Method for beam alignment in optical wireless communication system

Abstract

An optical wireless communication system (100) comprising: an optical transmitter (200) comprising: a light source (210) configured to emit a light beam for optical data communication; a subsystem (220) configured to perform a beam alignment process based on incident light received from the remote optical receiver (300); and a remote optical receiver (300) comprising: a photodetector (310) configured to detect the light beam transmitted by the optical transmitter (200); and a semi-spherical mirror (320) configured to reflect a portion of the light beam received from the optical transmitter (200) to facilitate a light beam alignment process performed by the optical transmitter (200).

Description

Technical Field

[0001] The present invention relates to the field of free space optical wireless communication. More particularly, 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 an increasing number of electronic devices (such as laptops, tablets, and smartphones) to wirelessly connect to the Internet, wireless communication faces unprecedented requirements for data rate as well as link quality, and these requirements continue to grow year by year considering the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency technologies (such as Wi-Fi) have limited spectral capacity and cannot meet this revolution. Meanwhile, Li-Fi is attracting increasing attention due to its inherent security enhancement and its ability to support higher data rates over the available bandwidth in the visible, ultraviolet (UV), and infrared (IR) spectra.

[0003] However, to establish a point-to-point optical wireless communication link with high data rate over large separation distances, optical wireless communication systems or Li-Fi systems typically have a narrow beam angle (on the order of a few degrees), which is caused by the properties of the light source and the actual power budget. In addition, to reliably achieve such a high-speed link, two remote communication devices need to be accurately aligned, which can be quite challenging due to the combination of narrow beam width and large separation. To assist this alignment, different methods have been proposed, such as by means of a camera, a pilot light from a remote device, or using feedback information from a remote device. These systems either suffer from long latency to reach the final alignment or suffer from additional complexity of the system.

[0004] For example, in a pilot light-based beam alignment system, the pilot light is typically placed in front of a photodetector in an 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 needs a small surface to obtain low parasitic capacitance. Therefore, this requirement is difficult to meet in practice, or it may have a negative impact on the bandwidth to be supported by the data link.

[0005] US8160452B1 relates to an acquisition, pointing, and tracking system for a free space optical communication system that performs pointing and tracking functions internally by translating an internal optical fiber in the focal plane of a transceiver telescope by using a mirror in the focal plane of the telescope of each linked transceiver.

[0006] US2002033981A1 relates to an optical communication transmitter, receiver, and transceiver having a unique retroreflective element and / or a reflectivity that can be modulated.

[0007] EP1191715A2 relates to an optical wireless network system, comprising: a transmitter including a laser for generating a light beam reflected from a micromirror towards a receiver; a receiver including a lens for receiving incident light and directing the light towards a photodiode; and a reflection ring surrounding the lens at the receiver to reflect the light back to the transmitter.

[0008] CN113176534A relates to a Gaussian beam tracking method based on free space optical (FSO) communication. Summary of the Invention

[0009] In view of the limitations of traditional indicator-based systems, in the present invention, a hemispherical mirror is deployed in a target device to reflect a portion of the light beam received from an optical transmitter to assist the beam alignment process in the optical transmitter, such that the light beam reflected from the target device is used as an indicator in a traditional system.

[0010] More particularly, the object of the present invention is achieved by an optical wireless communication system as claimed in claim 1, a method of an optical wireless communication system as claimed in claim 8, and an optical receiver as claimed in claim 10.

[0011] According to a first aspect of the present invention, there is provided an optical wireless communication system. An optical wireless communication system comprises:

[0012] An optical transmitter, comprising:

[0013] - a light source configured to emit a light beam for optical data communication,

[0014] - a subsystem configured to perform a beam alignment process based on incident light received from a remote optical receiver; and

[0015] A remote optical receiver, comprising:

[0016] - a photodetector configured to detect the light beam transmitted by the optical transmitter,

[0017] - a hemispherical mirror configured to reflect a portion of the light beam received from the optical transmitter to assist the beam alignment process performed by the optical transmitter;

[0018] wherein the hemispherical mirror is semi-transparent and semi-reflective, and the photodetector is placed behind the hemispherical mirror with respect to the incident direction of the light beam and at the center of the hemisphere.

[0019] 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 the optical band, such as in the visible light, ultraviolet (UV), and infrared (IR) spectra. Optical data communication can be based on optical wireless communication standards. For example, the system can comply with the IEEE 802.11 standard (e.g., IEEE802.11bb) or the ITU G.9991 standard for high-speed optical wireless data communication.

