Optical-based validation of parallelism between internal facets

An optical-based system for metrology of a sample having a substrate, with a refractive index ns, and two or more internal facets, which are embedded in the substrate and nominally oriented at an acute nominal angle μnom relative to an external and flat surface of the sample, the system comprising a light transmissive optical element and an optical setup comprising a light source and a light sensing component, wherein the optical element has a refractive index about equal to ns and comprises an external and flat first surface and an external and flat second surface, which are opposite to one another and define an angle therebetween about equal to the nominal angle μnom;

• wherein the optical setup is configured to enable positioning the sample and/or the optical element, such that (i) the second surface of the optical element is parallel and adjacent to the surface of the sample, and (ii) when so positioned, light beams, generated by the light source, are incident on the first surface of the optical element about normally thereto;
• wherein the optical setup is further configured to focus on the light sensing component returned light beams, so as to enable determination of angular deviation between the returned light beams;
• and
• wherein the returned light beams are obtained following passage of the incident light beams through the optical element, transmission thereof into the sample and reflection off the internal facets, repassage through the optical element, and exit out of the optical element via the first surface of the optical element, the angular deviation thus being indicative of a deviation from parallelism between the internal facets.