Automatic probe focal length measurement system and method

Abstract

The invention relates to an automatic probe focal length measurement system and method. A measurement system for focal length measurement of an optical device includes: a translation stage including a base and a platform configured to be driven by a linear actuator to translate in a linear motion relative to each other in an automatic manner; a reference material disposed on the translation stage and having a surface opposite the optical device to be measured; a measuring device configured to automatically measure a gap between a surface of the reference material and a distal tip of the optical device; a spectrometer in optical communication with the optics; and a controller configured to operate the translation stage, the measurement device, and the spectrometer, and determine a focal length of the optical device based on a spectral characteristic of the measurement spectrum and based on a final gap between a surface of the reference material and a distal tip of the optical device when the spectral characteristic is determined.

Description

Technical Field

[0001] The present disclosure relates generally to optical probe assemblies, and more particularly to optical assemblies for spectroscopy. Background Art

[0002] Spectrometers, such as dispersive spectrometers, are included in, for example, absorption measurement instruments, vibrational spectroscopy instruments, non-rotational spectroscopy techniques, and Raman spectroscopy instruments, which are currently employed in a variety of applications, including industrial and laboratory applications, to determine and provide measurement results for various measured values ​​of a medium. For example, an absorption spectrum of a medium determined by a dispersive spectrometer of an absorption measurement device is employed to determine and provide measurement results for the concentration of a component included in the medium, the turbidity of the medium, and / or at least one other measured value. For another example, a Raman spectrum of a sample of a medium determined by a dispersive spectrometer of a Raman spectroscopy device is employed to determine and provide measurement results for the concentration of a component included in the medium, the pH value of the medium, the melt index of the medium, the cell motility of the medium, and / or at least one other measured value. Raman spectroscopy has become a powerful tool for use in conjunction with in-situ process analysis.

[0003] A dispersive spectrometer typically includes a disperser (e.g., a diffraction or holographic grating), dispersed incident light, and a detector comprising an array of detection elements (e.g., a CCD camera, a photodiode array, or another type of detector array). The detection elements are arranged so that each receives a different portion of the dispersed light and determines and provides a detection signal corresponding to the intensity of the received portion of the dispersed light. For example, the detection signal is provided to a signal processor, which, based on the detection signal, determines and provides a spectral intensity value for the intensity spectrum of the light received by the detector.

[0004] Raman spectroscopy is based on an effect known as Raman scattering. Raman scattering is a type of inelastic scattering of electromagnetic radiation (such as excitation light from a laser) as it passes through a medium. The effect can be summarized as follows: Most incident photons of the excitation undergo elastic scattering (known as Rayleigh scattering), resulting in scattered radiation with the same wavelength as the incident radiation. However, a minority of incident photons undergo inelastic scattering, producing emitted photons with lower or higher energy, resulting in emission wavelengths (e.g., frequencies) above and / or below that of the incident radiation, known as Raman shifts.

[0005] Inelastic Raman scattering results from a selective interaction between incident radiation and molecules, an interaction that is specific to each chemical bond. The wavelength shift observed in the inelastically scattered radiation (i.e., the Raman shift) can be collected and separated from the strong Rayleigh scattered light to generate information about the composition of the medium, such as the concentration of specific molecules. However, because the fraction of radiation that undergoes a Raman shift is small, the resulting signal is relatively weak. Therefore, it is necessary to properly focus the excitation light at or near a nominal design focal point or area to maximize the intensity of the excitation light on the medium sample being investigated, and thus maximize its effect, and to maximize the signal strength (e.g., signal-to-noise ratio, SNR) within the collected light. Furthermore, poor optical focusing can lead to chromatic aberration of the signal.

[0006] Furthermore, probe optics are typically designed with a specified focal length, but the true focal length must be measured after the probe is manufactured to obtain an accurate number and determine whether the probe is built within quality control specifications. For at least these reasons, manufacturers of such optical probes may perform a quality check on the probe's focal length to confirm that the probe assembly is within design specifications. Traditionally, such quality checks are highly labor-intensive, requiring a skilled operator to use manual adjustments to determine the true focal length and manual data recording.

[0007] Therefore, further contributions are still needed in this area of ​​technology. Summary of the Invention

[0008] In at least one aspect of the present disclosure, a measurement system for measuring the focal length of an optical device to be measured includes: a translation stage including a base and a platform configured to translate relative to each other via a guide rail and connected such that the platform is constrained to linear motion relative to the base along an axis of the guide rail, wherein the translation stage further includes a linear actuator configured to automatically move the platform along the axis; a reference material disposed on the base of the translation stage and having a surface opposite to the optical device to be measured; a measurement device configured to automatically measure a gap between the surface of the reference material and a distal tip of the optical device to be measured; a spectrometer in optical communication with the optical device; and a controller configured to operate the translation stage, the measurement device, and the spectrometer and determine the focal length of the optical device based on spectral characteristics of a measured spectrum generated by the spectrometer and based on a final gap between the surface of the reference material and the distal tip of the optical device when the spectral characteristics are determined. The spectral characteristics are based on at least one of maximum intensity, band peak ratio, band area, and band area ratio.

[0009] In an embodiment, the controller is configured to determine the final gap based on an initial gap between a surface of a reference material and the distal tip of the optical device (which defines a starting point) and based on a net travel distance between the platform and the starting point. In another embodiment, the controller is configured to determine the final gap based on measurements taken by a measurement device.

[0010] In an embodiment, the measuring apparatus includes a first optical micrometer operable to generate a first light curtain between a first light source unit and a first receiver unit disposed on opposite sides of the translation stage, the first optical micrometer being configured such that a first portion of the first light curtain intersects a reference material and the optical device, wherein the first receiver unit is configured to measure the initial gap based on a second portion of the first light curtain incident on the first receiver unit.

