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EP-4741896-A1 - ADAPTER FOR COUPLING LIGHT FROM A PHOTONIC CIRCUIT

EP4741896A1EP 4741896 A1EP4741896 A1EP 4741896A1EP-4741896-A1

Abstract

This description relates to an optical adapter (100) intended to serve as an interface with an integrated optical circuit (101) to produce a broadened beam of light (108) and thus facilitate coupling with optical fibers (509) and/or an optical connector (505). The optical adapter (100) has a plane mirror on its upper face and a converging mirror on its lower face. The beam of light (108) propagates, broadening as it does so between the integrated optical circuit (101) and the converging mirror inside the transparent optical adapter (100), the path being folded back by the upper plane mirror.

Inventors

  • CASTANY, OLIVIER

Assignees

  • Commissariat à l'Energie Atomique et aux Energies Alternatives

Dates

Publication Date
20260513
Application Date
20251105

Claims (11)

  1. Optical adapter (100) including: - a transparent region (111); - a converging mirror (113) located on the side of a first face (111B) of the transparent region (111) and turned towards a second face (111T) of the transparent region (111), opposite the first face (111B); - a first plane mirror (115) located on the side of the second face (111T) of the transparent region (111) and turned towards the first face (111B); - a first optical port (117) located on the side of the first face (111B) and intended to be positioned opposite one end of a waveguide (201; 203) of an integrated optical circuit (101); - a second optical port (119) located on the second side (111T); and - a second plane mirror (109) located on a part (111S) of the transparent region (111) protruding from its first face (111B), said part (111S) being intended to be inserted into a cavity (107) of the integrated optical circuit (101), the optical adapter (100) being intended to ensure propagation of a light beam (108) between said end of the waveguide (201; 203) and the second optical port (119), the first plane mirror (115) and the converging mirror (113) being arranged so that the light beam (108) propagates between the first (117) and second (119) optical ports, through the transparent region (111), by reflection on the first plane mirror (115) and on the converging mirror (113), the light beam (108) having, at the level of the second optical port (119), a size ( d3 ) greater than that ( d1 ) which it has at the level of the first optical port (117).
  2. Adapter (100) according to claim 1, wherein the transparent region (111) further comprises at least one mechanical positioning element (301; 401) of the adapter (100) relative to the integrated optical circuit (101).
  3. Adapter (100) according to claim 2, wherein said at least one mechanical positioning element (301; 401) protrudes from the first face (111B) of the transparent region (111).
  4. Adapter (100) according to claim 2 or 3, wherein said at least one mechanical positioning element (301; 401) comprises at least one pad (301) without optical function intended to bear against the integrated optical circuit (101).
  5. Adapter (100) according to any one of claims 2 to 4, wherein said at least one mechanical positioning element (301; 401) further comprises at least one finger (401) devoid of optical function and intended to be inserted into a cavity (403) of the integrated optical circuit (101).
  6. Adapter (100) according to any one of claims 1 to 5, wherein the first (117) and second (119) optical ports are respectively adapted to receive and emit the light beam (108).
  7. Adapter (100) according to any one of claims 1 to 6, wherein the first face (111B) of the transparent region (111) is parallel to its second face (111T), the first plane mirror (115) being parallel to the second face (111T).
  8. Adapter (100) according to any one of claims 1 to 7, wherein the second optical port (119) is intended to be positioned opposite an optical connector (505) into which one end of an optical fiber (509) terminates.
  9. Optical device (500) comprising an integrated optical circuit (101) and the optical adapter (100) according to any one of claims 1 to 8, the optical adapter (100) being mechanically attached to the integrated optical circuit (101).
  10. Device (500) according to claim 9, wherein the optical adapter (100) is fixed to the integrated optical circuit (101) by an optically transparent layer of adhesive (207).
  11. Device (500) according to claim 9 or 10, further comprising at least one optical connector (505) positioned opposite the second optical port (119) and into which the end of an optical fiber (509) terminates.

