Abstract: There is described a method for determining a refractive index of a medium. The method generally has providing a substrate having a surface, the surface having a first surface portion and a second surface portion spaced-apart from the first surface portion and recessed of a depth relative to the first surface portion; receiving the medium at least on the second surface portion; propagating a first optical beam towards the first surface portion and a second optical beam towards the second surface portion; collecting the first and second optical beams after said propagating and generating first and second signals being indicative of a phase of a respective one of the first and second collected optical beams; and determining a refractive index of said medium based on the first and second signals, the depth, a wavelength associated to the first and second optical beams and a refractive index of the substrate.

Abstract: Polarization compensation in optical system having a primary optical element having polarization-altering characteristics, such as a dichroic element, is provided. A compensation optical element having substantially the same polarization-altering characteristics as the primary optical element is provided in the path of the light beam whose polarization state is to be conserved. The compensation optical element is oriented with respect to the light beam such that by transmitting or reflecting the light beam, it alters its polarization state in a manner opposite to the altering of this polarization state by the primary optical element. Advantageously, this is true for any orientation of the polarization state of the light beam.