JP4590610B2 - Multi-beam laser communication device - Google Patents

Description

  The present invention relates to a multi-beam laser communication apparatus that includes a plurality of communication laser light sources and performs communication using a plurality of laser beams between spatially separated points.

  Multi-beam laser transmission using a plurality of laser beams has been proposed for the purpose of suppressing fluctuations in received intensity in spatial laser communication (see Non-Patent Document 1).

Bee. Strickland, M.C. M. Lavan, e. Woodbridge, Vui. V. Chan, “Effects of the bit-error of the free-space laser communication system”, Applied Optics (Applied Optics (Applied of Fog on the Bit-Error Rate of Free-space Laser Communication System), Applied Optics (Applied) optics), USA, January 1999, Vol. 38, No. 3, p. 424-431

  However, in the laser beam transmission described in Non-Patent Document 1, the beam divergence angle is sufficiently wide, and special consideration is given to the fine angle adjustment in the transmission direction and the angular relationship in the transmission direction between the beams. It wasn't. For this reason, no consideration has been given to techniques for stabilizing fluctuations in received light intensity at the other party when performing spatial laser communication using a laser beam with a narrow divergence angle, such as between the ground and an artificial satellite. .

  In view of the problems as described above, an object of the present invention is to provide a multi-beam laser communication apparatus that can stabilize fluctuations in received light intensity.

In order to solve the above-mentioned problem, the invention according to claim 1 is a variable condition setting means for setting, as a variable condition , at least an average intensity and intensity dispersion in a beam axis deviation angle direction based on communication conditions with a communication partner ; condition setting means to a more set preset meet desired average intensity and intensity distribution of a communication partner under variation conditions beam divergence angle and one among the combinations of the number of beams et al smallest combination of a number of beams, feeding Beam condition determining means for determining the beam divergence angle of the trusted laser light source and the number of beams of the multi-beam, and communication control means for performing communication with the communication partner based on the beam conditions determined by the beam condition determining means. It is characterized by providing.

The invention according to claim 2 is the multi-beam laser communication apparatus according to claim 1, wherein the communication laser light source is capable of irradiating a beam having a narrow divergence angle of about several tens of μrad. The communication control means is characterized in that the irradiation direction of the communication laser light source is controlled so that the optical axis of each beam is on-axis transmission penetrating the receiver of the communication partner.

According to a third aspect of the present invention, in the multi-beam laser communication apparatus according to the first or second aspect, the variation condition setting means can set the pointing error to the communication partner as one of the variation conditions. The beam condition determining means is a combination of a preset beam divergence angle and the number of beams that satisfy the desired average intensity and intensity dispersion and pointing error of the communication partner under the fluctuation conditions set in the fluctuation condition setting means. From the above , the minimum beam number combination is determined as the beam divergence angle of the transmitting laser light source and the number of multi-beam beams .

According to a fourth aspect of the present invention, in the multi-beam laser communication device according to any one of the first to third aspects, the state of fluctuation is most severe during uplink transmission from the ground to the artificial satellite. wherein the variable condition of a minimum elevation angle, that it has to affect a small beam divergence angle of the air fluctuation is set to bi chromatography beam conditions so as to satisfy both the variable condition of a relatively small maximum elevation .

According to a fifth aspect of the present invention, in the multi-beam laser communication apparatus according to any one of the first to fourth aspects, the communication control means is a receiver for performing bidirectional laser communication. When receiving a laser beam from a communication partner, it comprises a received light intensity fluctuation information acquiring means for acquiring information on the received light intensity fluctuation, and the communication control means includes the received light intensity fluctuation information acquiring means. The acquired received light intensity fluctuation information is transmitted on a laser to be transmitted to the other party, and the received light intensity fluctuation information included in the laser received from the other party is supplied to the beam condition determining means. the light-receiving intensity variation information supplied from the communication control means reduces the number of beams as long as greater than the required value enough, if conversely falls below the required value, and in increasing the number of beams It allows characterized in that so as to optimize the state of the light receiver at the other party.

