JP2002118516A - Optical space transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical space transmission device which restrains a spherical aberration from being worsened, which restrains a light receiving optical system from becoming large-sized and high-cost, and which can enhance the directivity of the light receiving optical system. SOLUTION: A light receiving element 13 is arranged at a position which is defocused on the side of a light receiving optical system 12 from the focal position of the optical system 12. The focal position refers to the position at which a projection optical system 11 is installed at the most distant position from the optical system 12 in the specifications of a product. The defocused position refers to the position at which the spot diameter of a light beam becomes 75% of the diameter of an effective light receiving part in the light receiving element 13 when the light beam emitted from the optical system 11 is converged by the optical system 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light for performing optical communication by emitting a light beam from a light projecting means comprising a signal generating section and a light projecting optical system and receiving the light beam by a light receiving means comprising a light receiving optical system and a signal detecting section. The present invention relates to a spatial transmission device.

[0002]

2. Description of the Related Art A conventional optical space transmission apparatus of this type is shown in FIG.
As shown in (1), the light receiving means comprises a light projecting optical system 1 of the light projecting means and a light receiving optical system 2 of the light receiving means. Such an optical space transmission device includes a shift amount detecting means for detecting a shift amount between the optical axis of the light projecting optical system 1 and the optical axis of the light receiving optical system 2, and an optical signal based on the shift amount detected by the detecting means. If there is no optical axis correction means for correcting the deviation of the axis, it is not possible to correct the bending of the beam due to the fluctuation of the atmosphere or the like. Therefore, it is desirable to further widen the directivity of the light receiving optical system 2.

FIG. 7 is a schematic diagram of the light receiving optical system 2. A light beam La indicated by a solid line is incident on an optical axis of an effective light receiving portion 3 'of the light receiving element 3, and a light beam Lb indicated by a chain line is effective. A light beam L which is incident on almost the end of the light receiving section 3 'and is indicated by a two-dot chain line
“c” indicates a state in which the light is incident off the end of the effective light receiving unit 3 ′. These light beams La to Lc are almost in focus.

FIG. 8 is a schematic diagram showing the positional relationship between the light beams La to Lc and the effective light receiving portion 3 '. In FIG. 8A, the entire spot of the light beam La is contained in the effective light receiving portion 3'. Thus, the effective light receiving section 3 'is in a state capable of detecting all of the captured light beam La. In FIG. 8B, almost half of the spot of the light beam Lb deviates from the effective light receiving unit 3 ',
The effective light receiving section 3 'is in a state capable of detecting substantially half of the light beam Lb taken in. Then, in FIG. 8C, the entire spot of the light beam Lc deviates from the effective light receiving unit 3 ', and the effective light receiving unit 3' cannot detect the light beam Lc.

FIG. 9 is a graph showing the positional relationship between the light beams La to Lc and the effective light receiving section 3 ', and FIG. 8 is graphed. The horizontal axis is the distance between the center of the spot of the light beams La to Lc and the optical axis of the light receiving optical system 2, that is, the ratio between the image height h and the radius of the effective light receiving unit 3 ', and the position corresponding to FIG. 1
00%. The vertical axis represents the ratio of the portion where the light beams La to Lc overlap the effective light receiving portion 3 ', that is, the output ratio,
Assuming that the position of the point A corresponding to FIG.
Is 0%. At positions before and after point B corresponding to FIG.
% Has changed. FIG. 9 shows that when the focus of the light receiving optical system 2 is substantially focused on the light receiving element 3, almost 100% output is obtained up to the end of the effective light receiving unit 3 '. Indicates that no output can be obtained if the value is slightly out of the range.

[0006]

In such a conventional example, as shown in FIG. 6, the directivity of the light receiving optical system 2 is perpendicular to its optical axis and the light receiving region Ra However, if the opening of the light projecting optical system 1 does not exist in the light receiving area Ra, communication becomes impossible.
On the other hand, in the case of including the displacement amount detecting means and the optical axis correcting means, it is possible to direct at least the optical axis of the light receiving optical system 2 into the opening of the light projecting optical system 1 as shown in FIG. Even if the directivity of the light receiving optical system 2 is narrow, the light receiving area Ra can be brought into a communication-enabled state in accordance with the opening of the light projecting optical system 1.

