JP2016164816A - Holographic memory device, optical system used for the same, and intensity distribution conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To convert a non-uniform intensity distribution into a desired intensity distribution with high light use efficiency, in an optical system using a coherent light beam.SOLUTION: The optical system using the coherent light beam includes a light source which emits a light beam, an intensity distribution conversion part which converts the intensity distribution of the light beam emitted from the light source, and an irradiation part which irradiates a desired object with the light beam emitted from the intensity distribution conversion part. The intensity distribution conversion part includes a phase modulation part which performs the phase modulation and collection of the light beam and a diffraction element which is arranged in the phase modulation part. Thus, the intensity distribution can be converted while keeping the high light use efficiency. Even when the intensity distribution is complex, the intensity distribution can be converted inexpensively and easily.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an apparatus and method for converting the intensity distribution of coherent light.

  As a background art in this technical field, there is JP 2012-243355 A (Patent Document 1). Japanese Patent Laid-Open No. 2004-228688 has a problem that “in an optical information recording / reproducing apparatus that records information on a hologram recording medium or reproduces information from a hologram recording medium, recording / reproduction is performed using a light beam with a non-uniform light intensity distribution. As a solution, “the intensity distribution of the signal light is detected by a photodetector and the intensity distribution conversion element is used based on the detected information.” Information is recorded or reproduced by controlling the intensity distribution of the laser beam and irradiating the hologram recording medium with the laser beam having the intensity distribution controlled. "

  There is also JP-A-8-94839 (Patent Document 2). Japanese Patent Application Laid-Open No. 2004-228561 has a problem that “in the light beam conversion device, an incident light beam having a non-uniform energy distribution is converted into a light beam having a substantially uniform energy distribution on the exit surface”. As a means, “a light beam conversion device (or beam homogenizer) 10 is a holographic element having an array (matrix) facet 12 which is a sub-hologram. A light beam 14 having a non-uniform energy distribution is applied to the holographic element 10. When passed, an exit beam 22 having a substantially uniform energy distribution is obtained on the exit surface or target region 16 by superimposing facets having a low energy distribution. "

  Herwig Kogelnik, “Coupled Wave Theory for Thick Hologram Gratings”, Bell System Technical Journal Volume 48, Issue 9, pages 2909-2947, November 1969 (Non-Patent Document 1) describes Kogelnik's coupled wave theory. Yes.

  Masanori Takabayashi and Atsushi Okamoto, “Self-referential holography and its applications to data storage and phase-to-intensity conversion”, Optics Express, Vol. 21, Issue 3, pp. 3669-3681 (2013) 2) describes self-referencing holography.

JP 2012-243355 A JP-A-8-94839

Herwig Kogelnik, “Coupled Wave Theory for Thick Hologram Gratings”, Bell System Technical Journal Volume 48, Issue 9, pages 2909-2947, November 1969 Masanori Takabayashi and Atsushi Okamoto, “Self-referential holography and its applications to data storage and phase-to-intensity conversion”, Optics Express, Vol. 21, Issue 3, pp. 3669-3681 (2013)

  In a holographic memory that is an optical information recording system, signal light and reference light interfere with each other, and the interference fringes are recorded as a hologram on an optical information recording medium. However, the intensity of the signal light and reference light is not uniform. May cause deterioration of recording / reproducing performance. This non-uniform intensity distribution occurs, for example, because the laser light emitted from the semiconductor laser chip has a distribution with a strong intensity at the center. Further, it occurs due to dust and dirt adhering to the optical component, scratches and processing residue, diffraction at the opening, interference with stray light, and the like. This problem becomes a problem because, for example, in an optical system using a coherent light beam such as a laser processing machine, it causes a decrease in processing accuracy and processing efficiency.

  As a method for uniforming the intensity distribution, for example, Patent Document 1 uses an intensity distribution correction element having a transmittance distribution. However, this method has a problem that the light utilization efficiency is lowered because the intensity in the light beam is adjusted to a weak part.

  For example, in Patent Document 2, the intensity distribution is made uniform by a holographic element. However, when the incident intensity distribution is complicated, the production of the holographic element takes time to calculate the diffraction grating pattern and increases the cost. There are challenges.

  In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above-mentioned problems. To give an example, an optical system using a coherent light beam is a light source that emits a light beam, and a light beam emitted from the light source. An intensity distribution conversion unit that converts the intensity distribution and an irradiation unit that irradiates a desired object with the light beam emitted from the intensity distribution conversion unit, the intensity distribution conversion unit performs phase modulation and condensing of the light beam The phase modulation unit and a diffraction element disposed in the phase modulation unit are used.

According to the present invention, it is possible to convert the intensity distribution while maintaining high light utilization efficiency. Furthermore, even when the intensity distribution is complicated, the intensity distribution can be easily converted at a low cost.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is a block diagram showing a holographic memory device in Embodiment 1. FIG. 1 is a schematic diagram showing an optical system at the time of recording in a holographic memory device in Example 1. FIG. 1 is a schematic diagram showing an optical system during reproduction of a holographic memory device in Example 1. FIG. It is a conceptual diagram which shows the intensity distribution conversion method in Example 1. FIG. FIG. 3 is a schematic diagram illustrating the principle of intensity distribution conversion in the first embodiment. It is an operation | movement flow which performs intensity distribution conversion in Example 1. FIG. FIG. 3 is a schematic diagram illustrating an optical system at the time of obtaining an intensity distribution before conversion of the holographic memory device according to the first embodiment. 1 is a schematic diagram showing an optical system for producing an intensity distribution conversion element in Example 1. FIG. It is a figure which shows the phase distribution used for intensity distribution conversion element in Example 1, and phase modulation element manufacture. 1 is a schematic diagram illustrating an optical system that performs phase detection in Embodiment 1. FIG. It is a figure which shows the phase distribution used for intensity distribution conversion element in Example 1, and phase modulation element manufacture. It is a conceptual diagram which shows the intensity distribution conversion method in Example 2. FIG. It is an operation | movement flow which performs intensity distribution conversion in Example 2. FIG. FIG. 6 is a schematic diagram showing an optical system at the time of recording with an intensity distribution before conversion of the holographic memory device in Example 2. 6 is a schematic diagram illustrating an optical system during recording in a holographic memory device according to Embodiment 3. FIG. FIG. 10 is a schematic diagram showing another optical system at the time of recording in the holographic memory device in Example 3. 6 is a schematic view showing an optical system for producing an intensity distribution conversion element in Example 4. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  The intensity distribution of the signal light in the holographic memory greatly affects the SN (Signal to Noise ratio) which is an index indicating the quality of the reproduction signal. In particular, a reading error is likely to occur in a portion where the light intensity is low. For this reason, if the intensity distribution is not uniform, a portion having a low light intensity is generated, and the reading error rate is increased accordingly. On the other hand, when the intensity distribution is uniform, the reading error rate can be reduced, and a high SN can be obtained. In this embodiment, the intensity distribution is made uniform by using an intensity distribution converting optical system. A holographic memory device equipped with an intensity distribution conversion optical system will be described below.

