JPS625105A - Waveguide type photo-displacement sensor - Google Patents

Abstract

PURPOSE:To assure a sensor of longer distance of displacement measurement and available for identification of displacement direction, by installing means of parallelling means for a signal light and phase-shifting means of waveguide light between the discharging end of photo-waveguide path and reflecting surface of a specimen. CONSTITUTION:Asymmetric X dividing type photo-waveguide paths 10, 20 are formed, a beam of light guided into waveguide paths 11, 21 are divided equally at the X-shaped jointing members, the beams of the waveguide paths 13, 23 are reflected as the reference light by a reflecting film 2, the beams of light of the waveguide paths 14, 24 are reflected as the reflecting light by a movable mirror 4 and an output beam of intensity following a phase difference of the reflecting light is fed out from the waveguide paths 12, 22. As phase-shifting grooves 25 are made in the waveguide path 23, the output beam of the waveguide path 22 generates a phase deviation from the output beam of the waveguide path 12 for identification of the moving direction of the mirror 4. A rod lens 3 converts the light into parallel beams and the intensity of the light can be maintained regardless of a displacement of the mirror 4 connected to the specimen, and thus the distance of displacement measurement can be increased and the displacement direction can be identified.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention At least two optical waveguides for optical interference are formed on a substrate, and a lens means is provided between the output end of the optical waveguide of the substrate and a reflective surface on an object to be measured. are respectively provided, and the signal light emitted from the output end is collimated by these lens means, and the reflected light from the reflective surface is focused, and further a phase shift means is provided in one of the at least two optical waveguides. A waveguide-type optical displacement sensor characterized by being provided with.

BACKGROUND OF THE INVENTION This invention fabricates a Michelson interferometer using an optical waveguide on a substrate, and combines a reference beam reflected by a reflective surface on the substrate and a signal beam reflected by a reflective surface on a measured object outside the substrate. The present invention relates to a waveguide type optical displacement sensor that measures the amount of displacement of an object to be measured based on changes in light intensity caused by interference.

In such a waveguide type optical displacement sensor, it is inevitable that the signal light emitted from the three-dimensional optical waveguide of the substrate is diffused, and therefore is reflected by the reflective surface of the object to be measured and returned to the optical waveguide of the substrate. There is a problem in that the amount of incident light decreases. If the amount of displacement of the object to be measured is extremely small (for example, on the order of tens of micrometers), a considerable amount of reflected light will return to the optical waveguide of the substrate, but if the displacement of the object to be measured becomes large, it is no longer possible to obtain a measurable amount of signal light. I can't do it anymore.

Furthermore, with conventional waveguide type optical displacement sensors, it has not been possible to determine the direction of displacement of the object to be measured.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type optical displacement sensor that has a long displacement n1 constant distance and is capable of determining the displacement direction.

The waveguide type optical displacement sensor according to the present invention includes a substrate on which at least two optical waveguides for optical interference are formed, each provided between the output end of the optical waveguide of this substrate and a reflective surface on a measured object. , two lens means for collimating the signal light output from the output end and for condensing the reflected light on the reflecting surface, and a phase of the guided light provided in one of the at least two optical waveguides. It is characterized by comprising a shift means and a reflection means formed on the end face of the optical waveguide of the substrate in order to obtain reference light.

During the process in which the signal light and the reference light propagate through the optical waveguide of the substrate, these two lights interfere, and interference light with an intensity corresponding to the phase difference between these two lights is obtained.

The phase of the reference target is always constant, and the phase of the signal light changes depending on the position of the object to be measured. Therefore, the amount of displacement of the object to be measured is measured based on the change in the intensity of the interference light.

The signal light emitted from the two optical waveguides of the substrate is collimated by the two lens means and hits the reflective surface on the object to be measured, and the reflected light from the reflective surface is condensed by the lens means and reflected on the substrate. They are respectively incident on the optical waveguide. Since the amount of signal light incident on each optical waveguide of the substrate hardly changes even if the object to be measured is largely displaced, a long measurement distance can be obtained.