[0011] In some such embodiments, the measurement device includes a second optical micrometer disposed in the same plane as the first optical micrometer but at an angle to the first optical micrometer, the second optical micrometer being operable to generate a second light curtain between a second light source unit and a second receiver unit disposed on opposite sides of the translation stage, wherein the second light curtain is angled relative to the first light curtain, wherein the second optical micrometer is configured such that a first portion of the second light curtain intersects the reference material and the optical device, and wherein the second receiver unit is configured to determine the final gap based on a second portion of the second light curtain incident on the second receiver unit.

[0012] In another embodiment, the linear actuator is a stepper motor, and wherein the controller is configured to determine the net travel distance by counting the net number of steps taken by the stepper motor from the starting point to the final gap. In such an embodiment, wherein the linear actuator is operable to an accuracy of 5 micrometers (μm), the determined focal length is accurate to within 12.5 μm.

[0013] In an embodiment, the translation stage is configured with one degree of freedom.

[0014] In another aspect of the present disclosure, a method for measuring the focal length of an optical device in an automated manner includes: providing a measurement system according to the present disclosure; translating the optical device to be measured to a starting point via a platform, wherein the starting point defines an initial gap between the distal tip of the optical device and a reference material; transmitting excitation light onto the surface of the reference material so that measurement light is scattered, emitted and / or absorbed from the reference material; collecting the measurement light, transmitting the measurement light to a spectrometer, and generating a measurement spectrum of the collected measurement light; using feedback from the spectrometer to translate the platform in a first direction while sequentially and repeatedly transmitting excitation light, collecting measurement light and generating a measurement spectrum until a specified spectral characteristic of the measurement spectrum is determined; using feedback from the spectrometer to translate the platform in an opposite second direction until the spectral characteristic is determined in the second direction; and determining the focal length of the optical device based on the final gap between the distal tip of the optical device and the surface of the reference material when the spectral characteristic is determined.

[0015] Embodiments of the present disclosure also include determining a final gap based on the initial gap at the starting point and the net travel distance between the platform and the starting point.

[0016] In certain embodiments, wherein the linear actuator of the translation stage is a stepper motor, the stepper motor being configured to translate the optical device via the stage in incremental steps, the net travel distance is calculated by counting a net number of steps taken by the stepper motor in a first direction from a starting point to a final gap relative to a second direction. In certain such embodiments, the incremental steps are larger in the first direction than in the second direction.

[0017] In one embodiment, the starting point is specified and determined by measuring the initial gap using a measuring device. In another embodiment, the starting point is selected to be greater than the designed nominal focal length of the optical device. In yet another embodiment, the starting point is selected such that the first direction is toward the base of the translation stage. In yet another embodiment, the starting point is selected such that the first direction extends away from the base of the translation stage.

[0018] At least one embodiment further comprises: comparing the determined focal length to a specified focal length range for the optical device; and generating a message when the determined focal length is outside the specified range. At least one embodiment further comprises generating a message when the determined focal length is within the specified range. At least one embodiment further comprises recording the determined focal length for the optical device.

[0019] In another aspect of the present disclosure, a computer program product for operating the measurement system of the present disclosure includes a non-transitory machine-readable storage medium encoding instructions that, when executed by one or more programmable processors of a controller, cause the one or more programmable processors to perform operations including: translating an optical device to be measured to a starting point via a platform; transmitting excitation light onto a surface of a reference material so that measurement light is scattered, emitted, and / or absorbed from the reference material; collecting the measurement light, transmitting the measurement light to a spectrometer, and generating a measurement spectrum of the collected measurement light; translating the platform in a first direction using feedback from the spectrometer while sequentially and repeatedly transmitting excitation light, collecting measurement light, and generating a measurement spectrum until a prescribed spectral characteristic of the measurement spectrum is determined; translating the platform in an opposite second direction using feedback from the spectrometer until the spectral characteristic is determined in the second direction; and determining a focal length of the optical device based on a final gap between the distal tip of the optical device and the reference material when the spectral characteristic is determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The described embodiments and other features, advantages, and disclosures contained herein, as well as the manner in which they are achieved, will become apparent, and the present disclosure will be better understood, by referring to the following description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A schematic diagram illustrating an embodiment of a measurement system according to the present disclosure is shown;

[0022] Figure 2 shows a schematic plan view of another embodiment of a measurement system according to the present disclosure;

[0023] Figure 3 shows a schematic diagram of a spectrometer;

[0024] Figure 4 An exemplary Raman spectroscopy signal spectrum of a silicon reference material is shown, expressed as Raman shift (cm -1 ) is expressed for intensity (arbitrary units);

[0025] Figure 5 A method for measuring the focal length of a probe to be measured according to the present disclosure is shown; and

[0026] Figure 6 An exemplary measured spectrum according to the disclosed method is shown, with Raman shift (cm -1 ) is expressed in terms of intensity (arbitrary units).

[0027] In the figures, like features are identified by like reference numerals. DETAILED DESCRIPTION

[0028] The present disclosure discloses various embodiments of a focus measurement system for an optical probe and methods of using the same. According to one aspect of the present disclosure, a focus measurement system for an optical probe configured for Raman spectroscopy is disclosed. According to another aspect of the present disclosure, a method of using the measurement system to perform a measurement of the focus of an optical probe configured for Raman spectroscopy is disclosed. Although the focus measurement system and methods of using the same are described in the context of Raman spectroscopy, it will be understood that the structures and methods disclosed herein can be applied to optical probes configured for other types of spectroscopy and analytical optical sensors, such as absorption spectroscopy and vibrational spectroscopy in general.

[0029] Depending on the intended application of the probe, the systems and methods of the present disclosure are applicable to optical probes having different design focal lengths. For example, a probe designed for a bioprocessing application may have a relatively short focal length, and the overall length of such a probe may be relatively short. In addition, a probe manufactured for an industrial chemical application (sometimes referred to as an "immersion optic") may have a relatively long focal length and a relatively long overall length. Those skilled in the art will understand that the terms probe, optical probe, optics, and terminal optics are sometimes used interchangeably in this disclosure.

[0030] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe these embodiments. It will be understood, however, that this is not intended to limit the scope of the disclosure.

