Low-bulk interferometric sensor

An objective for a confocal system for spectral interferometric measurement comprising:

• a source hole;
• a first beam splitter having a face configured to form a reference surface, wherein the first beam splitter comprises at least one of the following elements:
• an assembly formed of a lens and a partially reflective plate, a lens having a face devoid of anti-reflective treatment, and an assembly comprising a mirror attached and fixed to a lens, an area of the mirror being less than an area of the lens;
• a second beam splitter having a partially reflective face, the second beam splitter being positioned downstream of the first beam splitter such that the first beam splitter is located between the source hole and the second beam splitter and that an optical distance between the reference surface and the partially reflective surface is substantially equal to an optical distance between the partially reflective surface and a focal plane of the objective;
• and
• a first lens positioned between the first beam splitter and the second beam splitter and a second lens positioned downstream of the second beam splitter, an optical distance between the first lens and the second beam splitter being equal to an optical distance between the second beam splitter and the second lens;
• wherein the first beam splitter, the second beam splitter, the first lens and the second lens are coaxial such that optical axes of the first beam splitter, of the second beam splitter, the first lens and the second lens are coincident.