Embodiments of the present disclosure are directed toward techniques and configurations for a photonic apparatus with a photodetector with bias control to provide substantially constant responsivity. The apparatus includes a first photodetector, to receive an optical input and provide a corresponding electrical output; a second photodetector coupled with the first photodetector, wherein the second photodetector is free from receipt of the optical input; and circuitry coupled with the first and second photodetectors, to generate a bias voltage, based at least in part on a dark current generated by the second photodetector in an absence of the optical input, and provide the generated bias voltage to the first photodetector. The first photodetector is to provide a substantially constant ratio of the electrical output to optical input in response to the provision of the generated bias voltage. Additional embodiments may be described and claimed.