Fabrication-tolerant waveguides and resonators
An optical waveguide having a core region with a substantially rectangular cross-section with a selected aspect ratio of width to height. Embodiments include devices incorporating the optical waveguide and methods for using the optical waveguide.
1. A method of propagating optical signals through a waveguide, the method including the steps of:
providing an optical waveguide comprising a single core region consisting essentially of at least one material layer, each material layer consisting essentially of a material (i) substantially transparent within an operating wavelength range having a free-space center wavelength, and (ii) selected from the group consisting of a group IV semiconductor element or compound, a III-V semiconductor compound, a II-VI semiconductor compound, and silicon nitride, the single core region having a substantially rectangular cross-section with an aspect ratio of width to height selected from a range of about 1.8:1 to 3:1, the cross-section supporting at least two TE modes and only one TM mode in the operating wavelength range, and the optical waveguide having at least one TE mode with a higher effective index than the TM mode; and
propagating light in the optical waveguide solely in the TM mode.
2. The method of claim 1 , wherein each material layer consists essentially of a group IV semiconductor element or compound and the aspect ratio is about 1.8:1.
3. The method of claim 2 , wherein the free-space center wavelength is about 1.5 μm.
4. The method of claim 1 , wherein a core refractive index of each core material of each material layer is approximately equal to a refractive index of crystalline silicon.
5. The method of claim 1 , wherein the optical waveguide further comprises a cladding region surrounding the core region, the cladding region (i) comprising at least one cladding material having a refractive index, and (ii) having a maximum cladding refractive index equal to the largest refractive index of the at least one cladding material.
6. The method of claim 5 , wherein a core refractive index of the material in the core region is at least 1.5 times as large as the maximum cladding refractive index.
7. The method of claim 5 , wherein the maximum cladding refractive index is approximately equal to a refractive index of silica.
8. The method of claim 1 , wherein the aspect ratio, the height, and the width of the cross-section cooperate to support the single TM mode.
9. The method of claim 8 , wherein the cross-section encompasses a largest possible area corresponding to the given aspect ratio.
10. The method of claim 1 , wherein the optical waveguide comprises:
a slanted sidewall defining a sidewall angle with respect to a top portion of the optical waveguide,
wherein the sidewall angle is less than 5 degrees.
11. The method of claim 1 , wherein an area of the cross-section is less than or equal to about 0.403−0.285×[sech(1.65×A R )] 0.36 square micrometers.
12. The method of claim 11 , wherein the area of the cross-section is equal to or greater than about 0.047+0.057×[sech(3×A R )] 0.44 square micrometers.