JP2010210326A - Interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy-to-measure interferometer even when its installation space is limited. <P>SOLUTION: A light beam L1 from a laser light source 2 is introduced into a reference plane 721 and an object under measurement 4 to obtain a reference light beam L4 and a measuring light beam L5 of which the polarization planes are orthogonal to each other. A sensor head 7 for emitting their combined light beam L6 is connected to a body 10 having the laser light source 2 through a flexible polarization reserving fiber 309, thereby allowing the sensor head 7 to be placed at an appropriate position and the displacement of the object under measurement 4 to be measured easily even when the installation space is limited. The sensor head 7 is connected to the body 10 through the polarization reserving fiber 309 which guides light with the polarization plane maintained, thereby allowing the polarization planes of the reference light beam L4 and the measuring light beam L5 to be reserved to be orthogonal to each other when the combined light beam L6 emitted from the sensor head 7 propagates through the polarization reserving fiber 309. The displacement of the object under measurement 4 is therefore measured accurately through the combined light beam L6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an interferometer.

  Conventionally, the light emitted from the light source is divided, one is made incident on the reference surface to obtain the reference light, and the other is made incident on the object to be measured to obtain the measurement light. There is known an interferometer that measures the amount of displacement of an object to be measured by analyzing interference generated by a difference in optical path length. As such an interferometer, there are known a homodyne interferometer that causes reference light and measurement light to interfere with each other at the same wavelength, and a heterodyne interferometer that causes reference light and measurement light to interfere with each other at different wavelengths. As a typical homodyne interferometer, for example, a Michelson interferometer is known (for example, see Patent Documents 1 to 3).

FIG. 7 is a diagram showing a configuration of a conventional Michelson interferometer 1E.
As shown in FIG. 7, a conventional Michelson interferometer 1E (hereinafter referred to as a Michelson interferometer) includes a laser light source 2, a probe optical system 3, an acquisition unit 5, a calculation unit 6, and And have an integrated configuration. In such an interferometer 1E, the laser light L1 emitted from the laser light source 2 enters the probe optical system 3. The light L1 incident on the stylus optical system 3 is adjusted by the half-wave plate 301 after the ratio of the S wave component and the P wave component with respect to the polarizing film 303 of the polarizing beam splitter 302 disposed downstream of the optical path is adjusted. The polarized beam splitter 302 divides the light into S-wave light L 2 reflected by the polarized beam splitter 302 and P-wave light L 3 transmitted through the polarized beam splitter 302.

The light L2 passes through the quarter-wave plate 304 and is then reflected by the reference surface 305 to become reference light L4. The reference light L4 passes through the quarter wavelength plate 304, is converted into P-wave light with respect to the polarizing beam splitter 302, and passes through the polarizing beam splitter 302.
The light L3 passes through the quarter-wave plate 306, and then is reflected by the DUT 4 to become measurement light L5. The measurement light L5 passes through the quarter-wave plate 306, is converted into S-wave light with respect to the polarization beam splitter 302, is reflected by the polarization beam splitter 302, and is combined with the reference light L4.

  The combined light L6 (interference light) of the reference light L4 and the measurement light L5 is incident on the acquisition unit 5, and the polarizing films 504 and 504 of the polarizing beam splitters 503 and 508 disposed downstream of the optical path by the half-wave plate 501. After the ratio of the P wave component and the S wave component with respect to 509 is adjusted, the light is split into light L7 and light L8 by the non-polarizing beam splitter 502.

  The light L7 is split by the polarization beam splitter 503 into P-wave light L71 and S-wave light L72. That is, the light L7 is a P-wave light L71 serving as a phase reference of each of the lights L72, L81, and L82, which will be described later, and a phase difference delayed by 180 ° with respect to the light L71 when reflected by the polarization beam splitter 508. The light is divided into 180 ° S-wave light L72. The divided lights L71 and L72 are received by the photodetectors 505 and 506, respectively. Thereby, when the DUT 4 is displaced, the photodetector 505 obtains a sinusoidal interference signal A1 indicating the intensity of the light L71 (interference), and the photodetector 506 provides the intensity of the light L72 having a phase difference of 180 °. A sinusoidal interference signal A2 is obtained.

  On the other hand, the light L8 passes through the quarter-wave plate 507, and after the phase is delayed by 90 ° with respect to the light L7 (reference light L71), the polarization beam splitter 508 causes the P-wave light L81 and the S-wave light. Divided into light L82. That is, the light L6 has a phase difference of 90 ° with respect to the light L71 and a phase difference of 90 ° with respect to the light L71, and is reflected by the polarization beam splitter 508 so that the phase is 180 ° behind the light L81. In other words, the light is divided into light L82 having a phase difference of 270 °, the phase of which is delayed by 270 °. The divided lights L81 and L82 are received by the photodetectors 510 and 511, respectively. As a result, when the DUT 4 is displaced, an interference signal A3 indicating the intensity of the light L81 having a phase difference of 90 ° is obtained by the photodetector 510, and the intensity of the light L82 having a phase difference of 270 ° is obtained by the photodetector 511. The interference signal A4 shown is obtained.

