JP5058935B2 - Optical modulator and image recording apparatus - Google Patents

Description

  The present invention relates to an optical modulator that modulates incident light, and an image recording apparatus that records an image on a recording material by irradiating the recording material with 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 the main surface of a thick plate-like electro-optic substrate. In this optical modulator, electrodes adjacent to each other are disclosed. By applying a voltage between the elements to generate an electric field inside the substrate, it is possible to diffract the light traveling inside the electro-optic substrate. Actually, in the electro-optic substrate, the range in which the refractive index changes (thickness range) depends on the voltage applied between the electrode elements, from the viewpoint of preventing the occurrence of discharge between the electrode elements. There is a certain limit to the increase in voltage. 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.
JP 2000-313141 A

  By the way, in order to reduce the size and improve the safety of the optical modulator, it is necessary to shorten the length of the electrode elements or to reduce the voltage applied between the electrode elements. However, in the optical modulator disclosed in Patent Document 1, as described above, in order to generate a phase difference necessary for diffraction in incident light, the electrode elements are elongated in the light traveling direction and relatively between the electrode elements. It is necessary to apply a large voltage, and the electrode elements cannot be shortened or the voltage between the electrode elements cannot be reduced.

  In addition, in the optical modulator of Patent Document 1, a lens for shaping light incident on the optical modulator is required on the rear side of the optical modulator with respect to the traveling direction of light, and from the optical modulator on the front side of the optical modulator. Another lens for shaping the emitted light is required. Therefore, when the shaping lens is also considered as a component of the optical modulator, the presence of these lenses limits the miniaturization of the optical modulator.

  The present invention has been made in view of the above problems, and aims to reduce the size of an optical modulator or to lower the voltage applied to an electrode in the optical modulator.

  The invention according to 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 is configured to receive light incident on the inside from an incident surface which is one end surface. A base portion that leads to another end surface opposite to the incident surface along a moving direction parallel to one main surface; and the other end surface of the base portion or the vicinity of the other end surface. A mirror that reflects light guided to the other end surface and guides the light to the incident surface along the moving direction, and the main surface of the base portion or both main surfaces of the base portion; A plurality of electrode elements arranged in a direction perpendicular to the electrode, and by applying a voltage between the electrode elements of the electrodes, the light path in the base portion from the incident surface to the other end surface At least partly and from the other end surface to the incident surface In at least a part of both of the light path in the serial base unit, and a modulation unit to diffract light incident causes a change in the periodic refractive index in the arrangement direction within the base unit.

  A second aspect of the present invention is the optical modulator according to the first aspect, wherein the light is made to enter the base portion from the incident surface while being converged in a direction perpendicular to the main surface, and the other. And a shaping lens for receiving and shaping light emitted from the incident surface via the end face.

  The invention according to claim 3 is an optical modulator, which is a plate-like member formed of a material whose refractive index changes by an electric field, and is configured to receive light incident on the inside from an incident surface which is one end surface. A base portion that leads to another end surface opposite to the incident surface along a moving direction parallel to one main surface; and the other end surface of the base portion or the vicinity of the other end surface. A mirror that reflects light guided to the other end surface and guides the light to the incident surface along the moving direction, and the main surface of the base portion or both main surfaces of the base portion; A plurality of electrode elements are arranged in a direction perpendicular to the electrode, and a voltage is applied between the electrode elements of the electrodes, thereby causing a periodic refractive index change in the arrangement direction within the base portion in the vicinity of the electrodes. It is generated at the site of and enters into the base part A modulator that diffracts the light, and makes the light enter the base portion from the incident surface while converging light in a direction perpendicular to the main surface, and light emitted from the incident surface via the other end surface And a shaping lens for receiving and shaping.

  Invention of Claim 4 is an optical modulator of Claim 2 or 3, Comprising: The light which injects into the said base part reflects in the electrode vicinity of the said main surface or both said main surfaces, The said In the vicinity of the electrode in the base portion, a region through which the light passes in a cross section perpendicular to the light path is smaller than the region in the vicinity of the incident surface.

  The invention according to claim 5 is the optical modulator according to claim 4, wherein an optical path length of light from the shaping lens to the mirror and an optical path of light from the mirror to the shaping lens Lights that are equal in length and incident on the base are collected on the mirror with respect to the vertical direction.

  A sixth aspect of the present invention is the optical modulator according to any one of the first to fifth aspects, wherein the light path in the base portion extends from the incident surface to the other end surface, and the other The light path in the base portion from the end surface to the incident surface is the same.

  The invention according to claim 7 is the optical modulator according to claim 6, wherein the mirror is formed on the other end face, and the other end face is inclined with respect to the main face.

  The invention according to claim 8 is the optical modulator according to any one of claims 1 to 3, wherein the base portion is a thin plate member.

  A ninth aspect of the present invention is the optical modulator according to the eighth aspect of the present invention, wherein the electrodes are a set of electrode element pairs formed on both the main surfaces with the base portion interposed therebetween.

  A tenth aspect of the present invention is the optical modulator according to any one of the first to third aspects, wherein the refractive index decreases as the base portion moves away from the main surface in a cross section perpendicular to the moving direction. The refractive index distribution is as follows.

  An eleventh aspect of the present invention is the optical modulator according to any one of the first to third aspects, wherein the base portion is formed on a plate-shaped main body, the main body, and the main surface. A thin layer having a refractive index distribution in which a refractive index decreases as the main body moves away from the thin layer in a cross section perpendicular to the moving direction, and the refractive index of the thin layer is the refractive index distribution. Smaller than the maximum refractive index.

  According to a twelfth aspect of the present invention, in the optical modulator according to any one of the eighth to eleventh aspects, the base portion guides light incident therein to the moving direction in a single mode.

  A thirteenth aspect of the present invention is the optical modulator according to any one of the first to twelfth aspects, wherein the modulation unit includes the electrodes and includes a plurality of electrodes arranged in the arrangement direction.

  The invention described in claim 14 is an image recording apparatus for recording an image on the recording material by irradiating the recording material with light, wherein the light source unit and the light from the light source unit are incident thereon. 14. An optical modulator according to any one of claims 13, an optical system for guiding one of zero-order light or (± 1) -order diffracted light from the optical modulator onto a recording material, and the optical modulator on the recording material A scanning mechanism that moves the irradiation position of light from the recording material relative to the recording material, and a control unit that controls the optical modulator in synchronization with the relative movement of the irradiation position relative to the recording material.

  According to the present invention, it is possible to reduce the size of the optical modulator by efficiently generating a phase change of light, or to reduce the voltage applied to the electrode in the optical modulator, or to converge the light incident on the base portion. In addition, the shaping of the light emitted from the base portion can be realized with one shaping lens, and the light modulator having the shaping lens can be miniaturized.

  Further, in the invention of claim 4, it is possible to efficiently generate a phase change of light by reducing a region through which light passes in the vicinity of the electrode in the base portion. It is possible to simplify the configuration of the optical modulator in which the path from the other end surface to the incident surface is the same.

  In the invention of claim 9, periodic refractive index changes in the arrangement direction can be efficiently generated in the base portion, and in the invention of claim 10, light loss in the base portion can be reduced. .

  Further, in the invention of claim 11, it is possible to reduce the asymmetry of the shape of the region through which light passes in the base portion, and in the invention of claim 12, the intensity distribution of the emitted light can be in a preferable state. In the invention of claim 13, optical modulation in a plurality of channels can be realized.

  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 includes an optical head 2 that emits drawing light along the X direction in FIG. 1, a holding drum 70 that is a holding unit that holds a recording material 9 on which an image is recorded, and an image. A control unit 4 responsible for overall control of the recording apparatus 1 is 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 Y 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 an internal configuration of the optical head 2 when the optical head 2 is viewed from above (that is, (+ Z) side in FIG. 1) along the Z direction perpendicular to the X direction and the Y direction in FIG. 3 shows the optical head 2 side viewed from the opposite side of the holding drum 70 of FIG. 1 along the X direction (that is, viewed from the (−X) side of the optical head 2 toward the (+ X) direction). The internal structure of the optical head 2 in the case) is shown.

