Theoretical analysis of gain characteristics of Er/sup 3+/-Tm/sup 3+/-codoped tellurite fiber amplifier

The rate and power propagation equations of Er/sup 3+/ and Tm/sup 3+/-codoped tellurite fiber amplifier pumped by 800-nm laser are presented and solved to analyze the dependences of gain at both 1470 and 1530 nm on the codoping concentration of Er/sup 3+/ and Tm/sup 3+/, fiber length, and input signal power. The numerical results show that with pump power of 200 mW and fiber length of 1.5 m, the gain at both 1470 and 1530 nm may reach 12.0 dB when the codoping concentration of Er/sup 3+/ and Tm/sup 3+/ reach 4.0/spl times/10/sup 25/ ions/m/sup 3/, 3.2/spl times/10/sup 25/ ions/m/sup 3/, respectively. The fiber length and codopant concentrations are proposed to make the two channels equivalently amplified.     

Pr/sup 3+/-doped fluoride fiber amplifier module pumped by a fiber coupled master oscillator/power amplifier laser diode

We constructed the first Pr/sup 3+/-doped fluoride fiber amplifier (PDFA) module pumped by a fiber-coupled master oscillator/power amplifier laser diode (MOPA-LD) operating at 1.017 /spl mu/m. The maximum signal gain and noise figure were 30.5 and 5.5 dB, respectively. An output power of 18 dBm was achieved at an input signal power of 0 dBm. Furthermore, we showed that the use of MOPA-LD pumping, rather than conventional Nd-YLF laser pumping, makes it possible to halve the length of the Pr/sup 3+/-doped fluoride required in the amplifier module and also allows a broader spectral bandwidth to be achieved.     

Multiwavelength diode-cladding-pumped Nd/sup 3+/-doped germano-aluminosilicate fiber laser

Simultaneous multiwavelength oscillation at 1060 and 1090 nm has been produced from a free-running Nd/sup 3+/-doped multicomponent silica fiber laser. As a result of co-doping with both Al/sub 2/O/sub 3/ and GeO/sub 2/, the Nd/sup 3+/ ions are situated at separate sites relating to either Al/sup 3+/-rich or Ge/sup 4+/-rich regions of the germano-aluminosilicate glass. The slope efficiency of the combined /spl sim/1-/spl mu/m output was /spl sim/52% (56%) with respect to the launched (absorbed) pump power. The 1060-nm emission reaches threshold first because of the greater number of Nd/sup 3+/ ions that are located at Al/sup 3+/-rich sites. On chopping the pump light the relaxation oscillations relating to the 1090-nm emission are antiphase with the oscillations observed with the 1060-nm emission. A degree of spectral overlap exists between the fluorescence emitted from Nd/sup 3+/ ions located at each site. Power equalization (to /spl sim/1 W each) of the 1060- and 1090-nm emissions was carried out by way of Raman amplification that occurred either internally or externally to the Nd/sup 3+/-doped silica fiber laser.     

Modeling and experiments of actively Q-switched Er/sup 3+/-Yb/sup 3+/ codoped clad-pumped fiber lasers

Two models are presented to describe the complex dynamics of Q-switched clad-pumped Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers (EYDFLs): the full model that includes the full wavelength-dependence of parameters in the 1550- and the 1080-nm band due to Er/sup 3+/ and Yb/sup 3+/, respectively, and the simplified model that assumes single wavelengths for both bands. The models are based on detailed rate equations that include energy transfer between Er/sup 3+/ and Yb/sup 3+/ ions, and spontaneous emission due to both Er/sup 3+/ and Yb/sup 3+/. The simplified model is shown to agree with the full model within 10% difference. Experiments are performed using a 4-m-long single-mode clad-pumped EYDFL, and pulse energy of 14.5 /spl mu/J is achieved. Excellent agreement is shown between the simplified model and experiments. The model is further used to study the extractable energy of the laser and show limiting factors: amplified spontaneous emission (ASE) and energy storage in Yb/sup 3+/ ions. The model is also used to optimize the pulse energy in terms of fiber length, pump power, and Er/sup 3+/-Yb/sup 3+/ concentrations.     

1.65 /spl mu/m-band optical amplification with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping

In order to expand the available bandwidth for wavelength division multiplexing transmission systems, a 1.65 /spl mu/m-band optical fibre amplifier with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping has been demonstrated. The positive gain, 3.8 dB, is the first ever achieved by means of (/sup 2/H/sub 11/2/, /sup 4/S/sub 3/2/) /spl rarr/ /sup 4/I/sub 9/2/ stimulated emission transition.     

