Pilot optical offset compensation method in optical wireless communication systems

Abstract

An optical receiver (300) comprising: a photodetector (310) configured to detect a data beam transmitted by an optical transmitter (200); and at least two pilot light sources (321, 322) configured to emit pilot light to assist a beam alignment procedure performed by the optical transmitter (200), wherein the at least two pilot light sources are located on different sides of the photodetector (310); and 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 according to the determined corresponding individual pilot light intensity such that the centroid of the combination of pilot light intensities of the pilot light sources (321, 322) provides an indication to the optical transmitter (200) about the desired direction of movement of the data beam.

Description

Technical Field

[0001] The present invention relates to the field of free space optical wireless communication. In particular, various methods, apparatuses, systems, and computer-readable media related to methods for beam alignment in optical wireless communication systems are disclosed herein.

Background Art

[0002] To enable more electronic devices such as laptops, tablets, smartphones, etc. to connect to the Internet wirelessly, wireless communication is facing unprecedented requirements regarding data rate and link quality. Considering the new digital revolution related to the Internet of Things (IoT), such requirements continue to increase year by year. Wireless frequency technologies such as Wi-Fi (registered trademark) have limited spectrum capacity to embrace this revolution. On the other hand, Li-Fi (light fidelity) is attracting increasing attention due to its intrinsic security enhancement and its capability to support higher data rates with the available bandwidth in the visible light, ultraviolet (UV), and infrared (IR) spectra.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, to establish point-to-point optical wireless communication links with high data rates over large distances, optical wireless communication systems or Li-Fi systems typically use narrow beam angles (on the order of several degrees) due to the characteristics of the light source and practical power budgets. Furthermore, to ensure such high-speed links are reliably achieved, the two remote communication devices must be precisely aligned, which can be extremely difficult given the combination of narrow beam width and large distance. Various methods have been proposed to assist with this alignment, such as using camera assistance, pilot light from the remote device, or feedback information from the remote device. These systems suffer from long latency to achieve final alignment or additional complexity to the system.

[0004] For example, in a pilot light-based beam alignment system, the pilot light should ideally be positioned to receive the maximum signal. Naturally, it is impossible to have both the receiver and the pilot light in the same position. In practice, the pilot light is usually placed in front of the photodetector in the optical receiver. The surface of the pilot light should be much smaller than the surface of the photodetector. However, to support high data rates, the photodetector requires a small surface area to obtain low parasitic capacitance. Thus, the requirements are difficult to meet in practice or may negatively impact the bandwidth supported by the data link. Alternatively, the pilot light may be positioned in the same virtual location using a translucent or dichroic mirror.

[0005] A further alternative option is to split the pilot light into multiple smaller pilot lights placed symmetrically around the data receiver detector. One challenge in this setup is alignment accuracy. Slight mechanical misalignment, dirt on the optical window, or emission asymmetry of these pilot lights can result in an offset from the data beam on the data receiver, leading to a decrease in the signal-to-noise ratio of the data signal, or even failure of data reception. [Means for solving the problem]

[0006] Given the limitations of conventional pilot light-based systems, the present invention proposes a more accurate alignment scheme that compensates for offsets in pilot light-based beam steering systems without requiring a return channel. Feedback to the optical transmitter for beam alignment is provided by the optical receiver by changing the centroid of the combined light intensities from multiple pilot light sources.

[0007] In particular, the object of the present invention is achieved by the optical receiver described in claim 1, the optical wireless communication system described in claim 12, and the method performed by the optical receiver described in claim 15.

[0008] According to a first aspect of the present invention, an optical receiver is provided. The optical receiver is A photodetector configured to detect a data beam transmitted by an optical transmitter, At least two pilot light sources configured to emit pilot light to assist a beam alignment procedure performed by an optical transmitter, wherein the at least two pilot light sources are located on different sides of the photodetector, For each of at least two pilot light sources, the individual pilot light intensity is determined based on the received beam intensity of the data beam detected by the photodetector, and The center of gravity of the combined pilot light intensities of at least two pilot light sources is controlled to emit pilot light according to the determined corresponding individual pilot light intensities, so as to provide an indication to the optical transmitter about the desired direction of movement of the data beam. A controller configured as follows, Includes.