According to the invention of claim 1, the communication condition with the communication partner, and set at least as a beam axis deviation angle direction of the average intensity and intensity variance variation condition setting means varies the conditions, the more set the variation condition setting means varying a desired average intensity and intensity distribution of dynamic conditions communications under party from the combinations of beam spread angle a beam number previously set to satisfy the combination that minimizes the number of beams, beam spread angle of the transmitting laser light source Since the beam condition determining means determines the number of beams of the multi-beam, and the communication control means communicates with the communication partner based on the beam condition, the beam suitable for suppressing fluctuations in the received light intensity on the partner side Laser transmission can be performed under certain conditions. Therefore, it is easy to hold the laser line in an environment in which atmospheric fluctuations and pointing errors exist, and the practical value is great.

According to the second aspect of the present invention, a communication laser light source that can irradiate a beam with a narrow divergence angle of about several tens of μrad is used, and the communication control means has an optical axis of each beam of a communication partner. Since the irradiation direction of the communication laser light source is controlled so as to be on-axis transmission through the light receiver, the dispersion of intensity fluctuations can be kept small while maintaining the average intensity with respect to the beam axis deviation angle, Effective fluctuation of received light intensity can be suppressed.

Further, the invention according to claim 3, variation condition setting means allows setting the pointing error of the communication partner as a variable condition, the beam condition determining means, fluctuation is set to change condition setting section The combination of the beam divergence angle and the number of beams set in advance that satisfies the desired average intensity, intensity dispersion, and pointing error of the communication partner under the conditions is selected as the beam divergence angle of the transmitting laser light source. Since the number of beams is determined as the number of multi-beams, fluctuations in received light intensity can be more effectively suppressed.

According to the fourth aspect of the present invention, when the elevation angle when the satellite is pointed at the time of uplink transmission from the ground to the artificial satellite is small, the path in the atmosphere is long and the intensity fluctuation is large, and the elevation angle is If it is high, the influence of atmospheric fluctuations is small and the beam divergence angle is relatively small. Therefore , the beam condition determining means is designed to satisfy both the minimum elevation angle variation condition and the maximum elevation angle variation condition. Since the beam divergence angle and the number of multi-beams are determined, it is possible to perform good uplink transmission over all paths.

According to the invention of claim 5, the communication control means performs reception control for performing bidirectional laser communication. When a laser beam is received from a communication partner, the received light intensity fluctuations are received. The communication control means transmits the received light intensity fluctuation information acquired by the received light intensity fluctuation information acquisition means on a laser to be transmitted to the other party, and from the other party. The received light intensity fluctuation information included in the received laser is supplied to the beam condition determining means, and the beam condition determining means determines the number of beams if the received light intensity fluctuation information supplied from the communication control means sufficiently exceeds the required value. reduce, by increasing the number of beams in the case below the required value in the reverse, since so as to optimize the state of the light receiver at the other party, the received light intensity variation to the communication partner suppressed Since such beam conditions are set to each other, it can be maintained laser line efficiently.

  Next, an embodiment of a multi-beam laser communication apparatus according to the present invention will be described based on the attached drawings.

  FIG. 1 shows a schematic configuration of a multi-beam laser communication apparatus 1 capable of irradiating four laser beams. A first telescope 2a, a second telescope 2b, a third telescope 2c, and a fourth telescope for transmitting laser beams. 2d, a laser directing device 3 for directing a laser beam emitted from a laser light source provided in the first to fourth telescopes 2a to 2d to a communication partner, a light receiving telescope 4 for receiving a laser beam from the communication partner, and a transmission / reception direction And a gimbal mechanism 5 for adjusting the elevation angle, and a control unit 6 for controlling them.

  The main communication function of the control unit 6 is comprehensively handled by the communication control means 61, but the basic transmission / reception function is omitted. At the time of transmission, the laser light source to be used is selected from the first to fourth telescopes 2a to 2d according to the beam conditions and irradiated with the laser beam, and the beam divergence angle is adjusted to change the received light intensity on the other side. Can be suppressed. In FIG. 1, the configuration of four laser beam transmitting telescopes is shown as an example, but the number of laser beam transmitting telescopes is not limited to this, and can be arbitrarily set.

