JP3128029B2 - Optical IC displacement meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As a conventional example of such an optical IC displacement meter, there is an optical IC interferometer disclosed in Japanese Patent Application Laid-Open No. 64-12204. FIG. 3 is a configuration diagram of the embodiment. In FIG. 3, an optical waveguide 22 and reference optical waveguides 31 and 3 are provided on a substrate 21.
2, 33, 34 and interference waveguides 41, 42, 43, 44
And the branch waveguide 23, and the reference optical waveguides 32, 3
The optical path lengths of the optical waveguides 3 and 34 are longer than the optical path lengths of the reference optical waveguides 31, 32 and 33 by λ / 8. 24 is a light emitting element, 25, 26, 27 and 28 are mirrors, 29 is a power distributor, 35 is an optical fiber that emits a light beam propagating through the optical waveguide 22 toward the corner cube 30, and 36 is a corner cube 30. An optical fiber for introducing the reflected light beam into the branch waveguide 23, 37, 38, 3
Reference numerals 9 and 40 are light receiving elements.

[0003] In such a configuration, FIG.
FIG. 5 shows a signal processing circuit for calculating a moving distance of the corner cube 30 using a C interferometer. The signal processing circuit will be briefly described with reference to FIG.

When the corner cube 30 moves in the X direction, the square wave signals S ₁ to S _{1 are} output from the respective Schmitt circuits 52 to 55.
S ₄ is output. By the way, the reference optical waveguides 32 to 34
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 in the order of λ / 4. There are differences. Further, the square wave signals S _{1 to} S ₃ and the square wave signal S ₂
To S ₄ is a phase difference of lambda / 8, respectively.

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

Similarly, when the corner cube 30 moves in the -X direction, the count pulse is similarly supplied to the one-shot circuits 57 to 60, every time the corner cube 30 moves by λ / 4.
61 to 64, and the count pulses are supplied to AND circuits 79 and 84 via AND circuits 75 to 78 and 80 to 83, respectively.
Output from Since the count pulse output from the OR circuit 79 and the count pulse output from the OR circuit 84 have a phase difference of λ / 8, the count pulse output from the OR circuit 86 is counted. Makes the moving distance of the corner cube 30 λ / 8
In the order of.

As described above, in the above 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, the "optical IC interferometer" described in the above-mentioned prior art has the following disadvantages. (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. In addition, since power loss (scattering) is integrated in each element, it is difficult to obtain a signal having a good S / N. (2) When reflected light is generated by the mirrors 25 to 28 and the cross waveguide, and the reflected light returns to the light emitting element 24, the oscillation wavelength becomes unstable, so that the operation of the device becomes unstable. 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) Although the phase shifter is realized by utilizing the electro-optic effect of lithium niobate, it is difficult to operate stably because of DC drift. There were drawbacks such as.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a small-sized optical IC displacement meter capable of measuring displacement with high accuracy.

[0010]

To solve the above-mentioned problems, the present invention provides a laser diode (hereinafter simply referred to as an LD).
), A collimator lens attached to one side of the LD and collimating the output light of the LD, a measurement target to which light from the collimator lens is incident, and reflected light from the measurement target via the lens. A measuring optical waveguide that guides light from the other exit surface of the LD, and a phase modulation for modulating the phase of light propagating through the reference optical waveguide or the measuring optical waveguide. An optical IC-based interferometer having a configuration including a detector, a coupling optical waveguide for coupling the measurement optical waveguide and the reference optical waveguide, and a light receiving element to which 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 in a sine wave shape with the phase modulator. Characterized in that was. The reference optical waveguide, the measurement optical waveguide, and the coupling optical waveguide are each configured by a glass waveguide manufactured by a flame deposition method, and the phase modulator is configured by using a thermo-optic effect. . The reference optical waveguide, the measurement optical waveguide, and the coupling optical waveguide are manufactured by diffusion of titanium on a lithium niobate substrate, and the phase modulator is configured using an electro-optic effect. Further, the end faces of the reference optical waveguide, the measurement optical waveguide and the coupling optical waveguide are processed obliquely.

[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 a reduction in size and cost and minimizing power loss. (2) By adopting a configuration in which one of the lights emitted from both sides of the LD is used as reference light and the other is used as measurement light,
This essentially eliminates the generation of return light and coherent noise. (3) As a method for measuring the interference phase, a signal can be put on the modulation frequency by using a phase modulation method in which the phase of the reference optical path is sine-wave-shaped, so that stable operation without the influence of DC drift can be achieved. I have.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of an optical IC-based displacement meter of the present invention. In FIG. 1, a reference optical waveguide 1, a measurement optical waveguide 2, and a Y-shaped optical waveguide 3 are manufactured by using a flame deposition method disclosed in Japanese Patent Publication No. Sho 62-48806, "Method for Manufacturing Thin Film for Optical Waveguide". The phase modulator 4 made of a glass waveguide and using the thermo-optic effect is configured by adding a heater electrode such as Cr on the reference optical waveguide 1 by sputtering or vapor deposition.

The light emitted from the LD 5 is collimated by a selfoc lens 6 attached to one side of the LD 5,
The light is reflected by a corner cube (hereinafter simply referred to as CC) 8, which is a measurement object placed at the measurement point. The reflected light is
The light 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 enters the reference optical waveguide 1 and is multiplexed with the light from the measurement optical waveguide 2 in 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
Are added, and the phase of the guided light is modulated in a sine wave shape by the signal source 18. 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 through the low-pass filter 15 to detect the sine component of the interference signal.

On the other hand, the multiplier 12 doubles the frequency of the signal source 18 with a frequency doubler 17 and multiplies the signal source 18 with the interference signal, and passes the low-pass filter 13 to detect the cosine component of the interference signal.

