JP4969057B2 - Displacement detection device, displacement measurement device, and fixed point detection device - Google Patents

Description

  The present invention provides a displacement detection device that detects displacement by detecting diffracted light from a diffraction grating, a displacement measuring device that measures the amount of displacement using interference of diffracted light by the diffraction grating, and a fixed point for obtaining a fixed point by the diffracted light. The present invention relates to a detection device.

  Conventionally, there is a grating interferometer that detects the displacement of the position of a diffraction grating mounted on a moving scale by using interference of light. Hereinafter, the displacement detection device will be described with reference to FIG. FIG. 18 shows a displacement detection device using a transmission type diffraction grating.

  As shown in FIG. 18, the displacement detection device includes a coherent light source unit 90, a first lens 91, a first polarization beam splitter (PBS) 92, and a first quarter-wave plate. 93, a reflecting prism 94, a second quarter-wave plate 95, a second lens 96, a beam splitter (BS) 97, a second PBS 98, and a first photoelectric converter 99. The second photoelectric converter 100, the third quarter wave plate 101, the third PBS 102, the third photoelectric converter 103, the fourth photoelectric converter 104, and the first difference. A dynamic amplifier 105, a second differential amplifier 106, and an incremental signal generator 107 are provided, and a transmission type diffraction grating disposed on the scale 108 is read.

  The coherent light source unit 90 emits light to the first lens 91. The first lens 91 narrows the incident light into an appropriate beam and emits it to the first PBS 92. The first PBS 92 divides the incident light into two lights, a light having an S-polarized component and a light having a P-polarized component. S-polarized light is a polarization component that vibrates perpendicularly to an incident plane formed by light incident on and reflected from the boundary surface of light. P-polarized light is a polarization component that vibrates horizontally with respect to the incident plane. The light having the S polarization component is reflected by the first PBS 92, and the light having the P polarization component is transmitted through the first PBS 92. If the light from the coherent light source 90 is linearly polarized light, the polarization direction is inclined by 45 degrees and is incident on the first PBS 92. By so doing, the intensity of the light of the S-polarized component and the light of the P-polarized component can be made equal.

The light having the S-polarized component reflected by the first PBS 92 is incident on the point P of the diffraction grating recorded on the scale 108, and the light having the P-polarized component transmitted through the first PBS 92 is The light enters the point Q of the diffraction grating and is diffracted in the directions indicated by the following equations.
sinθ ₁ + sinθ ₂ = n · λ / Λ
Θ ₁ represents an incident angle on the scale 108, θ ₂ represents a diffraction angle from the scale 108, Λ represents a grating pitch (width), λ represents a wavelength of light, and n represents a diffraction order. Is shown.

In the conventional displacement detection apparatus shown in FIG. 18, the incident angle to the point P is θ ₁ p, the diffraction angle is θ ₂ p, the incident angle to the point Q is θ ₁ q, and the diffraction angle is θ When ₂ q, are adjusted to be _{θ 1 p = θ 2 p =} θ 1 q = θ 2 q. The diffraction orders are the same at the P point and the Q point.

  The light (S-polarized component) diffracted at the point P passes through the first quarter-wave plate 93, is reflected vertically by the reflecting prism 94, returns to the point P again, and is diffracted by the diffraction grating. At this time, since the optical axis of the first quarter-wave plate 93 is inclined 45 degrees with respect to the polarization direction of the incident light, the light returned to the P point is light of the P-polarized component. .

  Similarly, the light (P-polarized component) diffracted at the Q point passes through the second quarter-wave plate 95, is reflected vertically by the reflecting prism 94, returns to the Q point again, and is diffracted by the diffraction grating. The At this time, the optical axis of the second quarter-wave plate 95 is inclined 45 degrees with respect to the polarization direction of the incident light, so that the light returned to the Q point is light of the S polarization component. .

  Thus, the light diffracted again at the P point and the Q point returns to the first PBS 92. Since the light returned from the point P has a P-polarized component, it passes through the first PBS 92. Further, since the light returned from the Q point has an S-polarized component, it is reflected by the first PBS 92. Therefore, the light returned from the point P and the point Q is overlapped by the first PBS 92, is narrowed down to an appropriate beam by the second lens 96, and enters the BS 97.

  The BS 97 divides the incident light into two, one light is incident on the second PBS 98 and the other light is incident on the third quarter-wave plate 101. The second PBS 98 and the third quarter-wave plate 101 are inclined at 45 degrees with respect to the polarization direction of incident light.

  The light incident on the second PBS 98 is divided into light having an S-polarized component and light having a P-polarized component. The light having an S-polarized component is incident on the first photoelectric converter 99, and the P-polarized component is converted into light. The incident light is incident on the second photoelectric converter 100. Further, in the first photoelectric converter 99 and the second photoelectric converter 100, an interference signal of Acos (4Kx + δ) is obtained. K represents 2π / Λ, x represents the amount of movement, and δ represents the initial phase. In the first photoelectric converter 99, a signal having a phase difference of 180 degrees from that of the second photoelectric converter 100 is obtained.

  In addition, the light incident on the third quarter-wave plate 101 is light having a P-polarized component and light having an S-polarized component, which are circularly polarized in the opposite directions, and superimposed to become linearly polarized light. Enter the PBS 102. The light incident on the third PBS 102 is divided into light having an S-polarized component and light having a P-polarized component, and the light having an S-polarized component is incident on the third photoelectric converter 103, and the P-polarized component is converted into light. The incident light enters the fourth photoelectric converter 104. Note that the polarization direction of the linearly polarized light incident on the third PBS 102 rotates once when the diffraction grating moves by Λ / 2 in the x direction. Therefore, the third photoelectric converter 103 and the fourth photoelectric converter 104 can obtain an interference signal of Acos (4Kx + δ ′), similarly to the first photoelectric converter 99 and the second photoelectric converter 100. . In the third photoelectric converter 103, a signal that is 180 degrees out of phase with the fourth photoelectric converter 104 is obtained.

  The third PBS 102 is inclined 45 degrees with respect to the second PBS 98. Therefore, the signals obtained by the third photoelectric converter 103 and the fourth photoelectric converter 104 are 90 degrees out of phase with the signals obtained by the first photoelectric converter 99 and the second photoelectric converter 100. ing.

  The first differential amplifier 105 differentially amplifies the electrical signal input from the first photoelectric converter 99 and the second photoelectric converter 100, and incrementally outputs a signal obtained by canceling the DC (direct current) component of the interference signal. Output to the signal generator 107. Similarly, the second differential amplifier 106 also differentially amplifies the electric signal input from the third photoelectric converter 103 and the fourth photoelectric converter 104, and cancels the DC (direct current) component of the interference signal. The signal is output to the incremental signal generator 107.

  Next, FIG. 19 shows an example of a conventional fixed point detection apparatus disclosed in the following Patent Document 1 by the applicant of the present application. This fixed point detection apparatus has a fixed part 110 and a movable part 130 movable along a measurement direction (X direction). The fixed part 110 includes an optical system 111 and a detection system 121, and the movable part 130 is a substrate 131. And two volume holographic diffraction gratings 132 and 133 arranged on the upper surface thereof.

  The optical system 111 includes a light source 112 that outputs laser light such as a semiconductor laser, a collimator lens 113, and a condenser lens 114. The detection system 121 includes two light receivers 122 and 123 and an electric processing circuit 129.

  FIG. 20 shows holographic diffraction gratings 132 and 133 used in this example. The holographic diffraction gratings 132 and 133 are formed by a transmission type volume hologram. Hereinafter, the holographic diffraction gratings 132 and 133 are sometimes simply referred to as holograms. As shown in the figure, the grating interval or grating pitch d of each of the holograms 132 and 133 changes successively in the measurement direction. In addition, the distribution surfaces 142 and 143 forming the grating interval or grating pitch d of the respective holograms 132 and 133 are inclined with respect to the upper surface of the holograms 132 and 133, and the inclination angles are successively changed in the measurement direction. is doing. When incident light is diffracted by each of the holograms 132 and 133, the diffraction efficiency changes continuously in the measurement direction.

  FIG. 21 shows a main part of the fixed point detection apparatus of FIG. As shown in the drawing, two holograms 132 and 133 are arranged on the upper surface 131A of the substrate 131 so as to be adjacent to each other in the horizontal direction. The two holograms 132 and 133 are configured symmetrically with respect to the center plane 135. That is, the inclination angles of the distribution planes 142 and 143 of the holograms 132 and 133 are sequentially and continuously changed to both sides symmetrically with respect to the center plane 135, and the lattice interval or the grating pitch d is relative to the center plane 135. Symmetrically and continuously changing on both sides. The two holograms 132 and 133 are arranged so that the diffraction efficiency of each of the holograms 132 and 133 is different from each other in the measurement direction.

