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

Patent metadata

Field	Value
Publication number	US-2018252984-A1
Application number	US-201815970530-A
Country	US
Kind code	A1
Filing date	May 3, 2018
Priority date	Aug 29, 2012
Publication date	Sep 6, 2018
Grant date	—

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.

First claim

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

Assignees

• Lockheed Corp

Inventors

• Hu Yongdan
• Xing Andrew
• Henderson Angus J

Classifications

• H01S3/0092

  Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity (nonlinear frequency conversion per se G02F1/35) · CPC title

• G02F1/3532

  Arrangements of plural nonlinear devices for generating multi-colour light beams, e.g. arrangements of SHG, SFG, OPO devices for generating RGB light beams · CPC title

• G02F1/39

  for parametric generation or amplification of light, infrared or ultraviolet waves · CPC title

• H01S3/0675

  Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers · CPC title

• G02F2001/3503

  Physics · mapped topic