JPH0642910A - Optical interference apparatus - Google Patents

Abstract

PURPOSE:To reduce the number of optical elements and to make an apparatus light- weight, compact and to enable mass production with the present processing techniques, by dividing a beam of light into two at two surfaces of a plane parallel plate and by causing the two beam to interfere with each other. CONSTITUTION:Light from a light source 1 is converted to a parallel beam L0 by a lens 2 and enters a plane parallel plate 3, forming beam L1-L4. The beam L1 is a portion of the beam L0 which passes surface A, B, and the beam L2 is light passing the face A, reflected at the face B and further reflected at the face A to pass through the face B. The beam L3 is reflected light from the face A. The beam L4 is light emerging from the face A after passing through the face A and reflected at the face B. The beams L1, L2 are condensed by a lens 4 turned to electric signals by a first photodetector 5. Similarly, the beams L3, L4 are changed to electric signals by a second photodetector 7. Since the beam L2 is reflected twice by the plane parallel plate 3, the optical path is longer than that of the beam L1, resulting in a phase difference. The interference of the beams can be accordingly detected by the intensity, strong or weak of the electric signals of the photodetector 5. The same gone true for the detector 7. Since the lights are made to interfere with each other within the plate 3, the lights are not affected by the fluctuation of the outside air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical interference device used for measuring angles, temperatures and the like.

[0002]

2. Description of the Related Art An optical interference device forms interference fringes by utilizing the interference of light, analyzes the fringes, and measures various physical quantities such as distance, temperature, angle, refractive index of medium, and accuracy of optical elements. It is a device that does. The optical interferometer combines a plurality of mirrors to divide the light flux from the light source into two, give an optical path difference to them, and then cause them to interfere with each other, and two interferometers with different distances in a transparent substrate. There is a waveguide type interferometer in which the optical waveguide is formed and the optical path difference is used to interfere the light flux.

FIG. 8 shows an optical system of a well-known Michelson interferometer, which is an example of an interferometer using a mirror.

As shown in the figure, this conventional interferometer includes a laser light source 101, a first mirror 102 through which a light beam from the laser light source 101 is guided, a first convex lens 103,
The second convex lens 104 and the half mirror 105 are provided,
The half mirror 105 is arranged with its optical axis shifted with respect to the second convex lens 104. A mirror 106 is provided on the side where the light flux from the laser light source 101 is reflected by the half mirror 105, and a mirror 107 is provided on the side that transmits the half mirror 105. Mirrors 106, 1
A screen 108 is provided where the luminous flux is guided by the 07 and the half mirror 105.

In the interferometer having the above-described structure, the coherent light beam emitted from the laser light source 101 is reflected by the mirror 102 and converted into a parallel light beam having a large diameter by the two convex lenses 103 and 104. .
A part of this light flux is reflected by the half mirror 105, reaches the mirror 106, is further reflected by the mirror 106, and then is transmitted through the half mirror 105 to be reflected on the screen 10.
Up to 8. On the other hand, of the light flux entering the half mirror 105 from the second convex lens 104, the half mirror 105
The light flux that has passed through reaches the mirror 107 and is further reflected by the mirror 1.
It is reflected by 07. After that, the reflected light flux reaches the half mirror 105, is reflected by the half mirror 105, and reaches the screen 108. In this way, the light flux reflected by the mirror 106 and the light flux reflected by the mirror 107 interfere with each other on the screen 108, and as a result, interference fringes are observed.

A case where this interferometer is used as a highly accurate range finder will be described.

In this case, the optical parts other than the mirror 107 are fixed and the position of the mirror 107 is changed.
When the distance D between the end of the illustrated half mirror 105 and the mirror 107 changes by ¼ of the wavelength of the laser light source 101, the brightness of the interference fringes on the screen 108 is reversed.
Therefore, by measuring the number of times the light and dark are inverted, it is possible to measure a minute displacement of the laser light source 101 in the wavelength order.

FIG. 9 shows a case where an example of a waveguide type interferometer is used for temperature measurement.

This interferometer includes a laser light source 111 and a condenser lens 1 for receiving a light beam emitted from the laser light source 111.
12, a transparent substrate 113 having two curved waveguides 113a and 113b on which the light flux focused by the condenser lens 112 is incident, and a lens 114 for focusing the light flux emitted from the substrate 113, And a photodetector 115.

