J.R. Talman

2-Gbit/s signal amplification at lambda =1.53 mu m in an erbium-doped single-mode fiber amplifier

The gain, saturation power, and noise of an erbium-doped single-mode traveling-wave fiber amplifier operating at a wavelength lambda =1.53 mu m are characterized. In continuous-wave (CW) measurements amplification at 2 Gbit/s was demonstrated with up to 17-dB gain for 1*10/sup -9/ bit error rate at 1.531 mu m and a 3-dB full bandwidth of 14 nm. From the determination of the fiber-amplifiers output signal-to-noise ratio versus input signal power during data transmission, it was concluded that, with signal levels used here, signal-spontaneous beat noise limited the receiver sensitivity improvement. With the fiber amplifier acting as an optical preamplifier of the receiver, the best sensitivity was -30 dBm, obtained after installing a polarizer at the fiber amplifier output to reject half of the applied spontaneous emission power. This sensitivity was 6 dB better than without the fiber amplifier, proving that the fiber amplifier can be used as a preamplifier. >

Wide-band lightwave distribution system using subcarrier multiplexing

A description is given of a bidirectional lightwave distribution system based on subcarrier multiplexing. Eight independent wideband channels (180 Mb/s/channel) are transmitted from the head-end on one 1.3- mu m wavelength laser as frequency-shift-keyed (FSK) subcarriers, between 2.6 and 4.7 GHz. Each receiving node uses a parallel-resonant p-i-n FET receiver, a microwave bandpass filter and a limiter-discriminator demodulator to select and demodulate the appropriate channel. A 45-Mb/s return channel is provided from each node to the head-end on a separate subcarrier frequency. Error-free bidirectional transmission is obtained without penalties from laser nonlinearities, optical reflections or interference, or interchannel interference from closely spaced subcarrier channels. >

Resonant p-i-n-FET receivers for lightwave subcarrier systems

A theoretical and experimental analysis of narrowband resonant direct-detection p-i-n-FET receivers for subcarrier multiple-access networks is described. It is shown how a small inductance can be used to optimize the coupling between the p-i-n and FET, over a range of microwave subcarrier frequencies, minimizing the frequency-dependent thermal noise and leaving shot-noise as the ultimate limitation. Shot-noise then establishes a fixed ratio of the total usable bandwidth to the minimum received power per channel, which for the binary FSK system considered is 6.1 GHz/ mu mW. A resonant p-i-n-FET receiver, designed to provide maximum sensitivity between 2.5 and 5.0 GHz, has been constructed. The measured signal-to-noise ratio is in excellent agreement with that predicted by the noise analysis. >

An APD/FET optical receiver operating at 8 Gbit/s

A high-sensitivity optical receiver has been designed for a bit rate of 8 Gbit/s and wavelengths of 1.3-1.55\mu m. The receiver uses a 60-GHz gain-bandwidth-product InGaAs/InGaAsP/InP avalanche photodiode followed by a high-impedance hybrid GaAs MESFET preamplifier. A bandwidth of 6.9 GHz was measured, with flat frequency response ±2 dB being obtained through the use of a 3-tap transversal equalizer. A sensitivity \bar{P} as high as -25.8 dBm was measured for 10-9bit-error rate.

An optical-feedback transimpedance receiver for high sensitivity and wide dynamic range at low bit rates

A novel transimpedance optical receiver using optically coupled feedback rather than a conventional feedback resistor is described. The optically coupled feedback has a number of advantages, including: (1) elimination of feedback-resistor Johnson noise for higher sensitivity; (2) elimination of feedback capacitance for higher bandwidth; and (3) the capability of large feedback current with low output voltage for wide dynamic range. A theoretical analysis is presented, along with experimental results for a long-wavelength optical-feedback receiver at a bit rate of 1.5 Mb/s. The experimental receiver uses InGaAs p-i-n photodiodes and a silicon JFET preamplifier and obtains a maximum sensitivity of -63.8 dBm for an error rate of 1*10/sup -7/. When the receiver is optimized for high level signals, an optical dynamic range of 40 dB is attained with no preamplifier automatic gain control (AGC). The results of a transmission experiment over a length of 303 km of single-mode optical fiber at a wavelength of 1.55 mu m are presented. >