A method and apparatus for encoding data. A first pair of optical signals having a first phase difference is generated in response to receiving an input signal having a voltage. A second pair of optical signals having a second phase difference is generated in response to receiving an input signal having a voltage. The first pair of optical signals is combined to form a first optical signal having a first intensity. The second pair of optical signals is combined to form a second optical signal having a second intensity. The first intensity of the first optical signal reaches a peak at a different time from the second intensity of the second optical signal.