The waveguide 11 provided in the substrate 113
3a and 113b have a refractive index of the substrate 113 within the substrate 113.
A slightly higher portion is provided so that light propagates only in that portion. In the conventional example shown in FIG. 9, LiNbO ₃ is used as the substrate 113, and two curved waveguides 113a and 113b and two waveguides 1 having different distances are formed in the substrate 113 by a method called proton exchange.
Branching waveguide 1 which is a part for branching into 13a and 113b
13c and a multiplexing waveguide 113d, which is a portion where the two waveguides 113a and 113b merge, are manufactured. The width of these waveguides 113a, 113b, 113c, 113d is usually 3 to 4 μm.

In the interferometer having the structure as described above, the coherent light emitted from the laser light source 111 is guided from the end face of the substrate 113 into the waveguide by the condenser lens 112. The light guided into the waveguide is the branched waveguide 1
13c is divided into two, one of which is a curved waveguide 113a
And the other passes through another curved waveguide 113b, is multiplexed again by the multiplexing waveguide 113c, and is output from the end face of the substrate 113. The output light is focused on the photodetector 115 by the condenser lens 114, and the light intensity is measured by the photodetector 115.

The principle of temperature measurement by this interferometer will be described.

Since there is an optical path difference between the light passing through the curved waveguide 113a in the substrate 113 and the light passing through the curved waveguide 113b, there is a phase difference φ. When this optical path difference is 2L, the phase difference φ is expressed by the following equation.

[0014]

[Equation 1]

Since the substrate 113 made of LiNbO ₃ has a different refractive index n depending on temperature, as can be seen from the above equation,
The phase difference φ changes with temperature, and the signal detected by the photodetector 115 changes. The temperature can be measured from the change in this signal.

[0016]

In addition to the interferometer shown in FIG. 8, there are interferometers that use several types of mirrors such as the Maha-Zehnder type. However, all of them use optical elements such as several mirrors. It requires a space of several tens of cm square as a whole. The mirror support mechanism is required to have a fine adjustment mechanism for keeping the positional relationship between the mirrors stable with an accuracy equal to or less than the wavelength of the light source used, and for adjusting the optical axis of each mirror with high accuracy. Becomes large in size. Also, a strong surface plate for fixing the support mechanism and the fine adjustment mechanism is required. In addition, since the interference fringes also fluctuate when the air in the optical path fluctuates, some kind of enclosure surrounding the interferometer is also necessary.

On the other hand, the waveguide type interferometer shown in FIG. 9 can solve all the above problems, but the width of the waveguide is only 3 to 4 μm.
Since the distance is m, the alignment between the light flux output from the substrate 113 and the condenser lens 112 is delicate. Further, although research on optical waveguides has been vigorously pursued, the reality is that an industrial mass production method suitable for mass production has not been established.

The present invention has been made to solve the above-mentioned problems of the prior art, is a compact and lightweight device, can obtain a stable interferometer, and is mass-produced by the current optical element processing technology. It is an object of the present invention to provide an optical interference device that can be used.

[0019]

The optical interference device of the present invention comprises:
A light source; and a parallel plate having a first surface on which light from the light source is incident and a second surface parallel to the first surface. The light which is emitted without being reflected by either the first surface or the second surface and the light which is reflected by the second surface and the first surface in this order and is emitted from the second surface is separated. And / or the light reflected by the first surface among the light incident on the first surface and the second light that is not reflected by the first surface.
And is separated from the light emitted from the first surface and emitted from the first surface to cause interference, whereby the above object is achieved.

Alternatively, a light source, a parallel plate having a first surface on the side on which light from the light source is incident, and a second surface parallel to the first surface, and the first parallel plate. A first diffraction grating provided on the surface and a second diffraction grating provided on the second surface, and the first diffraction grating and the second diffraction grating among the incident light to the first diffraction grating Light which is diffracted and emitted in this order by the second diffraction grating and light which is reflected in this order by the second diffraction grating and the first diffraction grating and emitted from the second diffraction grating, And / or light incident on the first diffraction grating that is reflected by the first diffraction grating and the light that is diffracted by the first diffraction grating and reflected by the second diffraction grating The light is diffracted by the diffractive grating and is separated from the emitted light to generate interference, which achieves the above object.

[0021]

[Function] The incident light beam is divided into two by the two surfaces of the parallel plate,
Since the light flux divided in two is caused to interfere in the parallel plate,
The number of optical elements is significantly reduced, and the mutual positional relationship between the two planes of the parallel plate is kept stable.

