A system can include a transmitter that produces an optical signal having a plurality of carrier frequencies and a receiver separated from the transmitter by free space through which the optical signal propagates. The receiver includes an array of detectors of multiple types, with the types being capable of detecting light respectively having the carrier frequencies. A location of an incident area where the optical signal is incident on the detector array generally depends on a misalignment of the receiver relative to the transmitter, but the detectors in the detector array are arranged so that at least one detector of each of the types detects light from the optical signal regardless of where the incident area is on the detector array.