JP4949917B2 - Optical space transmission system - Google Patents

Description

  The present invention relates to an optical space transmission system that performs data communication using an optical beam that transmits an optical space, and more specifically, an optical space transmission in which deterioration of transmission characteristics due to unnecessary reflection of the light beam is reduced. About the system.

Optical space transmission technology that radiates a light beam to free space and performs data communication allows information processing terminals and AV equipment to be connected without cables in offices and homes, making high-speed communication utilizing the broadband nature of light In recent years, it has been attracting attention because of the high possibility that it can be realized. In addition, optical space transmission has higher directivity and does not affect adjacent wireless networks, in addition to no legal restrictions on frequency usage, compared to wireless LAN and UWB wireless communication methods. It has a great advantage in terms of confidentiality and security.
For these reasons, recently, a higher-speed optical space transmission system has been demanded in accordance with an increase in the capacity of transfer data.

However, in order to perform data communication at a higher speed, a high-performance light source (light emitting element) or light receiving element capable of high-speed response is required. In particular, the light receiving element has a reduced light receiving area because it is necessary to reduce parasitic capacitance in order to obtain high frequency response characteristics. For example, the diameter of the light receiving element for 1.25 Gbps data communication is 200 μm, and the diameter of the light receiving element for 10 Gbps data communication is 60 μm (manufactured by Albis as of February 2006).
However, in the optical space transmission system, when the light receiving area of the light receiving element is reduced, the total received power is reduced, so that high speed transmission becomes difficult.

  In order to solve this problem, a multiplex transmission method has been proposed in which parallel data communication is performed between a plurality of light sources and a plurality of light receiving elements to improve the overall transmission rate (see Patent Document 1). In this method, a plurality of optical links are provided to reduce the transmission rate per link.

  FIG. 16 is a diagram showing a configuration of a conventional optical spatial connection device described in Patent Document 1. In FIG. Patent Document 1 shows a technique for performing signal transmission in a computer or a communication processing device, but it can also be applied to an optical space transmission system.

  In FIG. 16, a plurality of electric signals input to the optical transmission module 30 are converted into optical signals by the LD driver array 32 and the light emitting element array 33, respectively, and further converted into light beams having different angles by the collimating lens 34, To be released. In the light receiving module 35, the light signal is condensed by the condenser lens 39 to each light receiving element in the light receiving element array 38 according to the incident angle of the light beam. The light receiving element array 38 converts the input optical signal into an electric signal and sends it to the amplifier array 37. Thereafter, the amplifier array 37 amplifies each electrical signal and then outputs the amplified signal from the light receiving module 35.

  In this conventional optical spatial connection device, the arrangement of the light emitting elements on the focal plane viewed from the collimating lens 34 is transmitted as the emission angle of the light beam output from the collimating lens 34. Further, the condensing position of the light beam incident on the light receiving module 35 on the light receiving surface is determined by the incident angle of the light beam. That is, in this conventional optical spatial connection device, the element arrangement of the light emitting element array 33 is transmitted after being converted into the angle information of the light beam. As long as the light can be condensed by the condensing lens 39, the condensing position on the light receiving surface is not affected at all. Therefore, it is described that the positional deviation tolerance between the modules can be improved as compared with the configuration using the conventional lens array.

However, the configuration shown in FIG. 16 has a problem that the collimating lens 34 and the condensing lens 39 increase as the number of light sources and light receiving elements increases and the mounting area thereof increases. Further, since the light beams emitted from the light emitting element array 33 are incident on the collimating lens 34 perpendicularly, the reflected return light is incident on the light emitting element array 33 again, and the operation of the light emitting element array 33 is unstable. May be. Of the light beam incident on the light receiving element array 38, the light beam is once reflected on the surface of the light receiving element, and the reflected light is further reflected on the front surface of the condenser lens 39 and may be incident on the light receiving element array 38 again. . Since this multiple reflected light becomes delayed light, it becomes a big problem as the data rate becomes high.
Thus, in the optical space transmission system, reflected return light from each reflection point in the optical transmission path and multiple reflections affect the transmission quality.

Therefore, in order to solve the influence of the reflected light, a technique of performing noise cancellation with a receiver has been proposed (see Patent Document 2).
FIG. 17 is a diagram showing a configuration of a conventional optical space transmission system described in Patent Document 2. In FIG.

