Pilot light offset compensation method in optical wireless communication system

Abstract

An optical receiver (300) comprising: a photodetector (310) configured to detect a data beam transmitted by an optical transmitter (200); at least two pilot light sources (321, 322) configured to emit pilot light to assist a beam alignment process performed by the optical emitter (200); wherein at least two pilot light sources are placed on different sides of the photodetector (310); a controller (330) configured to determine an individual pilot light intensity for each of the pilot light sources based on the received beam intensity of the data beam detected by the photodetector (310), and to control each of the pilot light sources to emit pilot light in accordance with the determined corresponding individual pilot light intensity, the pilot light sources (321, 322) are arranged such that the center of gravity of the combined pilot light intensity of the pilot light sources (321, 322) provides an indication to the optical emitter (200) regarding the desired direction of movement of the data beam.

Description

Technical Field

[0002] This invention relates to the field of free-space optical wireless communication. More particularly, this document discloses various methods, apparatuses, systems, and computer-readable media related to beam alignment methods in optical wireless communication systems. Background Technology

[0004] To enable an increasing number of electronic devices, such as laptops, tablets, and smartphones, to wirelessly connect to the internet, wireless communication is placing unprecedented demands on data rates and link quality, and these demands are growing year by year, given the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency technologies (such as Wi-Fi) have limited spectrum capabilities to embrace this revolution. Meanwhile, Li-Fi (Light Fidelity) is attracting increasing attention due to its inherent security enhancements and its ability to support higher data rates across the available bandwidth of the visible, ultraviolet (UV), and infrared (IR) spectra.

[0005] However, to establish high-data-rate point-to-point optical wireless communication links over large spacing distances, optical wireless communication systems, or Li-Fi systems, typically use narrow beam angles (approximately a few degrees) due to the properties of the light source and practical power budgets. Furthermore, reliably achieving such high-speed links requires precise alignment of the two remote communication devices, which can be very challenging due to the combination of narrow beam width and large spacing. Different methods have been proposed to assist in this alignment, such as using cameras, pilot lights from the remote devices, or feedback information from the remote devices. These systems either suffer from long delays in achieving final alignment or introduce additional complexity to the system.

[0006] For example, in a pilot-based beam alignment system, ideally, the pilot light should be positioned at the same location as the receiver to receive the maximum signal. Of course, it's impossible to place both the receiver and the pilot light in the same location. In practice, the pilot light is typically placed in front of the photodetector within the optical receiver. The surface area of ​​the pilot light should be much smaller than that of the photodetector. However, to support high data rates, the photodetector requires a small surface area to achieve low parasitic capacitance. Therefore, meeting this requirement is difficult in practice and could negatively impact the bandwidth supported by the data link. Alternatively, a semi-transparent mirror or a dichroic mirror can be used to position the pilot light in the same virtual location.

[0007] Another alternative is to split the pilot light into multiple smaller pilot beams, which are symmetrically positioned around the data receiver detector. One of the challenges of this setup is alignment accuracy. Small mechanical displacements or contamination on the optical window, or asymmetries in the light emission of the pilot beams, will create a deflection of the data beam from the data receiver, resulting in a lower signal-to-noise ratio (S / N) or even no data reception. Summary of the Invention

[0009] Given the limitations of traditional pilot-based systems, this invention proposes a more precise alignment scheme to compensate for offsets in pilot-based beam manipulation systems without requiring a return channel. By altering the centroid of the combined light intensity from multiple pilot light sources, the optical receiver provides feedback to the optical transmitter for beam alignment.

[0010] More specifically, the object of the present invention is achieved by the optical receiver as claimed in claim 1, by the optical wireless communication system as claimed in claim 12, and by the method performed by the optical receiver as claimed in claim 15.

[0011] According to a first aspect of the present invention, an optical receiver is provided. An optical receiver includes: - A photodetector is configured to detect a data beam transmitted by an optical transmitter; - At least two pilot light sources are configured to emit pilot light to assist in a beam alignment process performed by an optical emitter; wherein the at least two pilot light sources are placed on different sides of the photodetector; - The controller is configured as -Based on the received beam intensity of the data beam detected by the photodetector, determine the individual pilot light intensity for each of at least two pilot light sources, and - Control each of at least two pilot light sources to emit pilot light according to the determined corresponding individual pilot light intensities, such that the centroid of the combined pilot light intensity of the at least two pilot light sources provides an indication to the optical transmitter of the desired direction of movement of the data beam.

