System for free space optical communication using active beam steering

Abstract

The optical receiver (2) comprises a translucent retroreflector (1; 100, 100; 101; 101; 102, 104; 103, 103; 104) configured to assist in a retroreflector-based beam alignment procedure for the optical receiver (2). A photodetector (12) of the receiver is placed behind the retroreflector. The translucent retroreflector (1; 101; 101; 102) comprises a coating (5) applied to an optical component of the optical receiver (2), or a translucent retroreflector (100; 103, 103; 104) comprises an optical material introduced by replacing at least a portion of an original optical material of an optical component of the optical receiver (2). An optical wireless communication system includes an optical receiver.

Description

Technical Field

[0001] The present invention generally relates to a system for free - space optical communication using active beam steering. More particularly, the present invention relates to a semi - transparent retro - reflector configured to assist in retro - reflector - based beam alignment in an optical wireless communication (OWC) system, the OWC system including an optical receiver that includes one or more optical components. Background Art

[0002] The present invention is generally for Li - Fi communication applications and in particular for Li - Fi communication applications with active beam steering. Li - Fi is a wireless communication technology that uses light to transmit data between devices. A Li - Fi communication system is an optical communication system capable of transmitting data at high speed in the visible, ultraviolet, and infrared spectral ranges. A Li - Fi communication system uses light from light - emitting diodes (LEDs) as a medium to provide network, mobile, and high - speed communication in a manner similar to Wi - Fi.

[0003] As the required data rate increases and the distance increases, more and more power is needed in the data - carrying beam. One way to reduce the required power is to reduce the beam width of the beam (illuminating a smaller area). One disadvantage of a narrow beam is that the beam needs to be accurately aimed at the direction of the opposing receiver. This can be done manually or automatically. For automatic alignment of the beam, a signal is needed to determine in which direction the beam should move.

[0004] A well - known method of aiming a beam at a target is by placing a retro - reflector at the location of the target. By scanning the beam, the position of the retro - reflector can be found by observing the reflected light that returns to the beam - steering device. To maintain tracking of the position of the retro - reflector, small changes can be made in the beam direction, the result of which is modulation of the returned signal strength. The small changes in the beam direction can have different shapes. If the same beam is also used to transmit data to the target, a photodetector must be placed near the retro - reflector so that when the beam is aimed at the retro - reflector, the data - receiving receiver is also illuminated. For this purpose, a retro - reflecting foil with a hole in the center can be used, in which the data receiver can be placed.

[0005] US 11,177,879 B2 discloses systems and methods for free space optical communication with multiple street lamp assemblies. The method includes transmitting a light beam from a first free space optical (FSO) unit of a first street lamp assembly to a second FSO unit of a second street lamp assembly along a transmission path. A transmission error is detected while transmitting the light beam along the transmission path. Positions of one or more smart mirrors are obtained. An alternative transmission path from the first FSO unit to the second FSO unit or a third FSO unit is determined. The alternative transmission path includes reflection of the light beam from one or more smart mirrors. The smart mirror can be semi-transparent. The shape of the reflective surface of the smart mirror can be curved.

[0006] WO 2017098220 A1 relates to a system for remotely sensing light emitted from a monitored environment. The system includes one or more retroreflective optical elements having a reflective optical coating on a surface and having a position within the environment to be monitored.

[0007] US 2018128951 A1 relates to an apparatus for a transmitting and receiving unit of a communication arrangement. Nor can D3 disclose a retroreflector-based beam alignment system in which a photodetector is placed behind a semi-transparent retroreflector for optical data communication.

[0008] However, a problem associated with the solutions of the retroreflector and data receiver described above is that they are rather large. This results in a need for a wider light beam to illuminate both the receiver and the retroreflector. SUMMARY OF THE INVENTION

[0009] An object of the present invention is to overcome this problem and provide a semi-transparent retroreflector configured to assist in retroreflector-based beam alignment in an optical wireless communication (OWC) system, the retroreflector being compact, and using which a narrower light beam is required to illuminate both the receiver and the retroreflector compared to prior art solutions.

[0010] A further object of the present invention is to provide such a semi-transparent retroreflector, using which a smaller amount of power is required for data transmission in an OWC system, and which is cost-effectively implemented.

