JPH03142317A - Optical gyro - Google Patents

Abstract

PURPOSE:To obtain an optical gyro which is free from the reduction of the optical coupling efficiency and the deviation of the optical axis and is reasonably integrated by forming a semiconductor light emitting element, a light receiving element an optical waveguide coil and optical waveguides integrally. CONSTITUTION:In the case of the use of, for example, laser beam in a short wavelength band, a thin film formed by growing compound semiconductor crystal having a superlattice structure is laminated on a silicon substrate 3 to form a laser element 10 and the light receiving element 12, and optical waveguides 14, 14a, and 14b are formed by a thin film formed by growing ferroelectric crystal on the substrate 3. Thus, the laser element 10 and the light receiving element 12 are formed integrally and the optical waveguide 14 and the second branching optical waveguide 14b are formed integrally. A high refractive index is given to the ferroelectic thin film or the compound semiconductor thin film to form a sensing coil 7 on the substrate 3 as an optical waveguide maintaining the single mode polarization plane in the same manner as optical waveguides 14, 14a, and 14b. Thus, the coupling efficiency and the degree of accuracy of optical axis alignment between the semiconductor light emitting element as well as the light receiving element and optical waveguides are improved to miniaturize the optical gyro.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention is a method for controlling a fixed cover of an optical waveguide coil based on the phase difference between laser beams traveling in mutually opposite directions within the optical waveguide coil. This invention relates to an optical gyro that detects the rotational angular velocity of a detection object.

[Prior Art] Conventionally, as shown in FIG. 6, a laser beam emitted from a laser light source 72 is split into two by a beam splitter 76, and one of the laser beams is sent to an optical waveguide via a coupling lens 78a. 80, the laser beam is emitted to one end of the optical fiber coil 82 and propagated clockwise, and the other laser beam is
propagates to the optical phase modulator 84 via the coupling lens 78b,
After being phase modulated by the optical phase modulator 84, the light is output to the other end of the optical fiber coil 82 and propagated counterclockwise, thereby causing the optical fiber coil 82 to propagate in mutually opposite directions. The laser beams incident from both ends of the beam splitter 76
An optical gyro 70 is known that is configured to integrate two laser beams, receive the light with a light receiver 74, and output an electric signal according to the phase difference between the two laser beams.

In this optical gyro 70, when the object to be detected (the path shown in the figure) on which the optical gyro 70 is mounted rotates at a rotational angular velocity Ω on the coil forming surface of the optical fiber coil 82, the laser beam CW traveling in the clockwise direction and the laser beam CW traveling in the counterclockwise direction Laser light CCW that advances to
A phase difference Δφ expressed by the following equation is generated between

Δφ=4πLRΩ/(Cλ) where: is the length of the optical fiber coil, R is the radius of the optical fiber coil, C is the speed of light in vacuum, and λ is the wavelength of the light.

Then, when the light receiver 74 outputs an electrical signal according to the phase difference Δφ, an electrical signal processing circuit (the path shown in the figure) detects the rotational angular velocity Ω of the detected object based on this electrical signal. However, when the rotational angular velocity of the object to be detected is small, the resulting phase difference Δφ is extremely small and does not appear as an electrical output of the light receiver 74. Therefore, in this optical gyro 70, the detection sensitivity is improved by phase modulating the laser light CCW traveling in the counterclockwise direction using the optical phase modulator 84.

Therefore, as is well known, the voltage output of the photodetector 74 is superimposed with a DC component as well as a high-order component expressed by a Bessel function, and when this voltage output is synchronously detected, a voltage signal corresponding to the rotational angular velocity Ω is generated. A V-shaped mouth is obtained. This voltage signal VO is expressed by the following equation.

VD=Csin(Δφ) =Csin (4yr L RΩ/(Cλ)) However,
C is a predetermined constant.

In this way, by increasing the detection sensitivity through phase modulation and synchronously detecting the output electrical signal of the light receiver 74, even minute movements of the object to be detected can be detected.

By the way, this type of optical gyro is manufactured by assembling the laser light source 72, the light receiver 74, the optical systems 76 to 82, etc., which are made as independent components, so there is a risk of misalignment of each component due to vibration or temperature changes. A problem occurs in the bonding between the laser light source and the optical waveguide. Therefore, the laser light source 7
2 (or the light receiver 74) and the optical waveguide 80 and the overlapping area of the two laser beams CW and CCW on the light receiving surface of the light receiver 74 change, and the voltage signal output from the light receiver 74 drifts. Problems such as this occur.

