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开展了1 915 nm高功率、高效率、窄谱宽输出的掺铥光纤激光器（TDFL）研究。基于全光纤主振荡功率放大（MOPA）结构，采用40 W的793 nm半导体激光器泵浦纤芯直径25 m的双包层大模场面积（LMA）掺铥光纤，获得了最高功率12.1 W的1 915 nm窄谱宽连续种子激光输出。将8 W种子光注入掺铥光纤放大器，在793 nm激光泵浦功率为142.9 W时，获得了平均功率90 W的激光输出，其中心波长为1 915.051 nm，3 dB谱宽仅为94 pm，斜率效率为60.2%，光-光转换效率达63.0%。该系统在40 min运行考核时间内输出激光稳定性良好。

An all-fiber multiwavelength Tm-doped laser based on four-wave mixing in highly-germania-doped-highly-nonlinear-fiber (HG-HNLF) has been demonstrated. By using 50-m HG-HNLF to provide intensity-depended gain, 36 lasing lines with wavelength spacing of 0.86 nm within 30-dB bandwidth is obtained.

We propose an all-fiber Tm-doped fiber laser with a tunable and narrow laser line generated in a wavelength region of 2 µm. A single laser line with a linewidth below 0.05 nm, tunable in a wavelength range of 44.25 nm, is obtained. The laser linewidth and the discrete wavelength tuning range depend on the characteristics of the two fiber optical loop mirrors with high birefringence in the loop that forms the cavity. Dual-wavelength laser operation is also observed at tuning range limits with a wavelength separation of 47 nm. Alternate wavelength switching is also observed.

All-fiber Tm3+-doped silica fiber laser operating at 2 μm region was demonstrated. The wavelength of the fiber laser can be selected from 1925 nm to 2200 nm by using different fiber Bragg gratings (FBGs) as wavelength selection elements. By employing a FBG arrays in the laser cavity, six switchable lasing wavelengths were achieved. The presented fiber laser can be useful for dense wavelength division multiplexing systems.

A graphene-based saturable absorber was fabricated by optically depositing layers of graphene onto the end tip of single mode fiber, and it was used to passively Q-switch thulium-doped fiber laser at 2 µm pumped by EDFA. The spectrum of the graphene Q-switched thulium-doped fiber laser and the relationship between the output power, repetition rate and pump strength are studied and presented.

We report a dissipative dispersion-managed mode-locked thulium-doped fiber laser. 40 kW peak power is obtained after one-stage single-mode thulium-doped fiber amplifier with pulse duration of 285 fs.

We investigated characteristics of two typical pulses in passively mode-locked thulium-doped fiber lasers. The dissipative soliton pulse-shaping operation without additional spectral filter in the thulium-doped fiber laser was demonstrated in numerical simulation

We report stabilization of a thulium-holmium codoped fiber soliton laser with a saturable absorber based on carbon nanotubes. The laser generates transform-limited 750-fs pulses with 0.5-nJ energy.

We successfully demonstrated a simple, compact and low cost passive Q-switched Thulium doped fiber laser (TDFL) at long wavelength of 1854.3 nm regions in conjunction with 1552 nm pump excitation. A stable pulse has been generated using graphene film based saturable absorber (SA). The graphene is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulphate (SDS) aqueous solution. Graphene flakes obtained from the process are mixed with polyethylene oxide (PEO) as the host polymer to produce free standing composite thin film which acts as a passive Q-switcher in the TDFL ring cavity. The SA is fabricated by sandwiching the graphene thin film between two fiber connectors. At 1552 nm pump power of 498 mW, a stable pulse train has been observed with a repetition rate of 6.51 kHz and pulse duration of 11.51 μs. The high performances of Q-switched laser suggest that the new type of saturable absorber based on electrochemical exfoliation in conjunction with all-fiber ring cavity configuration is suitable for a Q-switcher near 1900 nm wavelength.

We report a supercontinuum spanning well over an octave of measurable bandwidth from about 1 to 3.7 μm in a 2.1 mm long As₂S₃ fiber taper using the in situ tapering method. A sub-100-fs mode-locked thulium-doped fiber laser system with ~300 pJ of pulse energy was used as the pump source. Third-harmonic generation was observed and currently limits the pump pulse energy and achievable spectral bandwidth.