Fiber length dependence of phase change induced by laser-diode pumping in Yb/sup 3+/-Al/sup 3+/ co-doped optical fibers

We investigated the fiber length dependence of the phase change near 1580 nm induced by 980-nm pump beam in Yb/sup 3+/-Al/sup 3+/ co-doped optical glass fibers by use of a long-period fiber grating pair. As the pumping power increased, the phase change linearly increased and then was gradually saturated. Both the saturated phase change and the saturation pump power increased with the increase of the fiber length. The saturated phase change in Yb/sup 3+/-Al/sup 3+/ co-doped fibers of 16.7, 33.2, and 43.5 cm was found to be /spl sim/0.5, /spl sim/0.8, and /spl sim/1.0 rad, respectively. The saturation of the phase change is attributed to the saturation of the absorption from the finite ytterbium ions doped in the fibers.     

A high gain, high output saturation power Pr/sup 3+/-doped fluoride fiber amplifier operating at 1.3 mu m

A high net gain of 30.1 dB at 1.309 mu m and an output saturation of 13 dBm are obtained using a Pr/sup 3+/-doped fluoride fiber amplifier pumped at 1.017 mu m. The critical Pr/sup 3+/ concentration at which concentration quenching begins to occur was obtained by fluorescence lifetime measurement. The Pr/sup 3+/ concentration should be less than 1000 ppm to suppress the concentration quenching by cross relaxation. A high signal output power of 17.8 dBm was extracted from the Pr/sup 3+/-doped fluoride fiber. The Pr/sup 3+/-doped fluoride amplifier shows good potential for use in 13. mu m telecommunication systems.<>     

Gain-flattened Er/sup 3+/-doped fiber amplifier for a WDM signal in the 1.57-1.60-/spl mu/m wavelength region

A gain-flattened Er/sup 3+/-doped silica-based fiber amplifier (EDFA) has been constructed for a 1.58-/spl mu/m band WDM signal. This EDFA exhibits uniform amplification characteristics with a gain excursion of 0.9 dB for a four-channel WDM signal in the 1.57-1.60 /spl mu/m wavelength region. The average signal gain and the noise figure for the WDM signal are 29.5 dB and less than 6.3 dB, respectively. The use of this EDFA in parallel with a 1.55-/spl mu/m band EDFA will expand the WDM transmission wavelength region.     

35-dB gain Tm-doped ZBLYAN fiber amplifier operating at 1.65 /spl mu/m

We demonstrate the first high gain rare-earth-doped fiber amplifier operating at 1.65 /spl mu/m. It consists of ZBLYAN fiber with a Tm/sup 3+/-doped core and Tb/sup 3+/-doped cladding, pumped by 1.22 /spl mu/m laser diodes. It is possible to achieve efficient amplification with Tm/sup 3+/ ions if their amplified spontaneous emission (ASE) in the 1.75 to 2.0 /spl mu/m wavelength region is suppressed by doping Tb/sup 3+/ ions in the cladding. A two-stage-type fiber amplifier is constructed and a signal gain of 35 dB is achieved for a pump power of 140 mW. A gain over 25 dB is realized in the 1.65 /spl mu/m to 1.67 /spl mu/m wavelength region.     

Performance of a high concentration Er/sup 3+/-doped alumino silicate fiber amplifier

We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length.     

Optimum parameter design of Er/sup 3+/-doped fiber for optical amplifiers

The parameters of Er/sup 3+/-doped fiber which optimize the signal gain of a fiber amplifier pumped by a 1.48- mu m laser diode are theoretically determined using the rate equation for a three-level laser system. The basic parameters specified are the relative-index difference and the cutoff wavelength. The optimum cutoff wavelength of a completely Er/sup 3+/-doped core fiber with a step-index profile is 0.8 mu m regardless of the value of the relative-index difference. The optimum cutoff wavelength depends on the Er/sup 3+/-doped area radius.<>     

High-power broadly tunable Ho/sup 3+/-doped silica fibre laser

Tuning of the 2.1 /spl mu/m Ho/sup 3+/-doped silica fibre laser is demonstrated for the first time. The /sup 5/I/sub 7//spl rarr//sup 5/I/sub 8/ transition provides tuning over 144 nm, from 2019 to 2163 nm, and a maximum pump-limited output power of 1.58 W at 2100 nm was produced.     

