Dual comb spectroscopy for web thickness measurement

Abstract

The present disclosure provides a method comprising generating, by a dual-frequency comb source, a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate. The method comprises directing one or more of the first optical frequency comb or the second optical frequency comb toward a material using one or more optical elements. The method comprises detecting, using a diode photodetector, optical signals from the first optical frequency comb and the second optical frequency comb after one or more of the first optical frequency comb or the second optical frequency comb interact with the material. The method comprises generating, using the diode photodetector, a radio frequency signal corresponding to the optical signals. The method comprises determining, based on the radio frequency signal, a thickness of the material.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 744,299, filed January 12, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The embodiments of this disclosure relate generally to material thickness measurement techniques, and more particularly, to dual-comb spectroscopy techniques for web thickness measurement. Example embodiments relate to systems, apparatus, and methods for web thickness measurement, such as the measurement of the thickness of flat sheets. Background Technology

[0003] The applicant has recognized the numerous technical challenges associated with material thickness measurement, such as the measurement of the thickness of flat sheets. Through effort, ingenuity, and innovation, the applicant has addressed these material measurement-related problems by developing solutions included in the embodiments of this disclosure, many examples of which are described in detail herein. Summary of the Invention

[0004] Various embodiments of this disclosure relate generally to material thickness measurement techniques, and more particularly to dual-comb spectroscopy techniques for material thickness measurement.

[0005] According to one aspect of this disclosure, a computer-implemented method is provided. In some embodiments, the method includes: generating a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate from a dual-frequency comb source. The method includes: guiding one or more of the first or second optical frequency combs toward a material using one or more optical elements. The method includes: detecting optical signals from the first and second optical frequency combs using a diode photodetector after one or more of the first or second optical frequency combs has interacted with the material. The method includes: generating a radio frequency (RF) signal corresponding to the optical signal using the diode photodetector. The method includes: determining the thickness of the material based on the RF signal.

[0006] According to other aspects of this disclosure, the computer-implemented method may include one or more of the following features: Determining the thickness of the material may include: extracting spectral information from an RF signal, wherein the spectral information includes one or more of an interference fringe pattern or absorption features, and determining the thickness based on the spectral information. Guiding one or more of a first optical frequency comb or a second optical frequency comb toward the material may include: allowing both the first optical frequency comb and the second optical frequency comb to propagate through the material. Guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material may include: combining the first optical frequency comb and the second optical frequency comb, and guiding the combined optical frequency comb toward the material. In some embodiments, the dual frequency comb source may be positioned on a first side relative to the material, and the diode photodetector may be positioned on a second side relative to the material. In some embodiments, both the dual frequency comb source and the diode photodetector may be positioned on the first side relative to the material. In some embodiments, one or more of the first optical frequency comb or the second optical frequency comb may operate in a wavelength range of 1 micrometer to 2 micrometers. One or more of the first optical frequency comb or the second optical frequency comb may operate in a wavelength range of 2 micrometers to 9 micrometers. In some embodiments, the dual-frequency comb source may be an optical fiber-based source. In some embodiments, the dual-frequency comb source may be a photonic chip-based source. A photonic chip-based source may include one or more silicon nitride waveguides. The first and second optical frequency combs may be generated by a dual-frequency comb spectrometer including the dual-frequency comb source. Determining the thickness may include applying an algorithm configured to select either an interferometric or absorption-based measurement. In response to indicating the selection of an interferometric measurement, an example method may include applying one or more interferometric algorithms to an RF signal, wherein the one or more interferometric algorithms are configured to identify interference fringes reflected within the RF signal, and analyzing the interference fringes to determine the thickness of the material. In response to indicating the selection of an absorption-based measurement, the method may include applying one or more absorption algorithms to an RF signal, wherein the one or more absorption algorithms are configured to identify absorption features from the RF signal, and analyzing the absorption features to determine the thickness of the material.

[0007] According to another aspect of this disclosure, a system is provided. The system includes an apparatus configured to generate a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate. The system includes one or more optical components configured to guide one or more of the first or second optical frequency comb toward a material. The system includes a diode photodetector configured to detect optical signals from the first and second optical frequency combs after one or more of the first or second optical frequency combs interact with the material, and to generate an RF signal corresponding to the optical signals. The system includes a signal processor configured to determine the thickness of the material based on the RF signal.

[0008] According to other aspects of this disclosure, the system may include one or more of the following features. Determining the thickness of the material may include: extracting spectral information from an RF signal, wherein the spectral information includes one or more of an interference fringe pattern or absorption features, and determining the thickness based on the spectral information. Guiding one or more of a first optical frequency comb or a second optical frequency comb toward the material may include: allowing both the first optical frequency comb and the second optical frequency comb to propagate through the material. Guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material may include: combining the first optical frequency comb and the second optical frequency comb, and guiding the combined optical frequency comb toward the material. The dual frequency comb source may be positioned on a first side relative to the material, and the diode photodetector may be positioned on a second side relative to the material.

[0009] The above description of the invention is provided merely to outline some exemplary embodiments in order to provide a basic understanding of some aspects of this disclosure. Therefore, it should be understood that the above embodiments are merely illustrative and should not be construed as limiting the scope or substance of this disclosure in any way. It should be understood that, in addition to those outlined herein, the scope of this disclosure covers many possible embodiments, some of which will be further described below. Attached Figure Description

[0010] The description of the exemplary embodiments can be read in conjunction with the accompanying drawings. It should be understood that, for simplicity and clarity of illustration, the elements illustrated in the figures are not necessarily drawn to scale unless otherwise described. For example, unless otherwise described, the dimensions of some elements may be exaggerated relative to others. Embodiments incorporating the teachings of this disclosure are shown and described with reference to the accompanying drawings, in which:

[0011] Figure 1A An example scanner for measuring material thickness using a dual-frequency comb, in combination with at least some example embodiments of the present disclosure, is illustrated.

[0012] Figure 1B An example dual-frequency comb measurement system according to at least some example embodiments of the present disclosure is illustrated.

[0013] Figures 2A to 2B Frequency domain examples of at least some example embodiments according to this disclosure are illustrated.

[0014] Figures 3A to 3C The double-comb interference fringes are illustrated according to at least some example embodiments of the present disclosure.

[0015] Figure 3D Example absorption spectra and features are illustrated according to at least some example embodiments of this disclosure.

[0016] Figure 4 Block diagrams of example apparatuses according to at least some example embodiments of the present disclosure are illustrated.

[0017] Figure 5 Example procedures for measuring material thickness using dual-frequency comb spectroscopy are illustrated according to at least some example embodiments of the present disclosure. Detailed Implementation

[0018] Some embodiments of this disclosure will be described more fully below with reference to the accompanying drawings, which illustrate some, but not all, embodiments of this disclosure. In fact, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will meet applicable legal requirements. Similar reference numerals always refer to similar elements.

[0019] As used herein, terms such as “front,” “rear,” “top,” “bottom,” “left,” “right,” etc., in the examples provided below, are used for illustrative purposes to describe the relative positions of certain components or portions of components. Furthermore, as will be apparent to those skilled in the art based on this disclosure, the terms “substantially” and “approximately” indicate that the referenced element or associated description is accurate within applicable engineering tolerances.

[0020] As used herein, the term “comprising” means including but not limited to, and should be interpreted in the manner in which it is typically used in the patent context. The use of broader terms such as “comprising,” “including,” and “having” should be understood to provide support for narrower terms such as “consisting of,” “substantially composed of,” and “substantially constituted by.”

[0021] The phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally mean that the specific feature, structure, or characteristic following the phrase may be included in at least one embodiment of this disclosure, and may be included in more than one embodiment of this disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

[0022] The phrases “in one example,” “according to one example,” “in some examples,” etc. generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one example of this disclosure, and may be included in more than one example of this disclosure (importantly, such phrases do not necessarily refer to the same example).

[0023] If the specification states that a component or feature “may,” “can,” “should,” “will,” “preferably,” “possibly,” “usually,” “optionally,” “for example,” “as an example,” “in some examples,” “often,” or “may” (or other such language) be included or have that feature, then the specific component or feature is not required to be included or have that feature. Such a component or feature may be optionally included in some examples or excluded.

[0024] The terms “example” or “exemplary” as used herein mean “used as an example, instance, or illustration.” Any specific implementation described herein as an “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other specific implementations.

[0025] The terms “electrical connection,” “electrical coupling,” “communication with,” “electronic communication with,” or “connection” in this disclosure mean two or more elements or components connected by wired and / or wireless means, such that signals, voltages / currents, data, and / or information can be sent to and / or received from these elements or components.

[0026] The term "component" can refer to an article of writing, device, or apparatus that may include one or more surfaces, portions, layers, and / or elements. For example, an example component may include one or more substrates that may provide one or more underlying layers for the component, and may include one or more elements that may form a portion on top of the substrate and / or one or more elements that may be disposed on top of the substrate. The term "element" can refer to an article of writing, device, or apparatus that may provide one or more functions.

[0027] The terms “computing entity,” “device,” “system,” and / or similar terms used interchangeably herein can refer to, for example, one or more computers, computing entities, desktop computers, mobile phones, tablets, phablets, laptops, distributed systems, products / devices, terminals, servers or server networks, blade servers, gateways, switches, processing devices, processing entities, set-top boxes, repeaters, routers, network access points, base stations, etc., and / or any combination of devices or entities suitable for performing the functions, operations, and / or processes described herein. Such functions, operations, and / or processes can include, for example, sending, receiving, operating, processing, displaying, storing, determining, creating / generating, monitoring, evaluating, comparing, and / or similar terms used interchangeably herein. In one embodiment, these functions, operations, and / or processes can be performed on data, content, information, and / or similar terms used interchangeably herein. In this regard, apparatus 400 embodies a specific computing entity specially configured to implement the specific operations described herein and provide the associated specific advantages, as described herein.

[0028] The term "circuit" refers only to a hardware circuit implementation (e.g., an implementation in analog and / or digital circuitry); a combination of a circuit and one or more computer program products, the computer program products including software and / or firmware instructions stored on one or more computer-readable storage devices that work together to enable a device to perform one or more functions described herein; or an integrated circuit, such as a processor, multiple processors, a portion of a single processor, a multi-core processor, which requires software or firmware to operate, even if the software or firmware is not physically present. This definition of "circuit" applies to all uses of the term herein (including in any claims). Additionally, the term "circuit" may refer to a specially designed circuit attached to one or more circuit boards, such as a baseband integrated circuit, a cellular network device or other connectivity device (e.g., a Wi-Fi card, Bluetooth circuitry, etc.), a sound card, a video card, a motherboard, and / or other computing devices. In particular, the term "circuit" should be broadly understood to include hardware, and in some embodiments, includes software for configuring the hardware. For example, in some embodiments, "circuit" includes processing circuitry, storage media, network interfaces, input / output devices, etc.

[0029] Overview

[0030] The various embodiments disclosed herein address the technical challenges associated with material measurement, including flat sheet thickness measurement. Conventional measurement techniques typically require costly components and technologies, posing a significant cost barrier to widespread industrial implementation. Additionally, conventional measurement systems often lack the accuracy and speed required for real-time monitoring of moving materials during the manufacturing process, where measurement times are too slow for continuous production line monitoring. Furthermore, existing measurement systems typically require complex optical configurations and lack the portability and integration capabilities needed for a wide variety of industrial applications.

[0031] Various implementations address these technical challenges by providing systems, apparatus, and methods for measuring the thickness of flat sheets or other materials using interferometric and absorption spectra using dual-frequency comb (DFCS) technology. In various implementations, the dual-frequency comb is generated in the range of approximately 1 micrometer to 9 micrometers. 1 micrometer to 2 micrometers can be generated using a basic system, while 2 micrometers to 9 micrometers can be generated by extending the wavelength range using nonlinear wavelength conversion. In various implementations, the dual-frequency comb is generated in the range of approximately 2 micrometers to 4 micrometers. In various implementations, the dual-frequency comb is generated in the range of approximately 3 micrometers to 6 micrometers. In various implementations, the dual-frequency comb is generated in the range of approximately 4.5 micrometers to 9 micrometers. The frequency comb may comprise a beam formed by multiple synchronized, discrete, and narrow wavelengths. In some implementations, one frequency comb passes through the material to be measured (e.g., the flat sheet to be measured). The frequency comb may interact with the material in a reflective or transmissive manner. In some implementations, the frequency comb / beam is collected and mixed with light from another synchronized comb. The frequency of the other comb may be slightly different. When these combs / two beams are mixed, an RF signal is generated, and the RF signal can be measured at different frequencies. In some implementations, RF signals can be measured using diodes at different frequencies.