To solve this problem, ferroelectric materials such as lithium oxide L+NbO3, bismuth silicon oxide Bi2SiO2, etc.
A semiconductor light-emitting element and a light-receiving element are pasted on a substrate, or a thin film of a compound semiconductor is laminated by crystal growth on a substrate of a compound semiconductor (gallium arsenide GaAs, indium phosphide InP, etc.). (For example, a 1'L gallium aluminum arsenide GaAQAs semiconductor light emitting element and a light receiving element) are formed by forming a ferroelectric thin film on the same compound semiconductor substrate for an optical waveguide. Then, the thin film was made with a high refractive index by the titanium TI thermal diffusion method,
An optical fiber gyro that prevents the effects of vibration and temperature changes by integrating each element and optical system has been proposed (Japanese Patent Laid-Open No. 58-216909).

[Problems to be Solved by the Invention] However, in the optical fiber gyro described above, since the semiconductor light emitting element and the light receiving element, which are manufactured separately, are attached on the substrate, the cleavage plane (laser light) of the semiconductor light emitting element and the light receiving element is Another problem was that it was difficult to bring the light-emitting surface or light-receiving surface of the optical waveguide into close contact with the end surface of the optical waveguide and to align them with high precision, and it was not possible to sufficiently prevent a decrease in optical coupling efficiency and misalignment of the optical axis. Furthermore, compound semiconductor substrates have the property that lattice defects are likely to occur in the crystals when a compound semiconductor of a different type is grown on the substrate, so the formed thin film is easily broken. When a ferroelectric thin film is formed on a compound semiconductor substrate and this thin film is doped by thermal diffusion or ion implantation, distortion may occur in the thin film. Forming optical waveguides and other optical devices with dielectric thin films requires
There's a problem.

SUMMARY OF THE INVENTION Therefore, the present invention has been made with the object of providing an optical gyro that does not cause a decrease in optical coupling efficiency or shift of the optical axis, and is easy to integrate.

[Means for Solving the Problems] The gist of the present invention is to emit laser light to both ends of an optical waveguide coil, and to emit laser light to each end of the optical waveguide coil based on the mutual phase difference between the laser lights incident from both ends. This is an optical gyro that detects the rotational angular velocity of a detected object to which an optical waveguide coil is fixed, and is made from a thin film formed by growing a compound semiconductor crystal with a superlattice structure on a single substrate of an elemental semiconductor single crystal. an optical waveguide coil consisting of a thin film of ferroelectric or compound semiconductor formed by crystal growth on the single substrate; and an optical waveguide coil consisting of the same thin film as the optical waveguide coil; An optical gyro characterized by comprising an optical waveguide connecting each of both ends of the optical waveguide coil to the semiconductor light emitting device and the semiconductor light receiving device.

[Function] According to the optical gyro of the present invention configured as described above, the laser light emitted by the semiconductor light emitting element travels through the optical waveguide to each end of the optical waveguide coil, and mutually travels within the optical waveguide coil. propagate in the opposite direction. The light is then received from each end of the optical waveguide coil through the optical waveguide to the semiconductor light receiving element.

Here, a superlattice is a crystal lattice formed by stacking lattices of different elements or compounds, and is a crystal lattice that is formed by stacking lattices of different elements or compounds, and is a superlattice that supports dislocations caused by lattice mismatch between elemental semiconductors and compound semiconductors (deformation due to slipping of compound semiconductor crystals). It has a suppressive effect. Therefore, a compound semiconductor crystal with a superlattice structure is
It is possible to grow regularly even on substrates of elemental semiconductor single crystals with different lattice constants. therefore,
A high-quality compound semiconductor thin film free of lattice defects can be formed on an elemental semiconductor single crystal substrate, and by stacking these thin films, semiconductor light-emitting devices and semiconductor light-receiving devices can be manufactured.

In addition, forming optical waveguide coils and optical waveguides by forming thin films of compound semiconductors or ferroelectrics on single-crystal substrates of elemental semiconductors produces thin films with a regular crystal structure without lattice defects, which allows thermal diffusion. This is because the thin film is not distorted by ion implantation or ion implantation.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 is an explanatory diagram showing the optical configuration of an optical gyro according to an embodiment of the present invention.

