Modeling high-power Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers

High-power cladding-pumped Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers (EYDFL) are analyzed with a detailed rate-equations model that takes into account the energy transfer between Yb/sup 3+/ and Er/sup 3+/. Examples of EYDFL with distributed Bragg reflector (DBR) mirrors at both fiber ends are demonstrated. Approximate quasi-analytical solutions to the rate equations show good agreement with the exact numerical solutions for practical operating conditions. An "optimum design" of the laser is discussed in relation to the fiber length that maximizes the output power.     

Modeling and optimization of short Er/sup 3+/-Yb/sup 3+/ codoped fiber lasers

A theoretical study of short Er/sup 3+/- Yb/sup 3+/ codoped fiber lasers (EYDFLs) is presented. Examples include centimeter-length EYDFLs pumped at 978 nm, with distributed Bragg reflector (DBR) mirrors at both fiber ends. Approximate quasi-analytical solutions are shown to be in excellent agreement with the exact numerical solution of the rate equations. Using the quasi-analytical model, we demonstrate a design optimization of a short EYDFL. The effects of the Yb/sup 3+/ concentration, laser wavelength, output mirror reflectivity, and pump wavelength are considered and discussed with relation to the optimal laser length and output efficiency.     

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.     

Numerical analysis of optical amplification in Er/sup 3+/-Yb/sup 3+/ codoped Ti:LiNbO/sub 3/ strip waveguides

Optical amplification at 1530 nm in 980-nm pumped Er/sup 3+/-Yb/sup 3+/-diffused Ti:LiNbO/sub 3/ strip waveguides was numerically analyzed on the basis of rate equation model of Er/sup 3+/-Yb/sup 3+/ system and pump/signal power propagation equations. The model includes total eight energy levels of the Er/sup 3+/-Yb/sup 3+/ system and simultaneously takes into account the excited state absorption (ESA) and upconversion processes within the Er/sup 3+/ ions as well as possible energy transfer processes between Yb/sup 3+/ and Er/sup 3+/ ions. A comparison of numerical results from the eight-level model and highly simplified five-level model has indicated that the /sup 4/S/sub 3/2/ manifold of Er /sup 3+/ ion must be included in the rate equation model. Dependences of threshold pump power and amplification gain on pump power (for gain only), Yb/sup 3+/ surface concentration and waveguide length were calculated and discussed. The characteristics of pump power evolution along the waveguide axis and population density distribution, as well as the influences of energy transfer coefficient from Yb/sup 3+/ to Er/sup 3+/, 550-nm (Er/sup 3+/), and 1060-nm (Yb/sup 3+/) fluorescence lifetime and above-mentioned detrimental processes including ESA, upconversion, and cross-relaxation processes on numerical result were studied. The role of Yb/sup 3+/ is demonstrated. A novel design idea that Yb/sup 3+/ is only incorporated at the end of the waveguide is proposed.     

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.     

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.     

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.     

Laser diode pumped Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fluoride fiber amplifiers operating at 1.3 mu m

Both Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped singlemode fibres with high numerical apertures are pumped by laser diodes with InGaAs/GaAs strained quantum well structures. A net gain of 5.2 dB is obtained from Pr/sup 3+/-doped fluoride fibre pumped by laser diodes operating at 1.1017 mu m and a net gain of 3.2 dB is obtained from Pr/sup 3+/-Yb/sup 3+/-codoped fibre pumped by laser diodes operating at 0.98 mu m. The pumping efficiency difference between Pr/sup 3+/-doped and Pr/sup 3+/-Yb/sup 3+/-codoped fibre is discussed.<>     

High repetition rate passively Q-switched Nd/sup 3+/:Cr/sup 4+/ all-fibre laser

A passively Q-switched fibre laser comprising an Nd/sup 3+/-doped gain fibre spliced to a new Cr/sup 4+/-doped saturable absorber fibre delivers 0.3 nm-bandwidth continuous pulsed laser beam at 1084 nm, with 38 to 84 kHz repetition rate, and 3.0 to 6.4 /spl mu/s pulse duration.     

High-performance integrated erbium/sup +3/-ytterbium/sup +3/ codoped glass waveguide laser

We report the design and characterization of an efficient erbium/sup +3/-ytterbium/sup +3/ codoped ion exchanged glass distributed Bragg reflector (DBR) laser pumped by a 980-nm pigtailed laser source. Laser oscillation at 1536 nm is demonstrated with a pump threshold of 35 mW and a slope efficiency of 10.6%. The dependence of lasing performance on pump wavelength detuning is examined for different cavity designs.     

Tunable Pr/sup 3+/-doped silica-based fibre laser

The tunability of the Pr/sup 3+/-doped silica-based fibre laser has been investigated. A broad tuning range of 86 nm is obtained for the transition /sup 1/D/sub 2/-/sup 3/F/sub 3,4/ in the band centred at 1048 nm. Factors limiting tunability, and effects of host matrix and broadening mechanisms are discussed.<>     

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.<>     

Low-loss Cu/sup +/-Na/sup +/ ion exchanged optical channel waveguides in glass

Electric field assisted Cu/sup +/-Na/sup +/ ion exchanged optical channel waveguides have been produced in Corning 7740 borosilicate glass using a Cu film source. Average losses of 1.0, 0.45 and 0.3 dB/cm, at wavelengths of 633, 850 and 1300 nm, respectively, have been measured.     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

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.     

High-power multiwavelength Er/sup 3+/-Yb/sup 3+/ codoped double-cladding fiber ring laser

A high-power simultaneous multiwavelength lasing in an Er/sup 3+/-Yb/sup 3+/ codoped double-cladding fiber (EYCDF) ring laser is demonstrated based on a wavelength-dependent filter through spatial mode beating within the multimode fiber section. We have investigated the relationship between the lasing wavelengths and the length of the EYCDFs. The experimental results indicate that both the number of lasing wavelength lines and the spacing between two adjacent lasing lines can be controlled by the changes of the lasing light polarization states.     

16-channel optical FDM distribution/transmission experiment utilising Er/sup 3+/-doped fibre amplifier

A 16-channel optical FDM distribution/transmission experiment at around 1534 nm wavelength is demonstrated utilising an Er/sup 3+/-doped fibre amplifier. 16 intensity-modulated optical signals at 622 Mbit/s were amplified simultaneously at a gain of 15.2-18.5 dB. One of the amplified signals is selected using the waveguide frequency selection switch and directly detected with a receiver sensitivity of -38 dBm (P/sub e/=10/sup -9/).<>     

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.     

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.<>     

Tunable Nd/sup 3+/-doped fibre ring laser

A novel tunable all-fibre laser using a Nd/sup 3+/-doped single mode fibre ring resonator is reported. End pumped by an argon laser of 514.5 nm wavelength, the laser threshold was 1.45 mw, and a tuning range of 60 nm is obtained.<>