Thulium-doped Silica Fiber Laser Research Articles

Amplification at 2.3-µm in 1.9-µm thulium-doped silica fiber laser

A high-power 1.9-µm Tm3+-doped silica fiber laser generates 7.3-dB of gain at 2.3 µm when cladding- pumped with 207 W of power at 793 nm. We attribute the 2.3-µm gain to the transition 3H4 → 3H5 of Tm3+.

Monolithic ultrashort-cavity DBR gain-switched thulium doped fiber laser made by high-precision femtosecond laser direct-writing

We demonstrate a novel monolithic ultrashort-cavity distributed Bragg reflector (DBR) gain-switched thulium doped silica fiber laser. Commercial heavily thulium doped non-polarization-maintaining silica fiber was selected as the gain medium. Monolithic linear laser resonator, which includes a pair of uniform fiber Bragg gratings (FBGs) with a space of 1.0-mm inbetween, was inscribed in the thulium fiber by femtosecond-laser point-by-point (PbP) writing method. The reflectivity of either FBG is close to 100 % and the effective cavity length is calculated to be 3.5 mm. Such an ultrashort-DBR-cavity fiber laser exhibited high Q factor and low cavity loss, allowing the efficient utilization of pump power within the millimeter-long cavity. Single-longitudinal, linearly polarized, gain-switched TDFL at 2003 nm, with a recorded shortest pulse duration of 4.3 ns, a repetition rate of 50 kHz, a maximum peak power of 500 W, and single pulse energy of 2.14 μJ, has been realized, benefitted from the ultrashort cavity length.

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing.

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

Ultrathin gold nanowires as broadband saturable absorbers for ultrashort pulsed lasers

Ultrathin gold nanowires (UGNWs) with a diameter of ⩽2 nm have attracted much attention because of their high aspect ratios, unusual physical properties and potential applications in nanoelectronics, sensors and photonics. Despite recent advances on UGNWs and the related devices, nonlinear optical properties of UGNWs and their application on photonic devices (e.g. ultrashort pulsed lasers) remain largely unexplored. Here we show that UGNWs can be used as broadband saturable absorbers (SAs) for constructing ultrashort pulsed lasers with an operating wavelength range from near-infrared to mid-infrared (MIR). UGNWs are prepared by using a silane-mediated approach, and then mixed with polyvinyl alcohol to form the UGNWs film. The UGNWs film not only show strong absorption from visible to MIR spectral region (over 25 μm), but also possess the nonlinear saturable absorption properties in the spectral region. As the UGNWs film SA is inserted into an erbium or thulium doped silica fiber laser cavity, stable passively mode-locked lasers at 1562.2 or 1970 nm with a pulse width of a few hundreds of femtoseconds is obtained, respectively. Especially, by inserting the UGNWs film SA into a holmium/praseodymium codoped fluoride fiber laser cavity, stable passively mode-locked laser at 2864 nm is achieved. Our results show that the UGNWs film are promising SAs for constructing broadband ultrashort pulsed lasers.

Flexible chalcogenide glass large-core multimode fibers for hundred-watt-level mid-infrared 2-5 µm laser transmission

The rapidly-developed high-power mid-infrared 2-5 µm laser technology requires a compact, flexible low-loss glass fiber for power delivery or laser generation. With the broadest bandwidth of low-loss transmission window in mid-infrared region amongst all mid-infrared glass fibers, chalcogenide glass fiber is the best candidate covering the whole 2-5 µm range. Multi-hundred-watt high-power delivery for 5.4-µm CO laser was previously demonstrated in a multimode chalcogenide fiber with a 1-mm-diameter large core, at the cost of giving up one of the most desirable fiber advantages, the flexibility. Indeed, chalcogenide glass fibers with decent flexibility have never exhibited hundred-watt-level power transmitting capability in the 2-5 µm range. In this paper, we have experimentally demonstrated 100-watt-level power transmission in multimode As2S3 chalcogenide fibers, using a customized high-power 2-µm thulium doped silica fiber laser source. With effective forced cooling, the multimode As2S3 fiber with 200 µm core diameter can resist incident laser power of 120 W and deliver transmitted power of 63 W. Nano-sized scattering center related laser damage mechanism and the cylindrical heat transfer model have been proposed to explain the high-power damage process of chalcogenide glass fibers. The calculation is in good agreement with the experiments. It is promising to further enhance the transmitted power above 100 W in flexible chalcogenide glass large-core fibers.

