Measurement system

Abstract

In a system capable of determining the distance to multiple points on a workpiece surface, this invention provides a configuration that improves or strengthens a key portion of the effective measurement range. [Solution] The device has an optical unit that outputs light, a branching unit, and a detection / processing unit. The branching unit includes an interferometer unit 101 that branches light along a reference optical path as reference light and branches it along a measurement optical path as measurement light and reflects it onto a workpiece to be measured. The device also includes an analog-to-digital converter configured to receive composite light including the reference light and the measurement light and convert the composite light into a composite photoelectrical signal, and a sample-and-hold unit. The sample-and-hold unit consists of i) at least a first sample-and-hold circuit and a second sample-and-hold circuit, and ii) a circuit unit 102 connected to sample the composite photoelectrical signal (for example, at first and second sample rates respectively) and provide the output to the analog-to-digital converter.

Description

Technical Field

[0001] The present disclosure relates to precision measurement, and more particularly to a precision workpiece surface measurement apparatus and system.

Background Art

[0002] Quality control of an object (e.g., a workpiece) having a specific surface shape (e.g., manufactured by molding and / or machining, etc.) has become increasingly required with respect to throughput, measurement resolution, and accuracy. Ideally, such a workpiece should be measured / inspected to ensure appropriate dimensions, functions, etc. However, very precise measurement tolerances (e.g., in some cases, at the micron level or finer) may be required to confirm a workpiece surface having desired characteristics for some applications.

Summary of the Invention

Problems to be Solved by the Invention

[0003] For the measurement and inspection of a workpiece surface, various precision measurement systems can be used. For example, in some cases, a measurement system that performs such processing may utilize a type of optical coherence tomography (OCT) that can determine the distance to a target, e.g., frequency-modulated continuous wave (FMCW) technology (e.g., determine the distance to a point on the workpiece surface and, as part of the measurement process of the workpiece surface, determine the distances to multiple points on the workpiece surface). An important part of such a system and / or other equivalent measurement systems is the effective measurement range. A configuration that can improve or enhance such a measurement system (e.g., for measuring and inspecting the surface of a workpiece, etc.) is desirable.

Means for Solving the Problems

[0004] This summary is provided to introduce, in simplified form, a selection of concepts that are further described below in the detailed description of embodiments of the invention. 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, there is provided a measurement system including a light unit that outputs light, a branching unit, and a detection / processing unit. The branching unit branches a part of the light output from the light unit as reference light guided along a reference optical path, and branches at least a part of the remaining light as measurement light guided along a measurement optical path and reflects it off a workpiece to be measured. The detection / processing unit is configured to receive a combined light including the reference light from the reference optical path and the measurement light from the measurement optical path reflected by the workpiece, and to convert the combined light into a combined optoelectrical signal. The detection / processing unit has an analog-to-digital converter and a sample-and-hold unit. The sample-and-hold unit includes at least a first sample-and-hold circuit and a second sample-and-hold circuit, and the sample-and-hold unit is connected to provide an output to the analog-to-digital converter.

[0006] According to another aspect, there is provided a method of operating a measurement system. The method includes - receiving a combined light including the reference light from the reference optical path and the measurement light from the measurement optical path reflected by the workpiece, - converting the combined light into a combined optoelectrical signal, - using a first sample-and-hold circuit to sample the combined optoelectrical signal at a first sampling rate and providing a corresponding first output to an analog-to-digital converter, - using a second sample-and-hold circuit to sample the combined optoelectrical signal at a second sampling rate lower than the first sampling rate and supplying a corresponding second output to the analog-to-digital converter, and includes.

[0007] In yet another embodiment, a measurement system is provided that receives composite light including reference light from a reference optical path and measurement light from a measurement optical path reflected by a workpiece, converts the composite light into a composite photoelectrical signal, samples the composite photoelectrical signal at a first sample rate using a first sample-and-hold circuit and provides a corresponding first output to an analog-to-digital converter, and samples the composite photoelectrical signal at a second sample rate lower than the first sample rate using a second sample-and-hold circuit and provides a corresponding second output to an analog-to-digital converter. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram of the measurement system, including the interferometer and circuitry sections. [Figure 2] This block diagram shows a first implementation configuration of an interferometer unit that may be included in a measurement system like the one shown in Figure 1. [Figure 3] This block diagram shows a second implementation configuration of the interferometer unit that may be included in a measurement system like the one shown in Figure 1. [Figure 4] Figure 1 is a block diagram showing possible implementation configurations of circuit components included in a measurement system. [Figure 5A] Figure 1 illustrates the specific operating principle of a measurement system, where the measurement optical path length is longer than the reference optical path length. [Figure 5B] Figure 1 illustrates the specific operating principle of a measurement system, where the measurement optical path length is longer than the reference optical path length. [Figure 5C] Figure 1 illustrates the specific operating principle of a measurement system, where the measurement optical path length is longer than the reference optical path length. [Figure 5D] Figure 1 illustrates the specific operating principle of a measurement system, where the measurement optical path length is longer than the reference optical path length. [Figure 6A] Figure 1 illustrates the specific operating principle of a measurement system, where the reference optical path length is longer than the measurement optical path length. [Figure 6B] Figure 1 illustrates the specific operating principle of a measurement system, where the reference optical path length is longer than the measurement optical path length. [Figure 6C] Figure 1 illustrates the specific operating principle of a measurement system, where the reference optical path length is longer than the measurement optical path length. [Figure 6D] Figure 1 illustrates the specific operating principle of a measurement system, where the reference optical path length is longer than the measurement optical path length. [Figure 7A] This figure shows the first implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 7B] This figure shows the first implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 8A] This figure shows a second implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 8B] This figure shows a second implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 9A] This figure shows a third implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 9B] This figure shows a third implementation configuration of the sample-and-hold section and the corresponding signal timing. [Figure 10] This flowchart illustrates an example implementation of routines for operating a measurement system. [Modes for carrying out the invention]

[0009] Figure 1 is a block diagram showing the measurement system 100 together with the workpiece WP to be measured. As shown in Figure 1, the measurement system 100 includes an interferometer unit 101 and a circuit unit 102. The measurement system utilizes optical coherence tomography (OCT) techniques, such as frequency-modulated continuous wave (FMCW) techniques, as will be described in more detail below. Specific implementation configurations of the interferometer unit 101 will be described in more detail below with respect to Figures 2 and 3. Implementation configurations of the circuit unit 102 will be described in more detail below with respect to Figure 4.

[0010] In various implementations, the measurement system 100 is configured to determine the distance D to the workpiece. More specifically, the measurement system 100 optically measures the distance between the measurement system 100 and the workpiece WP. The measurement system 100 may also measure the three-dimensional shape and / or surface properties of the workpiece WP (for example, by scanning the illumination position on the workpiece WP to measure different points on the surface of the workpiece WP).

[0011] Figure 2 shows an interferometer unit 101 that may be included in the measurement system 100 as shown in Figure 1. M This is a block diagram showing the first implementation form. As shown in Figure 2, the interferometer unit 101 M The light section 110 and the branching section 120 M It has a reference mirror 136 and, as will be described in more detail below, the interferometer unit 101 M This directs light to the workpiece WP (for example, to measure the distance to the workpiece WP).

[0012] In various implementations, the optical unit 110 includes a laser resonator and outputs laser light (for example, the optical unit 110 in Figures 2 and 3 may be similarly or alternatively referred to as the laser unit 110 in some implementations). The optical unit 110 outputs, for example, frequency-modulated laser light. The optical unit 110 has a frequency shifter provided in the resonator and can output a laser whose oscillation frequency changes linearly with time. In various implementations, the optical unit 110 may include a frequency-shifted feedback laser.

[0013] Branch section 120 M The optical unit 110 splits the light emitted into a portion of the reference light and at least a portion of the remaining light as measurement light. As will be explained in more detail below, the reference light is connected to the reference optical path ROP M Guided along the measurement light path MOP M It is led along. In various embodiments, branch 120 M It comprises a beam splitter component (e.g., a beam splitter). In various embodiments, the splitter element has a specified splitting ratio (e.g., reference optical path ROPM and the measurement optical path MOP M are each adjusted to have approximately the same amount of light (1:1).

[0014] Reference optical path ROP M In the reference optical path ROP, the reference light branched from the branching portion 120 M is irradiated toward the reference mirror 136, and the reference light is reflected toward the branching portion 120 M . In the measurement optical path MOP M the measurement light branched from the branching portion 120 M is irradiated toward the workpiece WP. The measurement light reflected by the workpiece WP is received by the branching portion 120 M . In various embodiments, the distance between at least a part of the branching portion 120 M and the workpiece WP can be set as the distance D measured by the measurement system 100.

[0015] The branching portion 120 M combines the reflected measurement light and the reference light reflected by the reference mirror 136. Thus, in FIG. 2, an example is shown in which the branching portion 120 M also functions as a combining portion (for example, in some implementations, the branching portion may be further or alternatively referred to as the branching / combining portion 120 M or simply the combining portion 120 M ). The branching portion 120 M outputs the combined light (e.g., including the reference light and the measurement light) to the circuit portion 102 (e.g., the detection portion 140 within the circuit portion 102, which will be described in more detail below with respect to FIG. 4).

