Semiconductor optical waveguide device
View Patent ↗A semiconductor waveguide optical device and a method of manufacturing of a semiconductor optical device are disclosed. The semiconductor waveguide optical device may include a gradient index waveguide for mode conversion and/or vertical translation of optical modes of step-index waveguides, which may be disposed on or over a same substrate as the gradient index waveguide. The gradient index waveguide may be epitaxially grown.
1. A method of manufacturing a semiconductor optical waveguide device, the method comprising:
growing on a substrate a base waveguide comprising one of:
i) a gradient index waveguide comprising a local refractive index depending on a growth parameter, wherein the growing comprises varying the growth parameter so as to gradually increase the local refractive index to a maximum value, and then to gradually decrease the local refractive index, whereby upon completion of the growing, the gradient index waveguide comprises a transversal bell-shaped refractive index profile defining an optical axis comprising the maximum value of the transversal bell-shaped refractive index profile;
ii) a first step index waveguide comprising a first waveguide core comprising a first core thickness and a first refractive index; and
iii) a second step index waveguide comprising a second waveguide core comprising a second core thickness and a second refractive index;
forming a first recess in the base waveguide by removing a first portion thereof to a first depth;
forming a different one of the gradient index waveguide, the first step index waveguide, and the second step index waveguide in the first recess;
forming a second recess in at least one of the waveguides formed heretofore on the substrate, by removing a second portion thereof to a second depth; and
forming the remaining one of the gradient index waveguide, the first step index waveguide, and the second step index waveguide in the second recess;
wherein upon growing the gradient index waveguide and the first and second step index waveguides, an optical path is formed comprising in sequence the first waveguide core, the gradient index waveguide, and the second waveguide core.
2. The method of claim 1 , wherein the first and second recesses are formed in the gradient index waveguide, wherein the first step index waveguide is formed in the first recess, and the second step index waveguide is formed in the second recess.
3. The method of claim 2 , wherein forming at least one of: the gradient index waveguide, the first step index waveguide, and the second step index waveguide comprises epitaxial growing.
4. The method of claim 3 , wherein the growth parameter is selected from the group consisting of reactive gas pressure, deposition rate, a ratio of precursor gases, and a source element temperature.
5. The method of claim 1 , wherein forming the first recess comprises forming a first mask layer over a length of the gradient index waveguide and a second portion of the gradient index waveguide and etching a first portion of the gradient index waveguide; and
wherein forming the second recess comprises forming a second mask layer over the length of the gradient index waveguide and the first step index waveguide, and etching the second portion of the gradient index waveguide.
6. The method of claim 1 , wherein the growth parameter is varied so that the transversal bell-shaped refractive index profile comprises a substantially parabolic refractive index profile characterized by a repeat length L of an optical field propagating in the gradient index waveguide,
wherein the length of the gradient index waveguide between the first and second step index waveguides is LM/4, wherein M is an integer.
7. The method of claim 6 , wherein the optical field comprises at least two optical modes, wherein L=2π/δn eff k 0 , wherein δn eff is an effective refractive index step between the at least two optical modes, and k 0 is a wavenumber of a zero-order optical mode for propagating in the gradient index waveguide.
8. The method of claim 7 , wherein the first and second step index waveguides are formed such that a center of the first waveguide core is disposed above the optical axis, and a center of the second waveguide core is disposed below the optical axis.
9. The method of claim 7 , wherein M is an odd number; and wherein the first core thickness is larger than the second core thickness, or wherein the first refractive index is smaller than the second refractive index.
10. The method of claim 9 , wherein the first and second step index waveguides are formed such that the first and second waveguide cores are centered on the optical axis, and
wherein the method further comprises butt-coupling an optical fiber to the first step index waveguide.
11. The method of claim 1 , wherein growing the gradient index waveguide comprises growing a first gradient index waveguide portion and growing a second gradient index waveguide portion abutting the first gradient index waveguide portion;
wherein growing the first gradient index waveguide portion comprises varying the growth parameter so as to gradually increase the local refractive index to a maximum value, and then to gradually decrease the local refractive index, whereby upon completion of the growing the first gradient index waveguide portion, the first gradient index waveguide portion comprises a transversal bell-shaped refractive index profile comprising a first width;
wherein growing the second gradient index waveguide portion comprises varying the growth parameter so as to gradually increase the local refractive index to a maximum value, and then to gradually decrease the local refractive index, whereby upon completion of the growing the second gradient index waveguide portion, the second gradient index waveguide portion comprises a transversal bell-shaped refractive index profile comprising a second width; and
wherein the first width is bigger than the second width.