JPH0652163B2 - Waveguide optical displacement sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION At least two optical waveguides for optical interference are formed on a substrate, and a movable mirror that moves together with an object to be measured has a V-shaped reflecting surface. , Lens means is provided between the emitting end of the optical waveguide of the substrate and the emitting surface of the movable mirror,
The lens means collimates the signal light emitted from the emitting end toward the reflecting surface, collects the reflected light from the reflecting surface at the emitting end, and further collects the at least two light guides. A waveguide type optical displacement sensor, wherein a phase shift means is provided on one side of the waveguide.

BACKGROUND OF THE INVENTION The present invention produces a Michelson interferometer using an optical waveguide on a substrate, and a reference light reflected by a reflection surface on the substrate and a signal light reflected by a reflection surface on an object to be measured outside the substrate. The present invention relates to a waveguide type optical displacement sensor that measures a displacement amount of an object to be measured based on a change in light intensity due to interference of light.

In such a waveguide type optical displacement sensor, it is unavoidable that the signal light emitted from the three-dimensional optical waveguide of the substrate is diffused, and therefore is reflected by the reflection surface of the object to be measured and returned to the optical waveguide of the substrate. There is a problem that the amount of incident light is reduced. If the displacement of the measured object is extremely small (for example, about several tens of μm), a considerable amount of reflected light returns to the optical waveguide of the substrate, but when the displacement of the measured object becomes large, a measurable amount of signal light is no longer obtained. I will not be able to.

In addition, the conventional guided-wave optical displacement sensor cannot determine the displacement direction of the measured object.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a waveguide type optical displacement sensor having a long displacement measuring distance and capable of discriminating a displacement direction.

A waveguide type optical displacement sensor according to the present invention has a substrate on which at least two optical waveguides for optical interference are formed, two inclined reflecting surfaces intersecting at an angle smaller than 180 °,
A movable mirror that moves together with the object to be measured, provided between the emitting ends of the two optical waveguides of the substrate and the reflecting surface of the movable mirror,
Lens means for collimating the signal light output from the emitting end toward the reflecting surface and condensing the reflected light on the reflecting surface at the emitting end, and the at least two optical waveguides. It is characterized in that it is provided with a phase shift means for the guided light provided on one side and a reflecting means formed on the end face of the optical waveguide of the substrate for obtaining the reference light.

In the process in which the signal light and the reference light propagate through the optical waveguide of the substrate, these two lights interfere with each other, and interference light having 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 measured object. Therefore, the displacement amount of the measured object is measured by 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 lens means and hits the reflecting surface of the movable mirror. The reflected light from the reflecting surface is condensed by the lens means and the two optical waveguides of the substrate. Incident on each. Since the amount of signal light incident on each of the optical waveguides of the substrate hardly changes even when the object to be measured, that is, the movable mirror is largely displaced, a long measurement distance can be obtained.

Since one lens means is sufficient for two signal lights, the structure is simple.

Phase shift means is provided on one of the at least two optical waveguides. Therefore, the periodic changes in the interference light intensity obtained from both optical waveguides are shifted from each other by the phase amount corresponding to the phase forcedly shifted by the phase shift means. It is possible to discriminate the moving direction of the measured object by the phase shift of these two interference lights.

The reflection 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 the metal thin film, the amount of light reflected by the metal thin film, that is, the reference light intensity can be controlled. By setting the reference light intensity to be approximately the same as the signal light intensity, it is possible to improve the extinction ratio of the change in the light intensity of the interference light. If the extinction ratio is good, the subsequent optical signal processing will be easy.

Description of Embodiments FIG. 1 shows an example of a waveguide type optical displacement sensor according to the present invention.
FIG. 2 shows the entire displacement measuring system.

Two asymmetric X-branch optical waveguides 10 and 20 are formed by thermally diffusing Ti into the substrate 1, for example, LiNbO ₃ . The optical waveguide 10 includes four optical waveguides 11 to 14, and the optical waveguide 10 has these optical waveguides 11 to 14 at X at one end thereof.
The optical waveguide 12
Is made narrower than the widths of the other optical waveguides 11, 13, and 14. Similarly, the optical waveguide 20 has four optical waveguides 21 to 24.
It consists of The optical waveguides 11 and 21 are commonly formed at their input ends, and are branched into Y-shapes toward their X-shaped coupling portions. Details of such an asymmetric X-branch optical waveguide are disclosed in Japanese Patent Application Laid-Open No. 58-202406 (Japanese Patent Application No. 57-86178) as a waveguide type optical beam splitter.

