JPS6288385A - Semiconductor laser gyroscope - Google Patents

Abstract

PURPOSE:To implement a laser gyroscope, in which mode coupling is hard to occur even if the size is compact, by assigning polarization modes, which are crossed at a right angle, in the opposite propagating directions. CONSTITUTION:In this semiconductor laser gyroscope, polarized light beams, which are crossed at a right angle, are proparated in the reverse directions in a ring laser. Namely, the ring laser includes a single-mode lightguide having a degenerate mode. The laser has a propagating-direction polarization control means 12. the means 12 makes the light beam, which is propagated in the reverse direction, to be the polarization components that are crossed at a right angle. It is desirable that the propagating- direction polarization control means 12 has the following parts: two Farady rotors, which have a 45 deg. polarization-plane rotating function in the reverse direction; and a polarizer, which is inserted between the two Farady rotors and whose maximum transmitting polarization plane is rotated by about 45 deg. with respect to the perpendicular polarizing component. The polarized light beams, which are crossed at a right angle, are propagated in the reverse directions in the ring laser. Thus mode coupling in a low angular speed region can be suppressed. Therefore, the semiconductor laser gyroscope, which can be sufficiently used in practical application, can be fabricated even if the size is made compact.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser gyroscope that is small, lightweight, and has low power consumption.

[Conventional technology]

FIG. 8 is a diagram showing the basic configuration of a conventional ring laser. Here, the ring laser refers to a laser having a closed optical path. Four laser tubes T+~T are placed in a square on a disk (not shown), and four reflecting mirrors M1~M3 and a semi-transparent mirror M4 are placed at the four corners of the square to create a resonance system with a ring optical path. Configure the vessel. The reflectors M1 to M3 have a reflectance of 1 (
) 0% plane mirror, and the semi-transparent mirror M4 is a plane mirror that transmits part of the light. The ring optical path itself forms a resonator, so in that optical path, light that travels clockwise (→) and light that travels counterclockwise (+-) coexist, and each light is reflected by the semitransparent mirror M. , are emitted in different directions.

These two lights are detected by a superimposed photodetector using reflecting mirrors Ms, Mb and a semi-transparent reflecting mirror M.

When the ring laser shown in FIG. 8 is stationary (the disk is stationary), a constant electrical signal proportional to the square of the amplitude of the combined light is generated at the photodetector. On the other hand, when this ring laser is rotated in a plane that includes the optical path (rotated around the center O), a relativistic effect creates a gap between the light that travels clockwise and the light that travels counterclockwise along the optical path. A phenomenon in which the oscillation frequency shifts occurs due to the optical path difference. Therefore, the rotational angular velocity can be measured by mixing these lights propagating in opposite directions and measuring the frequency of the beat signal having the difference frequency between the two lights. This is the principle of a laser gyroscope. References: ■ Supervised by Kenji Sakurai, “Practical Laser Technology,” Institute of Electronics and Communication Engineers (
19B3), ■ Kei Tanaka-1 “Laser and Measurement”, Kyoritsu Shuppan (1983).

[Problem that the invention seeks to solve]

However, in such conventional laser gyroscopes, although theoretically there is a strict proportional relationship between the rotational angular velocity of the ring laser and the beat frequency, in reality, when the angular velocity falls below a certain level, the retrograde light There is a problem in that mode coupling occurs, resulting in the same frequency, and the beat signal disappears, making it impossible to measure the beat frequency.

For example, a square helium neon (lle
-Ne) Ring laser (wave N: 0.1 at a point of 35°45° north latitude in case of [i33pm>)! !
The beat frequency number due to the rotation of the sphere is approximately 67 tlz, but with an ordinary ring laser, it is said that it is almost impossible to observe a beat frequency of less than 1001)z culm due to the above-mentioned modulus coupling. (Literature: Inaba, Shimoda, eds., Laser Handbook, Breakfast Shoten, pp. 57
9-5 old, 1975).

When forming a ring laser on a semiconductor substrate, the oscillation wavelength is 1.3 μl (refractive index 3
．． 6), the beat frequency due to the above rotation is 0.
It becomes 09Hz. As a rotation detector using integration, it is calculated that 149 beat signals can be obtained per skin groove, which is sufficient sensitivity for consumer use.

Laser gyroscopes are originally highly sensitive, so
The problem when introducing this into consumer equipment is not a decrease in sensitivity due to miniaturization, but a relative expansion of the angular velocity 6a region where the beat signal disappears due to mode coupling.

The present invention solves these conventional problems,
The purpose of the present invention is to provide a compact semiconductor laser gyroscope that enables low angular velocity detection.

[Means for solving problems]

The semiconductor laser gyroscope of the present invention is characterized in that mutually orthogonal polarized light propagates in opposite directions within a ring laser.

In other words, the present invention provides a ring laser formed by a circularly closed optical path on a semiconductor substrate, a light mixing section that mixes and interferes light propagating in opposite directions in the ring laser, and a beat of the interfered light. In the semiconductor laser gyroscope equipped with a photodetector for detecting a signal, the ring laser includes a single mode waveguide having a degenerate mode, and converts the light propagating in opposite directions into mutually orthogonal polarization components. It is characterized by comprising a propagation direction polarization control means.

