JP2011234071A - Optical wireless apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical wireless apparatus with a simplified configuration facilitating adjustment of an optical axis and capable of a tolerance for a displacement of extending a receiving unit.SOLUTION: An optical wireless transmission apparatus 1 includes a transmitting unit 10 and a receiving unit 20. The transmitting unit 10 includes an SLD 11 that emits light having a first wavelength band and that performs laser oscillation due to externally returned light, a collimator lens 13 that converts the light emitted from the SLD 11 to parallel light, and a diffraction grating 14 that has different diffraction angles for wavelengths of light and that diffuses the parallel light from the collimator lens 13 in a predetermined angle range corresponding to the first wavelength band in a first plane. The receiving unit 20 is disposed in the predetermined angle range in the first plane, and includes a CCP 21 that, by reflecting part of light arriving via the diffraction grating 14 in the original direction, returns the part of light to the SLD 11, and a light receiving element 22 that converts the other part of light arriving via the diffraction grating 14 into an electric signal.

Description

  The present invention relates to an optical wireless transmission apparatus that performs spatial transmission of information using light, and particularly relates to a technique that can be suitably applied to laser power transmission and optical communication.

  Conventionally, there are the following two types of optical wireless transmission apparatuses that use a space as a transmission path. One is a diffused light type optical wireless transmission apparatus that performs communication using light having a spread angle. This diffused light type optical wireless transmission device has the advantage of not requiring precise optical axis alignment, but has a problem that it cannot be applied to long-distance communication because light is diffused and attenuated. The other is a parallel light type optical wireless transmission apparatus that performs communication using parallel rays. Although this parallel light type optical wireless transmission device can perform long-distance communication by precisely aligning the optical axis, there is a problem that precise optical axis alignment is not easy.

  In this regard, Patent Document 1 discloses a parallel light type communication device in which a two-dimensional scanner is provided on the transmitter side and the optical axis misalignment between the transmitter and the receiver is corrected using the two-dimensional scanner.

JP-A-5-346467

  However, in the communication device disclosed in Patent Document 1, it is necessary to incorporate a two-dimensional scanner, which is a mechanical and electrical drive mechanism, on the transmitter side, which increases the cost of the communication device and increases the size of the device. There's a problem. Therefore, a configuration that does not require a mechanical and electrical search mechanism, that is, an optical wireless transmission device that facilitates optical axis alignment with a simpler configuration has been demanded.

  The present invention has been made in view of the above circumstances. As an example of the problem, light that can easily adjust the optical axis with a simple configuration and can increase the tolerance of positional deviation of the receiving unit. It is to provide a wireless transmission device.

  In order to achieve the above object, one aspect of the present invention is an optical wireless transmission apparatus including a transmission unit and a reception unit, wherein the transmission unit emits light in a first wavelength band and is externally supplied. A light source that oscillates with the return light, a collimator element that collimates the light emitted from the light source, a diffraction angle varies according to the wavelength of the light, and the collimated light from the collimator element is converted into the first plane. A dispersion optical element that disperses within a predetermined angle range corresponding to the first wavelength band, and the receiving unit is disposed within the predetermined angle range in the first plane. A part of the light that has reached through the dispersion optical element is reflected in the original direction and returned to the light source, and the remainder of the light that has reached through the dispersion optical element is converted into an electrical signal. A light receiving element.

1 is a schematic configuration diagram of an optical wireless transmission apparatus according to a first embodiment of the present invention. It is a figure which shows the diffraction direction of the light which injects into a diffraction grating. In the optical wireless transmission apparatus which concerns on the 1st Embodiment of this invention, it is a figure which shows the diffusion direction of the light radiate | emitted from the light source. 5 is a graph showing the relationship between the ratio of extracting light to the outside and the light output of the light receiving element in the optical wireless transmission apparatus according to the first embodiment of the present invention. It is a figure which shows the external appearance of the retroreflection material of the optical wireless transmission apparatus which concerns on the 2nd Embodiment of this invention. In the optical wireless transmission apparatus according to the second embodiment of the present invention, how the light travels when the receiving unit is displaced in the direction in which light is not dispersed is compared with the optical wireless transmission apparatus according to the first embodiment. FIG. It is a schematic block diagram of the optical wireless transmission apparatus which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram of the receiving part of the optical wireless transmission apparatus which concerns on the 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a schematic configuration diagram of an optical wireless transmission device 1 according to the first embodiment of the present invention. The optical wireless transmission device 1 illustrated in FIG. 1 includes a transmission unit 10 and a reception unit 20, and a signal is transmitted when the reception unit 20 receives laser light emitted from the transmission unit 10. The optical wireless transmission device 1 is assumed to be, for example, an optical communication device or a laser power transmission device.

