Abstract: An optical device comprises: an active semiconductor region (130), for providing gain to signal light (170) passing through said active region (130); a signal-light reflector (120), for reflecting the signal light (170) through the active region (130) in a direction out of the plane of the active region (130); a pump-light reflector (120), the pump-light reflector (120) being arranged to reflect pump light so as to form a standing wave (160) in the device; and an absorber (191) that absorbs light at a wavelength of the signal light. The absorber (191) is arranged at a position in the device at which there is no or substantially no pump light.