  Then, the calculation means 6 performs a first sine wave signal obtained by taking a difference between the interference signal A2 having a phase difference of 180 ° and the reference interference signal A1 by an electrical signal process, an interference signal A2 having a phase difference of 270 °, and By generating a second sinusoidal signal obtained by taking the difference of the interference signal A1 having a phase difference of 90 °, and counting the repetition of intensity changes of the first and second sinusoidal signals having the phase difference of 90 °. The amount of displacement of the DUT 4 is calculated with high accuracy.

JP-A-2-22503 Quantitative Research Institute Vol.49, (2000) pp. 38-39 M.J Downs and K.W.Raine: Anunmodulated bidirectional fringe-counting interferometer system for measuring displacement, precis.eng, Vol.1, No2 (1979) 85

  However, such an interferometer 1E has a configuration in which the laser light source 2, the probe optical system 3, the acquisition unit 5, and the calculation unit 6 are integrated, and tends to be large. Therefore, in order to apply the light L3 to the object 4 to be measured and obtain the measurement light L5, it is necessary to adjust the positional relationship between the interferometer 1E and the object 4 to be measured. The interferometer 1E has a problem that since the interferometer 1E is large, the positional relationship cannot be adjusted well and it is difficult to measure.

  An object of the present invention is to provide an interferometer that is easy to measure even when the installation space is limited.

  The interferometer of the present invention causes a laser light source and light from the laser light source to be incident on a reference surface and incident on a measurement object, and is reflected by the reference light reflected on the reference surface and the measurement object. A sensor head that obtains the measured light, multiplexes the measurement light and the reference light after orthogonalizing the polarization plane of the measurement light and the polarization plane of the reference light, and emits the combined light; and the laser While transmitting light from the light source to the sensor head side, guiding the light emitted from the sensor head, and guiding the light emitted from the light guide means to the sensor head, A polarization-maintaining fiber that guides the combined light emitted from the sensor head to the light guide unit while preserving the polarization plane of the combined light, and interference from the combined light extracted by the light guide unit Characterized in that it comprises an acquisition unit configured to acquire items, and a calculating means for calculating a displacement amount of the object to be measured based on the interference signal.

According to the present invention, the sensor head is connected to the main body unit including the laser light source, the light guide unit, the acquisition unit, the calculation unit, and the like by the polarization maintaining fiber. The light emitted from the laser light source of the main body is guided to the sensor head via the polarization maintaining fiber. Thus, since the sensor head and the main body having the laser light source and the like are connected by the polarization maintaining fiber, the sensor head can be arranged at an appropriate position, and it is easy even if the installation space is limited. In addition, the amount of displacement of the object to be measured can be measured.
In addition, when the sensor head is connected to the main body by an optical fiber that guides light without preserving the plane of polarization, the reference light in the combined light is transmitted when the combined light emitted from the sensor head passes through the optical fiber. Further, since the polarization planes of the measurement light are respectively rotated (because the phases of the respective lights are shifted), the calculation means cannot accurately measure the displacement amount of the object to be measured from the combined light. On the other hand, in the present invention, since the sensor head is connected to the main body by a polarization maintaining fiber that preserves and guides the polarization plane, the combined light is transmitted when the combined light passes through the polarization maintaining fiber. The polarization planes of the reference light and the measurement light are stored in a state where they are orthogonal to each other. Therefore, the calculating means can accurately measure the displacement amount of the object to be measured from the combined light.

  In the interferometer according to the aspect of the invention, the sensor head includes a quarter-wave plate disposed downstream of the optical path of the reference surface, and the reference surface is a part of the light from the laser light source incident on the reference surface. Is preferably reflected as the reference light and the remaining light is transmitted.

In the present invention, the sensor head includes, for example, a lens, a translucent member, and a quarter wavelength plate. Then, the light from the laser light source is collected and collimated by the lens, and then enters the translucent member. A part of the light is reflected on the surface (reference surface) to become reference light, and the rest is the surface and translucent. The light passes through the member, passes through the quarter-wave plate, and then enters the object to be measured and is reflected to become measurement light. The measurement light is transmitted through the quarter-wave plate, converted into linearly polarized light in which the reference light and the polarization plane are orthogonal, and then transmitted through the reference surface and combined with the reference light.
Here, in the conventional interferometer, the light from the laser light source is divided into two directions using a polarization beam splitter, a quarter wavelength plate and a reference surface are arranged on one optical path, and 1 on the other optical path. By arranging the / 4 wavelength plate and the object to be measured, reference light and measurement light whose polarization planes are orthogonal to each other are obtained, and two quarter wavelength plates are required.
On the other hand, in the present invention, as described above, since only one quarter-wave plate is required to obtain the reference light and the measurement light whose polarization planes are orthogonal to each other, the conventional configuration is applied to the sensor head. Compared to the case, the sensor head can be miniaturized, and measurement is easier even if the space is limited.

  The interferometer of the present invention includes a refractive index gradient type lens whose refractive index continuously changes along a radial direction, and the refractive index gradient type lens includes an incident surface on which light from the laser light source is incident, It is preferable that a part of the light incident on the incident surface is reflected as the reference light, and an emission surface that is the reference surface for emitting the remaining light is provided.

