A method for optical wireless beam alignment using multicore fiber

Abstract

An OWC subsystem (400) to establish bidirectional optical data communication with a remote OWC subsystem comprises: a bundle of fiber cores (405) arranged in a predetermined shape; an optical transceiver (401) to transmit and receive data beams via a first fiber core; an auxiliary beacon transmitter (402); at least two auxiliary beacon receivers (403) each to receive a respective beacon beam from the remote OWC subsystem via a respective fiber core; the fiber splitter (404) to split a beacon beam from the auxiliary beacon transmitter (402) into at least two transmit beacon beams and provide each of these transmit beacon beams to a respective fiber core; and a collimator (407) to focus the data and / or beacon beams from the remote OWC subsystem towards a common end core face (406) of the bundle (405) and collimate the data and / or transmit beacon beams from the common end core face (406).

Description

[0001] A method for optical wireless beam alignment using multicore fiber

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of optical wireless communication, such as Li-Fi communication. More particularly, various devices, systems, and methods are disclosed herein related to a secure optical wireless communication system.

[0004] BACKGROUND OF THE INVENTION

[0005] To enable more and more electronic devices like laptops, tablets, and smartphones to connect wirelessly to the Internet, wireless communication confronts unprecedented requirements on data rates and link qualities, and such requirements keep on growing year over year, considering the emerging digital revolution related to Intemet-of- things (loT). Radio frequency technology like Wi-Fi has limited spectrum capacity to embrace this revolution. In the meanwhile, light fidelity (Li-Fi) is drawing more and more attention with its intrinsic security enhancement and capability to support higher data rates over the available bandwidth in visible light, ultraviolet (UV), and infrared (IR) spectra. Furthermore, Li-Fi is directional and shielded by light blocking materials, which provides it with the potential to deploy a larger number of access points, as compared to Wi-Fi, in a dense area of users by spatially reusing the same bandwidth. These key advantages over wireless radio frequency communication make Li-Fi a promising secure solution to mitigate the pressure on the crowded radio spectrum for loT applications and indoor wireless access. Other possible benefits of Li-Fi may include guaranteed bandwidth for a certain user, and the ability to function safely in areas otherwise susceptible to electromagnetic interference. Therefore, Li-Fi is a very promising technology to enable the next generation of immersive connectivity.

[0006] To achieve a high data throughput in short-range point-to-point optical links, a narrow beam transmitter source is used, together with a small low capacitance photoreceiver. Due to this narrow beam characteristic, a precise alignment between transmitter and receiver is necessary. For non-static systems, this may be solved by different types of electromechanical actuators and beam tracking methods. One low-cost and compact method for optical beam tracking can be realized with an additional low-frequency beacon transmitter. This system operates properly when there is a long separation distance between the optical transmitter and the optical receiver. For short distances, due to the high-speed optical transceiver being physically separated from the low-frequency beacon-based tracking system, the deviation in the tracking can be significant due to near-field transmission characteristics. To solve this problem, the units can be calibrated to compensate for the deviation for a specific communication distance d. However, the calibration will only work for systems that operate at a fixed communication distance and not for fully dynamic ones.

[0007] US2020366371A1 relates to systems and methods for providing high throughput connectivity between multiple network nodes, such as satellites in Earth orbit or ground stations, using a multi-access free space optical communications transceiver. The transceiver includes a focal plane assembly with an array of moveable optical fibers or fiber bundles, multi-core fibers, or a combination thereof. Each optical fiber bundle may include a centrally located data fiber with guide fibers disposed around the data fiber.

[0008] US5777768A relates to a method for establishing a laser link communications system in free space, which includes first and second terminals that are distanced from each other on an optical path. Each terminal includes a plurality of laser transmitters which together generate a plurality of laser beams, with each of the laser beams carrying a communication signal.

[0009] US2022107473A1 relates to a free-space optical communication device including an optical fiber bundle and one or more processors. The optical fiber bundle includes a central fiber connected to a first photodetector, and a plurality of surrounding fibers, each surrounding fiber connected to a corresponding second photodetector.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention aims to solve the problem of reducing, in a high-speed narrow beam optical communication (sub)system, arrangement constraints for discrete data and beacon / pilot transceivers (or transmitters / receivers), including associated optics, used for beam alignment and acquisition, pointing and tracking, while enhancing compactness of the high-speed narrow beam optical communication (sub)system.