[0012] A photodetector in an optical receiver is a semiconductor device that converts light into current or voltage based on the device's operating mode. A photodetector can also be called a photodiode, light detector, or light sensor. A photodetector may include optical filters, built-in lenses, and may have a large or small surface area. Depending on the device's structure, photodetectors can be classified into different types, such as PN photodiodes, Schottky photodiodes, PIN photodiodes, and avalanche photodiodes.

[0013] Preferably, the two pilot light sources are symmetrically placed on opposite sides of the photodetector. Alternatively, at least two pilot light sources may be placed asymmetrically on opposite sides of the photodetector, such as at different distances from the photodetector. The controller then needs to account for these different distances when determining the individual pilot light intensities, ensuring that the centroid of the combined pilot light intensities provides a good indication for the optical emitter. For example, compared to a symmetrical deployment, the different distances between the at least two pilot light sources and the photodetector can be compensated for by applying one or more additional correction factors to the individual pilot light intensities.

[0014] When the optical receiver is not aligned with the remote optical transmitter, the data beam from the optical transmitter can be aimed near the detection area of ​​the optical receiver. For example, there may be an offset between the center of the injected data beam and the center of the photodetector's detection area. Such an offset reduces the intensity of the received beam, resulting in suboptimal received data signal. The greater the offset, the worse the received signal quality.

[0015] The center of gravity, also known as the centroid, of an object or system is the point at which the weight of the object or system can be considered concentrated. In other words, if the object or system were suspended from this point, it would reach a point of equilibrium. Here, the center of gravity of a collection of pilot light sources with different intensities depends on the geometry and distribution of the pilot light sources, as well as the individual intensity of each pilot light source, making it closer to the source with the greater intensity.

[0016] By introducing asymmetry into the pilot light intensity, the centroid of the combined pilot light provides an indication of the desired direction of movement of the data beam toward the optical transmitter. The optical transmitter can then adjust the emitted data beam to minimize offset or to better align the center of the injected data beam with the center of the detection area of ​​the photodetector. In this way, beam alignment feedback is carried within the pilot light itself, eliminating the need for a separate return channel or feedback signal from the optical receiver to the optical transmitter.

[0017] Advantageously, the controller is also configured to control each of at least two pilot light sources to maintain individual pilot light intensity when the received beam intensity is higher than a first predetermined threshold.

[0018] The first predetermined threshold can be a value on a linear or decibel scale, indicating that the intensity of the received beam is sufficient for further processing at the optical receiver, such as demodulation and decoding of the data included in the optical data beam.

[0019] Advantageously, the controller is also configured to control at least two pilot light sources to change the intensity of the individual pilot light, thereby initiating a scanning of the centroid of the pilot light intensity on the detection surface of the optical receiver when the intensity of the received beam is below a second predetermined threshold.

[0020] When only two pilot light sources are deployed, scanning can be performed by shifting the center of gravity to the line between the two pilot light sources.

[0021] Preferably, the controller is also configured to stop scanning when the intensity of the received beam is higher than a third predetermined threshold.

[0022] The third predetermined threshold can be a value scaled linearly or in decibels. When the received beam intensity is higher than the third predetermined threshold, this indicates that the data beam is roughly aligned with the detection area of ​​the optical receiver, and fine-tuning may still be necessary. Depending on the application, the third predetermined threshold can be lower than the first predetermined threshold, such as a few dB lower if scaled in decibels.

[0023] In the preferred configuration, the controller is configured to control the pilot light sources to perform grating scanning on the detection surface using the centroid of the pilot light intensity when there are more than two pilot light sources.

[0024] With more than two pilot light sources deployed, two-dimensional grating scanning can be performed on the detection surface.

[0025] Advantageously, the controller is configured to control at least two pilot light sources to perform an iterative local search using the centroid of the combined pilot light intensity when the received beam intensity is below a first predetermined threshold but above a fourth predetermined threshold; wherein the iterative local search is achieved by measuring the local derivative of the received beam intensity of the data beam with respect to the centroid of the combined pilot light intensity, and then changing the centroid of the combined pilot light intensity in a direction toward a higher received beam intensity of the data beam.

[0026] Iterative local searches can be performed after an initial search or a new search (raster search), allowing the initial or new search to be used for acquisition, and iterative local searches to be used for fine-tuning or tracking. This is also helpful when a data communication link has already been established between the optical transmitter and the optical receiver. For example, if there is a small movement in at least one of the optical transmitter and the optical receiver, the link quality may be degraded due to the small misalignment, and iterative local searches can help the two communicating devices return to a better alignment for higher data rates.

