Metrology system utilizing multiple measurements

Abstract

A metrology system includes: an optical section that outputs light; a branching section; and a detector and a processing section. The branching section branches the light into a reference light along a reference optical path and a measurement light along a measurement optical path for reflection by a workpiece to be measured. The detector and processing section are configured to: receive a combination of light including the reference light and the measurement light; and convert the combination of light into a combined photoelectric signal. The detector and processing section includes: an analog-to-digital converter; and a sampling and holding section. The sampling and holding section includes at least a first sampling and holding circuit and a second sampling and holding circuit, and is coupled to sample the combined photoelectric signal (e.g., at corresponding first and second sampling rates) and provide an output to the analog-to-digital converter.

Description

Technical Field

[0001] This disclosure relates to precision metrology, and more specifically, to apparatus and systems for measuring the surface of precision workpieces. Background Technology

[0002] For quality control of objects (e.g., workpieces) that include specific surface profiles (e.g., produced through molding and / or machining), there are increasingly higher requirements in terms of throughput, measurement resolution, and accuracy. Ideally, such workpieces should be measured / inspected to ensure correct dimensions, functionality, etc. However, very precise measurement tolerances (e.g., in some instances at the micrometer level or finer) may be required to confirm that the workpiece surface has the desired characteristics for some applications.

[0003] Various precision metrology systems can be used for measuring and inspecting workpiece surfaces. For example, in some instances, metrology systems performing such operations can utilize an optical coherence tomography (OCT) technique, such as frequency modulated continuous wave (FMCW), which can determine the distance to a target (e.g., the distance to a point on the workpiece surface; distances to multiple points on the workpiece surface can be determined as part of a workpiece surface measurement operation). An important component of such systems and / or other equivalent measurement systems is their effective measurement range. It would be desirable to improve or otherwise enhance the configuration of such metrology systems (e.g., for measuring and inspecting workpiece surfaces, etc.). Summary of the Invention

[0004] This summary is provided to introduce, in a simplified form, the concept choices further described below in the detailed embodiments. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0005] According to one aspect, a measurement system is provided, comprising: an optical section that outputs light; a branching section; and a detector and a processing section. The branching section branches a portion of the light output from the optical section into reference light guided along a reference optical path, and branches at least a portion of the remaining light into measurement light guided along a measurement optical path for reflection by a workpiece to be measured. The detector and processing section are configured to: receive a combined light comprising the reference light from the reference optical path and the measurement light reflected from the workpiece from the measurement optical path; and convert the combined light into a combined photoelectric signal. The detector and processing section includes: an analog-to-digital converter; and a sampling and holding section. The sampling and holding section includes at least a first sampling and holding circuit and a second sampling and holding circuit, wherein the sampling and holding section is coupled to provide an output to the analog-to-digital converter.

[0006] According to another aspect, a method for operating a metering system is provided. The method includes:

[0007] - Receives a combination of light including reference light from the reference optical path and measurement light reflected from the workpiece from the measurement optical path;

[0008] - Convert combined light into combined photoelectric signals;

[0009] - The combined photoelectric signal is sampled at a first sampling rate using a first sampling and holding circuit, and the corresponding first output is provided to the analog-to-digital converter; and

[0010] - The combined photoelectric signal is sampled at a second sampling rate lower than the first sampling rate using a second sampling and holding circuit, and the corresponding second output is provided to the analog-to-digital converter.

[0011] According to another aspect, a metrology system is provided, the metrology system being configured to: receive a combination of light including reference light from a reference optical path and measurement light reflected from a workpiece from a measurement optical path; convert the combination of light into a combination of photoelectric signals; sample the combination of photoelectric signals at a first sampling rate using a first sampling and holding circuit, and provide a corresponding first output to an analog-to-digital converter; and sample the combination of photoelectric signals at a second sampling rate lower than the first sampling rate using a second sampling and holding circuit, and provide a corresponding second output to the analog-to-digital converter. Attached Figure Description

[0012] Figure 1 It is a block diagram of a metrology system that includes the interferometer and the circuit system.

[0013] Figure 2 It is shown that it can be included in, for example, Figure 1 A block diagram of the first embodiment of the interferometer part in a metrology system, such as a metrology system;

[0014] Figure 3 It is shown that it can be included in, for example, Figure 1 A block diagram of the second embodiment of the interferometer part in a metrology system, such as a metrology system;

[0015] Figure 4 It is shown that it can be included in, for example, Figure 1 A block diagram illustrating the implementation of the circuit system portion of a metering system, such as a metering system.

[0016] Figures 5A to 5D It shows things like Figure 1 A diagram illustrating certain operating principles of a measurement system, such as a measurement system, wherein the length of the measuring optical path is longer than the length of the reference optical path;

[0017] Figures 6A to 6D It shows things like Figure 1The diagram illustrates certain operating principles of measurement systems, such as the measurement system, in which the reference optical path length is longer than the measurement optical path length.

[0018] Figure 7A and Figure 7B This is a diagram illustrating a first embodiment of the sampling and holding section and the corresponding signal timing;

[0019] Figure 8A and Figure 8B This is a diagram illustrating a second embodiment of the sampling and holding section and the corresponding signal timing;

[0020] Figure 9A and Figure 9B This is a diagram illustrating the third embodiment of the sampling and holding section and the corresponding signal timing; and

[0021] Figure 10 This is a flowchart illustrating an exemplary implementation of a routine for operating a metering system. Detailed Implementation

[0022] Figure 1 This is a block diagram showing the measuring system 100 and the workpiece WP to be measured. (Example) Figure 1 As shown, the metrology system 100 includes an interferometer section 101 and a circuit system section 102. This metrology system utilizes optical coherence tomography (OCT) techniques, such as frequency modulated continuous wave (FMCW) techniques, as will be described in more detail below. References will be made below. Figure 2 and Figure 3 Some embodiments of the interferometer section 101 are described in more detail below. Reference will be made to... Figure 4 The implementation of the circuit system section 102 is described in more detail.

[0023] In various embodiments, the metrology system 100 is configured to determine the distance D to the workpiece. More specifically, the metrology system 100 optically measures the distance between the metrology system 100 and the workpiece WP. The metrology system 100 may also measure the three-dimensional shape and / or surface characteristics of the workpiece WP (e.g., by scanning the position of light illuminating the workpiece WP, such as for measuring different points on the surface of the workpiece WP).

[0024] Figure 2 It is shown that it can be included in, for example, Figure 1 The interferometer part 101 in the measurement system 100, etc. M A block diagram of the first embodiment. (See diagram below.) Figure 2 As shown, interferometer section 101 M Includes light section 110 and branch section 120 M And reference mirror 136. Interferometer section 101, which will be described in more detail below.M Direct the light toward the workpiece WP (e.g., to measure the distance to the workpiece WP).

[0025] In various embodiments, the optical section 110 includes a laser resonator and outputs laser light (e.g., Figure 2 and Figure 3 The optical portion 110 in some embodiments may also be referred to as the laser portion 110. The optical portion 110 can output, for example, frequency-modulated laser light. The optical portion 110 can provide a frequency shifter in a resonator and can output laser light with an oscillation frequency that varies linearly with time. In various embodiments, the optical portion 110 may include a frequency-shift feedback laser.

[0026] Branch section 120 M A portion of the light output from the light section 110 is split into a reference light, and at least a portion of the remaining light is split into a measurement light. This will be described in more detail below, along the reference light path ROP. M Guide the reference light and along the measurement optical path MOP M Guide the measuring light. In various embodiments, branch 120 M This may include beam splitter components (e.g., beam splitters, etc.). In various embodiments, the beam splitter components may have a specified splitting ratio (e.g., 1:1, such that beam splitting can be achieved along the reference optical path ROP). M and measurement optical path MOP M Each of them guides approximately the same amount of light.

[0027] Reference optical path ROP M In the middle, from branch 120 M The branched reference light shines toward the reference mirror 136, which reflects the reference light back to the branch portion 120. M In measuring the optical path MOP M In the middle, from branch 120 M The branched measuring light shines towards the workpiece WP. The measuring light reflected from the workpiece WP at the branch section 120... M The branch is received back. In various implementations, branch 120 M The distance between at least a portion of the workpiece WP and the workpiece can be set as the distance D to be measured by the metering system 100.

[0028] Branch section 120 M The reflected measurement light is combined with the reference light reflected by reference mirror 136. In this way, Figure 2 Branch section 120 is shown. M Examples that also serve as combining parts (e.g., in some embodiments, branch parts may also or alternatively be referred to as branch and combining parts 120) MOr simply referred to as Combination Part 120 M Branch section 120 M The combined light (e.g., including a reference light and a measurement light) is output to the circuit system section 102 (e.g., output to the detector section 140 in the circuit system section 102, as will be referred to below). Figure 4 (A more detailed description follows).

[0029] In various implementation methods, the reference optical path ROP is used. M It can have a reference optical path length (e.g., including the round-trip travel of the reference light to and from reference mirror 136). Similarly, the measurement optical path MOP M It can include a measurement optical path length (e.g., including the travel distance of the measuring light to and from the workpiece WP). Generally, there may be a difference between the reference optical path length and the measurement optical path length. Figure 2 In the example, a reference marker RM is provided, which indicates the reference optical path ROP. M The length representation, such as relative to the measurement optical path MOP M As shown. In this example, the measurement optical path MOP... M Indicated to have a higher ROP than the reference optical path M Greater length. In the reference optical path ROP M The length is greater than the measurement optical path MOP M In the alternative scenario, the measurement surface of the workpiece WP will be shown before the reference mark RM (i.e., in Figure 2 (Left side of the reference mark RM). As will be described in more detail below, the circuit system portion 102 can be configured to receive combined light (i.e., including a combined reference light and a measuring light) and generate an output (e.g., indicating the distance to the workpiece and correspondingly indicating the difference between the length of the reference optical path and the length of the measuring optical path).