[0020] The photodetector of the optical receiver is a semiconductor device that converts light into current or voltage based on the operating mode of the device. The photodetector can also be referred to as a photodiode, a light detector, or a photosensor. The photodetector can include a filter, a built-in lens, and can have a large or small surface area. Depending on the structure of the device, the photodetector can be classified into different types, such as PN photodiodes, Schottky photodiodes, PIN photodiodes, and avalanche photodiodes.

[0021] Beam alignment is achieved on the transmitter side by means of a reflected beam from a remote receiver.

[0022] For the high-speed optical wireless communication proposed in the present invention, preferably, the optical transmitter has a small beam angle. The beam angle or beam width is the aperture angle from 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. For the horizontal plane, the beam angle or beam width is usually expressed in degrees. Preferably, the beam angle of the optical transmitter is not greater than 30 degrees. And even more advantageously, the narrow beam has a half-angle not greater than 10 degrees. Such a narrow beam is of practical consideration for supporting long-distance and high-data-rate communication within a reasonable power budget.

[0023] In a system with two-way optical wireless communication, two remote devices can have both transmitting and receiving capabilities. Thus, the first device can have an optical transmitter and a conventional receiver according to the present invention, and the second device can have a conventional transmitter and an optical receiver according to the present invention. It can also be the option that both devices include an optical transmitter and an optical receiver according to the present invention. And then, the beam alignment process can be enabled unidirectionally, where during the beam alignment process, one device acts as a transmitter and the other device acts as a receiver.

[0024] In a preferred arrangement, the subsystem includes:

[0025] A tiltable mirror configured to reflect incident light to a beam splitter;

[0026] The beam splitter, which is configured to selectively:

[0027] - Direct the reflected light from the tiltable mirror to a multi-element detector, or

[0028] - Direct the light beam from the light source to a remote optical receiver;

[0029] The multi-element detector, which is configured to:

[0030] - Detect the incident reflected light guided by the beam splitter, and

[0031] - Provide a control signal to steer the tiltable mirror such that the incident reflected light falls in the center of the multi-element detector.

[0032] The multi-element detector is a photoelectric detector including 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 helpful it is for the beam alignment process. However, the cost of the system may also increase accordingly. Therefore, the selection of the multi-element detector is a design choice between performance and cost.

[0033] Advantageously, the hemispherical mirror is semi-transparent and semi-reflective, and the photoelectric detector is placed behind the hemispherical mirror relative to the incident direction of the light beam and at the center of the hemisphere.

[0034] Advantageously, a part of the light beam transmitted through the hemispherical mirror is greater than the remaining part of the light beam reflected back to the optical transmitter.

[0035] Since only this part of the light beam transmitted through the hemispherical mirror contributes to optical data communication, while the reflected part is only used for beam alignment, it is preferred that this part of the light beam transmitted through the hemispherical mirror is greater than the remaining part reflected back to the optical transmitter. The ratio between these two parts can be controlled by the type of coating on the hemispherical mirror, the thickness of the coating on the hemispherical mirror, or the composition of the coating on the hemispherical mirror.

[0036] Even more advantageously, this part of the light beam transmitted through the hemispherical mirror is at least twice the remaining part reflected back to the optical transmitter.

[0037] Alternatively, the hemispherical mirror is reflective, and the photoelectric detector is placed closely near the hemispherical mirror such that both the hemispherical mirror and the photoelectric detector are within the coverage area of the light beam from the optical transmitter.

[0038] In this setup, the hemispherical mirror is no longer semi-transparent but purely reflective and is placed adjacent to the photodetector. The beam from the optical transmitter should be wide enough to cover both the hemispherical mirror and the photodetector, and the reflective hemispherical mirror reflects part of the beam back to the optical transmitter to assist in the beam alignment process. To reduce the unnecessary power consumption of the optical transmitter due to the wide beam width, it is beneficial to place the hemispherical mirror as close as possible to the photodetector. The photodetector and the hemispherical mirror can be mounted on the same surface in the optical receiver.

[0039] Advantageously, the light source is configured to emit a beam with non-uniform intensity in cross-section, and the intensity is highest at the center.

[0040] To assist in the beam alignment process, it is beneficial to add additional information to the beam emitted by the optical transmitter. This additional information can be a predefined intensity distribution of the beam cross-section.