  The beam conditions used for transmission by the communication control means are from the fluctuation condition setting means 62 in which the fluctuation conditions are set based on the basic data input by the external input means 7 operated by the user of the multi-beam laser communication apparatus 1. Based on the supplied fluctuation conditions (directing error, average intensity, intensity dispersion), the beam condition determining means 63 sets. In other words, beam axis misalignment takes into account communication conditions with the communication partner (in the case of communication with an artificial satellite, the influence of atmospheric fluctuations according to the pointing position of the artificial satellite, satellite orbit information, desired irradiance, etc.) The intensity fluctuation in the angular direction and the pointing error on the laser transmission side are determined as the fluctuation condition, and the received light intensity fluctuation of the communication partner under this fluctuation condition is optimized (the desired average intensity and intensity dispersion are satisfied and transmitted) The beam divergence angle of the multi-beam that can minimize the total output of multiple beams (when the radius of curvature of the wavefront of the beam at the time of emission is infinite, the beam divergence angle is uniquely determined by the beam radius) and the number of beams By setting as a condition and performing communication under this beam condition, fluctuations in received light intensity on the other side can be suppressed and communication can be stabilized.

  Note that the fluctuation condition set in the fluctuation condition setting means 62 is not limited to the one directly input from the external input means 7, and the fluctuation condition storage means 64 for storing the main fluctuation condition pattern is provided, and this fluctuation is set. The variable condition may be called from the condition storage means 64 and set. The beam condition determining means 63 for determining the beam condition based on the variation condition may determine the beam condition with reference to a correspondence table in which the beam condition corresponding to the variation condition is determined. Alternatively, the beam condition may be derived by performing a predetermined calculation.

  Furthermore, the multi-beam laser communication apparatus 1 according to the present embodiment includes a received light intensity fluctuation information acquisition unit 65 that is capable of bidirectional communication and acquires information on the received light intensity fluctuation when a laser beam is received from the partner side. It is assumed that the communication control means 61 transmits the received light intensity fluctuation information (average intensity and intensity dispersion) acquired by the received light intensity fluctuation information acquiring means 65 on a laser to the other party. On the other hand, the communication control means 61 that has extracted the received light intensity fluctuation information (average intensity and intensity variance) included in the laser received from the other side supplies the received light intensity fluctuation information to the beam condition determining means 63, thereby The determination means 63 adjusts the value of the margin added to the desired average received light intensity and the variance value of the fluctuation, which is correction of the beam condition.

  That is, since the beam condition is optimized by feedback control by transmitting the received light intensity fluctuation when the laser beam actually transmitted from the communication partner is received to the communication partner, it is set in the fluctuation condition setting means 62. Even when the actual fluctuation condition greatly changes from the above fluctuation condition, the beam condition is optimized so as to complementarily suppress the fluctuation of the received light intensity, so that the laser line can be efficiently maintained.

  In the above embodiment, the correspondence method between the variation condition set in the variation condition setting unit 62 and the beam condition determined by the beam condition determination unit 63 is not particularly limited and belongs to design know-how. However, the basic concept of setting the conditions of the beam divergence angle and the number of beams will be described below.

(Beam axis deviation angle characteristics of average intensity with a single beam)
When a light wave propagates through a medium whose refractive index fluctuates, the phase of the wave front changes and the intensity distribution of the light wave fluctuates. Here, using the existing theory, the beam axis deviation angle characteristic of the fluctuation of the received light intensity when the beam wave propagates through the slant path between the ground and the artificial satellite is calculated. Here, the beam axis deviation angle is defined as an angle formed by a beam optical axis connecting the transmission point and the center of the beam pattern during long exposure and a straight line connecting the light receiving point and the transmission point.

  As a premise of analysis of received light intensity fluctuation, the scale size of the refractive index non-uniformity is sufficiently larger than the wavelength, the state of the refractive index fluctuation is weak and isotropic, and the Rytov conversion And the Born approximation is established, and the change in the refractive index fluctuation on the propagation path is gradual.

  The time average of the intensity I (ρ, L) of the light wave at the distance ρ from the center of the beam pattern at the time of long-time exposure in the plane perpendicular to the propagation direction when the beam wave having a Gaussian intensity distribution propagates the distance L is When normalized by the intensity at the center of the beam at the exit position, it can be expressed as Equation (1).