[0009] A photodetector in an optical receiver is a semiconductor device that converts light into an electric current or voltage based on the device's operating mode. A photodetector may also be called a photodiode, light detector, or photosensor. A photodetector may include optical filters and built-in lenses, and may have a large or small surface area. Depending on the device structure, photodetectors can be classified into different types, such as PN photodiodes, Schottky photodiodes, PIN photodiodes, and avalanche photodiodes.

[0010] Preferably, the two pilot light sources are placed symmetrically on different sides of the photodetector. In some cases, at least two pilot light sources may be placed asymmetrically on different sides of the photodetector, such as at different distances to the photodetector. In this case, the controller must take the different distances into account when determining the individual pilot light intensity so that the centroid of the combination of pilot light intensity provides good indication to the optical transmitter. For example, the different distances between at least two pilot light sources and the photodetector may be compensated by applying one or more additional correction factors to the individual pilot light intensity compared to a symmetrical deployment.

[0011] If the optical receiver is not aligned with the remote optical transmitter, the data beam coming from the optical transmitter may be directed to the side of the optical receiver's detection area. For example, there may be an offset between the center of the incident data beam and the center of the photodetector's detection area. Such an offset leads to a decrease in the received beam intensity, resulting in, for example, a suboptimal received data signal. The larger the offset, the worse the received signal quality.

[0012] The center of gravity of an object or system, also known as the center of mass, refers to the point from which the weight of the object or system is considered to be concentrated. In other words, it is the point from which the object or system would be balanced if it were suspended. Here, the center of gravity of a collection of pilot light sources with varying intensities depends on the geometry and distribution of these pilot light sources, as well as the individual intensities of these pilot light sources, and will be closer to the strongest light source.

[0013] By introducing asymmetry in the pilot light intensity, the centroid of the pilot light combination provides the optical transmitter with an indication regarding the desired direction of data beam movement. This allows the optical transmitter to adjust the emitted data beam so that the offset is minimized, or the center of the incident data beam and the center of the photodetector's detection area are better aligned. In this way, the feedback for beam alignment is piggybacked to the pilot light itself, eliminating the need for a separate return channel or feedback signal from the optical receiver to the optical transmitter.

[0014] Advantageously, the controller is further configured to control each of at least two pilot light sources to maintain individual pilot light intensity if the received beam intensity exceeds a first predetermined threshold.

[0015] The first predetermined threshold may be a value on either a linear or decibel scale, indicating that the received beam intensity is sufficient for further processing in the optical receiver, such as demodulating and decoding the data contained in the optical data beam.

[0016] Beneficially, the controller is further configured to control at least two pilot light sources to vary the individual pilot light intensity to initiate a scan of the centroid of the pilot light intensity on the detection surface of the optical receiver if the received beam intensity falls below a second predetermined threshold.

[0017] If only two pilot light sources are deployed, the scan may be performed by shifting the center of gravity along the line between the two pilot light sources.

[0018] Preferably, the controller is further configured to stop scanning if the received beam intensity exceeds a third predetermined threshold.

[0019] The third predetermined threshold may be a value on either a linear or decibel scale. If the received beam intensity exceeds the third predetermined threshold, this indicates that the data beam is roughly aligned with the detection area of ​​the optical receiver, although fine-tuning may still be required. Depending on the application, the third predetermined threshold may be lower than the first predetermined threshold, for example, several dB lower on a decibel scale.

[0020] In a preferred setup, the controller is configured to control the pilot light sources to perform a raster scan on the detection surface based on the centroid of the pilot light intensity when three or more pilot light sources are present.

[0021] If three or more pilot light sources are deployed, a two-dimensional raster scan can be performed on the detection surface.

[0022] Beneficially, the controller is configured to control at least two pilot light sources to perform an iterative local search on the centroid of the pilot light intensity combination if the received beam intensity is below a first predetermined threshold but above a fourth predetermined threshold, the iterative local search is performed by measuring the local derivative between the received beam intensity of the data beam and the centroid of the pilot light intensity combination, and then changing the centroid of the pilot light intensity combination in the direction of increasing the received beam intensity of the data beam.

