Jonathan A. Nagel

Dispersion penalty reduction using an optical modulator with adjustable chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value. >

Equalization in amplified WDM lightwave transmission systems

The authors introduce simple techniques to solve gain equalization problems in amplified wavelength-multiplexed lightwave transmission systems. By adjusting the channel powers at the terminals in a prescribed way, either the output powers or the output signal-to-noise ratios of all the channels can be equalized. All adjustments can be made using information provided by system telemetry. No new equipment, upgrades, or adjustments are required at intermediate amplifier sites.<<ETX>>

Degradations due to stimulated Brillouin scattering in multigigabit intensity-modulated fiber-optic systems

The stimulated Brillouin scattering (SBS) process limits the maximum power that can be transmitted in low-loss optical fibers in multigigabit fiber optic systems. It is shown that recently observed large optical fluctuations resulting from SBS degrade the signal-to-noise ratio and consequently the system bit error rate. Since SBS has potentially the lowest power threshold of all fiber nonlinearities: it is critical that it be addressed. It is shown that the SBS threshold can be increased by providing a low frequency sine wave dither to the laser pre-bias current. It is found that a modulation index as low as 2% can quadruple the SBS threshold. Measurements with a 1.5- mu m externally modulated laser at 2.5 Gb/s indicate that this dither in no way degrades the performance in the presence of chromatic dispersion. >

A compensator for the effects of high-order polarization mode dispersion in optical fibers

We present a polarization mode dispersion compensator for the rotation of the principal states with frequency. This compensator requires only two control elements more than existing first-order compensators. These are the position of one polarization controller and the setting of a single delay. With the proposed scheme, compensation for first order can be decoupled from the compensation for higher orders and controlled independently. The effect of the compensator on signal transmission is evaluated with extensive numerical simulations.

Multi-stage erbium-doped fiber amplifier designs

Applications for erbium-doped fiber optical amplifiers have been multiplying in recent years, and increasingly complex structures have been introduced. We review characteristics and design parameters, the use of interstage elements, and various digital transmissions systems applications for multi-stage amplifiers. A notation is introduced to describe multi-stage fiber amplifiers. >

End-to-end equalization experiments in amplified WDM lightwave systems

It is experimentally verified that signal-to-noise ratio equalization in amplified wavelength-multiplexed lightwave systems can be achieved by adjusting input optical signal powers according to a simple algorithm. The experiment involved four channels spaced by 2 nm transmitted through 550 km of fiber with the aid of eight erbium-doped optical amplifiers.<<ETX>>

Measurements and simulation of multipath interference for 1.7-Gb/s lightwave transmission systems using single- and multifrequency lasers

Power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers. Systems that use SF lasers potentially exhibit worse degradation than those using MF lasers. Bit-error-rate (BER) floors occur only under the worse-case conditions of poor receiver margin and large multiple reflections. The use of optical isolation to reduce laser feedback is ineffective in reducing multipath interference, and in many cases may worsen the penalty. It is shown that for a typical transmission system, these degradations are reduced if optical interconnection reflections are maintained below -20.5 dB. The experimental study is in good agreement with theoretical predictions using an analytic expression of the MPI noise power spectral density and with computer simulations using multimode laser rate equations. >

A high capacity noncoherent FSK lightwave field experiment using Er/sup 3+/-doped fiber optical amplifiers

A description is given of high-bit-rate fiber-optic noncoherent frequency-shift keying (FSK) transmission field experiments using Er/sup 3+/-doped optical amplifiers. Transmission distances of 70 km for a four-channel 6.8-Gb/s capacity experiment and 177 km for single-channel 1.7-Gb/s transmissions were demonstrated in a typical field environment. Measurements of receiver sensitivity dispersion penalty, interchannel crosstalk, and long-term bit-error-rate performance are presented. Results show negligible degradations due to >3000-ps/nm dispersion and interchannel crosstalk, in addition to stable long-term performance. This performance demonstrates the applicability of noncoherent FSK and fiber amplifier technologies.<<ETX>>

Dispersion Penalty Reduction using a Optical Modulator with Adjustable Chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value.<<ETX>>

Wavelength division multiplexing applications for optically amplified systems

1.5 pm, each carrying 1.7 Gb/s ofinformation for a totalsystem capacity of 3.4 Gb/s. The use of WDM to increase system capacity has not been attractive for manyreasons, but mostly due to the fact that losses in the optical multiplexors and demultiplexors required tocombine and split the signals reduces the available system gain.The use of Erbium-doped optical amplifiers makes WDM transmission a practical method ofincreasing system capacity without sacrificing system gain. A basic WDM system is shown in Figure 1.