JP2013122548A - Optical deflection element and optical deflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical deflection element having an optical waveguide layer made of an electrooptical material on which a laser beam is incident and an electrode for applying voltage to the optical waveguide layer so as to deflect the laser beam, and allowing two dimensional deflection without using a prism or using two separately manufactured optical deflection elements, and to provide an optical deflector having the optical deflection element.SOLUTION: An optical deflection element includes: an optical waveguide layer 21 made of an electrooptical material; and voltage application parts 31, 41 provided in a direction Y of travel of a laser beam L in the optical waveguide layer 21 and configured to apply voltage to the optical waveguide layer 21. The voltage application part 31 has an electrode 32 configured to apply voltage to the optical waveguide layer 21 to form a refractive index modulation area 33 that deflects the laser beam L in a direction X intersecting the direction Y. The voltage application part 41 has an electrode 42 configured to apply voltage to the optical waveguide layer 21 to form an electric field distribution in a direction Z intersecting a plane XY inside the optical waveguide layer 21 so as to deflect the laser beam L in the direction Z.

Description

  The present invention relates to an optical deflecting element comprising an optical waveguide layer formed of an electro-optic material and receiving laser light, and an electrode for deflecting the laser light by applying a voltage to the optical waveguide layer, and light having the same The present invention relates to a deflection apparatus.

In various fields such as a laser printer, laser processing, display, measurement, optical communication, and the like, a light beam scanner that is a light deflection device that scans a laser beam that is laser light is used.
The light beam scanner generally includes a laser oscillation device serving as a light source and a light deflection element that scans the laser beam. The light beam scanner further includes an optical coupling optical system for shaping a light beam, which is a laser beam generated from a laser light source, into a beam shape suitable for the light beam deflecting element, which is a light deflecting element, and a light beam deflecting element. In some cases, an output optical system for shaping the light beam profile output from the light source or for expanding or reducing the deflection angle given by the light beam deflecting element may be provided.

  Conventionally used light beam deflectors that are light beam deflecting elements include those that perform light scanning by controlling the reflection angle of a light beam, such as a rotating polygon mirror, galvanometer mirror, and MEMS mirror. In addition, there are known ones that utilize a change in the refractive index of a material due to an acousto-optic (AO) effect or an electro-optic (EO) effect.

  Among these, the EO effect has an extremely high response speed in principle, and a light beam deflecting element using an electro-optic material (see, for example, [Patent Document 1] and [Patent Document 2]) is effective for high-speed beam scanning. is there. In addition, the scanning angle can be controlled arbitrarily according to the voltage applied to the optical waveguide layer that is made of EO material and receives laser light, so that a desired deflection angle can be instantaneously given to the light beam. It is. The light source of the light deflecting element has various wavelengths and light intensities depending on the use of the light deflecting element. In particular, the light deflecting element is used for distance measurement by laser processing or laser radar, or for laser projection. As the light source, a high-intensity laser light source of several hundred mW to 1 W or more is selected.

  As described above, there is known an optical deflection element that includes an optical waveguide layer that is formed of an electro-optic material and receives laser light, and an electrode that deflects the laser light by applying a voltage to the optical waveguide layer. However, this conventional optical deflection element can only deflect in one dimension (see, for example, [Patent Document 1] and [Patent Document 2]) and deflects in two dimensions. Nothing has been proposed yet.

  A configuration has been proposed in which an optical deflecting element using an electro-optic material can be used for a two-dimensional deflection, but this configuration can also be deflected only in one dimension by an optical deflecting device using an electro-optic material. This is only possible, and is two-dimensionally deflected in combination with a prism (see, for example, [Patent Document 1]).

  In the configuration combining the optical deflection element and the prism, it is necessary to position the prism to adjust the optical axis, and there are manufacturing problems such as difficulty in securing positioning accuracy and the time required for positioning. In addition, there is a concern that the cost is increased because the prism is expensive, there is a problem that it is not suitable for integration, the configuration becomes complicated, and the size reduction is difficult due to this problem.

  In order to be able to deflect two-dimensionally by using an optical deflecting element using an electro-optic material without using a prism, two optical deflecting elements manufactured separately using an electro-optic material are used for two-dimensional deflection. However, in this case as well, it is necessary to perform positioning for optical axis adjustment, and it is expected that it will be difficult to secure positioning accuracy, and it will take time for positioning. In addition, there are concerns about higher costs, problems that are not suitable for integration, that the configuration becomes complicated, and that miniaturization is difficult due to this problem. .

