JP2001159520A - Ring laser gyro and its signal detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the change of a beat frequency in a short time, even if a ratio S/L is small, assuming an optical path length of a ring laser as L and a closed area enclosed by an optical path as S. SOLUTION: Figures 1, 2 are ring laser gyros having different sizes, respectively. Only a counterclockwise laser beam is shown by an arrow for simplification. For example, when S's are equal mutually, l1, l2 are selected so that S/L's do not become integer-fold mutually. When signals of the ring laser gyros 1, 2 are synchronized and overlapped, overlapping of the two signals is changed in response to the difference between beat frequencies of the ring laser gyros 1, 2. The height and the width of the pulse of the signal are measured relative to plural pulses, then the difference between beat frequencies is known, to thereby detect the angular velocity of rotation. A measuring time can be shortened in this way, compared with the case where the beat frequency is obtained by counting the number of pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring resonator type laser gyro.

[0002]

2. Description of the Related Art Conventionally, as a gyro for detecting an angular velocity of a moving object, a mechanical gyro having a rotor and a vibrator and an optical gyro are known. In particular, optical gyros are being revolutionized in the gyro technical field because they can be activated instantaneously and have a wide dynamic range. The optical gyro includes a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro, and the like. Of these, the first to be developed is a ring laser type gyro using a gas laser, which has already been put to practical use in aircraft and the like. Recently, a semiconductor ring laser gyro integrated on a semiconductor substrate as a small, high-precision ring laser type gyro is, for example,
It is disclosed in JP-A-5-288556. In the ring laser gyro, the oscillation frequency of the clockwise laser light and the counterclockwise laser light shift with rotation. Then, the beat frequency generated from the difference between the oscillation frequencies is measured to detect the angular velocity of rotation.

[0003]

However, since the beat frequency is proportional to the ratio S / L of the optical path length L of the ring laser and the closed area S surrounded by the optical path, the S / L is smaller than that of a small ring laser. As the frequency decreases, the beat frequency decreases.
Therefore, when the S / L is small, there is a problem that it takes time to measure the change in the beat frequency.

Accordingly, an object of the present invention is to detect a change in beat frequency in a short time even when the S / L is small as in a small ring laser.

[0005]

An optical gyro according to the present invention for solving the above-mentioned problems includes a plurality of ring lasers, and a beat frequency generated at the time of rotation becomes a non-integer multiple.

In the method of the present invention, the signals of a plurality of ring laser gyros are superposed in synchronization with each other using the above-mentioned laser gyro, and the intensity and pulse width of the superposed signal pulses are detected. .

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a top view of the ring laser gyro of the present invention. For simplicity, only the counterclockwise laser light is indicated by arrows. Reference numerals 1 and 2 denote ring laser gyros having different sizes. For example, when S is equal to each other, l ₁ and l ₂ are selected so that S / L does not become an integral multiple of each other. In general, S / L is not set to be an integral multiple of each other. This is to prevent beat signals from overlapping at an integral multiple of a certain period. This is because if the beat signal overlaps at an integral multiple, it is impossible to detect a pulse shift.

FIG. 2 is a plan view and a cross-sectional view for explaining a manufacturing process of the semiconductor ring laser. In order to manufacture this semiconductor ring laser, first, an n-InP substrate 21 (having a thickness of 350 μm) was formed using a metal organic chemical vapor deposition method.
m) on the InP buffer layer 21 (0.05 μm thick).
m) 1.3 μm undoped InGaAsP light guide layer 23 (0.15 μm thickness), 1.55 μm undoped InGaAsP active layer 24 (0.1 μm thickness)
m) 1.3-μm undoped InGaAsP optical guide layer 25 (0.15 μm thickness), P-InP cladding layer 26 (2 μm thickness), 1.4 μm P-InGa composition
A AsP cap layer 27 (0.3 μm thick) is grown.
After crystal growth, Cr / Au is formed as an anode material 28 on the P-InP cap 27 layer by vapor deposition. Then, using a spin coater, AZ-1350 (made by Hoechst) is applied as a photoresist 31 on the anode material 28 so as to have a film thickness of 1 μm. After pre-baking at 80 ° C. for 30 minutes, the wafer is exposed with a mask. The photoresist 31 after development and rinsing has a slightly tapered shape. The width of the stripe is 5
μm, the length of one side of the optical path of the ring laser gyro is
L ₁ = 110 μm and l ₂ = 100 μm, respectively.
Thereafter, the wafer is introduced into a reactive ion etching apparatus, and Cr / Au of the anode material 28 is dry-etched using the photoresist 31 as an etching mask. The gas used for etching is Au
CF ₄ is used for r and Cr. Next, after the semiconductor layer is etched using chlorine gas so that the height of the optical waveguide becomes 3.2 μm, the photoresist 31 is peeled off.
Thereafter, the anode 28 is annealed in a hydrogen atmosphere to realize ohmic contact. Next, AuGe / Ni / Au is deposited on the n-InP substrate 21 as the cathode 11. Finally, annealing is performed in a hydrogen atmosphere to obtain ohmic contact.