[0023] Iterative local search may occur after an initial search or a new search (raster search), whereby the initial search or new search may be used for acquisition, and the iterative local search may be used for fine tuning or tracking. This is also useful when a data communication link has already been established between an optical transmitter and an optical receiver. For example, if at least one of the optical transmitter and the optical receiver has moved slightly, the link quality may degrade due to a slight misalignment, and the iterative local search may help the two communication devices to return to a better alignment for a higher data rate.

[0024] The fourth predetermined threshold may be a value close to or equal to the minimum received beam intensity for maintaining an optical wireless link, such as the signal strength required for the optical receiver to demodulate and decode a received data signal at the lowest data rate.

[0025] Preferably, the iterative local search follows a hill climbing algorithm.

[0026] Hill climbing is a mathematical optimization for local search, such as finding the maximum or minimum value of a given function. The algorithm typically starts from a random point on the function and repeatedly moves in the steepest upward or downward direction until it reaches a local maximum or minimum.

[0027] Here, the algorithm may start from the point where the center of gravity of the combination of pilot lights is located when the rough search ends, and the hill climbing algorithm improves the alignment by fine-tuning the center of gravity of the combination of pilot lights to further maximize the received beam intensity detected by the photo-detector. For example, iterative local search may be performed by measuring the local derivative between the received beam intensity of the data beam and the center of gravity of the combination of pilot light intensities, and then changing the center of gravity of the combination of pilot light intensities in the direction where the received beam intensity of the data beam increases.

[0028] Advantageously, the optical receiver according to the present invention includes at least three pilot light sources to assist the optical transmitter in two-dimensionally adjusting the data beam.

[0029] Beneficially, the optical receiver according to the present invention includes one or more pilot light drivers configured to adjust the supply voltage and / or current connected to two or more pilot light sources to apply two or more pilot light intensities determined by the controller.

[0030] In one example, the pilot light is a continuous wave.

[0031] The pilot light may be an un-modulated continuous wave (CW) such that the amplitude and frequency are constant.

[0032] In another example, the pilot light is a modulated wave.

[0033] The pilot light may be a modulated wave, and the modulation may be applied to at least one of the amplitude, frequency, and phase of the emitted pilot light. Also, the pilot light may be an amplitude-modulated or frequency-modulated continuous wave.

[0034] According to a second aspect of the present invention, an optical wireless communication system is provided. The optical wireless communication (OWC) system is A light source configured to emit a data beam for optical data communication, and A subsystem configured to perform a data beam alignment procedure based on pilot light received from a remote optical receiver. Including an optical transmitter, The remote optical receiver according to the present invention, Includes.

[0035] Optical data communication may conform to optical wireless communication standards. For example, the system may 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.

[0036] In the high-speed optical wireless communication targeted by the present invention, it is preferable that the optical transmitter has a small beam angle. The beam angle or beam width is the aperture angle from which the majority 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 usually expressed in degrees. It is preferable that the beam angle of the optical transmitter is 30 degrees or less. More beneficially, a narrow beam is a half-angle of 10 degrees or less. Such a narrow beam is a practical consideration for supporting long-distance and high-data-rate communication within a reasonable power budget.

[0037] The light source of the optical transmitter may be a light-emitting diode (LED), a laser diode, or a vertical-cavity surface-emitting laser (VCSEL). Optical data communication is performed in optical bands such as visible light, ultraviolet (UV), and infrared (IR) spectra.

[0038] Beneficial subsystems are A multi-element detector configured to detect pilot light from a remote optical receiver, A beam steering unit configured to steer a data beam emitted by a light source, A controller configured to control the beam steering unit based on an indication provided by the centroid of the pilot light detected by a multi-element detector, Includes.