The parallelism required for the two surfaces of the parallel plate is several seconds, which is a level that can be mass-produced by the current optical element processing technology.

[0023]

EXAMPLES The present invention will be described below with reference to examples.

(First Embodiment) FIG. 1A shows a schematic view of an optical interference device in an embodiment of the present invention.

The optical interference device of the present embodiment comprises a light source 1, a collimator lens 2 on which light from the light source 1 is incident, and a parallel plate 3 on which light from the collimator lens 2 is incident. On the side opposite to the collimator lens 2
Convex lens 4 and the first photodetector 5 are arranged in this order from the parallel plate 3 side, and in the direction of the light reflected by the parallel plate 3 among the light from the collimator lens 2, the second convex lens 4 and The two photodetectors 5 are arranged in this order from the side of the parallel plate 3.

The light source 1 emits coherent light and is, for example, a semiconductor laser. The parallel plate 3 is the light source 1
It is made of a material that is transparent to the light from, for example, glass, and has a thickness t1 and two opposing surfaces A and B. The surfaces A and B are optically polished and have a parallelism of several seconds. Such a parallel plate 3 can be sufficiently obtained by the current optical element processing technology.

The operation of the optical interference device having the above structure will be described.

The light emitted from the light source 1 is converted by the collimator lens 2 into a parallel light flux L0 and enters the parallel plate 3 as shown in the figure. A part of the light beam L0 incident on the parallel plate 3 is generated by the parallel plate 3 into light beams L1 to L4.

The light beam L1 is the light beam that passes through the surfaces A and B of the light beam L0. Of the light flux L0, the light flux L2 passes through the surface A, is reflected by the surface B, is further reflected by the surface A, and is reflected by the surface B.
Is the light that passes through. The light flux L3 is the light reflected by the surface A of the light flux L0. The light beam L4 is a light beam of the light beam L0 that has passed through the surface A, is reflected by the surface B, and is emitted from the surface A again. Since the surface A and the surface B are parallel to each other, the light flux L is inevitable.
1 and the light flux L2, and the light flux L3 and the light flux L4 are parallel to each other.

The light beams L1 and L2 are formed by the first convex lens 4
Is focused on the first photodetector 5 and converted into an electric signal by the first photodetector 5. On the other hand, the light flux L3 and the light flux L4 are condensed on the second photodetector 7 by the second convex lens 6 and converted into an electric signal by the second photodetector 7.

The interference of the light beams L1 and L2 detected by the first photodetector 5 will be described with reference to FIG. FIG. 1B is a diagram schematically showing the light reaching the first convex lens 4 in the optical interference device shown in FIG. The drawing shows the lens surface of the first convex lens 4, the circle on the lower side of the drawing shows the range reached by the light beam L1, and the circle on the upper side of the drawing shows the range reached by the light beam L2.

When the light flux L1 and the light flux L2 are compared, the light flux L
Since 2 is reflected twice in the parallel plate 3, the optical path of the light beam L2 is longer than that of the light beam L1. Therefore, a phase difference φ1 occurs between the light flux L2 and the light flux L1. The phase difference φ1 is expressed by the following equation.

[0033]

[Equation 2]

This phase difference φ1 is

[0035]

[Equation 3]

When the condition is satisfied, the portion where the light flux L1 and the light flux L2 overlap (shaded portion in FIG. 1B) becomes bright.
Also, the phase difference φ1 is

[0037]

[Equation 4]

When satisfying the condition, the portion where the light flux L1 and the light flux L2 overlap becomes dark. Therefore, the luminous flux L1 and the luminous flux L2 are changed depending on the strength of the electric signal obtained by the first photodetector 5.
Interference with can be detected.

A phase difference similar to the phase difference φ1 generated between the light flux L1 and the light flux L2 is also generated between the light flux L3 and the light flux L4 detected by the second photodetector 7. Therefore, as in the case of the interference between the light flux L1 and the light flux L2, the interference between the light flux L3 and the light flux L4 can be detected by the strength of the electric signal obtained by the second photodetector 7.

As described above, in the optical interference device of the present embodiment, since the light is interfered within the parallel plate 3, it is not affected by the fluctuation of the outside air.