[0016] In various implementations, the reference optical path ROP M may have a reference optical path length (e.g., including the propagation of the reference light to the reference mirror 136 and the propagation of the reference light from the reference mirror). Similarly, the measurement optical path MOP M may have a measurement optical path length (e.g., including the propagation of the measurement 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. In the example of FIG. 2, as shown in relation to the measurement optical path MOP M the reference optical path ROPM A reference marker RM is provided to indicate the length of the measurement optical path MOP. M The length of the reference optical path ROP M It has been shown to be greater than the length of the reference optical path ROP. M The length of the measured optical path MOP M Under another condition, where the length is greater than the reference marker RM, the measuring surface of the workpiece WP is shown in front of the reference marker RM (i.e., to the left of the reference marker RM in Figure 2). As will be described in more detail below, the circuit 102 may be configured to receive the combined light (i.e., including the combined reference light and the measuring light) and generate an output (for example, indicating the distance to the workpiece and correspondingly the difference between the reference optical path length and the measuring optical path length).

[0017] In various implementation configurations, the difference in optical path length between the reference optical path length and the measurement optical path length may correspond to the propagation difference between the reference light and the measurement light, resulting in a propagation delay corresponding to the optical path length difference between the reference light and the measurement light. As will be explained in more detail below, the distance to the workpiece WP can be determined by determining a signal corresponding to the propagation delay (for example, as determined using circuit section 102). More specifically, as described above, the measurement optical path length is a result of the distance to the workpiece (for example, the measurement optical path length increases as the distance to the workpiece increases and decreases as the distance to the workpiece decreases). Correspondingly, the propagation delay (for example, corresponding to the difference between the measurement optical path length and the known fixed reference optical path length) will differ depending on the distance to the workpiece. As will be explained in more detail below, such a relationship may be used to determine the measurement distance to the workpiece (for example, according to a determination signal corresponding to the propagation delay that indicates the optical path length difference indicating the measurement distance to the workpiece).

[0018] In various implementation configurations, the interferometer unit 101 of the measurement system M The distributed part DP M It may include the distributed part DP. M The reference optical path ROP M Although included in one implementation, in another implementation, the dispersion part is the measurement optical path MOP FIt may be included in the example shown, the distributed part DP. M This includes a high-dispersion optical element OE1. In various implementations, the optical element OE1 may be at least semi-transparent, allowing light (e.g., reference light in the illustrated example) to pass through it, and the optical element OE1 causes dispersion of light. In various implementations, the dispersion imbalance between the reference optical path and the measurement optical path arises at least partly from the dispersion (e.g., it may be used as part of a process to determine the measurement distance to the workpiece WP).

[0019] Figure 3 shows an interferometer unit 101 that may be included in the measurement system 100 as shown in Figure 1. F This is a block diagram showing the second implementation form. As shown in Figure 3, the interferometer unit 101 F The light section 110 and the branching section 120 F It includes a circulator section 125, an optical head section 134, and a combining section 139. Optical fibers OF1 to OF6 are shown connecting different sections to provide light to and / or from different sections. More specifically, the optical section 110 is connected by optical fiber OF1 to branch section 120 F It is connected to the branch section 120. F The optical fiber OF2 connects to the composite unit 139, and the optical fiber OF3 connects to the circulator unit 125. The circulator unit 125 is connected to the optical head unit 134 by the optical fiber OF4, and the optical fiber OF5 connects to the composite unit 139. The composite unit 139 is connected to the circuit unit 102 by the optical fiber OF6.

[0020] As will be explained in more detail below, the interferometer unit 101 F This irradiates light toward the workpiece WP (for example, to measure the distance to the workpiece WP). In various implementation configurations, the measurement system includes the interferometer unit 101 F The distance between the device and the workpiece WP can be measured optically (for example, in various mounting configurations, the three-dimensional shape and / or surface characteristics of the workpiece WP can also be measured by scanning the irradiation position on the workpiece WP to measure different points on the surface of the workpiece WP).

[0021] Branch section 120 F The light output from the optical unit 110 is split, with a portion used as reference light and at least a portion of the remaining light used as measurement light. F For example, this is an optical fiber splitter (which can be similarly or alternatively called an optical fiber coupler). In the example in Figure 3, branching section 120 F The system supplies measurement light to the circulator unit 125 and reference light to the synthesis unit 139.

[0022] The circulator unit 125 has multiple input / output ports. For example, the circulator unit 125 takes light from one port and outputs light from the next port, takes light from the next port and outputs light from the next port. Figure 3 shows an example in which the circulator unit 125 has three input / output ports. In this case, the circulator unit 125 has a branching unit 120 F The measurement light supplied from the optical head unit 134 is output to the optical head unit 134. The circulator unit 125 also outputs the light input from the optical head unit 134 (reflected light from the workpiece WP) to the synthesis unit 139.

[0023] The optical head unit 134 directs the light input from the circulator unit 125 toward the workpiece WP. The optical head unit 134 includes, for example, a collimator lens. In this case, the optical head unit 134 first adjusts the light input from the circulator unit 125 via the optical fiber OF4 into a beam shape using the collimator lens and outputs it.

[0024] Furthermore, the optical head unit 134 receives reflected light from the measurement light irradiated onto the workpiece WP. The optical head unit 134 focuses the received reflected light onto the optical fiber OF4 using a collimator lens and supplies it to the circulator unit 125. In this case, the optical head unit 134 may have one common collimator lens, which irradiates the workpiece WP with measurement light and receives reflected light from the workpiece WP. In various mounting configurations, the distance between at least a portion of the optical head unit 134 and the workpiece WP can be defined as distance D (for example, in some mounting configurations, it may be characterized as the measurement distance D).

[0025] Alternatively, the optical head unit 134 may include a focusing lens. In this case, the optical head unit 134 focuses the light input from the circulator unit 125 via the optical fiber OF4 onto the surface of the workpiece WP. The optical head unit 134 receives at least a portion of the reflected light reflected from the surface of the workpiece WP. The optical head unit 134 focuses the received reflected light onto the optical fiber OF4 using the focusing lens and supplies it to the circulator unit 125. In this case as well, the optical head unit 134 may include one common focusing lens, which may irradiate the workpiece WP with measurement light and receive the reflected light from the workpiece WP.

[0026] The combining unit 139 receives the reflected light, which is the measurement light that is irradiated onto the workpiece WP from the circulator unit 125 and reflected back. The combining unit 139 also receives the branching unit 120 F The device receives a reference light from the optical fiber. The combining unit 139 combines / mixes the reflected measurement light and the reference light and provides the corresponding output to the circuit unit 102 (for example, the detection unit 140 in the circuit unit 102, as will be described in more detail below with respect to Figure 4). In various implementations, the combining unit 139 may be an optical fiber splitter (for example, also called an optical fiber coupler and / or optical fiber combiner).

[0027] Reference optical path ROP F For the reference light traveling along (and corresponding to the reference optical path length ROPL), the reference light is branched at branch 120 FFrom there, the optical fiber OF2 is passed through to the synthesis unit 139. Measurement optical path MOP F The measurement light traveling along (and corresponding to the measurement optical path length MOPL) is directed to the branching section 120 F From there, the signal passes through optical fiber OF3, circulator section 125, optical fiber OF4, optical head section 134, (for example, according to the distance D from optical head section 134 to workpiece WP) through free space FS to workpiece WP, (for example, according to the distance D from optical head section 134 to workpiece WP) is reflected by workpiece WP so as to return to optical head section 134 through free space FS, passes through optical head section 134, optical fiber OF4, circulator section 125, optical fiber OF5 to the synthesis section 139.

[0028] In various implementation configurations, the oscillation frequency of the light output from the optical unit 110 changes linearly over time (for example, it can be characterized as a frequency sweep), and a frequency difference arises between the oscillation frequency of the reference light (received by the combining unit 139) and the oscillation frequency of the measurement light, depending on the propagation delay corresponding to the difference in propagation distance. A beat signal can be generated in response to such a frequency difference (for example, the combining unit 139 in Figure 3 or the branching / combining unit 120 in Figure 2). M (This is generated by combining the reference light and the measurement light). As will be explained in more detail below with respect to Figure 4, the detection and processing unit DPP of the circuit unit 102 may also include a detection unit 140 which can provide a signal corresponding to the difference in propagation distance between the reference light and the measurement light.

[0029] In various implementation configurations, as will be explained in more detail below with respect to Figure 4, the detection and processing unit DPP detects the difference in propagation distance between the reference light and the measurement light by frequency analysis of the generated beat signal. More specifically, in various implementation configurations, the combined light (e.g., from the combining unit 139) is received by the detection unit 140 (e.g., of the detection and processing unit DPP), which can output a combined photoelectric signal (e.g., which may be a sine wave), and this combined photoelectric signal is digitized using an analog-to-digital converter (e.g., which may be included in the processing unit 150 of the detection and processing unit DPP in some implementation configurations). This digitized signal may then be analyzed through a fast Fourier transform algorithm (e.g., performed by the processing unit 150, and additional processing to determine the distance to the workpiece may be performed in various implementation configurations).

[0030] In various implementation configurations, the display unit 160 of the circuit unit 102 is controlled by the control unit 180 to display the analysis results of the detection / processing unit DPP (for example, displaying the distance to the workpiece, or displaying it in a different way). In various embodiments, the display unit 160 may include a display or the like and display the detection results, and the control unit 180 may store the analysis results in a storage unit or the like. Generally, the measurement system can measure the distance between the interferometer unit 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.

