JP2007271354A - Ring laser gyroscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel ring laser gyroscope using a semiconductor laser. <P>SOLUTION: The ring laser gyroscope includes a surface light emitting laser element 100, a plurality of mirrors 12 and 13, and a photodetector 15. The surface light emitting laser element 100 and the plurality of mirrors 12 and 13 are arranged so as to constitute a polygonal optical path 20. By exciting the surface light emitting laser element 100, a first laser beam 31 clockwise propagated by the polygonal optical path 20 and a second laser beam 32 counterclockwise propagated by the polygonal optical path 20 are excited. The photodetector 15 is disposed at a position where the first laser beam 31 and the second laser beam 32 interfere with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ring laser gyro.

  Among the gyros for detecting the angular velocity of the rotating object, the optical gyro has a feature of high accuracy. In the optical gyro, the angular velocity is detected using a frequency difference between two laser beams traveling in opposite directions along an annular optical path. As such an optical gyro, an optical gyro using a rare gas laser has been proposed (for example, Patent Document 1). In these optical gyros, laser beams that circulate in the opposite directions on the same path are extracted to form interference fringes. By detecting the moving speed and moving direction of the interference fringes, the rotating speed and rotating direction of the gyro are detected. However, an optical gyro using a rare gas laser has a problem that a high voltage is required for driving and power consumption is large, and a problem that the apparatus is large and weak against heat.

As a gyro for solving such a problem, a gyro using a semiconductor ring laser having an annular (triangular or square) waveguide has been proposed (for example, Patent Document 2). The semiconductor laser used in this gyro has an annular waveguide having a substantially constant width. Then, two laser beams that circulate in the opposite directions in the annular waveguide are extracted to detect the interference fringes. However, since the laser beam confined using a thin waveguide spreads greatly when emitted to the outside of the waveguide, it is difficult to actually detect the interference fringes with high accuracy. Therefore, in a gyro using a semiconductor laser, a gyro (for example, Patent Document 3) that detects a beat frequency corresponding to a frequency difference between two laser beams from a voltage change between two electrodes of the semiconductor laser, or an end face of a resonator. A gyro (for example, Patent Document 4) that detects a beat frequency by using exuded evanescent light is generally used.
Japanese Patent Laid-Open No. 11-351881 JP 2000-230831 A JP-A-4-174317 JP 2000-121367 A

  However, a gyro that detects the beat frequency requires a special device for detecting the rotational direction.

  Under such circumstances, an object of the present invention is to provide a novel ring laser gyro using a semiconductor laser.

  In order to achieve the above object, a ring laser gyro according to the present invention includes a surface emitting laser element, a plurality of mirrors, and a photodetector, and the surface emitting laser element and the plurality of mirrors form a polygonal optical path. When the surface emitting laser element is excited, the first laser beam propagating clockwise through the polygonal optical path and the first laser beam propagating counterclockwise through the polygonal optical path are excited. The second laser beam is excited, and the photodetector is disposed at a position where the first laser beam and the second laser beam interfere with each other.

  According to the present invention, it is possible to obtain a ring laser gyro that is small in size, consumes less power, and can obtain information on the rotation direction and rotation speed.

  Hereinafter, the present invention will be described with examples. However, the present invention is not limited to the examples given below. In the following description, specific materials and numerical values may be exemplified, but other materials and other numerical values may be used as long as the effects of the present invention can be obtained.

[Ring laser gyro]
The ring laser gyro of the present invention includes a surface emitting laser element, a plurality of mirrors, and a photodetector. A surface emitting laser element (Vertical Cavity Surface Emitting Laser: VCSEL) is a semiconductor laser element, and includes a highly reflective mirror and an active layer (gain region) for amplifying light. The mirror is constituted by, for example, a semiconductor multilayer film or a dielectric multilayer film.

  The surface emitting laser element and the plurality of mirrors are arranged to form a polygonal optical path. The polygonal optical path is usually a triangular or square optical path.

  When the surface emitting laser element is excited, the first laser light propagating clockwise in the polygonal optical path and the second laser light propagating counterclockwise in the polygonal optical path are excited. In other words, the surface emitting laser element and the plurality of mirrors are arranged so that these first and second laser beams are excited.