  When the movable part 130 moves relative to the fixed part 110, that is, when the movable part 130 moves relative to the stationary light receivers 122 and 123 and the light source 112 in FIG. The light diffracted by the hologram 132 is detected by the first light receiver 122, and the light diffracted by the second hologram 133 is detected by the second light receiver 123.

  Since the two holograms 132 and 133 are different from each other in that the diffraction efficiency is maximized, the peak position of the light intensity curve of the diffracted light detected by the first light receiver 122 and the diffraction detected by the second light receiver 123 are different. The peak position of the light intensity curve of light is different. Therefore, there is an intersection of two light intensity curves, that is, a point where the two light intensities are equal. Such a point is a fixed point obtained by the fixed point detection device.

JP-A-4-324316

  By the way, recent fixed point detection devices and displacement measuring devices using light emitting diodes and lasers have been improved in resolution and are capable of measuring 1 nm or less. On the other hand, in such a measurement, heat generation of the sensor itself is not allowed, and in particular, a means for separating the light source from the sensor and transmitting the beam by the optical fiber is often used.

  FIG. 22 is a diagram showing a fixed point detection device 160 that detects a fixed point by transmitting an outgoing beam from the light source 161 to the detection unit 164 through the polarization maintaining type optical fiber 163. The outgoing beam from the light source 161 is transmitted to the condensing lens 162 via the polarization maintaining optical fiber 163, and irradiated to the two diffraction gratings 166 and 167 arranged on the measurement object 169 adjacent to each other. The diffracted light diffracted by the edges 168 of the diffraction gratings 166 and 167 is received by the two light receiving elements 170 and 171, and the amounts of light received by the two light receiving elements 170 and 171 are compared by the comparator 172. A fixed point is defined as a point that becomes the size of.

  As described above, the fixed point detection device 160 of FIG. 22 uses the polarization maintaining type optical fiber 163 in order to transmit the outgoing beam from the light source 161 while maintaining the polarization component. However, the polarization is disturbed due to the effects of fiber stress and bending, which affects the detection unit 164 side, and stable measurement may not be possible.

  Specifically, it is as follows. This means that when the polarization axis of the beam emitted from the optical fiber 163 is slightly changed due to bending or stress of the optical fiber 163, the polarization component of the beam incident on the diffraction gratings 166 and 167 is changed. In general, the diffraction efficiency of a diffraction grating is not only different depending on the polarization component of the incident beam, but also has individual differences, so that the amount of light entering the light receiving elements 170 and 171 changes, and it is recognized that the fixed point has shifted. End up.

  Therefore, in order to stably detect the fixed point in the fixed point detection device 160, it is necessary to stabilize the polarization axis of the beam emitted from the optical fiber 163 as much as possible.

  Next, FIG. 23 is a diagram showing a displacement measuring device 180 that transmits the outgoing beam from the light source 181 to the detection unit 184 through the polarization maintaining optical fiber 183 and measures the displacement of the measurement object by the detection unit 184. . The outgoing beam from the light source 181 is transmitted to the condenser lens 185 via the polarization maintaining optical fiber 183 and then incident on the polarization beam splitter 186. The polarization beam splitter 186 bisects the incident beam and enters the diffraction grating scale 187. The diffracted light obtained here passes through the λ / 4 wave plates 188 and 189, is reflected by the mirror surfaces 191 and 192, returns to the polarization beam splitter 186 through the same optical path. Here, the two beams are combined again and travel toward the polarizing element side 193. In this way, the interference signal after passing through the polarizing element 193 is converted into an electric signal by the light receiving element 194, whereby the movement amount of the diffraction grating can be measured.

  However, even in this displacement measuring apparatus 180, when the polarization is disturbed due to the stress or bending of the optical fiber 183, the light quantity ratio divided by the polarization beam splitter 186 changes accordingly. The change in the light amount ratio between the two beams appears as a change in the modulation rate when coupled again by the polarization beam splitter 186 and becomes an interference signal, which causes the output fluctuation of the signal output. Since these adversely affect the accuracy of displacement measurement, it is necessary to stabilize the polarization axis of the beam emitted from the optical transmission unit as much as possible.

  The present invention has been made in view of the above circumstances, and is capable of detecting and displacing a fixed point with high accuracy by reducing polarization disturbance due to bending or stress of an optical fiber that transmits light emitted from a light source to a detection side. An object is to provide a displacement detection device, a displacement measurement device, and a fixed point detection device that enable measurement.

  In order to solve the above problems, a displacement detection apparatus according to the present invention includes a light source that emits light, an extinction ratio conversion unit that increases an extinction ratio of light emitted from the light source to 20 dB or more, and the extinction ratio conversion unit. Is attached to a measurement object, a condenser lens that collects the light whose extinction ratio is 20 dB or more, a polarization maintaining optical fiber that transmits the light collected by the condenser lens, and the light A diffraction grating that irradiates and diffracts the light transmitted by the fiber; and a light receiving means that receives the light diffracted by the diffraction grating; the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means; Receiving the diffracted light incident on the optical fiber with the polarization axis of the light collected by the optical means aligned with the optical axis of the optical fiber or an axis orthogonal to the optical axis, and received by the light receiving means Detecting the displacement of the measurement object in size.

  According to this displacement detection device, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is the optical axis of the optical fiber or an axis orthogonal to the optical axis. Therefore, it is possible to reduce polarization disturbance due to bending or stress of the optical fiber.

  In order to solve the above problems, a displacement measuring apparatus according to the present invention is a light source that emits light, an extinction ratio conversion unit that converts the light emitted from the light source into linearly polarized light and increases its extinction ratio to 20 dB or more, A condensing lens that condenses light having an extinction ratio of 20 dB or more by the extinction ratio conversion means, a polarization-maintaining optical fiber that transmits the light collected by the condensing lens, and the optical fiber A polarizing beam splitter that bisects the light transmitted by the beam, a diffraction grating that is attached to a measurement object and that receives the light bisected by the polarizing beam splitter to obtain diffracted light, and the bisected beam obtained by the diffraction grating. A phase plate that changes the polarization of the diffracted light, and the diffraction grating that reflects the two diffracted lights whose polarization is changed by the phase plate and passes through the phase plate again. The two reflecting mirrors to be guided to the diffraction grating by the two reflecting mirrors, diffracted by the diffraction grating and incident on the polarizing beam splitter, and the two diffracted lights reflected and transmitted by the polarizing beam splitter A polarizing element that causes interference, and a light receiving element that receives interference light obtained by the polarizing element, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the light collected by the condensing means The polarization axis is aligned with the optical axis of the optical fiber or an axis orthogonal to the optical axis, and is incident on the optical fiber, and the displacement of the measurement object is measured by the amount of received diffracted light received by the light receiving means.

  According to this displacement measuring apparatus, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is the optical axis of the optical fiber or an axis orthogonal to the optical axis. Therefore, it is possible to reduce polarization disturbance due to bending or stress of the optical fiber.

  In order to solve the above problems, a fixed point detection apparatus according to the present invention is a light source that emits light, an extinction ratio conversion unit that converts the light emitted from the light source into linearly polarized light and increases its extinction ratio to 20 dB or more, A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio converting means, and a polarization maintaining optical fiber for transmitting the light condensed by the condensing lens are adjacent to each other. And two diffraction gratings that are irradiated and diffracted by the light transmitted by the optical fiber, two light receiving means that receive the light diffracted by the two diffraction gratings, and the amount of light received by the two light receiving means And the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is the optical axis of the optical fiber or the light. In accordance with the axis perpendicular to the axis incident to the optical fiber, it said comparison means determining a fixed point on the basis of a result of comparing the amount of light received by the two light receiving means.

  According to this fixed point detection apparatus, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light collected by the condensing means is an optical axis of the optical fiber or an axis orthogonal to the optical axis. Therefore, it is possible to reduce polarization disturbance due to bending or stress of the optical fiber.

  In order to solve the above problems, a displacement detection apparatus according to the present invention includes a light source that emits light, an extinction ratio conversion unit that increases an extinction ratio of light emitted from the light source to 20 dB or more, and the extinction ratio conversion unit. Accordingly, the condenser lens that collects the light whose extinction ratio is 20 dB or more, the polarization maintaining optical fiber that transmits the light collected by the condenser lens, and the optical fiber that is transmitted by the optical fiber. A depolarizing element that depolarizes light, a diffraction grating that is attached to a measurement object and diffracts when irradiated with light depolarized by the depolarizing element, and a light receiving means that receives light diffracted by the diffraction grating The extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is set to the optical axis or the optical axis of the optical fiber. In accordance with the interlinking axis incident on said optical fiber, said light receiving means detects the displacement of the measurement target in the size of the light receiving amount of the diffracted light received.

