Generation of broadband coherent laser pulses based on adiabatic four-wave mixing in waveguides and fiber
The technology disclosed in this patent document can be used to implement an optical device for generating broadband optical pulses, including an optical waveguide having different waveguide structures at different locations along the optical waveguide and with varying dimensions or pressure gradient that change adiabatically along the different locations to enable non-linear four wave mixing over a broad spectral range.
1. An optical device for frequency conversion based on adiabatic four wave mixing to produce an idler laser beam, comprising:
a pump laser module to produce a pump laser beam having pump laser pulses at pump laser wavelengths;
a signal laser beam module to produce a signal laser beam having signal laser pulses at a signal laser wavelength;
a segment of fiber having an input port and an output port, the input port coupled to receive the signal laser beam and the pump laser beam to exhibit a spatially varying optical dispersion as an adiabatic four wave mixing medium to convert energy at the signal laser wavelength into the idler laser beam at an idler wavelength shorter than the signal laser wavelength, wherein the input port of the segment of fiber has a negative wave-vector mismatch and the output port of the segment of fiber has a positive wave-vector mismatch, or the input port of the segment of fiber has a positive wave-vector mismatch and the output port of the segment of fiber has a negative wave-vector mismatch; and
an output port coupled to the output port of the segment of fiber to select the idler laser beam as an output of the optical device.
2. The device as in claim 1 , wherein the segment of fiber includes a spatially tapered fiber with an adiabatic taper rate satisfying a condition for adiabatic four wave mixing, wherein the condition for adiabatic four wave mixing includes
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wherein Δk eff is an effective wave-vector mismatch, wherein κ is a coupling coefficient, and wherein the derivatives are with respect to a propagation distance of light in the tapered fiber.
3. The device as in claim 1 , wherein a photon conversion ratio (PCR) of the segment of fiber is expressed by 1−exp(−8πκ 2 /|dΔk/dz|), wherein κ=2√{square root over (γ sig γ idl P A P B )} represents a nonlinear coupling strength and |dΔk/dz| represents a sweeping rate of Δk, which is wave-vector mismatch for adiabatic four wave mixing,
wherein y sig and y idl are nonlinear coefficients for signal and idler waves, respective,
and wherein P A and P B are pump powers for pump light beams for the non-linear four wave mixing.
4. The device as in claim 1 , wherein the segment of fiber tapers from the input port towards the output port of the segment of fiber.
5. The device as in claim 1 , wherein the segment of fiber includes a photonic crystal fiber (PCF).
6. The device as in claim 5 , wherein the PCF includes an air-core.
7. The device as in claim 5 , wherein the PCF includes a solid core with high numerical apertures.
8. The device as in claim 1 , wherein the segment of fiber includes a hollow capillary fiber.
9. The device as in claim 1 , wherein the segment of fiber includes a spatially untapered fiber with an adiabatic pressure gradient with rate satisfying a condition for adiabatic four wave mixing, wherein the condition for adiabatic four wave mixing includes
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wherein Δk eff is an effective wave-vector mismatch, wherein κ is a coupling coefficient, and wherein the derivatives are with respect to a propagation distance of light in the fiber.
10. The device as in claim 1 , wherein the segment of fiber includes a type of fiber in which a longitudinally varying spatial structure or pressure gradient are used to satisfy a condition for adiabatic four wave mixing, wherein the condition for adiabatic four wave mixing includes
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wherein Δk eff is an effective wave-vector mismatch, wherein κ is a coupling coefficient, and wherein the derivatives are with respect to a propagation distance of light in the fiber.
11. An optical device for adiabatic frequency conversion of light, comprising:
an optical path to combine signal beam and first and second pump beams; and
an optical waveguide including an input port and an output port, the input port directing the combined signal beam and first and second pump beams, the optical waveguide structured to have a spatial tapering from the input port towards the output port with an adiabatic taper rate to cause adiabatic four wave mixing which produces an idler beam at an idler wavelength different from wavelengths of the signal beam and the first and second pump beams,
wherein the input port of the optical waveguide has a negative wave-vector mismatch and the output port of the segment of fiber has a positive wave-vector mismatch, or the input port of the optical waveguide has a positive wave-vector mismatch and the output port of the segment of fiber has a positive wave-vector mismatch.
12. The device as in claim 11 , wherein the optical waveguide is structured for the adiabatic four wave mixing to satisfy
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wherein Δk eff is an effective wave-vector mismatch, wherein κ is a coupling coefficient, and wherein the derivatives are with respect to a propagation distance of light in the tapering.
13. The device as in claim 11 , wherein the optical waveguide includes a fiber that has a fiber core that has a spatially varying core size along the fiber to enable the non-linear four wave mixing over the broad spectral range.
14. The device as in claim 11 , wherein the fiber includes a photonic crystal fiber (PCF).
15. The device as in claim 14 , wherein the PCF includes an air-core.
16. The device as in claim 14 , wherein the PCF includes a solid core with high numerical apertures.
17. The device as in claim 11 , wherein the fiber includes a hollow capillary fiber.