JP2008242098A - Polarizing rotary element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a longitudinal electric field type polarizing rotary element which has rectangularly sectioned electrooptical crystal, and can improve uniformity of an electric field distribution in a cross section of the electrooptical crystal when a high voltage is applied with a simple structure. <P>SOLUTION: On flanks of large-sized optical crystal 1 except two surfaces perpendicular to an optical axis, an A electrode 2 and a B electrode 3 are formed. The A electrode 2 and B electrode 3 are formed so as to have a small electrode width on an end side of each flank and a large electrode width at the center part of the flank to enclose a circumference of the large-sized optical crystal 1. One of edges of the A electrode 2 and B electrode 3 is linear and the other is in a mountain shape such that the electrode width smoothly varies according to a curve or straight line, a fixed spacing being provided between the A electrode 2 and B electrode 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarization rotation element, and more particularly to a vertical electric field type polarization rotation element having a rectangular cross section.

  2. Description of the Related Art In recent years, laser devices that emit laser light having a rectangular beam cross section have been increasing in diameter and output. Such a laser device is used as, for example, a high-power pulse laser device. In these applications, as the diameter of the laser apparatus is increased, a large-sized polarization rotation element that supports a large-diameter rectangular beam is also required.

  Conventionally, a laser beam having a circular beam cross section has been generally used for a vertical electric field type polarization rotation element using an electro-optic effect such as the Pockels effect. For this reason, an electro-optic crystal having a circular cross section has been used for the polarization rotation element. In the present specification, the vertical electric field means that the direction of the electric field applied to the polarization rotation element is parallel to the optical axis of the laser light incident on the element.

  FIG. 3 is a perspective view showing a conventional polarization rotation element. As shown in FIG. 3, in order to make the polarization rotation element having the electro-optic crystal 7 having a circular cross section correspond to the incident light of the rectangular beam section 5, the cross-sectional diameter of the electro-optic crystal 7 is at least a diagonal line of the rectangular beam section 5. It must be longer than the length. In addition, due to the relationship between crystal cutout orientations, crystals that are actually the base material must be larger.

  However, the large crystal has a problem that it is difficult to manufacture due to limitations due to its growth rate and cost. In view of this, it has been considered that the shape of the electro-optic crystal is a rectangular column having a rectangular cross section. Accordingly, since the electro-optic crystal can be grown with a minimum cross-sectional dimension with respect to the shape of the incident light beam, the electro-optic crystal can be reduced in size and the manufacturing period thereof can be shortened.

  On the other hand, as an example of an optical device using a longitudinal electric field type electro-optic crystal, for example, Patent Document 1 discloses an optical device in which an electrode layer is laminated in the optical axis direction. Further, as shown in FIG. 3, the electrode pair 8 may be formed on the side surface of the electro-optic crystal 7 so as to be wound around the electro-optic crystal 7.

JP-A-2005-181503

  However, when an electrode pair as shown in FIG. 3 is provided for a polarization rotation element having an electro-optic crystal having a rectangular cross section, there are the following problems. In the electro-optic crystal 7 having a circular cross section shown in FIG. 3, by forming a pair of electrodes 8 side by side in the direction of the optical axis direction 4, when a high voltage is applied to the polarization rotator, A vertical electric field (electric field direction 6) is generated inside. Here, by making the width of each electrode of the electrode pair 8 constant, the electric field distribution in the circular cross section of the electro-optic crystal 7 can be obtained with good uniformity. Further, it has advantages such as simplification of the structure as compared with the type in which the electrode layers of Patent Document 1 are laminated. However, when an electrode of the type wound around the crystal is applied to an electro-optic crystal having a rectangular cross section, a band electrode pair having a constant width is formed as in the case of a circular cross section. There has been a problem that the electric field distribution in the rectangular cross section of the film is not uniform. For this reason, the polarization rotation characteristic of the outgoing light with respect to the incident light of the rectangular beam is not uniform within the cross section of the electro-optic crystal.