[0041] In one setup, the subsystem uses information related to this non-uniform intensity to assist in the beam alignment process.

[0042] The beam alignment subsystem in the optical transmitter can compare the intensity distribution of the cross-section of the reflected light with the intensity distribution of the beam initially emitted by the optical transmitter. Then, the orientation of the light source and / or the tiltable mirror or the entire optical transmitter can be adjusted based on the comparison result.

[0043] Advantageously, the intensity in the cross-section follows a Gaussian distribution.

[0044] According to a second aspect of the present invention, a method is provided. A method for an optical wireless communication system includes the following steps:

[0045] - Emitting a beam by an optical transmitter for optical data communication;

[0046] - Reflecting a part of the beam by a hemispherical mirror included in a remote optical receiver to assist in the beam alignment process performed by the optical transmitter;

[0047] - Performing a beam alignment process by the optical transmitter based on the incident light received from the remote optical receiver;

[0048] - Detecting the beam from the optical transmitter by the remote optical receiver.

[0049] In one example, the method further includes the following steps for the optical transmitter:

[0050] - Reflecting the incident light to a beam splitter by a tiltable mirror;

[0051] - The beam splitter selectively directs the reflected light from the tiltable mirror to the multi-element detector or directs the light beam to the remote optical receiver;

[0052] - The multi-element detector detects the incident reflected light guided by the beam splitter; and

[0053] - A control signal is provided to manipulate the tiltable mirror such that the incident reflected light falls in the center of the multi-element detector;

[0054] wherein the hemispherical mirror is semi-transparent and semi-reflective, and the photodetector of the remote optical receiver is placed behind the hemispherical mirror relative to the incident direction of the light beam and at the center of the hemisphere.

[0055] According to a further aspect of the present invention, an optical receiver is provided. An optical receiver includes:

[0056] - A photodetector configured to detect a light beam transmitted by a remote optical transmitter;

[0057] - A hemispherical mirror configured to reflect a portion of the light beam received from the optical transmitter to assist in the beam alignment process performed by the optical transmitter;

[0058] wherein the hemispherical mirror is semi-transparent and semi-reflective, and the photodetector is placed behind the hemispherical mirror relative to the incident direction of the light beam and at the center of the hemisphere.

[0059] According to a further aspect of the present invention, an optical receiver is provided. An optical receiver includes:

[0060] - A photodetector configured to detect a light beam transmitted by a remote optical transmitter;

[0061] - A hemispherical mirror configured to reflect a portion of the light beam received from the optical transmitter to assist in the beam alignment process performed by the optical transmitter;

[0062] wherein the hemispherical mirror is reflective, and the photodetector is placed closely adjacent to the hemispherical mirror such that both the hemispherical mirror and the photodetector are within the coverage area of the light beam from the optical transmitter. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In the drawings, like reference numerals generally refer to the same parts throughout the different Figure 1 views. Further, the drawings are not necessarily to scale; instead, emphasis is generally placed upon illustrating the principles of the invention.

[0064] Figure 1 A conventional one-way beam steering system for optical wireless communication is shown;

[0065] Figure 2 Shows the basic components of an optical transmitter and a remote optical receiver in an optical wireless communication system according to the present invention;

[0066] Figure 3 Shows an example of the basic components included in the beam alignment subsystem of an optical transmitter;

[0067] Figure 4 Shows an example of implementing an optical receiver;

[0068] Figure 5 Shows the arrangement of the beam manipulation system when the optical transmitter and the optical receiver are aligned;

[0069] Figure 6 Shows the arrangement of the beam manipulation system when the optical transmitter and the optical receiver are not aligned;

[0070] Figure 7 Shows another example of implementing an optical receiver and the scenario when the beam is aligned;

[0071] Figure 8 Shows another example of implementing an optical receiver and the scenario when the beam is not aligned; and

[0072] Figure 9 Shows a flowchart of the method of an optical wireless communication system. Detailed Description

[0073] The embodiments set forth below represent information that enables those skilled in the art to practice these embodiments and illustrate the best mode of practicing these embodiments. After reading the following description in accordance with the accompanying drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize the applications of these concepts that are not specifically set forth herein. It should be understood that these concepts and applications fall within the scope of the present disclosure.

[0074] For optical wireless communication such as LiFi, it is known that for a specific separation distance between the transmitter and the receiver, if the radiation beam from the transmitter is narrow, much less transmitted power is required. As the transmitter beam becomes narrower and narrower, it is necessary to direct the beam more precisely to the receiver.