The optical head 2 shown in FIGS. 2 and 3 includes a semiconductor laser (semiconductor laser array in which a plurality of semiconductor lasers are arrayed) that emits a light beam having a predetermined wavelength (for example, 830, 635, and 405 nanometers (nm)). Alternatively, the light source unit 21 may include a solid-state laser that emits light of 355 nanometers (nm) subjected to wavelength conversion of a YAG laser, or another type of light-emitting element such as a lamp. The optical modulator 3 in which the light beam from 21 injects along the optical axis J1 is provided. The optical modulator 3 is a thin plate-like (slab-like) member formed of a material whose refractive index changes with an electric field, and a main surface 311 of the base portion 31 that is perpendicular to the optical axis J1. A plurality of electrodes 33 arranged in a proper arrangement direction (X direction in FIGS. 2 and 3). In the present embodiment, the base portion 31 is formed of an electro-optic crystal of lithium niobate (LiNbO ₃ ) (that is, lithium niobate, abbreviated as LN). Note that the base portion 31 is polarized in the crystal by an electric field such as an electro-optic crystal of lithium tantalate (LiTaO ₃ ) (that is, lithium tantalate, abbreviated as LT), and the refractive index changes. You may form with another material.

  4 is a cross-sectional view of the optical modulator 3 at the position indicated by the arrow AA in FIG. 2. In FIG. 4, illustration of parallel oblique lines in the cross section of the base portion 31 is omitted. Each electrode 33 is a set of a plurality of electrode elements 331 connected to a potential applying unit 41 (see FIG. 2) of the control unit 4 and a plurality of electrode elements 332 connected to a grounding unit 34 for applying a ground potential. The electrode elements 331 and the electrode elements 332 are alternately arranged at a constant pitch in the X direction. In the present embodiment, six electrode elements 331 and 332 (that is, three electrode elements 331 and three electrode elements 332) that are continuous in the arrangement direction form one electrode 33, A potential can be individually applied to the electrode 33. In FIG. 4, the electrode elements 331 and 332 included in one electrode 33 are surrounded by a two-dot chain line rectangle.

  Actually, each of the electrode elements 331 and 332 has a long shape in the optical axis J1 direction (Y direction) (for example, a length of 5 millimeters (mm)), and the electrode elements adjacent to each other in the X direction. The distance between the 331 and 332 (center distance) is 5 to 20 micrometers (μm), and the width of the gap between the electrode elements 331 and 332 and the width of the electrode elements 331 and 332 are substantially the same.

  When a predetermined potential is applied from the potential applying unit 41 to the electrode element 331, an electric field is formed from each electrode element 331 toward the adjacent electrode element 332 through the base portion 31. The base portion 31 formed of lithium niobate is refracted by an electric field in the Z direction (that is, the direction corresponding to the electro-optic coefficient r33) in FIG. 4 perpendicular to the arrangement direction (X direction) of the electrode elements 331 and 332. The rate is greatly changed, and a voltage (potential difference) is applied between the electrode elements 331 and 332, and an arrow E1 is added in the vicinity of the electrode elements 331 and 332 inside the base portion 31 in FIG. By generating an electric field in the Z direction, a periodic refractive index change in the arrangement direction occurs in a portion in the base portion 31 in the vicinity of the electrode 33 (similarly in FIG. 15 described later).

  In the present embodiment, the thickness of the base portion 31 (thickness in the Z direction indicated by reference sign D1 in FIG. 4) is, for example, 30 to 50 μm, and the refractive index changes inside the base portion 31. The range in the Z direction (also referred to as the electric field penetration depth) is 30 to 50 μm from the main surface 311 to the (−Z) side, and the change in the refractive index due to the electric field between the electrode elements 331 and 332 is the main surface 311. This occurs up to the vicinity of the main surface 312 on the opposite side.

  The light source unit 21 shown in FIGS. 2 and 3 has a collimator lens (not shown), and the light beam emitted from the semiconductor 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 beam 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 has an elliptical shape with a constant cross-section having a long cross section in the X direction. The light passes through the mirror 231 and enters the cylindrical 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 that has passed through the cylindrical lens 223 in FIG. 3 shows an outer shape with a thin solid line in FIG. In this way, the light enters the end surface (hereinafter referred to as “incident surface”) 313 of the base portion 31 of the optical modulator 3 while condensing. For the X direction, light from the cylindrical lens 223 shown in FIG. 2 enters the light modulator 3 as parallel light. Thus, in the optical head 2, the illumination optical system 22 is constructed by the cylindrical lenses 221 to 223.

  The light that has entered the inside of the base portion 31 is subjected to multiple reflections at the two main surfaces 311 and 312 parallel to each other (the main surfaces 311 and 312 whose normal lines are parallel to the Z direction) of the base portion 31, and the two main surfaces 311. , 312 travels (propagates) along the Y direction (optical axis J1) parallel to the horizontal axis. In addition, a mirror 36 is provided on an end surface 314 (a surface facing the incident surface 313, hereinafter referred to as an “opposing surface 314”) on the opposite side ((+ Y) side) to the incident surface 313 in the base portion 31. The light guided from the incident surface 313 to the opposing surface 314 is reflected by the mirror 36 and guided to the incident surface 313 along the Y direction. Thus, the light reciprocates in the Y direction inside the base portion 31. In the following description relating to the optical modulator 3, the Y direction is also referred to as a moving direction.

  At this time, a state in which the potential from the potential applying unit 41 is not applied to each electrode 33 (more precisely, the electrode element 331) in the optical modulator 3 (that is, a state in which the potential of the electrode element 331 is set to the ground potential). Then, the light passing through the site in the vicinity of the electrode 33 travels inside the base portion 31 while being in a parallel state with respect to the X direction. On the other hand, in a state in which the potential from the potential applying unit 41 is applied to the electrode 33, a periodic refractive index change in the arrangement direction occurs in the base portion 31 in the vicinity of the electrode 33 due to the electro-optic effect. In this case, a periodic phase difference occurs in the light passing through the part, and diffraction occurs (that is, the optical modulator 3 functions as a diffraction grating). As described above, in each electrode 33 of the optical modulator 3, light in a state parallel to the X direction is emitted from the end surface (that is, the incident surface 313) of the base portion 31 on the (−Y) side as zero-order light. It is possible to switch between a state and a state in which (± 1) order diffracted light (of course, higher order diffracted light is also emitted) deviating from the optical axis J1 in the X direction as it travels along the optical axis J1. The

  The 0th-order light or (± 1) -order diffracted light corresponding to each grid-shaped electrode 33 of the optical modulator 3 is substantially parallel to the Z direction by the cylindrical lens 223 having a positive power only in the Z direction described above. After being reflected by the half mirror 231 in FIG. 2, the light enters the lens 232 having a positive power along the optical axis J2 parallel to the X direction. Here, when the change in the optical axis J1 or J2 direction by the half mirror 231 is taken into consideration, the position on the optical axis J1 in the vicinity of the (−Y) side end of the electrode 33 corresponds to the front focal point of the lens 232, and the lens A minute shielding plate 233 is disposed at the rear focal point of H.232. Therefore, the 0th order light that is substantially parallel to both the Y direction and the Z direction is condensed and shielded on the shielding plate 233 via the lens 232. In FIG. 2, the outer shape of light (zero-order light) when no voltage is applied to all the electrodes 33 is indicated by a thin solid line.

  Further, the (± 1) -order diffracted light enters a position away from the optical axis J2 of the lens 232 as will be described later, and enters the lens 234 along a path avoiding the shielding plate 233. The lens 234 is disposed so that the front focal point is located in the vicinity of the shielding plate 233 and the rear focal point is on the recording material 9 of the holding drum 70, and (± 1) -order diffracted light is collected via the lens 234. The recording material 9 is irradiated with light. As described above, in the optical head 2, the projection optical system 23 is constructed by the cylindrical lens 223, the half mirror 231, the shielding plate 233, and the lenses 232 and 234.

