JPH11271016A - Interference measurement signal forming device - Google Patents

Abstract

(57) [Problem] To make the optical adjustment simple and ultra-compact, and to minimize the influence on the wavelength fluctuation of the laser light source. SOLUTION: Coherent light output from a light source unit 1 is input to a light emitting system 3 through a coupling unit 2 while maintaining a polarization plane. In the light emitting system 3, each light beam is subjected to phase modulation of substantially the same amplitude and opposite sign to emit at least two irradiation light beams. The irradiation optical system 4 condenses and deflects these irradiation light beams, respectively, and irradiates the measurement points of the scale unit 5. In the scale unit 5, at least two irradiation light beams are diffracted in substantially the same direction, and these two diffracted light beams are both incident on the light receiving system 6. In the light receiving system 6, the diffracted light beam is received and guided to the light receiving unit 7, and the light receiving unit 7 receives the light and converts it into an electric reception signal. Based on the signal received by the light receiving unit 7,
The components are analyzed by the displacement measuring section 8 and the displacement of the scale section 5 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference measurement signal forming apparatus, and more particularly to an interference measurement signal forming apparatus used for an interference measurement apparatus for measuring a displacement of a scale section.

2. Description of the Related Art FIG. 16 shows a configuration diagram of a conventional interference measuring device.

A conventional interference measuring device (encoder)
Laser diode 101, collimating lens 102, deflection beam splitter 103, reflecting members 104a and 104
4b, diffraction gratings 105a and 105b, scale 10
6, 1/4 wavelength plate 107, beam splitter 108, polarizing plates 109a and 109b, detectors 110a and 110
b, a reflecting mirror 111 is provided.

The coherent light emitted from the laser diode 101 is collimated (parallel luminous flux) by a collimating lens 102 and split by a deflection beam splitter 103 into P deflection in the transmission direction and S deflection in the reflection direction. The deflected light flux is reflected by the reflection members 104a and 104
b irradiates the diffraction gratings 105a and 105b vertically. The diffracted light beams LD2 and LD1 are emitted from two directions of the measurement diffraction grating 106A on the scale 6, diffracted and reflected, reflected in the vertical direction of the measurement diffraction grating 106A of the scale 106, and re-diffraction of ± m order. Optical LD1 (m) and LD
2 (-m) travels on the same optical path toward the detection system. These re-diffracted lights are orthogonally polarized, pass through the quarter-wave plate 107 via the reflecting mirror 111, and become mutually circularly polarized. The beam is split into two optical paths by a beam splitter 108 and the detector 11
Photoelectrically detected by 0a and 110b.

[0004]

However, in the conventional interferometer, although a countermeasure is taken against the wavelength fluctuation of the laser as a light source, since a large number of individual components are required as described above, There were restrictions on miniaturization. Conventionally, since a large number of components are mounted, it has been difficult to adjust the optical arrangement of these components.

Further, in the prior art, in view of the above, it is an object of the present invention to reduce the number of optical components to reduce the size and to make optical adjustment simple and easy. It is another object of the present invention to provide a highly accurate and inexpensive interference measurement signal forming apparatus capable of realizing an ultra-compact and rigid interference optical system, stabilizing an output signal. Another object of the present invention is to minimize the influence of the wavelength variation of the laser light source as much as possible and achieve excellent stability.

Further, in the present invention, by using a waveguide device to which the phase modulation type heterodyne interferometry is applied, it is resistant to the fluctuation of the amount of received light, only one detector is used, and the direction of the displacement can be discriminated. It is an object of the present invention to provide a simple interference measurement signal forming apparatus.

Further, according to the present invention, by using a zone plate lens (ZPL), both the condensing and deflecting functions are realized by a single element, whereby the mounting is simplified and the whole module is reduced in size. The purpose is to make.

