Integration of photonics optical gyroscopes with micro-electro-mechanical sensors
Aspects of the present disclosure are directed to monolithically integrating an optical gyroscope fabricated on a planar silicon platform as a photonic integrated circuit with a MEMS accelerometer on the same die. The accelerometer can be controlled by electronic circuitry that controls the optical gyroscope. The optical gyroscope may have a microresonator ring or a multi-turn waveguide coil. Gaps may be introduced between adjacent waveguide turns to reduce cross-talk and improve sensitivity and packing density of the optical gyroscope.
1. A method for monolithically fabricating an integrated photonics chip comprising an optical waveguide-based rotation-sensing loop of an optical gyroscope and a micro-electro-mechanical-systems (MEMS)-based motion sensing device on a common platform, the method comprising:
designating a central area on the common platform to fabricate the MEMS-based motion sensing device, wherein the central area is to be enclosed by the optical waveguide-based rotation-sensing loop;
fabricating the optical waveguide-based rotation-sensing loop on the common platform;
protecting the fabricated waveguide-based rotation-sensing loop by depositing an etch-stop layer above the waveguide-based rotation-sensing loop; and
fabricating the MEMS-based motion sensing device in the designated central area.
2. The method of claim 1 , wherein fabricating the MEMS-based motion sensing device further comprises:
depositing and patterning electrodes on top of the etch-stop layer in the designated central area.
3. The method of claim 2 , further comprising:
depositing and patterning a first sacrificial layer on top of the etch-stop layer and the patterned electrodes.
4. The method of claim 3 , further comprising:
depositing and patterning a structural layer on top of the patterned sacrificial layer and the patterned electrodes.
5. The method of claim 4 , further comprising:
depositing and patterning a second sacrificial layer on top of the patterned structural layer.
6. The method of claim 5 , further comprising:
patterning the structural layer to create columns as parts of the MEMS-based motion sensing device, wherein the second sacrificial layer also gets patterned on top of the columns.
7. The method of claim 6 , further comprising:
removing the first and the second sacrificial layers, thereby creating a suspending structure that acts as a motion sensing element of the MEMS-based device.
8. The method of claim 1 , wherein fabricating the optical waveguide-based rotation-sensing loop further comprises:
fabricating a first portion of the loop on a first plane; and
fabricating a second portion of the loop on a second plane, wherein light couples evanescently between the first portion of the loop on the first plane and the second portion of the loop on the second plane.
9. The method of claim 1 , wherein the optical waveguide-based rotation-sensing loop comprises a microresonator ring.
10. The method of claim 1 , wherein the optical waveguide-based rotation-sensing loop comprises a a waveguide coil, wherein the loop comprises a plurality of waveguide turns, each waveguide turn being parallel to adjacent waveguide turns.
11. The method of claim 10 , wherein fabricating the optical waveguide-based rotation-sensing loop on the common platform further comprises:
forming gaps on either side of each waveguide turn to reduce crosstalk between the adjacent waveguide turns, thereby increasing a spatial density of waveguide turns that can be fabricated within a predetermined area on the common platform.
12. The method of claim 11 , wherein each of the gaps comprises one of: an air gap, a gap filled with metal, or, a gap filled with an inert gas or liquid.
13. The method of claim 11 , wherein the predetermined area depends on an exposure field of a reticle used to fabricate the optical waveguide-based rotation-sensing loop and the MEMS-based motion sensing device.
14. The method of claim 7 , further comprising:
packaging the optical gyroscope and the MEMS-based motion sensing device together as a modularized integrated inertial measurement unit (IMU).
15. The method of claim 14 , wherein the MEMS-based motion sensing device provides coarse rotational sensing reading for all axes of motion, and the optical gyroscope provides a higher-precision rotational sensing reading for one or more selected axes of motion.
16. The method of claim 15 , wherein the MEMS-based motion sensing device comprises an accelerometer for one or more axes of motion.
17. The method of claim 1 , wherein the common platform is a silicon photonics platform.
18. The method of claim 15 , wherein the optical waveguide comprises a waveguide core sandwiched between an upper cladding and a lower cladding, and the waveguide core comprises silicon nitride and the upper cladding and lower cladding comprise oxide.