JP2005065131A - Capture and tracking apparatus for spatial laser communication - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform proper capture and tracking by preventing a sum signal of outputs of a QD photodetector from becoming zero-cross even when a receiving strength of laser beams from an opposite station is lowered when a communication station which performs spatial laser communication, comprises a capture and tracking apparatus for precisely tracking the opposite station using the QD photodetector. <P>SOLUTION: A precise tracking control means 17 of the capture and tracking apparatus comprises first to fourth band limiting means 21a-21d corresponding to output signals (a)-(d) of first to fourth photo-detecting means 16a-16d of a QD photodetector 16, and a level discriminator 24 performs control to convert the first to fourth band limiting means 21a-21d from a through state into a band-limiting state through an LPF 26 (the state of cutting high-frequency noise components from the output signals (a)-(d)) when a sum signal Σ of the output signals (a)-(d) reaches a band limitation starting level with the reduction of the received light intensity or to convert the first to fourth band limiting means 21a-21d from the band limiting state into the through state when the received signal intensity increases and the sum signal Σ reaches a band limitation canceling level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a capture and tracking device for space laser communication that captures and tracks a partner station by space optical communication performed between a moving body or between a moving body and a fixed body.

  2. Description of the Related Art Conventionally, a capture tracking device for spatial laser communication has been used to capture and track each other between two stations that perform laser communication. This spatial laser communication acquisition and tracking device includes a coarse tracking control means for controlling the direction of a transmission / reception telescope by a laser beam from a partner station, and a four-quadrant light receiver (the light receiving surface is divided into four parts). And a fine tracking control means for receiving a laser beam from a partner station and adjusting and controlling the light receiving position so that the light receiving spot is at the center.

  In the acquisition and tracking device that performs fine tracking with the four-quadrant light receiver as described above, when the received light intensity is significantly attenuated, the random noise (thermal noise or shot noise) included in the preamplifier output from the four elements causes 4 A phenomenon occurs in which the sum signal of the element is zero-crossed (changes from positive to negative or from negative to positive). Since the sum signal is input to the denominator of the subsequent divider and the difference value is input to the numerator of the divider, the output from the divider is an abnormal value that can be alternately swung up to the positive / negative limit value of the divider. A phenomenon occurred. Since the light emission intensity of the laser element used for optical communication is limited at present, a high-power laser beam cannot be used for communication in order to avoid attenuation of the light reception intensity.

  As a method for calculating the output from the four-quadrant light receiver to obtain the light receiving spot position, a method of normalizing the position change using a divider has been conventionally performed, and the division provided in the light spot position detection unit is conventionally performed. There is a conventional technique in which a function of responding to fluctuations in received light intensity is provided in a detector (see, for example, Patent Document 1). However, the method described in Patent Document 1 inevitably has a problem that the error increases when the received light intensity decreases.

  In addition, as a method of avoiding the above-described abnormal phenomenon that occurs when the received light intensity decreases, the incident light to the tracking optical sensor is attenuated and the influence of noise becomes significant, and a predetermined threshold value is set. When it exceeds, the mirror adjustment operation for fine tracking is stopped and the movable mirror is fixed.After that, when the incident light becomes stronger and the influence of noise is reduced and falls below the threshold, the movable mirror is stopped. There is a conventional technique for resuming an automatic tracking operation from a position (see, for example, Patent Document 2). However, in the method described in Patent Document 2, since the control is not performed after the mirror adjustment operation for fine tracking is stopped and the movable mirror is fixed, the disturbance of posture change is directly directed. There is a possibility that the communication partner is lost due to an error.

JP-A-10-190549 JP 2001-333017 A

  That is, in these methods, there is a limit in reducing the pointing error when the received signal is attenuated, and it is not possible to realize highly reliable acquisition and tracking.

  The problem to be solved by the present invention is that even if the received light intensity of the laser beam is reduced and the influence of noise is increased, the phenomenon that the sum signal of the four elements becomes zero crossing does not occur, and proper acquisition and tracking is achieved. It is to provide a capture and tracking device for possible spatial laser communication.