[0032] Some implementations provide a flat sheet measurement technique that includes directing a first optical frequency comb beam of a dual-frequency comb to the sheet and interfering the first optical frequency comb beam with a second optical frequency comb having a wavelength repetition rate offset. Example implementations measure RF generated using a radio frequency (RF) diode and calculate or otherwise determine the thickness of the flat sheet based on the RF. For example, some implementations evaluate the RF signal to determine an interference spectrum and / or an absorption spectrum, and calculate or otherwise determine the sheet thickness based on the interference determination. In this respect, some implementations calculate or otherwise determine the thickness of the sheet (or other material) based on interference fringes. Some implementations utilize specially configured algorithms to determine whether interference or absorption should be used to measure the sheet.

[0033] Some implementations calculate or otherwise determine the thickness of the sheet (or other material) based on absorption. Some implementations guide the two combs of a dual-frequency comb substantially simultaneously through the sheet. In some implementations, the sheet is positioned between the dual-frequency comb source and the detector. In such implementations, a first side of the sheet may face the dual-frequency comb source, and a second side of the sheet may face the detector. In some implementations, the detector and the dual-frequency comb source are positioned on the same side of the sheet. In some implementations, the comb source is based on an optical fiber. In some implementations, the comb source is a photonic chip. In some implementations, the sheet to be measured is a moving sheet. In some implementations, the sheet is a sheet moving in the longitudinal direction (MD), and the scanner is in the transverse direction (CD). In some implementations, multiple thin layers can be detected.

[0034] The exemplary embodiments of this disclosure offer several technical advantages. The dual-frequency comb approach provides broad spectral coverage across hundreds of nanometers or larger, enabling the simultaneous measurement of multiple material properties, including thickness, composition, and moisture content, using a single measurement system. This comprehensive characterization capability reduces or eliminates the need for multiple separate measurement instruments and provides a more complete material analysis. Some exemplary embodiments achieve high measurement speeds (e.g., compared to existing web / sheet thickness measurement systems), enabling real-time monitoring of moving web material (flat sheets, etc.) during the manufacturing process without interrupting production. Some exemplary embodiments utilize photoelectric detection instead of complex imaging optics, reducing system cost and complexity while maintaining high measurement accuracy. The dual-frequency comb technology provides high spectral resolution and high sensitivity to material absorption characteristics in both the near-infrared and infrared wavelength ranges, enabling precise detection of thickness variations and changes in material properties. Some embodiments include automatic selection between interferometric and absorption-based measurement techniques, thus optimizing measurement accuracy for different material types and thickness ranges without manual intervention. Compared to conventional measurement systems, implementations based on compact photonic chips offer the potential for significant reductions in size, weight, power consumption, and manufacturing costs, enabling portable and cost-effective deployment in a variety of industrial applications. These technological advantages collectively contribute to improved material thickness measurement technologies, devices, and systems that provide comprehensive, rapid, and cost-effective material characterization capabilities for web / sheet manufacturing applications.

[0035] Example systems disclosed herein

[0036] Figure 1A Scanner 101 is illustrated according to at least some example embodiments of the present disclosure. Figure 1BA dual-frequency comb measurement system 100 according to at least some example embodiments of the present disclosure is illustrated. In some embodiments, the dual-frequency comb measurement system 100 (or a portion thereof) is combined with and / or embodied by a device such as scanner 101. It should be understood that Figure 1A The configuration of scanner 101 depicted is not intended to be limiting. In some embodiments, scanner 101 may include other configurations. For example, scanner 101 may exclude... Figure 1A One or more of the components described and / or may include Figure 1A One or more other components not described in the text.

[0037] The dual-frequency comb measurement system 100 can be configured to provide measurement capabilities that enable comprehensive characterization of materials, including web thickness measurement during the manufacturing process. The web may include continuous material sheets, including but not limited to plastic films, polymer sheets, paper, textiles, or other flat sheet products. The manufacturing process may include industrial production operations involved in producing the web material through continuous or batch methods. The manufacturing process may include shaping, handling, and disposing of the web material as it moves through production equipment. The manufacturing process may involve multiple stages, such as material preparation, web formation, coating, drying, cooling, and / or winding operations. During the manufacturing process, material properties such as thickness, composition, and moisture content can be monitored and controlled in real time via devices such as scanner 101 (e.g., its dual-frequency comb measurement system 100) to maintain product quality specifications and optimize production efficiency.

[0038] The dual-frequency comb measurement system 100 can be configured to scan across the material laterally as the material moves longitudinally, thereby providing a spatial mapping of material properties across the entire width of the material. This lateral scanning capability enables the detection of thickness variations, compositional changes, and other material property variations that occur across the width of the material during manufacturing.

[0039] Lateral scanning can be achieved through a mechanical positioning system that moves one or more optical components across the width of the material as it continues to move longitudinally. The scanning system (such as scanner 101 embodying the dual-frequency comb measurement system 100) may include a motorized translation stage, rotating mirror system, or other beam-directing mechanism that guides a frequency comb beam (e.g., an optical frequency comb) across the width of the material to different locations, as further described herein. The scanning rate can be coordinated with the material velocity to ensure sufficient measurement coverage and spatial resolution across the material surface.

[0040] The longitudinal movement of the material can be accommodated by the ability to continuously measure material properties as it passes through the measurement zone. The dual-frequency comb measurement system 100 provides a rapid measurement speed for multiple measurements per unit length of material, thereby generating a two-dimensional mapping of material properties across both the longitudinal and transverse dimensions. The combination of transverse scanning and longitudinal web movement enables comprehensive quality monitoring of the material surface.

[0041] Scanning configurations provide enhanced process control for materials manufacturing applications. Lateral thickness variations can indicate problems with manufacturing equipment, such as die lip adjustment, temperature variations, or material flow irregularities. Thickness measurements can provide feedback to automated process control systems that adjust manufacturing parameters to maintain uniform material properties across the material width. Spatial resolution of thickness measurements can be optimized to detect localized defects or variations while maintaining sufficient measurement speed for continuous monitoring.

[0042] In this regard, in some embodiments, the dual-frequency comb measurement system 100 (or a portion thereof) may be embodied by a device such as a scanner 101, wherein material moves between scanner heads (described further below) in the scanner direction, the scanner heads moving synchronously in the lateral direction. The scanner 101 (e.g., via its dual-frequency comb measurement system 100) may be configured to generate a thickness map of the material during material production.

[0043] In some embodiments, scanner 101 includes, or otherwise represents, a measuring device (or apparatus) configured to perform thickness measurements (e.g., continuous or periodic thickness measurements) on a moving material (e.g., material 110) during the manufacture (e.g., production) of the material. In some embodiments, material 110 comprises a flat sheet, such as a plastic film, polymer sheet, paper, textile, or other flat sheet product, as described above. In some embodiments, scanner 101 may be configured to perform thickness measurements (e.g., continuous or periodic thickness measurements of material 110) across the entire width of the moving material 110. Scanner 101 may include one or more scanner heads 98 that repeatedly move back and forth in a transverse (CD) direction perpendicular to the longitudinal (MD) direction of the moving material 110, thereby enabling the measurement of the entire width of material 110 or at least substantially the entire width of material 110.

[0044] The lateral direction may include a direction perpendicular to the longitudinal direction of the moving material 110. The lateral direction may represent the width dimension of the material 110, wherein thickness measurement can be performed by moving one or more scanner heads 98 back and forth across the lateral direction to obtain a thickness measurement across the entire width of the material (or at least across substantially the entire width of the material). The longitudinal direction may include, for example, the primary direction of movement of the material 110 through the scanner during manufacturing. The longitudinal direction may correspond to the length dimension of the material as it moves through the scanner 101 or during the manufacturing process.

[0045] Scanner 101 may incorporate dual-frequency comb spectral components, such as an optical frequency comb source, a diode photodetector, optical elements, and / or signal processing elements (e.g., signal processing electronics), for performing interferometric measurements and / or absorption-based thickness measurements. In some embodiments, the dual-frequency comb measurement system 100 (or a portion thereof) is incorporated into one or more scanner heads 98. In this regard, in some embodiments, one or more scanner heads 98 may accommodate one or more measurement components including one or more dual-frequency comb spectral components and may be configured to move across the width of material 110 (or at least substantially across the width of the material). In some embodiments, one or more scanner heads 98 may include a frequency comb source, a diode photodetector, optical elements for beamforming and guiding, and / or signal processing elements.

[0046] In some embodiments, one or more scanner heads 98 include a plurality of scanner heads. In such embodiments, one or more scanner heads 98 may include a first scanner head 88 and a second scanner head 86 employed in a synchronous manner, wherein the first scanner head 88 and the second scanner head 86 are positioned on opposite sides of the material 110 to define a measurement gap through which the material 110 passes. In some embodiments, the first scanner head 88 may represent an upper scanner head, and the second scanner head 86 may represent a lower scanner head. In some embodiments, one or more scanner heads 98 may be supported by two crossbeams (e.g., a first crossbeam 92 and a second crossbeam 94), on which the first scanner head 88 and the second scanner head 86 are mounted.

[0047] One or more scanner heads 98 may have operating surfaces that define a measurement gap for receiving the material 110 to be measured. In some embodiments, the dual-frequency comb measurement system 100 (or a portion thereof) may be incorporated into a first scanner head 88. The first scanner head 88 may be configured to repeatedly move back and forth in the transverse direction across the width of the longitudinally moving material 110, such that the thickness of the entire material (or substantially the entire material) can be measured. In some embodiments, one or more components of the dual-frequency comb measurement system 100 (e.g., a dual-frequency comb source, such as a dual-frequency comb spectrometer or other components) may be received within the first scanner head 88. Alternatively or additionally, in some embodiments, one or more components of the dual-frequency comb measurement system 100 (e.g., a dual-frequency comb source, such as a dual-frequency comb spectrometer or other components) may be received within a second scanner head 86. In some embodiments, one or more components of the dual-frequency comb measurement system 100 may be positioned in the first scanner head 88, and one or more other components of the dual-frequency comb measurement system 100 may be positioned in the second scanner head 86. The movement of the first scanner head 88 and the second scanner head 86 is synchronized in terms of speed and direction, so that they are aligned with each other.

[0048] The dual-frequency comb measurement system 100 enables dual-frequency comb spectroscopy (DFCS) to provide a method for measuring the thickness and / or other properties of material 110. The dual-frequency comb measurement system 100 utilizes two optical frequency combs with slightly different repetition rates to generate spectral information about material 110. Thickness measurements using the DFCS approach can be based on interference fringes present in the RF signal, which, as further described herein, are generated due to optical interference effects within the material. Alternatively or additionally, thickness measurements using the DFCS approach can be based on absorption features in the RF signal corresponding to specific material absorption characteristics. In some embodiments, the dual-frequency comb measurement system 100 can be configured to analyze both types of spectral information to provide a comprehensive material characterization including thickness, composition, and / or other material properties.

[0049] DFCS technology facilitates and / or enables accurate thickness measurements of various types of materials, including plastic films, paper, and other web-based products. The DFCS approach offers several advantages over conventional measurement techniques. It provides broad spectral coverage across hundreds of nanometers or larger, enabling the simultaneous measurement of multiple material properties. High measurement speeds are achievable, with measurement times less than one millisecond. The DFCS approach utilizes photoelectric detection instead of complex imaging optics, reducing system cost and complexity. Additionally, the DFCS approach provides high spectral resolution and sensitivity to material absorption characteristics in both the near-infrared and infrared wavelength ranges.