[0075] To establish stable communication with high throughput, the two devices need to face each other and be correctly aligned. Due to the combination of narrow beams and large separations, this can be quite challenging in practice.

[0076] For this purpose, a pilot light can be used, which is positioned close to the photodetector in the receiver and transmits a pilot light signal back to the transmitter. The pilot light signal can be an out-of-band signal that uses a frequency band different from the communication signal. Then, the transmitter will detect the pilot signal and use the detected information to direct the transmitted light beam more precisely towards the receiver.

[0077] Figure 1 An example of a pilot light-based beam alignment setup in an optical wireless communication system is shown. In 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 send an optical data signal to a remote optical receiver. The tiltable mirror (M / Ma) can be adjusted in both the X and Y directions to achieve full 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 from the light source (LS) to the remote optical receiver. In Figure 1 The remote optical receiver or target device shown in the right box includes at least a photodetector (D) and a pilot light (PL). The photodetector (D) is used to receive the optical data signal from the optical transmitter. The pilot light (PL) is used to assist the transmitter in detecting the position of the optical receiver or target device and at the same time direct the light from the light source (LS) to the photodetector (D) of the target device.

[0078] For such a pilot light-based beam alignment system, the design challenges are as follows:

[0079] - The surface of the pilot light (PL) must be much smaller than the surface of the photodetector (D), as shown in the figure. In practice, this may be difficult to achieve when the communication link requires a high data rate because the detector (D) (usually a photodiode or an avalanche photodiode) must have a small surface to obtain a low parasitic capacitance, which directly affects the bandwidth of the receiver in the target device.

[0080] - When the surface of the detector (D) is smaller than the surface of the pilot light (PL), the light 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 sizes of the pilot light (PL) and the detector (D) and the distance between them.

[0081] In view of the limitations of the conventional pilot light-based system, in the present invention, a hemispherical mirror is proposed to be deployed in the target device to reflect a part of the light beam received from the transmitter to assist the beam alignment process in the transmitter, such that the light beam reflected from the target device is used as a kind of pilot light in the conventional system.

[0082] Figure 2Shows the basic components of the optical transmitter 200 and the remote optical receiver 300 in the optical wireless communication system 100 according to the present invention. The optical transmitter 200 includes a light source 210 configured to emit a light beam for optical data communication, and a subsystem 220 configured to perform a beam alignment process based on the incident light received from the remote optical receiver 300. The remote optical receiver 300 includes a photodetector 310 configured to detect the light beam transmitted by the optical transmitter 200; a hemispherical mirror 320 configured to reflect a portion of the light beam received from the optical transmitter 200 to assist the beam alignment process performed by the optical transmitter 200.

[0083] These pairs of remote communication devices 200, 300 operate in the optical band, such as in 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 two remote receivers is usually no greater than 30 degrees or 15 degrees half-angle. To support high data rate and long-distance communication, the beam angle can be on the order of 1 to 5 degrees half-angle, and even reach and include a non-divergent beam. Therefore, it is important to accurately align the light beam emitted from the light source 210 of the optical transmitter 200 towards the photodetector 310 of the optical receiver 300.

[0084] Figure 3 Shows an 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 221, a beam splitter 222, and a multi-element detector 223. The tiltable mirror 221 is configured to reflect the incident light to the beam splitter 222. The beam splitter 222 is configured to selectively direct the reflected light from the tiltable mirror 221 to the multi-element detector 223, or direct the light beam from the light source 210 to the remote optical receiver 300. The multi-element detector 223 is configured to detect the reflected incident light guided by the beam splitter 222 and provide a control signal to manipulate the tiltable mirror 221 such that the reflected incident light falls in the center of the multi-element detector 223.

[0085] Figure 4 Shows an example of implementing the optical receiver 300. The hemispherical mirror 320 is semi-transparent and semi-reflective, and the photodetector 310 is placed behind the hemispherical mirror 320 relative to the incident direction of the light beam and at the center of the hemisphere. The solid line with an arrow represents the incident light beam on the mirror 320 and the reflected light beam from the mirror 320, where the arrow shows the direction of the light beam.

[0086] Figure 4 (a) Shows a scenario where the incident light beam is reflected in the same direction, which gives an indication to the beam alignment subsystem in the optical transmitter that the optical receiver is aligned with the optical transmitter.

