JP5249008B2 - Light modulator - Google Patents

Description

  The present invention relates to an optical modulator that modulates incident light.

Conventionally, a method of performing light modulation using a material whose refractive index changes by an electric field such as lithium niobate (LiNbO ₃ ) is known. For example, Patent Document 1 discloses an optical modulator in which a plurality of electrode elements are arranged in one direction on one main surface of a thick plate-like electro-optic substrate. By applying a voltage between the electrode elements to generate an electric field inside the substrate, it is possible to diffract the light traveling inside the electro-optic substrate.

  Actually, the range in which the refractive index changes (range in the thickness direction) inside the electro-optic substrate depends on the voltage applied between the electrode elements. Therefore, in the optical modulator of Patent Document 1, the electrode element is elongated in the light traveling direction, and light that is incident from one end surface of the electro-optic substrate and travels inside the main surface is formed on the electrode element. On the other hand, the light is incident at a small angle (at a large incident angle) and totally reflected by the main surface, thereby realizing a phase difference necessary for diffracting light. At this time, it is necessary to apply a relatively large voltage of 60 V to 100 V between the electrode elements.

  In Non-Patent Document 1, in a polarizer, one electrode is provided on each of the upper and lower surfaces of a lithium niobate substrate on which a periodically poled structure is formed, and a voltage applied between the upper electrode and the lower electrode is set. A technique is disclosed in which light incident on the substrate is emitted as 0th-order diffracted light by changing, or is emitted as (± 1) -order diffracted light by Bragg diffraction.

On the other hand, in Patent Document 2, a diffraction grating type in which a fixed ribbon and a flexible ribbon are alternately formed on a substrate and the depth of the diffraction grating can be changed by bending the flexible ribbon with respect to the fixed ribbon. The light modulation element is disclosed. In the light modulation element of Patent Document 2, one adjacent fixed ribbon and one flexible ribbon are used as one grating element, and each grating element can be independently shifted between a reflection state and a diffraction state. Accordingly, a technique is disclosed in which the address resolution in drawing on the photosensitive material is set to a size corresponding to the width of one lattice element of the irradiation region on the photosensitive material.
JP 2000-313141 A JP 2007-121881 A Harald Gnewuch, Christopher N. Pannell, Graeme W. Ross, Peter GR Smith, and Harald Geiger, "Nanosecond Response of Bragg Deflectors in Periodically Poled LiNbO3", IEEE PHOTONICS TECHNOLOGY LETTERS, DECEMBER 1998, VOL. 10, NO. 12, p .1730-1732

  By the way, in order to realize high-speed modulation in the optical modulator, it is necessary to reduce the voltage applied between the electrode elements. In addition, when such an optical modulator is used in an image recording apparatus that records an image on a recording material by irradiating the recording material with light, the distance between the electrode elements is increased in correspondence with higher definition of the image. In this case, it is necessary to shorten the voltage applied between the electrode elements. However, in Patent Document 1, it is necessary to apply a relatively large voltage (for example, 100 V) between the electrode elements in order to cause a phase difference necessary for diffraction in incident light, thereby reducing the voltage between the electrode elements. I can't. In addition, the distance between the electrode elements cannot be shortened in order to prevent the occurrence of discharge (leakage) between the electrode elements.

  The present invention has been made in view of the above problems, and aims to reduce the voltage applied between electrodes in an optical modulator and reduce the control pitch.

The invention described in claim 1 is an optical modulator, which is a plate-like member formed of a material whose refractive index changes by an electric field, and the direction of polarization generated when an electric field is applied is opposite A first polarization part and a second polarization part, which have a periodically poled structure in which the first polarization part and the second polarization part are alternately arranged in a predetermined polarization part arrangement direction, and extend in the polarization part arrangement direction that enters the inside from one end face The light is guided along a traveling direction which is a direction perpendicular to the polarization portion arrangement direction or is inclined at a predetermined angle with respect to the direction perpendicular to the polarization portion arrangement direction, and the periodic polarization inversion structure And a first base portion provided on one main surface and the other main surface of the base portion with the periodic polarization reversal structure interposed therebetween, respectively, and a base portion that leads to the other end surface opposite to the one end surface. An electrode portion and a second electrode portion, the first electrode portion and the front A modulation unit that diffracts light incident on the base unit by applying a voltage between the second electrode unit and causing a periodic refractive index change in the polarization unit arrangement direction in the periodic domain-inverted structure. And the first electrode portion includes a plurality of first electrodes arranged in an electrode arrangement direction that is a direction parallel to the polarization portion arrangement direction or a direction perpendicular to the traveling direction, a plurality of first electrodes each first electrode is the Rukoto disposed in the polarized portion arranged first polarized portion of the 4 following a predetermined number of consecutive in the direction and the polarized portion on group as a second polarization unit, the a plurality of first electrodes corresponding to the plurality of polarized portion group, before Symbol base portion, in the state where voltage is not applied between the second electrode portion and the first electrode, wherein the first electrode Zero-order diffracted light is emitted from the polarized portion group corresponding to In a state where a voltage is applied between each first electrode and the second electrode portion, the polarization unit group corresponding to each first electrode functions as a phase diffraction grating, and each first electrode from the polarized portion groups corresponding to the diffracted light is emitted, application of voltage between each of the said and the plurality of first electrode the second electrode portion by being controlled by independent, said plurality of light emitted from the other end face through said plurality of polarized portion group corresponding to the first electrode is individually modulated, the two or more first electrode voltage between the second electrode portion In the applied state, the voltages applied between the two or more first electrodes and the second electrode portion are equal .