[0050] In some embodiments, the dual-frequency comb measurement system 100 can operate by generating a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate. Each optical frequency comb may include a series of discrete, regularly spaced optical frequencies spanning a wide wavelength range. For example, in some embodiments, each optical frequency comb may include a beam formed by a plurality of synchronized, discrete, and narrow wavelengths. For example, each optical frequency comb may include directional electromagnetic radiation (e.g., light) that maintains spatial coherence and defined propagation characteristics as it travels from a source (e.g., a dual-frequency comb source) to a target or across an optical path.

[0051] The difference between the first and second repetition rates can be in the radio frequency range, such as kilohertz, which allows for the generation of a detectable electronic signal. When light from one or both optical frequency combs interacts with material 110, the transmitted or reflected light carries information about the material's properties. A diode photodetector can detect the optical signals from the two frequency combs after interaction with the web material and generate an RF signal. The RF signal contains spectral information that can be analyzed to determine the thickness of the web material.

[0052] The generation of dual optical frequency combs can be achieved through various techniques for producing two synchronous frequency combs with different repetition rates. In some implementations, a mode-locked laser system (or other laser systems, such as fiber-based laser configurations or photonic chip implementations) can be used to generate a first optical frequency comb with a first repetition rate. Similar techniques can be used to generate a second optical frequency comb with a second repetition rate different from the first repetition rate, wherein the second repetition rate is offset from the first repetition rate by a controlled amount.

[0053] The timing characteristics of the dual-frequency comb measurement system 100 can be configured to provide rapid spectral measurements. In some embodiments, the dual-frequency comb measurement system 100 can operate using pulses emitted approximately every 7 nanoseconds (e.g., short-duration bursts of electromagnetic radiation / light), where each pulse includes a frequency comb with discrete optical frequencies. In some embodiments, for fiber-optic frequency comb sources, the pulse timing can correspond to a repetition rate in the range of approximately 100 MHz. The repetition rate difference between the two optical frequency combs can be approximately in the kilohertz range, thereby producing a measurable offset between the two optical frequency combs. For example, a kilohertz-range repetition rate difference allows the dual-frequency comb measurement system 100 to sweep across a variety of wavelengths (e.g., substantially all wavelengths) within approximately 3 milliseconds. Rapid wavelength sweeping can occur or otherwise be achieved by gradually traversing different relative timing positions of the pulses from the two optical frequency combs based on the slight difference in repetition rate. As the pulses from the two optical frequency combs overlap and separate in time, an optical mixing process samples different portions of the spectral content, thereby effectively producing a time-domain representation of the optical spectrum that can be detected as an RF signal.

[0054] The spectral characteristics of an optical frequency comb can be configured to optimize measurement performance. In some examples, the dual-frequency comb measurement system 100 can be configured to provide a relatively wide spacing between spectral lines in exchange for improved averaging processing and response time. Wider spectral line spacing reduces the total number of spectral elements that need to be processed, allowing for faster signal processing and improved signal-to-noise ratio through enhanced averaging. This configuration flexibility allows the dual-frequency comb measurement system 100 to be optimized for different measurement requirements, thus balancing spectral resolution with measurement speed and sensitivity.

[0055] In some embodiments, a first optical frequency comb and a second optical frequency comb with different repetition rates can be provided in the wavelength range of 1 micrometer to 9 micrometers to enable the measurement of various material properties. In some embodiments, the wavelength range of 1 micrometer to 2 micrometers can be generated using an optical fiber-based frequency comb source, while the extended wavelength range of 2 micrometers to 9 micrometers can be achieved using nonlinear wavelength conversion techniques. This broad wavelength coverage allows the dual-frequency comb measurement system 100 to probe different absorption characteristics of the material 110, thereby providing comprehensive spectral information for thickness and composition analysis. In some embodiments, a first optical frequency comb and a second optical frequency comb with different repetition rates can be provided in the wavelength range of 2 micrometers to 4 micrometers. In some embodiments, a first optical frequency comb and a second optical frequency comb with different repetition rates can be provided in the wavelength range of 3 micrometers to 6 micrometers. In some embodiments, a first optical frequency comb and a second optical frequency comb with different repetition rates can be provided in the wavelength range of 4.5 micrometers to 9 micrometers.

[0056] In some embodiments, the dual-frequency comb measurement system 100 includes a dual-frequency comb source 104 configured to generate dual-frequency combs (e.g., two optical frequency combs including a first optical frequency comb and a second optical frequency comb). The dual-frequency comb source 104 may be embodied in or be embodied as a dual-frequency comb spectrometer configured to generate a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate. For example, a dual-frequency comb spectrometer may include the dual-frequency comb source 104. The dual-frequency comb spectrometer or its dual-frequency comb source 104 may utilize different technical approaches to achieve the generation of a pair of synchronized optical frequency combs with a controlled repetition rate difference.

[0057] In some embodiments, the dual-frequency comb spectrometer or dual-frequency comb source 104 includes two pulsed lasers that generate a pair of optical frequency combs having a controlled repetition rate difference. In some embodiments, the pair of optical frequency combs can be characterized in their spectral content by a large set of regularly spaced frequencies and in the time domain by short pulses. The comb tooth frequencies of the optical frequency combs can be derived from the reciprocal of the round-trip time of the laser cavity (f...). rep Separate. For example, longer cavities in fiber-optic systems can provide spacing at the 100MHz level. Smaller combs can generate higher frequency spacing of tens to hundreds of GHz. Lower f rep It can provide a denser spectrum and higher spectral resolution.

[0058] As noted above, the pair of optical frequency combs may have different repetition rates. In some examples, the repetition rate difference (Dfrep) can be in the radio frequency (RF) range, such as kHz, and when combined at the photodiode, it can result in a beat-frequency comb at the RF frequency. When light from one or both combs propagates through material 110, the resulting electronic signal can show an RF spectrum, which reveals (e.g., through signal processing) data / information that can be used to determine the thickness of material 110. For example, one or more of a pair of optical frequency combs with different pulse repetition rates can be directed toward material 110 and propagate a distance within material 110. Photodetection and data / signal processing of the propagating light can be performed to convert the optical absorption into an RF signal, which can be used to determine the thickness of material 110. As a non-limiting example, the repetition rate can be about 80 MHz, and the time between pulses can be between about 12.5 ns.

[0059] In this regard, in some implementations, the dual-frequency comb source 104 is configured to emit pulses at intervals, each pulse including a frequency comb. For example, in some exemplary implementations, the dual-frequency comb source 104 (e.g., its two pulsed lasers) may be configured to emit pulses at intervals of about 7 ns (or other intervals), wherein each pulse includes a frequency comb, and the generated pulses sweep across the full wavelength in about 3 microseconds (µs) at least in part based on the repetition rate difference.

[0060] An optical frequency comb structure can be characterized by its spectral properties, wherein each individual frequency component of the optical frequency comb (e.g., tooth, comb tooth, or similar term) is precisely defined and stable. In some embodiments, the frequency spacing between adjacent comb teeth corresponds to the repetition rate of the pulsed laser source, which can be expressed as... ,in This represents the time interval between consecutive pulses. For the example implementation above with a 7ns interval, this corresponds to a repetition rate of approximately 143MHz. In some implementations, the optical frequency of each comb tooth can be expressed as... , where n is an integer representing the number of teeth, and This indicates the carrier envelope offset frequency.

[0061] In some implementations, the dual-frequency comb configuration utilizes slightly different repetition rates, such as and Two frequency combs, where the difference For example, this can be in the range of Hz to kHz. The repetition rate difference allows for the time mapping of the optical spectrum to the radio frequency domain via heterodyne detection processes or other techniques. In some implementations, the time required for two pulse trains to sweep across all relative time positions (e.g., corresponding to full wavelength coverage) can be calculated as... For the 3-microsecond sweep time in Example 3 above, this would correspond to a repetition rate difference of approximately 333 kHz.

[0062] In some implementations, the coherence of the optical frequency comb is maintained throughout the measurement process, thereby achieving a precise phase relationship between different spectral components. The coherence length of each comb tooth can be determined by the linewidth of the respective frequency component, which may depend on the stability and noise characteristics of the laser source (e.g., the optical frequency comb source). In some implementations, the coherence length is sufficient to maintain phase coherence over the optical path length encountered in material thickness measurement applications, thereby enabling interferometric measurements based on the phase relationship between different spectral components.

[0063] In some implementations, the bandwidth of the optical frequency comb can span multiple octaves, thereby providing broad spectral coverage for simultaneous measurements of multiple material properties. In some examples, the spectral bandwidth may depend on the gain bandwidth of the laser medium, the dispersion characteristics of the optical cavity, and / or nonlinear optical processes that contribute to spectral broadening. In some implementations, the optical frequency comb may be spectrally shaped or filtered to optimize measurements for specific material absorption characteristics or to avoid spectral regions with strong gas absorption that may interfere with measurements.

[0064] As described above, in some embodiments, different technical approaches can be used to implement a dual-frequency comb spectrometer (or its dual-frequency comb source 104). In some embodiments, the dual-frequency comb source 104 includes a fiber-based dual-frequency comb source (fiber-based source). In this regard, in some embodiments, a fiber-based source can be used to generate a first optical frequency comb and a second optical frequency comb. The fiber-based frequency comb source can utilize a mode-locked fiber laser architecture that provides stable and reliable frequency comb generation. In some examples, the fiber-based source may include an erbium-doped fiber laser system that generates frequency combs spanning octaves in the near-infrared wavelength range. Fiber-based implementations can offer advantages in terms of stability, robustness, reliability for harsh manufacturing environments, and mature manufacturing processes. Fiber-based configurations provide stable operation and a mature technology platform suitable for industrial applications. In some examples, the fiber-based source can operate at a repetition rate in the approximately 100 MHz range, which corresponds to the round-trip time of the laser cavity of the fiber-based laser. The fiber-based frequency comb source can provide dense spectral content with closely spaced frequency lines, thereby enabling high spectral resolution measurements.

[0065] In some embodiments, the dual-frequency comb spectrometer may include a photonic chip. In some embodiments, the dual-frequency comb source 104 may be embodied as a photonic chip-based dual-frequency comb source. Compared to some other sources, the photonic chip implementation offers advantages in size, weight, power consumption, and manufacturing cost. The photonic chip can integrate optical components on a single substrate, thereby enabling a compact and portable optical frequency comb generation system or configuration. In some embodiments, the photonic chip may include a silicon nitride waveguide. For example, in some embodiments, the photonic chip may utilize a silicon nitride (SiN) waveguide resonator to generate dual optical frequency combs. Silicon nitride waveguide technology provides a fabricatable platform for generating wide optical frequency combs through nonlinear optical processes. The silicon nitride platform offers compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication processes, thereby enabling the potential for large-scale production and cost reduction. Silicon nitride materials offer favorable dispersive and nonlinear properties, which, for example, enable efficient optical frequency comb generation when combined with high-quality factor resonator structures. In some implementations, the photonic chip may include a high-Q resonator that enables low-threshold broadband comb generation.

[0066] In some examples, photonic chips incorporating silicon nitride waveguides can generate frequency combs via a four-wave mixing process within a microresonator structure. The silicon nitride waveguide can be configured as a ring resonator or other cavity geometries supporting multiple optical modes. When optical power is coupled into the resonator structure, the nonlinearity of the silicon nitride material can combine with its dispersive properties to generate light across a wide range of cavity modes, thus producing an optical frequency comb structure. Photonic chip implementations offer higher repetition rates compared to some other sources. Higher repetition rates enable faster measurement speeds. The chip-scale approach offers the possibility of low-cost, high-volume manufacturing using semiconductor fabrication processes compatible with CMOS technology.

[0067] The dual-frequency comb measurement system 100 can be configured to operate across multiple wavelength ranges to probe the absorption characteristics of different materials and optimize measurement performance for various materials. The selection of wavelength ranges can depend on the specific material properties of the material 110 being measured and the absorption characteristics of interest used for thickness determination. For example, a dual-frequency comb spectrometer (or its dual-frequency comb source 104) can be configured to operate across different spectral regions according to specific measurement requirements.

[0068] In some embodiments, the first and second optical frequency combs can operate in a wavelength range of 1 to 2 micrometers. This 1- to 2-micrometer wavelength range corresponds to the near-infrared spectral region. In this regard, for measurements in the near-infrared region, the dual-frequency comb source 104 can be configured to generate optical frequency combs in a wavelength range of approximately 1 to 2 micrometers. The 1- to 2-micrometer wavelength range provides the detection of overtones and combined absorption bands of various molecular species present in material 110. This 1- to 2-micrometer wavelength range is particularly suitable for measuring organic polymer films and other materials exhibiting absorption characteristics in the near-infrared region.

