Patent ID: 12206450

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

FIG.1is a diagram illustrating the configuration of a communication apparatus1according to a first embodiment.

The communication apparatus1includes a signal output unit10, a transmission-side oscillation light output unit11, an optical modulation unit12, a spatial optical communication unit13, a reception-side oscillation light output unit14, an optical demodulation unit15, and a signal input unit16(an optical receiver).

The signal output unit10outputs an electric signal indicating information to be transmitted to a communication partner to the optical modulation unit12. That is, an output end of the signal output unit10is connected to an input end of the optical modulation unit12via an electric cable.

The transmission-side oscillation light output unit11outputs oscillation light serving as a carrier of an optical signal to the optical modulation unit12. That is, an output end of the transmission-side oscillation light output unit11is connected to the input end of the optical modulation unit12via an optical cable.

The optical modulation unit12modulates the oscillation light input from the transmission-side oscillation light output unit11by using a signal input from the signal output unit10. The optical modulation unit12outputs an optical signal generated by the optical modulation to the spatial optical communication unit13. That is, an output end of the optical modulation unit12is connected to an input end of the spatial optical communication unit13via an optical cable.

The spatial optical communication unit13is an optical antenna provided so as to face a communication partner. The spatial optical communication unit13converts an optical signal input to a transmission port into an optical wireless signal and transmits the optical wireless signal. On the other hand, the spatial optical communication unit13converts a received optical wireless signal into an optical signal and outputs the optical signal from a reception port. A transmission port of the spatial optical communication unit13is connected to the optical modulation unit12via an optical cable, and the reception port is connected to an input end of the optical demodulation unit15via an optical cable.

The reception-side oscillation light output unit14outputs oscillation light to the optical demodulation unit15. The optical demodulation unit15demodulates the optical signal input from the spatial optical communication unit13by using the oscillation light input from the reception-side oscillation light output unit14, and outputs the demodulated signal to the signal input unit16. The signal input unit16receives the signal from the optical demodulation unit15. The optical demodulation unit15generates an electric signal by demodulating the optical signal input from the spatial optical communication unit13, using the oscillation light input from the reception-side oscillation light output unit14. The optical demodulation unit15outputs the generated electric signal to the signal input unit16. An output end of the optical demodulation unit15is connected to an input end of the signal input unit16via an electric cable.

The signal input unit16receives the signal from the optical demodulation unit15.

FIG.2is a configuration example of the spatial optical communication unit13according to the first embodiment.

The spatial optical communication unit13includes an antenna131, a focus adjustment unit132, a wavefront shaping unit133, a half mirror134A, a half mirror134B, a wavefront detection unit135, a wavefront control unit136, an optical axis adjustment unit137, and a control information generation unit138.

The antenna131allows a received optical wireless signal to be incident on the focus adjustment unit132. The antenna131transmits an optical wireless signal incident from the focus adjustment unit132to a communication partner. The antenna131includes a plurality of mirrors. The focus adjustment unit132adjusts the focus of an optical wireless signal incident from the antenna131and the wavefront shaping unit133, under the control of the wavefront control unit136. The focus adjustment unit132allows the optical wireless signal incident from the wavefront shaping unit133to be incident on the antenna131and allows the optical wireless signal incident from the antenna131to be incident on the wavefront shaping unit133. The wavefront shaping unit133corrects the wavefront of an optical wireless signal incident from the half mirror134A and the focus adjustment unit132, under the control of the wavefront control unit136. The wavefront shaping unit133allows the optical wireless signal incident from the focus adjustment unit132to be incident on the half mirror134A and allows the optical wireless signal incident from the half mirror134A to be incident on the focus adjustment unit132. Configuration examples of the wavefront shaping unit133include a variable mirror.

The half mirror134A reflects a part of the optical wireless signal incident from the wavefront shaping unit133. The half mirror134A is placed such that the reflected light is incident on the half mirror134B. The half mirror134A transmits a part of the optical wireless signal incident from the optical modulation unit12to be incident on the wavefront shaping unit133. The half mirror134B reflects a part of the optical wireless signal incident from the half mirror134A to be incident on the optical demodulation unit15. The half mirror134B transmits a part of the optical wireless signal incident from the half mirror134A to be incident on the wavefront detection unit135. The wavefront detection unit135detects a wavefront of the optical wireless signal incident from the half mirror134B.

