EP4652689A1

EP4652689A1 - Free-space optical communication

Info

Publication number: EP4652689A1
Application number: EP24700149.8A
Authority: EP
Inventors: Haimin Tao; Matthias Wendt
Original assignee: Signify Holding BV
Current assignee: Signify Holding BV
Priority date: 2023-01-18
Filing date: 2024-01-10
Publication date: 2025-11-26
Also published as: CN120569919A; WO2024153510A1

Abstract

A mechanism for setting up a communication from a Free-Space Optical Communication (FSOC) device and another communication device. A light beam, output by the FSOC device, is steered so as to continuously repeat a fine sweeping pattern whilst moving through a coarse sweeping pattern.

Description

Free-space optical communication

FIELD OF THE INVENTION

The present invention relates to the field of Free-Space Optical Communication.

BACKGROUND OF THE INVENTION

Free-Space Optical Communication (FSOC) strategies facilitate communication between different devices using the transmission of directed light, particularly light beams such as laser beams or other forms of collimated light beam. A laser beam has an extremely narrow beam divergence (e.g., <4mrad). Devices that operate using an FSOC strategy can achieve very high throughput and/or communicate over a very long distance through use of laser beams, as optical power is concentrated over a very small beam diameter. However, for smaller scale applications (e.g., within a building) it is possible to make use of FSOC strategies/techniques using other forms of collimated light (i.e., light beams).

However, for a FSOC-based system to work, beam steering technology is necessary. In particular, it is essential to keep a light beam, produced by a first device, aligned with a beam sensing arrangement of a second device. For stationary applications, beam steering can be used to initiate and maintain this alignment regardless of environmental conditions such as vibration and (outdoor) atmosphere conditions. For mobile or quasi - stationary applications, beam steering is naturally more important to maintain the alignment during movement.

There is a desire to improve the beam steering of a light beam for an FSOC device to increase the speed and ease of alignment.

International patent application WO 2020/214234 Al discloses a method and system for adaptive FSOC using a digital micro mirror assembly in communication with a controller. A laser is included which is configured to generate an optical beam which may be applied to select ones of first sub-pluralities of micromirror elements to generate a transmitted free space optical signal along a selected vector. A detector is included for receiving an incoming free space optical signal imaged by at least one of the micromirror elements. Disclosed is a method that involves sweeping using a broad spot to detect a communications partner and then subsequently narrowing the field of search to around a location in a subsequent scan.

International patent application WO 2018/231152 Al likewise discloses a method and system for high-speed communication, whereby a coarse scan using a gimbal system is performed to point into a one degree FOV accuracy of a partner beacon, followed by a fine angular adjustment using electronic beam steering which does corrections for 1/10^th of the beam width.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a Free-Space Optical Communication device.

The Free-Space Optical Communication (FSOC) device comprises a beam generator configured to generate a light beam for communicating with a second, different communication device comprising a beam sensing arrangement; and a beam steering system configured to steer a beam output direction, being a direction in which the light beam is output by the beam generator, the beam steering system being operable in at least an acquisition mode.

When operating in the acquisition mode, the beam steering system is configured to steer the movement of the beam output direction to follow a continuous sweeping pattern corresponding with a superimposed coarse sweeping pattern and a continually repeated fine sweeping pattern, whereby the beam output direction substantially follows the coarse sweeping pattern but deviates from the coarse sweeping pattern based on the superimposed fine sweeping pattern; and the fine sweeping pattern is defined by one or more sinusoidal functions.

The present disclosure proposes a technique for controlling the direction of a light beam of a Free-Space Optical Communication (FSOC) device, e.g., during initializing or set-up of inter-device communication in an FSOC system. The direction of the light beam is controlled or steered using a beam steering system, which is operable in at least an acquisition mode.

During the acquisition mode, the beam steering system moves the light beam to follow a coarse sweeping pattern. Whilst following the overall coarse sweeping pattern, the beam steering system also performs (at a smaller scale) steering of the light beam according to a fine sweeping pattern. Thus, the beam is deviated away from the coarse sweeping pattern to perform a fine sweeping pattern (within a small region visited during the coarse sweeping pattern). As a result, acquisition may be achieved using the single superimposed sweeping pattern.

The proposed approach shows improved speed of aligning a light beam with a beam sensing arrangement of the second communication device, as a greater spread of possible locations are visited/covered in less time during the process of a coarse sweeping pattern. In particular, the effective spot size of the light beam is increased by iteratively performing the fine sweeping pattern.

It will be appreciated that the beam steering system may also be operable in other modes. For instance, the beam steering system may also be operable in at least a tracking mode, in which the beam is steered to track or maintain communication with the beam sensing arrangement. As another example, the beam steering system may be operable in a tuning mode, in which the beam is steered to maximize a signal strength of the beam received by the beam sensing arrangement of the second communication device.

Defining the fine sweeping pattern with a sinusoidal function reduces any sudden jerks or changes of the beam steering system. This significantly reduces wear and/or stress on the beam steering system.

For the sake of completeness, it is noted that superimposing the fine sweeping pattern on the coarse sweeping pattern represents a scenario in which the fine sweeping pattern is continually repeated by continuously superposing the fine sweeping pattern on to the coarse sweeping pattern.

The fine sweeping pattern may preferably be defined using a Lissajous curve. This provides a shape that explores a small region with a high level of efficiency using two independent sinusoidal functions. This maintains the improved reduction to wear and/or stress on the beam steering system.

In some examples, the size of the footprint area of the fine sweeping pattern is more than 10 times smaller than the coarse sweeping pattern. This ensures more purposive and accurate searching of the second communication device by the FSOC device.

In some embodiments, the coarse sweeping pattern is a raster or zig-zag pattern. This approach provides a reliable technique for investigating a search area.

