Optical system, optical device, computer program product and measurement method

Abstract

Optical system comprising: an optical circuit (2) with phase shift of polarized light; and an information processing device (3) which processes data acquired by the phase-shift polarized light optical circuit (2); wherein the optical circuit (2) with phase shift of polarized light comprises: a polarizing beam splitter (21a) which splits light having a coherence length shorter than a difference in optical path length between a normal optical path and a delayed optical path having an optical path length longer than the normal optical path, the light being split into normal light traveling along the normal optical path and delayed light traveling along the delayed optical path; a separating device (23), wherein the normal light and the delayed light are individually emitted to a reference surface (10), and the separating device (23) separates the reflected light reflected from the reference surface (10) into a plurality of light beams; and a plurality of image capture elements (24) each capturing the intensities of the plurality of split light beams, the information processing device (3) comprises a processor (32) and a memory (31) which stores an instruction, wherein the information processing device further comprises, as a configuration when the processor (32) executes the instruction stored in the memory (31): a calibration device (322) which individually identifies calibration parameters for calibrating optical properties of the plurality of reflected light beams separated by the separation device (23), wherein the calibration device (322) further identifies the calibration parameters based on the intensity of normal reflected light traveling along the normal optical path and reflected at the reference surface (10) and further based on the intensity of delayed reflected light traveling along the delayed optical path and reflected at the reference surface (10), wherein the normal reflected light and the delayed reflected light are each detected by the plurality of image detection elements (24).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This invention claims priority to Japanese Application No. 2017-151864, filed on August 4, 2017, the disclosure of which is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] This invention relates to an optical system, an optical device, a computer program product and a measuring method for measuring a shape of a measuring object. 2. Description of related technology

[0003] A Fizeau interferometer is known as an example of an apparatus for observing, for example, a surface shape of an optical component. The interferometer is configured such that light from a light source is converted into parallel light, the parallel light is emitted onto a reference plate, and, in addition, parallel light passing through the reference plate strikes a test object parallel to and spaced apart from the reference plate by a predetermined distance; and two beams of reflected light from the parallel light reflected from a reference surface of the reference plate and a test surface of the test object are used to generate interference fringes having equal thicknesses (Japanese Patent Laid-Open No. JP H09-21606 A).

[0004] It is known that measurement results of the interferometer are affected by errors resulting from external factors, such as fluctuations in the air or vibration, variations in the manufacturing of the various components of the interferometer, or variations during assembly.

[0005] US 10 088 291 B2 discloses an instantaneous phase-shift interferometer using a light source with a coherence length shorter than the difference in optical path length between the light reflected from a reference surface and the light reflected from a measured surface. A beam originating from the light source is split, and using an adjustable optical delay path, a first beam is delayed to cause a difference in optical path length and is superimposed on the same optical axis as a second beam, whereupon the reference beam and the measurement beam are generated. The optical path length of the delayed optical path is changed during adjustment, a plurality of interference fringe images are individually acquired, and at least one of the bias voltage, amplitude, and phase shift of the interference fringes obtained in each of the interference fringe images is calculated.The shape of a measured object is measured based on the results of bias calculation, amplitude calculation and phase shift amount calculation.

[0006] EP 1 717 546 A1 discloses an interferometer comprising a variable-wavelength light source. A reference light and a measurement light are synthesized, and the synthesized light is split into a plurality of split lights. A specific phase difference is provided between the split lights by phase-shifting optical elements. A plurality of interference fringe images formed by the phase-shifted split lights are captured by an imaging unit.Bias voltages, amplitudes, and the amounts of phase shift of the interference fringes formed by the plurality of split lights are calculated based on interference fringe intensities of the imaged interference fringes obtained by placing a calibration substrate in place of the measurement object, varying the wavelength of the emitted light to several values, and operating the imaging unit to capture a plurality of images of interference fringes obtained by the split lights. SUMMARY OF THE INVENTION

[0007] In view of these circumstances, this invention provides a technology that reduces the influence of errors.

[0008] This object is achieved according to the invention by the features of the independent claims. Specific embodiments of the invention are the subject of the dependent claims.

[0009] An optical system according to one aspect of this invention is an optical system equipped with a phase-shift polarized light optical circuit and an information processing device that processes data acquired by the phase-shift polarized light optical circuit.The phase-shift polarized light optical circuit includes a polarizing beam splitter that splits light having a coherence length shorter than a difference in optical path length between a normal optical path and a delayed optical path longer than the normal optical path, splitting the light into normal light traveling along the normal optical path and delayed light traveling along the delayed optical path; a separator where the normal light and the delayed light are individually emitted onto a reference surface, and the separator separates the reflected light reflected from the reference surface into a plurality of light beams; and a plurality of image detecting elements that respectively detect the intensities of the plurality of separated light beams.The information processing apparatus includes a calibration device that individually identifies calibration parameters that calibrate optical properties of the plurality of reflected light beams separated by the separation device, wherein the calibration device identifies the calibration parameters based on the intensity of reflected normal light traveling along the normal optical path and reflected from the reference surface and the intensity of reflected delayed light traveling along the delayed optical path and reflected from the reference surface, wherein the reflected normal light and the reflected delayed light are respectively detected by the plurality of image detection elements.

[0010] According to a specific embodiment, the plurality of image capture elements can also capture interference light for measurement light traveling along the normal optical path and reflected from a measurement object, and reference light traveling along the delayed optical path and reflected from the reference surface.

[0011] In particular, the calibration device may also identify, for each of the plurality of image sensing elements, a phase value corresponding to each of the plurality of image sensing elements by using a plurality of beams of interference light received by the plurality of light sensing elements and having a phase difference changed by modifying the length of the delayed optical path.

[0012] Furthermore, the information processing device may in particular include a measuring device which measures a shape of the measurement object by using the intensity of the interference light detected by the light detecting elements and calibration parameters and the phase value which have been identified by the calibration device.