Here, the brackets represent a time average. In the above equation, W ₀ is the beam radius at the exit position (the distance from the center of the beam to the position where the intensity is 1 / e ^{2 of the} peak value).

W _e (L) is the beam radius at the distance L, and can be expressed as the following formula (2) using the beam radius W (L) when there is no atmospheric fluctuation.

Here, k is the wave number of the light wave, η is the distance in the propagation direction from the transmission point, κ is the wave number of refractive index fluctuation, and Φ _n (η, κ) is the three-dimensional power spectrum of refractive index fluctuation.

Further, the beam radius W (L) when there is no atmospheric fluctuation can be expressed as the following formula (3) using the beam radius W ₀ at the exit position and the curvature radius R ₀ of the wave front at the exit position. .

This R ₀ is a positive value when a narrow beam having a center of curvature in the beam traveling direction is emitted, and a negative value in the case of a spread beam. When R ₀ is infinite, that is, when emitted with a parallel wavefront, the beam divergence angle is uniquely determined by the beam radius at the time of emission. Further, using the beam radius at the light receiving position and the distance to the light receiving position, the beam divergence angle θ of all angles (both sides of the beam) can be expressed as “θ = 2W _e (L) / L”.

In the case of the uplink from the ground to the satellite, _assuming that Φ _n (η, κ) can be expressed by a Kolmogorov spectrum model, the above equation (2) can be expressed as the following equation (4): I can express.

Here, Θ is the zenith angle, H ₀ is the altitude of the transmission point, H is the satellite altitude, and C _n ² (h) is the refractive index structure constant at altitude h. Further, when considering the theoretical consideration of turbulence, when the inner scale that represents the minimum size of the refractive index fluctuation lump is l ₀ and the outer scale that represents the maximum size is L ₀ , κ ₀ = 2π / Let L ₀ , κ _max = 2π / l ₀ .

Time average intensity <I (ρ, L)> of uplink (with atmospheric fluctuation) at the time of collimation transmission with W ₀ of 0.055 m, and time average intensity distribution <I (ρ, L)> without atmospheric fluctuation Is shown in FIG. These calculation conditions are shown in Table 1.

In this calculation, the effect of atmospheric fluctuations was included up to an altitude of 20 km. Further, v = 24.6 m / s, AHV = 3 × 10 ⁻¹³ m ^{− in the} HV model of C _n ² (h) so that W _e (L) is about 5 times W (L). ^2/3 . This model setting of C _n ² (h) is similar to the value estimated from stellar observation in another time zone.

  The horizontal axis in FIG. 2 is the beam axis deviation angle, and the vertical axis is normalized by the peak intensity when there is no fluctuation. Uplink <I (ρ, L)> is a value independent of the satellite altitude, and can be expressed as <I (φ)> = <I (ρ, L)>. As shown in FIG. 2, the beam spreads and propagates due to atmospheric fluctuations.

The downlink W _e (L) can be expressed as the following formula (5).

図２と同じ条件で、ダウンリンクの＜Ｉ（ρ，Ｌ）＞を計算すると、Ｗ_e（Ｌ）は限りなくＷ（Ｌ）に近づく。すなわち、ダウンリンクは、伝搬によって拡がった光波が対流圏に入射し、地上で受光される間際に大気揺らぎの影響を受けるため、Ｗ_e（Ｌ）は揺らぎの無い場合とほぼ等しくなるのである。

When the downlink <I (ρ, L)> is calculated under the same conditions as in FIG. 2, W _e (L) approaches W (L) as much as possible. That is, in the downlink, since light waves spread by propagation enter the troposphere and are affected by atmospheric fluctuations just before being received on the ground, W _e (L) is almost the same as when there is no fluctuations.

(Characteristic of beam axis deviation angle of logarithmic intensity dispersion in single beam)
The logarithmic intensity dispersion B _I (ρ, L) of the uplink due to atmospheric fluctuation can be expressed as the following formula (6).

Here, γ _r and γ _i are real numbers having a relationship of the following formula (7) with λ as a wavelength, and I ₀ (·) represents a modified Bessel function.

