Cladding-pumped Fiber Laser Research Articles

A 43-W<tex>$C$</tex>-Band Tunable Narrow-Linewidth Erbium–Ytterbium Codoped Large-Core Fiber Laser

The authors report a widely tunable and highly efficient cladding-pumped erbium-ytterbium codoped large-core fiber laser, generating up to 43 W of output power at /spl sim/1.5 /spl mu/m with a narrow linewidth (0.16-nm full-width at half-maximum) and a good beam quality (M/sup 2/<1.7). By use of a tunable narrow-band fiber Bragg grating, the laser wavelength was tuned from 1532 to 1567 nm, limited upwards by the tuning range of the fiber grating. The overall slope efficiency was 32% with respect to launched pump power.

Cladding-pumped ytterbium-doped large-core fiber laser with 610 W of output power

We report a cladding-pumped ytterbium-doped fiber laser, generating up to 610 W of continuous-wave (cw) output power at 1.09 μm with a slope efficiency of 82% and with a good beam quality ( M 2=2.7). The core diameter was 43 μm and the inner cladding diameter was 650 μm. Even at this high power, the maximum output power was still limited by the available pump power, and no undesirable roll-over was observed in output power with increasing pump power.

A Cladding-Pumped Fiber Laser With Pump-Reflecting Inner-Cladding Bragg Grating

A fiber Bragg grating (FBG) was inscribed in the inner cladding of a double-clad fiber, in order to reflect, and thus, double-pass, the pump radiation in a cladding-pumped fiber laser. The effective pump reflectivity of the inner-cladding FBG was /spl sim/46.4%. This increased the slope efficiency of a Yb-doped cladding-pumped fiber laser by up to 8.5%, and the output power increased by 45% with a 3-W pump source. The FBG provides stable and robust pump reflection, while leaving the fiber end free, for example, so that a signal transmission fiber can be spliced to the double-clad fiber.

Experimental study of stimulated Brillouin and Raman scatterings in a Q-switched cladding-pumped fiber laser

Characteristics of stimulated Brillouin and Raman scatterings (SBS and SRS) in a Q-switched cladding-pumped ytterbium (Yb)-doped fiber laser are experimentally investigated. A stable SBS pulse train with a width of ∼2 ns and a peak power of ∼1.0 kW can be generated in regular Q-switching processes under certain conditions. The time jitter and intensity fluctuation of SBS pulses are presented, and their mechanism and statistics are discussed. The accompanied Raman–Stokes waves in regular Q-switched pulses and SBS pulses are quantitatively compared.

Ytterbium-doped large-core fiber laser with 1.36 kW continuous-wave output power

We have demonstrated a highly-efficient cladding-pumped ytterbium-doped fiber laser generating 1.36 kW of continuous-wave output power at 1.1 mum with 83% slope efficiency and near diffraction-limited beam quality. The laser was end-pumped through both fiber ends and showed no evidence of roll-over even at the highest output power, which was limited only by available pump power.

Ytterbium-doped large-core fibre laser with 610 W of near diffraction-limited output power

A cladding-pumped ytterbium-doped fibre laser, generating up to 610 W of continuous-wave output power at 1.1 µm with slope efficiency of 80% and near diffraction-limited beam quality (M2=1.3) is reported. No undesirable roll-over was observed in output power with increasing pump power.

High-power wavelength-tunable cladding-pumped rare-earth-doped silica fiber lasers

We describe the design and performance of cladding-pumped silica fiber lasers with high continuous-wave output powers and broad wavelength tunability in the 1, 1.5, and 2 μm spectral ranges. An ytterbium-doped fiber laser was tuned via wavelength dependent feedback provided by an external cavity containing a diffraction grating from 1027 to 1105 nm at multi-watt power levels. Similarly, high output power and wide wavelength tunability from 1540 to 1600 nm and from 1860 to 2090 nm at multi-watt output power levels has been achieved in Er-Yb co-doped and Tm-doped silica fiber lasers, respectively. A neodymium doped fiber laser was tuned from 1057 to 1118 nm at a lower power level. Limiting factors and the prospects for further improvements in performance are considered.

High-power and tunable operation of erbium-ytterbium co-doped cladding-pumped fiber lasers

We describe erbium-ytterbium co-doped fiber lasers in different free-running and tunable configurations. The lasers were cladding-pumped by high-power multimode diode sources. We compare pumping at 915 and 980 nm. With a free-running laser, we obtained slope efficiencies of up to 50% with 915-nm pumping and 38% with 980-nm pumping, with respect to absorbed pump power. We reached a double-ended output power of 16.8 W from the free-running laser. Thanks to a high rare-earth concentration and a small inner cladding area (possible with the high-brightness pump sources we used), the operating pump absorption of the fiber reached 8 dB/m. With such high absorption, short fibers with high nonlinear thresholds are possible even with cladding pumping. The tunable fiber laser had a tuning range from 1533 to 1600 nm and emitted 6.7 W of output power at 1550nm in a high-brightness, single-polarization, narrow linewidth beam.

