JPH06258018A - Optical ic displacement measuring equipment - Google Patents

Abstract

PURPOSE:To allow highly accurate measurement of displacement through a downsized equipment by constituting an optical IC interferometer part only of one coupling optical guide and a phase shifter and subjecting the phase of a reference light or a measuring light to sinusoidal modulation. CONSTITUTION:Light emitted from a laser diode(LD) 5 is collimated 6 and the light reflected from the corner cube 8 of an object is condensed 7 and made to enter a measuring light waveguide 2. Light emitted from the other side of the LD 5 is made to enter a reference light waveguide 1 and combined with the light entered to the waveguide 2 to cause interference. The interference wave propagates through a waveguide 3 and converted into an electric signal by a light receiving element 9. The propagated light is subjected to sinusoidal phase modulation by a phase modulator 4 using a signal source 18 while a detected interference signal is multiplied 16 by a signal 18 and a low-pass filter 15 detects cosine component. On the other hand, the frequency of the signal source 18 doubled by a frequency doubler 17 with its interference is multiplied 12 and a low-pass filter 13 detects sine component. Interference phase phi is operated 14 based on the signals sinphi and cosphi.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical IC type displacement meter for measuring the displacement of a measurement object, which is small in size and enables highly accurate measurement.

[0002]

2. Description of the Related Art As a conventional example of such an optical IC type displacement meter, there is JP-A 64-12204, "Optical IC interferometer". FIG. 3 is a block diagram of the embodiment. In FIG. 3, an optical waveguide 22 and reference optical waveguides 31, 3 are provided on a substrate 21.
2, 33, 34 and interference waveguides 41, 42, 43, 44
And the branch waveguide 23 are formed, and the reference optical waveguides 32 and 3 are formed.
The optical path lengths of 3, 34 are respectively formed longer than the optical path lengths of the reference optical waveguides 31, 32, 33 by λ / 8. Reference numeral 24 is a light emitting element, 25, 26, 27, 28 are mirrors, 29 is a power distributor, 35 is an optical fiber for emitting the light beam propagating through the optical waveguide 22 toward the corner cube 30, and 36 is a corner cube 30. Optical fibers for introducing the reflected light flux into the branch waveguide 23, 37, 38, 3
Reference numerals 9 and 40 are light receiving elements.

In such a structure, FIG.
The signal processing circuit for obtaining the moving distance of the corner cube 30 using the C interferometer is shown, which will be briefly described with reference to the output signal of each circuit of the signal processing circuit shown in FIG.

By moving the corner cube 30 in the X direction, the square wave signals S _1-
S ₄ is output. By the way, the reference optical waveguides 32 to 34
Of the reference optical waveguides 31 to 33 are formed to be λ / 8 longer than the optical path lengths of the reference optical waveguides 31 to 33, respectively, so that the square wave signals S ₁ and S ₃ and the square wave signals S ₂ and S ₄ are respectively at the positions of λ / 4. There is a phase difference. In addition, the square wave signals S _{1 to} S ₃ and the square wave signal S _{2 are}
Each of S ₄ has a phase difference of λ / 8.

Then, the one-shot circuits 57 to 6 at the rising and falling edges of the square wave signals S _{1 to} S ₄ , respectively.
Count pulses are generated from 0, 61 to 64, and the count pulses are output from the OR circuits 69 and 74 via the AND circuits 65 to 68, 70 to 73. This OR circuit 6
The count pulses output from the reference numerals 9, 74 are generated each time the corner cube 30 moves by λ / 4, and the count pulse output by the OR circuit 69 and the count pulse output by the OR circuit 74 are λ / 8. There is a phase difference of.
Therefore, a count pulse is output from the OR circuit 85 every time the corner cube 30 moves by λ / 8, and the moving distance of the corner cube 30 can be obtained on the order of λ / 8.

Even when the corner cube 30 is moved in the -X direction, the count pulse is similarly changed every time the corner cube 30 is moved by λ / 4, the one-shot circuits 57-60 ,.
61-64, and the count pulse is generated from the OR circuits 79, 84 via the AND circuits 75-78, 80-83.
Is output from. Since the phase difference between the count pulse output from the OR circuit 79 and the count pulse output from the OR circuit 84 is λ / 8 as in the above case, the count pulse output from the OR circuit 86 should be counted. The corner cube 30 movement distance by λ / 8
It can be calculated on the order of.