[0007] When the displacement amount detecting means and the optical axis correcting means are not provided, the displacement between the optical axis of the light projecting optical system 1 and the optical axis of the light receiving optical system 2 cannot be corrected. The directivity of the light receiving optical system 2 is expanded as
It is necessary that a ′ includes the opening of the light projecting optical system 1.

However, at present, the size of the light receiving element 3 cannot be freely selected. Therefore, in order to guide the light beams La to Lc to the light receiving element 3, it is necessary to shorten the focal length of the light receiving optical system 2. In order not to reduce the absolute value of the light energy required by the light receiving optical system 2, the light receiving optical system 2
Cannot be made smaller. Therefore, in order to guide the light beams La to Lc to the light receiving element 3, the light receiving optical system 2
The focal length is shortened without changing the size of the aperture, which is equivalent to reducing the F value.

For example, specific numerical values are shown below. The communication distance (D) between the light projecting optical system 1 and the light receiving optical system 2 is 1 k
m, the aperture (O ₁ ) of the light projecting optical system 1 is 60 mm, and the beam diameter (O ₂ ) of the light projecting optical system 1 at the position of the light receiving optical system 2
Is 2 m, the effective diameter (R) of the light receiving element 3 is 0.2 mm, and the directivity of the light receiving optical system 2 is equivalent to that of the light projecting optical system 1. Since the maximum deviation (E) from the optical axis of the optical system 2 is 1 m and R / (2E) ≪1, the required focal length (f) of the light receiving optical system 2 is substantially f / {O _2. D / (O ₂ −O ₁ )} = R / (2E), and f = 103 mm. On the other hand, in order to maintain the light receiving sensitivity of the light receiving optical system 2, the aperture of the light receiving optical system 2 cannot be made too small. Here, assuming that the opening of the light receiving optical system 2 is 60 mm, which is the same as the opening (O ₁ ) of the light projecting optical system 1,
The F value required for the light receiving optical system 2 is 1.7.

As described above, in order to secure the energy of the received light while expanding the directivity, a lens having a small F value is required. Further, when the directivity is widened or the F-number is further reduced to secure more light energy, deterioration of spherical aberration cannot be ignored. In order to suppress the deterioration of the spherical aberration, the number of lenses must be increased, or an expensive aspherical lens must be used. As a result, the apparatus becomes large and the manufacturing cost increases. Occurs.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide an optical space transmission device capable of improving the directivity of a light receiving optical system while suppressing an increase in size and cost of the light receiving optical system.

[0012]

According to the present invention, there is provided a space optical transmission apparatus according to the present invention, which emits a light beam from a light projecting means comprising a signal generating section and a light projecting optical system, and transmits a signal to a light receiving optical system. In an optical space transmission device that performs optical communication by receiving light with a light receiving unit including a detecting unit, the light receiving element that constitutes the signal detecting unit is set to the maximum within a range where the light projecting optical system and the light receiving optical system can perform optical communication. It is characterized in that defocusing is performed from the focal position of the light receiving optical system when it is located at a distance.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a schematic diagram for explaining the configuration of the first embodiment. An optical space transmission apparatus includes a light emitting unit including a signal generating unit (not shown) and a light emitting optical system 11, a light receiving optical system 12, and a light receiving unit 12. And light receiving means including the element 13. FIG. 2 is a schematic diagram of the light receiving optical system 12 for explaining the position of the light receiving element 13, and the effective light receiving section 13 'of the light receiving element 13 is arranged on the optical axis.
Among the light beams La to Lc emitted from the light projecting optical system 11, the center of the light beam La indicated by a solid line is incident on the optical axis,
The center of the light beam Lb indicated by the dashed line is the effective light receiving portion 13 '.
And the center of the light beam Lc indicated by the two-dot chain line completely passes through the effective light receiving portion 13 '.