  In the present invention, the voltage applied between the electrodes in the optical modulator can be lowered.

  FIG. 1 is a diagram showing a configuration of an image recording apparatus 1 according to the first embodiment of the present invention. The image recording apparatus 1 has an optical head 2 that emits drawing light along the Y direction in FIG. 1 (a direction parallel to the optical axis J1 of the optical head 2), and a recording material 9 on which an image is recorded. A holding drum 70 that is a holding unit to hold, and a control unit 4 that performs overall control of the image recording apparatus 1 are provided. The recording material 9 is irradiated with drawing light from the optical head 2 while being scanned, whereby an image is recorded (that is, an image is drawn by light irradiation). As the recording material 9, for example, a photosensitive material such as a printing plate and a plate forming film is used. A photosensitive drum for plateless printing may be used as the holding drum 70. In this case, the recording material 9 corresponds to the surface of the photosensitive drum, and the holding drum 70 is regarded as holding the recording material 9 integrally. be able to.

  The holding drum 70 is rotated by the motor 81 about the central axis of the cylindrical surface, so that the optical head 2 is relative to the recording material 9 in the main scanning direction (that is, the direction perpendicular to the rotation axis of the holding drum 70). Move at a constant speed. The optical head 2 can be moved by a motor 82 and a ball screw 83 in a sub-scanning direction parallel to the rotation axis of the holding drum 70 (that is, the X direction in FIG. 1 perpendicular to the main scanning direction). Is detected by the encoder 84. In this manner, the scanning mechanism including the motors 81 and 82 and the ball screw 83 causes the irradiation position on the recording material 9 of the light from the optical head 2 to be relative to the recording material 9 in the main scanning direction at a constant speed. And move relatively in the sub-scanning direction intersecting the main scanning direction.

  2 and 3 are diagrams showing the internal configuration of the optical head 2 in a simplified manner. 2 shows the optical head 2 upward (ie, the Z direction perpendicular to the X direction and the Y direction in FIG. 1) perpendicular to the optical axis J1 and the sub-scanning direction of the optical head 2 in FIG. 1 shows the internal configuration of the optical head 2 when viewed from the (+ Z) side in FIG. 1, and FIG. 3 shows the optical head 2 side viewed from the side opposite to the motor 82 in FIG. 1 along the sub-scanning direction. 2 shows the internal configuration of the optical head 2 (when viewed from the (−X) side of the optical head 2 toward the (+ X) direction).

  The optical head 2 shown in FIGS. 2 and 3 is a laser that emits a light beam having a predetermined wavelength (for example, 830, 635, 405, or 355 nanometers (nm)) (a semiconductor in which a plurality of semiconductor lasers are arranged). A light source unit 21 having a laser array or another type of light emitting element such as a lamp) and a light modulator 3 on which a light beam from the light source unit 21 is incident. The optical modulator 3 is a thin plate-like (slab-like) member formed of an electro-optic crystal that is a material whose refractive index changes with an electric field, and light that enters the base portion 31. A modulation unit 32 for diffraction is provided.

In the present embodiment, base portion 31 is formed of a single crystal of lithium niobate (LiNbO ₃ ) (that is, lithium niobate, abbreviated as LN). The base portion 31 is a single crystal of lithium tantalate (LiTaO ₃ ) (that is, lithium tantalate, abbreviated as LT), etc. It may be formed of the material.

  2 and 3, the modulation unit 32 includes a first electrode unit 33 provided on a main surface 311 on the (+ Z) side of the base unit 31 (hereinafter referred to as an “upper surface 311”). 3, the second electrode portion 34 is provided on the (−Z) side main surface 312 (hereinafter referred to as “lower surface 312”) of the base portion 31. As shown in FIG. 2, the first electrode portions 33 are arranged in a predetermined electrode arrangement direction (that is, the X direction in FIGS. 2 and 3) and each is in the optical axis J1 direction (that is, the light traveling direction). ) And extending in the Y direction, and the plurality of first electrodes 331 are individually connected to the potential applying unit 41 of the control unit 4. In the present embodiment, the first electrode portion 33 is described as including 15 first electrodes 331, but actually, a larger number of first electrodes 331 are provided on the upper surface 311 of the base portion 31. The second electrode portion 34 shown in FIG. 3 includes a single second electrode 341 (that is, a common electrode) that faces the plurality of first electrodes 331 of the first electrode portion 33 with the base portion 31 interposed therebetween, and has a ground potential. Is connected to the grounding portion 5 for providing

  4 is a cross-sectional view of the optical modulator 3 at the position AA in FIG. 2. In FIG. 4, illustration of parallel oblique lines in the cross section of the base portion 31 is omitted (the same applies to FIG. 11). . As shown in FIG. 4, the base portion 31 includes a plurality of first polarization portions 3111 and a plurality of second polarization portions 3112 in a predetermined polarization portion arrangement direction (that is, the X direction in FIG. 4). The periodic polarization inversion structures 310 are alternately arranged in a direction parallel to the arrangement direction. The plurality of first polarization units 3111 and the plurality of second polarization units 3112 are band-shaped portions extending in the Y direction perpendicular to the polarization unit arrangement direction. In the first polarization unit 3111 and the second polarization unit 3112, the crystal axis Therefore, the direction of polarization generated when an electric field in the Z direction is applied to the periodically poled structure 310 is reversed. In addition, the orientation of the crystal axis in the portion around the periodically poled structure 310 of the base portion 31 is the same as that of the second polarization portion 3112. The periodic polarization reversal structure 310 of the base portion 31 applies a very high voltage in the Z direction to a site to be the first polarization portion 3111 of the base portion 31 before the periodic polarization reversal structure 310 is formed. It is formed by reversing the direction of polarization at a site that is to become the one polarization portion 3111.