In FIG. 17, the optical transmission unit 44 of the base unit 41 transmits the transmission lights LPa and LPb having different emission spectra from the LEDs 54 and 55 in phase according to the signal P to be transmitted. The optical receiver 46 of the slave unit 42 photoelectrically converts the transmission lights LPa and LPb with the PD 67 and takes out only the signal P with the operational amplifier 68. Further, the optical transmission unit 45 of the slave unit 42 differentially transmits transmission light beams (−LCb, LCa) having different emission spectra from the LEDs 61 and 63 according to the signal C to be transmitted. The optical receiver 43 of the parent device 41 photoelectrically converts the transmission light beam (−LCb, LCa) by the PDs 52 and 53 according to the emission spectrum, and takes out only the signal C by the operational amplifier 51.

  Therefore, the signal transmitted from the PD 52 of the optical receiver 43 to the inverting input terminal of the operational amplifier 51 is the signal (−C) obtained by photoelectrically converting the transmission light beam (−LCb) transmitted from the optical transmitter 45. The noise component (N) obtained by photoelectrically converting the disturbance light LN and the noise component (P) obtained by photoelectrically converting the light reflected by the reflector 47 from the transmission light LPb transmitted from the optical transmitter 44 are superimposed. Signal (N + (− C) + P). Further, the signal sent from the PD 53 of the optical receiver 43 to the non-inverting input terminal of the operational amplifier 51 is the signal (+ C) obtained by photoelectrically converting the transmission light beam (LCa) transmitted from the optical transmitter 45. The noise component (N) obtained by photoelectrically converting the disturbance light LN and the noise component (P) obtained by photoelectrically converting the light reflected by the reflector 47 from the transmission light LPa transmitted from the light transmitting unit 44 are superimposed. Signal (N + C + P).

  On the other hand, the operational amplifier 51 subtracts the output signal (N + C + P) of the PD 52 input to the inverting input terminal from the output signal (N + (− C) + P) of the PD 53 input to the non-inverting input terminal (N− N + C − (− C) + P−P = 2C).

That is, as can be seen from the calculation result, the signal output from the operational amplifier 51 and sent from the terminal 50 to the subsequent signal processing unit is reflected by the noise component (N) caused by the disturbance light LN and the reflector 47. Only the signal (2C) from which the noise component (P) caused by the light is completely removed is obtained.
JP-A-8-237204 (page 8, Fig. 1) Japanese Patent Laid-Open No. 2002-111585 (page 10, FIG. 1) “Pencil of Light” by Tatsuta Tatsuo, New Technology Communication, published on June 20, 1989, 7th edition (page 167)

  However, in the conventional optical space transmission system described in Patent Document 2, in order for noise components (N) and (P) to be accurately and completely removed from the signal output from the operational amplifier 51, the master unit 41 is used. The LEDs 54 and 55 included in the optical transmitter 44 of the first and second optical transmitters 44 must be installed close to each other. This is because, when installed separately, the reflected light power changes because the incident conditions (for example, incident angle and incident power) of the transmission light beam transmitted from each light source are different. Further, since a difference in optical path length until reaching the PD is also caused through the reflector, a noise component (P) caused by reflected light incident on the PDs 52 and 53 provided in the light receiving unit 43 of the parent device 41 is also generated. Will be different in size and phase. Therefore, the noise component is not completely removed when the calculation is performed.

  Further, in the conventional optical space transmission system described in Patent Document 2, the output signal obtained by the slave unit 42 is 2P which is twice the output signal P obtained from one LED. However, when the LEDs 54 and 55 are installed adjacent to each other for the reasons described above, the output power per LED is reduced or the diffusion plate or the like is used so that the radiation intensity density of the light beam is increased and the eye-safe condition is satisfied. Since it is necessary to reduce the radiation intensity density of the light beam, it is not possible to simply obtain a large output signal.

  As described above, the conventional optical space transmission system described in Patent Document 2 has an increase in the number of components such as light sources of two different wavelengths and an arithmetic circuit for noise cancellation, as compared with a normal optical space transmission system. However, there is a problem that the effect of speeding up data transmission is small.

  Therefore, an object of the present invention is to prevent a light beam emitted from a light emitting element from being reflected back to the light emitting element or incident on a light receiving element other than the target, thereby enabling stable high speed data communication. It is to provide an optical space transmission system that can be realized.

