Abstract: A technique is disclosed for optically trimming a sensor (10) to account for manufacturing variations in the losses of the sensor. As a result, the sensor can be used interchangeably, without requiring adjustment of the processing system (12) the sensor is used with. More particularly, in one embodiment, variably transmissive optical filters 72 and 74 are positioned inside the sensor to effectively alter or standardize the losses of the sensor. Various other arrangements, including the use of variably reflective mirrors, wavelength selective elements, blocking elements, and path adjustment elements, are also described in which the characteristics of the sensor's optical paths are altered.