Abstract
Optical parametric amplifiers provide gain to an input signal in a phase-sensitive fashion; hence the name phase-sensitive amplifiers (PSAs). Recently, quantum-limited PSAs with large gains and phase-sensitive signal amplification at 1.06 μm have been demonstrated.1,2 PSAs possess many properties that make them attractive for use in ultrahigh-speed communications and networks: They do not add any spontaneous-emission noise, and the signal-to-noise ratio is preserved as the signal is amplified. In this sense they make an ideal amplifier with a 0-dB theoretical noise figure.1 They are unidirectional in that the gain exists only for light propagating in the same direction as the pump light in the amplifier. PSAs can be designed for operation at any wavelength; hence the full low-loss window of the fused-silica fiber becomes usable. In contrast, the erbium-fiber amplifier provides gain over a relatively narrow wavelength range (≃40 nm). In a fiber/amplifier line the use of PSAs automatically compensates for the degrading effects of dispersion; there is no need for extra dispersion-compensating devices.3 Short pulses can propagate without significant broadening over distances up to 100 times the dispersion length of the fiber. Moreover, dispersion can be compensated in both the positive and the negative group-velocity-dispersion (GVD) regions of the fused-silica fiber. When used with solitons, PSAs can reduce the Gordon–Haus timing jitter without the need for extra filters.4 Solitons can propagate over long distances without generating dispersive radiation during amplification and decay between the amplifiers.5 The preceding properties can be very useful for upgrading the capacity of the existing 1.3-μm fiber plant.
© 1994 Optical Society of America
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