FIG. 3 shows the characteristics of the uplink logarithmic intensity dispersion B _I (ρ, L) with the axis deviation angle φ as the horizontal axis. Here, the beam radius W ₀ at the emission position is 0.01 m, 0.02 m, and 0.055 m, and the emission is performed in a collimated state. In this case, the beam divergence angles were 51.9 μrad, 38.3 μrad, and 28.8 μrad, respectively. Other calculation conditions are the same as in Table 1. From the results of FIG. 3, the uplink B _I (ρ, L) changes sharply with respect to φ as the beam divergence angle decreases. Since this uplink B _I (ρ, L) is also a value almost independent of the satellite altitude, B _I (φ) is as close as possible to B _I (ρ, L).

The downlink B _I (ρ, L) can be expressed as the following formula (8) when the averaging effect at the light receiving aperture is not taken into consideration.

The downlink B _I (ρ, L) calculated under the same conditions as in Table 1 at λ = 0.51 μm is almost uniform regardless of ρ and L, and is related to the value of W _0. In other words, the value was almost equal to the calculated value 0.41 in the case of a plane wave.

[Multi-beam beam interval]
For light waves that have propagated through a medium with atmospheric fluctuations, the distance between the two points where the correlation between the intensity fluctuations at the two points on the light-receiving surface is sufficiently small (correlation length for atmospheric fluctuations) is the propagation distance l in the fluctuation medium. Since (λl) ^1/2 is given using the wavelength λ, the correlation length of the light wave having λ of 0.51 μm propagated through the slant path is about 0.1 m. The divergence angle of the uplink beam is assumed to be several tens of μrad in order to secure a desired irradiance. If a beam interval of about 1 m is set on the ground, each laser beam is in the troposphere that is subject to atmospheric fluctuations. It can be considered that the correlation of intensity fluctuations due to atmospheric fluctuations when propagating while maintaining the correlation length and receiving each beam by a satellite is sufficiently small.

[Example of calculation of uplink axis deviation angle characteristics during two-beam transmission]
For the case where two laser beams are emitted with an interval sufficiently longer than the correlation length, an uplink time average intensity distribution <I (φ)> and logarithmic intensity dispersion B _I (φ) are calculated using existing theory. The fluctuations in received light intensity due to atmospheric fluctuations of each beam were calculated on the assumption that they were independent of each other. At this time, the two beams were collimated with the same W ₀ and the output power was also the same.

  As shown in FIG. 4, the positional relationship between the optical axis of each beam and the optical receiver is emitted in parallel with the case where the optical receiver is on the optical axis of each beam (on-axis transmission) and is intermediate between the optical axes of the two beams. Let us consider a case where a light receiver is positioned at (parallel transmission). The beam axis deviation angle φ at the time of on-axis transmission corresponds to the case where both beams make an angle φ in the same direction from the state of φ = 0 shown in FIG. Φ at the time of parallel transmission corresponds to the case where the axis deviation angle of each beam changes from the initial state shown in FIG.

FIG. 5 shows the characteristics of the time average intensity distribution <I (φ)> with respect to the off-axis angle when W _{0 of} both beams is 0.02 m, 0.01 m, and 0.005 m. The vertical axis is normalized by the peak value when the beam divergence angle is 38.6 μrad. In the calculation, H was set to 500 km assuming a low orbiting orbiting satellite, and other calculation conditions were the same as in Table 1. Since the change of <I (φ)> with respect to φ is moderate, parallel transmission and on-axis transmission have almost the same shape. When W ₀ is small, the peak value decreases, and the 1 / e ² beam divergence angle is a full angle value, 38.6 μrad (W ₀ = 0.02 m) and 51.7 μrad (W ₀ = 0.01 m, respectively). ), 79.8 μrad (W ₀ = 0.005 m).

Next, FIG. 6 shows the characteristics of logarithmic intensity dispersion B _I (φ) with respect to the off-axis angle when W _{0 of} both beams is 0.02 m, 0.01 m, and 0.005 m. In this case, the beam divergence angles are 38.6 μrad, 51.7 μrad, and 79.8 μrad, respectively, as in FIG. FIG. 6A shows the characteristics during on-axis transmission, and FIG. 6B shows the characteristics during parallel transmission. Since H was set to 500 km, the difference between on-axis transmission and parallel transmission became significant, and the logarithmic intensity dispersion B _I (φ) overall increased in parallel transmission. As in the case of a single beam, when the beam divergence angle is increased, the rate of change of the logarithmic intensity dispersion B _I (φ) with respect to the axis deviation angle from the center of the beam becomes slow. In addition, B _I (0) at the time of on-axis transmission is a half value of B _I (0) when two beams are transmitted in an overlapping manner. As the number of beams is increased, B _I (0) for on-axis transmission decreases.