  According to the present invention, the light incident on the entrance surface of the gradient index lens and collimated by the gradient index lens is reflected by the exit surface (reference surface) on the exit surface; The light is divided into light that is transmitted to the quarter-wave plate side. Therefore, since the function of collimating and dividing light can be realized only by the gradient index lens, the number of parts can be reduced as compared with the above-described configuration in which the function of collimating and dividing light is realized by the lens and the translucent member. .

  In the interferometer of the present invention, the reference surface is a wire grid surface in which a plurality of wires are provided in parallel, and out of light incident on the reference surface, light whose polarization plane is parallel to the wire is the reference light. It is preferable that the plane of polarization transmits light perpendicular to the wire.

  According to the present invention, among the light incident on the reference surface which is the wire grid surface, a part of the light whose polarization plane is parallel to the wire is reflected by the reference surface to become reference light, and the polarization plane is perpendicular to the wire. Passes through the reference surface and is reflected by the object to be measured to become measurement light. Then, the measurement light passes through the reference surface and is combined with the reference light in which the measurement light and the polarization plane are orthogonal to each other. Therefore, a quarter wave plate for rotating the polarization plane of the light transmitted through the reference surface is not necessary, and the number of parts can be reduced.

  In the interferometer of the present invention, the reference surface is an exit end surface of the polarization maintaining fiber on the sensor head side, reflects a part of incident light as the reference light and transmits the remaining light on the sensor head side. It is preferable to inject.

  In general, the exit end face of the optical fiber is subjected to an oblique polishing process or an antireflection film so that reflected light as noise is not generated. In the present invention, such a special one is applied to the exit end face of the polarization maintaining fiber. By not intentionally performing the processing, the exit end surface is caused to function as a reference surface that reflects a part of light from the laser light source as reference light. Thereby, a member such as a translucent member for dividing the light from the laser light source into the reference light and the measurement light can be eliminated, and the configuration can be simplified.

  In the interferometer of the present invention, the light guide means is an optical circulator that emits light from the laser light source only to the sensor head side and emits the combined light from the sensor head side only to the acquisition means side. Preferably there is.

  According to the present invention, since the optical circulator that emits the combined light from the sensor head side only to the acquisition means side is used as the light guide means, it is possible to prevent the combined light from returning to the laser light source side. The return light (combined light) can prevent the laser light source from becoming unstable, or noise included in the light emitted from the laser light source from increasing, thereby reducing the measurement accuracy. Further, since the number of flexible fiber portions increases, it becomes easier to handle the sensor head and the main body, and convenience can be improved.

  In the interferometer of the present invention, the laser light source includes a first laser light source that emits light of a first wavelength, and a second laser light source that emits light of a second wavelength different from the first wavelength, The light emitted from the first and second laser light sources is combined between the light guide means and the acquisition means, and is combined with the polarization planes being orthogonal to each other and emitted to the light guide means side. And the light extracted by the light guide means from the first combined light composed of the reference light of the first wavelength and the measurement light, and the reference light of the second wavelength and the measurement light. Splitting into the second combined light, and the acquiring means includes a first acquiring means for acquiring a first interference signal from the first combined light emitted from the splitting means, and the splitting means. A second acquisition of a second interference signal from the emitted second combined light Obtaining means, wherein the calculating means calculates displacement amounts of the object to be measured from the first and second interference signals, and the polarization-maintaining fiber included in the displacement amounts from the displacement amounts. It is preferable that the amount of displacement of the object to be measured is calculated by offsetting the error due to.

  According to the present invention, the displacement amount of the object to be measured calculated from the first and second combined lights is added and divided by 2, for example, to compensate for errors caused by bending or twisting of the polarization maintaining fiber. Since the displacement amount of the measurement object is calculated, the measurement accuracy can be improved.

[First Embodiment]
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of an interferometer 1 according to the first embodiment. In the following description, elements having the same functions as those of the conventional interferometer 1E are denoted by the same reference numerals, and the description thereof is omitted or simplified. In FIG. 1, the optical axis of the light emitted from the laser light source 2 is indicated by a solid line, and the optical path is indicated by a one-dotted line for easy understanding.

As shown in FIG. 1, the interferometer 1 includes a laser light source 2, a probe optical system 3, an acquisition unit 5, and a calculation unit 6.
The laser light source 2 emits linearly polarized laser light L1.
The probe optical system 3 includes a non-polarizing beam splitter 307 as a light guiding unit, a lens 308, a polarization maintaining fiber 309, and a sensor head 7. In the present embodiment, the main body 10 includes the laser light source 2, the non-polarizing beam splitter 307, the lens 308, the acquisition unit 5, and the calculation unit 6.

  The polarization maintaining fiber 309 has flexibility and connects the main body 10 and the sensor head 7. The polarization maintaining fiber 309 stores the polarization plane of light incident from the main body 10 side or the sensor head 7 side, and emits it to the other side. As such a polarization maintaining fiber 309, for example, a structure in which a core is formed in an elliptical shape, or a so-called PANDA fiber in which a stress applying portion is provided around the core, is propagated in a biaxial direction perpendicular to the cross section. What maintains a mode etc. can be employ | adopted.

  The sensor head 7 includes a lens 71, a translucent member 72, and a ¼ wavelength plate 73. In the translucent member 72, the surface on which the light L <b> 1 from the laser light source 2 is incident reflects the light L <b> 1 as the reference light L <b> 4 and the reference surface 721 that transmits the remaining light L <b> 3 to the quarter wavelength plate 73 side. It has become.

