High-power double-clad fiber lasers

Rare-earth doped, laser-diode-pumped, single-mode, double-clad fiber lasers are studied in detail, experimentally and theoretically, with particular attention to properties of scaling to higher output powers. Gain saturation, spontaneous emission, fiber propagation loss, and the optimum output coupler are considered for oscillator design and laser performance. Thermal properties are investigated, including the thermal fracture limit, the decrease of quantum efficiency with increasing pump power through the temperature dependence of multiphonon decay and ion-ion energy transfer, and thermal lensing. Self-focusing and Raman effects are briefly considered. It is shown that output powers in the tens of watts range are readily feasible with available double-clad fiber lasers     

83-W single-frequency narrow-linewidth MOPA using large-core erbium-ytterbium Co-doped fiber

We demonstrate a continuous-wave (CW) single-frequency narrow-linewidth laser at 1552 nm with an output power of 83 W using a master-oscillator power amplifier configuration. A seed from an all-fiber distributed feedback-laser with a linewidth of 13 kHz was polarization scrambled and boosted through a chain of amplifiers in an all-fiber configuration. The last amplification stage consisted of a highly efficient cladding-pumped large-core erbium-ytterbium co-doped fiber which helped increase nonlinear thresholds.     

Novel performance of fiber lasers: tunable operation in visible range

A review of the main physical processes important for frequency doubling of fiber lasers and the results of development by the Novosibirsk group of the fiber lasers operating from blue-green to yellow-red spectral ranges with a potential of the broad continuous tuning are presented. These lasers with ～100 mW power are treated to be attractive light sources for applications in medicine, especially in confocal microscopy and flow cytometry.     

A 43-W C-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.     

Widely tunable single-frequency erbium-doped fiber lasers

In this letter, we report on experimental results on a 70-nm-wide quasi-continuously tunable single-frequency erbium-doped fiber (EDF) laser, in which the laser produced a single-longitudinal mode oscillation between 1510-1580 nm, an output power of 0.5 mW, and a tuning step of about 25 MHz. The cavity incorporates three tunable bandpass filters (TBFs): a bulk-grating-based TBF, a fiber-ring-cavity filter, and an autotracking saturable absorption-induced grating filter generated by an unpumped EDF. This laser had a frequency drift of 100 MHz and a signal-to-source spontaneous emission ratio higher than 60 dB.     

Experimental demonstration of enhancing pump absorption rate in cladding-pumped ytterbium-doped fiber lasers using pump-coupling long-period fiber gratings

A long-period fiber grating (LPFG) was inscribed in a single-mode fiber and was spliced with a ytterbium (Yb)-doped double-clad fiber in order to couple pump radiation of the inner cladding into the core in a cladding-pumped fiber laser. The use of an LPFG permits a partial core-pumping scheme in a cladding-pumping fiber laser because a portion of the pump radiation can be coupled to the core by LPFG. The enhancement of the pump absorption of a Yb-doped cladding-pumped fiber laser as the result of pump coupling by LPFG was 35%, and the maximal output power increased by up to 55% when a 20-W pump source is used.     

Efficient and tunable Er/Yb fiber grating lasers

Efficient and tunable single-frequency fiber Bragg grating (FBG) lasers are demonstrated using a novel photosensitive Er/Yb fiber design. Both sub-mW threshold pump power, and high slope efficiencies of ~31% at 1536 nm and ~26.1% at 1562 nm were achieved. Wavelength tuning could be obtained over 11 and 25 nm in 1535 and 1550 nm wavelength regions, respectively, by cavity-length tuning     

High-power, high-temperature operation of AlInGaAs-AlGaAs strained single-quantum-well diode lasers

Strained layer AlInGaAs-AlGaAs graded-index separate-confinement heterostructure single-quantum-well diode lasers with cavity width and length of 500 and 1000 mu m, respectively, have been operated continuous-wave (CW) at heatsink temperatures up to 125 degrees C, with output power up to 4.9 W per facet and power efficiency as high as 49% measured at 10 degrees C. Promising results have been obtained in initial reliability tests on uncoated devices at heatsink temperatures of 10 and 50 degrees C.<>     

High-power single-mode operation in DFB and FP lasers usingdiffused quantum-well structure

Distributed feedback (DFB) and Fabry-Perot (FP) semiconductor lasers with step and periodic interdiffusion quantum-well structures are proposed for high-power single-longitudinal-mode operation. It is shown that the phase-adjustment region formed by the diffusion step (i.e., step change in optical gain and refractive index) counteracts the influence of spatial hole burning, especially for DFB lasers with large coupling-length products biased at high injection current. Furthermore, it is found that with careful design of the diffusion grating (i.e., grating period and amount of diffusion extent) of FP lasers, side-mode suppression ratio can be enhanced and threshold current density can be minimized to a satisfied level     

Derivation of the mode build-up time of tunable fiber lasers

An analytical expression for the mode build-up time of tunable fiber lasers is derived, based on a plane-wave lumped-circuit laser model and a two-level atomic system. Limiting parameters for the design of a high-speed tunable fiber laser can therefore be identified.     