[0031] Figure 1 A measurement system 100 for measuring the focal length of an optical device 10 (e.g., an optical device of a probe head or, more generally, an optical probe) to be measured according to at least one embodiment of the present disclosure is shown. The measurement system 100 includes a translation stage 20 on which the optical device 10, whose focal length is to be measured, can be rigidly and reversibly mounted. The translation stage 20 can include a base 24 and a platform 22, which are configured to translate relative to each other and are connected via one or more rails 26 such that the platform 22 is constrained to linear motion relative to the base 24. The measurement system 100 includes a reference material 50 disposed on the base 24, the reference material 50 having a surface facing the optical device 10 such that light emitted from the optical device 10 is incident on the surface.

[0032] In at least one embodiment according to the present disclosure, the measurement system 100 includes a spectrometer 300, which is in optical communication with the optical device 10 to be measured via an optical fiber 18, such as Figure 110. The optical fiber 18 can be reversibly connected to the optical device 10 at one end via a connector 16 and reversibly connected to the spectrometer 300 at the other end via a similar or different connector. The spectrometer 300 is operable to generate and transmit excitation light to the optical device 10 and to receive and operate on measurement light from the optical device 10, both via the optical fiber 18.

[0033] The measurement system 100 includes at least one measurement device 30 configured to measure, in an automated manner, a gap 38 between a surface of a reference material 50 and the distal tip 14 of the optical device 10 to be measured. Figure 1 As shown, the measurement device 30 can be an optical micrometer (e.g., a precision laser micrometer, a laser caliper) that is operable and configured to generate a light curtain 36 between a light source unit 32 and a receiver unit 34 of the optical micrometer, the light source unit 32 and the receiver unit 34 being disposed on opposite sides of the translation stage 20 such that a first portion of the light curtain 36 intersects and is blocked by the reference material 50 and the optical device 10. In such a configuration, the receiver unit 34 is configured to measure the gap 38 based on a second portion of the light curtain 36 incident on the receiver unit 34. In at least one embodiment, the light source unit 32 and the receiver unit 34 can be mounted to a common track that supports each unit 32, 34 and fixes their relative positions to each other and to the translation stage 20.

[0034] In at least one embodiment according to the present disclosure, the measurement system 100 includes a controller 40 that communicates (e.g., digitally) with the translation stage 20, the spectrometer 300, and the at least one measurement device 30. The controller can be configured to operate the translation stage 20, the measurement device 30, and the spectrometer 300, and determine the focal length of the optical device 10 based on the spectral characteristics (e.g., maximum intensity) of the spectral signal from the reference material 50 detected by the spectrometer 300 and the final gap 38 between the surface of the reference material 50 and the distal tip 14 of the optical device 10 when the maximum intensity is detected.

[0035] Controller 40 can be configured to perform certain operations and includes control structures for providing the functionality described herein. In certain embodiments, controller 40 forms part of a processing subsystem comprising one or more computing devices with memory 42 and processing and / or communication hardware 44. For example, the processor of spectrometer 300 and / or its functionality may be included in controller 40. Controller 40 may be a single device or a distributed device, and its functionality may be performed by hardware and / or software. Controller 40 may include one or more arithmetic logic units (ALUs), central processing units (CPUs), memory, limiters, regulators, filters, format converters, and the like, which are not shown for clarity. In at least one embodiment, controller 40 is programmable to execute algorithms and process data according to operational logic defined by programmed instructions (such as software or firmware). Alternatively or additionally, the operational logic of controller 40 can be defined at least in part by hardwired logic or other hardware, for example, using any suitable type of application-specific integrated circuit (ASIC). Controller 40 can be dedicated to the functionality described herein or may further be used to regulate, control, and activate one or more other subsystems or aspects of the measurement systems and methods of the present disclosure.

[0036] The translation stage 20 also includes a linear actuator 28 connected to the platform 22 and configured to automatically move (e.g., translate) the platform 22 along the axis 25 within the guide rail 26 based on commands from a controller 40. In at least one embodiment, the controller 40 communicates with the linear actuator 28 and is configured to control the linear actuator 28 to determine the travel distance, position, starting point, and generally the current position of the platform 22. The linear actuator 28 may be a stepper motor that drives a lead screw in fixed increments called steps. In such linear actuators 28, the travel distance of the lead screw, and therefore the platform 22, per incremental step depends on the resolution of the stepper motor. For example, some commercially available motors are capable of half-stepping at a rate of 1 μm / pulse (micrometers / pulse), with a positioning accuracy of 5 μm, a repeatability of 3 μm, a backlash of 3 μm, and a total range of 35 mm. The minimum resolution of the linear actuator 28 is within the ±10 μm range and is at least ±12.5 μm. In another embodiment, the linear actuator 28 may be a piezoelectric motor configured to move the platform via an applied voltage or electric field.

[0037] The translation stage 20 may further include a bracket 23 (e.g., a securing mechanism such as a collar and set screw, a spring-loaded or friction-fit latch, or other suitable mechanism) configured to rigidly and reversibly secure the optical device 10 to the platform 22. The bracket 23 may include an index or reference surface configured to interface with the probe body 12 of the probe 10, thereby enabling repeatable and reproducible positioning and holding of the probe 10 relative to the platform 22.

[0038] In at least one embodiment of the translation stage 20, the platform 22 is constrained to linear motion (e.g., one degree of freedom) relative to the base 24 along the axis 25 of the guide rail 26. For example, the platform 22 and the base 24 can be arranged orthogonally to each other. In at least one embodiment, as Figure 1 As shown, the base 24 is oriented horizontally and the platform 22 is oriented vertically, e.g. Figure 1 2. The translation stage 20 is oriented vertically along the z-axis of the xyz coordinate system shown. In such an embodiment, at least one guide rail 26 can be oriented vertically, thereby limiting the linear motion of the platform 22 to vertical motion along the axis 25 of the guide rail 26. This embodiment of the translation stage 20 is generally referred to as a z-axis stage, and the base 24 is stationary, e.g., does not translate. In an alternative embodiment, the base 24 can be oriented vertically, while the platform 22 can be oriented horizontally (e.g., on the x-axis) to limit horizontal linear motion.

