Gigahertz to terahertz frequency signal generation using OPO and DFG

Patent metadata

Field	Value
Publication number	US-9588398-B2
Application number	US-201514740257-A
Country	US
Kind code	B2
Filing date	Jun 16, 2015
Priority date	Jul 8, 2005
Publication date	Mar 7, 2017
Grant date	Mar 7, 2017

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 I P having pump-light frequency and generates two different lower intermediate frequencies of light—an OPO-signal beam I S and a spatially/temporally overlapping OPO-idler beam I I . A difference-frequency generator non-linear material then receives the two intermediate-frequency beams I I and I S , 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 I P -beam-entry mirror, an I P -light-extraction mirror to remove unconverted I P -beam, an I I -beam-extraction mirror, and an I S -beam-extraction mirror, and a fifth I THz -beam-extraction mirror.

First claim

What is claimed is:

1. An apparatus for generating a gigahertz-terahertz-range signal having a first frequency in a gigahertz to terahertz frequency range, the apparatus comprising:
a pump laser that outputs pump light having a pump frequency; and
a single cavity, operably coupled to the pump laser to receive the pump light,
wherein the single cavity includes a first non-linear material in an optical path in the single cavity that receives the pump light and generates light that includes a first intermediate frequency and a second intermediate frequency,
wherein the single cavity includes a first etalon tuned to pass just the first intermediate frequency, and
wherein the single cavity includes a second non-linear material in the optical path in the single cavity that uses the light of the first intermediate frequency and the light of the second intermediate frequency to generate the gigahertz-terahertz-range signal, wherein the gigahertz-terahertz-range signal has a frequency that is equal to a difference between the two intermediate frequencies.

2. The apparatus of claim 1 , wherein the pump laser is configured to controllably vary the pump frequency, wherein the cavity is tuned to resonate at the first intermediate frequency, such that the second intermediate frequency varies based on the varied pump frequency, and such that the frequency of the terahertz-range signal is controllably varied based on the varied pump frequency.

3. The apparatus of claim 1 , wherein the optical path has a bow-tie ring topology, and wherein the single cavity further includes:
a first frequency-selective mirror that is transparent to the frequency of the pump light and through which unconverted pump light is removed from the cavity,
a second mirror that is reflective to the first intermediate frequency, such that between 1% and 5% of the second intermediate frequency is transmitted through the second mirror,
a third mirror that is reflective to the second intermediate frequency,
a frequency-selective Fabry-Perot etalon located in the optical path between the second mirror and the third mirror, and that is configured to pass the first and second intermediate frequencies,
a fourth frequency-selective mirror that is reflective to the first and second intermediate frequencies and transparent to the frequency of the pump light and through which the pump light is introduced into the cavity,
wherein the first non-linear material includes a first non-linear optical (NLO) crystal that acts as an optical parametric oscillator, and
wherein the second non-linear material includes a second non-linear optical (NLO) crystal that acts as a difference frequency generator, wherein the first NLO crystal and the second NLO crystal are located in the optical path between the fourth mirror and the first mirror.

4. The apparatus of claim 1 , wherein the single cavity is arranged in a ring topology and further includes:
a first frequency-selective mirror that is transparent to the frequency of the pump light and through which unconverted pump light is removed from the cavity, and transparent to the frequency of the gigahertz-terahertz-range signal and through which the gigahertz-terahertz-range signal is removed from the cavity,
a second mirror that is reflective to at least a fixed frequency of the two intermediate frequencies, such that between 1% and 5% of the other of the two intermediate frequencies is transmitted through the second mirror,
a third mirror that is reflective to the fixed frequency of the two intermediate frequencies,
a frequency-selective Fabry-Perot etalon located in the optical path between the second mirror and the third mirror, and that is configured to pass the fixed frequency of the two intermediate frequencies,
a fourth frequency-selective mirror that is reflective to at least the fixed frequency of the two intermediate frequencies and transparent to the frequency of the pump light and through which the pump light is introduced into the cavity,
wherein the first non-linear material and the second non-linear material are both part of a single non-linear optical (NLO) crystal that acts both as an optical parametric oscillator, and as a difference frequency generator, wherein the single NLO crystal is located in the optical path between the fourth mirror and the first mirror.

5. The apparatus of claim 1 , further comprising a piezo-electric element, wherein the pump laser is configured to controllably vary the pump frequency using the piezo-electric element.

6. The apparatus of claim 1 , wherein the single cavity includes a wavelength separator-combiner that spatially separates the light of the first intermediate frequency from light of the second intermediate frequency, and that recombines the spatially separated light into a single beam.

7. The apparatus of claim 6 , wherein the wavelength separator-combiner includes at least one diffraction grating.

8. The apparatus of claim 1 , wherein the first non-linear material and the second non-linear material are both part of a single non-linear optical (NLO) crystal that acts both as an optical parametric oscillator and as a difference frequency generator.

9. The apparatus of claim 1 ,
wherein the first non-linear material includes a first non-linear optical (NLO) crystal that acts as an optical parametric oscillator,
wherein the second non-linear material includes a second non-linear optical (NLO) crystal that acts as a difference frequency generator,
wherein the first NLO crystal and the second NLO crystal are spatially separated from one another, and
wherein the apparatus further includes:
a first mirror located in the optical path between the first NLO crystal and the second NLO crystal, wherein the first mirror is reflective at both the first intermediate frequency and the second intermediate frequency and transmissive at the pump frequency.

10. The apparatus of claim 1 , wherein the pump laser further includes:
a distributed-feedback (DFB) fiber laser that receives input pump light at a first pump wavelength and emits output pump light at a second pump wavelength, wherein the DFB fiber laser includes:
a fiber having a core and at least a first cladding layer, wherein the core includes a signal-amplifying dopant; and
a DFB grating operatively coupled to a portion of the fiber.

11. The apparatus of claim 1 ,
wherein the first non-linear material includes a first non-linear optical (NLO) crystal that acts as an optical parametric oscillator,
wherein the second non-linear material includes a second non-linear optical (NLO) crystal that acts as a difference frequency generator,
wherein the first NLO crystal and the second NLO crystal are spatially separated from one another, and
wherein the apparatus further includes:
a first mirror located in the optical path between the first NLO crystal and the second NLO crystal, wherein the first mirror is reflective at both the first intermediate frequency and the second intermediate frequency and transmissive at the pump frequency, and
a second reflector located in the optical path facing the second face of the second NLO crystal, wherein the second reflector is reflective at the gigahertz-terahertz-frequency range, such that the gigahertz-terahertz-range signal is reflected by the second reflector and exits the cavity.

12. The apparatus of claim 1 , wherein the optical path in the single cavity is configured to have a bow-tie ring topology.

13. The apparatus of claim 1 , further comprising a plurality of piezo-electric elements, wherein the pump laser is configured to controllably vary the pump frequency using the plurality of piezo-electric element

Assignees

• Lockheed Corp

Inventors

• Hu Yongdan
• Xing Andrew
• Henderson Angus J

Classifications

• G02F1/3534 Primary

  Three-wave interaction, e.g. sum-difference frequency generation (G02F1/3532 takes precedence) · CPC title

• G02F2001/3507

  Physics · mapped topic

• G02F1/3501

  Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals · CPC title

• G02F1/39

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

• 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