One of the at least two optical waveguides is provided with phase shift means. Therefore, the periodic changes in the intensity of the interference light obtained from the nine optical waveguides are shifted from each other by a phase amount corresponding to the phase forcibly shifted by the phase shift means. It becomes possible to determine the moving direction of the object to be measured based on the phase shift between these two interference lights.

The reflecting means formed on the end face of the optical waveguide of the substrate can be realized by vapor deposition of a metal thin film or the like. By changing the thickness of this metal thin film, it is possible to control the amount of light reflected by the metal thin film, that is, the reference light intensity. By setting the reference light intensity to approximately the same level as the signal light intensity, it is possible to improve the extinction ratio of the change in the light intensity of the interference light. A good extinction ratio facilitates subsequent optical signal processing.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an example of a waveguide type optical displacement sensor according to the present invention.
FIG. 2 each shows the entire displacement measuring system.

Substrate 1. For example, by thermally diffusing TL into L i N b Oa, two asymmetrical X-branched optical waveguides 10 and 2
0 is formed. The optical waveguide 10 includes four optical waveguides 1
1 to 14, and the optical waveguide 10 includes these optical waveguides 11
-14 are connected at one end in an X-shape, and the width of the optical waveguide 12 is the same as that of the other optical waveguide 11.
It is made narrower than the width of 13.14. Optical waveguide 2
0 is similarly composed of four optical waveguides 21 to 24. The optical waveguides 11 and 21 are formed in common at their input ends, and branch into a Y-shape toward their respective X-shape filling portions. The details of such an asymmetrical
-202406 (Japanese Patent Application No. 57-86178).

The operation of the asymmetrical X-branched optical waveguide 10 (same as the optical waveguide 20) will be explained as follows within the scope related to this embodiment. The light propagating through the optical waveguide 11 is transmitted through two optical waveguides 13.
The process branches equally to 14 and progresses. Light propagating through the optical waveguides 13 and 14 toward the X-shaped packing section returns to the optical waveguide 11 when the phases of these lights are equal. Optical waveguide 1
When the lights 3 and 14 have opposite phases (the phases differ by 180"), these lights proceed to the optical waveguide 12. Therefore, the optical waveguide 12 includes the light that goes through the optical waveguides 13 and 14 toward the X-shaped packing part. Light with an intensity corresponding to the phase difference is obtained.

The above description is based on the optical waveguide 11.12 and the optical waveguide 13°1.
The same holds true even if 4 is exchanged.

An input optical fiber 31 is connected to the common input end of the optical waveguides 11 and 21, and an output optical fiber 32.33 is connected to the end of the optical waveguide 12.22.

As the input optical fiber 31, a polarization maintaining optical fiber is used. Laser light from a laser light source 41 passes through an isolator 42 and a lens 43 to an optical fiber 31.
will be introduced in The isolator 42 allows light to travel from the laser 41 to the optical fiber 31 and blocks light traveling in the opposite direction, and performs this action based on the polarization direction of the light. A multimode optical fiber is used as the output optical fiber /<32.33. Output light guided through these optical fibers 32, 33+ enters the light receiving elements 44A and 44B, respectively, and is converted into electrical signals representing the light intensity thereof.

A reflective film 2 is formed on the end face of the optical waveguide 13.23 of the substrate 1 by depositing Au. In the asymmetrical X-branch type optical waveguide 10, among the light guided to the optical waveguide 11 and equally branched into the optical waveguides 13 and 14, the optical waveguide 13
The light traveling through is reflected by this reflective film 2 and goes toward the X-shaped block.

This light is the reference light. The intensity of the reference light can be determined by the thickness of the reflective film. Asymmetrical X-branched optical waveguide 2
0, reference light can be obtained from the optical waveguide 23 in the same manner.

A movable mirror 4 is fixedly attached to the tip of a rod 6 of an actuator (not shown) that is the object to be measured or is attached to or in contact with the object to be measured. Rod lenses (gradient index lenses) 3 are provided between the end faces of the optical waveguides 14 and 24 of the substrate 1 and the movable mirror 4, respectively, and are fixed by suitable fixing means. The focal planes of this rod lens 3 are located at the output ends of the optical waveguides 14 and 24, respectively. In other words, one rod
As shown in FIG. 4(B) for the lens.