[0013] For example, the phase-shift polarized light optical circuit may include at least four of the image sensing elements, and the measuring device may calculate modeling parameters of an approximate function using the least square method, wherein the modeling parameters use the calibration parameters to model a data array including the intensities of the interference light for the measuring light and the reference light.

[0014] An optical device according to another aspect of this invention includes a detecting means that individually detects the intensities of a plurality of divided light beams, wherein light divided into normal light traveling along a normal optical path and delayed light traveling along a delayed optical path having a longer optical path length than the normal optical path is individually emitted to a reference surface, and the reflected light reflected from the reference surface is divided into the plurality of beams;and a calibration device that individually identifies calibration parameters that calibrate optical properties of the plurality of split light beams based on the intensity of normal reflected light traveling along the normal optical path and reflected from the reference surface and the intensity of delayed reflected light traveling along the delayed optical path and reflected from the reference surface;

[0015] According to a specific embodiment, the calibration device can detect at least one phase value of interference light for measurement light traveling along the normal optical path and reflected from a measurement object and reference light traveling along the delayed optical path and reflected from the reference surface by using a plurality of beams of interference light having a phase difference that has been changed by modifying the length of the delayed optical path.

[0016] Furthermore, the optical device may in particular include a measuring device which measures a shape of the measurement object by using the intensity of the interference light detected by the image detection elements and the calibration parameters and the phase value identified by the calibration device.

[0017] A computer program product according to another aspect of this invention, which is particularly embodied as a fixed, non-transitory computer-readable storage medium, comprises computer-readable instructions that cause a computer to perform a detection that individually detects the intensities of a plurality of split light beams, wherein light split into normal light traveling along a normal optical path and delayed light traveling along a delayed optical path having a longer optical path length than the normal optical path is individually emitted to a reference surface, and the reflected light reflected from the reference surface is split into the plurality of beams;and perform an identification which individually identifies calibration parameters that calibrate optical properties of the plurality of split light beams based on the intensity of normal reflected light traveling along the normal optical path and reflected from the reference surface and the intensity of delayed reflected light traveling along the delayed optical path and reflected from the reference surface;

[0018] A measuring method according to another aspect of this invention comprises the steps of: individually detecting the intensities of a plurality of divided light beams, wherein light divided into normal light traveling along a normal optical path and delayed light traveling along a delayed optical path having a longer optical path length than the normal optical path is individually emitted to a reference surface, and the reflected light reflected from the reference surface is divided into the plurality of beams;and individually identifying calibration parameters that calibrate optical properties of the plurality of split light beams based on the intensity of normal reflected light traveling along the normal optical path and reflected from the reference surface, and further based on the intensity of delayed reflected light traveling along the delayed optical path and reflected from the reference surface;

[0019] According to the above, the influence of errors can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] This invention will be further described in the following detailed description with reference to the accompanying several drawings, using non-limiting examples of exemplary embodiments of this invention, wherein like reference numerals represent similar parts throughout the various views of the drawings. It should be noted that while embodiments are described separately, individual features thereof may be combined to form further embodiments. Fig. 1 gives an overview of an optical system; Fig. 2A to Fig. 2G shows interference and measurement data for two beams of reflected light; Fig. 3 provides an overview of an optical system according to an embodiment; Fig. 4 shows a configuration of functions of a phase-shift polarized light optical circuit according to the embodiment; Fig. 5 shows a configuration of functions of an information processing apparatus according to the embodiment; Fig. 6 is a flowchart for a process of calibrating the light intensity; and Fig. 7 is a flowchart for a process of measuring a shape of a measurement object. DETAILED DESCRIPTION OF THE INVENTION

[0021] The details shown herein are exemplary and merely illustrative of embodiments of this invention and are presented to provide what is believed to be the most useful and comprehensive description of the principles and conceptual aspects of this invention. In this regard, no attempt is made to describe structural details of this invention in more detail than is necessary for a basic understanding of this invention, since the description, together with the drawings, will clearly indicate to those skilled in the art how the forms of this invention may be practiced. EmbodimentRequired technology for the embodiment

[0022] An optical system S' using a Fizeau interferometer is described with reference to Fig. 1 described. Fig. 1 provides an overview of the optical system S'. The optical system S' includes a light source 1, an information processing device (information processor 3), an image capture device 4, and / or a beam splitter 5. The information processing device 3 is to be connected to the light source 1 and the image capture device 4, respectively, in such a way that it is capable of communicating with each of them. The information processing device 3 can displace a measurement object 11 or control or regulate its displacement as appropriate. The information processing device 3 can further displace a reference surface 10 instead of, or in addition to, displacing the measurement object 11.

[0023] The light source 1 can, for example, be a laser oscillator that emits a laser of a specific (predetermined or predeterminable) wavelength based on a command from the information processing device 3. The laser emitted by the light source 1 passes through the beam splitter 5 and travels to the reference surface 10 and the measurement object 11. Reflected light, which is reflected from the surfaces of the reference surface 10 and the measurement object 11, travels through the beam splitter 5 and to the image capture device 4. In Fig. 1, Wr denotes reference light, which is the reflected light reflected from the surface of the reference surface 10, while Wt denotes measurement light, which is the reflected light reflected from the surface of the measurement object 11.

[0024] The image capture device 4 detects the intensity of the received light and thereby generates measurement data. The information processing device 3 displaces (or controls the displacement of) the measurement object 11 by a displacement distance, which is determined, in particular, as a function of the wavelength of the laser light. In this way, the information processing device 3 can change the phase difference between the two beams of reflected light. The information processing device 3 controls or regulates the image capture device 4 and generates measurement data, in particular, each time the measurement object 11 is displaced. In this way, the information processing device 3 can then acquire measurement data (the intensity of interference light for the two beams of reflected light) in states in which the two beams of reflected light have different phase differences.

[0025] The interference light for the reference light reflected from the surface of the reference surface 10 and the measurement light reflected from the surface of the measurement object 11, as well as the measurement data acquired by the image acquisition device 4 are calculated with reference to the Fig. 2A to 2G. The Fig. Figures 2A to 2G show interference light and measurement data for the two beams of reflected light. As in Fig. 1, referred to in the Fig. 2A to 2G Wr is the reference light, and Wt is the measuring light.