[0087] Figure 4 (b) shows a scenario where the incident light beam is reflected in different directions, which gives an indication to the beam alignment subsystem in the optical transmitter that the optical receiver is not aligned with the optical transmitter. The optical transmitter will accordingly adjust the direction of the output light beam, such as by controlling a tiltable mirror or adjusting the light source, until the subsystem detects that the reflected light beam from the optical receiver has the same direction as the transmitted light beam.

[0088] Note that for this setup, the semi-transparent mirror has an exact spherical shape, and the detector 310 is placed in the center of the hemisphere.

[0089] Figure 5 Shows the arrangement of the beam manipulation system according to the present invention when the optical transmitter and the optical receiver are aligned. As compared with the conventional beam alignment setup shown in Figure 1 , the pilot light (PL) in the target is replaced by a semi-transparent mirror (SM) in the shape of a hemisphere. The SM reflects a part of the light beam received from the LS. Only when the light beam is aligned in such a way that it directly hits the center of the detector (D) in the optical receiver, the light will be reflected to the beam manipulation unit on the left side. The center of this detector (D) is preferably located in the center of the hemisphere. In other cases, the light will be reflected in some other direction, so no light will be detected at the quadrant detector (QD).

[0090] Figure 6 Shows a scenario when the optical transmitter and the optical receiver are not aligned. In this example, only the light beam very close to the center of the semi-transparent mirror (SM) will be reflected back in a slightly offset direction to be detected by the quadrant detector (QD). This slightly offset direction deviates from the center of the quadrant detector (QD), and this information can be used for fine-tuning of the light beam direction.

[0091] Figure 7 Shows another example of implementing the optical receiver 300 and a scenario when the light beam is aligned. In this setup, the hemispherical mirror 320 is reflective, and the photodetector 310 is placed closely adjacent to the hemispherical mirror 320 such that both the hemispherical mirror 320 and the photodetector 310 are in the coverage area of the light beam from the optical transmitter 200. The solid line with an arrow represents the incident light beam on the mirror 320 and the reflected light beam from the mirror 320, where the arrow shows the direction of the light beam.

[0092] The coverage areas of the light beam from the optical transmitter and the reflected light beam from the optical receiver are shown by the triangles with dashed lines. In this case, the light beam from the light source should be wide enough so that when it reaches the optical receiver 300, it covers both the hemispherical mirror 320 and the photodetector 310. When the optical transmitter and the optical receiver are aligned, the optical transmitter will also be located in the center of the reflected light beam, as Figure 7 shown in

[0093] Figure 8 Figure shows the scenario when the light beams are misaligned. Due to the reflection on the surface of the hemispherical mirror 320, the reflected light beam received by the subsystem of the optical transmitter will be even more divergent.

[0094] Note that for the setup shown in Figure 7 and Figure 8 the accuracy of the light beam manipulation may be affected by the width of the reflected light beam. Preferably, additional information can be added to the light beam from the light source to assist the light beam alignment process.

[0095] In one example, the light beam from the light source can be configured to be non-uniform in cross-section but have the highest intensity in the center. This additional information can be used for more precise light beam manipulation. When the optical transmitter slightly changes the direction of the transmitted light beam, due to the intensity non-uniformity, the intensity of the reflected light beam will further change. This information can be used to determine which movement of the light source or the tiltable mirror of the optical transmitter is preferred and perform several movements until the maximum intensity is reached, which indicates that the optical transmitter and the optical receiver are accurately aligned. An example of a non-uniform cross-section can be a Gaussian distribution cross-section, which is also easy to implement.

[0096] Figure 9 Figure shows a flowchart of method 500 of the optical wireless communication system 100. Method 500 includes the following steps of the optical wireless communication system 100:

[0097] - In step S501, a light beam is transmitted by the optical transmitter 200 for optical data communication;

[0098] - In step S502, a part of the light beam is reflected by the hemispherical mirror 320 included in the remote optical receiver 300 to assist the light beam alignment process performed by the optical transmitter 200;

[0099] - In step S503, based on the incident light received from the remote optical receiver 300, the optical transmitter 200 performs a light beam alignment process;

[0100] - In step S504, the remote optical receiver 300 detects the light beam from the optical transmitter 200.