  As the light source 11 of the transmission unit 10, for example, a super-luminescent diode (hereinafter referred to as SLD) having a wider spectral line width than a normal semiconductor laser (hereinafter referred to as LD) is preferable. is there. The SLD 11 emits light having a broad spectrum (determined by the laser medium. For example, the center wavelength is 950 nm and the line width is 60 nm) based on the control of the light source driving unit 12. The SLD 11 is manufactured by applying an antireflection coating that makes the reflectance as close to zero as possible on one end face of the laser medium of the LD. That is, the antireflection coating is applied to one end surface of the SLD 11 on the laser beam emission side, and the antireflection coating is not applied to the other end surface. For this reason, the SLD 11 alone does not oscillate. In the present embodiment, as will be described later, the SLD 11 is used as an external resonator type laser.

  The light emitted from the SLD 11 is converted into parallel light by a collimator lens 13 which is a collimator element, and the parallel light is diffracted by a diffraction grating 14 which is a dispersion optical element.

Here, the diffraction direction (strengthening direction) of the light passing through the diffraction grating 14 will be described with reference to FIG. FIG. 2 is a diagram showing the diffraction direction of light incident on the diffraction grating 14 having a grating pitch of N (the number of gratings per unit length. The grating interval is 1 / N). When the wavelength of incident light is λ, the incident angle is α, the diffraction angle is β, and the diffraction order is m,
sin α + sin β = Nmλ (1)
Therefore, the diffraction angle β differs for each wavelength.

  That is, when light having a wide spectrum is incident on the diffraction grating 14, the diffracted light is diffused and propagated as shown in FIG. FIG. 3 is a diagram illustrating the diffusion direction of the light emitted from the SLD 11. More specifically, from the above equation (1), the longer the wavelength, the larger the diffraction angle β. Therefore, when the wavelength λ of the incident light is λ1 ≦ λ ≦ λ2, the light of wavelength λ1 is the A direction and the light of wavelength λ2 is The S region traveling in the B direction and surrounded by the A direction and the B direction becomes the traveling direction of the diffracted light. In the present embodiment, as shown in FIGS. 1 and 3, the light emitted from the SLD 11 will be described as being dispersed in a direction (paper surface direction) parallel to the XY plane.

  In general, when light emitted from the SLD 11 is reflected by a reflecting member (reflector) disposed outside the SLD 11 and returned to the SLD 11, it becomes an external resonator type LD light source, and it is known that the SLD 11 oscillates. ing. As an application example using this characteristic and a diffraction grating, there is a wavelength-tunable external resonator laser. In the case of a tunable external resonator type laser, light is dispersed by a diffraction grating to select the wavelength, and only light of a specific wavelength is returned to the LD light source, thereby realizing laser oscillation with a narrow band spectrum selectively. ing. Based on the principle of this wavelength-tunable external cavity laser, the traveling region of diffused light dispersed by the diffraction grating 14 (hereinafter referred to as the diffusion region, specifically, the S region in FIG. 3) By arranging a reflecting member 21 such as a mirror and returning the light reflected by the reflecting member 21 to the SLD 11, laser oscillation can be caused. That is, if the receiving unit 20 provided with the reflecting member 21 is arranged in any of the diffusion regions, a laser resonator is automatically constructed by the transmitting unit 10 and the receiving unit 20, and the transmitting unit 10 moves to the receiving unit 20. Laser light can be transmitted. When laser oscillation occurs, the spectrum of the light emitted from the SLD 11 becomes a narrow band, so that the diffusion angle of the light dispersed by the diffraction grating 14 becomes narrow.

  As the reflecting member 21 of the receiving unit 20, a retroreflecting material such as a corner cube prism (hereinafter referred to as CCP) is suitable. The CCP 21 has a recursive property of reflecting incident light in the original direction (the same direction as the incident light). In the present embodiment, by utilizing the characteristics of the CCP 21, a part of the light incident on the CCP 21 from the diffraction grating 14 is reflected in the same direction, and the reflected light is returned to the SLD 11 through the diffraction grating 14. It has become.