[0027] The fourth predetermined threshold may be a value close to or equal to the minimum received beam intensity required to maintain the optical wireless link, such as the signal strength required for the optical receiver to demodulate and decode the received data signal at the lowest data rate.

[0028] Preferably, the iterative local search is performed using a hill-climbing algorithm.

[0029] Hill climbing is a mathematical optimization technique used for local searches, such as finding the maximum or minimum value of a given function. The algorithm typically starts at a random point on the function and iteratively moves in the steepest ascending or descending direction until a local maximum or minimum is reached.

[0030] Here, the algorithm can start from the point where the centroid of the combined pilot light is located at the end of the coarse search, and the hill-climbing algorithm improves alignment by fine-tuning the centroid of the combined pilot light to further maximize the received beam intensity detected by the photodetector. For example, the iterative local search can be achieved by measuring the local derivative of the received beam intensity of the data beam with respect to the centroid of the combined pilot light intensity, and then changing the centroid of the combined pilot light intensity in a direction toward a higher received beam intensity of the data beam.

[0031] Advantageously, the optical receiver according to the invention includes at least three pilot light sources to assist the optical transmitter in adjusting the data beam in two dimensions.

[0032] Advantageously, the optical receiver according to the invention includes one or more pilot light drivers configured to adjust the power supply voltage and / or current connected to more than one pilot light source to apply more than one pilot light intensity determined by a controller.

[0033] In one example, the pilot light is a continuous wave.

[0034] Pilot light can be an unmodulated continuous wave (CW) with a constant amplitude and frequency.

[0035] In another example, the pilot light is a modulated wave.

[0036] The pilot light can also be a modulated wave, and modulation can be applied to at least one of the amplitude, frequency, or phase of the emitted pilot light. It is also possible that the pilot light is an amplitude-modulated or frequency-modulated continuous wave.

[0037] According to a second aspect of the present invention, an optical wireless communication system is provided. An optical wireless communication (OWC) system includes: - Optical emitter, including: - A light source, configured to emit a data beam for optical data communication; - A subsystem configured to perform a data beam alignment process based on pilot light received from a remote optical receiver; and - A remote optical receiver according to the present invention.

[0038] Optical data communication can be based on optical wireless communication standards. For example, the system can conform to the IEEE 802.11 standard (e.g., IEEE 802.11bb) or the ITU G.9991 standard for high-speed optical wireless data communication.

[0039] For the high-speed optical wireless communication mentioned in this invention, preferably, the optical transmitter has a small beam angle. The beam angle, or beam width, is the aperture angle at which most of the transmitted 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. The beam angle or beam width is typically expressed in degrees. Preferably, the beam angle of the optical transmitter is no greater than 30 degrees. And even more advantageously, the narrow beam angle is no greater than 10.5 degrees. Such a narrow beam is practically advantageous for supporting long-distance and high-data-rate communication within a reasonable power budget.

[0040] The light source of the optical transmitter can be one of a light-emitting diode (LED), a laser diode, or a vertical-cavity surface-emitting laser (VCSEL). Optical data communication is performed in optical frequency bands, such as in the visible, ultraviolet (UV), and infrared (IR) spectra.

[0041] Beneficially, the subsystem includes: - A multi-element detector is configured to detect pilot light from a remote optical receiver; - Beam manipulation unit, configured to manipulate a data beam emitted by a light source; - The controller is configured to control the beam manipulation unit based on an indication provided by the centroid of the pilot light detected by the multi-element detector.

[0042] A multi-element detector is a photodetector that includes more than one detector element. In one example, a multi-element detector is a quadrant detector. Advantageously, the more elements included in a multi-element detector, the better it assists the beam alignment process. However, the cost of the system may also increase accordingly. Therefore, the choice of a multi-element detector is a design choice between performance and cost.

[0043] The beam manipulation unit may include one or more mirrors, prisms, lenses or rotating diffraction gratings.

[0044] In one example, the subsystem includes: - A tiltable reflector is configured to reflect pilot light to a beam splitter; - The beam splitter is configured to selectively guide: -Guide the reflected pilot light from the tiltable mirror to the multi-element detector; or -Guide the beam of light from the light source to a remote optical receiver; - The multi-element detector is configured as follows: - Detect the reflected pilot light guided by the beam splitter; and - Provide control signals to manipulate the tiltable mirror based on the center of gravity of the reflected pilot light.