[0101] The beam alignment process may further include the following steps for the optical transmitter 200:

[0102] - Reflecting the incident light to a beam splitter through a tiltable mirror;

[0103] - Selectively directing the reflected light from the tiltable mirror by the beam splitter to a multi-element detector or directing the light beam to a remote optical receiver;

[0104] - Detecting the reflected incident light directed by the beam splitter by the multi-element detector; and

[0105] - Providing a control signal to manipulate the tiltable mirror such that the reflected incident light falls in the center of the multi-element detector.

[0106] Those skilled in the art will recognize that the present invention is in no way limited to the above preferred embodiments. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0107] Additionally, by studying the drawings, the disclosure, and the appended claims, those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. An optical wireless communication system (100), comprising: An optical transmitter (200), comprising: - A light source (210) configured to emit a light beam for optical data communication, - A subsystem (220) configured to perform a beam alignment process based on incident light received from a remote optical receiver (300); and A remote optical receiver (300), comprising: - A photodetector (310) configured to detect the light beam transmitted by the optical transmitter (200), - A hemispherical mirror (320) configured to reflect a portion of the light beam received from the optical transmitter (200) to assist the beam alignment process performed by the optical transmitter (200); wherein the hemispherical mirror (320) is semi-transparent and semi-reflective, and the photodetector (310) is placed behind the hemispherical mirror (320) with respect to the incident direction of the light beam and at the center of the hemisphere.

2. The optical wireless communication system (100) according to claim 1, wherein the subsystem (220) comprises: A tiltable mirror (221) configured to reflect the incident light onto a beam splitter (222); The beam splitter (222), configured to selectively: - Direct the reflected light from the tiltable mirror (221) to a multi-element detector (223), or - Direct the light beam from the light source (210) to the remote optical receiver (300); The multi-element detector (223), configured to: - Detect the reflected incident light guided by the beam splitter (222), and - Provide a control signal to manipulate the tiltable mirror (221) such that the reflected incident light falls in the center of the multi-element detector (223).

3. The optical wireless communication system (100) according to claim 1 or 2, wherein a portion of the light beam transmitted through the hemispherical mirror (320) is greater than the remaining portion of the light beam reflected back to the optical transmitter (200).

4. The optical wireless communication system (100) according to claim 3, wherein the portion of the light beam transmitted through the hemispherical mirror (320) is at least twice the remaining portion reflected back to the optical transmitter (200).

5. The optical wireless communication system (100) according to any one of the preceding claims, wherein the light source (210) is configured to emit a light beam with non-uniform intensity in cross-section, and the intensity is highest at the center.

6. The optical wireless communication system (100) according to claim 5, wherein the subsystem (220) uses information related to the non-uniform intensity to assist the beam alignment process.

7. The optical wireless communication system (100) according to claim 5 or 6, wherein the intensity in cross-section conforms to a Gaussian distribution.

8. A method (500) for an optical wireless communication system (100), comprising the following steps: - Transmitting (S501) a light beam by the optical transmitter (200) for optical data communication; - Reflecting (S502) a portion of the light beam by a hemispherical mirror (320) included in the remote optical receiver (300) to assist the beam alignment process performed by the optical transmitter (200); - Based on the incident light received from the remote optical receiver (300), the optical transmitter (200) performs (S503) a beam alignment process; - The remote optical receiver (300) detects (S504) the beam from the optical transmitter (200); wherein the hemispherical mirror (320) is semi-transparent and semi-reflective, and the photodetector (310) of the remote optical receiver (300) is placed behind the hemispherical mirror (320) with respect to the incident direction of the beam and at the center of the hemisphere.

9. The method (500) according to claim 8, further comprising the following steps for the optical transmitter (200): - Reflecting the incident light to the beam splitter (222) through the tiltable mirror (221); - The beam splitter (222) selectively directs the reflected light from the tiltable mirror (221) to the multi-element detector (223), or directs the beam to the remote optical receiver (300); - The multi-element detector (223) detects the reflected incident light guided by the beam splitter (222); and - Providing a control signal to manipulate the tiltable mirror (221) such that the reflected incident light falls in the center of the multi-element detector (223).

10. An optical receiver (300), comprising: - A photodetector (310) configured to detect the beam transmitted by the remote optical transmitter (200); - A hemispherical mirror (320) configured to reflect a part of the beam received from the optical transmitter (200) to assist the beam alignment process performed by the optical transmitter (200); wherein the hemispherical mirror (320) is semi-transparent and semi-reflective, and the photodetector (310) is placed behind the hemispherical mirror (320) with respect to the incident direction of the beam and at the center of the hemisphere.

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