JPH042172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electro-optic optical deflector that electro-optically deflects a light beam using an electro-optic crystal.
Regarding a crystal composite electro-optic optical deflector that combines multiple electro-optic crystals to obtain good optical deflection performance, it is easy to manufacture and provides stable performance.
This allows for high-speed optical deflection with efficient band usage.

Prior Art In general, optical deflectors are broadly classified into mechanical optical deflectors and acousto-optic optical deflectors in addition to the electro-optic optical deflectors mentioned above. Of these three types of optical deflectors, the ones that have reached the stage of practical use are mechanical optical deflectors represented by polygons, and acousto-optic devices that use ultrasonic waves to form a diffraction grating on a dielectric material surface. The electro-optical optical deflector has not yet left the laboratory stage.

However, among the three types of optical deflectors mentioned above, each of which has its own advantages and disadvantages, the electro-optic optical deflector that is currently at the research stage is the one that can theoretically be expected to have the highest speed. Conventional technology related to the present invention, which aims to put into practical use an optical deflector that is much faster than the conventional art, will also be described exclusively with respect to this electro-optical optical deflector.

Therefore, in certain types of crystals and substances, the effect of changing the refractive index by applying an electric field can be obtained. Generally, such an effect is referred to as an electro-optic effect, and a crystal or substance that provides such an effect is referred to as an electro-optic crystal or an electro-optic substance. The above-mentioned electro-optic light deflector is a general term for optical deflectors that utilize this electro-optic effect, and generally, if an electrode is attached to a material exhibiting an electro-optic effect such as an electro-optic crystal and a voltage or electric field is applied, It is possible to cause a change in the refractive index in an appropriate manner depending on the material or the shape of the electrode, and as a result, the traveling direction of light passing through the material is changed to perform so-called deflection, thereby forming an optical deflector. be able to.

Typical conventional configurations of electro-optic light deflectors having such basic configurations are listed and shown in FIGS. 1 to 5, respectively.

First, the conventional electro-optic optical deflector shown in FIG. A phase diffraction grating is formed within the electro-optic crystal 1 by application of an alternating electric field, and the light beam is deflected by its diffraction action. This conventional configuration has the advantage that it is suitable for integration because the electrodes for applying an electric field can be gathered on one side of the electro-optic crystal 1.
In addition to requiring advanced technology to manufacture, the light beam can only be deflected in a specific direction, so although it can be used as a deflection switch, it is impossible to sweep the light beam with continuous analog deflection. It has its drawbacks.

Next, the conventional electro-optic light deflector shown in FIG. 2 consists of quadrupole electrode rods arranged on four sides of an electro-optic crystal 1 having a rectangular cross section, with electrodes of the same polarity arranged on opposite sides. 2a to 2b as AC voltage source 3
By connecting to , a linearly changing electric field distribution is generated within the crystal cross section according to the applied voltage, and as a result, a linearly changing refractive index distribution is generated, and the refractive index is shifted toward the side with a larger refractive index. It is designed to deflect a light beam. This conventional configuration has drawbacks such as the difficulty of applying high-frequency voltage due to the structure of the electrode, making it impossible to perform high-speed deflection, and the strong electric field concentrating near the electrode rod, which tends to cause crystal distortion. .

Next, the conventional electro-optic optical deflectors shown in FIGS. 3a to 3-c each have extremely simple-shaped electrode plates 2a, 2b, That is, it has the simplest structure in which electrode plates 2a and 2b are attached, for example, in a triangular shape as shown in the figure, or a trapezoidal or home base shape that acts equivalently to a triangular shape, and these electrode plates 2a and 2b are connected. In response to the voltage applied by the AC voltage source 3, a triangular prism having a refractive index different from other parts is formed in the crystal 1 under the electrode plate, so that the light beam passing through the triangular prism is deflected. This is what I did. In this conventional configuration, when a light beam is deflected by applying a voltage, an optical phase shift occurs in the entire light beam, which varies in magnitude depending on the position but always in the same direction.
As a result, an extra phase modulation is added to the light beam simultaneously with the deflection. Therefore, when using an optical deflector with this conventional configuration for high-speed deflection or high-speed modulation,
Since it becomes necessary to provide an extra optical frequency band for passing the above-mentioned extra phase modulation component, there is a drawback that the band utilization efficiency of the optical signal is reduced.

