Nd-doped Fiber Research Articles

Compact high-power tunable three-level operation of double cladding Nd-doped fiber laser

We present a compact high-power continuous-wave tunable neodymium-doped double cladding fiber laser operating on three-level /sup 4/F/sub 3/2/-I/sub 9/2/ transition with a maximum output power up to 810 mW. At 926.7 nm, it has a maximum slope efficiency of 49.3% against absorbed 808-nm pump. By compressing the fiber Bragg grating, 15-nm tuning range is achieved.

Femtosecond Neodymium-doped microstructure fiber laser

We demonstrate femtosecond operation of a Nd-doped mi-crostructure fiber laser. The fiber provides gain and anomalous dispersion at the lasing wavelength of 1.06 microm and enables the construction of short and simple cavity designs. The laser is passively mode-locked by the combined action of a saturable absorber mirror, fiber nonlinearity, and dispersion and produces transform limited sub-400-fs pulses with a pulse energy as high as 100 pJ.

Large-mode-area Nd-doped single-transversemode dual-wavelength microstructure fiber laser

A novel design for a microstructure fiber (MSF) laser consisting of a large core and a single annulus of 5 air holes is described. The fiber design incorporates a silica core that was doped in the liquid phase with 1300 ppm Nd2O3. The light guiding losses in the structurally very simple MSF are approximately 0.7 dB/m. Single transverse mode emission is demonstrated with a mode field area larger than 200 microm2. The laser simultaneously emits at two groups of wavelengths centered at 1060 nm and 1090 nm. Pumped by a cw Ti:sapphire laser, the fiber laser yields a maximum output power of 280 mW (pump power limited) at a slope efficiency of 52%. Our results indicate how the advanced possibilities of MSF's can be used for optimized fiber laser designs.

Analysis of W-type waveguide for Nd-doped fiber laser operating near 940 nm

We propose a three-layered W-type structure for laser fiber to facilitate the three-level radiative transition near 940 nm region of Nd ion, while suppressing the competing four-level transition near 1060 nm by introducing a novel highly wavelength selective loss mechanism. In order to achieve a net gain around 940 nm, requirements in fiber waveguide parameters for the LP01 mode cut-off and bending loss were theoretically investigated. The waveguide designs were experimentally confirmed generating stable CW single mode output power of 705 mW.

Growth and characterization of Nd-doped SBN single crystal fibers

The growth from ceramic pedestals of single crystal fibers of strontium barium niobate (SBN), doped with different Nd concentrations, was studied. High-quality fibers were grown for Nd doping levels of up to 4.2 at. %, and doping levels as high as 9.9 at. % were reached. No signs of core effects were observed, even for the highest concentration samples. The emission spectra of Nd3+ ions in the fibers did not differ from those obtained from bulk SBN crystals, showing very broad bands due to the typical disorder of the crystallographic tungsten-bronze structure. Fluorescence quenching was clearly observed for Nd doping levels above 2 at. %.

Femtosecond Neodymium-Doped Fiber Laser Operating in the 894–909-nm Spectral Range

We demonstrate a practical ultrafast Nd-doped fiber laser operating in the 894-909-nm spectral range. Using purposely designed semiconductor saturable absorbers, a truly self-started mode-locking regime of operation with clean transform-limited 360-fs pulses was achieved.

A Nd doped Multimode-Fiber-Laser with D-Shape Large Clad under Quasi-Solar-Pumping

We observed laser oscillation for a multimode Nd-doped fiber laser with D-shaped cladding under quasi-solar-pumping simulated by an intense halogen lamp with a color temperature of 5,600 Kelvin. The fiber had a millimeter-scale diameter and was 78 m long, and the doping rate was 3000 ppm of Nd ions in silica core-glass. Results show that the output power obtained was 300 mW when the injected power of the lamplight was 1.1 W at an entrance to the fiber, and the optical-optical conversion efficiency was 27 %. The threshold of laser oscillation is 24 times for the solar constant (0.14 W/cm2), a value which is one order of magnitude lower than the case of crystal lasers reported under solar-pumping.