[0045] In a system with bidirectional optical wireless communication, two remote devices can have transmitting and receiving capabilities, such as transceivers. Therefore, the first device can have an optical transmitter according to the invention and a conventional receiver, and the second device can have a conventional transmitter and an optical receiver according to the invention. Alternatively, both devices can be included in an optical transmitter and optical receiver according to the invention. And then, a bidirectional beam alignment process can be enabled.

[0046] According to a third aspect of the present invention, a method is provided. A method performed by an optical receiver includes the following steps: - The data beam transmitted by the optical transmitter is detected by the photodetector of the optical receiver; - Pilot light is emitted by at least two pilot light sources of the optical receiver to assist the beam alignment process performed by the optical transmitter; wherein the at least two pilot light sources are placed on different sides of the photodetector; - The controller of the optical receiver determines an individual pilot light intensity for each of the at least two pilot light sources based on the received beam intensity of the data beam detected by the photodetector, and controls each of the at least two pilot light sources to emit pilot light according to the determined corresponding individual pilot light intensity, such that the centroid of the combined pilot light intensity of the at least two pilot light sources provides an indication to the optical transmitter of the desired direction of movement of the data beam. Attached Figure Description

[0048] In the accompanying drawings, similar reference numerals typically refer to the same parts throughout the different figures. Furthermore, the drawings are not necessarily drawn to scale; instead, the focus is usually on illustrating the principles of the invention.

[0049] Figure 1 A conventional one-way beam manipulation system for optical wireless communication is demonstrated. Figure 2 The figure illustrates the basic components of the optical receiver according to the present invention; Figure 3 An example arrangement of at least two pilot light sources and a photodetector in an optical receiver is shown; Figure 4 The figure shows an example of the receiving plane of an optical receiver, in which a data beam from an optical transmitter is aimed next to a photodetector due to offset; Figure 5 An implementation of an optical receiver that applies the intensity of more than one pilot light via a pilot optical driver is demonstrated; Figure 6 The figure illustrates an optical wireless communication system; Figure 7 The figure illustrates an example of implementing a subsystem in an optical transmitter; Figure 8 The figure illustrates another example of implementing a subsystem in an optical transmitter; and Figure 9 A flowchart of a method for using an optical receiver is shown. Detailed Implementation

[0051] The embodiments described below represent information enabling those skilled in the art to practice the embodiments and illustrate the best mode for practicing the embodiments. Upon reading the following description with reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and recognize the application of these concepts not specifically mentioned herein. It should be understood that these concepts and applications fall within the scope of this disclosure.

[0052] For optical wireless communications, such as LiFi, it is well known that for a certain separation distance between the transmitter and receiver, a narrower radiated beam from the transmitter requires less transmission power. As the transmitter beam becomes narrower, it becomes necessary to point the beam more precisely at the receiver.

[0053] To establish stable communication with high throughput, the two devices need to face each other and be properly aligned. This can be very challenging in practice due to the combination of narrow beams and large spacing.

[0054] For this purpose, pilot light can be used, which is positioned close to the photodetector in the receiver and transmits the pilot light signal back to the transmitter. The pilot light signal can be an out-of-band signal using a frequency band different from the communication signal. Alternatively, the pilot light can have a different wavelength or wavelength band than the communication signal, allowing them to be separated by optical filters. The transmitter then detects the pilot signal and uses the detection information to more accurately direct the transmitted beam to the receiver.

[0055] Figure 1 An example of beam alignment setup for pilot light in an optical wireless communication system is shown. Figure 1 The transmitter shown in the left box includes a light source (LS), a beam splitter (BS), a quadrant detector (QD), and a beam splitter (BS). The light source (LS) is used to transmit optical data signals to a remote optical receiver. A tiltable mirror (M / Ma) is adjustable in the X and Y directions to achieve complete spatial coverage. The beam splitter (BS) is used to selectively direct the light received by the tiltable mirror (M / Ma) to the quadrant detector (QD) and the light from the light source (LS) to the remote optical receiver. Figure 1The remote optical receiver or target device shown in the right-hand box includes at least a photodetector (D) and a pilot light (PL). The photodetector (D) is used to receive optical data signals from the optical transmitter. The pilot light (PL) assists the transmitter in detecting the position of the optical receiver or target device and simultaneously guides light from the light source (LS) to the photodetector (D) of the target device.