Hereinafter, the optical path of the light L1 emitted from the laser light source 2 will be described.
The linearly polarized light L1 emitted from the laser light source 2 passes through the non-polarizing beam splitter 307, is condensed and collimated by the lens 308, and then enters the polarization maintaining fiber 309. Is emitted toward the lens 71 of the sensor head 7. The light L1 emitted from the polarization maintaining fiber 309 from the laser light source 2 is condensed and collimated again by the lens 71, and then enters the reference surface 721. A part of the light L1 is reflected as the reference light L4, and the rest The light L3 passes through the reference surface 721.

  The light L3 that has passed through the reference surface 721 passes through the quarter-wave plate 73, is converted into circularly polarized light, and then is reflected by the DUT 4 to become measurement light L5. Then, the measurement light L5 is transmitted through the quarter-wave plate 73 to be converted into linearly polarized light whose plane of polarization is rotated by 90 °, that is, linearly polarized light in which the plane of polarization of the reference light L4 and the plane of polarization are orthogonal to each other. The light is combined with the reference light L4 that is transmitted through the surface 721 and reflected by the reference surface 721.

  The combined light L6 composed of the reference light L4 and the measurement light L5 passes through the lens 71 and then enters the polarization preserving fiber 309, and the polarization planes of the reference light L4 and the measurement light L5 in the combined light L6 are stored. In this state, the light is guided to the polarization maintaining fiber 309 and emitted toward the lens 308. The combined light L6 passes through the lens 308 and is then reflected by the non-polarizing beam splitter 307 toward the acquisition means 5 side.

As described in the background art, the acquisition unit 5 divides the combined light L6 (interference light) into four lights L71, L72, L81, and L82 having different phases every 90 °, thereby receiving the light L71. , L72, L81, and L82, the four interference signals A1 to A4 having different phases are output every 90 °.
Then, the calculation means 6 generates the first interference signal from the interference signal A1 and the interference signal A2 that is 180 degrees out of phase with respect to the interference signal A1, and the 90 degrees out of phase with respect to the interference signal A1. A second interference signal is generated from the interference signal A3 and the interference signal A4 delayed in phase by 270 ° with respect to the interference signal A1, and the device under test 4 in the optical axis direction of the light L3 is generated from these first and second interference signals. The amount of displacement is calculated.

According to the above embodiment, the following effects can be obtained.
Since the sensor head 7 is connected to the main body 10 having the laser light source 2 and the like by the flexible polarization-maintaining fiber 309, the sensor head 7 can be disposed at an appropriate position, and the installation space is reduced. Even if it is limited, the amount of displacement of the DUT 4 can be measured easily.

  Since the sensor head 7 is connected to the main body 10 by a polarization maintaining fiber 309 that stores and guides the polarization plane, the combined light L6 emitted from the sensor head 7 passes through the polarization maintaining fiber 309. In addition, the polarization planes of the reference light L4 and the measurement light L5 in the combined light L6 are stored while being orthogonal to each other. Therefore, the calculation means 6 can accurately measure the amount of displacement of the DUT 4.

  The sensor head 7 causes the light L1 from the laser light source 2 to enter the reference surface 721, obtains the reference light L4 by a part of the reflected light, and transmits the remaining light L3 that has passed through the reference surface 721 to the quarter wavelength plate. The measurement light L5 is obtained by transmitting the light 73 and then reflecting the light by the object 4 to be measured. Then, the measurement light L5 reflected by the DUT 4 is transmitted through the quarter-wave plate 73 so that the polarization plane of the measurement light L5 is orthogonal to the polarization plane of the reference light L4. Therefore, in the present embodiment, only one quarter-wave plate 73 is required to obtain the reference light L4 and the measurement light L5 whose polarization planes are orthogonal to each other, and therefore the reference light L4 whose polarization planes are orthogonal to each other. Compared with the case where the conventional configuration, which requires two quarter-wave plates 304 and 306 to obtain the measurement light L5, is applied to the sensor head 7, this embodiment can reduce the size of the sensor head 7 and reduce the space. It becomes easier to measure even if is limited.

[Second Embodiment]
FIG. 2 is a diagram illustrating a configuration of an interferometer 1A according to the second embodiment.
As shown in FIG. 2, the interferometer 1A of the present embodiment is provided with a refractive index gradient lens 74 (Grin lens) in the sensor head 7A instead of the lens 71 and the light transmitting member 72 of the first embodiment. This is a feature. The refractive index gradient lens 74 is formed in a cylindrical shape, and its refractive index gradually changes along the radial direction to collimate incident light. One end surface of the gradient index lens 74 is an incident surface 741 on which light from the laser light source 2 is incident, and the other end surface is incident from the incident surface 741 and is made parallel to the optical axis direction. A part of the reflected light is reflected as the reference light L4, and the remaining light L3 is an emission surface 742 for emitting the light to the quarter wavelength plate 73 side. In the present embodiment, the emission surface 742 functions as a reference surface.

  In this embodiment as well, the same effect can be obtained with the same configuration as that of the embodiment. In addition, since it has an exit surface 742 that functions as a reference surface and a refractive index gradient lens 74 that collimates incident light, the incident that is realized by the lens 71 and the translucent member 72 in the first embodiment. The function of collimating and dividing the light can be realized by only the refractive index gradient lens 74, and the number of parts can be reduced as compared with the first embodiment.