  The present invention is directed to an optical space transmission system that performs data communication using a light beam that transmits an optical space. And in order to achieve the said objective, the optical space transmission system of this invention is a transmission terminal provided with the at least 1 light emission part which radiate | emits a light beam to optical space, and at least receives the light beam radiate | emitted to optical space. A receiving terminal including one light receiving unit, and a terminal fixing auxiliary tool that is attached to the transmitting terminal and the receiving terminal and fixes the positional relationship between at least one light emitting unit and at least one light receiving unit. Further, at least one light-emitting unit and at least one light-receiving unit are connected, and the light beam emitted from at least one light-emitting unit is at least one light-receiving unit in a state where the transmitting terminal and the receiving terminal are mounted on the terminal fixing auxiliary tool. And is provided at a position where it does not return to at least one light emitting portion.

  For example, when at least one light emitting unit and at least one light receiving unit face each other in a state where the transmission terminal and the reception terminal are mounted on the terminal fixing auxiliary tool, one light emitting unit and one light transmission pair are paired for transmission and reception. When the vertical distance from the light receiving unit is L, the horizontal interval is W, and the directivity angle of the light beam is θ, the light beam irradiation angle α of this one light emitting unit with respect to the vertical direction from the transmitting terminal to the receiving terminal is , Given by equation (1) described in the embodiment.

  Typically, each of the at least one light emitting unit is connected to a light emitting element that emits light according to communication data and the light emitting element, and condenses the light emitted from the light emitting element and emits a light beam into an optical space. And an outgoing optical fiber. Alternatively, each of the at least one light emitting unit is connected to a light emitting element that emits light corresponding to communication data and the light emitting element, and emits light emitted from the light emitting element to an optical space through an optical waveguide. And an optical waveguide substrate.

When a plurality of light beams are irradiated from at least one light emitting unit, the receiving terminal further includes a lens that collects the plurality of incident light beams, and at least one light receiving unit includes the light beam collected by the lens. And at least one light receiving element for receiving light. Alternatively, the receiving terminal further includes a lens that condenses a plurality of incident light beams, and the at least one light receiving unit passes at least one light beam having a desired wavelength among the light beams collected by the lens. A wavelength filter and at least one light receiving element that receives only the light beam that has passed through the at least one wavelength filter may be included. The allowable passband Δλ of the wavelength filter is defined such that the wavelength of the light beam emitted from each of the at least one light emitting unit is λ _n , the directivity angle is θ _n, and the incident angle with respect to at least one light receiving unit is α _n . Is given by equation (2) described in the embodiment.

Preferably, the receiving terminal further includes a second at least one light emitting unit that emits a light beam to the optical space, and the transmitting terminal receives a second at least one light receiving unit that receives the light beam emitted from the receiving terminal. May be further provided. Similarly, in this case, the second at least one light emitting unit and the second at least one light receiving unit have the second at least one light emitting unit in a state where the transmitting terminal and the receiving terminal are mounted on the terminal fixing auxiliary tool. the light beam emitted from the part may the second of the at least one provided also do not return position to any of the second at least one light emitting portion is reflected by the light receiving portion.

Furthermore, at least two of the plurality of light beams emitted from the at least one light emitting unit may be condensed on any one of the at least one light receiving unit, and the at least one light emitting unit may be any two If the spacing of the light emitting portion and a d (d> 0.15 mm), the distance L to the optical axis intersecting point of the light beam, each emitted from the two light emitting portions are described in embodiment formula (3) Is preferably given by:

  Note that the terminal-fixing auxiliary tool that fixes the positional relationship between at least one light emitting unit and at least one light receiving unit may be integrally formed on the transmitting terminal side, not on an individual configuration, or on the receiving terminal side. It may be integrally formed.

  According to the present invention, it is possible to prevent the light beam emitted from the light emitting element from being reflected back to the light emitting element or entering a light receiving element other than the intended purpose. As a result, good transmission characteristics can be obtained by a simple method, and stable high-speed data communication can be realized.

  The technology of the present invention can be applied to various optical space transmission systems that transmit and receive light beams through free space. The optical space transmission system shown in FIGS. 1 and 2 will be described as a specific example.

  The optical space transmission system shown in FIG. 1 includes a transmission terminal 10 and a reception terminal 20 (such as a portable terminal) and a terminal fixing auxiliary tool 70. The transmission terminal 10 includes an optical transmission unit 11 for optically transmitting data. The receiving terminal 20 includes an optical receiving unit 21 for optically receiving data. The terminal fixing auxiliary tool 70 includes a guide 71 for mounting the transmitting terminal 10 and a guide 72 for mounting the receiving terminal 20.

