Multi-channel optical equalizer for intersymbol interference mitigation

An optical signal equalizer for equalizing a received optical signal modulated at a preselected modulation bit rate, the equalizer comprising two or more equalizer units,

• the first equalizer unit including
• a first coupler for splitting the light into two portions and for adjusting the phase of one of the first or second light portions;
• a controllable interferometer unit including two arms, the first arm receiving the first of the two portions, the second arm receiving the second of the two light portions, the first arm having an additional delay which is approximately equal to one modulation bit period, and further including a controllable delay unit located in the first or second arm for adjusting the magnitude of the first or second light portions passing therethrough;
• a second coupler for receiving the two light two portions and further adjusting the phase of the same first or second light portions adjusted by the first coupler and for combining first or second light portions into a single output signal;
• and
• the second equalizer unit including
• a first coupler connected to the single output of the first equalizer unit for splitting the light into two portions and for adjusting the phase of one of the first or second light portions;
• a controllable interferometer unit including two arms, the first arm receiving the first of the two portions, the second arm receiving the second of the two light portions, the first arm having an additional delay which is approximately equal to one modulation bit period, and further including a controllable delay unit located in the first or second arm for adjusting the magnitude of the first or second light portions passing therethrough;
• and
• a second coupler for receiving the two light two portions and further adjusting the phase of the same first or second light portions adjusted by the first coupler and for combining first or second light portions into an output signal of the optical signal equalizer.

A method for equalizing a received multiwavelength optical signal modulated at a preselected modulation bit rate, comprising the steps of

• splitting the light into two or more variable portions;
• creating a differential delay between the two or more of the portions, which is approximately is equal to an integer multiple of 1/Δf, where Δf is the channel spacing of the multiwavelength system,
• adjusting the phase of the light in one of the two or more portions
• combining the signals into a single output
• whereby the variable adjustments are made so as to mitigate intersymbol interference impairments in the received optical signal.