[Third Embodiment]
FIG. 3 is a diagram illustrating a configuration of an interferometer 1B according to the third embodiment.
In the interferometer 1B of the present embodiment, as shown in FIG. 3, the light incident surface of the translucent member 72A is provided in parallel with a plurality of wires made of metal such as aluminum at a minute interval sufficiently shorter than the wavelength of the light L1. This is characterized in that the wire grid surface 721A is formed. Of the incident light L1, the wire grid surface 721A reflects light (linearly polarized light) whose polarization plane is parallel to the wire as reference light L4, and functions as a reference surface. In addition, the wire grid surface 721A transmits light L3 (linearly polarized light) of which incident light L1 has a polarization plane perpendicular to the wire. The light L3 that has passed through the wire grid surface 721A is reflected by the object to be measured 4 and becomes measurement light L5. The measurement light L5 passes through the wire grid surface 721A and is combined with the reference light L4 whose polarization plane is orthogonal.

  Thus, in this embodiment, the wire grid surface 721A that reflects the incident light L1 as the reference light L4 transmits only the light L3 whose polarization plane is orthogonal to the reference light L4. Even without providing a quarter-wave plate for rotating the polarization plane of the light L3, the measurement light L5 in which the polarization plane is orthogonal to the reference light L4 is obtained simply by reflecting the light L3 with the measurement object 4. Can do. Therefore, the number of parts can be reduced by the amount that the quarter wavelength plate can be dispensed with.

[Fourth Embodiment]
FIG. 4 is a diagram illustrating a configuration of an interferometer 1C according to the fourth embodiment.
As shown in FIG. 4, the interferometer 1 </ b> C of the present embodiment is characterized in that the return light L <b> 6 (combined light L <b> 6) from the sensor head 7 is extracted to the acquisition unit 5 side by an optical circulator 8 as a light guide unit. is there.

The optical circulator 8 emits the light L1 from the laser light source 2 only to the sensor head 7 side, and emits the combined light L6 from the sensor head 7 side only to the acquisition means 5 side. The optical circulator 8 includes a first surface 81, a second surface 82, and a third surface 83 formed at different positions, although the drawing is simplified. A polarization maintaining fiber 84 is attached to the first surface 81. The second surface 82 is connected to the sensor head 7 by a polarization maintaining fiber 309. A polarization maintaining fiber 85 is attached to the third surface 83. In such an optical circulator 8, the light L1 emitted from the laser light source 2 and guided to the first surface 81 through the polarization maintaining fiber 84 is emitted only from the second surface 82 to the sensor head 7 side. Further, the combined light L6 emitted from the sensor head 7 and guided to the second surface 82 through the polarization maintaining fiber 309 is emitted only from the third surface 83 to the acquisition means 5 side. The combined light L <b> 6 emitted from the third surface 83 is collected and collimated by the lens 310 and then enters the acquisition unit 5.
In the present embodiment, the main body 10 includes the laser light source 2, the lenses 308 and 310, the polarization maintaining fibers 84 and 85, the optical circulator 8, the acquisition unit 5, and the calculation unit 6.

  In this embodiment as well, the same effect can be obtained with the same configuration as in the first embodiment. In addition, since the optical circulator 8 that emits the combined light L6 from the sensor head 7 side only to the acquisition unit 5 side is used as the light guide unit, the combined light L6 can be prevented from returning to the laser light source 2 side. The return light L6 from the sensor head 7 can prevent the laser light source 2 from becoming unstable or the noise included in the light L1 emitted from the laser light source 2 from increasing, thereby reducing the measurement accuracy. .

[Fifth Embodiment]
FIG. 5 is a diagram illustrating a configuration of an interferometer 1D according to the fifth embodiment.
The interferometer 1D of this embodiment is characterized in that the laser light sources 21 and 22 having different wavelengths λ1 and λ2 are used, the measurement error due to the deflection of the polarization maintaining fiber 309 is removed, and the displacement amount of the DUT 4 is calculated. is there.

As shown in FIG. 5, the interferometer 1 </ b> D of this embodiment includes a laser light source 2, a probe optical system 3, a dividing unit 9, an acquiring unit 5, and a calculating unit 6.
The laser light source 2 has a predetermined wavelength λ1 (first wavelength), and a first laser light source 21 that emits a laser beam L1A that is a P wave to a polarization beam splitter 311 to be described later, and the laser beam L1A And a second laser light source 22 that has a different wavelength λ2 (second wavelength) and emits a laser beam L1B that is an S wave to the polarization beam splitter 311.

  The wavelengths λ1 and λ2 of the laser beams L1A and L1B are desirably relatively close to each other so that the refractive index of the core inside the polarization maintaining fiber 309 with respect to the laser beams L1A and L1B can be regarded as substantially equal. Between the wavelengths λ 1 and λ 2, the combined light of the wavelengths λ 1 and λ 2 can be separated into light of the wavelengths λ 1 and λ 2 by an element such as a circuit grid, a prism, and bandpass filters 92 and 93 described later. It is desirable that there is a difference in degree.

