Method and apparatus for calibrating a wavelength-tuning interferometer

An interferometry method comprising:

• forming an optical interference image by combining different portions of an optical wave front reflected from multiple surfaces;
• varying a frequency of the optical wave front at each of multiple constant tuning rates;
• for each constant frequency tuning rate, recording an interference signal at at least one location of the optical interference image in response to the varying frequency and transforming the interference signal to produce a corresponding spectrum;
• identifying a peak corresponding to a pair of the multiple surfaces in at least one spectrum;
• selecting a frequency tuning rate based on a spectral coordinate of the peak;
• and
• recording an interference signal at a plurality of locations of the optical interference image in response to varying the frequency at the selected tuning rate.

An interferometry method comprising:

• forming an optical interference image by combining different portions of an optical wave front reflected from multiple surfaces;
• varying a frequency of the optical wave front over a range of tuning rates recording an interference signal at at least one location of the optical interference image in response to the varying frequency;
• monitoring a reference phase from a reference cavity produced in response to an additional portion of the optical wave front;
• and
• transforming the interference signal for the at least one location into an optical path length (OPL) domain based on the monitored reference phase to produce a spectrum having a peak at an OPL corresponding to a pair of the multiple surfaces.

A system comprising:

• a frequency-tunable light source;
• an interferometer which during operation directs different portions of an optical wave front derived from the light source to multiple surfaces and recombines the different portions to form an optical interference image;
• a multi-element photo-detector positioned to measure an interference signal at different locations of the optical interference image in response to varying the frequency of the light source;
• and
• an electronic controller coupled to the light source and the photo-detector, wherein during operation the controller:
• i) varies the frequency of the light source at a plurality of different tuning rates;
• ii) records an interference signal at least one of the locations in response to varying the frequency at the plurality of different tuning rates;
• iii) transforms at least a portion of the interference signal corresponding to the plurality of different tuning rates to produce a spectrum having a peak at a spectral coordinate corresponding to a pair of the multiple surfaces;
• iv) selects a frequency tuning rate based on the spectral coordinate of the peak;
• v) varies the frequency of the light source at the selected frequency tuning rate;
• and
• vi) records the interference signal for each of the different locations of the optical interference image in response to varying the frequency at the selected frequency tuning rate.

A system comprising:

• a frequency-tunable light source;
• an interferometer which during operation directs different portions of an optical wave front derived from the light source to multiple surfaces and recombines the different portions to form an optical interference image;
• a multi-element photo-detector positioned to measure an interference signal at different locations of the optical interference image in response to varying the frequency of the light source;
• and
• an electronic controller coupled to the light source and the photo-detector, wherein during operation the controller:
• i) varies the frequency of the light source at each of multiple constant tuning rates;
• ii) for each constant frequency tuning rate, records an interference signal at at least one location of the optical interference image in response to the varying frequency and transforms the interference signal to produce a corresponding spectrum;
• iii) identifies a peak corresponding to a pair of the multiple surfaces in at least one spectrum;
• iv) selects a frequency tuning rate based on a spectral coordinate of the peak;
• and
• v) records an interference signal at a plurality of locations of the optical interference image in response to varying the frequency at the selected tuning rate.

A system comprising:

• a frequency-tunable light source;
• an interferometer which during operation directs different portions of an optical wave front derived from the light source to multiple surfaces and recombines the different portions to form an optical interference image;
• a multi-element photo-detector positioned to measure an interference signal at different locations of the optical interference image in response to varying the frequency of the light source;
• and
• an electronic controller coupled to the light source and the photo-detector, wherein during operation the controller:
• i) varies the frequency of the light source over a range of tuning rates;
• ii) records an interference signal for at least one of the locations in response the varying the frequency over the range of tuning rates;
• iii) monitors a reference phase from a reference cavity produced in response to an additional portion of the optical wave front;
• and
• iv) transforms the interference signal for the at least one location into an optical path length (OPL) domain based on the monitored reference phase to produce a spectrum having a peak at an OPL corresponding to a pair of the multiple surfaces.