[0056] The design challenges for such a pilot-based beam alignment system are as follows: As shown in the figure, the surface of the pilot light (PL) must be much smaller than the surface of the photodetector (D). In practice, this can be difficult to achieve when high data rates are required for communication links because the detector (D) (typically a photodiode or avalanche photodiode) must have a small surface area to achieve low parasitic capacitance, which directly affects the bandwidth of the receiver in the target device.

[0057] When the surface of the detector (D) is smaller than the surface of the pilot light (PL), the beam from the light source (LS) must be large enough to cover the detector (D). This limits the beam width to a certain extent determined by the dimensions of the pilot light (PL) and the detector (D) and the distance between them.

[0058] Given the limitations of traditional pilot-based systems, in practice, pilot light is typically split into multiple smaller pilot beams placed around the data receiver detector. However, one challenge of such a setup is the accuracy of alignment between the transmitting source and the QD. Small mechanical displacements or contamination on the optical window, or asymmetries in the light emission of the pilot light, will create a deflection of the data beam from the optical receiver, resulting in a lower signal-to-noise ratio (S / N) or even failure to receive optical data.

[0059] Figure 2 The figure illustrates the basic components of an optical receiver 300 according to the present invention. The optical receiver 300 includes a photodetector 310, at least two pilot light sources 321, 322, and a controller 330.

[0060] A photodetector 310 is configured to detect a data beam transmitted by an optical transmitter 200 for optical data communication. At least two pilot light sources 321, 322 are configured to emit pilot light to assist in a beam alignment process performed by the optical transmitter 200. The at least two pilot light sources 321, 322 are positioned on different sides of the photodetector 310. A controller 330 is configured to determine an individual pilot light intensity for each of the at least two pilot light sources 321, 322 based on the received beam intensity of the data beam detected by the photodetector 310, and to control each of the at least two pilot light sources 321, 322 to emit pilot light according to the determined corresponding individual pilot light intensity, such that the centroid of the combined pilot light intensity of the at least two pilot light sources 321, 332 provides the optical transmitter 200 with an indication of the desired direction of movement of the data beam.

[0061] Figure 3 An example arrangement of at least two pilot light sources 321, 322 and a photodetector 310 in an optical receiver 300 is shown. Figure 3 As shown, at least two pilot light sources 321 and 322 are placed on different sides of the photodetector 310 with separation distances d1 and d2, respectively. Note that d1 and d2 can be different, such that the at least two pilot light sources are placed on different sides of the photodetector in an asymmetrical manner. The controller then needs to consider the different distances when determining the individual pilot light intensities, so that the centroid of the combined pilot light intensities provides a good indication for the optical emitter. For example, the different distances between the at least two pilot light sources and the photodetector can be compensated for by applying one or more correction factors to the individual pilot light intensities, compared to a symmetrical deployment.

[0062] Preferably, the two pilot light sources are symmetrically placed on different sides of the photodetector, such that d1=d2.

[0063] Figure 4 The figure illustrates an example of the receiving plane of the optical receiver 300. For clarity, in this example, four pilot light sources A, B, C, and D are deployed around the photodetector 310. As shown, the data beam from the optical transmitter 200 is aimed adjacent to the detection area of ​​the optical receiver 300, resulting in an offset between the center of the injected data beam and the center of the detection area of ​​the photodetector 310. This offset leads to a reduction in the intensity of the received beam, such as an unsatisfactory received data signal. The greater the offset, the worse the received signal quality.

[0064] By introducing asymmetry into the pilot light intensity or pilot light signal intensity (in this case, increasing the light from pilot light D and decreasing the light from pilot light A), the center of gravity of all pilot lights shifts towards pilot light D. Upon receiving the pilot light from optical receiver 300, transmitter 200 then controls the emitted data beam to follow the center of gravity for better alignment with the detection area in optical receiver 300. Controller 330 of the optical receiver can control the center of gravity to move in small directions, such as the X and Y directions, and iteratively detect in which directions it should move to increase the intensity of the received beam.

[0065] The controller 330 is also configured to control each of at least two pilot light sources 321, 322 to maintain an individual pilot light intensity when the received beam intensity is higher than a first predetermined threshold. The first predetermined threshold may be a value scaled linearly or in decibels, indicating that the received beam intensity is sufficient for further processing at the optical receiver, such as demodulating and decoding data included in the optical data beam.

