NL2028816B1 - Method for determining a position of a target by optical interferometry and device for doing the same - Google Patents

Method for determining a position of a target by optical interferometry and device for doing the same Download PDF

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Publication number
NL2028816B1
NL2028816B1 NL2028816A NL2028816A NL2028816B1 NL 2028816 B1 NL2028816 B1 NL 2028816B1 NL 2028816 A NL2028816 A NL 2028816A NL 2028816 A NL2028816 A NL 2028816A NL 2028816 B1 NL2028816 B1 NL 2028816B1
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Netherlands
Prior art keywords
light
optical path
optical
reference signal
beam splitter
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NL2028816A
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Dutch (nl)
Inventor
Pieter Christiaan Van De Sande Willem
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Prodrive Tech Innovation Services B V
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Priority to NL2028816A priority Critical patent/NL2028816B1/en
Priority to PCT/EP2022/070702 priority patent/WO2023002050A1/en
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Publication of NL2028816B1 publication Critical patent/NL2028816B1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/0207—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer
    • G01B9/02071—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer by measuring path difference independently from interferometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
    • G01B9/02018—Multipass interferometers, e.g. double-pass
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
    • G01B9/02019—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations contacting different points on same face of object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02056—Passive reduction of errors
    • G01B9/02057—Passive reduction of errors by using common path configuration, i.e. reference and object path almost entirely overlapping
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02075—Reduction or prevention of errors; Testing; Calibration of particular errors
    • G01B9/02078—Caused by ambiguity
    • G01B9/02079—Quadrature detection, i.e. detecting relatively phase-shifted signals
    • G01B9/02081—Quadrature detection, i.e. detecting relatively phase-shifted signals simultaneous quadrature detection, e.g. by spatial phase shifting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/15—Cat eye, i.e. reflection always parallel to incoming beam
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/45—Multiple detectors for detecting interferometer signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/60—Reference interferometer, i.e. additional interferometer not interacting with object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/70—Using polarization in the interferometer

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

A method for determining a position of a target by optical interferometry comprises several steps. A first, a second and a third coherent light beam is generated at a first wavelength at a first instance and at a second wavelength different from the first wavelength at a second instance. A first reference signal is generated by guiding the first coherent light beam along a first optical path, a measure signal is generated by guiding the second coherent light beam along a second optical path comprising a target, and a second reference signal is generated by guiding the third coherent light beam along a third optical path, wherein the third optical path has an optical distance different from the first optical path and the second optical path. A first interference signal is generated from the first reference signal and a first portion of the second reference signal at the first instance and at the second instance. A second interference signal is generated from the measure signal and a second portion of the second reference signal at the first instance and the second instance. A position of the target can be determined by calculating a difference between the optical distance of the first optical path and the optical distance of the second optical path based on the first and the second interference signal both in the first and the second instance.

Description

METHOD FOR DETERMINING A POSITION OF A TARGET BY OPTICAL
INTERFEROMETRY AND DEVICE FOR DOING THE SAME
Technical field
[0001] The present invention relates to method for high stability and high precision interferometry and an interferometer for doing the same.
Background art
[0002] Interferometers may be used for measuring a difference in an optical path length towards a movable target with respect to an optical path length towards a reference by generating an interference signal from an interaction between light that has travelled the reference optical path and light that has travelled a target optical path. A generic concern with interferometry and interferometers are changes in optical path length caused by environmental factors such as temperature changes, because this may affect the length of the beam’s path and the refractive indices of the medium through which the beam passes which both determine the optical path length. Other generic concerns are providing adequate spatial resolution, preferably uniform spatial resolution, determining a phase and a direction of travel.
[0003] US 8,570,529 B2 describes a position detection device comprising an interferometer to produce an interference pattern dependent on the length of the measurement section and a detector, which takes the detected interference pattern as a basis for producing a measuement signal. The position detection device further comprises a source, for producing a wave field in the measurement section, a wave field variation device for varying the wavelength of the wave field over time, and an evaluation circuit for evaluating the measurement signal on the basis of the variation over time. A disadvantage of this solution is that it may require a relatively large dynamic range on the modulation input which introduces noise in the measurements. A further disadvantage of this solution is that it is complex to implement in a system wherein the position is detected along multiple axes, particularly when a same modulation depth is desired along multiple axes. Furthermore, it does not allow to determine an accurate position in situations where the reference distance and the target distance may be equal, which may typically occur in free-space solutions.
Summary of the invention
[0004] It is an object of the invention to solve at least one, preferably all of the disadvantages related to the prior art.
[0005] According to a first aspect of the invention the object is achieved by providing a method according to the appended claims. The method achieves the object of the invention by generating two interference patterns, a first one between a first reference signal and a second reference signal and a second one between a measure signal and the second reference signal, wherein the second reference signal is generated by guiding the third coherent light beam along a third optical path having a second reference distance, wherein the second reference distance is different from the first reference distance and the measure distance. This enables reducing the noise in measurements, because this enables reducing the required variation in modulation input by reducing the relative variation in the measured distances. Furthermore, it is advantageous to minimize the variation in modulation depth especially in case measurements are performed for multiple axes, since this improves the contrast of the interference between the different signals.
[0006] By switching the wavelength between two states the sign information of the phase difference may be resolved. It may also improve the resolution of the pathlength difference, by levelling the resolution throughout the range of pathlength differences. Preferably, the change of the wavelength during the transition between the two states follows a sine wave. This may simplify the generation and/or processing of signals. However, any other transition of the laser wavelength will also be possible.
[0007] Preferably, a low cost light source is used. A suitable light source is configured for emitting light having a single wavelength at a time and is capable of changing the single wavelength between two or more states. Preferably, the light source generates light having a single wavelength at a time and is capable of changing the single wavelength between two or more states. The light source may be configured for changing between the two or more states by means of adapting a parameter of the light source, such as a current, a voltage or a temperature. Beneficially, the light source is configured for having a linear correlation between an adaptation of the parameter and a change of the single wavelength. The light source may for instance comprise a tuneable homodyne laser source, such as a semiconductor or diode laser, which typically offer a low cost light source. Examples of an advantageous light source are a distributed feedback (DFB) laser and a vertical-cavity surface-emitting laser (VCSEL).
[0008] Advantageously, one of the third optical path and both the first and the second optical path (i.e. the third optical path or both the first and the second optical path) comprises a delay path. Such delay path may comprise a light guide for offering a simple and compact means for providing a delay to a signal. Preferably, the third optical path comprises such a delay path. In such coinciding or averlapping optical paths, the first coherent light beam may comprise light of a first polarization direction and the second coherent light beam may comprise light of a second polarization direction different from the first polarization direction. Typically, the first polarization direction is orthogonal to the second polarization direction.
