Method for gigahertz to terahertz frequency signal generation using opo and dfg

Abstract

Apparatus and method for high-power multi-function millimeter-wavelength (THz-frequency) signal generation using OPO and DFG in a single cavity. In some embodiments, the OPO-DFG cavity includes an optical parametric oscillator (OPO) non-linear material that receives pump light IP having pump-light frequency and generates two different lower intermediate frequencies of light—an OPO-signal beam IS and a spatially/temporally overlapping OPO-idler beam II. A difference-frequency generator non-linear material then receives the two intermediate-frequency beams II and IS, and the DFG then generates a THz-frequency output signal that has a frequency equal to the difference between the two intermediate frequencies. In some embodiments, a single-piece crystal of non-linear material is used for both OPO and DFG functions. Some embodiments use a bow-tie ring having four mirrors that define the optical path: an IP-beam-entry mirror, an IP-light-extraction mirror to remove unconverted IP-beam, an II-beam-extraction mirror, and an IS-beam-extraction mirror, and a fifth ITHz-beam-extraction mirror.

What is claimed is: 
     
         1 . A method for generating a gigahertz-terahertz-range signal having a frequency in a gigahertz to terahertz frequency range, the method comprising:
 receiving pump light having a pump frequency into a single optical cavity having an optical path;   generating light that includes a first intermediate frequency and a second intermediate frequency within the single optical cavity by using energy from the pump light;   spatially separating the light of the first intermediate frequency from the light of the second intermediate frequency such that the light of the first intermediate frequency propagates along a first segment of the optical path and the light of the second intermediate frequency propagates along a second segment of the optical path, and recombining the spatially separated light into a single beam; and   generating the gigahertz-terahertz-range signal within the single optical cavity by using the light of the two intermediate frequencies, wherein the frequency of the gigahertz-terahertz-range signal is equal to a difference between the two intermediate frequencies.   
     
     
         2 . The method of  claim 1 , wherein the optical path has a bow-tie ring topology, and wherein the method further includes:
 reflecting light of the first intermediate frequency at a first frequency-selective reflector, and removing unconverted pump light from the single optical cavity through the first frequency-selective reflector;   reflecting light of the first intermediate frequency at a second reflector;   reflecting light of the first intermediate frequency at a third reflector;   passing light of the first intermediate frequency through a frequency-selective Fabry-Perot etalon located in the optical path between the second reflector and the third reflector while blocking light of the second intermediate frequency;   reflecting light of the first intermediate frequency at a fourth frequency-selective reflector;   introducing the pump light through the fourth frequency-selective reflector into the single optical cavity;   converting the pump light into light of the first intermediate frequency and light of the second intermediate frequency using non-linear optical parametric oscillation in the optical path between the fourth reflector and the first reflector; and   converting light of the first intermediate frequency and light of the second intermediate frequency to electromagnetic radiation having a gigahertz-terahertz frequency using non-linear difference frequency generation in the optical path.   
     
     
         3 . The method of  claim 1 , further comprising:
 removing the pump light and the gigahertz-terahertz-range signal through a single port; and   separating the pump light and the gigahertz-terahertz-range signal outside of the single optical cavity.   
     
     
         4 . The method of  claim 1 , further comprising:
 tuning the pump frequency using a piezo-electric element in order to change the frequency of the gigahertz-terahertz-range signal.   
     
     
         5 . The method of  claim 1 , further comprising:
 reflecting light of the first intermediate frequency at a first frequency-selective reflector, and removing unconverted pump light from the single optical cavity through the first frequency-selective reflector;   reflecting light of the first intermediate frequency at a second reflector;   reflecting light of the first intermediate frequency at a third reflector;   reflecting light of the first intermediate frequency at a fourth reflector;   passing light of the first intermediate frequency through a frequency-selective Fabry-Perot etalon located in the optical path between the third reflector and the fourth reflector while blocking light of the second intermediate frequency;   reflecting light of the first intermediate frequency at a fifth frequency-selective reflector;   reflecting light of the first intermediate frequency at a sixth frequency-selective reflector;   introducing the pump light through the sixth frequency-selective reflector into the single optical cavity;   converting the pump light into light of the first intermediate frequency and light of the second intermediate frequency using non-linear optical parametric oscillation in the optical path between the sixth reflector and the first reflector; and   converting light of the first intermediate frequency and light of the second intermediate frequency to electromagnetic radiation having a gigahertz-terahertz frequency using non-linear difference frequency generation in the optical path.   
     
