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 the TM0 mode 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 integrated on-chip optical polarizer, comprising:
a mode converting waveguide disposed to receive light comprising a first mode and a second mode and configured to selectively convert the second mode into a third mode while preserving the first mode;
a mode squeezing waveguide disposed to receive light from the mode converting waveguide and configured to lessen an optical confinement of the third mode to a greater degree than that of the first mode; and,
a dump waveguide disposed to receive light from the mode squeezing waveguide and configured to dump the third mode while allowing light in the first mode to propagate to an output.
2. The polarizer of claim 1 comprising a support substrate, wherein at least one of the mode converting waveguide, the mode squeezing waveguide, and the dump waveguide comprises a planar waveguide formed in or upon the support substrate.
3. The polarizer of claim 2 , wherein the support substrate comprises a semiconductor wafer comprising an A3B5 semiconductor material or an A2B6 semiconductor material.
4. The polarizer of claim 1 , wherein the mode converting waveguide comprises a first waveguide taper that widens in a direction of light propagation.
5. The polarizer of claim 4 , wherein the first waveguide taper is vertically asymmetric.
6. The polarizer of claim 5 , wherein the first waveguide taper comprises a bi-level rib waveguide taper.
7. The polarizer of claim 5 , wherein the first waveguide taper comprises a lower cladding and an upper cladding, and wherein the lower cladding is characterized by a refraction index that differs from a refraction index of the upper cladding.
8. The polarizer of claim 4 , wherein the mode squeezing waveguide comprises a second waveguide taper that narrows in the direction of light propagation.
9. The polarizer of claim 8 , wherein the second waveguide taper comprises a ridge waveguide.
10. The polarizer of claim 1 , wherein the dump waveguide comprises an input end, an output end, and a waveguide bend therebetween, the waveguide bend having a bend radius selected to radiate the third mode while allowing the first mode to propagate along the dump waveguide towards the output end thereof.
11. The polarizer of claim 10 , further comprising an output waveguide taper disposed at the output end of the dump waveguide.
12. The polarizer of claim 1 wherein the support substrate comprises a silicon-on-isolator wafer comprising a silicon layer, and wherein the mode converting waveguide, mode squeezing waveguide, and dump waveguide each comprise a planar waveguide defined in the silicon layer.
13. The polarizer of claim 1 wherein the support substrate comprises a silicon-on-isolator wafer comprising a silicon layer and a second layer disposed over the silicon layer, and wherein at least one of the mode converting waveguide, mode squeezing waveguide, and dump waveguide comprises at least a portion of the second layer.
14. The polarizer of claim 1 , wherein the first mode comprises a TE0 mode, and the second mode comprises a TM0 mode.
15. The polarizer of claim 14 , wherein the third mode comprises a higher-order TE mode.
16. The polarizer of claim 1 , wherein the first mode is characterized by a larger effective refractive index than the second and third modes.
17. A photonic integrated circuit (PIC) chip comprising:
an optical waveguide interconnect disposed to provide an optical connection between a first optical device and a second optical device and comprising one or more integrated on-chip optical polarizers of claim 1 , each configured to suppress light propagating in the optical waveguide interconnect in the second mode while passing through light in the first mode, so as to reduce mode crosstalk downstream from the one or more integrated on-chip polarizers.
18. A method for on-chip polarization filtering comprising:
receiving light comprising first and second modes into a mode converting waveguide;
using the mode converting waveguide to selectively convert light received in the second mode into a third mode while maintaining light received in the first mode to remain in the first mode;
using a mode squeezing waveguide to at least partially squeeze out the third mode so as to lessen an optical confinement thereof within the mode squeezing waveguide to a greater degree than an optical confinement of the first mode; and,
selectively attenuating the third mode using a dump waveguide configured to dump light of the third mode received from the mode squeezing waveguide while allowing light in the first mode to propagate to an output.
19. The method of claim 18 wherein the first mode is a fundamental TE mode, the second mode is a fundamental TM mode, and the third mode is a higher-order TE mode.
20. The method of claim 18 , wherein the first mode is characterized by a greater effective index than the second and third modes.