  FIG. 5 is a diagram for explaining a light path between the optical modulator 3 and the recording material 9. In FIG. 5, the cylindrical lens 223 and the half mirror 231 are not shown, and the optical axes J1 and J2 of FIG. 2 are arranged on the same line J3, and each component is illustrated.

  As shown in FIG. 5, the lens 232 is actually sufficiently larger than the optical modulator 3 (the same applies to the cylindrical lens 223 and the half mirror 231 in FIG. 2), and any electrode 33 (see FIG. 5, light (0th-order light or (± 1) th-order diffracted light) from each electrode 33 is also incident on the lens 232. For example, the 0th-order light from the electrodes 33 located at both ends is guided to the shielding plate 233 by the lens 232 along the path K2 indicated by a thin solid line in FIG. Further, the (± 1) -order diffracted light enters the position away from the optical axis J3 of the lens 232 along the path K3 indicated by a thin broken line in FIG. 5 and reaches the lens 234 without being blocked by the shielding plate 233. To do. The shielding plate is the same size as the lens 234, and the portion that shields the 0th-order light is used as an opening, so that the (± 1) -order light can be shielded and the 0th-order light is used as the lens. 234. In FIG. 5, such a shielding plate 233a is illustrated by a two-dot chain line. The optical system constructed by the lenses 232 and 234 (which can also be regarded as a schlieren optical system) is bilateral telecentric, and (± 1) -order diffracted light is zero-order light if the shielding plate 233 is omitted. It is guided to a position guided on the recording material 9. In FIG. 5, the principal ray of the zero-order light when the shielding plate 233 is omitted is indicated by a two-dot chain line denoted by reference numeral M <b> 1, and the principal ray M <b> 1 is perpendicular to the recording material 9. In the present embodiment, a reduction optical system is formed by the lenses 232 and 234, and the recording material 9 has a pitch smaller than the arrangement pitch of the electrodes 33 in the optical modulator 3 and is near the plurality of electrodes 33. Are arranged in a sub-scanning direction perpendicular to the main scanning direction.

  FIG. 6 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 relative movement of the irradiation position on the recording material 9 (that is, the irradiation position on the assumption that light from the electrode 33 of the light modulator 3 is always guided to the recording material 9) with respect to the recording material 9. In synchronization, ON / OFF control is performed to individually switch the ON state in which light ((± 1) -order diffracted light) is guided to the recording material 9 and the OFF state in which light is not guided in the plurality of electrodes 33 (step). S13), an image is recorded on the recording material 9. In this way, when an image is recorded on the entire recording material 9 while scanning the irradiation position of the light from the optical head 2, the rotation of the holding drum 70, the movement of the optical head 2 in the sub-scanning direction, and the light source The emission of light from the unit 21 is stopped (steps S14 and S15), and the operation of recording an image in the image recording apparatus 1 is completed.

  By the way, in the optical modulator 91 of the comparative example shown in FIG. 7 having the same configuration as that of the optical modulator in Japanese Patent Application Laid-Open No. 2000-313141 (Patent Document 1), the thickness of the base portion 92 (electro-optic substrate) is large. Therefore, light that is incident from one end face 921 and travels inside the base portion 92 has a plurality of electrode elements (however, in FIG. 7, only one electrode element is denoted by reference numeral 93). Is incident on the main surface 922 on which the array is formed at a small angle (at a large incident angle), is reflected by the main surface 922, and is emitted from the other end surface 923. In the base portion 92, the depth at which the refractive index changes due to the voltage between the electrode elements 93 adjacent to each other (the depth from the main surface 922) is proportional to the square of the voltage, and the distance between the centers of the electrode elements 93 adjacent to each other. Inversely proportional to When the distance between the centers of the electrode elements 93 (the pitch of the electrode elements 93) is about 20 μm, the voltage that can be applied between the electrode elements 93 is from the viewpoint of preventing discharge between the electrode elements 93. The maximum is about 100 volts (V) (usually 80 to 100 V). In this case, the depth at which the refractive index changes due to the electro-optic effect is about 30 μm. As described above, since the portion where the refractive index changes due to the electric field formed by the electrode element 93 on the main surface 922 is only in the vicinity of the main surface 922 in the base portion 92, the base portion 92 proceeds inside the base portion 92. Light is affected by the change in refractive index only in the vicinity of the reflection position on the main surface 922.

  Therefore, in order to cause a phase difference necessary for diffracting the light traveling inside the base portion 92 by a change in the refractive index inside the base portion 92, the main surface 922 on which the electrode element 93 is formed is defined. It is necessary to lengthen the electrode element 93 in the light traveling direction while making light incident at a small angle, and to increase the distance that causes a phase change in the light. In the optical modulator 91 of FIG. 7, in the base portion 92, the angle formed between each of the end surfaces 921, 923 and the main surface 922 is set to an acute angle so that the end surface 921 extends along the direction parallel to the main surface 922. The light incident on the inside is reflected from the main surface 922 only once and emitted from the end surface 923 along the direction parallel to the main surface 922 (that is, the incident optical axis and the outgoing optical axis are matched). Realized.

  On the other hand, in the optical modulator 3 shown in FIGS. 2 and 3, the electrode 33 is formed in the Y direction by using the base portion 31 that is thin enough to allow incident light to be multiple-reflected by the two main surfaces 311 and 312. In almost the entire range, the phase of the light can be changed by the action of the electric field. In other words, the light is allowed to enter the range where the refractive index change occurs in the thickness direction of the base portion 31 a plurality of times, or the light is allowed to stay within this range, and the distance at which the phase change occurs (due to the action of the electric field). The distance at which the change in the refractive index affects the light can be ensured. Further, by providing the mirror 36 on the facing surface 314, a part of the light path (hereinafter referred to as “outward path”) in the base portion 31 from the incident surface 313 to the facing surface 314 and the facing surface 314. In both of part of the light path (hereinafter referred to as “return path”) in the base portion 31 from the first to the incident surface 313, a periodic refractive index change in the arrangement direction can be caused. As a result, the phase change of the light can be generated very efficiently (that is, the diffraction efficiency is improved), and the electrode elements 331 and 332 are shortened in the moving direction as compared with the optical modulator 91 of the comparative example ( For example, by reducing the size of the optical modulator 3 (by reducing the length to half or less), or by reducing the voltage applied between the electrode elements 331 and 332, the safety of handling the optical modulator 3 can be improved. Can do.

  For example, in the optical modulator 91 of the comparative example, the voltage applied between the electrode elements 93 adjacent to each other when the incident light is diffracted is 80 to 100 V. In this embodiment, the electrode element 331 of the electrode 33 is used. , 332 can be set to 60 V or less (40 V or less depending on various conditions), so that the voltage applied between the electrode elements can be compared with the case where the optical modulator 91 of the comparative example is used. The safety concerning the handling of the optical modulator 3 can be improved reliably. In addition, by making the electrode 33 longer in the direction of the optical axis J1, the potential applied to the electrode element 331 can be reduced to 15 V or less (10 V or less depending on various conditions). It is possible to perform modulation at high speed. The reduction of the voltage applied between the electrode elements 331 and 332 can be similarly applied to the second and third embodiments described later.

  In the optical modulator 91 of the comparative example of FIG. 7, the light traveling into the base portion 92 is converged and the light travels with respect to the base portion 92 in order to shape the light emitted from the base portion 92. Lenses 941 and 942 need to be provided as shaping lenses on the rear side and the front side in the direction. Therefore, when the shaping lens is regarded as a constituent element of the optical modulator, the optical modulator 91 of the comparative example has a certain limit in miniaturization due to the presence of these lenses 941 and 942.

  On the other hand, in the optical modulator 3 of FIG. 3, one cylindrical lens 223 causes the light from the light source unit 21 to enter the base unit 31 from the incident surface 313 while converging the light from the light source unit 21. It serves as a shaping lens that receives light emitted from the incident surface 313 via the light and shapes it in a state parallel to the Z direction. Thus, by realizing the convergence of the light incident on the base portion 31 and the shaping of the light emitted from the base portion 31 with one shaping lens, an optical modulator having a shaping lens as a component (and, The optical head 2) can be reduced in size (the same applies to the optical modulator 3 in FIGS. 8, 13, 14, 17, and 19 described later).