[0012] In view of the above, the present invention is directed to an optical wireless communication, OWC, subsystem as claimed in claim 1, by an OWC system as claimed in claim 13, and by a method as claimed in claim 14. In accordance with a first aspect of the invention, an OWC subsystem is provided. The OWC subsystem, which is configured to establish bidirectional optical data communication with a remote OWC subsystem for point-to-point narrow beam optical wireless communication, comprises: a bundle of fiber cores comprising a common end core face facing a collimator; an optical transceiver configured to transmit to the remote OWC subsystem and receive from the remote OWC subsystem, respective transit and receive data beams via a first fiber core of the bundle; an auxiliary beacon transmitter configured to provide a beacon beam to a fiber splitter; at least two auxiliary beacon receivers each configured to receive a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle; the fiber splitter directly coupled to at least the auxiliary beacon transmitter, and configured to split the beacon beam from the auxiliary beacon transmitter into at least two transmit beacon beams with each transmit beacon beam having a same amount of output power and provide each of the at least two transmit beacon beams to a respective fiber core of the bundle; and the collimator configured to focus the data and / or beacon beams received from the remote OWC subsystem towards the common end core face, and to collimate the data and / or at least two transmit beacon beams from the common end core face for transmission towards the remote OWC subsystem, wherein the fiber cores of the bundle are arranged in a predetermined shape, and wherein the beacon beams are used for bidirectional beam alignment between the OWC subsystem and the remote OWC subsystem, such that the alignment of the OWC subsystem (400) with the remote OWC subsystem is obtained when a respective amount of optical power received at each of the fiber cores carrying the beacon beams from the remote OWC subsystem is determined to be equal.

[0013] Thus, instead of using a specific arrangement of discrete beacon / pilot beam transmitters and receivers, including associated optics, located, e.g., symmetrically around the aperture of the data beam from a discrete optical transceiver, a bundle of fiber cores is used such that the different cores of the bundle serve the different purposes of an alignment procedure based on beacon / pilot and data transmission and reception / detection. Thereby, the arrangement constraints for these discrete devices can be avoided in the context of the alignment procedure by transferring these arrangement constraints to the bundle of fiber cores that are then required to be arranged in a predetermined shape. Easier electromagnetic compatibility (EMC) shielding and better usage of existing space due to intrinsic flexibility of the fiber core may thus be obtained.

[0014] Advantageously, the predetermined shape of said fiber core arrangement may be defined by different arrangements of the fiber cores carrying the transmit beacon beams and the fiber cores carrying the beacon beams from the remote OWC subsystem respectively around the first fiber core carrying the respective transmit and receive data beams. Thereby, the arrangement constraints may be directed to the fiber cores and not to the discrete auxiliary beacon transmi tter / recei vers and discrete optical transceiver.

[0015] Advantageously, the different arrangements may comprise a symmetrical arrangement and / or an arrangement based on circle-packing-in-a-circle problem. Thereby, the fiber cores carrying the transmit beacon beams and the fiber cores carrying the beacon beams from the remote OWC subsystem may be symmetrically arranged around the first fiber core, and / or the fiber cores carrying the transmit beacon beams and the fiber cores carrying the beacon beams from the remote OWC subsystem may be arranged to enhance compactness based on the circle packing in a circle. It is noted that, although the two- dimensional circle packing is directed to packing of unit circles into the smallest possible larger circle, the fiber cores (corresponding to the smaller circles) of the bundle (corresponding to the larger circle inside which the smaller circles are packed) may have any diameter of a same or different size.

[0016] Preferably, the symmetrical arrangement may define, at the common end core face, at least one of a round data beam and oval beacon beam arrangement, an oval data beam and round beacon beam arrangement, and a round data beam and round beacon beam arrangement.

[0017] Advantageously, the first fiber core carrying the respective transmit and receive data beams may be placed at the center of the bundle. Thereby, the position of the first fiber core at the common end core face facing the collimator may be predetermined to be advantageously used by the collimator for mitigating any data beam divergence.

[0018] Advantageously, the first fiber core at the common end core face may be placed at the focal point of the collimator. Thereby, lowest data beam divergence may be achieved. Preferably, the bundle of fiber cores may comprise an optical multi-core fiber or a bundle of multiple optical single-core fibers.