The probe optical system 3 includes a polarization beam splitter 311, a non-polarization beam splitter 307, a lens 308, a polarization preserving fiber 309, and a sensor head 7 as multiplexing means.
The splitting unit 9 includes a non-polarizing beam splitter 91, a band-pass filter 92 that transmits only light having a wavelength λ1, and a band-pass filter 93 that transmits only light having a wavelength λ2. The emitted combined light L6 is divided into a first combined light L6A having a wavelength λ1 and a second combined light L6B having a wavelength λ2.

The acquisition unit 5 includes an acquisition unit 5A on which the first combined light L6A having the wavelength λ1 is incident and an acquisition unit 5B on which the second combined light L6B having the wavelength λ2 is incident. These acquisition means 5A and 5B have the same configuration as the acquisition means 5 in the back technique.
In the present embodiment, the main body 10 includes a laser light source 2, a polarizing beam splitter 311, a non-polarizing beam splitter 307, a lens 308, a dividing unit 9, an acquiring unit 5, and a calculating unit 6.

  In such an interferometer 1 </ b> D, the laser beam L <b> 1 </ b> A that is emitted from the laser light source 21, has a wavelength λ <b> 1, and is a P wave with respect to the polarization beam splitter 311 passes through the polarization beam splitter 311. The laser light L1B emitted from the laser light source 22 and having a wavelength λ2 and being S-waves with respect to the polarization beam splitter 311 is reflected by the polarization beam splitter 311 and the light L1A from the laser light source 21 whose polarization planes are orthogonal to each other. Combine. The combined light L1 by the lights L1A and L1B passes through the non-polarizing beam splitter 307 and the lens 308, and enters the sensor head 7 in a state where the polarization planes of the lights L1A and L1B are stored by the polarization maintaining fiber 309.

  The sensor head 7 obtains the reference light L4A from the light L1A having the wavelength λ1 and the measurement light L5A in which the polarization plane is orthogonal to the reference light L4A, and the reference light L4B and the reference light L4B are polarized from the light L1B having the wavelength λ2. The orthogonal measurement light L5B is obtained. At this time, since the polarization planes of the lights L1A and L1B from the laser light sources 21 and 22 are orthogonal to each other, the reference light L4A of the light L1A having the wavelength λ1 and the measurement light L5B of the light L1B having the wavelength λ2 are parallel. The measurement light L5A of the light L1A having the wavelength λ1 is parallel to the reference light L4B of the light L1B having the wavelength λ2.

  The combined light L6 of these lights L4A, L4B, L5A, and L5B, that is, the combined light L4A and L4B of light L4A and L5A obtained from the light L1A of wavelength λ1 and the light L1B of wavelength λ2 The combined light L6 from L6B is emitted toward the lens 308 with the polarization plane preserved by the sensor head 7, passes through the lens 308, and is then transmitted to the non-polarizing beam splitter 307 by the non-polarizing beam splitter 91 of the dividing unit 9. Reflected to the side.

The combined light L6 reflected by the non-polarizing beam splitter 307 is split into two lights L61 and L62 by the non-polarizing beam splitter 91.
The light L61 that passes through the non-polarizing beam splitter 91 passes through the bandpass filter 92, so that only the combined light L6A having the wavelength λ1 is extracted. The combined light L6A having the wavelength λ1 extracted from the light L61 enters the acquisition unit 5A. The acquisition unit 5A obtains four interference signals A1 to A4 whose phases are different every 90 ° from the combined light L6A and outputs the four interference signals A1 to A4 to the calculation unit 6. Then, the calculation means 6 generates first and second interference signals whose phases are different from each other by 90 ° from these four interference signals A1 to A4, and counts repetition of intensity changes of these first and second interference signals. Then, the displacement amount of the DUT 4 is calculated.

Here, when the polarization maintaining fiber 309 bends and the refractive indexes in the two orthogonal directions in the cross section of the cladding inside the polarization maintaining fiber 309 change, the combined light L6A having the wavelength λ1 emitted from the sensor head 7 is obtained. When passing through the polarization-maintaining fiber 309, an optical path length difference occurs between the reference light L4A and the measurement light L5A whose polarization planes are orthogonal to each other, and an error occurs in the calculated displacement amount of the measured object 4. That is, the displacement amount of the device under test 4 calculated based on the combined light L6A of the wavelength λ1 is m1, the displacement amount of the actual device under test 4 is L, the reference light L4A generated by the deflection of the polarization maintaining fiber 309, and the measurement The optical path length difference between the lights L5A is n. Then, if the optical path length of the measurement light L5A is increased by n with respect to the reference light L4A, the displacement m1 of the DUT 4 calculated from the combined light L6A having the wavelength λ1 is expressed by the following equation (1). .
m1 = L + n (1)

  In addition, from the light L62 reflected by the non-polarizing beam splitter 91, only the combined light L6B having the wavelength λ2 is extracted by the bandpass filter 93, and the acquisition unit 5B has a phase that differs every 90 ° from the combined light L6B. Two interference signals A1 to A4 are output, and the calculation means 6 calculates the displacement amount of the DUT 4 from these interference signals A1 to A4.