[0008]

According to the present invention, there is provided an incident waveguide for guiding a coherent irradiation light beam from a light source unit, and a branch waveguide for branching the light beam from the incident waveguide into at least two light beams. And at least two emission waveguides branched by the branch waveguide, and a phase modulator for phase-modulating a light flux of at least one emission waveguide are formed on one surface of the optical substrate, and at least two irradiations are performed. A light-emitting system that forms a light beam, and an irradiation optical system that has a diffractive lens such as a Fresnel zone plate, and irradiates at least two irradiation light beams emitted from the light-emitting system to measurement points of the diffraction grating in the scale section; At least two irradiation light beams, which are disposed so as to be displaceable with respect to the light emitting system and are irradiated by the irradiation optical system, are diffracted by a diffraction grating formed on the surface, and are substantially in the same direction. A scale section that forms a diffracted light beam,
Provided is an interference measurement signal forming apparatus, comprising: a light receiving system that receives a diffracted light beam diffracted by the scale unit; and a light receiving unit that receives the diffracted light beam received by the light receiving system and forms a light receiving signal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Interference Measurement Signal Forming Apparatus FIG. 1 shows a configuration diagram of an interference measurement signal forming apparatus according to the present invention. FIG. 1A shows a plan view thereof, and FIG.
(B) shows a side view thereof.

The interference measurement signal forming apparatus includes a light source unit 1, a coupling unit 2, a light emitting system 3, an irradiation optical system 4, a scale unit 5, a light receiving system 6, a light receiving unit 7, and a displacement measuring unit 8.

The light source unit 1 is composed of, for example, a light emitting element for outputting coherent light such as a laser diode. The coupling unit 2 includes, for example, a lens and a polarization-maintaining single-mode fiber and the like. The coupling unit 2 inputs coherent light from the light source unit 1 to the coupling unit 3, and emits laser light emitted from the light source unit 1 to a light emitting unit. Supply 3 When a laser emitting random polarized light is used as the light source 1,
By providing a polarizer or the like, it is possible to appropriately convert the light into linearly polarized light having a polarization direction in the X or Y direction and to enter the light.

The light emitting system 3 is formed on an optical substrate 31 having an electro-optical effect, such as a lithium niobate crystal substrate or a lithium tantalate crystal substrate. On the optical substrate 31, for example, one X-cut type, Z-propagation type straight incident waveguide 32 is formed, and the optical waveguide 31 is further branched by a branch waveguide 33 into emission waveguides 34 and 35. A pair of electrodes for modulating the refractive index in the Y direction are arranged near the emission waveguides 34 and 35, and phase modulators 36 and 37 are formed, respectively. For example, a sine wave signal of a predetermined frequency and a phase modulation signal of substantially the same amplitude and opposite sign are applied to the electrodes of the phase modulators 36 and 37, respectively, to change the phase of the incident light beam. An example of the phase modulation signal, + sin (2πf _M t) and -sin (2πf _M t) and the like are used.

The irradiation optical system 4 is composed of, for example, a diffractive lens such as a Fresnel zone plate, a grating lens, and a diffractive zone plate lens (ZPL).
A diffraction grating is formed on the front or back surface of the scale section 5 at the position where light is irradiated, and the scale section 5 is displaced in the direction of the arrow.

In this example, the light receiving system 6 includes a block 61 composed of a socket or a ferrule of glass, plastic or the like, and an optical fiber 62 such as a multimode fiber. The light receiving unit 7 is configured by a light receiving element such as a photodiode. When the amount of light is insufficient, a condenser lens may be provided in front of the light receiving unit 7 or the like. The displacement measuring unit 8 performs a process of calculating the displacement of the scale 5 indicated by the arrow in the figure based on the received interference light.

Next, the operation of the above-described interference measurement signal forming apparatus will be described. First, the coherent light output from the light source unit 1 is input to the light emitting system 3 via the coupling unit 2 while maintaining the polarization plane. As described above, the light emitting system 3 emits at least two irradiation light beams by subjecting one light beam to phase modulation and applying the other light beam to phase modulation of substantially the same amplitude and opposite sign. In the irradiation optical system 4,
These irradiation light beams are condensed and deflected, respectively, and are irradiated on the measurement points of the scale section 5. In the scale unit 5, at least two irradiation light beams are diffracted in substantially the same direction, and these two diffracted light beams are both incident on the light receiving system 6. In the light receiving system 6, the diffracted light beam is received and guided to the light receiving unit 7, and the light receiving unit 7 receives the light and converts it into an electric reception signal. The displacement measuring unit 8 analyzes the components of the signal received by the light receiving unit 7 to determine the displacement of the scale unit 5.