[0019] Preferably, the collimator may comprise an imaging optical part or a nonimaging optical part or a combination thereof. For example, the collimator may comprise a normal lens or an optical system like an air space doublet or a coaxial optics.

[0020] Preferably, each of the at least two auxiliary beacon receivers at least may comprise one of a photodiode, a camera sensor (e.g., a CMOS or InGaAs image sensor), an endoscopic sensor, a silicon photomultiplier (SiPM) and a single photon avalanche diode (SPAD). It is noted that the photodiode may also designate a light detector, a photodetector or a photoelectric sensor, which may be a PIN diode, an avalanche photodiode (APD), or a photomultiplier, and that an array of SiPMs may be an array of SPADs connected in parallel.

[0021] Preferably, the fiber cores carrying the beacon beams from the remote OWC subsystem may be coupled to the at least two auxiliary beacon receivers. Thereby, two options are possible. In the first option, said coupling may be carried out “directly”, i.e., without passing through the fiber splitter when an amount of those fiber cores carrying the beacon beams from the remote OWC subsystem is equal to an amount of these auxiliary beacon receivers. In this first option, each of the fiber cores carrying the beacon beams from the remote OWC subsystem is directly coupled to a respective auxiliary beacon receiver (i.e., in a coupling ratio of 1 : 1). In the second option, said coupling may be carried out “indirectly”, i.e., through the fiber splitter, when an amount of those fiber cores carrying the beacon beams from the remote OWC subsystem is different from an amount of these auxiliary beacon receivers. In this second option, splitting is then needed and the fiber splitter may be directly coupled to the auxiliary beacon receivers.

[0022] Advantageously, the OWC subsystem may comprise an actuator system configured to steer the transmit data beam and / or the transmit beacon beams. Steering may be achieved using fast steering mirrors (FSM’s), voice-coil mirrors, prisms, and so on.

[0023] Advantageously, the optical transceiver and at least three of the at least two auxiliary beacon receivers may be further configured to detect an angle of incidence of the respective data and beacon beams from the remote OWC subsystem based on at least the predetermined shape of said fiber core arrangement at the common end core face. Thus, in the example case of three auxiliary beacon receivers, the corresponding three fiber cores carrying their respective beacon beam from the remote OWC subsystem may be spaced two by two at an angle of 120 degrees at the common end core face. In the example case where a fast steering system for steering the data and beacon beams received from the remote OWC is used in combination with the possibility to detect the angle of incidence, the corresponding steering algorithm does not have to determine the beam position based on the maximum received optical power. Instead, it steers directly in the direction of the received beam and therefore enables a faster response when finding and tracking a beam.

[0024] Advantageously, the alignment of the OWC subsystem with the remote OWC subsystem may be obtained when a respective amount of optical power received at each of the fiber cores carrying the beacon beams from the remote OWC subsystem is determined to be equal.

[0025] In accordance with a second aspect of the invention, an OWC system is provided. The OWC system comprises: an OWC subsystem according to the first aspect or any combinations of the first aspect, that is configured to establish bidirectional optical data communication with a remote OWC subsystem for use in bidirectional beam alignment; and the remote OWC subsystem, wherein the OWC subsystem and the remote OWC subsystem are configured to comprise all other components of each other.

[0026] Thus, it is beneficial that the OWC system and the remote OWC system are identical to allow the beam alignment procedure to be implemented by both sides.

[0027] In accordance with a third aspect of the invention, a method performed at an OWC subsystem for establishing bidirectional optical data communication with a remote OWC subsystem for point-to-point narrow beam optical wireless communication is provided, wherein the OWC subsystem comprises an optical transceiver, at least two auxiliary beacon receivers, an auxiliary beacon transmitter, a fiber splitter directly coupled to at least the auxiliary beacon transmitter, a bundle of fiber cores comprising a common end core face facing a collimator, and the collimator. The method comprises: transmitting and receiving, by the optical transceiver, respective transmit and receive data beams via a first fiber core of the bundle, respectively to and from the remote OWC subsystem; providing, by the auxiliary beacon transmitter, a beacon beam to the fiber splitter; receiving, by the two auxiliary beacon receivers, a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle; splitting, by the fiber splitter, the beacon beam from the auxiliary beacon transmitter into at least two transmit beacon beams with each transmit beacon beam having a same amount of output power; providing, by the fiber splitter, each of the at least two transmit beacon beams to a respective fiber core of the bundle; and focusing, by the collimator, the data and / or beacon beams received from the remote OWC subsystem towards the common end core face, and collimating, by the collimator, the data and / or at least two transmit beacon beams from the common end core face for transmission towards the remote OWC subsystem, wherein the fiber cores of the bundle are arranged in a predetermined shape, and wherein the beacon beams are used for bidirectional beam alignment between the OWC subsystem and the remote OWC subsystem, such that the alignment of the OWC subsystem (400) with the remote OWC subsystem is obtained when a respective amount of optical power received at each of the fiber cores carrying the beacon beams from the remote OWC subsystem is determined to be equal.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings, like reference characters generally refer to the same parts throughout the different figures. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the present invention.