47 W continuous-wave 1726 nm thulium fiber laser core-pumped by an erbium fiber laser.

The high-power, short-wavelength operation of a thulium-doped silica fiber laser at 1726nm has been demonstrated in a core-pumped monolithic (all-fiber) resonator configuration, in-band pumped by a high-power erbium-only fiber laser operating at 1580nm. The thulium fiber laser yielded 47W in a single-spatial-mode output beam for 60-W absorbed pump power. The corresponding slope efficiency, with respect to an absorbed pump power of 80%, compares favorably with the theoretical maximum (Stokes) efficiency of 91.5%. The prospects for further scaling of single-mode power in this wavelength regime to >100 W are considered, as well as the potential applications for high-power lasers operating in this difficult-to-reach wavelength band.

All-fiberized single-frequency silica fiber laser operating above 2 μm based on SMS fiber devices

In this paper, a single-frequency thulium-doped silica fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode (SMS) structures incorporating a Sagnac loop was experimentally demonstrated. Based on the analysis of the transmission properties of the SMS fiber structure and the mode selection characteristic of the Sagnac loop, two cascaded SMS fiber devices with the same multimode fiber length of approximately 3.25 cm were used in our laser system, to select the specific lasing wavelength above 2 μm, as well as enhance the suppression of lasing around 1900 nm. A 6.5-m-long unpumped thulium-doped silica fiber was employed in the Sagnac loop as a saturable absorber to achieve single-longitudinal-mode operation. Single-frequency operation of the fiber laser at 2004.9 nm has been achieved with a maximum output power of 20.9 mW.

3 W narrow-linewidth ultra-short wavelength operation near 1707 nm in thulium-doped silica fiber laser with bidirectional pumping

We have developed an ultra-short wavelength operation of all-fiber Tm-doped laser system, in which the laser system was structured in a FBGs based linear cavity with FBG associated bidirectional pump mechanism at 1550 nm. The laser yielded 3.15 W of continuous-wave output at 1706.75 nm with a narrow-linewidth of ~50 pm. A high reflectivity FBG (HR-FBG) at 1550 nm was used to reflect the residual pump light and achieve the bidirectional pump mechanism. The maximum slope efficiency was improved from 23.2% without HR-FBG to 42.1% with HR-FBG at 1550 nm and the lowest pump threshold was reduced from 1.6 to 0.8 W accordingly. In the experiment, we have also investigated the dependencies of the slope efficiencies and pump threshold of the laser versus the length of active fiber and reflectivity of the output mirror (FBG) in detail. It is indisputable that the development of 1.7 μm silicate fiber lasers with Watt-level output power will open up a number of promising application windows.

High-peak-power single-oscillator actively Q-switched mode-locked Tm3+-doped fiber laser and its application for high-average output power mid-IR supercontinuum generation in a ZBLAN fiber.

A single-oscillator actively Q-switched mode-locked (QML) thulium-doped silica fiber laser is presented and used to pump a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber for mid-infrared (mid-IR) supercontinuum (SC) generation. The fiber laser provided high-peak-power levels directly from the oscillator delivering single mode-locked pulse energies up to 48 μJ, being 2-4 orders of magnitude higher than conventional continuous wave mode-locked lasers. By pumping a ZBLAN fiber specially designed for high-output-power SC generation, 7.8 W have been achieved in all spectral bands with a spectrum extending to 4.2 μm.