  FIG. 1 is a block diagram showing a configuration of a holographic memory device 10 that records / reproduces digital information as an optical information recording medium 1 as a hologram.

  In FIG. 1, the holographic memory device 10 is connected to an external control device 91 via an input / output control circuit 90. In the case of recording, the holographic memory device 10 receives an information signal to be recorded from the external control device 91 by the input / output control circuit 90. When reproducing, the holographic memory device 10 transmits the reproduced information signal to the external control device 91 by the input / output control circuit 90.

The holographic memory device 10 includes an optical system 11, a reproduction optical system 12, a disk cure optical system 13, a disk rotation angle detection optical system 14, and a rotation motor 50, and the optical information recording medium 1 is a rotation motor 50. It is the structure which can be rotated by.
The optical system 11 plays a role of irradiating the optical information recording medium 1 with reference light and signal light and recording digital information on the recording medium as a hologram. At this time, an information signal to be recorded is sent by a controller 89 to a spatial light modulator (to be described later) in the optical system 11 via a signal generation circuit 86, and the signal light is modulated by the spatial light modulator.

  When reproducing the information recorded on the optical information recording medium 1, the reproduction optical system 12 connected to the access control circuit 81 emits the reference light emitted from the optical system 11 in the direction opposite to that at the time of recording. It converts so that it may inject into the information recording medium 1. FIG. Reproduction light reproduced by the reproduction reference light is detected by a photodetector described later in the optical system 11, and a signal is reproduced by the signal processing circuit 85.

  The irradiation time of the reference light and the signal light applied to the optical information recording medium 1 can be adjusted by controlling the opening / closing time of the shutter in the optical system 11 via the shutter control circuit 87 by the controller 89.

  The disc cure optical system 13 plays a role of generating light used for pre-cure and post-cure of the optical information recording medium 1. Precure is a pre-process of irradiating predetermined light in advance before irradiating the desired position with reference light and signal light when recording information at a desired position in the optical information recording medium 1. Post-cure is a post-process in which information is recorded at a desired position in the optical information recording medium 1 and then irradiated with a predetermined light so that additional recording cannot be performed at the desired position.

  The disk rotation angle detection optical system 14 is used to detect the rotation angle of the optical information recording medium 1. When the optical information recording medium 1 is set to a predetermined rotation angle, a signal corresponding to the rotation angle is detected by the disk rotation angle detection optical system 14, and the controller 89 controls the disk rotation motor by using the detected signal. The rotation angle of the optical information recording medium 1 can be controlled via the access control circuit 88.

  A predetermined light source driving current is supplied from the light source driving circuit 82 to the light sources in the optical system 11, the cure optical system 13, and the disk rotation angle detection optical system 14, and each light source emits a light beam with a predetermined intensity. be able to.

  The rotation motor 50 is provided with a mechanism capable of sliding the position in the radial direction of the optical information recording medium 1, and position control is performed via a disk rotation motor / access control circuit 88.

  By the way, the recording technique using the principle of hologram angle multiplexing tends to have a very small tolerance for the deviation of the reference beam angle. Therefore, a mechanism for detecting the deviation amount of the reference beam angle is provided in the optical system 11, a servo control signal is generated by the servo signal generation circuit 83, and the deviation amount is corrected via the servo control circuit 84. It is necessary to provide the holographic memory device 10 with a servo mechanism for this purpose.

  The optical system 11, the disk cure optical system 13, and the disk rotation angle detection optical system 14 may be simplified by combining several optical system configurations or all optical system configurations into one.

  FIG. 2 shows a recording principle in an example of a basic optical system configuration of the optical system 11 in the holographic memory device 10. The light beam emitted from the light source 201 passes through the collimator lens 202 and enters the shutter 203. When the shutter 203 is open, after the light beam passes through the shutter 203, the intensity ratio of the p-polarized light and the s-polarized light is adjusted to a desired ratio by the polarization direction conversion element 204 composed of, for example, a half-wave plate. Thus, the polarization direction is controlled. Thereafter, the light beam enters a polarization beam splitter 205 that is an optical element that separates the light beam into the signal light 206 and the reference light 207.

The light beam that has passed through the polarization beam splitter 205 functions as signal light 206, and after the light beam diameter is expanded by the beam expander 208, the light beam is arranged near the condensing point of the phase modulation element 209, the relay lens 210, and the relay lens 210 The intensity distribution conversion element 229 and the polarization beam splitter 211 that have been transmitted are incident on the spatial light modulator 212. The spatial light modulator 212 is a device that spatially modulates light intensity, and uses this to add two-dimensional digital information to signal light. -
The signal light to which information is added by the spatial light modulator 212 is reflected by the polarization beam splitter 211 and passes through the relay lens 213 and the spatial filter 214. Thereafter, the signal light is irradiated onto the optical information recording medium 1 by the objective lens 215 and condensed.

  On the other hand, the light beam reflected by the polarization beam splitter 205 acts as reference light 207, and is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 216, and then the mirror 217 and the light beam of the reference light. The light enters the galvano mirror 219 via an iris 226 defining a shape and a mirror 218. Since the angle of the galvanometer mirror 219 can be set by the actuator 220, the incident angle of the reference light incident on the optical information recording medium 1 after passing through the scanner lens 227 including the lens 221 and the lens 222 is set to a desired angle. Can do.

  By causing the signal light 206 and the reference light 207 to enter the optical information recording medium 1 so as to overlap each other, an interference fringe pattern is formed in the optical information recording medium 1, and this pattern is written into the optical information recording medium 1. To record information. In addition, since the incident angle of the reference beam 207 incident on the optical information recording medium 1 can be changed by the galvanometer mirror 219, recording by angle multiplexing is possible.

  Hereinafter, among the holograms recorded in the same area while changing the reference beam angle, a hologram corresponding to each reference beam angle is called a page, and a set of pages angle-multiplexed in the same area is called a book. To do.