  That is, from the comparison of characteristics between FIG. 6A and FIG. 6B, the irradiation direction of the communication laser light source is controlled so that the optical axis of each beam is on-axis penetrating the receiver of the communication partner. However, it can be understood that the dispersion of intensity fluctuations is kept small while maintaining the average intensity with respect to the beam axis deviation angle.

[Setting the number of beams]
In actual uplink transmission, the logarithmic intensity dispersion of the received light intensity is affected by the pointing error to the satellite when the beam is emitted from the ground device. Therefore, the effect of reducing the variation in received light intensity when the number of multi-beams is changed, including pointing errors, will be examined. The causes of this pointing error are listed in Table 2.

  The causes of pointing errors can be broadly classified into satellite tracking errors, errors in optical travel differences, and errors in the optical axis. The value of each error depends on the individual satellite and the ground station. Here, it is assumed that the divergence angle of the laser beam is several tens of μrad, and the pointing error of ± 3 μrad (peak value) which is smaller by one digit than this value. It was set. In this way, if the beam condition is determined in consideration of the pointing error with respect to the communication partner, the variation in received light intensity can be more effectively suppressed.

FIG. 7 shows the characteristics of the uplink normalized time average intensity distribution <I (3 μrad)> and logarithmic intensity dispersion B _I (3 μrad) when the number of beams is changed based on the calculation at the time of two-beam transmission. Here, the positional relationship between each beam and the light receiver is assumed to be on-axis transmission, and the beam divergence angle is calculated for each of 40 μrad, 50 μrad, 60 μrad, 70 μrad, and 80 μrad. Further, the beam radius at the time of emission corresponding to each beam divergence angle is as described in the figure. Other calculation conditions were the same as those in the calculation of FIG.

A specific example of the procedure for determining the beam condition of the actual beam divergence angle and the number of beams is as follows.
(1) Setting of pointing error angle (example 3μrad)
(2) Drawing of normalized light reception average intensity and number of beams in the direction of beam axis deviation angle of setting directivity error angle (3) Extracting combination of beam divergence angle and number of beams satisfying desired average intensity (4) Setting directivity Drawing of logarithmic intensity dispersion and beam number in the direction of the beam axis deviation angle of error angle (5) Extracting combinations of beam divergence angle and beam number satisfying desired logarithmic intensity dispersion (6) (3) and (5) Select the combination of the beam divergence angle and the number of beams that satisfies both conditions and the smallest number of beams.

According to the above procedure, FIG. 7A is created by setting the pointing error angle to 3 μrad. For example, when the required value of <I (3 μrad)> is 0.1 or more, the beam divergence angle to satisfy the required value The combination of the number of beams is 1 beam at 40 μrad, 1 beam at 50 μrad, 2 beams at 60 μrad, 3 beams at 70 μrad, and 6 beams at 80 μrad. Then, in FIG. 7B, for example, if B _I (3 μrad) = 0.2 or less is a required value, the combination of the beam divergence angle and the number of beams to satisfy the desired required value is 8 beams at 40 μrad, There are 2 beams at 50 μrad, 2 beams at 60 μrad, 2 beams at 70 μrad, and 2 beams at 80 μrad. Among the above combinations, a combination that satisfies both the conditions of average intensity and dispersion and has a small number of beams has two beams at 50 μrad or two beams at 60 μrad. In addition, when a plurality of beam conditions remain as selection targets in this way, it may be finally narrowed down to one combination on the condition of the beam divergence angle, or the average value of the beam divergence angles in the combination remaining as the selection target (In the case of 50 μrad and 60 μrad, 55 μrad) may be used.

  As described above, if there is no relative change between the communication station including the multi-beam laser communication apparatus 1 and the communication target, a good link can be maintained for a relatively long time depending on the beam conditions determined once. However, the direction from the ground to the artificial satellite depends on the position of the ground station, the orbit of the artificial satellite, and the time, and in particular, the pointing direction to the low-orbit artificial satellite varies greatly with time.