In the present embodiment, the widths in the polarization portion arrangement direction (X direction) of each first polarization portion 3111 and each second polarization portion 3112 in the periodically poled structure 310 are 1.25 μm to 5 μm (in this embodiment, The first polarization part 3111 and the second polarization part 3112 are both set to 5 μm.), The pitch of the plurality of first polarization parts 3111 in the polarization part arrangement direction, and the polarization part arrangement direction of the plurality of second polarization parts 3112 The pitch in each is 2.5 to 10 μm. In the following description, one first polarization portion 3111 and one second polarization portion 3112 adjacent in the polarization portion arrangement direction are collectively referred to as one polarization pair 3110, and a plurality of polarization pairs 3110 in the polarization portion arrangement direction. The pitch (in this embodiment, 10 μm) is called polarization versus pitch.

  The first electrode part 33 and the second electrode part 34 are arranged with the periodic polarization reversal structure 310 of the base part 31 interposed therebetween, and each first electrode 331 of the first electrode part 33 is continuous 2 in the polarization part arrangement direction. The first polarization unit 3111 and the second polarization unit 3112 (that is, one polarization pair 3110) are arranged on a polarization unit group.

  In the optical modulator 3, a plus (+) potential (for example, 2 V to 25 V) is applied from the potential applying unit 41 to the first electrode 331 of the first electrode unit 33 (that is, the first electrode unit 33 and the second electrode 3). By applying a voltage in the Z direction between the electrode part 34), in the polarization part group corresponding to the first electrode 331, the polarization direction of the first polarization part 3111 becomes the (−Z) direction, and the second polarization The polarization direction of the portion 3112 is the (+ Z) direction. In FIG. 4, the direction of polarization of each polarization part is indicated by an arrow.

  Assuming that the refractive index of the base portion 31 in a state where no electric field is generated therein is n, as described above, a potential is applied to the first electrode 331, thereby causing a gap between the first electrode 331 and the second electrode 341. In FIG. 2, an electric field is generated inside the base portion 31 and the direction of polarization of the first polarization portion 3111 becomes the (−Z) direction, whereby the refractive index of the first polarization portion 3111 decreases by Δn to become n−Δn. . Further, when the polarization direction of the second polarization part 3112 becomes the (+ Z) direction, the refractive index of the second polarization part 3112 increases by Δn to become n + Δn. Thereby, between the 1st electrode 331 and the 2nd electrode 341, as shown in FIG. 5, the change of the periodic refractive index in a polarization part arrangement | sequence direction arises. In FIG. 5, the horizontal axis indicates the position in the X direction, and the vertical axis indicates the refractive index. In addition, a first polarization unit 3111 and a second polarization unit 3112 arranged at the position in the X direction on the horizontal axis are shown in the upper part. In the optical modulator 3, when a potential is applied to the plurality of first electrodes 331 of the first electrode portion 33, a periodic refractive index change in the polarization portion arrangement direction occurs in the periodic polarization inversion structure 310.

  The light source unit 21 shown in FIGS. 2 and 3 has a collimator lens (not shown), and the light beam emitted from the laser is converted into parallel light through the collimator lens and enters the cylindrical lens 221. The light that has passed through the cylindrical lens 221 changes from a circular cross section perpendicular to the optical axis J1 to an ellipse that is long in the X direction. That is, the cylindrical lens 221 has a negative power only in the X direction, and the width of the light beam cross section of the light passing through the cylindrical lens 221 is (almost) constant with respect to the optical axis J1 and the Z direction perpendicular to the X direction. .

  The light from the cylindrical lens 221 is incident on the cylindrical lens 222 having a positive power only in the X direction, and the light that has passed through the cylindrical lens 222 is formed into an elliptical shape having a constant cross-section with a long beam cross section in the X direction. The light enters the lens 223. The cylindrical lens 223 has a positive power only in the Z direction, and when attention is paid only to the Z direction, the light passing through the cylindrical lens 223 shown in FIG. (−Y) side end surface (hereinafter referred to as “incident surface”) 313. For the X direction, light from the cylindrical lens 223 shown in FIG. 2 enters the light modulator 3 as parallel light. As described above, in the optical head 2, the illumination optical system 22 is constructed by the cylindrical lenses 221 to 223, and the light from the light source unit 21 extends in the X direction (that is, the polarization unit arrangement direction) by the illumination optical system 22. After being converted to light, the light enters the base portion 31 from the incident surface 313 of the base portion 31 of the optical modulator 3.

