lasing is 615 mW, with 10% of optical conversion efficiency. Moreover, a tunable cascaded RRFL is performed by tuning the wavelength of pump laser or tilting the etalon. Dual-wavelength emission for each order of random lasing can also be realized at specific pump wavelengths. We also verified, by employing shorter fiber (10 km), more than 1.5 W output power of high-order RRFL can be achieved with -3 dB bandwidths less than 0.6 nm. To the best of our knowledge, this is the first demonstration of tunable sub-1 nm narrowband cascaded RRFL with single- or dual-wavelength emission for each order of random lasing.