JP4596468B2 - Magneto-optic spatial light modulator - Google Patents

Description

  The present invention relates to a magneto-optic spatial light modulator that individually controls the magnetization direction of each pixel by a combined magnetic field generated by drive currents on the X side and the Y side. The drive line is arranged in the shape of a “well” on the periphery excluding the center of the pixel, and the direction of the magnetic field generated from the drive line surrounding the target pixel in the shape of a “well” is made to coincide with the center of the target pixel. Thus, the present invention relates to a magneto-optical spatial light modulator that is intended to reduce malfunctions due to leakage magnetic fields at corners of pixels other than the target pixel.

  A magneto-optical spatial light modulator is a magneto-optical device that spatially modulates the amplitude, phase, and polarization state of light using the Faraday effect of the magnetic film, and can independently control the magnetization direction of the magnetic film. A large number of pixels (pixels) are two-dimensionally arranged in the X and Y directions. Since the spatial light modulator having such a two-dimensional array of pixels can process information in parallel at high speed, an optical information processing system, optical computing, projector TV, moving image hologram recording, optical volume recording, etc. In recent years, research and development has been advanced as a key device to be realized.

  An example of a magneto-optic spatial light modulator is shown in FIG. The spatial light modulator 10 is mainly composed of a magnetic film (magneto-optic material) 12, and a number of pixels 14 whose rotation direction is rotated by the Faraday effect are spaced apart from each other in the X direction (horizontal direction) and the Y direction (vertical direction). ) In two dimensions, and X-side and Y-side drive lines are wired along the pixels 12. The X side drive pulse current is supplied from the X side drive unit 16 to the X side predetermined drive line, and the Y side drive pulse current is supplied from the Y side drive unit 18 to the Y side predetermined drive line. The operations of the X-side drive unit 16 and the Y-side drive unit 18 are controlled by the control unit 20. The magnetic fields generated by the drive pulse currents flowing through the selected X-side drive line and Y-side drive line are combined, and the magnetization direction of each pixel is individually controlled by the combined magnetic field.

FIG. 5 is an explanatory diagram of the basic operation. Only two pixels are drawn to simplify the drawing. Incident light that has passed through the first polarizer 22 and has become linearly polarized light enters each pixel 14 of the spatial light modulator. Incident light passes through the transparent substrate 24 and the magnetic film 12, is reflected by the metal film 28, passes through the magnetic film 12 and the transparent substrate 24 again, and is emitted. At this time, due to the Faraday effect of the magnetic film 12, the polarization direction of the light reflected by each pixel 14 is rotated by a predetermined angle. Here, if a Faraday rotation of + θ _F (for example, +45 degrees) occurs when a positive magnetic field (+ H) is applied to the upper pixel, a negative magnetic field (−H) is applied to the lower pixel. Sometimes a Faraday rotation of -θ _F (eg, -45 degrees) occurs. These reflected lights reach the second polarizer 30. If the polarization transmission plane is set to +45 degrees, the upper stage light rotated by +45 degrees Faraday is transmitted (ON), but is rotated by -45 degrees Faraday. The lower light is blocked (OFF). In this way, by controlling the direction of the magnetic field applied to each pixel, on / off of the reflected light by each pixel can be controlled.

  By the way, each pixel in the spatial light modulator is not an individual element that is completely independent of each other. Actually, a magnetic film is grown on the entire surface of the substrate by the LPE method or the like. This is a state in which the pixel is magnetically partitioned. This is because it is necessary to arrange each pixel very small and accurately. For example, in Patent Document 1, an oxidizable film pattern such as Si is formed in a region corresponding to a pixel on a magnetic garnet material, and the whole is subjected to heat treatment to reduce the magnetic garnet material directly under the Si film and change the quality. In other words, a technique for forming a large number of pixels capable of reversal of magnetization in units of pixels is disclosed. In this way, the polarization direction of light passing through each pixel can be rotated by a predetermined angle due to the Faraday effect, and thus spatially modulated by arbitrarily selecting the direction of magnetization in each pixel. Light can be generated.