  That is, as shown in FIG. 8, when a terrestrial optical station equipped with the multi-beam laser communication device 1 communicates with an artificial satellite equipped with an optical communication function, an artificial satellite located at S1 is used for uplink transmission from the ground. When the elevation angle when the satellite is pointed is small (the zenith angle is large), the path in the atmosphere is long and the intensity fluctuation is large. Further, when the elevation angle when pointing to the artificial satellite located at S2 is large (the zenith angle is small), the influence of atmospheric fluctuation is small, and the beam spread is suppressed. Further, when the artificial satellite moves on the satellite orbit and points to the artificial satellite located in S3, the path in the atmosphere is long and the intensity fluctuation becomes large, as in the case of directing the artificial satellite located in S1. FIG. 9 shows the relationship between the zenith angle and the beam divergence angle.

As shown in FIG. 9, even if the exit beam diameter is the same, the beam divergence angle changes depending on the change in the zenith angle. Therefore, in order to continue the laser link between the ground and the satellite when the elevation angle changes greatly, the fluctuation condition at the minimum elevation angle where the fluctuation state is the most severe and the influence of atmospheric fluctuations are small and the beam divergence angle is relatively in both variable condition with small maximum elevation, the desired average received light intensity so as to satisfy the dispersion fluctuations, Ru necessary to set the number of beams of the beam condition of the beam divergence angle and multi-beam transmitting laser is Ah.

As an example, FIG. 10A shows the relationship between the normalized received light average intensity and the number of beams when the zenith angle is 60 degrees with the same configuration as FIG. 7, and FIG. 10 shows the relationship between the logarithmic intensity dispersion and the number of beams. Shown in b). At this time, the emission beam radius was set to the same value as in FIG. As in the case of FIG. 7, the required conditions for light reception by the satellite are set such that <I (3 μrad)> is 0.1 or more and B _I (3 μrad) is 0.2 or less. When the setting of the angle (in this case, the beam diameter) and the number of beams is obtained, the condition for using five beams having a beam diameter of 0.0105 m is the minimum beam number setting. Since this setting exceeds the setting value of the number of beams according to FIG. 7, even when the elevation angle is as shown in FIG. 7, the light reception request by the satellite can be cleared.

  Further, in the spatial laser communication, the atmospheric fluctuation state of the propagation path and the pointing error to the other party of communication are statistical values, and actually change depending on the time and position. Therefore, it is desirable to set the beam conditions with a certain margin for the required value of the received light intensity in communication. Therefore, the information on the average intensity and the intensity dispersion value in the received light is sent to the communication partner side, and when the laser beam from the partner side is received, the received light intensity fluctuation information on the average intensity and the intensity dispersion value on the partner side is acquired. Accordingly, a desired average received light intensity and a margin value to be added to the variance value of fluctuation may be adjusted when determining the beam condition. For example, reduce the number of beams if the average intensity and intensity dispersion on the other side are sufficiently higher than the required values, and conversely increase the number of beams if they are lower than the required values, thereby optimizing the light reception state on the other side. The laser line can be efficiently maintained.

  After determining the beam condition as described above, in order to adjust the actual beam divergence angle, an optical system composed of a plurality of lenses is provided with a zoom function, and the beam emitted by fine adjustment of the lens interval is provided. The divergence angle can be set, and the number of beams can be set by selecting the first to fourth telescopes 2a to 2d for laser beam transmission.