The optical space transmission system shown in FIG. 2 includes a terminal fixing auxiliary tool 70 that can be connected to a data storage device 80 (such as a DVD recorder) corresponding to the transmission terminal 10 and a reception terminal 20 (such as a portable terminal). Is done. The receiving terminal 20 includes an optical receiving unit 21 for optically receiving data. The terminal fixing auxiliary tool 70 includes an optical transmission unit 11 for optically transmitting data stored in the data storage device 80 and a guide 72 for mounting the receiving terminal 20.
Of course, the terminal fixing auxiliary tool 70 may be integrally formed with the data storage device 80.

  In the present invention, in the system of FIG. 1, the optical transmitter 11 and the optical receiver 21 are aligned in a foolproof manner by simply mounting the transmitting terminal 10 and the receiving terminal 20 on the terminal fixing auxiliary tool 70, respectively. Is realized. In addition, as in the system of FIG. 2, even when the optical transmission unit 11 is integrally formed with the terminal fixing auxiliary tool 70, the optical transmission unit 11 can be simply attached to the terminal fixing auxiliary tool 70. And the optical receiver 21 are realized in a foolproof manner. In addition, the distance between the optical transmission unit 11 and the optical reception unit 21 in a state where the terminal is mounted on the terminal fixing auxiliary tool 70 is about several millimeters to several tens of centimeters.

  Hereinafter, various characteristic structures provided by the present invention will be described in detail in the order of an example in which the structure is applied to the optical space transmission system of FIG. The drawings used in each embodiment are diagrams illustrating the positional relationship between the transmission terminal 10 and the reception terminal 20 in a state where the transmission terminal 10 and the reception terminal 20 are respectively attached to the terminal fixing auxiliary tool 70 (terminals). The illustration of the fixing auxiliary tool 70 is omitted).

[First Embodiment]
FIG. 3 is a perspective view for explaining the optical space transmission system according to the first embodiment of the present invention. 4 is a cross-sectional view of the optical space transmission system shown in FIG. 3 taken along the line AA. 3 and 4, the optical transmission unit 11 of the transmission terminal 10 includes a light emitting unit 13 provided on the mounting substrate 12. In addition, the optical receiving unit 21 of the receiving terminal 20 includes a light receiving unit 23 provided on the mounting substrate 22.

  The light emitting unit 13 includes a light emitting element such as a semiconductor laser, and emits a light beam according to communication data. The light receiving unit 23 includes a light receiving element such as a photodiode, and receives the light beam emitted from the light emitting unit 13. In the present invention, the light emitting unit 13 and the light receiving unit are prevented so that the light beam emitted from the light emitting unit 13 toward the light receiving unit 23 is reflected by the surface of the light receiving unit 21 or the mounting substrate 22 and does not return to the light emitting unit 13. 23, the light beam emission angle and the incident angle are determined.

For example, as in the optical space transmission system shown in FIG. 4, consider a case where the optical transmission unit 11 of the transmission terminal 10 and the optical reception unit 21 of the reception terminal 20 face each other in parallel by the terminal fixing auxiliary tool 70 . In this case, the vertical distance between the light emitting unit 13 and the light receiving unit 23 that form a pair of transmission and reception is “L”, the horizontal distance between the light emitting unit 13 and the light receiving unit 23 is “W”, and the directivity angle of the light beam is Assuming that “θ”, the light beam irradiation angle “α” of the light emitting unit 13 with respect to the vertical direction from the transmission terminal 10 toward the reception terminal 20 can be obtained by the following equation (1).
α> tan ⁻¹ (W / 2L) + θ (1)

  With the above structure, stable light transmission is performed even when a light-emitting element such as a DFB (Distributed Feedback) laser or a VCSEL (Vertical Cavity Surface Emitting Laser), whose operation is likely to be unstable due to reflected return light, is used. be able to.

Next, a structural example of the light emitting unit 13 for satisfying the above formula (1) will be specifically described.
5 to 7 are structural cross-sectional views of the transmission terminal 10 for explaining structural examples 1 to 3 of the light emitting unit 13.

(1) Structural example 1
As shown in FIG. 5, Structural Example 1 is a structure in which the light emitting element 14 constituting the light emitting unit 13 is mounted in a state inclined in advance with respect to the mounting substrate 12. With this structure, the irradiation direction of the light beam can be easily changed. In addition, when the mounted light emitting element 14 becomes unstable without being fixed, a component for supporting the light emitting element 14 may be separately provided.

