JPH02222922A - Electrooptic lens device - Google Patents

Abstract

PURPOSE:To obtain a light beam which has aberrations improved by using an electrooptic medium and an electrooptic lens consisting of an electrode couple and a power source means, and obtained lens operation in a desired direction. CONSTITUTION:The electrooptic lens 3 is formed by using the rectangular electrooptic medium 5 as a base. The electrode couple are formed on the optical path of the electrooptic medium 5 and the power source means 7 is connected between electrode films 6a and 6b. A linear polarized light beam which is made incident on the electrooptic medium 5 of the electrooptic lens 3 is converged and flattened by a 1st lens in a 1st direction crossing a 2nd direction of convergence or divergence by the electrooptic lens 3. Consequently, when the lens operation by the electrooptic lens 3 is provided, the light beam has a refractive index close to a square distribution in the electrooptic medium 5 to have small aberrations.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF APPLICATION IN INDUSTRIES - (1) The present invention relates to an electro-optic lens device such as an optical head of an optical information recording/reproducing device using an electro-optic lens.

2. Description of the Related Art In general, electro-optic crystals are one of the important materials in optical devices. Here, the conventional method of changing the focal length using an electro-optic crystal is described, for example, in the 1985 Institute of Electrical Engineers of Japan Electromagnetic Field Theory Study Group Materials (EMT-85° & 16-20.
It is described in [Active transmission characteristics of gradient index flat plate microlens for image processing] in pages 25 to 33).

This is LiNb0. A minute graded refractive index flat plate microlens of 2501 Im or less is fabricated on a crystal plate by proton exchange, an electrode is further formed on the surface, and a voltage is applied to this electrode to create an electric current (by changing the refractive index by an optical effect to create a focal point). It changes the distance, and its theoretical analysis has been carried out.

In addition, literature (Ar'PI, IIED OPT+C5/V
ol, 24. No. 9/1, May 1985) rTotal 1internal ra "1ectio
n1ensJ describes a total internal reflection lens using an electro-optic crystal L i Ta O. First, LiTa0. A fine electrode array is formed on the X or Z plane of the crystal. The incident laser beam is focused to a beam diameter of about 20 μm at a small angle of 1.4° with respect to the X plane or the four planes. When a voltage is applied to the electrodes, the refractive index changes due to the electro-optic effect, resulting in a change in the position of the beam waist.

Problems to be Solved by the Invention The former method, in which a minute graded index flat plate microlens is fabricated in an electro-optic crystal [,iNbO, by proton exchange, is not easy to fabricate.

■ The incident beam is limited to 250 μm or less.

Therefore, applicable optical devices are also subject to restrictions.

■ Based on theoretical analysis, 20011mL cannot change the focal position.

■ Currently, only calculation results are available, and convergence performance is unknown.

There is a drawback.

In the case of the latter, a total internal reflection lens using an electro-optic crystal LjTaO, there is the restriction that the laser beam must be incident at an angle (1° to 4°) almost parallel to the crystal plane (reflecting surface). .

(2) The diameter of the incident beam at the reflecting surface must be narrowed to, for example, 20 μm.

There is a drawback.

Therefore, by applying a voltage to a pair of electrodes formed to sandwich an electro-optic medium such as P[, ZT, etc., a refractive index distribution is generated in the electro-optic medium by the electro-optic effect, and it is made to have a lens function. Electro-optic lenses are being considered. According to such an electro-optic lens, the h'q structure is simple and easy to manufacture, and the incident beam conditions are not severe.

However, it has problems in convergence performance and has the disadvantage of producing aberrations.

Means for Solving the Problems In the invention as set forth in claim 1, a linearly transmitted light beam is
a first lens that converges the light beam in the same direction;
an electro-optic medium disposed at a beam waist position on the optical axis of the light beam emitted from the first lens, between the second lens for converging the light beam in the direction; Shaped on both opposing sides? ■Electricity consisting of a pair of electrodes with a size and shape that provides a lens effect that converges or diverges the light beam in a second direction orthogonal to the first direction by applying pressure, and a power supply means that applies voltage to this pair of electrodes. An optical lens was installed.