  Conventionally, in order to transmit laser light from a transmission unit to a reception unit, it has been necessary to incorporate a search mechanism such as a two-dimensional scanner on the transmission unit side to perform precise optical axis alignment. However, in the present embodiment, it is only necessary to arrange the receiving unit 20 (CCP 21) somewhere in the diffusion region (S region in FIG. 3) having a predetermined angle spread, so there is no need for precise optical axis alignment. . That is, the optical wireless transmission device 1 can easily adjust the optical axis with a simple configuration in which a dispersion optical element is provided on the transmission unit 10 side and a retroreflecting material is provided on the reception unit 20 side. It is possible to increase the tolerance of positional deviation with respect to the light dispersion direction (direction parallel to the XY plane).

  A light receiving element 22 is disposed on the reflection surface of the CCP 21 of the receiving unit 20. The light receiving element 22 is a photoelectric conversion element that converts light into an electrical signal. The light receiving element 22 extracts a part of the light incident on the reflection surface of the CCP 21 and performs photoelectric conversion. As the photoelectric conversion element, for example, a photodiode or a solar cell is assumed. In the case of a photodiode, a light modulation signal is converted into an electric modulation signal. In the case of a solar cell, light energy is converted into electric energy. Convert. The converted electrical modulation signal or electrical energy is sent to the operating unit 23.

  Here, the magnitude of the light output taken out by the light receiving element 22 is the ratio η (= externally) of the light taken out from the laser resonator out of the light emitted from the laser resonator constructed by the transmitter 10 and the receiver 20. The total amount of light inside the laser resonator, which will be referred to as the light extraction efficiency hereinafter). FIG. 4 is a graph showing the relationship between the light extraction efficiency η and the light output extracted by the light receiving element 22 obtained by experiments. The light output taken out by the light receiving element 22 is standardized, and the light output when the light extraction efficiency η = 0.8 is 1.

  As shown in FIG. 4, if the light extraction efficiency η is too small, the amount of light extracted outside the laser resonator is small, and the light output of the light receiving element 22 is also small. On the other hand, when the light extraction efficiency η is too large, the amount of light returning to the SLD 11 is reduced, so that the laser oscillation is weakened, and thereby the light output of the light receiving element 22 is also reduced. Therefore, by selecting an appropriate light extraction efficiency η, the light receiving element 22 can obtain the maximum light output (η = 0.8 in FIG. 4). In the receiving unit 20 of the present embodiment, the light extraction efficiency η is set in advance so that the light output of the light receiving element 22 is maximized. Specifically, since the reflectance of the back surface of the CCP 21 is adjusted in advance so as to have an appropriate value, the light output of the light receiving element 22 is maximized.

  As described above, according to the optical wireless transmission device 1 of the present embodiment, the transmission unit 10 emits light in the first wavelength band and emits laser light from the SLD 11 that oscillates with return light from the outside. The diffraction angle differs depending on the wavelength of the light and the collimator lens 13 that converts the collimated light into parallel light, and the parallel light from the collimator lens 13 has a predetermined angle corresponding to the first wavelength band in the first plane. And the receiving unit 20 is disposed within a range of a predetermined angle in the first plane, and a part of the light that has reached through the diffraction grating 14 is in the original direction. The CCP 21 is reflected back to the SLD 11 and the light receiving element 22 that converts the remainder of the light that has reached via the diffraction grating 14 into an electric signal. Therefore, the optical axis can be easily adjusted with a simple configuration. Light dispersion of receiver 20 It is possible to increase the tolerance of the positional deviation with respect to that direction.

  The size of the diffusion region is determined from the above equation (1) using the incident angle α and wavelength λ of light incident on the CCP 21 and the value of the grating pitch N as parameters. In the present embodiment, The value of this parameter is determined according to the use of the optical wireless transmission apparatus 1, and a suitable size of the diffusion region is set.

  In the optical transmission according to the present embodiment, the specific wavelength that causes laser oscillation is meaningless. In other words, in the present embodiment, it is meaningful that the transmission unit 10 causes laser oscillation by arranging the reception unit 20 on a predetermined spread area, and a specific wavelength selected as a result is selected. Has no particular meaning.

