WO2022196337A1

WO2022196337A1 - Optical transmission apparatus

Info

Publication number: WO2022196337A1
Application number: PCT/JP2022/008529
Authority: WO
Inventors: 悠宮島; 雄一富岡
Original assignee: キヤノン株式会社
Priority date: 2021-03-16
Filing date: 2022-03-01
Publication date: 2022-09-22

Abstract

The purpose of the present invention is to provide an optical transmission apparatus that can be adjusted to a good divergence in order to ensure the stability of communication. The optical transmission apparatus performs optical communication between a light projection unit, which includes an emission means for emitting communication light and a light projection optical system, and a light reception unit, which includes a light reception optical system and a communication light reception means for receiving the communication light, the optical transmission apparatus being characterized in that: the light projection unit includes a detection light emission unit for emitting detection light; the light projection optical system has an adjustment optical system for changing the divergence of light flux; the light reception unit includes a detection light reception means for receiving the detection light; and the optical transmission apparatus includes a divergence control unit for controlling the adjustment optical system on the basis of information from the detection light reception means.

Description

optical transmission equipment

The present invention relates to an optical transmission device that is arranged at a distance and transmits and receives light to transmit information.

An optical transmission device consists of a light projecting part that transmits communication light and a light receiving part that receives communication light. In order to perform stable communication, it is necessary to align the optical axes of the optical system of the light-projecting section and the optical system of the light-receiving section.

Spatial optical transmission equipment (optical transmission equipment) has the problem that the direction of communication light changes due to vibrations at the installation location, atmospheric fluctuations, environmental temperature changes, etc., and communication becomes unstable.

In Patent Document 1, the amount of positional deviation between a receiving telescope and a transmitting telescope is estimated from the amount of received light (received signal power), and an optical fiber, which is a light projecting part, is moved according to the estimated amount of positional deviation. A technique is disclosed for uninterrupted communication by increasing the cross-sectional area of the transmitted beam incident on the receiving telescope.
The optical transmission device includes a light projecting section for transmitting communication light and a light receiving section for receiving communication light. In order to perform communication, it is necessary to correct the eccentricity of the communication light beam caused by disturbance.
Therefore, especially in an optical transmission device, correcting the eccentricity of a communication light beam is a problem. Patent Documents 2 and 3 disclose techniques for correcting eccentricity of communication light beams caused by vibration of a lens portion using a plurality of vibration isolation mechanisms.

JP-A-2002-164853 JP 2017-161567 A JP-A-07-027978

However, in the prior art disclosed in Patent Document 1, if the amount of positional deviation is estimated based on the amount of received light, it is difficult to determine the shift direction of the optical fiber, and adjustment takes time or cannot be completely adjusted. Therefore, the communication light is diverged more than necessary, and there is a possibility that the amount of received light is reduced. Further, the frequency that can be vibrated by shifting the optical fiber is not clear, and the amount of positional deviation that can be corrected by shifting the optical fiber and the amount of positional deviation that cannot be corrected are not clear.
Even if an antivibration mechanism is used as in the prior arts of Patent Documents 2 and 3, it is difficult to completely eliminate the eccentricity of the light flux. In addition, since there is an intensity distribution in the light flux, there is a problem that the amount of light fluctuates due to a change in the amount of vignetting at the opening of the light receiving section. Good communication quality cannot be obtained when the amount of light fluctuates greatly or when the amount of light is insufficient.

Accordingly, it is an object of the present invention to solve the above problems and to provide an optical transmission device that can be adjusted to a good degree of divergence in order to ensure communication stability.

An optical transmission device according to the present invention for achieving the above object is a light projecting section including emitting means for emitting communication light and a light projecting optical system, a light receiving optical system, and communication light receiving means for receiving the communication light. and an optical transmission device for performing optical communication between a light receiving unit including An adjusting optical system is provided, the light receiving unit includes detection light receiving means for receiving the detection light, and the optical transmission device controls the divergence of the adjusting optical system based on information from the detection light receiving means. A control unit is provided.
An optical transmission device according to the present invention for achieving the above object comprises a first light projecting section including first emitting means for emitting first communication light and a first light projecting optical system; a light receiving optical system, a first light receiving unit including a first communication light receiving means for receiving the first communication light, a second emitting means for emitting the second communication light, and a second light projecting optical system and a second light receiving unit including a second light receiving optical system and second communication light receiving means for receiving the second communication light, An optical transmission device for performing optical communication between one light projecting unit and the first light receiving unit, and performing optical communication between the second light projecting unit and the second light receiving unit, The first light projecting part has a detection light emitting part for emitting detection light, the second light projecting optical system has an adjusting optical system for changing the divergence of the light flux, and the first light receiving part has detection light receiving means for receiving the detection light, and the optical transmission device has a divergence control section for controlling the adjustment optical system based on information obtained by the detection light receiving means. characterized by
An optical transmission apparatus according to the present invention for achieving the above object includes a first light emitting/receiving means for emitting a first communication light and receiving a second communication light, and a first optical system. a second light projecting/receiving unit including one light projecting/receiving unit, second light emitting/receiving means for emitting the second communication light and receiving the first communication light, and a second optical system; and performing bidirectional optical communication between the first and second light projecting and receiving sections, wherein the first light projecting and receiving section includes a detection light emitting section for emitting detection light. the second optical system has an adjusting optical system for changing the divergence of the light beam; the second light projecting and receiving unit has detection light receiving means for receiving the detection light; The transmission device is characterized by comprising a divergence control section for controlling the adjustment optical system based on information from the detection light receiving means.

With the above configuration, it is possible to provide an optical transmission device that can be adjusted to a good degree of divergence in order to ensure communication stability.

1 is a configuration diagram of an optical transmission device according to a first embodiment; FIG. FIG. 2 is a detailed configuration diagram of a light projecting unit according to the first embodiment; 4 is an enlarged view of a main portion of the light projecting section of Example 1. FIG. 4 is a detailed configuration diagram of a light receiving unit of Example 1. FIG. 4 is an enlarged view of a main portion of the light receiving portion of Example 1. FIG. FIG. 4 is a longitudinal aberration diagram for a wavelength of 1550 nm during focusing at infinity in the light receiving optical system of Example 1; 4 is a lateral aberration diagram for a wavelength of 1550 nm during focusing at infinity of the light receiving optical system of Example 1. FIG. 4 is an explanatory diagram of the amount of received light at the aperture diameter D of the light receiving optical system of Example 1. FIG. 4 is an explanatory diagram of a method for calculating an additional divergence angle β in Example 1. FIG. FIG. 4 is a diagram showing the relationship of required beam waist _wn with respect to communication distance L in Example 1; 4 is a diagram showing the relationship of parallel light beam waist _wp to communication distance L in Example 1. FIG. 4 is a diagram showing the relationship of the divergent light beam waist _wx to the communication distance L in Example 1. FIG. FIG. 11 is a detailed configuration diagram of a light projecting unit according to the second embodiment; FIG. 11 is a detailed configuration diagram of a light receiving unit of Example 2; FIG. 10 is a view of the second embodiment in which the replaceable holding member of the light receiving unit is removed and the camera is attached; FIG. 10 is a longitudinal aberration diagram for the e-line during focusing at infinity of the light receiving optical system of Example 2; FIG. 10 is a lateral aberration diagram for the e-line during focusing at infinity of the light receiving optical system of Example 2; It is the intensity distribution of the luminous flux immediately after the opening of the light projecting part in Example 2. It is the intensity distribution of the luminous flux at the opening of the light-receiving part 2 km away from the light-projecting part in Example 2. It is the intensity distribution of the luminous flux at the opening of the light-receiving part which is 5 km away from the light-projecting part in Example 2. 4 is a transmittance distribution of the light intensity conversion element of Example 2. FIG. 10 shows the intensity distribution of the luminous flux immediately after the opening of the light projecting section in Example 3. FIG. It is the intensity distribution of the luminous flux at the opening of the light-receiving part 2 km away from the light-projecting part of Example 3. It is the intensity distribution of the luminous flux at the opening of the light-receiving part which is 5 km away from the light-projecting part in Example 3. 10 shows the transmittance distribution of the light intensity conversion element of Example 3. FIG. FIG. 11 is a detailed configuration diagram of a light projecting unit of Example 4; FIG. 11 is a detailed configuration diagram of a light projecting unit of Example 5; It is the transmittance distribution of the light intensity conversion element of the modification. It is the transmittance distribution of the light intensity conversion element of the modification.

The present invention will be described below using specific examples. In the explanatory diagrams, the scale may differ from the actual scale for the sake of clarity.

FIG. 1 is a schematic configuration diagram of an optical transmission device showing an embodiment of the present invention. Description is made from one direction (optical transmission device 1000 (light projecting unit, first light projecting unit, first light projecting/receiving unit) to optical transmission device 2000 (light receiving unit, first light receiving unit, second light projecting/receiving unit). ))), the same applies to communication in the reverse direction (from the optical transmission device 2000 to the optical transmission device 1000).

The communication light transmitted from the optical transmission device 1000 on the transmission side is received by the optical transmission device 2000 on the reception side at a distance, and communication is performed.

