JPH0440122A - Projector for spatial optical transmission - Google Patents

Abstract

PURPOSE:To enable communication continuously for long time in a daytime without providing an automatic tracking device by making the beam cross section shape of a laser beam elliptical long in a perpendicular direction. CONSTITUTION:A semiconductor laser 10 is arranged so as to make perpendicular the direction having the enlarging angle of the laser beam to be outputted from this, and beam cross section 14A of a laser beam 14 passing through a projecting lens 12 is made elliptical long in the perpendicular direction so as shown by an alternate long and two short clashes line. At this time, at the position a Fresnel lens 4 at a light receiving device 3, the cross section shape of the laser beam 14 is set so that a long diameter in the perpendicular direction can be almost equal to a distance subtracting the length of the Fresnel lens 4 in the perpendicular direction from the amount of diurnal fluctuation at the position of the laser beam 14 in the perpendicular direction.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a light projection device for spatial light transmission using laser light.

[Conventional technology]

In spatial light transmission, light is projected from a light projecting device toward a light receiving device installed at a position more than f in number, and a signal is propagated. At this time, as shown in FIG. 6, for example, a laser beam 5 is projected from a semiconductor laser 1 through a light projecting lens 2 to a Fresnel lens 4 which is a light receiving surface of a light receiving device 3. 3A and converts it into an electrical signal. Here, the output beam of the semiconductor laser 1 has a different spread angle depending on the emission direction. That is, the beam shape in a cross section perpendicular to the central optical axis of the output beam is approximately elliptical. For this reason, conventionally, as shown in FIGS. 7 and 8,
A collimator lens 6, a cylindrical lens pair 7, and a lens 8 are interposed between the semiconductor laser 1 and the projection lens 2, so that the beam cross section 5A is circular.

[Problem to be solved by the invention]

In the spatial light transmission system as described above, the laser beam 5 emitted from the projection lens 2 shown in FIG. By the way, while the laser beam 5 propagates through the atmosphere,
refracted by the atmosphere. Since the temperature of the atmosphere fluctuates diurnally, the vertical position of the laser beam 5 at the light-receiving surface position of the light-receiving device 3 causes diurnal fluctuations due to changes in the vertical refractive index gradient of the atmosphere. FIG. 9 shows the variation in the height position of the laser beam 5 on the light receiving surface on a sunny day when the distance between the semiconductor laser 1 and the light receiving bags W, 3 is 8 Kl. FIG. 10 shows the position of the laser beam 5 in relation to the Fresnel lens 4 which is the light receiving surface. In this case, the transmission distance is 8 m as described above, the output power of the projection lens Pa is 151 W, and the size of the Fresnel lens 4 is 30 c + m x 30 cn.
The beam diameter at the position is 70C1 even when stopped down to the smallest
In this state, the relative positional fluctuation with respect to the light receiving surface is as shown in FIG. Therefore, as can be seen from FIG. 10, the Fresnel lens 4 can only receive the laser beam 5 from 8 o'clock to 12 o'clock. In other words, continuous communication is only possible for about 4 hours during the day. In order to solve this problem, either a tracking device for automatically tracking the laser beam 5 is provided in the light-receiving bag f3 shown in FIG. 6, or the beam diameter is increased. In the former case, there is a problem that the automatic tracking device becomes large-scale. In the latter case, for example, as shown in FIG. 11, if the beam diameter at the light receiving device is expanded to D = 2.5 m,
Light can be received continuously between 8:00 and 16:00, that is, during the day. However, as mentioned above, the projection lens output power P
When o = 1511W and propagation distance is 8Kn, the incident power to the light receiving device is as small as 0.40μW,
If the beam diameter at the light receiving position is increased, communication, etc. becomes impossible. This invention has been made in view of the above-mentioned conventional problems, and it can be used continuously for long periods of time during the day without significantly reducing the incident power to the light receiving device or without providing an automatic tracking device for the light receiving device. An object of the present invention is to provide a light projecting device for spatial light transmission that enables communication using the following methods.