[0031] In various implementation configurations, the interferometer unit 101 of the measurement system F The distributed part DP F It may include the distributed part DP. F The reference optical path ROP F Although included in one implementation, in another implementation, the dispersion part is the measurement optical path MOP F It may be included in the example shown, the distributed part DP. F This includes a high-dispersion optical fiber OF2 (i.e., branch section 120 as described above) FThe optical fiber OF2 connecting the composite section 139 is a high-dispersion optical fiber. In various implementation configurations, other optical paths (for example, the measurement optical path MOP) F ) is one or more low-dispersion optical fibers (e.g., dispersion DP) F This may include high-dispersion optical fibers (lower than OF2). For example, some or all of the optical fibers OF3, OF4, or OF5 may be relatively low-dispersion optical fibers. This is in contrast to a conventional configuration in which both optical paths may include optical fibers with similar / matched (e.g., identical) dispersion characteristics. In various implementations, the dispersion imbalance between the reference optical path and the measurement optical path arises at least partly from the dispersion (e.g., it may be used as part of the process for determining the measurement distance to the workpiece WP).

[0032] In other words, in some conventional configurations, matching optical fibers (e.g., having similar dispersion characteristics) in the reference and measurement optical paths typically minimize cumulative dispersion imbalance. Using optical fibers with different dispersion characteristics in the two optical paths results in dispersion imbalance (e.g., in some cases, this may correspond to an increase in dispersion imbalance). Even in such configurations, matching the baseline optical path length (OPL) is still desirable to obtain the desired interference effect (e.g., resulting from the combination of the reference and measurement light in the combining unit 139), although higher-order phases may be added due to dispersion.

[0033] In various implementations, a gap (e.g., through free space FS between the optical head 134 and the workpiece WP) may be used to deliver the measurement light to the workpiece WP. In some such configurations, including a relatively low-dispersion optical fiber in the measurement optical path MOP may be considered relatively more efficient (e.g., to increase the dispersion imbalance caused by free space FS / gap, compared to a reference optical path that may include a higher-dispersion optical fiber). However, it should be understood that other configurations may also be available. The primary purpose of some such implementations is to make the dispersion / optical fibers in the two optical paths different (e.g., to have different dispersion characteristics), and generally, a greater dispersion imbalance can improve the identification of signal peaks.

[0034] Figure 4 is a block diagram showing possible implementation configurations of the circuit unit 102 that may be included in the measurement system shown in Figure 1. As shown in Figure 4, the circuit unit 102 includes a detection / processing unit DPP (e.g., including a detection unit 140 and a processing unit 150), a display unit 160, and a control unit 180. In various implementation configurations, the detection unit 140 of the detection / processing unit DPP uses a combined reference light and a measurement light (e.g., the branching unit 120 in Figure 2). M Alternatively, the combined light (received from the combining unit 139 in Figure 3) is received / detected, and the combined light is converted into an electrical signal. In various implementation configurations, the detection unit 140 detects a beat signal generated by combining and interfering the reference light and the measurement light. The detection unit 140 may have, for example, a photoelectric conversion element that can convert the beat signal into an electrical signal. An example of a photoelectric conversion element is a photodiode. The detection / processing unit DPP may also have an analog-to-digital converter (ADC) that can convert the beat signal converted into an electrical signal into a digital signal.

[0035] As described above, in various implementation configurations, the oscillation frequency of the light output by the optical unit 110 changes linearly with time. Therefore, a frequency difference arises between the oscillation frequency of the reference light and the oscillation frequency of the measurement light according to the propagation delay. A beat signal is generated in response to this frequency difference.

[0036] The processing unit 150 analyzes the detected electrical signal and calculates the distance D to the workpiece WP. The processing unit 150 analyzes the frequency at which the beat signal was generated using a frequency transformation such as FFT. Then, the processing unit 150 calculates the optical path length difference corresponding to the frequency of the beat signal.

[0037] In various embodiments, the control unit 180 receives the output from the processing unit 150 of the detection / 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 accept instructions from the user. In various implementations, the control unit 180 may be configured to control some operations of the optical unit 110, the display unit 160, and / or the detection / processing unit DPP. In various implementations, the control unit 180 may control the optical unit 110 to output light to the branching unit 120 (for example, in Figure 2 or Figure 3). Generally, it should be noted that the measurement system 100, including the interferometer unit 101 and the circuit unit 102, can measure the distance between the measurement system 100 and the workpiece WP (for example, by analyzing the frequency difference between the measurement light reflected by the workpiece WP and the reference light).

[0038] As described above, in various implementation configurations, the interferometer unit 101 of the measurement system (for example, the interferometer unit 101 in Figure 2) M Or the interferometer unit 101 in Figure 3 F ) is the distributed part DP (for example, the distributed part DP in Figure 2) M Or the DP in Figure 3 F ) may include. An imbalance in dispersion between the reference optical path ROP and the measurement optical path MOP can arise, at least in part, from the dispersion component. More specifically, the dispersion component DP can cause the dispersion of light in the reference optical path ROP to be different from the dispersion of light in the measurement optical path MOP, which corresponds to an imbalance in dispersion between the reference optical path ROP and the measurement optical path MOP (which can be used, for example, as part of the process of determining the measurement distance to the workpiece WP).

[0039] Figures 5A to 5D illustrate the specific operating principles of the measurement system shown in Figure 1. As described above, in various implementations, the measurement system including the optical unit 110 operates according to optical coherence tomography (OCT), such as frequency-modulated continuous wave (FMCW), which is sometimes called swept optical coherence tomography (SS-OCT) in some implementations. Figure 5A shows a state where the measurement distance of the measurement optical path length MOPL (e.g., to the workpiece) is longer than the reference optical path length ROPL. The optical path length difference DIFF is shown, which corresponds to the difference in length between the optical paths. For example, if the MOPL is 1.5 mm longer than the ROPL, the MOPL corresponds to a position of 1.5 mm within the range of -4.0 mm to +4.0 mm. In this case, the distance D from the interferometer unit 101 (see Figure 4) may be +5.5 mm, which corresponds to spanning the range from the negative end of -4.0 mm to the positive end of +1.5 mm (for example, in a configuration where the range starts from the end of the interferometer unit 101).

[0040] Figure 5B is a graph showing the change in frequency over time, where the dotted signal corresponds to the measurement light ML and the solid signal corresponds to the reference light RL (e.g., received by a combining unit such as the combining unit 139). The shape of each signal corresponds to the frequency sweep of the optical unit 110 (for example, the frequency of each signal increases linearly with time, returns to the baseline level when it reaches a maximum value, and then the process can be repeated in subsequent periods). The time delay ΔT between signals is shown to be greater than 0 to correspond to the propagation delay (e.g., due to the measurement optical path length MOPL being longer than the reference optical path length ROPL). Beat frequency f b Furthermore, as shown in Figure 5B, it has been shown to be greater than 0, corresponding to the frequency difference between the two signals at a given time.

[0041] Figure 5C is a graph of the combined signal (e.g., from the combining unit), showing that the amplitude oscillates over time. When the reference light and the measurement light are combined (e.g., by the combining unit) by the frequency sweep of the optical unit 110, the beat frequency f of the signal in Figure 5C bA time delay (for example, as illustrated in Figure 5B) is encoded. In various implementations, the beat frequency can be detected as a function of time (for example, by the detection unit 140 of the detection / processing unit DPP). In various implementations, the Fourier transform (for example, used by the processing unit 150) can evaluate the time-domain data and extract arbitrary frequency information. Since the rate of change of frequency (i.e., the slope of the frequency sweep) is known, the frequency information can be mapped to the propagation distance of light (for example, as shown in Figure 5D, the signal peaks correspond to different distances / positions D of the workpiece).

[0042] Furthermore, with respect to Figure 5D (i.e., the x-axis extends from -4.0 mm to +4.0 mm), the Fourier transform used to convert the frequency space to distance generates a pair of positive and negative conjugate peaks (i.e., corresponding to the positive position peak PPP and the negative position peak NPP, respectively, with a positive beat frequency +f b and negative beat frequency -f b It should be noted that this corresponds to the following: Generally, standard processing for such systems typically ignores the negative component (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 within the negative distance range has been considered undesirable due to signal peak ambiguity (i.e., with respect to which signal peak corresponds to the current measurement). In such systems, the practically usable distance range was reduced to about half (e.g., in this embodiment, only the 4 mm distance range corresponding to the positive signal range from 0 to 4 mm was used, rather than the full 8 mm distance range combining the negative and positive distance ranges from -4.0 mm to +4.0 mm). In various implementations, to address such problems, the measurement system may include a dispersive section (e.g., enabling deambiguation between signal peaks). In various implementations, alternatively, other techniques may be used to achieve such deambiguation (e.g., the quadrature processing technique, which will be described in more detail below with respect to Figures 9A and 9B).

[0043] Figures 6A to 6D are similar to Figures 5A to 5D, respectively, except that they represent the reverse state (i.e., with respect to lengths MOPL and ROPL). More specifically, Figure 6A shows a state where the measurement distance of the measurement optical path length MOPL (e.g., to the workpiece) is shorter than the reference optical path length ROPL. The optical path length difference DIFF corresponding to the difference in optical path lengths is shown (for example, in a simplified example, the magnitude of the optical path length difference DIFF in Figure 6A may be the same as the magnitude of the optical path length difference DIFF in Figure 5A). For example, if MOPL is 1.5 mm shorter than ROPL, MOPL corresponds to a position of -1.5 mm within the range of -4.0 mm to 4.0 mm, and in this case, the distance D from the interferometer unit 101 (see Figure 4) may be +2.5 mm, which corresponds to spanning the range from the negative end of -4.0 mm to the negative end of -1.5 mm (for example, in a configuration where the range starts from the end of the interferometer unit 101).

