JP2009092995A - Electro-optic element and light beam deflector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact electro-optical device and a light beam deflector that are driven by a low voltage and cause a light beam to scan at a wide angle. <P>SOLUTION: The electro-optical device is operated by application of a voltage from both surfaces of an optical material substrate having an electro-optical effect, and light deflection is achievable by a combination of the electro-optical effect with a spatial field effect. A distribution of changes in refractive index occurring in a crystal is controlled to cause a light beam to scan in a breadthwise direction of the substrate. Thus the compact electro-optical device and the light beam deflector are provided which are driven by a low voltage and are capable of causing the light beam to scan at a wide angle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electro-optic element and an optical beam deflector using an electro-optic crystal material, and more particularly to a scanner unit such as a laser printer, a laser scanning microscope, and a barcode reader, an electro-optic element used for an optical communication switch element, and The present invention relates to a light beam deflector.

  Electro-optical elements that can scan a light beam at an arbitrary angle according to an input signal are used in various applications, for example, video equipment such as laser printers, projectors, and displays, optical communication, optical recording, optical modeling, and various types of sensing. It is a basic element for configuring devices and the like.

The performance required for electro-optic elements is that it can be scanned at a wide angle, that it can be scanned at high speed, that it can operate with low power consumption or low-voltage input signals, that it is compact, and that it is shock resistant. It is excellent.
Various electro-optic elements have been proposed so far, but all of the above requirements cannot be satisfied.
The typical prior art currently used as an electro-optical element will be described below.

As a light deflection technique capable of scanning a light beam at a wide angle, there is a method of mechanically driving a polygon mirror or a galvanometer mirror.
However, since the mirror is driven by motor driving, the operation speed is as slow as several hundred Hz at the maximum, and it is difficult to reduce the size of the element and power consumption is high.
In addition, if a mirror formed by MEMS (Micro Electro Mechanical Systems) technology is used, it is possible to reduce the size of the element and integrate a plurality of elements, but it is difficult to drive at a high speed of MHz or more, and mechanically. Low reliability for strong strength.

As a method without a mechanical drive unit, there is an optical deflection element using an acousto-optic effect (AO (Acousto-Optic) effect). The AO deflector operates at a relatively high speed of about several hundred kHz, and can obtain a large deflection angle with a high acoustic frequency.
However, since the AO deflector has an ultrasonic wave generation part, it is difficult to reduce the size of the element. Further, since the AO deflector requires an elastic wave excitation signal of several hundred MHz, the drive system cannot be complicated and large. Absent.

Further, as a technique capable of scanning a light beam at high speed, there is an optical deflection element that uses a change in refractive index of an optical material due to an electro-optic effect (EO (Electro-Optic) effect). For example, a prism-shaped electrode is formed on the surface of an electro-optic crystal substrate such as lithium niobate (LiNbO ₃ : LN) or lithium tantalate (LiTaO ₃ : LT), or a polarization inversion region such as a prism shape is patterned on the electro-optic crystal. The beam is deflected by causing a refractive index change by applying a voltage.
For example, Patent Document 1 uses this principle to report a multi-beam compatible optical switch element provided with a plurality of prismatic electrodes.
However, since the amount of change in the refractive index due to the electro-optic effect is generally very small, it is necessary to increase the element size and to increase the driving voltage in order to obtain a large deflection angle.

In addition to the above optical deflection technique, Non-Patent Document 1 reports a beam deflection element using space charge controlled electrical conduction. This is a phenomenon in which, due to electron injection into the electro-optic crystal, the refractive index change due to the electro-optic effect is inclined, and wide-angle light deflection occurs. In Non-Patent Document 1, by forming metal electrodes on the upper and lower surfaces of a KTN crystal substrate having a large EO effect and applying a voltage, a large beam deflection of about 10 ° in the entire film thickness direction is realized. Yes.
The operation principle of the beam deflection element using the space charge controlled electric conduction will be described below with reference to FIGS. 22 (a) to 22 (c).

FIG. 22A is a diagram showing a conventional electro-optic element viewed from the side. The electro-optic element is formed by forming a metal thin film as an electrode on both surfaces (upper and lower faces in the figure) of a substrate made of an electro-optic crystal. Configured.
Here, when the contact between the electrode and the crystal is ohmic contact, electrons are injected into the crystal. The space charge effect is an effect in which the electric field emitted from the anode is terminated by electrons injected into the crystal. This effect makes the electric field between the electrodes non-uniform. The electric field distribution when electrons are injected into the optical crystal is given by equation (1).

  Here, V represents an applied voltage, d represents the thickness of the crystal, and x represents coordinates in the thickness direction of the crystal (0 ≦ x ≦ d). Therefore, the electric field distribution in the electro-optic crystal shown in FIG. 22A has different values in the thickness direction of the crystal as shown in FIG. When the electro-optic crystal exhibits a refractive index change due to the Kerr effect, the refractive index change amount Δn of the crystal when an electric field is formed inside the crystal is given by equation (2).

n ₀ is the refractive index of the crystal and s _ij is the Kerr constant. From the equations (1) and (2), the refractive index change amount in the electro-optic crystal caused by the space charge effect has a distribution as shown in FIG. That is, the refractive index is the lowest near the electrode to which a positive voltage is applied, and the refractive index is the highest near the opposite electrode. When the refractive index of a crystal material to which a voltage is applied changes due to the Kerr effect, the refractive index changes linearly in the thickness direction of the crystal.
Here, when a light beam is inputted from the cross section of the crystal, the light propagates while being deflected in a direction having a high refractive index. When the interaction length, that is, the length of propagation in the crystal having a refractive index distribution is L, the deflection angle θi inside the crystal is given by the following equation (3).

  Further, when the deflection angle is small, the deflection angle θ when emitted from the crystal is given by the equation (4) from Snell's law.

An example in which the refractive index distribution and the beam deflection angle inside the crystal are specifically calculated from the above principle will be shown.
Here, the refractive index of the crystal is n ₀ = 2.2, the Kerr constant is s _ij = 1.0 × 10 ⁻¹⁴ m ² / V ² , the crystal thickness is d = 500 μm, and the interaction length is L = 5 mm. It was.
JP 2007-114446 A K. Nakamura, et.al., “Wide-angle low-voltage electro-optic beam deflection based on space-charge-controlled mode of electrical condition in KTa1-xNbxO3,” Applied Phys. Lett., 89, 131115 (2006)

Here, the distribution of the refractive index change in the crystal caused by the voltage application is shown in FIG. In FIG. 23, the horizontal axis indicates the refractive index difference, and the vertical axis indicates the displacement.
A negative refractive index change occurs when a positive voltage is applied, and a positive refractive index change occurs when a negative voltage is applied. Further, by increasing the applied voltage, the amount of change in refraction inside the crystal also increases.
24A shows a cross section of the electro-optic element, and FIG. 24B shows the deflection angle of the emitted beam with respect to the applied voltage of the electro-optic element shown in FIG. 24A and the beam in the film thickness direction accompanying the beam deflection. The position shift amount, that is, the difference between the incident position and the exit position of the light beam in the film thickness direction is shown. In FIG. 24B, the horizontal axis represents the applied voltage, the left vertical axis represents the deflection angle, and the right vertical axis represents the displacement amount.
The deflection angle increases in proportion to the square of the applied voltage. Theoretically, a beam deflection of ± 10 ° or more becomes possible by applying a voltage of ± 200V. However, when the light beam is incident from the center in the thickness direction of the crystal, the shift amount of the beam position accompanying the beam deflection needs to be 1/2 or less of the crystal thickness, that is, 250 μm or less in this example. When the amount of displacement is 250 μm or more, the light beam is reflected on the upper and lower surfaces of the crystal before the light propagated inside the crystal reaches the emission end face.
The amount of voltage that can be applied to the crystal is limited by the amount of shift of the beam position. In this example, it is necessary to operate the device at about ± 200 V or less.