The light propagating through the optical waveguide 14 and exiting from its end is collimated by the rod lens 3 and hits the movable mirror 4, and the reflected light is focused by the rod lens 3 exactly near the output end of the optical waveguide 14. incident on the optical waveguide 14 and
It propagates toward the character-filled part. This light is signal light. Signal light is obtained not only from the optical waveguide 14 of one asymmetrical X-branching optical waveguide 10 but also from the optical waveguide 24 of the other asymmetrical X-branching optical waveguide 20 in the same manner.

First, the principle of displacement measurement will be explained. One optical waveguide I
Focus only on O.

As described above, the reference light of the optical waveguide 13 and the optical waveguide 14
The output light with an intensity corresponding to the phase difference with the signal light is outputted to the optical waveguide 1.
2, and this output light is guided to the light receiving element 44A by the optical fiber 32. The phase difference between the reference light and the signal light depends on the optical path difference between these two lights, that is, the amount of displacement of the movable mirror 4. The change in the output light intensity with respect to the displacement f1 (optical path difference) is shown by a solid line in FIG. The output light intensity changes sinusoidally with a period of λ (light wavelength) with respect to changes in the optical path difference. Signal light is transmitted through rod lens 3 and movable mirror 4
The optical path difference is equal to twice the amount of displacement of the movable mirror 4.

The output optical signal is converted into an electric signal by the light receiving element 44A, and then level-discriminated and binarized by a circuit 45A having two high and low thresholds ◆level 81 and S2 (third
(see figure). The rise and/or fall of this binary signal is counted by counter 46A. Therefore, the amount of displacement of the movable mirror 4 is measured in units of λ/2- or λ/4. For example, when a laser diode with a wavelength of λ-0.8 μm is used as the light source 41, displacement measurement can be performed in units of 0.4 μm or 0.2 μm.

Next, the principle of determining the displacement direction will be explained.

In the other optical waveguide 20, basically the same operation as in the optical waveguide 10 is performed, and for the output light guided by the optical fiber 33, the light receiving element 44B, threshold circuit 45B, and counter 4BB are also operated as described above. works the same way.

In the asymmetric X-branch type optical waveguide 20, phase shifting grooves 2 are formed in the substrate 1 at positions on both sides of the optical waveguide 23.
5 is formed, and the phase of the reference light propagating through the optical waveguide 23 is shifted by a predetermined amount. As a result, the optical waveguide 2
The output light obtained from the optical waveguide 12 is out of phase with respect to the output light obtained from the optical waveguide 12, as shown by the broken line in FIG. In this embodiment, a phase shift is applied by 178 cycles of the output light intensity. Therefore, the binary signal obtained from the threshold circuit 45B is also out of phase with the binary signal output from the threshold circuit 45A, as shown by the broken line.

The rising and/or falling of such a binary signal is detected by differentiating circuits 47A and 47B, and this differentiated signal is input to direction determining circuit 48.

When the movable mirror 4 moves in a direction away from the substrate 1, the rising edge (falling edge) of the output signal of the threshold circuit 45A appears before the rising edge (falling edge) of the output signal of the threshold circuit 45B, and the movable mirror 4 When moving in the opposite direction, the order of change of these two signals is reversed. The determining circuit 48 determines the moving direction of the movable mirror 4 based on the order in which changes in the outputs of the two differentiating circuits 47A and 47B appear. The direction determination circuit 48 can also be configured by a CPU.

In addition to the above-mentioned grooves, means for imparting a phase shift to the light propagating through the optical waveguide of the substrate include means for applying voltage or pressure to the optical waveguide, a thin film such as SiO□ loaded on the optical waveguide, and the like.

The reflectance and transmittance of light at the output end of the optical waveguide 13.23 are determined by the thickness of the reflective film 2. Therefore, by controlling the thickness of the two reflective films 2, the ratio of the intensity of the reference light and the signal light can be arbitrarily determined, and this can also be set to 1=1. This makes it possible to improve the extinction ratio of changes in the light intensity of the output light.