An interference phase φ is calculated from a cosine signal cos φ obtained from the low-pass filter 13 and a sine signal sin φ obtained from the low-pass filter 15 by an arithmetic unit 14.
Is calculated.

In such a configuration, the optical path of the measuring light emitted from the LD 5, passing through the SELFOC lens 6 → CC 8 → the SELFOC lens 7 → the measuring optical waveguide 2, and reaching the multiplexing point of the Y-shaped optical waveguide 3 is changed. L _m , the optical path of the reference light emitted from the other end of the LD 5, passing through the phase modulator 4 → the reference optical waveguide 1, and reaching the multiplexing point of the Y-shaped optical waveguide 3 is represented by L _r .
After passing through the Y-shaped optical waveguide 3, the light is detected by the light receiving element 9 and the I / V
The interference signal I ₀ amplified by the conversion circuit 11 is represented by the following equation. Note that A in the expression 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 or changes in the reflectance when the CC 8 is moved, and the moving direction cannot be determined. Therefore, in order to overcome these disadvantages, the phase of the reference light is modulated into a sine wave using the phase modulator 4. The modulation frequency omega _m, When the modulation depth xi], the interference signal I _m obtained from the light receiving element 9 is represented by the following equation. I _m = A · cos ｛φ + K · cos (ω _mt )｝ Ｋ K = 4 · π · ξ / λ

This equation is expanded using a Bessel function,
When the component of the modulation frequency ω _m is detected by the multiplier 16 and the low-pass filter 15, and the frequency component 2ω _m twice the modulation frequency is extracted by the multiplier 12 and the low-pass filter 13, the following equation is obtained. I _m (ω _m ) = 2A · J ₁ (K) sinφ I _m (2ω _m ) = 2A · 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 by adjusting the gains of the low-pass filters 13 and 15 and calculating the following expression by the computing unit 14, it becomes possible to measure the interference phase φ with high accuracy and detect the displacement. L _m = (λ / 2π) · tan ^-1 ｛I _m (ω _m ) / I
_m (2ω _m )｝ + L _r

FIG. 1 shows an optical waveguide pattern.
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 a method of measuring the interference phase φ, not only the phase modulation method of modulating the phase of the reference light in a sine wave shape but also the phase shift given to the reference light can be fixed at 90 deg. In this case, the signals of sinφ and cosφ can be directly output by the I / V conversion circuit 11. Further, a configuration using a directional coupler instead of the Y-shaped optical waveguide may be adopted.

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

Further, by processing the end face of the optical waveguide portion obliquely, it is possible to reduce the return light to the LD and the light receiving element, thereby preventing the output loss of the LD and the entry of noise into the light receiving element.

Further, in the above-described embodiment, an example has been described in which the light emitted from the LD 5 is converted into parallel light using the SELFOC lens 6 and propagated in the space, but the light from the LD 5 is made incident on an optical waveguide such as a fiber. It is also possible to detect the reflected light by guiding it to an object to be measured and making the reflected light incident on an optical waveguide such as a fiber.

[0025]

As described above in detail with the embodiments, according to the present invention, (1) the optical IC-based interferometer is constituted by only one coupling optical waveguide and phase shifter. It is possible to reduce the size and cost. (2) One of the lights emitted from both sides of the LD is used as a reference light,
Since the other is used as measurement light, LD
And the generation of coherent noise and return light to the light source can be essentially eliminated. (3) As a method for measuring the interference phase, a signal can be put on the modulation frequency by using a phase modulation method in which the phase of the reference optical path is sine-wave-shaped, and a stable operation free from the influence of DC drift is realized. it can. It is possible to realize an optical IC-based displacement meter having the above effects.

[Brief description of the drawings]

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

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

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

FIG. 4 is a circuit configuration diagram of a signal processing circuit of the optical IC interferometer of FIG. 3;

FIG. 5 is an explanatory diagram of an output signal of each circuit of the signal processing circuit of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reference optical waveguide 2 Measurement optical waveguide 3 Y-shaped optical waveguide (coupling optical waveguide) 4 Phase modulator 5 Laser diode 6, 7 Selfoc lens 8 Corner cube (measurement object) 9 Light receiving element

Claims (4)

(57) [Claims] 1. A laser diode (5), a collimator lens (6) attached to one surface of the laser diode (5), and collimating output light of the laser diode (5); A measuring object (8) into which light is incident, a measuring optical waveguide (2) for guiding reflected light from the measuring object (8) through a lens (7), and a laser diode (5). A reference optical waveguide (1) for guiding light from the other exit surface; and the reference optical waveguide (1) or the measurement optical waveguide (2).
Modulator for modulating the phase of light propagating through the optical path (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) to which light coupled by the coupling optical waveguide (3) is incident. An interferometer having an optical IC configuration having the following configuration: the phase modulator (4) modulates the phase of the reference light or the measurement light into a sinusoidal waveform to obtain the interference obtained from the light receiving element (9). An optical IC displacement meter, wherein the displacement of the object to be measured (8) is measured from the spectrum phase of a signal. 2. The reference optical waveguide (1), the measuring optical waveguide (2), and the coupling optical waveguide (3) are formed of a glass waveguide manufactured by a flame deposition method, and the phase modulator (4). 2. An optical IC-based displacement meter according to claim 1, wherein the sensor is configured using a thermo-optic 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 2. An optical IC-based displacement meter according to claim 1, wherein the displacement meter is configured using an electro-optic effect. 4. An optical IC displacement meter according to claim 1, wherein end faces of said reference optical waveguide (1), said measuring optical waveguide (2) and said coupling optical waveguide (3) are processed obliquely.