[0039] A multi-element detector is a type of photodetector that contains two or more detector elements. One example of a multi-element detector is a quadrant detector. Beneficially, the more elements a multi-element detector contains, the better it assists in beam alignment procedures. However, the system cost can also increase accordingly. Therefore, the choice of a multi-element detector is a design choice between performance and cost.

[0040] A beam-steering unit may include one or more mirrors, prisms, lenses, or rotating diffraction gratings.

[0041] In one example, the subsystem is: A tiltable mirror configured to reflect pilot light to a beam splitter, The reflected pilot light from the tiltable mirror is sent to the multi-element detector, or The beam from the light source is sent to the remote optical receiver. A beam splitter configured to selectively direct beams, Detects reflected pilot light directed by a beam splitter, and Provides a control signal for steering a tiltable mirror based on the center of gravity of a reflected pilot light. A multi-element detector configured as follows, Includes.

[0042] In a system with bidirectional optical wireless communication, the two remote devices may have both transmit and receive capabilities, such as transceivers. Therefore, the first device may have an optical transmitter and a conventional receiver according to the present invention, and the second device may have a conventional transmitter and an optical receiver according to the present invention. Alternatively, both devices may include an optical transmitter and an optical receiver according to the present invention. In this case, the beam alignment procedure can be performed bidirectionally.

[0043] A third aspect of the present invention provides a method. The method performed by an optical receiver is: The steps include detecting the data beam transmitted by the optical transmitter using the photodetector of the optical receiver, A step of emitting pilot light to assist a beam alignment procedure performed by an optical transmitter using at least two pilot light sources of an optical receiver, wherein the at least two pilot light sources are located on different sides of the photodetector, The optical receiver controller determines individual pilot light intensity for each of 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 combination of pilot light intensities of the at least two pilot light sources provides an indication to the optical transmitter about the desired direction of movement of the data beam. Includes. [Brief explanation of the drawing]

[0044] In the drawings, similar reference letters generally refer to the same part throughout different drawings. Furthermore, these drawings are not necessarily to scale; instead, the emphasis is generally on illustrating the principles of the invention. [Figure 1] This shows a conventional unidirectional beam steering system for optical wireless communication. [Figure 2] The basic components of the optical receiver according to the present invention are shown. [Figure 3] An example of the arrangement of at least two pilot light sources and a photodetector in an optical receiver is shown. [Figure 4] This shows an example of the light-receiving surface of an optical receiver where the data beam from the optical transmitter is directed to the side of the photodetector due to an offset. [Figure 5] This shows an implementation of an optical receiver that applies two or more pilot light intensities via a pilot optical driver. [Figure 6] This shows an optical wireless communication system. [Figure 7] This shows an example of implementing a subsystem in an optical transmitter. [Figure 8] Here is another example of implementing a subsystem in an optical transmitter. [Figure 9]A flowchart of the optical receiver method is shown. [Modes for carrying out the invention]

[0045] The embodiments described below are intended to provide information that will enable those skilled in the art to practice the embodiments and to represent the best modes of practice. By reading the following description in reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and recognize applications of these concepts that are not specifically addressed herein. It should be understood that these concepts and applications fall within the scope of this disclosure.

[0046] In optical wireless communications such as LiFi, it is known that at a certain distance between the transmitter and receiver, the narrower the beam emitted from the transmitter, the significantly less transmission power is required. As the transmitter beam narrows, it becomes necessary to direct the beam more precisely towards the receiver.

[0047] To establish high-throughput and stable communication, both devices must face each other and be properly aligned. This is actually very difficult due to the combination of narrow beams and large gaps.

[0048] For this purpose, a pilot light may be used, located near the photodetector in the receiver, to transmit a pilot light signal to the transmitter. The pilot light signal may be an out-of-band signal using a different frequency band than the communication signal. Alternatively, the pilot light may have a different wavelength or wavelength band than the communication signal, which can be separated by an optical filter. The transmitter detects the pilot signal and uses the detection information to more accurately direct the transmit beam toward the receiver.