[0009] Preferably, the coherent light beam corresponding to the first and the second optical path is collimated along at least a part of the coinciding optical path.
This is particularly beneficial for parts of the respective optical paths relating to free- space interferometry. Preferably, the first and second coherent light beam are generated from a single coherent light source, because changes in the light source (e.g. switching of frequencies between states) influence both coherent light beams simultaneously without requiring any additional means for instance for synchronization. For the same reason, it is preferred that in addition the third coherent light beam is generated from the single coherent light source.
[0010] In a preferred embodiment, both the first and the second optical path pass a polarizing beam splitter, wherein the polarizing beam splitter is configured for splitting the first and the second optical path. Following a non-coinciding part of the first and second optical path, the beam splitter may be used for re-joining the first and second optical path.
[0011] According to a second aspect of the invention the object is achieved by a sensing unit according to the appended claims. The sensing unit reaches the object of the invention in a similar way as the method according to the present invention.
[0012] In a preferred embodiment, the sensing unit further comprises a light guide, wherein the third optical path comprises the light guide. Advantageously, the first and second optical path comprise a coinciding part wherein a part of the first and the second optical path coincide wherein in the coinciding part the first coherent light beam has a first polarization direction and the second coherent light beam has a second polarization direction different (e.g. orthogonal to) from the first polarization direction.
[0013] The sensing unit preferably comprises a light source for generating a source light beam, and a first optical element configured for generating the first coherent light beam and the second coherent light beam. The light source may be configured for collimating the source light beam.
[0014] The first optical element may comprise a polarizing beam splitter configured for interacting with the source light beam and generating the first light beam and the second light beam.
[0015] The first optical element comprises at least one of a single pass interferometer and a dual pass interferometer, for instance comprising a retroreflector.
Preferably, the first optical element comprises a dual pass interferometer, because a reflective target of the interferometer only has to be used to fold the beam towards the retroreflector. As a result, the target mirror can be a plane mirror with a less stringent tolerances on the rotation. For metrology of stage position this advantage is critical as a plane mirror can translate in a direction orthogonal to the measurement direction without affecting the measurement, creating the possibility for a decoupled orthogonal displacement measurement. The less stringent tolerance on the rotation of the mirror translates to an acceptance for a rotation of the measured stage.
[0016] Typically, a dual pass interferometer comprises at least two reflectors (e.g. mirrors) configured orthogonal from one another and facing opposing sides of the polarizing beam splitter, wherein each reflector of the two reflectors is configured for reflecting a different one of the first and the second light beam towards the polarizing beam splitter. Furthermore, the optical path between the polarizing beam splitter and a corresponding reflector may comprise a means for switching a polarization direction between the first and the second direction of polarization. Such means for instance comprise a quarter wave plate configured for interacting with the corresponding first and second light beam before and after reflection by the corresponding reflector of the two reflectors.
[0017] Advantageously, a sensing unit according to the present invention further comprises a beam splitter configured for interacting with the source light beam and generating the third light beam. Examples of suitable beam splitters comprise fiber- based beam splitters and free-space beam splitters.
[0018] In an embodiment according to the invention, the means advantageously comprise a second optical element downstream of the first optical element configured for generating interference between the first reference signal and the second reference signal and the second interference pattern, wherein the second optical element comprises a first output connected to the first detector and a second output connected to the second detector.
[0019] The second optical element preferably comprises a further polarizing beam splitter configured for splitting the first and the second optical path, a first polarizer downstream from the further polarizing beam splitter configured for generating the first interference signal and a second polarizer downstream from the further polarizing beam splitter configured for generating the second interference signal.
[0020] Sensing units according to the present invention are particularly beneficial in situations wherein multiple measurements need to be compared, such as in situations where distances are determined along multiple axes. Such a system, for instance comprises a plurality of sensing units as described herein. Preferably, individual ones of the plurality of sensing units are configured for measuring a distance along a plurality of axes. Advantageously, such a system comprises a common light source for generating a source light beam, wherein the common light source is configured upstream of the plurality of sensing units. The benefit of such a system, for instance comprising a 5 single laser source (e.g modulated line locked laser source) as the common light source, is suitable for performing a number of independent position measurements each with approximately the same (optimized) modulation depth.
[0021] As will be evident to the person skilled in the art, various segments along the different optical paths may be configured in a free-space or fiber-based solution. Preferably, polarizing maintaining fibers are used to make the measurements less sensitive to fiber deformation.
Brief description of the figures
[0022] Aspects of the invention will now be described in more detail with reference to the appended drawings, wherein same reference numerals illustrate same features and wherein:
[0023] Fig. 1 represents a generic schematic overview of an embodiment according to the present invention.
[0024] Fig. 2 represents a schematic overview of a first embodiment according to the present invention.
[0025] Fig. 3 represents a schematic overview of a second embodiment according to the present invention.
[0026] Fig. 4 represents a schematic overview of a third embodiment according to the present invention.
[0027] Fig. 5A and B represent schematic overviews of a fourth embodiment according to the present invention.
[0028] Fig. 6 represents a schematic overview of measured signals between the first and the second state.
Detailed description of embodiments
[0029] Referring to Fig. 1, embodiments of an interferometer 100 according to the present invention may comprise a single light source 101 (e.g. a laser) providing light to a splitter 102 (e.g a fiber coupler) configured to split the light and guide a first portion towards a sensor head 105 for instance via a first fiber 103 and guide a second portion towards a second fiber 104 configured as a delay line.
[0030] The sensor head 105 splits the light into a first reference signal 106 and a measurement signal 108. The first reference signal travels back and forth from between the sensor head 105 and a reflective reference 107 {e.g. a mirror) along a first optical path and the measurement signal travels back and forth between the sensor head 105 and a movable reflective target 109 (e.g. a mirror).
[0031] The second fiber 104 is configured to generate a second reference signal which is split by a further beam splitter 114 into a first portion 110 being guided towards a first detector 112 and a second portion 111 being guided towards a second detector 113.
[0032] The first reference signal 106 and the measurement signal 108, after traveling back and forth between the sensor head 105 and the corresponding reflective surface 107, 109, leave the sensor head and are guided towards the first detector 112 and the second detector 113, respectively.
[0033] The first detector 112 is configured to generate and measure a first interference signal between the first reference signal 106 and the first portion of the second reference signal 110. The second detector 113 is configured to generate and measure a second interference signal between the measurement signal 108 and the second portion of the second reference signal 111.