The operation of the asymmetrical X-branch optical waveguide 10 (same for the same 20) will be described below in the range related to this embodiment. The light propagating through the optical waveguide 11 equally branches into the two optical waveguides 13 and 14 and proceeds. The light propagating through the optical waveguides 13 and 14 toward the X-shaped coupling portion returns to the optical waveguide 11 when the phases of these lights are the same. When the light in the optical waveguides 13 and 14 have opposite phases (phases differ by 180 °), these lights travel to the optical waveguide 12. Therefore, the optical waveguide 12,
Light having an intensity corresponding to the phase difference of the light traveling from 14 to the X-shaped coupling portion can be obtained.

The above description is similarly applied even if the optical waveguides 11 and 12 and the optical waveguides 13 and 14 are exchanged.

An input optical fiber 31 is provided at the ends of the common input ends of the optical waveguides 11 and 21, and an output optical fiber 3 is provided at the ends of the optical waveguides 12 and 22.
2 and 33 are connected respectively. Input optical fiber 31
For this, a polarization-maintaining optical fiber is used. The laser light from the laser light source 41 is isolated by the isolator 42 and the lens.
It is introduced into the optical fiber 31 via 43. Isolator 42
Allows the light to travel from the laser 41 to the optical fiber 31, and blocks the light traveling in the opposite direction, and performs this action based on the polarization direction of the light. Output optical fiber 32,
A multi-marred optical fiber is used as 33.
The output lights guided by these optical fibers 32 and 33 are incident on the light receiving elements 44A and 44B, respectively, and are converted into electric signals representing their light intensities.

Reflective films 5 and 6 are formed on the end faces of the optical waveguides 13 and 23 of the substrate 1 by depositing Au. In the asymmetric X-branch optical waveguide 10, the optical waveguide is guided to the optical waveguide 11 and
Of the light equally branched to 13 and 14, the light traveling through the optical waveguide 14 is reflected by the reflective film 5 and goes to the X-shaped coupling portion. This light is the reference light. The intensity of the reference light can be determined by the film thickness of the reflective film 5. Also in the asymmetrical X-branch optical waveguide 20, the reference light can be similarly obtained from the optical waveguide 24.

The movable mirror 4, which is the object to be measured itself or is attached to or in contact with the object to be measured, has two reflecting surfaces intersecting at an angle of 180 ° or less. Board 1
A rod lens (gradient index lens) 3 is provided between the end faces of the optical waveguides 13 and 23 and the movable mirror 4, and is fixed by an appropriate fixing means. Third
As shown in the enlarged view of the figure, the light emitted from the optical waveguide 13 is collimated by the lens 3 and the movable mirror 4
Toward one of the reflective surfaces. The light emitted from the optical waveguide 23 is collimated by the lens 3 and goes to the other reflecting surface of the movable mirror 4. These lights are reflected vertically by the reflecting surface of the movable mirror 4 and follow the same optical path as the rod.
The light returns to the lens 3, is condensed by the lens 3, and enters the optical waveguides 13 and 23, respectively. Optical waveguide 13,
The light incident on 23 propagates toward the X-shaped coupling portion. These lights are signal lights.

Since the light traveling from the rod lens 3 to the movable mirror 4 and the reflected light from the movable mirror 4 are collimated, even if the movable mirror 4 is largely displaced, there is almost no change in the amount of light incident on the optical waveguides 13 and 23. Moreover, since the light incident on the optical waveguides 13 and 23 is condensed, the coupling efficiency is high and a large amount of output light can be obtained.

First, the displacement measurement principle will be described. One optical waveguide 10
Only pay attention to.

As described above, the output light having the intensity corresponding to the phase difference between the reference light of the optical waveguide 14 and the signal light of the optical waveguide 13 is obtained in the optical waveguide 12, and this output light is guided to the light receiving element 44A by the optical fiber 32. Get burned. 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. A change in the output light intensity with respect to the displacement amount (optical path difference) is shown by a solid line in FIG. The output light intensity changes sinusoidally with a cycle of λ (light wavelength) with respect to a change in optical path difference.

The displacement L of the movable mirror 4 and the optical path difference Δl have the following relationship. FIG. 4 schematically shows light that reciprocates between the rod lens 3 and the movable mirror 4. The angle formed by the moving direction of the movable mirror 4 and the collimated signal light is θ. Then, the following equation holds.

Δl / 2 = L · cos θ (1) From this, the displacement amount L is expressed as L = Δl / 2 · cos θ (2).