As described above, in the above-mentioned conventional example, the moving distance of the object can be obtained on the order of λ / 2 or more, and the moving direction of the object can be determined.

[0008]

However, in the "optical IC interferometer" shown in the above-mentioned prior art, (1) it is composed of many elements such as a directional coupler, a Y demultiplexer / coupler, and a cross waveguide. Therefore, it is complicated and it is difficult to reduce the size and cost. Moreover, since the power loss (scattering) is integrated in each element, it is difficult to obtain a signal with good S / N. (2) Reflected light is generated by the mirrors 25 to 28 and the cross waveguide, and when the reflected light returns to the light emitting element 24, the oscillation wavelength becomes unstable, so that the operation of the device becomes unstable. Further, when the reflected light enters the light receiving elements 37 to 40, it becomes coherent noise, and a periodic error occurs in the measured value. (3) The phase shifter is realized by utilizing the electro-optic effect of lithium niobate, but it is difficult to operate stably because of DC drift. There were drawbacks such as.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a small-sized optical IC displacement meter capable of highly accurate displacement measurement.

[0010]

The structure of the present invention for solving the above-mentioned problems is a laser diode (hereinafter, simply referred to as LD
That is, the collimator lens attached to one side of the LD for collimating the output light of the LD, the measurement target on which the light from the collimator lens is incident, and the reflected light from the measurement target through the lens. Measurement optical waveguide that guides the light from the other side, a reference optical waveguide that guides the light from the other emission surface of the LD, and a phase modulation for modulating the phase of the light propagating in the reference optical waveguide or the measurement optical waveguide. And an optical IC interferometer section having a configuration including a coupling optical waveguide that couples the measurement optical waveguide and the reference optical waveguide, and a light receiving element on which the light coupled by the coupling optical waveguide is incident. Then, the displacement of the measurement object is measured from the spectrum phase of the interference signal obtained from the light receiving element by modulating the phase of the reference light or the measurement light into a sine wave by the phase modulator. Characterized in that was. Further, the reference optical waveguide, the measurement optical waveguide, and the coupling optical waveguide are configured by glass waveguides manufactured by a flame deposition method, and the phase modulator is configured by utilizing a thermo-optical effect. . Further, the reference optical waveguide, the measurement optical waveguide, and the coupling optical waveguide are manufactured by titanium diffusion on a lithium niobate substrate, and the phase modulator is configured by utilizing an electro-optical effect. The end faces of the reference optical waveguide, the measurement optical waveguide, and the coupling optical waveguide are obliquely processed.

[0011]

According to the present invention, (1) the optical IC interferometer section is composed of only one coupling optical waveguide and a phase shifter, thereby realizing downsizing and cost reduction, and minimizing power loss. (2) By using one of the lights emitted from both sides of the LD as the reference light and the other as the measurement light, the LD
The generation of return light and coherent noise is essentially eliminated. (3) As a method of measuring the interference phase, by using a phase modulation method in which the phase of the reference optical path is sine wave-shaped, a signal can be placed on the modulation frequency, and stable operation that is not affected by DC drift is performed. There is.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical IC type displacement meter of the present invention. In FIG. 1, the reference optical waveguide 1, the measurement optical waveguide 2, and the Y-shaped optical waveguide 3 were manufactured by using the flame deposition method disclosed in Japanese Patent Publication No. 62-48806, "Method for manufacturing thin film for optical waveguide". The phase modulator 4 formed of a glass waveguide and utilizing the thermo-optic effect is formed by adding a heater electrode such as Cr on the reference optical waveguide 1 by sputtering or vapor deposition.

Light emitted from the LD 5 is collimated by a SELFOC lens 6 attached to one side of the LD 5,
It is reflected by a corner cube (hereinafter, simply referred to as CC) 8 which is a measurement object installed at a measurement point. The reflected light is
It is condensed by the SELFOC lens 7 and enters the measurement optical waveguide 2. On the other hand, the light emitted from the other surface of the LD 5 is
The light is incident on the reference optical waveguide 1, is combined with the light from the measurement optical waveguide 2 by the Y-shaped optical waveguide 3, and interferes. The interference wave propagates through the Y-shaped optical waveguide 3, is received by the light receiving element 9, and is converted into an electric signal.