In addition to the first lens, the first electro-optic lens, and the second lens according to the invention as claimed in claim 1, the invention also includes a second lens that converges the light beam emitted from the second lens in the second direction. 3 lenses and a fourth lens that converges in the same second direction, and are arranged between the third lens and the fourth lens at a beam waist position on the optical path of the light beam emitted from the third lens. an electro-optic medium having a size and shape formed on opposite surfaces of the electro-optic medium along the light beam transmission direction to provide a lens action to converge or diverge the light beam in the first direction when a voltage is applied. A second electro-optical lens was provided, which consisted of a pair of electrodes and power supply means for applying a voltage to the pair of electrodes.

According to the first aspect of the invention, when a predetermined voltage is applied to the electrode pair by the power supply means in the electro-optic lens, a refractive index distribution is generated in the electro-optic medium due to the electro-optic effect.

At this time,? The size and shape of the Li:m pair give this crystal a lens action that converges or diverges the light beam in a predetermined second direction, and the light beam incident as linearly polarized light receives this lens action. Converge or diverge in the second direction. Therefore, the light beam used only needs to be linearly polarized light, and is not subject to any other special restrictions. At this time, the linearly polarized light beam incident on the electro-optic crystal of such an electro-optic lens will cause aberrations due to differences in refractive index distribution depending on the passing position, but the first lens will cause aberrations in the first direction,
That is, it is converged and flattened in a first direction perpendicular to a second direction in which it is converged or diverged by the electro-optic lens. Therefore, when subjected to a lens action by the electro-optic lens, the light beam in the electro-optic medium experiences a refractive index close to a square distribution, resulting in small aberrations. Thereafter, the second lens converges the light beam in the first direction and converts the beam, so that the light beam is emitted as a convergent or diverging light beam with reduced aberrations. The focal length in the first direction can be controlled by varying the voltage applied to the electrode pair by the power supply means in the electro-optic lens.

Furthermore, according to the invention as claimed in claim 2, the lens system consisting of the first lens, the first electro-optic lens, and the second lens according to the invention as claimed in claim 1 has a similar 41-lens structure, and the first,
A lens system consisting of a third lens, a second electro-optic lens, and a fourth lens with the two directions reversed is provided, so
The aberration can also be reduced in a direction orthogonal to the direction according to the first aspect of the invention. Therefore, it is emitted as a convergent or diverging light beam with reduced aberrations in both the first and second directions.

Embodiment The first embodiment of the invention recited in claim 1 is shown in FIGS. 1 to 5.
This will be explained based on the diagram.

Roughly, as shown by arrow A, on the optical path (y-axis direction) of a linearly polarized light beam 1, there are a cylindrical lens 2 as a first lens, an electro-optic lens 3, and a second lens.
A cylindrical lens 4 as a lens is provided in this order. Here, both the cylindrical lenses 2 and 4 have a convergence effect in the X-axis direction, which is the first direction.

Further, the electro-optic lens 3 has a rectangular electro-optic medium 5.
, for example, is formed based on a p + , Z T electro-optic crystal. Its composition is 9.0/65/3
5 is suitable, but other compositions are possible. Here,
The electro-optic medium 5 is placed at the beam waist position of the convergent light beam produced by the cylindrical lens 2, and the surface on which the light beam enters and enters is optically polished. Electrode pairs 6 are formed on both surfaces of the electro-optic medium 5 in the y-axis direction, which face each other along the optical path (light beam transmission direction=y-axis direction). Here, the electrode pair 6 is an electrode film 6a.