[0011] According to a first aspect of the present invention, this and other objects are achieved by an optical receiver comprising: a translucent retroreflector configured to assist a retroreflector-based beam alignment procedure for the optical receiver; a photodetector configured to detect a beam for optical wireless communication; wherein the photodetector is placed behind the translucent retroreflector; and an optical component; wherein the translucent retroreflector comprises a coating applied to the optical component, or wherein the translucent retroreflector comprises an optical material that is at least part of the optical component.

[0012] Thus, in particular, by either providing a translucent retroreflector comprising a coating applied to the optical component of the optical receiver or providing a translucent retroreflector comprising an optical material introduced by replacing at least part of the original optical material of the optical component of the optical receiver, a translucent retroreflector is provided that is configured to assist retroreflector-based beam alignment in an optical wireless communication (OWC) system. This retroreflector is very compact, and using this retroreflector, a narrower beam is required compared to prior art solutions to illuminate both the receiver and the retroreflector.

[0013] It should be noted that in the case where the translucent retroreflector comprises an optical material introduced by replacing at least part of the original optical material of the optical component of the optical receiver, the part being replaced can in principle be any part, but preferably it is part of the surface of the optical component in question that is intended to face the light source when the translucent retroreflector is mounted in the use position.

[0014] Such a translucent retroreflector further requires a small amount of power for data transmission in the OWC system and is cost-effectively implemented.

[0015] The coating can comprise a thickness configured to allow a part of the beam emitted by the light source to transmit through the coating and a part of the beam emitted by the light source to be reflected by the coating.

[0016] Thus, the coating provides the appropriate translucent properties for the translucent retroreflector. Especially for a metal coating, the amount of light transmitted through the coating relative to the amount of light reflected by the coating can be controlled by adjusting the thickness of the coating, since a thicker coating will increase reflection and decrease transmission.

[0017] The coating can comprise a thickness configured to allow at least 50% or at least 70% of the light of the beam emitted by the light source of the OWC system to transmit through the coating and allow at most 50% or at most 30% of the light of the beam emitted by the light source of the OWC system to be reflected by the coating.

[0018] 50% or more, or 70% or more, of the transmitted light is used for signal detection in the OWC system. 50% or less, or 30% or less, of the reflected light ensures the proper retroreflector function of the translucent retroreflector. Thus, it becomes possible to control reflection and transmission as a function of the wavelength of the light. Especially in the case of a metal coating, absorption may also play a role.

[0019] The coating can be a metal, such as gold.

[0020] Thus, a coating that is simple and easy to apply is provided. If such a coating is made thin enough, the coating becomes translucent to ensure the proper retroreflector function of the translucent retroreflector. In this regard, "thin enough" can be understood to include a thickness suitable for obtaining any of the above requirements for the light beam emitted by the light source, or can be understood to include a thickness of 2 μm or less, such as a thickness between 1 nm and 2 μm. It can also be understood that the suitable thickness of the coating to be made translucent for the light of the light beam emitted by the light source can depend on factors such as the wavelength of the light and the specific type of material used for the coating.

[0021] The coating can include a stack of dielectric material layers.

[0022] Thus, the coating can be provided in a simple and easy-to-produce manner. For a dielectric coating, the amount of reflected light relative to the amount of transmitted light depends on the stack design, which is a function of the materials used, the thickness of each layer, and the number of layers.

[0023] The coating can include a curved surface, or can be provided on a curved surface.

[0024] The translucent retroreflector can include a lens, and the curved surface can include a curvature corresponding to the curvature of the focal plane of the lens.

[0025] By providing such a curved surface, and especially if the curved surface is further placed at the focus of the lens, the light reflected by the translucent retroreflector follows the same or almost the same optical path as the incident light and is sent back towards the beam steering device. By placing such a translucent retroreflector at the position of the target, aiming the light beam at the translucent retroreflector, and scanning the light beam, the position of the translucent retroreflector can be determined with high precision by observing the light returning to the beam steering device.