  In order to independently control the magnetization direction of each pixel, a drive line routed along each pixel is selected and a drive current is supplied, and a resultant magnetic field generated thereby is used. Specifically, the magnetization direction of the pixel is not changed by the magnetic field generated by the drive pulse current flowing through either the X-side or Y-side drive line, but the drive flows through the selected X-side and Y-side drive lines. When the timings of the pulse currents coincide, the magnetic fields generated by both drive pulse currents are combined, and when the combined magnetic field is applied to the target pixel, the magnetization direction of the target pixel is controlled.

  For example, Patent Document 2 describes a technique for linearly wiring X-side and Y-side drive lines in a gap between pixels. According to this, when a driving pulse current is supplied to each selected one of the X-side driving line and the Y-side driving line, the four pixels in the vicinity where they intersect each other have a positive positional relationship. A region where the magnetic flux in the opposite direction passes and two regions where the magnetic flux does not pass are generated. That is, even if two drive lines are selected to control the magnetization direction of only one target pixel, the magnetic flux in the opposite direction leaks to the diagonally located pixels. This leakage magnetic field is particularly concentrated at the corner of the pixel. Since the reversal of the magnetic domain in the pixel is likely to occur from a corner having a high magnetic flux density, unnecessary magnetization reversal (bit rate error) occurs in the pixels other than the target pixel.

Therefore, in Patent Document 2, in order to prevent unnecessary magnetization reversal (bit rate error) in pixels other than the target pixel, a small region with a small coercive force is provided at a specific one of the four corners of the pixel. In this case, an inversion nucleus is formed by a weak magnetic field from the drive line, and an external bias magnetic field that works favorably on the target pixel is applied. However, when using the external bias magnetic field, extra control is required, and it is difficult to switch the external bias magnetic field at high speed, which hinders high-speed switching of the spatial light modulator. In addition, the structure in which the wiring is embedded in the gap and the magnetic field is applied from the side surface of the pixel is complicated and difficult to manufacture, and it is very difficult to realize high density by narrowing the pixel interval. Incidentally, if the pixel interval is large, the information density is lowered, which makes it unsuitable for use in processing a large amount of information at high speed.
US Pat. No. 5,473,466 U.S. Pat. No. 4,578,321

  The problem to be solved by the present invention is that the pixel interval can be narrowed, unnecessary magnetization reversal in pixels other than the target pixel does not occur, the occurrence of bit rate errors can be drastically reduced, and a large amount of information can be processed at high speed The realization of a magneto-optic spatial light modulator.

  In the present invention, a large number of pixels that rotate the polarization direction by the Faraday effect are two-dimensionally arranged in the X direction and the Y direction in a state of being separated from each other, and the X side drive line and the Y side are wired along the pixels. In the magneto-optic spatial light modulator of the type in which the magnetization direction of each pixel is individually controlled by the combined magnetic field generated by the drive current flowing through the drive line, the X side drive line and the Y side drive line are respectively in the X direction. The pixels arranged in the Y direction and the pixels arranged in the Y direction extend straight on the peripheral edge (not in a zigzag or spiral shape), and each pixel is removed from the center by drive lines on the X side and the Y side. The direction of the magnetic field generated from the drive lines on the X side and the Y side that surround the target pixel in the shape of a “well” is aligned at the center of the target pixel. A magneto-optic spatial light modulator, characterized in that had Unishi.

  Here, the two X-side drive lines and the two Y-side drive lines arranged on both sides of the pixel are paired and short-circuited at one end to form a loop. In this case, it is preferable to use a reciprocating type folded back. In that case, it is preferable that the short-circuit portions of each drive line pair appear alternately on both sides of the pixel array region on the X side and the Y side.