Next, the electro-optic optical deflector shown in FIGS. 4a and 4b is an improved version that eliminates the above-mentioned drawbacks of the conventional configuration shown in FIG. Electro-optic crystals 1a and 1b having similar shapes are joined together with their optical axes reversed to have opposite polarities to form a flat rectangle as a whole, and the entire top and bottom surfaces of the electro-optic crystals 1a and 1b are adhered. Both rectangular electrode plates 2
a and 2b are connected to an AC voltage source 3.
Therefore, each electro-optic crystal is constructed under the same conditions as the electro-optic crystal shown in FIG. 3, except that the optical axes are of opposite polarity. That is, when a light beam passes through an electro-optic crystal pair having such a configuration when a voltage is applied, a linear optical length change or optical phase change is exhibited within the cross section of the light beam, just as in the conventional configuration shown in FIG. The light beam is deflected to the side with the longer optical length. However, such a change in optical length is caused by a pair of electro-optic crystals 1
Since it acts differentially between a and 1b, the polarity of the change in optical length within the cross section of the light beam is reversed on the left and right, and becomes zero at the center. Therefore, no phase modulation occurs in the optical beam as a whole, no extra optical frequency band is required, and band utilization efficiency is improved. Also, from the point of view of deflection sensitivity, the longer the crystal length in the direction along the optical axis, the better.
Electro-optic crystal 1a having the configuration shown in FIGS. 4a and 4b,
When the crystal length of 1b in the optical axis direction is increased, the triangular hypotenuse formed by the bonding surface between crystals 1a and 1b becomes a significantly acute angle, and the incident angle of the light beam to the bonding surface of crystals 1a and 1b approaches 90°. Therefore, the light is incident almost parallel to the bonded surface. Therefore, if there is a slight gap between the bonded surfaces of the crystals 1a and 1b, or a difference in refractive index due to a misalignment of the optical matching agent used to alleviate the effect of the difference in refractive index between the two, In this case, the incident light beam is totally reflected on the bonded surface and cannot pass through the optical deflector. In order to prevent such a situation from occurring, conventionally, so-called optical contacts, which do not use an optical matching agent and which do not cause refractive index mismatch, have been developed using advanced and expensive manufacturing technology, that is, highly smooth contacts. The bonding process was carried out in such a way that the bonding surfaces, which had a mirror finish, could be self-retained simply by adhering them tightly. However, electro-optic crystals generally
It is also a piezo crystal, and when an electric field is applied, the refractive index changes and the physical dimensions of the crystal also change. As a result, in the configuration shown in FIG.
By applying a voltage, the two crystals 1a and 1b undergo dimensional changes of opposite polarity, that is, elongation and shrinkage reciprocally, and the bonded surfaces tend to peel off.

In summary, the problems with the conventional electro-optic optical deflector of the type constructed by bonding a plurality of electro-optic crystals as shown in Figure 4 are the technical difficulty of the optical contact surfaces between the crystals and It lies in stability and reliability.

Next, the electro-optic optical deflector shown in FIG.
In order to solve the problems described above with respect to the conventional configuration shown in the figure, a plurality of crystal pairs having the configuration shown in the fourth figure are connected in series. In other words, since the same deflection effect as in the configuration shown in FIG. 4 is obtained using multiple stages, the crystal length per stage can be shortened, and the bonding surface between the crystal pairs can be shortened. The incident angle of the light beam relative to the surface is small, so that the problem of total internal reflection as described above does not occur even when an optical matching agent is used without using an optical contact.

However, even in the conventional configuration shown in FIG. 5, since a large number of electro-optic crystal prisms each consisting of five electro-optic crystals 1a to 1e are used as shown in the figure, the structure is not only complicated and expensive, but also Since there are many discontinuous surfaces in the optical path due to bonding, many drawbacks remain, such as increased light transmission loss.

As detailed above, all of the conventional electro-optic optical deflectors of this type have some kind of drawback, and none of them have reached the level of practical use.

Summary of the Invention An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, use a simple shape or structure, especially an electrode layer of a simple shape, and create an optical contact that is technically difficult and unstable to manufacture. An object of the present invention is to provide an electro-optic optical deflector capable of high-speed deflection with excellent utilization efficiency of an optical frequency band without using.

Another object of the present invention is to provide an electro-optic optical deflector with a new structure that eliminates the disadvantages of the conventional structure described above with reference to FIGS. 3 to 5 and takes advantage of its advantages.

Still another object of the present invention is to provide an electro-optic optical deflector that not only has the original function of an optical deflector but also is suitable for application as an optical pulse generator, a streak camera, an optical gate, a high-speed camera, a range finder, etc. It is about providing the equipment.