It is not necessary to provide the set of the first convex lens 4 and the first photodetector 5 and the set of the second convex lens 6 and the second photodetector 7 at the same time. Even if only provided, it functions as an optical interference device. When both sets are provided, the output signals of the first photodetector 5 and the second photodetector 7 are in opposite phase, and it is possible to obtain a larger electric signal by taking the difference between the two. Is.

In the optical interference device of this embodiment, as can be seen from the above equation 2, when any of the incident angle θi1, the refractive index n, and the wavelength λ changes, the phase difference φ1 also changes, and the brightness of the interference fringes changes. To do. By utilizing this action, the optical interference device can be used as an angle sensor, a temperature sensor, or the like.

FIG. 2 shows a schematic diagram in the case of measuring rotation or temperature using the light flux L1 and the light flux L2 in the optical interference device shown in FIG.

In this optical interferometer, the set of the first convex lens 4 and the first photodetector 5 is used in the optical interferometer shown in FIG. 1, and the second convex lens 6 and the second photodetector 7 are used.
Is not used. A semiconductor laser is used as the light source 1. Since the oscillation wavelength λ of the semiconductor laser fluctuates depending on the ambient temperature, the light source 1 uses the heat sink 8 in order to avoid this.
It is attached to the Peltier element 9 via the and is kept at a constant temperature.

In this optical interferometer, the planes A and B of the parallel plate 3 are used to cause the light beams to interfere in the plane parallel plate 3, and the plane A and the plane B of the parallel plate 3 are mutually interfering with each other. The positional relationship is kept stable. As a result, the large-scale support mechanism and surface plate which are required in the conventional optical interference device are not required.

A case of measuring rotation using the optical interference device shown in FIG. 2 will be described.

When the parallel plate 3 rotates and the incident angle θi1 changes, the phase difference φ1 shown in Formula 2 increases and decreases, and the output obtained by the photodetector 5 becomes a sinusoidal waveform as shown in FIG. The period Xθi1 of the sine wave of FIG.

[0048]

[Equation 5]

Is given by With this optical interference device,
The rotation angle can be measured up to the order of the cycle Xθi1. For example, the wavelength λ of the light source 1 is 0.78 μm, the refractive index of the parallel plate 3 is n = 1.5, and the thickness of the parallel plate 3 is t1 = 1 m.
When m and the incident angle θi1 = 60 °, the output period Xθi1 = 1.10 (mrad) (about 0.063 deg) obtained by the photodetector 5 is obtained.

A case of measuring the temperature T using the optical interference device shown in FIG. 2 will be described.

When the temperature T changes, the refractive index n of the parallel plate 3
Changes. As a result, the phase difference φ1 shown in Formula 2 increases or decreases, and the output obtained by the photodetector 5 becomes a sinusoidal waveform as shown in FIG. 3, as in the case of measuring rotation. The cycle XT of the sine wave in FIG.

[0052]

[Equation 6]

Is given by With this optical interference device,
Temperatures can be measured up to the order of period XT.
For example, the wavelength λ of the light source 1 is 0.78 μm, the refractive index of the parallel plate 3 is n = 1.5, the thickness of the parallel plate 3 is t1 = 10 mm,
Incident angle θi1 = 60 °, (dn / dT) = 1 × 10 ⁻⁵ / d
Assuming that Eg, the period XT = 4.8 °.

Since these periods Xθi1 and XT are inversely proportional to the thickness t1 of the parallel plate 3 as apparent from the equations 5 and 6, by changing the thickness t1 of the parallel plate 3,
The periods Xθi1 and XT can be set freely. Therefore, by changing the settings of the cycles Xθi1 and XT, the measurement order of this optical interference device can be changed.

Further, as shown by the alternate long and short dash line in FIG.
By providing the slit 10 between the parallel plate 3 and the convex lenses 4 and 6, the S / N ratio of the electric signal obtained by the photodetectors 5 and 7 can be improved. The S / N ratio is the ratio between the amplitude of the signal to be received and the amplitude of the noise signal.

The method of setting the slit 10 and the S / N ratio will be described below.
The principle of improving the ratio will be described with reference to FIGS.

The positional deviation S between the light beam L1 and the light beam L2 shown in FIG.

[0058]

[Equation 7]

Is given by Since interference occurs only at the overlapping portion of the light flux L1 and the light flux L2, the light flux of the non-overlapping portion of the light flux L1 and the light flux L2 is shielded as shown in FIG.
The slit 10 shown in is added. As a result, unnecessary light is removed by the slit 10, and the S / N ratio of the signal obtained by the photodetector 5 can be improved.