[0030] FIG. 1 shows an example of a beam alignment setup according to prior art;

[0031] FIG. 2 shows an example of a control loop in an apparatus according to prior art;

[0032] FIG. 3 shows an example of a schematic free space optical communication system according to prior art;

[0033] FIG. 4 shows an example of an OWC subsystem according to the present invention;

[0034] FIG. 5 shows an example of different fiber core arrangements at a common end core face, according to the present invention;

[0035] FIG. 6 shows an example of scenario when an optical spot is received at the common end core face, according to the present invention;

[0036] FIG. 7 shows an example of flow chart of a method performed at an OWC subsystem, according to the present invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0037] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

[0038] To achieve a high data throughput in short-range point-to-point optical wireless communication, a narrow beam transmitter source is typically used, together with a small low capacitance (photo)receiver. Due to this narrow beam characteristics, a precise alignment between transmitter and receiver is necessary. For non-static systems, this requires different types of electromechanical actuators and beam tracking methods.

[0039] FIG. 1 shows an example of a beam alignment setup according to prior art. As illustrated, the point-to-point narrow beam OWC system 100 comprises two (first and second) identical OWC units 101, 102 that are placed facing each other. For clarity purposes, only the main components 103-107 of the first optical wireless unit 101 are demonstrated, the facing second OWC unit 102 correspondingly comprising the same main components 103- 107. The high-speed optical wireless transceiver 107, which comprises a narrow beam emitter and receiver, is placed in the center of the board or surface of the first OWC unit 101. Two auxiliary beacon transmitters 105, 106, which are configured to send low-frequency beacon signals with the same amount of output power, are placed next to the optical transceiver 107 with an equal distance b = b’ from the optical wireless transceiver 107, while two auxiliary four-quadrant (photo)receivers 103, 104, which are configured to detect the beacons from the facing OWC unit 102 for beam alignment, are placed next to the optical wireless transceiver 107 with an equal distance a = a’. Mechanical actuators (not shown in FIG. 1) will move each complete OWC unit 101, 102 independently in the x (roll)-y (pitch) axis to align the optical wireless transceiver 107 with the matching optical wireless transceiver 107 of the facing optical wireless communication unit 102- according to the received signal that is tracked in the two auxiliary four-quadrant (photo)receivers 103, 104 coming from the facing OWC unit 102.

[0040] As illustrated in FIG. 2 showing an implementation example of a control loop 200 in the OWC unit 101, 102 according to prior art, the signals received on the respective quadrants of the two auxiliary four-quadrant (photo)receivers 103, 104 are summed. This, together with the use of two auxiliary beacon transmitters used in the facing OWC unit 102 to generate the same beacon, will compensate for the tracking deviation produced by the physical separation between the auxiliary beacon transmitters / auxiliary four-quadrant (photo)receivers and the high-speed optical wireless transceiver.

[0041] The sum of the signals from the two four-quadrant (photo)receivers 103, 104 generates four signals, which are fed into analog-to-digital converters (ADCs) in a controller 201 of the OWC unit 101. This controller 201 will process the signals to generate error vectors and create a closed control loop with the mechanical actuator 202. The actuator will stop when the error is below a certain threshold or close to zero with a predefined tolerance, thereby resulting in an alignment of the two OWC units 101, 102.