That is, in the crystal composite electro-optic optical deflector of the present invention, at least one pair of electro-optic crystals are sequentially connected in series in the optical axis direction with the polarities of their crystal axes reversed to each other, and each electro-optic crystal is connected in series in the optical axis direction. electrodes are respectively deposited on crystal planes facing each other across the optical axis, and the shape of the electrodes deposited on the crystal planes on at least one side for each electro-optic crystal is such that at least It is a polygonal shape having parallel sides parallel to the axis and oblique sides obliquely intersecting the optical axis, and the polygonal shapes are antisymmetrical to each other with respect to the optical axis in a pair of electro-optic crystals, and the oblique sides are opposite to each other with respect to the optical axis. are parallel to each other and face each other.

EXAMPLES The present invention will be explained in detail below using examples with reference to the drawings.

First, an example of the basic configuration of the electro-optic light deflector of the present invention is shown in FIG. In the basic configuration shown, if rectangular coordinates x, y, z are provided as shown,
Electro-optic crystals 1a and 1b forming a pair of rectangular parallelepipeds are arranged cascaded in the y-axis direction along the optical path, and
The optical axes taken in the axial direction are reversed and are reversed to each other as shown. Note that among the end faces S ₁ , S ₃ and S ₂ , S ₄ through which the light beam passes in each crystal 1a and 1b, the end faces S ₁ and S ₂ that are in contact with each other are in close contact or adhered, and are coated with adhesive or optical matching. The end faces S ₁ and S ₂ are crimped with or without adhesive, or they are made into optical contacts (although this is not particularly necessary), or they are brought into close contact in an appropriate manner, such as by applying a non-reflective coating. .

Due to this configuration, an electrode layer in the shape of a parallelogram as shown in the figure is formed on one side of the electro-optic crystal composite, which forms a rectangular parallelepiped as a whole as shown in the figure, for example, on the top surface as shown in the figure, spanning both crystals 1a and 1b. 2
For each crystal, similar triangular electrode layers are deposited antisymmetrically to each other. That is, for example, as shown in the figure, crystal 1a
In the case of crystal 1b, the base of the triangle is in contact with the right side of the crystal and the apex is in contact with the left side, and in the case of crystal 1b, the base of the triangle is in contact with the left side and the apex is in contact with the right side. Therefore, in the illustrated example, the oblique sides of the triangular electrode layers on the upper surfaces of crystals 1a and 1b are opposed to each other in the optical path direction.

Note that on the other side of the illustrated electro-optic crystal composite, for example, on the lower surface shown in the figure, an electrode layer 2b of the same shape is deposited directly under the upper electrode layer 2a, or a rectangular electrode layer is formed over the entire lower surface. 2b is applied, and the electrode layers 2a and 2b on both the upper and lower surfaces are connected to an AC voltage source 3 and driven. In addition, the incident light beam enters from the end surface S ₃ of the crystal 1a and passes through the bonding surfaces S ₃ and S ₄ to the crystal 1a.
It is emitted from the end surface _S4 of b, but is deflected in the xy plane during that time, and becomes an emitted deflected light beam.

In this basic configuration, the direction of the optical axis of the electro-optic crystal and the polarization direction of the incident light beam are set depending on the type and properties of the electro-optic crystal used. For example, when using a LiTaO ₃ or LiNbO ₃ crystal, In this case, it is efficient to set the voltage application direction, which in the illustrated example is the z-axis direction, and the polarization direction of the incident light beam to be in the direction of the c-axis, which is the birefringent crystal axis of the electro-optic crystal. The electro-optic crystals 1a and 1b in the basic configuration shown in the figure are not only rectangular as shown in the figure, but also have a Brewster cut shape so that the incident light beam forms a Brewster angle with respect to the incident end surface. It is also possible to make the light incident by refraction.

In the electro-optic light deflector of the present invention having the basic configuration as described above, the electrode layers 2a and 2b on both the upper and lower surfaces
As in the conventional configuration, optical deflection is performed by applying an AC voltage of a desired waveform between the two. However, according to the above-described basic configuration of the present invention, the triangular electrode layer deposited on at least one surface, for example, the top surface, of the electro-optic crystal composite is configured antisymmetrically with respect to the optical path direction, so that An almost constant electric field is generated in the crystal,
A refractive index change occurs under such a constant electric field. Moreover, since the optical axes between adjacent crystals are reversed and have opposite polarities, for example, if the refractive index change that occurs under the electrode of crystal 1a is Δn, then
The refractive index change occurring under the electrode of the crystal 1b is -Δn.