  The present invention is an optical deflecting element comprising an optical waveguide layer formed of an electro-optic material and receiving laser light, and an electrode for deflecting the laser light by applying a voltage to the optical waveguide layer. It is an object of the present invention to provide an optical deflection element that can be deflected two-dimensionally and an optical deflection apparatus having the optical deflection element without using two optical deflection elements manufactured separately.

  In order to achieve the above object, the present invention is directed to an optical waveguide layer formed of an electro-optic material that receives laser light emitted from a laser light source, and a traveling direction of the laser light in the optical waveguide layer. A first voltage application unit configured to apply a voltage to the optical waveguide layer; and a second voltage application unit, wherein the first voltage application unit transmits the laser light incident on the optical waveguide layer to the optical waveguide layer. A first electrode that applies a voltage to the optical waveguide layer to form a refractive index modulation region that deflects in a first direction that intersects the traveling direction; and a second voltage application unit is provided on the optical waveguide layer. In order to form an electric field distribution along the second direction in the optical waveguide layer so that the incident laser light is deflected in a second direction intersecting the plane formed by the traveling direction and the first direction. A second electrode for applying a voltage to the optical waveguide layer is provided. There in that light deflection element.

  The present invention relates to an optical waveguide layer formed of an electro-optic material that receives laser light emitted from a laser light source, and the optical waveguide provided along the traveling direction of the laser light in the optical waveguide layer. A first voltage applying unit that applies a voltage to the layer, and a second voltage applying unit, wherein the first voltage applying unit intersects the traveling direction of the laser light incident on the optical waveguide layer. A first electrode that applies a voltage to the optical waveguide layer in order to form a refractive index modulation region that deflects in a direction, and the second voltage application unit includes the laser beam incident on the optical waveguide layer. A voltage is applied to the optical waveguide layer to form an electric field distribution along the second direction in the optical waveguide layer so as to be deflected in a second direction intersecting the plane formed by the traveling direction and the first direction. Since it is in the optical deflection element having the second electrode to be applied By using the first voltage application unit and the second voltage application unit without using a prism and without using two separately manufactured light deflecting elements, the deflection of each part is performed. It is possible to provide a two-dimensionally deflectable optical deflecting element suitable for integration, which can improve positioning accuracy and shorten positioning time, and can reduce cost and increase in size. .

It is a schematic front view of an example of the optical deflection apparatus to which the present invention is applied. It is a schematic perspective view of the 1st structural example of the optical deflection | deviation element which can be mounted in the optical deflection | deviation apparatus shown in FIG. FIG. 6 is a schematic diagram of a second configuration example of an optical deflection element that can be mounted on the optical deflection apparatus shown in FIG. 1. FIG. 7 is a schematic plan view of a third configuration example of an optical deflection element that can be mounted on the optical deflection apparatus shown in FIG. 1. It is a conceptual diagram for demonstrating the principle in which deflection | deviation is performed in the 2nd voltage application part of the optical deflection | deviation element which can be mounted in the optical deflection | deviation apparatus shown in FIG. It is a schematic front view of the other example of the optical deflection apparatus to which this invention is applied. It is a schematic perspective view of the 4th structural example of the optical deflection | deviation element which can be mounted in the optical deflection | deviation apparatus shown in FIG. It is a performance evaluation result of an example of the optical deflection | deviation element to which this invention is applied.

FIG. 1 shows an outline of an example of an optical device which is an optical deflecting device to which the present invention is applied.
The optical device 100 includes a light source 10 that is a laser beam source that emits a laser beam L, a light deflection element 20 that receives the laser beam L emitted from the light source 10, a light source 10, and a light deflection element 20 therein. The housing 50 has a housing 50 and an output hole 51 provided in the housing 50 for outputting the laser light L emitted from the light source 10 and transmitted through the light deflection element 20 to the outside of the housing 50.
As shown in FIG. 2, the optical device 100 also includes a power source 30 as a first voltage applying unit that applies a voltage to the optical deflection element 20, and a power source 40 as a second voltage applying unit. .

  In FIG. 1, an arrow Y indicates the traveling direction of the laser light L emitted from the light source 10, and the laser light in the light deflecting element 20 when the laser light L is not deflected in the light deflecting element 20. The traveling direction of L is shown. In the figure, an arrow X indicates a direction perpendicular to the paper surface of the figure and perpendicular to the Y direction. In the figure, an arrow Z indicates the vertical direction in the figure and the direction perpendicular to the X direction and the Y direction, that is, the direction perpendicular to the XY plane, which is a plane formed by the X direction and the Y direction.

