JP2014119553A - Optical deflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical deflector that reduces power source load by reducing electrostatic capacity and that prevents deflection displacement between incident light and emission light.SOLUTION: An optical deflector according to the invention comprises a pair of light incident/outgoing faces that sandwich an electro-optical crystal between a pair of parallel quadrangular electrode faces and that are perpendicular to the electrode faces and parallel to each other, each incident/outgoing face having a light non-reflection coat part and a high light reflection coat part identical in area such that light is made incident on the light non-reflection coat part and light made incident on the deflector is reflected from the high light reflection coat part. The deflection direction of light is perpendicular to the electrode face.

Description

The present invention relates to an optical deflector using a KLTN crystal having an electro-optic effect _{(K 1-y L y Ta} 1-x b x O 3).

Among optical deflectors that change the traveling direction of light, KTN (KTa _1-x Nb _x O ₃ ) optical deflectors that use internal charges and secondary electro-optic effects are galvanometer mirrors, polygon mirrors, MEMS mirrors, etc. In contrast, it is a solid element having no moving parts. The KTN crystal has an electro-optic effect by applying a voltage, and changing only the direction without changing the shape of light like a prism. In particular, the KTN crystal is known as a substance having a large change in refractive index at a low voltage, that is, a large electro-optic effect. Thus, with KTN, galvanometer mirrors that mechanically change the direction of light, can replace very common components such as lenses, prisms, and mirrors for applications where they need to move at high speeds, Compared with a polygon mirror and a MEMS mirror, it can operate at high speed.

  Further, unlike other solid-state optical deflectors such as an electro-optic prism and an acousto-optic deflector, the longer the light is transmitted through the element, the larger the deflection angle.

NTT Technical Journal, November 2009 "KTN crystals that open up new possibilities and their applied technologies" written by Takeshi Yagi

  A KTN crystal is a dielectric having a very large dielectric constant, and an element using KTN inevitably has a large capacitance. Therefore, a displacement current becomes large when used at a high frequency, and a large load is applied to a power supply circuit for controlling deflection. There is a disadvantage that it takes.

  Capacitance is given by (dielectric constant) x (electrode area) ÷ (distance between electrodes), so the light is reflected within the crystal without increasing the electrode area, and the light circulates multiple times in the same region in the crystal. Thus, a method of increasing the deflection angle as compared with the capacitance has been taken.

  FIG. 1 shows a structure of a conventional optical deflector 100 using KTN. An optical deflector 100 shown in FIG. 1 is formed in a hexahedral structure, and includes a KTN dielectric 101, a rectangular electrode surface 102, an incident light surface 103 formed on a side surface of the KTM dielectric 101, and an outgoing light surface. 104, a high reflection (HR) coat 105 applied to the incident light surface 102, an anti reflection (AR) coat 106, an HR coat 107 applied to the outgoing light surface 104, and an AR coat 108. . The KTN dielectric 101 is sandwiched between two electrode surfaces 102.

  Incident light enters the inside of the optical deflector 100 (dielectric 101) from a portion of the incident light surface 103 where the AR coating 104 is applied. Since a voltage is applied to the optical deflector 100, the light incident from the incident light surface 103 is refracted and deflected in the dielectric 101. The light deflection direction is perpendicular to the electrode surface 102. Reflected by the portion of the outgoing light surface 104 where the HR coating 107 is applied. Further, the light is reflected again at the portion of the incident light surface 103 where the HR coating 105 is applied, and the reflected light is emitted from the portion of the outgoing light surface 104 where the AR coating 108 is applied. In the hexahedron of the deflector 100, the optical path is folded twice, so that the optical path between the first reflection and the second reflection is shared by half before the first reflection and half after the second reflection.

  In the case of this structure, there remains a region that is not used for deflection in the deflector 100, and there is a disadvantage that the capacitance is unnecessarily increased and a load is applied to the power supply circuit.

  Further, the optical axes of the incident light and the outgoing light are shifted in a direction different from the deflection direction, and there is a drawback that it takes time to adjust the optical axis.

  The present invention has been made in view of such problems. The object of the present invention is to scrape off unnecessary portions of the crystal based on the structure of the optical deflector using the conventional KTN of FIG. Another object of the present invention is to provide an optical deflector that reduces the load on the power source by reducing the capacitance and eliminates the deviation of the deflection between the incident light and the outgoing light.

  Specifically, the optical deflector according to the first embodiment of the present invention includes a pair of light beams sandwiched between a pair of parallelogram electrode surfaces parallel to each other and perpendicular to the electrode surfaces and parallel to each other. A light non-reflective coating part and a light high-reflective coating part having the same area are formed in each of the light incident / exit surfaces, and light is incident from the outside in the light non-reflective coating part. The high reflection coating includes a light incident / exit surface on which light incident on the deflector is reflected, and a light deflection direction is perpendicular to the electrode surface.

  An optical deflector according to a second embodiment of the present invention includes five rectangular side surfaces sandwiching an electro-optic crystal between a pair of parallel pentagonal electrode surfaces and perpendicular to the pair of electrode surfaces, A pair of adjacent light incident / exit surfaces, which are formed into a seven-sided body surrounded by side surfaces formed with a light incident / exit surface and three light reflecting surfaces, which are provided with a light non-reflective coating. The light deflection direction is perpendicular to the electrode surface.

Further, the electro-optic crystal of the optical deflector according to the first and second embodiments of the present invention is a single crystal mainly composed of potassium tantalate niobate (KTa _1-x Nb _x O ₃ ). Features.

  The optical deflector of the present invention can reduce the capacitance by reducing the capacitance, and can eliminate the deviation of the deflection of the incident light and the emitted light.

