Fangzhou Tan

High power mid-infrared supercontinuum generation in a single-mode ZBLAN fiber with up to 21.8 W average output power

We report high power mid-infrared (mid-IR) supercontinuum (SC) generation in a single-mode ZBLAN (ZrF₄-BaF₂-LaF₃-AlF₃-NaF) fiber with up to 21.8 W average output power from 1.9 to beyond 3.8 μm pumped by amplified picosecond pulses from a single-mode thulium-doped fiber (TDF) master oscillator power amplifier (MOPA). The optical-optical conversion efficiency from the 793 nm pump laser of the last stage thulium-doped fiber amplifier (TDFA) to mid-IR SC output is 17%. It is, to the best of our knowledge, the highest average power mid-IR SC generation from a ZBLAN fiber to date.

Dissipative soliton generation from a graphene oxide mode-locked Er-doped fiber laser

We demonstrated dissipative soliton obtained from a graphene oxide mode-locked Er-doped fiber laser, which operated in normal dispersion cavity by employing the dispersion compensation fiber. The highly chirped pulses at the repetition rate of 19.5 MHz can be compressed from 11 ps to 542 fs by using single mode fiber. Numerical simulations were in good agreement with the experimental results. The hydrophilic graphene oxide with easier fabrication shows great potential to be a novel low-cost saturable absorber in reliable and compact mode-locked fiber laser system.

High-Power Thulium-Doped All-Fiber Superfluorescent Sources

Power scaling of broadband and narrowband thulium-doped all-fiber superfluorescent sources based on master-oscillator power-amplifier configuration is reported. For scaling the output-power of broadband superfluorescent fiber source, a stable low-power broadband superfluorescent fiber seed source and a two-stage cladding-pumped thulium-doped fiber amplifiers were adopted. The thulium-doped fiber power amplifier yielded 122 W of broadband superfluorescence output, and the wavelength range spanned from 1935-2075 nm with a full width at half maximum (FWHM) of 25 nm. To the best of our knowledge, this is the first demonstration of superfluorescence power exceeding 100 W from thulium-doped fiber amplifiers at 2 μm. In addition, we also investigate the power scaling of narrowband thulium-doped superfluorescent fiber source based on a tunable narrowband superfluorescent fiber seed source by selecting a small region out of a broadband superfluorescence spectrum using a narrowband fiber Bragg grating. The two-stage cladding-pumped thulium-doped all-fiber amplifiers were used directly to boost average power to 120 W, the center wavelength and the FWHM were 1963.5 and 1.2 nm, respectively. The presented high power broadband and narrowband superfluorescent fiber source could be of great interest and open up the prospect of many new applications such as laser materials processing and metrology.

Pulse-shaping mechanisms in passively mode-locked thulium-doped fiber lasers

Different pulse-shaping mechanisms were investigated experimentally and numerically in passively mode-locked thulium-doped fiber lasers. Conventional solitons were demonstrated in a passively semiconductor saturable absorber mirror mode-locked anomalous dispersion thulium-doped fiber laser. With normal dispersion fiber and spectral filter added in cavity, pulse-shaping processes were theoretically analyzed in the presence of dispersion map and dissipation in thulium-doped fiber lasers. The existence of parabolic pulse as nonlinear attraction was proved and distinct pulse intensity profiles evolution from Gaussian shape to parabolic shape was proposed in dissipative dispersion-managed thulium-doped fiber lasers.

High-power operation of silica-based Raman fiber amplifier at 2147 nm.

We demonstrated a 2147 nm silica-based Raman fiber amplifier with output power of 14.3 W directly pumped with a 1963 nm CW thulium-doped all-fiber MOPA. The 1963 nm thulium-doped all-fiber MOPA is seeded with a 2147 nm thulium-doped all-fiber laser at the same time. The Raman Stokes power shift from 1963 nm to 2147 nm is accomplished in a piece of 50 m silica-based highly nonlinear fiber (HNLF). The conversion efficiency was 38.5% from 1963 nm to 2147 nm in the HNLF. The output power achieved was only currently limited by available 1963 nm input power and the architecture has significant scaling potential. To the best of our knowledge, this is the highest power operation of a Raman fiber amplifier at >2 µm wavelength region.