In other embodiments, the coarse sweeping pattern is a spiral pattern. The spiral pattern may be a straight-line spiral or a spiral curve. This approach is particularly advantageous if the acquisition mode needs to be repeated after successful locating of the second communication device, as it can be assumed that the second communication device will still be near to its previous location.

The spiral pattern is a pattern that starts at a first location and gradually moves outwardly (in a spiral) away from the first location.

In preferred approaches, the speed of movement through the fine sweeping pattern is more than 3 times faster than the speed of movement through the coarse sweeping pattern. This ensures that the beam steering system will iteratively repeat the fine sweeping pattern or motion whilst moving through the coarse sweeping pattern. Conceptually the fine sweeping pattern, such as a Lissajous curve with the coarse sweeping pattern that scans a room, it will be clear that during the time-interval that the coarse sweeping pattern passes over the footprint of the fine sweeping pattern coverage area, the fine sweeping pattern passes several times through the footprint, thus moving faster through the fine-sweeping pattern coverage area and changing direction more rapidly than the coarse sweeping pattern does.

In preferred examples, the speed of movement through the fine sweeping pattern is more than 5 times faster than the speed of movement through the coarse sweeping pattern, e.g., more than 10 times faster, e.g., more than 20 times faster, e.g., more than 40 times faster.

The Free-Space Optical Communication device may further comprise a receiver configured to receive a response communication from the second communication device, wherein the beam steering system is configured to, responsive to the receiver receiving a response communication indicating that the second communication device has sensed the light beam, exit the acquisition mode.

This approach ensures that the beam steering system exits the acquisition mode (i.e., stops searching for the second communication device) once the light beam is correctly targeting or being directed towards the second communication device. This helps to avoid overshooting or missing of the second communication device in order to set up a communication link.

The receiver may be an FSOC beam sensing system configured to receive the response communication as a second light beam output by the second communication device. The FSOC beam sensing system may be functionally identical or similar to the beam sensing system of the second communication device. In particular, the second communication device may also be an FSOC communication device, such that the response communication is carried by a second light beam that facilitates bidirectional communication (using FSOC principles) between the FSOC device and the second communication device.

The receiver may be a broad beam FSOC sensing system (omnidirectional receiver) capable of detecting optical signals originating from the general direction in which the first light beams is directed, configured to receive a light of the first light beam reflected by a retroreflector mounted on the second communication device.

In another approach, the receiver is a radiofrequency sensing system configured to receive the response communication as a radiofrequency signal transmitted by the second communication device. This approach does not necessitate that the second communication device comprise a beam generator. Rather, the second communication device can be simpler in design.

There is also proposed a Free-Space Optical Communication system comprising: the Free-Space Optical Communication device previously described; and the second communication device. The second communication device thereby comprises at least the beam sensing system for sensing the light beam output by the Free-Space Optical Communication device.

In at least one embodiment, the second communication device comprises a response generating system configured to generate and transmit a response communication to the Free-Space Optical Communication device responsive to the beam sensing arrangement sensing the light beam. The response generating system may, for instance, be a second beam generator for generating a (second) light beam to be directed towards the Free-Space Optical Communication device or a retro-reflector mounted on the second communication device to at least partially reflect the light beam generated by the Free-Space Optical Communication device back. In alternative examples, the response generating system comprises an antenna or antenna system for generating a radiofrequency or microwave frequency signal for the Free- Space Optical Communication system.

Optionally, the second communication device further comprises a second beam generator for generating a second light beam; the beam sensing arrangement is configured to determine a direction from which the light beam of the Free-Space Optical Communication device is received by the beam sensing arrangement; and the second communication device further comprises a second beam steering system configured to direct the second light beam towards the direction from which the light beam of the Free-Space Optical Communication device is received by the beam sensing arrangement. This approach facilitates a co-operative or collaborative approach for two FSOC devices to direct light beams towards one another, e.g., to set up a communication pathway or channel.

In preferred examples, the second communication device is a Free-Space Optical Communication device.

There is also provided a computer-implemented method of controlling a beam output direction of a light beam output by a beam generator of a Free-Space Optical Communication device, the light beam being for communicating with a second, different communication device comprising a beam sensing arrangement.

The computer-implemented method comprises steering the movement of the beam output direction to follow a continuous sweeping pattern corresponding with a superimposed coarse sweeping pattern and a continually repeated fine sweeping pattern, whereby the beam output direction substantially follows the coarse sweeping pattern but deviates from the coarse sweeping pattern based on the superimposed fine sweeping pattern and the fine sweeping pattern is defined by one or more sinusoidal functions.

There is also provided a computer program comprising code means for implementing any herein described method when said program is run on a processing system.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. 1 illustrates a system in which embodiments can be employed;

Fig. 2 conceptually illustrates a coarse and fine sweeping pattern according to an embodiment;

Fig. 3 conceptually illustrates a coarse and fine sweeping pattern according to another embodiment;

Fig. 4 illustrates another system in which embodiments can be employed; and Fig. 5 is a flowchart illustrating a method according to an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The invention provides a mechanism for setting up a communication from a Free-Space Optical Communication (FSOC) device and another communication device. A light beam, output by the FSOC device, is steered so as to iteratively repeat a fine sweeping pattern whilst moving through a coarse sweeping pattern.

The present disclosure is based on the realization that superimposing a fine sweeping pattern on a coarse sweeping pattern when performing a search or sweep with the light beam significantly increases the chances of the light beam becoming incident on a light or beam sensing system of a different communication device (i.e., the device being searched), particularly for a bidirectional beam alignment. The proposed approach thereby improves an efficiency during an acquisition or searching mode of a beam steering system.

Embodiments may be employed in any suitable environment in which it is desired to communication between two communication devices, of which at least one is a FSOC device.