[0026] Fig. 2A is a schematic view illustrating a case where the phases of the two beams of reflected light are substantially the same. Fig. Figure 2B is a schematic view showing that the two beams of reflected light interfere, and the amplitudes of the two beams intensify each other to produce a larger amplitude. Fig. Figure 2C is a schematic view of the measurement data, expressed as a measurement image, for the measurement data acquired when the two beams of reflected light are substantially coincident. As shown in Fig. As shown in Figure 2C, the measurement image acquired when the phases of the two beams of reflected light substantially match produces an image with a strong light intensity (brightness) throughout the entire image.

[0027] Fig. Figure 2D is a schematic view illustrating a case where the phases of the two beams of reflected light are offset by approximately π (rad). Fig. Figure 2E is a schematic view showing that the two beams of reflected light interfere, and the amplitudes of the two beams attenuate each other, producing a smaller amplitude. Fig. Figure 2F is a schematic view of the measurement data, expressed as a measurement image, for the measurement data acquired when the two beams of reflected light are offset by approximately π (rad). As shown in Fig. As shown in Figure 2F, the measurement image acquired when the phases of the two beams of reflected light are offset by approximately π (rad) produces an image with a low light intensity (darkness) over the entire measurement image.

[0028] In this example, when the height of the measurement object 11 (or a position of a surface of the measurement object 11 along the direction or axis of the light coming from the light source 1 and incident on the measurement object 11) is constant, the phase difference in the interference light incident on each pixel of an image sensing element is the same. Therefore, theoretically, each pixel of each image sensing element in the image sensing device 4 detects an identical intensity of interference light. Meanwhile, when the height of the measurement object 11 is not constant (as in Fig. 1), the phase difference in the interference light incident on each pixel of the image sensing element is different. Therefore, each pixel of the image sensing element detects a different intensity of interference light. The information processing device 3 identifies the phase difference in the interference light incident on each pixel or picture element of the image sensing element based on the intensity of the interference light detected by each pixel or picture element of the image sensing element in the image sensing device 4. Furthermore, the information processing device 3 can identify the height of the measurement object 11 based on the identified phase difference.

[0029] Fig. Figure 2G is a schematic view in which a data array is plotted in the order in which the light intensity detected at each pixel was recorded. The horizontal axis of the Fig. 2G indicates the phase difference between the two beams of reflected light resulting from the displacement of the measuring object 11, and the vertical axis indicates the magnitude of the light intensity.

[0030] In Fig. 2G, the intensities of the interference light with different phases, which are detected by certain pixels or picture elements in the image capture device 4, are each plotted with its own black circle. Each data item in the plotted data array contains a certain error from the time of measurement. Therefore, each data item does not necessarily correspond to an approximate value identified based on an approximate function corresponding to the data array. In view of this, the difference between each data item and the corresponding approximate value can be considered as an error ε i (x, y) from the time of measurement, and by identifying modeling parameters that determine the sum of the squares of the error ε i (x, y), the approximation function can be adapted to the plotted data arrangement.

[0031] A process of the information processing device 3 which identifies the modeling parameters will be described with reference to Fig. 2G. A function f(x,y), denoted by a dashed line, is an approximate function of the data arrangement, where the intensities of light detected by pixels corresponding to coordinates (x, y) are arranged in the detected order. In Fig. 2G, an amplitude V denotes the amplitude of the approximate function, a deviation I'(x, y) denotes a center of oscillation of the approximate function, and an offset A denotes the offset of the approximate function. In addition, the errors ε i (i = 1 to 4) a distance from each data element to the corresponding approximate value.

[0032] The reference light Wr is represented by the expression (1), where the phase of the reference light Wr is defined as ϕ rThe measuring light Wt is represented by the expression (2), where the phase of the measuring light Wt is ϕ t and a phase difference resulting from the displacement of the measuring object 11 is expressed as δ i An intensity I i The interference light for the reference light Wr and the measurement light Wt is represented by expression (3). Expression (4) is obtained by expanding expression (3). [Formula 1] Wr=Ireiϕr Wt=Itei(ϕr−δi) Ii=|Wr+Wt|2 Ii=Ir2+It2+2IrIt cos(ϕt−ϕr−δi)

[0033] In this example, in expression (4) I r 2 + I t 2 the average intensity of the interference light and 2I r It is the intensity modulation of the interference light. If a difference between the intensity modulation known as ϕ r phase defined as ϕ tdefined phase is defined as a phase difference ϕ, the phase difference ϕ also indicates the height of the measuring object 11.

[0034] Expression (5) is obtained by expanding expression (4). [Formula 2] Ii=Ir2+It2+2IrItcos ϕ cos δi−2IrIt sin ϕ sin δi where ϕ = ϕ t - ϕ r . In this example, each element of expression (5) can be substituted as shown in expressions (6) to (8). Expression (5) is represented in expression (9) using expressions (6) to (8). [Formula 3] a0=Ir2+It2 a1=2IrIt cos ϕ a2=−2IrIt sin ϕ Ii=a0+a1 cos δi+a2 sin δi

[0035] The intensity I i of the light detected by a particular pixel is given by expression (10) using a matrix, by writing out expression (9) for each δ i represents. [Formula 4] [I1I2⋮IN]=[1cos δ1sin δ11cos δ2sin δ2⋮⋮⋮1cos δNsin δN][a0a1a2]

[0036] Expression (10) can be reformulated as I = Xa. Here, a vector a that is optimal in the sense of minimizing the 2-norm of I - Xa is already known as a least square solution and can be written as a = (X T X) -1 X T I. Here X is T X is represented by expression (11). Furthermore, X T I is represented by expression (12). Unless otherwise noted, in the following expressions, Σ without an index is treated as a summation of i = 1 ~ N. [Formula 5] XTX=[N∑cos δi∑sin δi∑cos δi∑cos2 δi∑cos δi sin δi∑sin δi∑cos δi sin δi∑sin2 δi] XTI=[∑Ii∑Iicosδi∑Iisinδi]

