A receiver for demodulating a DPSK optical signal, the receiver comprising: an optical interferometer configured to receive the DPSK optical signal and interfere the DPSK optical signal with itself, the optical interferometer comprising: a constructive output port for outputting a first signal, and a destructive output port for outputting a second signal; a differential detector for generating an analog electrical signal responsive to a difference between the first signal and the second signal, the differential detector comprising: a first photodetector coupled to the constructive port of the interferometer to receive the first signal and generate a first photocurrent, and a second photodetector coupled to the destructive port of the interferometer to receive the second signal and generate a second photocurrent; a clock and data recovery, CDR, module for converting the analog electrical signal generated by the differential detector into a digital electrical output signal; a controller for determining a ratio of the first photocurrent to the second photocurrent, wherein the controller is further adapted to determine an amount of the optical spectral filtering experienced by the DPSK optical signal along a communication link based on said ratio, to select a predetermined value for a characteristic of the receiver based on said amount of optical filtering, and to adjust the characteristic of the receiver based on the selected predetermined value. an optical interferometer configured to receive the DPSK optical signal and interfere the DPSK optical signal with itself, the optical interferometer comprising: a constructive output port for outputting a first signal, and a destructive output port for outputting a second signal; a constructive output port for outputting a first signal, and a destructive output port for outputting a second signal; a differential detector for generating an analog electrical signal responsive to a difference between the first signal and the second signal, the differential detector comprising: a first photodetector coupled to the constructive port of the interferometer to receive the first signal and generate a first photocurrent, and a second photodetector coupled to the destructive port of the interferometer to receive the second signal and generate a second photocurrent; a first photodetector coupled to the constructive port of the interferometer to receive the first signal and generate a first photocurrent, and a second photodetector coupled to the destructive port of the interferometer to receive the second signal and generate a second photocurrent; a clock and data recovery, CDR, module for converting the analog electrical signal generated by the differential detector into a digital electrical output signal; a controller for determining a ratio of the first photocurrent to the second photocurrent, wherein the controller is further adapted to determine an amount of the optical spectral filtering experienced by the DPSK optical signal along a communication link based on said ratio, to select a predetermined value for a characteristic of the receiver based on said amount of optical filtering, and to adjust the characteristic of the receiver based on the selected predetermined value.