[0039] The guide rail 26 may include a linear bearing operable to constrain the platform 22 to linear motion in a stable, repeatable, and reliable manner. As non-limiting examples, the guide rail 26 may include at least one roller (e.g., a ball bearing and a crossed roller bearing), a slide rail, a cylindrical sleeve, a dovetail track, or a flexure mechanism in which elastic deformation of the material of the mechanism effects translation.

[0040] In the context of the present disclosure, the optical device 10 to be measured may include an assembly of one or more lenses fixed within a probe body 12, which includes an internal volume in which the one or more lenses are disposed. The optical device 10 may include other optical devices ( Figure 11 ), such as, for example: a collimating lens for collimating excitation light entering the optical device 10 along a beam path within the probe body 12, e.g., via an optical fiber (e.g., optical fiber 18); one or more bandpass filters for removing undesired wavelengths generated en route to the light source generating the excitation light (e.g., those caused by the optical fiber transmitting the excitation light from the light source) and / or Rayleigh scattered light having the same wavelength as the excitation light after the excitation laser interacts with the analyte; and an objective lens configured to focus the excitation light from the beam path into a sample to be investigated or to a focal point or region to be illuminated, the focal point or region being a defined external focal distance from the distal tip 14 of the optical device 10, e.g., an outer surface of the objective lens or a transparent window of the optical device 10 distal to the objective lens. In at least one embodiment, the optical device 10 can be a terminal optical device (or simply "optical device") of a larger probe assembly to which the terminal optical device can be physically and optically connected.

[0041] The optical device 10 is configured to collect light scattered or emitted by the sample resulting from incident excitation light and direct the collected light through the probe body 12. In certain embodiments, the lens of the optical device 10 can both focus the collimated excitation light into the sample and collimate the collected light from the sample into a counter-propagating beam path within the probe body 12. The collected light (referred to herein as measurement light) can then be transmitted to the spectrometer 300 for spectral detection.

[0042] Figure 3 An exemplary and non-limiting schematic diagram of a spectrometer suitable for use with the measurement systems and methods of the present disclosure is shown. For example, spectrometer 300 can include a monochromatic light source 1, such as a laser, configured to transmit excitation light L0 having an excitation wavelength λ0 to a measurement region 3, which is configured to accommodate a sample S of a medium. In the context of the present disclosure, sample S is a reference material 50, and measurement region 3 is a base 24 of a translation stage 20 on which the reference material 50 is placed. In certain embodiments, the excitation wavelength λ0 is, for example, a wavelength within the visible or near-infrared wavelength range. As a non-limiting example, the excitation wavelength λ0 is, for example, a wavelength from 400 nm to 1300 nm, and may be 1064 nm, 993 nm, 785 nm, 632.8 nm, 532 nm, 405 nm, or other wavelengths within the visible or near-infrared wavelength range.

[0043] In certain embodiments, the spectrometer 300 may include a filter 5 , such as a notch filter, configured to filter out the measurement signal LR included in the measurement light L1 emitted from the measurement region 3 .

[0044] The spectrometer 300 further comprises a spectrometric unit 7 configured to receive a measurement signal LR radiating from the illuminated sample S and to determine and provide an intensity spectrum I(λ) of the measurement signal LR within a spectral measurement range Δλ of the spectrometer 300 .

[0045] In certain embodiments, the spectrometric unit 7 includes a scatterer 9, such as a diffraction grating or a holographic grating, configured to scatter an incident measurement signal LR; a detector 11, such as an array of charge-coupled devices (CCDs) or an array of photodiodes, such as silicon photodiodes or avalanche photodiodes, configured to receive the scattered measurement signal LR; and a signal processor 13, such as a microprocessor, connected to the detector 11. The detector 11 is configured to determine and provide a detector signal corresponding to the spectral intensity of the incident scattered measurement signal LR. The signal processor 13 is configured to determine and provide an intensity spectrum I(λ) of the measurement signal LR based on the detector signal. In certain embodiments, the spectrometer 300 can be configured to operate for Raman or other spectroscopic techniques, such as Fourier transform infrared spectroscopy (FT-IR), absorbance, or ultraviolet light. Any spectrometer operable to capture intensity variations in the optical components required to focus incident light (e.g., excitation light) on an analyte is suitable for use with the measurement systems and methods of the present disclosure.

[0046] According to at least one embodiment of the present disclosure, the optical device 10 is specifically configured for Raman spectroscopy, and the spectrometer 300 is a Raman spectrometer configured for Raman spectroscopy. In such an embodiment, during measurement of the focal length of the optical device 10, the reference material 50 is located in the measurement region 3 (e.g., on the base 24) and is illuminated by the light source 1. In this case, the measurement signal LR is the Raman scattered light emitted from the illuminated reference material 50, and the intensity spectrum I(λ) provided by the spectrometry unit 7 is the Raman spectrum of the reference material 50. The Raman spectrum thus determined is provided to the controller 40, for example, which determines and provides a measurement result mv of the intensity value of the intensity spectrum I(λ) based on a previously determined model M of the reference material 50, the model M being used to determine the measurement result mv based on the spectral intensity of the Raman spectrum provided by the spectrometry unit 7. In this regard, the controller 40 is an integral part of the Raman spectrometer 300, or is an external unit configured to receive the intensity spectrum I(λ) determined by the spectrometry unit 7, such as Figure 1 In either case, the controller 40 is connected to or in communication with the spectrometric unit 7, for example.