An optical transmission device 1000 on the transmission side is configured by mounting a light projection unit 100 for emitting communication light on an angle adjustment base 101 . The orientation of the light projecting unit 100 can be adjusted on two axes.

An optical transmission device 2000 on the receiving side is configured such that a light receiving section 200 for receiving communication light is mounted on an angle adjustment base (angle adjustment section) 201 . The orientation of the light receiving section 200 can be adjusted on two axes.

In order to align the optical axes of the light projecting optical system 120 (not shown in FIG. 1) of the light projecting unit 100 and the light receiving optical system 220 (not shown in FIG. 1) of the light receiving unit 200 at the time of installation. Then, the angle is adjusted by the angle adjustment table 101 and the angle adjustment table 201. FIG. This ensures communication once.

However, if the

optical transmission devices

1000 and 2000 continue to be used as they are, atmospheric fluctuations, vibrations of members (not shown) holding the angle adjustment base 101 and the light receiving optical system 220, environmental temperature fluctuations, etc. , the optical path of communication light fluctuates, and communication is not stable. Therefore, fluctuations in the communication light are grasped by the transmission light detection unit of the light projection unit 100 and the reception light detection unit of the light reception unit 200 (composed of a transmission wedge prism 231 and a position detection sensor 232, which will be described later). and corrects the optical path of communication light to stabilize communication. Specifically, the transmission light control unit (divergence control unit) 140, the focus mechanism (correction optical system, both of which are not shown in FIG. 1) in the projection optical system 120, the angle adjustment base 201, the reception light control unit ( A divergence control unit 240 and an image blur correction mechanism (correction optical system, both of which are not shown in FIG. 1) in the light receiving optical system 220 correct the optical path of communication light and stabilize communication.

The configuration of the optical transmission device of the present invention will be described in detail below with reference to FIGS. 2A to 21. FIG.

(Example 1)
FIG. 2A is a detailed configuration diagram of the optical transmission device 1000 .
The light projecting section 100 has a communication light emitting means 110, a light projecting optical system 120 (first optical system), a transmission light detection section, a transmission light control section 140, and a holding section 150 (not shown). . A communication light emitting means (ejecting means, a detection light emitting part, a first emitting and receiving means) 110 emits communication light, and a light projecting optical system 120 converts the communication light emitted from the communication light emitting means 110 into substantially parallel light. Send. The transmitted light detection section detects the state of the communication light transmitted from the projection optical system 120, and the transmitted light control section 140 controls the communication light.

In Example 1, the communication light emitting means 110 is an optical fiber, and emits communication light having a wavelength in the wavelength band of 1540 nm to 1560 nm, which is incident from the other end (not shown). Communication light receiving means 210 (not shown in FIG. 2A), which will be described later, is also an optical fiber, and receives communication light at the other end (not shown). Thus, the optical transmission device 1000 on the transmission side and the optical transmission device 2000 on the reception side have substantially the same structure, and if the direction of the communication light in the optical fiber is reversed, the relationship between transmission and reception is reversed. become. Thereby, two-way communication is established.

The light projecting optical system 120 includes a lens 121, a lens 122, a lens 123, a secondary mirror (reflective curved surface) 124, and a primary mirror (reflective curved surface) 125. The lens 121 (movable optical member, transmissive optical member, second adjustment optical system) has an image blur correction mechanism (correction optical system, double-lined frame in the drawing), and shifts in a direction perpendicular to the optical axis. This makes it possible to finely adjust the direction of the communication light (angle of incidence on the communication light receiving means 210). In this embodiment, the image blur correction mechanism (correction optical system) is composed of a lens 121 that is a single optical element. In addition, the lens 123 (movable optical member, transmissive optical member) has a focus mechanism (correction optical system, double-lined frame in the figure), and by shifting in the optical axis direction, the degree of divergence of communication light can be minimized. can be adjusted. The primary mirror 125 has an opening with a diameter of 30 mm at its center.

The transmitted light detector includes reflecting

prisms

131a and 131b that return part of the transmitted communication light, and position detection sensors (second detection light receiving means) 132a and 132b that detect the condensing positions of the returned light beams. Consists of

FIG. 2B is an enlarged view of reflecting

prisms

131a and 131b. By using a prism with an apex angle of θ _α =89.9°, the communication light is shifted by 0.2° and folded back (180.2° with respect to the original direction). The folded light beam enters the light projecting optical system 120 again and is shifted by 0.2° as described above. means) are focused on 132a and 132b. The direction of the light beam can be calculated from the imaging positions (information) detected by the

position detection sensors

132a and 132b. The reflecting

prisms

131a and 131b are installed so as to reflect the communication light within a range of 1 mm at each end of the communication light beam and within a range of 5 mm in the circumferential direction around the optical axis in one cross section including the optical axis. , the divergence of the communication light can be calculated from the directions (information) of the light rays at both ends.

The

position detection sensors

132a and 132b have wavelength selection filters, and the light having the wavelength of the detection light emitted by the communication light emitting means 110 of the optical transmission device 1000 is transmitted therethrough. Light at the wavelength of the communication light or detection light coming from is blocked. Such a configuration reduces erroneous detection due to stray light. In this embodiment, the wavelength of the detection light is the same as the wavelength of the communication light.

The transmission light control unit 140 is connected to the

position detection sensors

132a and 132b and performs the above calculations. Moreover, the calculation result is fed back to the focus mechanism of the projection optical system 120 .

The holding part 150 (not shown) has a replaceable holding member 151 and a fixed holding member 152 . The communication light emitting means 110 , the

position detection sensors

132 a and 132 b that are part of the transmission light detection section, and the transmission light control section 140 are held by a replaceable holding member 151 . The projection optical system 120 and the reflecting

prisms

131 a and 131 b that are part of the transmitted light detection section are held by a fixed holding member 152 together with a dustproof glass 153 . The detachable portion 151a of the exchangeable holding member 151 and the detachable portion 152a of the fixed holding member 152 are detachable. The control signal from the transmission light control unit 140 is transmitted to and received from the light projecting optical system 120 by a mechanism (electrical contact, optical coupling, etc.) capable of transmitting and receiving signals, which is configured in the detachable unit 151a and the detachable unit 152a. transmitted to the internal focus mechanism. The fixed holding member 152 is held by the angle adjustment table 101 , and thus the light projecting section 100 is placed on the angle adjustment table 101 in the optical transmission device 1000 .

FIG. 3A is a detailed configuration diagram of the optical transmission device 2000 on the receiving side.
The light-receiving unit 200 includes a light-receiving optical system 220 (second optical system) that receives and condenses communication light, and communication light-receiving means 210 (second emission light) that receives the communication light condensed by the light-receiving optical system 220 . a light receiving means), a received light detection section for detecting the state of incoming communication light, a received light control section 240 for controlling the communication light, and a holding section. The holding portion is composed of a replaceable holding member (light receiving means holding member) 251 and a fixed holding member (optical system holding member) 252 .

The light receiving optical system 220 has a primary mirror (reflective curved surface) 225 , a secondary mirror (reflective curved surface) 224 , a lens 223 , a lens 222 , and a lens 221 . The lens 221 (movable optical member, transmissive optical member) has an image blur correction mechanism (double frame in the figure), and by shifting in a direction perpendicular to the optical axis, the direction of communication light can be finely adjusted. can be done. In this embodiment, the image blur correction mechanism (correction optical system) is composed of a lens 221 that is a single optical element. Also, the lens 223 (movable optical member, transmissive optical member) has a focus mechanism (double frame in the figure), and by shifting in the optical axis direction, it is possible to finely adjust the degree of divergence of the communication light. . The primary mirror 225 has an opening with a diameter of 30 mm at its center.

The communication light receiving means 210 is an optical fiber as described above, and receives communication light at the other end (not shown). The spot diameter of the communication light condensed by the light receiving optical system 220 is 44 μm for the core diameter of the optical fiber of the communication light receiving means 210 of 50 μm. there is The communication light receiving means 210 is arranged on the optical axis of the light receiving optical system 220 .

The received light detection unit includes a translucent wedge prism 231 that refracts a portion of the incoming communication light, and a position detection sensor (detection light receiving means) 232 that detects the condensing position of the refracted light beam. consists of

FIG. 3B is an enlarged view of transmission wedge prism 231 . Material s-bls7 (manufactured by Ohara, refractive index n=1.500252 at a wavelength of 1550 nm) and a prism shape with an apex angle θ _β =0.40° refracts communication light by 0.2°. . The refracted light beam enters the light receiving optical system 220 and is condensed on the position detection sensor 232 located at a different position from the communication light receiving means 210 because of the 0.2° deviation described above. The direction of the light beam can be calculated from the imaging position (information) detected by the position detection sensor 232 . The transmission wedge prism 231 is installed so as to refract the communication light within a range of 3 mm at one end of the communication light and 5 mm in the circumferential direction around the optical axis in one cross section including the optical axis. From the ray orientation, the angle of arrival of the communication light can be calculated.

