JPS625104A - Waveguide type photo-displacement sensor - Google Patents

Abstract

PURPOSE:To obtain a photo-displacement sensor of long distance of displacement measurement, by installing a lens means to convert into parallel beams of light a signal light between discharging end of photo-waveguide path and reflecting surface on the specimen. CONSTITUTION:An asymmetrical X dividing type photo-waveguide path 20 is formed on a substrate 11, a beam of light guided into a waveguide path 21 is divided equally at the X-shaped jointing member, the beam on a waveguide path 23 is reflected as the reference beam of light by a reflecting film 12, that on a waveguide path 24 is reflected as a signal light by a movable mirror 14, and an output beam of light with an intensity corresponding to these two reflected beams is guided to a light-receiving element through waveguide path 22 and output fiber 32. As a rod lens 13 serves for parallelling of the beams of light, the light intensity can be maintained constant regardless of a displacement of the mirror 14 connected to the sample the film thickness of the film 12 controls reflecting and transmission coefficients. Consequently, distance displacement measurement becomes longer and amount of damping of the intensity of the signal light can be limited to a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION Summary of the Invention At least one optical waveguide for optical interference is 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. A waveguide type optical displacement sensor characterized in that the signal light emitted from the output end is collimated by the lens means, and the reflected light from the reflective surface is collected.

BACKGROUND OF THE INVENTION This invention fabricates a Michelson interferometer using an optical waveguide on a substrate, and combines a reference target 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.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type optical displacement sensor that can measure displacement over a long distance.

A waveguide type optical displacement sensor according to the present invention includes a substrate on which at least one optical waveguide for optical interference is formed, a substrate provided between the output end of the optical waveguide of this substrate and a reflective surface on a measured object, A lens means for collimating the signal light outputted from the output end and condensing the reflected light on the reflecting surface, and a reflecting means formed on the end face of the optical waveguide of the substrate for obtaining reference light. It is characterized by having the following.

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 light is always constant, and the phase of the signal light changes depending on the position on 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 optical waveguide of the substrate is collimated by the lens means and hits a reflective surface on the object to be measured, and the reflected light from this reflective surface is collected by the lens means and enters the optical waveguide of the substrate. . Since the amount of signal light incident on the optical waveguide of the substrate hardly changes even if the object to be measured is largely displaced, a long measurement distance can be obtained.

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.

A board 11 built into the sensor case 10. For example, L
The asymmetrical X-branched optical waveguide 20 is formed by thermally diffusing Ti into LNbO. This optical waveguide 20 has 4
The optical waveguide 20 includes two optical waveguides 21 to 24, and the optical waveguide 20 is constructed by coupling these optical waveguides 21 to 24 at one end in an X-shape.

The width of the optical waveguide 24 is made narrower than the widths of the other optical waveguides 21 to 23. Details of such an asymmetrical X-branch type optical waveguide are disclosed in Japanese Patent Application Laid-Open No. 58-2024H (Japanese Patent Application No. 57-88178) as a waveguide optical beam splitter.

The operation of this asymmetrical X-branched optical waveguide 20 will be explained as follows within the scope related to this embodiment. Optical waveguide 2
The light propagating through 1 is split equally into two optical waveguides 23 and 24 and proceeds. The light propagating through the optical waveguides 23 and 24 toward the X-shaped packing section returns to the optical waveguide 21 when the phases of these lights are equal.

When the lights in the optical waveguides 23 and 24 have opposite phases (the phases differ by 180°), these lights proceed to the optical waveguide 22. Therefore, in the optical waveguide 22, light having an intensity corresponding to the phase difference of the light traveling through the optical waveguides 23 and 24 toward the X-shaped packing portion is obtained.

The above description is based on the optical waveguides 21 and 22 and the optical waveguides 23 and 2.
The same holds true even if 4 is exchanged.

Input and output optical fibers 31.32 are connected to the ends of the optical waveguides 21.22 via connectors 33.34, respectively. As the input optical fiber 31, a polarization maintaining optical fiber is used. Laser light from laser light source 4I is introduced into optical fiber 31 via isolator 42 and lens 43. 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. The output light guided by this optical fiber 32 is transmitted to a light receiving element 44.
2 is converted into an electrical signal representing the light intensity.

A reflective film 12 is formed on the end face of the optical waveguide 23 of the substrate 11 by depositing Au. Of the light guided to the optical waveguide 21 and equally branched into the optical waveguides 23 and 24, the light traveling through the optical waveguide 23 is reflected by the reflective film 12 and heads toward the X-shaped junction. This light is the reference light. The intensity of the reference target can be determined by the thickness of the reflective film 12.

The rod 1B of the actuator 15, which is the object to be measured or is attached to or in contact with the object to be measured, passes loosely through the hole in the case IO and protrudes into the case 10, and the movable mirror 14 is fixedly attached to the tip of the rod 1B. has been done. The end face of the optical waveguide 24 of the substrate 11 and the movable mirror 14
A rod lens (gradient index lens) 13 is provided between the two and fixed to the case 10 by suitable fixing means. The focal plane of this rod lens 13 is located at the output end of the optical waveguide 24. That is, FIG. 4(B)
As shown in , the light propagating through the optical waveguide 24 and exiting from the end thereof is collimated by the rod lens 13 and hits the movable mirror 14 , and the reflected light is reflected by the rod lens 13 and exiting from the optical waveguide 24 . The light is focused exactly near the edge.