[0047] Reference material 50 can be any suitable substance that exhibits a unique spectral peak intensity and can be formed into a very flat wafer (e.g., a plate or disk). Having a unique maximum intensity peak enables good resolution of focus measurements. Non-limiting examples of suitable reference materials include silicon and diamond, such as synthetic diamond. Figure 4 An exemplary intensity spectrum (expressed in arbitrary units) of the Raman signal of a silicon wafer reference material using 785 nm excitation is shown, although spectrometer 300 may be based on any suitable light source wavelength known to those skilled in the art. -1 ) achieves good resolution of focus measurement. When the optical device is not focused, the energy density of the excitation light L1 in the measurement area 3 is reduced, and the maximum (e.g., peak) intensity of the spectral signal may be reduced, or the relative intensities at different wavelengths in the spectrum (e.g., band area, peak ratio, and band area ratio) may be distorted. For example, Figure 4 In such cases, the band area at peak intensity may be distorted relative to the nominal band area at the true focus.

[0048] In embodiments where the optical device 10 includes an external window that generates its own spectral signal within the measurement signal LR (e.g., a unique peak intensity separated from (e.g., having a different Raman shift than) the peak of the reference material 50), the ratio of intensities at corresponding wavelengths or the ratio of band areas at these peak intensities can be used to determine the focal length of the optical device 10. The band-peak ratio and band-area ratio can also be determined for only the reference material 50, e.g., when the reference material 50 exhibits two or more local peak intensities (e.g., bands) at different wavelengths. For example, Figure 4 As shown, silicon has a peak at about 405 cm -1 The ratio of the peak intensities and / or the ratio of the band areas of the two peaks can be spectral characteristics used to determine the focal length.

[0049] As used in the context of this disclosure, such spectral characteristics (e.g., peak intensity, band-to-peak ratio, band area, and band-to-area ratio) are referred to as spectral characteristics of the measured spectrum. The spectral characteristics can be selected relative to the spectral characteristics of the reference material 50 and its spectral characteristics at a given excitation light wavelength, L0. In certain embodiments, the spectral characteristics can be further selected relative to the spectral characteristics of the optical device 10, such as the spectral signal of an external window of the optical device 10.

[0050] According to at least one embodiment of the present disclosure, the measurement system 200 includes a first measurement device 30a and a second measurement device 30b, such as Figure 2 In such an embodiment, other elements of the measurement system 200, such as the translation stage 20 having the platform 22 and the base 24 on which the reference material 50 is placed, may be coupled to the measurement system 200. Figure 1 Similarly, the optical device 10 to be measured can be connected to the spectrometer 300 and the controller 40 ( Figure 2 ). However, in such an embodiment, the controller 40 may be configured differently to operate and communicate with the second measurement device 30b, as further described herein.

[0051] The first measurement device 30a and the second measurement device 30b can be identical, or they can be different, for example, having different measurement ranges. The first and second measurement devices 30a and 30b can be arranged in different planes at an angle a relative to each other. In some embodiments, angle a can be 90° or less. The first measurement device 30a can be selected and configured to measure the initial gap (e.g., at a starting position or point) between the surface of the reference material 50 and the distal tip 14 of the optical device 10, and the second measurement device 30b can be selected and configured to measure the final gap between the surface of the reference material 50 and the distal tip 14 of the optical device 10 after the focal length has been determined. In another embodiment, the second measurement device 30b can be capable of performing both initial and final gap measurements for a probe having a relatively long focal length, and the first measurement device 30a can be capable of performing only the final gap measurement for a probe having a relatively short focal length, while the second measurement device 30b is used to measure the initial gap for such a relatively short focal length probe. The measurement system 200 including the first and second measurement devices 30a, 30b may facilitate measuring different probes having a wide range of focal lengths.

[0052] In embodiments of the present disclosure in which the optical device 10 is used for Raman spectroscopy, the focal length (e.g., focal length) of the optical device 10 during assembly is of critical importance. Because the Raman signal from inelastic scattering is relatively weak, it is necessary to properly focus the optical device 10 at or near a nominal design focal point or area to maximize the intensity of the excitation light, thereby maximizing the effect of the excitation light, and to maximize the intensity of the Raman signal within the collected light (e.g., signal-to-noise ratio, SNR). Furthermore, poor optical focus may result in chromatic and / or spherical aberration of the signal, whereby the intensity of longer wavelengths within the signal is disproportionately reduced compared to shorter wavelengths, which may distort the band intensity ratio or band area ratio between reference bands within the measured spectrum of the optical device 10. As a non-limiting example, embodiments of the optical device 10 having a relatively short focal length may include a specified nominal focal length range of 25–250 μm (approximately 0.001–0.010 inches). Embodiments of the optical device 10 having a relatively long focal length may include a specified nominal focal length range of 2500-5600 μm (approximately 0.10-0.22 inches).

[0053] Another aspect of the present disclosure includes a method of measuring the focal length of an optical device (eg, an end optic) using the measurement system 100 according to the present disclosure. Figure 5 This method 500 is shown in . The method 500 and its embodiments may be performed to verify the quality of a probe (eg, whether it functions properly) as part of a probe manufacturing process or as part of a failure analysis, as non-limiting examples.

[0054] According to one embodiment of the present disclosure, the method 500 may include a step 510 of providing the measurement system 100, such as Figure 1 As shown. Step 510 includes introducing the optical device 10 to be measured into the translation stage 20 and securing the optical device 10 therein. Method 500 includes the following step 520 of translating the optical device 10 along axis 25 via the platform 22 to a starting point, which defines the distance between the optical device 10 and the reference material 50. The starting point can be selected such that the optical device 10 is out of focus, such that the gap 38 between the distal tip 14 of the optical device 10 and the surface of the reference material 50 disposed on the base 24 of the translation stage 20 is greater than or less than the nominal design focal length. In at least one embodiment, the starting point is selected such that the gap 38 is greater than the nominal design focal length. Such an embodiment can ensure that the optical device 10 does not inadvertently collide with the reference material 50 or the base 24 when translating to or from the starting point.

[0055] The starting point can be determined by measuring a gap 38 between the distal tip 14 of the optical device 10 and the incident surface of a reference material 50 disposed on the base 24 of the translation stage 20, where the starting point coincides with a specified gap distance therebetween. The gap 38 can be continuously measured while the optical device 10 is translated until it reaches the starting point, which defines the initial gap for the controller 40. In at least one embodiment, the gap 38 is measured using a measurement device 30, which continuously transmits the measured values ​​of the gap 38 to the controller 40.

