A waveguide structure (IOO) for a photonic integrated circuit, comprising: a substrate; an active region (102) comprising a diode junction, the active region comprising: a light emission portion (102a) to emit light in a first direction and a second direction perpendicular the first direction; and a light absorption portion (102b) to absorb light emitted from the light emission portion (102a) in the second direction; a first contact corresponding to the light emission portion (102a); and a second contact corresponding to the light absorption portion (102b).