[0069] In some implementations, the first and second optical frequency combs can operate in a wavelength range of 2 to 9 micrometers. This 2- to 9-micrometer band covers the mid-infrared spectral region, where many materials exhibit strong intrinsic absorption bands. This wavelength range allows for the detection of characteristic molecular fingerprint regions, enabling precise material identification and compositional analysis in addition to thickness measurement. The 2- to 9-micrometer wavelength range can be achieved using nonlinear wavelength conversion techniques applied to base frequency comb systems operating in the 1- to 2-micrometer range. For example, through nonlinear wavelength conversion techniques, the 1- to 2-micrometer wavelength range can be extended to approximately 2 to 9 micrometers. This wavelength extension provides enhanced sensitivity for thickness measurements based on absorption spectroscopy.

[0070] Nonlinear wavelength conversion can extend the spectral coverage of an optical frequency comb by utilizing optical processes such as difference frequency generation, optical parameter amplification, or other nonlinear optical phenomena. The nonlinear wavelength conversion process can acquire the output from a 1-micron to 2-micron frequency comb source and generate a corresponding frequency comb structure at longer wavelengths in the 2-micron to 9-micron range. This approach allows a dual-frequency-comb measurement system 100 to probe the mid-infrared spectral region while utilizing near-infrared frequency comb technology. The nonlinear wavelength conversion approach can utilize nonlinear optical crystals or waveguide structures that facilitate efficient frequency conversion processes. Conversion efficiency and spectral characteristics can be optimized through careful selection of nonlinear materials, phase-matching conditions, and optical power levels. Nonlinear wavelength conversion can convert the spectral content to longer wavelengths while preserving the original 1-micron to 2-micron source's optical frequency comb structure and timing characteristics.

[0071] In this regard, in some embodiments, a dual-frequency comb spectrometer or dual-frequency comb source 104 can be configured to emit a light beam (e.g., a dual optical frequency comb) in the region of interest. In some embodiments, the region of interest is 1 micrometer to 9 micrometers. In some embodiments, a frequency comb in the range of 1 to 2 micrometers is generated using a fundamental frequency comb system, and a nonlinear wavelength conversion (as discussed above) is applied to extend the wavelength range from 1 to 2 micrometers to 1 to 9 micrometers. In some embodiments, the selection of the spectral region of interest can be determined based on the specific material properties and measurement requirements of the application. For example, for the near-infrared, a 1 to 2 micrometer range can provide sufficient spectral coverage for a variety of polymers and plastic sheets.

[0072] In some implementations, a dual-frequency comb spectrum analyzer or dual-frequency comb source 104 can be configured to provide wavelength tunability within a specified spectral region. This tunability enables optimization of thickness measurements for specific material types or thickness ranges. Wavelength selection can be controlled electronically or through optical filtering techniques to target specific absorption lines or spectral regions that provide the optimal signal-to-noise ratio for thickness measurements.

[0073] The repetition rate difference between the two frequency combs can be precisely controlled to optimize measurement speed and / or spectral resolution. For example, the repetition rate difference can be adjusted in the range of approximately 1 Hz to 10 kHz, depending on the specific measurement requirements. A smaller repetition rate difference provides higher spectral resolution but may require a longer measurement time, while a larger difference can correspondingly achieve faster measurements with lower spectral resolution. The optimal repetition rate difference can be selected based on factors such as material thickness range, desired measurement accuracy, and / or manufacturing line speed. The dual-frequency comb spectrometer (or dual-frequency comb source 104) can be configured with specific repetition rate parameters optimized for the intended measurement application. As a non-limiting example, in some specific implementations, the first optical frequency comb may have a repetition rate of approximately 80 MHz, while the second optical frequency comb may have a repetition rate of approximately 80.005 MHz, wherein the repetition rate difference enables the generation of an RF signal (e.g., including RF beat frequency), which is detected using one or more electronic detection techniques (such as photodetection) and processed using one or more signal processing techniques.

[0074] In some embodiments, the light beam emitted by the dual-frequency comb spectrometer or dual-frequency comb source 104 (e.g., a dual optical frequency comb) can be extended, collimated, and / or combined to cover the region of interest. In some embodiments, one or more optical components 106 of system 100 are used to extend, collimate, and / or combine the light beam. In some embodiments, one or more optical components 106 include one or more lenses.

[0075] like Figure 1BAs shown, the dual-frequency comb source 104 may include a first source 104a (e.g., a first optical frequency comb source) and a second source 104b (e.g., a second optical frequency comb source) configured to emit dual-frequency combs. For example, the first source 104a may be configured to emit a first optical frequency comb 105a, and the second source 104b may be configured to emit a second optical frequency comb 105b. Figure 1B In the example depicted, the dual-frequency comb source 104 may include two fiber-based frequency comb lasers (e.g., a first fiber-based frequency comb laser and a second fiber-based frequency comb laser) configured to emit two short-pulse frequency comb laser beams corresponding to the dual optical frequency combs, as described above.

[0076] As described above, the dual-frequency comb measurement system 100 may include one or more optical components 106. In some embodiments, at least a portion of the one or more optical components 106 may be configured to guide at least one of a first optical frequency comb 105a or a second optical frequency comb 105b toward the material 110, enabling spectral measurements and analysis to determine the thickness or other properties of the material 110. The one or more optical components 106 may include one or more beam steering elements, focusing and / or collecting elements that control the propagation path of the optical frequency comb (e.g., frequency comb light) through or around the material. The optical configuration may be designed to optimize the interaction between the optical frequency comb and the material 110 while maintaining coherence and timing characteristics for dual-frequency comb spectral measurements to generate thickness measurement data for the material 110.

[0077] In some embodiments, the dual-frequency comb measurement system 100 can realize a single-comb interaction framework. In some such embodiments, one optical frequency comb passes through the material 110, while the other optical frequency comb does not pass through the material 110. In some such embodiments, one or more optical components 106 (or portions thereof) can be used to guide one optical frequency comb from the pair of optical frequency combs toward the material 110, while the second optical frequency comb serves as a reference optical frequency comb that does not interact with the material 110.

[0078] In some such embodiments, an optical frequency comb guided to and through material 110 can interact with material 110 in a reflective and / or transmissive manner. For example, in some such embodiments, one of a first optical frequency comb 105a or a second optical frequency comb 105b may be guided toward material 110 such that the optical frequency comb interacts with material 110 in a reflective and / or transmissive manner, while the other optical frequency comb retains its original spectral characteristics. The single-comb interaction pathway can provide spectral information about material 110 by comparing the optical frequency comb interacting with the material (e.g., the optical frequency comb obtained after passing through material 110) with a reference optical frequency comb during an optical mixing process at diode photodetector 114. In this regard, in some embodiments, after the interaction, an optical signal (e.g., light) corresponding to the optical frequency comb interacting with the material is collected and mixed (e.g., combined or similar terms) with another optical frequency comb (e.g., a reference optical frequency comb). For example, the reference optical frequency comb may be used to interfere with the optical frequency comb interacting with the material after passing through material 110. In some implementations, the mixed optical signal after interference can be converted into an RF signal, which is used to determine the thickness of material 110 or otherwise generate thickness data including a measurement of the thickness of material 110.

[0079] In some embodiments, the dual-frequency comb measurement system 100 can realize a dual-comb interaction framework. In such embodiments, two optical frequency combs (e.g., both a first optical frequency comb 105a and a second optical frequency comb 105b) emitted by a dual-frequency comb spectrometer or dual-frequency comb source 104 are combined and guided toward material 110, wherein at least a portion of the combined optical frequency combs passes through material 110. In some examples, a portion of the combined optical frequency combs may be internally reflected relative to material 110. In such embodiments, one or more optical components 106 (or portions thereof) may be used to guide both the first and second optical frequency combs of a pair of optical frequency combs through material 110. For example, both the first optical frequency comb 105a and the second optical frequency comb 105b may be guided toward material 110 to pass through material 110, thereby causing the two optical frequency combs to interact with material 110 in a reflective or transmissive manner. Both optical frequency combs can acquire spectral information about the properties of the material.

[0080] In some embodiments, one or more optical components 106 may be configured to support the combination of a first optical frequency comb 105a and a second optical frequency comb 105b prior to interaction with the material 110. In some embodiments, the dual-frequency comb measurement system 100 or one or more optical components 106 thereof may include one or more beamforming elements configured to optimize the interaction between the optical frequency combs and the material 110. Beamforming may be optimized to balance measurement sensitivity with spatial resolution, where tighter focusing provides higher intensity for an improved signal-to-noise ratio. In some embodiments, the dual-frequency comb measurement system 100 or one or more optical components 106 thereof may include one or more focusing lenses or mirrors configured to control the beam size and intensity distribution at the material surface. In some embodiments, the dual-frequency comb measurement system 100 or one or more optical components 106 thereof may include one or more collimating optics to maintain parallel beam propagation over the propagation distance between the dual-frequency comb source 104 and the material 110, and subsequently to the diode photodetector 114.

[0081] In some embodiments, the dual-frequency comb measurement system 100 or one or more optical components 106 may include a beam expander configured to increase the diameter of the optical frequency comb beam to, for example, provide adequate coverage of the material 110 being measured. In some embodiments, beam expansion can ensure that the measurement area covers a representative portion of the material 110, thereby providing a statistically meaningful thickness measurement across the width or region of interest. In some embodiments, the beam expansion ratio can be selected based on the specific dimensions of the material being measured and the desired spatial resolution of the thickness measurement.

[0082] In some embodiments, the dual-frequency comb measurement system 100 may include one or more collecting optics configured to efficiently focus transmitted light passing through material 110 and direct the light toward diode photodetector 114. Collection efficiency can be optimized by appropriately selecting the numerical aperture, focal length, and / or positioning of the one or more collecting optics relative to material 110 and diode photodetector 114. In some embodiments, the one or more collecting optics include one or more lenses. In some embodiments, the dual-frequency comb measurement system 100 may include one or more collecting optics configured to efficiently focus reflected light from material 110.

[0083] One or more optical components 106 (e.g., a portion thereof) or other components of the dual-frequency comb measurement system 100 may be configured to support transmission-based measurements, wherein light from the optical frequency comb propagates from one side of material 110 through material 110 to the other side of material 110 and is collected after passing through material 110. The transmission-based measurement approach can provide information about the thickness of material 110 through absorption analysis of how material 110 modifies the transmitted light spectrum. Transmission-based measurements are particularly suitable for measuring the thickness of materials that are sufficiently transparent at the operating wavelength to allow sufficient light transmission for detection.

[0084] Alternatively or additionally, one or more optical components 106 (e.g., a portion thereof) or other components of the dual-frequency comb measurement system 100 may be configured to support reflection-based measurements, wherein light from the optical frequency comb is reflected from the material 110 during interaction with the material 110. Reflection-based measurements can provide information about the thickness of the material 110 by analyzing the interference effects between light reflected from different interfaces within the material structure.

[0085] In some embodiments, the optical frequency comb may pass through the material 110 once or multiple times. In some embodiments, the optical frequency comb may pass through the material 110 multiple times using a retroreflector, a mirror, or other optical elements positioned to redirect light back through the material 110. Such a multiple-pass configuration can increase the effective path length and enhance the measurement sensitivity for materials with weak absorption characteristics. The multiple-pass approach is particularly suitable for measuring very thin materials or detecting small variations in material thickness.

[0086] like Figure 1B As shown, the dual-frequency comb measurement system 100 may include a diode photodetector 114 (e.g., a photodiode, RF diode, etc.). The diode photodetector 114 may be configured to detect optical signals and convert them into electrical signals. The diode photodetector 114 may be configured to measure or otherwise determine RF signals at various frequencies. For example, after one or both optical frequency combs of the dual-frequency comb emitted by the dual-frequency comb source 104 interact with the material 110 (as described above), the diode photodetector 114 may be used to detect, extract, map, or otherwise generate RF signals corresponding to the optical frequency combs. For example, the RF signals may correspond to light from a combined optical frequency comb passing through the material 110, or light from an optical frequency comb passing through the material 110 and mixed with the other optical frequency comb of the pair of optical frequency combs.

