Optical multiplexer
An optical multiplexer includes a substrate into which are integrated a polarization rotator and a polarization coupler. The polarization coupler and the polarization rotator are in optical communication with each other.
1. An optical multiplexer comprising:
a substrate;
a first polarization coupler integrated into the substrate, the first polarization coupler having
first and second input waveguides for receiving first and second polarized light beams, respectively, and
an output waveguide for transmitting a first polarization combined light beam;
a first polarization rotator integrated into the substrate in an optical path of the first polarized light beam to the first input waveguide so as to rotate polarization of the first polarized light beam relative to the second polarized light beam; and,
a wavelength coupler integrated into the substrate and disposed to receive the first polarization combined light beam for combining it with a second polarization combined light beam for forming a wavelength multiplexed beam.
2. An optical multiplexer of claim 1 , wherein the first polarization rotator comprises:
a. a stressinducing element disposed to generate a stress-field in the substrate for forming a birefringent portion having a principal axis slanted with respect to a polarization axis of the first polarized light beam; and,
b. a waveguide having a portion that passes through the stressfield.
3. An optical multiplexer of claim 2 , wherein the stressinducing feature is laterally offset with respect to the portion of the waveguide passing therethrough.
4. An optical multiplexer of claim 3 , wherein the stress-inducing feature comprises a stress-inducing strip disposed on a surface of the substrate and having a coefficient of expansion different from the coefficient of expansion of the substrate.
5. An optical multiplexer of claim 3 , wherein the stress-inducing feature comprises walls forming one of a trench and a ledge in the substrate.
6. An optical multiplexer of claim 3 , wherein the stress-inducing feature has a length selected so as to rotate polarization of the first polarized beam by 90 degrees with respect to the polarization of the second polarized beam so as to provide orthogonally polarized beams at the inputs of the polarization coupler.
7. An optical multiplexer of claim 3 , further comprising:
a. first and second pump lasers optically coupled to the substrate for providing the first and second polarized beams, respectively; and,
b. an output port for providing a polarization multiplexed Raman pump beam.
8. An optical multiplexer of claim 1 , further comprising a second polarization coupler integrated into the substrate, the second polarization coupler having
i. first and second input waveguides for receiving third and forth polarized light beams, respectively, and
ii. an output waveguide for transmitting the second polarization combined light beam;
b. a second polarization rotator integrated into the substrate in an optical path of the third polarized light beam so as to rotate polarization of the third polarized light beam relative to the forth polarized light beam;
c. wherein the first a second polarized beams have a first central wavelength; and the third and forth polarized beams have a second central wavelength different from the first central wavelength.
9. An optical multiplexer of claim 8 , further comprising an input tap waveguide formed in the substrate for controlling light entering the substrate.
10. An optical multiplexer of claim 8 , further comprising an output tap waveguide formed in the substrate, the output tap waveguide being disposed to detect reflected light at an output of the substrate.
11. An optical multiplexer according to claim 1 , further comprising:
a. a second polarization coupler integrated into the substrate, the second polarization coupler having
i. first and second input waveguides for receiving third and forth polarized light beams, respectively, and
ii. an output waveguide for transmitting the second polarization combined light beam;
b. a second polarization rotator integrated into the substrate in an optical path of the third polarized light beam so as to rotate polarization of the third polarized light beam relative to the forth polarized light beam;
c. wherein the first and second polarized beams have a first central wavelength, and the third and forth polarized beams have a second central wavelength different from the first central wavelength;
d. wherein each of the first and second polarization rotators comprises a stress-inducing element generating a slanted stressfield in the substrate, and a waveguide having a portion that passes through the slanted stress-field.
12. An optical multiplexer according to claim 11 further comprising:
a. first, second, third and fourth pump lasers optically coupled to the substrate for providing the first, second, third and fourth polarized beams, and
b. an output waveguide formed in the substrate for providing a polarization and wavelength multiplexed Raman pump beam.
13. An optical multiplexer according to claim 12 , further comprising at least one of an input tap waveguide and an output tap waveguide for controlling light entering the substrate at an input or output thereof, respectively.