US-20260128791-A1 - System for free space optical communication using active beam steering

US20260128791A1US 20260128791 A1US20260128791 A1US 20260128791A1US-20260128791-A1

Abstract

Optical receiver ( 2 ) comprising a semitransparent retroreflector ( 1; 100; 101; 102; 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 semitransparent retroreflector ( 1; 101; 102 ) comprises a coating ( 5 ) applied to an optical component of the optical receiver ( 2 ), or the semitransparent retroreflector ( 100; 103; 104 ) comprises an optical material introduced by replacing at least a part of an original optical material of an optical component of the optical receiver ( 2 ). Optical wireless communication system comprising the optical receiver.

Inventors

Joris Jan Vrehen

Assignees

SIGNIFY HOLDING B.V.

Dates

Publication Date: 20260507
Application Date: 20231016
Priority Date: 20221021

Claims (15)

1 . An optical receiver comprising: a semitransparent retroreflector configured to assist a retroreflector based beam alignment procedure for the optical receiver; a photodetector configured to detect optical beams for optical wireless communication; wherein the photodetector is placed behind the semitransparent retroreflector; and an optical component; wherein the semitransparent retroreflector comprises a coating applied to the optical component, or wherein the semitransparent retroreflector comprises an optical material being at least a part of the optical component.
2 . The optical receiver according to claim 1 , wherein the coating comprises a thickness configured to allow a part of a light beam emitted by a light source to be transmitted through the coating and a part of the light beam emitted by the light source to be reflected by the coating, or wherein the coating comprises a thickness configured to allow at least 50% or at least 70% of the light of a light beam emitted by a light source to be transmitted through the coating and to allow at most 50% or at most 30% of the light of a light beam emitted by the light source to be reflected by the coating.
3 . The optical receiver according to claim 1 , wherein the coating is a metal, such as gold, or wherein the coating further comprises a stack of layers of a dielectric material.
4 . The optical receiver according to claim 1 , wherein the coating comprises or is provided on a curved surface.
5 . The optical receiver according to claim 4 , wherein the semitransparent retroreflector comprises a lens, and wherein the curved surface comprises a curvature corresponding to the curvature of a focal plane of the lens.
6 . The optical receiver according to claim 1 , wherein the semitransparent retroreflector comprises a lens and an optical substrate, wherein the coating is applied to the optical substrate, and wherein: the optical substrate is placed in the focal point (F) of the lens, or the optical substrate is placed in a distance from the focal point (F) of the lens being smaller than 5 mm or 2 mm or 1 mm.
7 . The optical receiver according to claim 1 , wherein the coating is applied directly onto the optical component of the optical receiver.
8 . The optical receiver according to claim 1 , wherein the optical material being at least a part of the optical component comprises a Fresnel reflectivity of between 3% and 5%, or of 4%.
9 . The optical receiver according to claim 1 , wherein the optical material being at least a part of the optical component is introduced by providing a layer of the optical material on the optical component.
10 . The optical receiver according to claim 1 , wherein the optical material introduced by replacing at least a part of the original optical material of the optical component is provided with or on a curved surface.
11 . The optical receiver according to claim 10 , wherein the semitransparent retroreflector comprises a lens, and wherein the curved surface comprises a curvature corresponding to the curvature of a focal plane of the lens.
12 . The optical receiver according to claim 1 , wherein the optical component being at least a part of is any one of a cover glass, a part of a housing and a part of a surface of the photodetector.
13 . The optical receiver according to claim 1 , wherein the semitransparent retroreflector further comprises an optical material being at least part of the optical component, and wherein the optical component is any one of: at least a part of the photodetector, at least a part of a surface of the photodetector, at least a part of a cover glass of the optical receiver, and at least a part of a housing of the optical receiver.
14 . The optical receiver according to claim 1 , wherein the photodetector is placed in the focal point (F) of a lens of the semitransparent retroreflector.
15 . An optical wireless communication, OWC, system, comprising an optical receiver according to claim 1 .

Description

FIELD OF THE INVENTION 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 semitransparent retroreflector configured to assist a retroreflector based beam alignment in an optical wireless communication, OWC, system, the OWC system comprising an optical receiver, the optical receiver comprising one or more optical components. BACKGROUND OF THE INVENTION This invention is generally employed in Li-Fi communication applications and in particular to Li-Fi communication applications with active beam steering. Li-Fi is a wireless communication technology which utilizes light to transmit data between devices. Li-Fi communication systems are light communication systems capable of transmitting data at high speeds over the visible light, ultraviolet, and infrared spectrums. Li-Fi communication systems use light from light-emitting diodes (LEDs) as a medium to deliver network, mobile, high-speed communication in a similar manner to Wi-Fi. With the increase of required data rates and increasing distances more and more power is needed in the optical beam that carries the data. A way to lower the needed power is to reduce the beam width of the beam (illuminating a smaller area). A drawback of a narrow beam is that the beam needs to be aimed accurately in the direction of the opposite receiver. This can be done manually, or automatically. For an automatic alignment of the beam a signal is needed to establish in which direction the beam should be moved. One well known method to aim the beam at a target is by placing a retroreflector at the position of the target. By scanning the beam one can find the position of the retroreflector by looking at the reflected light returning to the beam steering device. To keep track of the position of the retroreflector, small variations can be made in the beam direction resulting in a modulation of the returned signal strength. The small variation in beam direction can have different shapes. If the same beam is also used to transfer data to the target, a photo detector must be placed near the retroreflector such that the data receiving receiver is also illuminated when the beam is aimed at the retroreflector. For this one can use a retroreflective foil with a hole in the center where the data receiver can be placed. U.S. Pat. No. 11,177,879 B2 discloses a system and method for performing free space optical communication with a plurality of streetlamp assemblies. The method includes transmitting a light beam from a first free space optical (FSO) unit of a first streetlamp assembly to a second FSO unit of a second streetlamp assembly along a transmission path. A transmission error is detected while transmitting the light beam along the transmission path. A location of one or more smart mirrors is obtained. An alternate transmission path is determined from the first FSO unit to the second FSO unit or a third FSO unit. The alternate transmission path includes a reflection of the light beam from the one or more smart mirrors. The smart mirrors may be semi-transparent. The shape of the reflective surface of the smart mirror may be curved. WO2017098220A1 relates to a system for remotely sensing light emanating from within a monitored environment. The system comprises one or more retro-reflective optical elements bearing a reflective optical coating upon a surface and position within the environment to be monitored. US2018128951A1 relates to a device for a sending and receiving unit of a communication arrangement. D3 also fails to disclose a retroreflector based beam alignment system, with the photodetector placed behind the semitransparent retroreflectors for optical data communication. However, a problem related to the above described retroreflectors and data receiver solutions is that they are rather large. This has the consequence that a wider light beam is needed to illuminate both the receiver and the retro reflector. SUMMARY OF THE INVENTION It is an object of the present invention to overcome this problem, and to provide a semitransparent retroreflector configured to assist a retroreflector based beam alignment in an optical wireless communication, OWC, system, which retroreflector is compact and with which a narrower light beam as compared to the prior art solutions is needed to illuminate both the receiver and the retroreflector. It is a further object of the present invention to provide such a semitransparent retroreflector with which smaller amounts of power is needed for data transmission in the OWC system and which is cost-effective to implement. According to a first aspect of the invention, this and other objects are achieved by means of an optical receiver comprising a semitransparent retroreflector configured to assist a retroreflector based beam alignment procedure for the optical receiver; a photodetector configured to detect optical beams for optical wireless c