[0087] The diode photodetector 114 can be used as a photoelectric conversion element that supports dual-frequency comb spectral measurements by converting the optical frequency difference between two optical frequency combs into an RF signal that can be detected electronically. For example, the diode photodetector 114 can be configured to detect or otherwise receive optical signals corresponding to the optical frequency combs and generate an electrical output signal (e.g., an RF signal) that includes spectral information about the material 110 based on the optical frequency difference between the two optical signals.

[0088] In some embodiments, the diode photodetector 114 may be configured to detect optical signals corresponding to the first optical frequency comb 105a and the second optical frequency comb 105b after optical mixing of the first optical frequency comb 105a and the second optical frequency comb 105b and after the interaction of one or both of them with the material 110, and to generate an RF signal based on the optical frequency difference between the detected optical signals. Optical mixing may occur before any of the optical frequency combs interacts with the material 110, or after one or both of the first optical frequency combs interact with the material 110, depending on the comb interaction framework (e.g., single-comb interaction or dual-comb interaction). In this regard, the diode photodetector 114 may be used to map the optical frequency combs (in some embodiments, one optical frequency comb, or in some embodiments, two optical frequency combs) after interacting with the material 110 to the RF spectrum.

[0089] In some embodiments, the dual-frequency comb measurement system 100 may be configured to perform optical mixing of the material-interacting optical frequency comb and a reference optical frequency comb at a diode photodetector 114 or at another location after the optical frequency comb interacts with the material 110. In such embodiments, a mixing process may occur when the material-interacting optical frequency comb and the reference optical frequency illuminate the diode photodetector 114 (e.g., a photodiode, etc.), causing the diode photodetector 114 to generate an electrical signal proportional to the optical power incident on it. Based on the different repetition rates of the first optical frequency comb 105a and the second optical frequency comb 105b, the optical mixing at the diode photodetector may produce a beat frequency corresponding to the difference between corresponding optical frequencies in the two optical frequency combs. The diode photodetector 114 may convert the optical beat frequency into an electrical signal in the RF range for processing using electronic signal processing techniques or other techniques.

[0090] In some embodiments, the dual-frequency comb measurement system 100 may be configured to perform optical mixing of a first optical frequency comb 105a and a second optical frequency comb 105b prior to interaction with the material 110 to generate a combined optical frequency comb 108. In some embodiments, the optical mixing may be performed such that the combined optical frequency comb 108 maintains temporal coherence between the pair of optical frequency combs throughout the optical path to maintain interference properties.

[0091] In some embodiments, one or more optical components 106 may include one or more beam combining elements configured to spatially and temporally combine a first optical frequency comb 105a and a second optical frequency comb 105b prior to interaction to generate a combined optical frequency comb 108. For example, one or more optical components 106 may include beam splitters, dichroic mirrors, polarizing beam splitters, and / or fiber couplers configured to mix the first optical frequency comb 105a and the second optical frequency comb 105b to generate the combined optical frequency comb 108.

[0092] Based on the different repetition rates of the first optical frequency comb 105a and the second optical frequency comb 105b, when the combined optical frequency comb 108 illuminates the diode photodetector 114, the diode photodetector 114 can generate a beat frequency corresponding to the difference between the corresponding optical frequencies of the two optical frequency combs. The diode photodetector 114 can convert the optical beat frequency into an electrical signal in the RF range for processing using electronic signal processing techniques or other techniques.

[0093] In some implementations, the diode photodetector 114 can measure signals in the MHz radio frequency range. The RF signal generated by the diode photodetector 114 may include frequency components spanning from kilohertz to megahertz frequencies, depending on the repetition rate difference between the two optical frequency combs and / or the number of optical frequency components being detected. The MHz radio frequency range provides a frequency range that facilitates electronic signal processing. The RF signal may contain multiple frequency components, where each component corresponds to a beat frequency between a pair of optical frequencies from the two optical frequency combs.

[0094] The repetition rate difference between two optical frequency combs enables rapid spectral acquisition by generating time-varying interference patterns that sweep across different combinations of optical frequencies. As pulses from the two frequency combs gradually shift in relative timing due to the repetition rate difference, different portions of the optical spectrum can be sampled and converted into RF signals. This time-scanning process allows a diode photodetector to capture spectral information across the entire optical bandwidth of the frequency comb within a short measurement time, such as milliseconds.

[0095] The diode photodetector 114 may include various types of photodiode technologies suitable for light in the wavelength range used by the detection system 100. In some embodiments, the diode photodetector may include an InGaAs photodiode for detecting near-infrared light in the 1-micrometer to 2-micrometer wavelength range. InGaAs photodiodes offer high sensitivity and fast response times, making them suitable for detecting rapid time changes in optical signals from a dual-frequency comb. InGaAs materials offer favorable absorption characteristics in the near-infrared range and provide sufficient bandwidth to detect RF signals generated through the frequency comb mixing process. For applications operating in the mid-infrared wavelength range of 2-micrometer to 9-micrometer, the diode photodetector 114 may include photodiode technologies such as mercury cadmium telluride (MCT) detectors, indium antimonide (InSb) detectors, or other mid-infrared sensitive materials. These detector types can provide the spectral sensitivity required to detect frequency comb light at longer wavelengths while maintaining sufficient speed and sensitivity for RF signal generation. The choice of diode photodetector technology may depend on the specific wavelength range, required sensitivity, operating temperature, and cost considerations for the specific application.

[0096] The diode photodetector 114 may be coupled (e.g., at least communicatively coupled) to signal processing electronics that amplifies, filters, and / or digitizes the RF signal for subsequent analysis. The signal processing electronics may include an RF amplifier for boosting the signal level, a bandpass filter for selecting a specific frequency range of interest, and / or an analog-to-digital converter for digitizing the RF signal for computer-based analysis. Signal processing may include Fourier transform processing to convert the time-domain RF signal into frequency-domain spectral information that reveals the absorption and / or interference properties / features of the material.

[0097] The diode photodetector configuration can be optimized for specific measurement geometries. The effective area of ​​the diode photodetector can be sized to efficiently collect optical signals while maintaining a fast response time, and the diode photodetector 114 can be positioned at an appropriate distance from the material to optimize signal collection efficiency. In some embodiments, an optical focusing element can be used to focus the optical signal onto the effective area of ​​the diode photodetector to improve the signal-to-noise ratio and measurement sensitivity.

[0098] The positioning of the diode photodetector 114 relative to the material 110 and the dual-frequency comb source 104 can be configured to adapt to different measurement geometries. In some embodiments, the diode photodetector 114 may be positioned on the side of the material 110 opposite to the source of the first and second optical frequency combs (e.g., the first source 104a or the second source 104b). Opposite-side detector positioning allows for the detection of light from the first or second optical frequency comb 105a that has passed through the material 110, thereby providing detection of material properties and absorption characteristics. Opposite-side detector positioning is suitable for materials with sufficient transparency and for applications where the optical components can be accessed from both sides of the material.

[0099] In some embodiments, the diode photodetector 114 may be positioned on the same side of the material 110 as the source of the first optical frequency comb 105a and the second optical frequency comb 105b. Same-side detector positioning (e.g., reflection-based detector positioning) enables the detection of light reflected from the material surface or from internal interfaces within the material structure. Same-side detector positioning is suitable for applications where only one side of the material is accessible. In some embodiments, the same-side detector configuration may utilize beam-splitting or beam-directing optics to separate the incident frequency comb light from the reflected light, thereby ensuring that the diode photodetector receives the reflected signal without interference from the source light. Optical elements such as beam splitters, mirrors, or directional couplers may be used to achieve optical isolation and signal routing. The same-side detector configuration may also incorporate focusing optics to concentrate the reflected light onto the diode photodetector and collecting optics to focus the light reflected from the surface of the web material.

[0100] Now for reference Figures 2A to 2B This provides the frequency domain according to at least some example embodiments of this disclosure. Specifically, Figure 2A An example is illustrated of the collected optical signal 204 (e.g., optical spectrum) corresponding to the first optical frequency comb 105a and the second optical frequency comb 105b after at least one of the first optical frequency comb 105a or the second optical frequency comb 105b has interacted with the material 110 and after optical mixing. As described above, in some embodiments, optical mixing may occur before the interaction, and in some embodiments, optical mixing may occur after the interaction.

[0101] The collected optical signal 204 may include a first optical signal 210 and a second optical signal 220. In some embodiments, the first optical signal 210 may correspond to light from an optical frequency comb passing through material 110, and the second optical signal 220 may correspond to light from a second optical frequency comb passing through material 110, wherein both the first and second optical frequency combs originate from a pair of frequency combs emitted by dual frequency comb source 104. In some embodiments, the first optical signal 210 may correspond to light from an optical frequency comb passing through material 110, and the second optical signal 220 may correspond to a second optical frequency comb (e.g., a reference optical frequency comb) that is not guided through material 110, wherein both the first and second optical frequency combs originate from a pair of frequency combs emitted by dual frequency comb source 104, and the second optical frequency comb light (e.g., the reference optical frequency comb) is configured to interfere with the first optical frequency comb.

[0102] refer to Figure 2B The collected optical signal 204 can be converted into an RF signal 230 (e.g., RF spectrum) corresponding to the collected optical signal 204. In some embodiments, the collected optical signal 204 (e.g., first optical signal 210 and second optical signal 220) is detected by a diode photodetector 114. In some embodiments, the collected optical signal 204 can be collected using one or more optical elements of the system 100. In some embodiments, the one or more optical elements may include one or more lenses. In some embodiments, the first optical signal 210 and the second optical signal 220 are directed to the diode photodetector 114, and the RF signal 230 is generated by the diode photodetector 114 based on the first optical signal 210 and the second optical signal 220. In this respect, in some embodiments, the collected optical signal 204 can be detected, extracted, and / or received by the diode photodetector 114.

[0103] Light from the optical frequency combs guided to material 110 can travel through the material and maintain a certain coherence. In some embodiments, the coherence allows the diode photodetector 114 to generate an RF signal 230 as a difference between optical signals (e.g., the difference between the first optical signal 210 and the second optical signal 220). In this regard, in some embodiments, generating the RF signal 230 includes performing heterodyne detection. In such embodiments, when light from the dual optical frequency combs is incident on the diode photodetector 114 after interacting with material 110, or when the diode photodetector 114 receives or detects the collected optical signal 204, the diode photodetector 114 can generate an RF signal 230, which includes a beat frequency corresponding to the difference between the optical frequencies of the first optical signal 210 and the second optical signal 220 and corresponding to a pair of optical frequency combs 105a, 105b. This is based on the fact that the pair of optical frequency combs 105a, 105b have different repetition rates (…). and Each pair of corresponding optical frequencies from these two optical frequency combs can generate a unique RF beat frequency. In this respect, the resulting RF signal 230 can include signals generated by the repetition rate difference. Interval frequency combs.

[0104] In some embodiments, electronic signal processing techniques and / or other techniques are used to process the RF signal 230 generated by the diode photodetector 114 to support the extraction of spectral information from the RF signal 230. RF signal processing may include amplification, filtering, and / or analog-to-digital conversion to achieve digital signal processing. In some embodiments, Fast Fourier Transform (FFT) techniques and / or other techniques may be used to analyze the RF signal 230 to extract spectral information from the RF signal. In some embodiments, the intensity at each frequency in the RF signal 230 may be determined by applying a Fourier Transform (FFT) to the detected optical signals (e.g., the first optical signal 210 and the second optical signal 220). In some embodiments, the intensity at each frequency is approximately proportional to the square of the transmitted intensity.

[0105] In some embodiments, the bandwidth of the diode photodetector 114 can be selected to adapt to the RF frequency. For example, if the repetition difference is in the kHz range and the number of comb teeth spans several MHz in the RF domain, the bandwidth of the diode photodetector can be selected such that it is sufficient to capture the RF spectrum of interest. In some embodiments, the signal-to-noise ratio of the RF signal 230 can be optimized by carefully selecting diode photodetector characteristics such as responsivity, noise equivalent power, and / or bandwidth. The diode photodetector 114 can operate while maximizing signal strength and minimizing noise contributions from sources such as thermal noise, shot noise, and amplifier noise. In some embodiments, the diode photodetector 114 can be temperature-stable or cooled to reduce thermal noise and improve overall system sensitivity.