Non-Patent Document 1, using a _{KTN (KTa lx Nb x O 3} ) crystal as the electro-optical crystal, employs a Ti as an electrode material in order to achieve the ohmic contact. Furthermore, a large deflection angle is obtained by bringing the operating temperature close to the Curie temperature. The beam deflection due to the space charge effect is not a phenomenon peculiar to KTN, and the same beam deflection is possible if the material has a large electro-optic effect. For example, strontium barium niobate (Sr _x Ba _1-x NbO ₃ : SBN) crystal has a high electro-optic coefficient and is suitable as an electro-optic material for configuring light deflection utilizing the space charge effect.

FIG. 25 shows the result of measuring the beam deflection angle by forming a Ti electrode on SBN (x = 61) and applying a voltage. In the figure, the horizontal axis indicates the applied voltage, and the vertical axis indicates the deflection angle.
Here, the thickness of the crystal was d = 500 μm, and the interaction length was L = 7 mm. Further, the relationship between the applied voltage and the beam deflection angle was plotted at operating temperatures of 75 ° C. and 87 ° C., respectively.
SBN (x = 61) has a Curie temperature of 80 ° C., and when the operating temperature is equal to or lower than the Curie temperature, the refractive index of the electro-optic crystal changes due to the Pockels effect. At this time, there is a relationship of the formula (5) between the electric field amount in the crystal and the refractive index change amount.

Here, r _ij is a Pockels coefficient. In addition, when the Pockels effect and the space charge effect are combined, it is theoretically derived that the beam deflection angle changes almost linearly with respect to the applied voltage, but it is operated at 75 ° C. as shown in FIG. In the experimental results, the beam deflection angle changes linearly with respect to the applied voltage in the range where the applied voltage is about ± 50 V or less.
The beam deflection angle is proportional to the square of the voltage application amount at an operating temperature equal to or higher than the Curie temperature, but the measurement result when operating at 87 ° C., which is equal to or higher than the Curie temperature, also indicates that the beam deflection angle is the square of the voltage application amount. It turns out that it is almost proportional. Further, since any operating temperature was operated at a temperature close to the Curie temperature, a large beam deflection angle of ± 4 ° or more was obtained.

  The beam deflection element using space charge controlled electrical conduction does not have a mechanical drive, so it is superior in impact resistance compared to the mirror drive type and MEMS (Micro Electro Mechanical System) type, and can operate at high speed. . In addition, since it can be operated simply by applying a voltage to the solid optical crystal substrate, the drive system can be simplified compared to an AO deflector, and the deflection angle is small despite the device length being only a few millimeters. It can be increased to about 10 °.

However, in order to drive the beam deflection element using space charge controlled electrical conduction, it is necessary to apply a high voltage of about several hundred volts. Theoretically, the drive voltage can be reduced by reducing the thickness of the electro-optic crystal, as can be seen from equation (1). As an example, the relationship between the voltage application amount and the beam deflection angle when the crystal thickness is 100 μm is estimated.
Here, considering the case where beam deflection occurs by combining the Kerr effect and space charge, the refractive index of the crystal is n ₀ = 2.2, and the Kerr constant is s _ij = 1.0 × 10 ⁻¹⁴ m ² / V. ^{2 is} assumed, the crystal thickness is d = 100 μm, and the interaction length is L = 5 mm.

FIG. 26 shows the relationship between the applied voltage, the deflection angle, and the shift amount of the beam position in the film thickness direction accompanying the beam deflection in the above parameters. In the figure, the horizontal axis indicates the applied voltage, and the vertical axis indicates the deflection angle.
Compared with the case of FIG. 24 in which the thickness of the crystal is 500 μm, a deflection angle of about ± 2 ° is obtained at a low voltage of about 8V. However, when the voltage application amount exceeds 8 V, the beam emission position moves in the film thickness direction by 50 μm or more, that is, ½ or more of the crystal thickness. Therefore, when a voltage of 8 V or more is applied, the light beam is reflected on the upper and lower surfaces of the crystal before reaching the emission end face. As a result, it is possible to drive at a low voltage by reducing the thickness of the crystal, but it is difficult to realize a beam deflecting element having a large deflection angle because the beam moves in the crystal thickness direction. .

  As described above, it has been difficult to achieve both low-voltage driving and wide-angle beam scanning in a beam deflection element using space charge controlled electrical conduction.

  An object of the present invention is to solve these problems and to provide a small electro-optic element and a light beam deflector that can be driven at a low voltage and can scan a light beam at a wide angle. To do.

  In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention is directed to a substrate made of an electro-optic material, electrode regions formed on both sides of the substrate, and light passing through the electro-optic material between the electrode regions. In the electro-optic element in which the light propagates, the refractive index of the light propagation region is variable.

  According to a second aspect of the present invention, in the electro-optical element according to the first aspect, the structure in which the refractive index that changes the thickness of the electro-optic crystal is variable is a structure in which the thickness of the substrate is changed. It is characterized by that.

  According to a third aspect of the present invention, in the electro-optic element according to the second aspect, the change rate of the thickness of the substrate gradually changes.

  According to a fourth aspect of the present invention, in the electro-optical element according to the second aspect, the thickness of the substrate changes stepwise.

  According to a fifth aspect of the present invention, in the electro-optical element according to any one of the first to fourth aspects, the structure in which the refractive index is variable is a structure in which the density of the substrate is changed. Features.

  According to a sixth aspect of the present invention, in the electro-optic element according to any one of the first to fifth aspects, the structure in which the refractive index is variable is a structure in which the density of the domain-inverted region of the substrate is changed. It is characterized by being.

  According to a seventh aspect of the present invention, in the electro-optic element according to any one of the first to sixth aspects, the structure in which the refractive index is variable is a structure in which the electric resistance of the electrode region is changed. It is characterized by that.

  According to an eighth aspect of the present invention, in the electro-optic element according to any one of the first to seventh aspects, the electrode region has minute holes, and the surface density of the minute holes gradually changes. And

  According to a ninth aspect of the present invention, in the electro-optic element according to any one of the first to seventh aspects, the electrode region comprises a plurality of stripe-shaped aggregates, and the line width of the stripe shape gradually changes. It is characterized by doing.

  According to a tenth aspect of the present invention, in the electro-optical element according to the eighth or ninth aspect, the electrode region is made of at least two kinds of conductive materials, and the work functions of the conductive materials are different from each other. To do.

  According to an eleventh aspect of the present invention, in the electro-optic element according to the seventh aspect, the electrode region has a laminated structure of a conductive material and an electric resistor material.

  According to a twelfth aspect of the present invention, in the electro-optic element according to the eleventh aspect, the thickness of the electric resistor material gradually changes.

  According to a thirteenth aspect of the present invention, in the electro-optic element according to the eleventh aspect, the thickness of the electric resistor material changes stepwise.

  A fourteenth aspect of the present invention is a light beam deflector using the electro-optic element according to any one of the first to thirteenth aspects.

  According to the present invention, operation is performed by applying a voltage from both surfaces of an optical material substrate having an electro-optic effect, and light deflection is possible by a combination of the electro-optic effect and the spatial electric field effect. The light beam is scanned in the substrate width direction by controlling the distribution of the change in refractive index generated in the crystal. Accordingly, it is possible to provide a compact electro-optical element and a light beam deflector that can be driven at a low voltage and can scan a light beam at a wide angle.