[0034] Referring to Fig. 2, an embodiment of a device 201 according to the present invention comprises a sensor head comprising a first optical assembly 202 based on a Michelson interferometer and a second optical assembly 203. In the first optical assembly a bundle of light 204 is split using a first polarizing beam splitter (PBS) 205. The first PBS 205 may for instance be provided in a cube shaped configuration.
Such PBS's as the first PBS 205 may comprise a beam splitter coating, for instance configured diagonally from one edge to another edge of a cube shaped PBS. The bundle of light 204 may be directed to a first side 208 of the first PBS 205. A first reference beam 2086 exiting the first PBS 205 and having a first polarization state is directed to a reference reflector 207 (e.g. a reference mirror, such as an internal reference mirror) provided at a second side 209 of the first PBS 205. A target beam 210 exiting the first PBS having a second polarization state is directed towards a reflective target 211 at a third side 212 of the first PBS 205. A double pass arrangement may be created by providing a first quarter wave plate (QWP) 213 at the second side 209 and a second QWP 214 at the third side 212 and by providing a retroreflector (RR) 215 at a fourth side 216 of the first PBS 205.
In such an embodiment the first reference beam 206 and the target beam 210 pass the first QWP 213 and the second QWP 214 respectively two times thereby switching the polarization state between the first and the second state.
[0035] A light source 217 configured for oscillating at a single frequency (e.g. a diode) at a time is provided. The light source is switchable between a first state having a first wavelength and a second state having a second wavelength. The light source 217 for instance provides a bundle of light 204, for instance a bundle of collimated light generated by a laser. The bundle of light 204 may travel in free-space or may at least in part travel through a fiber for instance comprising an angle polished fiber end, wherein a collimator may be provided downstream of the angle polished fiber end. The bundle of light 204 comprises light having multiple polarization states for instance light having a first polarization state (e.g. P-polarized light) and light having a second polarization state (e.g. S-polarized light). The bundle of light is directed towards an off- center location of the first side 208 of the first PBS 205. The first PBS 205 splits the bundle of light into a first light beam 206 (e.g. first reference beam) having the first polarization state (e.g. P-polarized light) and a second light beam 210 (e.g. target beam) having the second polarization state (e.g. S-polarized light).
[0036] The first reference beam 206 is generated by an interaction of the bundle of light 204 with the first PBS 205 (e.g. a beam splitter coating provided in the first PBS), which is configured to reflect light in the first polarization state. The first QWP 213 changes the linear first polarization state of the reference beam 206 into a circular polarization state. The reflective first reference reflector 207 then changes the propagation direction of the reference beam 206 without changing the rotation of the polarization, which changes the handedness of the circular polarization. A consecutive pass through the first QWP 213 changes the polarization state from circular polarized light into light having a linear second polarization state. The reference beam 206 in the second polarization state is transmitted through the first PBS 205 and is reflected at the
RR 215. The reference beam 206 reflected by the RR 215 retains its second polarization state and is transmitted back towards the first PBS 205 and enters the first PBS 205 at a location offset from where it emerged from the first PBS 205 just before being reflected by RR 215. The reference beam 206 is then transmitted through the first PBS 205 towards the reflective first target 207. The first QWP 213 transforms the second polarization state into a circular polarization, the reflection at the reflective reference reflector 207 changes the handedness and a consecutive pass through the first QWP 213 transforms the polarization state from this circular polarization into a linear first polarization state. This light having a first polarization state is then reflected by the first
PBS 205 (e.g. the beam splitter coating of the first PBS) and is directed to a second optical assembly 203 arranged at another off-center location of the first side 208 of the first PBS 205 next to the off-center location.
[0037] The target beam 210 is also generated by the first PBS 205 (e.g. the beam splitter coating provided in the first PBS), which is configured to transmit light in the second polarization state. The same principle as for the first reference beam 206 is used here to create a double pass arrangement for this target beam. The second QWP 214 changes the linear second polarization state of the target beam into a circular polarization state. The reflective target 211 then changes the propagation direction of the target beam without changing the rotation of the polarization, which changes the handedness of the circular polarization. A consecutive pass through the second QWP 214 changes the polarization state of the light from a circular polarized state into a linear first polarization state. The light in the first polarization state is reflected by the beam splitter coating of the first PBS 205 towards the RR 215, which in turn reflects the target beam towards the first PBS 205 retaining the first polarization state. The target beam is then reflected by the beam splitter coating of the first PBS 205 towards the reflective target 211. The second QWP 214 transforms the first polarization state of the light of the target beam into a circular polarization, the reflection at the reflective target 211 changes the handedness and a consecutive pass through the second QWP 214 transforms this circular polarization state into a linear second polarization state. This light having a second polarization state is then transmitted by the first PBS 205 and directed towards the second optical assembly 203 arranged at the other off-center location of the first side 208 of the first PBS 205 next to the off-center location.
[0038] The advantage of such a first optical assembly 202 providing a double pass arrangement is that the reflective target 211 is only used to fold the beam towards the retroreflector. As a result, the target mirror can be a plane mirror with a less stringent tolerances on the rotation. For metrology of stage position this advantage is critical as a plane mirror can translate in a direction orthogonal to the measurement direction without affecting the measurement, creating the possibility for a decoupled orthogonal displacement measurement. The less stringent tolerance on the rotation of the mirror translates to an acceptance for a rotation of the measured stage.
[0039] Another advantage is that an equal amount of glass length for both beams or optical paths offers a high thermal stability. Both the first reference beam 206 and the target beam 210 travel an equal distance through the first PBS 205, respective
QWP 213, 214 and RR 215, a thermal expansion or a change in refractive index of the glass of these components is then compensated.
[0040] The detecting means comprises a second optical assembly 203 comprising a second PBS 219, which may have a cube shaped configuration, for instance similar to the first PBS 205. The first reference beam 206 and the target beam 210 are directed co-linearly to a first side 218 of the second PBS 219 and are separated from each other by a beam splitter coating of the second PBS 219. A second collimated reference beam 220, that may have been split off the bundle of coherent laser light generated by the laser 217 using a beam splitter 228 (e.g. fiber coupler) and has travelled through a separate optical path configured for providing a delay 229 for instance comprising a delay line (e.g. a fiber), is directed towards a second side 221 of the second
PBS 219, such that this light strikes the beam splitter coating of the second PBS 219 at a same location as the both the first reference beam 206 and the target beam 210 but at opposing sides of the beam splitter coating of the second PBS 219. Embodiments comprising a fiber-based delay may comprise an angle polished fiber end and a collimator configured to direct the second collimated reference beam 220 towards the second side 221 of the second PBS 219.