  The linear light incident on the inside of the base portion 31 is reflected while being multiple-reflected by the upper surface 311 and the lower surface 312 (that is, the main surfaces 311 and 312 whose normal lines are parallel to the Z direction) of the base portion 31. It travels along the axis J1 (that is, guided along the traveling direction that is perpendicular to the polarization portion arrangement direction) and passes through the periodic polarization reversal structure 310. In the optical modulator 3, control is performed so that an equal potential is applied to each of the three first electrodes 331 (hereinafter referred to as “first electrode group”) that are continuous in the electrode arrangement direction. Here, when attention is paid to one first electrode group (that is, three consecutive first electrodes 331) of the first polarization unit 3111, the potential from the potential applying unit 41 is not applied to the first electrode group. (In other words, in the state where the potentials of the three first electrodes 331 of the first electrode group are set to the ground potential), between the first electrode group and the second electrode 341 in the linear light parallel to the X direction ( That is, the light passing through the three polarization unit groups (polarization pair 3110) corresponding to the first electrode group travels inside the base unit 31 while being in a parallel state with respect to the X direction, and (+ Y ) Side end face (that is, the other end face opposite to the incident face 313, hereinafter referred to as “exit face”) 314 and is emitted from the exit face 314 as zero-order diffracted light.

  Further, in a state where the potential from the potential applying unit 41 is applied to one first electrode group, periodic refraction in the polarization unit arrangement direction due to the electro-optic effect between the first electrode group and the second electrode 341. A change in the rate occurs, and among the linear light parallel to the X direction, light that passes through the three polarization unit groups corresponding to the first electrode group has a periodic phase difference, and diffraction occurs. That is, the portion between the first electrode group and the second electrode 341 of the periodic polarization reversal structure 310 functions as a phase diffraction grating. As a result, the light passing through between the first electrode group and the second electrode 341 among the linear light parallel to the X direction travels in the (+ Y) direction along the optical axis J1 with respect to the X direction. The light is emitted from the emission surface 314 as (± 1) -order diffracted light (of course, higher-order diffracted light is also emitted) away from J1. In the present embodiment, the periodically poled structure 310 functions as a diffraction grating that causes Ramanus diffraction.

  As described above, in the optical modulator 3, the light that passes through between the first electrode group and the second electrode 341 among the linear light and is emitted from the emission surface 314 is expressed as zero-order diffracted light (± 1). Transition to the next diffracted light is possible. As described above, in the optical head 2, the potential applying unit 41 is controlled by the control unit 4, so that a plurality of (in the present embodiment, five) first electrode groups of the first electrode unit 33 are used. A potential is applied individually. Thereby, the light passing through the three polarization unit groups corresponding to the first electrode groups is controlled independently from the light passing through the three polarization unit groups corresponding to the other first electrode groups, and the 0th-order diffracted light Or (± 1) order diffracted light. Thus, the optical modulator 3 according to the present embodiment is a multi-channel optical modulator.

  The zero-order diffracted light from the optical modulator 3 is made substantially parallel to the Y direction by a cylindrical lens 231 having a positive power only in the Y direction, as shown by a thin solid line in FIG. The light enters a lens 232 having a positive power. Here, the front focal point of the lens 232 is a position in the base 31 near the (+ Y) side end of the first electrode 331, and the aperture of the aperture plate 233 is disposed at the rear focal point of the lens 232. Therefore, the 0th-order diffracted light emitted from the emission surface 314 of the base portion 31 is condensed on the aperture plate 233 via the lens 232 as shown by the thin solid line in FIG. Through the lens 234.

  The lens 234 is disposed so that the front focal point is located in the vicinity of the aperture plate 233 and the rear focal point is on the recording material 9 of the holding drum 70 (see FIG. 1), and the 0th-order diffracted light passes through the lens 234. Then, the light is irradiated onto the recording material 9 while condensing in the Z direction at a position where the optical axis J1 and the recording material 9 as the exposure surface intersect.

  Further, the 0th-order diffracted light that has passed between the five first electrode groups and the second electrode 341 enters the lens 234 through the openings of the cylindrical lens 231, the lens 232, and the aperture plate 233, as shown in FIG. The recording material 9 is irradiated through the lens 234 in parallel with the optical axis J1. In FIG. 2, the outer shape of the light from the light source unit 21 is drawn on the (−Y) side of the base unit 31, and the first electrode group and the second electrode 341 are drawn on the (+ Y) side of the base unit 31. A center line J2 of the light beam cross section of the 0th-order diffracted light passing between the two is drawn.

  On the other hand, the (± 1) -order diffracted light that has passed between each first electrode group and the second electrode 341 spreads away from each center line J2 as it moves away from the base portion 31, and is blocked by the aperture plate 233. The recording material 9 is not irradiated. In the optical head 2, a projection optical system 23 (which can be regarded as a schlieren optical system that is telecentric on both sides) is constructed by the cylindrical lens 231, the aperture plate 233, and the lenses 232 and 234.

  In the image recording apparatus 1, for example, among the five first electrode groups of the first electrode unit 33, no potential is applied to the first, third, and fifth first electrode groups from the (+ X) side, and (+ X ) When a predetermined potential is applied to the second and fourth first electrode groups from the side, as shown in FIG. 6, the first, third, and fifth from the (+ X) side on the recording material 9 Three irradiation regions 91 corresponding to the light passing between the first electrode group and the second electrode 341 are formed. In the optical modulator 3, when the zero-order diffracted light is obtained by the three polarization unit groups (polarization pairs 3110) corresponding to the first electrode groups, the potentials applied to the first electrode groups are equalized (this embodiment) In this form, it is 0 V.) Also, the potential applied to each first electrode group when obtaining the (± 1) -order diffracted light is made equal.