6b, these electrode films 6a and 6b have a relatively narrow electrode width d1 in the center of the electro-optic medium 5, as shown in the figure.
, in the shape of a straight rectangle with a length Ql,
A power supply means 7 having a voltage v1 is connected between these electrode films 6a and 6b, and is configured such that the voltage V1 can be selectively applied by a control system and switching means (not shown). For example, gold (Au) is used as such an electrode material, but other conductive materials may be used. Also,
The electrode film is formed by vacuum evaporation.

In such a configuration, a light beam 1 linearly polarized in the y-axis direction is converged in the X-axis direction by the cylindrical lens 2, and enters the electro-optic medium 5 of the electro-optic lens 3 as a convergent light beam 8. The convergent light beam 8 that has entered the electro-optic lens 3 becomes a diverging light beam 9 (in the x-axis direction) and is emitted again. Assuming that no voltage is applied to the electrode pair 6, the diverging light beam 9 emitted from the electro-optic lens 3 is converged in the X-axis direction by the cylindrical lens 4 and converted into a parallel beam. However, when a voltage is applied to the electrode pair 6, the refractive index in the electro-optic medium 5 changes due to the electro-optic effect, resulting in a lens action (convergence action) in the y-axis direction, and in this state, the cylindrical lens 4 When it passes through, it becomes a convergent beam IO as shown in FIG. 1(a) and converges at the focal point F (however, the converging direction is only in two axial directions).

Here, regarding the electro-optic lens 3 in this embodiment, the linearly polarized light beam 1 enters from the end surface of the electro-optic medium 5, and i'! ! The light passes through the area affected by the polar films 6a and 6b and is emitted from the other end face. Now, when no voltage is applied to the electrode pair 6, the electro-optic medium 5 exists as a mere optical medium, and the light beam 1 directly passes through the electro-optic medium 5 without undergoing any change.
It is emitted from. Therefore, it does not have a lens effect. −
On the other hand, when a voltage 1 is applied to the electrode pair 6, a predetermined refractive index distribution is generated in the electro-optic medium 5 in the area affected by the electrode pair 6, and a lens effect is imparted to the electro-optic medium 5.

Therefore, the linearly polarized light beam 1 incident on the electro-optic medium 5 under such voltage application conditions is emitted after being subjected to a predetermined lens action.

Here, the lens action of the electro-optic lens 2 of this embodiment will be explained in more detail. First, a voltage v1 is applied to the electrode pair 6.
When this is applied, an electric field distribution as shown by the broken line E1 in FIG. Based on such electric field distribution, P L Z T
? ! ! Electro-optic effect of pneumatic crystal (secondary electro-optic effect)
This causes a refractive index distribution in the crystal. Now, the direction of the electric field and the linear polarization direction are the y-axis direction, and the traveling direction of the light beam 1 is the y-axis direction.
Assuming that the axial direction is the Z-axis component of the refractive index in the electric field as nz, the following equation is obtained. However, n is P L7゜1 in the electric field E=O
The refractive index of the electro-optic crystal, I, 3, is a matrix component of the second-order electro-optic constant.

From equation (1), the refractive index change Δn due to the electric field [ra2] 7. is proportional to the square of the electric field strength. And since the refractive index is small where the electric field is strong, I) I, ZT
The refractive index distribution is such that the refractive index is low near the electrode portions in the electro-optic crystal and becomes high near the center of the crystal.

Therefore, a lens effect occurs toward the center in the second direction, the y-axis direction. And this lens action is caused by the electrode length Q
The longer the period, the greater the effect.

Therefore, when the light beam 1 linearly polarized in the Z-axis direction is incident on the electro-optic medium 5, it is subjected to a lens action in the Z-axis direction by the voltage V1 applied to the electrode pair 6 having the electrode width d1 and length Q. . Under such lens action, the light converges at the focal point F.