In the above, the interference between the light flux L1 and the light flux L2 has been described, but the same applies to the light flux L3 and the light flux L4.

The degree of modulation of the signal due to the interference obtained by the photodetectors 5 and 7 is determined by the transmittance T of the plane A of the parallel plate 3.
_{It is determined by A} and the reflectance R _A, and the transmittance T _B and the reflectance R _{B of the} surface B. If the intensities of the light beams L0 to L4 are I0 to I4, the intensities I0 to I4 can be expressed as follows.

[0062]

[Equation 8]

The modulation m12 of the interference signal obtained by the photodetector 5 is

[0064]

[Equation 9]

Therefore, the maximum value should be obtained when I1 = I2. However, in this case, from equations 8 (1) and (2),

[0066]

[Equation 10]

Thus, R _A = R _B = 1 (T _A = T _B = 0). This cannot be achieved in practice. Therefore, in this case, T _A = R _A = 0.
5, T _B = R _B = 0.5 is preferable.

On the other hand, similarly, the modulation degree m34 of the interference signal obtained by the photodetector 7 becomes maximum when I3 = I4. At this time, the reflectances R _A and R _B and the transmittances T _A and T _B are

[0069]

[Equation 11]

It is obtained by solving For example, R
_{If B} = 1 then T _A = 0.618 and R _A = 0.382. That is, surface A functions as a beam splitter and surface B
Acts as a mirror.

(Second Embodiment) FIG. 4 shows an optical interference device according to another embodiment of the present invention. The same members as those in FIG. 1 have the same reference numerals.

The optical interference device of this embodiment uses a parallel plate 11 having a structure different from that of the parallel plate 3 instead of the parallel plate 3 shown in FIG.

The parallel plate 11 is made of a material transparent to the light from the light source 1, for example, glass, and has a thickness t2 and two opposite surfaces C and D. The surfaces C and D are optically polished and have a parallelism of several seconds. The surface C and the surface D are provided with fine diffraction gratings 12C and 12D, respectively, each having a grating spacing of about the same as the wavelength of light. When the grating spacing of the diffraction gratings 12C and 12D is reduced to the wavelength of light, the diffraction gratings 12C and 12D have so-called polarization characteristics, and diffraction may or may not occur depending on the polarization direction of the light (“Dielectric surcure”).
face-relief gratings with
high diffraction effect
ncy ”, K. Yokomori, Applied
Optics Vol. 23, No. 14, p2
302 (1984)).

The diffraction grating 12 having the above structure
In C and 12D, among the light fluxes incident on the diffraction gratings 12C and 12D, as shown by the arrows in FIG. 5, in the case of P waves whose polarization directions are up and down in the plane of the drawing, no diffraction occurs. The light passes through the diffraction gratings 12C and 12D. However, in the case of an S wave whose polarization direction is perpendicular to the paper surface, diffraction is caused by the diffraction gratings 12C and 12D. If the diffraction grating 12C and the diffraction grating 12D are equivalent, the light beam L21 is emitted by two times of diffraction, and the light beam L22 is emitted by two times of diffraction and two reflections on the surfaces C and D ( Japanese Patent Application No. 1-81707).

When light having a wavelength of 0.78 μm is incident on such diffraction gratings 12C and 12D, the refractive index n = 1.45 of the parallel plate 11, the incident angle θi2 = 58 °, the grating interval 0.46 μm, the grating Is 1 μm, the transmittance T _P = P wave in the diffraction gratings 12C and 12D
0.99, reflectance R _P is almost 0, diffraction efficiency n _p = 0.01
The transmittance T _s for S wave is approximately 0.01, the reflectance R _s = 0.07, and the diffraction efficiency n _s = 0.92.

The operation of the optical interference device having the above structure will be described below.

As shown in FIG. 4, the S wave emitted from the light source 1 is converted into a parallel light beam L20 by the collimator lens 2 and diffracted or reflected by the diffraction gratings 12C and 12D to generate light beams L21 to L24.