[Means to solve the problem]

The present invention provides a light projecting device for spatial light transmission that transmits a signal by projecting a laser beam output from a light source to a light receiving device, in which the cross-sectional shape of the laser beam is an ellipse that is long in the vertical direction. The above object is achieved by a light projecting device for spatial light transmission, which is characterized in that it has a shape. Further, the above object is achieved by using a semiconductor laser as the light source and arranging the semiconductor laser so that the direction in which the divergence angle of its output beam is large is the vertical direction. Further, the above object is achieved by providing a cylindrical lens that expands the diameter of the laser beam from the light source in the vertical direction and reduces the diameter in the horizontal direction. Furthermore, the vertical cross-sectional shape of the laser beam at the light-receiving device position is determined by subtracting the vertical length of the light-receiving surface of the light-receiving device from the diurnal fluctuation amount of the vertical position of the laser beam. The above objective is achieved by making the distance approximately equal to the distance shown in FIG.

[Action and effect]

In this invention, since the cross-sectional shape of the laser beam emitted from the spatial light transmission projector is an ellipse that is long in the vertical direction, the refractive index gradient in the vertical direction of the atmosphere in the laser beam propagation path changes. This allows the light receiving surface to be always located within the laser beam even when the position of the light receiving surface changes in the vertical direction of the laser beam. Communication can be performed for long periods of time during the day without increasing the beam diameter unnecessarily. In addition, since the light source is a semiconductor laser and the direction in which the output beam of the semiconductor laser has a large divergence angle is the vertical direction, the laser beam can be shaped into an ellipse that is long in the vertical direction without providing a special lens. . Furthermore, the diameter of the laser beam from the light source is expanded in the vertical direction,
In addition, by using a cylindrical lens whose diameter is reduced in the horizontal direction, the laser beam can be shaped into an elliptical shape that is long in any vertical direction, and the ratio of the major axis to the minor axis can be optimized, allowing efficient optical transmission. Furthermore, since the vertical major axis of the laser beam at the light-receiving surface position is approximately equal to the distance obtained by subtracting the length of the light-receiving surface from the diurnal variation in the vertical direction of the laser beam, the laser beam at the light-receiving surface position Optical transmission can be performed efficiently without unnecessarily increasing the vertical length of the optical fiber.