[0044] In Figure 6B (which is the same as Figure 5B except that the relative signal positions are reversed), the dotted line signal corresponds to the measurement light ML, and the solid line signal corresponds to the reference light RL (e.g., received in the combiner). The time delay ΔT between signals is shown to be less than 0, corresponding to the propagation delay (e.g., due to the measurement optical path length MOPL being shorter than the reference optical path length ROPL). Beat frequency f b Furthermore, as shown in Figure 6B, it is shown to be less than 0, corresponding to the frequency difference between the two signals at a given time.

[0045] In Figure 6C, when the reference light and the measurement light are combined (for example, by the combining unit), the beat frequency f of the signal in Figure 6C is b A time delay (for example, as illustrated in Figure 6B) is encoded. In various implementations, the beat frequency can be detected as a function of time (for example, by the detection unit 140 of the detection / processing unit DPP), similar to the process described above with respect to Figures 5C and 5D. The frequency information can be mapped to the propagation distance of light (for example, as shown in Figure 6D, the signal peaks correspond to different distances / positions D of the workpiece).

[0046] Furthermore, with respect to Figure 6D, the Fourier transform used to convert the frequency space into distance generates a pair of conjugate peaks of + and - (positive and negative) (i.e., corresponding to the positive position peak PPP and the negative position peak NPP, respectively, with a positive beat frequency +f b and negative beat frequency -f b It should be noted that the generated positive and negative signal peaks are essentially the same as those in Figure 5B. As mentioned above (i.e., with respect to standard processing in certain conventional systems), collecting data in the negative distance range has been considered undesirable, at least in part, due to ambiguity in the correspondence between signal peaks (i.e., from the standpoint that it becomes unclear which signal peak corresponds to the current measurement). More specifically, if the measurement process yields a positive position peak PPP and a negative position peak NPP at the positions shown in Figures 5D and 6D (i.e., positions corresponding to +1.5 mm and -1.5 mm, respectively), it can become unclear whether the measurement corresponds to the positive position peak PPP at +1.5 mm or the negative position peak NPP at -1.5 mm (for example, when it corresponds to the difference between the measurement optical path length MOPL and the reference optical path length ROPL). As mentioned above, in various embodiments, to solve this problem, the measurement system may include a dispersive unit (for example, one that enables identification between signal peaks). In various embodiments, other techniques may be used as alternatives to achieve identification (for example, the orthogonal processing technique which will be described in more detail below with respect to Figures 9A and 9B).

[0047] As described above with respect to Figures 2, 3, 5A-5D, and 6A-6D, in various implementations, the measurement system may include a dispersive section (for example, enabling identification between signal peaks). Techniques and configurations utilizing such dispersive sections are described in further detail in the U.S. Patent Application 19 / 005,052 (December 30, 2024), entitled "METROLOGY SYSTEM UTILIZING FULL RANGE DETECTION" (Agent Reference No. 660051.578), which was assigned and filed concurrently with this Specified and is incorporated herein by reference in its entirety.

[0048] As will be explained in more detail below with respect to Figures 7A to 10, as part of the processing of a measurement system as described herein, the synthesized light (e.g., from the synthesis unit 139) is received by a detection unit 140 which can output a synthesized photoelectric signal (e.g., which may be a sine wave), and this synthesized photoelectric signal is digitized using an analog-to-digital converter (e.g., which may be included in the processing unit 150 in some implementations). This digitized signal can then be analyzed through a Fast Fourier Transform algorithm (e.g., performed by the processing unit 150). Figures 7A to 9B show specific implementations of a sample-and-hold unit SHP (e.g., which may be included between the detection unit 140 and the analog-to-digital converter, as will be explained in more detail below).

[0049] As a general principle, it should be noted that in some conventional systems, the FMCW absolute value (ABS) range has been limited by the minimum frequency step size (dF) in the sample. This requires that the dynamic range (e.g., maximum distance for multi-target resolution) is equal to the number of samples per sweep (e.g., macro 10m / 10μm requires 1 million samples per sweep). Over a wide range, the beat frequency can become excessively high, making digital conversion difficult (e.g., in terms of analog-to-digital converter and processing speed).

[0050] There is uncertainty regarding the position beyond the conventional FMCW absolute value range until an integer multiple of the absolute value range is reached. The range may be extended by using a second measurement (e.g., corresponding to a second measurement track) with a slightly different period, according to the principles described herein. In various implementations, the period that can be modified is the period related to the FMCW absolute value range.

[0051] In various implementations, the two measurements may be performed with different sample frequency intervals dF1 and dF2 (for example, to correspond to different sample rates). Configurations utilizing different sample rates are described in more detail below with respect to Figures 7A to 9B. In various implementations, it may be desirable to make full use of the Nyquist measurement range (+ / - range) in such techniques. As mentioned above, this can be achieved by certain techniques such as the introduction of a dispersion section, or by utilizing quadrature detection of the beat signal (for example, according to the embodiments of Figures 9A and 9B, which are described in more detail below).

[0052] Acquiring high-bandwidth signals using a low-bandwidth analog-to-digital converter, according to the principles described herein and as will be explained in more detail below, is achieved by placing a high-bandwidth sample-and-hold unit (SHP) prior to the analog-to-digital converter (for example, as shown in the examples in Figures 7A, 8A, and 9A, which will be explained in more detail below). Generally, the techniques described herein may have various advantages, such as enabling measurements over a longer range, requiring fewer samples, and / or enabling the use of slower electronic equipment (e.g., a slow analog-to-digital converter used in combination with a relatively fast sample-and-hold unit (SHP)).

[0053] Figures 7A and 7B show a first implementation of the sample-and-hold unit SHP' and the corresponding signal timing. As shown in Figure 7A, the sample-and-hold unit SHP' (e.g., part of the processing unit 150' of the detection-processing unit DPP) is coupled to the detection unit 140 (e.g., to receive a signal from the detection unit 140, such as a synthesized photoelectric signal from the detection unit 140). In various implementations, as will be described in more detail below, the sample-and-hold unit SHP' may be configured to sample the synthesized photoelectric signal from the detection unit. The sample-and-hold unit SHP' is coupled to provide an output (e.g., a sample) to the analog-to-digital converter 152 (e.g., part of the processing unit 150' of the detection-processing unit DPP). In various implementations, according to the principles described herein, the processing unit may further be configured to perform a Fast Fourier Transform on each digitized signal (i.e., for analysis) to determine at least one peak corresponding to the beat frequency. In addition, the distance to the workpiece may be determined at least in part based on the determined peak corresponding to the beat frequency.

[0054] As shown in Figure 7A, the sample-and-hold unit SHP' includes a first sample-and-hold circuit SH1 and a second sample-and-hold circuit SH2. The first and second sample-and-hold circuits SH1 and SH2 are connected in parallel between the detection unit 140 and the analog-to-digital converter 152. The first sample-and-hold circuit SH1 includes a first input switch SW1in, a first capacitor C1, and a first output switch SW1out. The first input switch SW1in is connected to the detection unit 140 (for example, on the input side) and to the first capacitor C1 (for example, on the output side). The first output switch SW1out is connected to the first capacitor C1 (for example, on the input side) and to the analog-to-digital converter 152 (for example, on the output side). The operation of the sample-and-hold unit SHP' (including, for example, the control of switches SW1in and SW1out by control signals Trig1in and Trig1out) will be described in more detail below with reference to Figure 7B.

[0055] The second sample-and-hold circuit SH2 includes a second input switch SW2in, a second capacitor C2, and a second output switch SW2out. The second input switch SW2in is connected to the detection unit 140 (e.g., on the input side) and to the second capacitor C2 (e.g., on the output side). The second output switch SW2out is connected to the second capacitor C2 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP' (including control of switches SW2in and SW2out by control signals Trig2in and Trig2out) will be described in more detail below with reference to Figure 7B.

[0056] Figure 7B shows specific signals related to the operation of the sample-and-hold unit SHP' in Figure 7A. Figure 7B shows the relationship between signals and time for the laser frequency, control signals Trig1in, Trig1out, Trig2in and Trig2out, and a typical combined signal Trig1out+Trig2out. As described herein, the light output by the optical unit (e.g., optical unit 110) includes laser light whose oscillation frequency changes linearly with time (e.g., according to a “chirped” laser), and in Figure 7B, it is shown that the laser frequency increases linearly with time. Note that this is similar to the plots in Figures 5B and 6B (i.e., the reference light and measurement light originate from the light from optical unit 110). Note that the other signals in Figure 7B described below are provided during the period in which the laser frequency is increasing. Thus, in various implementations, as time increases, the signals may correspond to sampling when the laser frequency is at a higher frequency. As will be explained in more detail below, the conversion from analog to digital (e.g., digitization of the signal) is performed alternately (interlaced) between the first and second sample-and-hold circuits SH1 and SH2.

[0057] The control signals Trig1in, Trig1out, Trig2in, and Trig2out are used to control the switches SW1in, SW1out, SW2in, and SW2out of the sample-and-hold unit SHP', respectively. The first input control signal Trig1in is indicated to be supplied according to the first sample rate SR1 for operating the first input switch SW1in, and the second input control signal Trig2in is indicated to be supplied according to the second sample rate SR2 for operating the second input switch SW2in. Note that the second sample rate SR2 is lower than the first sample rate SR1, as will be explained in more detail below.