  FIG. 3 shows a reproduction principle in an example of a basic optical system configuration of the optical system 11 in the holographic memory device 10. When reproducing the recorded information, only the reference light 207 is obtained using the polarization direction conversion element 204, and the polarization direction is rotated 90 degrees with respect to the time of recording using the polarization direction conversion element 216. The reference light is incident on the galvano mirror 219 via the mirror 217, the iris 226, and the mirror 218, is set to a desired reference light angle, and then enters the optical information recording medium 1. The light beam transmitted through the optical information recording medium 1 is reflected by a galvanometer mirror 224 whose angle can be set, and becomes reference light for reproduction. The reproduction light 228 diffracted by the reproduction reference light passes through the objective lens 215, the relay lens 213, and the spatial filter 214. Thereafter, the reproduction light passes through the polarization beam splitter 211 and enters the photodetector 225, and the recorded signal can be reproduced. As the photodetector 225, for example, an image sensor such as a CMOS image sensor or a CCD image sensor can be used, but any element may be used as long as page data can be reproduced.

  Hereinafter, the features of this embodiment will be described in more detail.

  The feature of the present embodiment is that an intensity distribution conversion element 229 for making the intensity distribution of laser light substantially uniform is disposed. The nonuniform intensity distribution occurs, for example, because the laser light emitted from the chip has a distribution with a strong intensity at the center. Further, it occurs due to dust and dirt adhering to the optical component, scratches and processing residue, diffraction at the opening, interference with stray light, and the like. On the other hand, in this embodiment, the intensity distribution is made substantially uniform by using the phase modulation element 209, the relay lens 210, and the intensity distribution conversion element 229. The principle and method will be described below.

  First, the principle of intensity distribution conversion will be described. FIG. 4 is a conceptual diagram for explaining the concept of the intensity distribution conversion principle. (A) is intensity distribution before conversion, (B) is intensity distribution uniformization using the transmittance filter of patent document 1, (C) is intensity distribution equalization of an intensity | strength of a present Example. It is a conceptual diagram regarding each intensity | strength at the time of performing using the distribution conversion method. In the intensity distribution conversion method of Patent Document 1, the non-uniform intensity distribution shown in (A) is reduced to an intensity distribution so that it becomes a post-conversion intensity distribution 904 that matches the minimum intensity value as shown in (B). Conversion is performed using a filter having an inversely proportional transmittance. Since there is an intensity portion 901 that is not used, light utilization efficiency is reduced. On the other hand, in the intensity distribution conversion method of this embodiment, as shown in (C), the intensity distribution of the intensity portion 902 to be converted is set so that the average value 905 of the intensity distribution before conversion becomes the intensity distribution after conversion. Move the light intensity of the strong part to the weak part. High light utilization efficiency can be realized by this method.

  FIG. 5 is a schematic diagram of an optical system used to explain the principle of intensity distribution conversion. The phase modulation element 209, the relay lens 210, the intensity distribution conversion element 229, and the spatial light modulator in the optical system 11 shown in FIG. Only the portion 212 is shown, and the phase modulation element 209, the Fourier lenses 103 and 104 in the relay lens 210, and the spatial light modulator 212 constitute a 4f system. For simplicity of explanation, the phase modulation element 209 is assumed to be capable of arbitrary phase modulation at an arbitrary position on the element. The intensity distribution conversion unit includes a phase modulation unit and an intensity distribution conversion element. The phase modulation unit includes a relay lens 210 including a phase modulation element 209 and Fourier lenses 103 and 104. Since the intensity distribution conversion element 229 is arranged in the vicinity of the point, the intensity distribution conversion unit has a phase modulation unit and an intensity distribution conversion element arranged in the phase modulation unit.

  As shown in FIG. 5A, the signal light 206 is incident on the phase modulation element 209. When light emitted from an arbitrary point of the phase modulation element 209 is considered as a spherical wave in accordance with Huygens' principle, the emitted light from a certain point becomes parallel light by the Fourier lens 103 and enters the intensity distribution conversion element 229. The intensity distribution conversion element 229 is a volume type holographic optical element, and emits parallel light incident from an arbitrary angle within a predetermined range as parallel light of almost all angles within the predetermined angle range. Therefore, one point of light on the phase modulation element 209 is dispersed on the entire surface of the spatial light modulator 212. By adjusting the phase distribution of the phase modulation element 209, the intensity distribution on the spatial light modulator 212 can be made uniform. Hereinafter, the relationship between the phase distribution of the phase modulation element 209 and the intensity distribution on the spatial light modulator 212 will be described in detail.

First, as shown in FIG. 5B, the intensity at two points B1 and B2 on the spatial light modulator 212 of light emitted from two points A1 and A2 on the phase modulation element 209 will be considered. The intensity distribution conversion element 229 is a diffractive element in which a hologram of parallel light beams from light emitted from almost all points on the phase modulation element 209 exists. Here, the two lights emitted from A1 and A2 are used. Pay attention to the hologram of parallel light made by. When light emitted from two points A1 and A2 becomes parallel light by the Fourier lens 103 and enters the intensity distribution conversion element 229, transmitted light and diffracted light are generated by Bragg diffraction of the hologram, respectively. The transmitted light and diffracted light emitted from A1 reach two points B1 and B2 on the spatial light modulator 212, respectively (FIG. 5B), and the transmitted light and diffracted light emitted from A2 are respectively B2 and B1 are reached (FIG. 5C), and these two lights interfere with each other at B1 and B2. The diffracted light of the hologram that satisfies the Bragg condition has a phase difference of + π / 2 or −π / 2 with respect to the transmitted light. About this, it can derive | lead-out from the formula described in the nonpatent literature 1, for example. From the above, the light intensity at B1 and B2 can be calculated by the following equation (1) in consideration of the interference between the transmitted light and diffracted light from A1 and A2.

Here, i is an imaginary unit √-1, and the sign of ± is determined by the hologram recording condition of the diffraction element. Further, a1, a2, b1, and b2 are complex amplitudes of light at A1, A2, B1, and B2, respectively, and the light intensity at these positions can be calculated as | a1 | ^ 2.

When phase differences between recording and reproduction (phase during reproduction−phase during recording) δ1 and δ2 are given to A1 and A2, Equation (1) expresses this phase difference, and the following Equation (2)

And the light intensity is expressed by the following formula (3) under the recording condition where the sign of i is “+”.

Can be written. From this equation, it can be seen that if δ1 and δ2 are appropriately selected, the light intensities of B1 and B2 can be changed with respect to A1 and A2.

  If the phase at the two points A1 and A2 on the phase modulation element 209 is the same as that at the time of recording, that is, δ1 = δ2, the light intensities at B1 and B2 are also the same. If δ1 = 0 and δ2 = π / 2, the light intensity of B2 is stronger than that of B1, and the light intensity of A1 moves to A2. Conversely, if δ1 = π / 2 and δ2 = 0, the light intensity of B2 is weaker than B1, and the light intensity of A2 moves to A1. From the above, the light intensity can be moved between any two points on the phase modulation element 209 with the configuration of FIG.

Further, when the light intensity is differentiated by the phase difference δ1, δ2 from the recording at each corresponding point, the following equation (4) is obtained.