The position detection sensor 232 has a wavelength selection filter, and the light having the wavelength of the detection light emitted by the communication light emitting means 110 of the optical transmission device 1000 is transmitted therethrough. Alternatively, the light of the wavelength of the detection light is shielded. Such a configuration reduces erroneous detection due to stray light. In this embodiment, the wavelength of the detection light is the same as the wavelength of the communication light.

The received light controller 240 (optical characteristic controller) is connected to the position detection sensor 232 and performs the above calculations. Further, the calculation result is fed back to the image blur correction mechanism of the light receiving optical system 220 and the angle adjustment table 201 (the adjustment portion is indicated by a double-lined frame in the drawing). Specifically, when the fluctuation of the correction angle of the communication light is at a frequency of less than 10 Hz, correction is performed by the angle adjustment table 201, and when the frequency is from 10 to 50 Hz, the image blur correction mechanism of the light receiving optical system 220 is used. to correct.

A holding portion that holds the light receiving portion is composed of a replaceable holding member 251 and a fixed holding member 252 . The communication light receiving means 210 and the position detection sensor 232 which is part of the received light detection section are held by a replaceable holding member 251 . The light receiving optical system 220 , the transmission wedge prism 231 that is part of the received light detection section, and the received light control section 240 are held by a fixed holding member 252 together with a dustproof glass 253 . The detachable portion 251a of the exchangeable holding member 251 and the detachable portion 252a of the fixed holding member 252 are detachably connected. The control signal from the received light control unit 240 is transmitted to and received from the light receiving optical system 220 by signal transmission/reception by a mechanism (electrical contact, optical coupling, etc.) configured in the attachment/detachment portion 151a and the attachment/detachment portion 152a. is transmitted to the focus mechanism and the angle adjustment base 201 . The fixed holding member 252 is held by the angle adjustment table 201 , and thus the light receiving section 200 is placed on the angle adjustment table 201 in the optical transmission device 2000 .

As described above, in this embodiment, part of the communication light is utilized as the detected light detected by the transmitted light detector and the received light detector. Therefore, the communication light emitting means 110 also serves as a detection light emitting section. Also, for the sake of clarity, it should be noted that the "communication light" discussed thus far includes not only light that communicates, but also detection light.

Here, optical detailed values of the light receiving optical system 220 are shown below. As mentioned above, due to the symmetry, the optical details of the projection optics 120 are also similar. In numerical examples, for surface number i which is the order of surfaces (optical surfaces) from the object side, ri is the radius of curvature of the i-th surface from the object side, di is the i-th surface from the object side, and It shows the distance (on the optical axis) from the (i+1)th surface. Also, ndi and νdi represent the refractive index and Abbe number of the medium (optical member) between the i-th surface and the (i+1)-th surface. The symbol * attached to the right of the surface number indicates that the surface is an aspherical surface.

The aspheric shape is expressed by the following equation, where the X axis is in the direction of the optical axis, the H axis is in the direction perpendicular to the optical axis, the traveling direction of light is positive, R is the paraxial radius of curvature, and K is the conic constant. Also, “eZ” means “×10 ^−Z ”.

<Numeric data>
unit mm
Surface data Surface number r d nd vd Glass material 1 (Aperture) ∞ 1.10 1.51633 64.1 s-bsl7 (ohara)
2 ∞ 150.00
3* -385.051 -140.00
4* -133.630 155.00
5 1644.588 2.00 1.56883 56.4 s-bal14 (ohara)
6 -104.907 20.00
7 -152.756 0.80 1.61800 63.3 s-phm52 (ohara)
8 29.125 16.70
9 38.931 2.50 1.56883 56.4 s-bal14 (ohara)
10 100.000 100.00
Image plane ∞

Aspheric data 3rd surface
K=-1.00000e+000
4th side
K=-2.32216e+000

Various data Focal length 1600.00
F number 16.00
Half angle of view 0.53
Image height 14.80
Lens length 308.10

4 and 5 are longitudinal aberration diagrams at a communication wavelength (1540 nm to 1560 nm) and a focal length f = 1599.999 mm as optical performance values of the light receiving optical system 220 when focused on infinity (the same applies to the light projecting optical system 120). Fig. 4 shows a lateral aberration diagram; A solid line and a dotted line in the astigmatism diagram of the longitudinal aberration diagram and the lateral aberration diagram show aberrations on the meridional image plane and the sagittal image plane, respectively. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.4 mm, astigmatism is drawn on a scale of 0.4 mm, and distortion is drawn on a scale of 5%. FIG. 5 shows transverse aberration diagrams at an image height of 14.8000 mm, an image height of 11.1000 mm, an image height of 7.4000 mm, an image height of 3.7000 mm, and an image height of 0.0000 mm.

As shown in FIGS. 4 and 5, the aberration can be reduced at the central angle of view of the communication light receiving means 210 at the communication wavelength (1540 nm to 1560 nm).

The features of the configuration of the present invention will be described below.
First, the subject and principle of the present invention will be explained.
As described above, the direction (arrival angle) of the communication light emitted from the projection optical system fluctuates due to environmental temperature changes, device vibrations, atmospheric fluctuations, and the like. In general, the fluctuation frequency depends on the cause of occurrence.

The effects of fluctuations in the optical performance of the light-receiving optical system and the light-projecting optical system and positional fluctuations of the optical transmission device due to environmental temperature changes result in arrival angle fluctuations with a fluctuation frequency of 10 Hz or less. The influence of vibrations in the installation environment of the optical transmission device (vibrations caused by the traffic of people and vehicles) results in arrival angle fluctuations with a fluctuation frequency of less than 50 Hz. The effect of atmospheric fluctuations is arrival angle fluctuation with a fluctuation frequency of 50 Hz or more.

In this embodiment, the image blur correction mechanism can only correct image blur with a fluctuation frequency of less than 50 Hz due to limitations of the drive mechanism. Therefore, arrival angle fluctuations of 50 Hz or more, which are mainly caused by atmospheric fluctuations, cannot be corrected. If the amount of received light becomes unstable due to this influence, communication becomes unstable. Specifically, when the ratio of the amount of received light when there is variation in the arrival angle to the amount of received light when there is no variation in the angle of arrival (hereinafter referred to as the variation in the amount of received light) falls below a certain value, the received signal cannot be processed correctly. communication becomes unstable. It is an object of the present invention to reduce this.

In the present invention, as a solution to the above problem, communication instability is reduced by adjusting the degree of divergence for arrival angle fluctuations of fluctuation frequencies of 50 Hz or higher. Specifically, when the arrival angle variation is small, the divergence is decreased, and when the arrival angle variation is large, the divergence is increased, thereby reducing the variation in the amount of received light while securing the amount of received light as much as possible. there is This is the principle idea of the present invention.

Details will be described below.
First, consider a parallel Gaussian beam emitted from the projection optical system. The intensity distribution I _t of the Gaussian beam is represented by Equation (2). Here, r is the distance in the radial direction, and _w0 is the exit light beam waist (radius) immediately after exiting the projection optical system.

The parallel light beam waist _wp when the Gaussian beam of parallel light reaches the light-receiving optical system separated by the communication distance L is expressed by Equation (3). Here, λ is the wavelength of communication light.

Further, the divergent light beam waist w _x when the divergence is adjusted in the projection optical system and changed by the additional divergence angle (half angle) β [rad] (≧0) is given by Equation (4).

The intensity distribution _Ir of the Gaussian beam that has reached the light receiving optical system is similarly expressed by Equation (5).

Let α [rad] (≧0) (hereinafter referred to as a high-frequency arrival angle fluctuation amount) be an arrival angle fluctuation amount having a fluctuation frequency of 50 Hz or more that cannot be corrected by the image blur correction mechanism. The amount of deviation Δ of the light arrival position above is represented by Equation (6) with respect to the communication distance L.

The amount of received light received at the aperture diameter D of the light receiving optical system is as shown in FIG. A two-dot chain line indicates the intensity distribution when there is no shift in the light arrival position, and a broken line indicates the intensity distribution when there is a shift amount Δ in the light arrival position. The amount of received light is obtained by multiplying these intensity distributions by the area integral of the aperture diameter D. FIG. For the sake of explanation, FIG. 6 shows the intensity distribution as the intensity in one dimension (one direction perpendicular to the traveling direction of the light ray), but the actual intensity distribution is two-dimensional (in the plane perpendicular to the traveling direction of the light ray). is the strength against

Here, let us consider the received light amount variation γ, which is the ratio of the received light amount AΔ when the arrival angle varies by the high-frequency arrival angle variation α to the received light amount A0 when there is no arrival angle variation. Strictly speaking, the variation γ in the amount of received light changes depending on the relationship between the divergent light beam waist _wx and the aperture diameter D, but it does not change much with the aperture diameter D. Therefore, considering the case where the aperture diameter D is extremely small, it is represented by the formula (7).

In general, if the received light amount variation γ is less than 5 dB (=31.6%), communication tends to become unstable, which is not preferable. In other words, the condition for stable communication is given by equation (8).

With k=1/0.759=1.32, we obtain equation (10).