A rod φ lens 3 is provided between the output end of the optical waveguide 14.24 and the movable mirror 4, and the light emitted from the optical waveguide 14.24 is converted into parallel light by this lens 3. Even if the distance between the lens 3 and the mirror 4 changes due to the movement of the movable mirror 4, the light directed toward and reflected by the mirror 4 is parallel light and is hardly diffused. In addition, the reflected light from the mirror 4 is condensed by the lens 3 and passes through the optical waveguide 1.
4.24, respectively. Therefore, the intensity of the reflected light returning to the optical waveguide 14, 24 can be kept almost constant regardless of the position of the mirror 4. Since the signal light intensity can be maintained substantially constant with respect to the displacement of the movable mirror 4, accurate displacement measurement becomes possible, and the measurable range of displacement amount is expanded.

FIG. 4 shows a state in which the rod lens 3 is interposed between the output end of the optical waveguide 14 and the movable mirror 4 according to the present invention (FIG. 4(B)), and a state in which the rod lens 3 is not interposed (FIG. 4(B)). A
)) is shown. Conventional example without lens (Fig. 4 (A)
)), the light emitted from the optical waveguide 14 is diffused, and most of the reflected light from the movable mirror 4 is directed to a location other than the end face of the optical waveguide 14.

FIG. 5 shows changes in the intensity of the signal light returning to the optical waveguide 14 with respect to the amount of displacement of the movable mirror in a conventional example without a lens and in a case with a lens according to the present invention. According to the experimental results, in the conventional example without a lens, the signal light intensity is halved even if the distance between the end face of the optical waveguide 14 and the movable mirror 4 is about 50 μm (black circle), whereas in the present invention, the signal light intensity is halved (black circle). When a lens is used, the amount of attenuation of the signal light intensity is extremely small even when the distance reaches 10 mm.

Figure 6 is a trace of an experiment in which the movable mirror 4 was periodically vibrated, and the changes in the output light intensity and the amount of movement of the mirror 4 during this vibration were reflected on an oscilloscope and photographed. . A is movable mirror 4
amount of movement.

B shows the change in output light intensity.

It can be seen that the output light intensity (midrange value) hardly changes with respect to the amount of movement of the movable mirror 4.

In the above embodiment, the substrate 1 is provided with an asymmetrical X-branched optical waveguide 10.
20 is formed, but a Michelson type interferometer can also be constructed using other optical waveguides. For example, a Y-shaped optical waveguide as shown in FIG. 7(A),
An optical waveguide including a directional coupler as shown in the same figure (C)
It may also be a single optical waveguide as shown in FIG. Figure 7 (
In the configuration C), the reflective film 2 has a considerably high transmittance, and the light transmitted through the reflective film 2 becomes signal light.

Also, the rod lens is omitted in these figures.

As for the lens means, in addition to rod lenses, ordinary convex lenses, micro lenses, etc. can be used.

[Brief explanation of the drawing]

Figure 1 is a plan view showing an example of a waveguide type optical displacement sensor;
The figure is a block diagram showing the entire optical displacement measurement system, Figure 3 is a waveform diagram showing the output light intensity and a binary signal created based on it, and Figure 4 is a diagram showing the difference between the configuration of the conventional example and the present invention. , Fig. 5 is a graph showing the influence of this difference in configuration on the light intensity, Fig. 6 is a diagram tracing the waveform of the oscilloscope and shows the displacement amount and output light intensity change, and Fig.
The figure is a schematic plan view showing another example of the optical waveguide on the substrate. 1... Substrate, 2... Reflective film. 3...Rod lens, 4...Movable mirror. l0120...Asymmetrical X-branch optical waveguide. 11-14.21-24... Optical waveguide. 25... Phase shift groove. Applicant for the above patent: Tateishi Electric Co., Ltd. Agent: Kenji Ushiku and one other person 3rd FIA Figure 4 Figure 6WJ-1111, ?

Claims (1)

[Claims] A substrate on which at least two optical waveguides for optical interference are formed, each provided between an output end of the optical waveguide of this substrate and a reflective surface on a measured object, and from the output end to the reflective surface on the object to be measured. two lens means for collimating the output signal light and for condensing the reflected light on the reflecting surface; a waveguide light phase shifting means provided in one of the at least two optical waveguides; and a reference. A waveguide type optical displacement sensor comprising a reflecting means formed on an end face of an optical waveguide of a substrate to obtain light.