Here, the reference light L4B of the combined light L6B having the wavelength λ2 is parallel to the measurement light L5A of the combined light L6A having the wavelength λ1, and the measurement light L5B of the combined light L6B having the wavelength λ2 is the reference light of the combined light L6A having the wavelength λ1. Parallel to L4A. Accordingly, in the combined light L6A having the wavelength λ1, the optical path length of the measurement light L5A is increased by n with respect to the reference light L4A due to the deflection of the polarization maintaining fiber 309. However, in the combined light L6B having the wavelength λ2, The optical path length of the reference light L4B having parallel surfaces is increased by n with respect to the measurement light L5B. That is, the optical path length of the measurement light L5B is reduced by n with respect to the reference light L4B. Accordingly, when the displacement amount of the DUT 4 calculated from the combined light L6B having the wavelength λ2 is m2, m2 is expressed by the following equation (2).
m2 = L-n (2)

Therefore, the calculation means 6 adds 2 to the displacements m1 and m2 of the DUT 4 calculated based on the combined lights L6A and L6B of the wavelengths λ1 and λ2, as shown in the following equation (3). The actual displacement amount L of the object to be measured 4 is obtained by dividing by.
L = (m1 + m2) / 2 (3)

  As described above, in the present embodiment, the calculation unit 6 uses the displacement amount m1 of the DUT 4 calculated from the combined light L6A and the displacement amount M2 of the DUT 4 calculated from the combined light L6B. Since the actual displacement L of the DUT 4 is calculated by offsetting the error n caused by the deflection of the polarization maintaining fiber 309 included in the variation amounts m1 and m2, the measurement accuracy can be improved.

[Sixth Embodiment]
FIG. 6 is a diagram illustrating a configuration of a main part of an interferometer 1E according to the sixth embodiment.
As shown in FIG. 6, the interferometer 1E of this embodiment is characterized in that the exit end face 313 of the polarization maintaining fiber 309 functions as a reference plane. That is, normally, the exit end face of the polarization maintaining fiber 309 is applied to the exit end face 313 of the polarization-maintaining fiber 309 when the exit end face of the optical fiber is subjected to an oblique polishing process or an antireflection film so that the reflected light as noise is not generated. By not performing such special processing, the light L1 from the laser light source 2 is partially reflected by the emission end face 313, and this reflected light is used as the reference light L4. Thereby, in this embodiment, the translucent member 72 required in the said 1st Embodiment can be made unnecessary and a structure can be simplified.

  Note that the reflectance of the exit end face 313 is improved by applying a reflection coat or the like to the exit end face 313 of the polarization-maintaining fiber 309, thereby making the intensity ratio of the reference light 4 and the measurement light L 5 close to each other and outputting by the acquisition means 5. The S / N ratio of the interference signals A1 to A4 to be generated may be increased. In FIG. 6, 309A is a core of the polarization maintaining fiber 309, and 309B is a cladding of the polarization maintaining fiber 309.

[Modification of Embodiment]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
In each of the embodiments described above, the sensor head 7 divides the light L1 from the laser light source 2 by reflecting a part of the light L1 from the reference surfaces 721, 721A, and 742 and transmitting the remaining light. 7 may divide the light L1 from the laser light source 2 by the polarization beam splitter 302 as in the conventional interferometer 1E.
The sensor head 7A of the second embodiment may be applied to the sensor head 7 of the fourth and fifth embodiments, or the sensor head 7B of the third embodiment may be applied.

  In the second embodiment, the gradient index lens 74 and the quarter-wave plate 73 are spaced apart from each other, but the gradient index lens 74 and the quarter-wave plate 73 are bonded together, The sensor head 7A may be downsized. In this case, an optical coat that increases the reflectance may be applied to either one of the surfaces of the gradient index lens 74 and the quarter-wave plate 73 to be bonded.

In the second embodiment, no optical element is disposed between the gradient index lens 74 and the quarter wavelength plate 73, but the lens is disposed between the gradient index lens 74 and the quarter wavelength plate 73. This lens may be used to finely adjust the convergence, divergence, and collimation of the light L3 emitted from the gradient index lens 74.
In the third embodiment, the wire grid surface 721A is provided on the incident surface of the translucent member 72A. However, the wire grid surface 721A is provided, for example, on the exit surface of the polarization maintaining fiber 309 on the sensor head 7B side. It may be provided and may be provided at an appropriate position.

  In the fifth embodiment, the wavelengths λ1 and λ2 of the laser beams L1A and L1B have substantially the same refractive index of the clad inside the polarization maintaining fiber 309 with respect to the laser beams L1A and L1B, and the bandpass filters 92 and 93 The wavelength is such that only the light of one wavelength λ1, λ2 can be extracted from the light L61, L62 transmitted through the filters 92, 93, and the difference between the wavelengths λ1, λ2 is slight. There may be some difference between the wavelengths λ1 and λ2 of the laser beams L1A and L1B. In this case, due to the difference between the wavelengths λ1 and λ2, a difference occurs in the refractive index of the core inside the polarization maintaining fiber 309 with respect to the light of the wavelengths λ1 and λ2, and thus, for example, the combined light L6A of the wavelength λ1 and the wavelength λ2 When the combined light L6B is guided to the polarization maintaining fiber 309, an optical path length difference is generated between the combined light L6A and L6B. An optical element for correcting such an optical path length difference is provided to correct the optical path length difference. Alternatively, it may be numerically corrected by the refractive index for each light of wavelengths λ1 and λ2 at the time of calculation.