  Each of the first and second laser beams travels in the opposite directions along the polygonal optical path. When the gyro rotates, a difference occurs between the frequency of the first laser beam and the frequency of the second laser beam due to the Sagnac effect. Therefore, it is possible to detect the rotation of the gyro by observing the interference fringes at the position where the first laser beam and the second laser beam interfere with each other. In order to observe the interference fringes, the photodetector is disposed at a position where the first laser beam and the second laser beam interfere with each other.

  The ring laser gyro of the present invention may further include an excitation laser element that emits pump light for exciting the surface emitting laser element. This excitation laser element emits laser light having a shorter wavelength than the oscillation wavelength of the surface emitting laser element. The excitation laser element is not limited as long as the surface emitting laser element can be excited, and a general semiconductor laser element can be applied. The surface emitting laser element may be excited by current injection without using the excitation laser element.

  The surface-emitting laser element may include a mirror layer and a gain region disposed closer to the center of the optical path than the mirror layer. The gain region is a layer that generates gain by absorbing the pump light emitted from the excitation laser light.

  The surface emitting laser element is a semiconductor laser that emits laser light from its main surface, not from the side surface (end surface) of the semiconductor multilayer film. The wavelength of the laser light output from the surface emitting laser element is not particularly limited, and can be selected from wavelengths from the ultraviolet region to the infrared region (for example, 400 nm to 1600 nm). The material of the gain region is selected according to the wavelength of the laser beam. One preferred material is a III-V compound semiconductor composed of a group III element such as Ga, In and Al and a group V element such as As, N and P. When a long wavelength laser beam is used, a III-V group compound semiconductor containing Ga and As is usually used as a material for the quantum well layer. In addition, when using short-wavelength laser light, a III-V group compound semiconductor containing Ga and N is usually used as the material of the quantum well layer.

  The mirror layer includes at least a layer for reflecting the first and second laser beams. An external resonator is constituted by the mirror layer of the surface emitting laser element and another mirror.

The light that reaches the mirror layer without being absorbed in the gain region is preferably reflected by the mirror layer and incident on the gain region again. However, since the wavelength of the pump light and the wavelengths of the first and second laser lights are different, it may be difficult to realize a mirror that reflects both with high reflectivity. In such a case, the mirror layer may include a first mirror layer that reflects 99% or more of the pump light and a second mirror layer that reflects 99% or more of the first and second laser lights. . According to this configuration, the ratio of pump light absorbed in the gain region can be increased. For example, the first mirror layer is a layer in which 30 pairs of Al _0.87 Ga _0.13 As layers (thickness 66.3 nm) and GaAs layers (thickness 57.3 nm) are alternately laminated (60 layers in total). The mirror layer may be a layer in which 30 sets of Al _0.87 Ga _0.13 As layers (thickness 80.7 nm) and GaAs layers (thickness 69.9 nm) are alternately stacked (total of 60 layers). . In this case, the reflectance of the first mirror layer at 805 to 860 nm is 99% or more, and the reflectance of the second mirror layer at 960 to 1020 nm is 99% or more.

  The plurality of mirrors constituting the polygonal optical path may include output mirrors that transmit part of the first and second laser beams. The gyro of the present invention may further include a prism for causing the first and second laser beams transmitted through the output mirror to interfere with each other. Instead of the prism, another optical element that can superimpose the first and second laser beams may be used.

  The output mirror is, for example, a mirror that reflects 96% to 98% of the first and second laser beams and transmits 4% to 2%. Further, the mirror other than the output mirror is preferably a mirror that reflects 99% or more (for example, 99.9% or more) of the first and second laser beams.

  The gyro photodetector of the present invention may include only one light receiving element (for example, a photodiode or a phototransistor) or may include a plurality of light receiving elements. By using two or more light receiving elements, the moving speed and moving direction of the interference fringes can be detected. As a result, it is possible to detect the rotational direction and rotational speed of the gyro.

  The ring laser gyro of the present invention may include other optical elements as necessary. For example, a lens may be disposed between the excitation laser element and the surface emitting laser element. Further, a pinhole for suppressing oscillation of an unnecessary mode of laser light may be disposed on the optical path. In addition, an element that generates SHG may be disposed on the optical path.

