A waveguide structure for a photonic integrated circuit, comprising: a substrate; an active region comprising a diode junction, the active region comprising: a light emission portion to emit light in a first direction and a second direction perpendicular the first direction; and a light absorption portion to absorb light emitted from the light emission portion in the second direction; a first contact corresponding to the light emission portion ; and a second contact corresponding to the light absorption portion , characterised in that the waveguide structure comprises: a driven waveguide having a longitudinal axis substantially parallel to the first direction and for guiding light; and an absorber structure having a longitudinal axis substantially parallel to the first direction, and the absorber structure for absorbing light unguided by the driven waveguide , wherein the driven waveguide is separated from the absorber structure in the second direction by a recess in the waveguide structure , the recess comprising a first sidewall on a first side of the driven waveguide , a second sidewall on a first side of the absorber structure , and a base portion joining the first sidewall and the second sidewall . a substrate; an active region comprising a diode junction, the active region comprising: a light emission portion to emit light in a first direction and a second direction perpendicular the first direction; and a light absorption portion to absorb light emitted from the light emission portion in the second direction; a light emission portion to emit light in a first direction and a second direction perpendicular the first direction; and a light absorption portion to absorb light emitted from the light emission portion in the second direction; a first contact corresponding to the light emission portion ; and a second contact corresponding to the light absorption portion , characterised in that the waveguide structure comprises: a driven waveguide having a longitudinal axis substantially parallel to the first direction and for guiding light; and an absorber structure having a longitudinal axis substantially parallel to the first direction, and the absorber structure for absorbing light unguided by the driven waveguide , wherein the driven waveguide is separated from the absorber structure in the second direction by a recess in the waveguide structure , the recess comprising a first sidewall on a first side of the driven waveguide , a second sidewall on a first side of the absorber structure , and a base portion joining the first sidewall and the second sidewall . a driven waveguide having a longitudinal axis substantially parallel to the first direction and for guiding light; and an absorber structure having a longitudinal axis substantially parallel to the first direction, and the absorber structure for absorbing light unguided by the driven waveguide , wherein the driven waveguide is separated from the absorber structure in the second direction by a recess in the waveguide structure , the recess comprising a first sidewall on a first side of the driven waveguide , a second sidewall on a first side of the absorber structure , and a base portion joining the first sidewall and the second sidewall . <EOS>