It can be seen that | b1 | ^ 2 and | b2 | ^ 2 monotonically increase with respect to δ1 and δ2 in the range of 0 to π / 2. Therefore, when the signal light 206 is non-uniform, the phase of the portion where the intensity is to be increased is set to a value larger than the phase of the portion where the intensity is to be decreased, so that the light intensity is moved and the intensity distribution is made uniform. It can be carried out.

When the expression (1) is expanded with respect to the complex amplitudes a1,..., An of all points on the phase modulation element 209 and the complex amplitudes b1,. )

It can be seen that the light intensity can be moved between any two points in accordance with the phases of a1,.

  From the above, the light intensity on the spatial light modulator 212 can be uniformly converted by determining the phase distribution of the phase modulation element 209 in advance using the phase modulation element 209, the intensity distribution conversion element 229, and the Fourier lenses 103 and 104. It has been shown.

  Next, the intensity distribution conversion method in the holographic memory device 10 will be described according to the operation flow.

  FIG. 6 shows an operation flow for performing intensity distribution conversion. In FIG. 6, first, steps 401 and 402 are processes for acquiring the intensity distribution before conversion, and will be described with reference to FIG. FIG. 7 shows a configuration in which a polarization direction conversion element 230 is added except for the intensity distribution conversion element 229, as compared with the optical configuration of FIG. In FIG. 7, the polarization of the signal light 206 is adjusted by the polarization direction conversion element 230 (401), and the signal light 206 is directly incident on the photodetector 225. Thereby, the intensity distribution on the spatial light modulator 212 is measured (402).

  Subsequently, in step 403 of FIG. 6, the acquired intensity distribution is evaluated. If the desired performance is not achieved, the intensity distribution conversion element 229 is manufactured as a reject using the intensity distribution conversion element manufacturing optical system 600 described later (406). Thereafter, a phase pattern of the phase modulation element 209 is obtained using a phase detection optical system 618 described later, and the phase modulation element 209 is manufactured (409).

  Next, the produced intensity distribution conversion element 229 and phase modulation element 209 are installed near the condensing point of the relay lens 210 in the optical system 11 of FIG. 5 (410). Then, the position / angle is adjusted, and whether or not the desired intensity distribution conversion performance is obtained is evaluated using the intensity distribution acquired by the photodetector 225 (411). If the desired performance does not appear even if the position and angle are adjusted, the result is “Reject”, which is a detailed step of the phase modulation element manufacturing step 409, which will be described later, and a phase modulation element 209 having a phase pattern conjugate to the phase pattern. Returning to step 807 for manufacturing the phase modulation element, the phase modulation element is manufactured again. If the desired performance is obtained, as an Accept, the polarization of the signal light is adjusted to return to the original state (412).

  By the above procedure, the intensity distribution of the signal light 206 of the holographic memory device 10 can be converted to low cost, and the error occurrence rate can be reduced to obtain a high SN. Further, in Patent Document 2, it is necessary to repeatedly calculate the diffraction grating pattern according to the intensity distribution before the conversion, whereas in the method of this embodiment, the phase modulation pattern can be easily calculated using Equation (5). Therefore, it can be easily realized as compared with the method of Patent Document 2.

  Next, a method for manufacturing the intensity distribution conversion element 229 in step 406 of FIG. 6 will be described. FIG. 8 is a schematic diagram showing an intensity distribution conversion element manufacturing optical system. This optical system is constructed independently of the holographic memory device 10.

  First, the configuration of the intensity distribution conversion element manufacturing optical system 600 will be described. The light beam emitted from the light source 601 passes through the collimator lens 602 and enters the shutter 610. When the shutter 610 is open, the light beam passes through the polarization direction conversion element 611, the relay lens 603, and the spatial filter 604 and enters the polarization beam splitter 606. By making the polarization direction conversion element 611 into s-polarized light, the light beam is incident on the quarter-wave plate 612 and the phase modulator 605. The light beam incident on the phase modulator 605 is made to have a substantially uniform intensity / phase distribution using the spatial filter 604. The phase modulation pattern 708 displayed on the phase modulator 605 has a reference phase distribution. This distribution is intentionally a distribution having a somewhat high spatial frequency of 0 to π. The reason is that since the M # of the recording medium is finite during hologram recording, effective hologram recording can be realized by making the intensity distribution on the Fourier plane substantially uniform. The phase modulator 605 is a reflective spatial light modulator and can multi-value modulate the two-dimensional spatial phase distribution of incident light in a range of at least 0 to 3π / 2. After conversion to p-polarized light and phase modulation by the quarter-wave plate 612 and the phase modulator 605, the light beam is incident on the hologram recording medium 105 disposed in the vicinity of the focal point using the Fourier lens 607. . Here, the phase modulator 605, the Fourier lenses 607 and 608, and the photodetector 609 constitute a 4f system.

  Using this optical system, the shutter 610 is opened for a desired time, and the hologram recording medium 105 is exposed to produce the intensity distribution conversion element 229 from the hologram recording medium 105. The intensity distribution conversion element 229 produced here is produced by light from each pixel of the phase modulator 605 interfering in the hologram recording medium 105 to generate a hologram between the pixels. This method applies the concept of self-referenced holography described in Non-Patent Document 2. Further, since the intensity distribution conversion element 229 does not require information on the intensity distribution before conversion, it can be mass-produced in advance.

  Next, a method for manufacturing the phase modulation element 209 in Step 409 of FIG. 6 will be described. The phase modulation pattern of the phase modulation element 209 needs to be prepared in accordance with a reference phase distribution that is an arbitrary phase modulation pattern used when the intensity distribution conversion element 229 is manufactured. This pattern can be calculated on the computer using equation (5).

  The following method can also be used to absorb the deviation from the ideal state of the intensity distribution conversion element 229 and the optical system calculation model, which is difficult to calculate. That is, light having a uniform intensity distribution is incident on the intensity distribution conversion element 229 produced above using the optical system of FIG. 8, and the emitted light is converted into substantially parallel light by the Fourier lens 608 and the intensity on the photodetector 609. Get the distribution. Then, the phase distribution of the phase modulator 605 is selected so that the intensity distribution substantially matches the intensity distribution before conversion measured in the flow 402 of FIG. At this time, the intensity distribution conversion element 229 converts the uniform intensity distribution into the intensity distribution before conversion. In other words, considering this in reverse, if the phase distribution on the spatial light modulator 609 is measured and a conjugate phase distribution of this phase distribution is added to the signal light, the light after passing through the intensity distribution conversion element 229 The intensity distribution should be uniform. Hereinafter, a method for manufacturing the phase modulation element 209 using this concept will be described.