[0058] As a more specific description of a particular operation, in various implementations, the first input switch SW1in is operated (e.g., closed or conducted) according to the first input control signal Trig1in, and the output of the detection unit 140 (e.g., the combined photoelectric signal) is sampled into the first capacitor C1 (e.g., while the first output switch SW1out is open or non-conductive according to the first output control signal Trig1out). More specifically, while the first input switch SW1in is closed or conducted and the first output switch SW1out is open or non-conductive, the first capacitor C1 is charged to a level corresponding to the signal from the detection unit 140, and therefore samples the signal (e.g., the combined photoelectric signal) at that corresponding time.

[0059] Then, the first input switch SW1in is operated (e.g., open or non-conductive) according to the first input control signal Trig1in, and then the first output switch SW1out is operated (e.g., closed or conductive) according to the first output control signal Trig1out, connecting the first capacitor C1 (e.g., providing the sampled value stored in the first capacitor C1) to the input of the analog-to-digital converter 152 (e.g., operating accordingly and digitizing the sampled value held in the first capacitor C1). By repeating this process (i.e., according to the indicated transitions of the control signals Trig1in and Trig1out), the signal from the detection unit 140 (e.g., the combined photoelectric signal) can be sampled by the first sample-and-hold circuit SH1 and digitized by the analog-to-digital converter 152.

[0060] It will be understood that a similar operation can be performed with respect to the second sample-and-hold circuit SH2. In short, according to the control signals Trig2in and Trig2out, switches SW2in and SW2out can be controlled to hold a sample in capacitor C2, and then the sample can be provided to be digitized by the analog-to-digital converter 152. Following this process (i.e., according to the indicated transitions of the control signals Trig2in and Trig2out), the signal from the detection unit 140 (e.g., a composite photoelectric signal) can be sampled by the second sample-and-hold circuit SH2 and digitized by the analog-to-digital converter 152.

[0061] As mentioned above, the second sample rate SR2 is lower than the first sample rate SR1. In a specific example in Figure 7B, 29 cycles of the first input control signal Trig1in are shown according to the first sample rate SR1 in the illustrated period (for example, 29 instances where the first input control signal Trig1in cycles from low to high and then from high to low). 28 cycles of the second input control signal Trig2in are shown according to the second sample rate SR2 (for example, 28 instances where the second input control signal Trig2in cycles from low to high and then from high to low). As a specific numerical example, this could represent a ratio of SR2 / SR1 = 28 / 29 = 0.97. Design considerations regarding setting a relatively small difference between the first and second sample rates will be discussed in more detail below, following the explanation of Figure 9B.

[0062] As shown in the lower part of Figure 7B, the sample rate SRADC of the analog-to-digital converter corresponds to the combination of the first and second output control signals Trig1out and Trig2out. Note that in the illustrated example, the sample rate SRADC of the analog-to-digital converter is approximately twice the first sample rate SR1. The timing of the first and second output control signals Trig1out and Trig2out is configured such that the sample rate SRADC of the analog-to-digital converter is preferably sampled at equal intervals (for example, thus reducing the requirements for the analog-to-digital converter). Note that such operation may occur even if the combination of the first and second input control signals Trig1in and Trig2in is not configured similarly. Note that if the current circuit configuration illustrated and described herein does not exist, the intervals between control signal combinations will not be constant and may include extremely short intervals, which may increase the processing load.

[0063] In this embodiment, the desired effect is achieved in part by configuring the second output control signal Trig2out to provide a regular interval contribution to the sample rate SRADC of the analog-to-digital converter, but not to perfectly match the timing of the second input control signal Trig2in. For example, in contrast to the first output control signal Trig1out, which is configured to provide a transition immediately after each transition of the first input control signal Trig1in (for example, the small exemplary arrows shown between Trig1in and Trig1out illustrate the sampling and conversion timing relationship), the transitions of the second output control signal Trig2out occur at different intervals after the transitions of the second input control signal Trig2in (for example, the small exemplary arrows shown between Trig2in and Trig2out illustrate the sampling and conversion timing relationship). In some embodiments, as shown in Figure 7B, occasional skips may occur in the analog-to-digital conversion, as indicated by the empty box MK in the transition diagram for the second output control signal Trig2out and the corresponding Trig1out+Trig2out combination. In various implementations, this can also be characterized as corresponding to duplicate samples resulting from the Vernier effect between two sample rates.

[0064] As described above, the output control signals Trig1out and Trig2out (corresponding, for example, to providing samples to the analog-to-digital converter 152) are configured to reduce the requirements for the analog-to-digital converter. As can be seen from the figure, the output signals to the analog-to-digital converter 152 (i.e., the sample rate SRADC of the analog-to-digital converter at the bottom of Figure 7B) consist of specific intervals (i.e., specific regular intervals between transitions / samples), thus reducing the requirements for the analog-to-digital converter. This is in contrast to a configuration where there is no sample-and-hold circuit and the analog-to-digital converter must acquire data according to the first sample rate SR1 and the second sample rate SR2 on its own (for example, if the signal intervals are not regular and some of the acquired signals / timings for the second sample rate SR2 are very close to some of the acquired signals / timings for the first sample rate SR1, the operating requirements for the analog-to-digital converter increase significantly).

[0065] Figures 8A and 8B show a second implementation of the sample-and-hold unit SHP'' and the corresponding signal timing. As shown in Figure 8A, the sample-and-hold unit SHP'' (e.g., part of the processing unit 150'' of the detection-processing unit DPP) is coupled to the detection unit 140 (e.g., to receive a signal from the detection unit 140, such as a synthesized photoelectric signal from the detection unit 140). In various implementations, as will be described in more detail below, the sample-and-hold unit SHP'' may be configured to sample the synthesized photoelectric signal from the detection unit. The sample-and-hold unit SHP'' is coupled to provide an output (e.g., a sample) to the analog-to-digital converter 152 (e.g., part of the processing unit 150'' of the detection-processing unit DPP). In various implementations, according to the principles described herein, the processing unit may further be configured to perform a Fast Fourier Transform on each digitized signal (i.e., for analysis) to determine at least one peak corresponding to the beat frequency. In addition, the distance to the workpiece may be determined at least in part based on the determined peak corresponding to the beat frequency.

[0066] As shown in Figure 8A, the sample-and-hold unit SHP'' includes a first sample-and-hold circuit SH1, a second sample-and-hold circuit SH2, and a third sample-and-hold circuit SH3. The sample-and-hold circuits SH1, SH2, and SH3 are connected in parallel between the detection unit 140 and the analog-to-digital converter 152. The main difference between the sample-and-hold unit SHP'' in Figure 8A and the sample-and-hold unit SHP' in Figure 7A is the addition of the third sample-and-hold circuit SH3. The descriptions of the first and second sample-and-hold circuits SH1 and SH2 and their corresponding operations in the sample-and-hold unit SHP' described above should be understood to also apply to the first and second sample-and-hold circuits SH1 and SH2 in the sample-and-hold unit SHP'' in Figure 8A, unless otherwise stated below. Therefore, at least part of the following description mainly concerns the differences corresponding to the additional sample-and-hold circuit SH3.

[0067] The third sample-and-hold circuit SH3 includes a third input switch SW3in, a third capacitor C3, and a third output switch SW3out. The third input switch SW3in is connected to the detection unit 140 (e.g., on the input side) and to the third capacitor C3 (e.g., on the output side). The third output switch SW3out is connected to the third capacitor C3 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP'' (including control of switches SW3in and SW3out by control signals Trig3in and Trig3out) will be described in more detail below with reference to Figure 8B.

[0068] Figure 8B shows specific signals related to the operation of the sample-and-hold unit SHP'' in Figure 8A. Figure 8B shows the signal-time relationship for the laser frequency, the control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in and Trig3out, and a typical combined signal Trigout (i.e., Trig1out + Trig2out + Trig3out). The control signals Trig1in, Trig1out, Trig2in and Trig2out have some similarities to the control signals described above with respect to Figure 7B, and will be understood to have similar functions unless otherwise described below.

[0069] The laser frequencies shown in Figure 8B are identical to, and should be understood similarly to, those described in Figure 7B. As will be described in more detail below, the analog-to-digital conversion (e.g., digitization of the signal) is performed alternately between the first, second, and third sample-and-hold circuits SH1, SH2, and SH3. Each switch SW1in, SW1out, SW2in, SW2out, SW3in, and SW3out in the sample-and-hold section SHP'' is controlled by the corresponding control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, and Trig3out, respectively. The first input control signal Trig1in is shown to be provided according to a first sample rate SR1 for operating the first input switch SW1in, the second input control signal Trig2in is shown to be provided according to a second sample rate SR2 for operating the second input switch SW2in, and the third input control signal Trig3in is shown to be provided according to a third sample rate SR3 for operating the third input switch SW3in. As will be explained in more detail below, note that the second sample rate SR2 is lower than the first sample rate SR1, and the third sample rate SR3 is lower than the second sample rate SR2.

[0070] With respect to Figure 7B, the more specific operation of the first and second sample-and-hold circuits SH1 and SH2 as described above will be understood to be similar for the third sample-and-hold circuit SH3 in Figure 8B. In short, according to the control signals Trig3in and Trig3out, switches SW3in and SW3out can be controlled to hold the sample in capacitor C3, and then the sample can be provided to be digitized by the analog-to-digital converter 152. Following this process (i.e., according to the indicated transitions of the control signals Trig3in and Trig3out), the signal from the detection unit 140 (e.g., a composite photoelectric signal) can be sampled by the third sample-and-hold circuit SH3 and digitized by the analog-to-digital converter 152.