[0041] A first portion of the second reference beam 220 having a second polarization state is transmitted by the second PBS 219 and travels together with the first reference beam 206 having the first polarization state and being reflected by the second
PBS 219 towards a first sensor 225 arranged at a third side 224 of the second PBS 219 adjacent to the first side 218. A second portion of the second reference beam 220 having afirst polarization state is reflected by the second PBS 219 and travels together with the target beam 210 having a second polarization state and being transmitted by the second
PBS towards a second sensor 223 arranged at a fourth side 222 of the second PBS 219 opposite to the first side 218.
[0042] The second PBS 219 further comprises a first polarizer 227 and a second polarizer 226 provided at the third 224 and the fourth 222 side of the second
PBS, respectively. First and second polarizers 226, 227 can be linear polarizers. The first reference beam 206 and the first portion of the second reference beam 220 are directed though the first polarizer 227 to generate interference between the first reference beam 206 and the first portion of the second reference beam 220 that can be sensed by the first sensor 225. The target beam 210 and the second portion of the second reference beam 220 are directed though the second polarizer 226 to generate interference between the target beam 210 and the second portion of the second reference beam 220 that can be sensed by the second sensor 223. Optionally, such (linear) polarizer can be rotated to control the intensity ratio between the respective beams to optimize for maximum interference contrast. The first and/or second sensor 223, 225 may comprise a photodiode as a detector to detect the interference signal.
Furthermore, the first and/or second 223, 225 sensor may comprise one or more fiber optical pickups for picking up the interference signal and relaying it to the corresponding detector. In the second optical assembly 203 the optical path length for both the first reference beam 206 and the target beam 210 correspond in a part wherein these paths overlap. After these paths of the first reference beam 206 and the target beam 210 are split by a beam splitter coating of the second PBS, the optical path length of the target beam 210 and second portion of the second reference beam 220 correspond and the optical path length of the first reference beam 210 and first portion of the second reference beam 220 correspond. As a result, any path length deviation, for instance caused by environmental factors such as temperature changes, equally influence the first and the second, the first and the third and/or the second and the third optical path and can therefore be directly compensated for or can be measured and compensated for by a processing means.
[0043] The benefit of providing a delay line for creating the second reference beam 220 is that a long and identical path difference between the first reference beam 206 and the second reference beam 220 and between the target beam 210 and the second reference beam 220 can be created. If such delay line is much longer than the variation in target distance, the relative variation in path length difference for independent measurements axes is minimized.
[0044] Furthermore, since the modulation depth is proportional to the path length difference between the interfered beams the variation in modulation depth between independent sensors can also be minimized. With this setup one laser source (e.g. a modulated line locked laser source) can be used to provide the input for a number of independent position measurements, each with approximately the same optimal modulation depth. This is for instance ideally suitable for a system comprising sensing units for measuring a relative position along multiple axes.
[0045] The sensor head shown in Fig. 2 can be adapted to provide a differential measurement by removing the reflective reference 207 and folding both measurement paths, for instance by introducing a mirror, to align them parallel before travelling through the quarter wave plates.
[0046] Referring to Fig. 3, embodiments of a device 301 according to the present invention may also comprise solutions being primarily fiber-based. For example, the light from the source 302 is split by a first splitter, such as a first fiber coupler 303 configured to split the light and guide a first portion for instance via a first fiber 304 towards a sensor head 305. The first splitter is further configured to guide a second portion towards a second fiber 308, for instance configured as a delay line, thereby providing a second reference beam.
[0047] The sensor head 305 is configured to split the first portion into a first reference beam 306 having a first polarization state and a target beam 307 having a second polarization state. To this end, the sensor head 305 may comprise a reflective polarizer 312 for splitting the first portion into the first reference beam 306 and the target beam 307. The sensor head 305 can further comprise a second fiber coupler 309, a fiber end 310 (e.g. an angle polished fiber end) and a collimator 311. The first reference beam 306 is reflected by the reflective polarizer 312, which thereby acts as a reference reflector, and subsequently enters the second fiber coupler 309. The target beam 307 passes through the reflective polarizer 312 and is reflected by the reflective target 313 and subsequently enters the second fiber coupler 309.
[0048] The second fiber coupler 309 passes part of the reflected first reference beam 306 and part of the reflected target beam 312 towards a first fiber-based polarizing beam splitter 314, for instance via a third fiber 315. The first fiber-based polarizing beam splitter 314 splits the first reference beam and the target beam according to their polarization states and guides the first reference beam (e.g. in a first polarization state) towards a first sensor 316 and the target beam (e.g. in a second polarization state) towards a second sensor 317, for instance via a fourth and fifth fiber 318, 319, respectively.
[0049] The second fiber 308 is configured for guiding the second reference beam towards a second fiber-based polarizing beam splitter 320. The second fiber- based polarizing beam splitter 320 may be configured for splitting the second reference beam into a first portion 323 comprising light having a first polarization state (e.g. a P polarization state) and a second portion 324 comprising light having a second polarization state (e.g. an S polarization state). The first portion 323 is led to one of the first and second sensor and the second portion 324 is led to the other one of the first and second sensor. For instance, such that the first portion 323 of the second reference beam is combined with one of the first reference beam 306 and the target beam 307 (e.g. the target beam) having a same polarization state as the first portion 323 and such that the second portion 324 of the second reference beam is combined with another one of the first reference beam 306 and the target beam 307 (e.g. the first reference beam) having a same polarization state as the second portion 324.
[0050] The first and second sensor 318, 317 comprise a third and a fourth fiber coupler 321, 322, respectively. The fourth fiber coupler 322 may be configured for combining the first portion 323 with the one of the first reference beam 306 and the target beam 307. The third fiber coupler 321 may be configured for combining the second portion 324 with the other one of the first reference beam 306 and the target beam 307.
The third and fourth fiber coupler 321, 322 may be configured for generating an interference signal between the corresponding beams combined by the respective fiber coupler.
[0051] Referring to Fig. 4, embodiments of a device 401 according to the present invention may also comprise solutions being partly fiber-based and partly free- space. For example, the light from the source 402 is split by a first splitter, such as a first fiber coupler 403 configured to split the light and guide a first portion for instance via a first fiber 404 towards a first fiber-based polarizing beam splitter 405. The first fiber-based polarizing beam splitter 405 is configured for splitting the first portion into a first reference beam having a first polarization state (e.g. a P polarization state) and a target beam having a second polarization state (e.g. an S polarization state), the first reference beam being guided towards a first sensor 410 by for instance a second fiber 406 and the target beam being guided towards a sensor head 411 configured as a free-space optical assembly by for instance a third fiber 407.