In the detailed flow of the phase modulation element manufacturing step 409 in FIG. 6, first, the phase modulation pattern to be displayed on the phase modulator is calculated using the intensity distribution information before conversion (801). Then, the phase distribution is adjusted (802), and the phase modulation pattern is displayed on the phase modulator (803). Here, a method for producing a phase modulation pattern to be displayed on the phase modulator 605 will be described with reference to FIG. FIG. 9 shows a method for producing a phase modulation pattern displayed on the phase modulation element 605 when the intensity distribution conversion element is produced and when the phase modulation element is produced. When producing the intensity distribution conversion element, the reference phase distribution 705 (φref (x, y)) may be displayed as it is. On the other hand, when manufacturing the phase modulation element, it is necessary to calculate the phase distribution using the intensity distribution 701 (I (x, y)) of the signal light 206 before conversion acquired in the flow 402 of FIG. First, using the intensity distribution 701 (I (x, y)) before conversion and its substantially maximum value Imax, a phase distribution δ (x, y) is obtained as in the following equation (6).

  Next, the reference phase distribution 705 (φref (x, y)) is added to δ (x, y) to produce a phase modulation pattern 709. Therefore, the phase modulation pattern 709 is φref (x, y) + δ (x, y).

  The phase modulation pattern 709 thus obtained is displayed on the phase modulator 605 in the optical system shown in FIG. 10 (803). Here, the optical system of FIG. 10 is an optical system used when producing a phase modulation element, and is obtained by adding a later-described phase detection optical system 618 to the optical system of FIG. Next, using this optical system, the intensity distribution conversion element is regenerated (804), the intensity distribution on the photodetector 609 is acquired, and it is confirmed whether or not it substantially matches the signal light intensity distribution before conversion.

Here, when the relationship between the phase and the monotonic increase of the intensity shown in Equation (4) is approximated as a proportional relationship, the intensity distribution Iout (x, y) on the photodetector 609 becomes the phase distribution δ (x, y). It can be said that it is approximately proportional. That is, the intensity distribution Iout (x, y) on the photodetector 609 when light having a phase distribution having a phase difference δ (x, y) with respect to the reference phase is incident is obtained by using the constant C as (7)

It can be expressed. From this, the intensity distribution Iout (x, y) on the photodetector 609 should substantially match the signal light intensity distribution before conversion.

  Therefore, the intensity distribution is confirmed in step 805, and if OK, the phase distribution on the photodetector 609 is measured as Accept (806). If it is NG, it returns to 801 as Reject, calculates the phase modulation pattern, and repeats the phase distribution adjustment (802). Here, a phase detection method using the phase detection optical system 618 in FIG. 10 will be described. In FIG. 10, by adjusting the polarization direction conversion element 611, the light beam has both s-polarized light and p-polarized light components, and the p-polarized light component transmitted through the polarizing beam splitter 606 is converted into the phase detection optical system 618 and the half mirror. 619 is used to guide the light on the photodetector 609 and interfere with the emitted light 620 from the intensity distribution conversion element 229. The phase detection optical system 618 includes two mirrors 615 and 616 and an actuator 614 that moves the mirror 615 by a minute distance. By moving the mirror 615 by a minute distance, the phase is detected by a method called a phase shift method or a fringe scan method. Distribution can be detected. As the phase detection method, other methods such as a Fourier transform method may be used.

  A phase modulation element 209 having a phase pattern conjugate to the phase pattern obtained by the above method is manufactured (807, 808). In this embodiment, the phase modulation element is a transmissive type, and is an element that applies phase modulation to incident light, which is manufactured using an electron beam drawing apparatus or the like on a material such as a glass substrate. Can also be used. Further, the phase pattern of the phase modulation element has the purpose of making the phase distribution of the signal light 206 a conjugate phase distribution to the outgoing light 620 from the intensity distribution conversion element 229 in FIG. When the phase pattern of the light 206 is non-uniform, it is possible to improve the performance of uniform intensity distribution by adding a phase distribution for correcting the phase pattern.

  In the present embodiment, the intensity distribution conversion element 229 is a general-purpose element that can convert an arbitrary intensity distribution, whereas the phase modulation element 209 needs to be manufactured according to the intensity distribution before conversion. On the contrary, it is possible to make the phase modulation element 209 general-purpose and produce the intensity distribution conversion element 229 according to the intensity distribution before the conversion using the same concept. In this case, as shown in FIG. 11, the phase modulation pattern 706 at the time of manufacturing the intensity distribution conversion element may be φref (x, y) −δ (x, y).

  If φref (x, y) is a desired phase distribution by this method, the phase distribution on the spatial light modulator 212 becomes φref (x, y) and does not depend on the intensity distribution before conversion. Therefore, the phase distribution on the spatial light modulator 212 can be a desired phase distribution, which can be used, for example, as a conventional phase mask, can avoid local concentration of energy, and has a phase distribution with the highest SN. It can also be optimized. However, in that case, the phase modulation element 209 and the intensity distribution conversion element 229 need to be manufactured using information on the intensity distribution before conversion.

  As described above, the present embodiment is an optical system using a coherent light beam, and includes a light source that emits a light beam, an intensity distribution conversion unit that converts an intensity distribution of the light beam emitted from the light source, and an intensity. An irradiation unit that irradiates a desired object with the light beam emitted from the distribution conversion unit, and the intensity distribution conversion unit includes a phase modulation unit that performs phase modulation and condensing of the light beam, and a diffraction disposed in the phase modulation unit. A structure having elements is used.

  In addition, a holographic memory device using a hologram, a light source that emits light, an optical element that separates the light emitted from the light source into signal light and reference light, and spatial light for adding information to the signal light A modulation unit and an intensity distribution conversion unit that converts the intensity distribution of the light emitted from the light source unit, and the intensity distribution conversion unit is disposed in the phase modulation unit and the phase modulation unit that perform phase modulation and condensing of the light beam. The diffractive element is included.

  Also, an intensity distribution conversion method for converting the intensity distribution of a coherent light beam, using a phase distribution element, a relay lens, and an intensity distribution conversion unit in which a diffraction element is arranged near the condensing point of the relay lens, The light beam intensity distribution is converted by a combination of a phase modulation pattern, which is a phase distribution of the modulation element, and a hologram of the diffraction element.

  Thereby, according to the present embodiment, it is possible to convert the intensity distribution while maintaining high light utilization efficiency. Furthermore, even when the intensity distribution is complicated, the intensity distribution can be easily converted at a low cost. Therefore, SN improvement and light utilization efficiency improvement can be easily performed at low cost.

