Hanshuo Wu

414 W near-diffraction-limited all-fiberized single-frequency polarization-maintained fiber amplifier

A high-power 1064 nm single-frequency polarization-maintained fiber amplifier based on an all-fiber master oscillator power amplifier configuration is demonstrated. To mitigate the stimulated Brillouin scattering (SBS) and the mode instability (MI) effect, a polarization-maintained Yb-doped fiber with a high dopant concentration and a 25 μm core diameter is adopted in the main amplifier stage; in addition, step-distributed longitudinal strain is imposed on the active fiber to broaden its effective SBS gain spectrum and further increase the SBS threshold. As a result, a pump-limited 414 W single-frequency fiber laser is obtained without signs of SBS and MI. Experimental results show that the SBS threshold is increased by at least two times. The slope efficiency of the main amplifier is about 80%. The polarization degree is higher than 98% at all the power levels. The beam quality is measured with a M2 of 1.34. To the best of our knowledge, this is the highest output power of single-frequency polarization-maintained fiber amplifier based on an all-fiber structure.

Intrinsic Mechanism for Spectral Evolution in Single-Frequency Raman Fiber Amplifier

In this paper, the spectral evolution properties in single-frequency Raman fiber amplifier (RFA) based on different pump schemes are analyzed theoretically for the first time based on the gain dynamics. It reveals that the walk-off effect in counter-pumped scheme acts as a natural low-pass filter for single-frequency RFA. When multilongitudinal mode rare-earth-doped fiber laser is used as the pump source for RFA, strong temporal fluctuations of the pump source would lead to spectral broadening in copumped scheme, while single-frequency operation could be maintained in the countered-pumped case because of the natural low-pass filter.

A novel high-power all-fiberized flexible spectral filter for high power linearly-polarized Raman fiber laser

Power scaling of linearly polarized Raman fiber laser (LPRFL), which has wide application potentials, is mainly limited by the generation of high-order Stokes light. In this paper, we propose a novel flexible spectral filter with all-fiberized configuration and high-power handling. Combining with the polarization-dependence of Raman gain, the filter could be used to efficiently suppress high-order Stokes light in LPRFL and thus help further power scaling. The filter is fabricated by two 45° cross-splice of three pieces of polarization maintaining (PM) passive fibers. The bandwidth and central wavelength of transmission spectrum of the spectral filter could be flexibly tuned through changing the length and temperature of the cross-spliced fiber. The insertion loss of the filter fabricated in the lab is measured to be as low as 0.07 dB. The filter is employed in a LPRFL, and the maximum output power of the LPRFL is increased by 48.7%.

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

Fiber lasers with flexible spectral manipulation property could provide a flexible tool for scenes where the temporal coherence property accounts, for example, coherent sensing/communication and nonlinear frequency conversion. Due to the good laser performance and relative simplicity of implementation, random fiber lasers (RFLs) based on random distributed feedback and Raman gain have earned more and more attention in the past few years, and a variety of RFLs with substantially different spectral properties have been developed. In this presentation, we demonstrate a high power linearly polarized RFL with flexible spectral manipulation property, in which the central wavelength and the linewidth of the spectrum can be tuned independently through a bandwidth-adjustable tunable optical filter (BA-TOF). The central wavelength of the RFL can be continuously tuned from 1095 to 1115 nm, while the full width at half-maximum (FWHM) linewidth has a maximal tuning range from ~0.6 to more than 2 nm. Moreover, the output power of 1102.5–1112.5 nm reaches ~23 W with polarization extinction ratio (PER) value > 20 dB. To the best of our knowledge, this is the first demonstration of a powerful linearly polarized RFL with both wavelength and linewidth tunability.

High power high signal-to-noise ratio multiwavelength Raman fiber laser based on random distributed feedback

A multiwavelength Raman fiber laser based on random distributed feedback and a Sagnac fiber loop filter (SFLF) that can deliver 2.33 W output power is demonstrated. The effect of polarization state on the signal-to-noise ratio (SNR) of multiwavelength emission is investigated by the insertion and removal of a polarization beam splitter (PBS) in the cavity. With the help of a PBS and a polarization controller (PC), stable six-wavelength emission with SNR > 21 dB is achieved. To the best of our knowledge, this is the highest output power in a multiwavelength Raman fiber laser ever reported.

Hundred-watt level highly stable passively Q-switched fiber laser based on graphene saturable absorber

We demonstrate a monolayer graphene based passively Q-switched fiber laser with cascaded amplifiers that can deliver 84.1 W average power at 1064 nm, with pulse energy of 1.67 mJ. To the best of our knowledge, this is the first time for a high power passively Q-switched fiber laser in the 1 μm range reported so far. More importantly, the Q-switched fiber laser operates stably during a week few-hours-per-a-day tests, which proves the stability and practical application value of graphene in high power pulsed fiber lasers.

Passively q-switched fiber lasers based on concave gold bipyramids saturable absorbers

In our experiment, a kind of novel gold nanoparticles – concave gold bipyramids (CAuBPs) withlarge electromagnetic-field enhancement and broader plasmonic tuning rangehave been used as a saturable absorber (SA). Passively Q-switched thulium-doped and ytterbium-doped fiber lasers have been demonstrated based on CAuBPs SAs, the longitudinal surface plasmon resonance (LSPR) bands of which are located at 1 μm and 2 μm. In the 1 μm region, the maximum average output power of 9.61 mW is obtained with the shortest pulse width of 1.83 μs at the pulse repetition rate of 97.47 kHz.In the 2μm waveband, 9.72 mW average output power is obtained with the minimum pulse width of 4.56μs at the repetition rate of 19.9 kHz. To the best of our knowledge, it’s the first time that CAuBP has been used as SA, which verifies the saturable absorption properties of CAuBPs in the infrared range experimentally.

All-fiberized single-frequency polarization-maintained fiber amplifier with record power

A high power single-frequency fiber amplifier with linear polarization is demonstrated based on the master oscillator power amplifier configuration, consisting of a single-frequency seed laser at 1064.1 nm and three-stage amplifiers. To suppress stimulated Brillouin scattering, a short piece of polarization-maintaining active fiber with large core diameter of 25 μm and high pump absorption coefficient is adopted in the main amplifier. Besides, step-distributed longitudinal strain is intentionally imposed on the active fiber to broaden the effective SBS gain spectrum and correspondingly improve the SBS threshold. As a result, a pump-limited single-frequency output of 414 W is obtained with no sign of SBS and mode instability, experimentally showing that the SBS threshold is improved by at least two times through introducing extra strain.. The slope efficiency of the main amplifier is about 80 %. The polarization degree is better than 98 % at all the power levels. To the best of our knowledge, this is the highest output power of single-frequency polarization-maintained fiber amplifier based on all-fiber structure.