[0071] As described above, the second sample rate SR2 is lower than the first sample rate SR1, and the third sample rate SR3 is lower than the second sample rate SR2. In a specific example in Figure 8B, according to the illustrated period, 29 cycles of the first input control signal Trig1in are shown (for example, 29 instances where the first input control signal Trig1in cycles from low to high, and then from high to low). According to the second sample rate SR2, 28 cycles of the second input control signal Trig2in are shown (for example, 28 instances where the second input control signal Trig2in cycles from low to high, and then from high to low). As a specific numerical example, this can represent a ratio of SR2 / SR1 = 28 / 29 = 0.97. According to the third sample rate SR3, 27 cycles of the third input control signal Trig3in are shown (for example, 27 instances where the third input control signal Trig3in cycles from low to high, and then from high to low). As some specific numerical examples, this could represent a ratio of SR3 / SR2 = 27 / 28 = 0.96, or SR3 / SR1 = 27 / 29 = 0.93. Design considerations regarding setting relatively small differences between the first, second, and third sample rates are described in more detail below, following the explanation of Figure 9B.

[0072] As shown in the lower part of Figure 8B, the sample rate SRADC of the analog-to-digital converter corresponds to the combination of the first, second, and third output control signals Trig1out, Trig2out, and Trig3out. Note that in the illustrated example, the sample rate of the analog-to-digital converter is approximately three times the first sample rate SR1. The timing of the first, second, and third output control signals Trig1out, Trig2out, and Trig3out is configured such that the sample rate SRADC of the analog-to-digital converter is preferably sampled at equal intervals (for example, thus reducing the requirements for the analog-to-digital converter). Note that such operation may occur even if the combination of the first, second, and third input control signals Trig1in, Trig2in, and Trig3in is not configured similarly. Note that if the current circuit configuration illustrated and described herein does not exist, the intervals between control signal combinations will not be constant and may include extremely short intervals, which may increase the processing load.

[0073] In this embodiment, the desired effect is achieved in part by configuring the second and third output control signals Trig2out and Trig3out to contribute to the sample rate SRADC of the analog-to-digital converter at regular intervals, but not to perfectly match the timing of the second and third input control signals Trig2in and Trig3in. For example, in contrast to the first output control signal Trig1out, which is configured to provide a transition immediately after each transition of the first input control signal Trig1in (for example, the small exemplary arrows shown between Trig1in and Trig1out illustrate the sampling and conversion timing relationship), the transition of the second output control signal Trig2out occurs at a different interval after the transition of the second input control signal Trig2in (for example, the small exemplary arrows shown between Trig2in and Trig2out illustrate the sampling and conversion timing relationship). Similarly, the transition of the third output control signal Trig3out (partially illustrated by the small exemplary arrow shown between Trig3in and Trig3out, for example, illustrating the timing relationship between sampling and conversion) occurs at a different interval after the transition of the third input control signal Trig3in. In some embodiments, as shown in Figure 8B, occasional skips may occur in the analog-to-digital conversion, as indicated by the empty box MK in the transition diagram for the second or third output control signals Trig2out or Trig3out and the corresponding Trig1out+Trig2out+Trig3out combinations. In various implementations, this can also be characterized as corresponding to duplicate samples resulting from the Vernier effect between the three sample rates.

[0074] As described above, the output control signals Trig1out, Trig2out, and Trig3out (corresponding, for example, to the provision of samples to the analog-to-digital converter 152) are configured to reduce the requirements for the analog-to-digital converter. As can be seen from the figure, the output signals to the analog-to-digital converter 152 (i.e., the sample rate SRADC of the analog-to-digital converter at the bottom of Figure 8B) consist of specific intervals (i.e., specific regular intervals between transitions / samples), thus reducing the requirements for the analog-to-digital converter. This is in contrast to a configuration in which there is no sample-and-hold circuit and the analog-to-digital converter must acquire data independently according to the first, second, and third sample rates SR1, SR2, and SR3 (for example, if the signal intervals are not regular and some of the acquired signals / timings between sample rates are very close to each other, the operating requirements for the analog-to-digital converter increase significantly).

[0075] Figures 9A and 9B show a third implementation of the sample-and-hold section SHP''' and the corresponding signal timing. As will be described in more detail below, in various implementations, the sample-and-hold section SHP''' can be used for orthogonal processing. In some such implementations, orthogonal processing is used as an alternative to including a dispersion section in the interferometer section, which may enable similar resolution of ambiguities (e.g., signal peaks) as described above.

[0076] As shown in Figure 9A, the sample-and-hold unit SHP'''' (e.g., part of the processing unit 150'''' of the detection-processing unit DPP) is coupled to the detection unit 140 (e.g., to receive a signal from the detection unit 140, such as a synthesized photoelectric signal from the detection unit 140). In various implementations, as will be described in more detail below, the sample-and-hold unit SHP'''' may be configured to sample the synthesized photoelectric signal from the detection unit. The sample-and-hold unit SHP'''' is coupled to provide an output (e.g., a sample) to the analog-to-digital converter 152 (e.g., part of the processing unit 150'''' of the detection-processing unit DPP). In various implementations, according to the principles described herein, the processing unit may further be configured to perform a Fast Fourier Transform on each digitized signal (i.e., for analysis) to determine at least one peak corresponding to the beat frequency. In addition, the distance to the workpiece may be determined at least in part based on the determined peak corresponding to the beat frequency.

[0077] As shown in Figure 9A, the sample-and-hold unit SHP'''' has a first sample-and-hold circuit SH1, a second sample-and-hold circuit SH2, a third sample-and-hold circuit SH3, and a fourth sample-and-hold circuit SH4. The sample-and-hold circuits SH1, SH2, SH3, and SH4 are connected between the detection unit 140 and the analog-to-digital converter 152. The main difference between the sample-and-hold unit SHP'''' in Figure 9A and the sample-and-hold unit SHP'' in Figure 7A is the addition of the third and fourth sample-and-hold circuits SH3 and SH4, as well as the connection to the detection unit 140. In general, it will be understood that much of the description of the sample-and-hold circuits SH1 and SH2 and their corresponding operations in the sample-and-hold unit SHP'' described above also applies to the sample-and-hold circuits SH1, SH2, SH3, and SH4 in the sample-and-hold unit SHP'' in Figure 9A, unless otherwise stated below. Therefore, at least part of the following explanation concerns differences that primarily correspond to the sample-and-hold section SHP'''.

[0078] One difference (for example, in relation to potential quadrature processing) is that the detection unit 140 may include multiple detectors (for example, in one embodiment the detectors may be photodetectors, with a phase shift of optically generated quadrature signals in front of the detectors). In one implementation, the detection unit 140 may include first and second detectors (not shown), such that first and third sample-and-hold circuits SH1 and SH3 are coupled to the first detector, and second and fourth sample-and-hold circuits are coupled to the second detector. In such a configuration, as will be described in more detail below, each pair of quadrature measurements (including, for example, a first pair corresponding to the first and second sample-and-hold circuits SH1 and SH2, and a second pair corresponding to the third and fourth sample-and-hold circuits SH3 and SH4) may occur simultaneously. Therefore, the outputs of the first and second detectors can be measured simultaneously by the first and second sample-and-hold circuits SH1 and SH2, respectively, and then simultaneously again by the third and fourth sample-and-hold circuits SH3 and SH4, respectively.

[0079] In the implementation shown in Figure 9A, the first sample-and-hold circuit SH1 includes a first input switch SW1In, a first capacitor C1, and a first output switch SW1out. The first input switch SW1In is connected to the detection unit 140 (e.g., to the first detector of the detection unit 140) (e.g., on the input side) and to the first capacitor C1 (e.g., on the output side). The first output switch SW1out is connected to the first capacitor C1 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP'''' (including control of switches SW1In and SW1Out by control signals Trig1In and Trig1Out) will be described in more detail below with respect to Figure 9B.

[0080] The second sample-and-hold circuit SH2 includes a second input switch SW2in, a second capacitor C2, and a second output switch SW2out. The second input switch SW2in is connected to the detection unit 140 (e.g., to the second detector of the detection unit 140) (e.g., on the input side) and to the second capacitor C2 (e.g., on the output side). The second output switch SW2out is connected to the second capacitor C2 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP''' (including control of switches SW2in and SW2out by control signals Trig2in and Trig2out) will be described in more detail below with reference to Figure 9B.

[0081] The third sample-and-hold circuit SH3 includes a third input switch SW3in, a third capacitor C3, and a third output switch SW3out. The third input switch SW3in is connected to the detection unit 140 (e.g., to the first detector of the detection unit 140) (e.g., on the input side) and to the third capacitor C3 (e.g., on the output side). The third output switch SW3out is connected to the third capacitor C3 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP''' (including control of switches SW3in and SW3out by control signals Trig3in and Trig3out) will be described in more detail below with reference to Figure 9B.

[0082] The fourth sample-and-hold circuit SH4 includes a fourth input switch SW4in, a fourth capacitor C4, and a fourth output switch SW4out. The fourth input switch SW4in is connected to the detection unit 140 (e.g., to the second detector of the detection unit 140) (e.g., on the input side) and to the fourth capacitor C4 (e.g., on the output side). The fourth output switch SW4out is connected to the fourth capacitor C4 (e.g., on the input side) and to the analog-to-digital converter 152 (e.g., on the output side). The operation of the sample-and-hold unit SHP''' (including control of switches SW4in and SW4out by control signals Trig4in and Trig4out) will be described in more detail below with reference to Figure 9B.