  FIG. 8 is a diagram illustrating another example of the optical modulator 3. In the optical modulator 3 of FIG. 8, the (+ Y) side end of the electrode 33 in the Y direction is disposed at substantially the same position as the facing surface 314 of the base 31. As a result, in the optical modulator 3 of FIG. 8, the light phase change continuously occurs immediately before and immediately after the light incident on the base portion 31 from the incident surface 313 is reflected by the mirror 36. Further downsizing of the modulator 3 can be achieved.

  In the optical modulator 3 shown in FIGS. 2 and 8, the electrode elements 331 and 332 are formed on the (+ Z) side main surface 311 of the base portion 31 (of course, they may be formed on the main surface 312. In the optical modulator, electrode elements 331 and 332 may be formed on both main surfaces 311 and 312 of the base portion 31.

  FIG. 9 is a diagram for explaining another example of the electrode. 9 shows the electrode 33a on the base portion 31, and is a cross-sectional view corresponding to FIG. Further, the lower part of FIG. 9 is a diagram showing a change in the refractive index inside the base portion 31 caused by the electrode 33a. The vertical axis shows the amount of change in the refractive index, and the horizontal axis shows the position in the X direction. In the upper part of FIG. 9, the illustration of the parallel oblique lines indicating the cross section of the base portion 31 is omitted (the same applies to the upper part of FIG. 10 and FIG. 15 described later). Although only one electrode 33a is shown in FIG. 9, a plurality of electrodes 33a are actually arranged in the X direction (the same applies to FIG. 10 described later).

  One electrode 33a of the optical modulator 3 shown in the upper part of FIG. 9 includes a plurality of electrode elements 331 formed on one main surface 311 of the base portion 31 and connected to the potential applying portion 41, and the other main surface. A plurality of electrode elements 332 formed on 312 and connected to the ground portion 34. The plurality of electrode elements 332 are respectively arranged at positions facing the plurality of electrode elements 331 across the base portion 31. In the optical modulator 3 having the electrodes 33a, the plurality of electrode elements 332 are arranged in the Z direction perpendicular to both the main surfaces 311 and 312. A plurality of electrode element pairs are arranged in the X direction with the electrode elements 331 and 332 facing each other as one electrode element pair. In each electrode element pair, an electric field is formed in a direction perpendicular to both the main surfaces 311 and 312 (and the light moving direction (Y direction)), as indicated by the arrow E2 in the upper part of FIG. The

  As described above, in the optical modulator 3, when the electric field perpendicular to both the main surfaces 311 and 312 is formed to diffract the light incident on the base portion 31, the electrodes 33 a are connected to the base portion 31. As shown in the lower part of FIG. 9, the electrode element pair arrangement direction (X The periodic refractive index change in (direction) can be efficiently generated. As a result, the phase change of the light is efficiently generated in both the forward path and the return path of the light in the base portion 31, and the length of the electrode 33a in the light moving direction is further shortened or applied to the electrode 33a. Can be further reduced.

  FIG. 10 is a diagram for explaining still another example of the electrode. The upper part of FIG. 10 shows the electrode 33b on the base part 31, and is a cross-sectional view corresponding to FIG. Further, the lower part of FIG. 10 is a diagram showing a change in the refractive index inside the base portion 31 caused by the electrode 33b. The vertical axis shows the amount of change in the refractive index, and the horizontal axis shows the position in the X direction.

  In the electrode 33 b of the optical modulator 3 shown in the upper part of FIG. 10, the electrode element 331 connected to the potential applying unit 41 and the electrode element 332 connected to the ground unit 34 are X on each main surface 311, 312. They are alternately arranged at a constant pitch in the direction. In addition, electrode elements 332 are arranged at positions on the main surface 312 facing each electrode element 331 on the main surface 311, and electrodes are arranged at positions on the main surface 312 facing each electrode element 332 on the main surface 311. An element 331 is arranged, and two electrode elements 331 and 332 facing each other are used as electrode element pairs, and a plurality of electrode element pairs are arranged in the X direction on the electrode 33b. In the plurality of electrode element pairs, as shown by the arrow with the symbol E3 in the upper part of FIG. 10, with respect to both main surfaces 311 and 312 (and the light moving direction (Y direction)) inside the base portion 31. Electric fields directed in the vertical (+ Z) direction and the (−Z) direction are alternately formed. Accordingly, in the optical modulator 3 having the electrode 33b, when the electric field perpendicular to the main surfaces 311 and 312 is formed to diffract the light incident on the base portion 31, the lower part of FIG. As shown in FIG. 3, the degree (amplitude) of the periodic refractive index change in the arrangement direction of the electrode elements 331 and 332 can be increased inside the base portion 31, and the length of the electrode 33b in the light movement direction can be increased. Can be further shortened, or the voltage applied to the electrode 33b can be further reduced.

  As described above, in the optical modulator 3, a plurality of electrode elements are arranged on one main surface 311 of the base portion 31 or on both main surfaces 311 and 312 in the arrangement direction perpendicular to the light moving direction in the base portion 31. A plurality of electrodes 33, 33 a, 33 b in which 331, 332 are arranged are provided as a modulation part, and the electrodes 33, 33 a, 33 b are adjacent to each other between electrode elements 331, 332 (including the case where they are adjacent to each other with the base part 31 in between). By applying a voltage to the base portion 31, it is possible to cause a periodic refractive index change in the arrangement direction in the base portion 31 and diffract light incident on the base portion 31.

  FIG. 11 is a diagram showing a configuration of still another example of the optical modulator, and FIG. 12 is an exploded view of the optical modulator of FIG. The optical modulator 3 in FIG. 11 includes an auxiliary substrate 351 in which a plurality of electrode elements 331 are arranged in the X direction on one main surface, and a plurality of electrode elements 332 in the X direction on one main surface. As shown in FIGS. 11 and 12, the plurality of electrode elements 331 of the auxiliary substrate 351 abut on the main surface 311 of the base portion 31, and the plurality of electrode elements 332 of the auxiliary substrate 352 are provided. The optical modulator 3 is configured by sandwiching the base portion 31 between the two auxiliary boards 351 and 352 such that the base portion 31 is in contact with the main surface 312 of the base portion 31. In such an optical modulator 3, since it is not necessary to directly form electrode elements on the thin plate-like base portion 31, it is possible to easily manufacture the optical modulator.

  When an electric field is formed inside the base portion 31 using the electrode elements 331 and 332 formed on the auxiliary substrates 351 and 352, the electrode elements 331 and 332, the main surfaces 311 and 312 of the base portion 31, and There may be a minute gap between them. Further, by alternately forming the electrode elements 331 and 332 on the auxiliary substrates 351 and 352, the same one as the optical modulator 3 of FIG. 10 may be manufactured, and furthermore, only on one main surface 311. This method may be used in the optical modulator 3 having the electrode 33 on the surface. The method using the auxiliary substrate can also be employed in the second and third embodiments described later.

  FIG. 13 is a diagram illustrating still another example of the optical modulator. In the optical modulator 3 shown in FIG. 13, the base portion 31a is thinner than the base portion 31 shown in FIG. 3 (for example, 5 μm), and the light incident on the inside of the base portion 31a from the incident surface 313 is changed to a single mode. And reciprocates in the Y direction in FIG. When each electrode 33 on the main surface 311 is turned off, light passing through the vicinity of the electrode 33 is emitted from the incident surface 313 as zero-order light, and when the electrode 33 is turned on (mainly ) The light is emitted from the incident surface 313 as (± 1) -order diffracted light. Thus, in the optical modulator 3 of FIG. 13, the thickness of the base portion 31a (usually 50 μm or less) is a light beam from the light source portion 21 so that light propagates in a single mode inside the base portion 31a. It is determined according to the wavelength of

  Here, when the light is guided in the multimode as in the base portion 31 of FIG. 3, the intensity distribution in the direction perpendicular to the principal ray of the light emitted from the incident surface 313 is biased. On the other hand, in the base portion 31a of FIG. 13, by guiding light in a single mode, the intensity distribution in the direction perpendicular to the principal ray of the light emitted from the incident surface 313 is stably and preferably (Gaussian distribution). It becomes possible to do. In addition, the light propagation efficiency can be improved as compared with the multimode. However, in order to propagate a large amount of light (energy), it is preferable to use the base portion 31 that guides light incident on the inside from the incident surface 313 in a moving direction parallel to the main surface 311 while performing multiple reflection. 13 may be used in the optical modulator 3 of FIGS. 9, 10 and 11.