Continuous wave single transverse mode laser oscillation in a Nd-doped large core double clad fiber cavity with concatenated adiabatic tapers

A new cavity design for the clad-pumped fiber laser (CPFL) was proposed and experimentally demonstrated in a Nd-doped silica fiber with the single transverse mode output and an enhancement in the slope efficiency for butt-coupled end pumping. In a fiber cavity two concatenated adiabatic rectangular tapers were formed to remove the optical feedback in higher order modes as well as to provide a low splice loss to standard single mode fibers. Mode propagation along the composite cavity was theoretically analyzed using beam propagation method and continuous wave oscillation in the LP 01 mode at 1.06 μm was achieved with the output power over 1.3 W at the pump power of 3.67 W.

Performances of a polymer-cholesteric-liquidcrystal output-coupler in Nd-doped fiber lasers

The performances and characteristics of a polymer-cholestericliquid-crystal reflector, used as an output coupler in a Nd-doped fiber laser, are presented. We show that a judicious combination of a linear polarizer and a quarter wave plate with the cholesteric coupler allows for a continuous scanning of the output-intensity from zero to a maximum value following the well-known Malus law. The results are shown to be contained in a simple Jones Matrix formalism. The LP-QW-PCLC combination is characterized by a reflection coefficient that can be freely adjusted from 0 to 1 by a simple rotation of the quarter-wave plate.

Single Mode Laser Oscillation in an Nd-Doped Large Core Double Clad Fiber Cavity with Concatenated Adiabatic Tapers

ABSTRACT¾ We created a new design for an Nd-doped clad-pumped silica fiber laser to enhance the pump absor ption and lasing efficiency for a butt-coupled, end-pumped scheme. Two concatenated adiabatic tapers formed within the laser cavity simultaneously removed higher order modes and were spliced to conventional single mode fibers. We theoretically analyzed mode propagation along the composite cavity and experimentally achieved continuous wave oscillation in the LP 01 mode at 1.06 mm and a laser output power of over 820 mW with a slope e fficiency of 27%. I. INTRODUCTION The rapid development of arrayed semiconductor laser diodes (LDs) with high output power has influenced many applic ations in optical communications, especially high power fiber amplifiers and fiber lasers. The beam quality parameters of the arrayed LDs, however, are not compatible with those of conventional single mode fiber (SMF). To overcome this mode mismatch and increase power delivery, some researchers have developed laser cavities based on double clad fiber (DCF), in which the pump and signal beams have different optical paths interacting with each other over the length of the cavities [1], [2]. The pump is launched in the silica cladding waveguide with a large area and a high numerical aperture supported by a low refractive index polymer jacket.

Cladding pumped large-mode-area Nd-doped holey fiber laser

A large Nd-doped core placed in a microstructure cladding (holey fiber) was pumped with a low-brightness diode laser. The area ratio of the pump radiation on the fiber to the core was larger than 30. The fiber length was 38 cm. Butt coupled mirrors formed the laser cavity. The emitted radiation at ? = 1060 nm was single transverse mode, the output power amounted to about 10 mW.

Numerical analysis and experimental results of output performance for Nd-doped double-clad fiber lasers

Numerical analysis is investigated for the high-power double-clad fiber lasers and experimental results using different microscope objectives for focusing into a Nd-doped rectangular double-clad fiber also performed. The numerical analysis includes dependence of output power on output mirror reflectivity, absorbed pump power, loss, and fiber length and pump power distribution for the cases of one-end and two-end pumps with 20 dB/km loss. Calculated conversion efficiencies are 76.36%, 69.73%, and 63.84% for lossless, two-end pump, and one-end pump fiber lasers, respectively. Slope efficiencies from absorbed pump power/output powers measured using microscope objectives are 16.8%/182 mW, 53.8%/351 mW, 24.9%/1240 mW, and 13.9%/649 mW for magnifications of 5×, 10×, 20×, and 40×, respectively.