(2) Design Conditions of Diffractive Lens such as Fresnel Zone Plate Next, a diffractive lens (diffractive zone plate lens)
As one example, the design conditions of an off-axis off-axis Fresnel zone plate (FZP) will be described.

FIG. 2 is an explanatory plan view showing the design of the focal length of the FZP. FIG. 2A is an explanatory view of air length conversion (air path), and FIG. 2B is an explanatory view in consideration of the thickness of the FZP glass substrate.

The setting of the focal length of the FZP is as follows. First, the wavelength of the laser of the light source unit 1 to be used is λ ₀ ,
The distance between the two exit waveguides 34 and 35 of the optical substrate is d,
The grating pitch of the scale unit 5 as a linear encoder is p, and the diffraction angle of the principal ray by the scale unit 5 is θ. In this case, the condition that the ± 1st-order diffracted light reflected from the scale section 5 is vertically reflected to the light receiving system 6 is sin θ = ± λ ₀ / p, and the focal length f _{0 of the} FZP is f ₀ = (d / 2) / tanθ is determined.

Here, for example, λ ₀ = 830 nm, p
= 10 μm and d = 250 μm, θ = 4.76
°, and f ₀ = 1.5 mm. When the thickness of a quartz substrate (for example, refractive index n = 1.46) for manufacturing FZP is 1.0 mm, the dimensions of the optical arrangement are as shown in FIG.
(B).

Next, the setting of the effective diameter (minimum value) of the FZP will be described. When the effective beam divergence angle (numerical aperture) NA of the light beam emitted from the waveguide is α, the effective diameter of the FZP is
It is required as follows. That is, the effective diameter Dx in the x direction (y = 0 cross section) is Dx = 2 × (2f
₀ tanα) -dy The effective diameter Dy in the y direction (x = 0 cross section) is Dy = 2 × (2f
₀ tan α) Here, for example, NA = 0.1, that is, α = 5.74 °
In this case, Dx = 0.35 mm and Dy = 0.3 mm.

Next, the setting of the exit angle of the exit chief ray from the exit waveguides 34 and 35 and the capture into the light receiving optical system will be described. FIG. 3 is a side view illustrating the design of the focal length of the FZP. FIG. 3A is an explanatory diagram of air length conversion (air path), and FIG.
FIG. 3 shows an explanatory diagram in which the thickness of P is considered.

Normally, when the end face of the optical substrate 31 is vertically polished, the light reflected on the end face returns to the light source unit 1 and the wavelength and output of the semiconductor laser become unstable. Therefore, in the present invention, in order to remove such return light, the emission-side end face of the light emitting system 3 is subjected to oblique polishing so that the measurement point of the scale section 5 is appropriately irradiated with the irradiation light beam. On the other hand, the incident-side end face of the light receiving system 6 is obliquely polished so that the diffracted light beam from the scale portion 5 is
To be properly incident.

That is, the optical substrate 31 having the emission waveguides 34 and 35 of the light-emitting system 3 and the block 61 having the optical fiber 62 of the light-receiving system 6 in the inner hole have the respective end faces in the emission direction of the irradiation light beam. Orthogonal plane (scale part 5
(A plane perpendicular to the direction of displacement) is formed obliquely so as to project from the respective surfaces toward the center toward the scale portion 5. As a result, the irradiation light flux refracted on the exit side end faces of the exit waveguides 34 and 35 is reflected and diffracted by the scale section 5, then refracted on the incident side end face of the light receiving system 6 and enters the optical fiber 62. It is configured as follows.

In the present invention, the optical substrate 31 is set so that the reflected light from the scale section 6 as a linear encoder does not reach the effective section of the FZP by setting the exit angle of the exit chief ray from the waveguide of the optical substrate 31. The polishing angle of the end face 31 is set.

Next, the setting of the polishing angle will be described.
FIG. 4 is an explanatory diagram of the polishing angle of the optical substrate.