  FIGS. 14 and 15 are diagrams showing an optical modulator 3 according to the second embodiment of the present invention, and FIGS. 14 and 15 correspond to FIGS. 3 and 4, respectively. The optical modulator 3 shown in FIGS. 14 and 15 is different from the optical modulator 3 of FIG. 3 in that the base portion 32 is thickened in the Z direction (thickness direction). The configuration of each electrode 33 is the same as that of the electrode 33 in FIG.

  In the base portion 32 of FIG. 14 formed of the same material as the base portion 31 of FIG. 3, the thermal diffusion method (for example, titanium (Ti) diffusion method) or the entire (+ Z) main surface 321 is used. The proton exchange method is applied. As a result, the position of the main surface 321 (on the left side of FIG. 16) as shown on the left side of FIG. 16 showing the refractive index at each position in the Z direction in the cross section of the base portion 32 perpendicular to the Y direction, which is the light moving direction. The refractive index distribution is such that the refractive index (the refractive index in the state where no electric field is generated by the electrode 33) decreases as the distance from the main surface 321 in the Z direction increases to the (−Z) direction. Is formed in the same manner in the entire base portion 32. In addition, in the base part 32 shown in FIG. 14, it has shown that the refractive index becomes small gradually toward the (-Z) side by drawing a point so that a density may become low as it leaves | separates from the main surface 321. (The same applies to FIGS. 17 and 19 described later).

  Further, in the base portion 32, an air layer is present on the (+ Z) side of the main surface 321 (except for a portion where the electrode 33 is formed), and therefore, on the (+ Z) side of the main surface 321. The refractive index at the position is sufficiently lower than that of the base portion 32. As a result, light incident on the inside of the base portion 32 from the incident surface 323 that is the end surface on the (−Y) side passes only through a portion (thin plate-shaped portion) having a high refractive index near the main surface 321 in the Y direction. Led to. As described above, in the optical modulator 3 of FIG. 14, a portion in the vicinity of the main surface 321 of the base portion 32 is a slab waveguide.

  Also in the optical modulator 3 shown in FIGS. 14 and 15, the mirror 36 is provided on the facing surface 324 that is the end surface on the (+ Y) side of the base portion 32, and the incident surface 323 to the facing surface 324 in the base portion 32. Is reflected by the mirror 36 and returned to the incident surface 323 along the Y direction. When each electrode 33 is turned off, the light passing through the vicinity of the electrode 33 is emitted from the incident surface 323 (that is, the (−Y) side end face) as zero-order light and turned on. (Mainly) the light is emitted from the incident surface 323 as (± 1) order diffracted light.

  At this time, the light traveling inside the base portion 32 is guided in the moving direction parallel to the main surface 321 in the vicinity of the main surface 321 on which the electrode 33 is formed as described above, and thus from the incident surface 323. In both the forward path to the facing surface 324 and the return path from the facing surface 324 to the incident surface 323, the light is transmitted a plurality of times within a range in which the refractive index is changed by the electrode 33 in the thickness direction of the base portion 32. By entering or staying within this range, the phase change of the light can be efficiently generated. As a result, the length of the electrode 33 in the light moving direction can be shortened, or the voltage applied between the electrode elements 331 and 332 in the electrode 33 can be lowered. The operation of recording an image on the recording material 9 using the optical head 2 having the optical modulator 3 of FIG. 14 is the same as in the first embodiment.

  Here, in the base portion 31 of FIG. 3 (and the base portion 31a of FIG. 13) in the first embodiment, an air layer is formed on the outside of the main surfaces 311 and 312 (that is, the side opposite to the base portion 31). Therefore, the refractive index decreases stepwise (steeply) outside the positions of both main surfaces 311 and 312 in the refractive index distribution in the Z direction. As a result, the light incident on the inside from the incident surface 313 can be multiple-reflected by the main surfaces 311 and 312 and guided to the moving direction with a simple configuration. Light loss occurs when the light is reflected on the main surfaces 311 and 312.

  On the other hand, in the base portion 32 of FIG. 14, as shown on the left side of FIG. 16, the refractive index gradually decreases as the distance from the main surface 321 increases in the (−Z) direction. Light is prevented from leaving the vicinity of the main surface 321, and the loss of light in the base portion 32 is reduced as compared with the case of multiple reflection of light on both main surfaces (that is, the light is propagated efficiently). ) Is realized.

  By the way, in the base part 31 of FIG. 3 in the first embodiment, the incident light is guided in the moving direction while being multiple-reflected by both the main surfaces 311 and 312, and therefore, the region from the incident surface 313 to the electrode 33 ( Precisely, a region (hereinafter referred to as “light passage region”) through which the light passes in a cross section perpendicular to the light movement direction in a portion immediately before the position where the diffracted light is derived from the incident surface 313. The size is substantially constant, and the shape is symmetric in the thickness direction (the same applies to the base portion 31a that guides light in a single mode).

  Similarly, in the base portion 32 of FIG. 14, the size of the light passage region is constant in the portion from the incident surface 323 to the electrode 33, but as described above, the main surface is on the (−Z) side of the main surface 321. While the refractive index gradually decreases as the distance from 321 increases, the refractive index drastically decreases due to the air layer on the (+ Z) side of the main surface 321 (that is, the distribution of the refractive index in the vicinity of the light passage region). Actually, as shown by a thin line on the right side of FIG. 16, the shape of the light passage region A1 becomes asymmetric in the thickness direction (that is, the upper part and the lower part) (distorted). In the present embodiment, the distance L1 from the main surface 321 to the (+ Z) side edge of the light passage region A1 on the right side of FIG. 16 is 1 to 10 μm, and the width L2 in the thickness direction of the light passage region A1 is 30 to 40 μm.

  Next, a method for reducing the asymmetry of the light passage region in the base portion capable of efficiently transmitting light will be described. FIG. 17 is a diagram illustrating another example of the optical modulator 3, and corresponds to FIG. The optical modulator 3 shown in FIG. 17 is different from the optical modulator 3 of FIG. 14 in that the base portion 32a has a thin layer 325, and the other configurations are the same.

In the base portion 32a shown in FIG. 17, a thin layer 325 formed of, for example, silicon oxide (SiO ₂ ) or lithium niobate similar to the main body 320 on the (+ Z) side surface 320a of the plate-shaped main body 320. (For example, a layer having a thickness of 10 μm or less and 0.1 μm or more, and hereinafter referred to as “auxiliary layer 325”) is provided. Further, in the main body 320, the surface 320a is processed by the thermal diffusion method or the proton exchange method, like the base portion 32 of FIG.

  FIG. 18 is a diagram showing a refractive index distribution in the thickness direction in a cross section perpendicular to the Y direction of the base portion 32a. The vertical axis in FIG. 18 indicates the position in the Z direction, and the horizontal axis in FIG. 18 indicates the refractive index. In FIG. 18, the same reference numerals are given to the positions of the main surface 321 of the base portion 32 a that is the (+ Z) side surface of the auxiliary layer 325 and the surface 320 a of the main body 320 in the Z direction.

