Quantum defect (QD) is an important issue that demands prompt attention in high-power fiber laser. Large QD may aggravate the thermal load in the laser, which would impact the frequency and amplitude noise, mode stability and threaten the security of high-power laser system. Here, we propose and demonstrate a cladding-pumped Raman fiber laser (RFL) with QD <1%. Using the Raman gain of the boson peak in a phosphorusdoped fiber to enable the cladding pump, the QD is reduced to as low as 0.78% with a 23.7 W output power. To our knowledge, this is the lowest QD ever reported in claddingpumped RFL. Furthermore, the output power can be scaled to 47.7 W with a QD of 1.29%. This work not only offers a preliminary platform for the realization of high-power low-QD fiber laser, but also proves low-QD fiber laser's great potential in power scaling.
The phosphosilicate fiber-based Raman fiber laser (RFL) has great potential in achieving low-quantum defect (QD) high-power laser output. However, the laser’s performance could be seriously degraded by the Raman-assisted four-wave mixing (FWM) effect and spontaneous Raman generation at 14.7 THz. To find possible ways to suppress the Raman-assisted FWM effect and spontaneous Raman generation, here, we propose a revised power-balanced model to simulate the nonlinear process in the low-QD RFL. The power evolution characteristics in this low-QD RFL with different pump directions are calculated. The simulation results show that, compared to the forward-pumped low-QD RFL, the threshold powers of spontaneous Raman generation in the backward-pumped RFL are increased by 40% and the Raman-assisted FWM effect is well suppressed. Based on the simulation work, we change the pump direction of a forward-pumped low-QD RFL into backward pumping. As a result, the maximum signal power is increased by 20% and the corresponding spectral purity is increased to 99.8%. This work offers a way for nonlinear effects controlling in low-QD RFL, which is essential in its further performance scaling.
Interplay between dispersion and nonlinearity in optical fibers is a fundamental research topic of nonlinear fiber optics. Here we numerically and experimentally investigate an incoherent continuous-wave (CW) optical field propagating in the fiber with normal dispersion, and introduce a distinctive spectral evolution that differs from the previous reports with coherent mode-locked fiber lasers and partially coherent Raman fiber lasers [Nat. Photonics 9, 608 (2015).]. We further reveal that the underlying physical mechanism is attributed to a novel interplay between group-velocity dispersion (GVD), self-phase modulation (SPM) and inverse four-wave mixing (IFWM), in which SPM and GVD are responsible for the first spectral broadening, while the following spectral recompression is due to the GVD-assisted IFWM, and the eventual stationary spectrum is owing to the dominant contribution of GVD effect. We believe this work can not only expand the light propagation in the fiber to a more general case and help advance the physical understanding of light propagation with different statistical properties, but also benefit the applications in sensing, telecommunications and fiber lasers.
In this paper, we propose and experimentally demonstrate a vortex random fiber laser (RFL) with a controllable orbital angular momentum (OAM) mode. The topological charge of the vortex RFL can range from − 50 t o 50 with nearly watt-level output power. A triangular toroidal interferometer is constructed to verify the spiral phase structure of the generated vortex random laser with a special coherence property. Vortex RFLs with fractional topological charge are also performed in this work. As the first demonstration of a vortex RFL with a controllable OAM mode (to the best of our knowledge), this work may not only offer a valuable reference on temporal modulation of a vortex beam and optical field control of an RFL but also provide a potential vortex laser source for applications in imaging, sensing, and communication.
Multiwavelength fiber lasers, especially those operating at optical communication wavebands such as 1.3 μm and 1.5 μm wavebands, have huge demands in wavelength division multiplexing communications. In the past decade, multiwavelength fiber lasers operating at 1.5 μm waveband have been widely reported. Nevertheless, 1.3 μm waveband multiwavelength fiber laser is rarely studied due to the lack of proper gain mechanism. Random fiber laser (RFL), owing to its good temporal stability and flexible wavelength tunability, is a great candidate for multiwavelength generation. Here, we reported high power multiwavelength generation at 1.3 μm waveband in RFL for the first time. At first, we employed a section of 10 km G655C fiber to provide Raman gains, as a result of which, 1.07 W multiwavelength generation at 1.3 μm waveband with an optical to signal noise ratio of ∼33 dB is demonstrated. By tuning the pump wavelength from 1055 nm to 1070 nm, tunable multiwavelength output covering the range of 1300-1330 nm can be achieved. Furtherly, we realized 4.67 W multiwavelength generation at 1.3 μm waveband by shortening the fiber length to 4 km. To the best of our knowledge, this is the highest output power ever reported for multiwavelength fiber lasers.
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