[0049] Figure 1 shows an example of a beam alignment setup based on pilot light in an optical wireless communication system. The transmitter shown in the left block of Figure 1 includes a light source (LS), a beam splitter (BS), a quadrant detector (QD), and another beam splitter (BS). The light source (LS) is used to send optical data signals to a remote optical receiver. A tiltable mirror (M / Ma) is adjustable in both the X and Y directions to cover the entire space. 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. The remote optical receiver or target device (Target) shown in the right block of Figure 1 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. A pilot light (PL) is used to help the transmitter detect the position of the light receiver or target device, as well as to direct light from the light source (LS) towards the photodetector (D) of the target device.

[0050] The design challenges for such pilot light-based beam alignment systems are as follows: - As shown in the diagram, the surface area of ​​the pilot light (PL) must be much smaller than the surface area of ​​the photodetector (D). In practice, this can be difficult to achieve when high data rates are required for the communication link, because the detector (D) (usually a photodiode or avalanche photodiode) must have a small surface area to reduce parasitic capacitance, which directly affects the receiver bandwidth in the target device. - If 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 extend, determined by the sizes of the pilot lamp (PL) and the detector (D), and the distance between them.

[0051] Given the limitations of conventional pilot light-based systems, in practice, the pilot light is typically implemented by splitting it into multiple smaller pilot lights placed around the data receiving detector. However, one challenge with such a setup is the precision of the alignment between the light source and the QD. Slight mechanical misalignment, dirt on the optical window, or emission asymmetry of these pilot lights can result in an offset from the data beam on the data receiver, leading to a decrease in the signal-to-noise ratio of the data signal, or even failure to receive the optical data.

[0052] Figure 2 shows the basic components of the optical receiver 200 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.

[0053] The photodetector 310 is configured to detect a data beam transmitted by the 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 procedure performed by the optical transmitter 200. The at least two pilot light sources 321, 322 are located on different sides of the photodetector 310. The controller 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 combination of pilot light intensities of the at least two pilot light sources 321, 322 provides indication to the optical transmitter 200 about the desired direction of movement of the data beam.

[0054] Figure 3 shows an example arrangement of at least two pilot light sources 321, 322 and a photodetector 310 in the optical receiver 300. As shown in Figure 3, at least two pilot light sources 321, 322 are placed on different sides of the photodetector 310 at separations d1 and d2, respectively. Note that d1 and d2 may be different so that at least two pilot light sources are placed asymmetrically on different sides of the photodetector. In this case, the controller must take the different distances into account when determining the individual pilot light intensities so that the centroid of the combination of pilot light intensities provides good indication to the optical transmitter. For example, the different distances between the at least two pilot light sources and the photodetector may be compensated by applying one or more additional correction factors to the individual pilot light intensities compared to a symmetrical arrangement.

[0055] Preferably, the two pilot light sources are placed symmetrically on opposite sides of the photodetector such that d1 = d2.

[0056] Figure 4 shows an example of the light-receiving surface of the optical receiver 300. For simplicity of explanation, in this example, four pilot light sources A, B, C, and D are arranged around the photodetector 310. As shown in the figure, the data beam coming from the optical transmitter 200 is directed to the side of the detection area of ​​the optical receiver 300 such that there is an offset between the center of the incident data beam and the center of the detection area of ​​the photodetector 310. Such an offset leads to a decrease in the received beam intensity, resulting in, for example, a suboptimal received data signal. The larger the offset, the worse the received signal quality.

[0057] By introducing asymmetry in the pilot light intensity or pilot light signal intensity (in this example, increasing the light from pilot light D and decreasing the light from pilot light A), the centroid of the entire pilot light shifts toward pilot light D. Upon receiving pilot light from the optical receiver 300, the transmitter 200 controls the emitted data beam to follow the centroid in order to better align with the detection area in the optical receiver 300. The optical receiver controller 330 may control minute shifts of the centroid in certain directions, for example, in the X and Y directions, and iteratively detect which direction the centroid should shift in order to increase the received beam intensity.

[0058] The controller 330 is further configured to control each of the at least two pilot light sources 321, 322 to maintain their individual pilot light intensities if the received beam intensity exceeds a first predetermined threshold. The first predetermined threshold may be a value on either a linear or decibel scale, indicating that the received beam intensity is sufficient for further processing in the optical receiver, such as demodulating and decoding the data contained in the optical data beam.

