A variably-polarizing optical probe assembly. The assembly includes an optical probe having one or more optical light delivery channels that emit incident light from the sample end of the probe toward a sample being investigated, and one or more optical light-receiving channels that receive incident light from the sample. A variably-polarizing substrate assembly is coupled to the sample end of the probe. The substrate assembly includes an optically transmitting substrate and one or more discrete polarizer areas on a face of the substrate, each such polarizer area defining a polarization orientation, with the polarizer areas together defining one or more different polarization orientations. The substrate assembly is arranged relative to the probe such that one polarizer area covers at least one light delivery channel and one polarizer area covers at least one light-receiving channel.