First, assuming that the emission angle β, the thickness on the emission side of the optical substrate 31 is t ₁ , and the thickness on the light receiving side is t ₂ , the following equation is satisfied from FIG. That is, 2 · f ₀ tanβ = (t ₁ + t ₂ ) / 2 f ₀ tanβ ≧ Dy / 2 After obtaining the emission angle β satisfying such a condition, the polishing angle γ of the end face of the optical substrate is calculated as follows. decide. That is, n _s sin γ = sin (β + γ) (where n _s is the refractive index of the optical substrate 4) For example, when t ₁ = 1.0 mm and t ₂ = 0.4 mm are used as a guide, n _s = From 2.2, β = 13 °, γ = 1
0 °.

(3) Another Embodiment of Light Receiving System FIG. 5 shows a configuration diagram of an interference measurement signal forming apparatus according to a second embodiment of the present invention.

The first embodiment is an example in which a multi-mode fiber is attached to the back side of the optical substrate 31.
In the second embodiment shown in FIG. 5A, a waveguide 63 such as a three-dimensional waveguide is formed on the back surface of the optical substrate 31 as a light receiving system. This waveguide 63 is
The end face is obliquely polished so that the diffracted light beam received from the scale 5 easily enters the waveguide 63. An optical fiber 64 is provided in the waveguide 63 formed in the optical substrate 31.
Are connected and guided to the light receiving unit 7.

FIG. 5B shows a configuration diagram of a modification of the second embodiment of the interference measurement signal forming apparatus according to the present invention.
In this example, the light receiving element 73 is directly connected to the end surface of the waveguide 63 formed on the optical substrate 31 on the emission side. At this time, the light receiving element 73 such as a photodiode can be directly integrated on the optical substrate 31.

FIG. 6 shows a configuration diagram of a third embodiment of the interference measurement signal forming apparatus according to the present invention.

Here, the interdigital electrode (I
The optical spectrum analyzer 64 having the DT) is formed on the back surface of the optical substrate 31. In the third embodiment, by arranging such devices, optical integration up to a part of signal processing is realized. Such optical integration is made possible by adopting a phase modulation method.

The light receiving system of the optical spectrum analyzer 64 includes a two-dimensional device having an interdigital electrode (IDT) 65, two-dimensional waveguide lenses 66 and 67, and the like.
A two-dimensional waveguide device 68 is provided. The light receiving section 7 includes first and second light receiving elements 71 and 72, which are integrated or directly connected to the substrate end surface of the optical substrate 31. The connection may be made by an optical fiber.

The diffracted light beam received from the scale 5 is 3
The light enters the two-dimensional waveguide device 68. At this time, the end face of the three-dimensional waveguide device 68 is obliquely polished as described above so that the diffracted light beam is easily incident. Cross finger electrode 65
, A signal similar to the phase modulation frequency f _M of the phase modulators 36 and 37 of the light emitting system 3 is applied, and a surface acoustic wave (SAW) is formed. The diffracted light beam passes through the two-dimensional waveguide lens 66 and is diffracted by surface acoustic waves formed by the interdigital electrodes 65. Furthermore, through the two-dimensional waveguide lens 67, the phase modulation frequency f _M component is received by the first light receiving element 71, twice the 2f _M component of the phase modulation frequency is received by the second light receiving element 72 Is done.

FIG. 7 is a block diagram showing a fourth embodiment of the interference measurement signal forming apparatus according to the present invention.

In the above-described embodiment, the diffracted light beam is reflected by the stage 5, but in the fourth embodiment,
The stage 5 is of a transmission type, in which a diffracted light beam is transmitted. As the light receiving system 6, an optical fiber 69 is used.
By appropriately arranging with a block, ferrule, etc.,
The transmitted diffraction light beam is received. The light may be directly incident on the light receiving unit 7 and received without using the optical fiber 69. Also,
When the light receiving section is provided below the optical substrate, it can be mounted in a space-saving manner by appropriately installing a reflecting mirror.

(4) Stability to Wavelength Fluctuation FIG. 8 is an explanatory diagram of the stability to wavelength fluctuation according to the present invention. Here, an example of a transmission type will be described, but the same applies to a reflection type. In the figure, the principal ray is indicated by a dashed line.