  In the fifth embodiment, the splitting unit 9 includes a non-polarizing beam splitter 91 and bandpass filters 92 and 93, and these optical elements 91 to 93 allow the combined light L6 to be combined with different wavelengths λ1 and λ2. Although splitting into the wave lights L6A and L6B, the splitting unit 9 includes a spectral element such as a prism or a diffraction grating that changes the traveling direction (optical axis) of the incident light according to the wavelength. You may divide | segment into each multiplexed light L6A and L6B from which wavelength (lambda) 1, (lambda) 2 differs.

  The present invention can be used for an interferometer, and can be particularly preferably used for a Michelson interferometer.

The figure which shows the structure of the interferometer which concerns on 1st Embodiment. The figure which shows the structure of the interferometer which concerns on 2nd Embodiment. The figure which shows the structure of the interferometer which concerns on 3rd Embodiment. The figure which shows the structure of the interferometer which concerns on 4th Embodiment. The figure which shows the structure of the interferometer which concerns on 5th Embodiment. The figure which shows the structure of the principal part of the interferometer which concerns on 6th Embodiment. The figure which shows the structure of the conventional Michelson interferometer.

DESCRIPTION OF SYMBOLS 1, 1A-1E ... Interferometer 2 ... Laser light source 4 ... Object to be measured 5 ... Acquisition means 5A ... First acquisition means 5B ... Second acquisition means 6 ... Calculation means 7, 7A, 7B ... Sensor head 8 ... Optical circulator ( Light guiding means)
DESCRIPTION OF SYMBOLS 21 ... 1st laser light source 22 ... 2nd laser light source 73 ... 1/4 wavelength plate 74 ... Refractive index gradient type lens 307 ... Non-polarization beam splitter (light guide means)
309: Polarization-maintaining fiber 311: Polarizing beam splitter
313: Injection end surface (reference surface)
721 ... Reference plane 721A ... Wire grid plane (reference plane)
741... Entrance surface 742... Exit surface (reference surface)
L4, L4A, L4B ... reference light L5, L5A, L5B ... measurement light L6A ... first combined light L6B ... second combined light.

Claims (7)

A laser light source;
The light from the laser light source is incident on a reference surface and is incident on the object to be measured to obtain the reference light reflected on the reference surface and the measurement light reflected on the object to be measured. A sensor head for combining the measurement light and the reference light after orthogonalizing the polarization plane and the polarization plane of the reference light, and emitting the combined light;
A light guide means for transmitting light from the laser light source to the sensor head side and for extracting the combined light emitted from the sensor head;
The light emitted from the light guide means is guided to the sensor head, and the combined light emitted from the sensor head is guided to the light guide means while preserving the polarization plane of the combined light. Wave storage fiber,
Obtaining means for obtaining an interference signal from the combined light extracted by the light guiding means;
An interferometer, comprising: a calculating unit that calculates a displacement amount of the object to be measured based on the interference signal. The interferometer according to claim 1, wherein
The sensor head includes a ¼ wavelength plate disposed in the latter stage of the optical path of the reference surface,
The interferometer, wherein the reference surface reflects a part of light from the laser light source incident on the reference surface as the reference light and transmits the remaining light. The interferometer according to claim 2, wherein
A refractive index gradient type lens whose refractive index continuously changes along the radial direction,
The refractive index gradient lens includes an incident surface on which light from the laser light source is incident, and a reference surface that reflects part of the light incident on the incident surface as the reference light and emits the remaining light. An interferometer characterized by comprising an exit surface. The interferometer according to claim 1, wherein
The reference surface is a wire grid surface in which a plurality of wires are provided in parallel. Of the light incident on the reference surface, the polarization surface reflects light parallel to the wire as the reference light, and the polarization surface. Transmits light perpendicular to the wire. The interferometer according to claim 1, wherein
The reference surface is an emission end surface of the polarization maintaining fiber on the sensor head side, and reflects a part of incident light as the reference light and emits the remaining light to the sensor head side. Interferometer to do. The interferometer according to any one of claims 1 to 5,
The light guide means is an optical circulator that emits light from the laser light source only to the sensor head side and emits the combined light from the sensor head side only to the acquisition means side. Total. The interferometer according to any one of claims 1 to 6,
The laser light source includes a first laser light source that emits light of a first wavelength, and a second laser light source that emits light of a second wavelength different from the first wavelength,
A light combining means for combining the light emitted from the first and second laser light sources in a state where the polarization planes are orthogonal to each other, and emitting the light to the light guide means side;
Light arranged between the light guide means and the acquisition means and extracted by the light guide means is a first combined light composed of the reference light of the first wavelength and the measurement light, and the second Splitting means for splitting into the second combined light composed of the reference light of the wavelength and the measurement light,
The obtaining means obtains a first interference signal from the first combined light emitted from the dividing means and a second interference signal from the second combined light emitted from the dividing means. Second acquisition means for
The calculating means calculates a displacement amount of the object to be measured from the first and second interference signals, and cancels an error due to the polarization-maintaining fiber included in each displacement amount from each displacement amount. An interferometer characterized by calculating a displacement amount of the object to be measured.

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