It is a schematic block diagram of the multi-beam laser communication apparatus which can irradiate four laser beams. It is a characteristic view of time average intensity <I (ρ, L)> with respect to the beam axis deviation angle φ. It is a characteristic view of logarithmic intensity dispersion B _I (ρ, L) with respect to the beam axis deviation angle φ. It is explanatory drawing of on-axis transmission and parallel transmission. It is a characteristic view of time average intensity distribution <I (φ)> with respect to a beam axis deviation angle φ at the time of two-beam transmission. It is a characteristic view of logarithmic intensity dispersion B _I (φ) with respect to the beam axis deviation angle φ during two-beam transmission. FIG. 6 is a characteristic diagram of uplink normalized time average intensity distribution <I (3 μrad)> and logarithmic intensity dispersion B _I (3 μrad) when the number of beams is changed. It is explanatory drawing of the change state of an elevation angle and an intensity | strength fluctuation when directing the artificial satellite which moves on a satellite orbit from a ground optical station. It is a characteristic figure of a zenith angle and a beam divergence angle. (A) is a characteristic diagram of the normalized received light average intensity and the number of beams when the zenith angle is 60 degrees. (B) is a characteristic diagram of the logarithmic intensity dispersion and the number of beams when the zenith angle is 60 degrees.

Explanation of symbols

1 Multi-beam laser communication device 2a First telescope (for laser beam transmission)
2b Second telescope (for laser beam transmission)
2c Third telescope (for laser beam transmission)
2d 4th telescope (for laser beam transmission)
DESCRIPTION OF SYMBOLS 3 Laser directing device 4 Light receiving telescope 5 Gimbal mechanism 6 Control part 61 Communication control means 62 Fluctuation condition setting means 63 Beam condition determination means 64 Fluctuation condition storage means 65 Received light intensity fluctuation information acquisition means 7 External input means

Claims (5)

A plurality of communication laser light sources are provided, and the laser beams of the plurality of communication laser light sources are spaced apart sufficiently longer than the correlation length so that they propagate through the troposphere that is subject to atmospheric fluctuations while maintaining the correlation length. By parallel beam transmission that emits the optical axis of each beam in parallel toward the receiver of the communication partner or on-axis transmission in which the optical axis of each beam penetrates the receiver of the communication partner. A multi-beam laser communication device that performs communication between a plurality of distant points using a plurality of laser beams,
Fluctuation condition setting means for setting, as a fluctuation condition , at least the average intensity and intensity dispersion in the beam axis deviation angle direction from the communication condition with the communication partner ;
Desired average intensity and satisfy intensity variance preset beam divergence angle and one among the combinations of the number of beams these communication partners in more under the set change conditions in the change condition setting means, the minimum combination of the number of beams Beam condition determining means for determining the beam divergence angle of the transmitting laser light source and the number of multi-beams;
Based on the beam condition determined by the beam condition determining means, communication control means for communicating with a communication partner;
A multi-beam laser communication device comprising: As the communication laser light source, one that can irradiate a beam with a narrow divergence angle of about several tens of μrad,
The said communication control means controls the irradiation direction of the laser beam source for communication so that the optical axis of each beam is on-axis transmission penetrating the receiver of the communication partner. Multi-beam laser communication device. The fluctuation condition setting means can set the pointing error to the communication partner as one of the fluctuation conditions,
The beam condition determining means is a combination of a preset beam divergence angle and the number of beams satisfying desired average intensity and intensity dispersion and pointing error of a communication partner under the fluctuation condition set in the fluctuation condition setting means , 3. The multi-beam laser communication apparatus according to claim 1, wherein a combination that provides the minimum number of beams is determined as a beam divergence angle of the laser beam source for transmission and a beam number of multi-beams.   For uplink transmission from the ground to the satellite, both the fluctuation conditions at the minimum elevation angle where the fluctuation is the most severe and the fluctuation conditions at the maximum elevation angle where the influence of atmospheric fluctuation is small and the beam divergence angle is relatively small are satisfied. 4. The multi-beam laser communication apparatus according to claim 1, wherein the beam condition is set as described above. The communication control means performs reception control for performing bidirectional laser communication,
When receiving a laser beam from a communication partner, equipped with received light intensity fluctuation information acquisition means for acquiring information of the received light intensity fluctuation,
The communication control means transmits the received light intensity fluctuation information acquired by the received light intensity fluctuation information acquisition means on a laser to be transmitted to the other party, and also receives the received intensity fluctuation information contained in the laser received from the other party. Shall be supplied to the condition determining means,
The beam condition determining means reduces the number of beams if the received light intensity fluctuation information supplied from the communication control means sufficiently exceeds the required value, and conversely increases the number of beams if the information is below the required value. The multi-beam laser communication apparatus according to claim 1, wherein the state of light reception in the laser beam is optimized.

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