Free space optical coupling device capable of resisting incident angle jitter

Abstract

The invention discloses a free space optical coupling device capable of resisting incident angle jitter, and belongs to the field of optical communication. A plurality of convex lenses are adopted to realize a coupling lens group with an extremely short equivalent focal length, so that the influence of an incident light angle on a light spot position is as small as possible, and photodiodes with different sizes and bandwidths are mounted on a receiving plane and are respectively used for communication and light spot position monitoring, so that incident angle jitter which is difficult to avoid when a receiver moves is resisted, and the accuracy of communication is improved. And when the light spot deviates from the communication photodiode, the deviation direction of the light spot is detected, so that the direction of the incident light is quickly corrected, and a communication link is recovered.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a free-space optical coupling device capable of resisting incident angle jitter. Background Art

[0002] The coupling technology of spatial light to photodetectors is an important part of the free space optical communication (FSO) system. Its coupling efficiency determines the key indicators of the communication link, such as the bit error rate, interruption probability, and channel capacity. In the FSO system, typical coupling devices include optical components such as the pan / tilt, beam splitter, deflection mirror, and collimating lens. The receiver monitors the laser angle through an imaging device or a four-quadrant detector, controls the laser incident angle by adjusting the pan / tilt direction, and finally focuses the incident laser through a single convex lens or lens group and couples it into the optical fiber.

[0003] The existing solution uses a single lens as a fiber coupling lens. When the incident light angle is in error, that is, it is not parallel to the main optical axis of the lens, the spot point will shift significantly, resulting in the inability to couple the laser into the optical fiber or a small-area PD. If a high-reduction-ratio, high-precision electrically controlled deflection mirror is used to adjust the laser incident angle, the cost will be too high and the laser angle adjustment speed will be too slow, and it will not be able to cope with the high-speed movement of the receiver. When the receiving end moves, the direction of the incident light will change and jitter rapidly, causing the spot position to shift. Due to the limited maneuverability of the gimbal and the insufficient response speed of the imaging device, the offset of the spot position is difficult to be compensated in time, causing the spot to jitter near the end face of the optical fiber, resulting in communication interruption. Therefore, the existing spatial optical coupling device is difficult to solve the problem of stable reception of optical signals from moving targets. Summary of the invention

[0004] The present invention provides a free-space optical coupling device resistant to incident angle jitter, which can suppress the change of the light spot with the angle of the incident light and estimate the deviation direction when the light spot deviates from the communication PD, so as to timely and accurately adjust the light incident angle and restore the light spot position.

[0005] An embodiment of the present invention provides a free-space optical coupling device resistant to incident angle jitter, comprising:

[0006] A coupling lens group, including a plurality of convex lenses, for reducing the influence of the incident light angle on the light spot position;

[0007] Photodiodes (PD) of different sizes and bandwidths are arranged on the receiving plane and are used for high-speed optical communication and light spot position detection.

[0008] Optionally, in one embodiment of the present invention, in the coupling lens group, except for the first convex lens on which the light is incident, the distances between the remaining convex lenses and the previous imaging plane are greater than the distances between the remaining convex lenses and the next imaging plane.

[0009] Optionally, in one embodiment of the present invention, the large-bandwidth PD has a smaller area, the small-bandwidth PD has a larger area, and the small-area PD is placed in the middle of the large-area PD and is surrounded by the large-area PD.

[0010] Optionally, in one embodiment of the present invention, it further includes:

[0011] The transimpedance amplifier is used to estimate the output voltage of the comparison transimpedance amplifier, adjust the direction of the incident light according to the estimation result, and optimize the position of the light spot.

[0012] Optionally, in one embodiment of the present invention, there is a deviation between the receiving plane and the final imaging plane.

[0013] The free-space optical coupling device resistant to incident angle jitter of the embodiment of the present invention adopts multiple lenses to realize a coupling lens group with an extremely short focal length, so that the position of the light spot is affected as little as possible by the angle of the incident light, thereby resisting the inevitable incident angle jitter when the receiver moves, and detecting the direction of the light spot deviation when the light spot deviates from the communication PD, thereby quickly correcting the direction of the incident light and restoring the communication link.