The wavefront control unit136controls the focus adjustment unit132, the wavefront shaping unit133, and the optical axis adjustment unit137in accordance with data generated by the control information generation unit138. The optical axis adjustment unit137adjusts an optical axis of an optical wireless signal under the control of the wavefront control unit136. The optical axis adjustment unit137adjusts the optical axis by adjusting, for example, an angle of components constituting the communication apparatus1. The control information generation unit138estimates a wavefront after a certain period of time using the wavefront detected by the wavefront detection unit135, and outputs data indicating the estimated wavefront to the wavefront control unit136. The certain period of time described herein means, for example, a time obtained by adding half the time of a cycle of the wavefront detection process to a latency from detecting a wavefront to controlling the wavefront.

FIG.3is a diagram illustrating the configuration of the control information generation unit138according to the first embodiment.

The control information generation unit138includes a phase difference distribution storage unit141, an atmospheric layer calculation unit142, an atmospheric layer calculation result storage unit143, and a phase difference distribution estimation unit145.

The phase difference distribution storage unit141stores a phase difference distribution of the wavefront of the optical signal detected by the wavefront detection unit135. The atmospheric layer calculation unit142calculates the velocity of an atmospheric layer that affects an optical signal and measures (characteristic values related to the characteristics of the atmosphere) of the magnitude of the influence in accordance with the phase difference distribution stored in the phase difference distribution storage unit141. The atmospheric layer calculation unit142records data used by the phase difference distribution estimation unit145in an estimation use data storage unit144. The atmospheric layer calculation result storage unit143and the estimation use data storage unit144store results obtained by the calculation by the atmospheric layer calculation unit142. The phase difference distribution estimation unit145estimates a phase difference distribution after a certain period of time using the phase difference distribution of the wavefront of the optical signal recorded in the phase difference distribution storage unit141and the characteristic values related to the characteristics of the atmosphere recorded in the estimation use data storage unit144, and outputs the estimated phase difference distribution to the wavefront control unit136.

Calculation Method by Atmospheric Layer Calculation Unit142

The wavefront detection unit135detects a phase difference distribution of a wavefront according to a prescribed cycle. Two phase difference distributions detected at the latest time have been recorded in the phase difference distribution storage unit141. When the wavefront detection unit135newly detects a wavefront, data of a phase difference distribution with an earlier detection time between the two phase difference distributions is updated to data of the newly detected wavefront. The atmospheric layer calculation unit142calculates characteristic values related to the characteristics of the atmosphere using data of the two phase difference distributions.

The data of the two phase difference distributions are referred to as a “phase difference distribution A” and a “phase difference distribution B”, and it is assumed that the phase difference distribution B has an earlier observation time than the phase difference distribution A. The phase difference distribution A and the phase difference distribution B indicate phases of optical signals at detection positions on a two-dimensional plane in the wavefront detection unit135. The phase difference distribution A and the phase difference distribution B are represented as, for example, three-dimensional data (x, y, f(x, y). The symbols x and y are numerical values representing two-dimensional coordinates of a detection position in the wavefront detection unit135. The symbol x is an integer satisfying −n≤x≤n, y is an integer satisfying −m≤y≤m, and n and m are positive integers. Herein, f(x, y) is the phase of an optical signal detected at a detection position indicated by x and y.

FIG.4Ais a table illustrating an example of the phase difference distribution A.

FIG.4Bis a table illustrating an example of the phase difference distribution B.

FIGS.4A and4Billustrate matrices each indicating detection positions in a two-dimensional plane with y coordinates in rows and x coordinates in columns. In the matrix representing the phase difference distribution A, values of phase fA(x, y) at detection positions (x, y) are stored for each of the detection positions. Similarly, in the matrix representing the phase difference distribution B, values of phase fB(x, y) at detection positions (x, y) are stored for each of the detection positions.

The atmospheric layer calculation unit142calculates cross-correlation values between fA(x, y) and fB(x, y). The atmospheric layer calculation unit142calculates the cross-correlation values by using the following Equation (1).