The light beam L21 is a light beam which is diffracted by the diffraction grating 12C, then diffracted by the diffraction grating 12D, and immediately emitted. The light beam L22 is a light beam which is diffracted by the diffraction grating 12C, reflected by the diffraction grating 12D, further reflected by the diffraction grating 12C, diffracted by the diffraction grating 12D, and emitted. The light flux L23 is a light flux reflected by the diffraction grating 12C. The light beam L24 is a light beam which is diffracted by the diffraction grating 12C, reflected by the diffraction grating 12D, diffracted by the diffraction grating 12C again, and emitted. Since the surface C and the surface D are parallel to each other, the light fluxes L21 and L22, and the light fluxes L23 and L24 are inevitable.
And are parallel to each other.

The light beam L21 and the light beam L22 are condensed on the first photodetector 5 by the first convex lens 4 and converted into an electric signal by the first photodetector 5. On the other hand, the light flux L23 and the light flux L24 are condensed on the second photodetector 7 by the second convex lens 6 and converted into an electric signal by the second photodetector 7.

Comparing the light flux L21 and the light flux L22 detected by the first photodetector 5, the light flux L22 is reflected twice in the parallel plate 11, so that the optical path of the light flux L22 is the light flux L22.
It is longer than 21 optical paths. Therefore, a phase difference φ2 occurs between the light flux L22 and the light flux L21. The phase difference φ2 is expressed by the following equation.

[0081]

[Equation 12]

This phase difference φ2 is

[0083]

[Equation 13]

When the condition is satisfied, the overlapping portion of the light flux L21 and the light flux L22 becomes bright. Also, the phase difference φ2 is

[0085]

[Equation 14]

When satisfying the condition, the portion where the light flux L21 and the light flux L22 overlap becomes dark. Therefore, the interference between the light flux L21 and the light flux L22 can be detected depending on the strength of the electric signal obtained by the first photodetector 5.

A phase difference similar to the phase difference φ2 generated between the light flux L21 and the light flux L22 is also generated between the light flux L23 and the light flux L24 detected by the second photodetector 7. Therefore,
Similar to the case of the interference between the light flux L21 and the light flux L22, the interference between the light flux L23 and the light flux L24 can be detected by the strength of the electric signal obtained by the second photodetector 7.

As described above, also in the optical interference device of the present embodiment, as in the first embodiment, since the light is interfered within the parallel plate 11, it is not affected by the fluctuation of the outside air.

It is not necessary to provide the set of the first convex lens 4 and the first photodetector 5 and the set of the second convex lens 6 and the second photodetector 7 at the same time. Even if only provided, it functions as an optical interference device. When both sets are provided, the output signals of the first photodetector 5 and the second photodetector 7 are in opposite phase, and it is possible to obtain a larger electric signal by taking the difference between the two. Is.

In the optical interference device of the present embodiment, as can be seen from the above formula 12, the incident angle θi2, the refractive index n, the wavelength λ.
If any of the above changes, the phase difference φ2 also changes, and the contrast of the interference fringes changes. Utilizing this action, this optical interference device can be applied to, for example, an angle sensor, a temperature sensor, etc., as in the first embodiment.

FIG. 6 shows a schematic diagram in the case of measuring rotation or temperature using the light flux L21 and the light flux L22 in the optical interference device shown in FIG.

In this optical interference device, as in the first embodiment, a semiconductor laser is used as the light source 1, and the light source 1
The light source 1 is attached to the Peltier element 9 via a heat sink 8 in order to keep the temperature of the constant. In the optical interference device shown in FIG. 4, the set of the first convex lens 4 and the first photodetector 5 is used, and the set of the second convex lens 6 and the second photodetector 7 is not used. The photodetector 5 has two photodetectors 5a and 5b. An electric signal Sa is obtained from the photodetector 5a and an electric signal Sb is obtained from the photodetector 5b.

Also in this optical interference device, as in the first embodiment, the diffraction grating 12 provided on the parallel plate 11 is used.
C and the diffraction grating 12D are used to cause the light beams to interfere in the parallel plate 11, and the mutual positional relationship between the diffraction grating C and the diffraction grating D is kept stable. As a result, the large-scale support mechanism and surface plate which are required in the conventional optical interference device are not required.

The operation of the optical interference device having such a configuration will be described.

As described above, the light flux which has passed through the parallel plate 11 is focused on the photodetector 5 by the convex lens 4. At this time, the converging points of the P wave and the S wave can be changed by slightly differentiating the grating spacing between the diffraction grating 12C and the diffraction grating 12D or slightly shifting the grating direction (Japanese Patent Application No. 2- No. 158076, Japanese Patent Application No. 2-22632
No. 0). By utilizing this, the P wave shown by the one-dot chain line in FIG. 6 is focused on the photodetector 5a, and the S wave shown by the solid line is focused on the photodetector 5b. Therefore, the electric signal Sa represents the intensity of the P wave, and the electric signal Sb represents the intensity of the S wave.