[0030] In various embodiments, the optical path length difference between the reference optical path length and the measurement optical path length can correspond to the propagation difference between the reference light and the measurement light, for which a propagation delay corresponding to the optical path length difference occurs in both the reference light and the measurement light. As will be described in more detail below, the distance to the workpiece WP can be determined by determining a signal corresponding to the propagation delay (e.g., determined using circuit system section 102). More specifically, as mentioned above, the measurement optical path length is a result of the distance to the workpiece (e.g., the longer the distance to the workpiece, the larger the measurement optical path length, and vice versa). Correspondingly, the propagation delay (e.g., corresponding to the difference between the measurement optical path length and a known fixed reference optical path length) will be different for different distances to the workpiece. As will be described in more detail below, such a relationship can be used to determine the measurement distance to the workpiece (e.g., based on a determination signal corresponding to the propagation delay and correspondingly indicating the optical path length difference, which indicates the measurement distance to the workpiece).

[0031] In various implementations, the interferometer section 101 of the metrology system M It can include the dispersion part DP M .exist Figure 2 In the example, the dispersion part DP M Included in the reference optical path ROP M In some alternative implementations, the dispersion component may be included in the measurement optical path MOP. F In the example shown, the dispersion component DP... M This includes a high-dispersion optical element OE1. In various embodiments, the optical element OE1 may be at least semi-transparent, allowing light (e.g., the reference light in the illustrated example) to pass through it, and the optical element OE1 causes dispersion of the light. In various embodiments, the unbalanced dispersion between the reference optical path and the measurement optical path is at least partially caused by the dispersion portion (e.g., it can be used as part of the process of determining the measurement distance to the workpiece WP).

[0032] Figure 3 It is shown that it can be included in, for example, Figure 1 The interferometer part 101 in the measurement system 100, etc. F A block diagram of the second embodiment. (See diagram below.) Figure 3 As shown, interferometer section 101 F Includes light section 110 and branch section 120 F The optical section 110 comprises a circulator section 125, an optical head section 134, and a combination section 139. Optical fibers OF1 to OF6 are shown to connect the different sections for providing light to and from the different sections. More specifically, the optical section 110 is coupled to the branch section 120 via optical fiber OF1. F Branch section 120F The optical head section 134 is connected to the assemblies via fiber optic OF2 and to the circulator section 125 via fiber optic OF3. The circulator section 125 is connected to the optical head section 134 via fiber optic OF4 and to the assemblies 139 via fiber optic OF5. The assemblies 139 is connected to the circuitry section 102 via fiber optic OF6.

[0033] The interferometer section 101 will be described in more detail below. F The light is directed to the workpiece WP (e.g., to measure the distance to the workpiece WP). In various embodiments, the metrology system may optionally measure the interferometer section 101. F The distance between the workpiece WP and the workpiece WP (e.g., and in various embodiments, the three-dimensional shape and / or surface characteristics of the workpiece WP can also be measured, such as by scanning the position of light illuminating the workpiece WP, such as for measuring different points on the surface of the workpiece WP).

[0034] Branch section 120 F The light output from the light section 110 is branched, wherein a portion of the light is used as a reference light and at least some of the remaining light is used as a measurement light. Branch section 120 F For example, an optical fiber splitter (e.g., may also be called an optical fiber coupler or alternatively). Figure 3 In the example, branch 120 F The measuring light is supplied to the circulator section 125, and the reference light is supplied to the assembly section 139.

[0035] The circulator section 125 has multiple input / output ports. For example, the circulator section 125 inputs light from one port and outputs light from the next port, and inputs light from the next port and outputs light from the port after that. Figure 3 An example of a looper section 125 with three input / output ports is shown. In this case, the looper section 125 will generate from branch section 120. F The supplied measuring light is output to the optical head section 134. Furthermore, the circulator section 125 outputs the light input from the optical head section 134 (i.e., the light reflected from the workpiece WP) to the assembly section 139.

[0036] The optical head portion 134 provides / illuminates / guides the light input from the circulator portion 125 to the workpiece WP. The optical head portion 134 includes, for example, a collimating lens. In this case, the optical head portion 134 first uses the collimating lens to adjust the light input from the circulator portion 125 via the optical fiber OF4 into a beam shape, and then outputs the light.

[0037] Furthermore, the optical head portion 134 receives reflected light from the measurement light illuminating the workpiece WP. The optical head portion 134 uses a collimating lens to focus the received reflected light onto the optical fiber OF4 and supplies it to the circulator portion 125. In this case, the optical head portion 134 may include a common collimating lens that can illuminate the workpiece WP with the measurement light and receive reflected light from the workpiece WP. In various embodiments, the distance between at least a portion of the optical head portion 134 and the workpiece WP may be defined as a distance D (e.g., in some embodiments, it may be characterized as a measurement distance D).

[0038] Alternatively, the optical head portion 134 may include a focusing lens. In this case, the optical head portion 134 focuses light input from the circulator portion 125 via the fiber optic OF4 onto the surface of the workpiece WP. The optical head portion 134 receives at least a portion of the reflected light reflected from the surface of the workpiece WP. The optical head portion 134 uses the focusing lens to focus the received reflected light onto the fiber optic OF4 and supplies the light to the circulator portion 125. Also in this case, the optical head portion 134 may include a common focusing lens, which can illuminate the workpiece WP with measurement light and receive reflected light from the workpiece WP.

[0039] The assembly section 139 receives reflected light from the circulator section 125, namely, the measuring light that illuminates the workpiece WP and is reflected by the workpiece WP. Furthermore, the assembly section 139 receives light from the branch section 120. F The reference light is received. The combining section 139 combines / mixes the reflected measurement light and reference light and provides a corresponding output to the circuit system section 102 (e.g., to the detector section 140 in the circuit system section 102, as will be referred to below). Figure 4 (As described in more detail). In various embodiments, the combining portion 139 may be an optical fiber splitter (e.g., it may also be referred to as an optical fiber coupler and / or optical fiber combiner).

[0040] For ROP along the reference optical path F (and as corresponding to the reference optical path length ROPL) the reference light propagates, the reference light from branch 120 F Propagated through optical fiber OF2 to the assembly section 139. For the measurement optical path MOP... F The measurement light propagates (and corresponds to the measurement optical path length MOPL), the measurement light from branch 120 FThe light propagates through optical fiber OF3, through circulator section 125, through optical fiber OF4, through optical head section 134, and through free space FS to the workpiece WP (e.g., according to the distance D from optical head section 134 to workpiece WP), and is reflected by workpiece WP to propagate back to optical head section 134 through free space FS (e.g., according to the distance D from optical head section 134 to workpiece WP), and then through optical head section 134, through optical fiber OF4, through circulator section 125, and through optical fiber OF5 to reach assembly section 139.

[0041] In various embodiments, the oscillation frequency of the light output from the light section 110 varies linearly over time (e.g., it can be characterized as a frequency scan), depending on a frequency difference corresponding to a propagation delay between the reference light and the measurement light (e.g., received at the combination section 139). A beat frequency signal corresponding to this frequency difference can be generated (e.g., generated based on the combination of the reference light and the measurement light, such as via...). Figure 3 Combination part 139 or Figure 2 Branch / combination section 120 M The following text will refer to... Figure 4 In more detail, the detector and processing section DPP of the circuit system section 102 may include a detector section 140 and may provide a signal corresponding to the difference in propagation distance between the reference light and the measurement light.

[0042] In various implementations, reference will be made below. Figure 4 In more detail, the detector and processing section DPP detects the difference in propagation distance between the reference light and the measurement light by performing frequency analysis on the generated beat frequency signal. More specifically, in various embodiments, the combined light (e.g., from the combining section 139) is received by a detector section 140 (e.g., the detector section of the detector and processing section DPP), which can output a combined photoelectric signal (e.g., which may be a sine wave), which is digitized using an analog-to-digital converter (e.g., which may be included in the processing section 150 of the detector and processing section DPP in some embodiments). The digitized signal can then be analyzed using a Fast Fourier Transform algorithm (e.g., performed by the processing section 150, and additional processing may be performed in various embodiments to determine the distance to the workpiece).

[0043] In various embodiments, the display portion 160 of the circuit system portion 102 is controlled by the control portion 180 to display the analysis results of the detector and the processing portion DPP (e.g., the distance to the workpiece may be displayed or otherwise indicated). In various embodiments, the display portion 160 may include a display or the like and display the detection results, while the control portion 180 may store the analysis results in a storage unit or the like. Generally, the metrology system can measure the distance between the interferometer portion 101 and the workpiece WP by analyzing the frequency difference between the reference light and the measurement light reflected from the workpiece WP, as will be described in more detail below.

[0044] In various implementations, the interferometer section 101 of the metrology system F It can include the dispersion part DP F .exist Figure 3 In the example, the dispersion part DP F Included in the reference optical path ROP F In some alternative implementations, the dispersion component may be included in the measurement optical path MOP. F In the example shown, the dispersion component DP... F Including high-dispersion fiber OF2 (i.e., branched section 120 as described above) F The optical fiber OF2 connected to the assembly section 139 is a high-dispersion fiber. In various embodiments, another optical path (e.g., the measurement optical path MOP) F It may include one or more low-dispersion fibers (e.g., relative to the dispersion portion DP). F High-dispersion fiber OF2 has lower dispersion. For example, some or all of fibers OF3, OF4, or OF5 can be fibers with relatively low dispersion. This may contrast with some conventional configurations where fibers may be included in two optical paths with similar / matched (e.g., identical) dispersion characteristics. In various embodiments, the unbalanced dispersion between the reference optical path and the measurement optical path is at least partially caused by the dispersion portion (e.g., it can be used as part of the process of determining the measurement distance to the workpiece WP).