Now, in the basic configuration shown in Figure 6, the action of the optical deflector of the present invention on the xy coordinate plane parallel to the upper and lower surfaces of the crystal composite is as shown in Figure 7. If the width of the crystal composite in the x direction is D, the light beam incident parallel to the y-axis passes through the region under the electrode of length l/D (D/2+x) in crystal 1a, and Inside, it passes through an area under the electrode of length l/D (D/2-x). Therefore, the total optical length ΔLop where the optical beam is deflected by the application of the constant electric field mentioned above is as follows (1)
The formula becomes

ΔLop=Δn・l/D(D/2+x)−Δn・l/D(D/2−x)=2Δn・l/2・x(1
) Therefore, the total optical length ΔLop through which a light beam passing through point x is deflected is proportional to the lateral distance x from the center of the optical path to the point of incidence; The total optical length ΔLop changes linearly with the distance from the center. Note that l in the above formula is the light traveling direction of each electro-optic crystal 1a, 1b, that is, y in the figure.
This is each total length in the axial direction.

Therefore, since the light beam incident on the electro-optic crystal has the property of being deflected to the side with a longer optical length, if the value of the refractive index change Δn is positive, the value of the coordinate x will be positive. Conversely, if the value of the refractive index change Δn is negative, the beam is deflected to the side where the value of the coordinate x is negative. Note that the deflection angle θ at that time is expressed by the following equation (2).

θ=2・Δn・l/D (2) Therefore, when a linear light beam having a width approximately equal to the width D of the crystals 1a and 1b in the basic configuration shown in FIG. 6 is incident, the deflected output light beam The diffraction spread angle Δθ formed by

Δθ=0.886λ/D (3) Here, λ is the wavelength of the incident light.

Therefore, the deflection angle θ is determined by how many times the minimum value of the diffraction spread angle according to equation (3) is allowed relative to the beam spread angle of the incident light beam spot. The deflection angle θ according to equation (2) is equivalent to 2.26·Δn·l/λ times the beam spot, that is, the value obtained by dividing the right-hand side of equation (2) by the right-hand side of equation (3). become.

Furthermore, according to equation (2), no optical length change occurs at the center point of the crystal cross section, that is, the point at the coordinate x = 0, and the optical length changes symmetrically on the left and right of this center point at x = 0. It can be seen that this is occurring. Therefore, when a linear light beam that spreads symmetrically with x=0 as the central axis is incident, the average optical length change in the entire linear light beam is canceled out on the left and right sides, resulting in extra phase modulation. This significantly improves the efficiency of optical frequency band use.

Furthermore, in the electro-optic optical deflector configured according to the present invention, the angle of incidence of the light beam with respect to the end face of the intercrystalline junction is 0, and the junction surface between the crystals, which has been particularly problematic in the past, has a structure according to the present invention. Since the end face is perpendicular to the light traveling direction, at least no total reflection occurs. Note that although some reflections due to mismatching of refractive indexes remain, such residual reflections can be easily suppressed to a few percent or less by interposing an optical matching agent between the bonded surfaces. Also, if optical contacts are used, the problem of the bonding surface is completely eliminated, but
Since it is not essential, the present invention provides an optical deflector with excellent performance that is easy to manufacture and operates stably when a voltage is applied. That is, the electro-optic optical deflector according to the present invention has characteristics and performance that are almost equivalent to those of the optical deflector having the configuration shown in FIG. 4, which is recognized as having the best characteristics and performance among conventional devices, and furthermore, This is comparable to a state in which all of the above-mentioned drawbacks associated with this conventional configuration, particularly the problem of intercrystalline bonding end faces that require optical contact, have been solved.

Note that the basic configuration according to the present invention shown in the sixth figure and the third figure
As can be seen by comparing the conventional configuration shown in the figure, the optical deflector of the present invention performs a push-pull operation by reversing the polarities of the optical axes of the two optical deflectors according to the conventional configuration shown in the third figure, for example. It can also be considered that they are connected in a cascade arrangement.

The basic structure of the electro-optic light deflector of the present invention described in detail above can be modified in many ways without departing from its characteristics. Another example of the structure of the optical deflector of the present invention is shown in the eighth section.
They are shown in Figures a to c, Figures 9a and b, and Figure 10, respectively.