[0059] If the received beam intensity falls below a second predetermined threshold, the controller 330 is further configured to control at least two pilot light sources 321, 322 to vary the individual pilot light intensities to initiate a scan of the centroid of the pilot light intensity on the detection surface of the optical receiver 300. The second predetermined threshold may be a value on either a linear scale or a decibel scale. The second predetermined threshold may be less than or equal to the minimum beam intensity required by the optical receiver to maintain the data communication link even at the lowest data rate. If the received signal is too weak, or if the beam is not detected at all by the photodetector, a new scan is initiated by the controller.

[0060] If only two pilot light sources 321 and 322 are provided, the scan may be performed by moving the center of gravity along the line between the two pilot light sources 321 and 322. If three or more pilot light sources are provided, the controller 330 is configured to control the pilot light sources 321 and 322 to perform a raster scan on the detection surface by the center of gravity of the pilot light intensity, such as a two-dimensional scan.

[0061] Essentially, at least three pilot light sources 321, 322, and 323 assist the optical transmitter 200 in adjusting the data beam in two dimensions.

[0062] The controller 330 is further configured to stop scanning if the received beam intensity exceeds a third predetermined threshold. The third predetermined threshold may be a value on either a linear or decibel scale. If the received beam intensity exceeds the third predetermined threshold, this indicates that the data beam is substantially aligned with the detection area of ​​the optical receiver, although fine-tuning may still be required. Depending on the application, the third predetermined threshold may be lower than the first predetermined threshold, for example, several dB lower on a decibel scale.

[0063] The aforementioned scanning and stopping when sufficient signal strength is detected is one possible implementation. Alternatively, the offset may drift and shift during an active optical wireless data link. In this situation, a new full scan by the system could further degrade the data link, or even risk 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 iterative local search to track the beam. In this case, the controller 330 is configured to control at least two pilot light sources 321, 322 to perform iterative local search using the centroid of the pilot light intensity combination when the received beam intensity is below a first predetermined threshold but above a fourth predetermined threshold. The iterative local search is performed by measuring the local derivative between the received beam intensity of the data beam and the centroid of the pilot light intensity combination, and then changing the centroid of the pilot light intensity combination in the direction that increases the received beam intensity of the data beam.

[0064] In one example, the beam alignment procedure begins with a raster scan of the centroid until the data beam generates sufficient received beam intensity on the photodetector. The beam alignment procedure then switches to an iterative local search algorithm, such as a hill-climbing algorithm, which moves the centroid in small steps until the photodetector detects maximum signal intensity. In the hill-climbing algorithm, the local derivative between the signal intensity and the location of the pilot light's centroid is measured, and the controller then controls the pilot light source to move the pilot light's centroid in the direction of "uphill" (climbing towards higher signal levels). The local derivative can be determined by measuring whether the received beam intensity increases or decreases with each small movement (without losing the data link), and then moving in the direction of higher received beam intensity. This can be done if the transmitter or receiver moves or drifts. Such a tracking algorithm automatically optimizes the centroid of the received signal to the best position. If the data connection is lost, a new scan can be initiated to get in lock again.

[0065] The fourth predetermined threshold may be close to or equal to the minimum received beam intensity required to maintain the optical wireless link, such as the signal intensity required for the optical receiver to demodulate and decode the received data signal at the lowest data rate.

[0066] Figure 5 shows an implementation of an optical receiver 300 that applies two or more pilot light intensities via a pilot optical driver 340. The pilot optical driver 340 may be a programmable driver so that the individual light intensities of at least two pilot light sources can be precisely controlled. Alternatively, the pilot optical driver 340 may be 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. It is optional to deploy a single pilot optical driver 340 to control at least two pilot light sources 321, 322. It may also be optional to have a separate pilot optical driver 340 for each of the at least two pilot light sources 321, 322.

[0067] The pilot light may be either an unmodulated continuous wave or a modulated wave.