[0037] The information processing device 3 identifies a0 to a2 (modeling parameters) using the above expressions (11) and (12). The information processing device 3 identifies the phase difference φ using a1 and a2. The phase difference φ is represented by expression (13). Then, the information processing device 3 identifies a height h indicating the shape of the measurement object 11 using the phase difference φ and a wavelength λ of the light generated by the light source 1. The height h is represented by expression (14). [Formula 6] ϕ=arctan(−a2a1) h=λ4πϕ

[0038] Problems with the Prerequisite Technology for the Embodiment In the above description, the information processing device 3 shifts (controls or regulates the shift thereof) the measurement object 11 to cause two beams of reflected light to interfere with different phase differences. Thus, when the information processing device 3 modifies the length of an optical path of the reflected light and causes the interference with different phase differences, the time at which each beam of interference light is detected may be different. Therefore, the phase difference in the interference light detected by the image detection device 4 changes under the influence of atmospheric fluctuations over time. In addition, the background of the interference light detected by the image detection device 4 changes under the influence of changes in ambient light.The measurement accuracy for the measurement object 11 then deteriorates due to the changes in the phase difference and the background of the interference light detected by the image capture device 4.

[0039] In an optical system, reflected light from a reference surface or a measurement object is split, causing the multiple split light beams, each with a different phase difference, to interfere, and the intensity of the interference light is detected by each of a plurality of image detection elements. This can reduce the influence of environmental changes due to the passage of time. However, in the optical system, when the reflected light is split, the intensities of each of the multiple split light beams are not necessarily identical. This is because an optical circuit is affected by variations in the manufacturing of optical elements or variations in device assembly, and therefore a single light beam cannot be split into equal parts.

[0040] Consider an example where the intensities of the light beams detected by the multiple image sensing elements are different: for example, a case where the intensity of a light beam detected by any one of the image sensing elements is greater than the intensity of a light beam detected by another image sensing element. The least squares method calculates a vector that is optimal in terms of minimizing the 2-norm of I - Xa. Therefore, the larger the absolute value of a value, the more errors are considered to be incorporated. Therefore, if one image sensing element detects a greater light intensity than another image sensing element, the least squares method can calculate a result that weights the greater light intensity.

[0041] Overview of the Optical System According to the Embodiment In view of the above, an optical system S according to an embodiment of this invention calibrates modeling parameters that describe the intensities of split light beams captured by a plurality of image capture elements, wherein the calibration is performed using the intensities of light beams traveling along different paths. Thus, the optical system S can advantageously reduce the influence of errors resulting from variations in the optical system. An overview of the optical system S according to the embodiment of the invention will be described with reference to Fig. 3 described. Fig. 3 gives an overview of the optical system S according to the embodiment.

[0042] The optical system S includes the light source 1, an optical circuit 2 with phase-shift polarized light, and / or the information processing device 3 that processes data acquired by the optical circuit 2 with phase-shift polarized light. The information processing device 3 is connected so as to be capable of communication with the light source 1. The information processing device 3 can move (or control or regulate the movement of) the reference surface 10, the measurement object 11, and / or various structural components of the optical circuit 2 with phase-shift polarized light as required.

[0043] The phase-shift polarized light optical circuit 2 includes a normal optical path and a delayed optical path, which has a longer optical path length than the normal optical path. Light exiting the light source 1 is split into two light beams, each traveling along the two optical paths. The phase-shift polarized light optical circuit 2 emits each of the split light beams one by one onto the same reference surface. The phase-shift polarized light optical circuit 2 then splits the light reflected from the reference surface 10 and detects the intensity of each of the split light beams.Specifically, the information processing device 3 uses the intensity of each of the split light beams detected by the phase-shift polarized light optical circuit 2 to identify calibration parameters that calibrate the modeling parameters that model the intensity of the split light beams.

[0044] Below, various configurations included in the optical system S are described in detail. The light source 1 is, for example, a superluminescent diode (SLD). For example, the light source 1 emits light with a coherence length shorter than the difference in optical path length between the normal optical path and the delayed optical path, which has an optical path length longer than the normal optical path, with which the phase-shift polarized light optical circuit 2 is equipped. Specifically, the coherence length of the light emitted by the light source 1 is approximately 10 µm.

[0045] Configuration of the phase-shift polarized light optical circuit 2 according to the embodiment A configuration of functions of the phase-shift polarized light optical circuit 2 according to the embodiment will be described with reference to Fig. 4 describe. Fig. 4 shows a configuration of functions of the phase-shift polarized light optical circuit 2 according to the embodiment. The phase-shift polarized light optical circuit 2 includes polarizing beam splitters 21a and 21b, a corner cube 22, a separator 23, and / or one or more, specifically, a plurality of image sensing elements 24 (24a to 24d). In this embodiment, the phase-shift polarized light optical circuit 2 includes four of the image sensing elements 24, but may also include more than four image sensing elements 24. In addition, the phase-shift polarized light optical circuit 2 may also include a shielding plate that blocks light, and provide the shielding plate between the polarizing beam splitters 21a and 21b, between the polarizing beam splitter 21a and the corner cube 22, and / or between the corner cube 22 and the polarizing beam splitter 21b.

[0046] The polarizing beam splitter 21a splits the light emitted by the light source 1 into normal light, which travels along the normal optical path, and delayed light, which travels along the delayed optical path. More specifically, the polarizing beam splitter 21 causes light with an s-polarized component of the light emitted by the light source 1 to strike the corner cube 22 and light with a p-polarized component to strike the polarizing beam splitter 21b. The light with the s-polarized component and the light with the p-polarized component are linearly polarized light beams. The corner cube 22 is, in particular, or comprises a retroreflector that reflects incident light in a direction parallel to and in the opposite direction to an incident direction.The corner cube 22 at least partially reflects the incident light from the polarizing beam splitter 21a to the polarizing beam splitter 21b. In the following description, an optical path that passes from the polarizing beam splitter 21a through the corner cube 22 to reach the polarizing beam splitter 21b is referred to as the delayed optical path, while an optical path that passes from the polarizing beam splitter 21a to the polarizing beam splitter 21b without passing through the corner cube 22 is referred to as the normal optical path.

