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.