  In order to solve the above problem, the invention according to claim 1 is a coarse tracking control means for receiving a laser beam from a communication partner station that performs spatial laser communication and roughly adjusting the pointing direction based on the received laser beam. Then, the received laser beam is received by the four-quadrant light receiver, and a difference signal serving as an index of deviation from the center of the light receiving spot is obtained using the output signal from each light receiving element of the four-quadrant light receiver, and based on this difference signal Fine tracking control means for finely adjusting the directing direction, and in the capture tracking device for spatial laser communication, the fine tracking control means is a through state in which the signal from the light receiving element of the four-quadrant light receiver is passed as it is, Band limiting means capable of switching to a band limiting state in which a signal from the light receiving element of the four-quadrant light receiver passes through a low-frequency band pass filter, and each light receiving element that has passed through the band limiting means When the signal level of the sum signal, which is the sum of these signals, decreases and reaches a predetermined band limit start level, the band limit means is converted from the through state to the band limit state, and the band limit start level is exceeded. Band limiting control means for converting the band limiting means from the band limiting state to the through state when the signal level of the low sum signal rises and reaches a predetermined band limiting cancellation level is provided.

  According to a second aspect of the present invention, in the acquisition tracking device for spatial laser communication according to the first aspect, the band limiting means includes two or more band pass filters having different time constants, and the band limiting The control means sequentially switches from the short time constant to the long time constant according to the decrease in the signal level of the sum signal, and from the long time constant to the short time according to the increase of the signal level of the sum signal. It is characterized in that it is switched sequentially to return to the through state.

  According to the acquisition and tracking device for spatial laser communication according to claim 1, since the band limiting unit and the band limiting control unit are provided in the fine tracking control unit, the signal from each light receiving element that has passed through the band limiting unit in the through state. When the signal level of the sum signal, which is the sum, reaches the band limit start level, the band limit control unit converts the band limit unit from the through state to the band limit state, and cuts a high-frequency component that is highly likely to be a noise component. It is possible to prevent the sum signal from crossing zero and suppress the acquisition of an abnormal difference signal. As a result, even when the received light intensity of the received laser beam is reduced, proper acquisition and tracking can be continued without causing a significant pointing error.

  When the signal level of the sum signal that is lower than the band limitation start level rises and reaches the band limitation release level while the band limitation unit continues to capture and track in the band limitation state, the band limitation control unit Since the band limiting means is converted from the band limited state to the through state, when the received light intensity of the laser beam returns to an appropriate intensity, the normal capture and tracking operation can be quickly and automatically returned.

  As described above, if the communication tracking device for laser communication according to the present invention is used in both communication stations that perform spatial laser communication, the pointing error when the received laser beam is attenuated can be suppressed to be small, and light reception on the partner side can be suppressed. Since intensity fluctuation can be effectively suppressed, there is also an advantage that a stable laser link can be maintained.

  Further, according to the acquisition and tracking device for spatial laser communication according to claim 2, two or more band pass filters having different time constants are provided in the band limiting unit, and the bandwidth is reduced according to the decrease or increase of the signal level of the sum signal. Since the limit control means uses different band-pass filters with different time constants, the band limit frequency is set high while the signal level of the sum signal is relatively high, and the reliability of the differential signal used for directivity control is increased. By reducing the band limit frequency as the signal level of the sum signal decreases, an abnormal difference signal is acquired based on the zero cross of the sum signal caused by noise mixing while allowing an error factor due to smoothing. To prevent. Therefore, it is possible to further suppress the error factor due to the band limitation when the received light intensity is reduced, and it is possible to realize more suitable acquisition and tracking.

  Next, an embodiment of a capture and tracking device for spatial laser communication according to the present invention will be described based on the attached drawings.

  FIG. 1 shows a schematic configuration of a spatial optical communication system provided in both communication stations that perform spatial laser communication. This spatial optical communication system is configured by a capture and tracking device 1 for spatial laser communication according to the first embodiment, a telescope 2 for both transmission and reception, and a gimbal mechanism 3.

  In the acquisition and tracking device 1, a part of the laser beam received from the communication partner station received by the telescope 2 is separated by the first beam splitter 11, received by the CCD light receiver 12, and received from the CCD light receiver 12. The coarse tracking control means 13 that has received the light receiving signal drives the gimbal mechanism 3 to adjust the light receiving position of the laser beam. That is, the light receiving direction of the telescope 2 can be roughly adjusted to the communication partner station by the drive control of the gimbal mechanism 3 performed by the coarse tracking control means 13.

