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EP-4741894-A1 - PHOTONIC PRODUCT FOR IN-PLANE CHIP COUPLING OPERATING AT CRYOGENIC TEMPERATURES, AND METHOD OF MANUFACTURING THE SAME

EP4741894A1EP 4741894 A1EP4741894 A1EP 4741894A1EP-4741894-A1

Abstract

The present application pertains to a photonic in-plane chip coupling product including a support with a first and a second stack, each comprising a carrier and an optical component. The first stack has a carrier with a mounting surface and an opposing carrier surface carrying the first optical component, which has a first guided optical mode. Likewise, the second stack has a carrier and an optical component, featuring a second guided optical mode. These stacks are aligned so that the centers of their respective mode field distributions coincide. To minimize thermal deformation, at least one carrier in each stack includes layers of different materials with mutually different thermal expansion coefficients. Therewith a total thermal deformation between the mounting surfaces and the centers of the mode field distributions is minimized.

Inventors

  • TCHEBOTAREVA, Anna
  • VAN ESSEN, Bernard Henk Marius Francois
  • DE DOOD, MICHIEL JACOB ANDRIES

Assignees

  • Nederlandse Organisatie voor toegepast- natuurwetenschappelijk onderzoek TNO

Dates

Publication Date
20260513
Application Date
20241111

Claims (16)

  1. A photonic product, comprising: a support (5); a first stack (10) on the support that comprises a first carrier (11) and a first optical component (12), wherein the first carrier (11) has a first mounting surface (111) with which it is mounted on the support and, opposite the first mounting surface, a first carrier surface (112) carrying the first optical component, wherein the first optical component has a first guided optical mode; a second stack (20) on the support (5) that comprises a second carrier (21) and a second optical component (22), wherein the second carrier (21) has a second mounting surface (211) with which it is mounted on the support (5) and, opposite the second mounting surface, a second carrier surface (212) carrying the second optical component, wherein the second optical component has a second guided optical mode; wherein the first and the second stack (10, 20) are fixed against each other with a center (122) of a mode field distribution of the first guided optical mode being aligned with a center (221) of a mode field distribution of the second guided optical mode; wherein at least one of the first and the second carrier (11, 21) is provided with a first and a second layer (113, 114; 213, 214, 215, 216) of mutually different materials having mutually different thermal expansion coefficients, to minimize a difference between a total thermal deformation of a portion of the first stack (10) in a direction along a first reference line (RL1) between the first mounting surface (111) and the center (122) of the mode field distribution of the first guided optical mode and a total thermal deformation of a portion of the second stack (20) in a direction along a second reference line (RL2) between the second mounting surface (211) and the center (221) of the mode field distribution of the second guided optical mode.
  2. The photonic product according to claim 1, wherein a geometry of each of the stacks (10, 20) is symmetric with respect to the center position (122, 221) of the corresponding guided optical mode in a direction (X) transverse to a direction (Y) of the corresponding guided optical mode and to the direction (Z) of the respective reference line (RL1, RL2).
  3. The photonic product of claim 1, wherein the first optical component (12) is an optical fiber and the second optical component (22) is an on-chip photonic structure, the optical fiber preferably being a single mode optical fiber.
  4. The photonic product according to claim 3, wherein the optical fiber is accommodated in a V-groove (115) in the carrier surface (112) of the first carrier.
  5. The photonic product according to claim 4, wherein the V-groove (115) is provided in a carrier layer (114) from the same material as a material of a carrier layer (214, 216) in the second stack.
  6. The photonic product according to claim 3, 4 or 5, wherein the optical fiber (12a) is one of a plurality of optical fibers (12a, 12b, 12c).
  7. The photonic product according to claim 6, wherein the first carrier has a respective cantilever-like structure (115a, 115b, 115c) for each optical fiber.
  8. The photonic product according to claim 6, wherein the optical fibers (12a, 12b, 12c) each have a free end extending outside its respective groove towards the waveguide (223a, 223b, 223c).
  9. The photonic product according to claim 1, wherein second optical component comprises a first silicon oxide layer (222), an Si3N4 waveguide (223) and a second silicon oxide layer (224) provided on a silicon substrate (216) that is part of the carrier (21).
  10. The photonic product according to any of the preceding claims, wherein the carrier (21) of the second stack (20) comprises a layer (215) of beads adhered between the silicon substrate (216) and a lower arranged carrier layer (214).
  11. The photonic product, according to any of the preceding claims, wherein one or more of the optical components is a component of a quantum photonic processor.
  12. A method of manufacturing a photonic product (1), comprising: providing (S1) a support (5); providing (S2) a first stack (10) that comprises a first carrier (11) and a first optical component (12), the first optical component having a first guided optical mode with a mode field distribution having a first mode field distribution center (122), providing (S3) a second stack (20) that comprises a second carrier (21) and a second optical component (22), the second optical component having a second guided optical mode with a mode field distribution having a second mode field distribution center (221); adhering (S4) one (20) of the stacks on the support (5); holding (S5) the support in a fixed position, while controllably positioning the other one (10) of the stacks to align the first mode field distribution center (122) with the second mode field distribution center (221); adhering (S6) the other one (10) of the stacks on the support (5) when upon achieving alignment between the first mode field distribution center (122) with the second mode field distribution center (221); wherein at least one of the first and the second carrier (11, 21) is provided with a first and a second carrier layer (213, 214) of mutually different materials having mutually different thermal expansion coefficients, to minimize a difference between a total thermal deformation of a portion (10p) of the first stack (10) in a direction along a line between the first mounting surface (111) and the center (122) of the mode field distribution of the first guided optical mode and a total thermal deformation of a portion (20p) of the second stack (20) in a direction along a line between the second mounting surface (211) and the center (221) of the mode field distribution of the second guided optical mode.
  13. The method according to claim 12, comprising aligning the mode field distribution centers of the first optical component and the second optical component relative to each other so as to maximize the light coupling between said optical components.
  14. The method according to claim 12, using one of an on-chip spot-size converter, a WAFT (Waveguide Array to Fiber Transposer), and an interposer structure.
  15. The method according to any of the claims 12 to 14, wherein the alignment steps are performed at room temperature and wherein the difference between the total thermal deformation of the portion (10p) of the first stack (10) and the total thermal deformation of the portion (20p) of the second stack (20) is minimized for use of the photonic product at a cryogenic temperature.
  16. The method according to claim 12, the method comprises creating one or more cantilever-like structures (115a, 115b, 115c) for supporting a respective optical fiber by a dicing process.