[0045] In other words, in some existing conventional configurations, the matching fibers in the reference and measurement optical paths (e.g., having similar dispersion characteristics) typically minimize accumulated unbalanced dispersion. Using fibers with different dispersion characteristics in the two paths will result in dispersion imbalance (e.g., in some instances, this may correspond to an increase in dispersion imbalance). In such configurations, it remains desirable to match the baseline optical path length (OPL) to achieve the desired interference effect (e.g., produced by the combination of the reference and measurement beams in the combination section 139), but higher-order phase can be added via dispersion.

[0046] In various embodiments, measurement light can be delivered to the workpiece WP using an air gap (e.g., through the free space FS between the optical head portion 134 and the workpiece WP). In some such configurations, it can be considered more efficient to include a relatively low-dispersion fiber in the measurement optical path MOP (e.g., to enhance dispersion mismatch caused by the free space FS / air gap, such as relative to a reference optical path that may include a higher-dispersion fiber). That said, it should be understood that other configurations can also be used, and in some such embodiments, the primary objective is to make the dispersion / fibers in the two optical paths different (e.g., having different dispersion characteristics), and generally, the greater the dispersion mismatch, the better the disambiguation between signal peaks.

[0047] Figure 4 It is shown that it can be included in, for example, Figure 1 A block diagram illustrating an implementation of the circuit system portion 102 in a metering system, such as a metering system. Figure 4 As shown, the circuit system portion 102 includes a detector and processing portion DPP (e.g., including a detector portion 140 and a processing portion 150), a display portion 160, and a control portion 180. In various embodiments, the detector portion 140 of the detector and processing portion DPP receives / detects a combination of reference light and measurement light (e.g., from...). Figure 2 Branch 120 M or Figure 3 The combining section 139 receives the combined light and converts it into an electrical signal. In various embodiments, the detector section 140 detects the beat frequency signal generated by combining and interfering the reference light and the measurement light. In various embodiments, the detector section 140 may have, for example, a photoelectric conversion element and may convert the beat frequency signal into an electrical signal. An example of a photoelectric conversion element is a photodiode. The detector and processing section DPP may also have an analog-to-digital converter (ADC), which can convert / digitize the beat frequency signal converted into an electrical signal into a digital signal.

[0048] As described above, in various embodiments, the oscillation frequency of the light output by the light section 110 changes linearly with time. Therefore, a frequency difference appears between the oscillation frequency of the reference light and the oscillation frequency of the measurement light due to the propagation delay. A beat frequency signal is generated corresponding to this frequency difference.

[0049] The processing unit 150 (e.g., including a calculation unit) analyzes the detected electrical signal to calculate the distance D to the workpiece WP. The processing unit 150 analyzes the frequency of the generated beat frequency signal, for example, by using a frequency conversion such as FFT. Then, the processing unit 150 calculates the optical path length difference corresponding to the frequency of the beat frequency signal.

[0050] In various embodiments, the control unit 180 receives output from the detector and the processing unit 150 of the processing unit DPP, and controls the display unit 160 to display the analysis results of the processing unit 150. The display unit 160 may have a display or the like and display the detection results. The display unit 160 may also receive instructions from the user. In various embodiments, the control unit 180 may be configured to control certain operations of the light unit 110, the display unit 160, and / or the detector and the processing unit DPP. In various embodiments, the control unit 180 may control the light unit 110 to output light to the branch unit 120 (e.g., Figure 2 or Figure 3 Generally, it should be noted that the metrology system 100, including the interferometer section 101 and the circuit system section 102, is capable of measuring the distance between the metrology system 100 and the workpiece WP (e.g., by analyzing the frequency difference between the measurement light reflected by the workpiece WP and the reference light).

[0051] As described above, in various embodiments, the interferometer section 101 of the metrology system (e.g., Figure 2 Interferometer section 101 M or Figure 3 101 F ) may include the dispersive portion DP (e.g., Figure 2 The dispersion part DP M or Figure 3 DP F The unbalanced dispersion between the reference optical path (ROP) and the measurement optical path (MOP) may be at least partially caused by the dispersion component. More specifically, the dispersion component DP may cause the light dispersion in the reference optical path (ROP) to differ from that in the measurement optical path (MOP), which corresponds to the unbalanced dispersion between the ROP and the MOP (e.g., it can be used as part of a process for determining the measurement distance to the workpiece (WP).

[0052] Figures 5A to 5D It shows things like Figure 1 The diagram illustrates certain operating principles of metrology systems, such as metering systems. As described above, in various embodiments, the metrology system including the optical component 110 operates according to optical coherence tomography (OCT) such as frequency modulated continuous wave (FMCW). In some embodiments, the optical coherence tomography may also be referred to as swept-source optical coherence tomography (SS-OCT). Figure 5AThis illustrates a situation where the measurement distance (e.g., to the workpiece) causes the measuring optical path length MOPL to be longer than the reference optical path length ROPL. The optical path length difference DIFF is shown to correspond to the difference between the optical path lengths. For example, when MOPL is 1.5 mm longer than ROPL, MOPL may correspond to a 1.5 mm position within the range of -4.0 mm to +4.0 mm, at a distance of 101 from the interferometer section (see...). Figure 4 The distance D may be +5.5 mm, ranging from the negative range of -4.0 mm to the positive range of +1.5 mm (e.g., in a configuration where the range begins at the edge of the interferometer section 101).

[0053] Figure 5B This is a graph showing the frequency variation over time, where the dashed lines correspond to the measurement light ML, and the solid lines correspond to the reference light RL (e.g., received at a combination section such as combination section 139). The shape of each signal corresponds to the scanning frequency of the light section 110 (e.g., where the frequency of each signal increases linearly with time, reaches a maximum value, at which point the frequency returns to the baseline level, and this process can then be repeated over future time periods). The time delay between signals is shown. A T greater than 0 corresponds to a propagation delay (e.g., because the measuring optical path length MOPL is longer than the reference optical path length ROPL). The beat frequency f is also shown. b It is also correspondingly greater than zero, and corresponds to the frequency difference between two signals at a given time, such as Figure 5B As shown in the image.

[0054] Figure 5C This is a graph of the combined signal (e.g., from the combining section), indicating its amplitude oscillation over time. Due to the frequency sweep of the optical section 110, when the reference light and the measurement light are combined (e.g., through the combining section), the time delay (e.g., as...) Figure 5B (as shown) is encoded in Figure 5C The beat frequency f of the signal b In various embodiments, the beat frequency can be detected based on time (e.g., by a detector section 140 of the detector and processing section DPP). In various embodiments, a Fourier transform (e.g., utilized by the processing section 150) can evaluate the time-domain data and extract any frequency information. Because the rate of change of frequency (i.e., the slope of the frequency scan) is known, the frequency information can be mapped to the distance of light propagation (e.g., as shown in the diagram). Figure 5D As shown in the figure, it illustrates signal peaks corresponding to different workpiece distances / positions D.

[0055] Further reference Figure 5D(That is, the x-axis extends in the range from -4.0 mm to +4.0 mm). It should be noted that the Fourier transform used to convert the frequency space to distance produces + and - conjugate peak pairs (i.e., corresponding to the positive position peak PPP and the negative position peak NPP, respectively, and corresponding to the positive beat frequency +f). b and negative beat frequency -f b Generally, standard processing in such systems typically ignores negative components (e.g., the measurement optical path length MOPL is always assumed / configured to be greater than the reference optical path length ROPL). In such systems, collecting data over negative distance ranges is considered undesirable due to the uncertainty of signal peaks (i.e., which signal peak corresponds to the current measurement). This effectively reduces the available distance range by approximately half in such systems (e.g., in this example, only a 4mm distance range corresponding to a positive signal range from 0mm to 4mm is utilized, instead of the full 8mm distance range corresponding to a combination of negative and positive distance ranges from -4.0mm to +4.0mm). In various implementations, to address such issues, the metrology system may include a dispersive component (e.g., one that supports disambiguation between signal peaks). Alternatively, other techniques may be utilized to achieve this disambiguation in various implementations (e.g., orthogonal processing techniques, which will be referenced below). Figure 9A and Figure 9B (A more detailed description follows).

[0056] Figures 6A to 6D Is it separate from Figures 5A to 5D The diagram is similar to the one shown, but differs in that it corresponds to the opposite situation (i.e., relative to lengths MOPL and ROPL). More specifically, Figure 6A The diagram illustrates a situation where the measurement distance (e.g., to the workpiece) causes the measuring optical path length MOPL to be shorter than the reference optical path length ROPL. The diagram also shows the optical path length difference DIFF corresponding to the difference between the optical path lengths (e.g., as a simplified example). Figure 6A The amplitude of the optical path length difference DIFF can be compared with... Figure 5A The amplitude of the optical path length difference DIFF is the same. For example, when MOPL is 1.5 mm shorter than ROPL, MOPL may correspond to a position of -1.5 mm in the range of -4.0 mm to +4.0 mm, at which point the distance from the interferometer section 101 (see...) Figure 4 The distance D may be +2.5 mm, ranging from -4.0 mm at the negative end to -1.5 mm in the negative range (e.g., in a configuration where the range begins at the edge of the interferometer section 101).