Figure 1 illustrates a system 100 in which embodiments of the invention can be employed, for improved contextual understanding.

The system 100 is a Free-Space Optical Communication (FSOC) system, which comprises a Free-Space Optical Communication device (FSOC device) 110 and a second communication device (second device) 120.

The FSOC device 110 comprises a beam generator 111 and a beam steering system 112.

The beam generator 111 is configured to generate a light beam 150 for communication with the second communication device 120. The light beam 150 is a collimated beam of light, and may include a laser beam or another form of collimated light. The advantage in using a laser is that on account of the narrow beam nature, it generally does not require a complex collimator and may be used over longer distances. Conversely the relatively tight beam may cause eye-safety issues that a broader collimated light beam may not have.

Suitable examples of beam generators are well known in the art and include laser diodes, one or more LEDs with one or more accompanying collimators, VCSELs, gas lasers, chemical lasers, dye lasers, metal-vapor lasers, solid-state lasers, semiconductor lasers, free-electron lasers, a synchrotron light generator and so on. The beam may be controlled (e.g., by the beam generator 111 or a corresponding optional control system 119) so as to encode information to be transmitted from the FSOC device 110 to the second communication device 120, according to well-known principles.

The beam steering system 112 is configured to steer the generated light beam 150 to control or define a beam output direction. The beam output direction defines the direction in which the light beam 150 (generated by the beam generator 111) is output by the FSOC device 110.

The beam steering system 112 may, for instance, comprise a controllable mirror 112A (e.g., a fast-scanning mirror such as a MEMS mirror) and an associated controller 112B. Thus, each beam steering system may comprise a (e.g., MEMS) mirror 112A controlled by a (e.g., MEMS) controller 112B to steer the light beam. The direction of the beam can be controlled by controlling an angle that the mirror 112A makes with respect to the beam generator 111, which directs a light beam towards the mirror 112 A.

An alternative beam steering system may be configured to directly manipulate a direction in which the beam generator 111 faces. This is less preferred due to jostling, vibrating and/or potential damage of/to the beam generator 111.

Yet another beam steering system 112 may make use of one or more optical devices, e.g., lenses, to control the direction of the light beam. Such approaches will be readily apparent to the skilled person.

Of course, the FSOC device 110 may comprise further optical componentry for generating and/or outputting the light beams. Similarly, the FSOC device 110 may comprise any electronic components necessary for driving, powering, biasing, controlling and/or otherwise operating the other components of the FSOC device.

The second communication device 120 comprises a beam sensing system 125. The beam sensing system is configured to sense the light beam 150 generated by the beam generator 111 of the FSOC device 110 and steered by the beam steering system 112. The beam sensing system 125 may, for instance, generate an electrical signal responsive to the received light beam. Suitable examples of beam sensing systems 125 are well known in the art, and include any suited photosensitive device or photodetector, such as a photodiode, photoresistor, camera array (e.g., a two-dimensional photodetector array) and so on.

The second communication device 120 may further comprise a decoding system (not shown) configured to, for instance, decode information carried by the light beam 150 received at the beam sensing system 125. Approaches for encoding and decoding information using a light beam are well established in the field.

The FSOC system 100 thereby facilitates communication from the FSOC device 110 to the second communication device 120, in the form of a light beam. The illustrated FSOC system 100 is a unidirectional Free-Space Optical Communication system, in that a FSOC approach is used to communicate in a single direction.

It will be apparent that there is a need to correctly align or steer the light beam 150 output by the FSOC device 110 with the beam sensing system 125 of the second communication device 120.

Typically, this alignment is achieved by the beam steering system 112 operating in an acquisition mode, in which it steers the light beam 150 (i.e., changes the beam output direction) to follow a predetermined pattern. The beam output direction can follow this pattern at least until the light beam 150 is incident upon the beam sensing system 125 of the second communication device 120.

An alternative label for the acquisition mode is a searching mode, as the beam steering system is effectively steering or moving the beam output direction in search of the second communication device, and more specifically, the beam sensing system of the second communication device.

The predetermined pattern can be labelled a “sweeping pattern”, as the beam steering system sweeps the light beam in search of the beam sensing system of the second communication device, or a “search pattern”. A sweeping pattern is therefore a pattern of movement that the light beam takes (controlled by the beam steering system) in an effort to become incident upon the beam sensing system of the second communication device.

Further optional features of the FSOC device 110 and/or the second communication device 120 are hereafter described and can be employed in various embodiments of the present disclosure. In preferred approaches, the second communication device 120 is able to react or respond to sensing the presence or incidence of the beam (output by the FSOC device) at/on the beam sensing system 125.

In particular, the second communication device 120 may comprise a response generating system 126 configured to generate and transmit a response communication 160 to the FSOC device 110 responsive to the beam sensing system sensing the light beam. The response communication 160 may be iteratively or continually generated and/or output by the response generating system 126 as long as the light beam 150 is incident upon the beam sensing system 125 of the second communication device 120. This may follow well- established communication protocols.

The FSOC device 110 may correspondingly comprise a receiver 115 configured to receive a response communication 160 from the second communication device 120. Consequently, i.e. responsive to the receiver 115 receiving the response communication indicating that the second communication device has sensed the light beam, the beam steering system 112 may exit the acquisition mode. Thus, receipt of the response communication 160 by the FSOC device 110 may trigger the beam steering system 112 to exit the acquisition mode. This makes conceptual sense, as the response communication 160 indicates that the beam steering system 112 will have successfully completed its task of locating the beam sensing system 125 of the second communication device 120 (and therefore no longer needs to operate in the acquisition mode).

One example of a response communication is a second light beam, e.g., generated by a second light beam generator of the second device 120. In this way, the second device may effectively be a second FSOC device, so as to provide or facilitate bidirectional FSOC communication between the FSOC device 110 and the second device 120. A more detailed example of this approach is provided later in this description.