High-power all-fiber femtosecond chirped pulse amplification based on dispersive wave and chirped-volume Bragg grating

We report a high-power all-fiber-integrated femtosecond chirped pulse amplification system operating at 1064 nm, which consists of a dispersive wave source, a fiber stretcher, a series of ytterbium-doped amplifiers and a chirped volume Bragg grating (CVBG) compressor. The dispersive wave is generated by an erbium-doped mode-locked fiber laser with frequency shifted to the 1 μm region in a highly nonlinear fiber. With three stages of ytterbium-doped amplification, the average output power is scaled up to 125 W. Through CVBG, the pulse duration is compressed from 525 ps to 566 fs, the average output power of 107 W with a high compression efficiency of 86% is achieved, and the measured repetition rate is 17.57 MHz, corresponding to the peak power of 10.8 MW.

1 μJ, sub-300 fs pulse generation from a compact thulium-doped chirped pulse amplifier seeded by Raman shifted erbium-doped fiber laser

We present a compact thulium-doped chirped pulse amplifier producing 241 fs pulses with 1 μJ energy. The system is seeded with the Raman shifted soliton generated by the combination of an erbium-doped femtosecond laser and a nonlinear fiber. The Tm-doped large mode area fiber yields output power of 71 W, corresponding to pulse energy of 2.04 μJ, with a slope efficiency of 52.2%. The amplified pulses have been compressed to a duration time of 241 fs, using a folded Treacy grating setup. The pulse energy is measured to be 1.02 μJ, corresponding to a peak power of ~3 MW. To the best of our knowledge, this is the highest average power and pulse energy generated from an all-fiber, Raman shifted soliton seeded thulium-doped chirped pulse amplifier system.

Enhanced tunable Raman soliton source between 19 and 236 μm in a Tm-doped fiber amplifier

We demonstrate generation of widely tunable femtosecond pulses by utilizing the soliton self-frequency shift effect in a Tm-doped fiber amplifier, seeded by dispersion managed mode-locked Tm oscillator. The monochromatic soliton pulses with a duration of the order of 100 fs have been obtained and its wavelength can be adjusted continuously in the range of 1.9-2.36 μm by varying the pump power. The efficiency of Raman conversion is as high as 97% with output power up to 1.16 W. The experimental results are in good agreement with numerical simulations of pulse propagation in Tm-doped fiber amplifier.

Multi-watt mid-infrared supercontinuum generated from a dehydrated large-core tellurite glass fiber

We report for the first time multi-watt mid-infrared supercontinuum (SC) output from a dehydrated tellurite step-index fiber. The tellurite glass preform is melted in a dry-atmosphere filled glovebox and the water impurity in the glass has been reduced to 1ppm level. The fiber has a large core diameter of 12 µm and a numerical aperture (NA) of 0.21. Using the amplified Raman-shifted soliton pulses from a 1.55 µm erbium-doped fiber laser as the pump, a broadband 2-3 µm supercontinuum with a 3dB bandwidth of 985 nm has been generated from an 80cm-long dehydrated tellurite glass fiber. The power spectral density of the SC is above 3.5 dBm/nm in the whole range of 2-3 µm. The net output power of the supercontinuum from the tellurite fiber is measured to be 2.1 W. To the best of our knowledge, this is the highest average power of mid-IR SC generated from a tellurite fiber. The spectral density of above 3 dBm/nm is also one of the highest spectral densities of a SC achieved in 2.5-3 μm range from an oxide glass fiber.

Power Scaling of Linearly-polarized Thulium-doped All-fiber Picosecond MOPA

We demonstrated a linearly-polarized thulium-doped all-fiber picosecond MOPA with average power of 203 W at central wavelength of 1985 nm. The pulse duration and polarization extinction ratio (PER) were 15 ps and >15 dB respectively.