Methods, systems, and apparatus, including an optical receiver including a laser including a gain section; and a first tunable reflector configured to output a reference signal; a first coupler formed over the substrate; a shutter variable optical attenuator formed over the substrate, the shutter variable optical attenuator including an input port configured to receive the first portion of the reference signal from the laser; and an output port configured to provide or to block, based on a control signal, the first portion of the reference signal from the laser; and a second coupler including a first port configured to receive the first portion of the reference signal from the shutter variable optical attenuator; and a second port configured to (i) provide the first portion of the reference signal from the shutter variable optical attenuator to an optical analyzer or (ii) receive a data signal from a transmitter.