Multiwavelength thulium-doped silica fiber laser incorporating an all-fiber phase modulator

A novel multiwavelength thulium-doped silica fiber laser incorporating an all-fiber phase modulator is first presented in 2μm band. In the laser cavity, a phase modulator with a modulation frequency is efficient and beneficial to overcome the mode competitions. A polarization maintaining fiber Sagnac loop mirror is used as the filter. Large number of lasing wavelengths can easily and conveniently obtained at a proper modulation frequency under room temperature. The fiber laser can achieve ten output channels within a 15dB bandwidth from 1982nm to 1998nm.

Switchable and spacing-tunable dual-wavelength thulium-doped silica fiber laser based on a nonlinear amplifier loop mirror.

A kind of switchable and spacing-tunable dual-wavelength thulium-doped silica fiber laser based on a nonlinear amplifier loop mirror is presented and experimentally demonstrated. By adjusting the polarization controllers (PCs), stable dual-wavelength operation is obtained at the 2μm band. The optical signal-to-noise ratio (OSNR) is better than 56dB. The wavelength tuning is performed by applying static strain into the fiber Bragg grating. A tuning range from 0 to 5.14nm is achieved for the dual-wavelength spacing. By adjusting the PCs properly, the fiber laser can also operate in single-wavelength state with the OSNR for each wavelength more than 50dB.

Wavelength-swept Tm-doped fiber laser operating in the two-micron wavelength band.

A wavelength-swept thulium-doped silica fiber laser using an intracavity rotating slotted-disk wavelength scanning filter in combination with an intracavity solid etalon for passive control of temporal and spectral profiles is reported. The laser yielded a wavelength swept output in a step-wise fashion with each laser pulse separated from the previous pulse by a frequency interval equal to the free-spectral-range of the etalon and with an instantaneous linewidth of <0.05 nm. Scanning ranges from 1905 nm to 2049 nm for a cladding-pumping laser configuration, and from 1768 nm to 1956 nm for a core-pumping laser configuration were achieved at average output powers up to ~1 W.

A multiwavelength thulium-doped silica fiber laser incorporating a highly nonlinear fiber

A multiwavelength Tm3+-doped silica fiber laser incorporating a highly nonlinear fiber is presented. In the laser cavity, a nonlinear polarization rotation (NPR) based fiber loop mirror is used to overcome the mode competition and a polarization-maintaining fiber Sagnac loop mirror is used as the filter. The 150 m highly nonlinear fiber can improve the NPR effect in the laser cavity, which can increase the number of output channels. By adjusting the polarization state of the polarization controllers properly, stable multiwavelength operation at the 2 μm spectrum can be obtained at room temperature. It can achieve 15 output channels within a 10 dB bandwidth from 1990 to 2007.5 nm. The channel spacing of the multiwavelength Tm3+-doped silica fiber laser is 1.22 nm. Moreover, the performance of the laser is investigated for different pump powers and fibers.

A 1.97 μm multiwavelength thulium-doped silica fiber laser based on a nonlinear amplifier loop mirror

A 1.97 μm multiwavelength Tm-doped fiber laser based on a nonlinear amplifier loop mirror (NALM) has been experimentally demonstrated. The NALM with 500 m standard single mode fiber introduces intensity-dependent gain to alleviate mode competition caused by homogeneous gain broadening in Tm-doped fibers. At room temperature, up to 42 wavelengths with a wavelength spacing of 0.33 nm oscillate within a 10-dB bandwidth simultaneously. Repeat measurement of the laser spectrum shows the wavelength drift of a multiwavelength Tm-doped fiber laser is less than 0.05 nm in 40 min.