As shown in the figure, the optical gyro 1 includes an optical integrated circuit 5 formed on an n-type or p-type silicon single crystal substrate (hereinafter simply referred to as a silicon substrate) 3 doped with N elements, B elements, etc. A tag consisting of a sensing coil 7 is mounted on an object to be detected (not shown). Note that FIG. 1 shows the optical integrated circuit 5 enlarged with respect to the sensing coil 7.

The optical integrated circuit 5 includes a semiconductor laser device (hereinafter simply referred to as a laser device) 10 that emits highly coherent laser light.
, a semiconductor light-receiving element (hereinafter simply referred to as a light-receiving element) 12 that performs photoelectric conversion, and an optical waveguide 14 that guides laser light to a predetermined path.
・First branch optical waveguide 14a ・Second branch optical waveguide 14b,
It is composed of a directional coupler 16 that branches or integrates laser light, and a phase modulator 18 that modulates the laser light at a predetermined frequency.

As is well known, the laser element 10 has a double heterostructure (as shown) in which an active layer is sandwiched between cladding layers and bonded to each other, and positive and negative electrodes are formed on the surface (non-bonded surface) of the cladding layer. When a direct current is applied to the active layer, laser light is emitted from the active layer. As is well known, the light-receiving element 12 is a combination of a P-type semiconductor and an N-type semiconductor (shown in the figure), and when light hits the bonded surface, it outputs an electric signal depending on the intensity of the light.

The optical waveguide 14 guides the laser beam emitted from the laser element 10 to one end of the sensing coil 7, and the first branch optical waveguide 14a guides the laser beam emitted from the laser element 10 branched from the optical waveguide 14 by the directional coupler 16. The light is guided to the other end of the sensing coil 7, and the second branch optical waveguide 14b integrates the laser beams incident from both ends of the sensing coil 7 through the optical waveguide 14 and the first branch optical waveguide 14a. The light is guided to the light receiving element 12.

Here, the materials and manufacturing method of the laser element 10, the light receiving element 12, and each optical waveguide 14.14a, 14b will be explained.

First, when using a laser beam in a short wavelength band, a thin film is formed by growing a compound semiconductor crystal having a superlattice structure on a silicon substrate 3 by MOCVD (metal-organic chemical vapor deposition). By laminating (for example, laminating a GaAs thin film and a GaAQAs thin film), the laser element 10 and the light receiving element 12 are manufactured, and ferroelectric materials (L + NbO3, B i2s +
By forming each of the optical waveguides 14.14a and 14b with a thin film formed by crystal growth of 02, etc.), the laser element 10, the light receiving element 12, the optical waveguide 14, and the second branch optical waveguide 14b are integrally molded.

On the other hand, when using a long wavelength band laser beam, a thin film of a compound semiconductor (for example, 1nP) is formed on the silicon substrate 3 by MOCVD, and a compound semiconductor crystal having a superlattice structure is grown on this thin film. By laminating the thin films formed in this manner (for example, laminating a 1nP thin film and a 1nGaAsP thin film of indium, gallium arsenide, and phosphorus), each layer is made of the compound semiconductor thin film, together with the surface stone of the laser element 10 and the light receiving element 12. Optical waveguide 14.14a, 14
By manufacturing the laser element 10 and the light receiving element 1
2, the optical waveguide 14, and the second branch optical waveguide 14b are integrally molded.

For each optical waveguide 14.14a, 14b, a single-mode polarization-maintaining optical waveguide is formed by imparting a high refractive index to the ferroelectric thin film or compound semiconductor thin film by Tl thermal diffusion method or ion implantation. It is formed into a wave path.

The directional coupler 16 includes two optical waveguides arranged to sandwich a portion where the optical waveguide 14 and the first branch optical waveguide 14 or the second branch optical waveguide 14b are close to each other at a distance equivalent to the wavelength of the laser beam. A pair of positive and negative planar electrodes 16a and 16b
and 16c and 16d, the positive electrodes 16a, 16c and negative electrodes 16b of each of the planar electrodes 16a to 16d,
The planar electrodes 16a to 16d, which are arranged such that electrodes 16d are located opposite to each other, are made of aluminum or gold and are formed on a thin film of ferroelectric or compound semiconductor by a well-known photography technique.

Directional coupler 16 (operates as a beam splitter that separates circularly polarized light and linearly polarized light, and when a voltage is applied, splits the laser light from the laser element 10 into two and splits the laser light from the sensing coil 7 Combines laser beams incident from both ends.