  Arrows X, Y, and Z shown in FIG. 2 and the following indicate the same directions as the X direction, the Y direction, and the Z direction in FIG. 1, respectively. Further, in FIG. 2 and subsequent figures, the same reference numerals as those shown in the above-mentioned figures such as FIG. 1 are the same as those described along the above-mentioned figures. The description will be omitted as appropriate. Further, the illustration of the power supplies 30 and 40 is omitted as appropriate.

The light source 10 uses a laser diode and is configured to propagate a laser beam L having a wavelength of 650 nm in the Y direction. The polarization direction of the laser light L is the Z direction.
The optical deflection element 20 is provided along the Y direction in order to apply a voltage to the optical waveguide layer 21 and an optical waveguide portion 22 as an optical waveguide structure having an optical waveguide layer 21 that is a core layer that transmits the laser light L. The first voltage application unit 31 as a first voltage application unit, which is the first region, and the voltage application unit 41 as a second voltage application unit, which is a second region.

The optical waveguide layer 21 and the optical waveguide unit 22 have a planar shape parallel to the XY plane. The optical waveguide unit 21 receives the laser beam L emitted from the light source 10 and transmits the laser beam L toward the output hole 51. The optical waveguide layer 21 is magnesium-added lithium niobate (manufactured by Yamato Ceramics: Z-cut) in which magnesium is doped in lithium niobate (LiNbO ₃ ), which is an electro-optic material. However, the material of the optical waveguide layer 21 is not limited to this, and lithium tantalate (LiTaO ₃ ) may be used as the electro-optic material, and the doping material may be iron.

Lithium niobate and lithium tantalate are known to produce a photorefractive effect that distorts the beam even when light is transmitted without applying voltage, but they are useful because they are inexpensive, highly robust, and stable. In addition, the photorefractive effect is suppressed by doping with magnesium or the like. Magnesium-added lithium niobate (MgO-added LiNbO ₃ ) is known to improve photodamage resistance. When doping with magnesium, the magnesium concentration is preferably in the range of 4.5 mol% to 5.5 mol%, and particularly preferably 5.0 mol%.

  Such an electro-optic material is a ferroelectric, and has spontaneous polarization without applying an external electric field. A region where the directions of spontaneous polarization are aligned in one direction is called a domain. The optical waveguide layer 21 is formed so that the direction of spontaneous polarization is aligned in one direction as a whole. Note that a region having a region in which the direction of spontaneous polarization is aligned in one direction and a domain in which the direction of spontaneous polarization is different by 180 ° is called a domain wall.

  In the example shown in FIG. 2, the optical waveguide unit 22 is configured only by the optical waveguide layer 21, and the optical waveguide layer 21 is the optical waveguide unit 22 itself. 7 may include an insulating layer 23 provided so as to sandwich the optical waveguide layer 21 in the Z direction, as will be described later with reference to FIG.

  As shown in FIG. 2, the voltage applying unit 31 is used to form a refractive index modulation region that deflects the laser light L incident on the optical waveguide layer 21 in the X direction, which is the first direction intersecting the Y direction. As a first electrode for applying a voltage to the wave layer 21, an electrode 32 provided on both sides of the optical waveguide portion 22 in the Z direction and connected to the power supply 30 is provided.

  The electrodes 32 are provided as a pair so as to sandwich the optical waveguide unit 22 in the Z direction, are respectively connected to the power supply 30 and are integrated with the front and back surfaces of the optical waveguide unit 22 respectively. It has the upper electrode 32a and the lower electrode 32b which is a lower surface electrode. The upper electrode 32a is composed of a plurality of prism-shaped electrodes, specifically, equilateral triangle electrodes provided so as to be arranged along the Y direction. The lower electrode 32b is provided in a rectangular shape, specifically, a rectangular planar shape so as to include the arrangement region of the upper electrode 32a in the XY plane.

  The power source 30 is an AC power source supplied with power from an external voltage source, and applies a voltage signal based on the AC voltage to the electrode 32. In the optical waveguide layer 21, when a voltage is applied to the electrode 32, a primary electro-optic effect, that is, an EO effect appears in the crystal of the optical waveguide layer 21, and the refractive index in the crystal changes. A modulation region 33 is formed. The refractive index modulation region 33 is formed in a prism shape, specifically an equilateral triangle shape, corresponding to the prism type upper electrode 32a. Thus, a pseudo prism is formed in the optical waveguide layer 21 because the shape of the upper electrode 32a is a prism shape.