Here, the reference optical waveguide 4 has a phase modulator 4
Is added, and the phase of the guided light is modulated by the signal source 18 into a sinusoidal wave. The photocurrent (interference signal) detected by the light receiving element 9 is input to the multipliers 12 and 16 after being amplified by the I / V conversion circuit 11. The multiplier 16 multiplies the signal from the signal source 18 by the interference signal and passes the signal through the low-pass filter 15 to detect the sine component of the interference signal.

On the other hand, in the multiplier 12, the frequency of the signal source 18 is doubled by the frequency doubler 17 to perform multiplication with the interference signal, and the low-pass filter 13 is used to detect the cosine component of the interference signal.

From the sine signal sin φ obtained from the low pass filter 13 and the cosine signal cos φ obtained from the low pass filter 15, the interference phase φ is calculated by the arithmetic unit 14
Calculate with.

In such a configuration, the optical path of the measurement light that has been emitted from the LD 5, passed through the SELFOC lens 6 → CC8 → the SELFOC lens 7 → the measurement optical waveguide 2 and has reached the combining point of the Y-shaped optical waveguide 3 _Let L _{r be} the optical path of the reference light that is emitted from the other end of L _m , LD 5, passes through the phase modulator 4 → reference optical waveguide 1, and reaches the combining point of the Y-shaped optical waveguide 3.
The light passes through the Y-shaped optical waveguide 3 and is detected by the light receiving element 9, and the I / V
The interference signal I ₀ amplified by the conversion circuit 11 is expressed by the following equation. Note that A in the formula is a constant indicating the interference intensity. I ₀ = A · cos φ φ = 2 · π · (L _m −L _r ) / λ

Here, only by measuring the interference signal I ₀ , high-precision measurement cannot be performed due to fluctuations in the output of the light source, changes in reflectance when the CC 8 is moved, and the direction of movement cannot be determined. Therefore, in order to overcome these drawbacks, the phase of the reference light is modulated into a sine wave using the phase modulator 4. When the modulation frequency is ω _m and the modulation depth is ξ, the interference signal I _m obtained from the light receiving element 9 is given by the following equation. I _m = A · cos {φ + K · cos (ω _mt )} ─K = 4 · π · ξ / λ

This equation is expanded using the Bessel function,
The component of the modulation frequency ω _m is detected by the multiplier 12 and the low-pass filter 13, and the frequency component 2 which is twice the modulation frequency is detected.
When ω _m is extracted by the multiplier 16 and the low pass filter 15, the following equation is obtained. I _m (ω _m ) = 2 A · J ₁ (K) sin φ I _m (2ω _m ) = 2 A · J ₂ (K) cos φ

Here, the modulation depth ξ is adjusted so that J ₁ (K) = J ₂ (K) (ξ = 0.23)
λ) or the gains of the low-pass filters 13 and 15 are adjusted and the following equation is calculated by the computing unit 14, whereby the interference phase φ can be measured with high accuracy and the displacement can be detected. L _m = (λ / 2π) · tan ⁻¹ {I _m (ω _m ) / I
_m (2ω _m )} + L _r

Further, as a pattern of the optical waveguide portion, as shown in FIG.
In addition to the Y-shaped branch shown in FIG. 2, a 2 × 2 branch pattern as shown in FIG. 2 is also possible. In this case, as the method of measuring the interference phase φ, not only the phase modulation method of modulating the phase of the reference light into a sinusoidal shape but also the phase shift given to the reference light can be fixed to 90 deg and used. In this case, the signals of sin φ and cos φ can be directly output by the I / V conversion circuit 11. Furthermore, instead of the Y-shaped optical waveguide, a directional coupler may be used.

In the above embodiment, the base material is
The same effect can be obtained by using lithium niobate to fabricate the optical waveguide portion by titanium diffusion. In this case, since the substrate has an electro-optical effect, the phase modulation can be performed only by producing an electrode pattern and applying an electric field.