The propagation direction polarization control means is inserted between two Faraday rotators having a function of rotating the plane of polarization by 45 degrees in opposite directions and one Faraday rotator, and the maximum transmitted polarization 1fii is intersected. It is preferable to include a polarizer rotated by about 45 degrees with respect to the polarization component.

The propagation direction polarization control means includes a master laser for light injection provided separately from the ring laser, and a laser beam divided into mutually orthogonal polarization components from the master laser into the I-marked ring laser. It is preferable to include a light injection means for injecting light so as to propagate in the opposite direction.

[For production]

The present invention makes it possible to suppress mode coupling in the low angular velocity region by propagating 77 orthogonal polarized lights in opposite directions within the ring 1/-. A laser gyroscope can be configured.

There are several ways to cause orthogonal polarized light to propagate in opposite directions within a ring laser.

One method is to allocate orthogonal polarization components to mutually opposite propagation directions using a propagation general direction polarization control unit that is comprised of a Faraday rotator and a polarizer in a ring laser. It is. In another method, the polarization plane and the propagation direction are made to correspond without using a Faraday rotator, and a continuous wave master laser is prepared.
This is a method in which the output is polarized and separated into mutually orthogonal linearly polarized waves, and then light is injected so that they propagate in opposite directions.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the basic configuration of an embodiment of the present invention. In FIG. 1, reference number 1) is a semiconductor ring laser, reference number 12 is a propagation direction polarization control unit that allocates orthogonal polarization components to mutually opposite propagation directions, and reference number 13 is a device that controls these lights. This is an optical mixing detection section that performs mixing and detects a beat signal.

The semiconductor ring laser 1) that operates as a ring laser has degenerate polarization. That is, it is necessary that the two orthogonal polarization modes have the same propagation constant. By doing this, both the left and right rotation modes oscillate at the same frequency when the vehicle is stationary, and the beat signal disappears reliably when the vehicle is stationary. Specifically, the cross section of the waveguide may be square or circular.

FIG. 2 is a diagram showing an example of the configuration of a propagation direction polarization control section. In FIG. 2, the propagation direction polarization control unit 12 connects the semiconductor ring laser 1 with Faraday rotators 21 and 22 that rotate the plane of polarization by 45 degrees in opposite directions, and transmits only a predetermined polarization component between them. This is a configuration in which a polarizer 23 is arranged. When light passes through the Faraday rotators 21 and 22, there is no change in the polarization of the incident light and the output light, and as shown in Figure 2, for example, a polarized component horizontal to the plane of the paper enters from the right side, and a polarization component perpendicular to the plane of the paper from the left side. When a polarized component is incident, both lights become linearly polarized light tilted at 45 degrees between the Faraday rotators 21 and 22. By passing this linearly polarized light through the polarizer 23, one of the orthogonal polarized components is suppressed and emitted. That is, in this propagation direction polarization control section 12, the propagation direction and polarization can be made to correspond one-to-one.

However, the Faraday rotators 21 and 22 utilize magneto-optical effects, and cannot be realized using a normal semiconductor substrate.

To adopt this method, the propagation direction polarization control section 12:
Separately from the semiconductor substrate forming the semiconductor ring laser 1), it is necessary to fabricate and connect it on a magnetic material substrate.

FIG. 3 is a block diagram of an orthogonally polarized ring laser using a Faraday rotator. Reference number 31 is a semiconductor substrate, reference number 32 is a magnetic material substrate, and a propagation direction polarization control section 12 consisting of a Faraday rotator 21, 22 and a polarizer 23 is fabricated on the magnetic material substrate 32. It is.

There is an injection locking method as a method of matching the polarization plane and the propagation direction without using a Faraday rotator.

FIG. 4 is a diagram showing the basic configuration of the light injection type laser gyroscope of the present invention. In FIG. 4, the output of a continuously oscillating master laser 41 is separated into polarization components by a polarization separation/coupling unit 42 to form mutually orthogonal linearly polarized waves.
) is injected with light.

If a distributed coupling laser that oscillates in a single mode with a narrow spectrum is used as the mask laser 41, the oscillation of the ring laser can also be made into a single mode and a narrow spectrum, and measurement sensitivity can be improved.

FIG. 5 is a diagram showing an example of the arrangement of a light injection type semiconductor ring laser. In Figure 5, the master laser is oscillated with circularly polarized light, or the laser output is set to λ7 when oscillated with linearly polarized light.
The light is circularly polarized by a four-wavelength plate and joined to the incident waveguide 51. This light is split into orthogonal linearly polarized components by the polarization beam splitter 52, and oscillation modes in opposite directions are excited in the semiconductor ring laser 1). It is configured to be injected as follows.

FIG. 6 is a diagram showing an example of the arrangement of a light injection type semiconductor ring laser for integration. In FIG. 6, leakage light from a mask laser 41 oscillating in the TE mode is optically coupled to a waveguide 61, and both ends of the waveguide 61 are connected to a semiconductor ring laser 1) so that they can be excited in opposite propagation directions. let At this time, TE is applied to one optical path of the waveguide 61.
-7M mode converter 62 is inserted so that modes excited in opposite directions become mutually orthogonal linear polarization modes.