  Therefore, the optical deflection element 20 uses a prism-type refractive index modulation region 33 formed in the optical waveguide layer 21 when an AC voltage is applied to the electrode 32 by the power supply 30. The phase of the light L is modulated, and the laser light L is deflected in the X direction and emitted as indicated by an arrow in FIG.

  This is because the optical deflection element 20 can modulate the refractive index in the crystal of the optical waveguide layer 21 by the electro-optic effect, and functions as a phase modulation element that modulates the phase of the laser light L in the crystal. It is because it has become.

  In FIG. 2, the arrow indicating the laser beam L is illustrated so as to pass through the upper electrode 32 a, but actually, the laser beam L passes through the optical waveguide layer 21. If a voltage is applied by the power supply 30 at this time, the laser light L is transmitted through the refractive index modulation region 33 formed in the optical waveguide portion 22 with substantially the same shape as the upper electrode 32a, and the laser light L The light is refracted at the boundary position of the refractive index modulation region 33 and deflected in the X direction.

The deflection angle of the laser beam L in the X direction by the light deflection element 20 changes according to the voltage applied to the electrode 32 by the power supply 30. Therefore, when the power supply 30 applies an AC voltage to the electrode 32, the laser light L emitted from the light deflection element 20 is scanned in the X direction at a cycle corresponding to the cycle of the AC voltage of the power supply 30.
The power source 30 may be a DC power source as long as the deflection angle in the X direction is constant.

  In the configuration example shown in FIG. 2, the shape of the refractive index modulation region 33 is a prism type depending on the shape of the electrode 32. However, as shown in FIG. 3, the shape of the electrode 32 is the upper electrode 32a and the lower electrode 32b. As shown in FIG. 5A, the refractive index modulation region 33 is shaped by forming a prism-type, specifically equilateral triangular domain-inverted region 21a in the optical waveguide layer 21, as shown in FIG. You may make it be a prism type, specifically a regular triangle shape.

  The domain-inverted region 21a is a domain in which the direction of spontaneous polarization is inverted by 180 °, and forms a domain wall between the domain-inverted region 21b, which is a domain in which the direction of spontaneous polarization is not inverted in this way. In FIG. 3, the direction of the polarization axis of the polarization inversion region 21a is the -Z direction, and the direction of the polarization axis of the non-polarization inversion region 21b is the + Z direction. The upper electrode 32a and the lower electrode 32b are formed so as to cover the domain-inverted region 21a and the non-domain-inverted region 21b.

  When the electrode 32 is rectangular and the refractive index modulation region 33 is formed using the polarization inversion region 21a, the refractive index modulation region 33 is also formed by the non-polarization inversion region 21b. Therefore, a refractive index modulation region 33 formed by the polarization inversion region 21 a and a refractive index modulation region 33 formed by the non-polarization inversion region 21 b are formed in the optical waveguide unit 23, and is a boundary position between these refractive index modulation regions 33. Since the laser beam L is refracted at the domain wall, a deflection angle twice as large as that in the case where the refractive index modulation region 33 is formed by the shape of the electrode 32 can be obtained. The reason for this will be described in detail below.

First, a specific operation principle of the optical deflection element using the EO effect will be described in more detail.
When the electrode layers for forming an electric field are arranged facing each other on the front and back surfaces of the electro-optic material as in the above-described configuration, a voltage is applied to the deflection element through the electrode layers, so that the polarization axis of the electro-optic material Is formed, and its refractive index changes due to the electro-optic effect. When the refractive index change due to the Pockels effect is used, the refractive index change amount Δn of the electro-optic material is given by Expression (1).

In Equation (1), n is the refractive index of the electro-optic material, r _ij is the electro-optic constant, V is the applied voltage, and d is the crystal thickness.

Next, the deflection angle when the refractive index modulation region 33 is formed according to the shape of the electrode 32 will be described.
If a plurality of prism electrodes are formed so that the electrode shape on the region where the light beam propagates is composed of a plurality of triangles, the deflection angle of the emitted light is the sum of the refraction angles in each polarization inversion region. The deflection angle increases. This is because when a voltage is applied to the electrodes, the refractive index change region also has a triangular shape and each functions as a prism for the propagating beam. In other words, the propagating light beam is given a deflection angle in the X-axis direction as it propagates through the refractive index changing region. The deflection angle θ to which the laser beam output from the light beam deflection element is given is proportional to the amount of change in the refractive index of the electro-optic material, and is expressed by the following equation.