[0026] The translucent retroreflector may include a lens and an optical substrate, where a coating is applied to the optical substrate to render the optical substrate translucent, and where the optical substrate is placed at the focal point of the lens, or where the optical substrate is placed at a distance less than 5 mm or 2 mm or 1 mm from the focal point of the lens. The optimal distance between the focal point of the lens and the optical substrate depends on the focal length and diameter of the lens used in a particular translucent retroreflector. The distance of the optical substrate to the focal point of the lens can be determined as a function of the focal length of the lens, the lens diameter, and the maximum reflected beam angle.

[0027] The translucent retroreflector may include a lens and an optical substrate, where a coating is applied to the optical substrate to render the optical substrate translucent, and where the optical substrate is placed at a distance D from the focal point of the lens, the distance D being between

[0028]

[0029] where f is the focal length of the lens and d is the diameter of the lens. By satisfying this relationship for the distance D, the reflected beam angle is limited to 20° full width at half maximum (FWHM).

[0030] Thus, the lens and the optical substrate constitute the retroreflector. By applying a coating to the optical substrate, the retroreflector is made translucent. Thus, a portion of the light incident on the optical substrate is transmitted through to an optical receiver (such as a photodiode), effectively co - locating the retroreflector and the photodiode. This will allow for a much smaller and more compact retroreflector, which in turn results in lower power being required for data transmission.

[0031] By placing the optical substrate at a distance D that satisfies the above relationship or less than 5 mm or 2 mm or 1 mm from the focal point of the lens and thus being slightly defocused, a convergence of the diverging reflected beam is obtained such that a larger spot returns to the beam steering unit.

[0032] The optical substrate may include a curved surface on which the coating is applied, the curved surface including a curvature corresponding to the curvature of the focal plane of the lens.

[0033] Thus, and especially if the optical substrate is placed at the focal point of the lens, the light reflected by the optical substrate follows the same or nearly the same optical path as the incident light back towards the beam steering device of the OWC system. By placing such a translucent retroreflector at the location of the target, aiming the beam at the translucent retroreflector, and scanning the beam, the position of the translucent retroreflector can be determined with high precision by observing the light returning to the beam steering device.

[0034] The coating may be applied directly to the optical components of the optical receiver.

[0035] Thus, a translucent retroreflector with a particularly compact structure is obtained.

[0036] The optical material introduced by replacing at least a portion of the original optical material of the optical components of the optical receiver may include a Fresnel reflectivity between 3% and 5%, or 4%.

[0037] This Fresnel reflectivity can be obtained by using the inherent Fresnel reflectivity of a suitable optical medium. This in turn provides a translucent retroreflector with a particularly simple and compact structure. It should be noted that the above values are reasonable values for a glass-air transition. Higher values may be applicable if high-index materials, such as silicon photodetectors, are used.

[0038] The optical material introduced by replacing at least a portion of the original optical material of the optical components of the optical receiver can be introduced by providing a layer of the optical material on the optical components of the optical receiver.

[0039] Thus, a translucent retroreflector with a particularly compact structure is provided.

[0040] The optical material introduced by replacing at least a portion of the original optical material of the optical components can be provided with a curved surface or provided on a curved surface.

[0041] The translucent retroreflector can include a lens, and the curved surface can include a curvature corresponding to the curvature of the focal plane of the lens.

[0042] For example, the curvature can be molded in the optical components of the optical receiver, such as in a photodiode package. Thus, a very cost-effective implementation of such a curvature becomes possible.

[0043] The optical components of the optical receiver into which optical material is introduced by replacing at least a portion of the original optical material can be any one of a protective glass, a part of a housing, and a part of the surface of a photodetector or a photodiode.

[0044] Thus, a translucent retroreflector with a particularly simple and compact structure is provided, especially since no additional material needs to be added to the system.

[0045] The coating can further include a high reflectivity, such as a reflectivity of more than 80%, 90%, or 95% for light having a wavelength different from one or more wavelengths of the beam emitted by the light source.

[0046] Thus, interference from other light sources having wavelengths different from one or more wavelengths of the beam emitted by the light source is minimized or even completely eliminated.

[0047] The present invention also relates to an optical wireless communication (OWC) system, which includes an optical receiver according to the present invention.