Drive line of the X-side and Y-side, its shall be the wiring pattern line width at these intersections vicinity is widened towards the inside of the partially pixels. Specifically, the outer edge side of the pixel is linear, the inner side of the opposite pixel is uneven, and a narrow part and a wide part are formed, and the line width is linear between the narrow part and the wide part. The wiring pattern may be changed gradually or curvedly. In that case, the wide portion is preferably set to be 1.5 times wider than the narrow portion. For example, the pattern is such that corners are chamfered when viewed from a direction perpendicular to the main surface of the magneto-optical element portion. Further, the X-side and Y-side drive lines have a narrow portion covering 10-25% of one side of the pixel and a wide portion covering 25-45% of one side of the pixel. It is preferable that the X-side and Y-side drive lines viewed from the direction perpendicular to the main surface have a wiring pattern that coincides at the intersection.

  In the magneto-optic spatial light modulator according to the present invention, the drive lines on the X side and the Y side are wired so as to extend straight and surround each pixel in the shape of a “well” except for its center. Is wired so as to pass over the periphery of the pixels, so that the space between the pixels can be reduced. In addition, since the direction of the magnetic field generated from each drive line is configured to coincide with the center of the pixel, the necessary magnetic field effectively acts only on the target pixel, and unnecessary magnetization reversal occurs in pixels other than the target pixel. The occurrence of bit rate errors can be reduced without occurring. Therefore, a large amount of information can be processed at high speed.

  Furthermore, if the wiring pattern is such that the line width near the intersection of the drive lines on the X side and Y side is partially expanded toward the inside of the pixel, the leakage magnetic field at the corner of the pixel is further reduced. Since the extended drive line is located inside the corner of the pixel, local concentration of magnetic flux does not occur. Therefore, magnetization reversal does not occur in pixels other than the target pixel, and the bit rate error is drastically reduced. For these reasons, it is possible to reduce the size of the pixels and the interval between the pixels, and to process a large amount of information at high speed.

  FIG. 1 is an explanatory view showing an embodiment of a magneto-optic spatial light modulator according to the present invention, and shows a state in which a pixel formation region is viewed in a plan view. In a magnetic film (for example, a magnetic garnet single crystal film), a large number of minute pixels 14 that can set the magnetization direction independently of each other and rotate the polarization direction according to the magnetization direction with respect to incident light by the Faraday effect are mutually connected. The two-dimensional arrangement in the X direction (horizontal direction) and the Y direction (vertical direction) in a separated state, and the synthesis generated by the drive current flowing through the X side and Y side drive lines wired along the pixel 14 In this structure, the magnetization direction of each pixel is individually controlled by a magnetic field. Here, the X-side drive line (horizontal direction) 32 and the Y-side drive line (vertical direction) 34 are straight on the periphery of the pixels arranged in the X direction and the pixels arranged in the Y direction, respectively. The X- and Y-side drive lines are extended and wired so as to surround each pixel in a “well” shape except for its center, and the direction of the magnetic field generated from each drive line is aligned with the pixel center. It has become.

Specifically, the drive line 32 on the X side and the drive line 34 on the Y side are arranged so that the outer edge of the drive line 32 on the respective pixels 14 makes a half-round reciprocation along the periphery of the pixels. Wiring is performed to make one turn on the X side and Y side. In this embodiment, when the X-side and Y-side drive lines are wired, they are designed with the same line width throughout. The two X-side drive lines and the two Y-side drive lines arranged on both sides of the pixel make a pair, and are short-circuited at one end to form a loop, and the X side On the Y side, the short-circuit portions of the respective drive lines appear alternately on both sides of the pixel array region. Accordingly, when one X-side drive line is selected, the circuit circulates halfway back and forth with respect to the pixel located below the X-side drive line. The same applies to the drive line on the Y side. When the short-circuit portions are distributed and arranged in this way, the drive portions can be easily arranged even if the pixels and the pixel gaps are narrowed. Here, the state where the current I flows through the X ₁ drive line and the Y ₁ drive line is shown, and the pixel at the position where they intersect becomes the target pixel, and the current I makes one round around the target pixel. Become.