FIG. 8A shows a state where the wavelength λ of the laser light source is equal to the set reference wavelength λ ₀ . In this case, the principal rays of the two diffracted light beams diffracted by the scale overlap and exit perpendicularly from the scale and enter a fiber or a waveguide of the light receiving system.

Next, FIG. 8B shows a state where the wavelength λ of the laser light source is larger than the set reference wavelength λ ₀ . In this case, the two diffracted light beams are slightly converged, and their chief rays are slightly shifted, but are emitted perpendicularly from the scale and become parallel. Then, in the cross-section light beam, the overlapping portion is incident on the fiber or waveguide of the light receiving system.

FIG. 8C shows the wavelength λ of the laser light source.
Is smaller than the setting reference wavelength λ ₀ . In this case, the two diffracted light beams are slightly divergent, and their chief rays, though slightly shifted, exit perpendicularly from the scale and become parallel. Then, similarly, in the cross-section light beam, the overlapping portion is incident on the fiber or the waveguide of the light receiving system.

As described above, even if the laser wavelength of the light source unit fluctuates and the diffraction angle changes, a part of the common light beam can be received by the light receiving system 6 and the light receiving unit 7 via the fiber. Therefore, the received light amount and the efficiency due to the wavelength fluctuation do not change, and the stability is excellent.

(5) Detailed Description of Device First, the zone plate lens (ZPL) will be described. FIG. 9 is an explanatory view of a Fresnel zone plate that mainly constitutes the irradiation optical system.

The principal rays of the two irradiation light beams emitted from the emission waveguides 34 and 35 of the light emitting system 3 pass through the effective light beam diameters 41 and 42, not at the center of the ZPL. Further, the outer shape of the ZPL pattern may be an elliptical shape in the horizontal direction instead of the circular shape, whereby the thickness in the vertical direction can be reduced.

The diffraction-type ZPL is composed of (1) a computer-generated precision hologram (CGH) precise design process using a computer, (2) a super-precision original plate production process using an electron beam lithography system, and (3) transfer / photolithography. It can be manufactured from various processes such as a processing process. As described above, according to the present invention, as a collimating lens for projection, a diffractive zone plate lens (ZP
By using L), an ultra-small short focal length and
It is easy to manufacture an off-axis oblique incidence stigmatic lens. Further, it can be made of flat glass, and can be made so that there is almost no variation in focal length and eccentricity.

The diffracted light beam reflected from the scale passes through a portion 43 of the flat glass on which no ZPL is formed. In the portion 43 through which the diffracted light beam passes, the size of the flat glass may be reduced so that the flat glass is appropriately cut or does not exist.

Next, FIG. 10 shows an example of a manufacturing process diagram of the light emitting system.

First, as shown in FIG. 10A, a metal 312 (for example, a metal film 312 (for example, LiNbO ₃ or TaNbO ₃ ) is formed on a surface of a single-crystal substrate 311 (for example, LiNbO ₃ or TaNbO ₃ ) by photolithography. , Ti). Next, as shown in FIG. 10B, the single crystal substrate 311 is heated in an electric furnace or the like, so that the metal 3
12 is thermally diffused into the substrate, so that a buried waveguide 313 having a pattern shape is formed. In the case of modulating the light passing through the embedded waveguide as in the phase modulation method, after forming the waveguide 313, the light control electrodes 314 and 315 are desired as shown in FIG. Can be formed. Light control electrode section 314
And 315, a metal material having good electric conductivity is used, and generally, for example, Au which is stable over time is deposited and used.

In this manner, as shown in FIG. 10D, the incident waveguide 32 on which the coherent light from the light source unit 1 enters, and the at least two exit waveguides 3 for emitting light.
4 and 35 and a branching waveguide 33 for branching the light in the input waveguide 32 into at least two output waveguides 34 and 35 are formed. Further, phase modulators 36 and 37 for modulating at least two light beams branched by the branching waveguide 33 in the emission waveguides 34 and 35 can be formed.

Next, FIG. 11 shows a configuration diagram of a modification of the light emitting system. In FIGS. 11A and 11B, the left diagram is a plan view, and the right diagram is a cross-sectional view of a portion where electrodes exist.