Here, the required beam waist w _n is

is defined as

becomes. That is, the additional divergence angle β may be adjusted with respect to the parallel light beam waist _wp so as to exceed the required beam waist _wn .
For calculation purposes, equation (12) is expanded from equations (4) and (11) into equation (13).

Here, a method for calculating the additional divergence angle β will be described with reference to FIG.
First, the parallel light emitted with the emitted light beam waist w ₀ through the projection optical system (represented as a single lens) located at a position separated by the focal length f of the projection optical system from the communication light emission part is indicated by a dashed line. Further, the two-dot chain line indicates the optical path when the communication light emitting portion is shifted by _ΔZf . As can be seen from the figure, the optical path of the marginal ray at this time is the same as when the communication light emitting portion is not shifted and the light source is located at the angle of view ΔY. Since the direction of the marginal ray and the direction of the principal ray in this case are parallel to each other, the additional divergence angle β when the communication light emitting portion is shifted by ΔZ _f is given by equation (14).

here,

Than,

so that

becomes.
For the sake of clarity of explanation, the communication light emitting portion is shifted, but it is the same even if it is understood as a shift of the focal plane of the projection optical system. Thus, the additional divergence angle β can be calculated from the shift amount _ΔZf of the focal plane of the projection optical system.
A specific configuration of this embodiment will be described below.

Although it overlaps with the previous explanation, the high-frequency arrival angle fluctuation amount α [rad] fluctuates depending on the weather, the communication distance L, and the like. The high-frequency arrival angle fluctuation amount α is small when the wind is calm or the communication distance L is short, and the high-frequency arrival angle fluctuation amount α is large when the wind is strong or the communication distance L is long.

The received light control unit 240 calculates the arrival angle of the communication light and feeds it back to the image blur correction mechanism of the light receiving optical system 220 and the angle adjustment base 201 . However, even if these feedbacks are performed, the high-frequency arrival angle fluctuation amount α is calculated by the received light control section 240 as a correction remainder.

Information about the high-frequency arrival angle fluctuation amount α is transmitted to the transmission light control unit 140 via communication light. Based on the information on the high-frequency arrival angle fluctuation amount α, the transmission light control unit 140 calculates the additional divergence angle β and feeds it back to the focusing mechanism of the projection optical system 120 . This suppresses fluctuations in the amount of received light and ensures the stability of communication.

Here, the focus mechanism that changes the degree of divergence also has limitations on the drive frequency. The high-frequency arrival angle fluctuation amount α is the maximum value of the arrival angle fluctuation amount in the driving cycle of the focus mechanism. This makes it possible to set the optimum divergence, taking into consideration the limitation of the drive frequency of the focus mechanism. Note that the additional divergence angle β calculated by the transmission light control unit 140 may be increased or decreased depending on the purpose, such as suppressing fluctuations in the amount of received light or increasing the amount of received light.
The optical transmission device discussed in the present invention assumes the following specifications.
Communication distance L≤30km
High-frequency arrival angle fluctuation amount α≦100 μrad
Also, in this embodiment,
Output light beam waist w ₀ = 50 mm
is.

8A, 8B, and 8C respectively show the required beam waist _wn , the parallel light beam waist _wp , and the additional divergence angle β=3 for the communication distance L when the high-frequency arrival angle variation α=10 μrad, 50 μrad, and 100 μrad. Diverging light beam waists wx at .4 μrad, 58.0 _μrad and 125 μrad are shown.
With the additional divergence angle β, w _x ≧w _n is achieved, and the stability of communication can be secured.
By transforming the equation (16), the following equation (18) is obtained.

In this example,
Focal length f=1600mm
Output light beam waist w ₀ = 50 mm
Therefore, the focal plane shift amounts ΔZ required to secure the additional divergence angles β (3.4 μrad, 58.0 μrad, and 125 μrad) are 0.174 mm, 2.969 mm, and 6.411 mm, respectively.

Further, the focusing mechanism of the projection optical system 120 has the sensitivity to shift the focal plane by 4 mm when the lens is shifted by 1 mm in the optical axis direction. However, the lens shift amount is 1.6 mm, which is sufficient.
With the above configuration, the effects of the present invention can be obtained.

Although it depends on the environment, there are generally few cases where the high-frequency arrival angle fluctuation amount α exceeds 50 μrad. Therefore, when the high-frequency arrival angle fluctuation amount α=50 μrad,
w _n <w _p (19)
is achieved, it can be said that the need to change the divergence is low and the effect of the present invention is small.
Therefore, the conditional expression for sufficiently obtaining the effect of the present invention is the inverse of the expression (19),

Namely

Substitute k = 1.32 and α = 50 μrad into

The effect of the present invention can be sufficiently obtained when the following conditions are satisfied.

In this embodiment, it can be seen from FIG. 8B that the relationship of formula (20) is achieved over a wide range of communication distance L. FIG.
In this embodiment, the lens 123 and the lens 223 are used as a focusing mechanism as means for adjusting the degree of divergence of communication light. In this way, a low-cost configuration can be achieved by utilizing the technology that has been generalized in cameras and the like.
Further, it is desired that the divergence can be adjusted by the focus mechanism up to the high-frequency arrival angle fluctuation amount α=50 μrad.

than, at least

If,

is achieved.
Considering the above,

by transforming the

Substituting k = 1.32 and α = 50 µrad into equation (25) yields

becomes. Assuming that ΔZ _fmax is the maximum focal plane shift amount that can be adjusted by the focus mechanism,

A focusing mechanism that can achieve

Further, it is preferable that the correction resolution of the focus mechanism is high. Specifically, when the lens of the focus mechanism is moved (shifted) by 0.01 mm, the correction amount of the high-frequency arrival angle fluctuation amount α is preferably 1 μrad or less.
If the shift amount of the focal plane when the lens of the focus mechanism is moved (shifted) by 0.01 mm is ΔZ _fγ

If it is Namely

, substituting k = 1.32 and α = 1 μrad,

It suffices if there is a correction resolution of the focusing mechanism that satisfies the above.

In this embodiment, the focus mechanism of the projection optical system 120 has the sensitivity to shift the focal plane by 4 mm when the lens is shifted by 1 mm in the optical axis direction.
That is, for ΔZ _fγ =0.04 mm,
Focal length f=1600mm
Output light beam waist w ₀ = 50 mm
Therefore, the value of the right side of equation (30) is 0.068 mm, which satisfies equation (30).

In this embodiment, the focus mechanism is configured with only one optical member, each of the lens 123 and the lens 223 . By adopting such a configuration, compared with a configuration having a plurality of optical members, it is simpler and cheaper, and the adjustment accuracy when adjusting the degree of divergence can be improved.

In this embodiment, the

position detection sensors

132a and 132b detect the divergence of the communication light. Although not discussed so far, the divergence of the projection optical system may change due to environmental temperature changes, vibrations, and the like. With such a configuration, it is possible to improve the adjustment accuracy when adjusting the degree of divergence.

In this embodiment, the divergence of the communication light is detected using the light beams folded back by the reflecting

prisms

131a and 131b, but the method of detecting the divergence is not limited to this.
This embodiment has an angle adjustment table 201 and an image blur correction mechanism as means for correcting the direction of the communication light, and only the amount of arrival angle variation that cannot be corrected by these is dealt with by adjusting the degree of divergence. is doing. By adopting such a configuration, the divergence can be suppressed to be small compared to the corresponding configuration only by adjusting the divergence, and the amount of received light can be ensured.

In this embodiment, as a means for adjusting the direction of communication light, an image blur correction mechanism that can move the

lenses

121 and 221 in the direction perpendicular to the optical axis is used. In this way, a low-cost configuration can be achieved by utilizing the technology that has been generalized in cameras and the like.

As a means for adjusting the direction of communication light, a mechanism for changing the position and angle of a reflecting member such as a MEMS mirror may be used. In this case, it is possible to obtain the effect of not generating unnecessary light due to internal reflection of the lens, as compared with the case of using the transmissive member. Also, in general, the MEMS mirror can be driven at a higher speed than the image blur correction mechanism.

In this embodiment, the information of the high-frequency arrival angle fluctuation amount α calculated by the reception light control unit 240 (divergence control unit) is transmitted to the transmission light control unit 140 via the communication light, and the projection optical system It is fed back to the focusing mechanism of system 120 . However, the present invention is not limited to this. Information on the high-frequency arrival angle fluctuation amount α may be fed back to the focus mechanism of the light receiving optical system 220 . Since the optical transmission apparatus communicates bi-directionally and the arrival angle fluctuation amounts are relative deviations, the information of the high-frequency arrival angle fluctuation amount α of the communication light is substantially the same. The optical transmission devices mutually detect the high-frequency arrival angle fluctuation amount α and feed it back to their own focusing mechanisms, thereby mutually optimizing the degree of divergence.