The phase modulator 18 consists of positive and negative planar electrodes 18a and 18b arranged near one end of the sensing coil 7 of the second branched optical waveguide 12b to sandwich the second optical waveguide 12bfE. , when a voltage signal with a frequency fs from a signal processing electronic circuit is applied, the refractive index of the second branch optical waveguide 12b changes due to the electro-optic effect, and this change in refractive index causes the laser light to change to a modulation frequency fO.
phase modulated. Note that the phase modulator 18 may be provided on the optical waveguide 14 side.

The planar electrodes 18a, 18b of the phase modulator 18 are made in the same way as the planar electrodes 16a-16d of the directional coupler 16.

Sensing coil 7 (upper pot optical waveguide 14.14a, 14
Similarly to b, the Ti thermal diffusion method is used to impart a high refractive index to a ferroelectric thin film or a compound semiconductor thin film, and a single mode polarization-maintaining optical waveguide is formed on the silicon substrate 3. Further, the sensing coil 7 is formed in an external area of the optical integrated circuit 5, so that the total extension thereof is sufficiently long.

The optical integrated circuit 5 described above outputs a voltage signal to an electronic circuit 30 provided outside the silicon substrate 3, and each element of the optical integrated circuit 5 is driven by a drive signal from the electronic circuit 30.

As shown in FIG. 2, the electronic circuit 30 includes a laser element 10
a drive power supply circuit 32, a signal detection amplification circuit 34 that detects and amplifies the electrical signal from the light receiving element 12,
a light emission level control circuit 36 that controls the light emission level of the laser element 10 according to the output level of the laser element 10; a phase modulator drive circuit 40 that outputs a voltage signal based on the oscillation frequency fs of the oscillator 38 to the phase modulator 18; A synchronous detector 42 that synchronously detects the signal from the amplifier circuit 34 at a frequency fs, a filter 44 that filters high frequency components of the signal output from the synchronous detector 42, and a directional coupler that drives the directional coupler 16. The driving circuit 46 is the main part, and the light receiving element 12
A signal component corresponding to the rotational angular velocity of the detected object is detected from the electrical signal outputted by the sensor. The operation of each circuit in the electronic circuit 30 described above is well known as an electronic circuit for a phase modulation type optical gyro, so the details will be omitted.

In the optical gyro 1, a laser beam emitted from a laser element 10 is split into two by a directional coupler 9, one laser beam CW is emitted to one end of a sensing coil 7 and propagated clockwise, and the other laser beam is split into two by a directional coupler 9. The laser light CCW is phase modulated by the phase modulator 18, and is emitted to the other end of the sensing coil 7 and propagated counterclockwise, so that the colors within the sensing coil 7 are propagated in mutually opposite directions. An optical gyro 1 is placed between the two laser beams propagating within the sensing coil 7.
When the detected object equipped with the sensor rotates, a Sagnac phase difference occurs. One of the two laser beams CW having this phase difference is phase-modulated by the modulation frequency fO by the phase modulator 18, and further combined with the other laser beam CCW by the directional coupler 9, and then sent to the light receiving element 12. It is incident. Then, the light receiving element 12 outputs an electric signal according to the Sagnac phase difference between the two laser beams.

Then, the electronic circuit 30 synchronously detects the electric signal from the light receiving element 12 and outputs a signal corresponding to the rotational angular velocity.

As described above, in this example, a compound semiconductor thin film was formed on the silicon substrate 3 by crystal growth, so that a thin film having a regular superlattice crystal structure free of lattice defects could be obtained. Therefore, the semiconductor laser device 10 and the light-receiving device 12 can be made of a high-quality thin film of compound semiconductor crystal.

Furthermore, even if thermal diffusion or ion implantation is applied to a thin film of a high-quality compound semiconductor or a thin film formed by growing ferroelectric crystals, the crystal structure of the thin film will not be distorted. A thin film can be made to have a high refractive index by a diffusion method or an ion implantation method.

In addition, the laser element 10, the light receiving element 12, and each optical waveguide 1
4.14a, 14b and the sensing coil 7 can be integrally formed on the same silicon substrate 3, and the laser element 10, the light receiving element 13, and each optical waveguide 14.14a, 14
The optical coupling efficiency with b and the accuracy of optical axis alignment are improved, and furthermore, optical axis deviation and phase deviation due to vibrational temperature changes do not occur. Furthermore, since the optical system is integrated, it is effective in reducing the size of the device.

