High confinement waveguide on an electro-optic substrate
View Patent ↗The invention relates to an optical device including a passive high confinement waveguide, such as of silicon-rich silicon nitride, on an electro-optic substrate, like lithium niobate, optically coupled to a waveguide in the electro-optic substrate. A wide range of electro-optic devices are enabled by this high confinement waveguide structure, including: directional couplers, compact tap couplers, folded electro-optic devices, electro-optic modulators including ring resonators, electro-optic gratings. Further applications enabled by the present invention include hybrid passive planar lightwave circuits (PLC) integrated with electro-optically active waveguides, using the high confinement waveguide as an intermediary waveguide to transfer optical power between the passive and active components.
1. An electro-optic device comprising:
an electro-optic substrate having a refractive index n s ;
a first diffused waveguide within the electro-optic substrate for transmitting an optical signal through the device for electrically-induced modulation, the first diffused waveguide having a refractive index n w1 greater than n s ;
first and second separate high confinement waveguides having refractive indices n c1 and n c2 , respectively, wherein n c1 and n c2 are greater than n w1 , wherein the first and second high confinement waveguides are optically coupled to each other, forming a directional coupler comprising a taper for adiabatic transfer of the optical signal, wherein the first high confinement waveguide is optically coupled to the first diffused waveguide,
wherein the first high confinement waveguide and the first diffused waveguide form a first hybrid waveguide, wherein the first high confinement waveguide is at least partially disposed within the first diffused waveguide in the electro-optic substrate,
the electro-optic device further comprising a second diffused waveguide having a refractive index n w2 greater than n s , wherein the second high confinement waveguide and the second diffused waveguide form a second hybrid waveguide, wherein the second high confinement waveguide is at least partially disposed within the second diffused waveguide in the electro-optic substrate, and the first and second high confinement waveguides are disposed in a horizontally separated side-by-side configuration, and
wherein the first and second diffused optical waveguides of the first and second hybrid waveguides overlap in a coupling region.
2. An electro-optic device as defined in claim 1 , wherein the device comprises a Mach-Zehnder interferometer having an output optical waveguide comprising the first diffused waveguide, and an optical tap output waveguide comprising the second high confinement waveguide, whereby in operation, the directional coupler facilitates tapping of the optical signal from the output optical waveguide of the Mach-Zehnder interferometer into the optical tap output waveguide.
3. An optical device as defined in claim 1 , wherein the device comprises a ring resonator including a straight waveguide comprising the first hybrid waveguide and a ring waveguide disposed for evanescent coupling with the straight waveguide and comprising the second hybrid waveguide.
4. An electro-optic device as defined in claim 1 , wherein the first diffused waveguide forms a Mach-Zehnder interferometer comprising first and second arms, wherein the second high-confinement waveguide has separated first and second ring sections forming first and second ring resonators, respectively, optically coupled to the first and second arms, respectively, and disposed such that the first ring resonator coupled to the first arm and the second ring resonator coupled to the second arm have equal bias voltages and opposite signs thereof.
5. An electro-optic device as defined in claim 1 , wherein the device comprises a grating formed as a periodic structure along the length of the first high confinement waveguide.