FIG. 2 is a sectional view thereof. The magnetic film 12 is, for example, a Bi-substituted rare earth iron garnet film, which is formed on the GGG substrate 24 by about 3 μm by liquid phase epitaxial growth. Hereinafter, an example of the manufacturing process will be briefly described.
(A) An Al film is formed on the entire surface of the magnetic film 12 by sputtering or vapor deposition. Thereafter, a resist layer is formed only in the pixel formation region. The pixel size is, for example, a square of 16 μm in length and width, and the pixel interval is set to 2 μm. The number of pixels of the prototype was 16 × 16.
(B) Next, using the resist layer as a mask, the Al film in the gap region between the pixels is removed by ion milling, and further ion milling is performed to form the groove 42. Accordingly, the grooves 42 are formed in a lattice shape vertically and horizontally except for the region of the pixels 14. The depth of the groove is 3 μm. Thereafter, an annealing process is performed at 900 ° C. In the region corresponding to the pixel 14, the Al film 40 remains, which becomes a light reflecting film.
(C) After the SiO ₂ insulating film 44 is formed, a Cu film is formed in the lateral direction along the outer edge of the pixel 14 by sputtering, vapor deposition, plating, or the like, and the X-side drive line 32 is wired. The drive line may be made of Au, Al or the like in addition to Cu.
(D) Further, similarly, after the SiO ₂ insulating film 46 is formed, a Cu film is formed in the vertical direction along the outer edge of the pixel 14 by sputtering, vapor deposition, plating, or the like, and the Y side drive line 34 is wired. This drive line may also be made of Au, Al, etc. in addition to Cu.

  By doing so, the magneto-optic spatial light having a structure in which the X-side drive line 32 and the Y-side drive line 34 are formed on the pixel 14 so as to surround each pixel 14 in a “well” shape. A modulator is obtained. The direction of the current flowing through the drive lines on the X side and the Y side is applied to the target pixel in the same direction as the direction of the magnetic field generated by the current flowing through each drive line. Only by energizing the two drive lines (one loop) on the X side, the generated magnetic field cannot exceed the coercive force of the magnetic film, and the two drive lines (one loop) on the X side and the Y side Each current value is set so that magnetic saturation occurs only when the two drive lines (one loop) are energized simultaneously.

  In such a magneto-optical spatial light modulator, incident light is transmitted through the GGG substrate 24 and the magnetic film 12, totally reflected by the Al film 40 that performs a mirror function, and again transmitted through the magnetic film 12 and the GGG substrate 24. And exit. The light path is indicated by an arrow. When incident light travels back and forth through the portion of the magnetic film 12 corresponding to a pixel, rotation of the polarization direction is given by the Faraday effect.

  Leakage magnetic fields from two intersecting drive lines are concentrated near the intersection of the drive lines. In the present invention, both the X-side and Y-side drive lines are located on the pixel (because they are located closer to the center than the corner of the pixel), so the magnetic flux density at the corner of the pixel is reduced. To do. Since the reversal of the magnetic domain in the pixel generally starts from the corner, the reversal of the magnetization of the pixel in a diagonal position relative to the target pixel due to magnetic field leakage can be suppressed by using such a positional relationship between the pixel and the drive line. can do. In addition, since the current makes one turn around the periphery of the target pixel, the current value flowing through one drive line can be halved, and in that respect, unnecessary magnetization reversal is prevented in pixels other than the target pixel. it can.

FIG. 3 is an explanatory view showing another embodiment of the magneto-optic spatial light modulator according to the present invention, and shows a state in which the pixel array region is seen in a plan view. As shown in A, the X-side drive line 52 and the Y-side drive line 54 surround each pixel 14 in a “well” shape, and the X-side drive line 52 and the Y-side drive line 54 are pixels. The outer edge side of the pixel 14 is linear, and the inner side of the pixel on the opposite side is uneven, forming a narrow part and a wide part, and the line width gradually changes linearly between the narrow part and the wide part. A wiring pattern is used. That is, the pattern is such that the corners of the wide portion are chamfered when the pixel array region is viewed in plan (the state shown in FIG. 3). Each drive line is wired inside the pixel along the outer edge of the pixel. The X-side drive line 52 and the Y-side drive line 54 form a loop by forming a pair by short-circuiting at one end thereof. Here, the current I is flowing through the X ₁ drive line and the Y ₁ drive line.