  In the state where the electric field due to the electrode 33 is not generated in the base portion 32a, in the range in the Z direction corresponding to the main body 320 in FIG. 18 (on the (−Z) side from the position of the surface 320a), in the vicinity of the position of the surface 320a ( A refractive index distribution is formed in which the refractive index decreases toward the -Z) direction. That is, in the main body 320, a refractive index distribution is formed in which the refractive index decreases as the distance from the auxiliary layer 325 increases. Further, the range in the thickness direction (between the position of the surface 320a and the position of the main surface 321) corresponding to the auxiliary layer 325 in FIG. 18 is the maximum refractive index (that is, the surface 320a) in the refractive index distribution in the main body 320. The refractive index is constant at a refractive index smaller than the refractive index in the very vicinity of the position. Thus, in the base part 32a, it is considered that a portion where the refractive index gradually changes in the refractive index distribution due to the presence of the auxiliary layer 325 is embedded inside, or that the portion is covered by the auxiliary layer 325. be able to.

  Also in the optical modulator 3 of FIG. 17, the light incident on the inside of the base portion 32a passes only through the portion having a high refractive index near the main surface 321 (mainly, the portion of the main body 320 near the surface 320a) in the Y direction. Led to. At this time, as described above, since the auxiliary layer 325 is extremely thin, the phase change of the light due to the action of the electric field from the electrode 33 formed on the auxiliary layer 325 is efficient in both the outward path and the return path in the base portion 32a. Can often occur. As a result, the length of the electrode 33 in the light moving direction can be shortened, or the voltage applied to the electrode 33 can be lowered.

  Here, as described above, in the base portion 32 of FIG. 14, the shape of the light passage region A1 is asymmetric in the thickness direction as shown on the right side of FIG. 16 according to the refractive index distribution shown on the left side of FIG. In contrast, in the base portion 32a shown in FIG. 17, an auxiliary layer 325 having a refractive index smaller than the maximum refractive index of the refractive index distribution of the main body 320 in the vicinity of the surface 320a is formed on the surface 320a (a clad layer is formed). As a result, the amount of change in the refractive index in the vicinity of the (+ Z) side of the surface 320a is reduced, and the asymmetry of the refractive index distribution in the vicinity of the light passage region is reduced. As a result, compared with the light passage region A1 in the base portion 32 shown on the right side of FIG. 16, the base portion 32a in FIG. 17 can reduce asymmetry in the thickness direction of the shape of the light passage region (that is, The asymmetry of the cross-sectional shape of the light emitted from the light modulator 3 is reduced. Further, in the base portion 32 of FIG. 14, a loss occurs due to the reflection of light on the main surface 321, but in the base portion 32 a, the auxiliary layer 325 can suppress the loss of light on the surface 320 a of the main body 320. Can be propagated more efficiently.

  FIG. 19 is a diagram illustrating still another example of the optical modulator. In the base portion 32b of the optical modulator 3 shown in FIG. 19, the time for performing the processing by the thermal diffusion method or the proton exchange method on the main surface 321 is made shorter than the processing time in the base portion 32 of FIG. The thickness of the portion where the change (rise) is reduced. Thereby, the light incident on the inside of the base portion 32b from the incident surface 323 is guided in a moving direction parallel to the main surface 321 in a single mode.

  As described above, in the optical modulator 3 of FIG. 19, the light travels in the base portion 32b in the single mode (that is, the portion in the vicinity of the main surface 321 of the base portion 32b becomes a single mode waveguide). ), The thickness of the portion where the refractive index is changed in the base portion 32b is determined in accordance with the wavelength of the light beam from the light source portion 21 and the like. As a result, as compared with the case where the light travels in the multimode in the base portion 32 as in the optical modulator 3 of FIG. The intensity distribution in the direction perpendicular to can be stably set to a preferable state (Gaussian distribution). However, in order to propagate a large amount of light (energy), it is preferable to use the base portions 32 and 32a that guide the light incident inside from the incident surface 323 in a multimode. In the optical modulator 3 of FIG. 17, the thicknesses of the portions where the refractive index of the auxiliary layer 325 and the main body 320 have changed may be changed so that the light travels in the base portion 32a in a single mode.

  As described above, the thin optical base 31 and 31a are used in the optical modulator of the first embodiment, and the electrode 33 is provided in the optical modulator of the second embodiment. By using thick base portions 32, 32a, and 32b having a refractive index distribution that decreases as the distance from the main surface 321 (surface 320a in the base portion 32a) increases in the vicinity of the main surface 321, an incident surface is formed at the base portion. In the optical modulator, it is realized to move (reciprocate) the light incident on the inside in the Y direction parallel to the main surface in the vicinity of at least one main surface on which the electrode of the modulation unit is provided. It has been realized that the length of the electrode in the light moving direction is shortened or the voltage applied to the electrode is lowered.

  FIG. 20 is a diagram illustrating an optical modulator 3a according to the third embodiment of the present invention, and FIG. 20 corresponds to FIG. The base portion 30 of the optical modulator 3a in FIG. 20 is thickened in the Z direction (thickness direction) similarly to the base portion 32 in FIG. 14 (however, processing for forming a refractive index distribution is not performed). On the main surface 301, a plurality of electrodes 33 are arranged in the X direction as a modulation section. The configuration of each electrode 33 is the same as that of the electrode 33 in FIG.

  In the optical modulator 3a of FIG. 20, similarly to the optical modulator 3 of FIG. 2, the cylindrical lens 223 is disposed so as to face the incident surface 303 (that is, the (−Y) side end surface) of the base portion 30. Yes. In the present embodiment, light from the light source unit 21 is incident on the cylindrical lens 223 at a position shifted in the (−Z) direction from the optical axis J1. 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 that has passed through the cylindrical lens 223 shown in FIG. 20 shows an outer shape with a thin solid line in FIG. In this way, the light is incident on the incident surface 303 of the base portion 30 while being condensed. In FIG. 20, the light path K4 is indicated by a broken line while refracting light on the incident surface 303 is ignored.

  Light traveling inside the base portion 30 is incident on the main surface 301 on which the plurality of electrodes 33 are arranged at a small angle (at a large incident angle), and is reflected near the electrodes 33 on the main surface 301. The emitted light is guided to the mirror 36 on the facing surface 304. Actually, in the image recording apparatus 1 having the optical modulator 3a, when focusing only on the Z direction, a small amount of light (light incident on the (−Z) side of the optical axis J1) is incident on the cylindrical lens 223. The light that passes through the cylindrical lens 223 and enters the base portion 30 is collected on the mirror 36.

  The light reflected by the mirror 36 is further reflected by the main surface 302 opposite to the main surface 301 and emitted from the incident surface 303, and is shifted by the cylindrical lens 223 from the optical axis J 1 in the (+ Z) direction. Incident. Thus, in the cylindrical lens 223 of the light modulator 3a, the light from the base unit 30 is incident at a position different from the light incident from the light source unit 21. At this time, in the optical modulator 3a, the optical path length of the light from the cylindrical lens 223 to the mirror 36 via the main surface 301, and the optical path length of the light from the mirror 36 to the cylindrical lens 223 via the main surface 302 Are equal, the width in the Z direction of the light region in the cross section perpendicular to the path K4 at the position of the cylindrical lens 223 is equal to the incident light to the optical modulator 3a and the outgoing light from the optical modulator 3a ( (0th order light and 1st order diffracted light) are substantially equal (the same applies to the optical modulator 3c in FIG. 22 described later). The light that passes through the cylindrical lens 223 and travels in the (−Y) direction is disposed at a position that does not interfere with the light that is provided in place of the half mirror 231 in FIG. 2 (however, the light that travels from the light source unit 21 toward the cylindrical lens 223). ), The lens is guided to the lens 232 and used for image recording on the recording material 9 as in the first embodiment.

  As described above, in the optical modulator 3a, the cylindrical lens 223 causes the light from the light source unit 21 to enter the base unit 30 from the incident surface 303 while converging in the Z direction, and passes through the facing surface 304. Then, the light emitted from the incident surface 303 is received and shaped so as to converge in the Z direction. Thus, one cylindrical lens 223 has a shaping lens as a component by serving as a shaping lens for light incident on the base portion 30 and a shaping lens for light emitted from the base portion 30. The optical modulator can be miniaturized (the same applies to optical modulators 3b to 3e in FIGS. 21 to 24 described later).