[Math.1]Cor⁡(dx,dy)=∑y=-qq∑x=-pp2⁢fA(x,y)⁢fB(x+dx,y+dy)fA(x,y)2+fB(x+dx,y+dy)2(1)

In Equation (1) above, dx and dy denote an amount obtained by translating the value of fB(x, y) in an x direction and an amount obtained by translating the value of fB(x, y) in a y direction, respectively, and (dx, dy) is referred to as a “two-dimensional slide amount”. Herein, Cor (dx, dy) denotes cross-correlation values between fA(x, y) and fB(x, y) when fB(x, y) is moved by the two-dimensional slide amount (dx, dy). The symbols dx and dy are changed in the range of −p≤dx≤p and −q≤dy≤q. Here, p and q are positive integers. Furthermore, p≤n/2 and q≤m/2 are satisfied, and the sum of Cor (dx, dy) is calculated in the range of −p≤x≤p and −q≤y≤q. At this time, even though dx and dy are changed, −n≤x+dx≤n and −m≤y+dx≤m are satisfied, and values of fB(x+dx, y+dy) can be defined. Furthermore, the number of terms used in the sum calculation in Equation (1) above is the same regardless of the value of the two-dimensional slide amount (dx, dy).

FIG.5is a table illustrating an example of cross-correlation values between calculated phase difference distributions.

The atmospheric layer calculation unit142calculates the cross-correlation values Cor (dx, dy) between phase difference distributions by Equation (1) above for each combination of the two-dimensional slide amounts (dx, dy). The cross-correlation value for each two-dimensional slide amount is recorded in the atmospheric layer calculation result storage unit143. The atmospheric layer calculation unit142calculates a standard deviation of the cross-correlation values.

The phase difference distribution A and the phase difference distribution B recorded in the phase difference distribution storage unit141are updated at a certain cycle t1. Each time data is updated, the atmospheric layer calculation unit142calculates cross-correlation values and a standard deviation of the cross-correlation values. That is, a plurality of cross-correlation values based on phase difference distributions at different timings for one two-dimensional slide amount (dx, dy) are recorded in the atmospheric layer calculation result storage unit143. The atmospheric layer calculation unit142calculates an average value of cross-correlation values for each two-dimensional slide amount.

Then, the atmospheric layer calculation unit142selects an average value that is at least a constant multiple of a standard deviation of the most recently calculated cross-correlation values from the average values of the cross-correlation values. The constant multiple may be any value as long as it is a preset value. Then, the atmospheric layer calculation unit142records the average value and a two-dimensional slide amount (dx, dy) associated to the average value, in the estimation use data storage unit144. That is, the atmospheric layer calculation unit142checks to set the two-dimensional slide amount (dx, dy) such that the cross-correlation value is a relatively large value.

FIG.6Ais an example of a table illustrating average values of cross-correlation values between phase difference distributions.

FIG.6Bis an example of a table illustrating selected average values.

FIG.6Aillustrates average values of cross-correlation values between phase difference distributions when −2≤dx≤2 and −2≤dy≤2 are satisfied. An average value CorAve (dx, dy) of the cross-correlation values is an average value for each of the two-dimensional slide amounts (dx, dy) of the cross-correlation values Cor (dx, dy) between the phase difference distributions. At this time, a standard deviation of Cor (dx, dy) most recently calculated by the atmospheric layer calculation unit142is 0.005, and it is assumed that the atmospheric layer calculation unit142selects Corave (dx, dy) of 0.05 or more, which is 10 times this standard deviation.FIG.6Bis an example of a table illustrating the selected average values.

Of the average values of the cross-correlation values illustrated inFIG.6A, the average value is 0.05 or more when the two-dimensional slide amount (dx, dy) is (−2, 0), (−1, 1), and (2, −2). Each value of the average values CorAve (dx, dy) of the cross-correlation values at this time is 0.15, 0.2, and 0.09. This data is recorded in the estimation use data storage unit144.

Each time the data recorded in the phase difference distribution storage unit141is updated, an average value to be calculated by the atmospheric layer calculation unit142is also changed, and an average value to be selected is also different. The atmospheric layer calculation unit142updates the data recorded in the estimation use data storage unit144each time the calculation results are different.

Hereinafter, the reason why the atmospheric layer calculation unit142selects an average value that is at least a constant multiple of a standard deviation will be described. A phase difference in an optical signal may be affected by an atmospheric layer through which the optical signal propagates. The atmospheric layer includes layers of the atmosphere having a different movement speed, and optical signals undergo different phase changes by propagating through the atmospheric layer having a different movement speed. The number of average values to be selected associates to the number of atmospheric layers that affect optical signals. This is because a large cross-correlation value between a phase difference distribution translated by a specific two-dimensional slide amount and an immediately following phase difference distribution indicates the fact that the phase difference distribution has moved by the specific two-dimensional slide amount. Accordingly, the two-dimensional slide amount (dx, dy) represents a distance at which an air layer may travel during t1which is an interval between phase difference distribution observation times, and the average value CorAve (dx, dy) of the cross-correlation values represents a measure of the influence of the atmospheric layer on an optical signal detected. That is, the two-dimensional slide amount and the average value of the cross-correlation values are examples of characteristic values related to the characteristics of the atmosphere.

