JPH11174392A - Optical modulating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image on a binary sensitive material by using an optical modulating element which uses an electrooptic crystal. SOLUTION: In the optical modulating element 10 formed of an electrooptic crystal substrate 11 having individual electrodes 12 arrayed linearly on one surface and a common electrode 12 formed on the other surface, respective individual electrodes 13 are made trapezoid (parallelogram) having a couple of sides, crossing the array direction (x-axial direction) of the individual electrodes 13, at a specific angle to the traveling direction (z-axial direction) of light made incident on the optical modulating element. At this time, the angle of the sides of the individual electrodes crossing the x-axial direction to the z-axial direction is determined so that adjacent individual electrodes 13 share part of the x-axial area of the substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light modulator used in a recording apparatus such as a laser printer or a digital copying machine, and more particularly to a recording apparatus in the printing field for expressing a gray scale with a halftone dot on a binary photosensitive material. It is.

[0002]

2. Description of the Related Art Conventionally, in a recording apparatus such as a laser printer or a digital copier, a light modulation element array made of an electro-optic crystal is generally used.

[0003] Japanese Patent Application Laid-Open No. 4-372927 discloses an optical modulation element in which a drive voltage is lowered by increasing an optical path length, and an individual electrode is provided on one surface of an electro-optic crystal substrate and a common electrode is provided on the other surface. In particular, it discloses that it is desirable to provide a physical opening separation groove in the middle of each electrode in order to prevent crosstalk between pixels.

However, when the aperture separating groove structure for reducing crosstalk is used as described above, when the photosensitive material to be recorded is a binary photosensitive material used for forming a halftone image such as printing. This causes a problem that the formed image (line) becomes extremely thin. Even when the groove is not provided, a problem arises when the aspect ratio of the electrode width of the light modulation element / the thickness of the electro-optic crystal substrate becomes small. As the aspect ratio decreases, the transmitted modulated light deviates from the rectangular shape obtained from the ideal parallel plate approximation and becomes Gaussian, so that the image line becomes narrower in image formation on a binary photosensitive material. . It should be noted that the edge incidence type light modulation element is often used with such an aspect ratio.

FIG. 5 shows an example of such a light modulation element. The light modulation element 40 of the conventional example shown in FIG. 5A has a common electrode 42 on one surface of an electro-optic crystal substrate (PLZT plate) 41 and a plurality of individual electrodes 43 on the other surface. It is formed in a rectangular shape. FIG. 2B is a diagram of the light modulation element 40 of FIG. 1A viewed from above the individual electrodes. Opening pitch is 10
0 μm, electrode shape width (x-direction width) = 80 μm, length (z-direction length) = 2 mm, substrate thickness (y-direction thickness) = 250 μm
And the opening pitch / PLZT plate thickness ratio is 1 / 2.5.
In this light modulation element, the profile of the transmitted light when the continuous openings a, b, and c are set to the light transmitting state / light blocking state / light transmitting state is as shown in FIG. As shown in the figure, the beam profile has a shape close to a Gaussian distribution, not a rectangle expected from the parallel plate approximation. When exposing a binary photosensitive material or the like using a light modulation element having such a profile, for example, an image is formed only by light having a power equal to or higher than the threshold level Th in FIG. The resulting image line becomes narrower than the original aperture pitch. Specifically, when the power threshold level Th at which an image can be formed on a photosensitive material (sensitive material) used is 80% of the peak power, the width of the line image is 0.65 times the aperture pitch. When the adjacent openings are both in the light transmitting state, the lines are less thin because the transmitting states overlap at each end, but as described above, when both sides are in the non-transmitting state No good image can be obtained due to line thinning.

Japanese Patent Application Laid-Open No. 63-129318 is characterized in that the openings arranged one-dimensionally are trapezoidal when viewed on a plane (xy plane) perpendicular to the optical axis (z axis). Is disclosed. In general, when an image is formed by main-scanning a photosensitive material in a direction perpendicular to the row of openings, if the shape of each opening is configured as a simple separated rectangle, a blank portion that cannot be exposed between the openings occurs. As a result, vertical unevenness occurs in the main scanning direction of the image. In this JP-A-63-129318,
In order to solve this problem, it is disclosed that the shape of the opening is trapezoidal, and exposure from each opening is overlapped when the photosensitive material is scanned in the main scanning direction.