Since the optical path difference Δl is represented by the output of the counter described below, the displacement amount L of the movable mirror 4 can be measured from the equation (2).

The output optical signal of the optical waveguide 12 transmitted by the output optical fiber 32 is converted into an electric signal by the light receiving element 44A, and then level discrimination is performed by the circuit 45A having two threshold levels S1 and S2 of high and low. And binarized (see FIG. 5). The counter 46A counts the rising and / or falling of the binary signal. This count value represents the optical path difference Δl.

Next, the displacement direction determination principle will be described.

In the other optical waveguide 20, basically, the same operation as that of the optical waveguide 10 is performed, and the light receiving element 44B, the threshold circuit 45B and the counter 46B are the same as those described above for the output light guided by the optical fiber 33. Works the same as.

In the asymmetric X-branch optical waveguide 20, the optical waveguide 24
Grooves 25 for phase shift are formed in the substrate 1 at positions on both sides of, and the phase of the reference light propagating through the optical waveguide 24 is shifted by a predetermined amount. As a result, the output light obtained from the optical waveguide 22 is out of phase with the output light obtained from the optical waveguide 12, as shown by the broken line in FIG. In this embodiment, the output light intensity is phase-shifted by 1/8 cycle. Therefore, the binary signal obtained from the threshold circuit 45B is also out of phase with the output binary signal of the circuit 45A as indicated by the broken line.

Such a binary signal is detected by the differentiating circuits 47A and 47B to rise and / or fall, and the differentiated signal is input to the direction discriminating circuit 48.

When the movable mirror 4 moves 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 same circuit 45B, and the movable mirror 4 moves. When moving in the opposite direction, the order of change of these two signals is reversed. The discriminating circuit 48 discriminates the moving direction of the movable mirror 4 based on the order in which the outputs of the two differentiating circuits 47A and 47B appear. The direction discriminating circuit 48 can also be configured by a CPU.

As means for imparting a phase shift to the light propagating through the optical waveguide of the substrate, there are means for applying voltage or pressure to the optical waveguide, a thin film such as SiO ₂ loaded on the optical waveguide, in addition to the above-mentioned groove.

The reflectance and transmittance of light at the exit ends of the optical waveguides 14 and 24 are determined by the thickness of the reflective films 5 and 6. Therefore, the ratio of the intensity of the reference light to the intensity of the signal light can be arbitrarily determined by controlling the thickness of the reflective films 5 and 6, and can be set to 1: 1. As a result, the extinction ratio of the change in the light intensity of the output light can be improved.

In the above embodiment, the asymmetric X-branch optical waveguides 10, 20 are provided on the substrate 1.
However, a Michelson-type interferometer can be constructed by using other optical waveguides. For example, Figure 6
It may be a Y-shaped optical waveguide as shown in (A), an optical waveguide including a directional coupler as shown in (B), or a single optical waveguide as shown in (C). In the configuration of FIG. 7 (C), the reflection films 5 and 6 are assumed to have a considerably high transmittance, and the light transmitted through the reflection films 5 and 6 becomes the signal light. The rod lens is omitted in these figures.

As the lens means, an ordinary convex lens, a micro lens or the like can be used in addition to the rod lens.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an example of a waveguide type optical displacement sensor, and FIG.
The figure is a block diagram showing the entire optical displacement measuring system, FIG. 3 is an enlarged view showing how the signal light is collimated and condensed by the lens, and FIG. 4 shows the relationship between the optical path difference and the displacement amount of the movable mirror. FIG. 5 is a waveform diagram showing the output light intensity and a binary signal created based on it, and FIG. 6 is a schematic plan view showing another example of the optical waveguide on the substrate. 1 ... Substrate, 3 ... Rod lens, 4 ... Movable mirror, 5, 6 ... Reflective film, 10, 20 ... Asymmetric X-branch optical waveguide, 11-14, 21-24 ... Optical waveguide, 25 …… Phase shift groove.

Claims (1)

[Claims] 1. A substrate on which at least two optical waveguides for optical interference are formed, a movable mirror having two inclined reflecting surfaces intersecting at an angle smaller than 180 °, and moving together with an object to be measured. Are provided between the emitting ends of the two optical waveguides and the reflecting surface of the movable mirror, and are used to collimate the signal light output from the emitting ends toward the reflecting surface and the reflected light on the reflecting surface. Are formed on the end face of the optical waveguide of the substrate for obtaining the reference light and the lens means for condensing each of the light at the emission end, the phase shift means for the guided light provided on one of the at least two optical waveguides, and the reference light. A waveguide type optical displacement sensor including a reflection means.