  In Expression (2), L is the length of the entire plurality of prism portions, and D is the prism width. From equations (1) and (2), the deflection angle emitted from the optical deflection element is proportional to the applied voltage. Therefore, by controlling the voltage applied to the optical deflection element, it is possible to output the laser beam at an arbitrary deflection angle.

The deflection angle when the refractive index modulation region 33 is formed according to the shape of the domain-inverted region 21a is as follows.
Since the polarization axis of the electro-optic material forming the optical waveguide layer to be the core layer can generally be controlled, a prism domain is formed inside the core layer as shown in FIG. It becomes possible. In this way, by providing a domain-inverted region in which a plurality of prism shapes are arranged inside the core layer, a voltage is applied to the element through the electrode layer covering the entire domain-inverted prism region. Are formed.

  Since the sign of the refractive index change is different between the domain-inverted region and the other regions, the same effect as that provided with a plurality of prisms inside the electro-optic material is exhibited. The light beam input from the deflecting element end face is tilted in the X-axis direction by the prism portion, and a beam deflected at the element exit end is output. By reversing the sign of the refractive index change due to polarization reversal, the refractive index change amount becomes twice the refractive index change amount of the prismatic electrode, and the exit angle θ from the element is

Given in. As described above, the electrode 32 is formed in a rectangular shape so as to cover the prism domain. By making the refractive index modulation region 33 into a prism type depending on the shape of the domain-inverted region 21a, the electrode 32 can be formed in a square shape, and the electrode 32 can be easily formed.

  As shown in FIGS. 2 and 3, when a plurality of prism-type refractive index modulation regions 25 are formed along the Y direction, each refractive index modulation region 33 is located downstream in the Y direction as shown in FIG. The area may be gradually increased toward. The refractive index modulation regions 33 are preferably similar to each other. In the configuration shown in the figure, as in the example shown in FIG. 3, the refractive index modulation region 33 is a prism type and the electrode 32 is a square shape due to the shape of the domain-inverted region 21a. As in the example shown in FIG. 2, the refractive index modulation region 33 may be a prism type depending on the shape of the electrode 32.

  As shown in FIG. 4, the prism size is gradually increased, and the polarization inversion region 21 a is gradually increased from the incident side of the laser light L so that the deflection angle is increased. It is possible to make it larger.

According to non-patent literature (Yi Chiu, et al, Journal of Lightwave Technology, VOL17, No. 1 Jan 1999), the traveling distance z, the incident side prism width D ₀ , the maximum refractive change Δn _max , and the refractive index n ₀ are used. The prism width D (z) is

It is possible to obtain from The external deflection angle θ (z) at this time is

Given in.

In the configuration shown in FIG. 4, assuming that D ₀ = 0.5 mm, Δn _max = 3.83 × 10 ⁻³ , refractive index n = 2.203, and prism length L = 20 mm, the equations (4) and (5) The prism width D (z) is calculated by sequential calculation, and the exit side prism width is 1.56 mm.

  The prism width obtained by the equations (4) and (5) is represented by the distance between the two envelopes shown in FIG. These envelopes are envelopes of the horn prism. In order to produce a horn-type domain-inverted region, the size of the equilateral triangular domain-inverted region is sequentially determined from the incident side by this envelope, and the domain-inverted region 21a is formed without a gap as shown in FIG. It is preferable to do.

  As shown in FIG. 2, the voltage application unit 41 has a Z direction in the optical waveguide layer 21 so as to deflect the laser light L incident on the optical waveguide layer 21 in the Z direction that is the second direction intersecting the XY plane. As a second electrode for applying a voltage to the optical waveguide layer 21 in order to form an electric field distribution along the optical axis, an electrode 42 provided on both sides of the optical waveguide portion 22 in the Z direction and connected to the power supply 40 is provided. .

  The electrodes 42 are provided as a pair so as to sandwich the optical waveguide 22 in the Z direction, are connected to the power source 40 and are integrated with the front and back surfaces of the optical waveguide 22 by ohmic contact, respectively. It has the upper electrode 42a which is an electrode, and the lower electrode 42b which is a lower surface electrode. The upper electrode 42a and the lower electrode 42b are provided in a rectangular plane, specifically, a rectangular plane so as to include the transmission range of the laser light L deflected by the voltage application unit 31 in the XY plane.