Estimation Method by Phase Difference Distribution Estimation Unit145

The phase difference distribution estimation unit145estimates a phase after a certain period of time t2(for example, time obtained by adding half of a time interval to be controlled to a latency time from detecting a wavefront to controlling the wavefront) in accordance with the latest phase difference distribution A recorded in the phase difference distribution storage unit141, the average value of the cross-correlation values for each two-dimensional slide amount recorded in the estimation use data storage unit144, and a two-dimensional slide amount associated to the average value. A phase difference distribution fC(x, y) after the certain period of time t2is calculated by Equation (2) below.

[Math. 2]
fc(x,y)=ΣCorAve(dx,dy)×fA(x−δ×dx,y−δ×dy)  (2)

The symbol δ is a value obtained by dividing t2by the interval t1of phase difference distribution data update time. The phase difference distribution estimation unit145calculates the sum of products of the average values of the cross-correlation values for each two-dimensional slide amount recorded in the estimation use data storage unit144and phases slid by the two-dimensional slide amount associated to the average value.

For example, when the two-dimensional slide amounts illustrated inFIG.6Band the average values of the cross-correlation values at that time are selected, the phase difference distribution fC(x, y) after the certain period of time t2is calculated by Equation (3) below.

[Math.3]fc(x,y)=0.15×fA(x+2⁢t2t1,y)+0.2×fA(x+t2t1,y-t2t1)+0.09×fA(x-2⁢t2t1,y+2⁢t2t1)(3)

The phase difference distribution estimation unit145estimates a wavefront after the certain period of time t2in accordance with the calculation result. The wavefront control unit136adjusts a phase of the wavefront in accordance with the phase difference distribution estimated by the phase difference distribution estimation unit145. Specifically, the wavefront control unit136controls the wavefront shaping unit133such that the wavefront shaping unit133adds an opposite phase of an estimated phase difference to the wavefront.

Operation of System

Next, the estimation method according to the present embodiment will be described.

FIG.7is a flowchart illustrating an operation of the control information generation unit138according to the first embodiment.

The atmospheric layer calculation unit142first substitutes −q, which is a minimum value of values that dy can take, for a slide amount dy (step S1). Then, the atmospheric layer calculation unit142repeatedly performs step S3to step S8while dy≤q is satisfied (step S2).

The atmospheric layer calculation unit142substitutes −p, which is a minimum value of values that dx can take, for dx (step S3). The atmospheric layer calculation unit142repeatedly performs processing of step S5to step S7while dx≤p is satisfied (step S4). The atmospheric layer calculation unit142slides the phase difference distribution B by the two-dimensional slide amount (dx, dy) in accordance with the phase difference distribution A and the phase difference distribution B recorded in the phase difference distribution storage unit141, thereby calculating a cross-correlation value between the phase difference distribution A and the phase difference distribution B (step S5). The atmospheric layer calculation unit142records the calculated cross-correlation value in the atmospheric layer calculation result storage unit143in association with a slide amount (dx, dy) at this time (step S6). The atmospheric layer calculation unit142adds 1 to the value of dx (step S7).

When performing the processing of step S5to step S7until the slide amount dx reaches p, the atmospheric layer calculation unit142adds 1 to the value of dy (step S8).

That is, the atmospheric layer calculation unit142calculates cross-correlation values between phase difference distributions in all the two-dimensional slide amounts in the range of −p≤dx≤p and −q≤dy≤q in the processing in step S1to step S8.

Then, the atmospheric layer calculation unit142calculates a standard deviation of the most recently calculated cross-correlation values and average values of the cross-correlation values for each of the two-dimensional slide amounts (step S9). The atmospheric layer calculation unit142selects an average value that is at least a constant multiple of the most recently calculated standard deviation from the average values, and records the selected average value and a two-dimensional slide amount associated to the selected average value, in the estimation use data storage unit144(step S10).

The phase difference distribution estimation unit145estimates a phase difference distribution after a certain period of time from the phase difference distribution A recorded in the phase difference distribution storage unit141and the two-dimensional slide amount associated to the average value selected by the atmospheric layer calculation unit142in step S10(step S11). Then, the phase difference distribution estimation unit145generates control data in accordance with the estimation result and outputs the control data to the wavefront control unit136(step S12).