  The laser beam that has passed through the first beam splitter 11 is guided to an optical path fine adjustment unit 14 constituted by, for example, two movable mirrors, and the received light that has passed through the optical path fine adjustment unit 14 passes through the second beam splitter 15. The fine tracking control means 17 that has passed through and irradiated the light receiving surface of the QD light receiver 16 that is a four-quadrant light receiver and received the output signal from the QD light receiver 16 operates the movable mirror of the optical path fine adjustment means 14. Adjust the light receiving position with high accuracy.

  The QD light receiver 16 is composed of four light receiving elements (for example, photodiodes) having a light receiving surface divided into four parts. If the light receiving spot is at the center, the four light receiving elements are used. If the same current is obtained and the light receiving spot is off the center, a current corresponding to the deviation is obtained from each light receiving element. Therefore, the direction of deviation of the position of the light receiving spot can be identified based on the current obtained from each light receiving element. Since the standard QD light receiver 16 does not have an amplifying function, for example, a four-divided avalanche photodiode (QAPD) in which the element itself has an electric amplifying function by an avalanche effect may be used.

  The transmission laser beam emitted from the laser light source 18 included in the acquisition and tracking device 1 is directed to the optical path fine adjustment means 14 by the second beam splitter 15 and transmitted through the first beam splitter 11. Irradiated from the telescope 2.

  The cause of the fluctuation in received light intensity that occurs when performing spatial optical communication between the artificial satellite and the ground station is also due to fluctuations in the atmosphere, but is mainly due to the pointing error of the laser communication device on the other side. When this pointing error occurs in the partner station, the received light intensity decreases, and the received light intensity recovers as the pointing error is corrected in the partner station. As described above, in spatial optical communication in which both communication stations capture and track each other station, fluctuations in received light intensity generally occur. The pointing error corresponds to a control residual obtained by correcting the attitude variation of the satellite body by the acquisition and tracking device, and this pointing error increases when the received light intensity of light transmitted from the other side is attenuated. The acquisition and tracking device measures the position variation of the light receiving spot caused by the posture variation of the optical communication device, and controls the movable mirror and the driving device in order to correct the posture variation based on the measured value. Since the coarse tracking control detects light receiving spots with a large angular resolution at a long time interval, it is hardly affected by a short time drop in the light receiving intensity. On the other hand, it is a problem to improve the accuracy of position measurement and the accuracy of movable mirror control when the intensity of the light receiving spot is reduced in fine tracking control. Therefore, the fine tracking control means 17 of the acquisition tracking device 1 according to the first embodiment is configured as shown in FIG.

  The fine tracking control means 17 shown in FIG. 2 shows only a schematic configuration until a difference signal is acquired, and a known and existing technique can be applied as a method for controlling the optical path fine adjustment means 14 based on the acquired difference signal. Therefore, illustration was abbreviate | omitted.

  Currents proportional to the amount of received light (W) are output from the first light receiving element 16a, the second light receiving element 16b, the third light receiving element 16c, and the fourth light receiving element 16d, which are the four photodiodes constituting the QD light receiver 16, respectively. These are converted into voltage (V) by the preamplifier circuit 20 to obtain signal intensity as potential information. In the QD light receiver 16 shown in this figure, the arrangement of the first light receiving element 16a and the fourth light receiving element 16d, the arrangement of the second light receiving element 16b and the third light receiving element 16c are arranged in the x direction, respectively. The arrangement of the first light receiving element 16a and the second light receiving element 16b and the arrangement of the third light receiving element 16c and the fourth light receiving element 16d are arranged in the y direction.

  The received light signals of the first to fourth light receiving elements 16a to 16d output from the preamplifier circuit 20 are first band limiting means 21a, second band limiting means 21b, third band limiting means 21c, and fourth band limiting means 21d. Are supplied to the adder / subtracter circuit 22 via each of them. The details of the first to fourth band limiting units 21a to 21d will be described later.

  In the addition / subtraction circuit 22, the output signal a from the first light receiving element 16a, the output signal b from the second light receiving element 16b, the output signal c from the third light receiving element 16c, and the output from the fourth light receiving element 16d. Using the signal d, the sum signal Σ = a + b + c + d, the x-direction difference value Ex = a + b−c−d, and the y-direction difference value Ey = a + dc−b are calculated, and these Σ, Ex, and Ey are calculated. This is supplied to the divider 23. The sum signal Σ is also supplied to the level discriminator 24.