  In the first embodiment, the non-uniform intensity distribution of the signal light 206 in the optical system 11 of the holographic memory 10 is converted into a substantially uniform intensity distribution. However, in the present embodiment, the non-uniform intensity distribution is converted into a desired intensity distribution. Further SN improvements are being made.

  Even if the intensity distribution just before the spatial light modulator 212 in FIG. 2 is uniform, the signal light detected by the photodetector 225 during reproduction has a non-uniform intensity distribution for the following reason. For example, this occurs because the in-plane reflectance of the spatial light modulator 212 is not uniform. Alternatively, this is caused by non-uniform diffraction efficiency due to the overlap shift between the signal light 206 and the reference light 207 in the optical information recording medium 1. Or, it is caused by non-uniform diffraction efficiency due to a difference in polarization direction from the reference light 207 due to the signal light 206 being condensed. Or it is caused by non-uniformity of the sensitivity of the photodetector. In this embodiment, the SN improvement is performed by converting the intensity distribution in advance so that the signal light detected by the photodetector 225 during reproduction is substantially uniform.

  In this embodiment, the light beam shape is also deformed by the same intensity distribution conversion method in order to improve the light utilization efficiency. Although the photodetector 225 is generally rectangular, incident light from a laser used in the optical system 11 of the holographic memory 12 and optical elements such as lenses are circular. Therefore, the light use efficiency can be improved by making the round intensity distribution rectangular on the photodetector 225.

  In this embodiment, the contents of the holographic memory device and the intensity distribution conversion principle are the same as those in the first embodiment, but the phase distribution of the phase modulation element is different. FIG. 12 is a schematic diagram of conversion to a desired intensity distribution. In this embodiment, an arbitrary intensity distribution as shown in FIG. 12A is converted into a desired intensity distribution 907 as shown in FIG. That is, the intensity portion 906 to be converted is moved to a weak portion, and the average intensity value of the desired intensity distribution 907 and the average value before conversion are substantially the same. Thereby, the intensity distribution can be converted into a desired distribution with high light utilization efficiency.

  This embodiment will be described with reference to the operation flow shown in FIG.

  In Example 1, when measuring the intensity distribution before conversion, the signal light 206 was directly incident on the photodetector 225 using the polarization direction conversion element 204 as shown in FIG. 7 (401). On the other hand, in this embodiment, hologram recording / reproduction is performed once without the intensity distribution conversion element 229 (501 and 502), and the reproduced signal light is acquired by the photodetector 225, and the intensity distribution is uniform. Is evaluated (503). This operation is shown in FIG. In FIG. 14, the flow of signals when the solid line is recording and the dotted line is reproducing is shown. If the desired performance is not achieved, intensity distribution conversion is performed as a Reject.

  At this time, the images of the spatial light modulator 212 are all ON pixel images or data page patterns including both ON pixels and OFF pixels. In the case of the data page pattern, since the light intensity of the OFF pixel portion is not known, an inverted data page is also prepared, and recording and playback are performed for the two data pages before and after the inversion, and the playback image is turned on. The same evaluation is performed focusing on only the pixel portion. In addition, the phase modulation pattern of the phase modulation element 209 at this time uses a random phase distribution such that the highest frequency passes through the spatial filter 214. It is considered that the intensity distribution measured above includes all the influences due to the above-described nonuniformity of the intensity distribution. The intensity distribution of all ON pixels before conversion acquired above is assumed to be Iread (x, y).

  In the intensity distribution conversion, first, the polarization direction conversion element 230 is adjusted, and the intensity distribution I_SLM (x, y) of the direct signal light 206 is obtained directly by the photodetector 225 (504, 505).

Subsequently, using the intensity distribution Iread (x, y) acquired by recording / reproducing the hologram and the intensity distribution I_SLM (x, y) on the spatial light modulator 212 before conversion, the target intensity distribution after conversion is converted. Itarget (x, y) is calculated using the following equation (8).

Here, <> represents a spatial average. In addition, since a portion having a very small value of Iread has a very large value of Itarget, a predetermined threshold value may be provided so that a portion where Iread is equal to or less than the threshold value may not be converted.

Using the phase modulation pattern 708 shown in FIG. 9, the intensity distribution conversion element 229 is manufactured (506) by the same procedure as that of the first embodiment (506), and the phase modulation element 209 is manufactured so as to be Itarget (x, y) after the conversion. . In order to obtain a desired intensity distribution, the phase modulation pattern 710 (δ (x, y)) at the time of manufacturing the phase modulation element 209 is

  However, ΔI (x, y) = Itarget (x, y) −I_SLM (x, y). Here, c is a constant or a function of ΔI (x, y) set so that δ (x, y) does not exceed the range of 0 to π / 2.

  Similar to the first embodiment, the phase modulation pattern 709 (δ (x, y) + φref (x, y)) is displayed on the phase modulator 605 and is displayed on the photodetector 609 by the optical system shown in FIG. Get the phase distribution. Then, a phase modulation element having a conjugate phase of this phase distribution is manufactured (507).

  Next, the intensity distribution conversion element 229 and the phase modulation element 209 are mounted on the optical system 11 of the holographic memory device 10 to adjust the position and angle (508, 509). It is confirmed whether or not the desired intensity distribution Itarget is obtained by the photodetector 225. If it is obtained, the polarization direction of the signal light is adjusted as Accept (510), and the processing is finished (511). If not, “Reject” is repeated from the fabrication of the phase modulation element. The detailed steps of the phase modulation element manufacturing step 507 are the same as those in FIG.

  In addition to the above, the cause of non-uniformity in the intensity distribution of the signal light is, for example, quality deterioration of the recording hologram due to vibration during recording, aberration and intensity distribution of the reference light, incident angle dependency of the transmittance of the information recording medium 1, and the like Can be considered. According to the method of the present embodiment, the influence of nonuniform intensity distribution due to these factors can also be improved.

  As described above, the present embodiment is an optical system using a coherent light beam, and includes a light source that emits a light beam, an intensity distribution conversion unit that converts an intensity distribution of the light beam emitted from the light source, and an intensity. An irradiation unit that irradiates a desired object with the light beam emitted from the distribution conversion unit, and the intensity distribution conversion unit includes a phase modulation unit that performs phase modulation and condensing of the light beam, and a diffraction disposed in the phase modulation unit. An intensity distribution conversion unit is configured to convert the intensity distribution of the light beam into a desired intensity distribution.

  In addition, a holographic memory device using a hologram, a light source that emits light, an optical element that separates the light emitted from the light source into signal light and reference light, and spatial light for adding information to the signal light A modulation unit and an intensity distribution conversion unit that converts the intensity distribution of the light emitted from the light source unit, and the intensity distribution conversion unit is disposed in the phase modulation unit and the phase modulation unit that perform phase modulation and condensing of the light beam. The intensity distribution conversion unit converts the intensity distribution of the light beam into a desired intensity distribution.