[0048] The OWC system may include an optical receiver and at least one light source, and, in the propagation direction of the light emitted by the at least one light source, the optical receiver may be placed downstream of a translucent retroreflector.

[0049] The translucent retroreflector of the OWC system may include an optical material introduced by replacing the original optical material of an optical component of the optical receiver, and the optical component may be any one of the following: at least a part of a photodiode, at least a part of the surface of a photodetector, at least a part of the protective glass of the optical receiver, and at least a part of the housing of the optical receiver. The optical receiver of the OWC system may be placed at the focal point of the lens of the translucent retroreflector.

[0050] Therefore, the inherent reflectivity of the optical receiver and, if provided, the coating of the optical receiver can be utilized to provide the desired translucent retroreflector.

[0051] It should be noted that the present invention relates to all possible combinations of the features recited in the claims.

[0052] Advantageously, the present invention also relates to a method for manufacturing a translucent retroreflector for an optical receiver according to the present invention; the method includes:

[0053] - Replacing at least a part of the original optical material of an optical component of the optical receiver with another optical material to allow a part of the light beam incident on the translucent retroreflector to be transmitted therethrough and a part of the light beam to be reflected. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Now, this aspect and other aspects of the present invention will be described in more detail with reference to the accompanying drawings showing the (multiple) embodiments of the present invention.

[0055] Figure 1 A schematic side view showing an optical wireless communication (OWC) system including a translucent retroreflector according to the present invention.

[0056] Figure 2 Showing according to Figure 1 A schematic side view of a variant of the translucent retroreflector.

[0057] Figure 3 A schematic side view showing an optical wireless communication (OWC) system including another translucent retroreflector according to the present invention.

[0058] Figure 4 Showing according toFigure 3 Schematic side view of a variant of a translucent retroreflector.

[0059] Figure 5 Schematic side view showing another translucent retroreflector according to the present invention.

[0060] Figure 6 Showing according to Figure 5 Schematic side view of a variant of a translucent retroreflector.

[0061] Figure 7 Schematic side view showing another translucent retroreflector according to the present invention.

[0062] Figure 8 Showing according to Figure 7 Schematic side view of a variant of a translucent retroreflector.

[0063] As shown in the figures, the dimensions of the layers and regions are exaggerated for illustrative purposes and are thus provided to illustrate the general structure of embodiments of the present invention. Like reference numerals always refer to like elements. Detailed Description

[0064] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which current preferred embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the invention to those skilled in the art.

[0065] Figure 1 Schematic side view showing an optical wireless communication OWC system 8 including a translucent retroreflector 1 according to the present invention. The translucent retroreflector 1 according to the present invention is configured to assist in a retroreflector-based beam alignment procedure in the OWC system 8. Thus, the translucent retroreflector 1 according to the present invention may form part of the OWC system 8. The OWC system further includes a light source 7 and an optical receiver 2. In this figure, OA represents the optical axis of both the OWC system 8 and the translucent retroreflector 1.

[0066] The light source 7 is a laser light source such as an LED, a laser, or a semiconductor laser. The light source 7 is configured to emit a laser 6 during operation, particularly a highly collimated laser 6. In Figure 1 one light source 7 is shown. It is also feasible to provide more than one light source 7 (such as an array of light sources 7) for the OWC system 8.

[0067] The optical receiver 2 can be any type of optical receiver suitable for use in an OWC system. For example, Figure 1The optical receiver 2 shown in [Fig. 0] is a photodetector 12. The optical receiver 2 can also be a photodiode, which can include the photodetector 12. In any case, the optical receiver 2 includes one or more optical components. The optical components can include one or more of the photodetector 12 itself, the lens 3, the optical substrate 4, the protective glass 9, and the package 11.

[0068] The translucent retroreflector 1 is generally and regardless of the embodiment configured to assist in the retroreflector-based beam alignment in the OWC system 8.

[0069] As Figure 1 shown in [Fig. 8], the translucent retroreflector 1 can include a coating 5 applied to the optical components of the optical receiver 2 of the OWC system 8. Alternatively, as Figure 2 shown in [Fig. 10], the translucent retroreflector 1 can include an optical material 4 introduced by replacing at least a portion of the original optical material of the optical components of the optical receiver 2 of the OWC system 8.