[0066] When the received beam intensity is below a second predetermined threshold, the controller 330 is further configured to control at least two pilot light sources 321, 322 to change the individual pilot light intensity to begin scanning the centroid of the pilot light intensity on the detection surface of the optical receiver 300. The second predetermined threshold can be a value scaled linearly or in decibels. The second predetermined threshold can be equal to or less than the minimum beam intensity required by the optical receiver to maintain the data communication link even at the lowest data rate. When the received signal is too weak, or the photodetector does not detect the beam at all, the controller will initiate a new scan.

[0067] When only two pilot light sources 321 and 322 are deployed, scanning can be performed by moving the center of gravity to the line between the two pilot light sources 321 and 332. When more than two pilot light sources are deployed, the controller 330 is configured to control the pilot light sources 321 and 322 to perform grating scanning on the detection surface using the center of gravity of the pilot light intensity, such as two-dimensional scanning.

[0068] Basically, at least three pilot light sources 321, 322, and 323 assist the optical transmitter 200 in adjusting the data beam in two dimensions.

[0069] The controller 330 is also configured to stop scanning when the received beam intensity is higher than a third predetermined threshold. The third predetermined threshold can be a value scaled linearly or in decibels. When the received beam intensity is higher than the third predetermined threshold, this indicates that the data beam is roughly aligned with the detection area of ​​the optical receiver, and fine-tuning may still be necessary. Depending on the application, the third predetermined threshold can be lower than the first predetermined threshold, such as a few dB lower if scaled in decibels.

[0070] When sufficient signal strength is detected, the aforementioned scanning and stopping is one possible implementation. Alternatively, during an active optical wireless data link, it is possible that the offset is drifting, in which case performing a new full scan may risk further degrading the data link quality or even completely losing the data connection. Therefore, it may be beneficial to use a full scan (such as a raster scan) for acquisition and then use an iterative local search to track the beam. The controller 330 is then configured to control at least two pilot light sources 321, 322 to perform an iterative local search using the centroid of the combined pilot light intensity when the received beam intensity is below a first predetermined threshold but above a fourth predetermined threshold. The iterative local search is achieved by measuring the local derivative of the received beam intensity of the data beam with respect to the centroid of the combined pilot light intensity, and then changing the centroid of the combined pilot light intensity in a direction toward a higher received beam intensity of the data beam.

[0071] In one example, the beam alignment process begins with a grating scan of the centroid until the data beam generates sufficient received beam intensity on the photodetector. It then switches to an iterative local search algorithm, such as a hill-climbing algorithm, to move the centroid in small steps until maximum signal strength is detected on the photodetector. Using the hill-climbing algorithm, the local derivative of the signal strength with respect to the pilot beam centroid position is measured, and the controller then directs the pilot light source to move the pilot beam centroid uphill to a higher signal level. The local derivative can be determined by making small moves (without losing the data link), measuring whether the received beam intensity increases or decreases at each tiny move, and then moving in the direction of higher received beam intensity. This can be done as the transmitter or receiver moves or drifts. Using this tracking algorithm, the received signal automatically optimizes the centroid to the optimal position. If the data connection is lost, a new scan can be initiated to re-lock on.

[0072] The fourth predetermined threshold may be a value close to or equal to the minimum received beam intensity required to maintain the optical wireless link, such as the signal strength required for the optical receiver to demodulate and decode the received data signal at the lowest data rate.

[0073] Figure 5An implementation of an optical receiver 300 that applies the intensity of more than one pilot light source via a pilot optical driver 340 is demonstrated. The pilot optical driver 340 can be a programmable driver, allowing precise control of the individual light intensities of at least two pilot light sources. Alternatively, the pilot optical driver 340 is a conventional optical driver, and the individual light intensities of at least two pilot light sources 321, 322 are controlled by adjusting the bias of the pilot optical driver 340. A possible option is to deploy a single pilot optical driver 340 to control at least two pilot light sources 321, 322. Another possible option is to have a separate pilot optical driver 340 for each of the at least two pilot light sources 321, 322.

[0074] Pilot light can be an unmodulated continuous wave or a modulated wave.

[0075] Figure 6 The figure illustrates an optical wireless communication system 100. According to the present invention, the optical wireless communication (OWC) system 100 includes an optical transmitter 200 and a remote optical receiver 300. The optical transmitter 200 includes a light source 210 and a subsystem 220. The light source 210 is configured to emit a data beam for optical data communication. The subsystem 220 is configured to perform a data beam alignment process based on pilot light received from the remote optical receiver 300.

