Two-pump optical parametric devices having reduced stimulated Raman scattering noise levels
View Patent ↗Two-pump optical parametric devices (OPDs), and methods of operating the same, generate desired output signals and idlers having reduced stimulated Raman scattering (SRS) noise levels. When the two-pump OPD is used as a two-pump optical parametric amplifier (OPA), the pumps are polarized perpendicular to each other, and the lower-frequency sideband (signal or idler) is polarized parallel to the lower-frequency pump (perpendicular to the higher-frequency pump). The desired output may be an amplified signal or a generated idler. When the two-pump OPD is used as a two-pump optical frequency converter (OFC), the pumps can be polarized parallel to one another, in which case the signal and idler are both perpendicular to the pumps, or perpendicular to one another, in which case the lower-frequency sideband (signal or idler) is polarized parallel to the lower-frequency pump (perpendicular to the higher-frequency pump).
1. A two-pump optical parametric device, OPD, adapted to generate a desired output signal, comprising:
an optical medium that exhibits four-wave mixing;
one or more polarization couplers that apply a first polarized pump P 1 , a second polarized pump P 2 , and a polarized input signal S to the optical medium, wherein a frequency of the pump P 1 is lower than a frequency of the pump P 2 ; and
an optical filter that selects an idler I or an amplified signal S as the desired output signal, wherein:
the idler I is coupled to the pumps P 1 and P 2 and the signal S via said four-wave mixing; and
the one or more polarization couplers apply the pump P 1 , the pump P 2 , and the input signal S to the optical medium so that, in a set of four optical signals consisting of the pumps P 1 and P 2 , the signal S, and the idler I, two of the optical signals have a first polarization and the remaining two of the optical signals have a second polarization orthogonal to the first polarization.
2. The two-pump OPD of claim 1 , wherein:
the polarization of the pump P 1 is perpendicular to the polarization of the pump P 2 ;
the input signal S is configured as an inner sideband adjacent to a selected one of the pumps P 1 and P 2 ;
the desired output signal is output from a respective inner sideband adjacent to the pump P 1 or the pump P 2 , and
the inner sideband adjacent to the pump P 1 is polarized parallel to the pump P 1 ;
if the desired output is the amplified signal S, then the input signal S is configured as the inner sideband adjacent to the pump P 1 and the polarization of the input signal S is configured to be perpendicular to the polarization of the pump P 2 and
if the desired signal is the idler I, then the input signal S is configured as the inner sideband adjacent to the pump P 2 and the polarization of the input signal S is configured to be parallel to the polarization of the pump P 2 .
3. The two-pump OPD of claim 2 , wherein the frequencies of the pumps P 1 and P 2 are selected to minimize outer-band idlers.
4. The two-pump OPD of claim 2 , wherein the four-wave mixing is enabled by a phase-conjugating (PC) process.
5. The two-pump OPD of claim 1 , wherein:
the input signal S is configured as an inner sideband adjacent to the pump P 1 or an outer sideband adjacent to the pump P 2 ;
if the input signal S is configured as the inner sideband adjacent to the pump P 1 , then the OPD is configured to output the desired output signal from the outer sideband adjacent to the pump P 2 ; and
if the input signal S is configured as the outer sideband adjacent to the pump P 2 , then the OPD is configured to output the desired output signal from the inner sideband adjacent to the pump P 1 .
6. The two-pump OPD of claim 5 , wherein:
the polarizations of the pumps P 1 and P 2 are parallel to each other; and
the polarizations of the signal S and the idler I are both perpendicular to the polarizations of the pumps P 1 and P 2 .
7. The two-pump OPD of claim 5 , wherein:
the polarizations of the pumps P 1 and P 2 are perpendicular to each other; and
the polarization of the inner sideband is parallel to the polarization of the pump P 1 .
8. The two-pump OPD of claim 5 , wherein the frequencies of the pumps P 1 and P 2 are selected to minimize an outer sideband adjacent to the pump P 1 and an inner sideband adjacent to the pump P 2 .
9. The two-pump OPD of claim 5 , wherein the four-wave mixing is enabled by a Bragg scattering (BS) process.
10. The two-pump OPD of claim 1 , wherein the one or more polarization couplers comprise:
a first polarization coupler that applies the polarized input signal S to the optical medium;
a second polarization coupler that applies the first polarized pump P 1 to the optical medium; and
a third polarization coupler that applies the second polarized pump P 2 to the optical medium.