[0057] exist Figure 6B (That is, except that the relative signal positions are opposite, it is the same as...) Figure 5BIn the diagram (similar to the previous one), the dashed line signal corresponds to the measurement light ML, and the solid line signal corresponds to the reference light RL (e.g., received at the combined section). The time delay between the signals is shown. T less than 0 corresponds to a propagation delay (e.g., because the measuring optical path length MOPL is shorter than the reference optical path length ROPL). The beat frequency f is also shown. b It is also correspondingly less than zero, and corresponds to the frequency difference between two signals at a given time, such as Figure 6B As shown in the image.

[0058] exist Figure 6C In the process, when the reference light and the measurement light are combined (e.g., through a combination component), the time delay (e.g., as...) Figure 6B (as shown) is encoded in Figure 6C The beat frequency f of the signal b In various implementation methods, as described above... Figure 5C and Figure 5D The described process is similar; beat frequency can be detected based on time (e.g., via a detector and a detector section 140 of the processing section DPP). Frequency information can be mapped to the distance light travels (e.g., as...). Figure 6D As shown in the figure, it illustrates signal peaks corresponding to different workpiece distances / positions D.

[0059] Further reference Figure 6D It should be noted that the Fourier transform used to convert the frequency space to distance produces + and - conjugate peak pairs (i.e., corresponding to the positive position peak PPP and the negative position peak NPP, respectively, and corresponding to the positive beat frequency +f). b and negative beat frequency -f b It should be noted that the peak values ​​of the generated positive and negative signals are related to... Figure 5B The positive and negative signal peaks are essentially the same. As mentioned above, at least in part due to the uncertainty in the correspondence between signal peaks (i.e., relative to standard processing in some previous systems), collecting data in the negative distance range is considered undesirable (i.e., uncertainty about which signal peak corresponds to the current measurement). More specifically, if the performed measurement process results in a positive position peak PPP and a negative position peak NPP at the indicated position (i.e., corresponding to +1.5mm and -1.5mm respectively, as... Figure 5D and Figure 6DAs shown in the diagram, it may be unclear whether the measurement corresponds to a positive position peak PPP at the +1.5mm position or a negative position peak NPP at the -1.5mm position (e.g., corresponding to the difference between the measured optical path length MOPL and the reference optical path length ROPL). As mentioned above, in various embodiments, to address such issues, the metrology system may include a dispersive component (e.g., which supports disambiguation between signal peaks). In various embodiments, this disambiguation can alternatively be achieved using other techniques (e.g., orthogonal processing techniques, as described below regarding...). Figure 9A and Figure 9B (To be described in more detail).

[0060] As mentioned above Figure 2 , Figure 3 , Figures 5A to 5D and Figures 6A to 6D In various embodiments, the metrology system may include a dispersive component (e.g., one that supports disambiguation between signal peaks). The techniques and configurations utilizing such a dispersive component are described in more detail in U.S. Patent Application No. 660051.578, filed December 30, 2024, entitled “METROLOGY SYSTEM UTILIZING FULL RANGE DETECTION” (Attorney’s File No. 660051.578, U.S. Patent Application Serial No. 19 / 005,052), which is assigned and filed concurrently with this application and is hereby incorporated herein by reference in its entirety.

[0061] The following text will be about Figures 7A to 10 In more detail, as part of the processing of a metrology system such as the metrology system described herein, combined light (e.g., from combining section 139) is received by detector section 140, which can output a combined photoelectric signal (e.g., a sine wave), which is digitized using an analog-to-digital converter (e.g., which may be included in processing section 150 in some embodiments). The digitized signal can then be analyzed by a fast Fourier transform algorithm (e.g., performed by processing section 150). Figures 7A to 9B Some implementations of the sampling and holding section SHP are shown (e.g., it may be included between the detector section 140 and the analog-to-digital converter, as will be described in more detail below).

[0062] As a general principle, it should be noted that in some traditional systems, the absolute range of the FMCW (ABS) is limited by the minimum frequency step size in the sample. This imposes limitations. It requires the dynamic range (e.g., the maximum distance relative to multi-target resolution) to equal the number of samples per scan (e.g., a macro 10m / 10um requires 1 million samples per scan). For larger ranges, the beat frequency may also become too high for digital conversion (e.g., related to analog-to-digital converters and processing speed).

[0063] Beyond the traditional FMCW ABS range, positional uncertainty exists until an integer multiple of the ABS range is reached. Based on the principles described herein, the range can be extended by using a second measurement with a slightly different period (e.g., a similar second measurement trajectory). In various implementations, the period that can be varied falls within the FMCW ABS range.

[0064] In various implementations, two measurements can be performed at different sampling frequency intervals dF1 and dF2 (e.g., corresponding to different sampling rates). See below for reference. Figures 7A to 9B The configurations utilizing different sampling rates are described in more detail. In various implementations, it may be preferable to utilize the full Nyquist measurement range (+ / - range) of such techniques. As mentioned above, this can be achieved by certain techniques, such as including a dispersive component, or alternatively by utilizing orthogonal detection of the beat frequency signal (e.g., according to...). Figure 9A and Figure 9B The implementation method will be described in more detail below.

[0065] Based on the principles described herein, and as will be described in more detail below, obtaining a high-bandwidth signal using a low-bandwidth analog-to-digital converter (ADC) is achieved by including a high-bandwidth sampling and holding section (SHP) preceding the ADC (e.g., as shown below). Figure 7A , Figure 8A and Figure 9A As shown in the example below (which will be described in more detail below). In general, the techniques described herein can have various advantages, such as supporting a longer range of measurements, requiring fewer samples, and / or supporting the use of slower electronics (e.g., slower analog-to-digital converters used in conjunction with relatively fast sampling and holding sections of SHP).

[0066] Figure 7A and Figure 7B This is a diagram illustrating a first embodiment of the sampling and holding section SHP' and the corresponding signal timing. (See diagram for example.) Figure 7AAs shown, a sampling and holding section SHP' (e.g., as part of processing section 150' of detector and processing section DPP) is coupled to detector section 140 (e.g., receiving signals from detector section 140, such as combined photoelectric signals from detector section 140). As will be described in more detail below, in various embodiments, the sampling and holding section SHP' can be configured to sample the combined photoelectric signals from the detector section. The sampling and holding section SHP' is coupled to provide an output (e.g., a sample) to analog-to-digital converter 152 (e.g., as part of processing section 150' of detector and processing section DPP). According to the principles described herein, in various embodiments, the processing section can also be configured to perform a fast Fourier transform (i.e., for analysis) on each digitized signal to determine at least one peak corresponding to the beat frequency. Additionally, the distance to the workpiece can be determined at least in part based on the determined peak corresponding to the beat frequency.

[0067] like Figure 7A As shown, the sampling and holding section SHP' includes a first sampling and holding circuit SH1 and a second sampling and holding circuit SH2. The first sampling and holding circuit SH1 and the second sampling and holding circuit SH2 are connected in parallel between the detector section 140 and the analog-to-digital converter 152. The first sampling and holding circuit SH1 includes a first input switch SW1in, a first capacitor C1, and a first output switch SW1out. The first input switch SW1in (e.g., on the input side) is connected to the detector section 140 and (e.g., on the output side) is connected to the first capacitor C1. The first output switch SW1out (e.g., on the input side) is connected to the first capacitor C1 and (e.g., on the output side) is connected to the analog-to-digital converter 152. The operation of the sampling and holding section SHP' (e.g., including control of switches SW1in and SW1out via control signals Trig1in and Trig1out, respectively) will be referred to below. Figure 7B To provide a more detailed description.

[0068] The second sampling and holding circuit SH2 includes a second input switch SW2in, a second capacitor C2, and a second output switch SW2out. The second input switch SW2in (e.g., on the input side) is connected to the detector section 140 and (e.g., on the output side) to the second capacitor C2. The second output switch SW2out (e.g., on the input side) is connected to the second capacitor C2 and (e.g., on the output side) to the analog-to-digital converter 152. The operation of the sampling and holding section SHP' (e.g., including control of switches SW2in and SW2out via control signals Trig2in and Trig2out, respectively) will be referred to below. Figure 7B To provide a more detailed description.

[0069] Figure 7B It shows the relationship with Figure 7A The sampling and holding of certain signals are related to the operation of the SHP'. Figure 7B The relationship between the laser frequency, control signals Trig1in, Trig1out, Trig2in, and Trig2out, and the representative combined signal Trig1out+Trig2out, and time is shown. As described herein, the light output from the optical component (e.g., optical component 110) includes a laser whose oscillation frequency varies linearly with time (e.g., according to a "chirped" laser, etc.), and... Figure 7B The diagram shows that the laser frequency increases linearly with time. It should be noted that this is consistent with... Figure 5B and Figure 6B The drawing is similar (i.e., the reference light and the measuring light from the light section 110). It should be noted that, as described below... Figure 7B Other signals are provided during periods when the laser frequency increases. Therefore, in various implementations, as time increases, the signal may correspond to a sample taken at a higher laser frequency. As will be described in more detail below, the analog-to-digital conversion (e.g., signal digitization) is interleaved between the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2.

[0070] Control signals Trig1in, Trig1out, Trig2in, and Trig2out are used to control the switches SW1in, SW1out, SW2in, and SW2out of the sampling and holding section SHP', respectively. It is shown that the first input control signal Trig1in is provided according to the first sampling rate SR1 and is used to operate the first input switch SW1in, and the second input control signal Trig2in is shown to be provided according to the second sampling rate SR2 and is used to operate the second input switch SW2in. It should be noted that the second sampling rate SR2 is lower than the first sampling rate SR1, as will be described in more detail below.