  The divider 23 calculates Ex / Σ and Ey / Σ, and a differential signal indicating a deviation in the x direction (a signal indicating that there is no deviation as it approaches zero) and a differential signal (zero) indicating a deviation in the y direction. A signal indicating that there is no deviation as the value approaches. Thus, it is possible to acquire a differential signal that serves as an index for grasping the degree of deviation of the light receiving spot of the received laser beam irradiated to the QD light receiver 16 from the center of the light receiving surface of the QD light receiver 16. By moving the movable mirror of the optical path fine adjustment means 14 based on the value of the difference signal and finely adjusting the optical path of the received laser beam so that the light receiving spot hits the center of the QD light receiver 16, the fine tracking control means 17 A fine tracking operation is performed.

  FIG. 3A is a waveform diagram by simulation calculation when the sum signal Σ obtained from the adder / subtractor circuit 22 attenuates and recovers, and it can be seen that significant fine movement occurs in the signal level. This is because random noise (thermal noise or shot noise) included in the light receiving element and the preamplifier circuit 20 constituting the QD light receiver 16 is mixed. FIG. 3B shows an ideal differential signal (Ex / Σ or Ey / Σ) when there is no random noise for an example in which the position of the light receiving spot varies sinusoidally. When the received light intensity is significantly attenuated, the sum signal Σ (Σ = a + b + c + d, a signal that is not normally negative) is zero-crossed (changes from positive to negative or from negative to positive) due to the influence of random noise. Occurs. At the time of zero crossing, an abnormal difference signal was generated in which the output from the divider 23 was alternately swung up to the positive / negative limit value of the divider 23 (see FIG. 3C).

  Therefore, the first to fourth band limiting units 21a to 21d in the fine tracking control unit 17 of the acquisition and tracking device 1 according to the present embodiment include a switching unit 25 and a band pass filter (hereinafter referred to as an LPF) that transmits a low frequency component. ) 26 and a switching means 25 having a two-contact switching type switch, a through state in which the signal from the preamplifier circuit 20 is sent to the adder / subtractor circuit 22 as it is, and a band limited signal from the preamplifier circuit 20 through the LPF 26. The bandwidth limit state to be sent to is switched.

  That is, in the present embodiment, the first to fourth band limiting units 21a to 21d including the switching unit 25 and the LPF 26 are “through state in which a signal from the light receiving element of the four quadrant light receiver is passed as it is and four quadrant light reception. It functions as a band limiting means that can be switched between a band limiting state in which a signal from the light receiving element of the detector is passed through a low-frequency band pass filter.

  Further, the level discriminator 24 is configured such that the signal level of the sum signal Σ from the adder / subtractor circuit 22 is a specified value (predetermined band limit start level) as the intensity of the beam spot hitting the QD light receiver 16 decreases. Is detected, the switching signal is sent to each switching means 25 of the first to fourth band limiting means 21a to 21d to change the first to fourth band limiting means 21a to 21d to the band limiting state. The output signals a to d from which the high-frequency components have been cut are supplied to the addition / subtraction circuit 22.

  After the band limitation is performed as described above, the signal level of the sum signal Σ from the adder / subtractor circuit 22 becomes a predetermined value (predetermined band) as the intensity of the beam spot hitting the QD light receiver 16 increases. The level discriminator 24 that has detected that the limit release level has been reached sends a switching signal to each of the switching means 25 of the first to fourth band limiting means 21a to 21d, and the first to fourth band limiting means 21a. ˜21d is changed to the through state, and the output signals a to d from the preamplifier circuit 20 are supplied to the adder / subtractor circuit 22 as they are.

  That is, in the present embodiment, the level discriminator 24 that performs switching control of the switching means 25 of the first to fourth band limiting means 21a to 21d is “the sum of signals from each light receiving element that has passed through the band limiting means. When the signal level of the sum signal decreases and reaches a predetermined band limit start level, the band limit means is converted from the through state to the band limit state, and the signal level of the sum signal is lower than the band limit start level. Increases and reaches a predetermined band limit release level, and functions as a band limit control means for converting the band limit means from the band limit state to the through state.

  FIG. 3D shows the waveform of the sum signal Σ when the switching control by the level discriminator 24 is performed using the band limitation control method described above. For example, the level discriminator 24 determines that the signal level of the sum signal Σ has reached 0.3 [V], which is the band limitation start level, and switches the switching unit 25 of the first to fourth band limiting units 21a to 21d. By switching, the sum signal Σ is calculated on the basis of the band-limited output signals a to d in this figure in about 0.04 seconds, and the subsequent sum signal Σ is smoothed. I can see that

  Thereafter, the level discriminator 24 determines that the signal level of the sum signal Σ has reached 0.4 [V], which is the band limitation release level, and switches the switching unit 25 of the first to fourth band limiting units 21a to 21d. By switching, the sum signal Σ is calculated on the basis of the output signals a to d that are not band-limited in this figure, in the vicinity of approximately 0.076 seconds. It can be seen that a slight tremor has occurred.