Here, InGaAs is used as a semiconductor material.
Although a P type was used, a GaAs type, a ZnSe type, and an In type
Any material system such as a GaN system and an Al-GaN system may be used. The shape of the optical waveguide is not limited to a square as shown in FIG. 1, but may be a circle, a hexagon, a triangle, or the like, as shown in FIG. 1. In general, the shape is not limited. Further, the number of ring laser gyros does not need to be limited to two, but may be plural.

Next, the operation of the semiconductor ring laser gyro will be described. The oscillation threshold values of the ring laser gyros 1 and 2 at room temperature are 2.2 mA and 2.0 m, respectively.
A. The driving current is 3 mA, and when this laser is stationary, the oscillation wavelength λ _{0 in} vacuum is 1.55 μm.
m.

When the ring laser gyro is rotated clockwise at a rate of 30 degrees per second, such as camera shake or automobile vibration, the ring laser gyros 1 to 13 are rotated.
A beat frequency of 0.1 Hz is obtained. A beat frequency of 118.2 Hz is obtained from the ring laser gyro 2.

FIGS. 3A and 3B show signals of the ring laser gyros 1 and 2, respectively.

FIG. 3C shows a signal obtained by synchronizing these signals and superimposing them. When the signals of the ring laser gyros 1 and 2 are superposed in synchronization, the overlap of the two signals changes according to the difference in the beat cycle of the ring laser gyros 1 and 2. If the height and width of the pulse of this signal are measured for a plurality of pulses, the difference in beat frequency can be determined, and the angular velocity of rotation can be detected. By doing so, the measurement time is reduced as compared with the case where the beat frequency is obtained by counting the number of pulses.

FIG. 4 shows a signal obtained by inverting the signal of the ring laser gyro 2 on the signal of the ring laser gyro 1 and superimposing them. In this case as well, the difference in beat frequency can be determined by measuring the pulse amplitude and pulse width, so that the angular velocity of rotation can be determined.

[0015]

According to the present invention described above, the angular velocity of rotation can be detected in a short time even when the beat frequency accompanying rotation is small.

[Brief description of the drawings]

FIG. 1 is a top view illustrating the structure of a ring laser gyro according to the present invention.

FIG. 2 is a plan view and a cross-sectional view for explaining a manufacturing process of the ring laser gyro of the present invention.

FIG. 3 is a waveform diagram illustrating a signal of the ring laser gyro of the present invention.

FIG. 4 is a waveform diagram illustrating signals of the ring laser gyro of the present invention.

[Explanation of symbols]

 Reference Signs List 1, 2 Ring laser 10, 20 Optical path of laser beam 11 Cathode material 12 Ring laser 13 Optical memory 14 Ring laser 15 Optical memory 20 Signal output terminal 21 Substrate 22 Buffer layer 23 Optical guide layer 24 Active layer 25 Optical guide layer 26 Cladding layer 27 Cap layer 28 Anode material

Claims (4)

[Claims] 1. A ring laser gyro including a plurality of ring lasers, wherein a set of ring lasers whose beat frequencies generated during rotation are non-integer multiples is included. 2. A ratio S of an optical path length L to a closed area S surrounded by the optical path.
2. The ring laser gyro according to claim 1, wherein the ring laser gyro includes a plurality of ring lasers whose / L is a non-integer multiple. 3. A method for detecting a signal of a ring laser gyro using a ring laser gyro including a plurality of ring lasers and having a beat frequency generated at the time of rotation being a non-integer multiple, wherein the signals of the plurality of ring laser gyros are synchronized A method for detecting a signal of a ring laser gyro, characterized by detecting the intensity and pulse width of the superposed signal pulses. 4. A signal of at least one ring laser gyro of the plurality of ring laser gyros is inverted and synchronously superimposed, and the intensity and pulse width of the superimposed signal pulse are detected. 4. The signal detection method for a ring laser gyro according to claim 3, wherein: