For example, the light quantity control unit (13) performs biphase encoding for the communication information.

The control signal is then gated with the biphase encoded data to extract the clock edge after the time window has opened.

The expected level of the clock is gated with the biphase encoded data to generate a control signal in advance of the opening of the time window.

A method of extracting a clock from a biphase encoded bit stream includes the step of detecting a stream of samples each having a sample size measured between consecutive bit phase transitions.

differentially bi-phase coded binary data