Now, the refractive index distribution in the electro-optic medium 5 according to this example is as follows:
Figure 3 shows the results obtained using the finite element method. In FIG. 3, the coordinate origin 0 is the center position of the electro-optic medium 5, and X=O
M (indicated by ■), x=0°25mm (indicated by ■), x=
The refractive index distribution in the Z-axis direction at each position of 0.5 mm (indicated by ■) is shown. However, n, = 2.5, electric field strength E, = 1000 V/mm, electrode width d, = 1.1
mm% The thickness of the electro-optic medium in the Z-axis direction was 1.4M.

As a result, the refractive index distribution became a curved distribution as shown by ■■■. Based on this refractive index distribution,
Electrode length Q,,=8. When ray tracing was carried out using the Runge-Futter-Gill method and the convergence characteristics were examined when Omm, the light beam l incident on the electro-optic medium 5 was found to be
It has been found that convergence occurs due to the refractive index distribution in each region (2), which causes aberrations.

However, in this embodiment, the linearly polarized light beam l is not directly incident on the electro-optic medium 5 of the electro-optic lens 3;
The convergent light beam 8 is converged in the X-axis direction by the cylindrical lens 2 and is made incident at the beam waist position. That is, as shown in FIG. 4, it enters the electro-optic medium 5 as a convergent light beam 8 that is flattened in the X-axis force direction.

As a result, when compared with the refractive index distribution shown in FIG. 3, near the center of the electro-optic medium 5 (X=OM), the refractive index distribution approaches a square distribution over the entire Z-axis direction. The flat convergent light beam 8 is approximately 2
The refractive index of the power law distribution is sensed and converged, and aberrations are improved. In other words, by appropriately setting the relationship between the incident position X of the convergent light beam 8 converged by the cylindrical lens 2 and the electrode width d, convergence characteristics with less aberration can be obtained.

By the way, the electric field strength and focal length f of the electro-optical lens 3,
The actual measured values are shown in FIG. This actual measurement value is the electrode width d,
=0. 5nvn, electrode length Q, = 4.5mm and 8m+
2 types with n, beam diameter w of convergent light beam 8, = 1.2 m
This is an example in the case of m. According to this result, the focal length f becomes shorter in inverse proportion to the square of the electric field strength.

Next, a second embodiment of the invention according to claim 1 will be described with reference to FIGS. 6 to 10. Generally speaking, as in the case of the above embodiment, a cylindrical lens 12 as a first lens and an electro-optical lens are placed on the optical path (y-axis direction) of a linearly polarized light beam 11 as shown by arrow A. A lens 13 and a cylindrical lens 14 as a second lens are provided in this order.

Secondly, although the electro-optic lens 3 of the above embodiment had a convergence effect in the Z-axis direction, the electro-optic lens 1 of this embodiment
3 is designed to have a convergence effect in the X-axis direction. Therefore, the cylindrical lenses 12 and 14 have a convergence direction in the Z-axis direction, contrary to the case of the previous embodiment.

Similarly to the electro-optic lens 3 of the previous embodiment, the electro-optic lens 13 of this embodiment is based on an electro-optic medium 15 placed at the beam waist position of the cylindrical lens 12, and has electrode pairs 16 on both sides in the Z-axis direction. is formed. This pair of electrodes 16 each has a length Q formed on both sides with a gap g in the X-axis direction, and consists of four electrodes 16a, 16a, 2 each in the shape of a straight short plate.
16b, , 16b, and are connected to a power supply means 17 having a voltage V1.

In such a configuration, the light beam 11 polarized in the Z-axis direction is converged in the Z-axis direction by the cylindrical lens 12, and enters the electro-optic lens 13 at the beam waist position as a convergent light beam 18. This electro-optical lens 13
The convergent light beam 18 incident on the diverging light beam 19 (
z-axis direction). Assuming that no voltage is applied to the electrode pair 16, the diverging light beam 19 emitted from the electro-optic lens 13 is converged in the z-axis direction by the cylindrical lens 14 and converted into a parallel beam. However, when the voltage V2 is applied to the 7Tt pole pair 16, it is subjected to a lens action in the X-axis direction, and becomes a convergent light beam 20 converged in the X-axis direction as shown in FIG. 6(b). Converges to position F.