An all-fiber, resonantly pumped, gain-switched, 2 μm Tm-doped silica fiber laser

An all-fiber, gain-switched, single-mode, thulium-doped silica fiber laser operating at a wavelength of 1994.6 nm was developed. The laser was pumped by a 1.55 μm master oscillator power amplifier (MOPA) system and operated at a repetition rate ranging from 50 to 300 kHz. Different configurations of the laser cavity were tested. When operating at a 100 kHz repetition rate the laser delivered a maximum average power as high as 1.08 W with a slope efficiency of 49%. For a repetition rate of 50 kHz, stable 23 ns pulses with an energy of 15.3 μJ, corresponding to a peak power of 623 W, were achieved. We also report, to the best of our knowledge, the first demonstration of 2 μm gain-switched, mode-locked pulses with 100% modulation depth obtained in a Tm-doped fiber laser.

All-fiber Q-switched operation of thulium-doped silica fiber laser by piezoelectric microbending

We demonstrate an all-fiber Q-switched laser operation in the 2 µm region on the basis of a dynamic periodic microbend and pulsed-pump configuration. A single-mode thulium-doped silica fiber is pumped by 1.6 µm-band laser diodes, and the dynamic loss is introduced in the fiber ring resonator by the periodic microbend that is electrically controlled with a piezoelectric actuator. When the voltage-off period of the piezoelectric actuator is set at 20 µs for the pump power of 120 mW, the output pulse power is measured by 420 mW with a pulse width of 1.3 µs.

Spectral control of optical gain in a rare earth-doped optical fiber using novel triple layered structures

Novel techniques to control the effective emission cross section of a rare earth-doped optical fiber with a functional cladding structure are reviewed for applications in active fiber devices. We discuss evanescent wave filtering (EWF) technique based on the overlap in the radiative transition cross sections between the emitting ion in the core and the absorbing ion in the inner cladding. Experimental applications of EWF concept are reviewed for a composite gain medium with the erbium ions in the core and samarium ions in the inner cladding for self-gain flattening in C-band. W-type three layered fiber structure is also analyzed in terms of modal guidance and location of the LP 01 mode cut-off. Its application in neodymium and thulium-doped silica fiber laser is discussed to facilitate the radiative transition near 940 and 1600 nm region, respectively. The design concepts, fabrication process, and device performances are discussed for each application.

Single-frequency thulium-doped distributed-feedback fiber laser.

We have successfully demonstrated a single-frequency distributed-feedback (DFB) thulium-doped silica fiber laser emitting at a wavelength of 1735 nm. The laser cavity is less than 5 cm long and is formed by intracore UV-written Bragg gratings with a phase shift. The laser is pumped at 790 nm from a Ti:sapphire laser and has a threshold pump power of 59 mW. The laser has a maximum output power of 1 mW in a single-frequency, single-polarization radiation mode and is tunable over a few nanometers. To the best of the authors' knowledge, this is the first report of a single-frequency DFB fiber laser that uses thulium as the amplifying medium. The lasing wavelength is the longest demonstrated with DFB fiber lasers and yet is among the shortest obtained for thulium-doped silica fiber lasers.

Analysis and optimization of Q-switched operation of a Tm /sup 3+/ -doped silica fiber laser operating at 2 μm

Analysis and operation of a Q-switched Tm/sup 3+/-doped silica fiber laser in the wavelength region of 2 /spl mu/m is described when pumped with a Nd:YAG laser operating at 1.319 /spl mu/m. A large core of 17-/spl mu/m diameter was used to increase the laser gain volume, allowing high pump-power absorption and an output of high pulse energy and peak power. An acoustooptic modulator was used as Q-switching element and operated at repetition rates up to 30 kHz. A maximum peak output power of greater than 4 kW and a pulse duration at full-width at half-maximum of 150 ns has been obtained. This is the first report of high peak-power operation of the thulium-doped silica fiber laser.

190-fs passively mode-locked thulium fiber laser with a low threshold

We report a self-starting passively mode-locked thulium-doped silica fiber laser capable of 190-fs pulses. This practical, compact package is driven by a single 50-mW passively cooled diode laser, has a launched pumppower threshold of 18 mW for mode locking, and produces a 50-MHz train of mode-locked 20-pJ pulses at a wavelength near 1.9 microm.