In order to obtain high slope efficiency of 2 μm laser output, it is essential to design operating parameters of fiber laser prior to the experiment. Based on the rate equations, the pump and signal power equations of thulium doped fiber laser have been built. The effects of the cross relaxation coefficient K3101, the pump power filling factor Γp, the laser reflectivity of input mirror R3, the laser reflectivity of output mirror R4, and the Tm3+ concentration N of kilowatt level thulium doped fiber laser on the slope efficiency have been theoretically analyzed by an improved shooting algorithm. The results indicate that the slope efficiency decreases with the increasing laser reflectivity of output mirror, the pump power filling factor. Meanwhile, the slope efficiency increases with the increasing laser reflectivity of input mirror, the doping concentration and the cross relaxation coefficient, but the doping concentration and the cross relaxation coefficient have more obvious influence on the slope efficiency compared with the laser reflectivity of input mirror.

In this study, we demonstrate an S/S+ band discretely tunable thulium-doped fiber laser (TTDFL), locked to the 50-GHz ITU-T grid. By optimizing the inversion dynamics of the thulium-doped fiber while using a dual-wavelength (1.4 and 1.5 /spl mu/m) pumping scheme, 66.2 nm of tuning range (1452.2-1518.4 nm) that cover most of the thulium bandwidth, and more than 6.7 dBm of output power were obtained. By controlling the temperature of the fine grid filter, we also stabilized the output frequency of the TTDFL to within /spl plusmn/2 pm.

We report on ring thulium-doped fiber laser hybrid mode-locked by single-walled carbon nanotubes and nonlinear polarization evolution generating 600-fs pulses at 1910-1980nm wavelength band with 72.5MHz repetition rate. Average output power reached 300mW in single-pulse operation regime, corresponding to 4.88kW peak power and 2.93nJ pulse energy.

We demonstrated that SESAM mode-locked thulium-doped fiber laser produced stable nanosecond pulses from 2.5ns to 12.5ns at repetition rates between 1.72MHz and 258kHz. Average power of 5.6W at 1942nm was obtained by two-stage all-fiber amplifiers.

A mode-locked thulium-doped fiber laser (TDFL) based on nonlinear polarization rotation (NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is −1.425 ps2, the noise-like (NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 dB, and 0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.

In this work, a compact thulium-doped fiber laser with a Q-switched output is proposed and demonstrated. A thulium-doped fiber is used for the laser, with a peak absorption of 200 dB m−1 at 790 nm and a cutoff wavelength of 1350 nm as the primary gain medium, and a silver-based saturable absorber as the pulse generation mechanism. The pulses obtained from the proposed laser have repetition rates from 38.3 kHz up to 56.2 kHz, with a pulse width as low as 4.2 µs and pulse energy as high as 67.3 nJ at a maximum pump power of 228.8 mW. The generated pulses are highly stable, showing no changes or fluctuations over operation for a period of 60 min, and further validated with signal-to-noise ratios of 57.0 dB and 59.5 dB in the optical and frequency domains respectively. The proposed laser has high potential for eye-safe applications in manufacturing and medicine.

Optical parametric generation is demonstrated in orientation-patterned gallium arsenide, pumped by a novel single-oscillator simultaneously Q-switched and mode-locked thulium-doped fiber laser, downconverting the pump radiation into the mid-infrared wavelength regime. The maximum output energy reached is greater than 2.0 μJ per pump pulse.

A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single-and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single-and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873–1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.

We proposed a multimode interference (MMI) fiber based saturable absorber using bismuth telluride at ~2 μm region. Our MMI based saturable absorber was fabricated by fusion splicing with single mode fiber and null core fiber. The MMI functioned as both wavelength fixed filter and saturable absorber. The 3 dB bandwidth and insertion loss of MMI were 42 nm and 3.4 dB at wavelength of 1958 nm, respectively. We have also reported a passively mode locked thulium doped fiber laser operating at a wavelength of 1958 nm using a multimode interference. A temporal bandwidth of ~46 ps was experimentally obtained at a repetition rate of 8.58 MHz.