(2) Structural example 2
Structure example 2 is a structure in which the light emitting element 14 is mounted on the mounting substrate 12 in a normal state and the inclined optical fiber 15 is connected to the light emitting element 14 as shown in FIG. With this structure, the irradiation direction can be easily changed. In addition, in order to fix the optical fiber 15, you may provide the components to support separately. Note that the exit end face of the optical fiber 15 may be polished obliquely by about 7 ° so that the reflected return light does not return to the light emitting element 14.

  Usually, when the wiring from the light emitting element drive circuit to the light emitting element becomes long, there is a problem that the characteristics deteriorate during high-speed modulation. When the light emitting element 14 is inclined and mounted on the mounting substrate 12 as in the structure example 1, there is a problem that the lead wire on one side becomes long. However, by using the optical fiber 15 as in the structural example 2, the wiring can be shortened, so that deterioration of transmission characteristics during high-speed data transmission can be reduced.

(3) Structural example 3
In Structure Example 3, as shown in FIG. 7, the light emitting element 14 is mounted on the mounting substrate 12 in a normal state, and the optical waveguide substrate 17 having the inclined optical waveguide 16 is connected to the light emitting element 14. It is. With this structure, the irradiation direction can be easily changed.

  In general, when the optical fiber 15 is used inside the transmission terminal 10 as in the structural example 2, there is a problem that the transmission terminal 10 is enlarged due to the extra length processing portion. However, the transmission terminal 10 can be downsized by using the optical waveguide 16 as in Structural Example 3.

  With the structure of the first embodiment, it is possible to prevent the light beam emitted from the light emitting unit 13 from being reflected by the light receiving unit 23 or the like and returning to the light emitting unit 13. Thereby, stable high-speed data communication can be realized by a simple method.

[Second Embodiment]
In the first embodiment, the structure in which the light transmitting unit 11 includes one light emitting unit 13 and the light receiving unit 21 includes one light receiving unit 23 has been described.
In the following second to seventh embodiments, a structure in which the optical transmission unit 11 includes a plurality of light emitting units 13 and the optical reception unit 21 includes a plurality of light receiving units 23 will be described.

  FIG. 8 is a perspective view for explaining an optical space transmission system according to the second embodiment of the present invention. In the second embodiment illustrated in FIG. 8, the optical transmission unit 11 includes four light emitting units 13 a to 13 d on the mounting substrate 12, and the optical receiving unit 21 includes four light receiving units on the mounting substrate 22. 23a-23d.

  The light emitting unit 13a and the light receiving unit 23a satisfy the positional relationship of the first embodiment described above. Similarly, the light emitting unit 13b and the light receiving unit 23b, the light emitting unit 13c and the light receiving unit 23c, and the light emitting unit 13d and the light receiving unit 23d satisfy the positional relationship of the first embodiment described above.

[Third Embodiment]
FIG. 9 is a perspective view for explaining an optical space transmission system according to the third embodiment of the present invention. In the third embodiment illustrated in FIG. 9, the optical transmission unit 11 includes two light emitting units 13 a and 13 b on the mounting substrate 12, and the optical receiving unit 21 includes two light receiving units on the mounting substrate 22. 23a and 23b.

  The light emitting unit 13a and the light receiving unit 23a, and the light emitting unit 13b and the light receiving unit 23b satisfy the positional relationship of the first embodiment described above. Furthermore, the light emitting units 13a to 13b and the light receiving units 23a to 23b are arranged so that the light beam emitted from the light emitting unit 13a and the light beam emitted from the light emitting unit 13b intersect each other.

[Fourth Embodiment]
FIG. 10 is a perspective view for explaining an optical space transmission system according to the fourth embodiment of the present invention. In the fourth embodiment illustrated in FIG. 10, the light transmitting unit 11 includes eight light emitting units 13 a to 13 h on the mounting substrate 12, and the light receiving unit 21 includes eight light receiving units on the mounting substrate 22. 23a-23h. The fourth embodiment has a structure in which the second embodiment and the third embodiment are combined.

[Fifth Embodiment]
FIG. 11 is a perspective view for explaining an optical space transmission system according to the fifth embodiment of the present invention. In the fifth embodiment illustrated in FIG. 11, the light transmitting unit 11 includes four light emitting units 13 a to 13 d on the mounting substrate 12, and the light receiving unit 21 includes four light receiving units on the mounting substrate 22. 23a-23d.

  The light emitting unit 13a and the light receiving unit 23a satisfy the positional relationship of the first embodiment described above. Similarly, the light emitting unit 13b and the light receiving unit 23b, the light emitting unit 13c and the light receiving unit 23c, and the light emitting unit 13d and the light receiving unit 23d satisfy the positional relationship of the first embodiment described above. Furthermore, the light emitting units 13a to 13d and the light receiving units 23a to 23d are arranged so that a plurality of light beams emitted from the light emitting units 13a to 13d intersect at one point.