Embodiments of an optical deflector using an electro-optic element according to the present invention will be described below.
First Embodiment (Claims 1 and 2: Wedge Type Lateral Deflection Element)
A first embodiment of the present invention will be described with reference to FIG.
FIG. 1A is a top view of an electro-optical element according to the present invention, and FIG. 1B schematically shows a cross-sectional view of the electro-optical element taken along line Ib-Ib in FIG. It is a figure.
The electro-optic element is formed by forming an upper electrode 0102 and a lower electrode 0103 on both surfaces (the upper surface and the lower surface in FIG. 1B) of the electro-optic crystal substrate 0101, respectively. Further, the thickness of the electro-optic crystal substrate 0101 is gradually changed in the width direction of the electro-optic crystal substrate 0101.
That is, the electro-optic crystal substrate 0101 has a wedge shape.

Here, the larger the electro-optic constant (EO coefficient) of the electro-optic crystal, the larger the beam deflection angle after propagating in the electro-optic element. The electrode material is selected such that the contact with the crystal material is an ohmic contact. Specifically, KIN (KTa _1-x Nb _x O ₃ ) crystal, SBN (SrBa _1-x NbO ₃ ) crystal or the like is suitable as the optical crystal material, and Ti or the like is used as the electrode material for realizing ohmic contact. Cr or the like is preferred. These electrode materials can be formed as a thin film on the crystal plane by sputtering or vapor deposition.
Processing the optical crystal material into a wedge shape can be realized by, for example, a highly accurate polishing technique.
In FIGS. 1A and 1B, the upper electrode 0102 and the lower electrode 0103 are formed slightly smaller than the electro-optic crystal 0101. FIG. This has the effect of suppressing the generation of surface current on the side surface of the electro-optic crystal 0101 due to the voltage applied between the upper electrode 0102 and the lower electrode 0103.
In particular, when the electro-optic crystal 0101 is thin, the upper electrode 0102 and the lower electrode 0103 are easily short-circuited. Therefore, it is preferable that the dimensions of both the electrodes 0102 and 0103 be smaller than those of the electro-optic crystal 0101.
Specifically, it is sufficient to make the four sides of the electro-optic crystal 0101 wider than the size of both electrodes 0102 and 0103 by several hundred μm to 1 mm.

By applying a voltage between the upper electrode 0102 and the lower electrode 0103, electrons are injected into the electro-optic crystal 0101. The space charge effect and the electro-optic effect are combined, and the refractive index of the electro-optic crystal 0101 is changed by applying a voltage.
Here, applying a positive voltage to the electro-optic crystal 0101 causes a negative refractive index change. The smaller the distance between the upper electrode 0102 and the lower electrode 0103, the larger the electric field formed inside the electro-optic crystal 0101, and the greater the refractive index change.

When the thickness of the electro-optic crystal 0101 is changed as shown in FIG. 1B so as to have a wedge-shaped cross-sectional shape, the thickness of the electro-optic crystal 0101 varies on the Ib-Ib line. The amount of change in refractive index formed in 0101 is also different on the Ib-Ib line.
FIG. 13A is a diagram in which the electro-optic element shown in FIG. 1B is displayed in the first quadrant of the xy coordinates, and FIG. 13B is a refractive index along the line VII-VII in FIG. It is a figure showing the amount of change. In FIG. 13B, the horizontal axis indicates the position in the y coordinate, and the vertical axis indicates the refractive index change.
Here, a second-order Kerr effect is assumed as an electro-optic effect generated by forming an electric field inside the electro-optic crystal 0101, and a Kerr constant s _ij = 1.0 × 10 ⁻¹⁴ m ² / V ² is assumed.

In the following description, the x-axis is taken in the thickness direction of the electro-optic crystal, the y-axis is taken in the width direction of the electro-optic crystal, and the z-axis is taken parallel to the incident optical axis of the light beam.
The coordinate on the lower surface of the electro-optic crystal is x = 0, and the leftmost coordinate at which an electric field is formed on the electro-optic crystal is y = 0. The thickness of the electro-optic crystal was the smallest at 100 μm (d _min ) and the thickest at 500 μm (d _max ). The width of the electro-optic crystal was w = 500 μm, and the range between d _min and d _max was linearly changed in the range of y = 0 to w.
FIG. 13 shows the amount of change in the refractive index on the line of x = 80 μm. The voltage application amount was varied from 5 to 20 V as a parameter. It can be seen that the absolute value of the refractive index change amount increases as the voltage application amount increases, and the thickness of the electro-optic crystal is relatively small as the y coordinate decreases, so that the absolute value of the refractive index change amount also increases. .

  Consider inputting a light beam into a medium having a refractive index distribution as shown in FIG. As the y coordinate increases, the refractive index increases. Therefore, when the y coordinate is small, that is, when a light beam is input to a place where the thickness of the electro-optic crystal 0101 is thin, the direction in which the refractive index is relatively large (the y coordinate increases). The light beam propagates while deflecting. That is, the light beam is deflected in a direction horizontal to the width direction of the substrate of the electro-optic crystal 0101. When Δn changes depending on the y coordinate, the deflection angle of the beam in the lateral direction is given by equation (6).

  In equation (6), L is the interaction length.

  In a conventional deflection element using the space charge effect, the light beam is deflected in the thickness direction of the electro-optic crystal substrate, so that the thickness of the electro-optic crystal is limited and low voltage driving is difficult. On the other hand, in the lateral beam deflection as described above, the restriction on the thickness of the electro-optic crystal is relaxed, and low voltage driving becomes possible.

FIG. 14A is a diagram in which the electro-optic element shown in FIG. 1A is displayed in the first quadrant of the zy coordinates, and FIG. 14B shows the above structural parameters from the element to the beam with respect to the applied voltage amount. It is a figure showing the deflection angle when radiate | emits.
FIG. 14A also shows the beam position difference Δy accompanying the deflection.
Here, the beam incident coordinates (x _in , y _in ) are (80 μm, 0 μm), that is, the light beam is incident on the y axis from the thinnest crystal in the region where the electric field is applied.
The interaction length L was 4 mm. FIG. 14 shows that a large beam deflection angle of about 8 ° can be obtained with a relatively low applied voltage of about 20V. At this time, the beam position shift amount Δy is 200 μm, and it can be confirmed that it is sufficiently smaller than w which is the width of the substrate.

Increasing the beam deflection angle due to the passage of the light beam through the electro-optic element increases the thickness difference of the wedge-shaped electro-optic crystal, that is, the difference between d _max and d _min, and further increases the width w of the electro-optic crystal. This is possible by making it smaller.
Accordingly, as another example of the dimensions of the electro-optical element, it is assumed that d _max = 500 μm, d _min = 40 μm, w = 500 μm, and L = 2.5 mm.
FIG. 15 is a diagram illustrating the applied voltage, the beam deflection angle, and the displacement amount of the beam position of the electro-optic element according to the present invention.
In the figure, the horizontal axis represents the applied voltage, and the vertical axis represents the deflection angle and the amount of displacement.
By applying a voltage of about 25V, a large beam deflection of about 20 ° is possible. Even when beam light is scanned at a wide angle, the beam displacement is sufficiently smaller than the width of the electro-optic crystal.