[0052] The first splitter is further configured to guide a second portion towards a fourth fiber 408, for instance configured as a delay line, thereby providing a second reference beam. The second reference beam may be guided by the fourth fiber 408 towards a second fiber-based polarizing beam splitter 409. The second fiber-based polarizing beam splitter 409 may be configured for splitting the second reference beam into a first portion comprising light having a third polarization state (e.g. a P polarization state) and a second portion comprising light having a fourth polarization state (e.g. an S polarization state). The first portion is led to one of the first sensor 410 and the sensor head 411 and the second portion is led to the other one of the first sensor 410 and the sensor head 411. For instance, such that the first portion of the second reference beam is combined with one of the first reference beam and the target beam (e.g. the target beam) having a same polarization state as the first portion. For instance, the first portion is guided towards the first sensor 410 via a fifth fiber 412 and the second portion is guided towards the sensor head 411 via a sixth fiber 413. To that end, light travelling through the second fiber 406 and light traveling through the fifth fiber 412 may be combined by a second fiber coupler 425.
[0053] The sensor head 411 comprises a first input 414, a second input 415, an in-/output towards a reflective target 416 and an output towards a second sensor 417 and is configured for sensing an interference between the first and the second input.
The first input 414 is configured to receive the target beam and the second input 415 is configured to receive one of the first and the second portion of the second reference beam, preferably the one having a same polarization state as the target beam (e.g. the second portion). The first and the second input 414, 415 of the free-space optical assembly for instance each comprise a fiber end 418, 419 (e.g. an angle polished fiber end) and a collimator 420, 421. The optical assembly may further comprise a PBS 422,
a QWP 423 configured between the PBS 422 and the reflective target 416 and a polarizer 424 configured between the PBS 422 and the second sensor 417.
[0054] Referring to Fig. 5A and B, in a preferred embodiment of a device 500 according to the present invention a light generating means 501 configured to subsequently generate coherent light at a first wavelength and a second wavelength.
The light generated by the light generating means 501 travels along three optical paths, preferably each having a distinct optical path length, towards a detecting means 502 for detecting interference patterns. The first optical path may provide a first reference signal, the second optical path may provide a measure signal and the third optical path may provide a second reference signal. The detecting means 502 comprises two detectors 503, 503’, wherein one of the two detectors 503, 503’ is configured for determining a first interference signal between the first reference signal and the second reference signal and wherein another one of the two detectors 503, 503’ is configured for determining a second interference signal between the measure signal and the second reference signal.
In comparison to the example of Fig. 2, wherein the second PBS 219 of the detecting means itself is configured to split the second reference signal into a first portion and a second portion, in the example of Fig. 5, a beam splitting means 504 (forming the first
PBS 505 and the third PBS 506) of the optical means is configured for generating the first portion and the second portion of the second reference signals.
[0055] The coherent light generated by the light generating means 501 travels towards a first beam splitter 507 (e.g. fiber coupler) along a first joint optical path 508 that may comprise the first, the second and the third optical path. The first beam splitter 507 may then split the optical paths into a second joint optical path 509 that may comprise the first and the second optical path, and a third optical path 510. This embodiment may be configured in free-space, but may also be at least in part fiber- based.
[0056] For such an at least fiber-based solution, the first joint optical path 508, the second joint optical path 509 and/or the third optical path 510 may travel along a light guide. Such a light guide of the third optical path 509 or the second joint optical path 510 may comprise a delay path or line 511 to create a common delay between the third optical path 510 and the first optical path 512 an the one hand and the third optical path 510 and the second optical path 513 on the other hand. The light guides of the second joint optical path 509 and the third optical path 510 may each comprise a fiber end 514, 514’ (e.g. angle polished fiber end) and a collimator 515, 515’ configured to provide two collimated light beams, one comprising the first and the second coherent light beam and another one comprising the third coherent light beam.
[0057] The two collimated light beams travel towards the beam splitting means 504. The beam splitting means 504 may be configured to split each of the collimated light beams into two parallel spatially separated light beams, wherein the dashed and solid lines represent light traveling in different planes separated along a direction orthogonal to the image plane. Fig. 5B shows a top view of a suitable beam splitting means 504. The beam splitting means 504 (e.g. a modified cube beamsplitter or a Wollaston prism) may be configured to form a first PBS 505, wherein the first and the second optical path are split. The first PBS 505 of the beam splitting means 504 may be configured to generate the first and the second light beam, wherein light of the first polarization and the second polarization state travel towards the Michelson interferometer 516 along the first and the second optical path, respectively. The beam splitting means 504 may further be configured to form a third PBS 506, wherein the third optical path is split into two corresponding third optical paths 517, 517’. One of the two corresponding third optical paths 517, 517" may be configured for generating the first portion of the second coherent reference signal. Another one of the two corresponding third optical paths 517, 517° may be configured for generating the second portion of the second coherent reference signal. The first and the second portion may comprise light having a third and a fourth polarization state, respectively. Preferably, the third and fourth polarization state correspond to the first and the second polarization state, respectively.
[0058] The spatially separated and parallel first and second light beam are directed to a corresponding first and second off-center location of a first side 518 of a
PBS (e.g. a fourth PBS) of the Michelson interferometer 516, respectively. A mirror 519 may be provided to direct the first and the second light beam towards the Michelson interferometer 516 comprising a movable reflective target 522. The Michelson interferometer functions in a similar manner as the Michelson interferometer 202 of the example shown in Fig. 2, with the exception that the first and second optical path do not overlap within the interferometer 516 of the example shown in Fig. 5. The RR 520 in the example of Fig. 5 may for instance be a Cube corner retroreflector or a cat's eye retroreflector, thus changing the plane wherein light travels between entering and exiting the RR 520. After exiting the Michelson interferometer, both the first light beam and the second light beam enter the detecting means 502.
[0059] The detecting means 502 comprises a third beam splitter 521.
Preferably, the third beam splitter is a polarizing beam splitter (e.g. the second PBS), but can also be a non-polarizing beam splitter. The first optical path 512 and the second optical path 513 enter a first side (at respective non-overlapping locations) of the third beam splitter 521 and both of the two corresponding third optical paths 517, 517 enter a second side (at respective non-overlapping locations) of the third beam splitter 521 adjacent to the first side. The third beam splitter 521 may be configured such that the first optical path 512 and one of the two corresponding third optical paths 517, 517 overlap downstream of the third beam splitter 521 and may exit the third beam splitter at a third side. The third beam splitter may further be configured such that the second optical path 513 and another one of the two corresponding third optical paths 517, 517° overlap downstream of the third beam splitter 521 and may exit the third beam splitter at a fourth side. Linear polarizers may be provided between the third beam splitter and each of the two detectors 503, 503’, wherein the linear polarizers are configured to generate a first and a second interference signal.