[0014] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0016] Figure 1 A schematic structural diagram of a free-space optical coupling device resistant to incident angle jitter provided according to an embodiment of the present invention;

[0017] Figure 2 FIG. 4 is a schematic diagram of the arrangement of photodiodes on a receiving plane according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0019] The coupling technology of spatial light to photodetectors is an important component of the free space optical communication (FSO) system, and its coupling efficiency determines the key indicators of the communication link, such as the bit error rate, interruption probability, and channel capacity. The device of the present invention stably couples the spatial light signal into the photodetector, which can counteract the jitter generated by the receiver when it moves. The scheme adopts multiple convex lenses to realize a coupling lens group with an extremely short equivalent focal length, so that the position of the light spot is affected as little as possible by the angle of the incident light, and photodiodes of different sizes and bandwidths are installed on the receiving plane, which are used for communication and light spot position monitoring, respectively, so as to counteract the incident angle jitter that is difficult to avoid when the receiver moves. This scheme assumes that the total length of the lens group is known, and minimizes the equivalent focal length of the lens group by solving the optimization problem, and then determines the focal length, number, relative position and other indicators of the lens, thereby minimizing the interruption probability of the spatial light coupling system.

[0020] like Figure 1 As shown, the free-space optical coupling device resistant to incident angle jitter includes:

[0021] A coupling lens group, including a plurality of lenses, is used to reduce the influence of the incident light angle on the light spot position;

[0022] Photodiodes of different sizes and bandwidths are arranged on the receiving plane and are used for high-speed optical communication and light spot position detection.

[0023] The coupling lens group includes multiple coupling lenses, and their relative positions are optimized to make the light spot change as little as possible with the incident light angle; multiple photodiodes are installed on the receiving plane, and their areas and bandwidths are different, which can be used for high-speed optical communication and light spot position detection respectively.

[0024] Except for the first lens where the light is incident, the distance between the remaining lenses and the previous imaging plane is greater than the distance between them and the next imaging plane.

[0025] The large bandwidth PD has a smaller area, the small bandwidth PD has a larger area, and the small area PD is placed in the middle of the large area PD and surrounded by the large area PD. By optimizing the arrangement, the gap between the PDs should be as small as possible.

[0026] Furthermore, the communication PD can also be replaced by an optical fiber end face, and the photoelectric converter is located at the other end of the optical fiber. The spot position monitoring PD array can also be replaced by multiple optical fiber end faces, and these detection optical fibers surround the communication optical fiber.

[0027] There is a transimpedance amplifier after the PD. The light spot position can be estimated by comparing the output voltage of the transimpedance amplifier. The estimation result can be used to adjust the direction of the incident light and optimize the light spot position.

[0028] There can be a small deviation between the receiving plane and the final imaging plane to obtain a larger light spot and enhance the ability to resist the jitter of the incident angle of the optical signal.

[0029] In the embodiment of the present invention, a prism or a reflector is added in the middle of the optical path to fold the optical path, thereby reducing the size of the device. The lens of the coupling lens group is a convex lens, and some lenses can also be replaced by parabolic reflectors or optical metasurface lenses.

[0030] The free-space optical coupling device resistant to incident angle jitter of the embodiment of the present invention uses multiple lenses to realize a coupling lens group with an extremely short equivalent focal length, so that the light spot position is affected as little as possible by the angle of the incident light, and photodiodes of different sizes and bandwidths are installed on the receiving plane, which are used for communication and light spot position monitoring respectively. The PD used for communication usually has a very small area, so the junction capacitance is small and has a large bandwidth; while the PD used for light spot position monitoring usually has a large area and a wide detection range, so the junction capacitance is large, which results in a small bandwidth and is not suitable for communication. When the light spot accurately falls on a small PD for communication with a large bandwidth, the communication link is established, and there is no need to adjust the angle of the incident light; when the light spot leaves the photosensitive surface of the communication PD, the communication link is interrupted, and the large-area PD around it can detect the direction of the light spot offset, so that the angle of the receiver can be adjusted in time so that the light spot can fall on the small PD for communication again.

[0031] like Figure 1 As shown in the figure, it is proposed to use multiple lenses for optical signal coupling, so that when the incident light deviation θ1 caused by jitter is large, the light spot can also fall on a small area detector. The distance between the center of the spot of the inclined incident light and the center of the spot of the parallel incident light on imaging plane 1 is defined as Δ1, the distance between the center of the spot of the inclined incident light and the center of the spot of the parallel incident light on imaging plane 2 is defined as Δ2, and the distance between the center of the spot of the inclined incident light and the center of the spot of the parallel incident light on imaging plane 3 is defined as Δ3. According to Figure 1 It can be seen that Δ3<Δ2<Δ1, that is, the position of the light spot is gradually reduced under the influence of the incident light θ1.