[0068] Figure 6 shows an optical wireless communication system 100. The optical wireless communication (OWC) system 100 includes a remote optical receiver 300 and an optical transmitter 200 according to the present invention. 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 procedure based on pilot light received from the remote optical receiver 300.

[0069] The pair of remote communication devices 200 and 300 operate in optical bands such as the visible light, ultraviolet (UV), and infrared (IR) spectra. Point-to-point Li-Fi or optical wireless systems are typically narrow-angle systems. The beam angle between the two remote receivers is typically 30 degrees or less, or 15 degrees or less in half-angles. To support high data rates and long-distance communication, the beam angle may be on the order of 1 to 5 degrees in half-angles, or even lower, and may include non-divergent beams. Therefore, it is important to precisely align the beam emitted from the light source 210 of the optical transmitter 200 towards the photodetector 310 of the optical receiver 300.

[0070] In the optical wireless communication system 100 with bidirectional communication, the two remote devices 200 and 300 may have both transmit and receive capabilities as optical transceivers. Therefore, the first device may include an optical transmitter 200 and a conventional receiver according to the present invention, and the second device may have a conventional transmitter and an optical receiver 300 according to the present invention. Alternatively, both devices may include an optical transmitter and an optical receiver according to the present invention. In this case, the beam alignment procedure can be performed bidirectionally.

[0071] Figure 7 shows an example of implementing subsystem 220 in optical transmitter 200. The basic components included in subsystem 220 of optical transmitter 200 are a multi-element detector 221, a beam steering unit 222, and a controller 223.

[0072] The multi-element detector 221 is configured to detect pilot light from the remote optical receiver 300. The multi-element detector 221 is a type of photodetector that includes two or more detector elements. In one example, the multi-element detector is a quadrant detector. Beneficially, the more elements included in the multi-element detector, the better it is at assisting the beam alignment procedure. However, the cost of the system may also increase accordingly. The beam steering unit 222 is configured to steer the data beam emitted by the light source 210. The beam steering unit 222 may include one or more mirrors, prisms, lenses, or rotating diffraction gratings. The controller 223 is configured to control the beam steering unit based on an indication provided by the centroid of the pilot light detected by the multi-element detector 221.

[0073] Figure 8 shows another example of the basic components included in the beam alignment subsystem 220 of the optical transmitter 200. The beam alignment subsystem 220 may include a tiltable mirror 224, a beam splitter 225, and a multi-element detector 221. The tiltable mirror 22 is configured to reflect incident light to the beam splitter 225. The beam splitter 225 is configured to selectively direct the reflected light from the tiltable mirror 224 to the multi-element detector 221, or the 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 directed by the beam splitter 222 and to provide a control signal for steering the tiltable mirror 221 based on the centroid of the reflected pilot light.

[0074] Figure 9 shows a flowchart of Method 500 for the optical receiver 300. Method 500 is a step of the optical receiver 300, In step S501, the photodetector 310 of the optical receiver 300 detects the data beam transmitted by the optical transmitter 200, In step S502, at least two pilot light sources 321, 322 of the optical receiver 300 emit pilot light to assist the beam alignment procedure performed by the optical transmitter 200, wherein the at least two pilot light sources 321, 322 are located 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 and 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 and 322 to emit pilot light according to the determined corresponding individual pilot light intensity such that the centroid of the combination of pilot light intensities of the at least two pilot light sources 321 and 322 provides an indication to the optical transmitter 200 for the desired direction of movement of the data beam. Includes.

[0075] 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.

[0076] Furthermore, by examining the drawings, this disclosure, and the appended claims, variations of the disclosed embodiments can be understood by those skilled in the art and can be implemented in carrying out the claimed invention. In the claims, the word “comprising” does not exclude other components or steps, and the indefinite article “a” or “an” does not exclude plural. The mere fact that certain means are enumerated in different dependent claims does not imply that combinations of these means cannot be used advantageously.