[0007] The trapezoidal shape of the opening as described above is expected to improve the thinning of the image (line), which is a problem described in the above-mentioned JP-A-4-372927. on the other hand,
In order to realize such a shape and arrangement of the opening so as to use the secondary electro-optic effect of an electro-optic crystal such as a PLZT ceramic, a three-dimensionally formed opening shape is indispensable. In order to realize this structure, it is necessary to perform complicated processing such as forming an opening separation groove obliquely in the electro-optic crystal, which is not industrially practical.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an edge-incidence type light modulation element using the secondary electro-optic effect of an electro-optic crystal, particularly when a binary photosensitive material is exposed to light. In view of the problem in the conventional light modulation element that the line width of an image to be formed becomes extremely narrow, an object of the present invention is to provide a light modulation element in which the line width is not reduced even when an image is formed on a binary photosensitive material. I do.

[0009]

According to the present invention, there is provided an optical modulator comprising:
A plurality of individual electrodes are one-dimensionally arranged and formed on one surface, and the other surface is formed of an electro-optic crystal substrate in which a common electrode facing all of the plurality of individual electrodes is formed. An opening for switching between a state in which light is transmitted and a state in which light is blocked by controlling a voltage between the opposing electrodes; In a light modulation element that modulates light incident on the opening from a direction perpendicular to the arrangement direction of the individual electrodes from one end face of the optical crystal substrate, each of the individual electrodes occupies the individual electrode occupied by the individual electrode. A region on the electro-optic crystal substrate in the arrangement direction of the electrodes,
It is characterized in that it is formed in a shape that is partially shared with adjacent individual electrodes.

[0010] Here, the opening means a portion sandwiched between opposing electrodes. When this opening is set in a light transmitting state, the light transmittance in the opening is not always uniform over the entire opening and does not always coincide with the light transmitting region.

The shape of each individual electrode is a trapezoidal shape in which at least one of a pair of sides intersecting with the arrangement direction of the individual electrodes has a predetermined angle with respect to the traveling direction of the light. When a predetermined angle is θ and the length of the one side is L, it is preferable that a distance d between the adjacent individual electrodes satisfies d <L × sin θ.

The "trapezoidal shape" includes a rhombus and a parallelogram, and the arrangement may be such that the trapezoids are arranged in the same direction or nested.

[0013] When the predetermined angle is θ and the length of the one side is L, the interval d between the adjacent individual electrodes is d <L × sin θ. The predetermined angle θ means that electrodes adjacent to each other with an electrode distance d therebetween have an angle enough to overlap (share a region) at the distance d. In the above equation, the projection length of the length L of the one side in the optical axis direction is L ′.
Has the same meaning as d <L ′ × tan θ.

[0014]

According to the light modulation element of the present invention, each of the plurality of individual electrodes arranged on one surface of the electro-optic crystal substrate partially shares the area in the arrangement direction of the individual electrodes with the adjacent individual electrodes. When each opening is set in a light transmitting state, a portion showing a predetermined amount, for example, a transmitted light amount equal to or higher than a power threshold necessary for image formation on a binary photosensitive material, is formed by the electrode. Is wider than a conventional element having a rectangular shape and the same opening pitch. Therefore, when the present light modulation element is used even when exposing a binary photosensitive material, the width of the line image of the image formed by the light transmitted through each opening is smaller than that of a conventional light modulation element having rectangular individual electrodes. As compared with the case, the thinning is reduced, and as a result, a good image can be obtained.

[0015]

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

FIG. 1 shows an electrode arrangement of a light modulation device according to an embodiment of the present invention (bonding wires for power supply are not shown).
(FIGS. 3A and 3B) and a transmitted light profile (FIG. 3C).