[0071] As a more specific description of certain operations, in various embodiments, a first input switch SW1in is operated according to a first input control signal Trig1in (e.g., closed or otherwise turned on) to sample the output of detector section 140 (e.g., a combined photoelectric signal) onto a first capacitor C1 (e.g., according to the first output control signal Trig1out when the first output switch SW1out is off or otherwise turned off). More specifically, when the first input switch SW1in is closed or otherwise turned on, and the first output switch SW1out is off or otherwise turned off, the first capacitor C1 is charged to a level consistent with the signal from detector section 140, and thus the signal (e.g., the combined photoelectric signal) is sampled at the corresponding time.

[0072] Then, after operating the first input switch SW1in according to the first input control signal Trig1in (e.g., opening or otherwise placing it in a non-conducting state), the output switch SW1out is operated according to the first output control signal Trig1out (e.g., closing or otherwise placing it in a conducting state) to connect the first capacitor C1 (e.g., providing sample values ​​stored on the first capacitor C1) to the input of the analog-to-digital converter 152 (e.g., which correspondingly operates to digitize the sample values ​​stored on the first capacitor C1). By repeating this process (i.e., according to the transitions indicated by the control signals Trig1in and Trig1out), the signal (e.g., a combined photoelectric signal) sampled by the first sampling and holding circuit SH1 from the detector section 140 can be digitized by the analog-to-digital converter 152.

[0073] It should be understood that similar operations can be performed on the second sampling and holding circuit SH2. In short, switches SW2in and SW2out can be controlled according to control signals Trig2in and Trig2out to store samples on capacitor C2 and then provide the samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig2in and Trig2out), the signal (e.g., a combined photoelectric signal) sampled by the second sampling and holding circuit SH2 from detector section 140 can be digitized by analog-to-digital converter 152.

[0074] As mentioned above, the second sampling rate SR2 is lower than the first sampling rate SR1. Figure 7BIn a specific example, for the given time period, 29 cycles of the first input control signal Trig1in are shown according to the first sampling rate SR1 (e.g., corresponding to 29 instances of the first input control signal Trig1in cycling from low to high and from high to low). 28 cycles of the second input control signal Trig2in are shown according to the second sampling rate SR2 (e.g., corresponding to 28 instances of the second input control signal Trig2in cycling from low to high and from high to low). As a specific numerical example, this might indicate a ratio of SR2 / SR1 = 28 / 29 = 0.97. The following will be based on... Figure 9B The description provides a more detailed account of some design considerations that make the difference between the first and second sampling rates relatively small.

[0075] like Figure 7B As shown at the bottom, the analog-to-digital converter (ADC) sampling rate SRADC corresponds to a combination of the first output control signal Trig1out and the second output control signal Trig2out. In the example shown, the ADC sampling rate SRADC is approximately twice the first sampling rate SR1. The timing of the first output control signal Trig1out and the second output control signal Trig2out is configured such that the ADC sampling rate SRADC ideally appears with samples in regularly spaced intervals (e.g., thus reducing the requirements on the ADC). It should be noted that even if similar combinations of the first input control signal Trig1in and the second input control signal Trig2in were not configured in this way, and there were different intervals between the control signal combinations, including some intervals with very small intervals, this could still result in a significant processing burden without the current circuit structure shown and described herein.

[0076] In this example, the desired effect can be partially achieved by constructing the second output control signal Trig2out to provide a regularly spaced contribution to the analog-to-digital converter sampling rate (SRADC), rather than constructing it to perfectly match the timing of the second input control signal Trig2in. For example, compared to the first output control signal Trig1out, which is shown to provide a transition shortly after each transition of the first input control signal Trig1in (e.g., partially indicated by small example arrows between Trig1in and Trig1out, indicating sample-to-conversion timing), the transitions of the second output control signal Trig2out occur at different intervals after the transitions of the second input control signal Trig2in (e.g., partially indicated by small example arrows between Trig2in and Trig2out, indicating sample-to-conversion timing). In some implementations, this may occasionally result in skipping analog-to-digital conversions, as in... Figure 7BThe transition shown in the second output control signal Trig2out and the corresponding empty frame MK in the combination of Trig1out + Trig2out are illustrated. In various embodiments, this can also be characterized as corresponding to duplicate samples generated due to the vernier effect between the two sampling rates.

[0077] As described above, the output control signals Trig1out and Trig2out (e.g., corresponding to providing samples to the analog-to-digital converter 152) are constructed to reduce the requirements on the analog-to-digital converter. It can be seen that the output signals to the analog-to-digital converter 152 (i.e., as provided by...) Figure 7B The analog-to-digital converter (ADC) sampling rate (indicated by the SRADC at the bottom) is configured to be within a specified interval (i.e., with a specified regular interval between transitions / samples), which reduces the requirements on the ADC. This may contrast with a configuration without sampling and holding circuitry, and if the ADC's task is to acquire data itself according to a first sampling rate SR1 and a second sampling rate SR2 (e.g., the signal intervals are not regular, and some of the acquired signals / timings at the second sampling rate SR2 will be very close to some of the acquired signals / timings at the first sampling rate SR1), this would significantly increase the operational requirements of the ADC.

[0078] Figure 8A and Figure 8B This is a diagram illustrating a second embodiment of the sampling and holding section SHP'' and the corresponding signal timing. (See diagram for example.) Figure 8A As shown, the sampling and holding section SHP'' (e.g., as part of the processing section 150'' of the detector and processing section DPP) is coupled to the detector section 140 (e.g., receiving signals from the detector section 140, such as combined photoelectric signals from the detector section 140). As will be described in more detail below, in various embodiments, the sampling and holding section SHP'' can be configured to sample the combined photoelectric signals from the detector section. The sampling and holding section SHP'' is coupled to provide an output (e.g., a sample) to the analog-to-digital converter 152 (e.g., as part of the processing section 150'' of the detector and processing section DPP). According to the principles described herein, in various embodiments, the processing section can also be configured to perform a Fast Fourier Transform (i.e., for analysis) on each digitized signal to determine at least one peak corresponding to the beat frequency. Additionally, the distance to the workpiece can be determined at least in part based on the determined peak corresponding to the beat frequency.

[0079] like Figure 8AAs shown, the sampling and holding section SHP'' includes a first sampling and holding circuit SH1, a second sampling and holding circuit SH2, and a third sampling and holding circuit SH3. The sampling and holding circuits SH1, SH2, and SH3 are connected in parallel between the detector section 140 and the analog-to-digital converter 152. Figure 8A The sampling and holding part SHP and Figure 7A The main difference between the sampling and holding section SHP' and the previous one is the addition of a third sampling and holding circuit SH3. Unless otherwise stated below, the descriptions and corresponding operations of the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2 in the above sampling and holding section SHP' should also be understood to apply to... Figure 8A The sampling and holding section SHP'' contains a first sampling and holding circuit SH1 and a second sampling and holding circuit SH2. Therefore, at least a portion of the following description relates primarily to the differences corresponding to the additional sampling and holding circuit SH3.

[0080] The third sampling and holding circuit SH3 includes a third input switch SW3in, a third capacitor C3, and a third output switch SW3out. The third input switch SW3in (e.g., on the input side) is connected to the detector section 140 and (e.g., on the output side) to the third capacitor C3. The third output switch SW3out (e.g., on the input side) is connected to the third capacitor C3 and (e.g., on the output side) to the analog-to-digital converter 152. The operation of the sampling and holding section SHP'' (e.g., including control of switches SW3in and SW3out via control signals Trig3in and Trig3out respectively) will be referred to below. Figure 8B To provide a more detailed description.

[0081] Figure 8B It shows the relationship with Figure 8A The sampling and holding of certain signals are related to the operation of the SHP''. Figure 8B The diagram illustrates the signal-time relationship between the laser frequency, control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, and Trig3out, as well as a representative combination of Trigout (i.e., including Trig1out + Trig2out + Trig3out). The control signals Trig1in, Trig1out, Trig2in, and Trig2out are related to the signals mentioned above. Figure 7B The control signals described have some similarities and will be understood to have similar functions, unless otherwise stated below.

[0082] like Figure 8B The laser frequency shown is Figure 7BThe description of the laser frequency is the same, and will be based on Figure 7B The description of the laser frequency is used for understanding. As will be described in more detail below, the analog-to-digital conversion (e.g., signal digitization) is interleaved between the first sampling and holding circuit SH1, the second sampling and holding circuit SH2, and the third sampling and holding circuit SH3. Control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, and Trig3out are used to control the switches SW1in, SW1out, SW2in, SW2out, SW3in, and SW3out of the sampling and holding section SHP'', respectively. It is shown that the first input control signal Trig1in is provided according to the first sampling rate SR1 to operate the first input switch SW1in, the second input control signal Trig2in is provided according to the second sampling rate SR2 to operate the second input switch SW2in, and the third input control signal Trig3in is provided according to the third sampling rate SR3 to operate the third input switch SW3in. It should be noted that the second sampling rate SR2 is lower than the first sampling rate SR1, and it should also be noted that the third sampling rate SR3 is lower than the second sampling rate SR2, as will be described in more detail below.

[0083] Regarding the above reference Figure 7B The more specific operation of the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2 described herein should be understood, and can be applied to... Figure 8B The third sampling and holding circuit SH3 performs a similar operation. In short, switches SW3in and SW3out can be controlled according to control signals Trig3in and Trig3out to store samples on capacitor C3 and then provide the samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig3in and Trig3out), the signal (e.g., a combined photoelectric signal) sampled by the third sampling and holding circuit SH3 from detector section 140 can be digitized by analog-to-digital converter 152.

