Apparatus and method for measuring displacement

An apparatus for measuring displacement, comprising:

• a function generator;
• a light source coupled to said function generator, said light source outputting modulated output beam responsive to a wavelength modulating of said function generator;
• a beam splitter, splitting a modulated output beam from said light source into a first beam and a second beam, the first beam and the second beam having the same frequency;
• a first refection structure, reflecting said first beam to the surface of an object under test;
• a second reflection structure, reflecting said second beam to the surface of said object under test, said second reflection structure further having an extra reflector in comparison with said first reflection structure for providing said reflected first beam and said reflected second beam having an optical path length difference, said object under test scattering a scattering beam of gathering said first and second beams, and said scattering beam having an interference signal;
• a photodetector, receiving said interference signal of said scattering beam;
• and
• an operational unit, receiving and computing said interference signal for producing a displacement value.