[Example of ring laser gyro of the present invention]
The structure of an example of the ring laser gyro according to the present invention is schematically shown in FIG. In the drawings shown below, the scale of the members is appropriately changed for easy understanding. The gyro 10 of FIG. 1 includes an excitation laser element 11, a mirror 12, an output mirror 13, a prism 14, a photodetector 15, a pinhole 16, and a surface emitting laser element 100.

  The excitation laser device 11 is a high-power wide stripe semiconductor laser device that emits laser light having a wavelength of 808 nm.

  Both the mirror 12 and the output mirror 13 are curved mirrors. The radius of curvature of these mirror surfaces is, for example, in the range of 0.1 to 5 times the length L of the optical path 20 described later. Moreover, the diameter of the range substantially effective as a mirror surface among these mirrors is, for example, a range of 0.0005 to 0.01 times the length L of the optical path 20.

  The mirror 12 is a total reflection mirror that reflects the laser light emitted from the surface emitting laser element 100 with a high reflectance (for example, 99.5% or more). The output mirror 13 is a mirror that transmits about 2% to 4% of the laser light emitted from the surface emitting laser element 100 and reflects the rest. A known dielectric multilayer mirror can be applied to the mirror 12 and the output mirror 13.

  The surface emitting laser device 100 is an external cavity surface emitting laser (VECSEL) having an oscillation wavelength λ of about 980 nm. A cross-sectional view of an example of the surface emitting laser element 100 is shown in FIG.

  The surface emitting laser element 100 includes a heat sink 101 for cooling and a semiconductor multilayer film 110 disposed on the heat sink 101. The semiconductor multilayer film 110 includes a mirror layer 114, a gain region layer 113, and a window layer 112, which are sequentially stacked from the heat sink 101 side.

The window layer 112 is made of Al _0.3 Ga _0.7 As (thickness: about 0.4 μm). The window layer 112 preferably has as low a reflectance as possible for the pump light emitted from the excitation laser element 11. Therefore, it is preferable to apply AR coating on the surface of the window layer 112.

The gain region layer 113 includes an Al _0.08 Ga _0.92 As absorption layer (thickness: λ) adjacent to the window layer 112, and from the layer toward the mirror layer 114 side, an In _0.16 Ga _0.84 As strained quantum well layer ( (Thickness: 8 nm), GaAs _0.90 P _0.10 strain compensation layer (thickness: 25.7 nm), and Al _0.08 Ga _0.92 As absorption layer (thickness: λ / 2) are stacked 14 times in this order. Have That is, the gain region layer 113 is composed of a total of 43 semiconductor layers.

The mirror layer 114 includes 16 Al _0.87 Ga _0.13 As layers (thickness: λ / 4) and 15 GaAs layers (thickness: λ / 4), and an Al _0.87 Ga _0.13 As layer and a GaAs layer. It has a stacked structure so that they are alternately arranged.

  The semiconductor multilayer film 110 of the surface emitting laser element 100 can be formed, for example, by epitaxially growing a GaAs buffer layer, a window layer 112, a gain region layer 113, and a mirror layer 114 in this order on a single crystal GaAs substrate. Thereafter, the mirror layer 114 side is attached to the heat sink 101, and then the GaAs substrate and the buffer layer are removed by etching. In this way, the surface emitting laser element 100 can be formed.

Laser light (pump light) emitted from the excitation laser element 11 passes through the window layer 112 and is absorbed by the Al _0.08 Ga _0.92 As absorption layer of the gain region layer 113. As a result, the surface emitting laser element 100 is excited.

  As shown in FIG. 1, the surface emitting laser element 100, the mirror 12, and the output mirror 13 constitute a substantially equilateral triangular optical path 20. In order to excite the laser light propagating in the optical path 20, the surface emitting laser element 100 is arranged so that the angle formed by the surface of the mirror layer 114 of the surface emitting laser element 100 and the triangular surface of the optical path 20 is perpendicular. The Further, the surface emitting laser element 100 is arranged so that the gain region layer 113 is closer to the optical path 20 than the mirror layer 114.