[0083] Figure 9B shows specific signals related to the operation of the sample-and-hold unit SHP''' in Figure 9A. Figure 9B shows the signal-time relationship for the laser frequency, control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, Trig3out, Trig4in and Trig4out, and a typical combined signal Trigout (i.e., Trig1out + Trig2out + Trig3out + Trig4out). The control signals Trig1in, Trig1out, Trig2in and Trig2out have some similarities to the control signals described above with respect to Figure 7B and will be understood to have similar functions unless otherwise described below.

[0084] The laser frequencies shown in Figure 9B are identical to, and should be understood similarly to, those described in the laser frequency explanation in Figure 7B. As will be described in more detail below, the analog-to-digital conversion (e.g., digitization of the signal) is performed alternately between the first, second, third, and fourth sample-and-hold circuits SH1, SH2, SH3, and SH4. Each switch SW1in, SW1out, SW2in, SW2out, SW3in, SW3out, SW4in, and SW4out in the sample-and-hold section SHP'''' is controlled by the corresponding control signals Trig1in, Trig1out, Trig2in, Trig2out, Trig3in, Trig3out, Trig4in, and Trig4out, respectively. The first input control signal Trig1in and the second input control signal Trig2in are shown to be provided according to the first sample rate SR1 for operating the first input switch SW1in and the second input switch SW2in. The third and fourth input control signals Trig3in and Trig4in are provided according to a second sample rate SR2 for operating the third and fourth input switches SW3in and SW4in. Note that the second sample rate SR2 is lower than the first sample rate SR1, as will be explained in more detail below.

[0085] With respect to Figure 7B, the more specific operation of the first and second sample-and-hold circuits SH1 and SH2 as described above will be understood to be similar to the operation of the first and second, and third and fourth sample-and-hold circuits in Figure 9B. In short, according to the control signals Trig1in and Trig1out, switches SW1in and SW1out can be controlled to hold a sample in capacitor C1, and then the sample can be provided to be digitized by the analog-to-digital converter 152. Following this process (i.e., according to the indicated transitions of the control signals Trig1in and Trig1out), the signal from the detection unit 140 (e.g., the combined photoelectric signal from the first detector) can be sampled by the first sample-and-hold circuit SH1 and digitized by the analog-to-digital converter 152.

[0086] According to the control signals Trig2in and Trig2out, switches SW2in and SW2out can be controlled to hold a sample in capacitor C2, and then provide the sample to be digitized by the analog-to-digital converter 152. Following this process (i.e., according to the indicated transitions of the control signals Trig2in and Trig2out), a signal from the detection unit 140 (e.g., a composite photoelectric signal from the second detector) can be sampled by the second sample-and-hold circuit SH2 and digitized by the analog-to-digital converter 152.

[0087] According to the control signals Trig3in and Trig3out, switches SW3in and SW3out can be controlled to hold a sample in capacitor C3, and then provide the sample to be digitized by the analog-to-digital converter 152. In accordance with this process (i.e., according to the indicated transitions of the control signals Trig3in and Trig3out), a signal from the detection unit 140 (e.g., a composite photoelectric signal from the first detector) can be sampled by the third sample-and-hold circuit SH3 and digitized by the analog-to-digital converter 152.

[0088] According to the control signals Trig4in and Trig4out, switches SW4in and SW4out can be controlled to hold a sample on capacitor C4, and then provide the sample to be digitized by the analog-to-digital converter 152. Following this process (i.e., according to the indicated transitions of the control signals Trig4in and Trig4out), the signal from the detection unit 140 (e.g., a composite photoelectric signal from the second detector) can be sampled by the fourth sample-and-hold circuit SH4 and digitized by the analog-to-digital converter 152.

[0089] As described above, the second sample rate SR2 is lower than the first sample rate SR1. In a specific example in Figure 9B, the illustrated period shows 29 cycles of the first and second input control signals Trig1in and Trig2in according to the first sample rate SR1 (for example, 29 instances where the first and second input control signals Trig1in and Trig2in cycle from low to high and then from high to low). According to the second sample rate SR2, 28 cycles of the third and fourth input control signals Trig3in and Trig4in are shown (for example, 28 instances where the third and fourth input control signals Trig3in and Trig4in cycle from low to high and then from high to low). As a specific numerical example, this may result in a ratio of SR2 / SR1 = 28 / 29 = 0.97. Several design considerations for having a relatively small difference between the first and second sample rates are described in more detail below following the explanation of Figure 9B.

[0090] As shown at the bottom of Figure 9B, the sample rate SRADC of the analog-to-digital converter corresponds to the combination of the first, second, third, and fourth output control signals Trig1out, Trig2out, Trig3out, and Trig4out. Note that in the illustrated example, the sample rate of the analog-to-digital converter is approximately four times the first sample rate SR1. The timing of the first, second, third, and fourth output control signals Trig1out, Trig2out, Trig3out, and Trig4out is configured such that the sample rate SRADC of the analog-to-digital converter is preferably sampled at equal intervals (for example, thus reducing the requirements for the analog-to-digital converter). Note that this operation can occur even if the combinations of the first, second, third, and fourth input control signals Trig1in, Trig2in, Trig3in, and Trig4in are not configured similarly. If the current circuit configuration illustrated and described herein does not exist, the intervals between control signal combinations will not be constant and may include extremely short intervals, which may increase the processing load.

[0091] In this embodiment, the desired effect is achieved in part by configuring the third and fourth output control signals Trig3out and Trig4out to contribute to the sample rate SRADC of the analog-to-digital converter at regular intervals, but not to perfectly match the timing of the third and fourth input control signals Trig3in and Trig4in. For example, in contrast to the first and second output control signals Trig1out and Trig2out, which are configured to provide transitions immediately after the transitions of the first and second input control signals Trig1in and Trig2in (for example, the small exemplary arrows shown between Trig2in and Trig2out indicate the sampling and conversion timing relationship), the transition of the third output control signal Trig3out occurs at a different interval after the transition of the third input control signal Trig3in (for example, the small exemplary arrows shown between Trig3in and Trig3out indicate the sampling and conversion timing relationship). Similarly, the transition of the fourth output control signal Trig4out occurs at a different interval after the transition of the fourth input control signal Trig4in (partially indicated, for example, by the small exemplary arrow shown between Trig4in and Trig4out indicating the sample and conversion timing relationship). In some embodiments, as shown in Figure 9B, occasional skips may occur in the analog-to-digital conversion, as indicated by the empty box MK in the transition diagram for combinations of the third or fourth output control signal Trig3out or Trig4out and the corresponding Trigout (i.e., combined Trig1out + Trig2out + Trig3out + Trig4out). In various implementations, this can also be characterized as corresponding to duplicate samples resulting from the Vernier effect between sample rates.

[0092] As described above, the output control signals Trig1out, Trig2out, Trig3out, and Trig4out (corresponding, for example, to providing samples to the analog-to-digital converter 152) are configured to reduce the requirements for the analog-to-digital converter. As can be seen from the figure, the output signals to the analog-to-digital converter 152 (i.e., the sample rate SRADC of the analog-to-digital converter at the bottom of Figure 9B) consist of specific intervals (i.e., specific regular intervals between transitions / samples), thus reducing the requirements for the analog-to-digital converter. This is in contrast to a configuration where there is no sample-and-hold circuit and the analog-to-digital converter must perform data acquisition on its own (for example, if the signal intervals are not regular and some of the acquired signals / timings between sample rates are very close to each other, the operating requirements for the analog-to-digital converter increase significantly). Furthermore, orthogonal processing in various embodiments (using simultaneous input of input control signals Trig1in and Trig2in, and simultaneous input of input control signals Trig3in and Trig4in) is generally not achievable with a single analog-to-digital converter without a sample-and-hold circuit as shown and described herein. It will be understood that a configuration using a single analog-to-digital converter may offer certain advantages compared to using multiple analog-to-digital converters (for example, the potential for reduced cost and / or size of the configuration, and the potential for improved accuracy and avoidance of other differences that may arise from digitizing the signal with a single converter, whereas multiple converters may have slight differences in characteristics that could affect the converted signal differently).

[0093] With respect to the configurations in Figures 7A, 7B, 8A, 8B, 9A, and 9B, in various implementations, relatively small differences between sample rates (e.g., between the first and second sample rates in Figures 7B and 9B, or between the first, second, and third sample rates in Figure 8B, where the difference between sample rates is less than 10%) may be handled according to techniques for achieving a longer absolute range in the measurement (e.g., by having different measurement / measurement scales with slightly different periods / increments). With regard to using analog-to-digital converters to digitize signals associated with such slightly different measurement / sample rates, it will be understood that significant load may be placed on the analog-to-digital converter (e.g., when the circuit described herein is not provided). For example, because of the slight difference in rates, there may be periods in which some of the measured values / samples are very close in time, in which case the converter (such as the analog-to-digital converter) may require extremely high / fast operating characteristics. By using a sample-and-hold section according to the principles described herein, the sample-and-hold circuit can be used for sampling, and the output can be structured to reduce the requirements for the analog-to-digital converter (for example, as shown in the sample rate SRADC of the analog-to-digital converter in Figures 7B, 8B, and 9B, respectively).

[0094] It should be noted that the configurations in Figures 7A, 7B, 8A, 8B, 9A, and 9B offer specific advantages over conventional systems. As a general principle, in some conventional systems, the Nyquist frequency of the analog-to-digital converter used to digitize the composite photoelectric signal typically defines the maximum beat frequency and therefore the maximum measurable range for a given chart. When frequencies above the Nyquist frequency are sampled by the analog-to-digital converter, such frequencies may be detected as lower frequencies due to aliasing. Aliasing occurs because sampling a periodic function at short intervals of two or fewer times per period results in missing periods, which can lead to the appearance of lower frequencies. However, by using multiple measurements (e.g., performed by different sample-and-hold circuits) according to the principles described herein, the correct overall beat frequency can be determined, and correspondingly, accurate distance calculations can be performed.