  FIG. 7 is a diagram showing a flow of operations in which the image recording apparatus 1 records an image on the recording material 9. When recording an image, first, emission of light from the light source unit 21 is started (step S11). Subsequently, the holding drum 70 is rotated so that the optical head 2 is recorded at a constant speed in the main scanning direction. The optical head 2 moves in the sub-scanning direction in synchronization with the rotation of the holding drum 70 (step S12). In the control unit 4, the light irradiation position on the recording material 9 (that is, the irradiation position on the assumption that the light from the light modulator 3 is always guided to the recording material 9) is synchronized with the relative movement with respect to the recording material 9. Then, the ON state in which the light (that is, the 0th-order diffracted light) from the base portion 31 of the optical modulator 3 is guided to the recording material 9 and the OFF state in which the light is not guided are classified into five states of the first electrode portion 33. An ON / OFF control for switching each of the first electrode groups is performed (step S13), and an image is recorded on the recording material 9. In this way, when an image is recorded on the entire recording material 9 while raster-scanning the light irradiation position from the optical head 2, the holding drum 70 is rotated, the optical head 2 is moved in the sub-scanning direction, and The emission of light from the light source unit 21 is stopped (steps S14 and S15), and the operation of recording an image in the image recording apparatus 1 is completed.

  As described above, in the optical modulator 3, the first electrode portion 33 is provided on the upper surface 311 of the base portion 31 provided with the periodically poled structure 310, and the second electrode portion 34 is provided on the lower surface 312. By applying a voltage between the electrode part 33 and the second electrode part 34, the periodic polarization inversion structure 310 causes a periodic refractive index change in the polarization part arrangement direction, and the light incident on the base part 31 is generated. Diffraction. Thus, by applying a voltage between the first electrode part 33 and the second electrode part 34 provided with the base part 31 in between, a plurality of electrodes on the upper surface of the base part as in Patent Document 1 Unlike the structure in which a periodic refractive index change is caused in the base portion by applying a voltage between adjacent electrodes in FIG. 1, the voltage applied between the first electrode portion 33 and the second electrode portion 34 is reduced. However, a desired electric field in the Z direction can be formed inside the periodically poled structure 310. Then, by reducing the voltage applied between the first electrode portion 33 and the second electrode portion 34, the light modulation speed by the light modulator 3 can be improved. In the optical modulator 3, in order to form a desired electric field inside the periodically poled structure 310, the thickness of the base portion 31 is preferably 50 μm or less (more preferably 30 μm or less).

  In the optical modulator 3, voltages applied to three polarization unit groups (that is, three consecutive polarization pairs 3110) of the periodically poled structure 310 corresponding to the first electrode groups of the first electrode unit 33 are also determined. By independently controlling the voltages applied to the three polarization unit groups corresponding to the other first electrode groups, a plurality of outgoing lights are extracted from the incident light that is linear light, and each of the outgoing lights is turned on / off. OFF can be individually controlled.

  In the image recording apparatus 1, the pitches of the plurality of emitted lights that have passed between the plurality of first electrode groups and the second electrode 341 on the recording material 9 (that is, the recording material 9 having a cross section of the plurality of emitted light beams on the recording material 9). The distance between the central axes, hereinafter referred to as “recording light pitch”) is determined based on the polarization pair pitch of the periodic polarization reversal structure 310. Therefore, in order to reduce the recording light pitch, it is necessary to reduce the polarization pair pitch, and accordingly, the pitch of the plurality of first electrodes 331 is also reduced.

  Here, assuming a structure in which an electric field is generated in a base portion by applying a voltage between adjacent electrodes in a plurality of electrodes on the upper surface of the base portion as in Patent Document 1, in such a structure, If the pitch is reduced, discharge occurs between adjacent electrodes, and it is difficult to form a desired electric field in the base portion.

  On the other hand, in the optical modulator 3 according to the present embodiment, a plurality of first electrodes 331 are provided on the upper surface 311 of the base portion 31, and a second electrode 341 is provided on the lower surface 312 of the base portion 31. The voltage applied between the electrode 331 and the second electrode 341 is individually controlled, and the zero-order diffracted light from the light incident into the base portion 31 by the polarization portion group corresponding to each first electrode group, or ( ± 1) The potential applied to the first electrode group when obtaining the diffracted light is made equal. This makes it possible to reduce the distance between the first electrode groups while preventing discharge between adjacent first electrode groups (that is, to reduce the pitch of the first electrodes 331). As a result, the recording light pitch can be reduced. Reduction (that is, higher definition of an image) can be realized.

  As described above, in the optical modulator 3, the pitch of the plurality of first electrodes 331 of the first electrode portion 33 can be reduced. Therefore, the structure of the optical modulator 3 is an image recording apparatus 1 that requires high definition. Is particularly suitable for an optical modulator that modulates light from a light source. Further, from the viewpoint of high definition of the image recording apparatus 1, the polarization pair pitch is preferably 10 μm or less.

  In the light modulator 3, the light incident on the inside from the incident surface 313 in the base portion 31 is guided in the traveling direction parallel to the upper surface 311 and the lower surface 312 while being repeatedly totally reflected by the upper surface 311 and the lower surface 312. Thereby, it can guide | induce to the output surface 314, suppressing the energy loss of the light which injected into the base part 31 from the incident surface 313. FIG.

  In the optical modulator 3, as described above, a plurality of first electrodes 331 each provided on one polarization pair 3110 are individually connected to the potential applying unit 41, and are individually connected to the plurality of first electrodes 331. The structure is such that a potential can be applied (that is, the potential applied to each first electrode 331 can be controlled independently of the potential applied to the other first electrode 331). For this reason, by changing the control of the potential applying unit 41 by the control unit 4, the number of first electrodes 331 that are continuous in the electrode arrangement direction and always applied with the same potential (that is, included in one first electrode group). The number of first electrodes 331 to be changed) can be easily changed.

