Displacement sensing

A displacement sensor comprising:

• a silicon substrate;
• a silicon dioxide layer formed on a top surface of the silicon substrate;
• a lithium niobate layer formed on a top surface of the silicon dioxide layer;
• a first waveguide formed in the lithium niobate layer and comprising a first nonlinear optical element that is configured to receive a pump laser beam having a pump wavelength at a first waveguide end and configured to modify the pump laser beam to a first pump laser beam pulse with a first wavelength and configured to transmit the first pump laser beam pulse at a second waveguide end;
• a second waveguide formed in the lithium niobate layer and connected to the first waveguide and configured to receive the first pump laser beam pulse at a third waveguide end and comprising a second nonlinear optical element that is configured to modify the first laser beam pulse to a second pump laser beam pulse with a second wavelength and configured to transmit the second pump laser beam pulse at a fourth waveguide end and configured to reflect the second laser pulse based on an interface between the first waveguide and the second waveguide;
• a third waveguide configured direct the second laser pulse that is reflected to a first reflector that reflects the second laser pulse back through the third waveguide and through the second nonlinear optical element;
• a fourth waveguide;
• an optical switch;
• an interferometer formed in the lithium niobate layer and controlled by the optical switch and comprising a reference arm comprising a second reflector at a reference arm end and a sensor arm comprising a third reflector at a sensor arm end and configured to receive the second laser bean pulse from the fourth waveguide and based on a second beam pulse reflected path and a second beam pulse transmission path;
• a detector configured to detect an optical path length change in the sensor arm of the interferometer as measured by a beat frequency between the second laser beam pulse in the second beam pulse reflected path and the second beam pulse transmission path;
• and
• an amplifier connected to the detector and the optical switch and configured to amplify a detection signal from the detector and to control operations of the optical switch based on the detection signal.

A method of on-chip displacement sensing comprising:

• providing a plurality of pump laser beam pulses by a pump laser that formed in one or more layers on top a substrate;
• receiving the plurality of pump laser beam pulses and producing modified pump laser beam pulses for each of the plurality of pump laser beam pulses by a second-harmonic generator that is formed in the one or more layers;
• receiving the modified pump laser beam pulses by an optical parametric oscillator cavity of twice a length of a pump laser cavity of the pump laser that is formed in the one or more layers, wherein the optical parametric oscillator cavity comprises an optical parametric oscillator, a reflector, an interferometer that comprises a first interferometer reflector at an end of a reference arm and a second interferometer reflector at an end of a sensor arm that is controlled by an optical switch, wherein the method further comprises:
• receiving two successive modified pump laser beam pulses during a round-trip time of the optical parametric cavity, each of the two successive modified pump laser beam pulses creating successive optical pulses at frequency ωs separated by an optical parametric oscillator cavity length or separated in time by half of an optical parametric oscillator cavity round-trip time, wherein a first of the plurality of the modified pump laser beam pulses is split into a first optical signal pulse at frequency ωs and a second optical signal pulse at frequency op;
• receiving, by the interferometer, the first optical signal pulse at frequency ωs and reflects back through the first interferometer reflector the first optical signal pulse at frequency ωs that reaches an end of the optical parametric oscillator cavity at a reflector when the second optical signal pulse at frequency ωs has been sent to the sensor arm by an optical switch and reaches the second interferometer reflector;
• receiving and detecting, by the first detector, the second optical signal pulse and to produce a synchronization signal for the optical switch;
• amplifying and dividing by two, by the amplifier that is connected to the first detector, the synchronization signal and to produce an amplified detection signal to the optical switch and controlling operations of the optical switch based on the amplified detection signal;
• and
• receiving and detecting, by the second detector, an optical path length change in the sensor arm of the interferometer as measured by a beat frequency produced by the interferometer.