[0106] In some embodiments, the interaction of the first optical frequency comb 105a and / or the second optical frequency comb 105b with the material 110 can produce absorption and / or interference effects. In some embodiments, the first optical signal 210 and / or the second optical signal 220 include features resulting from interference and / or absorption. As described above, when the first optical frequency comb 105a and / or the second optical frequency comb 105b are directed to the material 110, a certain amount of light from the optical frequency combs can be internally reflected, while some or most of the frequency comb light can pass through the material 110. In this respect, the reflected light can be used to measure the thickness of the material 110 as an interference pattern observed at the measurement wavelength, and the transmitted light allows the thickness of the material 110 to be measured using optical absorption.

[0107] Interference patterns can represent and / or indicate the spatial or temporal distribution of optical intensity variations resulting from the superposition of two or more coherent light waves. In some examples, interference patterns can be generated when frequency comb light is reflected from within an interface of material 110, such as the inner surfaces of the first and second sides of material 110. Interference patterns can be caused by optical path differences between light waves that have traveled different distances through material 110, producing constructive and destructive interferences that manifest as periodic variations in the intensity of the detected optical signal. For example, the interference pattern can manifest as a periodic variation in the intensity of the RF signal 230 with respect to the optical frequency, where the periodicity is negatively correlated with the optical thickness of the material. The characteristics of the interference pattern (including the spacing between the maximum and minimum intensity values) can be correlated with the optical thickness of the material, thereby enabling precise determination of the material thickness by analyzing the interference pattern in the RF domain.

[0108] As described herein, the transmitted frequency comb light passing through material 110 can carry information about the material's absorption properties. The absorption spectrum corresponding to the detected optical signal can reveal absorption features characterizing the material's thickness and / or other properties. These absorption features may manifest as valleys or peaks in the RF spectrum. The intensity of these absorption features may be related to the material's thickness. In some embodiments, the choice between using an interferometric measurement approach or an absorption-based measurement approach may depend on the specific properties of material 110. For materials with strong absorption features in the wavelength range of the frequency comb, an absorption-based measurement approach utilizing absorption features can provide higher sensitivity and accuracy. For materials with weak absorption but significant refractive index contrast, an interferometric measurement approach utilizing internally reflected light may be more suitable for thickness determination.

[0109] In some embodiments, system 100 includes a signal processor configured to determine the thickness of material 110 based on an RF signal 230 generated by a diode photodetector 114. The signal processor may receive the RF signal 230 from the diode photodetector 114 and apply one or more signal processing algorithms to extract thickness information from spectral data, such as spectral information within the RF signal 230. In some embodiments, the signal processor may include digital signal processing hardware, software algorithms, or combinations thereof that enable real-time or near-real-time analysis of the RF signal 230 to provide a thickness measurement of material 110. The RF signal analysis process may include analyzing the RF signal 230 to determine the thickness and / or composition of material 110. The RF signal analysis process may involve converting the time-domain RF signal 230 into spectral information revealing material properties using various computational techniques. The signal processor may implement one or more RF signal analysis approaches to extract different types of information from the RF signal 230, thereby enabling a comprehensive characterization of the web material, rather than just a simple thickness measurement.

[0110] In some implementations, analyzing the RF signal 230 may include performing a Fourier transform on the RF signal 230 to extract spectral information. The Fourier transform process converts the time-domain RF signal 230 into frequency-domain spectral data, which reveals the optical absorption and / or interference properties / characteristics of the material 110. The Fourier transform decomposes the RF signal 230 into its constituent frequency components, where each frequency component corresponds to a specific optical wavelength or the frequency difference between two optical frequency combs. The spectral information extracted by the Fourier transform provides detailed information about how the material interacts with light across the optical bandwidth.

[0111] In some embodiments, the signal processor may be configured to determine the thickness of material 110 based on interference fringes in the RF signal. For example, in some embodiments, the method for determining the thickness of material 110 may be based at least in part on interference fringes in the RF signal generated by optical interference effects within the material structure. As described above, interference can occur between light rays traveling different optical path lengths through material 110 when light from an optical frequency comb passes through or is reflected from the material 110. These interference effects can cause periodic variations in the intensity of transmitted or reflected light with optical frequency, which can manifest as interference fringes in the spectral information extracted from the RF signal.

[0112] Spectral information can include interference fringes used to determine the thickness of the sheet material. Interference fringes can exhibit a periodic pattern in the frequency domain, where the period of the fringes is related to the optical thickness of the sheet material. A signal processor can analyze the fringe spacing and pattern to calculate the physical thickness of the material based on its known refractive index and the wavelength-dependent characteristics of the interference pattern. Interference fringe analysis provides high-precision thickness measurements, particularly for thin materials where optical path length differences produce well-defined fringe patterns.

[0113] In some implementations, the signal processor can be configured to determine the thickness of the web material based on absorption characteristics in the RF signal. The method for determining the thickness of the web material can be based on absorption characteristics in the RF signal that correspond to the wavelength-specific absorption properties of the web material. Different materials may exhibit characteristic absorption bands at specific light wavelengths, and the intensity of these absorption characteristics may be related to the amount of material present along the optical path length. The processor can analyze the depth and shape of the absorption characteristics in the spectral information to determine the thickness of the web material based on Beer's law or other absorption-based relationships.

[0114] In some implementations, available calibration data is determined based on the thickness of the absorption, which correlates the absorption intensity with the material thickness of the specific web material being measured. The processor can compare the measured absorption characteristics with a reference spectrum or calibration curve to determine the thickness that will produce the observed absorption properties. This approach is particularly suitable for materials with strong, well-defined absorption characteristics across the wavelength range of a dual-frequency comb system.

[0115] In some implementations, system 100 (or its signal processor) can implement an algorithm that automatically determines whether to use interferometric analysis or absorption analysis for thickness determination. In some implementations, the algorithm can evaluate the characteristics of the RF signal 230 to determine which analysis method provides a more accurate or reliable thickness measurement for a specific web material and measurement conditions. The automatic selection algorithm can analyze signal quality metrics, signal-to-noise ratio, fringe visibility, absorption characteristic intensity, and other parameters to determine the optimal analysis approach. The algorithm can assess the quality and characteristics of interference fringes present in the spectral information to determine whether interferometric analysis is appropriate. The algorithm can evaluate the fringe contrast, fringe spacing regularity, and signal-to-noise ratio of the fringe pattern to determine whether the interference fringes provide sufficient quality for accurate thickness determination. If the interference fringes meet predetermined quality criteria, the algorithm can select interferometric analysis as the primary thickness determination method.

[0116] In some implementations, the algorithm can evaluate the intensity and characteristics of absorption features in spectral information to determine whether absorption-based analysis is appropriate. The algorithm can assess the depth of the absorption features, spectral width, and signal-to-noise ratio to determine whether the absorption characteristics provide sufficient information for reliable thickness measurement. The algorithm can compare the absorption features with known material absorption characteristics to verify whether the observed features correspond to the desired material composition. An automatic selection algorithm implements decision logic that considers multiple factors simultaneously to select the optimal analysis method. The algorithm can weight different signal quality metrics based on specific measurement requirements and material properties. In some cases, the algorithm can determine that both interferometric analysis and absorption analysis provide reliable results, and can combine results from both methods to improve measurement accuracy and provide cross-validation for thickness determination.

[0117] In some implementations, the signal processor can also implement adaptive signal processing techniques that optimize analysis parameters based on the characteristics of the RF signal. Adaptive processing adjusts Fourier transform parameters, filtering characteristics, and analysis algorithms for specific web material and measurement conditions to maximize signal quality and measurement accuracy. This adaptive approach allows the system to maintain high measurement performance across different material types and varying measurement conditions without manual adjustment of system parameters. The thickness determination process provides real-time or near-real-time measurement results, enabling continuous monitoring of material thickness during manufacturing. The processor implements efficient algorithms that minimize computation time while maintaining measurement accuracy, enabling high-speed thickness monitoring of moving web material. Real-time capability provides immediate feedback for process control applications that require rapid detection and correction of thickness variations to maintain product quality.

[0118] Figures 3A to 3B Interference fringes are illustrated according to at least some example embodiments of this disclosure. Specifically, Figure 3A A graphical representation of the first interference fringe pattern 302 (e.g., a double comb fringe) is illustrated, and Figure 3B The graphic representation of the second interference fringe pattern 304 is illustrated. Figure 3C A graphical representation of the absorption spectrum 306 is shown, illustrating the interference fringes. It should be noted that, relative to... Figure 3C Regarding the interference fringes that are depicted and measured, Figures 3A to 3B A simplified calculation / representation of interference fringes is illustrated (for illustrative purposes). For example... Figures 3A to 3C As shown, the interference fringe pattern can change with the change of material thickness. Figure 3D An actual absorption spectrum 308 is illustrated, along with features that can be used to calculate or otherwise determine the absorption and therefore the thickness, as described herein. Specifically, Figure 3D The Fourier transform infrared (FTIR) absorption spectrum is illustrated.

[0119] In some implementations, interference fringe patterns can be characterized by their periodicity, amplitude, and phase relationships, which together provide quantitative information about the material thickness. The spacing between adjacent interference maxima and minima in the fringe pattern is inversely proportional to the optical thickness of the material, which is defined as the product of the material's physical thickness and refractive index. As the material thickness increases, the optical path difference between light rays that have traveled through the material along different paths also increases, resulting in a corresponding change in the fringe spacing observed in the radio frequency spectrum. Variations in the amplitude of the interference fringe pattern can provide additional information about material properties, including surface quality, internal structure, and optical losses within the material. Materials with smooth, parallel surfaces produce high-contrast interference fringes with well-defined maxima and minima, while materials with rough surfaces or internal scattering exhibit reduced fringe visibility. The phase relationships between the different spectral components of the interference pattern allow for the determination of absolute thickness values ​​rather than relative thickness changes, thus providing enhanced measurement capabilities for process control applications.

[0120] In some embodiments, the dual-frequency comb measurement system 100 can be configured to detect and measure multiple thin layers within a material structure. The multilayer material may include different material compositions in each layer, with each layer contributing unique spectral characteristics that can be identified by analyzing the corresponding RF signal. The wide spectral coverage of the dual-frequency comb measurement system 100 allows for the simultaneous measurement of different layers, as described herein, by probing the wavelength range in which each layer exhibits characteristic absorption or interference characteristics. Detection of multiple thin layers can utilize the wavelength-correlated penetration properties of the frequency comb light to probe different depths within the material structure. Shorter wavelengths may primarily interact with surface layers, while longer wavelengths penetrate deeper into the material structure and interact with underlying layers. The system 100 can analyze wavelength-correlated spectral information to separate contributions from different layers and determine the thickness and / or composition of individual layers. Multilayer measurements can provide valuable information for quality control of laminated materials, coated substrates, and other multi-component web products.

[0121] In some implementations, the dual-frequency comb measurement system 100 may include calibration capabilities to ensure accurate and traceable measurements across different operating conditions and material types. Calibration capabilities may include reference measurement procedures, standard material measurements, and / or system correction algorithms that account for instrument variations and environmental influences. The calibration process may establish a relationship between the RF signal properties and the actual material properties being measured. Calibration capabilities may utilize reference materials with known thickness and compositional properties to establish measurement accuracy and traceability. The reference materials may span the desired thickness range and material types in the intended application, thus providing calibration points across the entire measurement range. The calibration process may involve measuring the reference material under the same conditions as production measurements and establishing correction factors or calibration curves that correlate the measured RF signal properties with known material properties.

[0122] The calibration system enables an automated calibration process that periodically verifies measurement accuracy without interrupting production. Automated calibration can utilize built-in reference standards, movable calibration targets, or other mechanisms for periodic calibration checks. Calibration verification detects drift in system performance due to component aging, environmental changes, or other factors that can affect measurement accuracy over time. Calibration capabilities may include temperature compensation algorithms that take into account the thermal effects on both the measurement system and the web material properties. Temperature variations can affect the optical properties of the frequency comb source, the refractive index of the web material, and the response characteristics of the diode photodetector. Temperature compensation utilizes temperature sensors and calibration algorithms to maintain measurement accuracy across the desired operating temperature range.

