Erbium-doped fiber amplifier applications in WDM transport systems and networks.
Creators: name: Khaleghi, Farideh.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1996
Subjects: subject: Engineering, Electronics and Electrical.

description: New expressions are derived for wavelength-dependent gain variations of the EDFA due to changes in the pump power, total input power, and the power distribution among different wavelength channels in a wavelength-division multiplexing (WDM) system. A simple method is proposed to compensate for the changes in the amplifier gain spectrum. This method is based on adjusting the pump power. Two different novel gain equalization techniques are presented. A tunable coherent optical transversal filter is designed as a gain equalizer. The filter operation is based on coherently combining the tapped signals. It is shown that, although the N tapped signals after being weighted according to the filter parameters are recombined by a tree of 2 x 2 couplers, the coupling loss experienced at the output is much less than the noncoherent coupling loss (10log(N)). For a multi-wavelength input, the spectrum of the amplifier output power is evaluated before and after the equalizer, using the numerical full spectrum model of the amplifier. The impact of the laser phase noise on the performance of this equalizer is studied. Another gain equalization technique is presented where high- and moderate-inversion EDFAs are used alternatively in order to equalize both signal power and signal-to-noise ratio (SNR) of multiple wavelength channels in WDM transmission systems. This technique is based on the fact that the gain slope is a function of the inversion level in amplifiers. This is confirmed experimentally. The performance of the equalized WDM system is examined by a numerical analysis based on the full spectrum model of the amplifier. The interferometric conversion of the phase-to-intensity noise is studied. The probability density function (pdf) of the intensity noise at the output of a multi-tap filter is derived. The degradation of the filter response is evaluated. The power penalty due to this noise is derived for amplitude modulated signals modulated using different bit rates. The power penalty due to interferometric noise caused by multiple reflections is also derived. A novel bidirectional EDFA configuration is proposed where the power penalty associated with the amplifier due to both the signal-spontaneous noise and the interferometric noise is substantially reduced. The experimental results are presented where a gain of 36 dB is achieved, and a 2.5 Gb/s bidirectional transmission over 300 km is realized. The power penalty is as low as 0.5 dB. Application of EDFA in an optical network is presented. The multi-access scheme in this local network is code-division multiple access (CDMA). A new correlator receiver architecture for noncoherent optical CDMA networks is proposed based on a modified version of unipolar-bipolar correlation functions for known bipolar codes. These functions are studied. Average bit error rate (BER) performance is evaluated for this architecture. The results indicate that bipolar capacity can be achieved by this architecture.