Patent ID: 6400479
Filing Date: 2002-06-04
Classification: H04B,H04J

Abstract:
An optical communications network, comprising:a number of cascaded optical links extending between an optical transmitter and a corresponding optical receiver, each optical link having one or multiple fiber spans, each fiber span including (i) an optical fiber operative to carry wavelength-division multiplexed (WDM) optical communications signals in the direction from the transmitter to the receiver, and (ii) an optical amplifier coupled to the optical fiber, the optical amplifier being configured to supply a constant gain to each input optical signal over a specified range of input optical signal power, each optical link being configured such that the power level of each optical signal provided to each optical amplifier is within the specified range of input optical signal power to avoid attaining deep saturation of the cascaded optical amplifiers; optical signal-to-noise ratio (OSNR) measuring circuitry operative to measure the OSNR of an optical communications signal received at the receiver from the transmitter via the optical links by measuring amplified spontaneous emission (ASE) noise and optical signal power at the receiver, the OSNR measuring circuitry including a photodetector following a taper coupler and dual gain circuitry operative to selectively apply either a high gain or a low gain to the signal being measured; transmitter power adjusting circuitry operative to adjust the optical power of the optical communications signal transmitted by the transmitter to the receiver via the optical links; and a controller coupled between the OSNR measuring circuitry and the transmitter power adjusting circuitry, the controller being operative to control the dual-gain circuitry to apply high gain when the ASE noise is being measured and low gain when the optical signal power is being measured, the controller being further operative to adjust the optical power of the optical communications signal transmitted by the transmitter to attain a desired OSNR at the receiver independently of the optical power levels of the other optical communications signals carried on the path from the transmitter to the receiver.