A Chinese team has developed a 1.2μm band high-power tunable Raman fiber laser

Laser sources operating in the 1.2μm band have some unique applications in photodynamic therapy, biomedical diagnostics, and oxygen sensing. In addition, they can be used as pump sources for parametric generation of mid-infrared light and for generating visible light by frequency doubling. Lasers in the 1.2 μm band have been achieved with different solid-state lasers, including semiconductor lasers, diamond Raman lasers, and fiber lasers. Among these three lasers, fiber laser has the advantages of simple structure, good beam quality and flexible operation, which makes it the best choice to generate 1.2μm band laser.

Recently, the research team led by Professor Pu Zhou in China is interested in high-power fiber lasers in the 1.2μm band. The current high power fiber lasers are mainly ytterbium-doped fiber lasers in the 1 μm band, and the maximum output power in the 1.2 μm band is limited to the level of 10 W. Their work, entitled “High power tunable Raman fiber laser at 1.2μm waveband,” was published in Frontiers of Optoelectronics.

FIG. 1: (a) Experimental setup of a high-power tunable Raman fiber amplifier and (b) tunable random Raman fiber seed laser at 1.2 μm band. PDF: phosphorus-doped fiber; QBH: Quartz bulk; WDM: Wavelength division multiplexer; SFS: superfluorescent fiber light source; P1: port 1; P2: port 2. P3: indicates port 3. Source: Zhang Yang et al., High power tunable Raman fiber laser at 1.2μm waveband, Frontiers of Optoelectronics (2024).
The idea is to use the stimulated Raman scattering effect in a passive fiber to generate a high-power laser in the 1.2μm band. Stimulated Raman scattering is a third-order nonlinear effect that converts photons to longer wavelengths.

Figure 2: Tunable random RFL output spectra at (a) 1065-1074 nm and (b) 1077 nm pump wavelengths (Δλ refers to 3 dB linewidth). Source: Zhang Yang et al., High power tunable Raman fiber laser at 1.2μm waveband, Frontiers of Optoelectronics (2024).
The researchers used the stimulated Raman scattering effect in the phosphorus-doped fiber to convert a high-power ytterbium-doped fiber at 1 μm band to 1.2 μm band. A Raman signal with a power of up to 735.8 W was obtained at 1252.7 nm, which is the highest output power of a 1.2 μm band fiber laser reported to date.

Figure 3: (a) Maximum output power and normalized output spectrum at different signal wavelengths. (b) Full output spectrum at different signal wavelengths, in dB (Δλ refers to 3 dB linewidth). Source: Zhang Yang et al., High power tunable Raman fiber laser at 1.2μm waveband, Frontiers of Optoelectronics (2024).

Figure :4: (a) Spectrum and (b) power evolution characteristics of a high-power tunable Raman fiber amplifier at a pumping wavelength of 1074 nm. Source: Zhang Yang et al., High power tunable Raman fiber laser at 1.2μm waveband, Frontiers of Optoelectronics (2024)