Another example of a response communication is a radiofrequency or microwave frequency signal, e.g., generated at an antenna of the response generating system 126 of the second device 120. This approach has the advantage of not requiring specific directionality in order to transmit a communication to the FSOC device 110. Thus, the antenna may be an omnidirectional transmitter of a radiofrequency or micro-wave frequency signal for providing the response communication 160.

Yet another example of a response communication is a wide-angle light beam, e.g., wider than the light beam. For instance, the response communication may be carried by a light output by an omnidirectional optical wide-angle transmitter of the response generating system 126. The receiver of the FCOS device 110 may monitor for the emission of such a light output by the second device 120 in a direction at which the light beam 150 is output by the FCOS device.

Yet another example of a response communication is an indirect communication, e.g., a communication via the internet or other interconnected network of devices. Thus, the response generating system 126 may comprise a transceiver for communicating with the receiver 115 of the FCOS device over an existing communication channel or network, such as the internet.

Of course, the response communication may follow standard security or encryption protocols. The FSOC device 110 may, for instance, only exit the acquisition mode if an expected response communication is received (e.g., a response according to an expected encryption technique or protocol). This can reduce spoofing of the second communication device and/or interception of communications between the FSOC device 110 and the second communication device 120.

However it is not essential that the second communication device 120 actively generate and provide a response communication to the FSOC device.

In one alternative example, the beam steering system 112 may continually operate in the acquisition mode, i.e., there is no indication from the second device 120 that the light beam has been successfully received. This may be useful, for instance, when the purpose of the communication between the FSOC device and the second communication device is to simply identify the existence/presence/location of the FSOC device. This technique could, for instance, be used to identify the location of a surface ship (carrying the FSOC device) to a submarine (carrying the second communication device).

In another alternative example, the second communication device 120 may comprise a retroreflector, such as a comer cube reflector (not shown). The light beam generated by the FSOC device 110 may be (partially) reflected by the retroreflector and sensed by the receiver 115 (e.g., a corresponding sensing apparatus) of the FSOC device 110. Receipt of the reflected light beam may trigger the exiting of the acquisition mode by the beam steering system 112. This provides a passive technique for monitoring successful directing of the beam output direction towards the second device.

The present disclosure provides an improvement to the steering of the beam output direction at least when the beam steering system 112 is operating in the acquisition mode. In particular, the present disclosure effectively proposes a new pattern of movement that exhibits improved speed, reliability and/or efficiency of directing the light beam 150 generated by the FSOC device 110 to be incident upon the beam sensing system 125 of the second communication device 120.

In the proposed approach, in the acquisition mode, the beam steering system 112 is configured to steer the beam output direction to follow a coarse sweeping pattern. The beam steering system is also configured to, when steering the beam output direction to follow the coarse sweeping pattern, iteratively deviate the beam output direction from the coarse sweeping pattern to iteratively follow a fine sweeping pattern that is superimposed on the coarse sweeping pattern.

The beam output direction thereby conceptually modulates a first (coarse) sweeping pattern with a second (fine) sweeping pattern. Thus, the second (fine) sweeping pattern is effectively modulated onto the first (coarse) sweeping pattern.

The proposed approach facilitates improved coverage of the light beam as it moves through the coarse sweeping pattern.

The fine sweeping pattern is defined by one or more sinusoidal functions. This approach allows for improved coverage of the area or zone swept by the light beam during the acquisition mode of the beam steering system.

A sweeping pattern is a pattern of movement that aims to search or cover an area or zone with the light beam. Thus, the term “sweeping pattern” can be replaced by the term “pattern of movement” or “search pattern”, where appropriate.

The beam steering system may steer the light beam to move at different speeds through the coarse and fine sweeping patterns. In particular, the beam steering system may control the beam output direction to move more than 3 times faster (preferably more than 10 times faster, preferably more than 20 times faster, more preferably more than 50 times faster and even more preferably more than 100 times faster) through the fine sweeping pattern than through the coarse sweeping pattern. This will ensure that the fine sweeping pattern is repeated a plurality of times as the beam is steered through the coarse sweeping pattern.

Similarly, it will be appreciated that the fine sweeping pattern is smaller than the coarse sweeping pattern. The fine sweeping pattern may, for instance, be no less than 5 times smaller than the coarse sweeping pattern, e.g., no less than 10 times smaller, e.g., no less than 100 times smaller.

The coarse sweeping pattern may comprise a series or sequence of passes, tracks or edges. A track or pass represents a route taken by the light beam before reaching a vertex of the coarse sweeping pattern. A pass, track or edge may be substantially parallel to a previous and/or later pass, track edge in the sequence of passes/tracks that make up the coarse sweeping pattern. Conceptually, it will be understood that this approach can facilitate thorough or complete searching of a particular region.

Preferably, the size of the fine sweeping pattern is selected such that the area or region covered by (iteratively) performing the fine sweeping pattern along any given pass/track/edge of the coarse sweeping pattern abuts or overlaps a region covered when (iteratively) performing the fine sweeping pattern along a parallel pass/track/edge of the coarse sweeping pattern. This helps ensure that an entire area is covered when performing the sweep or search with the light beam.

The size of the coarse and/or fine sweeping pattern may be responsive to the size/diameter/divergence of the light beam. The size of the light beam is effectively proportional to the spot size of the light beam (i.e., the size of the area illuminated by the light beam when incident upon a surface). The size of the coarse and/or fine sweeping pattern may therefore be similarly responsive to the spot size.

In particular, the size of the fine sweeping pattern may be increased when the size of the light beam increases. This is to reduce overlapping of the light beam with previously illuminated area by the light beam when performing the fine sweeping pattern, thereby avoiding redundant investigation of previously explored areas.