[0070] As Figure 1 shown in [Fig. 15], the translucent retroreflector 1 includes the lens 3 and the optical substrate 4. The optical substrate 4 is placed at the focal point F of the lens 3, thereby creating a retroreflector. The coating 5 is applied to the optical substrate 4 and is configured to render the optical substrate 4 translucent or to make the optical substrate 4 semi-transparent, thereby creating the translucent retroreflector 1. Essentially, the optical substrate 4 and the coating 5 together constitute a semi-transparent mirror. Thus, a portion of the light 6 emitted by the light source 7 is transmitted through (see beam 61) to the optical receiver 2. In this way, the translucent retroreflector 1 and the optical receiver 2 are effectively co-located such that the optical components of the retroreflector 1, namely the lens 3 and the optical substrate 4, can also be considered as the optical components of the optical receiver 2. Additionally, the optical substrate 4, and thus the coating 5, is placed at a distance D from the optical receiver 2.

[0071] Viewed from the propagation direction of the light 6 and / or along the optical axis OA, the optical receiver 2, and in particular the photodetector 12, is generally and regardless of the embodiment arranged downstream of the translucent retroreflector 1, and in particular downstream of the optical substrate 4 and the coating 5. Thus, the optical receiver 2 is arranged to capture the light 61 transmitted through the translucent retroreflector 1.

[0072] Regardless of the embodiment, the coating 5 may include a thickness configured to allow a portion 61 of the light beam 6 emitted by the light source 7 of the OWC system 8 to transmit through the coating 5, and a portion of the light beam 6 emitted by the light source 7 of the OWC system 8 is reflected by the coating 5. The coating may include a thickness configured to allow 50%, 60%, or 70% of the light of the light beam 6 emitted by the light source 7 of the OWC system 8 to transmit through the coating 5, and allow 50% or 40% or 30% of the light of the light beam 6 emitted by the light source 7 of the OWC system 8 to be reflected by the coating 5. The coating 5 may include a thickness between 1 nm and 2 μm. The coating 5 may further include a high reflectivity to light having a wavelength different from one or more wavelengths of the light beam 6 emitted by the light source 7 of the OWC system 8. The coating 5 may be a metal, such as gold. Alternatively, the coating 5 may include a stack of dielectric material layers.

[0073] In Figure 2 the variant shown, the translucent retroreflector 1 likewise includes the coating 5 and the lens 3. For simplicity, the lens 3 is not shown in Figure 2 . The coating 5 is placed directly on the optical receiver 2 here. Thus, in this case, the distance D is zero. The optical receiver 2 includes a photodetector 12 and an encapsulation 11 encapsulating the photodetector 12. The encapsulation 11 may be plastic or epoxy resin molded over the photodetector 12. As Figure 2 shown, the encapsulation 11 includes a flat surface 14.

[0074] More particularly, in the assembled state of the translucent retroreflector 1, the coating 5 is placed on or at the surface 14 of the encapsulation 11 facing the lens 3, or replaces a portion of the surface 14. The coating 5 may simply be added to the surface 14. The coating 5 may be introduced as an optical material that replaces a part of the original optical material of the optical component in the form of the encapsulation 11 of the optical receiver 2 of the OWC system 8. The coating 5 is again placed in the focal point F of the lens 3, thereby creating a retroreflector. By utilizing the inherent reflectivity (Fresnel reflectivity) of the photodetector 12, the retroreflector presents the translucent retroreflector 1. In this case, the optical substrate 4 may thus be omitted.

[0075] Now turning to Figure 3 and Figure 4 , perspective side views showing two variants of the translucent retroreflector 100 are shown.

[0076] Figure 3 The variant of the translucent retroreflector 100 shown in Figure 1The described translucent retroreflector 1 generally differs in that the optical substrate 4 is a curved optical substrate 4. A coating 5 is applied to the curved optical substrate 4 and configured to render the curved optical substrate 4 translucent or to make the curved optical substrate 4 semi-transparent, thereby creating the translucent retroreflector 100. Generally and regardless of the embodiment, the curved optical substrate 4 may be provided with a surface having a curvature corresponding to the curved focal plane of the lens 3.