The light enters the optical waveguide 24 and propagates toward the X-shaped packing section. This light is signal light.

As described above, the reference light of the optical waveguide 23 and the optical waveguide 24
The output light with an intensity corresponding to the phase difference with the signal light is outputted to the optical waveguide 2.
2, and this output light is guided to the light receiving element 44 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 14. FIG. 3 shows the change in output light intensity with respect to the amount of displacement (optical path difference). The output light intensity changes sinusoidally with a period of λ (light wavelength) with respect to changes in the optical path difference. Since the signal light travels back and forth between the rod lens 13 and the movable mirror 14, the optical path difference is 2 times the amount of displacement of the movable mirror 14.
equals twice.

The output optical signal is converted into an electric signal by the light receiving element 44, and then level-discriminated and binarized by a circuit 45 having two high and low threshold ψ levels Sl and S2 (see FIG. 3). A counter 46 counts the rise and/or fall of this binary signal. Therefore, the amount of displacement of the movable mirror 14 is measured in units of λ/2 or λ/4. For example, when a laser diode with a wavelength λ-0.8 μm is used as the light source 41, the wavelength is 0.4 μm or 0.2 μm.
Displacement n1 can be constant in μm units.

The reflectance and transmittance of light at the output end of the optical waveguide 23 are determined by the thickness of the reflective film 12. Therefore, 2 reflective films 1
By controlling the thickness of 2, the intensity ratio of the reference light and the signal light can be arbitrarily determined.

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 lens 13 is provided between the output end of the optical waveguide 24 and the movable mirror 14, and the light emitted from the optical waveguide 24 is converted into parallel light by this lens 13. Even if the distance between the lens 13 and the mirror 14 changes due to the movement of the movable mirror 14, the light directed toward and reflected by the mirror 14 is parallel light, so it is hardly diffused. Also,
The reflected light from the mirror 14 is focused by the lens 13 and enters the optical waveguide 24 . Therefore, the intensity of the reflected light returning to the optical waveguide 24 can be kept almost constant regardless of the position of the mirror 14. Since the intensity of the signal light can be maintained substantially constant with respect to the displacement of the movable mirror 14, accurate displacement measurement becomes possible, and the measurable range of the amount of displacement is expanded.

FIG. 4 shows a state in which the rod lens 13 is interposed between the output end of the optical waveguide 24 and the movable mirror 14 according to the present invention (FIG. 4(B)), and a state in which it is not interposed (FIG. 4(B)).
A)) is shown. Conventional example without lens (Fig. 4)
In A)), the light emitted from the optical waveguide 24 is diffused.
Most of the reflected light from the movable mirror 14 is directed to a location other than the end face of the optical waveguide 24.

FIG. 5 shows changes in the intensity of the signal light returning to the optical waveguide 24 with respect to the amount of displacement of the movable mirror 14 in the conventional case without a lens and in the case of the present invention with a lens. According to the experimental results, in the conventional example without a lens, the signal light intensity is halved even when the distance between the end face of the optical waveguide 24 and the movable mirror 14 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.

FIG. 6 shows changes in the output light intensity and mirror 1 during this vibration in an experiment in which the movable mirror 14 was periodically vibrated.
The amount of movement shown in Figure 4 was reflected on an oscilloscope, and this was photographed and traced. A indicates the amount of movement of the movable mirror 14, and B indicates a change in the output light intensity. It will be seen that the output light intensity (midrange value) hardly changes with respect to the amount of movement of the movable mirror 14.

In the above embodiment, an asymmetrical X-branched optical waveguide 20 is provided on the substrate 11.
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 Figure 7(A), an optical waveguide including a directional coupler as shown in Figure 7(B), and a single optical waveguide as shown in Figure 7(C). An optical waveguide may also be used. In the configuration of FIG. 7(C).

The reflective film 12 has a fairly high transmittance, and the light transmitted through the reflective film 12 becomes signal light. In addition, the lens in the rod 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 drawings]

Figure 1 is a perspective view showing an example of a waveguide type optical displacement sensor;
The figure is a configuration 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 shows the difference between the configuration of the conventional example and the present invention. Figure 5 is a graph showing the influence of this difference in configuration on the light intensity, Figure 6 is a diagram tracing the waveform of the oscilloscope and shows the displacement and output light intensity change, and Figure 7 is a graph showing the influence of this difference in configuration on the light intensity. The figure is a schematic plan view showing another example of the optical waveguide on the substrate. 11... Substrate, 12... Reflective film, 13...
・Rod lens. 14... Movable mirror, 20... Asymmetrical X-branch optical waveguide. 21-24... Optical waveguide. Patent applicant: Tateishi Electric Co., Ltd. Agent: Kenji Ushiku et al.
Name 3rd FI! J Figure 4 Figure 6 Figure 5 Figure 5 0 50 100 150 200 250 Qam) 1
3m foot giant mountain reed Q Banquet-a-ri Figure 7

Claims (1)

[Claims] A substrate on which at least one optical waveguide for optical interference is formed, which is provided between an output end of the optical waveguide of this substrate and a reflective surface on a measured object, and outputs from the output end. a lens means for collimating the reflected signal light and for condensing the reflected light on the reflecting surface, and a reflecting means formed on the end face of the optical waveguide of the substrate to obtain a reference light. Wave type optical displacement sensor.