[0042] With respect to this point-to-point narrow beam OWC system 100, the solution of the present invention may present the following benefits: enhancing compactness by using the existing and needed collimator for focusing and collimating together the data and beacon beams; removing the constraints of placing the discrete beacon transmitter / receivers and optical transceiver in a specific arrangement, e.g., placing the discrete beacon transmitter and receivers symmetrically around the discrete optical transceiver, thereby allowing for an easier EMC shielding and a better usage of existing space due to the flexibility of the fiber; using smaller optically and electromechanically devices for steering the combined the beacon and data beams as these combined beams are collimated together by the collimator; avoiding the use of a costly beam splitter and other optical components that are used for the combination or separation of beacon and data beams; avoiding the use of an internal optical feedback mechanism in the auxiliary beacon transmitters of each unit for compensating for the difference in optical power due to LED / Laser binning and ageing, as one LED can be used by being connected to two fiber cores or a fiber splitter; manipulating characteristics (difference, beam shape) of the data and beacon beams by choosing a dedicated arrangement of the fiber cores at the end core face located in the area surrounding the focal point of the collimator.

[0043] FIG. 3 shows an example of a schematic free space optical (FSO) communication system 300 according to prior art. This schematic FSO communication system 300 is derived from a telescope control system as illustrated in: Qing Li et al, improved method for the position detection of a quadrant detector for free space optical communication”, Sensors 2019 (online published by MDPI), 19(1), 175, The FSO communication system 300, which is provided on each optical communication terminal (OCT), comprises a telescope 301, a fast steering mirror (FSM) 302 for combining a beam of light from the telescope 301, a beam splitter 303 with a half-mirror for splitting the combined beam of light into a reflected beacon beam as a beacon light independently received by each quadrant of a four-quadrant detector (QD) 304 and a transmitted data beam received by a data receiver 305, and a FSM control loop comprising an amplifier 306 for amplifying the respective photocurrent output from each quadrant of the QD 304 and whose amplitude corresponding to the energy of the beacon light respectively illuminates each quadrant, an analog-to-digital converter 307, a position calculation module 308 for estimating the beacon light according to the ratio of the photocurrent amplitudes, a controller 309, and a FSM driver 310 for driving the FSM 302.

[0044] With respect to this FSO communication system 300 using conventional beam splitter and (half-)mirrors approach, the solution of the present invention may present the following benefit: avoiding the use of a beam splitter and thereby, the additional use of absorptive materials needed to absorb optical power in specific branches and parts in order to minimize any misinterpretation by the beacon / pilot receiver.

[0045] FIG. 4 shows an example of an OWC subsystem 400 according to the present invention. In this setup, the OWC subsystem 400 is placed facing a remote identical OWC subsystem (not shown in FIG. 4) for establishing bidirectional optical data communication. The main components of the OWC subsystem 400 comprise: a bundle of fiber cores 405 comprising a common end core face 406 facing a collimator 407; an optical transceiver 401 configured to transmit to the remote OWC subsystem and receive from the remote OWC subsystem, respective transmit and receive data beams via a first fiber core of the bundle 405; an auxiliary beacon transmitter 402 configured to provide a beacon beam to a fiber splitter 404; at least two auxiliary beacon receivers 403 each configured to receive a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle 405; the fiber splitter 404 directly coupled to at least the auxiliary beacon transmitter 402, and configured to split the beacon beam from the auxiliary beacon transmitter 402 into at least two transmit beacon beams and provide each of the at least two transmit beacon beams to a respective fiber core of the bundle 405; and the collimator 407 configured to focus the data and / or beacon beams received from the remote OWC subsystem towards the common end core face 406, and to collimate the data and / or at least two transmit beacon beams from the common end core face 406 for transmission towards the remote OWC subsystem. The fiber cores of the bundle 405 are arranged in a predetermined shape, and the beacon beams are used for bidirectional beam alignment between the OWC subsystem 400 and the remote OWC subsystem.

[0046] The optical transceiver 401 may be an optical wireless high-speed transceiver used for high speed data communication, that may preferably comprise a narrow beam light source for data beam transmission. The light source may be one of a light-emitting diode (LED), a laser diode, a vertical-cavity surface-emitting laser (VCSEL), or an edge emitting laser diode (EELD). Preferably, the optical transceiver 401 may comprise at least one of a LED and a VCSEL, and the auxiliary beacon transmitter 402 may comprise a LED. The auxiliary beacon transmitter 402 and each auxiliary beacon receiver 403 may be a respective narrow beam emitter and receiver, which uses beacon / pilot light transmission and reception for beam alignment and acquisition, pointing and tracking. Beam angle or beam width is the aperture angle from where most of the power is radiated. For example, the half power beam width is the angle between the half-power (-3dB) points of the main lobe of the radiation pattern. For the horizontal plane, beam angle or beam width is usually expressed in degrees. A beam angle of 10 degrees or less is typically considered to be narrow.