Corresponding, the size and/or configuration of the coarse sweeping pattern may be similarly adapted. For instance, the distance between different passes/tracks/edges of the coarse sweeping pattern may be increased responsive to the size of the light beam increasing.

In some examples, the location of the coarse sweeping pattern can be controlled by the FSOC device 110. The location may, for instance, refer to a location of the center of the coarse sweeping pattern with respect to the FSOC device.

In one approach, the FSOC device 110 is configured to predict a direction of the second communication device 120. This can be achieved, for instance, responsive to a communication or signal produced by the second communication device, such as an omnidirectional transmission of an electromagnetic signal (e.g., light or a radiofrequency signal) by the second communication device.

By way of example, the second communication device may provide a communication for the FSOC device, which can be received by the receiver 115 of the FSOC device and used to approximate or predict a direction of the second communication device. The center of the coarse sweeping pattern may be set or defined responsive to the approximated direction. This can significantly reduce the required size or area that needs to be searched using the coarse sweeping pattern.

Another approach can be for a user input to provide an approximated direction for the second device from the FCOS device. This approach can be used to facilitate a guided set-up of the FCOS device.

Accordingly, in some examples, if the direction of the second communication device from the first communication device has been predicted (e.g., using an above described approach) the size of the coarse sweeping pattern may be reduced from a scenario when no direction has been predicted.

Figure 2 conceptually illustrates one approach for steering or maneuvering the beam output direction, by the beam steering system, during the acquisition mode.

The beam output direction of the light beam is moved to generally follow the coarse sweeping pattern 210, which is here a raster or zig-zag pattern. A raster or zig-zag pattern iteratively moves the light beam along a sequence of parallel lines, to provide improved coverage of a search area.

In following the coarse sweeping pattern 210, the beam output direction iteratively deviates to follow a fine sweeping pattern 220.

One suitable example of a fine sweeping pattern 220 is a pattern defined using a Lissajous curve, an example of which is illustrated in Figure 2. Thus, the fine sweeping pattern may be characterized or plottable using a function defined using a Lissajous curve. Thus, if the fine sweeping pattern were to be plotted or projected onto a 2D plane to form a shape, the shape would be a Lissajous figure.

An alternative to a Lissajous curve is any other function that is definable using one or more sinusoidal functions, such as a pattern definable using a single sinusoidal wave or a plurality of sinusoidal waves.

Figure 2 also illustrates how the coarse sweeping pattern can be formed from a series or sequence of tracks/passes/edges. In particular, the light beam is controlled to iteratively move along parallel tracks/edges when following the coarse sweeping pattern.

Figure 3 illustrates an alternative approach for steering or maneuvering the beam output direction, by the beam steering system, during the acquisition mode.

The approach of Figure 3 differs from that of Figure 2 in that the coarse sweeping pattern 310 is instead a spiral sweeping pattern. The fine sweeping pattern 320 is again a pattern defined using a Lissajous curve. The illustrated spiral sweeping pattern for the coarse sweeping pattern 310 is a straight-line spiral, but may be replaced by any other form of spiral, such as a curved spiral (or spiral curve). The term “spiral” is used in the present disclosure to refer to any line or sequence of connected lines that get(s) increasingly distant from a central point with distance along the line or sequence of lines.

Such a sweeping pattern is particularly advantageous if, for example, a communication from a FSOC device to the second device is lost, and the FSOC device is attempting to regain the connection (as it can be assumed that the second device will be proximate to the previous location of the FSOC device).

Figure 3 provides another illustrative example of how the coarse sweeping pattern can be formed from a series or sequence of tracks/passes. In particular, each track/pass/edge of the spiral sweeping pattern is parallel to another track/pass/edge of the spiral sweeping pattern.

As previously explained, the beam steering system is configured (when operating in the acquisition mode) to control the beam output direction using the coarse sweeping pattern and the fine sweeping pattern. This control is configured such that the fine sweeping pattern is iteratively superimposed over the coarse sweeping pattern.

In one example, this can be performed by iteratively/sequentially moving or stepping the direction of the beam output direction such that it follows the coarse sweeping pattern. Thus, the beam output direction may be moved in a sequence of discrete steps to follow the coarse sweeping direction.

In this example, for each iterative moment or step of the beam output direction, the beam steering system steers the beam output direction to follow the fine sweeping pattern. In this way, the fine sweeping pattern is iteratively repeated each time the beam output direction moves a step along the coarse sweeping pattern. More particularly, the beam steering system may be configured to (temporarily) pause progress through the coarse sweeping pattern for each iterative step through the coarse sweeping pattern in order to perform at least one iteration of the fine sweeping pattern.

In this way, a space through which the beam is moved (during the acquisition mode) is conceptually divided into a set of subspaces. The beam is sequentially moved into each subspace in turn, following the coarse sweeping pattern. Each time the beam is moved into a different subspace, it is moved according to the fine sweeping pattern, i.e., to explore the sub-space. This provides an improved chance that the beam sensing arrangement of the second device will receive and sense the beam output by the FSOC device. During the coarse steps, the fine sweeping pattern motion is continued, to avoid delays in having to start and/or stop the fine sweeping pattern.

In an alternative example, the beam steering system may be configured to control the beam output direction to (on average) continually follow the coarse sweeping pattern. In this approach, the beam steering system will continually also control the beam output direction to follow the fine sweeping pattern.

Referring back to Figure 1, it has previously been described how, in some embodiments, the beam steering apparatus 112 of the FSOC device 410 can operate in the acquisition mode until a response communication 160 is received from the second device 120. This response communication can indicate that the light beam 150 output by the FSOC device 410 is aligned with the sensing arrangement 125 of the second device 120, i.e., has successfully found the second device.

Thus, the beam steering apparatus 112 may exit the acquisition mode responsive to receiving a response communication 160 from the second device.

