Polarization independent multiplexer / demultiplexer

1. An integrated optical component comprising:

at least one input waveguide;

at least one output waveguide;

a first slab waveguide having a first refractive index, n1, the first slab waveguide being disposed between at least one of the input waveguides and at least one of the output waveguides, wherein the first slab waveguide includes SiN, wherein the first slab waveguide is at least 200 nanometers thick;

a second slab waveguide having a second refractive index, n2, that is uniform in the second slab waveguide, wherein the second slab waveguide comprises a sub-wavelength grating structure that comprises a first layer and a second layer, wherein the sub-wavelength grating structure comprises alternating layers of the first layer and the second layer, the first layer having a fourth refractive index, the second layer having a fifth refractive index, wherein the second refractive index is an effective refractive index based on the fourth refractive index and the fifth refractive index; and

a third cladding slab having a third refractive index, n3, the third cladding slab being disposed between the first slab and the second slab, wherein a thickness of the second slab waveguide and the thickness of the third cladding slab reduce a birefringence of the integrated optical component.

2. The integrated optical component of claim 1 , wherein n2 is greater than n1, and wherein n1 is greater than n3.

3. The integrated optical component of claim 1 , wherein the second slab waveguide includes Si and the third cladding slab includes SiO 2 .

4. The integrated optical component of claim 1 , wherein the birefringence is a difference between a transverse electric (TE) effective refractive index and a transverse magnetic (TM) effective refractive index.

5. The integrated optical component of claim 1 , wherein the second slab waveguide is between 40 and 160 nanometers thick and the third cladding slab is between 80 and 240 nanometers thick.

6. The integrated optical component of claim 5 further comprising a free-space slab propagation region that includes the first slab waveguide, the second slab waveguide and the third cladding slab, wherein the free-space slab propagation region is 600 nanometers thick.

7. The integrated optical component of claim 6 , wherein the second slab waveguide is between 80 and 100 nanometers thick and the third cladding slab is between 170 and 180 nanometers thick.

8. The integrated optical component of claim 7 , wherein the free-space slab propagation region comprises a birefringence below a threshold birefringence value, wherein the birefringence is a difference between a transverse electric (TE) effective refractive index and a transverse magnetic (TM) effective refractive index, wherein the threshold birefringence value is 1.

9. The integrated optical component of claim 1 , wherein the integrated optical component is one of: an Echelle Grating de-multiplexer, a delay line interferometer based de-multiplexer, an optical differential phase-shift keying demodulator, or an arrayed waveguide grating de-multiplexer.

10. The integrated optical component of claim 1 ,

wherein the first layer and the second layer alternate by a sub-wavelength periodicity.

11. The integrated optical component of claim 10 , the second slab waveguide having a second slab waveguide refractive index of between 2.4 and 2.6, wherein the second slab waveguide thickness is between 160 and 170 nanometers, wherein the third cladding slab thickness is between 205 and 215 nanometers.

12. A waveguide-based optical device, comprising:

an input waveguide configured to receive an input signal;

a signal splitter configured to divide the input signal into a plurality of beams;

a set of output waveguides configured to receive the plurality of beams from the signal splitter; and

a free-space slab propagation region disposed between the signal splitter and the set of output waveguides, wherein the free-space slab propagation region includes:

a silicon nitride (SiN) layer configured to permit the plurality of beams to pass through the SiN layer, wherein the SiN layer is at least 200 nanometers thick; and

a retarder layer disposed a particular distance from the SiN layer, wherein the retarder layer comprises a sub-wavelength structure that comprises a first layer with a first refractive index and a second layer with a second refractive index, wherein the sub-wavelength structure comprises alternating layers of the first layer and the second layer, the retarder layer having an effective refractive index based on the first refractive index and the second refractive index.

13. The waveguide-based optical device of claim 12 further comprising a spacer layer disposed between the SiN layer and the retarder layer.

14. The waveguide-based optical device of claim 13 , wherein the retarder layer is between 163 and 168 nanometers thick and the spacer layer is between 208 and 211 nanometers thick.

15. The waveguide-based optical device of claim 14 , wherein the free-space slab propagation region is 600 nanometers thick.

16. The waveguide-based optical device of claim 13 , wherein the retarder layer is between 160 and 170 nanometers thick and the spacer layer is between 205 and 215 nanometers thick.

17. The waveguide-based optical device of claim 13 , wherein the spacer layer includes silicon dioxide (SiO 2 ).

18. The waveguide-based optical device of claim 12 , wherein the free-space slab propagation region comprises a birefringence below a threshold birefringence value, wherein the birefringence is a difference between a transverse electric (TE) effective refractive index and a transverse magnetic (TM) effective refractive index.

19. The waveguide-based optical device of claim 18 , wherein threshold birefringence value is 0.3.