Thulium-doped fiber optic decay-time temperature sensors: Characterization of high temperature performance

The main objectives of this study were to investigate the thermometric potential of Tm-doped optical fiber and yttrium aluminum garnet (YAG) crystals for applications up to temperatures as high as 1300 °C, and to realize a prototype high temperature fluorescence fiber probe based on earlier Nd-doped fiber work for temperature measurement up to 750 °C. The research showed that the fluorescence characteristics of the Tm-doped YAG crystal were very stable at high temperatures and capable of providing a temperature measurement reproducibility better than ±6 °C over the region from room temperature up to 1350 °C.

Experimental and numerical results of optical preamplification in a laser Doppler anemometer receiving head

The first application of a fiber amplifier in a laser Doppler anemometer (LDA) system is presented. Using an Nd-doped fiber amplifier as optical preamplifier in a conventional 1064-nm LDA, a small signal gain of 30 and 35 dB signal-to-noise (SNR) enhancement of the LDA radiation are achieved. The amplifier model, numerical, and experimental results are described.

General model for a multimode Nd-doped fiber laser. II: Steady-state analysis of length-dependent polarization effects

We present a steady-state analysis of a general model for a bipolarized Nd-doped fiber laser including the slow longitudinal variations of the dynamical variables. The combined effects of pump-induced, distributed, and localized anisotropies are studied versus the fiber length. In particular, the evolution of the thresholds versus the pump-input polarization angle, for different fiber lengths, is investigated in depth. Approximate analytical results are derived for the thresholds and the output intensities. A good agreement with the numerical simulations is achieved in a large range of parameters.

General model for a multimode Nd-doped fiber laser. I: Construction of the model

We present a general modeling of a multi-longi-tudinal-mode bipolarized Nd-doped fiber laser which keeps both vectorial (polarization) and longitudinal properties in the dynamical equations. We use an approach based on random orientation of the microscopic dipoles and demonstrate that it is isomorphic to the model derived assuming a transverse two-site distribution function for the ions. This result is also true under the mean-field approximation. At steady-state, the model is the generalization of Rigrod’s theory to the case of a bipolarized laser.

Efficient amplification using the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd-doped silica fiber

Amplification characteristics of the three-level /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd-doped silica glass fiber are investigated under strong signal saturation and high pump power (150 mW). Aluminum codoped Nd-silica fibers exhibit strong superfluorescent behavior in the four-level /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 11/2/ transition which limits the optical conversion efficiency into the three-level transition. Ge-doped silica fibers do not exhibit this limitation and can efficiently amplify in the three-level transition with current laser-diode pump technology.

High energy, sub-picosecond pulses from a Nd-doped double-clad fiber laser

We report on the generation of high energy sub-picosecond optical pulses at 1.065 μm wavelength from a Nd 3+-doped double-clad fiber laser. The laser is passively mode-locked by nonlinear polarization evolution and produces, without any extra-cavity pulse compression, pulses with an energy content of 4 nJ and a pulse duration of 940 fs at a repetition rate of 17 MHz.

High-gain solid-state and fiber amplifier-chain for high-power coherent communication

We report on the experimental results of a dual-stage amplifier combining a Nd-doped double-clad fiber and a Nd-doped YAG crystal. We obtained up to 3.5-W single-mode single-frequency output power with 28-dB gain. This is, to the best of our knowledge, the first demonstration of a dual-stage amplifier combining doped fibers and solid-state amplifiers.

Ultranarrow-linewidth, efficient amplification of low-power seed sources by a fiber amplifier

We report efficient amplification of an external cavity diode laser in the 1.06-microm range. The diode laser radiation is coupled into a Nd-doped silica fiber. The fiber is pumped by a diode array with up to 6.15 W of power. After a single pass of the seed radiation through the fiber amplifier, we observe up to 1.74 W of single-mode, narrow-linewidth laser radiation that is tunable over a relatively wide range of 1.060-1.067 microm. The output from our amplifier has the same spectral characteristics as the seed beam.