An ultrafast thulium-doped fiber laser with stretched-pulse operation has been realized and investigated. The passively mode-locked oscillator emitted 119 fs pulses at a peak wavelength of 1912 nm. A normal-dispersion fiber with a high numerical aperture and small core was used for intracavity dispersion management and external compression. Numerical simulations were performed and are in good agreement with the experimental results.

Ultrashort pulses in a thulium-doped fiber laser were generated with a fiber based dispersion management. The laser emitted sub-500 fs pulses which were compressed externally with a normal dispersive fiber below 130 fs.

A high energy, high power ultrafast Tm doped fiber laser system was successfully developed. Pulse energy of 156 μJ and average power of 15.6 W were achieved. The laser system consisted of a mode-locked 2020 nm seed oscillator and multiple-stage power amplifiers. The seed included 30 m-long dispersion compensating fiber and emitted slightly chirped pulses with spectrum bandwidth of 8 nm. The mode-locking was stable and self-started. Repetition rate of seed oscillator was 2.5 MHz. The seed pulses were stretched with anomalous dispersion fiber to the duration of 320 ps. An AOM was used as a pulse picker to lower the repetition rate. A two-stage pre-amplifier was used to boost the pulse energy to 3 μJ. Pulse energies of up to 156 μJ were obtained from the final stage of power amplifier at a repetition rate of 100 kHz. Pulse durations of 780 fs were obtained after pulse compression. High OSNR and low background noise were also achieved at this low repetition rate.

Pulsed thulium-doped silica fiber laser operating at a wavelength of 1994.8 nm was developed. The laser was fast gain-switched by 1.55-μm radiation generated from a fiber amplifier system seeded by a directly modulated distributed feedback semiconductor laser. The Tm-doped fiber laser delivered stable nanosecond pulses at a repetition rate ranging from 50 kHz to 300 kHz. The maximum average output power as high as 1.08 W with a slope efficiency of 49% for the repetition rate of 100 kHz was reported. The shortest stable pulses recorded had a width of (20-25) ns and the energy of

In this paper it is shown that pumping at the excited state of Thulium high-power fibers leads to a significant cooling and efficiency improvement. Nearly a factor 2 higher efficiency is expected with this technique.

A broadband wavelength tunable mode-locked Tm3+-doped fiber laser operating in the 2 μm region based on a graphene saturable absorber is experimentally investigated. A section of graphene film is transferred on a microfiber, which allows light-graphene interaction via evanescent field. The microfiber based graphene not only acts as an excellent saturable absorber for mode-locking, but also induces a polarizing effect to form an artificial birefringent filter for wavelength selection. By tuning the polarization states in the laser cavity, the laser exhibits tunable wavelength mode-locked pulses over a wide range from 1880 to 1940 nm. Such a system provides a compact, user friendly and low cost wavelength tunable ultrashort pulse source in the 2 μm region.

We report on monotonically positively chirped pulse operation of a hybridly mode-locked thulium fiber laser. Dispersion management was realized with a small-core, high-NA fiber providing normal dispersion in the 2 μm wavelength region. The laser delivered pulses with 0.7 nJ energy at the 1927 nm center wavelength and sub-500-fs pulse duration after compression.

We report on a passively mode-locked thulium fiber laser with fiber based dispersion management. The laser delivers positively chirped pulses with 0.7 nJ of pulse energy, which can be compressed to sub-500 fs duration.

In this Letter we report on dispersion managed soliton thulium fiber laser operating at 1.93-1.97 µm and thulium-ytterbium amplifier. The anomalous dispersion in the laser cavity is compensated by the insertion of germanium-silicate fiber.

The steady-state gain distribution in cladding pumped thulium-doped fiber laser (TDFL) is analytically and numerically solved based on the rate equations including loss coefficients and cross relaxation effect. With the gain curve, a problem, which is named optical feedback inhibition (OFI) and always occurs in tandem TDFL-Ho:YAG laser system, is analyzed quantitatively. The actual characteristics of output spectra and power basically prove the conclusion of theoretical analysis. Then a simple mirror-deflected L-shaped cavity is employed to restrain the external feedback and simplify the structure of fiber-bulk Ho:YAG laser. Finally, 25 W of 2097-nm laser power and 51.2% of optical-to-optical conversion efficiency are obtained, and the beam quality factor is less than 1.43 obtained by knife-edge method.