[0047] The separator 23 individually emits normal light and delayed light onto the reference surface 10 and splits the light reflected by the reference surface 10 into a plurality of light beams. The separator 23 splits the reflected light into a plurality of light beams and allows the reflected light beams to impinge on the plurality of light-detecting elements 24. A specific structure in which the separator 23 individually emits normal light and delayed light onto a reference surface and splits the light reflected by the reference surface into a plurality of light beams will be described below. Specifically, the separator 23 includes a magnifying lens 231, a plurality of beam splitters 232, collimator lenses 233a and 233b, a quarter-wave plate 234, and / or a plurality of polarizing plates 235.

[0048] The magnifying lens 231 scatters incident light from the polarizing beam splitter 21b and allows the light to at least partially impinge on the image capture element 24a. The beam splitter 232a substantially allows incident light from the separator 23 to pass through and impinge on the collimator lens 233a. Furthermore, the beam splitter 232a at least partially reflects the light that has passed through the collimator lens 233a and been reflected from the reference surface 10 and / or the measurement object 11 to the collimator lens 233b. The collimator lens 233a converts incident light from the beam splitter 232a into a parallel light beam and allows the parallel light beam to impinge on the reference surface 10 and / or the measurement object 11. The collimator lens 233b converts incident light from the beam splitter 232a into a parallel light beam and allows the parallel light beam to strike the quarter-wave plate 234.

[0049] The quarter-wave plate 234 converts the linearly polarized light incident from the collimator lens 233b into circularly polarized light or elliptically polarized light and / or directs the polarized light to the beam splitter 232b. The beam splitter 232b splits the incident light from the quarter-wave plate 234 into light incident on a beam splitter 232c and light incident on a beam splitter 232d. The beam splitter 232c splits the incident light from the beam splitter 232b into light incident on a polarizing plate 235a and light incident on a polarizing plate 235b. The beam splitter 232d splits the incident light from the beam splitter 232b into light incident on a polarizing plate 235c and light incident on a polarizing plate 235d.

[0050] The polarizing plates 235a to 235d each convert the incident circularly polarized light or elliptically polarized light into linearly polarized light oriented in different directions. When the multiply split reference light and measurement light pass through the polarizing plates 235a to 235d and are polarized in different directions, the polarized light individually strikes the plurality of image sensing elements 24 as interference light with different phase differences δi. Specifically, the polarizing plate 235a allows incident light from the beam splitter 232c to strike the image sensing element 24a as interference light with a phase difference of approximately 0 (rad). The polarizing plate 235b allows incident light from the beam splitter 232c to strike the image sensing element 24b as interference light with a phase difference of approximately π / 2 (rad).The polarizing plate 235c allows incident light from the beam splitter 232d to strike the image capture element 24c as interference light with a phase difference of approximately π (rad). The polarizing plate 235d allows incident light from the beam splitter 232d to strike the image capture element 24d as interference light with a phase difference of approximately 3π / 2 (rad).

[0051] The image capture elements 24 are or include, for example, elements that convert received light into an electrical signal. Specifically, the image capture elements 24 may be or include a CCD image sensor or a CMOS image sensor, but the image capture elements 24 are not limited thereto. The plurality of image capture elements 24 each detects the intensity of a plurality of split light beams. Furthermore, the plurality of image capture elements 24 can also detect the intensity of interference light caused by the interference between the measurement light traveling along the normal optical path and reflected by the measurement object and the reference light traveling along the delayed optical path and reflected by the reference surface. The image capture elements 24 transmit the detected intensity of the light to the information processing device 3.

[0052] In this way, the phase-shift polarized light optical circuit 2 can cause the two split beams of reflected light to strike the plurality of image capture elements 24 as interference light with different phase differences. Therefore, the interference light with a plurality of different phase differences can be detected immediately or simultaneously, compared to a case where the optical system S' shifts the reference surface 10 or the measurement object 11 and thereby detects interference light with a plurality of different phase differences. Configuration of the information processing device 3 according to the embodiment

[0053] A configuration of functions of the information processing apparatus 3 according to the embodiment will first be described with reference to Fig. 5 described. Fig. Figure 5 shows the functional configuration of the information processing device 3 according to the embodiment. Specifically, the information processing device 3 includes a memory 31 and a controller 32. The memory 31 includes a storage medium such as ROM (Read Only Memory) and / or RAM (Random Access Memory). The memory 31 stores programs executed by the controller 32. The memory 31 can also store the light intensities or calibration parameters detected by the image sensing elements 24.

[0054] The controller 32 is or includes a computing resource that includes a processor, such as a CPU (central processing unit), not shown in the drawings. The controller 32 performs the functions of a detection device 321, a calibration device 322, and / or a measurement device 323 by executing a program stored in the memory 31.

[0055] Specifically, the detection device 321 detects the light intensity detected by the image detection elements 24. Specifically, light split into normal light traveling along the normal optical path and delayed light traveling along the delayed optical path, which has a longer optical path length than the normal optical path, is individually emitted onto the reference surface 10. The light reflected from the reference surface 10 is split into a plurality of light beams, and the detection device 321 individually detects the intensity of the plurality of split light beams. The detection device 321 informs the calibration device 322 of the detected light intensities.

[0056] In particular, the calibration device 322 individually identifies calibration parameters that calibrate optical properties of the plurality of reflected light beams split by the splitting device 23. Specifically, the calibration device 322 identifies parameters based on the intensity of the normal reflected light traveling along the normal path and reflected by the reference surface 10, and the intensity of the delayed reflected light traveling along the delayed optical path and reflected by the reference surface 10, wherein the normal reflected light and the delayed reflected light are each captured by a plurality of image capture elements.