Claims

1. A photodetector configured to detect a data beam transmitted by an optical transmitter, At least two pilot light sources configured to emit pilot light to assist a beam alignment procedure performed by the optical transmitter, wherein the at least two pilot light sources are located on different sides of the photodetector, For each of the at least two pilot light sources, individual pilot light intensities are determined based on the received beam intensity of the data beam detected by the photodetector, and the centroid of these pilot light intensities provides the optical transmitter with an indication for controlling the data beam to follow the centroid, and Control each of the at least two pilot light sources to emit pilot light according to the corresponding individual pilot light intensity determined above. A controller configured as follows, An optical receiver, including one.

2. The optical receiver according to claim 1, wherein the controller is configured to control each of the at least two pilot light sources to maintain individual pilot light intensities when the received beam intensity exceeds a first predetermined threshold.

3. The optical receiver according to claim 1 or 2, wherein the controller is configured to control the at least two pilot light sources to change the individual pilot light intensities to initiate a scan of the centroid of the pilot light intensities on the detection surface of the optical receiver when the received beam intensity falls below a second predetermined threshold.

4. The optical receiver according to claim 3, wherein the controller is configured to stop scanning when the received beam intensity exceeds a third predetermined threshold.

5. The optical receiver according to claim 3, wherein the controller is configured to control the pilot light sources to perform a raster scan on the detection surface based on the centroid of the pilot light intensity when three or more pilot light sources are present.

6. The optical receiver according to claim 3, wherein the controller is configured to control the at least two pilot light sources to perform an iterative local search using the centroid of the pilot light intensity when the received beam intensity falls below a first predetermined threshold but exceeds a fourth predetermined threshold, the iterative local search being performed by measuring the local derivative between the received beam intensity of the data beam and the centroid of the pilot light intensity, and then changing the centroid of the pilot light intensity in a direction that increases the received beam intensity of the data beam.

7. The optical receiver according to claim 6, wherein the iterative local search follows a hill-climbing algorithm.

8. The optical receiver according to claim 1, wherein the optical receiver includes at least three pilot light sources to assist the optical transmitter in adjusting the data beam in two dimensions.

9. The optical receiver according to claim 1, comprising one or more pilot optical drivers configured to adjust the supply voltage and / or current connected to two or more pilot light sources in order to apply two or more pilot optical intensities determined by the controller.

10. The optical receiver according to claim 1, wherein the pilot light is a continuous wave.

11. The optical receiver according to claim 1, wherein the pilot light is a modulated wave.

12. A light source configured to emit a data beam for optical data communication, and A subsystem configured to perform a data beam alignment procedure based on pilot light received from an optical receiver. Including an optical transmitter, The optical receiver according to claim 1, Optical wireless communication (OWC) systems, including [specific components / features].

13. The subsystem described above is A multi-element detector configured to detect pilot light from the optical receiver, A beam steering unit configured to steer the data beam emitted by the aforementioned light source, A controller configured to control the beam steering unit based on an indication provided by the centroid of the pilot light detected by the multi-element detector, The OWC system according to claim 12, including the following:

14. The subsystem described above is A tiltable mirror configured to reflect the aforementioned pilot light to a beam splitter, The reflected pilot light from the tiltable mirror is sent to the multi-element detector, or The beam from the light source is directed to the optical receiver. The beam splitter is configured to selectively direct the beam, The reflected pilot light directed by the beam splitter is detected, and A control signal is provided for steering the tiltable mirror based on the centroid of the reflected pilot light. The multi-element detector is configured as follows: The OWC system according to claim 12, including the following:

15. A method performed by an optical receiver, The steps include: detecting the data beam transmitted by the optical transmitter using the photodetector of the optical receiver; A step of emitting pilot light from at least two pilot light sources of the optical receiver to assist in a beam alignment procedure performed by the optical transmitter, wherein the at least two pilot light sources are located on different sides of the photodetector, The optical receiver controller determines individual pilot light intensities for each of the at least two pilot light sources based on the received beam intensity of the data beam detected by the photodetector, the centroid of these pilot light intensities provides an indication to the optical transmitter for controlling the data beam to follow the centroid, and controls each of the at least two pilot light sources to emit pilot light according to the determined corresponding individual pilot light intensities. Methods that include...

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