  For example, when control is performed such that one first electrode group is configured by four first electrodes 331 that are continuous in the electrode arrangement direction, the first electrode group and the second electrode 341 pass between the first electrode group and the second electrode 341. The length in the X direction of the irradiation region on the recording material 9 of the light guided to the recording material 9 is increased by about 4/3 times compared to the case where the first electrode group is composed of three first electrodes 331. Can be made. Further, when control is performed such that one first electrode group is configured by five first electrodes 331 that are continuous in the electrode arrangement direction, the length in the X direction of the irradiation region on the recording material 9 is the first Compared to the case where the electrode group is composed of three first electrodes 331, the number is about 5/3 times.

  Here, assuming an optical modulator having a structure in which the number of first electrodes included in the first electrode group cannot be changed, in such an optical modulator, an X-direction of an irradiation region on the recording material 9 is assumed. When the length is increased, the emitted light corresponding to two adjacent first electrode groups is turned on (that is, no potential is applied to the six first electrodes 331 included in the two first electrode groups). The length of the irradiation region on the recording material 9 in the X direction is approximately twice as long as the emission light corresponding to one first electrode group is turned on.

  On the other hand, in the optical modulator 3 according to the present embodiment, as described above, the number of the first electrodes 331 included in the first electrode group can be easily changed. The unit for changing the length of the region in the X direction can be reduced (that is, the address resolution is improved). In other words, the control pitch of the optical modulator 3 can be reduced.

  FIG. 8 is a side view showing another example of the optical modulator. In the optical modulator 3a shown in FIG. 8, the thickness of the base part 31a is made thinner than the base part 31 shown in FIG. 3 (for example, 5 μm), and the light incident on the inside of the base part 31a from the incident surface 313 is In the single mode, the light is guided in the Y direction in FIG. Similarly to the optical modulator 3 described above, when a potential is applied to the first electrode group on the upper surface 311, the three polarization unit groups corresponding to the three first electrode units 33 of the first electrode group are used. When (± 1) -order diffracted light is emitted and no potential is applied to the first electrode group, zero-order diffracted light is emitted. In the optical modulator 3a, the intensity distribution in the direction perpendicular to the principal ray of the light emitted from the emission surface 314 is stably brought into a preferable state (Gaussian distribution) by guiding the light in the single mode in the base portion 31a. It becomes possible.

  Further, in the optical modulator 3a, the distance in the Z direction between the first electrode portion 33 and the second electrode portion 34 is made smaller than that of the optical modulator 3 shown in FIG. The potential applied to the first electrode part 33 (that is, applied between the first electrode part 33 and the second electrode part 34 while maintaining the strength of the electric field formed between the second electrode part 34 and the second electrode part 34). Voltage) can be further reduced. On the other hand, in the optical modulator 3 shown in FIG. 3, a large amount of light energy can be propagated by guiding light in the multimode in the base portion 31.

  9 and 10 are side views showing still other examples of the optical modulator, respectively. In the optical modulator 3b shown in FIG. 9, a slab waveguide 315 is formed in the vicinity of the upper surface 311 of the base portion 31b by the annealing proton method. In the optical modulator 3b, the light incident on the inside of the base portion 31b from the incident surface 313 passes only through the slab waveguide 315 whose thickness (that is, the size in the Z direction) is smaller than that of the base portion 31b, and is an exit surface. Since it is radiate | emitted from 314, compared with the base part 31 shown in FIG. 3, the energy loss of the light at the time of passing through the base part 31b can be suppressed more.

  In the optical modulator 3c shown in FIG. 10, a slab waveguide 315a is formed near the center of the base portion 31c in the Z direction (thickness direction). The base portion 31c having the slab waveguide 315a forms a slab waveguide by the annealing proton method in the vicinity of one main surface of the electro-optic crystal half as thick as the base portion 31c. Another electro-optic crystal is formed by overlapping so that the main surface on which the slab waveguide is formed is brought into contact. In the optical modulator 3c, similarly to the optical modulator 3b shown in FIG. 9, the light incident on the inside of the base portion 31c passes through only the slab waveguide 315a and is emitted from the emission surface 314. Energy loss of light when passing can be further suppressed. Further, since the slab waveguide 315a is provided in the vicinity of the center of the base portion 31c in the Z direction, the waveform of light propagating through the slab waveguide 315a is symmetric in the Z direction as compared to the optical modulator 3b shown in FIG. Therefore, the energy loss of light when passing through the base portion 31c can be further suppressed.

  Next, an optical modulator according to the second embodiment of the present invention will be described. FIG. 11 is a diagram illustrating a cross section perpendicular to the Y direction of the optical modulator 3d according to the second embodiment, and corresponds to FIG. 4 that is a cross-sectional view of the optical modulator 3 according to the first embodiment. To do. As shown in FIG. 11, in the optical modulator 3d, the light shown in FIGS. 1 to 4 is different from the optical modulator 3 shown in FIG. 4 except that the shape and arrangement of the first electrode 331 of the first electrode portion 33 are different from those of the optical modulator 3 shown in FIG. It has the same structure as the modulator 3. In the following description, components corresponding to the optical modulator 3 of the optical modulator 3d are denoted by the same reference numerals.