In addition, since the directional coupler 16 and the phase modulator [8] are also integrally formed on the same silicon substrate 3, fluctuations in the operating point due to vibration and temperature are suppressed.

Here, in this embodiment, the electronic circuit 30 is provided outside the silicon substrate 3, and the sensing coil 7 is provided outside the optical integrated circuit 3.
0, but this (tL
As shown in FIG. 3, each circuit 32 to 46 of the electronic circuit 30
An optoelectronic integrated circuit 40 is fabricated by integrally integrating the optoelectronic integrated circuit 20 and the electronic circuit 30, which is composed of an electronic element formed of a thin film made by crystal growth on a silicon substrate 3. Similarly, the sensing coil 50 may be formed using ultra-fine processing techniques (micro-application techniques such as etching, doping, thin film formation, planar technology, etc.).

In this way, the sensing coil 50 can be made longer, so detection sensitivity can be improved. Further, since the optical integrated circuit 20 and the electronic circuit 30 can be integrated into one IC chip, the optical gyro can be made smaller.

In this case, the introduction portion 50a from one end of the sensing coil 50 to the coil body must cross over the coil, but the crossing of the sensing coil 50 can be done by the following formation method. You can construct the three-dimensional structure of a part.

That is, as shown in FIG. 4, first, the silicon substrate 3 is
Silicon chloride S + CQ 4, titanium chloride Ti on top
Upper claddings 52a and 54a and lower claddings 52b and 54b of silicon oxide 5102 are laminated and formed by using CQ a as a starting material and causing hydrolysis in a flame in an argon (Ar) gas atmosphere, and then , TiO, rich SiO2 (depending on the refractive index TiO2
An upper layer optical waveguide (optical waveguide in the overpassing portion) 50c (SiO2 containing a relatively large amount of kTi02) and a lower layer optical waveguide (optical waveguide in the coil forming portion) 50d are laminated by doping a predetermined amount of impurities such as By forming the sensing coil 50, the three-dimensional structure of the intersection portion of the sensing coil 50 can be constructed.

Alternatively, as shown in FIG. 5, the sensing coil 60 may be formed on a silicon single crystal cylinder 70, and the optoelectronic integrated circuit 40 may be integrated thereon using a part of the cylinder as a substrate.

In this case, since the total length of the sensing coil 60 can be increased, the detection sensitivity of the rotational angular velocity can be improved.

[Effects of the Invention] As explained above, according to the present invention, a semiconductor light-emitting device and a semiconductor light-receiving device are formed by growing a compound semiconductor crystal having a superlattice structure on a substrate of the same elemental semiconductor single crystal. At the same time, since the optical waveguide coil and the optical waveguide are formed by crystal growth of a compound semiconductor or ferroelectric thin film, the semiconductor light emitting element and light receiving element, the optical waveguide coil and the optical waveguide can be integrally formed. Therefore, the coupling efficiency between the semiconductor light emitting element and the light receiving element and the optical waveguide and the accuracy of optical axis alignment are improved, and the optical gyro can be made smaller. Furthermore, optical axis deviations and phase deviations due to vibrations and temperature changes do not occur.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the optical configuration of the optical gyro of the embodiment, Figure 2 is a block diagram of the electronic circuit, and Fig. 3 is an explanatory diagram showing the optical gyro in which a sensing coil is formed around an optoelectronic integrated circuit. FIG. 4 is an explanatory diagram showing the three-dimensional structure of the intersection of sensing coils, FIG. 5 is an explanatory diagram showing an optical gyro provided on a silicon cylinder, and FIG. 6 is an explanatory diagram showing a conventional optical gyro.

Claims (1)

[Claims] Laser light is emitted to both ends of the optical waveguide coil, and based on the phase difference between the laser beams incident from both ends, the detection target to which the optical waveguide coil is fixed is emitted. An optical gyro for detecting rotational angular velocity, which comprises a semiconductor light-emitting element and a semiconductor light-receiving element made of a thin film formed by growing a compound semiconductor crystal having a superlattice structure on a single substrate of an elemental semiconductor single crystal; an optical waveguide coil made of a thin film of ferroelectric or compound semiconductor formed by crystal growth on one substrate; and an optical waveguide coil made of the same thin film as the optical waveguide coil, each at each end of the optical waveguide coil and the semiconductor light emitting device. and an optical waveguide connecting the semiconductor light receiving element.