[0077] Figure 4 The variant of the translucent retroreflector 100 shown in is different from the translucent retroreflector 1 described above with reference to Figure 2 The described translucent retroreflector 1 generally differs in that the optical substrate 4 is a curved optical substrate 4, and a mirror is provided above or within or recessed into the curved surface 15 provided in the package 11 of the optical detector 2.

[0078] In the above variants of the translucent retroreflector 1 or 100, depending on the situation, the optical substrate 4 or the coating 5 is placed at the focus F of the lens 3 in all cases. Another option is, depending on the situation, to place the optical substrate 4 or the coating 5 slightly out of focus, i.e., slightly deviated from the focus F of the lens 3. This will result in a slightly converging or diverging reflected light beam, such that a larger light spot returns to the beam steering unit. In this regard, being slightly deviated from the focus F of the lens 3 can be understood to mean being placed at a distance D less than 5 mm or 2 mm or 1 mm from the focus F of the lens 3. Being slightly deviated from the focus F of the lens 3 can also and more generally be understood to mean being placed at a distance D from the focus of the lens 3, where the distance D is between

[0079]

[0080] where f is the focal length of the lens and d is the diameter of the lens 3. By satisfying this relationship for the distance D, the reflected light beam angle is limited to 20° full width at half maximum (FWHM).

[0081] Now turning to Figure 5 , a schematic side view of another translucent retroreflector 101 according to the present invention is shown. Due to the following features, Figure 5 The translucent retroreflector 101 shown in is different from the translucent retroreflector described above with reference to Figures 1 to 4 described.

[0082] The optical receiver 2 is a photodiode, which includes a photodetector 12 arranged in a housing 10. The housing includes: a bottom 13 on which the photodetector 12 is arranged; a wall 16 that extends from the bottom 13 so as to surround the photodetector 12; and a protective glass 9 that is arranged on the front surface of the wall 16 opposite to the bottom 13.

[0083] The coating 5 is applied to the surface 17 of the protective glass 9 such that the lens 3 (not shown for simplicity) and the protective glass 9 with the coating 5 together form a translucent retroreflector 101. The coating is placed at the focal point F of the lens 3.

[0084] Figure 6 A schematic side view of another translucent retroreflector 102 according to the present invention is shown. Due to the following features, Figure 6 the translucent retroreflector 103 shown in Figure 5 is different from the translucent retroreflector 101 described above with reference to

[0085] Now, the coating 5 is directly applied to the photodetector 12. The photodetector 12 is placed at the focal point F of the lens 3, in particular the coating 5 is placed at the focal point F of the lens 3. Thus, the inherent reflectivity (Fresnel reflectivity) of the photodetector 12 is utilized to render the translucent retroreflector 103 translucent. If the coating 5 is applied, the coating 5 determines the amount of light reflected. If the coating 5 is not applied, the inherent Fresnel reflection of the surface of the photodetector 12 (in particular the silicon surface) can be used to determine the amount of light reflected.

[0086] Figure 7 A schematic side view of another translucent retroreflector 103 according to the present invention is shown. Due to the following features, Figure 7 the translucent retroreflector 103 shown in Figure 5 and Figure 6 is different from the translucent retroreflectors 101 and 102 described above with reference to

[0087] The optical substrate 4 having a curved surface is arranged on the surface 17 of the protective glass 9 such that the lens 3 (not shown for simplicity) and the protective glass 9 with the optical substrate 4 together form a translucent retroreflector 102. The optical substrate 4 is placed at the focal point F of the lens 3, in particular the curved surface is placed at the focal point F of the lens 3. Alternatively, the optical substrate 4 having a curved surface can also be arranged within the surface 17 of the protective glass 9, such as being recessed therein.

[0088] Figure 8 A schematic side view of another translucent retroreflector 104 according to the present invention is shown. Due to the following features, Figure 8 the translucent retroreflector 104 shown in Figure 7 is different from the translucent retroreflector 103 described above with reference to

[0089] Now, the optical substrate 4 with a curved surface is directly disposed on the photodetector 12. The photodetector 12 is placed at the focal point F of the lens 3, and in particular, the optical substrate 4 is placed at the focal point F of the lens 3. Thus, the inherent reflectivity (Fresnel reflectivity) of the photodetector 12 is utilized to render the translucent retroreflector 104 translucent. Alternatively, the optical substrate 4 with a curved surface can also be directly disposed on the package of the photodetector 12, within the package of the photodetector 12, or recessed within the package of the photodetector 12.