[0084] As mentioned above, the second sampling rate SR2 is lower than the first sampling rate SR1, and the third sampling rate SR3 is lower than the second sampling rate SR2. Figure 8BIn a specific example, for the given time period, 29 cycles of the first input control signal Trig1in are shown according to the first sampling rate SR1 (e.g., corresponding to 29 instances of the first input control signal Trig1in cycling from low to high and from high to low). According to the second sampling rate SR2, 28 cycles of the second input control signal Trig2in are shown (e.g., corresponding to 28 instances of the second input control signal Trig2in cycling from low to high and from high to low). As a specific numerical example, this might indicate a ratio of SR2 / SR1 = 28 / 29 = 0.97. According to the third sampling rate SR3, 27 cycles of the third input control signal Trig3in are shown (e.g., corresponding to 27 instances of the third input control signal Trig3in cycling from low to high and from high to low). As some specific numerical examples, this might indicate a ratio of SR3 / SR2 = 27 / 28 = 0.96 or SR3 / SR1 = 27 / 29 = 0.93. The following will be based on... Figure 9B The description provides a more detailed account of some design considerations that make the differences between the first, second, and third sampling rates relatively small.

[0085] like Figure 8B As shown at the bottom, the analog-to-digital converter (ADC) sampling rate SRADC corresponds to a combination of the first output control signal Trig1out, the second output control signal Trig2out, and the third output control signal Trig3out. In the example shown, it should be noted that the ADC sampling rate is approximately three times the first sampling rate SR1. The timing of the first output control signal Trig1out, the second output control signal Trig2out, and the third output control signal Trig3out is configured such that the ADC sampling rate SRADC ideally appears with samples in regularly spaced intervals (e.g., thus reducing the requirements on the ADC). It should be noted that even if similar combinations of the first input control signal Trig1in, the second input control signal Trig2in, and the third input control signal Trig3in were not constructed in this way, and there were different intervals between the control signal combinations, including some intervals with very small intervals, this could result in a significant processing burden without the current circuit structure shown and described herein.

[0086] In this example, the desired effect can be partially achieved by constructing the second output control signal Trig2out and the third output control signal Trig3out to contribute regularly spaced contributions to the analog-to-digital converter sampling rate (SRADC), rather than constructing them to perfectly match the timing of the corresponding second input control signals Trig2in and Trig3in. For example, compared to the first output control signal Trig1out, which is shown to provide a transition shortly after each transition of the first input control signal Trig1in (e.g., partially indicated by small example arrows between Trig1in and Trig1out, indicating sample-to-transition timing), the transitions of the second output control signal Trig2out occur at different intervals after the transitions of the second input control signal Trig2in (e.g., partially indicated by small example arrows between Trig2in and Trig2out, indicating sample-to-transition timing). Similarly, the transition of the third output control signal Trig3out occurs at different intervals after the transition of the third input control signal Trig3in (e.g., as indicated by the small example arrows between Trig3in and Trig3out, indicating the sample-to-conversion timing relationship). In some implementations, this may occasionally result in skipping the analog-to-digital conversion, as in... Figure 8B The transitions shown by the second output control signal Trig2out or the third output control signal Trig3out, and the corresponding empty frame MK in the combination of Trig1out+Trig2out+Trig3out, are illustrated. In various embodiments, this can also be characterized as corresponding to duplicate samples generated due to the vernier effect between the three sampling rates.

[0087] As described above, the output control signals Trig1out, Trig2out, and Trig3out (e.g., corresponding to providing samples to the analog-to-digital converter 152) are constructed to reduce the requirements on the analog-to-digital converter. It can be seen that the output signals to the analog-to-digital converter 152 (i.e., as provided by...) Figure 8B The analog-to-digital converter (ADC) sampling rate (indicated by SRADC at the bottom) is configured to be within a specified interval (i.e., with a specified regular interval between transitions / samples), which reduces the requirements on the ADC. This may contrast with a configuration without sampling and holding circuitry, and if the ADC's task is to acquire data itself according to a first sampling rate SR1, a second sampling rate SR2, and a third sampling rate SR3 (e.g., the signal intervals are not regular, and some of the acquired signals / timings between sampling rates will be very close to each other, this would significantly increase the operational requirements of the ADC).

[0088] Figure 9A and Figure 9BThis is a diagram illustrating a third embodiment of the sampling and holding section ''' and the corresponding signal timing. As will be described in more detail below, in various embodiments, the sampling and holding section 'SHP''' can be used for orthogonal processing. In some such embodiments, orthogonal processing can be used as an alternative to including a dispersive component in the interferometer section, and similar disambiguation (e.g., disambiguation of signal peaks, etc.) can be achieved as described above.

[0089] like Figure 9A As shown, the sampling and holding section SHP''' (e.g., as part of the processing section 150''' of the detector and processing section DPP) is coupled to the detector section 140 (e.g., receiving signals from the detector section 140, such as combined photoelectric signals from the detector section 140). As will be described in more detail below, in various embodiments, the sampling and holding section SHP''' can be configured to sample the combined photoelectric signals from the detector section. The sampling and holding section SHP''' is coupled to provide an output (e.g., a sample) to the analog-to-digital converter 152 (e.g., as part of the processing section 150''' of the detector and processing section DPP). According to the principles described herein, in various embodiments, the processing section can also be configured to perform a fast Fourier transform (i.e., for analysis) on each digitized signal to determine at least one peak corresponding to the beat frequency. Additionally, the distance to the workpiece can be determined at least in part based on the determined peak corresponding to the beat frequency.

[0090] like Figure 9A As shown, the sampling and holding section SHP''' includes a first sampling and holding circuit SH1, a second sampling and holding circuit SH2, a third sampling and holding circuit SH3, and a fourth sampling and holding circuit SH4. The sampling and holding circuits SH1, SH2, SH3, and SH4 are connected between the detector section 140 and the analog-to-digital converter 152. Figure 9A The sampling and holding part SHP''' with Figure 7A The main difference between the sampling and holding section SHP' and the previous one is the addition of a third sampling and holding circuit SH3 and a fourth sampling and holding circuit SH4, as well as their connection to the detector section 140. Generally, unless otherwise stated below, the descriptions and corresponding operations of the sampling and holding circuits SH1 and SH2 in the above sampling and holding section SHP' should also be understood to apply to... Figure 9A The sampling and holding circuits SH1, SH2, SH3, and SH4 are in the sampling and holding section SHP'''. Therefore, at least a portion of the following description mainly relates to the differences corresponding to the sampling and holding section SHP'''.

[0091] As a distinction (e.g., in relation to potential orthogonal processing), detector section 140 may include multiple detectors (e.g., and have a phase shift in the orthogonal signals generated optically prior to the detectors; in some embodiments, the detectors may be photodetectors). In one embodiment, detector section 140 may include a first detector and a second detector (not shown), such that a first sampling and holding circuit SH1 and a third sampling and holding circuit SH3 are coupled to the first detector, and a second sampling and holding circuit and a fourth sampling and holding circuit are coupled to the second detector. As will be described in more detail below, in this configuration, each pair of orthogonal measurements (e.g., including a first pair of orthogonal measurements corresponding to the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2, and a second pair of orthogonal measurements corresponding to the third sampling and holding circuit SH3 and the fourth sampling and holding circuit SH4) can occur simultaneously. Therefore, the outputs of the first detector and the second detector can be simultaneously measured by the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2, respectively, and can then be simultaneously measured again by the third sampling and holding circuit SH3 and the fourth sampling and holding circuit SH4, respectively.

[0092] exist Figure 9A In the embodiment, the first sampling and holding circuit SH1 includes a first input switch SW1in, a first capacitor C1, and a first output switch SW1out. The first input switch SW1in (e.g., on the input side) is connected to the detector section 140 (e.g., a first detector connected to the detector section 140) and (e.g., on the output side) is connected to the first capacitor C1. The first output switch SW1out (e.g., on the input side) is connected to the first capacitor C1 and (e.g., on the output side) is connected to the analog-to-digital converter 152. The operation of the sampling and holding section SHP''' (e.g., including control of switches SW1in and SW1out via control signals Trig1in and Trig1out, respectively) will be referred to below. Figure 9B To provide a more detailed description.

[0093] The second sampling and holding circuit SH2 includes a second input switch SW2in, a second capacitor C2, and a second output switch SW2out. The second input switch SW2in (e.g., on the input side) is connected to detector section 140 (e.g., a second detector connected to detector section 140) and (e.g., on the output side) is connected to the second capacitor C2. The second output switch SW2out (e.g., on the input side) is connected to the second capacitor C2 and (e.g., on the output side) is connected to analog-to-digital converter 152. The operation of the sampling and holding section SHP''' (e.g., including control of switches SW2in and SW2out via control signals Trig2in and Trig2out respectively) will be referred to below. Figure 9B To provide a more detailed description.

[0094] The third sampling and holding circuit SH3 includes a third input switch SW3in, a third capacitor C3, and a third output switch SW3out. The third input switch SW3in (e.g., on the input side) is connected to detector section 140 (e.g., a first detector connected to detector section 140) and (e.g., on the output side) is connected to the third capacitor C3. The third output switch SW3out (e.g., on the input side) is connected to the third capacitor C3 and (e.g., on the output side) is connected to analog-to-digital converter 152. The operation of the sampling and holding section SHP''' (e.g., including control of switches SW3in and SW3out via control signals Trig3in and Trig3out respectively) will be referred to below. Figure 9B To provide a more detailed description.

[0095] The fourth sampling and holding circuit SH4 includes a fourth input switch SW4in, a fourth capacitor C4, and a fourth output switch SW4out. The fourth input switch SW4in (e.g., on the input side) is connected to detector section 140 (e.g., a second detector connected to detector section 140) and (e.g., on the output side) is connected to the fourth capacitor C4. The fourth output switch SW4out (e.g., on the input side) is connected to the fourth capacitor C4 and (e.g., on the output side) is connected to analog-to-digital converter 152. The operation of the sampling and holding section SHP''' (e.g., including control of switches SW4in and SW4out via control signals Trig4in and Trig4out respectively) will be referred to below. Figure 9B To provide a more detailed description.