When the beam steering apparatus 112 has exited the acquisition mode, it no longer performs the necessary steps for: steering the movement of the beam output direction to follow the coarse sweeping pattern; and, when steering the beam output direction to follow the coarse sweeping pattern, iteratively deviating the beam output direction from the coarse sweeping pattern to iteratively follow a fine sweeping pattern that is superimposed on the coarse sweeping pattern.

Thus, these steps may only be performed when the beam steering apparatus 112 operates in the acquisition mode. More particularly, when not operating in the acquisition mode, the beam steering apparatus 112 may be prevented from moving/steering the light beam along at least the coarse sweeping pattern.

In a preferred embodiment, the beam steering apparatus 112 may enter a tuning mode (after exiting the acquisition mode). When operating in the tuning mode, the beam steering apparatus may move the beam output direction to follow a fine tuning pattern.

The fine tuning pattern may be a sweeping or search pattern that is smaller than the fine sweeping pattern used in the acquisition mode. In particular, the fine tuning pattern may be defined by one or more sinusoidal functions, e.g., a Lissajous curve. For reduced storage/complexity, the fine tuning pattern may be a smaller or down-scaled version of the fine sweeping pattern.

The response communication 160 may carry signal strength information (e.g., light intensity) of the received light beam 150. The response communication 160 may be iteratively sent by the second device with updated signal strength information whilst the beam steering apparatus 112 is operating in the tuning mode.

The beam steering apparatus 112 may use this signal strength information to identify a beam output direction (within the fine tuning pattern) that provides the best signal strength intensity of the light beam to the second device. The beam steering apparatus may then set the beam output direction to be in a direction that achieves the best signal strength intensity of the light beam to the second device (i.e., the "best output direction”).

In some examples, when operating in the tuning mode, the beam steering apparatus 112 may be configured to iteratively repeat the fine tuning pattern, but re-centering the fine tuning pattern on the best output direction. In preferred approaches, the size of the fine tuning pattern is reduced each time it is repeated. This further optimizes the beam output direction, to further improve a signal strength of the light beam 150.

The beam steering apparatus may exit the fine tuning mode responsive to some predetermined criterion/criteria being met, e.g., a signal strength of the light beam reaching some predetermined value or reaching a local maximum. The signal strength may, for instance, be provided to the FSOC device 110 via a response communication 160 provided by the second device.

In the event that beam alignment is lost, as indicated in the response communication 160 or the loss of the response communication, the beam steering apparatus may re-enter the acquisition mode.

The technique of operating the beam steering system in the acquisition mode, and then the tuning mode effectively controls the beam output direction in a coarse-to-fine approach. This significantly improves the performance and signal strength between the FSOC device and the second communication device.

The beam steering apparatus may be operable in other or further modes, such as a tracking mode in which the light beam is steered to track a movement of the beam sensing apparatus of the second device.

A tracking mode may comprise, for instance, if a signal strength of the light beam reduces (e.g., as indicated in a response communication) moving the beam output direction according to a tracking pattern - such as one defined by one or more sinusoidal functions (e.g., a Lissajous curve). The tracking pattern may, for instance, be the same as the fine tuning pattern.

The beam steering apparatus may enter the tracking mode responsive, for example, the signal strength of the light beam failing to meet some predetermined criteria after it has previously met the predetermined criteria. Examples of suitable predetermined criterion/ criteria have been previously provided.

Another mode for the beam steering apparatus is an idle mode, in which the beam output direction is maintained. The beam steering apparatus may enter the idle mode responsive to a signal strength of the light beam (at the beam sensing apparatus of the second device) meeting some predetermined criteria. Examples of suitable predetermined criterion/ criteria have been previously provided e.g., a signal strength of the light beam reaching some predetermined value or reaching a local maximum.

Figure 4 illustrates another system 400 in which embodiments of the invention can be employed.

The system 400 comprises a first FSOC device 410 and a second FSOC device 420. The first FSOC device 410 comprises a first beam generator 411, a first beam steering system 412 and a first sensing arrangement 415. The second FSOC device 420 comprises a second beam generator 421, a second beam steering system 422 and a second sensing arrangement 425.

The system 400 is configured to operate as a bidirectional Free-Space Optical Communication system.

The components of the first FSOC device 410 and the second FSOC device 420 resemble those of the previously described FSOC device.

Thus, the first beam generator 411 is configured to generate a first light beam 451 carrying one or more communications for the second FSOC device. Similarly, the second beam generator 421 is configured to generate a second light beam 452 for carrying one or more communications for the first FSOC device 410. Suitable beam generators have been previously described.

The generation of the corresponding beam by each beam generator may be controlled (e.g., by a corresponding optional control system 419, 429) so as to encode information to be transmitted from the first/ second FSOC device 410, 420 to the other of the first/ second FSOC device, according to well-known principles.

The first beam steering system 412 is configured to control the beam output direction of the first light beam 451. The second beam steering system 422 is configured to control the beam output direction of the second light beam 452. Each beam steering system is operable in at least an acquisition mode, which may be embodied as previously described. The first beam sensing system 415 is configured to monitor for or sense the second light beam 452. Similarly, the second beam sensing system 425 is configured to monitor for or sense the first light beam 451.

The first beam sensing system 415 comprises at least a first beam sensor 415 A that detects the second light beam 452. In particular, the first beam sensor 415 A may generate an electric signal responsive to the second light beam such that a communication carried by the second light beam can be decoded (by decoding the second light beam).

Similarly, the second beam sensing system 425 comprises at least a second beam sensor 425 A that detects the first light beam 451. In particular, the second beam sensor 425 A may generate an electric signal responsive to the first light beam such that a communication carried by the first light beam can be decoded (by decoding the second light beam).