In the above example, a beam deflecting element based on a combination of the Kerr effect and space charge effect is shown. However, if the Pockels effect and space charge effect are combined, the beam deflection element is also in the horizontal direction (direction parallel to both electrodes of the electro-optic element). An optical deflection element that scans the light beam can be realized.
FIG. 16 is a diagram showing the applied voltage, the beam deflection angle, and the displacement amount of the beam position of the electro-optic element according to the present invention.
Here, as the structure of the electro-optic crystal substrate, d _max = 500 μm, d _min = 40 μm, w = 500 μm, and L = 4.0 mm were assumed. Regarding the value of the electro-optic constant, the Pockels coefficient r _ij is estimated to be about 4000 pm / V from the measurement result at 75 ° C. in FIG. 25, and therefore, r _ij = 4000 pm / V was assumed in the calculation in FIG. It can be seen from FIG. 16 that wide-angle beam scanning of 15 ° or more is possible by applying a voltage of about 25V. It can also be confirmed that the beam position shift amount can be made smaller than the width w of the electro-optic crystal.

[Second Embodiment (Claims 1, 3: Change in thickness of wedge-shaped crystal in curve)]
A second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a diagram schematically showing a cross-sectional view of the electro-optic element according to the present invention, in which an upper electrode 0202 and a lower electrode 0203 are formed on both surfaces (upper surface and lower surface in the figure) of the electro-optic crystal 0201, respectively. This is the same as in the first embodiment shown in FIG.
However, in FIG. 1B, the thickness of the electro-optic crystal 0101 changes in a linear shape, whereas in FIG. 2, the thickness of the electro-optic crystal 0201 changes in a curve (for example, an exponential function curve). Is different. In other words, in the first embodiment of the present invention, the rate of change of the thickness of the electro-optic crystal 0101 is constant, whereas in the second embodiment, the rate of change of the thickness of the electro-optic crystal 0201 varies depending on the location. It is characterized by being different.

Although it has been shown that wide-angle beam scanning is possible by applying a low voltage according to the first embodiment of the present invention, the following problems also exist. That is, if the incident position (y coordinate) of the light beam is different, the beam deflection angle at the emission position is also different.
FIG. 17A is a diagram in which the plan view of the electro-optic element shown in FIG. 2 is displayed in the first quadrant of the xy coordinates, and FIG. 17B is the emission when the incident y coordinate of the light beam is changed. It is a figure which shows the result of having compared the beam deflection angle in a position. In FIG. 17B, the horizontal axis represents the applied voltage, and the vertical axis represents the deflection angle.

Here, the structure of the optical deflection element is the same as that used when obtaining the characteristics shown in FIG. 15, and d _max = 500 μm, d _min = 40 μm, w = 500 μm, and L = 2.5 mm. Here, when the deflection angle when the incident y coordinate of the light beam is 0 μm, 10 μm, and 20 μm is compared, the larger the incident y coordinate, the smaller the deflection angle. That is, the deflection performance of the element depends on the incident position of the light beam.

The reason is as follows.
The deflection angle when the beam is emitted depends on the amount of change in the refractive index generated inside the crystal. More precisely, as shown in Expression (6), the deflection angle depends on the value of the derivative of the refractive index change amount in the y-axis direction.

Here, looking at FIG. 13B, which is the result of calculating the refractive index change inside the wedge-shaped optical crystal, it can be seen that the amount of change in the refractive index in the region where the y coordinate is small is large. Therefore, most of the beam deflection is caused by light propagating through a region having a small y-coordinate value. That is, in order to obtain a large deflection angle, it is desirable to input light from a portion having as small a y coordinate as possible.
In the region where the y coordinate is small, the differential amount of the refractive index change greatly depends on the coordinate, so that the difference in the deflection angle at the exit position becomes large with respect to the deviation of the incident position.

In order to prevent the beam deflection angle from changing with respect to the deviation of the incident position in the y-axis direction, the refractive index change amount Δn needs to change linearly with respect to the change in the y-direction. That is, dΔn / dy may be a constant value.
As shown in FIG. 2, the rate of change of Δn as described above can be controlled by changing the thickness of the electro-optic crystal in a curved line.
FIGS. 18A and 18B show an example.
18A is a diagram in which the side view of the electro-optic crystal shown in FIG. 2 is displayed in the first quadrant of the xy coordinates, and FIG. 18B is a graph corresponding to a change in the y-axis direction, that is, the width direction of the electro-optic crystal. It is the figure which showed the refractive index variation | change_quantity inside an electro-optic crystal, and applied voltage is made into the parameter. FIG. 18B also shows the thickness of the electro-optic crystal with respect to the change in the y-axis direction. In FIG. 18B, the horizontal axis indicates the position in the y coordinate, and the vertical axis indicates the refractive index change and the thickness.
Here, the thickness of the electro-optic crystal takes the thinnest value (= d _min ) at y = 0 and becomes the thickest value (= d _max ) at y = w. Changed in relationship.

Here, a case where a refractive change occurs inside the electro-optic crystal due to the Kerr effect and the space charge effect, the Kerr constant s _ij = 1.0 × 10 ⁻¹⁴ m ² / V ² was assumed. The dimensions of other electro-optic crystals were assumed to be d _max = 500 μm, d _min = 40 μm, and w = 500 μm. The incident x coordinate of the light beam was 20 μm.
FIG. 18B shows that the amount of change in the refractive index increases as the amount of applied voltage increases, and the refractive index of the electro-optic crystal also changes linearly with respect to the change in the y-axis direction. Accordingly, at this time, the beam deflection angle does not change with respect to the deviation of the incident position in the y-axis direction, and the tolerance of the incident position is increased.

FIG. 19 is a diagram showing the relationship between the applied voltage of the electro-optic element according to the present invention, the deflection amount of the beam deflection, and the shift amount of the beam position. In addition to the parameter values assumed above, the interaction length L is set to 6 mm. . In FIG. 19, the horizontal axis indicates the applied voltage, and the vertical axis indicates the deflection angle.
Wide-angle beam scanning of about 15 ° is possible with a voltage application amount of about 25 V, and the beam shift amount Δy at that time can also be made smaller than the crystal width w. From this result, it was shown that the second embodiment of the present invention can provide an optical deflection element that has a wide tolerance with respect to the deviation of the incident beam position and can scan the beam at a wide angle with low voltage driving.
In FIG. 2, only the upper surface of the optical crystal is curved to change the crystal thickness. However, the crystal thickness may be changed by giving curved surfaces only to the lower surface or both the upper and lower surfaces of the crystal.

[Third Embodiment (Claim 4: Wedge-shaped crystal thickness change is stepped)]
FIG. 3 shows a third embodiment of the present invention.
FIG. 3 schematically shows a cross-sectional view of an optical deflector using the electro-optic element according to the present invention.
The optical deflector shown in the figure is formed by forming an upper electrode 0302 and a lower electrode 0303 on both surfaces (upper surface and lower surface in the figure) of an electro-optic crystal 0301, respectively. Further, the thickness of the optical crystal 0301 changes stepwise with respect to the width direction of the electro-optic crystal 0301.

In order to realize a structure in which the thickness of the electro-optic crystal 0201 shown in FIG. 2 is changed in a curved shape, a highly accurate processing technique is required. Therefore, in order to simplify the processing, it is effective to change the thickness of the electro-optic crystal 0301 in a step shape as shown in FIG.
By narrowing the width of each step, the electro-optic crystal 0301 has a constant thickness when viewed locally, but the thickness of the electro-optic crystal 0301 changes in a curved shape when viewed as a whole electro-optic element. Is equivalent to that. That is, the same effect as changing the thickness of the electro-optic crystal 0301 in a curved shape can be obtained.