Although the discussion has so far been based on an ideal Gaussian beam, the actual intensity distribution is not strictly a Gaussian beam. In this embodiment, due to the light shielding by the secondary mirror 124, the intensity distribution of the communication light immediately after being emitted from the projection optical system 120 becomes a donut shape in the radial direction with the central part missing, and the intensity of the Gaussian beam is Different from distribution. However, in the use of an optical transmission device that propagates over a long distance of approximately 500 m or more, the intensity distribution of a substantially Gaussian beam is obtained when reaching the light receiving optical system due to diffraction of communication light. In addition, since the intensity distribution changes greatly depending on the refractive index distribution and transmittance distribution in the air through which the communication light propagates, there is little need to consider the strict intensity distribution. For these reasons, the above discussion considering the ideal Gaussian beam is sufficient, and the configuration of the present invention can ensure the stability of communication.

Similar to the discussion above, for non-ideal Gaussian beams, it may be difficult to define the exit light beam waist w ₀ . In that case, there is no problem in discussing the radial distance from the peak of the intensity distribution to 13.5% as the emitted light beam waist _w0 .

In this embodiment, part of the communication light emitted from the communication light emitting means 110 is used as the detection light, so the communication light emitting portion and the detection light emitting portion are the same. With such a configuration, the optical paths of the communication light and the detection light become closer, and the optical characteristics of the communication light can be detected more accurately.

Up to this point, the optical transmission device 2000 on the receiving side has been mainly discussed for the sake of explanation. It is the same. In particular, it should be noted that both devices have a transmitted light detector and a received light detector, although only one side is shown. In this embodiment, the reflective prism and the transmissive wedge prism are installed so as to be rotated 90° about the optical axis (in FIGS. 2A and 3A, the front side of the paper surface).

In the exemplified embodiment, the light projecting optical system and the light receiving optical system of the optical transmission device were basically optical systems having the same configuration, and the optical axes were substantially the same. is not limited to The light projecting optical system and the light receiving optical system of the optical transmission device may be optical systems having separate configurations, and the optical axes of both may not be coaxial.

Here, the "optical axis" discussed in the present invention means the central optical path of the communication light beam emitted from the emitting means and passing through the light projecting optical system, and the light receiving means passing through the light receiving optical system. It refers to the central optical path of the luminous flux of the communication light heading. Note that the definition is different from the optical axis of a general coaxial optical system.
In this embodiment, for the sake of clarity, the configuration is such that the emitting means exists on the optical axis of the coaxial light projecting optical system and the light receiving means exists on the optical axis of the coaxial light receiving optical system. I was explaining. However, in cases such as when there are no emitting means and light receiving means on the optical axes of the light projecting optical system and the light receiving optical system, communication cannot be established even if the optical axes of a general coaxial optical system are aligned. Further, when the light projecting optical system and the light receiving optical system are decentered optical systems, it is difficult to clearly define the "optical axis". It should be appreciated that the definition of "optical axis" is different for the above reasons.

In this embodiment, the detection light and the communication light similarly pass through all optical elements of the light projecting optical system 120 and the light receiving optical system 220, but are not limited to this. The effect of the present invention can be obtained by passing through at least part of the light projecting optical system and the light receiving optical system in the same way. However, as described above, it is preferable for the stability of communication that the number of optical elements that are similarly routed is as large as possible. Similarly, the detection light and the communication light may pass through different optical elements as the light projecting optical system and the light receiving optical system.

In this embodiment, both the reflective optical element and the transmissive optical element are used for the light projecting optical system 120 and the light receiving optical system 220, but the present invention is not limited to this, and only the reflective optical element, only the transmissive optical element, etc. may consist of

Here, in the present embodiment, part of the communication light emitted from the communication light emitting means 110 is used for detection, but it is not limited to this. For example, a dedicated detection light may be used, for example, a light having a different wavelength from the communication light may be incident from the other end (not shown) of the optical fiber of the communication light emitting means 110 and used as the detection light.

In this embodiment, the communication light emitted from the optical fiber is received by the optical fiber, but the present invention is not limited to this. For example, the communication light emitted from the semiconductor laser may be received by the sensor.

In the present embodiment, the position detection sensor is used as the detection light receiving means, but it is not limited to this, and may be a two-dimensional sensor or light amount detection sensor, for example.

In the illustrated embodiment, the optical transmission device 1000 and the optical transmission device 2000, which are spaced apart from each other, are capable of functioning as light projecting means and light receiving means, respectively. It has been described as a configuration in which communication is possible. However, the present invention is not premised on it.
a first light projecting unit including a first light emitting unit for emitting a first communication light and a first light projecting optical system; a first light receiving optical system; and a first light receiving unit for receiving the first communication light a first light receiving section including communication light receiving means; a second light projecting section including second emitting means for emitting the second communication light and a second light projecting optical system; and a second light receiving optical system. a system and a second light receiving section including second communication light receiving means for receiving the second communication light, wherein optical communication is performed between the first light projecting section and the first light receiving section; The present invention can be similarly applied to an optical transmission device that performs optical communication between a second light projecting section and a second light receiving section, and can enjoy its effects. In the optical transmission device having such a configuration, the first light projecting section has a detection light emitting section for emitting detection light, and the second light projecting optical system has an adjusting optical system for changing the degree of divergence of the light flux. The first light receiving section has detection light receiving means for receiving the detection light, and the optical transmission device has a divergence control section for controlling the adjustment optical system based on information obtained by the detection light receiving means. . In this configuration, the first light projecting section and the second light receiving section are arranged adjacent to each other, and the second light projecting section and the first light receiving section are arranged adjacent to each other. Here, "arranged adjacent to each other" means that the distance apart from each other is preferably 10 m or less, more preferably 2 m or less, and still more preferably 0.5 m or less.

(Example 2)
The configuration of the optical transmission device (spatial optical transmission device) according to the second embodiment of the present invention is the same as the configuration of the optical transmission device (spatial optical transmission device) of the first embodiment shown in FIG. Here, the description of the optical transmission apparatus according to the second embodiment is given for one-way communication, but the same applies to reverse-direction communication.

Embodiment 2 of the present invention provides an optical transmission device with small fluctuations in the amount of light due to disturbance for any communication distance.

The configuration of the optical transmission device (spatial optical transmission device) will be described in detail below with reference to FIGS.
FIG. 9 is a detailed configuration diagram of the light projection unit 100 (not shown) in the second embodiment of the optical transmission device 1000 shown in FIG. The same reference numerals are given to the same configurations as those of the light projecting unit 1100 according to the first embodiment shown in FIG. 2A, and the description thereof is omitted.
The light projecting section 100 includes a communication light emitting section (projecting means) 110, a light projecting optical system 120, a transmission light detection section, a transmission light control section 140, and a holding section 150 (not shown).

The projection optical system 120 of the second embodiment includes a lens 121, a lens 122, a lens 123, a secondary mirror 124, a primary mirror 125, and a light intensity conversion element, which are arranged in the optical path in this order from the communication light output side. 160. It differs from the projection optical system 120 of the first embodiment in that a light intensity conversion element 160 is provided. The light intensity conversion element 160 will be described later.

FIG. 10 is a detailed configuration diagram of the light receiving unit 200 (not shown) in the second embodiment of the optical transmission device 2000 shown in FIG. 1 on the receiving side. The same reference numerals are given to the same configurations as those of the light receiving unit 1200 in the first embodiment shown in FIG. 3A, and the description thereof is omitted.

The light-receiving optical system 220 of the second embodiment includes a light intensity conversion element 160, a primary mirror (reflecting curved surface) 225, a secondary mirror (reflecting curved surface) 224, a lens 223, a lens 222, a lens 223, a lens 222, a primary mirror (reflecting curved surface) 225, and a secondary mirror (reflecting curved surface) 224, which are arranged in the optical path in order from the communication light incident side. It has a lens 221 . It differs from the light receiving optical system 220 of the first embodiment in that a light intensity conversion element 160 is provided. The light intensity conversion element 160 will be described later.

The transmission wedge prism 231 is the same as the transmission wedge prism 231 of Example 1 shown in FIG.

As described above, the detachable portion 251a of the exchangeable holding member 251 and the detachable portion 252a of the fixed holding member 252 are detachably connected. Specifically, the detachable portion 251a is a C-mount female type, and the detachable portion 252a is a C-mount male type. Therefore, it is possible to remove the above coupling and couple a camera device 351 having a C-mount female type 351a and an imaging element 352 capable of capturing a two-dimensional image as shown in FIG.

4 and 5 are longitudinal aberration diagrams at a communication wavelength (1540 nm to 1560 nm) and a focal length f = 1599.999 mm as optical performance values of the light receiving optical system 220 when focused on infinity (the same applies to the light projecting optical system 120). Fig. 4 shows lateral aberration diagrams (showing the same optical performance values as in Example 1); 12 and 13 show longitudinal and lateral aberration diagrams at a visible light wavelength (e-line: wavelength 546 nm) and focal length f=1602.968 mm. A solid line and a dotted line in the astigmatism diagram of the longitudinal aberration diagram and the lateral aberration diagram show aberrations on the meridional image plane and the sagittal image plane, respectively. In the longitudinal aberration diagram, spherical aberration is drawn on a scale of 0.4 mm, astigmatism is drawn on a scale of 0.4 mm, and distortion is drawn on a scale of 5%. FIG. 13 shows lateral aberration diagrams at an image height of 14.8000 mm, an image height of 11.1000 mm, an image height of 7.4000 mm, an image height of 3.7000 mm, and an image height of 0.0000 mm.

