JPS6137010Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention sequentially transmits signals from a large number of holograms.
This relates to a device that reads data while keeping the timing. In other words, the present invention relates to a device for quickly and error-free reading of signals reproduced from a hologram by taking advantage of the fact that a large number of reproduced signals can be obtained simultaneously from a hologram. Magnetic tapes, magnetic drums, magnetic disks, etc. are currently used as large-capacity storage devices. In most of these, signals are recorded sequentially, and when reading them out, the signals are usually read out sequentially in time series. For the timing for reading, an external clock is used, or a method of generating the clock from the read signal by using magnetization reversal is used. It is also being considered to provide magnetic disks with tracks on which timing signals are recorded in addition to tracks on which ordinary signals are recorded. Like magnetic storage devices, holograms can also be used as memories with large storage capacities. A hologram differs from a magnetic storage device in that a large number of read signals can be obtained at the same time, and it is possible to record normal signals and timing signals in one hologram. The purpose of the present invention is to provide a device that can read information from a one-dimensional Fourier transform hologram by quickly knowing that the hologram and the readout light match, that the hologram can be read, and reading each bit without error. . A one-dimensional Fourier transform hologram is a hologram obtained by Fourier transforming information arranged in one dimension.
This has the advantage that components such as the spatial modulator and photodetector and the optical system can be simplified. A one-dimensional image Fourier transform hologram in which there is an imaging relationship between the hologram and an input pattern (or reproduced image) in a direction perpendicular to the Fourier transform direction is also used for storing time-series signals. (For example, Showa
Proceedings of the 23rd Applied Physics Association Conference 1951
(There is a description of the one-dimensional image Fourier transform hologram in "One-dimensional image Fourier transform hologram for recording time-series information" on page 97) Figure 1 shows the reproduction optical system of the one-dimensional image Fourier transform hologram. . 11 is a reading light, 12
1 is a film recording a hologram, 13 is a hologram to be read out, 14 is a cylindrical lens for reproduction, 1