By doing so, the master laser can be integrated on a single semiconductor substrate.

The method of mixing retrograde light and generating a beat signal is as follows.
Although a configuration using a conventional semi-transparent reflecting mirror as shown in FIG. 8 may be used, the external optical system can be simplified by adopting the following configuration.

FIG. 7 is a diagram showing an example of the configuration of the light mixing detection section.

In FIG. 7, another light mixing waveguide 71 is provided parallel to one side of the semiconductor ring laser 1) for leaking and coupling light, and light is mixed therein. The lens system 7
45 for two orthogonal modes.
The configuration is such that a beam analyzer 73 having a polarization angle of 1° is used to generate a beam signal.

This beat signal is focused by a lens system 74 onto the light receiving surface of a photodetector 75 and converted into an electrical signal. Optical mixing waveguide 71
may be a laser.

When the cross section of the semiconductor ring laser waveguide is rectangular or elliptical, the degeneracy between orthogonal polarizations can be solved. That is, the left and right polarization modes oscillate at different frequencies, and the beat signal does not disappear even when the device is stationary. In this case, the beat frequency increases or decreases depending on the rotation direction of the semiconductor ring laser, so not only the rotation speed but also the rotation direction can be known at the same time. However, in the case of injection type, the frequency of the master laser is forced to 5. Therefore, it is necessary to shift the frequency of the injected light in one direction using an A-0 modulator or the like.

〔Effect of the invention〕

As explained above, the present invention, by allocating mutually orthogonal polarization modes to mutually opposite directions of the Buddhist temple,
Even though it is small, a laser gyroscope that is less likely to cause mode coupling can be realized.

Furthermore, by using a semiconductor laser, it is possible to avoid the problem of beat generation at static 1) 1 due to Langmuir flow. Further, since all fine adjustment parts such as reflectors can be eliminated and integration is possible, economy through mass production can be achieved, and a semiconductor laser gyroscope can be provided at low cost and with high reliability.

This is not a pursuit of measurement sensitivity; it is small, lightweight,
It aims at low power consumption and no adjustment, and can be expected to be applied to consumer equipment. For example, it will become possible to introduce laser gyroscopes into automobiles, small ships, and small aircraft. In other words, by integrating the speed information from the speedometer and the angular velocity rotation information from the gyroscope,
The relative position from the starting point can be displayed in real time.
If displayed together with a map, the current location can be easily identified.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of an embodiment of the present invention. FIG. 2 is a diagram showing an example of the configuration of a propagation direction polarization control section. Figure 3 is a configuration diagram of an orthogonally polarized ring laser using a Faraday rotator. FIG. 4 is a diagram showing the basic configuration of the light injection type laser gyroscope 1) of the present invention. FIG. 5 is a diagram showing an example of the arrangement of a light injection type semiconductor ring laser'. FIG. 6 is a diagram showing an example of the arrangement of an optical H large semiconductor ring laser for integration. Fig. 7 is a diagram showing an example of the (h configuration) of the light mixing detection section. Fig. 8 is a diagram showing the basic configuration of a conventional ring laser. ... Propagation direction polarization control section, 13... Optical mixing detection section, 21.22.
・・Faraday rotator, 23... t'l+...
16 conductors, (plate, 32...magnetic V144 material board, old
... Master laser, 42 ... Polarization branch 1 coupling section, 51
...Waveguide, 52...1). optical beam J splitter, fil... waveguide, 62... TE-TM mode converter, 71... optical mixing waveguide, 72.74...
Lens system, 73... Analyzer, 75... Photodetector, M
1 to M3, M5, M6... Reflecting mirror, M4... Semi-transparent mirror, M7... Semi-transparent reflecting mirror. Patent Applicant: 1 Telegraph and Telephone Co., Ltd., 13゜Representative: Naotaka Ide, Patent Attorney, Figure 3: Loeco light-injected semiconductor ring-ray layout diagram: Figure 5: 9

Claims (3)

[Claims] (1) A ring laser formed by a circularly closed optical path on a semiconductor substrate, an optical mixing section that mixes and interferes light propagating in opposite directions within this ring laser, and a beat signal of the interfered light. In the semiconductor laser gyroscope, the ring laser includes a single mode waveguide having a degenerate mode, and the ring laser propagates the light propagating in opposite directions into mutually orthogonal polarization components. A semiconductor laser gyroscope characterized by comprising directional polarization control means. (2) The propagation direction polarization control means includes two Faraday rotators having a polarization plane rotation function of 45 degrees in opposite directions, and is inserted between these two Faraday rotators, so that the maximum transmission polarization planes are orthogonal to each other. The semiconductor laser gyroscope according to claim 1, further comprising a polarizer rotated by about 45 degrees with respect to a polarization component. (3) The propagation direction polarization control means includes a master laser for light injection provided separately from the ring laser, and laser beams separated into mutually orthogonal polarization components from the master laser into the ring laser. The semiconductor laser gyroscope according to claim 1, further comprising a light injection means for injecting light so as to propagate in a reverse direction.