This paper describes a low pass filter based on photonics crystal fiber (PCF) partial ASE suppression, and its application within a 1.7 µm to 1.8 µm band thulium-doped fiber amplifier (TDFA) and a thulium-doped fiber laser (TDFL). The enlargement of air holes around the doped core region of the PCF resulted in a low-pass filter device that was able to attenuate wavelengths above the conventional long cut-off wavelength. These ensuing long cut-off wavelengths were 1.85 μm and 1.75 μm, and enabled a transmission mechanism that possessed a number of desirable characteristics. The proposed optical low-pass filter was applied within a TDFA and TDFL system. Peak spectrum was observed at around 1.9 μm for conventional TDF lasers, while the proposed TDF laser with PCF setup had fiber laser peak wavelengths measured at downshifted values of 1.74 μm and 1.81 μm.

A high energy all-fiber format nanosecond thulium-doped fiber laser at 2050 nm with a master oscillator power amplifier (MOPA) configuration is presented in this paper. The seed oscillator is a linearly polarized gain-switched fiber laser pumped by a 1550 nm fiber laser. The output pulse of the seed has a polarization extinction ratio (PER) better than 16 dB with a maximal output power of 470 mW. After two-stage double- cladding fiber amplifiers, the average power at 40 kHz was boosted up to 40.5 W. The output pulse has a maximum pulse energy of 1 mJ with a pulse width of 100 ns, which corresponds to a peak power of 10 kW. To the best of our knowledge, it is the highest single pulse energy ever reported for a nanosecond thulium-doped all-fiber MOPA system at 2050 nm.

We propose and demonstrate a widely tunable multiwavelength thulium-doped fiber laser using a hybrid filter in order to expand the tuning range of a multiwavelength laser. The hybrid filter consists of an all-fiber interferometer and a tunable spatial mode-beating filter (SMBF). The operation principles of the interferometer and the tunable filter are analyzed. With a pump power of 200 mW, the number of wavelength can be tuned from one to nine by adjusting the polarization controller in the interferometer, and the multiwavelength laser can be tuned from 1896 to 1936 nm by adjusting the polarization controller in the SMBF. The wavelength spacing is 0.35 nm, and the linewidth of a single-wavelength is 0.03 nm. When pump power increases to 1 W, the spacing of dual-wavelength laser can be tuned from 6 to 36 nm.

We report mode-locking of an all-fiber thulium/holmium (Tm/Ho) co-doped laser with a saturable absorber based on a fiber taper embedded in carbon nanotube/polymer composite (FTCNTPC). 750fs soliton pulses are generated at wavelength around 1890nm.

In this paper, we apply a transverse mode propagation model of thulium-doped fiber laser based on propagation equations. Based on this model the behaviors of transverse mode propagation are demonstrated and individual transverse mode power distributions of output are simulated numerically under various conditions including bending radius, fiber length, and pump power. Furthermore, the output power and beam quality characteristic for the thulium-doped fiber laser are investigated experimentally, and the experimental results agree well with the numerical results.

We demonstrate highly efficient diode-pumped single-frequency fiber laser with 35% slope efficiency and 50mW output power operating near 2μm, which generated from a 2-cm long piece of highly Tm3+-doped germanate glass fiber pumped at 800nm.

We report the first demonstration of a unidirectional, isolator-free 2-mmthulium-doped fiber (TDF) laser, relying on the properties of the theta cavity (ring resonator with S-shaped feedback). The core pumped theta cavity TDF laser provides sub-Watt output power with a slope efficiency of 25%, a 2 dB flat tuning range of 1900–2050 nm, and a linewidth of 0.2 nm, and achieves the extinction ratio of 18– 25 dB (depending on the feedback value) between the favored and suppressed lasing directions. It is shown that these characteristics are competitive with, if not superior to, those of conventional ring cavities. The simulation results of the linear and Kerr-nonlinear theta cavities are also presented, explaining certain unexpected features of the laser behavior and establishing the importance of the doped fiber nonlinearity on the spectral shaping of the emitted signal.