[0123] In some implementations, the dual-frequency comb measurement system 100 can be configured to measure moisture content in addition to thickness measurement, thereby providing comprehensive material characterization capabilities. Moisture content measurement can utilize the specific absorption characteristics of water molecules presented in the spectral information extracted from the RF signal. Water molecules exhibit characteristic absorption bands in both the near-infrared and mid-infrared wavelength ranges detectable by the dual-frequency comb system. Moisture measurement capability can analyze the absorption characteristics at wavelengths where water exhibits strong absorption characteristics while the base fabric exhibits minimal absorption. The dual-frequency comb measurement system 100 can compare the intensity of the water absorption characteristics with calibration data to determine the moisture content of the fabric material. Moisture measurement can be performed simultaneously with thickness measurement, thus providing two parameters through a single measurement system.

[0124] Moisture content measurement provides process control information for web manufacturing applications where moisture content affects product quality, dimensional stability, or processing characteristics. Excessive moisture content can lead to dimensional changes, affect material strength, or cause processing difficulties in downstream operations. Real-time moisture monitoring capabilities enable immediate process adjustments to maintain optimal moisture levels throughout the manufacturing process. Combined thickness and moisture measurement capabilities allow for the detection of correlations between these parameters, providing additional insights into material quality and processing conditions. Moisture-induced thickness variations can be distinguished from other sources of thickness variation, enabling more precise process control and quality assessment. Simultaneous measurement of multiple parameters reduces the need for individual measurement systems and provides more comprehensive material characterization using a single instrument.

[0125] Example apparatus of this disclosure

[0126] Example systems according to some embodiments of this disclosure have been discussed, and example apparatuses according to some embodiments of this disclosure will now be described.

[0127] Figure 4 Block diagrams illustrating example apparatuses according to at least some example embodiments of the present disclosure are shown. Specifically, Figure 4 An example apparatus 400 (“Apparatus 400”) with a specific configuration according to at least some example embodiments of the present disclosure is depicted. In some embodiments, the dual-frequency comb measurement system 100 and / or a portion thereof comprises one or more systems (such as... Figure 4 The device 400 depicted and described is embodied therein. However, it should be noted that... Figure 4 The components or elements illustrated and described below with reference to the figures are not mandatory, and therefore one or more components or elements may be omitted in some embodiments. Additionally, besides Figure 4In addition to the components or elements illustrated and described below with reference to the figures, some embodiments may include additional or different components or elements. In some embodiments, the functionality of the dual-frequency comb measurement system 100 or any subset thereof may be performed by a single device 400 or multiple devices 400. In some embodiments, device 400 may include one or more physical devices.

[0128] Device 400 includes a processor 402, a memory 404, input / output circuitry 406, communication circuitry 408, a dual-frequency comb-source circuitry 410, a diode photodetector circuitry 412, and signal processing circuitry 414. Device 400 can be configured to perform the operations described herein. While the components are described with respect to functional limitations, it should be understood that a particular implementation must include the use of specific computing hardware. It should also be understood that in some embodiments, certain components of the components described herein include similar or common hardware. For example, in some embodiments, two circuit sets utilize the same processor, network interface, storage medium, etc., to perform their associated functions, such that each circuit set does not require duplicate hardware.

[0129] In some embodiments, processor 402 (and / or coprocessor, or assist processor, or any other processing circuitry otherwise associated with the processor) communicates with memory 404 via a bus to transfer information between components of device 400. In some embodiments, for example, memory 404 is non-transitory and may include, for example, one or more volatile and / or non-volatile memories. In other words, for example, in some embodiments, memory 404 includes or embodies an electronic storage device (e.g., a computer-readable storage medium). In some embodiments, memory 404 is configured to store information, data, content, applications, or instructions, etc., to enable device 400 to perform various functions according to example embodiments of this disclosure.

[0130] Processor 402 can be embodied in a variety of different ways. For example, in some example embodiments, processor 402 includes one or more processing devices configured to execute independently. Additionally or alternatively, in some embodiments, processor 402 includes one or more processors configured in series via a bus to enable independent execution of instructions, pipelined processes, and / or multithreading. The terms “processor” and “processing circuitry” should be understood to include single-core processors, multi-core processors, multiple processors within device 400, and / or one or more remote processors or “cloud” processors outside device 400.

[0131] In example embodiments, processor 402 is configured to execute instructions stored in memory 404 or otherwise accessible to the processor. Alternatively or additionally, in some embodiments, processor 402 is configured to perform hard-coded functionality. Thus, whether configured by hardware or software methods, or by a combination thereof, processor 402 represents an entity (e.g., physically embodied in circuit form) capable of performing operations according to embodiments of this disclosure. Alternatively or additionally, as another example, in some example embodiments, when processor 402 is embodied as an executor of software instructions, the instructions specifically configure processor 402 to execute algorithms specifically embodied in specific operations as described herein when executing such instructions. In some embodiments, processor 402 includes hardware, software, firmware, and / or combinations thereof that implement one or more operations described herein.

[0132] In some embodiments, device 400 includes input / output circuitry 406 that provides output to a user and, in some embodiments, receives indications of user input. In some embodiments, input / output circuitry 406 communicates with processor 402 to provide this functionality. Input / output circuitry 406 may include one or more user interfaces and, in some embodiments, includes a display that includes an interface presented as a web user interface, application user interface, user device, backend system, etc. In some embodiments, input / output circuitry 406 also includes a keyboard, mouse, joystick, touchscreen, touch area, softkeys, microphone, speaker, or other input / output mechanism. Processor 402 and / or input / output circuitry 406 including the processor may be configured to control one or more functions of one or more user interface elements via computer program instructions (e.g., software and / or firmware) stored in processor-accessible memory (e.g., memory 404, etc.). In some embodiments, input / output circuitry 406 includes or utilizes user-oriented applications to provide input / output functionality to client devices and / or other displays associated with the user.

[0133] In some embodiments, device 400 includes communication circuitry 408. Communication circuitry 408 includes any component (such as a device or circuit embodied in hardware or a combination of hardware and software) configured to receive data from a network and / or any other device, circuitry, or module communicating with device 400, and / or to a network and / or any other device, circuitry, or module communicating with the device. In this regard, in some embodiments, communication circuitry 408 includes, for example, a network interface for enabling communication with wired or wireless communication networks. Additionally or alternatively, in some embodiments, communication circuitry 408 includes one or more network interface cards, antennas, buses, switches, routers, modems, and any other supporting hardware, firmware, and / or software, or any other device suitable for enabling communication via one or more communication networks. Additionally or alternatively, communication circuitry 408 includes circuitry for interacting with antennas and / or other hardware or software to transmit signals via the antenna or to process signals received via the antenna. In some embodiments, communication circuitry 408 transmits data to and / or receives data from user equipment, one or more assets or accompanying sensors and / or other external computing devices communicating with device 400. In some embodiments, one or more circuit sets perform some or all of the described functionalities associated with another component.

[0134] In some embodiments, device 400 includes a dual-frequency comb source circuit 410. The dual-frequency comb source circuit 410 may include hardware components, software components, and / or combinations thereof, which are configured to work with processor 402, memory 404, input / output circuitry 406, and / or communication circuitry 408 to perform functions related to dual-frequency comb sources (such as those referenced above). Figure 1A This relates to one or more functions associated with the dual-frequency comb source 104 described in Figure 3. In some embodiments, the dual-frequency comb source circuit 410 may be configured to receive data, objects, etc. from one or more components of the device 400, and / or send data, objects, etc. to one or more components of the device, for example, using an application or API executed using a processor (such as processor 402). It should also be understood that in some embodiments, the dual-frequency comb source circuit 410 may include a separate processor, a specially configured field-programmable gate array (FPGA), or a dedicated interface circuit (ASIC) to provide or otherwise facilitate access to such data, objects, etc. used by one or more other components of the device 400. The dual-frequency comb source circuit 410 may also provide communication with other components of the device, system, and / or external systems via a network interface provided by communication circuit 408.

[0135] In some embodiments, device 400 includes a diode photodetector circuit 412. The diode photodetector circuit 412 may include hardware components, software components, and / or combinations thereof, which are configured to work with processor 402, memory 404, input / output circuitry 406, and / or communication circuitry 408 to perform functions related to a diode photodetector (such as those referenced above). Figure 1A This relates to one or more functions associated with the diode photodetector 114 described in Figure 3. In some embodiments, the diode photodetector circuit 412 may be configured to receive data, objects, etc. from one or more components of the device 400, and / or send data, objects, etc. to one or more components of the device, for example, using an application or API executed using a processor (such as processor 402). It should also be understood that in some embodiments, the diode photodetector circuit 412 may include a separate processor, a specially configured field-programmable gate array (FPGA), or a dedicated interface circuit (ASIC) to provide or otherwise facilitate access to such data, objects, etc. used by one or more other components of the device 400. The diode photodetector circuit 412 may also provide communication with other components of the device, system, and / or external systems via a network interface provided by communication circuit 408.

[0136] In some embodiments, device 400 includes signal processing circuitry 414. Signal processing circuitry 414 may include hardware components, software components, and / or combinations thereof, which are configured to work in conjunction with processor 402, memory 404, input / output circuitry 406, and / or communication circuitry 408 to perform operations related to signal processing circuitry 414 (such as those referenced above). Figure 1A The signal processing circuit 414 may be associated with one or more functions of the signal processing circuit described in Figure 3. In some embodiments, the signal processing circuit 414 may be configured to receive data, objects, etc. from one or more components of the device 400, and / or send data, objects, etc. to one or more components of the device, for example, using an application or API executed using a processor (such as processor 402). It should also be understood that in some embodiments, the signal processing circuit 414 may include a separate processor, a specially configured field-programmable gate array (FPGA), or a dedicated interface circuit (ASIC) to provide or otherwise facilitate access to such data, objects, etc. used by one or more other components of the device 400. The signal processing circuit 414 may also provide communication with other components of the device, system, and / or external systems via a network interface provided by the communication circuit 408.

[0137] Additionally or alternatively, in some embodiments, two or more sets of circuits embodying processor 402, memory 404, input / output circuitry 406, communication circuitry 408, dual-frequency comb-source circuitry 410, diode photodetector circuitry 412, and / or signal processing circuitry 414 are composable. Alternatively or additionally, in some embodiments, one or more sets of circuits perform some or all of the described functionality associated with another component. For example, in some embodiments, two or more sets of circuits embodying processor 402, memory 404, input / output circuitry 406, communication circuitry 408, dual-frequency comb-source circuitry 410, diode photodetector circuitry 412, and / or signal processing circuitry 414 are combined into a single module embodying hardware, software, firmware, and / or combinations thereof. Similarly, in some implementations, one or more sets of circuits (e.g., dual-frequency comb source circuit 410, diode photodetector circuit 412, signal processing circuit 414) are combined with processor 402 such that processor 402 performs one or more operations described above with respect to each of these sets of circuits embodied by dual-frequency comb source circuit 410, diode photodetector circuit 412, and / or signal processing circuit 414.

[0138] It should also be noted that all or part of the information discussed herein may be based on data received, generated, and / or maintained by one or more components of device 400. In some embodiments, one or more external systems, such as remote cloud computing and / or data storage systems, may also be utilized to provide at least some of the functionality discussed herein.

[0139] Example procedures disclosed herein

[0140] Figure 5 An example process 500 for measuring material thickness using dual-frequency comb spectroscopy is illustrated according to at least some example embodiments of the present disclosure. Process 500 may be implemented by one or more computing devices, entities, and / or systems described herein. Figure 5 Example process 500 is illustrated for illustrative purposes. Although example process 500 depicts a specific sequence of steps / operations, this sequence can be changed without departing from the scope of this disclosure. For example, some of the depicted steps / operations may be performed in parallel or in different sequences that do not substantially affect the functionality of process 500. In other examples, different components of the example device or system implementing process 500 may perform functions substantially simultaneously or in a specific sequence.