  Although it is possible to use a dispersion optical element as a lens instead of the diffraction grating 14 and generate diffused light using the lens, when a lens is used, a part of light for all wavelengths of incident light is used. Since it will return to SLD11, an energy loss will become large. On the other hand, when the dispersion optical element is the diffraction grating 14 as in the present embodiment, all the light having a specific wavelength of the incident light returns to the SLD 11, so that there is an effect that energy loss is small. is there. As a result, if the receiving unit 20 is arranged in the diffusion region, optical transmission is possible even if the distance between the transmitting unit 10 and the receiving unit 20 is a long distance.

  Furthermore, according to the optical wireless transmission device 1 of the present embodiment, since the reflectance control of the CCP 21 is performed in the reception unit 20, the reception unit 20 can obtain a suitable optical output, and the operation unit 23 A desired process can be executed in step (b).

<Second Embodiment>
In the first embodiment, the tolerance of positional deviation with respect to the light dispersion direction (direction parallel to the XY plane) of the receiving unit 20 is large, but the direction in which light reception is not performed (Z direction which is a direction perpendicular to the XY plane). ) With respect to the positional deviation of the receiving unit 20 was small. Therefore, in the second embodiment, as the retroreflecting material, using the CCP array 21A arrayed in the direction in which light is not dispersed (Z direction), the receiving unit 20 is also used in the direction in which light is not dispersed (Z direction). The tolerance of misalignment is increased.

  FIG. 5A is an external view of the CCP array 21A. As shown in FIG. 5A, the CCP array 21 </ b> A is configured by arraying a plurality of CCPs 24 that are sufficiently small with respect to the size of the diffraction grating 14 in the Z direction in the Z direction.

  FIG. 6A is a diagram illustrating how light travels when the CCP 21 is displaced in the direction in which light is not dispersed (Z direction) in the first embodiment, and FIG. In the second embodiment, it is a diagram showing how light travels when the CCP array 21A is displaced in a direction in which light is not dispersed (Z direction). As shown in FIG. 6A, when the CCP 21 is used as the retroreflecting material, the optical axis is shifted in the direction in which the light is not dispersed (Z direction), so that the light reflected by the CCP 21 Cannot pass through the diffraction grating 14. On the other hand, when the CCP array 21A is used, the optical axis deviation amount in the return path can be reduced by reducing the size of the CCP 24 even if the optical axis deviation occurs in the direction in which light is not dispersed (Z direction). Therefore, the loss of the return light amount can be reduced.

  Therefore, according to the optical wireless transmission device 2 of the second embodiment, the retroreflective members are arranged in an array in a direction (direction in which light is not dispersed) perpendicular to the first plane (direction in which light is dispersed). The size of each CCP 24 constituting the CCP array 21A is sufficiently small with respect to the size in the direction perpendicular to the first plane of the diffraction grating 14 (the direction in which no light is dispersed). In addition to the effect of the first embodiment, it is possible to expand the tolerance of the positional deviation of the receiving unit 20 in the direction in which light is not dispersed (Z direction).

  In the second embodiment, the light receiving element 22 is disposed on the reflection surface of the CCP 24 as in the first embodiment. However, a different configuration, for example, as shown in FIG. As described above, the CCP 24 and the light receiving element (photoelectric conversion element) 25 may be mixed in the Z direction to form an array. In this case, the value of the light extraction efficiency η can be controlled by the ratio of the areas of the CCP 24 and the light receiving element 25. The sizes of the CCP 24 and the light receiving element 25 are sufficiently small with respect to the beam diameter of the laser light reflected on the CCP array 21B.

<Third Embodiment>
FIG. 7 is a schematic configuration diagram of an optical wireless transmission device 3 according to the third embodiment. In the third embodiment, a plurality of light sources (SLD) 11 are arranged in an array in a direction (Z direction) in which light is not dispersed. Similarly to the second embodiment, a CCP array 21A arrayed in a direction in which light is not dispersed (Z direction) is provided.

  Therefore, according to the optical wireless transmission device 3 of the third embodiment, since the SLD 11 is arranged in the direction perpendicular to the first plane (the direction in which light is not dispersed), the effect of the second embodiment is achieved. In addition, high output can be realized and the amount of information to be transmitted can be increased.