It is a figure which shows the structure of the optical deflector 100 using the conventional KTN. It is a figure which shows the structure of the optical deflector 200 using KTN concerning the 1st Embodiment of this invention. It is a figure which shows the structure of the optical deflector 300 using KTN concerning the 2nd Embodiment of this invention.

[First Embodiment]
FIG. 2 shows the structure of an optical deflector 200 using KTN according to the first embodiment of the present invention. An optical deflector 200 shown in FIG. 2 is formed in a hexahedron, and has a structure in which a region not used for internal deflection of the conventional optical deflector shown in FIG.

  The optical deflector 200 shown in FIG. 2 has a KTN dielectric 201 and an electrode surface 202 formed in a parallelogram, and an incident light surface 203 and an outgoing light surface formed in a rectangular shape on the side surface of the KTM dielectric 201. 204. The incident light surface 203 is provided with a high reflection (HR) coating 205 and a non-reflection (AR) coating 206, and the outgoing light surface 204 is provided with an HR coating 207 and an AR coating 208. The KTN dielectric 201 is sandwiched between two electrode surfaces 202.

  Here, the ratio between the HR coat 205 (207) and the AR coat 206 (208) is 1: 1. The light incident surface 203 is a 3.4 mm × 1 mm rectangle, of which 1.7 mm × 1 mm is an AR-coated portion, and the remaining 1.7 mm × 1 mm is a HR-coated portion. The electrode surface 202 is a parallelogram obtained by cutting off two unnecessary parts (a right triangle with a base of 0.88 mm and a height of 4 mm) as shown in the optical deflector 100 shown in FIG. 1 from a rectangle of 4.4 mm × 4 mm. It is formed into a shape. As a result, the capacitance becomes 4/5 of the case where unnecessary portions are not removed, and the power load can be reduced.

  Incident light enters the inside of the optical deflector 200 to which a voltage is applied from the portion of the incident light surface 203 where the AR coating 206 is applied, and is refracted and deflected inside the optical deflector 200. The light deflection direction is perpendicular to the electrode surface 202. The incident light that has entered enters the portion of the outgoing light surface 204 where the HR coating 207 is applied, and is reflected for the first time. Next, the second reflection is performed at the portion of the incident light surface 203 where the HR coating 205 is applied. The reflected light is refracted and emitted from the portion of the outgoing light surface 204 where the AR coating 208 is applied. The deflector 200 has a structure in which the optical path between the first reflection and the second reflection is shared by half before and after the first reflection and half after the second reflection because the optical path is folded twice in the deflector 200. 100.

[Second Embodiment]
FIG. 3 shows the structure of an optical deflector 200 using KTN according to the second embodiment of the present invention. The optical deflector 300 shown in FIG. 3 is formed in a seven-sided body and has a pentagonal electrode structure.

  The optical deflector 300 shown in FIG. 3 has a pentagonal KTN dielectric 301 and an electrode surface 302 formed in a pentagon, and has side surfaces 303 to 307 perpendicular to the electrode surface. The KTN dielectric 301 is sandwiched between two electrode surfaces 302. A rectangular incident light surface (referred to as an incident light surface 303) is formed on one of the side surfaces 303 to 307 of the KTM dielectric 200, and a side surface 304 that is a side surface adjacent to the incident light surface 303. Is formed with an outgoing light surface (referred to as an outgoing light surface 304). Each side surface is a rectangle perpendicular to the electrode surface, and AR coating is applied to the incident light surface 303 and the outgoing light surface 304, but the other three side surfaces 305, 306, and 307 are not coated. The KTN dielectric 201 is sandwiched between two electrode surfaces 202.

  The incident light enters the optical deflector 300 to which a voltage is applied from the incident light surface 303 and is deflected inside the optical deflector 200. Next, of the three side surfaces, the light is totally reflected by the side surface 305, and the totally reflected light is further totally reflected by the side surface 306 and the side surface 307. The light totally reflected by the side surface 307 is emitted from the outgoing light surface 304. By making the optical path return three times in the deflector 300, the overlap of light increases in the KTN crystal, and not only can the increase in capacitance be suppressed, but also the deflection of incident light and outgoing light. It is possible to eliminate vertical axis misalignment.

100, 200, 300 Optical deflectors 101, 201, 301 KTN dielectrics 102, 202, 302 Electrode surfaces 103, 203, 303 Incident light surfaces 104, 204, 304 Emitted light surfaces 105, 107, 205, 207 HR coat 106, 108, 206, 208 AR coating 305-307 Side

Claims (3)

An optical deflector in which an electro-optic crystal is sandwiched between a pair of parallelogrammic electrode surfaces parallel to each other,
A pair of light incident / exit surfaces perpendicular to the electrode surface and parallel to each other, wherein a light non-reflective coating portion and a light high reflection coating portion having the same area are formed in each of the light incident / exit surfaces, A light incident / exit surface is provided in which light is incident from the outside in the reflective coating portion, and the light incident in the deflector is reflected in the high light reflective coating,
An optical deflector characterized in that a light deflection direction is perpendicular to the electrode surface. An optical deflector sandwiching an electro-optic crystal between a pair of parallel pentagonal electrode surfaces,
5 rectangular sides perpendicular to the pair of electrode surfaces,
A pair of adjacent light incident / exit surfaces, which are provided with a light non-reflective coating,
It is formed in a seven-sided body surrounded by three side surfaces formed with three light reflecting surfaces.
An optical deflector characterized in that a light deflection direction is perpendicular to the electrode surface. 3. The electro-optic crystal according to claim ₁ , wherein the electro-optic crystal is a single crystal mainly composed of potassium tantalate niobate (KTa _1-x Nb _x O ₃ ). 4. Optical deflector.

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