  Note that the bandwidth limit determined by the level discriminator 24 to end the bandwidth limit is higher than the bandwidth limit start level (threshold for switching from the through state to the bandwidth limit state) determined by the level discriminator 24 to start the bandwidth limit. The reason why the release level (threshold for switching from the band-limited state to the through state) is set large is to prevent chattering (a phenomenon in which the opening and closing of the contacts repeats within a short time).

  FIG. 3E shows the waveform of the difference signal acquired from the output signals a to d subjected to band limitation by switching to the LPF 26. This is more likely to contain errors than the ideal differential signal shown in FIG. 3B, and it cannot be denied that the measurement system has deteriorated, but the conventional method shown in FIG. 3C. It can be seen that an abnormal state such as (the waveform of the differential signal calculated by the zero-crossed sum signal) does not occur, and a differential signal that does not hinder the movable mirror control of the optical path fine adjustment unit 14 can be acquired.

  The specified values (band limit start level and band limit release level) that are discriminated by the level discriminator 24 in order to switch the band limit ON / OFF may be set as appropriate based on the noise characteristics according to the circuit configuration. The method is not particularly limited. Further, the band pass / cutoff characteristics used as the LPF 26 may be set as appropriate based on the noise characteristics according to the circuit configuration, but the random noise amplitude distribution can be estimated probabilistically, so avoiding zero crossing of the sum signal, In addition, it is desirable to use a filter having a characteristic capable of adding a frequency band restriction that minimizes a decrease in position measurement accuracy due to the band restriction.

  Next, a description will be given of a second embodiment in which the error of the difference signal can be suppressed more than the fine tracking control means 17 provided in the acquisition and tracking device 1 of the first embodiment described above while band limitation is applied. FIG. 4 shows a schematic configuration of fine tracking control means 17 ′ provided in the acquisition tracking device according to the second embodiment. In addition, about the structure similar to the fine tracking control means 17 shown in FIG. 2, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the fine tracking control means 17 ′, the output signals a to d supplied from the first to fourth light receiving elements 16a to 16d through the preamplifier circuit 20 are the first band limiting means 31a, the second band limiting means 31b, The third band limiting unit 31c and the fourth band limiting unit 31d are reached. The level discriminator 32 that receives the sum signal Σ from the adder / subtractor circuit that has received the output signals a to d from the first to fourth band limiting units 31a to 31d, according to the signal level of the sum signal Σ. The four-band limiting means 31a to 31d are controlled.

  These first to fourth band limiting units 31a to 31d are switched from a pre-amplifier circuit 20 to a first state by a switching state 33 having a three-contact switching type switch. A first-stage band-limited state in which a band-limited signal is sent to the adder / subtracter circuit 22 through a low-frequency pass filter (hereinafter referred to as first-stage LPF) 34a, and a band-limited signal from the preamplifier circuit 20 through the next-stage low-frequency pass filter (hereinafter referred to as next-stage LPF) 34b. It is possible to switch to a next-stage band-limited state in which the processed signal is sent to the adder / subtracter circuit 22.

  Here, the first-stage LPF 34a and the next-stage LPF 34b have different transmission / cutoff frequency bands, and the time constant of the next-stage LPF 34b is made longer than the time constant of the first-stage LPF 34a, so that The LPF 34b has a characteristic that the band limit frequency is lower (the output signals a to d are easier to smooth). If the first-stage LPF 34a and the next-stage LPF 34b having such characteristics are used, the first-stage LPF 34a is used when the light reception intensity of the QD light receiver 16 is high to some extent and the possibility of zero crossing is low even if some noise components remain. When the band of the output signals a to d can be limited, the received light intensity of the QD light receiver 16 is extremely low, and there is a risk that zero crossing may occur due to a minor noise component, the output signal is output using the next-stage LPF 34b. Bands a to d can be limited.