[Sixth Embodiment]
FIG. 12 is a structural sectional view for explaining an optical space transmission system according to the sixth embodiment of the present invention. In FIG. 12, the optical transmission unit 11 of the transmission terminal 10 includes light emitting units 13 a and 13 b provided on the mounting substrate 12. The light receiving unit 21 of the receiving terminal 20 includes light receiving units 23 a and 23 b provided on the mounting substrate 22 and a lens 24.

  The structure of the optical receiver 21 of the sixth embodiment is a structure to which the third embodiment is applied, and the lens 24 is different from the structure of the optical receiver 21 of the third embodiment. The structure of the optical transmission unit 11 according to the sixth embodiment is the same as the structure (structure examples 1 to 3) of the optical transmission unit 11 according to the first embodiment.

  The lens 24 is a lens for condensing the light beam transmitted from the transmission terminal 10, and a position where the light beam having the directivity angle θ emitted from the light emitting unit 13a can be condensed by the light receiving unit 23a, and The light beam having the directivity angle θ emitted from the light emitting unit 13b is provided at a position where the light receiving unit 23b can collect the light beam. That is, the lens 24 is a lens having a focal length f that is ½ of a linear distance from the light emitting unit 13a to the light receiving unit 23a.

  With the structure of the sixth embodiment, even when it is desired to condense light with high efficiency using a lens, the number of lenses can be reduced compared to the case where a lens is installed for each light receiving unit. Further, even when the number of light emitting units and light receiving units is increased and the mounting area of necessary optical elements is increased, it is not necessary to increase the size of the lens. Therefore, it becomes easy to manufacture the lens, and the cost can be reduced.

  Note that an antireflection film is preferably formed on the surface of the lens 24. This antireflection film can prevent the light beam emitted from the light emitting unit 13 from being reflected by the lens 24 and returning to the light emitting unit 13. Further, it is possible to prevent the light beam reflected by the surface of the light receiving unit 23 from being reflected again by the lens 24 and returning to the light receiving unit 23.

[Seventh Embodiment]
FIG. 13 is a structural sectional view for explaining an optical space transmission system according to the seventh embodiment of the present invention. In FIG. 13, the optical transmission unit 11 of the transmission terminal 10 includes light emitting units 13 a and 13 b provided on the mounting substrate 12. The light receiving unit 21 of the receiving terminal 20 includes light receiving units 23 a and 23 b provided on the mounting substrate 22, a lens 24, and wavelength filters 25 a and 25 b.

  The structure of the optical receiver 21 of the seventh embodiment is different from that of the optical receiver 21 of the sixth embodiment in the wavelength filters 25a and 25b. The structure of the optical transmitter 11 of the seventh embodiment is the same as the structure (structure examples 1 to 3) of the optical transmitter 11 of the first embodiment.

The light emitting units 13a and 13b emit light beams having different wavelengths. The wavelength filter 25a passes only the wavelength of the light beam emitted from the light emitting unit 13a. The wavelength filter 25b passes only the wavelength of the light beam emitted from the light emitting unit 13b.
When the wavelength of the light beam emitted from the light emitting unit 13 is λ _n , the directivity angle is θ _n, and the incident angle with respect to the light receiving unit 23 is α _n , the allowable passband Δλ of the wavelength filters 25a and 25b is as follows: It is represented by the relationship of Formula (2).
Δλ> sin α _n × λ _n × θ _n (2)

FIG. 14 is a diagram for explaining the effects of the wavelength filters 25a and 25b. FIG. 14 shows a case where the light beam having the directivity angle θ emitted from the light emitting unit 13a is collected by a lens (not shown) and incident on the light receiving unit 23a at an angle α. At this time, the light beam is incident on the wavelength filter 25a provided in the light receiving unit 23a with a deviation of angles θ _{1 to} θ ₂ .

Here, in a wavelength filter formed of a general dielectric multilayer film, when the reference wavelength for vertically incident light is λ ₀ , the passing wavelength λ with respect to the incident angle α is displaced to λ = cos α · λ _0. There are characteristics (see Non-Patent Document 1). Therefore, the wavelength filter is designed so that the desired wavelength λ ₀ passes with a minimum loss with respect to the incident angle α assumed in advance, but when the light beam has components θ ₁ to θ ₂ , There is a problem that the greater the deviation from the basic incident angle α, the greater the transmission loss for light of wavelength λ ₀ .

