J. Chrostowski

Effects of concentration on the performance of erbium-doped fiber amplifiers

The dependence of erbium-doped fiber amplifier (EDFA) performance on the erbium ion concentration is studied experimentally and theoretically. The quantum efficiency of the amplifier is found to he strongly dependent on the erbium ion concentration, the signal wavelength, and the relative propagation direction of the pump and signal beams. This dependence is fully explained by the presence of an upconversion mechanism between ions residing in pairs or larger clusters and suggests that other sources of amplifier performance degradation (back-ground loss, excited state absorption, homogenous upconversion) are negligible. The experimental data show that in the present EDFA designs with over 80% quantum/conversion efficiency, the aluminum co-doped fibers with erbium ion concentration less than 20/spl times/10/sup 24/ m/sup -3/ (900 molar ppm Er/sup 3+/) are most suitable.

Analytical model for rare-earth-doped fiber amplifiers and lasers

An analytical model for two-, three-, and four-level system rare-earth-doped fiber amplifiers and lasers is presented. The theory is applicable to dopants such as erbium, neodymium, thulium; praseodymium, and ytterbium. Fiber-amplifier gain is expressed in terms of attenuation coefficients, intrinsic saturation powers, and cross-saturation powers at the pump and signal wavelengths. These parameters can be directly determined from one- and two-beam fiber-transmission measurements. System-independent formulas are given for the slopes and thresholds of ring and linear fiber lasers. Good agreement between theory and experiment has been shown for erbium-doped fiber amplifiers and lasers and thulium-doped fiber lasers. Because of the finite-pump-level lifetime, three- and four-level models predict a flattening of the fiber laser slope at higher pumping powers when the fiber is shorter than the optimum length. Approximate system-independent solutions are also given for fiber amplifiers with excited-state absorption at either the pump or signal wavelengths. A novel technique, requiring only one tunable light source, is proposed for finding the best pump wavelength when pump ESA is present. The two-level analytical model recently developed for erbium-doped fibers is a special case of this theory. >

High power Q-switched erbium doped fiber laser

Rare-earth single-mode fibers are of specific interest in the field of optical communication as lasers or in-line optical amplifiers. High-power erbium-doped fiber lasers, operating in the eye safe wavelength region of 1.5 μm, are attractive not only in fiber communication but also for such applications as range finding.

A full-vectorial beam propagation method for anisotropic waveguides

An extension of the full-vectorial beam propagation method to anisotropic media is presented. Optical waveguides made of anisotropic materials can be modeled and simulated. The polarization dependence and coupling due to both the material and the geometric effects are considered. >

Self-mode locking in a Q-switched erbium-doped fiber laser

Stable and efficient self-mode locking in a Q-switched highly doped erbium fiber laser has been demonstrated. The proposed mechanism of the pulse formation based on self-phase modulation agrees well with the observed pulse characteristics.

Nonlinear guided waves coupled nonlinearly in a planar GaAs/GaAlAs multiple quantum well structure

A nonlinear guided‐wave concept and nonlinear coupled‐wave equations are used to study numerically the coupling characteristics of two planar waveguides in a GaAs/GaAlAs multiple quantum well structure with self‐defocusing nonlinearities. Both the mode‐intensity‐dependent critical power and the coupling length are calculated for the first time using the nonlinear field distributions. An optically controlled modulation/switching behavior is predicted.

Interboard optical data distribution by Bessel beam shadowing

We describe the efficient conversion of light from a laser diode into a Bessel beam whose axial intensity varies almost uniformly with distance using only a holographic optical element. An interesting shadowing property of the Bessel beam is demonstrated where on blocking the intense central spot the propagating ring pattern acts to reform the central spot a short distance following the obstruction. This behaviour together with the long propagation range for the Bessel beams central spot are considered for multiboard optical interconnects.

Optical pulse compression and breaking in nonlinear fibre couplers

Abstract The analysis of a curved, fibre coupler with a Kerr-type nonlinear medium between the fibres is presented. The nonlinear fibre coupler is seen to produce compression of optical pulses. A new feature, that of optical pulse breaking, is presented as well.

Bidirectional fiber amplifiers

The authors propose new bidirectional erbium-doped fiber amplifier repeaters for bidirectional fiber networks and OTDR fault detection. At each repeater the counterpropagating signals are separated, amplified separately, and then recombined. Signal separation is done by directional couplers with intrinsic 6-dB coupling loss, or by optical circulators with no intrinsic loss. Although the 3-dB input directional coupler loss can be compensated with a few milliwatts extra pump power, it increases the amplifier noise figure by 3 dB. The pump power required to compensate for the output directional coupler loss increases with the output signal power to 3 dB when the amplifier is saturated. The saturation output power of the directional coupler module is approximately 3 dB lower than the optical circulator. Multiple reflection induced relative intensity noise is reduced by assigning nonoverlapping optical bands to the signals in the two directions.<<ETX>>

Measuring the Raman time constant (T/sub R/) for soliton pulses in standard single-mode fiber

The Raman time constant (T/sub R/) used in the generalized nonlinear Schrodinger equation is determined experimentally at 1550 nm based on the Raman self-frequency shift in a standard single-mode fiber. The effective value of the T/sub R/ as measured is found to be 3.0 fs. Detailed error analysis shows that the uncertainty in the measurement is less than /spl plusmn/1.0 fs. The measured value of the T/sub R/ is approximately half of what is commonly used at present in theoretical simulations. Determined experimentally in this work the accurate value of T/sub R/=3.0 fs is essential in modeling pulse propagation in optical fibers.