Quantum-efficiency measurements in oxygen-containing gallium lanthanum sulphide glasses and fibers doped with Pr/sup 3+/

The production of competitive fiber amplifiers in the 1.3-/spl mu/m region requires both good quantum efficiency in the lasing ion and the capability to produce low-loss fibers. Oxygen-doped gallium lanthanum sulphide (GLS) doped with Pr/sup 3+/ may provide a route to both, We describe measurements of the quantum efficiency of Pr/sup 3+/ emission at 1.3 /spl mu/m from the /sup 1/G/sub 4/-/sup 3/H/sub 5/ transition in GLS glass and fiber containing varying quantities of lanthanum oxide. We show that oxide-containing GLS glasses, which are known to have considerably better thermal and glass-forming properties than pure GLS, can show quantum efficiencies of up to 84% of that of pure GLS, No degradation of quantum efficiency is seen when oxide-containing GLS glass is pulled into fiber form.     

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

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.     

85 W Tm/sup 3+/-doped silica fibre laser

An 85 W Tm/sup 3+/-doped silica fibre laser is presented. To the best of the authors' knowledge this is the highest output power achieved by pumping with 793 nm. The slope efficiency was 56%, the threshold 11 W and the output wavelength centred at 2.04 /spl mu/m. The high rate of cross relaxation in this laser provided a quantum efficiency of >130%.     

1.47 /spl mu/m Tm/sup 3+/:ZBLAN fibre laser pumped at 1.064 /spl mu/m

A large core area (1257 /spl mu/m/sup 2/) Tm/sup 3+/-doped ZBLAN fibre laser operated at 1.47 /spl mu/m is demonstrated. The pump source is a Nd:YAG laser operated at 1.064 /spl mu/m. A laser output power of 1.56 W continuous wave was obtained for 5.2 W of launched pump power. The slope efficiency with respect to the launched pump power was measured to be 33%.     

210 mW 2.84 /spl mu/m Ho/sup 3+/, Pr/sup 3+/-doped fluoride fibre laser

210 mW of unsaturated continuous-wave output from a Ho/sup 3+/, Pr/sup 3+/-doped fluoride fibre laser is demonstrated using the /spl sim/1100 nm output from a free-running diode-cladding-pumped Yb/sup 3+/-doped silica fibre laser as the pump source. A slope efficiency of 3.2% and an output wavelength of 2.84 /spl mu/m are obtained.     

Gain characteristics of Pr/sup 3+/-Yb/sup 3+/ codoped fluoride fiber for 1.3 mu m amplification

The authors report on the ability of the Pr/sup 3+/-Yb/sup 3+/ codoped system to move the pumping wavelength to wavelengths shorter than 1.017 mu m. It was demonstrated that, by codoping of Yb/sup 3+/ with Pr/sup 3+/-doped fluoride fiber, amplifiers can be moved to the spectral range where effective pumping can be done with InGaAs laser diodes that have strained-layer quantum-well structures that were developed as a pumping source for Er/sup 3+/-doped fiber amplifiers. The pumping wavelength range was extended down to 0.93 mu m.<>     

Pr/sup 3+/-doped fluoride single-mode fiber laser

Laser oscillation at 1.312 mu m was achieved using a Pr/sup 3+/-doped fluoride single-mode fiber laser pumped at 1.017 mu m. The operation of a rare-earth-doped fiber laser at 1.31 mu m, which is one of the central wavelengths in conventional optical telecommunication trunk line systems, was demonstrated for the first time using Pr/sup 3+/ ion as an active ion. The laser cavity consists of a mirror and a cleaved fiber facet used as an output mirror. The maximum output power, threshold pump, and slope efficiency are 26 mW, 370 mW, and 9.86%, respectively.<>     

Segmented-clad fiber design for inherently gain-flattened L/sup +/-band TDFA

We present here an efficient design for high gain, inherently gain-flattened L/sup +/-band thulium-doped fluoride fiber amplifier (TDFA), based on a novel segmented clad fiber refractive index profile. Detailed simulations show that the designed amplifier is able to achieve 20-dB gain, with /spl plusmn/0.7-dB gain ripple over 40-nm bandwidth (1600-1640) nm. Performance comparisons of the proposed module with an L/sup +/-TDFA based on conventional W-fiber designs and on a conventional step-index fiber have also been carried out.