[0057] In the optical system S' according to the assumed technique, the intensities of a plurality of interference light beams are detected by the single image detection device 4. In other words, in the optical system S', the element (I1 to I N ) on the left side of expression (10) indicate light intensities detected under identical conditions. Meanwhile, in the optical system S according to this embodiment, the reflected light is divided, and the intensities of a plurality of interference light beams are respectively detected by the plurality of image detecting elements 24. Therefore, in the optical system S, the elements (I1 to I N ) on the left side of the expression (10) shows light intensities recorded under different conditions.

[0058] The calibration parameters are parameters that calibrate, for example, a center of oscillation component, which specifies the center of oscillation of the approximate function, and an amplitude component, which specifies the amplitude of the approximate function. In expression (9), the center of oscillation component is a0, and the amplitude components are a1 and a2. Specifically, the calibration parameters calibrate the modeling parameters a0, a1, and a2 using a parameter p. i , which calibrates the center of oscillation component a0 of the approximation function that approximates the intensity of the light detected by an i-th image sensing element, and a parameter q i , which calibrates the amplitude component. The calibration parameter p i is represented by expression (15), and the calibration parameter q i is represented by expression (16). [Formula 7] pi=Csi+Cpi∑i(Cri+Cpi) qi=CsiCpi∑iCsiCpi

[0059] Where C s the intensity of the delayed reflected light, and C p is the intensity of the normal reflected light. Expression (9) is calculated using the parameters p i and q i represented in expression (17). [Formula 8] Ii=p'a0+qia1 cos δi+qia2 sin δi

[0060] In this way, the calibration device 322 can standardize the contribution rate of each of the plurality of detected light intensities by calibrating the modeling parameters. Furthermore, expression (18) can be generated by writing out expression (17) for each piece of measurement data. [Formula 9] ∑i[{pi}2piqicos δipiqisin δipiqicos δi{qi cos δi}2{qi}2sin δi cos δipiqisin δi{qi}2sin δi cos δi{qi sin δi}2][a0a1a2]=[ piIiqiIi cos δiqiIi cos δi]

[0061] The calibration device 322 can also identify a phase value corresponding to each of the plurality of image capture elements 24 for each of the plurality of image capture elements 24. A process for identifying the phase value corresponding to each of the plurality of image capture elements 24 is described below. In the following description, the measurement object is a measurement object used for calibration that has a controlled shape.

[0062] First, the calibration device 322 of the information processing device 3 determines whether the measurement object is installed. When the calibration device 322 determines that the measurement object is installed, the calibration device controls or regulates various structural components of the phase-shift polarized light optical circuit 2 and causes both reference light and measurement light to be emitted onto each of the plurality of image sensing elements 24. Further, the calibration device 322 shifts (or controls or regulates) the corner cube 22 of the phase-shift polarized light optical circuit 2, the reference surface 10, and / or the measurement object 11.controls the displacement of these elements) so that the optical path length difference (L1 + L2) of the normal optical path and the delayed optical path is equal to an optical path length (L3) which is twice the distance between the reference surface 10 and the measuring object 11.

[0063] The calibration device 322 determines whether the plurality of image capture elements 24 have detected interference light. If the calibration device 322 determines that the plurality of image capture elements 24 have detected interference light, the calibration device identifies a characteristic phase value θ i in particular for each of the plurality of image capture elements 24. A specific method by which the calibration device 322 determines the phase value θ iThe method by which a phase value is determined by the optical system S' using a Fizeau interferometer, which has already been described, is similar to the method by which the calibration device 322 determines a phase value. The calibration device 322 is not limited to this and may also determine a phase value using another known method.

[0064] The calibration device 322 can also measure a phase difference ψ i between the plurality of image capture elements 24 using the phase values ​​θ i of the plurality of image capture elements 24. For example, the calibration device 322 identifies the phase difference ψ i using the phase value θ ifrom one of the plurality of image sensing elements 24 as a standard reference. When the first image sensing element 24 is used as the reference, the phase difference ψ i Zero. In this way, the calibration device 322 can determine a phase difference δ i which is different within the plurality of image sensing elements 24 when the information processing device 3 measures an actual measurement object, and therefore the measurement accuracy in measuring the measurement object can be improved.

[0065] Specifically, the measuring device 323 measures the shape of the measurement object 11 using the intensity of the interference light received by the image sensing elements 24 and the calibration parameters and phase value identified by the calibration device 322. For example, the measuring device 323 calculates the modeling parameters of the approximate function using the least square method, wherein the modeling parameters use the calibration parameters to model a data array containing the intensities of the interference light for the measurement light and the reference light. An expression that finds the phase difference of each of the image sensing elements 24 is represented as the phase difference ψ i defined, and finding the modeling parameters (a0, a1 and a2) of the approximate function, which are modeled using the calibration parameters, is represented by the expression (19) below. [Formula 10] ∑i[{pi}2piqicos (δi+ψi)piqisin (δi+ψi)piqicos (δi+ψi){qi cos (δi+ψi)}2{qi}2sin (δi+ψi) cos (δi+ψi)piqisin (δi+ψi){qi}2sin (δi+ψi) cos (δi+ψi){qi sin (δi+ψi)}2][a0a1a2]=[ piIiqiIi cos (δi+ψi)qiIi sin (δi+ψi)]

[0066] The measuring device 323 can also identify the height h of the measurement object using the calculated modeling parameters. Specifically, the measuring device 323 identifies the height h, which indicates the shape of the measurement object, using the phase difference ϕ defined by the calculated modeling parameters and a wavelength λ of the light source 1. As described above, the phase difference ϕ is represented by Expression (13), and / or the height h is represented by Expression (14).

[0067] The measuring device 323 identifies the height h for each pixel corresponding to the plurality of image sensing elements 24. In this way, the measuring device 323 can identify the height of the measurement object 11 using the modeling parameters calibrated by the calibration parameters, and therefore the measurement accuracy can be improved.