Description

Field of the invention The present invention is directed at a photonic product for in-plane chip coupling operating at cryogenic temperatures. The present invention is further directed at a method of manufacturing the same. Background In Photonic Integrated Circuits (PICs), a plurality of components of a photonic circuit is integrated into a single chip. PICs offer many advantages over bulk optical systems, including small footprints, low weight and power consumption, better scalability and manufacturability, and better mechanical and optical stability. PIC technology is therefore considered crucial for applications in quantum and space-qualified devices. To couple light in and out of a PIC chip, a low-loss interface between the chip and an adjacent optical component is required. These devices must be able to operate in harsh conditions, i.e. in vacuum and at cryogenic temperatures down to 4 K and below. Ideally, PIC chips are manufactured and assembled with adjacent optical components at normal ambient temperatures, such as room temperatures, and only brought into cryogenic conditions thereafter. In the assembly process the adjacent optical components, e.g. the PIC chip and an optical fiber need to be aligned before they are fixed to each other. However, the adjacent optical components are typically not identical. For example, the adjacent optical components may be composed of mutually different materials which may have mutually different dimensions. Therewith, their introduction into cryogenic conditions would cause a temperature-dependent optical misalignment between the components to appear due to thermal deformation, which hampers their ability to function in these environments. The paper "Realignment-free cryogenic macroscopic optical cavity coupled to an optical fiber", written by Fedoseev et al. in 2022, arXiv:2301.06609v1 [physics.optics] 16 Jan 2023, is directed at a cryogenic set-up where an optical Fabry-Perot resonator is coupled to a single-mode optical fiber without realignment during cooling down. The system described therein maintains coupling efficiency through an axially symmetric design of the fiber-coupled resonator, such that the setup is rotationally symmetric around the optical axis. However, due to this restriction to a rotationally symmetric designs, this approach is less attractive for general application in PICs, because such assemblies typically cannot leverage this symmetry relation in the manner therein disclosed. There is therefore a need for an approach that is more generally applicable and scalable. At least the approach should be suitable for application in PICs. Summary of the invention In order to address the above-mentioned need, there is provided herewith, in accordance with a first aspect of the invention, a photonic product, comprising: a support, a first stack on the support and a second stack on the support. The first stack comprises a first carrier and a first optical component. The first carrier has a first mounting surface with which it is mounted on the support and, opposite the first mounting surface, a first carrier surface carrying the first optical component, wherein the first optical component has a first guided optical mode. The second stack comprises a second carrier and a second optical component, wherein the second carrier has a second mounting surface with which it is mounted on the support and, opposite the second mounting surface, a second carrier surface carrying the second optical component, wherein the second optical component has a second guided optical mode. The first and the second stack are fixed against each other with a center of a mode field distribution of the first guided optical mode being aligned with a center of a mode field distribution of the second guided optical mode. At least one of the first and the second carrier is provided with a first and a second layer of mutually different materials having mutually different thermal expansion coefficients, to minimize a difference between a total thermal deformation of a portion of the first stack in a direction along a first reference line between the first mounting surface and the center of the mode field distribution of the first guided optical mode and a total thermal deformation of a portion of the second stack in a direction along a second reference line between the second mounting surface and the center of the mode field distribution of the second guided optical mode. Although in practice it may not be possible to reduce the difference in thermal deformation to zero, nevertheless a substantial reduction of this difference, approaching zero, is achieved, i.e. a reduction of the difference in thermal deformation to at most 10% of the mode field size, preferably a reduction to at most 5% of the mode field size. The wording mode size is understood to be herein the size of the smallest mode in case the first guided mode and the second guided optical mode have a different mode size. By wa