[0060] Referring to Fig. 6, the following wave functions relate to two signals, for instance the measure signal and the first reference signal or to the first reference signal and the second reference signal: ai, re yr =1e za
SS{xecttAr) y, =loe *
Where A is the wavelength of the laser, and Ax is the difference in path length between the two signals. Once the two signals have travelled along their respective paths the total wavefunction becomes:
Wi geer) w=, ty, =I1,/e* +e*
The interference between these two signals is given by the following equation:
I,=wy* 2m x+et) 27 xtot+Ax) Jim ct) lg X+of+Ar) ne" Ve! " JE she +e © 7 ] ‚ Wx a =/,/|2+e* +e 7 2 =2/j tos Ear
A
Referring to this equation, the difference in the travelled distance between the two signals introduces a phase difference between the two signals, which results in an interference.
The phase difference between the two signals is given by the difference in travelled distance Ax. The resulting interference however does not carry information regarding the sign of the phase difference. By varying the laser wavelength between two states each having a different wavelength, the phase also passes between these two states.
This may be used to resolve the sign information of the phase difference and/or improving the resolution of Ax by levelling the resolution throughout the range of Ax.
The phase that can be measured in shown in Fig. BA. Each of the different arrows 601a- 601h denotes a different phase. The change in wavelength will result in a change in phase whichis shown in Fig, 6B. The length of the arrows relates to the modulation depth of the oscillation. This modulation depth is given by: 27 || Ax ZAAN oo; &D|[rad] = a] = vedan = en 53
ALA A
Where ÓP is the modulation depth in radians, OA is the change in wavelength of the source laser between the two different phases. A is the centre wavelength of the source laser. AX is the difference in path length between the two interference signals and mean is the refractive index of the medium.

Claims (1)

CONCLUSIESCONCLUSIONS 1. Werkwijze voor het bepalen van een positie van een doel door optische interferometrie omvattende de volgende stappen:A method for determining a position of a target by optical interferometry comprising the following steps: 5. het genereren van een eerste, een tweede en een derde coherente lichtbundel bij een eerste golflengte bij een eerste tijdsinstantie en bij een tweede golflengte die verschillend 1s van de eerste golflengte bij een tweede tijdsinstantie, ° het genereren van een eerste referentiesignaal door het geleiden van de eerste coherente lichtbundel langs een eerste optisch pad, © het genereren van een meetsignaal door het geleiden van de tweede coherente lichtbundel langs een tweede optisch pad omvattende een doel, ° het genereren van een tweede referentiesignaal door het geleiden van de derde coherente lichtbundel langs een derde optisch pad, waarbij het derde optische pad een optische afstand heeft die verschillend is van het eerste optische pad en het tweede optische pad, ° het genereren van een eerste interferentiesignaal op basis van het eerste referentiesignaal en een eerste deel van het tweede referentiesignaal bij de eerste tijdsinstantie en bij de tweede tijdsinstantie, ° het genereren van een tweede interferentiesignaal op basis van het meetsignaal en een tweede deel van het tweede referentiesignaal bij de eerste tijdsinstantie en de tweede tijdsinstantie, en ° het bepalen van een positie van het doel door het berekenen van een verschil tussen de optische afstand van het eerste optische pad en de optische afstand van het tweede optische pad gebaseerd op het eerste en het tweede interferentiesignaal zowel in de eerste als de tweede tijdsinstantie.5. generating a first, a second and a third coherent light beam at a first wavelength at a first time instance and at a second wavelength different from the first wavelength at a second time instance, ° generating a first reference signal by conducting of the first coherent light beam along a first optical path, © generating a measurement signal by guiding the second coherent light beam along a second optical path including a target, ° generating a second reference signal by guiding the third coherent light beam along a third optical path, the third optical path having an optical distance different from the first optical path and the second optical path, ° generating a first interference signal based on the first reference signal and a first portion of the second reference signal at the first time instance and at the second time instance, ° the generatere n of a second interference signal based on the measurement signal and a second portion of the second reference signal at the first time instance and the second time instance, and ° determining a position of the target by calculating a difference between the optical distance of the first optical path and the optical distance of the second optical path based on the first and second interference signals in both the first and second time instances. 2. Werkwijze volgens conclusie 1, waarbij een gemeenschappelijke vertraging wordt voorzien tussen het genereren van het tweede referentiesignaal en het genereren van het eerste referentiesignaal en tussen het genereren van het tweede referentiesignaal en het genereren van het meetsignaal.A method according to claim 1, wherein a common delay is provided between the generation of the second reference signal and the generation of the first reference signal and between the generation of the second reference signal and the generation of the measurement signal. 3. Werkwijze volgens conclusie 1 of 2, waarbij het genereren van de eerste coherente lichtbundel en de tweede coherente lichtbundel het splitsen van een door een lichtbron gegenereerd licht omvat, bij voorkeur waarbij het genereren van de derde coherente lichtbundel het splitsen van door de lichtbron gegenereerd licht omvat.A method according to claim 1 or 2, wherein generating the first coherent light beam and the second coherent light beam comprises splitting a light source generated light, preferably wherein generating the third coherent light beam comprises splitting a light source generated includes light. 4. Werkwijze volgens conclusie 3, waarbij het splitsen van licht voor het genereren van de eerste coherente lichtbundel en de tweede coherente lichtbundel het splitsen van door de lichtbron gegenereerd licht volgens respectievelijk een eerste en een tweede polarisatietoestand omvat, bij voorkeur waarbij het eerste deel en het tweede deel van het tweede referentiesignaal het splitsen van de derde coherente lichtbundel volgens respectievelijk een derde en een vierde polarisatietoestand omvat, bij voorkeur waarbij de eerste en de tweede polarisatietoestand overeenkomen met respectievelijk de derde en de vierde polarisatietoestand.A method according to claim 3, wherein splitting light to generate the first coherent light beam and the second coherent light beam comprises splitting light generated by the light source according to a first and a second polarization state, respectively, preferably wherein the first portion and the second part of the second reference signal comprises splitting the third coherent light beam according to a third and a fourth polarization state, respectively, preferably wherein the first and second polarization states correspond to the third and fourth polarization states, respectively. 