  The power source 40 is an AC power source supplied with power from an external voltage source, and applies a voltage signal based on the AC voltage to the electrode 42. When a voltage is applied to the electrode 42, the optical waveguide layer 21 is injected with electrons from the side of the upper electrode 42a and the lower electrode 42b that function as the cathode, and induces a refractive index change due to the space charge limiting current. Is done. The optical waveguide layer 21 emits the laser light L transmitted through the optical waveguide layer 21 by deflecting it in the Z direction by such a charge injection effect.

  In order to efficiently obtain this charge injection effect, the electrode 42 is preferably formed of a material that is easy to inject electrons, in other words, a metal material having a low work function. In this example, the electrode 42 is formed of Ti. For the same reason, the electrode 42 may be formed using Al or the like. In addition, when these materials are used, there is an advantage that film formation by sputtering is easy.

  In FIG. 2, the arrow indicating the laser beam L is illustrated as passing through the upper electrode 42 a, but actually the laser beam L passes through the optical waveguide layer 21. At this time, if a voltage is applied by the power supply 40, the laser light L is transmitted through the region where the charge injection effect is applied, and in this process, the laser light L is deflected in the Z direction.

The deflection angle of the laser beam L in the Z direction by the optical deflecting element 20 changes according to the voltage applied to the electrode 42 by the power source 40. Therefore, when the power supply 40 applies an AC voltage to the electrode 42, the laser light L emitted from the light deflection element 20 is scanned in the X direction at a cycle corresponding to the cycle of the AC voltage of the power supply 40.
The power source 40 may be a DC power source as long as the deflection angle in the Z direction is constant.

  A specific principle of operation of the optical deflection element utilizing the charge injection effect, in other words, the principle of beam deflection will be described in more detail.

  As described above, when a voltage is applied to the optical deflection element in which the electrode and the optical waveguide layer are in ohmic contact, electrons are injected from the electrode into the optical waveguide layer, thereby causing an electric field distribution in the Z direction of the optical waveguide layer. This electric field distribution causes light to be deflected.

The Z direction corresponds to the thickness direction of the electro-optic crystal. The refractive index n (z) that changes linearly in the thickness direction of the electro-optic crystal is n (z), where n is the refractive index at z = 0, and Δn (z) is the amount of change from the refractive index n at z. = N + Δn (z).
When a beam having a diameter D in a cross section perpendicular to the optical axis passes through the electro-optic crystal, the refractive index difference between the upper end and the lower end of the beam is Δn (D) −Δn (0).

  If the interaction length, which is the length of the part where the refractive index through which the beam passes, is L, the length L is shifted in the equiphase plane between the upper end and the lower end of the beam after propagation. The length of the deviation of the top and bottom equiphase surfaces is

It is. The inclination θ of the beam propagation direction at this time is such that the amount of deviation is sufficiently smaller than the diameter in the cross section perpendicular to the optical axis of the beam, and the refractive index is approximately 1 from the end face of the electro-optic crystal. Refracted at the interface between the electro-optic crystal and the outside, and the total deflection angle from the optical axis of the incident light is

It becomes. Here, since the refractive index change due to the electro-optic effect can be expressed by Equation (1),

It is represented by This equation (8) indicates that when the electric field E (z) depends on z, a non-zero deflection angle is generated in the Z direction. As shown in FIG. 5 (a), when no charge injection occurs, the electric field generated in the crystal is generally

Therefore, there is no deflection in the Z direction. On the other hand, as shown in FIG. 5B, when there is electron injection from the cathode, a space charge limited current is generated in the crystal, and the electric field is

It can be expressed. Thereby, the deflection angle in the z direction is

It is represented by

  As described above, when electrons are injected from the electrode into the electro-optic crystal by the applied voltage, the inside of the electro-optic crystal is in a space charge limited state, an electric field distribution is generated in the Z direction, and a refractive index distribution is generated by this electric field distribution. Is deflected in the Z direction.