That is, a voltage V is applied to the electrode pair 16 in the electro-optic lens 13.
When , is applied, an electric field distribution as shown by the broken line E3 in FIG. 7 is generated in the electro-optic medium 15 due to the shape and arrangement of the electrodes. As a result, due to the electro-optic effect of the PLZT@air-optic crystal, a refractive index distribution with a high refractive index near x=O (with the origin at the center of the electro-optic medium j5 shown in Figure 7) on the x''z plane is created. Such a refractive index distribution is given by equation (1).As a result, a lens effect occurs toward the center in the X direction.This lens effect becomes larger as the horizontal length Q becomes longer.

Therefore, when the light beam 11 linearly polarized in the z-axis direction is incident on the electro-optic medium 15, it is subjected to a lens action in the x-axis direction by the voltage V applied to the electrode pair 16. Under such lens action, the light converges at the focal point F.

Now, FIG. 8 shows the results of finding the refractive index distribution in the electromagnetic medium I5 according to this example by the finite element method. In FIG. 8, the coordinate origin 0 is the center position of the electro-optic medium 15, and z
The refractive index distribution in the X-axis direction at each position: =onwn (indicated by ■), Z=0.3mn+ (indicated by ■), and z=0.6mm (indicated by ■). However, n, =
2.5, electric field strength E7. :=1000V/mm, electrode gap g=1.5ax% The thickness of the electro-optic medium 15 in the Z-axis direction was 1.4 mm. As a result, the refractive index distribution became a curved distribution as shown by ■■■. Based on such a refractive index distribution, the electrode length Q, =8. When Om is assumed, ray tracing was performed using the Runge-Futter-Gill method and the convergence characteristics were examined. It has been found that each convergence causes aberrations.

However, in this embodiment, the linearly polarized light beam 11 is not made to directly enter the electro-optic medium 15, but is instead made into a convergent light beam 1 that is converged in the z-axis direction by the cylindrical lens 12.
8.

That is, as shown in FIG. 9, it enters the electro-optic medium 15 as a convergent light beam 18 that is flattened in two axial directions.

As a result, near the center of the electro-optic medium 15 (z=omm)
However, the refractive index distribution approaches a square distribution over the entire X-axis direction (in comparison with the refractive index distribution shown in FIG. 8, the flat convergent light beam 18 is The refractive index is sensed to have an approximately square-law distribution and is converged, thereby improving aberrations.

Incidentally, the actual measured values of the electric field strength and focal length f1 of the electro-optical lens 13 of this example are shown in FIG. This actual measurement value is electrode II'iJ gap g = 1.5 mm, electrode length a, = 8
Shizuku: Beam diameter W of convergent light beam 18.

This is an example of a case of 1.8 mm and a wavelength of 633 nm. In this case, as in the previous embodiment, the focal pressure if becomes shorter in inverse proportion to the square of the electric field strength.

Further, an embodiment of the invention according to claim 2 will be described with reference to FIG. 11. This embodiment is constructed by combining the two embodiments described above. That is, cylindrical lens (first lens) 2, electro-optic lens (first @ pneumatic lens) 3, cylindrical lens (second lens) 4, cylindrical lens (third lens) 12, electro-optic lens (second electro-optical lens) lens) 13, cylindrical lens (
4th lens) 14 are sequentially arranged on the same optical path. In this embodiment, the X-axis direction is the first direction, and the Z-axis direction is the second direction. Further, the light beam emitted from the cylindrical lens 4 corresponds to the light beam 11.

According to such a configuration, the effect of the above-described embodiment is exerted as is, and the convergent light beams 21 converged in the x and z moving image directions are focused at the same focal position F. In addition, in order to make the convergence position = focal position F in the X-axis force direction and Z-axis direction the same, the values of the voltages V, V, should be adjusted and set as appropriate, or,
If these voltages V1°Vt are the same, the shape of the electrodes in each electro-optical lens 3°13 may be determined appropriately.