5. Werkwijze volgens eender welke der voorgaande conclusies, waarbij het genereren van het eerste referentiesignaal en het meetsignaal het geleiden van de eerste en de tweede coherente lichtbundel gedeeltelijk langs een samenvallend optisch pad omvat.A method according to any one of the preceding claims, wherein generating the first reference signal and the measurement signal comprises guiding the first and second coherent light beams partially along a coincident optical path. 6. Werkwijze volgens eender welke der voorgaande conclusies, waarbij een Michelson- interferometer wordt gebruikt voor het genereren van het eerste referentiesignaal en het meetsignaal, bij voorkeur waarbij de gemeenschappelijke vertraging wordt voorzien buiten de Michelson-interferometer.A method according to any one of the preceding claims, wherein a Michelson interferometer is used to generate the first reference signal and the measurement signal, preferably wherein the common delay is provided outside the Michelson interferometer. 7. Inrichting voor het bepalen van een positie van een doel door optische interferometrie omvattende, een lichtgenererend middel dat een eerste en een tweede toestand heeft, waarbij, in de eerste status, het lichtgenererende middel is geconfigureerd voor het genereren van licht bij een eerste golflengte en, in de tweede status, het lichtgenererende middel is geconfigureerd voor het genereren van licht bij een tweede golflengte die verschillend is van de eerste golflengte, een optisch middel stroomafwaarts van het lichtgenererende middel dat is geconfigureerd voor het genereren van een eerste coherent referentiesignaal, een coherent meetsignaal en een tweede coherent referentiesignaal, waarbij het optische middel omvat een eerste optisch pad dat is geconfigureerd voor het genereren van het eerste coherente referentiesignaal door het geleiden van licht dat is gegenereerd door het lichtgenererende middel, een tweede optisch pad omvattende een verplaatsbaar doel en dat is geconfigureerd voor het genereren van het coherente meetsignaal door het geleiden van licht dat is gegenereerd door het lichtgenererende middel, een derde optisch pad dat is geconfigureerd voor het genereren van het tweede coherente referentiesignaal door het geleiden van licht dat is gegenereerd door het lichtgenererende middel, waarbij het derde optische pad een optische afstand heeft die verschillend is van het eerste optische pad en het tweede optische pad, een detectiemiddel stroomafwaarts van het optische middel geconfigureerd voor het genereren van een eerste interferentiesignaal tussen het eerste coherente referentiesignaal en een eerste deel van het tweede coherente referentiesignaal en voor het genereren van een tweede interferentiesignaal tussen het coherente meetsignaal en een tweede deel van het tweede coherente referentiesignaal, en omvattende een eerste detector, die is geconfigureerd voor het detecteren van het eerste interferentiesignaal, en een tweede detector, die is geconfigureerd voor het detecteren van het tweede interferentiesignaal, een verwerkingsmiddel dat 1s geconfigureerd voor het bepalen van een positie van het doel door het berekenen van een verschil tussen de eerste referentieafstand en de meetafstand gebaseerd op het eerste en tweede interferentiesignaal in zowel de eerste als de tweede toestand.Apparatus for determining a position of a target by optical interferometry comprising a light-generating means having a first and a second state, wherein, in the first state, the light-generating means is configured to generate light at a first wavelength and, in the second state, the light generating means is configured to generate light at a second wavelength different from the first wavelength, an optical means downstream of the light generating means configured to generate a first coherent reference signal, an coherent measurement signal and a second coherent reference signal, the optical means comprising a first optical path configured to generate the first coherent reference signal by guiding light generated by the light generating means, a second optical path comprising a movable target and that is configured vo or generating the coherent measurement signal by guiding light generated by the light generating means, a third optical path configured to generate the second coherent reference signal by guiding light generated by the light generating means, wherein the third optical path has an optical distance different from the first optical path and the second optical path, a detection means downstream of the optical means configured to generate a first interference signal between the first coherent reference signal and a first portion of the second coherent reference signal and for generating a second interference signal between the coherent measurement signal and a second portion of the second coherent reference signal, and comprising a first detector configured to detect the first interference signal and a second detector configured v for detecting the second interference signal, a processing means configured to determine a position of the target by calculating a difference between the first reference distance and the measurement distance based on the first and second interference signals in both the first and second states . 8. Inrichting volgens conclusie 7, waarbij het optische middel verder een lichtgeleider omvat die is geconfigureerd als een vertragingspad dat een gemeenschappelijke vertraging voorziet tussen het genereren van het tweede referentiesignaal en het genereren van het eerste referentiesignaal en tussen het genereren van het tweede referentiesignaal en het genereren van het meetsignaal.The apparatus of claim 7, wherein the optical means further comprises a light guide configured as a delay path that provides a common delay between the generation of the second reference signal and the generation of the first reference signal and between the generation of the second reference signal and the second reference signal. generating the measurement signal. 9. Inrichting volgens conclusie 7 of 8, waarbij het optische middel een eerste gezamenlijk optisch pad omvat waarbij het eerste, het tweede en het derde optische pad overlappen, waarbij het eerste gezamenlijke optische pad een eerste uiteinde omvattende een optische opname die optisch verbonden is met het lichtgenererende middel en een tweede uiteinde stroomafwaarts van het eerste uiteinde omvattende een eerste bundelsplitser omvat,An apparatus according to claim 7 or 8, wherein the optical means comprises a first common optical path with the first, second and third optical paths overlapping, the first common optical path having a first end comprising an optical receptacle optically connected to the light generating means and a second end downstream of the first end comprising a first beam splitter, waarbij de bundelsplitser is geconfigureerd voor het afsplitsen van het derde optische pad, bij voorkeur waarbij het derde optische pad stroomafwaarts van het eerste gezamenlijke optische pad de lichtgeleider omvat.wherein the beam splitter is configured to split off the third optical path, preferably wherein the third optical path downstream of the first common optical path comprises the light guide. 10. Inrichting volgens conclusie 9, waarbij het optische middel een tweede gezamenlijk optisch pad omvat, waarbij het eerste en tweede optische pad overlappen, waarbij het tweede gezamenlijke optische pad een eerste uiteinde dat optisch verbonden is met de eerste bundelsplitser en een tweede uiteinde stroomafwaarts van het eerste uiteinde omvattende een tweede bundelsplitser omvat, waarbij de tweede bundelsplitser is geconfigureerd voor het afsplitsen van het tweede optische pad, bij voorkeur waarbij het tweede gezamenlijke optische pad de lichtgeleider omvat.The apparatus of claim 9, wherein the optical means comprises a second common optical path, the first and second optical paths overlapping, the second common optical path having a first end optically connected to the first beam splitter and a second end downstream from the first end including a second beam splitter, the second beam splitter configured to split off the second optical path, preferably wherein the second common optical path includes the light guide. 