The light modulation element 10 of the present invention comprises an electro-optic crystal substrate 11 made of PLZT ceramic,
And a plurality of individual electrodes 13 formed on the upper surface (FIG. 1A). FIG.
FIG. 2B is a diagram of the light modulation element 10 shown in FIG. As shown in FIG. 1B, in the present light modulation element 10, the side of each individual electrode 13 that intersects the x-axis has a predetermined angle θ with respect to the z-axis, and the individual electrode 13 has a parallelogram shape. It is characterized by being formed. In addition,
As shown in FIG. 2, the light modulation element 10 of the present invention is disposed on a temperature adjusting assembly 20, and each individual electrode 13 is connected to a drive circuit (not shown). Note that the temperature control assembly 20
Includes a thermoelectronic element 21, a heat radiation fin 22, and a thermistor 23.

In the following, the structure of the present light modulation element will be described together with the manufacturing method.

As the electro-optical medium, (La _x Pb _1-x ) (Zr _y Ti
_1-y ) _{1-x / 4} O ₃ , using a PLZT ceramic having a composition ratio of x / y / 1-y = 9/65/35 in units of% and an average grain size of 4 μmφ. 250 PLZT ceramic
A wafer sliced to a thickness of μm and slightly polished on both sides is used.

First, a Cr / Au laminated film is formed as a common electrode 12 on one side of the wafer by a vacuum deposition method. At this time, the thickness of the Cr film is 50 A (angstrom), and the thickness of the Au film is 500 A. Next, an individual electrode group is formed by a lift-off method on the other surface opposite to the surface on which the common electrode 12 is formed.
A photoresist is applied to the surface on which the individual electrodes 13 are to be formed, and is exposed and developed using a photomask provided with a pattern such as an individual electrode pattern and a cutting mark for cutting into individual elements in advance. Form. Thereafter, a Cr / Au electrode is formed by a vacuum deposition method in the same manner as the formation of the common electrode. Finally, the wafer is immersed in acetone to dissolve the photoresist pattern, lift off the Cr / Au thin film deposited on the photoresist pattern, and form a desired electrode pattern (a plurality of individual electrodes 13). obtain.

In this embodiment, as the geometric dimensions of the light modulation element, the aperture pitch is 100 μm, and the shape of the individual electrodes is width (x direction) = 90 μm and length (z axis = projection in the direction of the optical axis). Length) = 2 mm, the angle θ between the optical axis (z-axis) and the side of the individual electrode was 1 °, and the distance between electrodes (x direction) was 10 μm.
The opening pitch / PLZT plate thickness ratio is 1 / 2.5.

Here, the angle θ formed between the optical axis and the side of the individual electrode is such that adjacent individual electrodes share a part of the region of the substrate in the x-axis direction, ie, when viewed from the z direction, An angle is required such that a part of the end overlaps with the adjacent electrode. As a lower limit, at least an angle at which adjacent electrodes overlap at one point is necessary. For example, in this embodiment, tan ^-1 (10 μm / 2 mm) = 0.
3 ° is required. Also, since the necessary amount of overlap differs depending on the type of photographic material to be recorded, the upper limit of the angle varies depending on the photographic material to be recorded, but it is preferable that the angle overlaps at about 1/3 of the aperture pitch. For the length of the light modulation element of this embodiment = 2 mm, tan
^-1 (60 μm / 2 mm) to about 2 °.

In this embodiment, the electrodes are parallelograms. However, as shown in FIG. 3A, the electrodes may be nested as trapezoids having similar angles. In addition,
Any shape may be used as long as the shapes overlap each other when viewed from the Z-axis direction.
The shape may be triangular or polygonal as shown in FIG. Next, the wafer is cut into each element by a dicer. Each element had a shape of width (x direction) = 26 mm (256 openings) and length (z direction) = 2 mm.

The light incident end face 15 and the output end face 16 of each cut element are optically polished, and then coated with a non-reflection coating for the wavelength of light actually used. Here, the SiO ₂ film is used for the anti-reflection coating, but may be made of other materials.

The surface on the side of the processed element 10 on which the common electrode 12 is formed (the surface of the common electrode 12) is attached to a temperature adjusting assembly.
It is fixed on a base plate (not shown) mounted on 20. Since the base plate also serves as an electrical terminal of the common electrode, a material having good electrical conductivity and good thermal conductivity is desirable. Here, a base plate made of aluminum (Al) is used.
A conductive adhesive material was used for bonding with FIG. 10 (FIG. 1). In addition,
For this bonding, solder or the like may be used. A hole for inserting a thermistor for temperature detection is provided in a portion of the base plate near the electro-optical element 10, and a thermistor 23 is inserted therein. Finally, each individual electrode 13 is connected to a bonding pad 24 connected to the drive circuit by wire bonding.