  According to this displacement detection device, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is the optical axis of the optical fiber or an axis orthogonal to the optical axis. Accordingly, the polarization of the light that is incident on the optical fiber and transmitted by the optical fiber is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber can be reduced.

  In order to solve the above problems, a displacement measuring apparatus according to the present invention is a light source that emits light, an extinction ratio conversion unit that converts the light emitted from the light source into linearly polarized light and increases its extinction ratio to 20 dB or more, A condensing lens that condenses light having an extinction ratio of 20 dB or more by the extinction ratio conversion means, a polarization-maintaining optical fiber that transmits the light collected by the condensing lens, and the optical fiber A depolarizing element that depolarizes the light transmitted by the light, a polarizing beam splitter that bisects the light depolarized by the depolarizing element, and a light that is attached to the measurement object and bisected by the polarizing beam splitter. Is incident on the diffraction grating to obtain the diffracted light, the phase plate for changing the polarization of the diffracted light of the bisected light obtained by the diffraction grating, and the phase plate Are reflected to the diffraction grating through the phase plate and guided again to the diffraction grating by the two reflection mirrors, and are diffracted by the diffraction grating and reflected by the diffraction grating. The extinction ratio converting means, comprising: a polarizing element that enters the polarizing beam splitter and interferes with two diffracted lights reflected and transmitted by the polarizing beam splitter; and a light receiving element that receives the interference light obtained by the polarizing element. , The extinction ratio is increased to 20 dB or more, and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis, and is incident on the optical fiber. The displacement of the measurement object is measured by the magnitude of the amount of diffracted light received by the light receiving means.

  According to this displacement measuring apparatus, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is the optical axis of the optical fiber or an axis orthogonal to the optical axis. Accordingly, the polarization of the light that is incident on the optical fiber and transmitted by the optical fiber is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber can be reduced.

  In order to solve the above problems, a fixed point detection apparatus according to the present invention is a light source that emits light, an extinction ratio conversion unit that converts the light emitted from the light source into linearly polarized light and increases its extinction ratio to 20 dB or more, A condensing lens that condenses light having an extinction ratio of 20 dB or more by the extinction ratio conversion means, a polarization-maintaining optical fiber that transmits the light collected by the condensing lens, and the optical fiber A depolarizing element for depolarizing the light transmitted by the optical element, two diffraction gratings disposed adjacent to each other and diffracted by the light depolarized by the depolarizing element, and the two diffractions Two light receiving means for receiving the light diffracted by the grating and a comparison means for comparing the light receiving amounts of the two light receiving means are provided, and the extinction ratio conversion means increases the extinction ratio to 20 dB or more. And the polarization axis of the light collected by the light collecting means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis, and is incident on the optical fiber, and the comparing means is the two light receiving means. A fixed point is determined based on the result of comparing the amount of received light.

  According to this fixed point detection apparatus, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light collected by the condensing means is an optical axis of the optical fiber or an axis orthogonal to the optical axis. Accordingly, the polarization of the light incident on the optical fiber and transmitted by the optical fiber is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber can be reduced.

  According to the displacement detection device of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is set to the optical axis or the optical axis of the optical fiber. Since the light is incident on the optical fiber in accordance with the orthogonal axes, polarization disturbance due to bending or stress of the optical fiber can be reduced, thereby enabling highly accurate displacement detection.

  According to the displacement measuring apparatus of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is set to the optical axis or the optical axis of the optical fiber. Since the light enters the optical fiber in accordance with the orthogonal axis, it is possible to reduce the polarization disturbance due to the bending or stress of the optical fiber, thereby enabling highly accurate displacement measurement.

  According to the fixed point detection apparatus of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is set to the optical axis or the optical axis of the optical fiber. Since the light is incident on the optical fiber in accordance with the orthogonal axis, it is possible to reduce the disturbance of the polarization due to the bending or stress of the optical fiber, thereby enabling high-precision fixed point detection.

  According to the displacement detection device of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is set to the optical axis or the optical axis of the optical fiber. The polarization of the light that is incident on the optical fiber and transmitted by the optical fiber along the orthogonal axis is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber is further reduced. Therefore, it is possible to detect displacement with higher accuracy.

  According to the displacement measuring apparatus of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light collected by the condensing means is set to the optical axis or the optical axis of the optical fiber. The polarization of the light that is incident on the optical fiber and transmitted by the optical fiber along the orthogonal axis is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber is further reduced. Therefore, it is possible to measure displacement with higher accuracy.

  According to the fixed point detection apparatus of the present invention, the extinction ratio is increased to 20 dB or more by the extinction ratio conversion means, and the polarization axis of the light condensed by the condensing means is set to the optical axis or the optical axis of the optical fiber. The polarization of the light that is incident on the optical fiber and transmitted by the optical fiber along the orthogonal axis is canceled by the depolarization element, so that the polarization disturbance due to bending or stress of the optical fiber is further reduced. Therefore, it is possible to detect a fixed point with higher accuracy.

  Hereinafter, the best mode of a displacement measuring device and a fixed point detecting device for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of the displacement measuring apparatus 10. The displacement measuring device 10 is used in the fields of semiconductor manufacturing, liquid crystal manufacturing, and the like that measure a movement amount of, for example, nanometers (nm) or less. Therefore, in this displacement measuring apparatus 10, the heat generated by the light source unit may affect the sensor of the detection unit, and stable measurement may not be possible. For this reason, it is necessary to prevent heat from being transmitted to the detection unit 16. Therefore, in particular, the light source 12 is separated from the detection unit 16, and the beam emitted from the light source 12 is transmitted to the detection unit 16 through the optical fiber 15.

  For this reason, the displacement measuring apparatus 10 includes a light source 12 that emits a beam, and a polarizing plate 13 that is a kind of polarizing element that is used as an extinction ratio conversion unit that converts the beam from the light source 12 into linearly polarized light with a high extinction ratio of 20 dB or more. And a condensing lens 14 for condensing linearly polarized light with a high extinction ratio from the polarizing plate 13 and a polarization maintaining optical fiber 15 for transmitting the linearly polarized light collected by the condensing lens 14.

  The displacement measuring apparatus 10 includes a condenser lens 17 that condenses the linearly polarized beam transmitted by the optical fiber 15, and a polarization beam splitter 18 that bisects the linearly polarized beam collected by the condenser lens 17. The diffraction beam 19 attached to the measurement object to which the beam divided by the polarization beam splitter 18 is incident and the polarization direction of the two diffracted lights obtained by the diffraction grating 19 are changed at an angle of 90 degrees with each other. The two phase plates 20 and 21 arranged at the same angle and the two phase plates 20 and 21 attached to each other are provided at an angle of 90 degrees with each other, and the diffracted light from the diffraction grating 19 is transmitted to the two phase plates. The reflection prism 24 having two mirror surfaces 22 and 23 reciprocated on the plate is recombined by the polarization beam splitter 18 and incident. A polarizing element 25 to interfere with the beam, comprising a light receiving element 26 for converting the received light amount of the interference light of the two beams into electrical signals.

  Here, the light source 12, the polarizing element 13, the condensing lens 14, and the polarization maintaining optical fiber 15 can be referred to as an optical transmission unit 11 because the beam emitted from the light source 12 is transmitted to the detection unit 16 side. The detection unit 16 includes a condenser lens 17, a polarizing beam splitter 18, a diffraction grating 19, two phase plates 20 and 21, two mirrors 22 and 23, a polarizing element 25, and a light receiving element 26.

  Hereinafter, details of each part which constitutes displacement measuring device 10 are explained. First, the light source 12 may emit a coherent beam or a light emitting diode that emits light having low coherence. Moreover, it may have polarization characteristics or may be non-polarized.

  A polarizing plate 13 which is a kind of polarizing element used as an extinction ratio converting means changes a beam from a light source to linearly polarized light having a high extinction ratio of 20 dB or more. An extinction ratio of 20 dB or more means that, as shown in FIG. 2, A: B, which is the ratio of short-axis light (B) that slightly leaks with respect to linearly polarized light (A) that is the long axis, is 100: 1 or more. It means that. The higher the extinction ratio, the better the quality of linearly polarized light. The polarizing element can also have an extinction ratio of about 30 dB when A: B is 1000: 1. As the polarizing element, an element that pulls a glass containing silver halide in a certain direction and causes the inner grain shape to be directed in a predetermined direction to function as a polarizing filter may be used. As the extinction ratio conversion means, a polarization beam splitter that changes the beam from the light source into linearly polarized light with a high extinction ratio of 20 dB or more may be used.