High-power operation and scaling behavior of CW optically pumped FIR waveguide lasers

High-power far infrared (FIR) laser operation at the 10- 100 mW level is described for wavelengths throughout the 40 μm-1.22 mm spectral region. These data correspond to order of magnitude improvements in converting CO2laser energy into FIR laser output. This improved FIR laser performance is attributed to a waveguide laser geometry with reduced losses for the CO2pump and also to a new method of output coupling. The basic design concept of the efficient laser resonator is discussed as well as the prospect for further increases in laser performance through improved efficiency and sealing.     

High-power operation of DCPBH lasers emitting at 1.52 ?m wavelength

Double-channel planar buried heterostructure (DCPBH) lasers emitting at 1.52 ?m wavelength have been made with considerably reduced current leakage. These devices have reached a maximum CW output power of 50 mW per facet at 20°C and have operated CW up to 125°C. Both these figures are the highest values yet achieved for lasers emitting in the 1.52 ?m wavelength region.     

Continuously tunable photopumped 1.3-μm fiber Fabry-Perotsurface-emitting lasers

Continuously tunable, single-frequency, optically pumped semiconductor-fiber lasers are demonstrated that embody a half-cavity, vertical-cavity surface-emitting laser within a fiber Fabry-Perot cavity. Continuous wavelength tuning over 40 nm at 1300-nm wavelength region is obtained under continuous-wave operation     

High-power operation of index-guided inverted channel substrate planar (ICSP) lasers

An easily fabricated high-power index-guided laser, the inverted channel substrate planar (ICSP) structure, has been developed using the two-step metal-organic chemical vapour deposition (MOCVD) technique. Linear output power characteristics were observed to 30 mW CW on submount with junction side up without facet coatings. The device operated in a stable single mode to a power >25 mW. Improved ICSP lasers with facet coatings demonstrate a stable high output power of 65 mW CW and a differential quantum efficiency of 60%.     

Simple and compact, all-fibre retro-reflector for cladding-pumped fibre lasers

Proposed is an all-fibre retro-reflector realised via shaping a fibre end into a right-angled cone for a pump reflector in cladding-pumped fibre lasers. The conical-shaped fibre-optic retro-reflector allows folded, total internal reflections for pump beams that propagate in the inner cladding of a double-clad fibre. The proposed scheme was applied to a cladding-pumped ytterbium-doped fibre laser and readily achieved over 55% of reflection for the unabsorbed pump throughput, thereby generating 29% more signal output power than without the pump retro-reflector     

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.     

Mid-infrared fluoride fiber lasers in multiple cascade operation

CW fiber laser cascades in an Er³⁺-doped fluorozirconate fiber operating simultaneously at 2.7 μm/1.55 μm or at 3.45 μm/2.7 μm/1.55 μm pumped around 650 nm are reported. Output powers of nearly 20 mW at 1.55 μm and 1.2 mW around 2.7 μm were obtained with a nonoptimized experimental setup for the 2.7 μm/1.55 μm cascade. At 1.55 μm a laser efficiency of 5% was achieved. By varying the parameters of the experimental setup, additional effective simultaneous laser action at 3.45 μm was demonstrated     

High-power operation in 0.98-μm strained-layer InGaAs-GaAssingle-quantum-well ridge waveguide lasers

High power strained-layer InGaAs-GaAs graded-index separate confinement heterostructure (GRIN-SCH) single-quantum-well (SQW) lasers at an emission wavelength of 0.98 μm have been fabricated. A light power as high as 270 mW and a maximum front power conversion efficiency of 51.5% have been obtained for the antireflective and highly-reflective coated laser with 9-μm-wide ridge and 600-μm-long cavity     

Widely tunable 1.55-μm lasers forwavelength-division-multiplexed optical fiber communications

Widely tunable lasers are essential components for high-capacity wavelength-division-multiplexed (WDM) transmission and photonic switching systems. For these optical fiber communication systems, they offer several advantages to increase the capacity, the functionality, and the flexibility of WDM networks. Nevertheless, these widely tunable transmitters must satisfy several stringent requirements depending on the specific application for which they are intended. Using criteria defined to compare the performances of several widely tunable laser structures reported in the literature, we pointed out a structure which presents a good tradeoff between high performances and technological processing simplicity. We designed and realized this component, the sampled-grating distributed Bragg reflector laser. Its tuning mechanism and main characteristics are first discussed. A short review is then made to compare these results to those measured on different widely tunable structures, and to propose improvements needed for practical implementation of these lasers for WDM optical fiber communications     

High-power, high-temperature operation of GaInAsSb-AlGaAsSbridge-waveguide lasers emitting at 1.9 μm

Ridge-waveguide lasers emitting at ~1.9 μm have been fabricated from a multiple-quantum-well heterostructure with an active region consisting of five GaInAsSb wells and six AlGaAsSb barriers. At room temperature, single-ended cw output power as high as 100 mW has been obtained. The maximum cw operating temperature is 130°C, with a characteristic temperature of 85 K between 20 and 80°C