  As an example of a processing method of the electro-optic crystal 0301, the electro-optic crystal is uniformly thinned by polishing or the like until the substrate is thickest, and then the electro-optic crystal is etched to a desired thickness by a dry etching technique. To do. A resist patterned by photolithography or the like can be used as a mask at the time of etching, and the thickness of the electro-optic crystal 0301 after etching can be changed by changing the thickness of the resist stepwise.

[Fourth Embodiment (Claim 5: Changing the density of an optical crystal (applying a minute pattern))]
4 (a) and 4 (b) show a fourth embodiment of the present invention.
FIG. 4A schematically shows a cross-sectional view of the electro-optical element according to the present invention, and FIG. 4B shows a modification of the fourth embodiment shown in FIG. 4A. It is sectional drawing.
The electro-optic element is formed by forming an upper electrode 402 and a lower electrode 0403 on both surfaces (upper surface and lower surface in the figure) of an electro-optic crystal 0401, respectively. An insulating layer 0406 is formed in the electro-optic crystal 0401 so as to penetrate the electro-optic crystal 0401 in the thickness direction. In addition, here, the density of the insulating layer 0406, that is, the ratio of the insulating layer 0406 included in the electro-optic crystal 0401 is larger toward the voltage source 0404 side (left side of the drawing) in the cross section of the electro-optic element, and is further away from the voltage source 0404 (see FIG. The smaller you go to the right).

The insulating layer 0406 is made of a material whose refractive index change amount when an electric field is formed inside the insulating layer 0406 is smaller than the refractive index change amount of the electro-optic crystal 0401. Furthermore, the refractive index of the insulating layer 0406 is preferably relatively close to that of the electro-optic crystal 0401. Specifically, quartz glass doped with tantalum pentoxide (Ta ₂ O ₅ ) at a high concentration, silicon nitride (SiN), or the like. The high refractive index glass and high refractive index polymer are suitable.

In the structure shown in FIG. 4A, when a voltage is applied from the voltage source 0404 between the upper electrode 0402 and the lower electrode 0403, a charge is injected into the electro-optic crystal 0401 to form an electric field, thereby changing the refractive index. Occurs. On the other hand, even if a voltage is applied to the insulating layer 0406, the refractive index does not change.
One possible reason for this is that charges are less likely to be injected into the material of the insulating layer 0406 than the electro-optic crystal 0401. Furthermore, even if charges are injected and an electric field is formed inside the insulating layer 0406, the amount of change in the refractive index due to that is extremely small compared to the amount of change in the refractive index of the electro-optic crystal 0401. Therefore, when a voltage is applied to the electro-optic element, the refractive index change amount is relatively small in the region where the ratio of the insulating layer 0406 is large compared to the region where the ratio of the insulating layer 0406 is small.

In FIG. 4A, the farther away from the voltage source 0404 of the electro-optic element, the more the insulating layer 0406 is contained (the region on the right side of the figure), so that a positive voltage is applied to the electro-optic crystal 0401 so as to give a negative refractive index change. When is applied, the absolute value of the equivalent refractive index variation is smaller in the relatively right region.
Therefore, the equivalent refractive index of the electro-optic element is smaller in the region on the left side of the figure and larger as it goes to the right side of the figure.
When the light beam is input from the left side of the cross section of the electro-optic element having a low equivalent refractive index, the light beam propagates while being deflected toward the right region having a high equivalent refractive index.

  The refractive index distribution created inside the electro-optic element can be controlled by adjusting the density of the insulating layer 0406. Therefore, a refractive index distribution similar to that when a voltage is applied to the curved surface of the electro-optic crystal as shown in the second embodiment of the present invention can be created.

An example of a manufacturing process for realizing the configuration shown in FIG.
First, the material of the electro-optic crystal 0401 is processed to a desired thickness by a polishing technique or the like. For driving at a low voltage, it is preferable to make the material of the electro-optic crystal 0401 thin. Specifically, a crystal thickness of about several tens of μm is suitable. Then, a part of the crystal material is dug out by dry etching techniques such as RIE (Reactive Ion Etching), ICP (Inductivity Coupled Plasma) etching, NLD (Neutral Loop Discharge) plasma etching, and focused ion (FIB (Focused Ion Beam)) etching. . Next, an insulating layer is formed so as to fill the dug portion. For the formation of the insulating film, sputtering or CVD (Chemical Vapor Deposition) is preferably used in the case of a high refractive index glass material, and dip coating or the like is easy in the case of a polymer material. Finally, the insulating material formed on the surface of the optical crystal material is removed. In this case, the entire element surface may be polished. Electrodes are formed on the upper and lower surfaces of the mixed substrate of optical crystal and insulating material manufactured by the above process.

  An upper electrode 0402 and a lower electrode 0403 are formed on both surfaces (the upper surface and the lower surface in FIG. 4B) of the electro-optic crystal 0401, respectively. Further, fine holes are provided from the upper surface of the electro-optic crystal 0401 to a certain thickness, and the holes are filled with an electrode material. Here, it is not always necessary to embed the entire depth of the hole with the electrode material, and it is sufficient to form a film thickness that covers the surface of the hole. The method of forming micropores in the material of the electro-optic crystal 0401 can be formed by dry etching technology as in the case of manufacturing the structure of FIG. 4A, and the electrode material can be formed by vapor deposition, sputtering, electrolytic plating, etc. A film formation technique can be used.

When a voltage is applied to the electro-optic element shown in FIG. 4B, the strength of the electric field formed is increased because the electro-optic crystal 0401 is relatively thin in the portion where the microhole is formed. Therefore, the amount of change in the refractive index is large. In FIG. 4B, since the hole density is increased in the region on the left side of the drawing, when a positive voltage is applied to the electro-optic crystal 0401 so as to give a negative refractive index change, the equivalent of the electro-optic element is obtained. The refractive index is smaller in the region on the left side of the figure and increases in the right direction.
If the light beam is input from the left side of the cross section of the electro-optic element having a low equivalent refractive index, the light beam propagates while being deflected toward the right region having a high equivalent refractive index.

The refractive index distribution created inside the electro-optic element can be controlled by adjusting the density of the insulating layer 0406. Therefore, a refractive index distribution similar to that when a voltage is applied to the curved surface of the electro-optic crystal as shown in the second embodiment of the present invention can be created.
In FIG. 4B, the pattern is applied only to the upper surface of the electro-optic crystal 0401. However, the pattern may be applied to only the lower surface or both upper and lower surfaces of the electro-optic crystal 0401.

[Fifth Embodiment (Claim 6: A polarization inversion pattern is applied to an optical crystal)]
FIG. 5 shows a fifth embodiment of the present invention.
FIG. 5 is a diagram schematically showing a cross-sectional view of the electro-optic element according to the present invention.
The electro-optic element is formed by forming an upper electrode 502 and a lower electrode 0503 on both surfaces (upper surface and lower surface in FIG. 5) of an electro-optic crystal 0501, respectively. In the electro-optic crystal 0501, a domain-inverted region 0506 in which the polarization direction of the electro-optic crystal 0501 is opposite to the other regions is provided. Also, the duty ratio of the domain-inverted region, that is, the ratio of the domain-inverted region included in the electro-optic crystal 0501 is smaller on the voltage source 0504 side (left side in the drawing) of the cross section of the electro-optic element and larger on the right side.