[0047] The fiber splitter 404 may be directly coupled to the optical transceiver 401 in the case where it is needed to split the transmit data beam into at least two transmit data beams and provide each of them to a respective first fiber core of the bundle 405.

[0048] In an example, the fiber splitter 404 may be directly coupled to the at least two auxiliary beacon receivers 403, provided that the amount of those fiber cores carrying the beacon beams from the remote OWC subsystem differs from the amount of the at least two auxiliary beacon receivers 403. Thereby, the fiber cores carrying the beacon beams from the remote OWC subsystem are coupled to the at least two auxiliary beacon receivers “indirectly”, i.e., by passing through the fiber splitter 404.

[0049] In an alternative example, the fiber splitter 404 may be not coupled to the at least two auxiliary beacon receivers 403, provided that the amount of those fiber cores carrying the beacon beams from the remote OWC subsystem equals the amount of the at least two auxiliary beacon receivers 403. Thereby, each of the fiber cores carrying the beacon beams from the remote OWC subsystem is coupled to a respective auxiliary beacon receiver 403 (i.e., in a coupling ratio of 1: 1) “directly”, i.e., without passing through the fiber splitter 404. To illustrate such an alternative example, FIG. 4 shows the bottom outline of the depicted fiber splitter 404 facing the auxiliary beacon receiver 403 with a dashed line. The bundle of fiber cores 405 may comprise an optical multi-core fiber or a bundle of multiple optical single-core fibers.

[0050] The collimator 407 may comprise an imaging optical part or a non-imaging optical part or a combination thereof. For example, the collimator 407 may comprise a normal lens or an optical system like an air space doublet or a coaxial optics.

[0051] FIG. 5 shows an example of different fiber cores arrangements 500 A, 500B, 500C at the common end core face 406, according to the present invention. As illustrated, each fiber core is associated with a dedicated function of transmission (TX) and / or reception (RX) of data and beacon beams. The fiber core arrangements 500A, 500B, 500C are symmetrical and comprise a round data beam and oval beacon beam arrangement 500A, an oval data beam and round beacon beam arrangement 500B, and a round data beam and round beacon beam arrangement 500C. Those skilled in the art will understand that other types of fiber core arrangements at the end core face 406 may be possible. For example, the fiber core arrangement may be based on the well-known circle-packing-in-a-circle problem directed to packing of unit circles into a smallest possible larger circle. In the present invention, the fiber cores may correspond to the smaller circles, the bundle 405 may correspond to the larger circle inside which the smaller circles are packed, and the fiber cores may have any diameter of a same or different size.

[0052] FIG. 6 shows an example of scenario when an optical spot is received at the common end core face 406, according to the present invention. In this example, the arrangement of the fiber cores TX carrying the transmit beacon beams (Beacon TX) and the fiber cores RX1, RX2, RX3 carrying the beacon beams (Beacon RX1 to Beacon RX3) from the remote facing OWC subsystem is respectively around the first fiber core TRX carrying the respective transmit and receive data beams (Data TRX), thereby defining a symmetrical fiber core arrangement. As depicted by a dashed grey circle, an optical spot transmitted from an auxiliary beacon transmitter 402 at the remote OWC subsystem is received at a location corresponding to the focal point of the collimator 407. Each fiber core carrying the beacon beams (Beacon RX1 to Beacon RX3) is assumed to be directly coupled to a respective auxiliary beacon receiver 403, e.g., a respective photodiode, for detecting the optical power transmitted by the optical spot. As shown in FIG. 6, the optical spot is not perfectly centered with respect to the first fiber core placed at the center of the bundle 405, so that the optical power is not equally received at the fiber cores RX1, RX2, and RX3. It results from said received optical power difference that the OWC subsystem 400 and the remote OWC subsystem are not (perfectly) aligned in the example of FIG. 6. It is noted that the received optical power difference may be also used by the auxiliary beacon receivers 403, e.g., the photodiodes, to determine a coarse value of an angle of incidence of the beams received from the remote OWC subsystem.