  Further, in the optical modulator 3a, in the vicinity of the electrode 33 in the base portion 30, the region through which the light passes in a cross section perpendicular to the light path K4 in the (+ Y) direction is the region in the vicinity of the incident surface 303 (that is, the region). , In the cross section perpendicular to the light path K4 in the vicinity of the incident surface 303). As a result, most of the light traveling inside the base portion 30 passes through a portion where the refractive index changes due to the electric field formed by the electrode 33 (portion in the vicinity of the main surface 301). It is realized that this occurs well (the same applies to optical modulators 3b to 3e in FIGS. 21 to 24 described later). Further, since the incident light and the outgoing light are separated in the optical modulator 3a, in the optical head 2 of FIG. 2, the outgoing light is recorded by using a general mirror or the like instead of the expensive half mirror 231. 9 and the manufacturing cost of the image recording apparatus 1 can be reduced (the same applies to the optical modulators 3b and 3c).

  FIG. 21 is a diagram illustrating another example of the optical modulator. In the optical modulator 3b of FIG. 21, the base portion 30, the electrode 33, and the mirror 36 are the same as those of the optical modulator 3a of FIG. 20, but the light incident on the base portion 30 is mainly formed with the electrode 33. The illumination optical system is designed so as to collect light in the Z direction on the surface 301. As a result, in the vicinity of the electrode 33 in the base portion 30, the region through which the light passes in a cross section perpendicular to the light path is made smaller (narrower) in the direction along the Z direction perpendicular to the main surface 301, and the light A phase change can be efficiently generated.

  FIG. 22 is a diagram illustrating still another example of the optical modulator. The optical modulator 3c of FIG. 22 is designed so that the light incident on the base portion 30 is condensed on the mirror 36 in the Z direction, similarly to the optical modulator 3a of FIG. A plurality of electrodes 33 are formed on both main surfaces 301 and 302 of the portion 30. Specifically, on each of the main surfaces 301 and 302, the electrode element 331 connected to the potential applying unit 41 (see FIG. 2) and the electrode element 332 connected to the grounding unit 34 applying the ground potential are X Alternatingly arranged in the direction at a constant pitch. As a result, with respect to the thickness direction (Z direction) of the base portion 30, a periodic refractive index change in the X direction occurs only in the vicinity of the main surfaces 301 and 302 in the base portion 30 (in practice, This occurs only in the vicinity of the electrode 33 in the ON state).

  Similar to the optical modulator 3 a in FIG. 20, in the optical modulator 3 c, light incident on the base portion 30 from the incident surface 303 is near the electrode 33 on the main surface 301, the mirror 36 on the opposing surface 304, and the main surface 302. The light is sequentially reflected in the vicinity of the electrode 33 and emitted from the incident surface 303. Thereby, a part of the light path (outward path) in the base portion 30 from the incident surface 303 to the opposing surface 304 and the light path (return path) in the base portion 30 from the opposing surface 304 to the incident surface 303. ) Can cause a periodic refractive index change in the arrangement direction (X direction). As a result, the phase change of light can be efficiently generated (that is, the diffraction efficiency can be improved), and the electrode 33 is shortened in the light moving direction to reduce the size of the optical modulator 3c, or the electrode 33 It is possible to improve the safety of handling the optical modulator 3c by lowering the voltage applied to the optical modulator 3c.

  FIG. 23 is a diagram illustrating still another example of the optical modulator. In the optical modulator 3d of FIG. 23, the mirror 36 is provided in the vicinity of the facing surface 304 of the base portion 30 with a gap between the mirror 36 and the facing surface 304. Actually, the light that enters the base portion 30 from the incident surface 303 and is guided to the mirror 36 through the main surface 301 and the opposing surface 304 is indicated by a principal ray M2 (shown by a broken line in FIG. 23). ) Is incident on the mirror 36 so as to be perpendicular to the reflecting surface, and is returned to the incident surface 303 through the same path as the path from the incident surface 303 to the mirror 36. Further, the light incident on the base portion 30 is condensed on the mirror 36 in the Z direction. As a result, both of a part of the light path in the base part 30 from the incident surface 303 to the opposing surface 304 and a part of the light path in the base part 30 from the opposing surface 304 to the incident surface 303. , It is possible to cause a periodic refractive index change in the arrangement direction, and to efficiently produce a light phase change. In the optical head having the optical modulator 3d of FIG. 23 (and the optical modulator 3e of FIG. 24 described later), the light incident on the optical modulator 3d and the optical modulator 3d are the same as the optical head 2 of FIG. It is necessary to separate the light emitted from the light by the half mirror 231 or the like.

  FIG. 24 is a diagram illustrating still another example of the optical modulator. In the optical modulator 3e of FIG. 24, the facing surface 304a of the base portion 30 is inclined with respect to the main surface 301, and a mirror 36a (in FIG. 24) is formed on the facing surface 304a by applying a reflective coating to the facing surface 304a. Is indicated by a thick line). In the optical modulators 3 and 3a to 3d, a mirror may be formed by coating in the same manner as the optical modulator 3e.

  Also in the light modulator 3e of FIG. 24, the light that enters the base portion 30 from the incident surface 303 and is guided to the mirror 36a is mirror 36a so that the principal ray M3 is perpendicular to the reflecting surface (opposing surface 304a). Is returned to the incident surface 303 through the same path as the path from the incident surface 303 to the mirror 36a. Further, the light incident on the base portion 30 is condensed with respect to the Z direction on the mirror 36a. As a result, in the optical modulator 3e, it is possible to cause a periodic refractive index change in the arrangement direction in both a part of the forward path and a part of the return path, and to efficiently generate a phase change of light. it can.

  In the optical modulator 3e, the (+ Y) side end of the electrode 33 is disposed in the vicinity of the facing surface 304a of the base portion 31 (in the vicinity of the (+ Z) side portion). Accordingly, in the optical modulator 3e of FIG. 24, the light phase change occurs immediately before and after the light incident on the base portion 30 from the incident surface 303 is reflected by the mirror 36a, and the optical modulator 3e. Further downsizing can be achieved. Furthermore, in the optical modulator 3e, the mirror 36a is formed on the facing surface 304a, so that the configuration of the optical modulator can be simplified compared to the optical modulator 3d in FIG.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  In the optical modulator 3 in the first and second embodiments, an electrode shorter than the base portion that forms the slab waveguide in the Y direction is provided. However, depending on the design of the optical modulator 3, it is the same as the base portion. An electrode having a length may be provided. In this case, light incident from the incident surface is affected by a change in refractive index in the entire path returning to the incident surface via the opposing surface.

  As described above, in the modulation unit of the optical modulator, at least a part of the light path in the base part from the incident surface to the opposing surface, and at least the light path in the base part from the opposing surface to the incident surface. In some cases, it is possible to reduce the size of the light modulator by efficiently changing the phase of the light by periodically changing the refractive index in the arrangement direction, or to apply to the electrode in the light modulator. It is possible to reduce the voltage to be applied.

  In the optical modulator 3 in the first and second embodiments and the optical modulators 3d and 3e in the third embodiment, the forward path and the backward path are the same path, so that the phase change of the light However, in the case where high energy (intensity) light is modulated by the optical modulator, the optical modulation shown in FIGS. As in the units 3a to 3c, it is preferable that the forward and backward paths of light in the base portion are different.

  In the first embodiment, the thickness of the base portion 31 is set to 30 to 50 μm. However, the light incident from the incident surface 313 is multiple-reflected by both the main surfaces 311 and 312, and the both main surfaces 311 and 312. The base portion 31 can be changed to various thicknesses as long as it leads in a direction parallel to the direction. However, in a general optical modulator, the depth at which the refractive index changes within the base portion is 30 to 50 μm, and therefore the refractive index changes almost entirely in the Z direction inside the base portion 31. In order to cause this, it is preferable that the thickness of the base portion 31 is 50 μm or less. In addition, from the viewpoint of ensuring a certain strength of the base portion 31 at the time of manufacturing the optical modulator 3, it is preferable that the thickness of the base portion 31 is 3 μm or more.