11. Inrichting volgens conclusie 10, waarbij de tweede bundelsplitser een eerste polariserende bundelsplitser omvat.The apparatus of claim 10, wherein the second beam splitter comprises a first polarizing beam splitter. 12. Inrichting volgens eender welke der conclusies 7 tot 11, waarbij het optische middel een Michelson-interferometer omvat en waarbij het eerste en tweede optische pad de Michelson-interferometer doorkruisen, bij voorkeur waarbij de Michelson-interferometer is geconfigureerd als één van een enkele-run spiegelinterferometer en een dubbele-run spiegelinterferometer.An apparatus according to any one of claims 7 to 11, wherein the optical means comprises a Michelson interferometer and wherein the first and second optical path traverse the Michelson interferometer, preferably wherein the Michelson interferometer is configured as one of a single- run mirror interferometer and a double-run mirror interferometer. 13. Inrichting volgens conclusie 12 samen met conclusie 10 of 11, waarbij de tweede bundelsplitser binnen de Michelson-interferometer is opgesteld en daarvan deel uitmaakt. 14 Inrichting volgens conclusie 12 samen met conclusie 10 of 11, waarbij de tweede bundelsplitser stroomopwaarts van de Michelson-interferometer is opgesteld en zodanig is geconfigureerd dat het eerste en tweede optische pad de Michelson-interferometer niet- overlappend doorkruisen.An apparatus according to claim 12 in conjunction with claim 10 or 11, wherein the second beam splitter is located within and forms part of the Michelson interferometer. The apparatus of claim 12 taken together with claim 10 or 11, wherein the second beam splitter is located upstream of the Michelson interferometer and is configured such that the first and second optical paths cross the Michelson interferometer non-overlapping. 15. Inrichting volgens eender welke der conclusies 7 tot 14, waarbij het optische middel een derde bundelsplitser omvat die is geconfigureerd voor het genereren van het eerste deel en het tweede deel van het tweede coherente referentiesignaal.An apparatus according to any one of claims 7 to 14, wherein the optical means comprises a third beam splitter configured to generate the first part and the second part of the second coherent reference signal. 16. Inrichting volgens conclusie 15 samen met conclusie 14, waarbij de derde bundelsplitser een derde polariserende bundelsplitser omvat, bij voorkeur waarbij de tweede bundelsplitser en de derde bundelsplitser een enkel bundelsplitsend middel vormen.An apparatus according to claim 15 taken together with claim 14, wherein the third beam splitter comprises a third polarizing beam splitter, preferably wherein the second beam splitter and the third beam splitter form a single beam splitter. 17. Inrichting volgens eender welke der conclusies 7 tot 16, waarbij het detectiemiddel een vierde bundelsplitser stroomafwaarts van de Michelson-interferometer omvat geconfigureerd voor het genereren van het eerste interferentiesignaal en het tweede interferentiesignaal, bij voorkeur waarbij de vierde bundelsplitser een tweede polariserende bundelsplitser omvat.Apparatus according to any one of claims 7 to 16, wherein the detection means comprises a fourth beam splitter downstream of the Michelson interferometer configured to generate the first interference signal and the second interference signal, preferably wherein the fourth beam splitter comprises a second polarizing beam splitter. 18. Inrichting volgens eender welke der conclusies 7 tot 17, waarbij het lichtgenererende middel een enkele lichtbron voor het genereren van licht in de eerste en de tweede toestand omvat, bij voorkeur waarbij de lichtbron een laser omvat.An apparatus according to any one of claims 7 to 17, wherein the light generating means comprises a single light source for generating light in the first and second states, preferably wherein the light source comprises a laser. 19. Inrichting volgens eender welke der conclusies 7 tot 18, waarbij het detectiemiddel een eerste polariseerder stroomopwaarts van de eerste detector geconfigureerd voor het genereren van het eerste interferentiesignaal en een tweede polariseerder stroomopwaarts van de tweede detector geconfigureerd voor het genereren van het eerste interferentiesignaal omvat.An apparatus according to any one of claims 7 to 18, wherein the detecting means comprises a first polarizer upstream of the first detector configured to generate the first interference signal and a second polarizer upstream of the second detector configured to generate the first interference signal. 20. Inrichting volgens eender welke der conclusies 7 tot 19, omvattende een verder optisch middel en een verder detectiemiddel, waarbij het verdere optische middel en het verdere detectiemiddel zijn geconfigureerd voor het meten van de positie van het doel langs een verschillende richting dan het optische middel en het detectiemiddel.An apparatus according to any one of claims 7 to 19, comprising a further optical means and a further detecting means, the further optical means and the further detecting means being configured to measure the position of the target along a different direction than the optical means and the detection means. 21. Inrichting volgens conclusie 20, omvattende een aanvullende bundelsplitser die is opgesteld voor het delen van het lichtgenererende middel tussen het optische middel en het verdere optische middel, waarbij de bundelsplitser is voorzien tussen het lichtgenererende middel en zowel het optische middel als het verdere optische middel.An apparatus according to claim 20, comprising an additional beam splitter arranged to share the light generating means between the optical means and the further optical means, the beam splitter being provided between the light generating means and both the optical means and the further optical means .
NL2028816A 2021-07-22 2021-07-22 Method for determining a position of a target by optical interferometry and device for doing the same NL2028816B1 (en)

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US20100259760A1 (en) * 2007-10-04 2010-10-14 Attocube Systems Ag Device for position detection
CN112432602A (en) * 2020-11-25 2021-03-02 中国航空工业集团公司北京长城计量测试技术研究所 Double-beam laser interferometry engine blade tip clearance measurement method and device
CN112857206A (en) * 2019-11-28 2021-05-28 余姚舜宇智能光学技术有限公司 Laser interferometer, optical system thereof, detection method and deflection detection equipment
US20210199418A1 (en) * 2019-07-26 2021-07-01 Zhejiang Sci-Tech University Differential sinusoidal phase modulation laser interferometric nanometer displacement measuring apparatus and method

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US20100259760A1 (en) * 2007-10-04 2010-10-14 Attocube Systems Ag Device for position detection
US8570529B2 (en) 2007-10-04 2013-10-29 Attocube Systems Ag Device for position detection
US20210199418A1 (en) * 2019-07-26 2021-07-01 Zhejiang Sci-Tech University Differential sinusoidal phase modulation laser interferometric nanometer displacement measuring apparatus and method
CN112857206A (en) * 2019-11-28 2021-05-28 余姚舜宇智能光学技术有限公司 Laser interferometer, optical system thereof, detection method and deflection detection equipment
CN112432602A (en) * 2020-11-25 2021-03-02 中国航空工业集团公司北京长城计量测试技术研究所 Double-beam laser interferometry engine blade tip clearance measurement method and device

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