10 (D) and 11 (A) show, in particular, a Z or Y propagation type waveguide using an X-cut substrate, or an X propagation type waveguide using a Y-cut substrate. This is a light emitting system 3 in which a wave path is formed. The phase modulators 36 and 37 in FIG. 10D each have independent electrodes, but connect the electrodes formed inside the emission waveguides 34 and 35 to the ground E in common, while connecting the electrodes outside these. By connecting the formed electrodes in common to the phase modulation voltage, voltages of substantially the same amplitude and opposite signs can be applied to the electrodes of the two phase modulators 36 and 37. FIG. 11A shows a structure in which electrodes inside the emission waveguides 34 and 35 are commonly formed in consideration of such electrical connection.

In the case shown in FIG. 11B, an X or Y propagation type waveguide is formed by using a Z-cut substrate, or a Z-propagation type waveguide is formed by using a Y-cut substrate. The light emitting system 3. This is because the electrodes of the phase modulators 36 and 37 are formed above the emission waveguides 34 and 35, and the phase modulation voltage is connected to one of the electrodes and the ground E is connected to the other. It is possible to apply voltages of substantially the same amplitude and opposite signs to the modulators 36 and 37.

(6) Operation of Displacement Measurement Next, the principle of operation of displacement measurement by the interference measurement device will be described. FIG. 12 is a diagram illustrating interference with the push-pull phase modulation method. The operation principle will be described below with reference to FIG.

The modulation operation of the optical waveguide portion 34 (first passage) and the optical waveguide portion 35 (second passage) utilizes the Pockels effect of the LiNbO3 single crystal substrate.

Where r is the Pockels effect of the LiNbO3 single crystal substrate d is the spacing between the electrodes of the waveguide Ω is the modulation angular frequency V is the applied voltage w is the electrode length of the waveguide.

Therefore, when a voltage is applied with the following sine wave, the phases of the light waves in the first path and the second path are
It becomes like the following formula.

[0055]

(Equation 1) Therefore, the phase change of the light waves in the first path and the second path is as follows.

[0056]

(Equation 2) As described above, a characteristic of the push-pull phase modulation method is that the phase changes of the light waves in the X direction and the Y direction take the opposite sign with the same amplitude.

As described above, the first diffracted light beam U1 that has passed through the first path and undergoes phase modulation and has been reflected from the diffraction grating scale of the scale section 5 and has undergone phase modulation through the second path. With respect to the second diffracted light beam U2 reflected from the diffraction grating scale of the scale section 5, a phase difference due to the displacement ΔL of the diffraction grating scale, ΔΦ = 2πΔL / p, is generated, and is expressed by the following equation.

[0058]

(Equation 3) The interference light I obtained by combining and interfering these two light waves is obtained as follows.

[0059]

(Equation 4) When this is calculated, the fundamental wave component I (Ω) and the second harmonic wave component I (2Ω) are respectively expressed by the following equations.

[0060]

(Equation 5) Therefore, in the push-pull type, the phase difference with respect to the displacement amount is π / 2, which enables the direction discrimination function.

Next, a detailed configuration of the displacement measuring section will be described. In the displacement measuring unit 8, the fundamental wave components I (Ω) and 2
The displacement is measured based on the harmonic component I (2Ω). FIG.
FIG. 3 shows a configuration diagram of the displacement measuring unit.

The displacement measuring section 8 includes a signal extracting section 81 and a displacement measuring section 82. The signal extraction unit 81 extracts a fundamental wave signal having a frequency equal to the modulation frequency of the phase modulation unit and a second harmonic signal having a frequency twice as high as the modulation frequency of the output signal of the light receiving unit 7. That is, the bandpass filters 811 and 812,
The detection circuit 813 and 814 extract the fundamental wave component I (Ω) and the second harmonic component I (2Ω) as described above. Further, the displacement measuring unit 82 obtains the displacement of the measuring object from the phase of the signal extracted by the signal extracting unit 81 as in the following equation.

ΔL = p / 2 · (N + ΔΦ / 2π) where N is an integer and the displacement is (（) p
It is a count number that is counted each time it changes. ΔΦ
Is the fraction of the phase displacement within 2π.