  Therefore, the level discriminator 32 that controls the first to fourth band limiting units 31a to 31d having the above-described configuration is supplied from the addition / subtraction circuit 22 as the intensity of the beam spot hitting the QD light receiver 16 decreases. When the signal level of the sum signal .SIGMA. Is reduced to a specified value (predetermined initial stage band limitation start level), a switching signal is sent to each of the switching units 33... Of the first to fourth band limiting units 31a to 31d. Thus, the first-stage LPF 34a, which is the first-stage filter, is switched so that the output signals a to d pass therethrough, and the first to fourth band-limiting means 31a to 31d are changed to the first-stage band-limited state, and high-frequency noise components are cut. The output signals a to d are supplied to the addition / subtraction circuit 22.

  After the switching to the first-stage LPF 34a, the signal level of the sum signal Σ from the adder / subtractor circuit 22 becomes a specified value (predetermined next-stage band limit) as the intensity of the beam spot hitting the QD light receiver 16 further decreases. When the level discriminating means 32 detects that the level has dropped to the start level), it sends a switching signal to each of the switching means 33... Of the first to fourth band limiting means 31a to 31d, and the next stage LPF 34b, which is the next stage filter, is sent. The output signals a to d are switched so that each of the output signals a to d passes, the first to fourth band limiting units 31 a to 31 d are changed to the next band limiting state, and the output signals a to d from which the low frequency noise components are further cut are obtained. It is supplied to the addition / subtraction circuit 22.

  After the band limitation is performed as described above, the signal level of the sum signal Σ from the adder / subtractor circuit 22 is increased to a specified value (predetermined next) as the intensity of the beam spot hitting the QD light receiver 16 increases. The level discriminator 32 that has detected that the first stage LPF 34a, which is the first stage filter, sends a switching signal to the switching means 33 of the first to fourth band limiting units 31a to 31d. Are switched so that the output signals a to d pass, and the first to fourth band limiting units 31a to 31d are returned from the next stage band limited state to the first stage band limited state.

  After the switching to the first-stage LPF 34a, the signal level of the sum signal Σ from the adder / subtractor circuit 22 is increased to a specified value (predetermined first-stage band limit release) as the intensity of the beam spot hitting the QD light receiver 16 further increases. The level discriminator 32, which has detected that the level has been reached, sends a switching signal to the switching means 33 of the first to fourth band limiting means 31a to 31d, and the first to fourth band limiting means 31a to 31d. Is changed to the through state, and the output signals a to d from the preamplifier circuit 20 are supplied to the adder / subtractor circuit 22 as they are.

  That is, the level discriminator 32 included in the fine tracking control unit of the acquisition and tracking device according to the present embodiment includes “two or more low-frequency bandpass filters having different time constants, and the band limiting control unit includes a sum signal. As the signal level decreases, the time constant is switched from the short time constant to the long time constant, and as the sum signal level increases, the time constant is switched from the long time constant to the short one. It functions as a "band limiting means for returning".

  FIG. 5 shows simulation waveforms of various signals in the fine tracking control means 17 ′ adopting the above-described two-stage filter switching method. For example, the level discriminator 32 determines that the signal level of the sum signal Σ has reached the first stage band restriction start level of 0.3 [V], and the switching means for the first to fourth band restriction means 31a to 31d. 33 is approximately 0.035 seconds for outputting a signal for switching to the first-stage LPF 34a (the first-stage filter switching signal is turned ON), and the sum calculated based on the band-limited output signals a to d thereafter. It can be seen that the signal Σ is somewhat smoothed.

  Furthermore, the level discriminator 32 discriminates that the intensity of the received light signal has decreased and the signal level of the sum signal Σ has reached 0.03 [V] which is the next band restriction start level. The switching means 33 of the limiting means 31a to 31d outputs a signal for switching to the next-stage LPF 34b (turning on the next-stage filter switching signal and turning off the first-stage filter switching signal) in about 0.046 seconds. Then, it can be seen that the sum signal Σ calculated based on the band-limited output signals a to d is further smoothed.

  Thereafter, the intensity of the received light signal increases, and the level discriminator 32 discriminates that the signal level of the sum signal Σ has reached the next-stage band restriction release level of 0.2 [V]. A signal for switching to the first-stage LPF 34a is output by the switching means 33 of the band limiting means 31a to 31d (the first-stage filter switching signal is turned on and the next-stage filter switching signal is turned off) in about 0.075 seconds. Then, it can be seen that fine movement due to noise occurs in the sum signal Σ calculated based on the band-limited output signals a to d.