[0076] The remote communication devices 200 and 300 operate within optical bands such as the visible, ultraviolet (UV), and infrared (IR) spectra. Point-to-point Li-Fi or optical wireless systems are typically narrow-angle systems. The beam angle between two remote receivers is typically no greater than 30 degrees or 15.5 degrees. To support high data rates and long-distance communication, the beam angle can be on the order of 1 to 5.5 degrees, and even downward and include non-divergent beams. Therefore, it is important that the beam emitted from the light source 210 of the optical transmitter 200 is precisely aligned toward the photodetector 310 of the optical receiver 300.

[0077] In the optical wireless communication system 100 with bidirectional communication, two remote devices 200 and 300, acting as optical transceivers, can have both transmitting and receiving capabilities. Therefore, the first device can include an optical transmitter 200 according to the invention and a conventional receiver, and the second device can have a conventional transmitter and an optical receiver 300 according to the invention. Alternatively, both devices can be included in the optical transmitter 200 and optical receiver 300 according to the invention. Then, a bidirectional beam alignment process can be enabled.

[0078] Figure 7The figure illustrates an example of implementing subsystem 220 in optical transmitter 200. The basic components included in subsystem 220 of optical transmitter 200 are multi-element detector 221, beam manipulation unit 222, and controller 223.

[0079] A multi-element detector 221 is configured to detect pilot light from a remote optical receiver 300. The multi-element detector 221 is a photodetector comprising more than one detector element. In one example, the multi-element detector is a quadrant detector. Advantageously, the more elements included in the multi-element detector, the more beneficial it is to assist the beam alignment process. However, the cost of the system may also increase accordingly. A beam manipulation unit 222 is configured to manipulate a data beam emitted by a light source 210. The beam manipulation unit 222 may include one or more mirrors, prisms, lenses, or rotating diffraction gratings. The controller 223 of the optical emitter 200 is configured to control the beam manipulation unit based on an indication provided by the centroid of the pilot light detected by the multi-element detector 221.

[0080] Figure 8 Another example of the basic components included in the beam alignment subsystem 220 of the optical transmitter 200 is shown. The beam alignment subsystem 220 may include a tiltable mirror 224, a beam splitter 225, and a multi-element detector 221. The tiltable mirror 224 is configured to reflect incident light to the beam splitter 225. The beam splitter 225 is configured to selectively direct reflected light from the tiltable mirror 224 to the multi-element detector 221, or to direct a beam from the light source 210 to the remote optical receiver 300. The multi-element detector 221 is configured to detect the reflected incident light guided by the beam splitter 222 and provide a control signal based on the centroid of the reflected pilot light to manipulate the tiltable mirror 221.

[0081] Figure 9 A flowchart of a method 500 for an optical receiver 300 is shown. Method 500 includes the following steps for the optical receiver 300: - In step S501, the data beam transmitted by the optical transmitter 200 is detected by the photodetector 310 of the optical receiver 300; - In step S502, pilot light is emitted by at least two pilot light sources 321, 322 of the optical receiver 300 to assist the beam alignment process performed by the optical transmitter 200; wherein the at least two pilot light sources 321, 322 are placed on different sides of the photodetector 310; - In step S503, the controller 330 of the optical receiver 300 determines an individual pilot light intensity for each of the at least two pilot light sources 321, 322 based on the received beam intensity of the data beam detected by the photodetector 310, and in step S504, controls each of the at least two pilot light sources 321, 322 to emit pilot light according to the determined corresponding individual pilot light intensity, such that the centroid of the combined pilot light intensity of the at least two pilot light sources 321, 332 provides the optical transmitter 200 with an indication of the desired direction of movement of the data beam.

[0082] Those skilled in the art will recognize that the present invention is by no means limited to the preferred embodiments described above. Rather, many modifications and variations are possible within the scope of the appended claims.

[0083] Additionally, through a study of the accompanying drawings, this disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are referenced in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

Claims

1. An optical receiver (300), comprising: - A photodetector (310) is configured to detect a data beam transmitted by an optical transmitter (200); - At least two pilot light sources (321, 322) are configured to emit pilot light to assist in a beam alignment process performed by an optical emitter (200); wherein the at least two pilot light sources (321, 322) are placed on different sides of a photodetector (310); - The controller (330) is configured as follows: -Based on the received beam intensity of the data beam detected by the photodetector (310), determine the individual pilot light intensity for each of the at least two pilot light sources (321, 322), and - Control each of at least two pilot light sources (321, 322) to emit pilot light according to the determined corresponding individual pilot light intensities, such that the centroid of the combined pilot light intensity of the at least two pilot light sources (321, 322) provides an indication to the optical transmitter (200) of the desired direction of movement of the data beam.

