Cascaded four-wave mixing in fiber optical parametric amplifiers: application to residual dispersion monitoring

This paper presents a parametric amplifier configuration that enables real-time monitoring of the net dispersion experienced by a pulse train. Fast detection or fast electronic signal processing is not required. The device exploits cascaded four-wave mixing (FWM) in an optical fiber and exhibits parametric gain and frequency conversion efficiency of more than 18 dB. Dispersion monitoring with 11-ps pulses that have experienced a net dispersion of ±180ps/nm are demonstrated. These pulses are similar to those to be used in high-bandwidth (∼40Gb/s) communication systems. The device is compatible with 160-Gb/s systems. Parametric amplification within the device enables simultaneous dispersion monitoring, wavelength conversion, and amplification. The monitor can be used in a feedback loop with a tunable dispersion compensator, allowing dispersion to be managed. Equations governing the FWM process are presented; there is good agreement between the simulated and measured results. The equations are further used to understand which of the several FWM processes within the device dominate.