JPS62242806A - Optical displacement sensor - Google Patents

Abstract

PURPOSE:To obtain an optical displacement sensor which is reducible in size and has a lens means by using a small-sized Fresnel lens. CONSTITUTION:An optical fiber 1 is fitted to a substrate 2 so that an end surface of the optical fiber contacts a half-mirror 2b. Part of light propagated in the fiber 1 is reflected by the mirror 2b and returns to the inside of the fiber 1 as irradiation light. Light transmitted through the mirror 2b, on the other hand, travels in the substrate 2, but made parallel by a lens 2a and projected from the lens to travel toward a body to be measured or a mirror 3 fitted thereto. Its reflected light is converged 2a and incident on the fiber 1. This light is used for reference measurement. The reference light and measurement light interfere with each other in the process of returning in the fiber 1 and interference light on which intensity modulation is imposed at the position of the mirror 3 is obtained at the other end and analyzed to measure the quantity of displacement of the mirror 3. The small-sized Fresnel lens is used, so the small-sized optical displacement sensor is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention The present invention utilizes a guiding waveguide formed in an optical fiber or a substrate to transmit a reference light beam reflected by a fixed mirror and a measurement light beam reflected by an object to be measured. The present invention relates to an optical displacement sensor that measures the amount of displacement of an object by interfering with each other and measuring the change in intensity of the interference light.

In such an optical displacement sensor, it is unavoidable that the measurement light emitted from the optical fiber or leading waveguide and directed toward the object to be measured is diffused, and therefore reflected from the reflective surface of the object to be measured and reflected back into the optical fiber or leading waveguide. There is a problem in that the amount of returning and incident light is reduced. If the amount of displacement of the object to be measured is extremely small (for example, several tens of μm), a considerable amount of reflected light will return to the optical fiber or optical waveguide, but if the displacement of the object to be measured becomes large, there will no longer be a measurable amount of signal light. You will no longer be able to obtain it.

The applicant has already proposed a waveguide type optical displacement sensor that solves these problems and has a long displacement measurement distance (for example, Japanese Patent Application No. 6O-142637). This waveguide type optical displacement sensor is
A substrate on which at least one leading wavepath for optical interference is formed; a substrate is provided between the output end of the leading wavepath of this substrate and a reflective surface on the object to be measured, and collimates the signal light output from the output end. The present invention is characterized in that it includes a lens means 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 for obtaining reference light.

During the process in which the signal light and the reference light propagate through the leading wavepath 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 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 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 leading waveguide of the substrate hardly changes even if the object to be measured is largely displaced, a long measurement distance can be obtained.

The specification of this prior invention shows a rod lens (gradient index type lens) as the lens means. Since the rod lens is large in shape, there is a problem in that the overall shape of the optical displacement sensor must also be increased in size. In particular, in an optical displacement sensor using an optical fiber, since the optical fiber has a small diameter, a large rod/lens is out of balance with the optical fiber. Also, using a rod lens increases the irradiation area on the object to be measured.

It becomes difficult to measure the amount of displacement of a small object to be measured or a minute area position. Furthermore, we have developed a twin type optical displacement sensor in which two optical interference paths are arranged side by side.
142638, which not only measures the amount of displacement of an object to be measured but also detects the direction of displacement, two large rod lenses must be arranged side by side. There is a problem in that the destination displacement sensor becomes larger.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an optical displacement sensor having a lens means that can be miniaturized.

Structure and Function of the Invention The present invention allows a reference light beam reflected by a fixed mirror and a measurement light beam reflected by an object to be measured to interfere with each other by using an optical fiber or a guiding wavepath formed on a substrate. In an optical displacement sensor that measures the amount of displacement of an object to be measured by measuring changes in the intensity of this interference light, a Fresnel lens formed in a flat plate is used as the lens means, and the measurement light beam is directed by the Fresnel lens. It is characterized by collimating the irradiation onto the object to be measured.

As shown in FIG. 1, a glass or plastic substrate 2
A Fresnel lens 2a is formed on one surface, and a half-shape mirror 2b is formed on the other surface by vapor deposition of a metal film such as Au.
is formed. Such a Fresnel lens can be made by patterning glass, plastic, etc. by molding a Fresnel lens pattern produced by electron beam drawing or the like as a mold, or by using an ultraviolet curing method.

A more detailed method for producing a Fresnel lens is described in the applicant's earlier application, Japanese Patent Application No. 61-3419 and Japanese Patent Application No. 61-3420.
detailed in.