The light modulation device 10 produced as described above
Is used in an optical system 30 as shown in FIG. FIG. 4 is a side view of the optical system 30 of the recording apparatus including the light modulation element 10. Laser light L emitted from laser light source 31
Is shaped into linear light for illuminating the entire light modulating element 10 by a lens group 33 including a cylindrical lens 32. The shaped light is passed through a polarizer (not shown in FIG. 3) when the polarization ratio is insufficient, and then the polarization direction is changed by the half-wave plate 34 to 45 with respect to the x-axis of the light modulation element 10. ° rotate the element
It is incident on 10. The light incident on the light modulation element 10 is emitted with its polarization plane rotated by birefringence generated in the electro-optic medium according to the voltage applied to the individual electrodes 13 of the modulation element 10.

In the present embodiment, 80 V was applied between the electrodes corresponding to the openings to be set in the light transmitting state.

The light transmitted through the light modulation element 10 is again reduced to a half.
The light is returned by 45 ° at the wave plate 35 (the half-wave plate 35 is not always necessary). The modulation is converted to a change in light intensity. afterwards,
The aperture image is reduced to a desired size by the imaging lens system 37, and is formed on the photosensitive material surface on the drum 38. In the present embodiment,
The aperture pitch of the light modulating element 10 was reduced from 100 μm to 30 μm.

FIG. 1C shows continuous openings a, b, and c.
2 shows an example of a transmitted light profile when is set to a light transmitting state / light blocking state / light transmitting state. in this way,
The amount of light transmitted through the openings a and c in the light transmitting state exceeds the threshold level Th of the light-sensitive material at a width substantially equal to the opening width, and the adjacent openings are continuously in the light transmitting state. Even if it is not, the image line formed by the light emitted from each opening has almost no thinning, and a good image can be obtained even on the binary photosensitive material. Specifically, the width of the line image when the threshold level Th of the power for forming an image was 80% was 1.0 times the aperture pitch.

[Brief description of the drawings]

FIG. 1 is a light modulation element according to an embodiment of the present invention.

FIG. 2 is a light modulation device in which a control circuit is arranged in the light modulation element of the present invention.

FIG. 3 is a diagram showing a shape of a light modulation element of the present invention.

FIG. 4 is a side view of an optical system of a recording apparatus provided with the light modulation element of the present invention.

FIG. 5 is a conventional end-surface incidence type light modulation element.

[Explanation of symbols]

 10 light modulation element 11 electro-optic crystal substrate 12 common electrode 13 individual electrode 20 temperature control assembly 21 thermoelectronic element 22 heat radiation fin 23 thermistor 24 bonding pad 31 laser light source 32 cylindrical lens 33 lens group 34, 35 λ / 2 plate 36 polarized light Child 37 Imaging lens system 38 Drum

Claims (2)

[Claims] 1. An electro-optic crystal substrate in which a plurality of individual electrodes are one-dimensionally arranged on one surface and a common electrode is formed on the other surface to face all of the plurality of individual electrodes. An opening for switching each part of the electro-optic crystal substrate sandwiched between the common electrode and each of the individual electrodes between a state in which light is transmitted and a state in which light is blocked by controlling a voltage between the opposing electrodes; A light modulator that modulates light incident on the opening from a direction perpendicular to the arrangement direction of the individual electrodes from one end surface of the electro-optic crystal substrate, wherein each of the individual electrodes is A light modulation element, wherein a region of an electrode on the electro-optic crystal substrate in the arrangement direction of the electrode is partially shared with an adjacent individual electrode. 2. Each of the individual electrodes has a trapezoidal shape in which at least one of a pair of sides intersecting with the arrangement direction of the individual electrodes has a predetermined angle with respect to a traveling direction of the light. 2. The light modulation element according to claim 1, wherein, when an angle is θ and a length of the one side is L, a distance d between the adjacent individual electrodes is d <L × sin θ.