  In the optical modulator 3 of FIGS. 14, 17 and 19, the refractive index distribution in the thickness direction in the base portions 32, 32a and 32b (the main body 320) is easily formed by the thermal diffusion method or the proton exchange method. The refractive index distribution may be formed by other methods.

  In the optical modulators 3, 3 d, 3 e of FIGS. 14, 17, 19, 23, and 24, the light incident on the base portions 32, 32 a, 32 b, 30 is the main surface 321 on which the electrode 33 is formed. Since only the vicinity of 301 is passed, the surfaces of the base portions 32, 32 a, 32 b, 30 opposite to the main surfaces 321, 301 do not necessarily have to be parallel to the main surfaces 321, 301.

  In the image recording apparatus 1, an optical modulator having only one electrode 33 may be provided. In this case, the width of the base portion in the arrangement direction is narrowed. However, in order to record an image at a high speed, it is preferable that an optical modulator having a plurality of electrodes is provided to enable optical modulation in a plurality of channels.

  In the first to third embodiments, the light modulators 3, 3 a to 3 e perform the light irradiation ON / OFF control with respect to the light irradiation position on the recording material 9. , 3a to 3e, multi-tone light irradiation control may be performed by adjusting a voltage applied between the electrode elements 331 and 332.

  In the image recording apparatus 1, only the (± 1) order diffracted light from the light modulators 3, 3 a to 3 e is guided onto the recording material 9 by the projection optical system 23, but depending on the design of the image recording apparatus, As described above, the (± 1) order diffracted light from the light modulators 3, 3a to 3e may be shielded, and the 0th order light may be guided onto the recording material. That is, one of the 0th-order light and (± 1) -order diffracted light from the light modulators 3, 3 a to 3 e 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 3e.

  The image recording apparatus provided with the optical modulators 3, 3a to 3e 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, 3a-3e while moving the irradiation positions of the light from the light modulators 3, 3a-3e relative to the recording material. . In the image recording apparatus, the light irradiation position on the recording material 9 may be moved by providing a polygon mirror or the like 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 3e 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 for demonstrating the path | route of the light between an optical modulator and 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 optical modulator of a comparative example. It is a figure which shows the other example of an optical modulator. It is a figure which shows the other example of an electrode. It is a figure which shows the further another example of an electrode. It is a figure which shows the further another example of an optical modulator. It is an exploded view of an optical modulator. It is a figure which shows the further another example of an optical modulator. It is a figure which shows the optical modulator which concerns on 2nd Embodiment. It is sectional drawing of an optical modulator. It is a figure which shows distribution of the refractive index and light passage area | region in a base part. It is a figure which shows the other example of an optical modulator. It is a figure which shows distribution of the refractive index in a base part. It is a figure which shows the further another example of an optical modulator. It is a figure which shows the optical modulator which concerns on 3rd Embodiment. It is a figure which shows the other example of an optical modulator. It is a figure which shows the further another example of an optical modulator. It is a figure which shows the further another example of an optical modulator. It is a figure which shows the further another example of an optical modulator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image recording device 3, 3a-3e Optical modulator 4 Control part 9 Recording material 21 Light source part 23 Projection optical system 30, 31, 31a, 32, 32a, 32b Base part 33, 33a, 33b Electrode 36, 36a Mirror 81, 82 Motor 83 Ball screw
223 Cylindrical lens 301, 302, 311, 312, 321 Main surface 303, 313, 323 Incident surface 304, 304a, 314, 324 Opposing surface 320 Main body 325 Auxiliary layer 331, 332 Electrode element

Claims (14)

An optical modulator,
It is a plate-like member formed of a material whose refractive index changes with an electric field, and light incident on the inside from an incident surface which is one end surface is aligned with the incident surface along a moving direction parallel to one main surface. Is the base that leads to the other end face on the opposite side,
A mirror that is provided in the vicinity of the other end surface of the base portion or near the other end surface, reflects light guided to the other end surface, and guides the light to the incident surface along the moving direction;
A plurality of electrode elements arranged in an arrangement direction perpendicular to the movement direction on the main surface of the base portion or both main surfaces of the base portion, and applying a voltage between the electrode elements of the electrodes; , At least a part of a light path in the base part from the incident surface to the other end surface, and at least a part of a light path in the base part from the other end surface to the incident surface. A modulation unit that causes a periodic refractive index change in the arrangement direction and diffracts light incident on the base unit;
An optical modulator comprising: The optical modulator according to claim 1, comprising:
A shaping lens that allows light to enter the base portion from the incident surface while converging in a direction perpendicular to the main surface, and receives and shapes light emitted from the incident surface via the other end surface An optical modulator further comprising: An optical modulator,
It is a plate-like member formed of a material whose refractive index changes with an electric field, and light incident on the inside from an incident surface which is one end surface is aligned with the incident surface along a moving direction parallel to one main surface. Is the base that leads to the other end face on the opposite side,
A mirror that is provided in the vicinity of the other end surface of the base portion or near the other end surface, reflects light guided to the other end surface, and guides the light to the incident surface along the moving direction;
A plurality of electrode elements arranged in an arrangement direction perpendicular to the movement direction on the main surface of the base portion or both main surfaces of the base portion, and applying a voltage between the electrode elements of the electrodes; A modulation unit that causes a periodic refractive index change in the arrangement direction to occur in a portion of the base unit in the vicinity of the electrode and diffracts light incident on the base unit;
A shaping lens that allows light to enter the base portion from the incident surface while converging in a direction perpendicular to the main surface, and receives and shapes light emitted from the incident surface via the other end surface When,
An optical modulator comprising: The optical modulator according to claim 2, wherein
Light incident on the base portion is reflected near the electrodes on the principal surface or both principal surfaces, and a region through which the light passes in a cross section perpendicular to the light path passes near the electrodes in the base portion. An optical modulator characterized by being smaller than the region in the vicinity of the incident surface. The optical modulator according to claim 4, comprising:
The optical path length of light from the shaping lens to the mirror, and the optical path length of light from the mirror to the shaping lens are equal,
An optical modulator characterized in that light incident on the base portion is condensed on the mirror in the vertical direction. An optical modulator according to any one of claims 1 to 5,
An optical modulation characterized in that a light path in the base portion from the incident surface to the other end surface is the same as a light path in the base portion from the other end surface to the incident surface. vessel. The optical modulator according to claim 6, comprising:
The optical modulator, wherein the mirror is formed on the other end surface, and the other end surface is inclined with respect to the main surface. The optical modulator according to any one of claims 1 to 3,
The optical modulator, wherein the base portion is a thin plate member. The optical modulator according to claim 8, comprising:
The optical modulator, wherein the electrode is a set of electrode element pairs respectively formed on the two principal surfaces with the base portion interposed therebetween. The optical modulator according to any one of claims 1 to 3,
The optical modulator, wherein the base portion has a refractive index distribution in which a refractive index decreases as the distance from the principal surface increases in a cross section perpendicular to the moving direction. The optical modulator according to any one of claims 1 to 3,
The base portion is
A plate-shaped body,
A thin layer formed on the body and having the major surface;
Have
The main body has a refractive index distribution in which a refractive index decreases as the distance from the thin layer in a cross section perpendicular to the moving direction is increased;
A light modulator, wherein a refractive index of the thin layer is smaller than a maximum refractive index in the refractive index distribution. The optical modulator according to any one of claims 8 to 11,
The optical modulator, wherein the base portion guides light incident therein to the moving direction in a single mode. The optical modulator according to any one of claims 1 to 12,
The optical modulator includes a plurality of electrodes including the electrodes and arranged in the arrangement direction. An image recording apparatus for recording an image on the recording material by irradiating the recording material with light,
A light source unit;
The light modulator according to any one of claims 1 to 13, wherein light from the light source unit is incident;
An optical system for guiding one of 0th-order light and (± 1) -order diffracted light from the light modulator onto a recording material;
A scanning mechanism for moving the irradiation position of light from the light modulator on the recording material relative to the recording material;
A control unit for controlling the optical modulator in synchronization with the relative movement of the irradiation position with respect to the recording material;
An image recording apparatus comprising:

Images