Patent ID: 8774320

Claim:
An apparatus, comprising: a plurality of photodiodes configured to receive optical signals, each of the optical signals being modulated in accordance with an m-QAM modulation format, where m is an integer greater than 4, the plurality of photodiodes supplying a plurality of outputs in response to the optical signals; and a rotation circuit configured to receive first data, the first data being supplied to the rotation circuit in response to the plurality of outputs, the first data having an associated first constellation, the first constellation including first points, each of which having a first magnitude relative to an origin and each of which having a corresponding one of a first plurality of phases relative to an axis, the first constellation also having second points, each of which having a second magnitude relative to the origin and a corresponding one of a second plurality of phases relative to the axis, each of the second plurality of phases being different than each of the first plurality of phases, the rotation circuit being configured to supply second data having an associated second constellation, the second constellation including third points, each of which having the first magnitude relative to the origin and a corresponding one of the first plurality of phases relative to the axis, the second constellation including fourth points, each of which having the second magnitude relative to the origin and a corresponding one of the first plurality of phases, wherein the rotation circuit includes: a selector circuit, wherein in response to a first control signal, the selector circuit passes a first portion of the first data as a first portion of the second data if the first portion of the first data has an associated magnitude that is less than a threshold magnitude, and, in response to a second control signal, the selector circuit supplying a second portion of the first data with a rotated phase relative to one of the second plurality of phases if the second portion of the first data has an associated magnitude that is greater than the threshold magnitude.