P. Myslinski

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. >

Performance of high-concentration erbium-doped fiber amplifiers

The full characteristics for two high-concentration erbium-doped fibers are reported. The comparison of the fibers characteristics indicates that design of fiber geometry can be used to partially compensate for the degradation of the amplifiers performance due to upconversion processes. For high NA fiber the 22-dB small-signal gain, and 3.5-dB noise figure are obtained from a 24-cm length of fiber. We report a photon quantum conversion efficiency of 28%, which corresponds to the highest efficiency obtained in heavily doped fibers.

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.

Q-switched thulium-doped fiber laser

A tunable Q-switched thulium-doped single-mode silica fiber laser is presented for the first time. Its performance is analyzed as a function of pulse repetition rate and pumping power. The optimization of laser parameters resulted in 4 W/1 30 ns, 1 .92-jrm wavelength pulses generated at a 4-kHz repetition rate. From the measured values of small- signal attenuation and intrinsic saturation power, the thulium ion param- eters at the pump and signal wavelength are derived and used in the- oretical modeling of the laser. The moderate power required from the Ti:sapphire pump laser used in the experiment suggests that similar re- suIts can be obtained using a laser diode pump.

Generation of multigigahertz bright and dark soliton pulse trains

Abstract A comprehensive study for generating trains of ultra-high speed bright and dark soliton pulses at 1553 nm using comblike dispersion profile fiber structures is presented. The comblike structure employed for generating bright solitons uses the lowest average power for the input signal ever reported. The generated bright soliton pulses have a full width at half maximum (FWHM) of 2.2 ps at a repetition rate of 49.3 GHz, while the generated dark soliton pulses have a FWHM of 3.8 ps at 47.6 GHz. The experimental results agree well with performed numerical simulations.

Upconversion dynamics of Er3+:YAlO3

The dynamics of the green (2H11/12, 4S3/2) and red (4F9/2) upconversion emission excited by 15 ns pulses from an Er:fibre laser at 1500 nm are presented and analyzed. The upconversion process is found to fit a kinetic model, which includes both cross relaxation and energy transfer.

Demonstration of all-optical demultiplexing of a multilevel soliton signal employing soliton decomposition and self-frequency shift

We report an experimental demonstration of an all optical demultiplexing a burst of 4/spl times/10-Gb/s multilevel TDM soliton signal using the soliton effect pulse compression and soliton self-frequency shift in a silica fiber.

Measurements of very low bit-error rates of optical switches based on semiconductor optical amplifiers

Very low bit-error-rate (BER) performance of an 8/spl times/8 nonblocking optical switch based on semiconductor optical amplifiers (SOAs) was measured using a simple extrapolation technique and optical disturbance. The results show the impact of SOAs amplified spontaneous emission and dynamic gain saturation on the low BER (<10/sup -12/) behavior of the optical switching system. The input dynamic ranges of 24 dB with a BER at 10/sup -15/ and of 20 dB with a BER at 10/sup -30/ were achieved for the bit rate at 1.0 Gb/s with less than 2-dB power penalty.

Nanosecond all-optical gain switching of an erbium-doped fibre amplifier

Abstract Optical gain switching of an erbium-doped fibre amplifier (EDFA) with short pulses at wavelengths within the amplifier bandwidth is demonstrated. Gain compression of 20 dB in 40 ns was experimentally obtained. Theoretical modelling agrees well with experimental results and concludes that gain compression is determined by pulse energy. Optimization of fibre length as well as signal and switching wavelengths predicts that 10 dB nanosecond switching can be obtained with sub-picojoule switching pulse energy. Theory also shows that a pump pulse can accelerate recovery to microseconds. The proposed switching scheme offers optical gain control many orders of magnitude faster than the fluorescence lifetime of erbium ions in a glass host, which limits the switching speed of an EDFA controlled by pump power modulation alone.