P.B. Hansen

Rayleigh scattering limitations in distributed Raman pre-amplifiers

The properties and fiber dependence of distributed Raman pre-amplifiers and, in particular, the effects of Rayleigh backscattering, which limits the sensitivity improvements that can be realized, is discussed. Bit-error-rate (BER) measurements show improvements In the effective receiver sensitivity of 6.2 and 7.0 dB for dispersion shifted fiber (DSF) and silica-core fiber (SCF), respectively. Theoretical predictions of the effective noise figure based on measured fiber parameters indicate improvements of 6.6 dB for DSF and 7.4 dB for SCF in good agreement with the measured optical SNR. The optimum receiver sensitivity is obtained in DSF with less than 600 mW of pump power, whereas the 0.8-dB superior performance of the SCF requires approximately 1 W.

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.

5.5-mm long InGaAsP monolithic extended-cavity laser with an integrated Bragg-reflector for active mode-locking

A 5.5-mm-long monolithic extended-cavity laser with an integrated Bragg-reflector in the InGaAsP system for active mode-locking at low repetition rates at a wavelength of 1.55 mu m has been fabricated. The device, which is designed to be used as a pulse source in long-distance soliton systems and optical time-division multiplexed systems, generates 20-ps-wide transform-limited pulses with a time-bandwidth product of 0.34 at a repetition rate of 8.1 GHz.<<ETX>>

A 1.54- mu m monolithic semiconductor ring laser: CW and mode-locked operation

The authors have fabricated a monolithic semiconductor ring laser with a diameter of 3.0 mm. A straight tangent waveguide provides two output ports through evanescent coupling. The laser, which exhibits a threshold current of 157 mA, operates in a single longitudinal mode with a linewidth of 900 kHz at a wavelength of 1.54 mu m. The device has been actively mode-locked at the fundamental resonance frequency of 9.0 GHz, yielding 27-ps pulses with a time-bandwidth product of 0.47. Differences in the characteristics of the pulses emitted from the two output ports indicate counterpropagating pulse trains, which because of the mode-locking scheme must collide in the modulated gain section.<<ETX>>

Loss compensation in dispersion compensation fiber modules by Raman amplification

Summary form only given. Dispersion-compensating fiber (DCF) devices relying on normal dispersion for the propagating mode are quite long (typically on the order of several kilometers) and therefore exhibit significant insertion loss. We propose and demonstrate Raman gain induced in the DCF as a simple and attractive method for obtaining lossless DCF modules. The Raman efficiency of the DCF is quite high because of the small mode-field diameter of the fiber, which leads to modest pump power requirements. A pump power of only 225 mW provides enough gain to offset the insertion loss of our 15.7-km DCF module with -1400 ps/nm of dispersion. We have also investigated the noise performance and verified penalty-free operation in a 9.953-Gbit/s transmission experiment.

InGaAsP monolithic extended‐cavity lasers with integrated saturable absorbers for active, passive, and hybrid mode locking at 8.6 GHz

Active, passive, and hybrid mode locking of a monolithic extended‐cavity semiconductor laser with an integrated saturable absorber have been demonstrated. Actively mode locked at a repetition rate of 8.6 GHz, 6.2 ps pulses were measured. Hybrid mode locking resulted in 4.4 ps pulses. The extended‐cavity laser also exhibits self‐starting passive mode locking at a repetition rate of 8.57 GHz with 5.5 ps pulses. A broad spectrum allows wavelength selectivity over a range of 15 nm with little change in the pulse width.

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/.

Dense wavelength-division multiplexed transmission in "zero-dispersion" DSF by means of hybrid Raman/erbium-doped fiber amplifiers

Transmission of 25 and 50 equally 100-GHz and 50-GHz spaced 10-Gb/s (OC-192) channels on the ITU grids is demonstrated over eight and four 83.8-km long spans, respectively, of DSF with the zero-dispersion wavelength within the signal wavelength band. Significant performance improvements are obtained with a pump power of only 440 mW with 55-/spl mu/m/sup 2/ dispersion-shifted fibers because of their relatively high Raman efficiency.

8 x 10 Gb/s 1.3-μm unrepeatered transmission over a distance of 141 km with Raman post- and pre-amplifiers

A repeaterless wavelength-division-multiplexed transmission system operating in the 1.3-/spl mu/m wavelength window is demonstrated by means of discrete Raman fiber amplifiers. The power budget is 45.1 dB, leaving a margin of 1.6 dB for a transmission distance of 141 km. The eight channels, which occupy a wavelength range from 1305.8 to 1311.6 nm, carry data at a rate of 10 Gb/s each. The Raman post- and pre-amplifier both employ a two-stage ring topology, which allows counterpropagating pumping.

A dual-drive Ti:LiNbO/sub 3/ Mach-Zehnder modulator used as an optoelectronic logic gate for 10-Gb/s simultaneous multiplexing and modulation

A dual-drive Ti:LiNbO/sub 3/ Mach-Zehnder modulator is used as an optoelectronic exclusive-OR gate. The logic capability is employed for simultaneously multiplexing and encoding two electrical 5-Gb/s signals on an optical beam. Demultiplexing schemes for differentially encoded signals involving optical or electrical time demultiplexing are presented. The dual-drive modulator offers a simple and relatively inexpensive way of encoding a 10-Gb/s pseudorandom bit string using one 5-Gb/s pattern generator.<<ETX>>