Free-space laser communication systems have the potential to provide flexible, high-speed connectivity suitable for long-haul intersatellite and deep-space links. For these applications, power-efficient transmitter and receiver designs are essential for cost-effective implementation. State-of-the-art designs can leverage many of the recent advances in optical communication technologies that have led to global wide-band fiber-optic networks with multiple Tbit/s capacities. While spectral efficiency has long been a key design parameter in the telecommunications industry, the many THz of excess channel bandwidth in the optical regime can be used to improve receiver sensitivities where photon efficiency is a design driver. Furthermore, the combination of excess bandwidth and average-power-limited optical transmitters has led to a new paradigm in transmitter and receiver design that can extend optimized performance of a single receiver to accommodate multiple data rates.

Laser communication transmitter and receiver design

The statistical properties, i.e. power spectral densities and probability density functions, of the noise due to Rayleigh backscattered light and due to interference of backscattered and reflected light are derived from the autocorrelation function of the optical source field. The crosstalk penalties due to Rayleigh backscattering in single- and double-source bidirectional systems are calculated. It is shown that it is possible to realize a bidirectional system with commercially available connectors in which Rayleigh backscattering is the dominant crosstalk contribution. The measured crosstalk penalties and bit-error probabilities in a double-source bidirectional system confirm the theoretical results. >

Crosstalk penalities due to coherent Rayleigh noise in bidirectional optical communication systems

An optical-preamplifier receiver with sensitivity of 137 photons/bit at 2.5 Gb/s and 1.530- mu m wavelength is presented. The sensitivity is 193 photons/bit at 10 Gb/s. The authors discuss the degradations from the quantum-limited value of 38 photons/bit. By employing an optical power amplifier at the transmitter, the authors demonstrate 2.5 Gb/s-250 km and 10 Gb/s-220 km transmission through dispersion-shifted fiber. >

2.5 and 10 Gb/s transmission experiments using a 137 photon/bit erbium-fiber preamplifier receiver

Strained InGaAs/AlGaAs double-quantum-well laser diodes (LDs) with GaInP buried waveguides operating at 0.98-1.02 mu m have been developed as light sources for pumping fiber amplifiers. These LDs have a flat surface and a low-loss real index waveguide that provides high differential quantum efficiency and efficient heat dissipation. For 0.98- mu m LDs, stable operation for over 10000 h under 100 mW conditions at 50 degrees C has been achieved, and the extrapolated lifetime is estimated to be 60000 h at 50 degrees C. For 1.02- mu m LDs, a maximum light output power of 415 mW, fiber output power as high as 70 mW, and stable operation for over 2300 h at 100 mW and 50 degrees C have been obtained. >

0.98-1.02 mu m strained InGaAs/AlGaAs double quantum-well high-power lasers with GaInP buried waveguides

The authors report an 8-Gb/s lightwave transmission system operating at 1.53- mu m wavelength through 130 km of single-mode fiber having a chromatic dispersion of zero at 1.3- mu m wavelength. A receiver sensitivity of -34.2 dBm (365 photons/bit) was achieved using an erbium-doped fiber preamplifier pumped at 980-nm wavelength. A sensitivity of -31.9 dBm (620 photons/bit) was reached by a preamplifier pumped at a 1480-nm wavelength. By employing a Ti:LiNbO/sub 3/ external modulator and a fiber Gires-Tournois interferometer to equalize fiber chromatic dispersion, the penalty for 130 km transmission was held to only 0.9 dB. >

8-Gb/s-130 km transmission experiment using Er-doped fiber preamplifier and optical dispersion equalization

The authors report the realization of an extremely high receiver sensitivity at 10 Gb/s by using an erbium doped fiber (EDF) preamplifier pumped with a 0.98 mu m laser diode. The obtained EDF input sensitivity is -37.2 dBm (147 photons/bit). In addition, the importance of minimizing reflection from amplifier fiber ends is shown. >

High receiver sensitivity at 10 Gb/s using an Er-doped fiber preamplifier pumped with a 0.98 mu m laser diode

The achievement of -30.8 dBm (630 photon/bit) receiver sensitivity at 10 Gb/s, with an Er/sup 3+/-doped optical fiber preamplifier, is discussed. This is an 8.3-dB sensitivity improvement over the avalanche-photodiode/FET receiver. Power penalties caused by a noise increase due to Rayleigh backscattering by the transmission optical fiber have been evaluated. Approximately -30-dB Rayleigh scattering from a 20-km optical fiber resulted in a 3.5-dB power penalty for a 25-dB-gain optical amplifier. >

Y. Sunohara

Papers

High receiver sensitivity at 10 Gb/s using an Er-doped fiber preamplifier pumped with a 0.98 mu m laser diode

Rayleigh scattering influence on performance of 10 Gb/s optical receiver with Er-doped optical fiber preamplifier