【Example】

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIGS. 1 and 2, a semiconductor laser 10 is arranged so that the direction in which the laser beam outputted from the laser beam has a large divergence angle is in the vertical direction. The beam cross section 14A of the laser beam 14 that has passed through the laser beam 14 is shaped like an ellipse that is elongated in the vertical direction, as shown by the two-dot chain line. At this time, the cross-sectional shape of the laser beam 14 at the position of the Fresnel lens 4 in the light receiving device 3 in FIG. The distance is set to be approximately equal to the distance obtained by subtracting the length in the vertical direction. That is, due to changes in the vertical refractive index gradient of the atmosphere in the propagation path of the laser beam 14, the propagated laser beam 14 changes diurnally in the vertical direction at the position of the light receiving surface, and on clear skies, the position of the propagated laser beam 14 changes daily in the vertical direction. It is at its lowest point at 4 p.m. and at its highest point at 4 p.m. Therefore, if the upper end of the laser beam 14 at 8:00 a.m. covers the Fresnel lens 4, which is the light receiving surface, and the lower end of the laser beam 14 at 16:00 covers the Fresnel lens 4, the Fresnel lens 4 will be The laser beam 14 is constantly received during the day. Moreover, compared to simply increasing the beam diameter with a circular cross section, the light on both sides in the horizontal direction is concentrated within the ellipse, so there is less loss of power incident on the Fresnel lens 4. Become. Therefore, it is preferable that the horizontal minor axis of the laser beam 14 be as close to the horizontal width of the Fresnel lens 4 as possible. According to the inventor's experiments, the output power Po of the projection lens
= 1511W, propagation distance #8 Kn, and the dimensions of the Fresnel lens 4 which is the light receiving lens are 30CIX 30C11, and the cross-sectional shape of the output laser beam 14 is set such that the major axis in the vertical direction is the position of the Fresnel lens 4. 2.5i, and the short axis in the horizontal direction is 70 cl, the laser beam 14 can be continuously incident on the Fresnel lens 4 from 8 a.m. to 4 p.m., and the incident power at that time is 1. .4μW, as shown in Figure 11, simply change the diameter of the laser beam to D = 2 with a circular cross section.
The incident power was 3.5 times that of the case where the angle was 511°, and communication was possible. In the above embodiment, the laser beam from the semiconductor laser 10 is emitted through the projection lens 12. However, as shown in FIGS. 3 and 4, for example, the cylindrical lens 16 is By interposing it between the laser 10 and the projection lens 12, the beam cross section 14A can be further reduced in length as shown by the two-dot chain line in FIG. In this way, the vertical width, that is, the major axis, of the beam cross section 14A can be made even longer, so that it is possible to cope with large fluctuations. Further, although the above embodiment uses the semiconductor laser 10 as the light source, the present invention is not limited to this, and other laser beam generating means such as a gas laser or a solid laser may be used. However, in this case, unlike the semiconductor laser 10, the spread angle of the output beam does not differ in the vertical and horizontal directions, so a cylindrical lens is essential.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view in the vertical direction of a floodlight device for spatial light transmission according to the present invention, FIG. 2 is a schematic cross-sectional view in the horizontal direction of the same embodiment, and FIG. FIG. 4 is a schematic horizontal cross-sectional view of the second embodiment of the lighting device, and FIG. 5 is a schematic cross-sectional view of the second embodiment of the same in the horizontal direction. FIG. 6 is a plan view showing the beam shape at the light receiving surface position of the laser beam and its relationship with the light receiving surface according to an example; FIG. 6 is an optical system diagram showing an outline of a conventional light projector and light receiving device for spatial light transmission; FIG. 7 8 is a schematic cross-sectional view showing the conventional light projecting device for spatial light transmission, FIG. 8 is a schematic cross-sectional view taken at a cross section perpendicular to FIG. 7, and FIG. 9 is a schematic cross-sectional view showing the light receiving surface position in the spatial light transmission system. Diagram showing the diurnal variation of the laser beam in the vertical direction, 1st
FIG. 0 is a plan view showing the relationship between the diurnal variation of the laser beam and the light receiving surface, and FIG. 11 is a plan view showing the relationship between the light receiving surface and the laser beam when the diameter of the laser beam is increased. 3... Light receiving device, 4... Fresnel lens, 5... Light receiver, 6... Collimator lens, 10... Semiconductor laser 12... - Projection lens, 14... Laser beam, 14A ...Beam cross section, 16...Cylindrical lens.

Claims (4)

[Claims] (1) In a light projector for spatial light transmission that transmits a signal by projecting a laser beam output from a light source to a light receiving device, the cross-sectional shape of the laser beam is an ellipse that is elongated in the vertical direction. A floodlight device for spatial light transmission, characterized by: (2) A device for spatial light transmission according to claim 1, wherein the light source is a semiconductor laser, and the semiconductor laser is arranged such that the direction in which the divergence angle of its output beam is large is the vertical direction. floodlight device. (3) A light projector for spatial light transmission according to claim 1 or 2, further comprising a cylindrical lens that expands the diameter of the laser beam from the light source in the vertical direction and reduces the diameter in the horizontal direction. (4) In claim 1, 2 or 3, the vertical cross-sectional shape of the laser beam at the position of the light receiving device is such that the major axis in the vertical direction is determined from the diurnal variation of the vertical position of the laser beam. A light projector for spatial light transmission, characterized in that the distance is approximately equal to the distance obtained by subtracting the vertical length of the light receiving surface.