  For example, as shown in FIG. 3B for the X-side drive line 52 and as shown in FIG. 3C for the Y-side drive line 54, the narrow width portion (width is indicated by a) is one side of the pixel. The size is such that it covers the inside of 10 to 25%, and the wide portion (width is indicated by b) is the size that covers the inside of 25 to 45% of one side of the pixel. The wide portion is set to be 1.5 times wider than the narrow portion. Further, the X-side drive line 52 and the Y-side drive line 54 are set to dimensions such that the corner chamfering pattern of the wide width portion overlaps when the pixel array region is viewed in a plan view.

  Leakage magnetic fields from two intersecting drive lines are concentrated near the intersection of the drive lines. In this embodiment, since the crossing portion is set wide, the cross section of the wiring becomes large, and the magnetic flux density at the corner of the pixel is reduced. Further, since the drive line having a wider width is located closer to the center than the corner of the pixel, the magnetic flux spreads and the local concentration (at the corner of the pixel) is small. Since the reversal of the magnetic domain in the pixel generally starts from the corner, such a wide chamfering pattern can suppress the magnetization reversal of the pixel in a diagonal position relative to the target pixel due to magnetic field leakage. In addition, since it is a narrow portion other than the corner of the pixel, a magnetic field is efficiently applied to the target pixel with a short magnetic path, and magnetization can be reversed with a small current.

  Spatial light modulators were prototyped by changing the X-side and Y-side drive line patterns (wide and narrow dimensions), and their operations were tested. As a result, when the pixel size was 16 μm and the pixel interval was 2 μm, a very good result was obtained in which no bit error occurred when the narrow width a was 4 μm and the wide width b was 6 μm or more. Further, when the narrow width dimension a was 2 μm, the bit width did not occur at all even when the wide dimension b was 4 μm or more.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows one Example of the magneto-optical spatial light modulator based on this invention. FIG. Explanatory drawing which shows the other Example of the magneto-optical spatial light modulator which concerns on this invention. An explanatory view showing an example of a magneto-optic spatial light modulator. Explanatory drawing of basic operation.

Explanation of symbols

14 pixels 32 X-side drive line 34 Y-side drive line

Claims (3)

A large number of pixels that rotate the polarization direction by the Faraday effect are two-dimensionally arranged in the X and Y directions in a state of being separated from each other, and the X-side drive line and the Y-side drive line wired along the pixels are arranged. In a magneto-optic spatial light modulator of a type that individually controls the magnetization direction of each pixel by a combined magnetic field generated by a flowing drive current,
The X-side drive line and the Y-side drive line extend straight on the periphery of the pixels arranged in the X direction and the pixels arranged in the Y direction, respectively , and the line width in the vicinity of the intersection is partially The X-side and Y-side drive lines are connected to surround each pixel in the shape of a “well” except for the center, and the target pixel is “well”. A magneto-optical spatial light modulator characterized in that the direction of the magnetic field generated from the X-side and Y-side drive lines enclosed in a letter-shape coincides with the center of the target pixel.   Two X-side drive lines and two Y-side drive lines arranged on both sides of the pixel are paired and short-circuited at one end to form a loop. 2. The magneto-optical spatial light modulator according to claim 1, wherein a short-circuit portion of each drive line pair alternately appears on both sides of the pixel array region. The drive lines on the X side and the Y side are linear on the outer edge side of the pixel, and have an uneven shape on the inner side of the opposite pixel to form a narrow part and a wide part, and between the narrow part and the wide part. 3. The magneto-optical spatial light modulator according to claim 1, wherein the wiring width is a wiring pattern that gradually changes linearly or curvedly.

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