[0096] Figure 9B It shows the relationship with Figure 9A The sampling and holding of certain signals are related to the operation of the SHP'''. Figure 9BThe diagram illustrates the signal-time relationship between the laser frequency, control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, Trig3out, Trig4in, and Trig4out, as well as a representative combination of Trigout (i.e., including Trig1out + Trig2out + Trig3out + Trig4out). The control signals Trig1in, Trig1out, Trig2in, and Trig2out are related to the signals mentioned above. Figure 7B The control signals described have some similarities and will be understood to have similar functions, unless otherwise stated below.

[0097] like Figure 9B The laser frequency shown is Figure 7B The description of the laser frequency is the same, and will be based on Figure 7B The description of the laser frequency is used for understanding. As will be described in more detail below, the analog-to-digital conversion (e.g., signal digitization) is interleaved between the first sampling and holding circuit SH1, the second sampling and holding circuit SH2, the third sampling and holding circuit SH3, and the fourth sampling and holding circuit SH4. Control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, Trig3out, Trig4in, and Trig4out are used to control the switches SW1in, SW1out, SW2in, SW2out, SW3in, SW3out, SW4in, and SW4out of the sampling and holding section SHP''', respectively. The first input control signal Trig1in and the second input control signal Trig2in are shown as being provided according to the first sampling rate SR1 for operating the first input switch SW1in and the second input switch SW2in. The third input control signal Trig3in and the fourth input control signal Trig4in are shown as being provided according to the second sampling rate SR2 for operating the third input switch SW3in and the fourth input switch SW4in. It should be noted that the second sampling rate SR2 is lower than the first sampling rate SR1, as will be described in more detail below.

[0098] Regarding the above reference Figure 7B The more specific operation of the first sampling and holding circuit SH1 and the second sampling and holding circuit SH2 described herein should be understood, and can be applied to... Figure 9BThe first and second, as well as the third and fourth sampling and holding circuits, perform similar operations. To summarize, switches SW1in and SW1out can be controlled according to control signals Trig1in and Trig1out to store samples on capacitor C1 and then provide the samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig1in and Trig1out), the signal from detector section 140 sampled by the first sampling and holding circuit SH1 (e.g., the combined photoelectric signal from the first detector) can be digitized by analog-to-digital converter 152.

[0099] Switches SW2in and SW2out can be controlled according to control signals Trig2in and Trig2out to store samples on capacitor C2 and then provide samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig2in and Trig2out), the signal from detector section 140 sampled by second sampling and holding circuit SH2 (e.g., combined photoelectric signal from second detector) can be digitized by analog-to-digital converter 152.

[0100] Switches SW3in and SW3out can be controlled according to control signals Trig3in and Trig3out to store samples on capacitor C3 and then provide samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig3in and Trig3out), the signal from detector section 140 sampled by third sampling and holding circuit SH3 (e.g., combined photoelectric signal from first detector) can be digitized by analog-to-digital converter 152.

[0101] Switches SW4in and SW4out can be controlled according to control signals Trig4in and Trig4out to store samples on capacitor C4 and then provide samples for digitization by analog-to-digital converter 152. According to this process (i.e., according to the transitions indicated by control signals Trig4in and Trig4out), the signal from detector section 140 sampled by fourth sampling and holding circuit SH4 (e.g., combined photoelectric signal from second detector) can be digitized by analog-to-digital converter 152.

[0102] As mentioned above, the second sampling rate SR2 is lower than the first sampling rate SR1. Figure 9BIn a specific example, for the given time period, 29 cycles of the first input control signal Trig1in and the second input control signal Trig2in are shown according to the first sampling rate SR1 (e.g., corresponding to 29 instances of the first input control signal Trig1in and the second input control signal Trig2in cycling from low to high and from high to low). According to the second sampling rate SR2, 28 cycles of the third input control signal Trig3in and the fourth input control signal Trig4in are shown (e.g., corresponding to 28 instances of the third input control signal Trig3in and the fourth input control signal Trig4in cycling from low to high and from high to low). As a specific numerical example, this might indicate a ratio of SR2 / SR1 = 28 / 29 = 0.97. The following will be based on... Figure 9B The description provides a more detailed account of some design considerations that make the difference between the first and second sampling rates relatively small.

[0103] like Figure 9B As shown at the bottom, the analog-to-digital converter (ADC) sampling rate SRADC corresponds to a combination of the first output control signal Trig1out, the second output control signal Trig2out, the third output control signal Trig3out, and the fourth output control signal Trig4out. In the example shown, it should be noted that the ADC sampling rate is approximately four times the first sampling rate SR1. The timing of the first output control signal Trig1out, the second output control signal Trig2out, the third output control signal Trig3out, and the fourth output control signal Trig4out is configured such that the ADC sampling rate SRADC ideally appears with samples in regularly spaced intervals (e.g., thus reducing the requirements on the ADC). It should be noted that even if similar combinations of the first input control signal Trig1in, the second input control signal Trig2in, the third input control signal Trig3in, and the fourth input control signal Trig4in were not constructed in this way, and there were different intervals between the control signal combinations, including some intervals with very small intervals, this could still result in a significant processing burden without the current circuit structure shown and described herein.

[0104] In this example, the desired effect can be partially achieved by constructing the third output control signal Trig3out and the fourth output control signal Trig4out to contribute regularly spaced contributions to the analog-to-digital converter sampling rate (SRADC), rather than constructing them to perfectly match the timing of the corresponding third input control signal Trig3in and the fourth input control signal Trig4in. For example, compared to the first output control signal Trig1out and the second output control signal Trig2out, which are shown to provide a transition shortly after each transition of the corresponding first input control signal Trig1in and the second input control signal Trig2in (e.g., partially indicated by small example arrows between Trig2in and Trig2out, indicating sample-to-transition timing relationships), the transition of the third output control signal Trig3out occurs at different intervals after the transition of the third input control signal Trig3in (e.g., partially indicated by small example arrows between Trig3in and Trig3out, indicating sample-to-transition timing relationships). Similarly, the transition of the fourth output control signal Trig4out occurs at different intervals after the transition of the fourth input control signal Trig4in (e.g., as indicated by the small example arrows between Trig4in and Trig4out, indicating the sample-to-conversion timing relationship). In some implementations, this may occasionally result in skipping the analog-to-digital conversion, as in... Figure 9B The empty frame MK is shown in the transitions illustrated by the third output control signal Trig3out or the fourth output control signal Trig4out, and in the corresponding combination of Trigout (i.e., the combination of Trig1out+Trig2out+Trig3out+Trig4out). In various embodiments, this can also be characterized as corresponding to duplicate samples generated due to the vernier effect between sampling rates.

[0105] As described above, the output control signals Trig1out, Trig2out, Trig3out, and Trig4out (e.g., corresponding to providing samples to the analog-to-digital converter 152) are configured to reduce the requirements on the analog-to-digital converter. It can be seen that the output signals to the analog-to-digital converter 152 (i.e., as provided by...) Figure 9BThe analog-to-digital converter (ADC) sampling rate (indicated by the SRADC at the bottom) is configured to be within a specified interval (i.e., with specified regular intervals between transitions / samples), which reduces the requirements on the ADC. This may contrast with a configuration without sampling and holding circuitry, and if the ADC's task is to acquire data itself (e.g., the signal intervals are not regular, and some of the acquired signals / timings between sampling rates will be very close to each other, which would significantly increase the operational requirements of the ADC). Furthermore, without the sampling and holding circuitry shown and described herein, quadrature processing (e.g., having simultaneous inputs for input control signals Trig1in and Trig2in, and simultaneous inputs for input control signals Trig3in and Trig4in) in various implementations may generally not be achievable with a single ADC. It is understood that, compared to multiple analog-to-digital converters, certain advantages may be associated with the configuration using a single analog-to-digital converter (e.g., since the signal is digitized using a single converter instead of multiple converters, which may have slightly different characteristics that may affect the converted signal differently and / or cause other differences, thus potentially reducing the cost and / or size of the configuration, potentially improving accuracy, etc.).

[0106] about Figure 7A , Figure 7B , Figure 8A , Figure 8B , Figure 9A and Figure 9B The configuration, in various implementations, exhibits relatively small differences in sampling rates (e.g., Figure 7B and Figure 9B Between the first sampling rate and the second sampling rate, or Figure 8B The difference between the first, second, and third sampling rates (e.g., in some instances, the difference between sampling rates is less than 10%) may be suitable for techniques used to achieve measurements over a longer absolute (ABS) distance range (e.g., different measurements / measurement scales with slightly different periods / increments). Regarding the use of analog-to-digital converters (ADCs) to digitize signals associated with such slightly different measurement / sampling rates, it should be understood that this could otherwise place a significant burden on the ADC (e.g., without the circuitry described herein). For example, due to subtle differences in rate, there may be some time-interval periods in the measurements / samples that are very close together, requiring very high / fast operating characteristics (e.g., ADCs or others). Based on the principles described herein, sampling can be performed using sampling and holding circuitry by utilizing sampling and holding sections, and the output can be constructed to reduce the requirements on the ADC (e.g., as described herein). Figure 7B , Figure 8B and Figure 9BThe sampling rate of the analog-to-digital converter in each of them is shown in the SRADC.