[0032] To achieve the above effect, the relative position of the lenses needs to be designed. First, calculate the k-th imaging plane spacing d k and the focal length of the lens f k When the imaging reduction factor of each level is Δ k / Δ k-1 Function expression of . According to Gauss's formula, we know that:

[0033]

[0034] Among them, d k,F and d k,B is the distance between the kth lens and the two imaging surfaces in front and behind. After solving equation (1), we can get:

[0035]

[0036] Increase imaging reduction condition d k,B <d k,F , we can get the unique solution:

[0037]

[0038] according to Figure 1 The similarity relationship in can be used to obtain the reduction factor of the k+1th level imaging:

[0039]

[0040] According to formula (4), assuming there are K lenses in total, the reduction factor of the cascade lens group is:

[0041]

[0042] Assume that the focal lengths of K lenses are f1...f K , the total length of the optical system is L, and the optimal position of the lens can be determined by solving the following optimization problem to minimize the impact of incident light jitter, that is, to minimize A 总 .

[0043]

[0044] This problem can be solved using tools such as CVX and Matlab.

[0045] For the special case of a double lens K = 2, we can directly obtain the following without solving the optimization problem:

[0046]

[0047] At this time, lens 2 should be placed behind lens 1 at f1+d 2,F The photodiode should be placed behind lens 2. 2,B When the incident light angle deviates, the displacement of the light spot decreases from Δ1 in the case of a single lens to It can be seen that the system's ability to resist changes in incident angle has been enhanced.

[0048] When the focal length of the lens is variable, equation (6) can also be modified to the following problem:

[0049]

[0050]

[0051] The constraint f k ≥f k,th Defines the focal length range of each lens, fk,th is the minimum focal length of the kth lens.

[0052] When the number of lenses K is variable, equation (6) can also be solved under different lens numbers, and the final objective function under different conditions can be compared. The value of determines the minimum number of lenses required.

[0053] like Figure 2 As shown in the figure, the PD areas on the receiving plane are different. The large-area PDs (labeled A, B, C, D) are used for spot position detection, while the small-area PDs (labeled E) are used for communication, that is, transmitting high-speed data streams. Assume that the photocurrents of PD A, PD B, PD C, PDD, and PD E are denoted as I A ,I B ,I C ,I D ,I E , then when:

[0054] I A +I B >I C +I D

[0055] When the light spot is moving downward, the receiving end pan / tilt should be adjusted; otherwise, if:

[0056] I A +I B C +I D

[0057] When the light spot moves upward, the receiving end pan / tilt should be adjusted.

[0058] I A +I D >I B +I C

[0059] When the light spot moves to the right, the receiving end pan / tilt should be adjusted; otherwise, if:

[0060] I A +I D B +I C

[0061] When the light spot moves to the left, the receiving end pan / tilt should be adjusted.

[0062] I A +I D =I B +I C ;I A +I B ​​=I C +I D

[0063] And I E >0, the communication link is established and there is no need to adjust the gimbal.

[0064] The free-space optical coupling device resistant to incident angle jitter in the embodiment of the present invention adopts multiple convex lenses to realize a coupling lens group with an extremely short equivalent focal length, so that the position of the light spot is affected as little as possible by the angle of the incident light, and photodiodes of different sizes and bandwidths are installed on the receiving plane, which are used for communication and light spot position monitoring respectively, so as to counteract the inevitable incident angle jitter when the receiver moves, and detect the direction of the light spot deviation when the light spot deviates from the communication photodiode, so as to quickly correct the direction of the incident light and restore the communication link.

[0065] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0066] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0067] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or N executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present invention belong.

Claims

1. A free-space optical coupling device resistant to incident angle jitter, characterized in that: include: A coupling lens group, including a plurality of convex lenses, for reducing the influence of the incident light angle on the light spot position; Photodiodes of different sizes and bandwidths are arranged on the receiving plane and are used for high-speed optical communication and light spot position detection.

2. The device according to claim 1, characterized in that In the coupling lens group, except for the first convex lens where light is incident, the distances between the remaining convex lenses and the previous imaging plane are greater than the distances between the remaining convex lenses and the next imaging plane.

3. The device according to claim 1, characterized in that The large-bandwidth PD has a smaller area, the small-bandwidth PD has a larger area, and the small-area PD is placed in the middle of the large-area PD and is surrounded by the large-area PD.

4. The device according to claim 1, characterized in that Also includes: The transimpedance amplifier is used to estimate the output voltage of the comparison transimpedance amplifier, adjust the direction of the incident light according to the estimation result, and optimize the position of the light spot.

5. The device according to claim 1, characterized in that There is a deviation between the receiving plane and the final imaging plane.

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