  As shown in FIG. 3, the polarization-maintaining optical fiber 15 has, for example, a concentric shape in which a circular core 30 having a diameter of 3 μm is wrapped by a clad 31 having a diameter of 100 μm. The core 30 and the clad 31 are, for example, quartz glass having different refractive indexes. The refractive index of the core 30 is higher than the refractive index of the clad 31. For example, when light having a wavelength of λ600 to 700 nm is sent to the core 30, the light propagates while reflecting the boundary between the core 30 and the clad 31 having a low refractive index. On both sides of the core 30, two glasses 32 and 33 having a circular cross section different from the core 30 and the clad 31 are provided so as to sandwich the core 30. The two glasses 32 and 33 have the same coefficient of thermal expansion and contract the entire clad 31. The entire clad 31 is cooled, and the stress applied to the core 30 is kept constant. An axis connecting the centers of the two glasses 32 and 33 and the centers of the core 30 and the clad 31 is an optical axis 34. The polarization axis of the beam emitted from the light source 12 is incident on the optical axis 34 of the polarization maintaining optical fiber 15 through the polarizing plate 13 and the condenser lens 14. An elliptical core type optical fiber having an elliptical cross section may be used.

  The polarization beam splitter 18 divides the beam transmitted by the polarization-maintaining optical fiber 15 and collected by the condenser lens 17 into two lights of light having an S-polarized component and light having a P-polarized component. . At this time, the polarization axis of the incident light is set to an angle such that the power of the outgoing light from the polarization beam splitter 18 is substantially equal between the S-polarized component and the P-polarized component. S-polarized light is a polarization component that vibrates perpendicularly to an incident plane formed by light incident on and reflected from the boundary surface of light. P-polarized light is a polarization component that vibrates horizontally with respect to the incident plane. The light having the S polarization component is reflected by the polarization beam splitter 18, and the light having the P polarization component is transmitted through the polarization beam splitter 18.

  The diffraction grating 19 may be a volume type hologram. The diffraction grating 19 is attached to an object to be measured. The diffraction grating 19 is movable in the direction of arrow A in the figure. The pitch of the diffraction grating 19 is, for example, 0.55 μm. The incident position (Q point) of the P-polarized component transmitted through the polarizing beam splitter 18 and the incident position (P point) of the S-polarized component reflected by the polarizing beam splitter 19 are different.

  The optical axis of the first quarter-wave plate 20 attached to the first mirror surface 22 of the reflecting prism 24 is inclined 45 degrees with respect to the polarization direction of the incident light. Similarly, the optical axis of the second quarter wave plate 21 attached to the second mirror surface 23 of the reflecting prism 24 is also inclined by 45 degrees with respect to the polarization direction of the incident light.

  The polarizing element 25 provided on the light receiving element 26 side is inclined 45 degrees with respect to the polarization direction of incident light. Therefore, the two lights from the polarization beam splitter 18 pass through the polarization element 25 and become interference waves. The light receiving element 26 converts the light amount of the interference wave into an electric signal.

  Next, the operation of the displacement measuring device 10 constituted by each of the above parts will be described. When the coherent or low coherent light emitted from the light source 12 enters the polarizing plate 13, it becomes linearly polarized light having a high extinction ratio of, for example, 30 dB. The linearly polarized light having a high extinction ratio is condensed by the condenser lens 14, and the polarization axis of the linearly polarized beam is set to the optical axis 34 of the polarization maintaining optical fiber 15 as described above with reference to FIG. The light is incident on the polarization-maintaining optical fiber 15 at the same time. As described above, when the beam that has been linearly polarized by the polarizing plate 13 is incident on the polarization-maintaining optical fiber 15, if the polarization axis of the beam is aligned with the optical axis 34 of the optical fiber 15, the light Variations in the extinction ratio due to bending or stress of the fiber 15 can be reduced. Further, the polarization axis of the beam may be incident so as to be aligned with an axis 35 orthogonal to the optical axis 34.

  In order to match the polarization axis of the beam with the optical axis of the polarization maintaining optical fiber 15, there is a method of adjusting so that the extinction ratio of the beam emitted from the emission end 15b of the optical fiber 15 is maximized. .

  Thus, the optical transmission unit 11 including the light source 12, the polarizing plate 13, the condensing lens 14, and the polarization maintaining optical fiber 15 has a high extinction ratio of the beam emitted from the emission end 15b of the optical fiber 15. In addition to this, fluctuations in the extinction ratio due to bending or stress of the optical fiber 15 can be reduced.

  The beam emitted from the polarization maintaining optical fiber 15 constituting the optical transmission unit 11 is collected by the condenser lens 17 on the detection unit 16 side and then enters the polarization beam splitter 18. As described above, the polarization beam splitter 18 divides the incident light into two lights, that is, light having an S polarization component and light having a P polarization component. The light having the S polarization component is reflected by the polarization beam splitter 18 and enters the point P of the diffraction grating 19. The light having the P-polarized light component passes through the polarization beam splitter 18 and enters the Q point of the diffraction grating 19.

Light incident on the point P and the point Q of the diffraction grating 19 is diffracted in the directions indicated by the following equations.
sinθ ₁ + sinθ ₂ = n · λ / Λ
Θ ₁ represents the incident angle to the diffraction grating, θ ₂ represents the diffraction angle from the diffraction grating, Λ represents the pitch (width) of the grating, λ represents the wavelength of light, and n represents the diffraction order. Show.

  The light (S-polarized component) diffracted at the point P of the diffraction grating passes through the first quarter-wave plate 20 attached to the first mirror surface 22 of the reflecting prism 24 and passes through the first mirror surface 22. , The light is reflected vertically and returned to the point P to be diffracted by the diffraction grating 19 again. At this time, the optical axis of the first quarter-wave plate 20 is inclined 45 degrees with respect to the polarization direction of the incident light, so that the light returned to the P point is light of the P-polarized component. . That is, the S-polarized light component diffracted at the point P of the diffraction grating 19 passes through the first quarter-wave plate 20, is reflected by the first mirror surface 22 of the reflecting prism 24, and is again the first 1 / Since it passes through the four-wave plate 20, the return polarization axis is at an angle orthogonal to the outgoing polarization axis.

  Similarly, the light diffracted at the Q point (P-polarized component) also passes through the second quarter-wave plate 21 attached to the second mirror surface 23 of the reflecting prism 24 and is vertically reflected by the reflecting prism 24. And is again diffracted by the diffraction grating 19. At this time, since the optical axis of the second quarter-wave plate 21 is inclined 45 degrees with respect to the polarization direction of the incident light, the light returned to the Q point is light of the S polarization component. . That is, the P-polarized light component diffracted at the S point of the diffraction grating 19 passes through the second quarter-wave plate 21, is reflected by the second mirror surface 23 of the reflecting prism 24, and again becomes the second 1 / Since it passes through the four-wave plate 21, the return polarization axis is at an angle orthogonal to the outgoing polarization axis.

  The light diffracted again at the points P and Q in this way returns to the polarization beam splitter 18. Since the light returned from the point P has a P-polarized component, it passes through the polarization beam splitter 18. Further, since the light returned from the point Q has an S-polarized component, it is reflected by the polarization beam splitter 18. Therefore, the light returned from the point P and the point Q is superimposed by the polarization beam splitter 18 and then enters the polarization element 25.

  The polarizing element 25 causes the two beams superimposed by the polarizing beam splitter 18 to interfere with each other. The light receiving element 26 converts the amount of interference light interfered by the polarizing element 25 into an electrical signal to obtain an interference signal. Based on this interference signal, the displacement measuring apparatus 10 measures the amount of movement of the diffraction grating 19 moving in the direction of arrow A, for example, on the order of nanometers (nm) or less.

  The interference signal can be expressed as A cos (4Kx + δ). K represents 2π / Λ, x represents the amount of movement, and δ represents the initial phase. For example, when the pitch Λ of the diffraction grating 19 is 0.55 μm, one period of the interference wave can be measured corresponding to the movement amount of the diffraction grating 19 of 0.1375 μm. Thus, for example, by interpolating 200 using A / D conversion or the like, a very fine resolution of about 0.6895 nm can be obtained. In particular, measurement of a fine displacement with a resolution of 10 nm or less requires a stable signal output. Needless to say, the fluctuation of the extinction ratio of the beam emitted from the optical transmission unit 11 is extremely small. The modulation factor of the interference wave obtained by passing through 25 can be stabilized, and displacement measurement with high resolution and high stability becomes possible.

