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EP-4175200-B1 - POINTING UNITS AND METHODS OF OPERATING POINTING UNITS

EP4175200B1EP 4175200 B1EP4175200 B1EP 4175200B1EP-4175200-B1

Inventors

  • QUINTANA SANCHEZ, Crisanto
  • ERRY, GAVIN
  • THUEUX, Yoann

Dates

Publication Date
20260506
Application Date
20221026

Claims (10)

  1. A pointing unit (100) for use with a free space optical communications terminal (105), the pointing unit comprising: an optical arrangement (101) comprising an optically transmissive steering element (101a, 101b) arranged in an optical path of an incident beam entering the optical arrangement, the optical arrangement comprising a principal axis (122) that is substantially parallel to an input direction of the incident beam (107), the optically transmissive steering element comprising: a first portion (703, 1005) configured to steer the incident beam by a first angle relative to the first portion, and a second portion (702, 1007) configured to steer the incident beam by a second angle, the second angle being variable according to electrical control of a refractive index of the second portion, the first angle being larger than the second angle; and wherein the first portion and the second portion are housed within a rotational support housing (507, 1017) to enable rotation of the steering element in a plane perpendicular to the principal axis, wherein, the optical arrangement is configured so that coarse steering of the incident beam is performable by rotation of the steering element in a plane perpendicular to the principal axis, and fine steering of the incident beam is performable by electrical control of the refractive index of the second portion such that the optical arrangement is thereby controllable to steer a beam towards a target.
  2. A pointing unit according to claim 1, wherein the first portion is a first metamaterial element (1005) and the second portion is a second metamaterial element (1007).
  3. A pointing unit according to claim 2, wherein the optically transmissive steering element is monolithic, the first metamaterial element forming a first layer of the optically transmissive steering element and the second metamaterial element forming a second layer of the optically transmissive steering element
  4. A pointing unit according to claim 3, wherein the first metamaterial element and the second metamaterial element are formed on a common substrate.
  5. A pointing unit according to any previous claim, wherein the coarse steering allows for steering through an opening angle of 90 degrees, and allows for fine steering through the second, variable angle of +/- 2 degrees.
  6. A pointing unit according to any one of claims 2 to 4, or claim 5 when dependent upon claim 2, wherein the steering angle resulting from the first and/or second metamaterial element is wavelength dependent, and the steering angle resulting from the first and/or second metamaterial element is polarisation dependent, and wherein the first and second metamaterial elements are arranged such that the steering element produces the same overall beam steering angle for a first incident beam of a first wavelength and a first polarisation and for a second incident beam of a second wavelength and a second polarisation, the first wavelength different to the second wavelength and the first polarisation orthogonal to the second polarisation.
  7. A pointing unit according to any previous claim, wherein the optically transmissive steering element is a first optically transmissive steering element of a pair of optically transmissive steering elements arranged as a Risley pair (1210).
  8. A pointing unit according to claim 7 further comprising a second pair of optically transmissive steering elements matching the first pair and arranged as a second Risley pair (1220).
  9. A pointing unit according to any one of claim 1 to 8, wherein the optical arrangement comprises a beam expander (118, 120) at an optical terminal, arranged to expand the beam diameter in the transmit direction and reduce the beam diameter in the receive direction, and wherein optionally the beam expander comprises a telescope arrangement.
  10. A vehicle equipped with the pointing unit according to any one of claims 1 to 9, wherein optionally the vehicle is an aircraft.

Description

Technical Field The present invention relates to pointing units and methods of operating pointing units, and more specifically to pointing units and methods of operating pointing units for use with free space optical communications terminals. Background Free space optical (FSO) communications uses light propagating in free space to transmit data. In the context of FSO communications, 'free space' refers to, for example, air, space, vacuum, or similar and is in contrast with communications via solids such as a fiber-optic cable. FSO communications can be useful for example in cases where communication via physical connections, such as fiber optic cables or other data cables, is impractical. One such case is, for example, communications between an aircraft such as a drone and a ground-based terminal. FSO communications ordinarily rely on direct line of sight between transmitter and receiver and so rely on directing an optical beam between FSO communication nodes. This demands pointing units which can steer a beam, received from another node, into a receiver module, and steer a transmitted beam towards a target node. FSO communications can offer higher data rates and improved security as compared to other wireless communication techniques. For example, FSO communications can achieve higher data rates, and can be less susceptible to jamming and interception compared to radio frequency (RF) communications. US 2017/025754 A1 relates to electromagnetic beam steering apparatuses comprising electromagnetic beam deflecting structures which include artificially structured effective media having at least two electronically-selectable tangential refractive index gradients. Non-patent literature "A Survey on Acquisition, Tracking, and Pointing Mechanisms for Mobile Free-Space Optical Communications", Kaymak et al., IEEE COMMUNICATIONS SURVEYS & TUTORIALS, vol. 20, no. 2, pages 1104-1123, XP011684306, DOI 10.1109/COMST.2018.2804323, relates to a variety of acquisition, tracking, and pointing mechanisms used in free-space optical communications systems. Non-patent literature "A hybrid system for beam steering and wavefront control", Nikulin, SPIE, XP040180910, 2004, relates to the use of a spatial light modulator to perform wavefront control and fine beam steering. US2019/025509A1 relates to a beam steering device comprising a plurality of transmission type optical modulation devices which include a phase modulator including a nanoantenna in which a plurality of nanostructure rows are arranged. US2020/025888A1 relates to a lidar device which comprises a metasurface for including a plurality of beam steering cells. Summary According to a first aspect of the present invention, there is provided the pointing unit of claim 1. According to a second aspect of the present invention, there is provided the vehicle of claim 10. Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings. Brief Description of the Drawings Figure 1 is a schematic diagram of an exemplary free space optical communications node comprising a pointing unit and terminal.Figure 2 is a schematic diagram of an exemplary steering element for use in a pointing unit.Figures 3a, 3b and 3c are schematic diagrams of examples of steering elements and various arrangements of electrical contacts for steering elements.Figures 4a, 4b and 4c are schematic diagrams of examples of various cross-sections of a steering element, and various arrangements of electrical contacts for a steering element.Figure 5 is a schematic diagram of an exemplary steering element housed in a slip ring architecture and rotational mount.Figures 6a and 6b are schematic diagrams of exemplary optical arrangements of steering elements arranged in a Risley topology.Figure 7 is a schematic diagram of an exemplary steering element comprising two portions, an electro-optic portion and an optical element.Figures 8a and 8b are schematic diagrams of exemplary steering elements comprising two portions, and various positions of electrical contacts applied thereto.Figure 9 is a schematic diagram of an exemplary Risley topology comprising four steering elements.Figure 10 is a schematic diagram of an exemplary steering element for use in a pointing unit, comprising a metasurface portion and a metadevice portion.Figure 10b is a schematic diagram of an exemplary steering element for use in a pointing unit, arranged to steer two beams at disparate wavelengths and polarisations.Figures 11a, 11b and 11c are schematic diagrams of various exemplary steering elements comprising various arrangements of metasurface portions and metadevice portions.Figure 12 is a schematic diagram of an exemplary Risley topology comprising four steering elements, the steering elements comprising a metasurface portion and a metadevice portion.Figure 13 is an example of an