Here, the effective light receiving portion 13 'of the light receiving element 13
In the prior art, the light beams La to Lc are arranged at a substantially focal position where the light beams converge in the light receiving optical system 12, but in the first embodiment, the light beams La to Lc are defocused toward the light receiving optical system 12 from the focal position. Is located in the position. At this time, the light projecting optical system 11 is installed at a position farthest from the light receiving optical system 12 in the product specifications. When the light beams La to Lc emitted from the light projecting optical system 11 converge in the light receiving optical system 12, the defocus position is such that the spot diameter of the light beams La to Lc is 75% of the diameter of the effective light receiving unit 13 '. Position.

FIG. 3 shows the light beams La to Lc and the effective light receiving section 1.
It is a schematic diagram of the positional relationship of 3 ', and (a) shows that all of the spots of the light beam La fall within the effective light receiving section 13'. (b) shows that almost half of the spot of the light beam Lb has deviated from the effective light receiving portion 13 ', and almost half of the taken light beam Lb is ready for signal detection. In (c), the center of the spot of the light beam Lc is deviated from the effective light receiving portion 13 ', but the effective light receiving portion 13'
Is located at the defocused position, which indicates that a part of the spot overlaps with the effective light receiving unit 13 '.

FIG. 4 is a graph showing the positional relationship between the light beams La to Lc of FIG. 3 and the effective light receiving section 13 '. The horizontal axis represents the center of the spot of the light beams La to Lc and the optical axis of the light receiving optical system 12. , Ie, the ratio between the image height h and the radius of the effective light receiving portion 13 '. The vertical axis represents the ratio of the portion where the light beams La to Lc overlap the effective light receiving portion 13 ', that is, the output ratio. The position of the point A corresponding to FIG.
The position before and after the point B corresponding to FIG. 3B is 100 to 5%, and the position of the point C corresponding to FIG. 3C is 5%.

As shown in FIG. 3A, when all the spots of the light beam La are completely contained in the effective light receiving portion 13 ', a reception level of 100% is obtained, and the image height h becomes large. Part of the spot of the light beam La is used as the effective light receiving portion 13 '.
Maintain that level until you start to fall off. Next, as shown in FIG. 3B, when the image height h becomes larger and a part of the spot of the light beam Lb starts to deviate from the effective light receiving portion 13 ', the output ratio gradually decreases to about 50%. Becomes Then, as shown in FIG. 3 (c), when the image height h further increases and the center of the spot of the light beam Lc is located substantially at the end of the effective light receiving portion 13 ', the output ratio becomes about 5% and thereafter. To 0%.

In the first embodiment, the light receiving element 13
When the light beams La to Lc emitted from the light projecting optical system 11 located at the farthest position converge in the light receiving optical system 12, light is received from the position where the spot diameter of the light beams La to Lc is minimized, that is, from the focal position. It was set at a position close to the optical system 12 side. Since the light projecting optical system 11 is not provided with a mechanism for changing the directivity of the light beams La to Lc, even if the light projecting optical system 11 and the light receiving optical system 12 are brought close to each other to shorten the communication distance, the light beam La The spot diameter of Lc does not become minimum on the light receiving element 13. Conversely, the light beam L on the light receiving element 13
Since the spot diameters a to Lc increase monotonically, the energy amount that increases in proportion to the square of the distance can be corrected.

On the other hand, when the communication distance is maintained as specified, the light beam L that should cover the conventional reception range is used.
Since the light energy amounts of a to Lb do not change significantly,
The burden on the circuit system is not increased. Also, without increasing the load on the light receiving optical system 12, for example, increasing the number of lenses,
The directivity of the light receiving optical system 12 can be extended to the range shown in FIG. If the circuit system can tolerate a reduction of the output ratio to 5%, the directivity of the light receiving optical system 12 can be increased to about 1.6 times the conventional value in terms of the image height h.