In this way, if the first light beam 451 is incident upon the second beam sensing system 425 and the second light beam 452 is incident upon the first beam sensing system 425, a bidirectional communication channel (that makes use of light beams, i.e., FSOC technology) is established between the first and second FSOC devices.

The first and second FSOC device may each perform the functions of the previously described FSOC device previously described, as well as (where appropriate for the other FSOC device), the functions of the second communication device. The first and second communication device may comprise appropriate circuitry for performing the same. These functions and/or components are not repeated for the sake of clarity.

The use of two FSOC devices (e.g., that are each searching for one another to establish a bidirectional communication channel) provides further opportunities for improvements and/or variations to approaches for beam steering, as set out below.

In particular, the beam steering arrangement of each FSOC device 410, 420 may be configured to, responsive to the beam sensing arrangement (of said device) receiving a light beam from the other FSOC device, redirect the light beam output by the said FSOC device towards the other FSOC device.

In particular, each beam sensing system 415, 425 may comprise a beam direction determiner 415B, 425B configured to determine a direction from which a light beam received by said beam sensing system 415, 425 is received. The beam direction determiner may, for instance, comprise a position sensitive device (PSD) or a quadrant photodetector (QPD), or a two-dimensional photodetector array. The beam steering arrangement of the corresponding FSOC device may use the determined direction to configure the light output direction to be directed towards the other FSOC device.

Put another way, once the beam from the other FSOC device is detected (an “incoming beam”), the beam direction determiner may provide the angle of the incoming beam to the beam steering arrangement. The beam steering arrangement may then immediately adjust the angle or direction of its own light beam such that it is pointed to the same angle as the incoming beam.

Thus, if the beam sensing system 415, 425 senses a beam from the other FSOC device 410, 420, then this detection may override the acquisition mode of the beam sensing system.

The beam direction determiner should have a sufficient field of view to be able to detect the incoming light incident angle when the light beam falls therein.

After redirecting the light beam towards the direction of the incoming beam, the beam steering system may enter the tuning mode.

In some examples, the response communication output by one FSOC device for use in controlling (in the other FSOC device) when the beam steering system of that other FSOC device exits the acquisition mode and/or provides information for use in the fine tuning mode (if performed) is a communication carried by a light beam output by the FSOC device.

In alternative examples, the response communication is carried by a different signal provided by the FSOC device, e.g., a radiofrequency or microwave frequency signal and/or an indirect signal such as an internet-based communication. The FSOC device(s) may be adapted accordingly, e.g., to have appropriate receivers, transmitters and/or transceivers.

Figure 5 is a flowchart 50 illustrating a method 500 according to an embodiment. The method is performed by an FSOC device, such as the FSOC device 110 illustrated in Figure 1 or the first/second FSOC device 410, 420 illustrated in Figure 4.

More particularly, the method 500 is a method of controlling a beam output direction of a light beam output by a beam generator of a Free-Space Optical Communication device. The light beam is configured for communicating with a second, different communication device comprising a beam sensing arrangement.

Method 500 effectively represents the procedure that is carried out by a/the beam steering system operating in the acquisition mode, as previously described.

The method 500 comprises a step 510 of steering the movement of the beam output direction to follow a coarse sweeping pattern (CSP). The method 500 further comprises a step 520 of (whilst steering the beam output direction to follow the coarse sweeping pattern) iteratively deviating the beam output direction from the coarse sweeping pattern to iteratively follow a fine sweeping pattern (FSP) that is superimposed on the coarse sweeping pattern.

Steps 510 and 520 are continually performed in parallel to one another.

The flowchart 50 illustrates further optional steps for methods according to further embodiments.

In particular, one proposed method comprises a step 530 of determining whether or not a response communication has been received (e.g., at a receiver) from a different communication device, such as a different FSOC device. Responsive to a response communication being received, the method may cause the beam steering system to exit the acquisition mode (i.e., stop performing steps 510, 520) in a step 590.

One proposed method comprises a step 540 of determining whether or not an incoming light beam (emitted by a different FSOC device) has been received at a beam sensing system. Responsive to detecting the presence of an incoming light beam, the method performs steps 545 and 590. Step 545 comprises redirecting or steering the light beam, using the beam steering system, emitted by the FSOC device towards a direction of the incoming light beam.

Responsive to a negative determination in steps 530 and/or 540 (if performed), the beam steering apparatus continues to operate in the acquisition mode, i.e., method 500 is continued.

In some embodiments, after performing step 590 (i.e., after exiting the acquisition mode), the method controls the beam steering apparatus to operate in a tuning mode 550.

When operating in the tuning mode 550, the beam steering apparatus is configured to move 551 the beam output direction according to a fine tuning pattern. Examples for a fine tuning pattern have been previously described.

The method then determines, in a step 552, whether there was an increased signal strength as a result of a beam output direction within the fine tuning pattern. This may comprise, for instance, receiving and analyzing a response communication from the different FSOC device.

Responsive to there being an increased signal strength, the method moves to step 553 of centering the fine tuning pattern at the beam output direction associated with the (largest) increased signal strength. The method may then revert back to repeating the fine tuning pattern.

In some examples, after performing step 553, the method may perform a step 554 of reducing the size of the fine tuning pattern, e.g., scaling the fine tuning pattern down. This approach aims to optimize or otherwise more accurately identify an optimal or improved beam output direction.

The method may repeat the steps of the tuning mode any number of times, e.g., up to a predetermined number of times, until a predetermined time period has elapsed and/or until a minimum signal strength level is reached.

The method may comprise, after the beam steering system exits the acquisition mode in step 590, determining whether or not there has been a loss or reduction of signal of the output light beam (in the other/different communication device). This may indicated in the absence of a response communication or by a signal strength carried by the response communication. This determination is performed in a step 560. If the beam steering system enters the tuning mode, step 560 may be performed after each iteration of steps 551-553 (and optional step 554).

