A received optical signal is coherently demodulated and converted into orthogonal x-polarization samples, and y-polarization samples. A plurality of logical units are accessible by one or more ports, a port being an addressable entity that sends commands. The FEM is then subjected to a sequence of pressure increments and the resultant profile is compared with empirical data to predict an onset of glaucoma. A clamping device is electrically coupled to the sensing device to control voltages across the sensing device during programming. The first and second delay circuits need only be substantially matched with one another to render the IQ generator amplitude and phase stable over a broad range of manufacturing process, operating temperature and input signal frequency variation.