A modular, hermetically sealed optical signal receiver subassembly for converting a modulated optical signal to a corresponding electrical signal including an optical demultiplexer coupled to a fiber optic connector receiving a multi-wavelength optical signal having a plurality of information-containing signals each with a different predetermined wavelength and functioning to demultiplex the optical signal into distinct first and second optical beams corresponding to the predetermined wavelength and substrate is provided that forms an optional reference path of the first and second beams respectively, the photodiodes functioning to convert the respective optical signals into an electrical signal.