[0090] Those skilled in the art will recognize that the present invention is in no way limited to the above-described preferred embodiments. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0091] 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 receiver (2), the optical receiver comprising: - a translucent retroreflector (1; 100； 101； 102； 103； 104), the translucent retroreflector configured to assist a retroreflector-based beam alignment procedure for the optical receiver (2); - a photodetector (12), the photodetector (12) configured to detect a beam for optical wireless communication; wherein the photodetector (12) is placed behind the translucent retroreflector (1; 100; 101; 102; 103; 104); and - an optical component; wherein the translucent retroreflector (1; 101; 102) comprises a coating (5) applied to the optical component, or wherein the translucent retroreflector (100; 103; 104) comprises an optical material that is at least part of the optical component.

2. The optical receiver (2) according to claim 1, wherein the coating (5) comprises a thickness configured to allow a portion of the beam (6) emitted by a light source (7) to transmit through the coating, and a portion of the beam emitted by the light source to be reflected by the coating, or wherein the coating (5) comprises a thickness configured to allow at least 50% or at least 70% of the light of the beam (6) emitted by a light source (7) to transmit through the coating, and to allow at most 50% or at most 30% of the light of the beam emitted by the light source to be reflected by the coating.

3. The optical receiver (2) according to any one of the preceding claims, wherein the coating (5) is a metal, such as gold, or wherein the coating (5) further comprises a stack of dielectric material layers.

4. The optical receiver (2) according to any one of the preceding claims, wherein the coating (5) comprises a curved surface (15) or is provided on a curved surface (15).

5. The optical receiver (2) according to claim 4, wherein the translucent retroreflector comprises a lens (3), and wherein the curved surface (15) comprises a curvature corresponding to the curvature of the focal plane of the lens (3).

6. The optical receiver (2) according to any one of the preceding claims, wherein the translucent retroreflector comprises a lens (3) and an optical substrate (4), wherein the coating (5) is applied to the optical substrate (4), and wherein: the optical substrate is placed at the focus (F) of the lens, or the optical substrate is placed at a distance less than 5 mm or 2 mm or 1 mm from the focus (F) of the lens.

7. The optical receiver (2) according to any one of the preceding claims, wherein the coating (5) is directly applied to the optical component of the optical receiver (2).

8. The optical receiver (2) according to claim 1, wherein the optical material that is at least part of the optical component has a Fresnel reflectivity between 3% and 5%, or 4%.

9. The optical receiver (2) according to claim 1 or 8, wherein The optical material, which is at least part of the optical component, is introduced by providing a layer of the optical material on the optical component.

10. The optical receiver (2) according to claim 1, 8 or 9, wherein, the optical material introduced by replacing at least part of the original optical material of the optical component is provided with a curved surface or provided on a curved surface.

11. The optical receiver (2) according to claim 10, wherein, the translucent retroreflector includes a lens (3), and wherein the curved surface includes a curvature corresponding to the curvature of the focal plane of the lens.

12. The optical receiver (2) according to claim 1, 8, 9, 10 or 11, wherein, the optical component, which is at least part of it, is any one of a protective glass (9), a part of the housing (10), and a part of the surface of the photodetector (12).

13. The optical receiver (2) according to any one of the preceding claims, wherein, the translucent retroreflector further includes an optical material that is at least part of the optical component, and wherein the optical component is any one of the following: at least part of the photodetector (12), at least part of the surface of the photodetector (12), at least part of the protective glass (9) of the optical receiver, and at least part of the housing (10) of the optical receiver.

14. The optical receiver (2) according to any one of the preceding claims, wherein, the photodetector (12) is placed at the focus (F) of the lens of the translucent retroreflector.

15. An optical wireless communication OWC system comprising an optical receiver (2) according to any one of the preceding claims.

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