S.G. Grubb

Stable single-mode erbium fiber-grating laser for digital communication

In this paper we report the fabrication of a short, robust, single-mode Er/sup 3+/ fiber-grating laser. This laser is proven by the successful outcome of a long-term bit-error-rate test at the 10/sup -15/ level in a 5- G/s fiber transmission experiment. In the process we present a new pumping geometry, the elucidation of one origin of relaxation oscillations that have plagued previous lasers and the demonstration of a simple electronic feedback scheme for suppressing them. This prototype source shows real promise for use in a high-speed communications system. >

Capacity upgrades of transmission systems by Raman amplification

Raman amplification is added to a transmission system to provide an increase in power budget allowing for a four-fold upgrade in capacity either by TDM or WDM. Here, a TDM upgrade from 2.5 to 10 Gb/s and a WDM upgrade from a single 10-Gb/s channel to four channels of 10 Gb/s each were experimentally verified with an improvement in the power budget of 7.4 dB. Raman gain is an attractive upgrade method for installed systems requiring no changes to the fiber span.

Raman amplifier with improved system performance

Summary form only given. We describe the predominant sources of noise for various amplifier configurations. In addition, we present the results of a successful 2.5 Gbit/s systems test of a two-stage Raman amplifier with net small signal gains of 29 dB and output powers exceeding + 15 dBm. Although Raman amplifiers do not suffer from increased noise figure due to incomplete population inversion, the passive loss of the amplifier does contribute to the noise figure through increased signal-spontaneous beating. Nonetheless, we have constructed a Raman amplifier with a noise figure contribution from signal-spontaneous beating that is less than 5 dB. A second source of noise in Raman amplifiers is the coupling of intensity fluctuations in the pump light to the signal. The fundamental cause of this noise is the lack of a long upper-state lifetime to buffer the Raman gain from fluctuations in the pump intensity. We present results demonstrating that the transit time through the amplifier can be used to average gain fluctuations if a strictly counterpropagating-pump geometry is employed. Lastly, double Rayleigh backscattering also contributes to the noise figure of the amplifier but can be reduced by decreasing fiber lengths and by constructing multistage amplifiers. Based on the above considerations, the two stage Raman amplifier with a counterpropagating pump was constructed. The requisite pump light was generated by a cascaded Raman laser operating at 1240 nm that was pumped by a cladding-pumped neodymium laser operating at 1060 nm. A 2.5 Gbit/s bit-error-rate test of this amplifier was performed.

Unrepeatered WDM transmission experiment with 8 channels of 10 Gb/s over 352 km

Remotely pumped post- and preamplifiers are employed in an 80-Gb/s wavelength-division multiplexed repeaterless transmission system with a transmission distance of 352 km and a fiber loss of 65.3 dB. Low-loss silica-core fiber combined with dispersion compensation in the receiver is used to maximize the transmission distance. The eight channels which range in wavelength from 1552.30 nm to 1559.56 nm exhibit sensitivities between -31.4 dBm and -30.5 dBm for error rates of 10/sup -9/.

405 km of repeaterless transmission at 5 Gb/s utilizing a post-amplifier and a remotely preamplified receiver with forward error correction

A repeaterless system enables transmission over 405 km of fiber at 5 Gb/s with 24.3 dBm of launch power and a remotely preamplified receiver sensitivity with FEC of -59 dBm for a total span budget of 83.3 dB.

Dispersion precompensated, high-power Er-Yb linear amplifier with gain tilt optimization over 11 nm

In this paper, we describe a high-power Er-Yb codoped optical fiber amplifier with flat gain tilt characteristics and low noise figure with mid-stage dispersion-compensating-fiber (DCF). The amplifier has been tested with a 77 NTSC channel matrix box, and showed its full compatibility for the US standard for cable TV applications.

465-km, 2.488 Gbit/s repeaterless transmission using a directly modulated DFB laser

Summary form only given. In this work, we experimentally demonstrate repeaterless transmission over distances as long as 465.6 km using a directly modulated distributed feedback (DFB) laser. Suppression of stimulated Brillouin scattering (SBS) is obtained by the frequency chirping of the laser diode itself when modulated without any additional manipulation of the transmitted signal spectrum.

Reduction of the noise power in rare-earth-doped fiber lasers by broadening; the laser linewidth

The results show for a Nd-cladding pumped fibre (CPF) laser an increase in the spectral width of the CPF laser from 0.254-0.577 nm results in a decrease in the relative intensity noise (RIN) of 10 dB.