Other configuration examples shown in FIGS. 8a to 8c are individual electro-optic crystals 1 in the basic configuration shown in FIG.
The triangular electrode layer 2a or 2a, 2b deposited on the upper surface or both upper and lower surfaces of a, 1b is shaped into a trapezoid, or a combination of a triangle or a right triangle in a rectangle, or an electrode layer having such a shape. The crystals 1a and 1b are integrally connected to each other. Electrode layer 2a in the basic configuration shown in FIG. 6
Alternatively, in 2a and 2b, since the hypotenuse where the optical length of the region under the electrode changes extends across the entire width of the crystal in the triangular shape, the number of deflection spots, that is, the number obtained by dividing the deflection angle by the beam spread angle, is In order to maximize the deflection angle and widen it, it is necessary to extend the deflection range to the side edges of the crystal, which causes disturbances in the deflection action near the side edges, resulting in disturbances in the cross-sectional shape of the output beam. On the other hand, Fig. 8 a to c
In the configuration example shown in , the shape of the electrode near the side edge of the crystal is rectangular, and the optical length of the area under the electrode is constant, so the area near the side edge of the crystal does not contribute to the deflection of the light beam. Therefore, in order to maximize the number of deflection spots, it is sufficient to extend the deflection spots to the full extent of the oblique side of the central region of the crystal, so there is no possibility that the cross-sectional shape of the output beam will be disturbed.

On the other hand, other configuration examples shown in FIGS. 9a, b and 10, respectively, are shown in FIGS.
The crystal pairs having the structure shown in 2 are connected in series in multiple stages, and the electrode layers 2a and 2b on both the upper and lower surfaces are continuous throughout the crystal composite. Among them, in the configuration example shown in FIG. 9a, a pair of crystals whose optical axes have opposite polarities are combined with adjacent crystals having the same optical axis polarity.
In the configuration example shown in Figure b, adjacent crystals are combined with their optical axis polarities reversed. Furthermore, in the configuration example shown in FIG. 10, each crystal pair is separated and combined into the front and rear parts of a crystal composite having the same optical axis polarity.

Note that in the electro-optical optical deflector of the present invention, unlike the conventional configuration shown in FIG. 4, the optical length of the entire crystal composite can be increased to increase the deflection sensitivity without essentially using a multi-stage configuration. When it is difficult to obtain a long electro-optic crystal as a single unit, it is extremely effective because short-sized electro-optic crystals can be combined in multiple stages to function equivalently.

Effects As is clear from the above explanation, according to the present invention, electro-optic crystals of simple shapes are appropriately combined and electrode layers of simple shapes are deposited on both the upper and lower surfaces of the electro-optic crystals. A special effect can be obtained in that it is possible to realize an electro-optic optical deflector that can be manufactured extremely easily, has excellent optical frequency band usage efficiency, and can operate at high speed without using unstable optical contacts.

[Brief explanation of drawings]

Figure 1, Figure 2, Figure 3 a-c, Figure 4 a, b
5 is a perspective view showing a typical structure of a conventional electro-optic light deflector, FIG. 6 is a perspective view showing an example of the basic structure of an electro-optic light deflector of the present invention, and FIG.
The figure is a top view showing an example of the light deflection operation, and FIGS. 8a to 8c, 9a and 9b, and 10 are perspective views showing examples of the specific structure. 1, 1a to 1e...electro-optic crystal, 2a, 2a
1, 2a2, 2b, 2b1, 2b2... electrode, 3...
AC voltage source, S ₁ to S ₄ ...crystal end face.

Claims (1)

[Claims] 1. At least one pair of electro-optic crystals are sequentially connected in cascade in the optical axis direction with the polarities of their crystal axes reversed to each other, and each electro-optic crystal is connected with the optical axis on both sides. electrodes are respectively deposited on crystal planes facing each other, and the shape of the electrodes deposited on each electro-optic crystal on at least one side of the crystal plane is at least parallel to the optical axis. It is a polygonal shape having oblique sides obliquely intersecting the optical axis, and the polygonal shapes are antisymmetrical to each other with respect to the optical axis in a pair of electro-optic crystals, and the oblique sides are parallel and opposite to each other. A crystal composite electro-optic optical deflector characterized by: 2. In the optical deflector according to claim 1, the end faces of the sequentially connected electro-optic crystals that intersect with the optical axis are formed directly, or with a refractive index matching agent interposed therebetween, or A crystal composite electro-optic optical deflector characterized by being in surface contact with each other by being coated with a non-reflective coating or by forming an optical contact. 3. In the optical deflector according to claim 1 or 2, for each electro-optic crystal, a crystal on the one side is attached to a crystal plane on the other side opposite to the crystal plane on the one side. 1. A crystal composite type electro-optic optical deflector, characterized in that the electrodes are deposited on a surface in a projected shape or over the entire surface of the crystal surface.