  Further, by increasing the number of times of diffraction, the same effect can be obtained even if the interference signal is applied to a detection optical system in which Acos (8Kx + δ) is used. FIG. 4 is a diagram showing a displacement measuring apparatus 200 (application example) having a configuration in which the number of diffractions is increased. The difference from FIG. 1 is that the two diffracted lights divided by the polarizing beam splitter 18 and diffracted by the diffraction grating 19 enter the reflecting prisms 201 and 202 from the incident surfaces 201a and 202a, and the reflecting surfaces 201b and 202b, reflecting surface The point is that the light is reflected by 201c and 202c, enters the diffraction grating 19 again, is further diffracted by the diffraction grating 19, and then reaches the two phase plates 20 and 21 and the reflection prism 24. The light reflected by the reflecting prism 24 passes through the two phase plates 20 and 21 again, passes through the diffraction grating 19, is diffracted, and is reflected again by the reflecting prisms 201 and 202, and then further diffraction grating. The light is diffracted at 19 and reaches the polarization beam splitter 18.

  The polarization beam splitter 18 superimposes the incident polarization components and then sends them to the beam splitter 203. The beam splitter 203 divides the incident light into two, makes one light incident on the polarization beam splitter 204, and sends the other light to the polarization element 25. The polarizing element 25 polarizes the light transmitted through the beam splitter 203 and makes it incident on the polarizing beam splitter 207.

  The light incident on the polarization beam splitter 204 is divided into light having an S-polarized component and light having a P-polarized component, and light having an S-polarized component is incident on the photoelectric converter 205, and light having a P-polarized component is converted into light. The light enters the photoelectric converter 206. The light incident on the polarization beam splitter 207 is divided into light having an S-polarized component and light having a P-polarized component. The light having an S-polarized component is incident on the photoelectric converter 208, and the light having a P-polarized component is converted into light. The light enters the photoelectric converter 209.

  Therefore, the photoelectric converter 205, the photoelectric converter 206, the photoelectric converter 208, and the photoelectric converter 209 can obtain an interference signal of Acos (8Kx + δ).

  FIG. 5 is a diagram showing the configuration of the fixed point detection device 40. The fixed point detection device 40 is used in the field of semiconductor manufacturing, liquid crystal manufacturing, or the like that measures a movement amount of, for example, nanometer nm or less. Therefore, neither the fixed point detection device 40 nor the sensor itself is allowed to generate heat. In particular, the light source 42 is disconnected from the detection unit 46 and the beam emitted from the light source 42 is transmitted to the detection unit 46 through the optical fiber 45.

  The fixed point detection device 40 is used together with the displacement measurement device 10 and detects, for example, an absolute position on the diffraction grating 19 of the displacement measurement device 10. As described above, the displacement measuring apparatus 10 uses a very small diffraction grating 19 such that the pitch Λ is 0.55 μm. If the power is turned off due to some accident while measuring the displacement on the diffraction grating 19 or the process is stopped, it becomes unclear which position on the diffraction grating was in the previous measurement after recovery. End up. Therefore, the fixed point detection device 40 has been developed for the purpose of always detecting the absolute position on the diffraction grating. For example, two hologram materials having different pitches are used as the two diffraction gratings 48 and 49, and a fixed point is detected by detecting the edge 50.

  As shown in FIG. 5, the fixed point detection device 40 is a kind of polarizing element used as an extinction ratio converting means for converting a light source 42 that emits a beam and linearly polarized light having a high extinction ratio of 20 dB or more. A polarizing plate 43, a condensing lens 44 that condenses linearly polarized light with a high extinction ratio from the polarizing plate 43, and a polarization-maintaining optical fiber 45 that transmits the linearly polarized light collected by the condensing lens 44. Prepare.

  Further, the fixed point detection device 40 includes a condenser lens 47 that condenses the linearly polarized beam transmitted by the optical fiber 45, and the linearly polarized beam collected by the condenser lens 47 is near the boundary (edge) 50. Two diffraction gratings 48 and 49 that are disposed adjacent to each other to form a focal point, two light receiving elements 52 and 53 that receive diffracted light diffracted by the two diffraction gratings 48 and 49, and the two light receiving elements A comparator 54 that compares the received light amounts of 52 and 53 is provided, and a fixed point is determined based on the compared signal.

  Hereinafter, details of each part constituting the fixed point detection apparatus will be described. First, the light source 42 emits a coherent or incoherent beam. Further, a beam having a polarization characteristic or a non-polarized beam may be emitted.

  The polarizing plate 43, which is a kind of polarizing element used as the extinction ratio converting means, changes the beam from the light source 42 into linearly polarized light having a high extinction ratio of 20 dB or more, as in the polarizing plate 13 described above. It is also possible to set the extinction ratio to about 30 dB. As the extinction ratio conversion means, a polarization beam splitter that changes the beam from the light source into linearly polarized light with a high extinction ratio of 20 dB or more may be used.

  The polarization maintaining optical fiber 45 is as already described with reference to FIG. Although not described here, the polarization axis of the beam emitted from the light source 42 is aligned with the optical axis 34 or 35 of the polarization maintaining optical fiber 45 via the polarizing plate 43 and the condenser lens 44. It is important to make it incident.

  This is because, when a beam that has been linearly polarized by the polarizing plate 434 enters the polarization-maintaining optical fiber 45, the polarization axis of the beam is aligned with the optical axis 34 of the optical fiber 45. This is because fluctuations in the extinction ratio due to bending or stress can be reduced.

  The two diffraction gratings 48 and 49 are arranged adjacent to each other so that the linearly polarized beam condensed by the condenser lens 47 is focused near the boundary (edge) 50. The two diffraction gratings 48 and 49 may have different grating vectors or may have different grating pitches. It also includes a reflective hologram and a blazed diffraction grating. In the configuration shown in FIG. 4, the two diffraction gratings 48 and 49 are of the reflection type, and each + 1st order diffracted light is emitted to the same side as the incident light. A transmission type diffraction grating may also be used.

  The two light receiving elements 52 and 53 convert the intensity of the diffracted light obtained from the two diffraction gratings 48 and 49 into electric signals. The two light receiving elements 52 and 53 are disposed on the same end side as the emission end side 45 b of the optical fiber 45 with respect to the two diffraction gratings 48 and 49.

  The comparator 54 compares the electric signals from the two light receiving elements 52 and 53. The comparison result by the comparator 54 is supplied to a control unit (not shown). Based on the comparison result by the comparator 54, the control unit determines a point at which the two signals have arbitrary magnitudes as a fixed point. Further, a point where two signals become the same output may be determined as a fixed point.

  Next, the operation of the fixed point detection apparatus 40 configured by the above-described units will be described. When the coherent or specific interference light emitted from the light source 42 enters the polarizing plate 43, it becomes linearly polarized light having a high extinction ratio of, for example, 30 dB. The linearly polarized light having a high extinction ratio is condensed by the condenser lens 44, and the polarization axis of the linearly polarized beam is set to the optical axis 34 of the polarization maintaining type optical fiber 45 as described above with reference to FIG. The light is incident on the polarization maintaining optical fiber 45 in accordance with the above. In this way, when the beam that has been linearly polarized by the polarizing plate 43 is incident on the polarization maintaining optical fiber 45, the polarization axis of the beam is aligned with the optical axis 34 of the optical fiber. The fluctuation of the extinction ratio due to the bending of 45 or stress can be reduced. Further, the polarization axis of the beam may be incident so as to be aligned with an axis 35 orthogonal to the optical axis 34.

  In order to match the polarization axis of the beam with the optical axis of the polarization maintaining optical fiber 45, there is a method of adjusting the extinction ratio of the beam emitted from the emission end 45b of the optical fiber 45 to be maximum. .

  Thus, the optical transmission unit 41 including the light source 42, the polarizing plate 43, the condensing lens 44, and the polarization maintaining optical fiber 45 has a high extinction ratio of the beam emitted from the emission end 45b of the optical fiber 45. In addition to this, fluctuations in the extinction ratio due to bending or stress of the optical fiber 45 can be reduced.

  The beams emitted from the polarization-maintaining optical fiber 45 constituting the optical transmission unit 41 are collected by the condenser lens 47 on the detection unit 46 side, and then moved to two diffraction gratings movable in the direction of arrow A in the figure. The focal point is set near the boundary (edge) 50 between 48 and 49.

  The intensity of the diffracted light obtained from the two diffraction gratings 48 and 49 is converted into an electric signal by the respective light receiving elements 52 and 53. A point at which the two signals are arbitrarily large is determined as a fixed point by the comparator 54 that compares the two signals. As described above, a point where two signals are the same output may be determined as a fixed point. However, when the two signals match, the comparison output of the comparator 54 becomes zero. Even when there is no diffracted light and the output of the light receiving element is 0, the comparison result is 0. Therefore, in order to prevent misrecognition, it is desirable to provide an offset, and therefore an arbitrary size with a certain numerical value. It is desirable to set and discriminate from 0.

