Method for determining a position by differential optical interferometry and differential interferometer for doing the same

A differential optical interferometer for determining a position of a target reflector in a measurement range, the differential optical interferometer comprising:

• a light generating means comprising a single frequency laser and being configured to generate a coherent source light beam being modulated between a first and a second wavelength;
• the light generating means further comprising a first and a second optical terminal, wherein the light generating means is configured to manipulate the coherent source light beam to generate a delayed light beam at the first optical terminal and a light beam at the second optical terminal, wherein the delayed light beam is delayed with respect to the light beam;
• a sensor head disposed downstream of the first and second optical terminal, wherein the delayed light beam is arranged in parallel to the light beam;
• wherein
• the sensor head comprises a first beam splitter and a second beam splitter disposed downstream of the first beam splitter, wherein
• the first beam splitter is configured to split each of the light beam and the delayed light beam into a first and second part, wherein
• the second beam splitter is configured to generate a first light signal by guiding the first part of one of the light beam and delayed light beam along a first path comprising a target reflector, configured to generate a second light signal by guiding the second part of the one of the light beam and delayed light beam along a second path comprising a reference reflector, wherein the second path is arranged in parallel to the first path, configured to generate a third light signal by allowing passage of at least part of the first part of the other one of the light beam and delayed light beam along a third path, and configured to generate a fourth light signal by allowing passage of at least part of the second part of the other one of the light beam and delayed light beam along a fourth path, wherein the fourth path is arranged in parallel to the third path;
• wherein
• the sensor head is configured to generate a first interference signal between the first light signal and the third light signal, and to generate a second interference signal between the second light signal and the fourth light signal;
• and wherein
• the sensor head comprises a detecting means configured to detect the first and the second interference signal, and
• a processing means configured to determine a position of the target reflector based on the first and second interference signal.