[0068] Hereinafter, a specific process of the data processing device 3 which calibrates the light intensity will be described with reference to Fig. 6 described. Fig. 6 is a flowchart for the light intensity calibration process. First, the calibration device 323 of the information processing device 3 controls the phase-shift polarized light optical circuit 2 and blocks the delayed optical path (step S1). Then, the calibration device 322 controls the light source 1 and emits light to the phase-shift polarized light optical circuit 2. The calibration device 322 controls the phase-shift polarized light optical circuit 2 and detects the intensity of the normal light traveling along the normal optical path (step S2). Then, the detection device 321 detects the intensity of the normal light detected by the phase-shift polarized light optical circuit 2.

[0069] When the detection device 321 detects the intensity of the light, the calibration device controls the phase-shift polarized light optical circuit 2 to stop blocking the delayed optical path and block the normal optical path (step S3). The calibration device 322 controls the phase-shift polarized light optical circuit 2 and detects the intensity of the delayed light traveling along the delayed optical path (step S4). Then, the detection device 321 detects the intensity of the delayed light detected by the phase-shift polarized light optical circuit 2. When the detection device 321 detects the intensity of the delayed light, the calibration device 322 controls the phase-shift polarized light optical circuit 2 and stops blocking the normal optical path (step S5).

[0070] The calibration device 322 identifies the calibration parameters using the normal light intensity and the delayed light intensity (step S6). Then, the calibration device 322 determines whether the measurement object for calibration is installed (step S7). If the calibration device 322 determines that the measurement object for calibration is not installed ("No" in step S7), the calibration device 322 waits until it determines that the measurement object for calibration is installed. If the calibration device 322 determines that the measurement object for calibration is installed ("Yes" in step S7), the process proceeds to step S8.

[0071] The calibration device 322 controls the phase-shift polarized light optical circuit 2 and shifts the corner cube 22 (controls the shift thereof), thereby modifying the distance or length of the delayed optical path (step S8). When the distance or length of the delayed optical path is modified, the calibration device controls the phase-shift polarized light optical circuit 2 and causes the phase-shift polarized light optical circuit 2 to detect the intensity of the reflected light that has been at least partially reflected by the reference surface 10 and the measurement object 11 (step S9). The detection device 321 detects the detected intensity of the reflected light.The calibration device 322 determines whether the intensity of the reflected light rays has been detected a certain (predetermined or predeterminable) number of times (step S10). If the calibration device 322 detects that the intensity of the reflected light rays has not been detected for the certain (predetermined or predeterminable) number of times ("No" in step S10), the process returns to step S8. The calibration device 322 repeats steps S8 to S10 until it detects that the intensity of the reflected light rays has been detected for the certain (predetermined or predeterminable) number of times.

[0072] If the calibration device 322 detects that the intensity of the reflected light rays has been detected a certain (predetermined or predeterminable) number of times ("Yes" at step S10), the calibration device 322 identifies the phase value for each image capture element 24 using the detected intensity of the reflected light (step S11). Once the phase value for each image capture element 24 is identified, the calibration device 322 identifies the phase difference between each image capture element 24 using the identified phase value (step S12). Then, the calibration device 322 stores the identified phase difference in the memory 31 (step S13).

[0073] Next, a process of the information processing device 3 in measuring the shape of the measurement object 11 will be described with reference to Fig. 7 described. Fig.7 is a flowchart for the process of measuring the shape of the measurement object. First, the measuring device 323 acquires the calibration parameters from the memory 31 (step S21). The measuring device 323 acquires the intensity of the reflected light detected by the image sensing elements 24 (step S22). The measuring device 323 identifies the phase value (modeling parameter) using the calibration parameters and the intensity of the reflected light (step S23). Then, the measuring device 323 measures the shape of the measurement object 11 using the phase value (step S24). Effect of the embodiment

[0074] As described above, the calibration device 322 of the information processing device 3 specifically identifies the calibration parameters that calibrate the modeling parameters that model the intensity of the plurality of split light beams. This allows the calibration device 322 to calibrate the optical properties of the plurality of split reflected light beams and thus reduce the influence of errors due to fluctuations in the optical system that receives the split light beams.

[0075] In particular, the calibration device 322 identifies the phase difference between the plurality of image capture elements 24 by identifying the phase values ​​of the plurality of image capture elements 24 using the calibration parameters. In this way, the calibration device 322 can determine the phase difference δ ibetween the plurality of image sensing elements 24 when the information processing device 3 measures an actual measurement object, and therefore the measurement accuracy in measuring the measurement object 11 can be improved.

[0076] Furthermore, the measuring device 323 measures in particular the shape of the measuring object 11 using the phase difference δ i between the plurality of image sensing elements 24, for which the influence of the fluctuation in the optical system between the image sensing elements 24 is reduced and corrected. In this way, the measuring device 323 can advantageously reduce the influence of errors, and therefore the accuracy in measuring the shape of the measurement object 11 can be improved.

[0077] Accordingly, an optical system is described which includes a phase-shift polarized light optical circuit comprising: a polarizing beam splitter which splits light having a coherence length shorter than a difference in optical path length between a normal optical path and a delayed optical path having an optical path length longer than the normal optical path, the light being split into normal light travelling along the normal optical path and delayed light travelling along the delayed optical path; a separator, wherein the normal light and the delayed light are individually emitted onto a reference surface, and the separator splits the reflected light reflected from the reference surface into a plurality of light beams;and a plurality of image detecting elements each detecting the intensities of the plurality of split light beams, and the optical system further includes an information processing device including a calibration device.;

[0078] This invention has been described above with reference to one embodiment, but the technical scope of this invention is not limited to that described in the above embodiment, and various modifications are possible within the scope of the description. For example, the specific embodiments of separate or integrated devices are not limited to the above-mentioned embodiment, and all or part of them may be configured to be functionally or physically separate or integrated into any desired units. In addition, novel embodiments produced by the arbitrary combination of a plurality of embodiments are also included in the scope of the embodiment of this invention. The advantages of a novel embodiment produced by such a combination also include the advantages of the original embodiment of this invention.