[0107] It should be noted that Figure 7A , Figure 7B , Figure 8A , Figure 8B , Figure 9A and Figure 9B The configuration offers certain advantages over existing systems. As some general principles, in some existing systems, the Nyquist frequency of the analog-to-digital converter (ADC) used to digitize combined optoelectronic signals typically sets the maximum beat frequency, and thus the maximum range that can be measured for a given frequency modulation. If the ADC samples frequencies higher than the Nyquist frequency, such frequencies may be detected as lower frequencies due to aliasing. Aliasing can occur because instantaneous sampling of the periodic function two or fewer times per cycle can lead to missed cycles and thus lower frequencies. However, according to the principles described herein, by utilizing multiple measurements (e.g., performed by different sampling and holding circuits), the correct overall beat frequency can be determined, and the corresponding accurate distance determination can be made.

[0108] Figure 10 This is a flowchart illustrating an exemplary implementation of a routine 1000 for operating a metrology system. At block 1010, the optical portion of the metrology system is controlled to output light. The metrology system includes a branching portion that branches a portion of the light output from the optical portion into reference light guided along a reference optical path; and branches at least a portion of the remaining light into measurement light guided along a measurement optical path for reflection by the workpiece to be measured. At block 1020, a combined light comprising the reference light from the reference optical path and the measurement light reflected from the workpiece from the measurement optical path is received (e.g., at detector section 140 of the detector and processing section DPP).

[0109] At block 1030, the combined light is converted (e.g., by detector section 140) into a combined photoelectric signal. At block 1040, the combined photoelectric signal is sampled (e.g., at a first sampling rate) using a first sampling and holding circuit (e.g., a first sampling and holding circuit of sampling and holding section SHP, which may be any one of sampling and holding sections SHP', SHP'', or SHP''') and a corresponding first output is provided to the analog-to-digital converter. At block 1050, the combined photoelectric signal is sampled (e.g., at a second sampling rate lower than the first sampling rate) using a second sampling and holding circuit (e.g., a second sampling and holding circuit of sampling and holding section SHP) and a corresponding second output is provided to the analog-to-digital converter.

[0110] In various embodiments, the method may further include performing a Fast Fourier Transform (FFT) for analyzing the digitized signal from the analog-to-digital converter to determine at least one peak corresponding to the beat frequency. For example, processing unit 150 may perform the FFT. In various embodiments, samples from each sampling and holding section may be digitized into a digitized signal by the analog-to-digital converter, and a FFT may be performed on the digitized signal (i.e., for analysis) to determine at least one peak corresponding to the beat frequency. In various embodiments, additional processing may be performed to determine a single peak / beat frequency corresponding to the distance to the workpiece. In various embodiments, the method further includes determining the distance to the workpiece based at least in part on the determined peak corresponding to the beat frequency (e.g., as may be performed by processing unit 150 or otherwise).

[0111] Various implementations of the metering system have been disclosed. The following features can be used alone or in combination with any of the implementations of the metering system.

[0112] For example, the light output from the optical component may include a laser whose oscillation frequency varies linearly with time. As another feature, the reference light may correspondingly include a laser whose oscillation frequency varies linearly with time; and the measurement light may correspondingly include a laser whose oscillation frequency varies linearly with time.

[0113] As another feature, the reference optical path has a reference optical path length; the measuring optical path has a measuring optical path length; and the difference in optical path length between the reference optical path length and the measuring optical path length corresponds to the propagation difference between the reference light and the measuring light and the corresponding propagation delay. The beat frequency corresponds to the propagation delay. The detector and the processing part of the metrology system can be configured to determine the distance to the workpiece at least in part based on a determined peak value corresponding to the beat frequency.

[0114] Although preferred embodiments of the present disclosure have been shown and described, those skilled in the art will appreciate, based on this disclosure, numerous variations in the arrangement of features and the order of operation shown and described. Various alternative forms can be employed to implement the principles disclosed herein. Furthermore, the various embodiments described above can be combined to provide additional embodiments.

[0115] Based on the detailed description above, these and other changes can be made to the implementation methods. Generally, the terminology used in the following claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible implementation methods and the full scope of the equivalents enjoyed by those claims.

Claims

1. A measurement system comprising: The light component outputs light; The branch portion, the branch portion: A portion of the light output from the light component branches into reference light guided along the reference optical path; and At least a portion of the remaining light is branched into measuring light guided along the measuring optical path, so as to be reflected by the workpiece to be measured; as well as The detector and processing unit are configured to: Receive a combination of reference light from the reference optical path and measurement light reflected from the workpiece from the measurement optical path; as well as The combined light is converted into a combined photoelectric signal; The detector and processing unit include: Analog-to-digital converter; as well as The sampling and holding section includes at least a first sampling and holding circuit and a second sampling and holding circuit, wherein the sampling and holding section is connected to provide an output to the analog-to-digital converter.

2. The metering system of claim 1, wherein the detector and processing section includes a detector section configured to detect the combined light and output the corresponding combined photoelectric signal, wherein the at least two sampling and holding circuits and the analog-to-digital converter are configured to digitize the combined photoelectric signal to generate a digital signal.

3. The metering system of claim 2, wherein the detector and processing section further comprises a processing section configured to perform a fast Fourier transform for analyzing the digitized signal to determine at least one peak corresponding to the beat frequency.

4. The metering system of claim 3, wherein the processing portion is configured to determine the distance to the workpiece at least in part based on a determined peak value corresponding to the beat frequency.

5. The metering system as described in claim 1, wherein: The first sampling and holding circuit is configured to operate at a first sampling rate; and The second sampling and holding circuit is configured to operate at a second sampling rate lower than the first sampling rate.

6. The metering system as described in claim 1, wherein: The first sampling and holding circuit includes a first capacitor; and The second sampling and holding circuit includes a second capacitor.

7. The metering system as described in claim 6, wherein: The first sampling and holding circuit includes a first input switch connected to the first capacitor; and The second sampling and holding circuit includes a second input switch connected to the second capacitor.

8. The metering system as described in claim 7, wherein: The first input switch operates according to the first sampling rate; and The second input switch operates according to a second sampling rate lower than the first sampling rate.

9. The metering system as claimed in claim 7, wherein: The first sampling and holding circuit includes a first output switch coupled to the first capacitor, wherein the first output switch is configured to operate to coupled the first capacitor to the analog-to-digital converter; and The second sampling and holding circuit includes a second output switch coupled to the second capacitor, wherein the second output switch is configured to operate to couple the second capacitor to the analog-to-digital converter.

10. The metrology system of claim 1, wherein at least one of the reference optical path or the measurement optical path includes a dispersion portion, wherein the unbalanced dispersion between the reference optical path and the measurement optical path is at least partially caused by the dispersion portion.

11. The metering system of claim 1, wherein the sampling and holding portion further includes a third sampling and holding circuit.

12. The metering system as claimed in claim 11, wherein: The first sampling and holding circuit is configured to operate at a first sampling rate; The second sampling and holding circuit is configured to operate at a second sampling rate lower than the first sampling rate; and The third sampling and holding circuit is configured to operate at a third sampling rate lower than the second sampling rate.

13. The metering system of claim 11, wherein the sampling and holding portion further includes a fourth sampling and holding circuit.

14. The metering system as claimed in claim 13, wherein: The sampling and holding portion is configured to operate for orthogonal processing; The first sampling and holding circuit and the second sampling and holding circuit are configured to operate at a first sampling rate; and The third sampling and holding circuit and the fourth sampling and holding circuit are configured to operate at a second sampling rate lower than the first sampling rate.

15. The metrology system of claim 1, further comprising a combining portion that receives and combines reference light from the reference optical path and measurement light from the measurement optical path, wherein the detector and processing portion receives the combined light from the combining portion.

16. The metering system of claim 1, wherein the light output by the optical portion comprises a laser whose oscillation frequency varies linearly with time.

17. A method for operating a metering system, The metering system includes: The light component outputs light; as well as The branch portion, the branch portion: A portion of the light output from the light component branches into reference light guided along the reference optical path; and At least a portion of the remaining light is branched into measuring light guided along the measuring optical path, so as to be reflected by the workpiece to be measured; The method includes: Receive a combination of reference light from the reference optical path and measurement light reflected from the workpiece from the measurement optical path; The combined light is converted into a combined photoelectric signal; The combined photoelectric signal is sampled at a first sampling rate using a first sampling and holding circuit, and the corresponding first output is provided to the analog-to-digital converter; and The combined photoelectric signal is sampled at a second sampling rate lower than the first sampling rate using a second sampling and holding circuit, and the corresponding second output is provided to the analog-to-digital converter.

18. The method of claim 17, further comprising performing a fast Fourier transform to analyze the digitized signal from the analog-to-digital converter to determine at least one peak corresponding to the beat frequency.

19. The method of claim 18, further comprising determining the distance to the workpiece based at least in part on a determined peak value corresponding to the beat frequency.

20. A measurement system comprising: The light component outputs light; The branch portion, the branch portion: A portion of the light output from the light component branches into reference light guided along the reference optical path; and At least a portion of the remaining light is branched into measuring light guided along the measuring optical path, so as to be reflected by the workpiece to be measured; as well as The detector and processing unit include: Analog-to-digital converters; and The sampling and holding section includes at least a first sampling and holding circuit and a second sampling and holding circuit, wherein the sampling and holding section is connected to provide an output to the analog-to-digital converter; The metering system is configured as follows: Receive a combination of reference light from the reference optical path and measurement light reflected from the workpiece from the measurement optical path; The combined light is converted into a combined photoelectric signal; The combined photoelectric signal is sampled at a first sampling rate using the first sampling and holding circuit, and the corresponding first output is provided to the analog-to-digital converter; and The combined photoelectric signal is sampled using the second sampling and holding circuit at a second sampling rate lower than the first sampling rate, and the corresponding second output is provided to the analog-to-digital converter.

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