     
         6 . The method of  claim 1 , wherein the spatially separating of the light includes reflecting the light at a first diffraction grating. 
     
     
         7 . The method of  claim 1 , further comprising passing light of the first intermediate frequency through a first frequency-selective Fabry-Perot etalon located in the first segment of the optical path. 
     
     
         8 . The method of  claim 1 , further comprising:
 passing light of the first intermediate frequency through a first frequency-selective Fabry-Perot etalon located in the first segment of the optical path; and   passing light of the second intermediate frequency through a second frequency-selective Fabry-Perot etalon located in the second segment of the optical path.   
     
     
         9 . The method of  claim 1 , wherein the generating of the light includes passing the light through a non-linear optical crystal that acts as an optical parametric oscillator. 
     
     
         10 . The method of  claim 1 , wherein the generating of the gigahertz-terahertz-range signal includes passing the light of the two intermediate frequencies through a non-linear optical crystal that acts as a difference frequency generator. 
     
     
         11 . The method of  claim 1 , wherein the generating of the light includes passing the light through a non-linear optical crystal that acts as both an optical parametric oscillator and as a difference frequency generator. 
     
     
         12 . The method of  claim 1 ,
 wherein the generating of the light includes passing the light through a first non-linear optical crystal that acts as an optical parametric oscillator,   wherein the generating of the gigahertz-terahertz-range signal includes passing the light of the two intermediate frequencies through a non-linear optical crystal that acts as a difference frequency generator, the method further comprising:   reflecting light at both the first intermediate frequency and the second intermediate frequency at a first frequency-selective reflector;   removing unconverted pump light from the single optical cavity through the first frequency-selective reflector; and   reflecting the gigahertz-terahertz-range signal out of the single optical cavity at a second frequency-selective reflector.   
     
     
         13 . The method of  claim 1 , further comprising:
 tuning a resonant cavity length of the single optical cavity using a piezo-electric element.   
     
     
         14 . The method of  claim 1 , further comprising:
 generating the pump light having the pump frequency, wherein the generating of the pump light includes:
 providing a distributed-feedback (DFB) fiber laser that emits the pump light at the pump frequency, and 
 controllably varying the pump frequency. 
   
     
     
         15 . The method of  claim 1 , further comprising providing a plurality of optical elements that define the optical path, wherein the providing of the plurality of optical elements includes arranging the plurality of optical elements in a single plane. 
     
     
         16 . The method of  claim 1 , further comprising:
 providing a unitary block housing;   surrounding the single optical cavity with the unitary block housing such that the optical path is completely within the unitary block housing.   
     
     
         17 . The method of  claim 1 , further comprising:
 reflecting light at both the first intermediate frequency and the second intermediate frequency at a first frequency-selective reflector; and   removing unconverted pump light from the single optical cavity through the first frequency-selective reflector.   
     
     
         18 . A method for generating a gigahertz-terahertz-range signal having a frequency in a gigahertz to terahertz frequency range, the method comprising:
 receiving pump light having a pump frequency into a single optical cavity having an optical path;   generating light that includes a first intermediate frequency and a second intermediate frequency within the single optical cavity by using energy from the pump light, wherein the generating includes passing the light through a non-linear optical crystal that acts as an optical parametric oscillator;   spatially separating the light of the first intermediate frequency from the light of the second intermediate frequency, and recombining the spatially separated light into a single beam; and   generating the gigahertz-terahertz-range signal within the single optical cavity by using the light of the two intermediate frequencies, wherein the frequency of the gigahertz-terahertz-range signal is equal to a difference between the two intermediate frequencies.   
     
     
         19 . The method of  claim 18 , further comprising:
 generating the pump light having the pump frequency, wherein the generating of the pump light includes:
 providing a distributed-feedback (DFB) fiber laser that emits the pump light at the pump frequency. 
   
     
     
         20 . A method for generating a gigahertz-terahertz-range signal having a frequency in a gigahertz to terahertz frequency range, the method comprising:
 generating pump light having a pump frequency using a distributed-feedback (DFB) fiber laser that emits the pump light at the pump frequency;   receiving the pump light into a single optical cavity having an optical path;   generating light that includes a first intermediate frequency and a second intermediate frequency within the single optical cavity by using energy from the pump light;   spatially separating the light of the first intermediate frequency from the light of the second intermediate frequency, and recombining the spatially separated light into a single beam; and   generating the gigahertz-terahertz-range signal within the single optical cavity by using the light of the two intermediate frequencies, wherein the frequency of the gigahertz-terahertz-range signal is equal to a difference between the two intermediate frequencies.