[0053] FIG. 7 shows an example of flow chart of a method 700 performed at an OWC subsystem 400 for establishing bidirectional optical data communication with a remote OWC subsystem, according to the present invention. The OWC subsystem 400 comprises an optical transceiver 401, an auxiliary beacon transmitter 402, at least two auxiliary beacon receivers 403, a fiber splitter 404 directly coupled to at least the auxiliary beacon transmitter 402, a bundle of fiber cores 405 comprising a common end core face 406 facing a collimator 407, and the collimator 407. The method 700 comprises the steps of: transmitting, in step S701, by the optical transceiver 401, a transmit data beam to the remote OWC subsystem via a first fiber core of the bundle 405, and receiving, in step S701’, by the optical transceiver 401, a receive data beam from the remote OWC subsystem via the first fiber core of the bundle 405; receiving, in step S702, by the two auxiliary beacon receivers 403, a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle 405; providing, in step S703, by the auxiliary beacon transmitter 402, a beacon beam to the fiber splitter 404; splitting, in step S704, by the fiber splitter 404, the beacon beam from the auxiliary beacon transmitter 402 into at least two transmit beacon beams; providing, in step S705, by the fiber splitter 404, each of the at least two transmit beacon beams to a respective fiber core of the bundle 405; and focusing, in step S706, by the collimator 407, the data and / or beacon beams received from the remote OWC subsystem towards the common end core face 406, and collimating, in step S706’, by the collimator 407, the data and / or at least two transmit beacon beams from the common end core face 406 for transmission towards the remote OWC subsystem, wherein the fiber cores of the bundle 405 are arranged in a predetermined shape, and wherein the beacon beams are used for bidirectional beam alignment between the OWC subsystem 400 and the remote OWC subsystem.

[0054] The method 700 according to the invention may be implemented on a computer as a computer implemented method, or in dedicated hardware, or in a combination of both. Executable code for the method 700 according to the invention may be stored on computer / machine readable storage means. Examples of computer / machine readable storage means include non-volatile memory devices, optical storage medium / devices, solid- state media, integrated circuits, servers, etc. Preferably, the computer program product comprises non-transitory program code means stored on a computer readable medium for performing the method 700 according to the invention when said program product is executed on a computer.

[0055] Methods, systems, and computer-readable media (transitory and non- transitory) may also be provided to implement selected aspects of the above-described embodiments.

Claims

CLAIMS:

1. An optical wireless communication, OWC, subsystem (400) configured to establish bidirectional optical data communication with a remote OWC subsystem for point- to-point narrow beam optical wireless communication, the OWC subsystem (400) comprising: a bundle of fiber cores (405) comprising a common end core face (406) facing a collimator (407); an optical transceiver (401) configured to transmit to the remote OWC subsystem and receive from the remote OWC subsystem, respective transmit and receive data beams via a first fiber core of the bundle (405); an auxiliary beacon transmitter (402) configured to provide a beacon beam to a fiber splitter (404); at least two auxiliary beacon receivers (403) each configured to receive a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle (405); the fiber splitter (404) directly coupled to at least the auxiliary beacon transmitter (402), and configured to split the beacon beam from the auxiliary beacon transmitter (402) into at least two transmit beacon beams with each transmit beacon beam having a same amount of output power and provide each of the at least two transmit beacon beams to a respective fiber core of the bundle (405); and the collimator (407) configured to focus the data and / or beacon beams received from the remote OWC subsystem towards the common end core face (406), and to collimate the data and / or at least two transmit beacon beams from the common end core face (406) for transmission towards the remote OWC subsystem, wherein the fiber cores of the bundle (405) are arranged in a predetermined shape, and wherein the beacon beams are used for bidirectional beam alignment between the OWC subsystem (400) and the remote OWC subsystem, such that the alignment of the OWC subsystem (400) with the remote OWC subsystem is obtained when a respectiveamount of optical power received at each of the fiber cores carrying the beacon beams from the remote OWC subsystem is determined to be equal.

2. The OWC subsystem of claim 1, wherein the predetermined shape of said fiber core arrangement is defined by different arrangements of the fiber cores carrying the transmit beacon beams and the fiber cores carrying the beacon beams from the remote OWC subsystem respectively around the first fiber core carrying the respective transmit and receive data beams.