[0141] In some embodiments, process 500 includes, at step / operation 502, generating a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate from a dual-frequency comb source. In some embodiments, the first and second optical frequency combs are generated by a dual-frequency comb spectrometer including a dual-frequency comb source.

[0142] In some embodiments, one or more of the first or second optical frequency comb operates in a wavelength range of 1 micrometer to 2 micrometers. In some embodiments, one or more of the first or second optical frequency comb operates in a wavelength range of 2 micrometers to 9 micrometers. In some embodiments, one or more of the first or second optical frequency comb operates in a wavelength range of 3 micrometers to 6 micrometers. In some embodiments, one or more of the first or second optical frequency comb operates in a wavelength range of 3 micrometers to 6 micrometers. In some embodiments, one or more of the first or second optical frequency comb operates in a wavelength range of 4.5 micrometers to 9 micrometers. In some embodiments, the dual-frequency comb source includes an optical fiber-based source. In some embodiments, the dual-frequency comb source includes a photonic chip-based source. In some embodiments, the photonic chip-based source may include one or more silicon nitride waveguides.

[0143] In some embodiments, process 500 includes, at step / operation 504, using one or more optical elements to guide one or more of a first optical frequency comb or a second optical frequency comb toward the material. In some embodiments, guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material includes: allowing both the first and second optical frequency combs to propagate through the material. In some embodiments, guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material includes: combining the first and second optical frequency combs, and guiding the combined optical frequency comb toward the material.

[0144] In some embodiments, process 500 includes, at step / operation 506, using a diode photodetector to detect optical signals from the first or second optical frequency comb after one or more of the first or second optical frequency combs have interacted with the material. For example, the diode photodetector may detect or otherwise receive light from the first or second optical frequency comb after one or more of the first or second optical frequency combs have interacted with the material.

[0145] In some embodiments, process 500 includes, at step / operation 508, generating an RF signal corresponding to the optical signal using a diode photodetector. In some embodiments, a dual-frequency comb source is positioned relative to the material on a first side, and a diode photodetector is positioned relative to the material on a second side. In some embodiments, both the dual-frequency comb source and the diode photodetector are positioned relative to the material on the first side.

[0146] In some embodiments, process 500 includes, at step / operation 510, determining the thickness of the material based on the RF signal. In some embodiments, determining the thickness of the material includes: extracting spectral information from the RF signal, wherein the spectral information includes one or more of interference fringe patterns or absorption features, and determining the thickness based on the spectral information.

[0147] In some embodiments, determining the thickness includes applying an algorithm configured to select either an interferometric measurement or an absorption-based measurement. In some embodiments, in response to indicating the selection of an interferometric measurement, process 500 may include applying one or more interferometric algorithms to an RF signal, wherein the one or more interferometric algorithms are configured to identify interference fringes reflected within the RF signal, and analyzing the interference fringes to determine the thickness of the material. In some embodiments, in response to indicating the selection of an absorption-based measurement, process 500 may include applying one or more absorption algorithms to an RF signal, wherein the one or more absorption algorithms are configured to identify absorption features from the RF signal, and analyzing the absorption features to determine the thickness of the material.

[0148] in conclusion

[0149] Those skilled in the art to which this disclosure pertains, benefiting from the teachings presented in the foregoing description and related drawings, will conceive of numerous modifications and other embodiments of the disclosure set forth herein. Therefore, it should be understood that embodiments are not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Furthermore, although the foregoing description and related drawings have described exemplary embodiments in the context of certain example combinations of elements and / or functions, it should be understood that different combinations of elements and / or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and / or functions expressly described above are also contemplated, as may be set forth in some of the appended claims. Although specific terms are used herein, they are used only in a general and descriptive sense and not for limiting purposes.

[0150] Although an example processing system has been described above, specific implementations of the subject matter and functional operations described herein may be implemented in other types of digital electronic circuits, or in computer software, firmware, or hardware (including the structures disclosed herein and their equivalents), or in a combination of one or more of them.

[0151] The embodiments of the subject matter and operations described herein can be implemented in digital electronic circuits, or in computer software, firmware, or hardware (including the structures disclosed herein and their equivalents), or in a combination of one or more of these. Embodiments of the subject matter described herein can be implemented as one or more computer programs (i.e., one or more modules of computer program instructions) encoded on a computer storage medium for execution by an information / data processing device or for controlling the operation of the information / data processing device. Alternatively or additionally, the program instructions can be encoded on artificially generated propagation signals (e.g., machine-generated electrical, optical, or electromagnetic signals) generated to encode information / data for transmission to a suitable receiver device for execution by the information / data processing device. The computer storage medium can be a computer-readable storage device, a computer-readable storage substrate, a random access memory array or device, or a serial access memory array or device, or a combination of one or more of these, or be included in a computer-readable storage device, a computer-readable storage substrate, a random access memory array or device, or a serial access memory array or device, or a combination of one or more of these. Furthermore, although computer storage media are not propagating signals, they can be a source or destination of computer program instructions encoded in artificially generated propagating signals. Computer storage media can also be one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices), or be included within such separate physical components or media.

[0152] The operations described herein can be implemented as operations performed by an information / data processing device on information / data stored on one or more computer-readable storage devices or received from other sources.

[0153] The term "data processing apparatus" encompasses all kinds of devices, apparatuses, and machines used for processing data, including, for example, programmable processors, computers, systems-on-a-chip, or one or more of the foregoing. Apparatus may include special-purpose logic circuitry, such as field-programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs). In addition to hardware, the apparatus may also include code that creates an execution environment for the computer program in question, such as code constituting processor firmware, protocol stacks, memory management systems, operating systems, cross-platform runtime environments, virtual machines, or combinations thereof. Apparatus and execution environments can implement a variety of different computing model infrastructures, such as web services, distributed computing infrastructures, and grid computing infrastructures.

[0154] Computer programs (also referred to as programs, software, software applications, scripts, or code) can be written in any programming language, including compiled or interpreted languages, declarative languages, or procedural languages, and can be deployed in any form, including as standalone programs or as modules, components, subroutines, objects, or other units suitable for use in a computing environment. A computer program may, but does not necessarily, correspond to a file in a file system. A program may be stored as part of a file that holds other programs or information / data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinating files (e.g., a file that stores one or more modules, subroutines, or portions of code). A computer program may be deployed to execute on a single computer, or on multiple computers located in one location or distributed across multiple locations and interconnected by a communications network.

[0155] The processes and logical flows described herein can be executed by one or more programmable processors that execute one or more computer programs to perform actions by manipulating input information / data and generating output. For example, processors suitable for executing computer programs include both general-purpose microprocessors and special-purpose microprocessors, as well as any one or more processors of any kind of digital computer. Generally, the processor receives instructions and information / data from read-only memory or random access memory, or both. The basic elements of a computer are a processor for performing actions according to instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to, one or more mass storage devices (e.g., magnetic disks, magneto-optical disks, or optical disks) for storing data, to receive information / data from or to such mass storage devices, or both. However, a computer does not need to have such devices. Devices suitable for storing computer program instructions and information / data include all forms of non-volatile memory, media, and memory devices, including (for example) semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Processors and memory may be supplemented by or integrated into dedicated logic circuitry.

[0156] To provide interaction with the user, embodiments of the subject matter described herein can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information / data to the user, and a keyboard and pointing device (e.g., a mouse or trackball through which the user provides input to the computer). Other types of devices can be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback, such as visual, auditory, or tactile feedback; and input from the user can be received in any form, including sound input, voice input, or tactile input. Furthermore, the computer can interact with the user by transmitting and receiving documents from a device used by the user; for example, by transmitting a web page to a web browser in response to a request received from a web browser on the user's client device.

[0157] Implementations of the subject matter described herein can be implemented in a computing system that includes backend components (e.g., as an information / data server), middleware components (e.g., an application server), frontend components (e.g., a client computer with a graphical user interface or web browser through which a user can interact with a specific implementation of the subject matter described herein), or any combination of one or more such backend, middleware, or frontend components. The components of the system can be interconnected via any form or medium of digital information / data communication (e.g., a communication network). Examples of communication networks include local area networks (“LANs”) and wide area networks (“WANs”), interconnected networks (e.g., the Internet), and peer-to-peer networks (e.g., self-organizing peer-to-peer networks).

[0158] A computing system may include clients and servers. Clients and servers are typically remote to each other and usually interact via a communication network. The client-server relationship is established by means of computer programs running on respective computers that have a client-server relationship with each other. In some implementations, the server sends information / data (e.g., HTML pages) to the client device (e.g., for the purpose of displaying information / data to a user interacting with the client device and receiving user input from the user interacting with the client device). Information / data generated at the client device (e.g., the result of user interaction) can be received from the client device at the server.

[0159] While this specification contains numerous specific implementation details, these details should not be construed as limiting the scope of any disclosure or claim, but rather as descriptions of features specific to particular embodiments of a particular disclosure. Certain features described herein in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may be implemented separately in multiple embodiments or in any suitable sub-combination. Furthermore, although features may be described above as functioning in certain combinations and even initially claimed as such, in some cases one or more features from the claimed combination may be removed from the combination, and the claimed combination may be for sub-combinations or variations thereof.

[0160] Similarly, although operations are depicted in a specific order in the accompanying drawings, this should not be construed as requiring such operations to be performed in the specific order shown or in sequential order, or to perform all illustrated operations to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the embodiments described above should not be construed as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or comprised of multiple software products.

[0161] Therefore, specific embodiments of this subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions stated in the claims may be performed in a different order and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific order or sequence shown to achieve the desired result. In some specific embodiments, multitasking and parallel processing may be advantageous.

[0162] Details of various embodiments of this disclosure are described in the documents on the following pages, which are incorporated herein by reference. In particular, the documents on the following pages, as appendices, exemplify various embodiments of this disclosure.

Claims

1. A method, the method comprising: A first optical frequency comb with a first repetition rate and a second optical frequency comb with a second repetition rate different from the first repetition rate are generated from a dual-frequency comb source; One or more of the first or second optical frequency combs are directed toward the material using one or more optical elements. A diode photodetector is used to detect optical signals from the first optical frequency comb and the second optical frequency comb after one or more of the first optical frequency comb or the second optical frequency comb interacts with the material. The diode photodetector is used to generate an RF signal corresponding to the optical signal; as well as The thickness of the material is determined based on the RF signal.

2. The method of claim 1, wherein determining the thickness of the material comprises: Spectral information is extracted from the RF signal, wherein the spectral information includes one or more of interference fringe patterns or absorption features; as well as The thickness is determined based on the spectral information.

3. The method of claim 1, wherein guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material comprises: Both the first optical frequency comb and the second optical frequency comb propagate through the material.

4. The method of claim 1, wherein guiding one or more of the first optical frequency comb or the second optical frequency comb toward the material comprises: The first optical frequency comb and the second optical frequency comb are combined to generate a combined optical frequency comb; as well as The optical frequency comb of the combination is directed toward the material.

5. The method of claim 1, wherein the dual-frequency comb source is positioned on a first side relative to the material, and wherein the diode photodetector is positioned on a second side relative to the material.

6. The method of claim 1, wherein both the dual-frequency comb source and the diode photodetector are positioned on a first side relative to the material.

7. The method of claim 1, wherein one or more of the first optical frequency comb or the second optical frequency comb operates in a wavelength range of 1 micrometer to 2 micrometers.

8. The method of claim 1, wherein one or more of the first optical frequency comb or the second optical frequency comb operates in a wavelength range of 2 micrometers to 9 micrometers.

9. The method according to claim 1, wherein the dual-frequency comb source is an optical fiber-based source.

10. A system comprising: The device is configured to generate a first optical frequency comb having a first repetition rate and a second optical frequency comb having a second repetition rate different from the first repetition rate; One or more optical components, the one or more optical components being configured to guide one or more of the first optical frequency comb or the second optical frequency comb toward the material; A diode photodetector configured to: (i) detect an optical signal from the first optical frequency comb and the second optical frequency comb after one or more of the first optical frequency comb or the second optical frequency comb interacts with the material, and (ii) generate an RF signal corresponding to the optical signal; and A signal processor configured to determine the thickness of the material based on the RF signal.

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