In the region where the polarization is reversed, the sign of the refractive index change with respect to the voltage application is reversed. That is, when a positive voltage is applied, a negative refractive index change usually occurs, whereas a positive refractive index change occurs in the domain-inverted region. When the applied voltages are equal, the absolute values of the refractive index change amounts are equal.
Therefore, when the domain-inverted region is formed with a duty ratio of 1: 1, the change in the positive and negative refractive indexes is canceled, and the equivalent amount of change in the refractive index becomes zero. In the electro-optic element shown in FIG. 5, there are few domain-inverted regions in the region on the left side of the diagram, and therefore a negative refractive index change occurs when a positive voltage is applied. On the other hand, since the region on the right side of the figure has more polarization inversion regions, the refractive index change amount is small, and the equivalent refractive index change amount is zero at the right end.

  If the light beam is input from the left side of the cross section of the electro-optic element having a low equivalent refractive index, the light beam propagates while being deflected toward the right region having a high equivalent refractive index. The equivalent refractive index inside the electro-optic crystal 0501 when a voltage is applied can be controlled by adjusting the duty ratio of the domain-inverted region, and therefore the same as when a voltage is applied to the curved surface of the complex electro-optic crystal 0501. It is also possible to create a refractive index distribution.

  As a specific method for forming a domain-inverted region, a method of applying an electric field application method widely applied in a quasi phase matching device using LN or LT, and forming an electric field by reducing the electrode width for voltage application In addition, the electron beam polarization reversal method that enables micro domain reversal without the need to form fine electrodes by directly irradiating a finely focused electron beam on the crystal surface, and local polarization reversal by femtosecond laser pulse irradiation A method of forming a region in a crystal can be considered.

[Modification (Claim 7: Resistivity of electrode material changes)]
In the examples from the first embodiment to the fifth embodiment of the present invention described above, any processing is performed on the electro-optic crystal substrate to control the refractive index change generated inside the electro-optic crystal, In the region closer to the voltage source (the left region in each figure), the refractive index was relatively low, and in the region far from the voltage source (the right region), a relatively high refractive index was created. In other words, the refractive index distribution is generated by controlling the thickness of the electro-optic crystal and the equivalent electro-optic effect.
Here, as a method for controlling the refractive index distribution inside the electro-optic crystal, unlike the above-described method, it is conceivable to change the applied voltage in accordance with the location of the electro-optic crystal. For example, the applied voltage may be increased in a region where the refractive index change amount is desired to be increased, and conversely, the applied voltage may be reduced in a region where the refractive index change amount is desired to be reduced.

FIG. 19 shows an example in which the amount of change in the refractive index inside the electro-optic crystal is calculated with respect to the width direction of the electro-optic crystal.
The horizontal axis is the coordinate in the width direction of the substrate as the y coordinate, and the vertical axis is the amount of change in the refractive index caused inside the electro-optic crystal on the left axis. On the right axis, the voltage application amount at a certain y coordinate is standardized by the maximum voltage V _max applied to the electro-optic crystal. Here, the applied voltage V (y) that changes depending on the y-coordinate is expressed by equation (8).

Here, a case where a refractive change occurs inside the electro-optic crystal due to the Kerr effect and the space charge effect is assumed, and a Kerr constant s _ij = 1.0 × 10 ⁻¹⁴ m ² / V ² is assumed. As for the dimensions of the other electro-optic crystals, the crystal thickness was assumed to be d = 40 μm and the crystal width w = 500 μm. The incident x coordinate of the light beam was 20 μm. From FIG. 19, it can be seen that the amount of change in refractive index increases as the amount of applied voltage increases, and the refractive index of the electro-optic crystal also changes linearly with respect to the change in the y-axis direction. Therefore, at this time, the beam deflection angle does not change with respect to the deviation of the incident position in the y-axis direction, and the tolerance of the incident position can be increased.

FIG. 20 is a diagram showing the relationship between the refractive index change in the width direction of the electro-optic crystal of the electro-optic element shown in FIG. 2 and the applied voltage. In FIG. 20, the horizontal axis indicates the y-coordinate position, and the vertical axis indicates the refractive index change and the applied voltage.
It can be seen that by changing the maximum applied voltage to 10V, 20V, and 30V, the refractive index change rate becomes steep.

FIG. 21 is a diagram showing the relationship between the applied voltage of the electro-optic element shown in FIG. 2, the beam deflection angle, and the beam position shift amount. In addition to the parameter values assumed above, the interaction length L is 8 mm. . Wide-angle beam scanning of about 15 ° is possible with a voltage application amount of about 20 V, and the beam shift amount Δy at that time can also be made smaller than the crystal width w.
As described above, by changing the voltage application amount in the width direction of the electro-optic crystal, an electro-optic element that has a wide tolerance against the deviation of the incident beam position and can scan the beam at a wide angle by driving at a low voltage is possible. It was shown that.
A method for changing the amount of voltage applied to the inside of the electro-optic crystal will be described below.

[Sixth embodiment]
FIG. 6 shows a sixth embodiment of the present invention.
FIG. 6 is a diagram schematically showing a cross-sectional view of the electro-optic element according to the present invention.
The electro-optic element is formed by forming an upper electrode 0602 and a lower electrode 0603 on both surfaces (upper surface and lower surface in the figure) of an electro-optic crystal 0601, respectively.
Here, the electrode material forming the upper electrode 0602 has a certain electric resistance value, and the resistance value changes in the width direction of the electro-optic crystal 0601. In the portion where the electrical resistance is large, the voltage drops when the current passes through the electrode. For example, in the electro-optic element shown in FIG. 6, the electrical resistance increases in the region farther from the voltage source 0604 (the region on the right side). If such an electrode material is formed, the voltage applied to the electro-optic crystal 0601 becomes smaller in the region on the right side. When a positive voltage is applied to the electro-optic crystal 0601, a negative refractive index change occurs. At this time, the refractive index becomes relatively larger in the right region.
Here, when the light beam is input from the left side of the cross section of the electro-optic element having an equivalent low refractive index, the light beam propagates while being deflected toward the right region having an equivalent high refractive index.

  As an example of controlling the magnitude of electric resistance, there is a method of doping a different material into an electrode material. For example, after an electrode is formed of a material having a low electrical resistance (resistivity 1 Ωcm or less, for example, copper), a material having a high electrical resistance value (resistivity 1 GΩcm or more, for example, Si) becomes higher in the right region. By doping in this way, the electrical resistance increases in the region on the right side of the entire electrode. Alternatively, two types of electrode materials having the same electrical resistance value but different temperature dependencies may be combined. For example, after an electrode is formed of a material having a small temperature dependency, the material having a large temperature dependency is doped so as to have a higher concentration in the right region. During the operation of the electro-optic element, the electric resistance of the electrode can be distributed by heating or cooling the electrode to a constant temperature.

[Seventh Embodiment (Claim 8: An equivalent electric field formation amount is controlled by applying a fine pattern to an electrode)]
A state similar to the fact that the electrical resistance varies from place to place can also be created with one kind of electrode material.
7A to 7C show a seventh embodiment of the electro-optic element according to the present invention. FIGS. 7A and 7B show the state of the electro-optic element when viewed from the top, and FIG. 7C shows the electricity at the line VIIc-VIIc in FIGS. 7A and 7B. It is the figure which represented the mode of the optical element cross section typically.
The electro-optic element is formed by forming an upper electrode 0702 and a lower electrode 0703 on both surfaces of the electro-optic crystal 0701 (upper surface and lower surface in FIG. 7C), respectively.
Here, a fine pattern is formed on the upper electrode 0702, and no electrode material is present on the surface of the electro-optic crystal 0701 in the pattern. In the fine pattern, the density of the region where no electrode material is present on the surface of the electro-optic crystal 0701 increases as the distance from the voltage source 0704 increases (the region on the right side of the drawing). As an example of changing the density, in FIG. 7A, the arrangement density of fine circular hole patterns is changed, and in FIG. 7B, the diameter of the holes forming the pattern is changed. 7A and 7B show examples of circular hole patterns, but the pattern shape is arbitrary as long as the surface density of the region where the electrode material is present varies depending on the region of the electro-optic element. is there.