[0056] Method 500 further includes step 530 of transmitting, after reaching the starting point, excitation light L0 from light source 1 of spectrometer 300 via optical fiber 18 and then through optical device 10 to the incident surface of reference material 50, such that measurement light L1 is scattered, emitted, and / or absorbed by reference material 50. Step 530 also includes collecting measurement light L1 using optical device 10 and transmitting measurement light L1 to spectrometer 300 via optical fiber 18. Whether measurement light L1 collected by optical device 10 is scattered, emitted, and / or absorbed depends on the type of spectrum for which spectrometer 300 and optical device 10 are configured, and to which method 500 is accordingly applicable.

[0057] Step 530 also includes generating a measurement spectrum I(λ) of the collected measurement light L1. In the case where the optical device 10 to be measured is a Raman optical device operable for Raman spectroscopy, the measurement light L1 includes a Raman signal (e.g., Figure 3 Because the measurement light L1 may include elastically scattered (Rayleigh) light, the optical device 10 or the spectrometer 300 may include a filter 5 configured to filter the measurement signal LR included in the measurement light L1 collected from the reference material 50. The measurement signal LR is then processed using the spectrometer 300 to generate a measurement spectrum I(λ) based on the spectral intensity at the wavelengths of the measurement range, as described with respect to Figure 3 As described, and determining the spectral characteristics of the measurement intensity spectrum, such as the measurement spectrum I(λ). Generating the measurement spectrum I(λ) may include spectrally dispersing and detecting the measurement signal LR (or measurement light L1) using the disperser 9 and detector 11 of the spectrometer 300, respectively, and generating the measurement spectrum I(λ) of the detected spectral intensity of the measurement signal LR.

[0058] Step 530 may also include determining the spectral characteristics of the measured spectrum I(λ) by analyzing (e.g., mathematically analyzing) the measured spectrum I(λ) at the current position of the optical device 10 (e.g., the current spectral characteristics). Those skilled in the art of the present disclosure will recognize and appreciate appropriate analytical mathematical tools and techniques for determining spectral characteristics based on data (e.g., spectral intensity) of the measured spectrum I(λ). In addition to tools and techniques for calculating spectral characteristics, determining the spectral characteristics may include comparing the determined value of the spectral characteristic at the current position of the optical device 10 (e.g., the current incremental step) with a previously determined value of the spectral characteristic. For example, when the currently determined value continues to increase relative to the previously determined value, such as when the spectral characteristic is at a maximum value for a selected spectral characteristic (e.g., intensity), the optical device 10 is translated in the current direction until a reverse trend is observed, causing the currently determined value to decrease relative to the previously determined value. In other embodiments, such as where the spectral characteristic is at a minimum value for a selected spectral characteristic (e.g., band area), a reverse trend may be used to determine the spectral characteristics. In such embodiments, the optical device 10 is translated in the current direction until a reverse trend is observed, causing the currently determined value to increase relative to the previously determined value.

[0059] Method 500 also includes a step 540 of translating optical device 10 from a starting point via platform 22 along axis 25 while sequentially and repeatedly performing the operations of step 530 until a spectral characteristic is determined. For example, the operations of transmitting excitation light, collecting measurement light, generating a measurement spectrum, and determining the spectral characteristic of step 530 are sequentially and repeatedly performed until at least one temporary spectral characteristic at the temporary position is determined. In at least one embodiment, linear actuator 28 can be used to translate optical device 10 in incremental steps, and at each incremental step, a measurement spectrum I(λ) of reference material 50 is generated and the current spectral characteristic is determined. For example, in an embodiment where linear actuator 28 is a stepper motor, optical device 10 can be moved in steps of 10-100 μm, and method steps 520 and 530 are sequentially performed at each incremental step.

[0060] Method 500 also includes step 550 of determining (e.g., identifying, calculating, or resolving) the temporary spectral characteristic of optical device 10 at the temporary position, translating optical device 10 along axis 25 via platform 22 in a second direction opposite the first direction using feedback from the spectrometer to confirm the final position of optical device 10 at which the spectral characteristic was determined, e.g., at or near the temporary position at which the temporary spectral characteristic was reacquired or determined. Step 550 may include translating optical device 10 in the second direction directly to the temporary position without performing steps 530 and 540 en route. For example, in step 540, optical device 10 may be translated in the first direction past the temporary position by a certain amount, e.g., to ensure that the temporary spectral characteristic is distinguished (e.g., identified). Then, in step 550, optical device 10 may be returned in the second direction to confirm the temporary position at which the spectral characteristic was determined. Step 550 may also include iteratively translating to either side of the temporary position (e.g., back and forth in the first and second directions) using feedback from the spectrometer until the final position at which the spectral characteristic was determined is confirmed to be at least within a specified range of values ​​or measurement tolerances. The final location can be the same as or different from the temporary location.

[0061] Figure 6 An exemplary set of measured spectra of a silicon reference material according to the present disclosure is illustrated. Figure 6In the illustrated example, the spectral characteristic is a maximum intensity at or about a Raman shift of 520 wavenumbers (in arbitrary units for this example). As shown, the maximum intensity at the starting point, Imax(f1), may be less than the maximum intensity, I(f2), at the true focal length. As optical device 10 is translated in a first direction, the maximum intensity may increase, and a maximum intensity, I(f2), at the true focal length will be observed. As optical device 10 is translated further past the true focal length, the maximum intensity may decrease to a lower maximum intensity value, I(f3). In this example, having observed a decrease in I(f3), optical device 12 may be translated back to the temporary position of I(f2), and optical device 12 may be iteratively translated around this position until a final position is identified at which the spectral characteristic is determined, as described herein.

[0062] Figure 6 This diagram illustrates how to use the same measured spectrum to determine the focal length where the spectral characteristic is the maximum band area. As shown in this example, the area under the curve is larger at the true focal length I(f2) than at the starting point I(f2), or when the gap is smaller than the true focal length, for example, the band area for I(f2) is larger than for I(f1) and I(f3).

