Method for production of optical waveguides and coupling and devices made from the same
Novel processing methods for production of high-refractive index contrast and low loss optical waveguides are disclosed. In one embodiment, a “channel” waveguide is produced by first depositing a lower cladding material layer with a low refractive index on a base substrate and a refractory metal layer. Then, an etch mask layer is deposited on the refractory layer, followed by selective etching of the refractory metal layer with a dry-etch tool with high selectivity to the etch mask layer. Then, the refractory metal layer is oxidized to form an oxidized refractory metal region, and a top cladding layer made of a second low refractive index material to encapsulate the oxidized refractory metal region. In another embodiment, a “ridge” waveguide is produced by using similar process steps with an added step of depositing a high-refractive-index material layer and an optional optically-transparent layer.
1. A method for producing a high-refractive index contrast and low loss optical waveguide, the method comprising the steps of:
depositing a lower cladding material layer with a first low refractive index on a silicon base substrate;
depositing or growing a refractory metal layer on top of the lower cladding material layer with the first low refractive index;
forming an etch mask layer deposited on the refractory metal layer;
selectively etching the refractory metal layer utilizing a dry-etching tool with high selectivity to the etch mask layer;
oxidizing the refractory metal layer in high-temperature ambient oxygen, wherein the refractory metal layer subsequently forms an oxidized refractory metal region; and
depositing a top cladding layer made of a second low refractive index material to encapsulate the oxidized refractory metal region on top of the lower cladding material layer.
2. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the oxidized refractory metal region is transparent for optical wavelength signals.
3. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the lower cladding material layer with the first low refractive index is made of silicon dioxide with an approximate thickness between 1 and 10 microns, and the first low refractive index of approximately 1.5.
4. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the lower cladding material layer with the first low refractive index is deposited by a deposition method or by oxidation of the silicon base substrate.
5. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the refractory metal layer on top of the lower cladding material layer with the first low refractive index is made of tantalum or niobium, with an approximate thickness between 50 nm and 1000 nm.
6. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the dry-etching tool utilizes chlorine and is highly effective in removing a thin layer of the refractory metal layer selectively, while preserving the etch mask layer.
7. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the high-temperature ambient oxygen is between 400 Celsius and 700 Celsius for a duration approximately between 30 minutes and 24 hours in the step of oxidizing the refractory metal layer.
8. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the second low refractive index material for the top cladding layer is based on silicon dioxide or polymers with a refractive index of approximately 1.5.
9. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 1 , wherein the oxidized refractory metal region forms tantalum pentoxide or niobium pentoxide with a refractive index of approximately 2.0 to 2.3.
10. A method for producing a high-refractive index contrast and low loss optical waveguide, the method comprising the steps of:
depositing or growing a low refractive index cladding layer on top of a silicon base substrate;
depositing or transferring a high refractive index material layer on top of the low refractive index cladding layer to form a slab core region;
depositing an optically-transparent layer on top of the slab core region;
depositing or growing a refractory metal layer on top of the optically-transparent layer;
forming an etch mask layer deposited on the refractory metal layer;
selectively etching the refractory metal layer utilizing a dry-etching tool with high selectivity to the etch mask layer;
oxidizing the refractory metal layer in high-temperature ambient oxygen, wherein the refractory metal layer subsequently forms an oxidized refractory metal region; and
depositing a top cladding layer made of a second low refractive index material to encapsulate the oxidized refractory metal region on top of the lower cladding layers.
11. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the low refractive index cladding layer is made of silicon dioxide, and wherein the high refractive index material layer is made of lithium niobate, lithium tantalate, tantalum pentoxide, or niobium pentoxide, with a refractive index approximately between 2 and 2.3 to match the oxidized refractory metal region's refractive index.
12. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 11 , wherein the step of depositing the high refractive index material layer utilizes an ion slicing technique if the lithium niobate or the lithium tantalate comprises the high refractive index material layer, and wherein the step of depositing the high refractive index material layer utilizes sputtering or oxidization of the refractory metal layer if tantalum pentoxide or niobium pentoxide comprises the high refractive index material layer.
13. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the optically-transparent layer is made of silicon dioxide with an approximate thickness between 3 nm and 100 nm.
14. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the slab core region has a thickness approximately between 100 nm and 2000 nm.
15. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the refractory metal layer is made of tantalum or niobium, with an approximate thickness between 50 nm and 1000 nm.
16. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the oxidized refractory metal region is transparent for optical wavelength signals.
17. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the dry-etching tool utilizes chlorine and is highly effective in removing a thin layer of the refractory metal layer selectively, while preserving the etch mask layer.
18. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the oxidized refractory metal region forms tantalum pentoxide or niobium pentoxide with a refractive index of approximately 2.0 to 2.3.
19. The method for producing the high-refractive index contrast and low loss optical waveguide of claim 10 , wherein the second low refractive index material for the top cladding layer is based on silicon dioxide or polymers with a refractive index of approximately 1.5.