The method for manufacturing a Fresnel lens disclosed in 1986-3419 is to apply an electron beam resist onto a substrate, draw a Fresnel lens pattern on the resist using an electron beam drawing method, and then develop the resist. Then, the remaining resist pattern on the substrate is transferred to the substrate by dry φ etching, and the substrate on which the Fresnel lens pattern is formed is used as a female mold to produce a Fresnel lens by injection molding or other methods. It is something to do.

The method for manufacturing a Fresnel lens disclosed in Japanese Patent Application No. 61-3420 is to apply an electron beam resist onto a substrate, draw a Fresnel lens pattern on the resist using an electron beam drawing method, and then develop the resist. Using the residual film resist pattern on this substrate as a male mold, a female mold is formed by electroforming, and this female mold is used to manufacture a Fresnel lens.

Figure 2 shows a Fresnel lens 2a and a half mirror 2b.
A circular substrate 2 having a shape shown in FIG. 1 is attached to an optical fiber type optical displacement sensor. For example, the diameter of the optical fiber 1 is 125 μm, and the diameter of the substrate 2 is 200 μm. A substrate 2 is attached to the end face of the optical fiber 1 so that the end face and the half mirror 2b are in close contact with each other.

A portion of the light introduced into the optical fiber 1 and propagated through the optical fiber 1 is reflected by the half mirror 2b and returns within the optical fiber 1 as a reference light.

The light transmitted through the half mirror 2b travels through the substrate 2 while being diverged due to the single diffraction effect, but the light passes through the Fresnel lens 2a.
The light is collimated by the lens and exits from this lens toward the object to be measured or the mirror 3 attached to it. The reflected light from the mirror 3 is also parallel light, and this parallel light is focused by the Fresnel lens 2a and enters the optical fiber 1.

This light is the measurement light.

The reference target and measurement light interfere with each other while returning through the optical fiber 1, and from the other end of the optical fiber 1, interference light whose intensity is modulated depending on the position of the mirror 3 is obtained.By analyzing this interference light, the mirror 3 displacement amounts are measured.

FIG. 3 shows an example of an optical displacement sensor using a so-called asymmetrical X-branch type optical waveguide 10 formed on a substrate 20. This X-branch optical waveguide 10 has four
It has two optical waveguides 11 to 14. Only a Fresnel lens 2a is formed on the substrate 2, and no double half mirrors are provided. This substrate 2 is bonded to the end face of the optical waveguide 4. A metal reflective film 21 is deposited on the end face of the optical waveguide 13 .

Light is introduced into the optical waveguide 11 from the optical fiber 31.

It divides equally into two leading wave paths 13 and 14 and proceeds. The light from the leading waveguide 13 is reflected by the reflective film 21 and becomes reference light.

Return through the optical waveguide 13.

The light that has advanced to the leading waveguide 14 exits from its end face, is collimated by the Fresnel lens 2a, is reflected by the mirror 3, and returns to the optical waveguide 14 from the Fresnel lens 2a again. This is the measurement light.

Light with an intensity corresponding to the phase difference between the reference light returning through the leading waveguide 13 and the measurement light returning through the optical waveguide 14 is obtained in the optical waveguide 12,
It is sent to a measuring device via an optical fiber 32.

In addition to the effects of the invention, this invention provides a compact Fresnel
Since a lens is used, a compact optical displacement sensor can be created. Furthermore, since the Fresnel lens formed on the substrate can be made using a female mold as mentioned above, it can be provided at a low cost, and with the electron beam lithography method, it is possible to make lenses with little aberration by controlling the CPU. It is possible. Since a small Fresnel lens is used, a parallel beam with a minute diameter of about several hundred μm can be formed, and the IJI area of the object to be measured can be made small.

Since two or more Fresnel lenses can be easily fabricated on one substrate, it can be applied to the above-mentioned twin type optical displacement sensor, and this optical displacement sensor can also be miniaturized. can.

[Brief explanation of drawings]

° Fig. 1 is a cross-sectional view showing a substrate on which a Fresnel lens is formed, Fig. 2 is a configuration diagram showing how the Fresnel lens formed on the substrate is applied to an optical fiber type optical displacement sensor; FIG. 3 is a configuration diagram showing how the same Fresnel lens is applied to a waveguide type optical displacement sensor. 2... Board. 2a...Fresnel lens. 2b...Half mirror. 3...Object to be measured or mirror. 21... Reflective film. that's all

Claims (1)

[Claims] In an optical displacement sensor that measures the displacement of an object to be measured using an intensity modulation signal resulting from interference between a reference beam reflected by a fixed mirror and a measurement beam reflected by an object to be measured, the measurement light beam is spread onto a flat plate. An optical displacement sensor characterized by collimating irradiation onto an object to be measured using a formed Fresnel lens.