[0063] In at least one embodiment, the spectral characteristic can be determined using a curve fit of data generated by repeatedly performing the operations of method 500 (e.g., steps 530 and 540). In such an embodiment, the first derivative of the fitted curve can be calculated and monitored to identify an inflection point of the fitted curve, at which location the temporary position is to be determined. In other embodiments, the spectral characteristic can be a target value, for example, a target value selected relative to a reference material 50 and its spectral characteristics at a given wavelength of excitation light L0.

[0064] In embodiments where the linear actuator 28 is a stepper motor, the incremental steps of method step 550 can be smaller than the incremental steps of method step 540. For example, in at least one embodiment, the steps of method step 550 can be 25% or 33% of the distance of the steps of method step 540 (as a non-limiting example, 150-200 μm compared to 50 μm). Such embodiments achieve finer resolution of the final position while reducing the overall cycle time of method 500 by determining the temporary position more quickly.

[0065] Method 500 further includes a step 560 of determining the focal length of optical device 10 based on a final gap between the distal tip of the probe and the surface of the reference material when the spectral characteristics are determined, after determining the spectral characteristics at the final position of optical device 10. Step 560 may include directly measuring the final gap or calculating the final gap.

[0066] In embodiments involving direct measurement, step 560 includes measuring the final gap using the measurement device 30 to directly measure the distance between the distal tip 14 of the optical device 10 and the opposing surface of the reference material 50 when the optical device 10 is in the final position determined by the spectral characteristics. For example, the reference Figure 1 In the illustrated embodiment of the measurement system 100, step 560 can include measuring the final gap using the measurement device 30. In some embodiments, both the initial gap and the final gap can be measured by the same measurement device 30. In such embodiments, the measurement device 30 can be configured to have sufficient range to measure a distance greater than the starting point (e.g., the initial gap) for both the short and long focal length configurations of the optical device 10, and to measure the final gap for both the short and long focal length configurations.

[0067] In another example, reference Figure 2 In the illustrated embodiment of measurement system 200, step 560 may include directly measuring the final gap using second measurement device 30b. Such an embodiment may be advantageous for probes to be measured having relatively long focal lengths. In such an embodiment, second measurement device 30b may be operable to further directly measure the initial gap for both the short and long focal length configurations of the probe to be measured. Furthermore, in such an embodiment, measurement device 30a may be operable to directly measure only the final gap for the short focal length configuration of the probe to be measured.

[0068] In at least one embodiment of method 500, the final gap is measured directly using measurement device 30; however, the initial gap, which defines the starting point, is not measured. In such an embodiment, an operator can manually set the initial gap, for example, by manually controlling a linear actuator. Such an embodiment simplifies measurement system 100 but may increase the risk of damage to the probe under test if improperly adjusted.

[0069] In accordance with at least one embodiment of the present disclosure, step 560 may include determining a final gap based on the initial gap at the starting point (e.g., as measured directly using measurement device 30) and the net travel distance of optical device 10 from the starting point via stage 22 during method steps 540 and 550. In such an embodiment, the net travel distance is calculated from the starting point by adding or subtracting the movement of stage 22 around the starting point (e.g., using controller 40). In embodiments of measurement system 100 where linear actuator 28 is a stepper motor, controller 40 may count the number of steps taken by the stepper motor during method steps 540 and 550 and convert the number of steps into a net travel distance based on the resolution of the stepper motor. As an example, steps away from the starting point may be counted as positive values, and steps toward the starting point may be counted as negative values, with the net travel distance determined by counting the net number of steps taken by the stepper motor from the starting point to the final gap. Such an embodiment enables the use of the measurement system 100 with a single, relatively low-range, low-cost measurement device 30 to measure the focal length of both short and long focal length configurations of the probe to be measured.

[0070] Method 500 may include a step 570 of recording the focal length in a memory of controller 40 after determining the focal length of optical device 10. In some embodiments, recording the focal length may include recording the focal length with a reference index associated with optical device 10. For example, the focal length with the reference index may be recorded in a spreadsheet stored in memory, such as by automatically populating the spreadsheet. As a non-limiting example, the reference index may be a serial number of a particular probe being tested.

[0071] Method 500 may include a step 580 of screening the probe under test by comparing the determined focal length to a specified focal length range for the probe. When the determined focal length is outside the specified range, a message may be generated alerting an operator or process control system to reject the probe. Similarly, when the determined focal length is within the specified range, a message may be generated alerting an operator or manufacturing system to accept the probe. Step 580 may include generating a message alerting an operator or process control system to reject the probe under test if the spectral characteristics are not identified (e.g., determined) before the distal tip 14 of the optical device 10 is within a minimum distance from the reference material 50. For example, the minimum distance may be the lower limit of the specified focal length range or a certain margin beyond the lower limit. Such an embodiment can ensure that the probe under test is not damaged, for example, by not colliding with the reference material 50 or the base 24 and not wasting additional production time on defective probes.

[0072] The measurement systems and methods of the present disclosure can be employed to inspect the quality of optical devices (and more generally, probes) during the manufacturing process (e.g., at the end of the assembly process) as one aspect of a quality control process. Furthermore, the measurement systems and methods of the present disclosure can be employed to facilitate the assembly process by notifying an operator of manufacturing adjustments to be applied to the probe during assembly, such as adding shims between the optical devices being manufactured or machining tolerance features in the probe.

[0073] Although various embodiments of a measurement system for optical probe focal length measurement and methods of using and constructing the measurement system have been described in considerable detail herein, these embodiments are provided by way of non-limiting examples of the disclosure described herein. It will therefore be understood that various changes and modifications may be made, and equivalents may be substituted for elements thereof, without departing from the scope of the disclosure. This disclosure is not intended to be exhaustive or to limit the scope of the disclosed subject matter.

[0074] Furthermore, when describing representative embodiments, the present disclosure may have presented methods and / or processes as a particular order of steps. However, to the extent that a method or process does not rely on the particular order of steps described herein, the method or process should not be limited to the particular order of steps described. Other order of steps are also possible and therefore still within the scope of the present disclosure.