The cause of the beam deflection is that electric charges are injected from the electrodes into the electro-optic crystal 0701. Accordingly, electric charges are not injected into a fine pattern in which no electrode is present on the surface of the electro-optic crystal 0701, and the electric field strength formed inside the electro-optic crystal 0701 even when the same voltage is applied in such a region. Becomes smaller.
Therefore, in the electro-optical element shown in FIG. 7, the amount of charge injection decreases as the region is on the right side, and the amount of change in refractive index caused by voltage application decreases. When a positive voltage is applied, a negative refractive index change occurs. Therefore, the refractive index increases relatively in the right region, and the light beam is equivalent to the left side of the cross section of the electro-optic element whose refractive index is low. Is input while being deflected toward the right region having a large refractive index equivalently.

[Eighth Embodiment (Claim 9: An equivalent electric field formation amount is controlled by applying a stripe pattern to an electrode)]
FIG. 8 shows an eighth embodiment of an electro-optic element according to the present invention.
FIG. 8 is a diagram schematically showing a state in which the electro-optic element is viewed from above. Although not shown here, the cross-sectional structure of the electro-optic element is equal to that shown in FIG. In the seventh embodiment shown in FIGS. 7A to 7C, a fine pattern is given to the electrode. However, a stripe shape as shown in FIG. 8 is also effective as the electrode pattern. At this time, the wider the width of the electrode, the larger the amount of injected charge, resulting in a larger amount of refractive index change caused by voltage application.
Therefore, as shown in FIG. 8, since the amount of change in the refractive index is smaller in the right region having a narrower stripe line width, the refractive index is larger in the right region when a positive voltage is applied.
Here, if the light beam is input from the side of the cross section of the electro-optic element having an equivalently low refractive index with a short stripe interval (the left side in the figure), it propagates while being deflected toward the right region having an equivalently large refractive index. .

[Ninth Embodiment (Claim 10: Electrode material comprises two or more kinds of materials)]
9 (a) and 9 (b) show a ninth embodiment of the present invention.
FIG. 9A shows a state of the electro-optic element according to the present invention as viewed from above, and FIG. 9B schematically shows a cross-sectional structure taken along line IXb-Ixb.
In the electro-optic element, the first upper electrode 0902 and the second upper electrode 0904 are formed on one surface of the electro-optic crystal 0901 (the upper surface in FIG. 9A), and the other surface of the electro-optic crystal 0901 ( A lower electrode 0905 is formed on the lower surface of FIG.
Here, a fine pattern is applied to the first upper electrode 0902, and a second upper electrode layer 0903 is formed so as to cover the electro-optic crystal 0901 and the first upper electrode 0902 simultaneously.

  As shown in the seventh embodiment, it is possible to control the electric field formed in the electro-optic crystal 0901 by forming a fine pattern on the electrode. May be divided, making it difficult to apply equal voltages to each other. For example, there may be a case where the fine pattern is not a circular hole but a circular dot. In this case, by embedding the fine pattern with the second upper electrode 0903, if a voltage is applied to the second upper electrode 0903, an equal voltage can be applied to the entire fine pattern forming the first upper electrode 0902. .

In order to generate the space charge effect, it is necessary that the electro-optic crystal 0901 and the electrode material are in contact by ohmic contact. Therefore, if an electrode material having a different work function is selected between the first upper electrode 0902 and the second upper electrode 0903, more electric charge is injected into the region to be in ohmic contact, and as a result The amount of change in the refractive index of the region increases. For example, in FIGS. 9A and 9B, as the material of the first upper electrode 0902, an electrode material having a large work function such as Ti or Cr is used so as to achieve ohmic contact with the electro-optic crystal 0901. In addition, an electrode material having a small work function such as Au or Pt is used as the material of the second upper electrode 0903. At this time, a large region where the material of the second upper electrode 0902 and the electro-optic crystal 0901 are in contact (the region on the right side of FIG. 9B) has a relatively small amount of charge injection, and thus the amount of change in refractive index. Becomes smaller.
Therefore, when a positive voltage is applied, the refractive index increases in the right region.
Here, when the light beam is input from the left side of the cross section of the electro-optic element having an equivalent low refractive index, the light beam propagates while being deflected toward the right region having an equivalent high refractive index.

  In FIGS. 6 to 9A and 9B described above, the pattern is applied only to the upper electrode, but the pattern may be applied only to the lower electrode or both the upper electrode and the lower electrode.

[Tenth embodiment (Claim 11: Inserting a resistor between an electrode and an optical crystal)]
As a method of applying different voltage amounts in the width direction of the electro-optic crystal, it is also effective to insert an electric resistor layer between the material of the upper electrode and the lower electrode and the electro-optic crystal.
FIG. 10 shows a tenth embodiment of the present invention.
FIG. 10 is a diagram schematically showing a cross-sectional structure of the electro-optic element according to the present invention.
In the electro-optic element, a lower electrode 1003 is formed on one surface (the lower surface in the drawing) of the electro-optic crystal 1001, and an electric resistor 1006 and an upper electrode 1002 are formed on the other surface (the upper surface in the drawing) of the electro-optic element 1001. Are sequentially stacked.
Here, the electric resistance value of the electric resistor 1006 changes in the width direction (the horizontal direction in the figure) of the electro-optic crystal 1001.

When a voltage is applied between the upper electrode 1002 and the lower electrode 1003, a voltage is applied to the electro-optic crystal 1001 via the electric resistor 1006. Depending on the resistance value when a current flows through the electric resistor 1006. Voltage drop occurs.
For example, in FIG. 10, assuming that the electric resistance increases as the distance from the voltage source 1004 increases (the region on the right side of the drawing), the voltage applied to the electro-optic crystal 1001 decreases in the region on the right side. That is, the electric field formed in the electro-optic crystal 1001 is reduced. Therefore, since the amount of injected charge is relatively smaller in the right region of the electro-optic element, the amount of change in the refractive index is smaller. Therefore, when a positive voltage is applied to the electro-optic element, the refractive index increases in the right region.
Here, when the light beam is input from the left side of the cross section of the electro-optic element having an equivalent low refractive index, the light beam propagates while being deflected toward the right region having an equivalent high refractive index.

[Eleventh embodiment (Claim 12: The thickness of the resistor inserted between the electrode and the optical crystal is changed)]
Even when the material constituting the electric resistor has the same resistivity in all regions, the same effect as described above can be obtained.
FIG. 11 shows an eleventh embodiment of the present invention.
FIG. 11 is a diagram schematically showing a cross-sectional structure of the electro-optic element according to the present invention.
In the electro-optic element, a lower electrode 1103 is formed on one surface (lower surface) of the electro-optic crystal 1101, and an electric resistor 1106 and an upper electrode 1102 are formed on the other surface (upper surface) of the electro-optic crystal 1101. Are sequentially stacked.
Here, the thickness of the electric resistor 1106 changes in the width direction of the electro-optic crystal 1101 (lateral direction in the figure).

  If the electrical resistivity of the material of the electrical resistor 1106 is constant, the thicker the portion, the greater the electrical resistance. Therefore, the voltage applied to the electro-optic crystal 1101 is lower, and the voltage is formed inside the electro-optic crystal 1101. The applied electric field is reduced. In FIG. 11, since the thickness of the layer of the electric resistor 1106 increases as the distance from the voltage source 1104 increases (the region on the right side), the amount of charge change is relatively small in the region on the right side. Get smaller. Therefore, when a positive voltage is applied to the electro-optic element, the refractive index increases in the right region. Here, when the light beam is input from the left side of the cross section of the electro-optic element having an equivalent low refractive index, the light beam propagates while being deflected toward the right region having an equivalent high refractive index.

