Method and apparatus for controlling waveguide birefringence by selection of a waveguide core width for a top cladding
View Patent ↗A method and apparatus for controlling waveguide birefringence by selection of a waveguide core width for a tuned top clad is described herein. In one example, a dopant concentration within a top cladding material is between 3-6% (wt.). Given a tuned top cladding composition, a width of the waveguide core is pre-selected such that birefringence is minimized, i.e., a zero, or near zero. The desirable width of the waveguide core is determined by calculating the distribution of stress in the top cladding over a change in temperature. From this distribution of stress, a relationship between the polarization dependent wavelength and variable widths of the waveguide in the arrayed waveguide grating are determined. This relationship determines a zero value, or near zero value, of polarization dependent wavelength for a given range of waveguide widths. Accordingly, the width of the waveguide may be selected such that the polarization dependent wavelength is minimized.
1. A method of controlling birefringence in an arrayed waveguide grating comprising:
determining a stress distribution in a top cladding layer and in at least one waveguide in the arrayed waveguide grating over a change in manufacturing temperature, the top cladding layer having a dopant in the range of 3-6% by weight;
determining a relationship between polarization dependent wavelength and a width of the waveguide from the stress distribution; and
selecting the width of the waveguide such that the polarization dependent wavelength is a predetermined value.
2. The method of claim 1 wherein the predetermined value is a minimized polarization dependent wavelength.
3. The method of claim 1 further comprising determining an elastic modulus of each of the top cladding layer and the waveguide prior to determining the stress distribution.
4. The method of claim 3 further comprising determining a coefficient of thermal expansion in each of the top cladding layer and the waveguide.
5. The method of claim 1 wherein determining the relationship between polarization dependent wavelength and the waveguide width from the stress distribution further comprises mapping the stress distribution into an index distribution.
6. The method of claim 5 further comprising determining an effective index of each of the waveguide and the top cladding.
7. The method of claim 1 wherein determining the relationship between polarization dependent wavelength and the waveguide width from the stress distribution further comprises determining a distribution of refractive index in the top cladding from the stress distribution.
8. The method of claim 2 wherein the minimized polarization dependent wavelength is zero.
9. The method of claim 1 wherein the top cladding layer is disposed over the waveguide.
10. The method of claim 9 wherein the top cladding layer is disposed over a substrate.
11. The method of claim 10 wherein the substrate comprises silicon.
12. The method of claim 10 wherein the substrate has a thickness of about 625 μm.
13. The method of claim 10 wherein the substrate is disposed over a first layer of SiO 2 .
14. The method of claim 13 wherein a second layer of SiO 2 is disposed over the substrate.
15. The method of claim 1 wherein the waveguide further comprises at least one dopant.
16. The method of claim 15 wherein the at least one dopant is selected from the group consisting of Germanium and Phosphorus.
17. The method of claim 1 wherein the waveguide comprises at least one material selected from the group consisting of polyacrylates, polymethacrylates, polysilicone, polyimide, epoxy, polyurethane, polyolefin, polycarbonate, polyamides, polyesters, acrylate-methacrylate copolymers, acrylic-silicone copolymers, epoxy-urethane copolymers, and amide-imide copolymers.
18. The method of claim 1 wherein the dopant comprises Boron.
19. The method of claim 1 wherein the change in manufacturing temperature is about 900° C.
20. An arrayed waveguide grating manufactured according to the method of claim 1 .