  Usually, the pass wavelength with respect to the wavelength filter is designed assuming a certain width. However, if the pass wavelength band is excessively widened, the light beam from other light emitting parts also passes, and the role of the wavelength filter is impaired. Therefore, in order to narrow the pass band of the wavelength filter, it is preferable to irradiate a light beam having a small directivity angle as much as possible. Therefore, it is desirable that the light emitting unit and the light receiving unit that are paired as far as possible to reduce the directivity angle θ while making the irradiation area of the light beam on the lens 24 the same area.

For example, consider a case where the oscillation wavelength of the light emitting units 13a and 13b is 850 nm, the distance from the light transmitting unit 11 to the light receiving unit 21 is 1 cm, and the irradiation area of the light beam at the lens 24 is 5 mm in diameter.
In this case, when the distance between the light emitting part 13a and the light emitting part 13b is 5 mm, the incident angle of the optical axis can be designed to be about 26.6 degrees and the directivity angle can be set to 12.5 degrees, and the maximum shift amount of the passing wavelength can be increased. 22.7 nm. On the other hand, when the distance between the light emitting part 13a and the light emitting part 13b is 10 mm, the incident angle of the optical axis can be designed to be about 45 degrees and the directivity angle is 8.1 degrees, and the maximum shift amount of the passing wavelength is 8.54 nm. It becomes. Therefore, in the latter case, the wavelength interval can be narrowed when wavelength multiplexing is performed, and wavelength setting in system design becomes easier.

  With the structure of the seventh embodiment, even if the light beam emitted from the light emitting unit is incident on a non-target light receiving unit due to surface reflection of the lens or the light receiving unit, unnecessary light is attenuated by the wavelength filter. Therefore, transmission characteristic deterioration can be reduced.

In addition, the said embodiment is an example, Comprising: The number of the light emission parts 13 and the number of the light-receiving parts 23 can be determined freely. For example, in order to secure a wider communication area, the number of the light emitting units 13 may be larger than the number of the light receiving units 23, or the light receiving units may be combined to obtain a larger received signal by combining the received signals. The number of 23 may be larger than the number of light emitting units 13.
The data signals transmitted from the plurality of light emitting units 13 may all be the same, or all or some of them may be different. Further, the emission angles of the light beams from the plurality of light emitting units 13 may all be the same, or all or some of them may be different.
Furthermore, the structure in which the optical transmission unit 11 is provided only on the transmission terminal 10 side and the optical reception unit 21 is provided only on the reception terminal 20 side has been described. However, the optical reception unit 21 is provided in both the transmission terminal 10 and the reception terminal 20. By providing the transmission unit 11, bidirectional communication can also be performed.

The optical space transmission system shown in FIGS. 1 and 2 is an example, and other system configurations and structures may be used as long as the optical transmission unit 11 and the optical reception unit 21 can be aligned in a foolproof manner. May be. For example, the transmitting terminal 10 may be provided with a retractable protrusion corresponding to the terminal fixing auxiliary tool 70 , and the optical transmitter 11 and the optical receiver 21 may be aligned by this protrusion.

  Furthermore, in the case of a structure that irradiates a plurality of light beams, a circle having a diameter of 7 mm at a position 10 cm away from the plurality of light sources (light emitting elements) in consideration of the international safety standard “IEC60825-1” for laser radiation. It is desirable to design so that a plurality of optical axes are not included in the range. This is because the worst exposure condition for retinal damage in the human eye is when the distance between the eye and the light source is 10 cm, and if it is closer than that, the retinal image is blurred and the danger is mitigated.

Specifically, if the distance between the two light sources was d (d> 0.15 mm), distance L from the two light sources to the optical axis intersecting point of the light beam that each emitted, by the following formula (3) It is preferable to design (FIG. 15).
L <(100 × d) / (7 + d) (3)
According to this formula (3), the place where the optical power is most concentrated is designed within 10 cm from the light source, and the light receiving unit is arranged at that place. As a result, the light receiving unit can be obtained in a large size without reducing the light beam power from the plurality of light sources under conditions that are safe for the eyes.

  The optical space transmission system of the present invention can be used in the field of high-speed optical space communication, etc., and is particularly useful when it is desired to reduce the deterioration of transmission characteristics by preventing the reflected light from being irradiated to an undesired optical element. is there.