As described above, the displacement measuring unit 8
The displacement amount ΔL of the scale unit 5 can be obtained directly from the type of signal. Further, the displacement measuring unit 8
By comparing the types of waveforms, it is possible to determine direction discrimination in which direction the displacement is occurring.

(7) Another Embodiment of Light Emitting System FIG. 14 shows a configuration diagram of a fifth embodiment of the interference measurement signal forming apparatus according to the present invention.

In the above embodiment, the optical substrate 31
A phase modulator 36 is provided in both of the two exit waveguides 34 and 35.
And 37 are provided. In the fifth embodiment shown in FIG. 14, the phase modulation is performed by providing the phase modulator 36 (or 37) only on one of the emission waveguides 34 (or 35) in the optical substrate 31 of the light emitting system 3. The other exit waveguide 35 (or 34) is not provided with a phase modulator, and the beam separated by the branch waveguide 33 is directly emitted. Emission waveguides 34 and 35
Are diffracted by the scale unit 5 and received by the light receiving system 6. For the scale unit 5, the light receiving system 6, and the displacement measuring unit 8, any one of the configurations of the above-described embodiments is used. Note that the scale section 5 and the light receiving system 6 are not limited to the reflection type, and may have a transmission type configuration as described in the fourth embodiment.

Next, the operation principle of displacement measurement by such an interference measurement signal forming apparatus will be described. Here, as an example, the optical waveguide section 34 (first path) allows the light beam to pass through without being phase-modulated, while the optical waveguide section 35 (second path) performs a modulation operation by the phase modulator 37. Will be described.

The first diffracted light beam E _A1 that has passed through the first passage and has been reflected from the diffraction grating scale of the scale section 5;
The phase difference due to the displacement ΔL of the diffraction grating scale and the second diffracted light beam E _A2 reflected from the diffraction grating scale of the scale unit 5 after undergoing the phase modulation through the second passage are represented by Δ
Φ = 2πΔL / p, which results in the following equation. In addition, each parameter is the same as the above definition.

[0069]

(Equation 6) The interference light I obtained by combining and interfering these two light waves is obtained as follows.

[0070]

(Equation 7) When this is calculated, the fundamental wave component I (Ω) and the second harmonic wave component I (2Ω) are respectively expressed by the following equations.

[0071]

(Equation 8) FIG. 15 shows the fundamental wave component I (Ω) and the second harmonic wave component I (2
Ω).

The displacement measuring section 8 can measure the displacement ΔL of the scale section 5 based on the fundamental wave component I (Ω) and the second harmonic component I (2Ω), as described above.

[0073]

As described above, according to the present invention, the number of optical components can be reduced to reduce the size, and the optical adjustment can be made simple and easy. Further, according to the present invention, an ultra-compact and rigid interference optical system can be realized, an output signal can be highly stabilized, and a highly accurate and inexpensive interference measurement signal forming apparatus can be provided. Further, according to the present invention,
The influence of the wavelength variation of the laser light source can be reduced as much as possible, and excellent stability can be obtained.

Further, according to the present invention, by using a waveguide device to which the phase modulation type heterodyne interferometry is applied, it is resistant to the fluctuation of the received light amount, only one detector is used, and the direction discrimination of the displacement amount can be performed. A possible interference measurement signal forming apparatus can be provided.

Further, according to the present invention, by using a diffractive lens, one light-collecting and deflecting function is realized by one element, thereby simplifying mounting and miniaturizing the entire module. be able to.

[0076]

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an interference measurement signal forming apparatus according to the present invention.

FIG. 2 is an explanatory plan view illustrating the design of the focal length of the FZP.

FIG. 3 is a side view illustrating the design of the focal length of the FZP.

FIG. 4 is an explanatory diagram of a polishing angle of an optical substrate.

FIG. 5 is a configuration diagram of an interference measurement signal forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an interference measurement signal forming apparatus according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of a fourth embodiment of an interference measurement signal forming apparatus according to the present invention.

FIG. 8 is a diagram illustrating the stability of the present invention with respect to wavelength fluctuation.