Further, by obliquely processing the end face of the optical waveguide portion, the return light to the LD and the light receiving element can be reduced, and the output loss of the LD and the mixing of noise into the light receiving element can be prevented.

Further, in the above-mentioned embodiment, an example in which the light emitted from the LD 5 is made into parallel light by using the SELFOC lens 6 and propagated in space is shown. It is also possible to guide the light to the measurement target and detect the reflected light by making it incident on an optical waveguide such as a fiber.

[0025]

As described above in detail with reference to the embodiments, according to the present invention, (1) the optical IC interferometer section is composed of only one coupling optical waveguide and phase shifter. It is possible to reduce the size and price. (2) One of the lights emitted from both sides of the LD is used as the reference light,
Since the other is used as the measurement light, the LD
The generation of return light and coherent noise can be essentially eliminated. (3) As a method of measuring the interference phase, by using a phase modulation method in which the phase of the reference optical path is sine wave-shaped, a signal can be placed on the modulation frequency, and stable operation that is not affected by DC drift is realized. it can. It is possible to realize an optical IC displacement meter having effects such as the above.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical IC displacement meter of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the optical IC displacement meter of the present invention.

FIG. 3 is a conventional example of an optical IC interferometer.

4 is a circuit configuration diagram of a signal processing circuit of the optical IC interferometer of FIG.

5 is an explanatory diagram of an output signal of each circuit of the signal processing circuit of FIG.

[Explanation of symbols]

 1 Reference Optical Waveguide 2 Measurement Optical Waveguide 3 Y-type Optical Waveguide (Coupling Optical Waveguide) 4 Phase Modulator 5 Laser Diode 6, 7 Selfoc Lens 8 Corner Cube (Measurement Target) 9 Photodetector

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[Procedure amendment]

[Submission date] June 2, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

From the cosine signal cosφ obtained from the low-pass filter 13 and the sine signal sinφ obtained from the low-pass filter 15, the interference phase φ is calculated by the arithmetic unit 14
Calculate with.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction content]

This equation is expanded using the Bessel function,
Modulation frequency ω_mComponent of the multiplier 16 and low-pass filter
-15, and a frequency component twice the modulation frequency
2ω _mIs extracted by the multiplier 12 and the low-pass filter 13.
Then, it becomes the following formula. I_m(Ω_m) = 2A ・ J₁(K) sinφ I_m(2ω_m) = 2A ・ J₂(K) cosφ

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (4)

[Claims] 1. A laser diode (5), a collimator lens (6) mounted on one surface of the laser diode (5) for collimating the output light of the laser diode (5), and a collimator lens (6) from the collimator lens (6). A measuring object (8) on which light is incident, a measuring optical waveguide (2) for guiding reflected light from the measuring object (8) through a lens (7), and the laser diode (5). A reference optical waveguide (1) for guiding light from the other emission surface, and the reference optical waveguide (1) or the measurement optical waveguide (2)
Phase modulator for modulating the phase of light propagating in light (4)
A coupling optical waveguide (3) for coupling the measurement optical waveguide (2) and the reference optical waveguide (1), and a light receiving element (9) on which the light coupled by the coupling optical waveguide (3) is incident. And an interferometer obtained from the light receiving element (9) by modulating the phase of the reference light or the measurement light into a sine wave by the phase modulator (4). An optical IC displacement meter, characterized in that the displacement of the measurement object (8) is measured from the spectrum phase of the signal. 2. The reference optical waveguide (1), the measuring optical waveguide (2) and the coupling optical waveguide (3) are glass waveguides manufactured by a flame deposition method, and the phase modulator (4). The optical IC-based displacement meter according to claim 1, wherein is configured by utilizing a thermo-optical effect. 3. The reference optical waveguide (1), the measurement optical waveguide (2) and the coupling optical waveguide (3) are manufactured by titanium diffusion on a lithium niobate substrate, and the phase modulator (4) is The optical IC-based displacement meter according to claim 1, wherein the displacement meter is configured by utilizing an electro-optical effect. 4. The optical IC integrated displacement meter according to claim 1, wherein end faces of the reference optical waveguide (1), the measurement optical waveguide (2), and the coupling optical waveguide (3) are obliquely processed.