  Therefore, according to the present embodiment, the intensity distribution of the signal light can be converted into a desired distribution, and the SN improvement and the light utilization efficiency can be easily and cost-effectively as in the first embodiment.

  In the first and second embodiments, the intensity distribution conversion is performed only on the signal light. However, in the present embodiment, the SN distribution is further improved by performing the intensity distribution conversion on the reference light.

  If the intensity distribution of the reference light is not uniform, the recorded hologram will be incomplete, increase in crosstalk between pages due to the deterioration of Bragg selectivity, and deterioration of signal quality due to insufficient overlap of signal light and reference light. Occur. By making the intensity distribution of the reference light substantially uniform, it is possible to eliminate the signal performance deterioration factor and to improve the SN.

  When the intensity distribution conversion of the reference light is performed using the same method as in the first and second embodiments, the phase distribution of the reference light becomes non-uniform. In this case, in order to avoid a change in intensity distribution due to diffraction, it is necessary to form an image with a relay lens up to the optical information recording medium 1, the number of optical elements increases, and the wavelength and angle of the reference light during reproduction are adjusted. Thus, there is a problem that it is difficult to correct the influence of the medium shrinkage.

  Therefore, in this embodiment, after the intensity distribution of the reference light is converted, a phase correction element is arranged to make the phase distribution uniform. Thereby, the intensity distribution can be converted while the reference light is parallel light.

  FIG. 15 shows a configuration for converting not only the signal light 206 but also the intensity distribution of the reference light 207. Although the basic optical configuration is the same as that of the first embodiment, an intensity distribution conversion unit 234 including an intensity distribution conversion element 235, a phase modulation element 231, a relay lens 233, and a phase correction element 232 is added to the reference optical path. The intensity distribution conversion element 235 and the phase modulation element 231 are produced in the same procedure as in the first and second embodiments. The intensity distribution before the conversion may be measured by placing a photodetector at the position of the phase modulation element 231. The phase correction element 232 may be manufactured so that the phase distribution of the emitted light is measured at the position of the phase correction element 232 and the measured phase distribution is substantially uniform. At this time, the angle of the galvanometer mirror 224 is adjusted to reflect the reference light 207 to a desired angle, and the phase distribution of this light is measured and fed back to finely adjust the phase distribution and position / angle of the phase correction element 232. The phase distribution of the reference beam 207 can be made uniform.

  FIG. 16 illustrates a configuration in which the intensity distribution of the signal light and the reference light is simultaneously converted by disposing the intensity distribution conversion unit 234 of FIG. 15 in front of the polarization beam splitter 205. Thereby, the intensity distribution conversion unit can be shared.

  As described above, the present embodiment is an optical system using a coherent light beam, and includes a light source that emits a light beam, an intensity distribution conversion unit that converts an intensity distribution of the light beam emitted from the light source, and an intensity. An irradiation unit that irradiates a desired object with the light beam emitted from the distribution conversion unit, and the intensity distribution conversion unit includes a phase modulation unit that performs phase modulation and condensing of the light beam, and a diffraction disposed in the phase modulation unit. And an optical element that separates the light emitted from the light source into signal light and reference light, and a spatial light modulator for adding information to the signal light. The intensity distribution conversion unit converts the intensity distribution of the holographic memory device using a hologram.

  In addition, a holographic memory device using a hologram, a light source that emits light, an optical element that separates the light emitted from the light source into signal light and reference light, and spatial light for adding information to the signal light A modulation unit and an intensity distribution conversion unit that converts the intensity distribution of the light emitted from the light source unit, and the intensity distribution conversion unit is disposed in the phase modulation unit and the phase modulation unit that perform phase modulation and condensing of the light beam. The intensity distribution conversion unit is an intensity distribution conversion unit that converts the intensity distribution of the reference light.

  Therefore, according to the present embodiment, it is possible to further improve the SN by performing the intensity distribution conversion on the reference light.

In the intensity distribution conversion methods of Examples 1 to 3, since a phase pattern is added to the converted intensity distribution, it is not possible to convert only the intensity distribution as parallel light. Therefore, in this embodiment, the phase modulation pattern 707 (φref (x, y)) in FIG. 11 is made to have a uniform phase distribution, so that the phase distribution of the emitted light is made uniform. However, here, when the phase modulation pattern 707 (φref (x, y)) has a uniform phase distribution, the phase pattern 706 (φref (x, y) −δ (x, y)) becomes a phase distribution from 0 to π / 2, and the intensity difference at the condensing point is larger than those in the first and second embodiments. Therefore, when the intensity distribution conversion element 229 is manufactured, there is a possibility that hologram recording cannot be performed efficiently because M # of the hologram recording medium is finite. Therefore, in this embodiment, defocus recording is performed to solve this problem. That is, as shown in FIG. 17, recording is performed by shifting the hologram recording medium from the focal point position. As a result, recording can be performed while avoiding a portion having a large intensity difference near the condensing point, and efficient hologram recording becomes possible.
When the parts of the optical system 11 are replaced with the change of the optical system over time or the consumption of parts, the intensity distribution may also change. In Examples 1 to 4, the intensity distribution is converted at the time of assembling the optical system, but the intensity distribution may be converted at the time of component replacement.

  In addition, in Examples 1 to 4, the intensity distribution can be made uniform not only in the holographic memory device but also in an optical system using a coherent light beam, for example, by making the intensity distribution uniform in a laser processing machine. In addition, machining accuracy and machining efficiency can be improved.

  In the holographic memory devices of Examples 1 to 4, even if the wavelength of the light source fluctuates, the performance of the intensity distribution conversion element 229 does not deteriorate within a practical range of the fluctuating wavelength range ± 5 nm. In the holographic memory devices according to the first to fourth embodiments, the mounting accuracy of the phase modulation element 209 and the intensity distribution conversion element 229 is about several to several tens μm and can be sufficiently adjusted. Further, in the holographic memory devices according to the first to fourth embodiments, the phase modulation element 209, the relay lens 210, and the intensity distribution conversion element 229 are configured as individual elements. It can also be replaced with a new element. In the holographic memory devices according to the first to fourth embodiments, the intensity distribution of substantially parallel light is converted. However, for example, conversion of light such as diverging light emitted from a laser can be realized based on the same concept.

  In the holographic memory devices of Examples 1 to 4, the intensity distribution conversion element 229 is a volume holographic optical element, but several thin phase types manufactured using a computer generated hologram (CGH) technique. It is also possible to replace it with a hologram.