Actions and Effects

In this way, according to the present embodiment, one of two phase difference distributions having different observation times is slid with different displacement amounts, and a cross-correlation value between the two phase difference distributions is calculated for each of the displacement amounts. Then, in accordance with an average value and a standard deviation of the cross-correlation values, a displacement amount in which a cross-correlation value becomes relatively large and the cross-correlation value are selected. This displacement amount is an index of the velocity of an atmospheric layer. The cross-correlation value in this displacement amount represents an index of the magnitude of the influence of the atmospheric layer on an optical signal. So, an atmospheric layer that affects an optical wireless signal is estimated by using this data, so that a phase difference distribution after a certain period of time can be estimated, and a control error in wavefront shaping can be reduced.

OTHER EMBODIMENTS

Hitherto, the embodiments of the present disclosure have been described in detail with reference to the drawings, but the specific configuration is not limited to the above description, and various design changes and the like can be made in a range without departing from the gist of the present disclosure.

The communication apparatus1according to the aforementioned embodiment corrects the influence of the atmosphere on the wavefront of an optical signal, but may correct the wavefront of an optical signal that propagates through a space other than the atmosphere. For example, when an optical signal propagates through a space filled with a medium other than air, such as underwater, the communication apparatus1may estimate a layer of the medium and the velocity of the layer in the same manner as in the present method and correct the optical signal.

The phase difference distribution storage unit141may record three or more phase difference distributions. In this case, the atmospheric layer calculation unit142selects two pieces of data from data recorded in the phase difference distribution storage unit141so that a detected time interval is constant. For example, when phase difference distribution data having a constant observation time interval are recorded as A0, A1, A2, A3, A4. . . in the order of earliest observation time, the atmospheric layer calculation unit142may select A0and A2or A1and A3, or may select A0and A3or A1and A4. At this time, the update time interval t1needs to be a difference between observation times of the two pieces of data selected by the atmospheric layer calculation unit142.

The phase difference distribution storage unit141, the atmospheric layer calculation result storage unit143, and the estimation use data storage unit144may be external databases, and the atmospheric layer calculation unit142and the phase difference distribution estimation unit145may acquire data from the external database.

Furthermore, the atmospheric layer calculation unit142and the phase difference distribution estimation unit145may not operate in cooperation with each other, and for example, the phase difference distribution estimation unit145may operate independently on the basis of data recorded in the estimation use data storage unit144.

The atmospheric layer calculation unit142calculates a cross-correlation value between phase difference distributions, but it may be calculated by an equation that divides Equation (1) above by the number of terms used in a sum calculation. In this case, since it is not necessary to make the number of terms used in the sum calculation the same depending on the value of the two-dimensional slide amount (dx, dy), values of p and q for determining the range of dx and dy are required to satisfy p≤n and q≤m, respectively.

Furthermore, the atmospheric layer calculation unit142selects an average value that is at least a constant multiple of a standard deviation of phase difference distributions among average values of cross-correlation values between the phase difference distributions, but the selection criterion may not be a constant multiple of the standard deviation. For example, the average value may be selected on the basis of a value calculated by a dispersion of the average value, or an average value of a certain constant or more may be selected without using a statistical value.

The control information generation unit includes a central processing unit (CPU) (a processor), a memory, an auxiliary storage device, and the like connected by a bus, and serves as a device including an atmospheric layer calculation unit and a phase difference distribution estimation unit by executing a program. All or a part of the functions of the phase difference distribution estimation device may be implemented by using hardware (a circuitry) such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The program may be recorded in a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disc, a ROM, or a CD-ROM, or a storage device such as a hard disk incorporated in a computer system. The program may be transmitted via an electrical communication line.

REFERENCE SIGNS LIST

1Communication apparatus10Signal output unit11Transmission-side oscillation light output unit12Optical modulation unit13Spatial optical communication unit14Reception-side oscillation light output unit15Optical demodulation unit16Signal input unit131Antenna132Focus adjustment unit133Wavefront shaping unit134A,134B Half mirror135Wavefront detection unit136Wavefront control unit137Optical axis adjustment unit138Control information generation unit141Phase difference distribution storage unit142Atmospheric layer calculation unit143Atmospheric layer calculation result storage unit144Estimation use data storage unit145Phase difference distribution estimation unit