  Further, the intensity of the received light signal is increased, and the level discriminator 32 determines that the signal level of the sum signal Σ has reached the first stage band restriction release level of 0.4 [V], and the first to fourth band restrictions. A signal for switching the switching means 33 of the means 31a to 31d to through is output (turning off the first stage filter switching signal) in about 0.78 seconds, and thereafter the output signals ad are not band-limited. It can be seen that the fine signal caused by the noise is generated again in the sum signal Σ calculated based on this.

  Also in the second embodiment, in order to prevent chattering, the first-stage band restriction release level is set higher than the first-stage band restriction start level, and the next-stage band restriction release level is set higher than the next-stage band restriction start level. is there.

  FIG. 5D shows the waveform of the differential signal acquired from the output signals a to d subjected to band limitation by switching to the first-stage LPF 34a and the next-stage LPF 34b. This also includes an error as compared with the ideal differential signal shown in FIG. 3B, and although it cannot be denied that the measurement system has deteriorated, the first difference shown in FIG. It can be seen that the error can be suppressed more than the difference signal acquired in the embodiment.

  The specified values (band limit start level and band limit release level of each stage) to be discriminated by the level discriminator 32 in order to switch ON / OFF of the band limit at each stage are appropriately set based on the noise characteristics according to the circuit configuration. The setting method is not particularly limited. The band pass / cutoff characteristics of the filters used as the first-stage LPF 34a and the next-stage LPF 34b may be set as appropriate based on the noise characteristics according to the circuit configuration, but the random noise amplitude distribution can be estimated probabilistically. It is desirable to use a filter having a characteristic capable of adding a frequency band limit that avoids zero crossing of the sum signal and minimizes a decrease in position measurement accuracy due to each band limit.

  In the second embodiment described above, two LPFs are used for switching according to strength reduction. However, three or more LPFs may be used for switching according to strength reduction.

It is a schematic block diagram of the optical communication system containing an acquisition tracking apparatus. It is a schematic block diagram of the fine tracking control means provided in the acquisition tracking apparatus which concerns on 1st Embodiment. It is a simulation waveform figure of various signals in fine tracking control means (mainly composition of Drawing 2). It is a schematic block diagram of the fine tracking control means provided in the acquisition tracking apparatus which concerns on 2nd Embodiment. It is a simulation waveform figure of various signals in fine tracking control means (configuration of Drawing 4).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acquisition tracking apparatus 2 Telescope 3 Gimbal mechanism 13 Coarse tracking control means 14 Optical path fine adjustment means 16 QD light receivers 16a to 16d First to fourth light receiving elements 17 Fine tracking control means 21a to 21d First to fourth band limiting means 24 Level discriminator 25 switching means 26 LPF
17 'fine tracking control means 31a to 31d first to fourth band limiting means 32 level discriminator 33 switching means 34a first stage LPF
34b Next stage LPF

Claims (2)

Coarse tracking control means for receiving a laser beam from a communication partner station that performs spatial laser communication and coarsely adjusting a directivity direction based on the received laser beam;
The received laser beam is received by a four-quadrant light receiver, and a differential signal that serves as an index of deviation from the center of the light-receiving spot is obtained using output signals from the respective light-receiving elements of the four-quadrant light receiver, and directed based on the difference signal. Fine tracking control means for finely adjusting the direction;
In space laser communication acquisition and tracking device comprising:
The fine tracking control means is
Band limiting means capable of switching between a through state in which the signal from the light receiving element of the four quadrant light receiver is passed as it is and a band limited state in which the signal from the light receiving element of the four quadrant light receiver is passed through the low frequency band pass filter; ,
When the signal level of the sum signal, which is the sum of the signals from the respective light receiving elements that have passed through the band limiting unit, decreases and reaches a predetermined band limiting start level, the band limiting unit is changed from the through state to the band limiting state. The band limiter converts the band limiter from the band limit state to the through state by increasing the signal level of the sum signal that is lower than the band limit start level and reaching a predetermined band limit release level. Control means;
A capture and tracking device for spatial laser communication. The band limiting means includes two or more band pass filters having different time constants,
The band limiting control means sequentially switches from the short time constant to the long time constant according to the decrease in the signal level of the sum signal, and from the long time constant according to the increase in the signal level of the sum signal. 2. The acquisition and tracking device for spatial laser communication according to claim 1, wherein the system is sequentially switched to a short one and returned to the through state.

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