  In this way, the fixed point detector 40 of the present embodiment detects the absolute positions of the diffraction gratings 48 and 49 attached to the measurement object 51. In general, a diffraction grating has a different amount of diffracted light depending on an incident polarization component. That is, the diffraction efficiencies of the S polarization component and the P polarization component are different. For example, when the diffraction efficiency of a reflection hologram is measured with a wavelength of a beam emitted from the light source of 780 nm and a grating pitch of 0.55 μm, as shown in FIG. Can be confirmed to be greatly different. In FIG. 6, the diffraction efficiency of the S-polarized component is between 46% and 41% when the incident angle is between 35 and 55 degrees, whereas the diffraction efficiency of the P-polarized component is between 91% and 92%. It can be confirmed that the diffraction efficiency of the P-polarized component is high. In addition, it can be said that there are individual differences in the manufacturing process, and these generally have a certain degree of variation.

  Therefore, by reducing the fluctuation of the extinction ratio of the beam incident on the diffraction grating, it has become possible to always perform stable fixed point detection without being affected by these effects.

  FIG. 7 shows how the fixed point detection position 40 changes with time when bending stress is applied to the polarization maintaining optical fiber 45 in the fixed point detection apparatus 40 of the present embodiment. FIG. In FIG. 7, the unit comprising the light source 42 + polarizing plate 43 + condensing lens 44 in FIG. 5 of the fixed point detection device 40 is used as a light incident part 55 for making the optical fiber 45 enter linearly polarized light having a predetermined extinction ratio. Yes. The light incident part 55 enters linearly polarized light having an extinction ratio of 12 dB or linearly polarized light having an extinction ratio of 29 dB into the polarization maintaining optical fiber 45. At this time, the bending radius and the detection position of the optical fiber 45 with respect to the fixed point detected based on the two diffracted lights from the boundary portion 50 on the two diffraction gratings 48 and 49 attached to the scale 51 are the time. It measures how it shifts over time.

  Therefore, this measurement system includes an encoder 56 that is attached to the scale 51 and detects an analog positional deviation amount as digital data, an interpolation circuit 57 that performs a predetermined number of interpolations on the digital value from the encoder 56, and an interpolation A personal computer (PC) 58 that counts the positional deviation data of the fixed point detection position 40 based on the numerical value from the circuit 57 is provided. The personal computer 58 is also supplied with the comparison result from the comparator 54 of the fixed point detection device 40.

  FIG. 8 is a characteristic diagram showing the fixed point detection position shift due to the fiber bending. The horizontal axis indicates time (minutes). The left vertical axis represents the detection position (nm), and the right vertical axis represents the bending radius (mm) of the optical fiber.

  First, the fixed point position detected by the fixed point detection device 40 when the bending radius of the optical fiber is 60 (mm) is set to zero. If linearly polarized light having extinction ratios of 12 dB and 29 dB is incident on the optical fiber 45, the fixed point position is not shifted until the elapsed time reaches 18 minutes (referred to as the first state). The bending radius of the optical fiber 45 is 28 (mm) until the time elapses from 18 minutes to 32 minutes (referred to as the second state). In this second state, when the light incident portion 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detection device 40 is shifted by −60 (nm). On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this second state, the fixed point detected by the fixed point detector 40 can be shifted by −35 (nm).

  The bending radius of the optical fiber 45 becomes 18 (mm) until the time elapses from 32 minutes to 48 minutes (referred to as the third state). In this third state, when the light incident part 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detector 40 is shifted by -130 (nm). On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this third state, the fixed point detected by the fixed point detector 40 can be shifted by −62 (nm).

  The bending radius of the optical fiber 45 becomes 28 (mm) until the time elapses from 48 minutes to 63 minutes (referred to as the fourth state). In this fourth state, when the light incident portion 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detector 40 is shifted by −58 (nm). On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this fourth state, the fixed point detected by the fixed point detection device 40 can be shifted by −35 (nm).

  The bending radius of the optical fiber 45 is 60 (mm) until the time elapses from 63 minutes to 78 minutes (referred to as the fifth state). In the fifth state, when the light incident part 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detection device 40 becomes 0 (nm) as in the first state. Further, even if linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this fifth state, the fixed point detected by the fixed point detection device 40 is similarly 0 (nm).

  The bending radius of the optical fiber 45 is 28 (mm) until the time elapses from 78 minutes to 93 minutes (referred to as the sixth state). In this sixth state, when the light incident part 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detector 40 is shifted by −60 (nm). On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this sixth state, the fixed point detected by the fixed point detection device 40 can be shifted by −35 (nm).

  The bending radius of the optical fiber 45 is 18 (mm) until the time elapses from 93 minutes to 108 minutes (referred to as the seventh state). In the seventh state, when the light incident portion 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detection device 40 is only −130 (nm) as in the third state. Shift. On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in the seventh state, the fixed point detected by the fixed point detection device 40 is only -62 (nm) as in the third state. It ’s not necessary.

  The bending radius of the optical fiber 45 is 28 (mm) until the time elapses from 108 minutes to 123 minutes (referred to as the eighth state). In the eighth state, when the light incident portion 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detection device 40 is only −60 (nm) as in the sixth state. Shift. On the other hand, when linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in the eighth state, the fixed point detected by the fixed point detection device 40 is only −35 (nm) as in the sixth state. It ’s not necessary.

  The bending radius of the optical fiber 45 is 60 (mm) until the time elapses from 123 minutes to 137 minutes (referred to as the ninth state). In the ninth state, when the light incident portion 55 enters linearly polarized light having an extinction ratio of 12 dB into the optical fiber 45, the fixed point detected by the fixed point detection device 40 becomes 0 (nm) as in the first state. Further, even if linearly polarized light having an extinction ratio of 29 dB is incident on the optical fiber 45 in this ninth state, the fixed point detected by the fixed point detection device 40 is similarly 0 (nm).

  That is, when bending stress is applied to the optical fiber 45, when linearly polarized light having an extinction ratio of 29 dB higher than the extinction ratio of 12 dB is incident on the optical fiber 45 by the light incident portion 55, it is understood that the positional deviation of the fixed point is small. The effect of using this embodiment is clear.

  As the optical transmission units 11 and 41 used in the displacement measuring device 10 and the fixed point detecting device 40, the following specific examples can be used in addition to the configurations shown in FIGS. FIG. 9 shows an optical transmission unit in which a polarizing plate and a condenser lens are integrated. In each specific example described below with reference to FIGS. 9 to 13, the light source 12, the polarizing plate 13, the condenser lens 14, the polarization maintaining optical fiber 15, and the optical transmission unit used in the displacement measuring apparatus 10. 11 codes are used. Of course, it can also be used in the fixed point detection device 40.

  Considering the packaging of the light incident portion of the light transmission unit 11 (the light incident portion 55 described in FIG. 7 applied to the displacement measuring device 10 and comprising the light source 12, the polarizing plate 13, and the condenser lens 14). In this case, it is necessary to reduce the number of parts. By integrating the polarizing plate 13 and the condenser lens 14, the number of parts can be reduced. Of course, the light from the light source 12 is converted into a linearly polarized light having a high extinction ratio by the polarizing plate 13 by the light transmission unit 11 in FIG. The optical axis 34 of the wave holding type optical fiber 15 can be aligned and incident on the incident end 15 a of the optical fiber 15. Therefore, the beam emitted from the emission end 15b of the optical fiber 15 has a high extinction ratio, and the fluctuation of the extinction ratio due to bending or stress of the optical fiber can be reduced.

  FIG. 10 shows an optical transmission unit 11 in which the polarizing plate 14 is integrated so as to be sandwiched between the collimator lens 61 and the condenser lens 14. In this specific example, the beam from the light source 12 is converted into parallel light by the collimator lens 61 and is incident on the polarizing plate 13 perpendicularly. Therefore, the performance of the polarizing plate 13 can be exhibited sufficiently. This specific example can also reduce the number of parts in packaging. Of course, the beam emitted from the emission end 15b of the optical fiber 15 has a high extinction ratio, and the fluctuation of the extinction ratio due to bending or stress of the optical fiber 15 can be reduced. As a modification of this specific example, the collimator lens 61, the polarizing plate 13, and the condenser lens 14 may be arranged apart from each other without being integrated.

  FIG. 11 shows an optical transmission unit 11 that does not use a polarizing plate but is formed so that the incident end face 15a of the polarization-maintaining optical fiber 15 has a Brewster angle instead of the polarizing plate. By making the incident end face 15a of the optical fiber 15 have a Brewster angle, the S-wave polarization component is reflected at the interface and the P-wave polarization component is incident on the core 30 in the optical fiber 15 in the same manner as the function of the polarization filter. Let That is, only the beam of the P wave polarization component can be incident on the optical fiber 15. The beam emitted from the light source 12 enters only the P wave component through the condenser lens 14 into the optical fiber 15 having the incident end face 15a formed at the Brewster angle. The S-wave polarization component is reflected by the incident end face 15a formed at the Brewster angle as indicated by an arrow in the figure and is not incident on the core 30 of the optical fiber 15, so that a beam having a high extinction ratio is incident. Therefore, even in this specific example, the beam from the light source 12 is converted into linearly polarized light having a high extinction ratio, and this beam is further condensed by the condenser lens 14 so that the polarization axis of the beam and the polarization maintaining type light The optical axis 34 of the fiber 15 can be aligned and incident on the optical fiber 15. Therefore, the beam emitted from the emission end 15b of the optical fiber 15 has a high extinction ratio, and the fluctuation of the extinction ratio due to bending or stress of the optical fiber 15 can be reduced. Further, since it is not necessary to use a polarizing element, space can be saved in packaging.