3. The OWC subsystem of claim 2, wherein the different arrangements comprise a symmetrical arrangement and / or an arrangement based on circle-packing-in-a-circle problem.

4. The OWC subsystem (400) of claim 3, wherein the symmetrical arrangement defines, at the common end core face (406), at least one of a round data beam and oval beacon beam arrangement (500A), an oval data beam and round beacon beam arrangement (500B), and a round data beam and round beacon beam arrangement (500C).

5. The OWC subsystem (400) of any of the preceding claims, wherein the first fiber core carrying the respective transmit and receive data beams is placed at the center of the bundle (405).

6. The OWC subsystem (400) of any of the preceding claims, wherein the first fiber core at the common end core face (406) is placed at the focal point of the collimator (407).

7. The OWC subsystem (400) of any of the preceding claims, wherein the bundle of fiber cores (405) comprises an optical multi-core fiber or a bundle of multiple optical single-core fibers.

8. The OWC subsystem (400) of any of the preceding claims, wherein the collimator (405) comprises an imaging optical part or a non-imaging optical part or a combination thereof.

9. The OWC subsystem (400) of any of the preceding claims, wherein each of the at least two auxiliary beacon receivers (403) at least comprises one of a photodiode, a camera sensor, an endoscopic sensor, a silicon photomultiplier and a single photon avalanche diode.

10. The OWC subsystem (400) of claim 9, wherein the fiber cores carrying the beacon beams from the remote OWC subsystem are coupled to the at least two auxiliary beacon receivers (403).

11. The OWC subsystem (400) of any of the preceding claims, further comprising an actuator system configured to steer the transmit data beam and / or the transmit beacon beams.

12. The OWC subsystem (400) of any of the preceding claims, wherein the optical transceiver (401) and at least three of the at least two auxiliary beacon receivers (403) are further configured to detect an angle of incidence of the respective data and beacon beams from the remote OWC subsystem based on at least the predetermined shape of said fiber core arrangement at the common end core face (406).

13. An OWC system, comprising: an OWC subsystem (400) according to any of the preceding claims configured to establish bidirectional optical data communication with a remote OWC subsystem for use in bidirectional beam alignment; and the remote OWC subsystem, wherein the OWC subsystem (400) and the remote OWC subsystem are configured to comprise all other components of each other.

14. A method (700) performed at an OWC subsystem (400) for establishing bidirectional optical data communication with a remote OWC subsystem for point-to-point narrow beam optical wireless communication, the OWC subsystem (400) comprising an optical transceiver (401), an auxiliary beacon transmitter (402), at least two auxiliary beacon receivers (403), a fiber splitter (404) directly coupled to at least the auxiliary beacon transmitter (402), a bundle of fiber cores (405) comprising a common end core face (406) facing a collimator (407), and the collimator (407), the method (700) comprising:transmitting (S701) and receiving (S70F), by the optical transceiver (401), respective transmit and receive data beams via a first fiber core of the bundle (405), respectively to and from the remote OWC subsystem; providing (S702), by the auxiliary beacon transmitter (402), a beacon beam to the fiber splitter (404); receiving (S703), by the two auxiliary beacon receivers (403), a respective beacon beam from the remote OWC subsystem via a respective fiber core of the bundle (405); splitting (S704), by the fiber splitter (404), the beacon beam from the auxiliary beacon transmitter (402) into at least two transmit beacon beams with each transmit beacon beam having a same amount of output power; providing (S705), by the fiber splitter (404), each of the at least two transmit beacon beams to a respective fiber core of the bundle (405); and focusing (S706), by the collimator (407), the data and / or beacon beams received from the remote OWC subsystem towards the common end core face (406), and collimating (S706’), by the collimator (407), the data and / or at least two transmit beacon beams from the common end core face (406) for transmission towards the remote OWC subsystem, wherein the fiber cores of the bundle (405) are arranged in a predetermined shape, and wherein the beacon beams are used for bidirectional beam alignment between the OWC subsystem (400) and the remote OWC subsystem, such that the alignment of the OWC subsystem (400) with the remote OWC subsystem is obtained when a respective amount of optical power received at each of the fiber cores carrying the beacon beams from the remote OWC subsystem is determined to be equal.

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