  The present invention has been made in view of such problems, and in a vertical electric field type polarization rotation element having a rectangular cross-section electro-optic crystal, when a high voltage is applied with a simple structure, the optical axis of incident light is applied. An object of the present invention is to provide a polarization rotation element capable of improving the uniformity of electric field distribution in a vertical cross section.

  The polarization rotator according to the present invention includes an electro-optic crystal having a rectangular cross section with respect to incident light, and the optical axis of the incident light on four surfaces parallel to the optical axis of the incident light of the electro-optic crystal. A pair of electrodes formed so as to be wound around the electro-optic crystal as a center, and the shape of each electrode on at least one pair of opposed surfaces of the four surfaces is the surface The electrode has a shape in which the electrode width on the end side is small and the electrode width at the center of the surface is large.

  In the present invention, the electrodes formed on the four surfaces (side surfaces) parallel to the optical axis of the incident light of the electro-optic crystal have at least one pair of side surfaces with a small electrode width on the end side of the surface and the center of the surface. The electrode width of the portion is formed to be large. Thereby, when a high voltage is applied to the electrode, the uniformity of the electric field distribution in the cross section of the electro-optic crystal can be improved. For this reason, according to the present invention, it is possible to obtain a polarization rotation characteristic with good uniformity for the outgoing light with respect to the incident light of the rectangular beam.

  In this case, the electro-optic crystal can be configured to be a KD * P crystal.

  The electro-optic crystal can be configured to exhibit an electro-optic effect when a longitudinal electric field parallel to the optical axis of the incident light is applied. In this case, the electro-optic effect can be a Pockels effect.

  According to the present invention, in a vertical electric field type polarization rotation element having an electro-optic crystal having a rectangular cross section, the uniformity of the electric field distribution in the cross section perpendicular to the optical axis of incident light when a high voltage is applied with a simple structure. Can be improved.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a side view of the polarization rotator according to the present embodiment as viewed from a direction perpendicular to the optical axis, and FIG. 2 is a perspective view showing the polarization rotator according to the present embodiment. In the following description, unless otherwise specified, the optical axis refers to the optical axis of incident light, and the cross section refers to a cross section perpendicular to the optical axis of incident light.

As shown in FIG. 1, a large optical crystal 1 is provided. The large optical crystal 1 has a quadrangular prism shape, and is arranged so that laser light is perpendicularly incident on the large optical crystal 1 inside a laser device (not shown). As the large optical crystal 1, a crystal using an electro-optical effect, for example, a KD * P (KD ₂ PO ₄ ) crystal using a Pockels effect is used.

  An A electrode 2 and a B electrode 3 are provided on the side surfaces of the large optical crystal 1 except for two surfaces perpendicular to the optical axis direction 4. The material of the A electrode 2 and the B electrode 3 is not limited, but a metal such as Au is used, for example, and is formed on the large optical crystal 1 by a technique such as vapor deposition and pressure bonding. The A electrode 2 is provided so as to be wound around the large-sized optical crystal 1 and is formed so that the electrode width at the end of the surface is small and the electrode width at the center of the surface is large on each side surface. ing. One of the edge portions of the A electrode 2 is linear, and the other has a mountain shape in which the electrode width changes smoothly according to the curve and the straight line. The dimensions of the electrode width are determined based on the dimensions of the large optical crystal 1 and conditions such as applied voltage. The B electrode 3 is formed so as to be symmetric with respect to the A electrode 2 with respect to a certain cross section perpendicular to the optical axis in the large optical crystal 1, and is constant between the A electrode 2 and the B electrode 3. Is provided. The film thicknesses of the A electrode 2 and the B electrode 3 are constant in each part.

  Next, the operation of the polarization rotation element of the present embodiment configured as described above will be described. As shown in FIG. 2, when a high voltage is applied to the A electrode 2 and the B electrode 3, a vertical electric field is generated parallel to the optical axis (electric field direction 6) in the cross section of the large optical crystal 1. In this state, when linearly polarized laser light is incident on the large optical crystal 1 in the direction of the optical axis 4, the laser light passing through the large optical crystal 1 changes to elliptically polarized light due to birefringence due to the Pockels effect. To do. Using this property, for example, the polarization direction can be rotated by 90 degrees depending on conditions. Since the Pockels effect has the property that the refractive index changes in proportion to the strength of the electric field, the polarization rotation of incident light can be controlled by the voltage applied to the polarization rotation element.