Claims

1. A measurement system for measuring the focal length of an optical device to be measured, the measurement system comprising: a translation stage comprising a base and a platform, the base and the platform being configured to translate relative to each other via a guide rail and connected such that the platform is constrained to linear motion relative to the base along an axis of the guide rail, wherein the translation stage further comprises a linear actuator configured to move the platform along the axis in an automated manner; a reference material disposed on the base of the translation stage and having a surface opposite to the optical device to be measured; a measuring device configured to measure, in an automated manner, a gap between the surface of the reference material and the distal tip of the optical device to be measured; a spectrometer in optical communication with the optical device; and a controller configured to operate the translation stage, the measurement device, and the spectrometer, and to determine a focal length of the optical device based on spectral characteristics of a measurement spectrum generated by the spectrometer and based on a resulting gap between the surface of the reference material and the distal tip of the optical device when the spectral characteristics are determined.

2. The measurement system according to claim 1, wherein: The spectral characteristic is based on at least one of a maximum intensity, a band peak ratio, a band area, and a band area ratio.

3. The measurement system according to claim 1 or 2, wherein: The controller is configured to determine the final gap based on an initial gap between the surface of the reference material and the distal tip of the optical device and based on a net travel distance of the platform from a starting point, the initial gap defining the starting point.

4. The measuring system according to any one of the preceding claims, wherein The controller is configured to determine the final gap based on measurements of the measuring device.

5. The measuring system according to any one of the preceding claims, wherein The measuring apparatus includes a first optical micrometer operable to generate a first light curtain between a first light source unit and a first receiver unit disposed on opposite sides of the translation stage, the first optical micrometer being configured such that a first portion of the first light curtain intersects the reference material and the optical device, wherein the first receiver unit is configured to measure the initial gap based on a second portion of the first light curtain incident on the first receiver unit.

6. The measurement system according to claim 5, wherein: The measuring device includes a second optical micrometer arranged in the same plane as the first optical micrometer but at an angle to the first optical micrometer, the second optical micrometer being operable to generate a second light curtain between a second light source unit and a second receiver unit disposed on opposite sides of the translation stage, wherein the second light curtain is at the angle relative to the first light curtain, wherein the second optical micrometer is configured such that a first portion of the second light curtain intersects the reference material and the optical device, and wherein the second receiver unit is configured to determine the final gap based on a second portion of the second light curtain incident on the second receiver unit.

7. The measuring system according to any one of the preceding claims, wherein The linear actuator is a stepper motor, and wherein the controller is configured to determine the net travel distance by calculating a net number of steps taken by the stepper motor from the starting point to the final gap.

8. The measurement system according to claim 7, wherein: The linear actuator is capable of operating to an accuracy of 5 μm, enabling the focal length to be determined to within 12.5 μm.

9. The measurement system according to claim 1, wherein: The translation stage is configured with one degree of freedom.

10. A method for measuring the focal length of an optical device in an automated manner, the method comprising: Providing a measurement system according to any one of the preceding claims; translating the optical device to be measured via the platform to a starting point, wherein the starting point defines an initial gap between the distal tip of the optical device and the reference material; transmitting excitation light onto the surface of the reference material such that measurement light is scattered, emitted, and / or absorbed from the reference material; collecting the measurement light, transmitting the measurement light to the spectrometer, and generating a measurement spectrum of the collected measurement light; translating the stage in a first direction using feedback from the spectrometer while sequentially and repeatedly transmitting the excitation light, collecting the measurement light, and generating the measurement spectrum until prescribed spectral characteristics of the measurement spectrum are determined; translating the platform in an opposite second direction using feedback from the spectrometer until the spectral characteristic is determined in the second direction; and The focal length of the optical device is determined based on a resulting gap between the distal tip of the optical device and the surface of a reference material when the spectral characteristic is determined. 11 . The method of claim 10 , further comprising determining the final gap based on the initial gap at the starting point and a net travel distance between the platform and the starting point.

12. The method according to claim 10, wherein: The linear actuator of the translation stage is a stepper motor configured to translate the optical device via the platform in incremental steps, and wherein the net travel distance is calculated by counting a net number of steps taken by the stepper motor in the first direction from the starting point to the final gap relative to the second direction.

13. The method according to claim 12, wherein: The incremental steps are larger in the first direction than in the second direction.

14. The method according to claim 10, wherein: The starting point is specified and determined by measuring the initial gap using the measuring device.

15. The method according to claim 10, wherein The starting point is selected to be larger than the designed nominal focal length of the optical device.

16. The method according to claim 10, wherein The starting point is selected such that the first direction is toward the base of the translation stage.

17. The method according to claim 10, wherein The starting point is selected such that the first direction extends away from the base of the translation stage.

18. The method according to claim 10, further comprising: comparing the determined focal length to a specified focal length range for the optical device; and Generates a message when the determined focal length is outside a specified range.

19. The method of claim 10, further comprising generating a message and / or recording the determined focal length of the optical device when the determined focal length is within a specified range.

20. A computer program product for operating the measurement system of claim 1, the computer program product comprising a non-transitory machine-readable storage medium encoding instructions that, when executed by one or more programmable processors of the controller, cause the one or more programmable processors to perform operations comprising: translating the optical device to be measured to a starting point via the platform; transmitting excitation light onto the surface of the reference material such that measurement light is scattered, emitted, and / or absorbed from the reference material; collecting the measurement light, transmitting the measurement light to the spectrometer, and generating a measurement spectrum of the collected measurement light; translating the stage in a first direction using feedback from the spectrometer while sequentially and repeatedly transmitting the excitation light, collecting the measurement light, and generating the measurement spectrum until prescribed spectral characteristics of the measurement spectrum are determined; translating the platform in an opposite second direction using feedback from the spectrometer until the spectral characteristic is determined in the second direction; and The focal length of the optical device is determined based on a resulting gap between the distal tip of the optical device and the reference material when the spectral characteristic is determined.

Images