  The optical device 100 including the optical deflection element 20 having the voltage application unit 31 and the voltage application unit 41 as described above, the power supply 30 and the power supply 40, converts the laser light L incident on the optical waveguide layer 21 into the voltage application unit. It functions as an optical deflecting device that deflects in the X direction at 31 and deflects in the Z direction at the voltage application unit 41 and emits it as deflected light that can be scanned two-dimensionally. Thus, the optical device 100 is a two-dimensional light deflection device, and the light deflection element 20 is a two-dimensional light deflection device. Further, since the optical waveguide layer 21 is made of magnesium-added lithium niobate, the optical deflection element 20 is an optical deflection element that can be used in the visible light range.

  As shown in FIG. 6, the optical device 100 is provided between the light source 10 and the light deflection element 20 and between the light deflection element 20 and the output hole 51 in order to improve the optical characteristics as the light deflection device. It is desirable that the lens 11 and the lens 12 are provided as optical elements.

  The lens 11 is a lens having a focal length of 8 mm that allows the laser light L emitted from the light source 10 to enter the optical waveguide layer 21. The lens 12 is a lens that collimates the deflected light, which is the laser light L emitted from the light deflecting element 20, and emits it out of the optical scanning device 100 from the output hole 51.

  As shown in FIG. 7, the voltage application unit 31 prevents or suppresses the deflection of the laser light L in the Z direction due to the charge injection into the optical waveguide unit 22. In order to ensure the deflection accuracy of the optical deflection element 20 in the Z direction by deflecting the laser light L in the Z direction by the voltage application unit 41 by charge injection into the wave unit 22, the voltage application unit in the Z direction. Insulating layers 23 may be provided on both sides of the optical waveguide layer 21 in 41, and the optical waveguide unit 22 may include the optical waveguide layer 21 and the insulating layer 23.

The insulating layer 23 includes an upper insulating layer 23a that is integral with the upper electrode 32a, and a lower insulating layer 23b that is integral with the lower electrode 32b. The material of the insulating layer 23 is Ta ₂ O ₅ , but other materials may be used. Each thickness of the upper insulating layer 23a and the lower insulating layer 23b is 1.5 μm, but can be changed as appropriate.

  The insulating layer 23 can also function as a cladding layer that improves the light utilization efficiency of the laser light L. The cladding layer is for reducing the optical loss of the guided light, and is formed between the optical waveguide layer 21 and the electrode 32 by a material having a refractive index lower than that of the optical waveguide layer 21.

  In the configuration shown in the figure, the electrode 23 has a rectangular shape as in the example shown in FIG. 3, and the shape of the domain-inverted region 21a as in the example shown in FIGS. Thus, the refractive index modulation region 33 is a prism type, but the refractive index modulation region 33 may be a prism type depending on the shape of the electrode 32 as in the example shown in FIG.

  Although not shown, the light deflection element 20 may integrally have a support substrate. By integrating the support substrate, it is possible to make the optical waveguide layer 21 and the optical waveguide portion 22 which are core layers thinner. When the optical waveguide layer 21 is thin, there is an advantage that it can be driven at a low voltage. The support substrate may be provided on at least one of the upper side of the upper electrode 32a and the lower side of the lower electrode 32b in the Z direction.

  When the support substrate is integrally formed, the optical deflection element 20 has a structure in which an adhesive layer is provided between the support substrate and the upper electrode and the lower electrode in addition to the support substrate, and the support substrate is integrated by the adhesive layer. Is possible.

An embodiment of the optical deflection element 20 and a manufacturing method thereof will be described.
First, as a wafer substrate constituting the optical waveguide layer 21, prism-type polarization inversion was formed using magnesium-added lithium niobate (φ3 “Z plate t = 0.5 mm manufactured by Yamato Ceramics).

  A method for inversion of polarization, that is, a method for forming a domain inversion region will be described. In the inversion process of an electro-optic substrate which is such a φ3 ″ wafer substrate, a photoresist film thickness of 2 μm was formed on this substrate by spin coating. As the pattern, a resist pattern of an equilateral triangle array (length: 20 mm) was prepared by + Z plane of the substrate and by photolithography, and at this time, the two sides of the equilateral triangle where light enters and exits were made parallel to the domain wall. Thereafter, a voltage corresponding to the coercive electric field was applied to the domain-inverted substrate by a direct electric field application method to produce an equilateral triangular domain-inverted region.