FIG. 5 is a graph corresponding to FIG. 4 for explaining the second embodiment, and is located at a position where the spot diameter of the light beams La to Lc is 20% of the diameter of the effective light receiving portion 13 '. The light receiving element 13 is defocused. In the second embodiment, the output ratio is set to 5 as in the first embodiment.
%, The directivity of the light receiving optical system 12 is changed to the first.
It can be expanded to about 1.15 times in the same conversion as in the embodiment.

When the light receiving element 13 is defocused at a position where the spot diameter of the light beams La to Lc is 20% or less of the effective light receiving portion 13 ', that is, at a position where the spot size is still extremely small, Since there is no difference from the case where there is a manufacturing error in the conventional method of arranging the light receiving element at the focal position, the light receiving element 13 has a spot diameter of the light beams La to Lc of 20 mm of the diameter of the effective light receiving section 13 '. % Must be defocused. The spot diameter at the time of defocusing is
If it is larger than that, even if it is placed at the position of the light beam La, the obtained energy will be lower than in the past, so it does not mean that defocusing should be performed without limit.

[0022]

As described above, in the optical space transmission apparatus according to the present invention, the light receiving element constituting the present signal detecting section is located at the most distant position within a range where the light projecting optical system and the light receiving optical system can perform optical communication. Since the focus is defocused from the focus position of the light receiving optical system when it is located, the spot diameter of the light beam does not become the minimum on the light receiving element even if the communication distance is shortened. Since the spot diameter increases monotonically, the energy amount of the light beam that increases in proportion to the square of the distance can be corrected. Further, when the communication distance is maintained as specified, the change in the energy amount of the light beam covering the conventional reception range is small, so that the load on the light receiving optical system, such as a lens, is not increased without increasing the load on the circuit system. It is not necessary to increase the number of sheets. For this reason, it is possible to improve the directivity of the light receiving optical system while suppressing an increase in the size and cost of the light receiving optical system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of a first embodiment.

FIG. 2 is a schematic diagram of a light receiving optical system for explaining a position of a light receiving element.

FIG. 3 is a schematic diagram of a positional relationship between a light beam spot and an effective light receiving section of a light receiving element.

FIG. 4 is a graph illustrating an image height / effective light receiving unit radius and an output ratio.

FIG. 5 is a graph for explaining the second embodiment and corresponding to FIG. 4;

FIG. 6 is a schematic diagram of a conventional example.

FIG. 7 is a schematic diagram of a light receiving optical system for explaining a position of a light receiving element in a conventional example.

FIG. 8 is a schematic diagram showing a relationship between a light beam spot and an effective light receiving section of a light receiving element in a conventional example.

FIG. 9 is a graph showing the relationship between image height / effective light receiving unit radius and output ratio in a conventional example.

FIG. 10 is a schematic diagram of a conventional example in which the directional direction is changed.

FIG. 11 is a schematic diagram of a conventional example in which the directivity is expanded.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Projection optical system 12 Light receiving optical system 13 Light receiving element 13 'Effective light receiving section La-Lc Light beam

Claims (4)

[Claims] 1. An optical space transmission apparatus for performing optical communication by emitting a light beam from a light projecting means comprising a signal generating unit and a light projecting optical system and receiving light by a light receiving means comprising a light receiving optical system and a signal detecting unit. A light receiving element constituting a signal detection unit is defocused from a focal position of the light receiving optical system when the light projecting optical system and the light receiving optical system are located farthest apart in a range where optical communication can be performed. Optical space transmission device. 2. The optical space transmission apparatus according to claim 1, wherein the light receiving element is defocused in a direction close to the light receiving optical system. 3. The light receiving element is defocused to a position where a spot diameter of a light beam converged by the light receiving optical system is approximately 20% or more of a diameter of an effective light receiving section of the light receiving element. Item 3. An optical space transmission device according to item 2. 4. The light receiving device according to claim 1, wherein a spot diameter of the light beam converged by the light receiving optical system is defocused to a position where the spot diameter is approximately 75% of a diameter of an effective light receiving portion of the light receiving device. 3. The optical space transmission device according to 2.