The figure explaining an example to which the optical space transmission system of this invention is applied The figure explaining an example to which the optical space transmission system of this invention is applied The perspective view explaining the optical space transmission system which concerns on the 1st Embodiment of this invention. Structural cross section explaining the optical space transmission system according to the first embodiment of the present invention Structural sectional view of the transmission terminal 10 for explaining the first structural example of the light emitting unit 13 Structural sectional view of the transmission terminal 10 for explaining the structural example 2 of the light emitting unit 13 Structural sectional view of the transmission terminal 10 for explaining the structural example 3 of the light emitting unit 13 The perspective view explaining the optical space transmission system which concerns on the 2nd Embodiment of this invention. The perspective view explaining the optical space transmission system which concerns on the 3rd Embodiment of this invention. The perspective view explaining the optical space transmission system which concerns on the 4th Embodiment of this invention. The perspective view explaining the optical space transmission system which concerns on the 5th Embodiment of this invention. Structural sectional view explaining an optical space transmission system according to a sixth embodiment of the present invention Structural sectional view explaining an optical space transmission system according to a seventh embodiment of the present invention The figure for demonstrating the effect of wavelength filter 25a and 25b The figure which shows the specific design example of the optical space transmission system of this invention The figure which shows the structure of the conventional optical space connection apparatus described in patent document 1 The figure which shows the structure of the conventional optical space transmission system described in patent document 2

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission terminal 11 Optical transmission part 12, 22 Mounting board 13, 13a-13h Light emission part 14 Light emitting element 15 Optical fiber 16 Optical waveguide 17 Optical waveguide board 20 Reception terminal 21 Optical reception part 23, 23a-23h Light reception part 24 Lens 25a, 25b Wavelength filter 70 Terminal fixing auxiliary tool 71, 72 Guide 80 Data storage device

Claims (5)

An optical space transmission system for performing data communication using a light beam transmitting in an optical space,
A transmission terminal including at least one light emitting unit that emits a light beam to an optical space;
A receiving terminal comprising at least one light receiving unit for receiving a light beam emitted into the optical space;
A terminal fixing auxiliary tool that is mounted with the transmitting terminal and the receiving terminal and fixes the positional relationship between the at least one light emitting unit and the at least one light receiving unit,
The at least one light emitting unit and the at least one light receiving unit are configured so that a light beam emitted from the at least one light emitting unit is in the state where the transmitting terminal and the receiving terminal are attached to the terminal fixing auxiliary tool. Provided at a position where it is reflected by at least one light receiving portion and does not return to any of the at least one light emitting portion ;
In a state where the transmitting terminal and the receiving terminal are mounted on the terminal fixing auxiliary tool, the emission surface of the at least one light emitting unit and the light receiving surface of the at least one light receiving unit face each other in parallel, When the vertical distance between one light emitting unit and one light receiving unit as a pair is L, the horizontal interval is W, and the directivity angle of the light beam is θ, the vertical direction from the transmitting terminal to the receiving terminal is An optical space transmission system characterized in that a light beam irradiation angle α of one light emitting unit is given by the following equation (1) .
α> tan ⁻¹ (W / 2L) + θ (1) The transmission terminal includes a plurality of light emitting units each emitting one light beam,
The receiving terminal further includes a lens that enters the plurality of light beams emitted from the plurality of light emitting units and collects the incident light beams.
Wherein the at least one light receiving unit, for receiving all of the condensed light beam by the lens, at least one light receiving element, an optical space transmission system according to claim 1. The transmission terminal includes a plurality of light emitting units that respectively emit light beams having different wavelengths.
The receiving terminal further includes a lens that enters the plurality of light beams emitted from the plurality of light emitting units and collects the incident light beams.
The at least one light receiving unit includes:
At least one wavelength filter that passes only a light beam having a desired wavelength among the light beams collected by the lens;
The optical space transmission system according to claim 1, further comprising: at least one light receiving element that receives only the light beam that has passed through the at least one wavelength filter. The transmission terminal includes a plurality of light emitting units each emitting one light beam,
Before SL plurality of multiple emitted from the light emitting portion of the light beam, said characterized in that it is any crab condensing at least one light receiving portion, the optical spatial transmission system according to claim 1. The transmission terminal includes a plurality of light emitting units each emitting one light beam,
When the interval between any two light emitting units is d (d> 0.15 mm), the plurality of light emitting units has a distance L from the two light emitting units to the optical axis intersection of the light beams respectively emitted from the two light emitting units. The optical space transmission system according to claim 1, characterized by being given by the following equation ( 2 ).
L <(100 × d) / (7 + d) ( 2 )

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