  With direct electric field application, the result was obtained that the domain-inverted region spreads outward by about 30 μm from the resist boundary. For this reason, it is desirable that the resist pattern be made 30 μm smaller than the desired prism domain. In order to produce the prism domain region with high accuracy, it is preferable to first apply a spike electric field to uniformly generate inversion nuclei, and then apply a constant electric field to widen the domain wall of the inversion nuclei. Specifically, when a spike electric field of 9 kV / mm is applied for 5 ms and a constant electric field of 5.5 kV / mm is applied for 5 seconds, the prism domain boundary side of the prism domain region becomes a straight line, and a prism domain region having a sharp apex angle is formed. Became possible.

Next, Ta ₂ O ₅ (thickness: 1.5 μm) was formed as the insulating layer 23 on the voltage application unit 31 by sputtering. As already described, the insulating layer 23 is formed to suppress the charge injection effect in the voltage application unit 31 and to have a deflection function only in the X direction.

  Subsequently, the upper electrode 32a, the lower electrode 32b, the upper electrode 42a, and the lower electrode 42b, which are upper and lower electrodes, were formed on the voltage application unit 31 and the voltage application unit 41 by sputtering. The electrode material is Ti for both the voltage application unit 31 and the voltage application unit 41.

The thicknesses of the upper electrode 32a, the lower electrode 32b, the upper electrode 42a, and the lower electrode 42b are 200 nm, the sizes of the upper electrode 32a are X = 3 mm, Y = 21 mm, and the size of the upper electrode 42a is X = 3 mm and Y = 3 mm.
5 mm × 25 mm was cut out from the substrate by a dicing saw, the end face was polished, and the optical deflection element 20 was manufactured through a reflective coating process.

  FIG. 8 shows a measurement result of the deflection angle with respect to the applied voltage in the Z direction and the X direction of the optical deflection element 20 thus produced. As shown in the figure, this optical deflecting device 20 obtains a result of a full angle of 1.16 mrad in the Z direction and 1.31 mrad in the X direction when a voltage of 200 Vpp is applied.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

For example, the deflection direction by the first voltage application unit and the deflection direction by the second voltage application unit are interchanged with the deflection direction by the first voltage application unit and the deflection direction by the second voltage application unit in the above example. Also good.
An optical device, a light deflection device, and a light modulation device to which the present invention is applied can be used in various fields such as a laser printer, laser processing, display, measurement, and optical communication.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 10 Laser light source 20 Optical deflecting element 21 Optical waveguide layer 21a Polarization inversion area | region 23 Insulating layer 31 1st voltage application part 32 1st electrode 33 Refractive index modulation area | region 41 2nd voltage application part 42 2nd electrode 100 Optical apparatus , Light deflection device, light modulation device L laser light X first direction Y traveling direction of laser light Z second direction

JP 2000-330143 A Japanese Patent No. 4663604

Claims (8)

An optical waveguide layer made of an electro-optic material that receives laser light emitted from a laser light source; and
A first voltage applying unit and a second voltage applying unit, which are provided along the traveling direction of the laser light in the optical waveguide layer and apply a voltage to the optical waveguide layer;
A first voltage application unit configured to apply a voltage to the optical waveguide layer in order to form a refractive index modulation region that deflects the laser light incident on the optical waveguide layer in a first direction intersecting the traveling direction; 1 electrode,
The second voltage application unit includes a second voltage application unit in the optical waveguide layer so that the laser light incident on the optical waveguide layer is deflected in a second direction intersecting a plane formed by the traveling direction and the first direction. An optical deflection element having a second electrode for applying a voltage to the optical waveguide layer in order to form an electric field distribution along the direction of 2. The optical deflection element according to claim 1, wherein
An optical deflection element comprising an insulating layer between a first electrode and the optical waveguide layer. The optical deflection element according to claim 1 or 2,
The optical deflection element, wherein the second electrode is Ti or Al. The optical deflection element according to any one of claims 1 to 3,
The refractive index modulation region is a prism type, and a plurality of the refractive index modulation regions are formed in the traveling direction in the optical waveguide layer. The optical deflection element according to claim 4, wherein
The optical deflection element, wherein the refractive index modulation region gradually increases in area toward the downstream side in the traveling direction. The optical deflection element according to claim 4 or 5,
The optical deflection element according to claim 1, wherein the refractive index modulation region has a prism shape depending on the shape of the electrode. The light deflection element according to any one of claims 4 to 6,
The optical deflecting element, wherein the shape of the refractive index modulation region is a prism type depending on the shape of the domain-inverted region provided in the optical waveguide layer.   An optical deflecting device comprising the optical deflecting element according to claim 1.

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