  In the third embodiment, the plurality of light sources 11 are arrayed in the direction in which light is not dispersed (Z direction), but the plurality of light sources 11 are arrayed in the direction in which light is dispersed (direction parallel to the XY plane). May be used. In this case, the CCP array 21A must also be arrayed in the direction in which light is dispersed (direction parallel to the XY plane).

<Fourth embodiment>
FIG. 8 is a schematic configuration diagram of the receiving units 30 and 40 of the optical wireless transmission device 4 according to the fourth embodiment. In the fourth embodiment, an optical element that makes the value of the light extraction efficiency η variable is added to the receiver. FIG. 8A is a configuration diagram of a receiving unit 30 that variably captures reflected light from the reflecting member 21 into the light receiving element 22, and FIG. 8B is a reception that variably captures incident light from the SLD 11 into the light receiving element 22. 4 is a configuration diagram of a unit 40. FIG.

  In the receiving unit 30, a PBS (polarization beam splitter) 26 and a quarter wavelength plate 27 are added to the configuration of the receiving unit 20 according to the first embodiment. Therefore, in the receiving unit 30, the amount of light incident on the light receiving element 22 through the PBS 26 and the CCP 21 can be controlled by rotating the quarter wavelength plate 27.

  On the other hand, in the receiving unit 40, a PBS (polarization beam splitter) 26 and a half-wave plate 28 are added to the configuration of the receiving unit 20 according to the first embodiment. Therefore, in the receiving unit 40, the amount of light incident on the light receiving element 22 from the PBS 26 can be controlled by rotating the half-wave plate 28.

  Therefore, according to the optical wireless transmission device 4 of the fourth embodiment, the receiving unit further includes an optical element that variably incorporates the light that has reached the receiving unit into the light receiving element 22. Even if the situation changes, the optimum light extraction efficiency η can be set, and the maximum light output can be obtained. Specifically, since the receiving unit 30 includes the PBS 26 and the quarter wavelength plate 27, the light after being reflected by the CCP 21 is rotated by rotating the quarter wavelength plate 27. The amount of light incident on can be adjusted. Further, since the receiving unit 40 includes the PBS 26 and the half-wave plate 28, the light before being reflected by the CCP 21 is incident on the light receiving element 22 by rotating the half-wave plate 28. The amount of light can be adjusted.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made to the embodiments of the present invention without departing from the gist of the present invention. Such modifications and changes can be made, and those accompanying such modifications and changes are also included in the technical scope of the present invention.

1, 2, 3, 4 Optical wireless transmission device 10 Transmitter 11 SLD (Light source)
12 Light source drive unit 13 Collimator lens (collimator element)
14 Diffraction grating (dispersion optical element)
20, 30, 40 Receiver 21, 24 CCP (reflective member)
21A, 21B CCP array (reflective member)
22, 25 Photoelectric conversion element (light receiving element)
23 Operation part 26 PBS
27 1/4 wavelength plate 28 1/2 wavelength plate

Claims (4)

An optical wireless transmission device including a transmission unit and a reception unit,
The transmitter is
A light source that emits light in the first wavelength band and that oscillates with return light from the outside;
A collimating element that collimates the light emitted from the light source;
A dispersion optical element having a diffraction angle different according to a wavelength of light, and dispersing the parallel light from the collimating element within a predetermined angle range corresponding to the first wavelength band in a first plane;
With
The receiver is
A retroreflecting material that is disposed within the range of the predetermined angle in the first plane, reflects a part of the light that has reached through the dispersion optical element in the original direction, and returns the light source to the light source;
A light receiving element that converts the remainder of the light that has reached through the dispersion optical element into an electrical signal;
An optical wireless transmission device comprising: The retroreflecting material is arranged in an array in a direction perpendicular to the first plane,
2. The light according to claim 1, wherein the size of each of the arrayed retroreflecting materials is sufficiently smaller than the size of the dispersion optical element in a direction perpendicular to the first plane. Wireless transmission device.   3. The optical wireless transmission apparatus according to claim 1, wherein the light sources are arranged in an array in a direction perpendicular to the first plane. The receiver is
4. The optical wireless transmission device according to claim 1, further comprising an optical element that variably takes light that has reached the receiving unit into the light receiving element. 5.

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