Modulated source interferometry with combined amputude & frequency modulation

An improved optical interferometer comprising:

• means for producing coherent light;
• means for generating a modulation signal;
• means for modulating the coherent light with combined amplitude and frequency modulation, wherein the combined amplitude and frequency modulation produces a broad, asymmetric output spectrum of the coherent light source;
• means for dividing the modulated coherent light into a reference light beam and a signal light beam;
• means for ensuring separation of the reference light beam and the signal light beam as they respectively traverse a reference arm and a signal arm of the interferometer;
• means for combining the reference light beam with the signal light beam allowing them to mutually interfere;
• means for detecting, in the interfering light beam, a signal having a frequency substantially equivalent to that of the modulation signal;
• means for measuring a phase difference between the detected interference signal and the modulation signal, the phase difference being indicative of an optical phase difference between the reference beam and the signal beam.

An improved optical interferometer comprising:

• means for providing a coherent light source;
• means for generating a modulation signal;
• means for modulating the coherent light source with combined amplitude and frequency modulation to produce more than two anti-phase side bands;
• a first polarizer for dividing the modulated coherent light into a reference light beam and a signal light beam plane polarized on mutually orthogonal axes;
• an optically transparent birefringent medium conducting the polarized light beams and ensuring separation of the reference light beam and the signal light beam;
• a second polarizer for combining the reference light beam with the signal light beam allowing them to mutually interfere;
• a photodetector for producing an electrical signal representative of a result of the mutual interference;
• means for detecting, in the electrical signal from the photodetector, a synchronous signal having a frequency substantially equivalent to that of the modulation signal;
• means for measuring a phase difference between the detected synchronous signal and the modulation signal, the phase difference being indicative of an optical phase difference between the reference beam and the signal beam.

An improved optical interferometer which can determine absolute distances, comprising:

• means for providing a single wavelength coherent light source;
• means for generating a modulation signal;
• means for modulating the coherent light source with combined amplitude and broadband frequency modulation, wherein the combined amplitude and frequency modulation produces a broad, asymmetric output spectrum of the coherent light source;
• a beam divider for dividing the modulated coherent light into a reference light beam and a signal light beam;
• a reference arm and a signal arm for providing physically separated paths for the reference light beam and signal light beam, respectively, the separated paths ensuring that the two light beams remain separated;
• a beam combiner for combining the reference light beam from the reference arm with the signal light beam from the signal arm allowing the beams to mutually interfere;
• a photodetector for producing an electrical signal representative of a result of the mutual interference;
• means for detecting, in the electrical signal from the photodetector, a synchronous signal having a frequency substantially equivalent to that of the modulation signal;
• means for measuring a phase difference between the detected synchronous signal and the modulation signal, the phase difference being indicative of an optical phase difference between the reference beam and the signal beam,
• wherein the optical interferometer can measure absolute distances using the single wavelength coherent light source.

An optical interferometer which can measure absolute differences consisting of:

• means for producing coherent light;
• means for generating a modulation signal;
• means for modulating the coherent light with combined amplitude and frequency modulation, wherein the combined amplitude and frequency modulation produces a broad, asymmetric output spectrum of the coherent light source;
• means for dividing the modulated coherent light into a reference light beam and a signal light beam;
• means for ensuring separation of the reference light beam and the signal light beam as they respectively traverse a reference arm and a signal arm of the interferometer;
• means for combining the reference light beam with the signal light beam allowing them to mutually interfere;
• means for detecting, in the interfering light beam, a signal having a frequency substantially equivalent to that of the modulation signal;
• means for measuring a phase difference between the detected interference signal and the modulation signal, the phase difference being indicative of an optical phase difference between the reference beam and the signal beam.