  In the first electrode portion 33 of the optical modulator 3d shown in FIG. 11, 30 strip-shaped first electrodes 331 extending in the Y direction are arranged in the X direction, which is the electrode arrangement direction, and each first electrode 331 is It is arranged on one first polarization part 3111 or second polarization part 3112. The plurality of first electrodes 331 are individually connected to the potential applying unit 41 (see FIGS. 2 and 3) of the control unit 4. In the optical modulator 3d, the six first electrodes 331 that are continuous in the electrode arrangement direction form a first electrode group that is controlled so that the potentials are always equal.

  In the optical modulator 3d, as in the first embodiment, the voltage applied between the first electrode portion 33 and the second electrode portion 34 is reduced, and the Z-direction inside the periodic polarization inversion structure 310 is reduced. A desired electric field can be formed. In addition, the voltages applied to the six polarization portions (that is, three consecutive polarization pairs 3110) of the periodic polarization reversal structure 310 corresponding to the first electrode groups of the first electrode portion 33 are set to the other first electrode groups. By independently controlling the voltages applied to the six polarization sections corresponding to the above, it is possible to extract a plurality of outgoing lights from the incident light that is linear light, and to individually control the ON / OFF of each outgoing light it can. Furthermore, the potential applied to the first electrode group when the 0th-order diffracted light or (± 1) th-order diffracted light is obtained from the light incident into the base portion 31 by the polarization unit corresponding to each first electrode group is equalized. Accordingly, it is possible to reduce the distance between the first electrode groups (that is, to reduce the pitch of the first electrodes 331) while preventing discharge between the adjacent first electrode groups, and as a result, the recording light pitch. Reduction (that is, higher definition) can be realized.

  In the optical modulator 3d, as described above, the plurality of first electrodes 331, each provided on one polarization unit, are individually connected to the potential applying unit 41, and potentials are individually applied to the plurality of first electrodes 331. (That is, the potential applied to each first electrode 331 can be controlled independently of the potential applied to the other first electrode 331). For this reason, by changing the control of the potential applying unit 41 by the control unit 4, the number of first electrodes 331 that are continuous in the electrode arrangement direction and always applied with the same potential (that is, included in one first electrode group). The number of first electrodes 331 to be changed) can be easily changed.

  For example, when control is performed such that one first electrode group is configured by seven first electrodes 331 that are continuous in the electrode arrangement direction, the first electrode group and the second electrode 341 pass between the first electrode group and the second electrode 341. The length in the X direction of the irradiation region on the recording material 9 of the light guided to the recording material 9 is increased by about 7/6 times compared to the case where the first electrode group is composed of six first electrodes 331. Can be made. When control is performed such that one first electrode group is configured by eight first electrodes 331 that are continuous in the electrode arrangement direction, the length of the irradiation region on the recording material 9 in the X direction is set to the first length. Compared to the case where the electrode group is composed of the six first electrodes 331, the number is about 4/3 times. As described above, in the optical modulator 3d, the unit for changing the length in the X direction of the irradiation region on the recording material 9 can be reduced (that is, the address resolution can be improved). In other words, the control pitch of the optical modulator 3d can be reduced.

  In the optical modulator 3d, as in the optical modulator 3 according to the first embodiment, the periodic polarization inversion structure 310 of the base portion 31 is the first of the base portion 31 before the periodic polarization inversion structure 310 is formed. It is formed by applying a very high voltage in the Z direction to a part to be the polarization part 3111 and inverting the polarization direction of the part to be the first polarization part 3111. When the periodic polarization reversal structure 310 is formed in the optical modulator 3d, the first electrode 331 (that is, a plurality of first electrodes arranged in the electrode arrangement direction) provided on a site to be the first polarization part 3111 is formed. Since the high voltage is applied using every other first electrode 331 of the one electrode 331, the optical modulator 3d can be easily manufactured.

  In the optical modulator 3d, instead of the base portion 31, base portions 31a to 31c shown in FIGS. 8 to 10 may be provided.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various change is possible.

  For example, in the optical modulator 3 according to the first embodiment, the first electrode 331 of the first electrode portion 33 may be provided on three or four polarization portions that are continuous in the polarization portion arrangement direction. Good. That is, the first electrode 331 is a polarization unit group (the optical modulator according to the second embodiment) that is a predetermined number of four or less first polarization units 3111 and second polarization units 3112 that are continuous in the polarization unit arrangement direction. Like 3d, it is arranged on one polarization part (including the case where the first polarization part 3111 or the second polarization part 3112 is a polarization part group). Further, in the second electrode portion 34, instead of the second electrode 341 that is a common electrode, a plurality of second electrodes that are opposed to each other with the base portion 31 sandwiched between the plurality of first electrodes 331 are provided. A voltage may be individually applied between the first electrode 331 and the second electrode 341 of the set.

  In the above-described optical modulators 3, 3a to 3d, the thickness of the base portion may be changed as appropriate. However, from the viewpoint of suppressing the energy loss of light when passing through the base portion, the thickness of the base portion is preferably 3 μm or more. The slab waveguides 315 and 315a of the optical modulators 3b and 3c may be formed by a method other than the annealing proton method.