Moreover, by making the convergence position=focus position F in the X-axis direction and the Z-axis direction different, it is possible to converge the beam into an arbitrary flat beam.

Effects of the Invention Since the present invention is constructed as described above, according to the invention described in claim 1, an electro-optic lens comprising an electro-optic medium, an electrode pair, and a power source means can be used to have a lens action in a desired direction. The structure is simple and easy to manufacture, and the focus position can also be applied. It can be easily variably controlled by one pressure, and the conditions for the light beam incident on the electro-optic lens can be relaxed to a state where only linearly polarized light is required. Although aberrations may occur due to differences in index distribution, since the first lens enters the electro-optic lens as a flat light beam that is converged in the orthogonal direction, a refractive index close to a square distribution can be sensed in the electro-optic medium. According to the invention as claimed in claim 2, it is possible to obtain a light beam with improved aberrations in both the first and second directions, and its focal length, light The beam shape can also be variably controlled by applying voltage and the like.

[Brief explanation of the drawing]

Fig. 1 shows a first embodiment of the invention as claimed in claim 1, in which Fig. 1(a) is a side view of the optical system, Fig. 2(b) is a plan view thereof, and Fig. 2 shows the state when voltage is applied. 3 is a characteristic diagram showing the refractive index distribution depending on the position in the electro-optic medium, FIG. 4 is a front view showing the shape of the incident beam on the electro-optic medium, and FIG. 5 is the electric field state. A characteristic diagram showing the focal length depending on the intensity, FIG. 6 shows a second embodiment of the invention as claimed in claim 1, in which (a) is a side view of the optical system, and (b) is a side view of the optical system. Its plan view, Fig. 7 is a cross-sectional view showing the electric field state when the voltage is applied, Fig. 8 is a characteristic diagram showing the refractive index distribution depending on the position in the electro-optic medium, and Fig. 9 is the incident light on the electro-optic medium. FIG. 10 is a front view showing the beam shape, FIG. 1O is a characteristic diagram showing the focal length depending on the electric field strength, and FIG.
1 is a side view of the optical system, and FIG. 3B is a plan view thereof.

Claims (1)

[Claims] 1. A first device for converging a linearly polarized light beam in a first direction.
A lens, an electro-optic medium disposed at the beam waist position on the optical axis of the light beam emitted from the first lens, and an electro-optic medium formed on both surfaces of the electro-optic medium facing each other along the light beam transmission direction, by applying a voltage. the light beam to the first
an electro-optic lens comprising an electrode pair having a size and shape to provide a lens effect of converging or diverging in a second direction perpendicular to the direction of the electro-optic lens; and a power source means for applying a voltage to the electrode pair; An electro-optic lens device comprising: a second lens that converges a light beam in the first direction. 2. A first converging light beam that is linearly polarized in a first direction.
A lens, an electro-optic medium disposed at the beam waist position on the optical axis of the light beam emitted from the first lens, and an electro-optic medium formed on both surfaces of the electro-optic medium facing each other along the light beam transmission direction, by applying a voltage. the light beam to the first
a first electro-optic lens comprising a pair of electrodes having a size and shape to provide a lens effect of convergence or divergence in a second direction perpendicular to the second direction; and a power supply means for applying a voltage to the pair of electrodes; a second lens that converges the emitted light beam in the first direction; a third lens that converges the light beam emitted from the second lens in the second direction; and an optical path of the light beam emitted from the third lens. an electro-optic medium disposed at the beam waist position of the electro-optic medium; and a lens action formed on both surfaces of the electro-optic medium facing each other along the light beam transmission direction to converge or diverge the light beam in the first direction by applying a voltage. a second electro-optic lens comprising an electrode pair having a given size and shape and a power source for applying a voltage to the electrode pair; An electro-optic lens device comprising: a fourth lens that converges in a direction.