Pump induced thermal effects in high power Tm3+ and Tm3+/Ho3+cladding-pumped fibre lasers

The operating temperatures of the actual fibre in Tm:silica and Tm/Ho:fluorozirconate(ZBLAN) fibre laser systems pumped by diode lasers have been measured using a thermalimaging technique. A maximum operating temperature of 192 °Cwas measured in the Tm:silica fibre and 75 °Cwas determined to be the highest temperature the ZBLAN fibre could withstandbefore damage became likely. The outer polymer jacket was found to considerablyincrease the fibre temperature. Periodic oscillations were found in the output ofthe Tm/Ho:ZBLAN fibre at high output powers with periods between 12and 27 ms. Both fibres were found to operate simultaneously at severalwavelengths a few nanometres apart and the output wavelength was constantlyfluctuating over time. The typical output wavelengths of the Tm:silica andTm/Ho:ZBLAN fibres were 1.96 and 2.07 µm.Thermal effects were found to be minimal in Tm:silica fibres for incident pumppowers of up to 36 W, whereas damage was possible in Tm/Ho:ZBLAN fibres atpump powers above 10 W.

Ytterbium-doped large-core fibre laser with 272 W output power

A highly efficient cladding-pumped Yb-doped large-core fibre laser, generating up to 272 W of continuous-wave output power at 1.08 /spl mu/m with a beam quality (M/sup 2/) of 3.2, is reported. The slope efficiency was 83% with respect to the launched pump power. No saturation (roll-off) was observed in output power with increasing pump power.

Self-Q-switched ytterbium-doped cladding-pumped fibre laser

A self-Q-switched ytterbium-doped double-clad fibre laser is described. A samarium-doped fibre is used as a filter for protecting a pump source. A fibre coupler is employed to obtain a nonlinear feedback. The mechanism of pulse formation in the laser is considered, and the dependence of its output pulse on the coupler parameters is studied.

High-power cladding-pumped Tm-doped silica fiber laser with wavelength tuning from 1860 to 2090 nm

A high-power double-clad Tm-doped silica fiber laser, pumped by two beam-shaped and polarization-coupled diode bars at 787 nm, was wavelength tuned by use of an external cavity containing a diffraction grating. The Tm fiber laser produced a maximum output power of 7 W at 1940 nm for 40 W of incident diode power and was tuned over a wavelength range of 230 nm from 1860 to 2090 nm, with >5-W output power over the range 1870-2040 nm. The prospects for further improvement in performance and extension of the tuning range are discussed.

Configurable three-wavelength Raman fiber laser for Raman amplification and dynamic gain flattening

A three-wavelength Raman fiber laser is presented that is suitable for the generation of a flattened Raman gain curve over a broad range of extended telecommunications bandwidths. This laser utilizes an 1100-nm Yb-doped cladding pumped fiber laser and a cascaded Raman resonator to generate output radiation at 1427, 1454, and 1480 nm. The slope efficiency for conversion from the 1100- to 14xx-nm radiation is 0.38, the total output power is 1.1 W, and the fiber laser "wall-plug" efficiency is 0.10. The output power at 1454 and 1480 nm is adjusted by varying the reflectivity of the fiber grating output couplers and the suppression of lower order spectral components is between 15 and 20 dB. Low frequency relative intensity noise (RIN) measurements indicate RIN values less than -90 dB/Hz below 100 kHz.

Jacketed air-clad cladding pumped ytterbium-doped fibre laser with wide tuning range

A tunable cladding-pumped ytterbium-doped fibre laser is presented. An air-clad inner cladding supported by a micro-structured silica mesh inside a silica jacket is used. A measured inner-cladding NA of 0.4 to 0.5 enables efficient pump launch into a 36 µm-diameter inner cladding. The small inner cladding area enables tuning from 1010 to 1120 nm.

Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs

We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality.

10 mJ total output from a gain-switched Tm-doped fibre laser

A gain-switched cladding-pumped Tm-doped silica fibre laser operating at a wavelength of approximately 2-μm with moderate output energy is reported. When pumped with the output from a gain-switched Ti:sapphire laser, a maximum total output energy of 10.1 mJ per pump pulse is produced at a slope efficiency of 30% (with respect to launched pump energy) and, at an overall optical-to-optical efficiency of 17%. For relatively short fibre lengths, saturation of the output energy is observed with an increase in launched pump energy because of pump-induced bleaching of the pump transition. The laser has been continuously tuned using an intracavity prism over a range of 109 nm, from 1909 nm to 2018 nm.

Efficient cladding-pumped Tm-doped silica fibre laser with high power singlemode output at 2 [micro sign

Continuous-wave operation of a double-clad Tm-doped silica fibre laser at 2 µm, pumped by two beam-shaped diode bars, yielded an output power of 14 W in a singlemode (M2 &lt; 1.1) beam for 36.5 W of launched pump power at 787 nm. The slope efficiency with respect to launched diode power was ~46%.

Compact high-energy Q-switched cladding-pumped fiber laser with a tuning range over 40 nm

We describe a compact Q-switched diode pumped double-clad ytterbium-doped fiber laser. The fiber laser was bidirectionally pumped by two laser diodes (2 W of output power each) via two side-injecting pump-couplers. We used a large multimode core of 15 μm diameter to increase the laser gain volume and thus to achieve higher pulse energy. Experimentally this laser produced pulses with energy up to 170 μJ with a peak power of 2 kW (at a low repetition rate of 500 Hz) and was tunable from 1060 to 1100 nm.

Highly efficient cladding-pumped fibre laser based on an ytterbium-doped optical fibre and a fibre Bragg grating

Ytterbium-ion-doped double-clad optical fibres were developed. The differential quantum efficiency of a diode-pumped fibre laser, fabricated on the basis of such optical fibres with a fibre Bragg grating, was 90%.

Ring-doped cladding-pumped single-mode three-level fiber laser

We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb(3+) -doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.