An optical data receiver comprises an optical input for receiving optical data signals, an optical sputter for splitting the optical signals into first and second receiver arms, an optical filter in the first receiver arm, means for increasing an intensity ratio of optical signal strength in the first receiver arm to optical signal strength in the second receiver arm, means for adjusting a phase difference between the first and second receiver arms, and an optical coupler for coupling outputs of the first and second receiver arms to a photodetector. The receiver of the present invention selectively filters a carrier component of received optical data signals, adjusts the relative strength of the carrier component and the received signal and then recombines them. In this way efficient optical transmission can be achieved with direct detection at the receiver, without the need for a complex receiver design including a local oscillator.