  In the optical modulators 3, 3a to 3d, the periodic polarization inversion structure may function as a diffraction grating that causes Bragg diffraction by applying a voltage to the periodic polarization inversion structure of the base portion. In this case, the traveling direction of the light incident on the periodically poled structure 310 is a direction inclined at a predetermined angle that satisfies the Bragg condition with respect to the direction perpendicular to the polarization portion arrangement direction. The electrode arrangement direction in which the plurality of first electrodes 331 are arranged may be parallel to the polarization portion arrangement direction, or may be a direction perpendicular to the light traveling direction.

  In the optical modulators 3, 3a to 3d, ON / OFF control of light irradiation with respect to the irradiation position of the light on the recording material 9 is performed. In the optical modulators 3, 3a to 3d, the first electrode unit 33 and the first light source 33 Multi-tone light irradiation control may be performed by adjusting a voltage applied between the two electrode portions 34.

  In the image recording apparatus 1, only the 0th-order diffracted light from the light modulators 3, 3a to 3d is guided onto the recording material 9 by the projection optical system 23. Depending on the design of the image recording apparatus, the light modulators 3, 3a The 0th order diffracted light from ˜3d may be shielded, and the (± 1) order diffracted light may be guided onto the recording material. That is, one of the 0th-order diffracted light and the (± 1) th-order diffracted light from the light modulators 3, 3 a to 3 d to which the light from the light source unit 21 is incident is guided onto the recording material 9 by the projection optical system 23. In the image recording apparatus, it is possible to record an image by modulation control of the optical modulators 3, 3a to 3d.

  The image recording apparatus provided with the optical modulators 3, 3a to 3d includes a recording material by a scanning mechanism that moves the optical head relative to the plate-shaped recording material placed on the stage along the recording material. An image may be recorded by controlling the light modulators 3, 3 a to 3 d while moving the irradiation positions of the light from the light modulators 3, 3 a to 3 d above relative to the recording material. . In the image recording apparatus 1 of FIG. 1, the light irradiation position on the recording material 9 may move in the X direction by providing a polygon mirror in the optical head.

  The recording material that holds the image information may be a photosensitive material such as a printed wiring board or a semiconductor substrate, or may be another photosensitive material, and is a material that reacts to heat due to light irradiation. It may be. The light modulators 3, 3a to 3d may be used for purposes other than image recording. In this case, the object to be irradiated with light may be other than the recording material.

1 is a diagram illustrating a configuration of an image recording apparatus according to a first embodiment. It is a figure which shows the internal structure of an optical head. It is a figure which shows the internal structure of an optical head. It is sectional drawing of an optical modulator. It is a figure which shows distribution of a refractive index. It is a figure which shows the light irradiation area | region on a recording material. It is a figure which shows the flow of the operation | movement which records an image on a recording material. It is a figure which shows the other example of an optical modulator. It is a figure which shows the other example of an optical modulator. It is a figure which shows the other example of an optical modulator. It is sectional drawing of the optical modulator which concerns on 2nd Embodiment.

Explanation of symbols

3, 3 a to 3 d Optical modulator 31, 31 a to 31 c Base part 32 Modulating part 33 First electrode part 34 Second electrode part 310 Periodic polarization inversion structure 311 Upper surface 312 Lower surface 313 Incident surface 314 Output surface 315, 315a Slab waveguide 331 1st electrode 341 2nd electrode 3110 Polarization pair 3111 1st polarization part 3112 2nd polarization part J1 Optical axis

Claims (1)

An optical modulator,
A plate-like member made of a material whose refractive index changes with an electric field, and a first polarization part and a second polarization part having opposite directions of polarization generated when an electric field is applied are predetermined polarizations. Having a periodically poled structure alternately arranged in the partial arrangement direction, and linear light extending in the polarization part arrangement direction that is incident on the inside from one end face is a direction perpendicular to the polarizing part arrangement direction, or Another end face that is guided along a traveling direction that is inclined at a predetermined angle with respect to the direction perpendicular to the polarization section arrangement direction, passes through the periodic polarization reversal structure, and is opposite to the one end face. A base that leads to
A first electrode portion and a second electrode portion provided respectively on one main surface and the other main surface of the base portion with the periodic polarization reversal structure interposed therebetween; the first electrode portion and the second electrode portion; A modulation unit that diffracts light incident into the base unit by causing a periodic refractive index change in the polarization unit arrangement direction in the periodic polarization inversion structure by applying a voltage between
With
The first electrode unit includes a plurality of first electrodes arranged in an electrode arrangement direction which is a direction parallel to the polarization part arrangement direction or a direction perpendicular to the traveling direction,
Wherein each of the first electrodes of the plurality of first electrodes, the Rukoto disposed in the polarized portion first polarized portion of the 4 following a predetermined number of contiguous in the array direction and polarized portion on group as a second polarization unit, The plurality of first electrodes correspond to a plurality of polarization unit groups,
In the previous Symbol base portion,
In a state where no voltage is applied between each first electrode and the second electrode portion, zero-order diffracted light is emitted from the polarization portion group corresponding to each first electrode,
In a state in which a voltage is applied between each first electrode and the second electrode portion, the polarization unit group corresponding to each first electrode functions as a phase diffraction grating, and each first electrode has Diffracted light is emitted from the corresponding polarized portion group,
By application of voltage between each of the said and the plurality of first electrode the second electrode portion is controlled by independent, passes through the plurality of polarized portion groups corresponding to the plurality of first electrode The light emitted from the other end face is individually modulated ,
In a state where a voltage is applied between two or more first electrodes and the second electrode part, a voltage applied between each of the two or more first electrodes and the second electrode part. An optical modulator characterized by equality .

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