FIG. 9 is an explanatory diagram of a Fresnel zone plate that mainly configures the irradiation optical system.

FIG. 10 is a manufacturing process diagram of a light emitting system.

FIG. 11 is a configuration diagram of a modified example of a light emitting system.

FIG. 12 is an explanatory diagram of interference of a push-pull type phase modulation method.

FIG. 13 is a configuration diagram of a displacement measurement unit.

FIG. 14 is a configuration diagram of a fifth embodiment of an interference measurement signal forming apparatus according to the present invention.

FIG. 15 shows a fundamental wave component I (Ω) and a second harmonic wave component I (2).
Ω) waveform diagram.

FIG. 16 is a configuration diagram of a conventional interference measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source part 2 Coupling part 3 Light emission system 4 Irradiation optical system 5 Scale part 6 Light receiving system 7 Light receiving part 8 Displacement measuring part

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Nobuo Hori 75-1 Hasunumacho, Itabashi-ku, Tokyo Topcon Corporation

Claims (10)

[Claims] An incident waveguide for guiding a coherent irradiation light beam from a light source unit, a branch waveguide for branching a light beam from the incident waveguide into at least two light beams, and at least two light beams branched by the branch waveguide. Two emission waveguides and a phase modulator for phase-modulating the light flux of at least one of the emission waveguides are formed on one surface of the optical substrate, and at least two
A light emitting system for forming two irradiation light beams, and an irradiation optical system having a diffractive lens such as a Fresnel zone plate and irradiating at least two irradiation light beams emitted from the light emitting system to a measurement point of a diffraction grating in the scale section And a scale portion displaceably disposed with respect to the light emitting system, diffracting at least two irradiation light beams irradiated by the irradiation optical system by a diffraction grating formed on the surface, and forming a diffracted light beam in substantially the same direction. An interference measurement signal forming device, comprising: a light receiving system that receives the diffracted light beam diffracted by the scale unit; and a light receiving unit that receives the diffracted light beam received by the light receiving system and forms a light receiving signal. 2. The interference measurement signal forming apparatus according to claim 1, further comprising a displacement measuring section for calculating a displacement between the irradiation optical system and the scale section based on a light receiving signal formed by the light receiving section. 3. The light receiving system according to claim 1, wherein the light receiving system is configured to receive the diffracted light beam reflected by the scale unit from the irradiation light beam irradiated by the irradiation optical system. Interference signal forming device. 4. The interference measurement signal according to claim 3, wherein the light receiving system includes a block provided on the other surface of the optical substrate, and a multimode fiber fixed by the block. Forming equipment. 5. The apparatus according to claim 3, wherein the light receiving system includes a waveguide formed on the other surface of the optical substrate. 6. The interference measurement signal forming apparatus according to claim 3, wherein the light receiving system includes a cross finger electrode formed on the other surface of the optical substrate and forming a surface acoustic wave. 7. The light receiving system according to claim 1, wherein the light receiving system is configured such that the irradiation light beam irradiated by the irradiation optical system receives the diffracted light beam transmitted through the scale section. Interference signal forming device. 8. The irradiating optical system is characterized in that a rear focal position is disposed near an exit end of the exit waveguide, and the scale section is disposed near a front focal position. The interference measurement signal forming device according to claim 1. 9. A diffractive lens such as a Fresnel zone plate included in the irradiation optical system such that an optical axis substantially coincides with a central portion of an emission position of at least two light beams emitted from an optical substrate of the light emitting system. The interference measurement signal forming apparatus according to any one of claims 1 to 8, wherein the apparatus is arranged. 10. The wavelength of the light source section is λ ₀ , the interval between the two emission waveguides of the optical substrate is d, the grating pitch of the scale section is p, and the diffraction angle of the principal ray by the scale section is When θ is set, the condition that the ± 1st-order diffracted light diffracted at the scale portion is vertically reflected is sin θ = ± λ ₀ / p, and the focal length f _{0 of} a diffractive lens such as a Fresnel zone plate
The interference measurement signal forming apparatus according to any one of claims 1 to 9, wherein is determined as f ₀ = (d / 2) / tan θ.