  The length L of the optical path 20 (the total of the three sides of the triangular optical path 20) is not limited as long as the effect of the present invention is obtained, but can be, for example, about 10 cm to 60 cm (in the example, about 20 cm to 40 cm). . The surface emitting laser element 100 is excited by the laser light 30 emitted from the excitation laser element 11, and the first laser light 31 propagating clockwise in the optical path 20 and the second propagating counterclockwise in the optical path 20. The laser beam 32 is excited.

  The pinhole 16 is disposed on the optical path 20 in order to suppress the oscillation in the high-order transverse mode. For example, the pinhole 16 is disposed in the vicinity of the beam waist, that is, in the vicinity of the center of the triangular side of the optical path 20 facing the surface emitting laser element 100 (side connecting the mirror 12 and the output mirror 13).

  A part of the laser beam 31 and a part of the laser beam 32 pass through the output mirror 13 and enter the prism 14. These two laser beams are superimposed on the prism 14 and enter the photodetector 15. The photodetector 15 includes two light receiving elements 15a and 15b, and detects the moving direction and moving speed of the interference fringes formed by the laser light 31 and the laser light 32. Then, the rotational direction and rotational speed of the gyro 10 are calculated from the output of the photodetector 15.

  Note that the principle of the gyro of the present invention for observing the interference fringes of two laser beams traveling in the opposite direction on the same optical path is the same as that of a conventional gyro using a rare gas laser. Therefore, conventional techniques can be applied to the method of monitoring interference fringes and the method of processing the output from the photodetector.

  In the gyro 10 shown in FIG. 1, the pump light is incident from the window layer 112 side. However, the pump light may be incident from the mirror layer 114 side as long as the effect of the present invention is obtained. In that case, a mirror layer 114 that reflects most of the first and second laser beams but transmits at least a part of the pump beam is used.

  In the ring laser gyro of the present invention, the length of the semiconductor region can be extremely shortened compared to the resonator length. Therefore, in the gyro according to the present invention, the effect of reducing the internal loss due to free carrier absorption and the effect of shortening the interaction length between the laser medium and light can be obtained.

  The ring laser gyro of the present invention can be applied to various devices that need to detect the rotation of an object. As a typical example, it can be used for an attitude control device, a navigation device, and a camera shake correction device. Specifically, the gyro of the present invention can be used for moving means such as aircraft such as rockets and airplanes, automobiles and motorcycles. Further, the gyro of the present invention can be used for a portable information terminal such as a mobile phone or a small personal computer, a toy, a camera, etc. by taking advantage of being ultra-small and easy to handle.

It is a schematic diagram which shows the structure of an example of the ring laser gyro of this invention. It is sectional drawing which shows typically an example of the surface emitting laser element used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gyro 11 Excitation laser element 12 Mirror 13 Output mirror 14 Prism 15 Photo detector 15a, 15b Light receiving element 16 Pinhole 20 Optical path 30 Laser light 31 1st laser light 32 2nd laser light 100 Surface emitting laser element 101 Heat sink 110 Semiconductor multilayer film 112 Window layer 113 Gain region layer 114 Mirror layer

Claims (5)

A ring laser gyro,
A surface emitting laser element, a plurality of mirrors and a photodetector;
The surface-emitting laser element and the plurality of mirrors are arranged to form a polygonal optical path,
Excitation of the surface-emitting laser element excites the first laser beam propagating clockwise in the polygonal optical path and the second laser beam propagating counterclockwise in the polygonal optical path. ,
The photodetector is a ring laser gyro, which is disposed at a position where the first laser light and the second laser light interfere with each other.   The ring laser gyro according to claim 1, further comprising an excitation laser element that emits pump light for exciting the surface emitting laser element. The surface-emitting laser element includes a mirror layer, and a gain region disposed closer to the center of the optical path than the mirror layer,
The gain region is a layer that generates a gain by absorbing the pump light,
The mirror layer includes a first mirror layer that reflects 99% or more of the pump light, and a second mirror layer that reflects 99% or more of the first and second laser lights. Ring laser gyro as described. The plurality of mirrors include an output mirror that transmits a part of the first and second laser beams,
The ring laser gyro according to any one of claims 1 to 3, further comprising a prism for causing the first and second laser beams transmitted through the output mirror to interfere with each other.   The ring laser gyro according to claim 1, wherein the photodetector includes a plurality of light receiving elements.

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