Responsive to a positive determination in step 560, the beam steering system may re-enter the acquisition mode (i.e., the method may revert back to step 510). Otherwise, the method may revert back to step 551, if the tuning mode is used. If the tuning mode is not used, the method may continue to monitor for any signal loss (i.e., iteratively repeat step 560).

The skilled person would be readily capable of developing a processing system for carrying out any herein described method. Thus, each step of the flow chart may represent a different action performed by a processing system, and may be performed by a respective module of the processing system.

Embodiments may therefore make use of a processing system. The processing system can be implemented in numerous ways, with software and/or hardware, to perform the various functions required. A processor is one example of a processing system which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A processing system may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of processing system components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

In various implementations, a processor or processing system may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and/or processing systems, perform the required functions. Various storage media may be fixed within a processor or processing system or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or processing system.

It will be understood that disclosed methods are preferably computer- implemented methods. As such, there is also proposed the concept of a computer program comprising code means for implementing any described method when said program is run on a processing system, such as a computer. Thus, different portions, lines or blocks of code of a computer program according to an embodiment may be executed by a processing system or computer to perform any herein described method.

There is also proposed a non-transitory storage medium that stores or carries a computer program or computer code that, when executed by a processing system, causes the processing system to carry out any herein described method.

In some alternative implementations, the functions noted in the block diagram(s) or flow chart(s) may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. If a computer program is discussed above, it may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A Free-Space Optical Communication, FSOC, device (110) comprising: a beam generator (111) configured to generate a light beam (150) for communicating with a second, different communication device (120) comprising a beam sensing arrangement (125); and a beam steering system (112) configured to steer a beam output direction, being a direction in which the light beam is output by the beam generator, the beam steering system being operable in at least an acquisition mode, wherein, when operating in the acquisition mode: the beam steering system (112) is configured to steer the movement of the beam output direction to follow a continuous sweeping pattern corresponding with a superimposed coarse sweeping pattern (210, 310) and a continually repeated fine sweeping pattern (220, 320), whereby the beam output direction substantially follows the coarse sweeping pattern (210, 310) but deviates from the coarse sweeping pattern (210, 310) based on the superimposed fine sweeping pattern (220, 320); and wherein the fine sweeping pattern (310) is defined by one or more sinusoidal functions.

2. The Free-Space Optical Communication device (110) of claim 1, wherein the fine sweeping pattern (220, 320) is defined using a Lissajous curve.

3. The Free-Space Optical Communication device (110) of any of claims 1 or 2, wherein the size of the fine sweeping pattern (220, 320) is more than 10 times smaller than the coarse sweeping pattern (210, 310).

4. The Free-Space Optical Communication device (110) of any of claims 1 to 3, wherein the coarse sweeping pattern is a raster or zig-zag pattern (210).

5. The Free-Space Optical Communication device (110) of any of claims 1 to 3, wherein the coarse sweeping pattern is a spiral pattern (310).

6. The Free-Space Optical Communication device (110) of any of claims 1 to 5, wherein the speed of movement through the fine sweeping pattern is more than 3 times faster than the speed of movement through the coarse sweeping pattern.

7. The Free-Space Optical Communication device (110, 410) of any of claims 1 to 6, further comprising a receiver (115, 415) configured to receive a response communication from the second communication device (120, 420), wherein the beam steering system (112, 412) is configured to, responsive to the receiver (125, 425) receiving a response communication indicating that the second communication device (120, 420) has sensed the light beam, exit the acquisition mode.

8. The Free-Space Optical Communication device (410) of claim 7, wherein the receiver (415) is an FSOC beam sensing system configured to receive the response communication as a second light beam (452) output by the second communication device (420).

9. The Free-Space Optical Communication device (110) of claim 7, wherein the receiver (115) is a radiofrequency sensing system configured to receive the response communication (160) as a radiofrequency signal transmitted by the second communication device (120).

10. A Free-Space Optical Communication system (100) comprising: the Free-Space Optical Communication device (110) of any of claims 1 to 9 ; and the second communication device (120).

11. The Free-Space Optical Communication system (100, 400) of claim 10, wherein the second communication device (120,420) comprises a response generating system configured to generate and transmit a response communication to the Free-Space Optical Communication device (110,410) responsive to the beam sensing arrangement (125,425) sensing the light beam (150, 450).

12. The Free-Space Optical Communication system (400) of claim 11, wherein: the second communication device (420) further comprises a second beam generator (421) for generating a second light beam (452); the beam sensing arrangement (425) is configured to determine a direction from which the light beam (451) of the Free-Space Optical Communication device (410) is received by the beam sensing arrangement (425); and the second communication device (420) further comprises a second beam steering system (422) configured to direct the second light beam (452) towards the direction from which the light beam (451) of the Free-Space Optical Communication device (410) is received by the beam sensing arrangement.

13. The Free-Space Optical Communication system (400) of any of claims 10 to 12, wherein the second communication device (120,420) is a Free-Space Optical Communication device.

14. A computer-implemented method of controlling a beam output direction of a light beam output by a beam generator (111) of a Free-Space Optical Communication device (110), the light beam (150) being for communicating with a second, different communication device (120) comprising a beam sensing arrangement (125), the computer-implemented method comprising: steering the movement of the beam output direction to follow a continuous sweeping pattern corresponding with a superimposed coarse sweeping pattern (210, 310) and a continually repeated fine sweeping pattern (220, 320), whereby the beam output direction substantially follows the coarse sweeping pattern (210, 310) but deviates from the coarse sweeping pattern (210, 310) based on the superimposed fine sweeping pattern (220, 320) and wherein the fine sweeping pattern is defined by one or more sinusoidal functions.