Optoelectronic device

An optoelectronic device includes an input waveguide 102 receiving an optical signal 104 and a multistage photodiode detector including photodiode elements 101a-n connected in series. One of the photodiode elements is connected to the input waveguide, receiving the optical signal. Each photodiode element has first and second contacts connected to first 120a and second 120b electrodes respectively. Each photodiode element may include a p-i-n junction extending across a waveguide. Each photodiode element may be located within a cavity 122a-n of a silicon-on-insulator wafer. The optoelectronic device may include passive waveguides 106a-n each connected to a pair of the photodiode elements. A final photodiode element may be connected at a terminating end to a high reflectivity mirror. The optoelectronic device may be a power monitor. An array may include such power monitors where each is connected to a respective laser or electro-absorption modulator. Power output monitoring of an electro-absorption modulator may use such a power monitor. A signal from the laser or electro-absorption modulator may be provided to the input waveguide and a power level of the signal detected using the multistage photodiode detector. A photonic integrated circuit used as a transmission device may also include the array of power monitors.