From FIGS. 4 and 5, it can be seen that the aberration can be reduced at the central angle of view where the communication light receiving section 210 is located at the communication wavelength (1540 nm to 1560 nm). 12 and 13, at the angle of view (23.4 × 16.7 mm = diagonal ± 14.2 mm) of the APS-C sensor (imaging element, two-dimensional image acquisition means) 352, even at visible light wavelengths, It can be seen that sufficient aberration is obtained.

That is, in the second embodiment, when the optical transmission device 1000 is installed, the camera device 351 for visible light is attached in place of the replaceable holding member 251, and two images captured by the imaging element on the optical axis of the light receiving optical system 220 are obtained. The angle of the light receiving optical system 220 can be adjusted while viewing the dimensional image. In this case, since the optical axis of the camera and the optical axis of the light-receiving optical system 220 are the same, the problem of the adjustment error due to the deviation between the optical axis of the camera and the optical axis of the light-receiving optical system as in Patent Document 2 is eliminated. be canceled.

Specifically, the adjustment procedure at the time of installation is as follows.
Step 1 Confirm with GPS or the like, and adjust the angle adjusting table 101 and the angle adjusting table 201 so that the light projecting unit 100 of the optical transmission device 1000 and the light receiving unit 200 of the optical transmission device 2000 face each other.

Step 2 In the optical transmission device 2000, the exchangeable holding member 251 is removed from the fixed holding member 252 together with the communication light receiving unit 210 and the position detection sensor 232 which is part of the received light detection unit, and the camera for visible light is fixed to the holding member. 252 is attached to the attaching/detaching portion 252a.

Step 3 While confirming the two-dimensional image captured by the camera, adjust the angle adjustment table 201 again so that the optical transmission device 1000 is at the center of the captured image.

Step 4 Remove the camera for visible light from the attachment/detachment portion 252a of the fixed holding member 252, and attach the exchangeable holding member 251 to the attachment/detachment portion 252a.

In the second embodiment, the position of the sensor in the camera in the optical axis direction is the same as the tip of the fiber of the communication light receiving unit 210. Therefore, from the design point of view, focus adjustment is performed after performing step 4. No need.

Here, the optical transmission device 2000 on the receiving side has been described, but the optical transmission device 1000 on the transmitting side can be similarly adjusted. As a result, the directions of the bidirectional optical axes are aligned, and communication is established.

The characteristic configuration of this embodiment will be described below.
When the optical transmission device of the second embodiment is used for optical communication, the installation interval between the light-projecting unit and the light-receiving unit, that is, the communication distance, varies depending on the conditions of the installation area. For example, it must be installed with a communication range of 2 km in one area and with a communication range of 5 km in another area. 14A, 14B, and 14C show the intensity distribution of the beam flux at each distance in Example 2. FIG. FIG. 14A shows the light intensity distribution of the emitted light flux at the opening position of the light projecting section of this embodiment. FIG. 14B shows the light intensity distribution of the light flux emitted from the light-projecting part at the opening position of the light-receiving part when the light-receiving part of this embodiment is installed at a position 2 km away from the light-projecting part. FIG. 14C shows the light intensity distribution of the light flux emitted from the light-projecting part at the opening position of the light-receiving part when the light-receiving part of this embodiment is installed at a position 5 km away from the light-projecting part. The solid lines in FIGS. 14A, 14B, and 14C are the light intensity distributions of the luminous flux of this embodiment. A dotted line is a comparative example for explaining the effect of the present invention, and shows the light intensity distribution when the light intensity conversion element (transmissive member) 160 of this embodiment is not used. Note that the light intensity was standardized by the maximum value.

In order to explain the effects of the present invention, a comparative example will be explained first. As can be seen from the dotted line in FIG. 14B, when the comparative example is installed at a distance of 2 km, the luminous flux that reaches the aperture is narrower than that of the light receiving aperture of φ100. Variation is small. On the other hand, as can be seen from the dotted line in FIG. 14C, when the comparative example is installed at a distance of 5 km, the luminous flux reaches a wider area than the aperture of the light receiving portion φ100, and the intensity distribution is steep near the edge of the aperture. Therefore, the amount of vignetting due to the opening of the light-receiving portion fluctuates greatly with respect to the deflection of the light beam due to the disturbance, resulting in large fluctuations in the amount of light. When optical transmission equipment with the same configuration is used for various communication distances in this way, there are cases where the light intensity distribution at the aperture position of the light receiving part is not optimal. There is a problem that cannot be solved.

Therefore, in this embodiment, as shown in FIG. 9, the light intensity conversion element 160 is arranged in the light projecting part according to the communication distance, and the light intensity distribution is optimized at the opening position of the light receiving part. is decreasing. FIG. 15 is a graph showing the transmittance distribution of the light intensity conversion element 160. As shown in FIG. As shown in FIG. 15, the transmittance is varied according to the position within the plane of the light intensity conversion element 160 . In this embodiment, by using such a light intensity conversion element 160, as shown in FIG. It reduces the light amount fluctuation when the light flux is swayed. In this embodiment, the transmittance of the light intensity conversion element 160 is set so as to decrease from the optical axis toward the end, thereby increasing the diameter of the light beam reaching the light receiving section aperture.

This principle is briefly explained below. In physical optics space propagation, the beam diameter (diameter) at the position of the beam waist is w ₀ , the beam diameter (diameter) at an arbitrary position x away from the beam waist is w, and the form of a Gaussian beam with a wavelength λ is as follows. A relational expression such as

In this example, since the beam is not an ideal Gaussian beam, w ₀ cannot be defined, and w does not completely match the above equation. relationship is established. For example, by narrowing the intensity distribution at the opening of the projection part corresponding to w ₀ , it is possible to widen the beam diameter w at a position x apart. Since the beam diameter w ₀ at the position of the beam waist at the projection aperture is usually determined by the characteristic values of the light source and the projection optical system, it is changed to the optimum beam diameter w according to each installed communication distance. It is difficult to Therefore, in this embodiment, the intensity distribution is converted by the light intensity conversion element ₁₆₀ , which is easy to change and remove the transmittance distribution. is doing. At this time, according to the above formula, the diameter of the light beam at the position of the opening of the light receiving portion that is x away can be made larger than in the case where the light intensity conversion element 160 is not provided.

In this embodiment, the light intensity conversion element 160 is configured with a transmission flat plate having a distribution of transmittance in order to convert the intensity at low cost and with high precision, but the effect of the present invention is not limited to this configuration. Further, in this embodiment, the transmittance continuously decreases from the optical axis of the light intensity conversion element 160 to the end, but the effect of the present invention is not limited to this. Also, in this embodiment, since the inner region of φ30 is an unused region due to obscuration by the mirror, the transmittance distribution of only the necessary region is drawn in FIG. Therefore, in this embodiment, the transmittance of the inner φ30 region, which is not used, may be a simple mountain shape obtained by extending the transmittance curve or any other shape.

Also, if the relative positions of the light intensity conversion element 160 and the light beam are shifted in the perpendicular direction, the intensity distribution after conversion tends to be tilted, making it impossible to obtain a good intensity distribution. For this reason, in this embodiment, the light intensity conversion element 160 is arranged at a position where the beam width is the largest, the beam becomes a parallel beam, and the influence of the decentering on the intensity distribution is the lowest. That is, it is arranged further downstream (farther from the light source) than the curved mirror, ie, the secondary mirror 124, which is the farthest from the light source. Further, this position can be said to be the downstream side of the optical element farthest from the light source among the optical elements having power in the light projecting section.

(Example 3)
A third embodiment is a modification of the second embodiment. The difference from Example 2 is that the transmittance distribution of the light intensity conversion element 160 is changed. 16A, 16B, and 16C show the intensity distributions of the light beams at respective distances of 0 km, 2 km, and 5 km in Example 3. FIG. Solid lines in FIGS. 16A, 16B, and 16C are intensity distributions of this example. A dotted line is a comparative example for explaining the effects of the present invention, and is a light intensity distribution when the light intensity conversion element 160 of Example 3 is not used. Here, FIG. 16B shows the intensity distribution when the light receiving unit is installed at a distance of 2 km. The incident light beam is vignetted from φ100, and the amount of received light fluctuates.

Therefore, in Example 3, as shown in FIG. 17, the transmittance of the light intensity conversion element 160 is set so as to increase from the optical axis toward the end, thereby reducing the divergence angle during space propagation. . As a result, as shown by the solid line in FIG. 16B, the luminous flux at the light receiving part opening position at the 2 km point can be made narrower, and the light amount fluctuation can be reduced even when used in an area where a larger disturbance occurs than in Example 2.

(Example 4)
Embodiment 4 is a modification of Embodiments 2 and 3, and differs from Embodiments 2 and 3 in that the light intensity conversion element 160 is placed in a different position, thereby obtaining another effect. . FIG. 18 is a layout diagram of this embodiment. As shown in FIG. 18, in the third embodiment, a light intensity conversion element 160 is arranged between two curved mirrors, that is, a primary mirror 125 and a secondary mirror 124 . As a result, since the light beam passes through the light intensity conversion element 160 twice, a stronger intensity conversion effect can be obtained with an element having a similar transmittance distribution.