DESCRIPTION OF SYMBOLS 1 ... Optical information recording medium, 10 ... Holographic memory device, 11 ... Optical system, 12 ... Reproduction optical system, 13 ... Disc cure optical system, 14 ... Optical system for disc rotation angle detection, 50 ... Rotation motor, 81 ... Access control circuit 82 ... Light source drive circuit 83 ... Servo signal generation circuit 84 ... Servo control circuit 85 ... Signal processing circuit 86 ... Signal generation circuit 87 ... Shutter control circuit 88 ... Disc rotation motor / access control circuit , 89 ... controller, 90 ... input / output control circuit, 91 ... external control device, ° 103 ... Fourier lens, 104 ... Fourier lens, 201 ... light source, 202 ... collimating lens, 203 ... shutter, 204 ... polarization direction conversion element, 205 ... Polarizing beam splitter, 206 ... Signal light, 207 ... Reference light, 208 ... Beam expander, 209 Phase modulation element 210 ... Relay lens 211 ... Polarization beam splitter 212 ... Spatial light modulator 213 ... Relay lens 214 ... Spatial filter 215 ... Objective lens 216 ... Polarization direction conversion element 217 ... Mirror 218 ... 219 ... Galvano mirror, 220 ... Actuator, 221 ... Lens, 222 ... Lens, 223 ... Actuator, 224 ... Galvano mirror, 225 ... Photo detector, 226 ... Iris, 227 ... Scanner lens, 228 ... Diffracted signal light 229, intensity distribution conversion element, 230, polarization direction conversion element, 231, phase modulation element, 232, phase correction element, 233, relay lens, 234, intensity distribution conversion unit, 235, intensity distribution conversion element, 600, intensity distribution Conversion element fabrication optical system, 601... Light source, 602. 603 ... Relay lens, 604 ... Spatial filter, 605 ... Phase modulator, 606 ... Polarization beam splitter, 607 ... Fourier lens, 608 ... Fourier lens, 609 ... Photo detector, 610 ... Shutter, 611 ... Polarization direction conversion element , 612 ... quarter wave plate, 614 ... actuator, 615 ... mirror, 616 ... mirror, 617 ... phase detection light, 618 ... phase detection optical system, 619 ... half mirror, 620 ... outgoing light, 701 ... intensity distribution, 702 ... Phase conversion, 703 ... Phase distribution, 704 ... Phase conversion, 705 ... Reference phase distribution, 706 ... Phase modulation pattern, 707 ... Phase modulation pattern, 708 ... Phase modulation pattern, 709 ... Phase modulation pattern, 710 ... Phase distribution, 901 ... Unused intensity part, 902 ... Intensity part to be converted, 904 ... Intensity distribution after conversion, 905 ... Intensity distribution after conversion, 906 ... Intensity part to be converted, 907 ... Intensity distribution after conversion

Claims (19)

An optical system using a coherent light beam,
A light source that emits the light beam;
An intensity distribution converter for converting the intensity distribution of the light beam emitted from the light source;
An irradiation unit for irradiating a desired object with the light beam emitted from the intensity distribution conversion unit,
The intensity distribution conversion unit includes an optical system including a phase modulation unit that performs phase modulation and condensing of a light beam, and a diffraction element disposed in the phase modulation unit. The optical system according to claim 1,
An optical element that separates light emitted from the light source into signal light and reference light;
A spatial light modulator for adding information to the signal light,
The intensity distribution converter is an intensity distribution converter that converts the intensity distribution of the signal light,
An optical system used for a holographic memory device using a hologram. The optical system according to claim 1,
An optical system characterized by being used in a laser processing machine. The optical system according to claim 1,
The phase modulation unit is composed of a phase modulation element and a relay lens,
The optical system, wherein the diffractive element is disposed near a condensing point of the relay lens. The optical system according to claim 4,
An optical system characterized in that a phase distribution of the phase modulation element is produced according to an intensity distribution before conversion and the intensity distribution of the light beam is converted. The optical system according to claim 1,
The optical system, wherein the diffraction element is a volume holographic optical element. The optical system according to claim 1,
The optical system according to claim 1, wherein the intensity distribution converter converts the intensity distribution of the light beam into a substantially uniform intensity distribution. The optical system according to claim 1,
The optical distribution system, wherein the intensity distribution conversion unit converts the intensity distribution of the light beam into a desired intensity distribution. The optical system according to claim 1,
An optical element that separates light emitted from the light source into signal light and reference light;
A spatial light modulator for adding information to the signal light,
The intensity distribution converter is an intensity distribution converter that converts the intensity distribution of the reference light,
An optical system used for a holographic memory device using a hologram. A holographic memory device using a hologram,
A light source that emits light;
An optical element that separates light emitted from the light source into signal light and reference light;
A spatial light modulator for adding information to the signal light;
An intensity distribution conversion unit that converts an intensity distribution of light emitted from the light source unit,
The holographic memory device, wherein the intensity distribution conversion unit includes a phase modulation unit that performs phase modulation and condensing of a light beam and a diffraction element disposed in the phase modulation unit. The holographic memory device according to claim 10, wherein
The holographic memory device, wherein the intensity distribution conversion unit is an intensity distribution conversion unit that converts an intensity distribution of the signal light. The holographic memory device according to claim 10, wherein
The phase modulation unit is composed of a phase modulation element and a relay lens,
A holographic memory device, wherein the diffractive element is disposed in the vicinity of a condensing point of the relay lens. A holographic memory device according to claim 12, comprising:
A holographic memory device, wherein a phase distribution of the phase modulation element is produced according to an intensity distribution before conversion to convert the intensity distribution of the light beam. The holographic memory device according to claim 10, wherein
A holographic memory device, wherein the diffractive element is a volume holographic optical element. The holographic memory device according to claim 10, wherein
The holographic memory device, wherein the intensity distribution conversion unit converts the intensity distribution of the light beam into a substantially uniform intensity distribution. The holographic memory device according to claim 10, wherein
The holographic memory device, wherein the intensity distribution conversion unit converts the intensity distribution of the light beam into a desired intensity distribution. The holographic memory device according to claim 10, wherein
The holographic memory device, wherein the intensity distribution conversion unit is an intensity distribution conversion unit that converts an intensity distribution of the reference light. An intensity distribution conversion method for converting the intensity distribution of a coherent light beam,
Using an intensity distribution conversion unit in which a diffraction element is arranged in the vicinity of a condensing point of a phase modulation element, a relay lens, and the relay lens,
An intensity distribution conversion method, wherein the intensity distribution of the light beam is converted by a combination of a phase modulation pattern which is a phase distribution of the phase modulation element and a hologram of the diffraction element. The intensity distribution conversion method according to claim 18,
An intensity distribution conversion method, wherein either the phase modulation pattern of the phase modulation element or the hologram of the diffraction element is produced according to an intensity distribution before conversion.

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