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 propagating in a direction of light propagation in an optical waveguide in a second mode while passing through light in a first mode; the optical polarizer comprises:
a mode converter comprising one or more parameters or characteristics that vary in the direction of light propagation, and configured whereby effective refractive indices of the second mode and a third mode, which may differ at input, become nearly equal at a location within the mode converter, so that the light that enters the mode converter in the second mode may effectively couple into the third mode; and
a mode squeezer comprising a waveguiding property that progressively weakens in the direction of light propagation, thereby lessening optical confinement of the third mode.
2 . The optical polarizer according to claim 1 , wherein the mode converter comprises: a first tapered waveguide including a width that widens from a first width to a second width in the direction of light propagation for converting the second mode to the third mode with a lower effective refractive index than the first mode; and
wherein the mode squeezer comprises a second tapered waveguide that narrows from the second width to a third width for squeezing the third mode out thereof.
3 . The optical polarizer according to claim 2 , wherein the mode squeezer also comprises a bend waveguide section for substantially eliminating the third mode therefrom, while preserving the first mode.
4 . The optical polarizer according to claim 1 , wherein the first mode is a fundamental TE mode and the third mode is a higher-order TE mode.
5 . The optical polarizer according to claim 2 , 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 2 , 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 3 , 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 3 , wherein the bend waveguide section comprises a dump waveguide configured for dumping the third mode while guiding the first mode therethrough.
18 . The optical polarizer according to claim 3 , wherein the bend waveguide section includes a bend with a bend radius, whereby the second mode and/or the third mode loses 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 3 , wherein the bend waveguide section comprises a dump waveguide configured for guiding the first mode with a highest effective index therethrough, and dump the second mode and the third mode with lower effective indexes.