[Table] The detection signal corresponding to bit A is shown by a curve 21, the detection signal corresponding to bit B is shown by a curve 22, and the threshold value for distinguishing between 1 and 0 is shown by a broken line 23. If the times at which the signals 21 and 22 cross the threshold 23 are t ₁ , t ₂ , t ₃ , t ₄ , t ₅ , t ₆ as shown in the figure, then t ₁ t ₂
If the signal is read once between t ₃ t ₄ and t ₄ t ₅ , it will match the previously recorded signal. However, between t ₂ t ₃ and t ₅ t ₆ , the signal is misread in the transition region. When a large number of bits are reproduced in parallel from one hologram, there are differences in the rise and magnitude of the analog output of each bit. Possible causes of this include the distribution of the amount of light for each bit of the input pattern during hologram photography and the arrangement of the reproduction optical system. To determine the timing of a hologram, the hologram to be read is provided with two timing signals that alternately become 1, and both detection signals are compared at the analog level, and when one becomes larger than the other, it is used as a timing reference. A differential timing image reproduction method (``Holographic issue retrieval device 2 hologram readout method'' Proceedings of the 1975 National Conference of the Institute of Electronics and Communication Engineers, Vol. 4, P110) is used.
The example in Figure 2 is not a signal that becomes 1 alternately, but
This is a signal in which 1 and 0 of A and B are inverted between t _{2 and} t ₃ . Between the transition regions t ₂ t ₃ , both detection signals are determined to be 0, resulting in signal misreading. Also,
There is a readout method that determines that the hologram has come to a readable position when a prerecorded timing signal and a detected signal match in the reproduced image. However, this method also requires that each bit of the reproduced image change in the same way over time as the film moves. However, as mentioned above, the temporal changes in each bit often differ. In particular, the arrangement of the cylindrical lens 14 shown in FIG.
If the arrangement is rotated around the optical axis, the reconstructed image and the photodetector will be misaligned. Figure 3 shows the misalignment between the photodetector and the reconstructed image.If there is a problem with the arrangement of the optical system, both the reconstructed image and the photodetector are usually in a straight line as shown in the figure. . 3
1 is a photodetector array, 32 is a reproduced image, 33, 34
are the bits at both ends of the photodetector array. When the film advances in the direction of arrow 16 in FIG. 1, the reconstructed image moves in the opposite direction. Therefore, if the reconstructed image and the photodetector are arranged as shown in FIG. Of the image, the bits detected by the 33rd photodetector are detected earlier than the bits detected by the 34th photodetector. Therefore, if a timing signal is recorded in the bit detected by the 33rd detector, even if the pre-recorded timing signal and the detected timing signal match, the other reproduced bits will be detected by the photodetector. Sometimes it doesn't reach the correct position.
This will be explained using FIG. 4. Figure 4 shows
It shows temporal changes in the detection output of bits at both ends of the reproduced image. 41 is a threshold value for distinguishing between 1 and 0, and when the bits at both ends of the reproduced image are 1, the signals detected by the detectors 33 and 34 in FIG. 3 are 42 and 43, respectively. Let T ₁ , T ₂ , T ₃ , and T ₄ be the times at which the signals 42 and 43 cross the threshold 41 . The bits at both ends are both recognized as 1 because
It is between T _{2 and} T ₃ , and in this interval, all reproduced images can be read correctly. This means that the reconstructed image is
(The detection signal is represented by 42) is detected early, and the detector 34 (detection signal 43) detects it late. Therefore, based on signal 42, T ₁ T ₃
When detecting a signal between T 1 and T 2, an error in reading the signal occurs between T ₁ and T ₂ . Also, the signal 4 from the detector 34
The signal readable area obtained only from 3 is T ₂ T ₄ , and in this case as well, signal reading errors occur between T ₃ T ₄ . Therefore, it is necessary to read the signals between T _{2 and} T ₃ when both the signals of the detectors 33 and 34 (detection signals 42 and 43) become readable. In other words,
The signals must be read when the signals at both ends of the reconstructed image become readable. For this purpose, it is necessary to find out as soon as possible without error that all bits of the reconstructed image can be read when the position of the reconstructed image is rotated relative to the detector.
Timing signals for determining whether the reproduced image can be read may be provided at both ends of the reproduced image. Furthermore, in the present invention, by providing timing signals at both ends of the reproduced image, it is also possible to set the optimum readout time for each bit of the detector.
The reconstructed image moves as the film on which the hologram is recorded moves, and if the reconstructed image and the detector are tilted as shown in FIG. The time at which the reproduced image can be optimally read differs depending on the case. In other words, for 33, the optimum read time is earlier, for 34, the optimum read time is later than 33, and for bit positions between 33 and 34, the optimum read time is the intermediate time between the respective optimum read times of 33 and 34. It's time. Both the reconstructed image in a one-dimensional Fourier transform hologram and the detector are linear, and the deviation between the two is often a relative minute rotation. In the present invention, by providing timing signals for the bits at both ends, the optimum read time for the intermediate bit can also be set by proportionally distributing the difference between the optimum read times for the bits at both ends. The present invention provides timing signals for controlling the readout of each hologram at both ends of the reproduced image.This allows the signal to be read out without error even if the reproduced image and the detector are relatively misaligned. Can be done.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the arrangement of the optical system when obtaining a reconstructed image from a one-dimensional image Fourier transform hologram, and Figure 2 is a diagram showing how the signal detected by the photodetector changes over time. , Figure 3 shows the relationship between the positions of the reproduced image and the detector when there is an error in the arrangement of the reproduction optical system, and Figure 4 shows the detection output of the bits at both ends of the reproduced image. It is a figure showing a temporal change of. In the figure, 11 is a reading light, 12 is a film recording a hologram, 13 is a hologram being read out, 14 is a cylindrical lens for reproduction, 15 is a photodetector, 16 is a moving direction of the film, 31 is a photodetector , 32 are reproduced images, and 33 and 34 are bits at both ends of the photodetector, respectively.

Claims (1)

[Scope of utility model registration request] Records bit images arranged in one dimension.
A one-dimensional hologram reading device for sequentially reading signals from a medium in which holograms are arranged, characterized in that each hologram is provided with a timing signal for controlling readout, and the timing signal is located at both ends of a reproduced image. .