We demonstrated a high-power, single-frequency (SF), all-fiber-format, thulium-doped master oscillator power amplifier (MOPA) system. The MOPA is seeded by a distributed feedback (DFB) diode laser and yields 75 W of SF laser output at a central wavelength of 2050.5 nm with a linewidth of 1 MHz. There is no indication of stimulated Brillouin scattering or gain saturation observed at the maximum output power, which means the output power was only limited by the available pump power. This is the highest output power, to the best of our knowledge, in the SF all-fiber thulium-doped MOPA at 2050 nm.

A thulium-doped fiber laser employing a Sagnac loop mirror made by a 145.5 cm polarization-maintaining fiber is demonstrated, which can operate with stable dual-wavelength lasing or tunable single-wavelength lasing around 1860 nm. Both stable dual-wavelength and tunable single-wavelength lasing are achieved by adjusting a polarization controller in the Sagnac loop mirror. The experimental results show that the output of the reported fiber laser with two different operation modes is rather stable at room temperature.

A 1,000 nm wide supercontinuum, spanning from 1470 nm in the telecom band to 2470 nm in the mid-infrared is demonstrated in a 800 nm x 220 nm 1 cm long hydrogenated amorphous silicon strip waveguide. The pump source was a picosecond Thulium doped fiber laser centered at 1950 nm. The real part of the nonlinear parameter of this waveguide at 1950 nm is measured to be 100 ± 10 W -1m-1, while the imaginary part of the nonlinear parameter is measured to be 1.2 ± 0.2 W-1m-1. The supercontinuum is stable over a period of at least several hours, as the hydrogenated amorphous silicon waveguides do not degrade when exposed to the high power picosecond pulse train.

The temporal output characteristics of an all-fiber gain-switched thulium-doped fiber laser near threshold are investigated experimentally and numerically. The pulse repetition rate and pulse energy of the 1550 nm pump source are found to be two important parameters that affect the laser performance. Adjusting these two parameters, three different output working states, namely no lasing state, unstable state, and steady state, are observed experimentally. Particularly, in the unstable state relatively stable output pulse trains with repetition rate trisecting (PRR 1/3) and halving (PRR 1/2) with respect to the pump source are found. The experimental results together with corresponding numerical simulation afford a deep insight into the related lasing mechanisms.

We demonstrate a simple, compact and low cost Q-switched thulium-doped fiber laser (TDFL) operating at 1844.1 nm by exploiting a graphene based saturable absorber (SA) in conjunction with 1552 nm pumping. The SA is fabricated by sandwiching the graphene thin film between two fiber connectors. The thin film was produced by mixing graphene flakes, synthesized by an electrochemical exfoliation process, with polyethylene oxide (PEO) solution. The TDFL generates a stable pulse train with 6.73 kHz repetition rate, 11.41 μs pulse width and 90.64 nJ pulse energy at 513 mW 1552 nm pump power. A higher performance Q-switched TDFL is expected to be achieved with the optimization of the SA and laser cavity.

We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser (TDFL) using a newly developed single-wall carbon nanotube-based saturable absorber. The TDFL generates the 25th harmonic mode-locked stretched pulse train with a high repetition rate of 213 MHz and a pulse duration of 710 fs. The laser operates at 1901.6 nm with an average power of 1.89 mW, which corresponds to the pulse energy of 0.008 nJ, at 1552 nm pump power of 719 mW. The peak-to-background ratio is measured to be 60 dB, which indicates the stability of the laser.

We report a supercontinuum spanning well over an octave of measurable bandwidth from about 1 to 3.7 μm in a 2.1 mm long As2S3 fiber taper using the in situ tapering method. A sub-100-fs mode-locked thulium-doped fiber laser system with ∼300 pJ of pulse energy was used as the pump source. Third-harmonic generation was observed and currently limits the pump pulse energy and achievable spectral bandwidth.

We have demonstrated an all-fiber mode-locked thulium-doped fiber laser with extremely long pulses, a very narrow spectrum and a high average power. The mode-locker is formed by a nonlinear loop mirror. The laser generates sinus-squared waveform with a repetition period of 82 ns and an average power between 100 and 150 mW. The wavelength is defined by the fiber Bragg grating and is 1956 nm.