(Example 5)
Example 5 is a modification of Examples 2, 3 and 4. FIG. The difference of the fifth embodiment from the second, third, and fourth embodiments is that the light intensity conversion element 160 is placed in a different position, thereby obtaining another effect. FIG. 19 is a layout diagram of the fifth embodiment. As shown in FIG. 19, in the fifth embodiment, the light intensity conversion element 160 is arranged on the light source side (upstream side) of the curved mirror closest to the light source, that is, the primary mirror 125 . Thereby, the size of the light intensity conversion element 160 can be reduced, and the cost can be reduced. On the other hand, there is a demerit that sensitivity to mounting errors increases due to the smaller size, but in a device that can sufficiently guarantee mounting accuracy, it is possible to obtain the effects of the present invention and reduce costs.
Also, in this embodiment, the lens 121 has an image blur correction mechanism (double-lined frame in the figure), and finely adjusts the direction of communication light by shifting (moving) in a direction perpendicular to the optical axis. be able to. When this adjustment value is large, the central axis of the intensity distribution of the luminous flux from the communication light emitting section 110 is greatly tilted after being emitted from the lens 121, and is then perpendicular to the optical axis of the projection optical system 120. shift sharply to In that case, if the light intensity conversion element 160 is arranged on the side away from the communication light emitting section 110 from the lens 121, the intensity distribution will be tilted and the intensity distribution will not be correctly converted. Therefore, in the fifth embodiment, the light intensity conversion element 160 is arranged between the lens 121 having an image blur correction mechanism and the light source, so that the intensity distribution can be satisfactorily converted even in a situation in which a large angular deviation due to disturbance is adjusted. It is possible to reduce fluctuations in the amount of light.

(Modification)
In Embodiments 2 to 5, the projection optical system using the curved mirror has been described, but the present invention can naturally obtain the same effect even in the projection optical system that does not use the curved mirror.
20 and 21 are examples of the transmittance distribution of the light intensity conversion element 160 used in the projection optical system. Even in the case of a general light projecting optical system without obscuration, if the light intensity conversion element 160 as shown in FIGS.

With the above configuration, the effects of the present invention can be obtained.
In the embodiment, a fixed holding member 252 that holds the light receiving optical system 220 is fixed to the angle adjustment table 201, and a replaceable holding member 251 that holds the communication light receiving section 210 is fixed to the fixed holding member 252. It's becoming With such a configuration, the angle of the light receiving optical system 220 can be determined by the angle adjustment table 201, and the determined angle is prevented from changing due to attachment and detachment of the camera.

Here, it should be noted that in the present invention, the optical transmission device does not necessarily have an angle adjustment table. For example, it is conceivable to use a tool for adjusting the angle only at the time of installation, perform the angle adjustment of the present invention, fix the position of the light receiving optical system, and then remove the angle adjustment table. Even in this case, the effects of the present invention can be obtained. However, it is preferable to have an angle adjusting base because the man-hours for attaching and removing the angle adjusting base can be reduced.

In the embodiment, a C mount is used as the detachable portion 251a and the detachable portion 252a. In this way, by using general-purpose technology (a mount part with multiple bayonet claws), it is easy to attach and detach, making it easier to attach a commercially available camera, avoiding the risk of high costs and difficulty in procurement. .

In the embodiment, the camera device is attached only when the optical transmission device 2000 is installed. Once the optical axis direction setting is completed and the communication state is established, the camera device needs to be connected all the time. and not. Such a configuration has the effect of reducing the cost of the optical transmission device.

In the embodiment, when a visible light camera is attached, the exchangeable holding member 251 can be removed from the fixed holding member 252 together with the communication light receiving unit 210 and the position detection sensor 232 which is part of the received light detection unit. . By adopting such a configuration, it is possible to obtain the effect of improving the attachment/detachment workability of the replaceable holding member 251 as compared with the configuration in which only the communication light receiving section 210 is replaced. In addition, since the relative positions of the communication light receiving unit 210 and the position detection sensor 232 are ensured, there is an effect of avoiding the adverse effect of deviation in the direction perpendicular to the optical axis due to attachment and detachment of the communication light receiving unit 210 described above. .

In the embodiment, there is a possibility that the position of the communication light receiving section 210 slightly shifts each time the communication light receiving section 210 is attached to or detached from the fixed holding member 252 . The shift in the optical axis direction is detected as divergence of the communication light from the optical transmission device 2000 when the direction of the communication light is reversed, and is corrected by the focusing mechanism of the light receiving optical system 220 . In other words, the focusing mechanism has the effect of correcting the shift.

In the embodiment, there is a possibility that the position of the communication light receiving section 210 slightly shifts each time the communication light receiving section 210 is attached to or detached from the fixed holding member 252 . A deviation in the direction perpendicular to the optical axis is detected as an angular deviation of the communication light and corrected by the image blur correction mechanism of the light receiving optical system 220 . In other words, the effect of correcting the shift is obtained by the image blur correction mechanism.

In the embodiment, by reducing the chromatic aberration in the visible light region from the communication wavelength (1540 to 1560 nm) of the light receiving optical system 220, it is possible to adjust the optical axis by visual confirmation with a commercially available visible light camera, improving workability. I am letting Also, in order to reduce chromatic aberration over a wide range from infrared wavelengths to visible light wavelengths, the optical system has a reflecting surface. If a refractive system were to be used, the number of lenses would increase.

Up to this point, the optical transmission device 2000 on the receiving side has been mainly discussed for the sake of explanation. It is the same. In particular, only one side of the transmission light detection section and the reception light detection section is shown, but it should be noted that both the

optical transmission apparatuses

1000 and 2000 have the transmission light detection section and the reception light detection section. . In the embodiment, the reflective prism and the transmissive wedge prism are installed at positions rotated by 90° around the optical axis (in FIGS. become).

In the embodiment, the light projecting optical system and the light receiving optical system of the optical transmission device are basically optical systems having the same configuration, and the optical axes are also substantially the same, but the present invention is not limited to this. do not have. The light-projecting optical system and the light-receiving optical system of the optical transmission device may be optical systems having separate configurations, and the optical axes of both may not be strictly coaxial.

Here, the "optical axis" discussed in the present invention means the central optical path of the communication light beam emitted from the emitting means and passing through the light projecting optical system, and the light receiving means passing through the light receiving optical system. It refers to the central optical path of the luminous flux of the communication light heading. Note that the definition is different from the optical axis of a general coaxial optical system.

In the embodiments, for the sake of clarity, a form in which the emitting means exists on the optical axis of the coaxial light-projecting optical system and the light receiving means exists on the optical axis of the coaxial light-receiving optical system is used. was explaining. However, in cases such as when there is no emitting means or light receiving means on the optical axes of the light projecting optical system and the light receiving optical system, communication cannot be established even if the optical axes of a general coaxial optical system are aligned. Further, when the light projecting optical system and the light receiving optical system are decentered optical systems, it is difficult to clearly define the "optical axis". It should be appreciated that the definition of "optical axis" is different for the above reasons.

In the embodiment, the communication light emitted from the optical fiber is received by the optical fiber, but it is not limited to this. For example, the communication light emitted from the semiconductor laser may be received by the sensor.

In the embodiment, the light receiving unit is composed only of optical fibers, and the camera device for adjustment is composed only of sensors, but they are not limited to this, and each may have a lens. For example, a fiber with a collimator may be used as the receiver, and a camera with a lens may be used as the camera for adjustment.

In the embodiment, the distance from the attachment/detachment portion 252a to the sensor surface of the camera device for adjustment and the distance from the attachment/detachment portion 252a to the tip of the fiber of the communication light receiving portion 210 are aligned. It doesn't matter if it's off.

In the embodiment, the center of the angle of view of the communication light receiving unit 210 is aligned with the center of the sensor of the camera device for adjustment. , but not limited to.

In the embodiment, adjustment was performed by a visible light camera device, but it is not limited to this, and the wavelength near the communication light (in the embodiment, the range of ±200 nm with respect to the wavelength of 1550 nm of the communication light It may be a camera device for wavelengths within the range). Adjustment with a camera device for visible light wavelengths has the advantage of being easy to recognize because it corresponds to visual observation. On the other hand, a camera device for wavelengths close to communication light has the advantage of easily reducing chromatic aberration in the design of the light receiving optical system 220 .

In the embodiment, part of the communication light emitted from the communication light emitting section 110 is used as detection light for adjusting the device, and the detection light is detected, but it is not limited to this. For example, a dedicated detection light may be used, for example, a light having a different wavelength from that of the communication light may be incident from the other end (not shown) of the optical fiber of the communication light emitting section 110 and used as the detection light.

In the embodiment, APS-C size is used as the sensor (imaging device). The larger the sensor size, the wider the field of view, which is advantageous for adjustment. However, the invention is not limited to this.