[Twelfth embodiment (Claim 13: The thickness of the resistor inserted between the electrode and the optical crystal is changed stepwise)]
FIG. 12 shows a twelfth embodiment of the present invention.
FIG. 12 is a diagram schematically showing a cross-sectional structure of the electro-optic element according to the present invention.
In the electro-optic element, a lower electrode 1203 is formed on one surface (lower surface) of the electro-optic crystal 1201, and an electric resistor 1206 and an upper electrode 1202 are formed on the other surface (upper surface) of the electro-optic crystal 1201. Are sequentially stacked.
Here, the thickness of the electric resistor 1206 changes stepwise in the width direction (lateral direction in the figure) of the electro-optic crystal 1201.

  In the eleventh embodiment, in order to control the electric field distribution formed in the electro-optic crystal with high accuracy, the film thickness of the electric resistor 1206 is not made linear as shown in FIG. It is necessary to change it to a curved shape. As shown in FIG. 12, by changing the film thickness of the layer of the electric resistor 1206 in a fine stepwise manner, the same effect as that of the electric resistor 1106 in which the film thickness equivalently changes in a curved shape can be expected.

The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there.
For example, although the case of the electro-optic element has been described in the above-described embodiment, the present invention may be applied to a light beam deflector provided with a light source (for example, a laser) that emits a light beam to the electro-optic element.

(A) is the figure which looked at the electro-optical element which concerns on this invention from the upper surface, (b) is the figure which showed typically sectional drawing of the electro-optical element in the Ib-Ib line | wire of (a). It is the figure which showed typically sectional drawing of the electro-optic element which concerns on this invention. 1 schematically shows a cross-sectional view of an optical deflector using an electro-optic element according to the present invention. (A) is a schematic cross-sectional view of an electro-optic element according to the present invention, and (b) is a cross-sectional view showing a modification of the fourth embodiment shown in (a). It is the figure which showed typically sectional drawing of the electro-optic element which concerns on this invention. It is the figure which showed typically sectional drawing of the electro-optic element which concerns on this invention. (A) and (b) show the state when the electro-optical element is viewed from above, and (c) schematically shows the state of the electro-optical element cross section taken along line VIIc-VIIc in (a) and (b). FIG. It is the figure which represented the mode that the electro-optic element was seen from the upper surface. (A) is a diagram showing a state of the electro-optic element as viewed from above, and (b) is a diagram schematically showing a cross-sectional structure taken along line IXb-Ixb in (a). FIG. 3 is a diagram schematically showing a cross-sectional structure of an electro-optic element according to the present invention. FIG. 3 is a diagram schematically showing a cross-sectional structure of an electro-optic element according to the present invention. FIG. 3 is a diagram schematically illustrating a cross-sectional structure of an electro-optical element according to the invention. (A) is the figure which displayed the electro-optic element shown in FIG.1 (b) in the 1st quadrant of xy coordinate, (b) represents the refractive index change amount in the VII-VII line of FIG.1 (b). FIG. (A) is the figure which displayed the electro-optic element shown to Fig.1 (a) in the 1st quadrant of zy coordinate, FIG.5 (b) emits a beam from the element with respect to an applied voltage amount about said structural parameter. It is a figure showing the deflection angle at the time. It is a figure showing the applied voltage of the electro-optic element which concerns on this invention, the amount of beam deflection angles, and the displacement of a beam position. It is a figure showing the applied voltage of the electro-optical element which concerns on this invention, a beam deflection angle, and the displacement amount of a beam position. (A) is a diagram in which the plan view of the electro-optic element shown in FIG. 2 is displayed in the first quadrant of the xy coordinates, and (b) is the beam deflection at the exit position when the incident y coordinate of the light beam is changed. It is a figure which shows the result of having compared the angle | corner. (A) is a diagram showing a side view of the electro-optic crystal shown in FIG. 2 in the first quadrant of the xy coordinates, and (b) is a refractive index inside the electro-optic crystal with respect to a change in the width direction of the electro-optic crystal. It is the figure which showed the variation | change_quantity. It is a figure which shows the relationship between the applied voltage of the electro-optic element which concerns on this invention, and the amount of deviation of a beam deflection angle and a beam position. FIG. 3 is a diagram showing a relationship between a change in refractive index in the width direction of an electro-optic crystal of the electro-optic element shown in FIG. 2 and an applied voltage. FIG. 3 is a diagram illustrating a relationship between an applied voltage of the electro-optic element illustrated in FIG. 2, a beam deflection angle, and a beam position shift amount. (A) represents a state of a conventional electro-optic element viewed from the side, (b) is a diagram showing an electric field distribution in the electro-optic crystal of (a), and (c) is an electricity diagram of (a). It is a figure which shows distribution of the refractive index change amount in an optical crystal. It is a distribution map of the refractive index change in the crystal | crystallization produced by voltage application. (A) shows a cross section of the electro-optic element, and (b) shows the deflection angle of the outgoing beam with respect to the applied voltage of the electro-optic element shown in (a) and the shift amount of the beam position in the film thickness direction accompanying the beam deflection. It is. It is a figure which shows the result of having formed Ti electrode in SBN (x = 61), applying a voltage, and measuring the beam deflection angle. It is a figure which shows the relationship between the applied voltage, the deflection angle, and the amount of change of the beam position of the film thickness direction accompanying beam deflection.

Explanation of symbols

0101 Electro-optic crystal 0102 Upper electrode 0103 Lower electrode 0104 Voltage source 0105 Light beam

Claims (14)

In an electro-optic element in which an electrode region is formed on both surfaces of the substrate made of an electro-optic material, and light propagates in the electro-optic material between the electrode regions,
An electro-optical element, wherein a refractive index of the light propagation region is variable.   2. The electro-optic element according to claim 1, wherein the structure in which the refractive index that changes the plate thickness of the electro-optic crystal is variable is a structure that changes the plate thickness of the substrate.   3. The electro-optic element according to claim 2, wherein a change rate of the thickness of the substrate is gradually changed.   3. The electro-optical element according to claim 2, wherein the thickness of the substrate changes stepwise.   5. The electro-optical element according to claim 1, wherein the structure in which the refractive index is variable is a structure in which the density of the substrate is changed.   6. The electro-optical element according to claim 1, wherein the structure having a variable refractive index is a structure in which a density of a domain-inverted region of the substrate is changed. element.   7. The electro-optical element according to claim 1, wherein the structure in which the refractive index is variable is a structure in which an electric resistance of the electrode region is changed.   8. The electro-optic element according to claim 1, wherein the electrode region has minute holes, and the surface density of the minute holes gradually changes.   8. The electro-optic element according to claim 1, wherein the electrode region is composed of a plurality of stripe-shaped aggregates, and the line width of the stripe-shape gradually changes. .   10. The electro-optic element according to claim 8, wherein the electrode region is made of at least two kinds of conductive materials, and the work functions of the conductive materials are different from each other.   8. The electro-optical element according to claim 7, wherein the electrode region has a laminated structure of a conductive material and an electric resistor material.   12. The electro-optical element according to claim 11, wherein the thickness of the electric resistor material gradually changes.   12. The electro-optic element according to claim 11, wherein the thickness of the electric resistor material changes stepwise.   A light beam deflector using the electro-optic element according to claim 1.

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