Integrated on-chip polarizer
A low loss high extinction ratio on-chip polarizer is disclosed. The polarizer is formed of a mode convertor followed by a mode squeezer and a dump waveguide, and may be configured to pass a desired waveguide mode and reject undesired modes. An embodiment is described that transmits a TE0 mode while blocking a TM0 mode by converting it into a higher-order TEn mode in a waveguide taper, squeezing out the TEn mode in a second waveguide taper to lessen its confinement, and then dumping the TEn mode in a waveguide bend that is configured to pass the TE0 mode.
1. An optical polarizer configured to suppress light in a second mode while passing through light in a first mode, comprising:
a first tapered waveguide including a width that widens from a first width to a second width in a direction of light propagation for converting the second mode to a third mode with a lower effective refractive index than the first mode;
a second tapered waveguide that narrows from the second width to a third width for squeezing the third mode out thereof; and
a bend waveguide section for substantially eliminating the third mode therefrom, while preserving the first mode.
2. The optical polarizer according to claim 1 , wherein the first mode is a TE mode and the second mode is a TM mode.
3. The optical polarizer according to claim 2 , wherein the first mode is a fundamental TE mode.
4. The optical polarizer according to claim 1 , wherein the first mode is a fundamental TE mode and the second mode is a higher-order TE mode.
5. The optical polarizer according to claim 1 , wherein the first tapered waveguide comprises a mode converter that widens in the direction of light propagation.
6. The optical polarizer according to claim 5 , wherein the first tapered waveguide widens non-linearly with length.
7. The optical polarizer according to claim 5 , wherein the first tapered waveguide is vertically asymmetric.
8. The optical polarizer according to claim 5 , wherein the first tapered waveguide comprises a bi-level rib waveguide.
9. The optical polarizer according to claim 5 , wherein the first tapered waveguide includes a lower cladding comprising a first refractive index, and an upper cladding comprising a second refractive index different than the first refractive index.
10. The optical polarizer according to claim 1 , wherein the second tapered waveguide comprises a mode squeezer including a width that narrows in the direction of light propagation.
11. The optical polarizer according to claim 10 , wherein the second tapered waveguide narrows non-linearly with length.
12. The optical polarizer according to claim 10 , wherein the second tapered waveguide includes a bi-level section.
13. The optical polarizer according to claim 12 , wherein the second tapered waveguide includes a ridge waveguide section.
14. The optical polarizer according to claim 10 , wherein the second tapered waveguide comprises a ridge waveguide.
15. The optical polarizer according to claim 1 , wherein the third width is smaller than the second width.
16. The optical polarizer according to claim 15 , wherein the bend waveguide section includes an output taper to provide an adiabatic transition between the bend waveguide section and a subsequent waveguide.
17. The optical polarizer according to claim 1 , wherein the bend waveguide section comprises a dump waveguide capable of dumping the third mode while guiding the first mode therethrough.
18. The optical polarizer according to claim 1 , wherein the bend waveguide section includes a bend with a bend radius, whereby the second and third modes lose coupling and are dumped from the bend waveguide section, while the first mode is guided therethrough.
19. The optical polarizer according to claim 18 , wherein the bend waveguide section comprises an S-bend including first and second turns.
20. The optical polarizer according to claim 1 , wherein the bend waveguide section comprises a dump waveguide capable of guiding the first mode with a highest effective index therethrough, and dump all modes other than the first mode with lower effective indexes.