Description

technical field This description relates in general to the field of integrated optical circuits, also called photonic integrated circuits ("Photonic Integrated Circuit" - PIC), and more particularly to the coupling of light, or optical coupling, between an integrated optical circuit and one or more optical fibers. Previous technique Integrated optical circuits, particularly silicon photonic circuits, can combine numerous functions on a single chip. This offers advantages, especially in terms of reduced size and optical losses, compared to assemblies made by assembling discrete components. In integrated photonic circuits, light is guided through small optical waveguides, typically less than a micrometer wide, enabling the creation of dense circuits. Integrated optical circuits communicate by exchanging light with external systems, coupling this light while minimizing optical losses. The issue of optical coupling is particularly critical in the case of single-mode optical beams, intended, for example, to be coupled in single-mode optical fibers, due to the small diameter of the light beams involved. In an integrated optical circuit, the coupling interfaces of optical guides are generally of two types: 1) Vertical grating couplers (VGCs) that operate by diffracting light on a periodic structure implemented at the end of the optical guide to direct the light upwards on the chip, and more precisely at an angle close to the vertical of the chip, for example an angle of 8° (angle considered in a medium with a refractive index equal to that of silica glass), the coupling gratings making it possible to form a beam of light with a diameter on the order of tens of micrometers, which is suitable for the single-mode optical fibers commonly used for optical communications; and 2) Edge-couplers, typically located at the edge of the circuit, consist of an optical waveguide that terminates at the chip edge, with the light exiting along the extension of the waveguide. The end of the waveguide may also have a structure that widens the optical mode before it exits the chip. The beam size is typically between two and ten micrometers. A variant of edge coupling may include a cavity, such as a well, formed in the top surface of the circuit to provide access to an exit of the optical waveguide. A mirror located in the cavity opposite the end of the optical waveguide then extracts the light by reflecting it off the plane of the chip, typically in a near-vertical direction. The two types of interfaces mentioned above allow the formation of single-mode light beams with a maximum diameter close to ten micrometers. In this case, direct coupling with optical fibers is possible, but the beam diameter remains small, requiring the optical fibers to be positioned with a precision of less than ±2 µm to achieve an acceptable coupling ratio. This positioning precision is difficult to achieve and requires the use of dedicated, expensive, and slow machines. To facilitate coupling and increase the tolerance of the For positioning, it is desirable to widen the diameter of the light beam exiting the integrated optical circuit to several tens of micrometers, for example about 50 µm, which allows the positioning tolerance to be relaxed to plus or minus 10 µm and consequently makes the assembly less delicate, thus allowing the use of less expensive and faster machines. Several techniques have been proposed for coupling light between an integrated optical circuit and optical fibers with an enlarged beam diameter. In all cases, a sufficiently long optical path is considered to allow the light beam to expand to the desired size. The different techniques are distinguished by the optical scheme used and the portion of the optical path over which the beam expands. Furthermore, edge-to-edge coupling involves attaching the optical fiber to the chip's edge, which is mechanically fragile. To avoid this drawback and attach the fiber to the chip's top surface while maintaining an optical configuration similar to edge-to-edge coupling, a cavity can be formed from the chip's top surface. This cavity has a vertical wall in front of the optical waveguide's tip, allowing the beam exiting the waveguide to pass through this wall and enter the cavity. Inside the cavity, a reflecting mirror intercepts the beam and deflects it upwards, exiting the chip's top surface in a near-vertical direction. Manufacturing this reflecting mirror can be achieved using various techniques and presents an industrial challenge. American patents US 9817193 , US 10209442 , US 10459163 And US 10690848 and the French patent FR 3066615 These designs describe integrated optical circuits where beam spreading is performed within the thickness of the chip substrate and where the back side of the chip incorporates an optical function, either a lens or a mirror. This solution allows the beam spreading function to be integrated inside the chip without additional components. However, a drawback is tha