  In the polarization rotation element of the present embodiment, the A electrode 2 and the B electrode 3 wound around the large optical crystal 1 have a small electrode width on the end side of the surface on each side surface, and an electrode in the center of the surface. The width is formed to be large. Thereby, good uniformity is obtained for the electric field distribution in each part in the cross section of the large optical crystal 1. For this reason, in this embodiment, even when laser light having a large rectangular beam cross section 5 close to the cross section of the large optical crystal 1 is incident, it is possible to obtain polarization rotation characteristics with good uniformity for the emitted light. Further, in the polarization rotation element of this embodiment, for example, it is not necessary to form a plurality of layers of electro-optic crystals and transparent electrodes in the optical axis direction, and the electrodes are formed on the side surfaces of the electro-optic crystals, so that the structure is simple. be able to.

  For the above-described embodiment, a polarization rotation element as shown in FIG. 1 was prototyped. As the large optical crystal 1, a 125 mm square cubic KD * P crystal was used. The dimensions of the A electrode 2 and the B electrode 3 on each side surface of the large optical crystal 1 were determined by simulating the electric field strength distribution based on conditions such as voltage. As a result of injecting a rectangular beam substantially equal to the cross-sectional dimension of the large optical crystal 1 into this prototype, the electric field distribution with good uniformity is obtained in each part in the cross-section, so that the emitted beam is good up to the edge of the beam cross-section. Uniform polarization rotation characteristics were obtained.

  As described above, according to the present embodiment, in the vertical electric field type polarization rotation element having a rectangular cross section, the uniformity of the electric field distribution in the cross section perpendicular to the optical axis when a high voltage is applied with a simple structure. Can be improved.

  In the above-described embodiment, the polarization rotation of incident light is controlled by the polarization rotation element using the Pockels effect, but the present invention is not limited to this. For example, the present invention can be applied to an element using another electro-optic effect due to the relationship with the electric field strength such as the electro-optic Kerr effect.

  Further, in the above-described embodiment, the KD * P crystal is used as the large-sized optical crystal 1, but the present invention is not limited to this. For example, another electro-optic crystal that can obtain the Pockels effect such as a BBO crystal or the other electro-optic effect described above may be used.

  Furthermore, in the above-described embodiment, the A electrode 2 and the B electrode 3 are formed so as to be targeted with respect to a cross section of the large optical crystal 1, but the present invention is not limited to this. . For example, it is not necessary to change the electrode width on all the side surfaces depending on conditions such as the size of the large optical crystal 1 and the desired electric field distribution uniformity, and the electrode width is changed only on a pair of opposing side surfaces. Also good.

  The present invention can be suitably used for, for example, a high-power pulse laser apparatus.

It is a side view which shows the polarization rotation element which concerns on embodiment of this invention. It is a perspective view which shows the polarization rotation element which concerns on embodiment of this invention. It is a perspective view which shows the conventional polarization rotation element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Large optical crystal 2; A electrode 3; B electrode 4; Optical axis direction 5; Rectangular beam cross section 6; Electric field direction 7;

Claims (4)

An electro-optic crystal having a rectangular cross-section with respect to incident light, and a periphery of the electro-optic crystal around the optical axis of the incident light on four surfaces parallel to the optical axis of the incident light of the electro-optic crystal. A pair of electrodes formed so as to be wound, and the shape of each electrode on at least one pair of opposing surfaces of the four surfaces is such that the electrode width on the end side of the surface is small A polarization rotation element characterized by having a shape in which the electrode width at the center of the surface is increased. The polarization rotator according to claim 1, wherein the electro-optic crystal is a KD * P crystal. The polarization rotator according to claim 1, wherein the electro-optic crystal exhibits an electro-optic effect when a longitudinal electric field parallel to the optical axis of the incident light is applied. The polarization rotation element according to claim 3, wherein the electro-optic effect is a Pockels effect.

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