  In FIG. 11, the incident end face 15a of the polarization maintaining optical fiber 15 may be formed by multilayer processing so that all the interfaces of the multilayer film have a Brewster angle. In this way, the S-wave polarization component can be reflected at the interface and the P-wave polarization component can be incident on the core 30 in the optical fiber 15 in the same manner as the function of the polarization filter. That is, only the beam of the P wave polarization component can be incident on the optical fiber 15. Further, the incident end face 15a of the optical fiber 15 may be formed to be a polarization beam splitter.

  FIG. 12 shows an optical transmission unit 11 in which a polarizing plate 63 is formed on the exit window of a semiconductor laser 62 used as a light source. The beam emitted from the semiconductor laser 62 has an extinction ratio of about 20 dB, but the extinction ratio can be set to about 30 dB by the polarizing plate 63 formed on the exit window. Also in this specific example, since it is not necessary to use a polarizing element in the external space of the semiconductor laser 62, space can be saved in packaging. Of course, the beam emitted from the emission end 15b of the optical fiber 15 has a high extinction ratio, and the fluctuation of the extinction ratio due to bending or stress of the optical fiber can be reduced.

  FIG. 13 shows an optical transmission unit 11 in which a window glass 64 for emitting a semiconductor laser 63 used as a light source is formed at a Brewster angle. In this semiconductor laser 63, the exit window is formed obliquely in order to prevent astigmatism from occurring due to the difference in divergence angle between the vertical direction and the horizontal direction of the beam. By forming the obliquely formed window glass 64 at a Brewster angle, the S wave polarization component is reflected at the interface in the same manner as the function of the polarization filter, and the P wave polarization component is reflected on the core 30 in the optical fiber 15. Make it incident. That is, only the beam of the P wave polarization component can be incident on the optical fiber 15. The P-polarized component emitted from the semiconductor laser 63 enters the optical fiber 15 through the condenser lens 14. Since the S wave polarization component is not incident, a beam having a high extinction ratio is incident. Therefore, even in this specific example, the beam from the semiconductor laser 63 is made into linearly polarized light having a high extinction ratio, and this beam is further condensed by the condenser lens 14 so that the polarization axis of the beam and the polarization holding type The optical axis 34 of the optical fiber 15 can be aligned and incident on the optical fiber 15. Therefore, the beam emitted from the emission end 15b of the optical fiber 15 has a high extinction ratio, and the fluctuation of the extinction ratio due to bending or stress of the optical fiber 15 can be reduced. Further, since it is not necessary to use a polarizing element outside the semiconductor laser 63, space can be saved in packaging.

  In FIG. 13, the window glass 64 of the semiconductor laser 63 may be formed by multilayer processing so that all interfaces of the multilayer film have a Brewster angle. In this way, the S-wave polarization component can be reflected at the interface and the P-wave polarization component can be incident on the core 30 in the optical fiber 15 in the same manner as the function of the polarization filter. That is, only the beam of the P wave polarization component can be incident on the optical fiber 15.

  The application of the present invention is not limited to the displacement measuring device 10 and the fixed point detecting device 40. At least a light source that emits light, an extinction ratio conversion unit that increases the extinction ratio of light emitted from the light source to 20 dB or more, and a collector that collects light having an extinction ratio of 20 dB or more by the extinction ratio conversion unit. An optical lens, a polarization-maintaining optical fiber that transmits the light collected by the condenser lens, and a diffraction grating that is attached to a measurement target and that is irradiated with and diffracted by the light transmitted by the optical fiber A light receiving means for receiving the light diffracted by the diffraction grating, the extinction ratio is increased to 20 dB or more by the extinction ratio converting means, and the polarization axis of the light condensed by the condensing means is set to the light The optical axis of the fiber or the axis perpendicular to the optical axis is incident on the optical fiber, and the displacement of the measurement object is detected by the magnitude of the amount of diffracted light received by the light receiving means. It can be applied to an apparatus for detecting a displacement due to optical adult. For example, there are a transmission type displacement detection device, a reflection type displacement detection device, a transmission type displacement measurement device, a transmission type fixed point detection device, and the like.

  Of course, the extinction ratio converting means may be a polarizing element. Further, the polarizing element which is the extinction ratio converting means may be integrated with the condenser lens.

  Further, the extinction ratio converting means may be formed by forming the light incident side end face of the optical fiber at a Brewster angle.

  Further, a semiconductor laser may be used as the light source, and the polarizing element may be formed on the exit window glass of the semiconductor laser.

  The extinction ratio converting means may be a polarization beam splitter. Further, a semiconductor laser may be used as the light source, and a polarization beam splitter may be formed on the exit window glass of the semiconductor laser.

  Alternatively, a semiconductor laser may be used as the light source, and the extinction ratio converting means may be formed by forming the exit window glass of the semiconductor laser at a Brewster angle. Further, the light incident side end face of the optical fiber may be used as a polarization beam splitter as the extinction ratio converting means.

  In the description so far, the displacement measuring devices 10 and 200 and the fixed point detection device 40 pass the beams from the light source 12 and the light source 42 through the polarizing plate 13 and the polarizing plate 43 and convert them into linearly polarized light having a high extinction ratio of 20 dB or more. Then, the light is condensed by the condensing lens 14 and the condensing lens 44, and is passed through the polarization maintaining optical fiber 15 and the optical fiber 45.

  Furthermore, in order to further reduce the disturbance of polarization due to bending or stress of the optical fiber, and thus to enable more accurate displacement measurement, a displacement measuring device 300 shown in FIG. 14 may be used.

  This displacement measuring device 300 is the outgoing end side 15b of the optical fiber 11 of the displacement measuring device 10 shown in FIG. 1, and the polarization of the beam transmitted by the optical fiber 15 between the condensing lens 17 is changed. This is a configuration including a depolarizing element 301 that makes no polarization.

  The depolarization element 301 depolarizes the beam transmitted through the optical fiber 15 and emitted. Crystal, mica or organic resin is used as the material. Here, a specific example of the depolarizing element 301 will be described with reference to FIG. The depolarizing element 301 whose cross section is shown in FIG. 15 is obtained by cutting a crystal 301a and a quartz glass 301b diagonally and bonding them using a transparent adhesive at a diagonal line 301c. In addition, mica or organic resin may be used as the material. Even if the incident light is, for example, linearly polarized light 131, the thicknesses of the quartz crystal 301a and the quartz glass 301b are different along the oblique line 301c, and λ / 4, 2λ / 4, 3λ /, depending on the position on the oblique line 301c. 4 thickness. For this reason, if the luminous flux has a width of, for example, about 1 mm, the light that is refracted by the quartz glass 301b becomes unpolarized random light 132. Based on this principle, the depolarizing element 301 can change the laser light whose polarization direction is fixed into non-polarized light such as natural light, that is, random light.

  The condensing lens 17 condenses the beam depolarized by the depolarization element 301 and makes it incident on the polarization beam splitter 18.

  As described above, the displacement measuring device 300 is provided with the depolarizing element 301 between the exit end 15b of the optical fiber 15 and the condensing lens 17, so that the bending or bending of the optical fiber 15 is greater than that of the displacement measuring device 10. Polarization disturbance due to stress can be further reduced. In addition, it is possible to detect displacement with higher accuracy.

  Similarly, FIG. 16 shows a displacement measuring device 350 having a configuration in which a depolarizing element 301 is provided between the output end side 15b of the optical fiber 15 and the condenser lens 17 in the displacement measuring device 200 having the configuration shown in FIG. . Also in this displacement measuring device 350, since the depolarizing element 301 is provided between the output end 15b of the optical fiber 15 and the condensing lens 17, the optical fiber 15 is bent more or more disturbed by stress than the displacement measuring device 200. It can be further reduced. In addition, it is possible to detect displacement with higher accuracy.