2. The optical receiver (300) of claim 1, wherein the controller (330) is further configured to control each of at least two pilot light sources (321, 322) to maintain individual pilot light intensity when the intensity of the received light beam is higher than a first predetermined threshold.

3. The optical receiver (300) according to claim 1 or 2, wherein the controller (330) is further configured to control at least two pilot light sources (321, 322) to change the individual pilot light intensity, thereby initiating scanning of the centroid of the pilot light intensity on the detection surface of the optical receiver (300) when the received beam intensity is below a second predetermined threshold.

4. The optical receiver (300) according to claim 3, wherein the controller (330) is further configured to stop scanning when the intensity of the received light beam is higher than a third predetermined threshold.

5. The optical receiver (300) according to claim 3 or 4, wherein the controller (330) is configured to control the pilot light sources to perform grating scanning on the detection surface using the centroid of the pilot light intensity when there are more than two pilot light sources (321, 322).

6. The optical receiver (300) according to any one of claims 3-5, wherein the controller (330) is configured to control at least two pilot light sources (321, 322) to perform an iterative local search using the centroid of the combined pilot light intensity when the received beam intensity is below a first predetermined threshold but above a fourth predetermined threshold; wherein the iterative local search is achieved by measuring the local derivative of the received beam intensity of the data beam with respect to the centroid of the combined pilot light intensity, and then changing the centroid of the combined pilot light intensity in a direction toward a higher received beam intensity of the data beam.

7. The optical receiver (300) according to claim 6, wherein the iterative local search is performed according to a hill-climbing algorithm.

8. The optical receiver (300) according to any one of the preceding claims includes at least three pilot light sources (321, 322, 323) to assist the optical transmitter (200) in adjusting the data beam in two dimensions.

9. The optical receiver (300) according to any one of the preceding claims includes one or more pilot light drivers (340) configured to adjust the power supply voltage and / or current connected to more than one pilot light source (321, 322, 323) to apply more than one pilot light intensity determined by the controller (330).

10. The optical receiver (300) according to any one of the preceding claims, wherein the pilot light is a continuous wave.

11. The optical receiver (300) according to any one of claims 1-9, wherein the pilot light is a modulated wave.

12. An optical wireless communication OWC system (100), comprising: - Optical transmitter (200), including: - The light source (210) is configured to emit a data beam for optical data communication; - Subsystem (220) is configured to perform a data beam alignment process based on pilot light received from a remote optical receiver (300); and -A remote optical receiver (300) according to any one of claims 1-8.

13. The OWC system (100) according to claim 12, wherein the subsystem (200) comprises: - A multi-element detector (221) is configured to detect pilot light from a remote optical receiver (300); - Beam manipulation unit (222) is configured to manipulate a data beam emitted by a light source (210); - The controller (223) is configured to control the beam manipulation unit based on an indication provided by the centroid of the pilot light detected by the multi-element detector (221).

14. The OWC system (100) according to claim 12, wherein the subsystem (200) comprises: - A tiltable reflector (224) is configured to reflect pilot light to a beam splitter (225). - The beam splitter (225) is configured to selectively guide: -Guide the reflected pilot light from the tiltable mirror (224) to the multi-element detector (221); or -Guide the beam from the light source (210) to the remote optical receiver (300); - The multi-element detector (221) is configured as follows: - Detect the reflected pilot light guided by the beam splitter; and - Provide control signals to manipulate the tiltable mirror based on the center of gravity of the reflected pilot light.

15. A method (500) performed by an optical receiver (300), comprising the following steps: - The data beam transmitted by the optical transmitter (200) is detected (S501) by the photodetector (310) of the optical receiver (300); - Pilot light is emitted (S502) by at least two pilot light sources (321, 322) of the optical receiver (300) to assist the beam alignment process performed by the optical transmitter (200); wherein at least two pilot light sources (321, 322) are placed on different sides of the photodetector (310); - The controller (330) of the optical receiver (300) determines (S503) an individual pilot light intensity for each of the at least two pilot light sources (321, 322) based on the received beam intensity of the data beam detected by the photodetector (310), and controls (S504) each of the at least two pilot light sources (321, 322) to emit pilot light according to the determined corresponding individual pilot light intensity, such that the centroid of the combined pilot light intensity of the at least two pilot light sources (321, 322) provides an indication to the optical transmitter (200) of the desired direction of movement of the data beam.

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