[0079] It should be understood that the foregoing examples are presented for the purpose of illustration only and are not to be construed as limiting this invention in any way. While this invention has been described with reference to exemplary embodiments, it is to be understood that the words used herein are words of description and illustration, not words of limitation. Changes may be made within the scope of the appended claims, as currently stated and as amended, without departing from the spirit and scope of this invention in its aspects.While this invention has been described herein with reference to specific structures, materials, and embodiments, this invention is not intended to be limited to the details disclosed herein; rather, this invention extends to all functionally equivalent structures, methods, and applications as come within the scope of the appended claims.

[0080] This invention is not limited to the embodiments described above, and various changes and modifications may be possible without departing from the scope of this invention.

Claims

[1] Optical system, comprising: an optical circuit (2) with phase shift of polarized light; and an information processing device (3) which processes data detected by the optical circuit (2) with phase shift polarized light; wherein the optical circuit (2) with phase shift of polarized light comprises: a polarizing beam splitter (21a) which splits light with a coherence length shorter than a difference in optical path length between a normal optical path and a retarded optical path which has an optical path length longer than the normal optical path, wherein the light is split into normal light which travels along the normal optical path and retarded light which travels along the retarded optical path; a separating device (23) wherein the normal light and the delayed light are emitted separately onto a reference surface (10), and the separating device (23) separates the reflected light reflected from the reference surface (10) into a plurality of light rays; and a multitude of image capture elements (24), each capturing the intensities of the multitude of split light rays, the information processing device (3) comprises a processor (32) and a memory (31) which stores an instruction, wherein the information processing device, as a configuration when the processor (32) executes the instruction stored in the memory (31), further comprises: a calibration device (322) which individually identifies calibration parameters for calibrating optical properties of the plurality of reflected light beams that have been separated by the separation device (23), wherein the calibration device (322) further identifies the calibration parameters starting from the intensity of normal reflected light which travels along the normal optical path and is reflected at the reference surface (10), and further from the intensity of delayed reflected light which travels along the delayed optical path and is reflected at the reference surface (10), wherein the normal reflected light and the delayed reflected light are each detected by the plurality of image acquisition elements (24). [2] Optical system according to claim 1, wherein: the multitude of image acquisition elements (24) captures interference light for measuring light, which travels along the normal optical path and is reflected at a measuring object (11), and reference light, which travels along the delayed optical path and is reflected at the reference surface (10). [3] Optical system according to claim 1 or 2, wherein: The calibration device (322) acquires a phase value for each of the plurality of image acquisition elements (24) corresponding to each of the plurality of image acquisition elements (24) by using a plurality of beams of interference light received by the plurality of image acquisition elements (24) and having a phase difference that has been changed by modifying the length of the delayed optical path. [4] Optical system according to claim 2 or 3, wherein the information processing device (3) further comprises a measuring device (323) which measures a shape of the object being measured (11) using the intensity of the interference light detected by the image acquisition elements (24) and the calibration parameters and phase value identified by the calibration device (322). [5] Optical system according to claim 4, wherein: the optical circuit (2) with phase shift of polarized light comprises at least four of the image acquisition elements (24), and the measuring device (323) calculates modeling parameters of an approximation function using the least squares method, wherein the modeling parameters use the calibration parameters to model a data arrangement containing the intensities of the interference light for the measuring light and the reference light. [6] Optical device comprising: a processor (32) and a memory (31) which stores an instruction, wherein the optical device, as a configuration when the processor (32) executes the instruction stored in the memory (31), further comprises: a detection device (321) which individually detects the intensities of a plurality of split light beams, wherein light which is split into normal light which travels along a normal optical path and delayed light which travels along a delayed optical path which is longer than the normal optical path is individually emitted to a reference surface (10) and the reflected light which is reflected from the reference surface (10) is split into the plurality of light beams; and a calibration device (322) which individually identifies calibration parameters for calibrating optical properties of the plurality of split light beams starting from the intensity of normal reflected light which travels along the normal optical path and is reflected at the reference surface (10) and further from the intensity of delayed reflected light which travels along the delayed optical path and is reflected at the reference surface (10). [7] Optical device according to claim 6, wherein: the calibration device (322) identifies at least one phase value of interference light for measuring light traveling along the normal optical path and reflected from a measuring object (11) and reference light traveling along the delayed optical path and reflected from the reference surface (10) using a plurality of beams of interference light having a phase difference that has been changed by modifying the length of the delayed optical path. [8] Optical device according to claim 7, further comprising a measuring device (323) which measures a shape of the object being measured (11) using the intensity of the interference light detected by the image acquisition elements (24) and the calibration parameters and phase value identified by the calibration device (322). [9] Computer program product comprising an executable set of instructions which, when loaded and executed by a suitable processor, causes the processor to perform operations which include: a detection system which individually detects the intensities of a plurality of split light rays, wherein light which is split into normal light which travels along a normal optical path and delayed light which travels along a delayed optical path which is longer than the normal optical path is individually emitted to a reference surface (10) and the reflected light which is reflected from the reference surface (10) is split into the plurality of light rays; and an identification which calibration parameters for calibrating optical properties of the plurality of split light beams starting from the intensity of normal reflected light which travels along the normal optical path and is reflected at the reference surface (10), and furthermore starting from the intensity of delayed reflected light which travels along the delayed optical path and is reflected at the reference surface (10), individually identified. [10] Measurement procedure comprising the following steps: Individual detection of the intensities of a plurality of split light rays, wherein light which is split into normal light traveling along a normal optical path and delayed light traveling along a delayed optical path which is longer than the normal optical path is individually emitted to a reference surface (10) and the reflected light which is reflected from the reference surface (10) is split into the plurality of light rays; and Individual identification of calibration parameters for calibrating optical properties of the plurality of split light beams starting from the intensity of normal reflected light which travels along the normal optical path and is reflected at the reference surface (10), and further starting from the intensity of delayed reflected light which travels along the delayed optical path and is reflected at the reference surface (10).

Images