  Similarly, FIG. 17 shows a fixed point detection apparatus 400 having a configuration in which a depolarization element 301 is provided between the exit end side 45b of the optical fiber 45 and the condenser lens 47 in the fixed point detection apparatus 40 having the configuration shown in FIG. . Also in this fixed point detection apparatus 400, since the depolarization element 301 is provided between the output end 45b of the optical fiber 45 and the condensing lens 47, the polarization of the optical fiber 45 is bent and stress is disturbed more than the fixed point detection apparatus 40. It can be further reduced. In addition, it is possible to detect a fixed point with higher accuracy.

It is a block diagram of a displacement measuring device. It is the figure used in order to explain an extinction ratio. It is sectional drawing of a polarization maintaining type optical fiber. It is an application example of a displacement measuring device. It is a block diagram of a fixed point detection apparatus. FIG. 6 is a characteristic diagram showing that diffraction efficiency differs greatly between an S-polarized component and a P-polarized component. It is a system configuration diagram for measuring how a fixed point detection position changes with time when bending stress is applied to a polarization maintaining optical fiber. It is a characteristic view which shows the fixed point detection position shift by fiber bending. It is a figure which shows the optical transmission unit which integrated the polarizing plate and the condensing lens. It is a figure which shows the optical transmission unit integrated so that a polarizing plate may be inserted | pinched between a collimator lens and a condensing lens. It is a figure which shows the optical transmission unit which formed the incident end surface of the polarization-maintaining type optical fiber so that it might become a Brewster angle instead of a polarizing plate. It is a figure which shows the optical transmission unit which formed the polarizing plate in the emission window of the semiconductor laser used as a light source. It is a figure which shows the optical transmission unit which formed the window glass for the emission of the semiconductor laser used as a light source in the Brewster angle. It is a block diagram of the displacement measuring device further provided with the depolarizing element. It is sectional drawing of a depolarizing element. It is a block diagram of the application example of the displacement measuring device further provided with the depolarizing element. It is a block diagram of the application example of the fixed point detection apparatus further provided with the depolarization element. It is a block diagram of the conventional displacement detection apparatus. It is a block diagram of the conventional fixed point detection apparatus described in patent document 1. It is a figure which shows the holographic diffraction structure used with the fixed point detection apparatus shown in the said FIG. It is a figure which shows the principal part of the fixed point detection apparatus shown in the said FIG. It is a block diagram of the fixed point detection apparatus which detects a fixed point using an optical fiber. It is a block diagram of the displacement measuring device which measures a displacement using an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Displacement measuring device, 11 Optical transmission unit, 12 Light source, 13 Phase plate, 14 Condensing lens, 15 Polarization holding type optical fiber, 16 Detection part, 17 Condensing lens, 18 Polarizing beam splitter, 19 Diffraction grating, 20 1st 1/4 phase plate, 21 2nd 1/4 phase plate, 22 1st reflection mirror surface, 23 2nd reflection mirror surface, 24 prism, 40 fixed point detection apparatus, 41 light transmission unit, 42 light source 43 phase plate, 44 condensing lens, 45 polarization maintaining optical fiber, 46 detector, 47 condensing lens, 48 diffraction grating, 49 diffraction grating, 50 edges, 52, 53 light receiving element, 54 comparator, 300 Displacement measuring device, 301 depolarization element, 400 fixed point detection device

Claims (16)

A light source that emits light;
An extinction ratio converting means for increasing the extinction ratio of the light emitted from the light source to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
A diffraction grating that is attached to a measurement object and is irradiated with light transmitted by the optical fiber and diffracted;
A light receiving means for receiving the light diffracted by the diffraction grating,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A displacement detection device that detects the displacement of the measurement object based on the amount of received diffracted light received by the light receiving means.   2. The displacement detection apparatus according to claim 1, wherein the extinction ratio converting means is a polarizing element.   3. The displacement detection apparatus according to claim 2, wherein the polarizing element as the extinction ratio converting means is integrated with the condenser lens.   2. The displacement detecting device according to claim 1, wherein the extinction ratio converting means is formed by forming a light incident side end face of the optical fiber at a Brewster angle.   3. The displacement detection apparatus according to claim 2, wherein a semiconductor laser is used as the light source, and the polarizing element is formed on an exit window glass of the semiconductor laser.   2. The displacement detection device according to claim 1, wherein the extinction ratio converting means is a polarization beam splitter.   7. The displacement detection device according to claim 6, wherein a semiconductor laser is used as the light source, and a polarizing beam splitter is formed on the exit window glass of the semiconductor laser.   2. The displacement detection device according to claim 1, wherein a semiconductor laser is used as the light source, and the exit window glass of the semiconductor laser is formed at a Brewster angle to form the extinction ratio converting means.   2. The displacement detection device according to claim 1, wherein the light incident side end face of the optical fiber is used as the extinction ratio converting means as a polarization beam splitter. A light source that emits light;
Extinction ratio converting means for converting the light emitted from the light source into linearly polarized light and increasing its extinction ratio to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
A polarizing beam splitter that bisects the light transmitted by the optical fiber;
A diffraction grating that is attached to a measurement target and that receives light bisected by the polarizing beam splitter to obtain diffracted light;
A phase plate that changes the polarization of the diffracted light of the bisected light obtained by the diffraction grating;
Two reflecting mirrors that reflect the two diffracted lights whose polarization has been changed by the phase plate and guide them again to the diffraction grating through the phase plate;
A polarizing element guided to the diffraction grating by the two reflecting mirrors, diffracted by the diffraction grating, incident on the polarizing beam splitter, and interfering two diffracted lights reflected and transmitted by the polarizing beam splitter;
A light receiving element that receives the interference light obtained by the polarizing element,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A displacement measuring device that measures the displacement of the measurement object by the magnitude of the amount of diffracted light received by the light receiving means. A light source that emits light;
Extinction ratio converting means for converting the light emitted from the light source into linearly polarized light and increasing its extinction ratio to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
Two diffraction gratings arranged adjacent to each other and diffracted by being irradiated with light transmitted by the optical fiber;
Two light receiving means for receiving light diffracted by the two diffraction gratings;
Comparing means for comparing the amount of light received by the two light receiving means,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A fixed point detecting device for determining a fixed point based on a result of comparison between the received light amounts of the two light receiving means.   12. The fixed point detection apparatus according to claim 11, wherein the comparison means determines a point at which a signal obtained by comparing the received light amounts of the two light receiving means has an arbitrary magnitude as a fixed point. A light source that emits light;
An extinction ratio converting means for increasing the extinction ratio of the light emitted from the light source to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
A depolarizing element for depolarizing the light transmitted by the optical fiber;
A diffraction grating that is attached to a measurement object and diffracts when irradiated with light depolarized by the depolarization element,
A light receiving means for receiving the light diffracted by the diffraction grating,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A displacement detection device that detects the displacement of the measurement object based on the amount of received diffracted light received by the light receiving means.   14. The displacement detecting device according to claim 13, wherein the depolarizing means is a depolarizing plate made of quartz, mica or organic resin. A light source that emits light;
Extinction ratio converting means for converting the light emitted from the light source into linearly polarized light and increasing its extinction ratio to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
A depolarizing element for depolarizing the light transmitted by the optical fiber;
A polarization beam splitter that bisects the light depolarized by the depolarization element;
A diffraction grating that is attached to a measurement target and that receives light bisected by the polarizing beam splitter to obtain diffracted light;
A phase plate that changes the polarization of the diffracted light of the bisected light obtained by the diffraction grating;
Two reflecting mirrors that reflect the two diffracted lights whose polarization has been changed by the phase plate and guide them again to the diffraction grating through the phase plate;
A polarizing element guided to the diffraction grating by the two reflecting mirrors, diffracted by the diffraction grating, incident on the polarizing beam splitter, and interfering two diffracted lights reflected and transmitted by the polarizing beam splitter;
A light receiving element that receives the interference light obtained by the polarizing element,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A displacement measuring device that measures the displacement of the measurement object by the magnitude of the amount of diffracted light received by the light receiving means. A light source that emits light;
Extinction ratio converting means for converting the light emitted from the light source into linearly polarized light and increasing its extinction ratio to 20 dB or more;
A condensing lens for condensing light having an extinction ratio of 20 dB or more by the extinction ratio conversion means;
A polarization-maintaining optical fiber that transmits the light collected by the condenser lens;
A depolarizing element for depolarizing the light transmitted by the optical fiber;
Two diffraction gratings arranged adjacent to each other and diffracted by being irradiated with light depolarized by the depolarization element,
Two light receiving means for receiving light diffracted by the two diffraction gratings;
Comparing means for comparing the amount of light received by the two light receiving means,
The optical fiber is adjusted so that the extinction ratio is increased to 20 dB or more by the extinction ratio converting means and the polarization axis of the light condensed by the condensing means is aligned with the optical axis of the optical fiber or an axis perpendicular to the optical axis. A fixed point detecting device for determining a fixed point based on a result of comparison between the received light amounts of the two light receiving means.

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