A case of measuring rotation or temperature using the optical interference device shown in FIG. 6 will be described.

When the parallel plate 11 is rotated to change the incident angle θi2 or the temperature T is changed to change the refractive index n, the phase difference φ3 shown in Formula 13 increases or decreases in the case of S wave.
The electric signal Sb obtained by the photodetector 5b changes in a sine wave shape as shown in FIG. On the other hand, in the case of P wave,
As described above, since the transmittances of the diffraction gratings 12C and 12D are almost 100%, no interference occurs, and the electric signal Sa obtained by the photodetector 5a is constant regardless of the incident angle θi2 and the temperature T. Therefore, by dividing the electric signal Sb by the electric signal Sa and normalizing the electric signal Sa, it is possible to remove an error caused by an output fluctuation of the light source 1.

The period Y of the sine wave of the electric signal Sb shown in FIG.
Is the change in the incident angle θi2,

[0099]

[Equation 15]

And, for temperature T,

[0101]

[Equation 16]

Thus, the cycle is almost the same as that of the first embodiment.

Further, similarly to the first embodiment, the diffraction grating 12
The degree of modulation of the electric signal Sb can be changed by changing the diffraction efficiency of C and 12D.

[0104]

As is apparent from the above description, according to the optical interference device of the present invention, the number of optical elements is reduced, so that not only the device can be made smaller and lighter, but also interference can be achieved in a parallel plate. As it is generated, the positional relationship between each optical element is kept stable and is not affected by the fluctuation of the outside air. As a result, a large supporting mechanism and a surface plate are not required, and a relatively high accuracy, such as an angle sensor, etc. Can be obtained.

Further, since the parallel plate, which is a constituent feature of the optical interference device of the present invention, can be mass-produced by the current optical element processing technology, the production cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical interference device according to a first embodiment of the present invention.

2 is a schematic diagram of an angle (temperature) sensor using the optical interference device shown in FIG.

FIG. 3 is a diagram showing an output signal of a photodetector with respect to an angle (temperature) of the optical interference device shown in FIG.

FIG. 4 is a schematic diagram of an optical interference device according to a second embodiment of the present invention.

5 is a schematic view of a diffraction grating used in the optical interference device shown in FIG.

6 is a schematic view of an angle (temperature) sensor using the optical interference device shown in FIG.

7 is a diagram showing an output signal of a photodetector with respect to an angle (temperature) of the optical interference device shown in FIG.

FIG. 8 is a diagram showing a conventional optical interference device.

FIG. 9 is a diagram showing another conventional optical interference device.

[Explanation of symbols]

 1 light source 2 collimator lens 3, 11 parallel plate 4, 6 convex lens 5, 7 photodetector 10 slit 12C, 12D diffraction grating L0 to L4, L20 to L24 luminous flux

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Ueyama 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Co., Ltd. Incorporated (72) Inventor Yukio Kurata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (2)

[Claims] 1. A light source and a first light source to which light from the light source is incident.
Surface and a parallel plate having a second surface parallel to the first surface, and reflects either of the first surface and the second surface of the incident light on the first surface. The light that is emitted without being separated from the light that is reflected by the second surface and the first surface in this order and emitted from the second surface, and / or is incident on the first surface. Interference occurs by separating the light reflected by the first surface from the light reflected by the second surface without being reflected by the first surface and emitted from the first surface. Optical interference device. 2. A light source, a parallel plate having a first surface on the side on which light from the light source enters, and a parallel plate having a second surface parallel to the first surface, and the first surface. A first diffraction grating provided above and a second diffraction grating provided on the second surface, wherein the first diffraction grating and the second diffraction grating among the incident light to the first diffraction grating Light which is diffracted and emitted in this order by the second diffraction grating and light which is reflected in this order by the second diffraction grating and the first diffraction grating and emitted from the second diffraction grating, and Or, of the incident light to the first diffraction grating, the light reflected by the first diffraction grating and the light reflected by the first diffraction grating and reflected by the second diffraction grating An optical interference device that generates interference by separating the light that is diffracted by the diffraction grating and emitted.