[0095] Figure 10 is a flowchart showing an exemplary implementation of routine 1000 for operating the measurement system. Block 1010 controls the optical unit of the measurement system to output light. The measurement system includes a branching unit that branches off a portion of the light output from the optical unit as reference light guided along a reference optical path, and branches off at least a portion of the remaining light as measurement light guided along a measurement optical path and reflected back to the workpiece to be measured. Block 1020 receives composite light, which includes the reference light from the reference optical path and the measurement light from the measurement optical path reflected by the workpiece (for example, in the detection unit 140 of the detection / processing unit DPP).

[0096] In block 1030, the synthesized light is converted into a synthesized photoelectric signal (for example, by the detection unit 140). In block 1040, the synthesized photoelectric signal is sampled (for example, at a first sample rate) using a first sample-and-hold circuit (which may be any of the sample-and-hold units SHP', SHP'', or SHP''') and the corresponding first output is provided to the analog-to-digital converter. In block 1050, the synthesized photoelectric signal is sampled (for example, at a second sample rate lower than the first sample rate) using a second sample-and-hold circuit (which may be any of the sample-and-hold units SHP) and the corresponding second output is provided to the analog-to-digital converter.

[0097] In various implementations, the method may further include performing a Fast Fourier Transform to analyze the digitized signal from the analog-to-digital converter and determining at least one peak corresponding to the beat frequency. For example, the processing unit 150 may perform the Fast Fourier Transform. In various implementations, samples from each sample-and-hold unit are digitized as a digitized signal by the analog-to-digital converter, and a Fast Fourier Transform is performed on the digitized signal (i.e., for analysis) to determine at least one peak corresponding to the beat frequency. In various implementations, additional processing may be performed to determine a single peak / beat frequency corresponding to the distance to the workpiece. In various implementations, the method may further include, at least in part, determining the distance to the workpiece based on the determined peak corresponding to the beat frequency (for example, by the processing unit 150 or otherwise).

[0098] Various embodiments of the measurement system are disclosed. The following features may be used individually or in any combination with any of the embodiments of the measurement system.

[0099] For example, the light output by the optical unit may include laser light whose oscillation frequency changes linearly with time. Other features include the fact that the reference light may include laser light whose oscillation frequency changes linearly with time, and the measurement light may include laser light whose oscillation frequency changes linearly with time.

[0100] Further features include the fact that the reference optical path has a reference optical path length, the measurement optical path has a measurement optical path length, and the difference in optical path length between the reference optical path length and the measurement optical path length corresponds to the propagation difference between the reference light and the measurement light and the corresponding propagation delay. The beat frequency corresponds to the propagation delay. The processing unit of the detection and processing unit of the measurement system may be configured to determine the distance to the workpiece based at least partially on a determined peak corresponding to the beat frequency.

[0101] While preferred implementations of the disclosure have been illustrated and described, numerous variations in the illustrated and described configurations and sequences of operation of the features will be apparent to those skilled in the art based on this disclosure. Various alternative configurations may be used to carry out the principles disclosed herein. In addition, the various implementations described above can be combined to provide further implementations.

[0102] In light of the detailed description above, these and other modifications can be made to the implementation. In general, the terms used in the following claims should not be construed as limiting the claims to the specific implementation disclosed herein and in the claims, but rather as encompassing all possible implementations along with the entire range of equivalents to which rights are granted.

Claims

1. The light-emitting part, A branching unit that branches off a portion of the light output from the optical unit as reference light guided along a reference optical path, and branches off at least a portion of the remaining light as measurement light guided along a measurement optical path and reflects it onto the workpiece to be measured, A detection and processing unit configured to receive composite light including reference light from the reference optical path and measurement light from the measurement optical path reflected by the workpiece, and to convert the composite light into a composite photoelectrical signal, Equipped with, The aforementioned detection and processing unit Analog-to-digital converter, A sample-and-hold unit comprising at least a first sample-and-hold circuit and a second sample-and-hold circuit, connected to the analog-to-digital converter to provide an output, Equipped with, Measurement system.

2. The detection and processing unit includes a detection unit configured to detect the synthesized light and output a corresponding synthesized photoelectric signal. The at least two sample-and-hold circuits and the analog-to-digital converter are configured to digitize the composite photoelectric signal and generate a digitized signal. The measurement system according to claim 1.

3. The detection and processing unit further comprises a processing unit configured to perform a fast Fourier transform for analyzing the digitized signal and to determine at least one peak corresponding to the beat frequency. The measurement system according to claim 2.

4. The processing unit is configured to determine the distance to the workpiece based at least partially on a determined peak corresponding to the beat frequency. The measurement system according to claim 3.

5. The first sample-and-hold circuit is configured to operate at a first sample rate. The second sample-and-hold circuit is configured to operate at a second sample rate lower than the first sample rate. The measurement system according to claim 1.

6. The first sample-and-hold circuit comprises a first capacitor, The second sample-and-hold circuit comprises a second capacitor, The measurement system according to claim 1.

7. The first sample-and-hold circuit includes a first input switch connected to the first capacitor, The second sample-and-hold circuit includes a second input switch connected to the second capacitor. The measurement system according to claim 6.

8. The first input switch operates according to the first sample rate, The second input switch operates according to a second sample rate lower than the first sample rate. The measurement system according to claim 7.

9. The first sample-and-hold circuit includes a first output switch connected to the first capacitor, and the first output switch is configured to operate to connect the first capacitor to the analog-to-digital converter. The second sample-and-hold circuit comprises a second output switch connected to the second capacitor, the second output switch being configured to operate in such a way as to connect the second capacitor to the analog-to-digital converter. The measurement system according to claim 7.

10. At least one of the reference optical path and the measurement optical path includes a dispersion section. The imbalance in dispersion between the reference optical path and the measurement optical path arises, at least partially, from the dispersion portion. The measurement system according to claim 1.

11. The sample-and-hold unit further comprises a third sample-and-hold circuit. The measurement system according to claim 1.

12. The first sample-and-hold circuit is configured to operate at a first sample rate. The second sample-and-hold circuit is configured to operate at a second sample rate lower than the first sample rate. The third sample-and-hold circuit is configured to operate at a third sample rate lower than the second sample rate. The measurement system according to claim 11.

13. The sample-and-hold unit further comprises a fourth sample-and-hold circuit. The measurement system according to claim 11.

14. The sample-and-hold unit is configured to operate for orthogonal processing, The first sample-and-hold circuit and the second sample-and-hold circuit are configured to operate at a first sample rate. The third sample-and-hold circuit and the fourth sample-and-hold circuit are configured to operate at a second sample rate lower than the first sample rate. The measurement system according to claim 13.

15. The system further includes a combining unit that receives and combines reference light from the aforementioned reference optical path and measurement light from the aforementioned measurement optical path. The detection and processing unit receives the synthesized light from the synthesis unit. The measurement system according to claim 1.

16. The light output by the optical unit includes laser light whose oscillation frequency changes linearly with time. The measurement system according to claim 1.

17. A method for operating a measurement system, The aforementioned measurement system is The light-emitting part, A branching unit that branches off a portion of the light output from the optical unit as reference light guided along a reference optical path, and branches off at least a portion of the remaining light as measurement light guided along a measurement optical path and reflects it onto the workpiece to be measured, Equipped with, The aforementioned method, Receiving composite light including the reference light from the reference optical path and the measurement light from the measurement optical path reflected by the workpiece, Converting the aforementioned synthesized light into a synthesized photoelectric signal, The first sample-and-hold circuit is used to sample the composite photoelectric signal at a first sample rate and provide the corresponding first output to the analog-to-digital converter. The composite photoelectric signal is sampled at a second sample rate lower than the first sample rate using a second sample-and-hold circuit, and the corresponding second output is provided to the analog-to-digital converter. Equipped with, method.

18. The method further comprises performing a fast Fourier transform to analyze the digitized signal from the analog-to-digital converter and determining at least one peak corresponding to the beat frequency. The method according to claim 17.

19. The method further comprises determining the distance to the workpiece based at least partially on a determined peak corresponding to the beat frequency. The method according to claim 18.

20. It is a measurement system, The light-emitting part, A branching unit that branches off a portion of the light output from the optical unit as reference light guided along a reference optical path, and branches off at least a portion of the remaining light as measurement light guided along a measurement optical path and reflects it onto the workpiece to be measured, A detection and processing unit comprising an analog-to-digital converter, a sample-and-hold unit comprising at least a first sample-and-hold circuit and a second sample-and-hold circuit, and connected to the analog-to-digital converter to provide an output, Equipped with, The aforementioned measurement system is The system receives composite light including the reference light from the reference optical path and the measurement light from the measurement optical path reflected by the workpiece. The aforementioned synthesized light is converted into a synthesized photoelectric signal, Using the first sample-and-hold circuit, the composite photoelectric signal is sampled at a first sample rate, and the corresponding first output is provided to the analog-to-digital converter. Using the second sample-and-hold circuit, the synthesized photoelectric signal is sampled at a second sample rate lower than the first sample rate, and the corresponding second output is provided to the analog-to-digital converter. It is configured in such a way. Measurement system.

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