In the embodiment, the light intensity distribution of the luminous flux is converted using the light intensity conversion element having different transmittance depending on the position in the plane of the element, but the present invention is not limited to this. The effects of the present invention can be obtained similarly even if a reflecting member having a different reflectance depending on the position in the plane is used as the light intensity conversion element.

The present invention is not limited to the above embodiments, and various changes and modifications are possible without departing from the spirit and scope of the present invention. Accordingly, the following claims are included to publicize the scope of the invention.

This application claims priority based on Japanese Patent Application No. 2021-042625 submitted on March 16, 2021 and Japanese Patent Application No. 2021-042700 submitted on March 16, 2021, The entire contents of that description are incorporated herein.

Claims

An optical transmission device for performing optical communication between a light projecting section including emitting means for emitting communication light and a light projecting optical system, and a light receiving section including a light receiving optical system and communication light receiving means for receiving the communication light. and
The light projecting unit includes a detection light emitting unit that emits detection light,
The projection optical system has an adjustment optical system that changes the divergence of the light flux,
The light receiving unit includes detection light receiving means for receiving the detection light,
The optical transmission device according to claim 1, further comprising a divergence control section for controlling the adjustment optical system based on information from the detection light receiving means.
a first light projecting unit including first emitting means for emitting the first communication light and a first light projecting optical system;
a first light receiving unit including a first light receiving optical system and a first communication light receiving means for receiving the first communication light;
a second light projecting section including a second projecting means for projecting the second communication light and a second projecting optical system;
a second light receiving unit including a second light receiving optical system and second communication light receiving means for receiving the second communication light;
wherein optical communication is performed between the first light projecting section and the first light receiving section, and optical communication is performed between the second light projecting section and the second light receiving section. and
The first light projecting section has a detection light emitting section for emitting detection light,
The second light projecting optical system has an adjusting optical system that changes the divergence of the luminous flux,
The first light receiving section has detection light receiving means for receiving the detection light,
The optical transmission device has a divergence control unit that controls the adjustment optical system based on information obtained by the detection light receiving means.
An optical transmission device characterized by:
a first light projecting/receiving section including a first light emitting/receiving means for emitting a first communication light and receiving a second communication light; and a first optical system;
a second light emitting/receiving unit including a second emitting/receiving means for emitting the second communication light and receiving the first communication light, and a second optical system;
and performing bidirectional optical communication between the first and second light projecting and receiving units,
The first light projecting/receiving unit has a detection light emitting unit for emitting detection light,
The second optical system has an adjustment optical system that changes the divergence of the luminous flux,
The second light projecting and receiving unit has detection light receiving means for receiving the detection light,
The optical transmission device has a divergence control unit that controls the adjustment optical system based on information from the detection light receiving means.
An optical transmission device characterized by:
w 0 (mm) is the beam waist of the communication light immediately after being emitted from the light projecting section, λ (mm) is the wavelength of the communication light, L (mm) is the distance between the light projecting section and the light receiving section, When

2. The optical transmission device according to claim 1, wherein the following conditional expression is satisfied.
The beam waist of the second communication light immediately after being emitted from the second light projecting section is w 0 (mm), the wavelength of the second communication light is λ (mm), and the second light projecting section and When the distance from the second light receiving part is L (mm),

3. The optical transmission device according to claim 2, wherein the following conditional expression is satisfied.
The beam waist of the second communication light immediately after being emitted from the second light projecting and receiving unit is w 0 (mm), the wavelength of the second communication light is λ (mm), and the first light projecting and receiving unit When the distance from the second light projecting and receiving part is L (mm),

4. The optical transmission device according to claim 3, wherein the following conditional expression is satisfied.
The beam waist of the communication light immediately after being emitted from the light projection unit is w 0 (mm), the focal length of the projection optical system is f (mm), and the projection when the divergence is adjusted by the adjustment optical system When the maximum shift amount of the focal plane of the optical system is ΔZ fmax (mm),

5. The optical transmission device according to claim 1, wherein the following conditional expression is satisfied.
The beam waist of the second communication light immediately after being emitted from the second light projecting unit is w 0 (mm), the focal length of the second light projecting optical system is f (mm), and the adjusting optical system When the maximum value of the shift amount of the focal plane of the second projection optical system when the divergence is adjusted is ΔZ fmax (mm),

6. The optical transmission device according to claim 2, wherein the following conditional expression is satisfied.
The beam waist of the second communication light immediately after being emitted from the second light projecting and receiving unit is w 0 (mm), the focal length of the second optical system is f (mm), and the divergence of the adjusting optical system is When the maximum value of the shift amount of the focal plane of the second optical system when adjusting is ΔZ fmax (mm),

7. The optical transmission device according to claim 3, wherein the following conditional expression is satisfied.
The adjustment optical system has a movable optical member,
ΔZ fγ (mm) is the shift amount of the focal plane when the movable optical member moves by 0.01 mm, w 0 (mm) is the beam waist of the communication light immediately after being emitted from the light projecting unit, and the projection optics When the focal length of the system is f (mm),

8. The optical transmission device according to claim 1, wherein the following conditional expression is satisfied.
The adjustment optical system has a movable optical member,
The shift amount of the focal plane when the movable optical member moves by 0.01 mm is ΔZ fγ (mm), and the beam waist of the second communication light immediately after being emitted from the second light projecting section is w 0 (mm ), and the focal length of the second projection optical system is f (mm),

9. The optical transmission device according to claim 2, wherein the following conditional expression is satisfied.
The adjustment optical system has a movable optical member,
The shift amount of the focal plane when the movable optical member moves by 0.01 mm is ΔZ fγ (mm), and the beam waist of the second communication light immediately after being emitted from the second light projecting/receiving unit is w 0 (mm ), and the focal length of the second optical system is f (mm),

10. The optical transmission device according to claim 3, wherein the following conditional expression is satisfied.
The optical transmission device according to any one of claims 1 to 12, wherein the adjustment optical system includes a transmissive optical member that changes its position and inclination.
The optical transmission device according to any one of claims 1 to 13, wherein the movable optical member of said adjustment optical system is composed of one optical element.
The light projecting unit having the light projecting optical system including the adjusting optical system has second detection light receiving means for receiving the detection light from the light projecting unit,
11. The divergence controller according to any one of claims 1, 4, 7, and 10, wherein the divergence controller controls the adjustment optical system based on information obtained by the second detection light receiving means. The optical transmission device according to .
The first projection optical system has a second adjustment optical system that changes the divergence of the luminous flux,
The first light projecting section having the first light projecting optical system including the second adjusting optical system includes second detection light receiving means for receiving the detection light from the first light projecting section. has
12. Any one of claims 2, 5, 8 and 11, wherein said divergence control section controls said second adjustment optical system based on information obtained by said second detection light receiving means. 1. The optical transmission device according to claim 1.
The first optical system has a second adjustment optical system that changes the divergence of the luminous flux,
The first light projecting/receiving section having the first optical system including the second adjustment optical system has second detection light receiving means for receiving the detection light from the first light projecting/receiving section. death,
13. The divergence controller according to any one of claims 3, 6, 9 and 12, wherein the divergence controller controls the second adjustment optical system based on information obtained by the second detection light receiving means. 1. The optical transmission device according to claim 1.
The light-receiving unit has a correction mechanism that changes the optical characteristics of the light-receiving optical system,
The optical transmission device has an optical characteristic control unit that controls the correction mechanism based on information obtained by the detection light receiving means.
16. The optical transmission device according to any one of claims 1, 4, 7, 10 and 15, characterized by:
The first light-receiving unit has a correction mechanism that changes optical characteristics of the first light-receiving optical system,
The optical transmission device has an optical characteristic control unit that controls the correction mechanism based on information obtained by the detection light receiving means.
17. The optical transmission device according to any one of claims 2, 5, 8, 11, and 16, characterized by:
The second light projecting and receiving unit has a correction mechanism that changes the optical characteristics of the second optical system,
The optical transmission device has an optical characteristic control unit that controls the correction mechanism based on information obtained by the detection light receiving means.
18. The optical transmission device according to any one of claims 3, 6, 9, 12, and 17, characterized by:
19. The optical transmission device according to claim 18, wherein the correction mechanism includes a transmissive optical member that changes position and inclination in order to change the incident angle of the communication light with respect to the communication light receiving means.
20. The correction mechanism according to claim 19, wherein the correcting mechanism includes a transmissive optical member that changes position and inclination in order to change the incident angle of the first communication light with respect to the first communication light receiving means. An optical transmission device as described.
21. The correcting mechanism according to claim 20, wherein the correcting mechanism includes a transmissive optical member that changes position and inclination in order to change the incident angle of the first communication light with respect to the second emitting and receiving means. optical transmission equipment.
The optical transmission device according to claim 18 or 21, wherein the correction mechanism includes a mechanism for changing the orientation of the light receiving optical system.
The optical transmission device according to claim 19 or 22, wherein the correction mechanism includes a mechanism for changing the orientation of the first light receiving optical system.
The optical transmission device according to claim 20 or 23, wherein the correction mechanism includes a mechanism for changing the orientation of the second optical system.