Method and apparatus for measuring distance

Abstract

An interferometry apparatus comprising: a laser source operable to emit a first light beam; a beam splitter arranged to split the first light beam into an object light beam and a reference light beam, the object light beam passing along an object light beam arm and the reference light beam passing along a reference light beam arm; an adaptive delay line located at a distance along the reference light beam arm, the adaptive delay line configured to provide, in use, one or more length-adjusted reference light beams; a beam splitter arranged to recombine the object light beam from the object light beam arm and the length-adjusted reference light beam(s) from the reference light beam arm; and a photodetector operable to detect interference between the object light beam and the length-adjusted reference light beam(s).

Description

Technical Field

[0001] This disclosure relates to apparatus for measuring distances, such as interferometric apparatus. This disclosure also relates to methods for measuring distances, including methods using the apparatus disclosed herein. Background Technology

[0002] Optical techniques for absolute distance measurement have been developed in many branches of science and engineering. Techniques based on tunable laser sources have been applied on length scales ranging from submillimeter (in the form of frequency-sweep optical coherence tomography (OCT)) to tens of meters or more in frequency-sweep interferometry (FSI) (often also known as frequency-modulated continuous wave (FMCW) lidar).

[0003] These techniques involve combining light reflected or scattered from a target (referred to as the object beam) with a local reference wave (referred to as the reference beam). Interference between the object beam and the reference beam can be detected. The object beam and the reference beam are separated from the initial beam of the laser source. There is an optical path difference between the travel distances of the object beam and the reference beam.

[0004] One issue is applying frequency-scanning interferometry to long-distance (approximately 10 meters) and high-speed (over 1000 rpm) operations. 5 Absolute distance measurement at any given coordinate is currently impractical at a reasonable cost due to the extremely high modulation frequencies (typically 100 GHz or higher). Summary of the Invention

[0005] A first aspect provides an interferometric measuring apparatus, comprising: a laser source operable to emit a first beam; a beam splitter arranged to split the first beam into an object beam and a reference beam, the object beam propagating along an object beam arm and the reference beam propagating along a reference beam arm; an adaptive delay line located at a distance along the reference beam arm, the adaptive delay line being configured to provide one or more length-adjusted reference beams in use; a beam splitter arranged to recombine the object beam from the object beam arm and one or more length-adjusted reference beams from the reference beam arm; and a photodetector operable to detect interference between the object beam and one or more length-adjusted reference beams.

[0006] Compared to devices without adaptive delay lines, the optical path difference between the target beam and (one or more) reference beams can be adjusted by providing one or more reference beams with adjustable lengths. Specifically, the optical path difference between the target beam and (one or more) reference beams can be reduced. For example, by adjusting the optical path distance of (one or more) reference beams to approximate the optical path distance of the target beam, the frequency of the interference signal can be reduced when measuring the distance to a distant target (e.g., a target 1 meter or more away from the device).

[0007] An adaptive delay line may include a series of N switches, where N ≥ 1, to allow selection of 2. N One of the optical path lengths of the interval, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide a reference beam for length adjustment.

[0008] The 2 N The optical path length of each interval can be equal or unequal.

[0009] An adaptive delay line can include any number of switches. An adaptive delay line can include multiple switches. An adaptive delay line can include up to or at least 100 switches, up to or at least 50 switches, up to or at least 20 switches, or up to or at least 10 switches. For example, an adaptive delay line can include one, two, three, four, five, six, seven, eight, nine, or ten switches.

[0010] Each switch in the adaptive delay line may include a rotating half-wave plate and a polarization beam splitter.

[0011] The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, can be adjustable.

[0012] The optical path length selectable by operating each switch within the adaptive delay line can be unique. In other words, the optical path length selectable by operating a given switch within the adaptive delay line can be different from the optical path length selectable by operating any other switch within the adaptive delay line.

[0013] In an example implementation, the adaptive delay lines can be configured such that the reference beam or the object beam passes through a series of N switchable delay lines, each with an exponentially increasing delay.

[0014] An adaptive delay line can include a series of N splitters to simultaneously provide 2-1 optical path lengths with spacing. N A reference beam, wherein N≥1, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams.

[0015] The 2 N The optical path length of each interval can be equal or unequal.

[0016] An adaptive delay line may include any number of splitters. An adaptive delay line may include multiple splitters. An adaptive delay line may include up to or at least 100 splitters, up to or at least 50 splitters, up to or at least 20 splitters, or up to or at least 10 splitters. For example, an adaptive delay line may include one, two, three, four, five, six, seven, eight, nine, or ten splitters.

[0017] An adaptive delay line may include one or more etalons, thereby enabling the adaptive delay line to operate in use to provide multiple reference beams with adjustable lengths.

[0018] The etalon, or each etalon, can have any suitable free spectral range.

[0019] One or more beamsplitters may include half-wave plates and polarization beamsplitters or 50:50 beamsplitters. Any given beamsplitter may have any suitable beam splitting ratio, such as 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, or 10:90.

[0020] The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, can be the same beam splitter.

[0021] The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, can be different beam splitters.

[0022] In an example implementation, the device may include: a first beam splitter arranged to split a first beam into a target beam and a reference beam; a second beam splitter located at a distance along the arm of the target beam and arranged to separate the target incident beam from the target beam; and a third beam splitter arranged to recombine the target beam and the adapted reference beam.

[0023] The laser source can be a tunable laser source. The laser source can be a VCSEL laser or an FDML laser.

[0024] The device may include a data logger operable to receive and record data from a photodetector. The data logger may include a data acquisition board (DAQ). The sampling rate of the DAQ may not exceed 100 gigabits per second (GS). -1 Up to 50GS s -1 Up to 20GS s -1 Up to 10GS s -1 Up to 5GS s -1 Up to 2GS s -1 or up to 1GSs -1 .

[0025] The target can include any suitable reflective surface. For example, a suitable target can be metallic, polymeric, or made of composite materials. They can have optically smooth or optically rough surface finishes. Alternatively, the target can include a weakly scattering medium, such as biological tissue.

[0026] The target can be at any distance from the device.

[0027] The apparatus may include a data processing device arranged to receive data from a data logger and process and / or analyze the received data.

[0028] Including an adaptive delay line in the reference beam arm of an interferometric apparatus can make the apparatus particularly suitable for high-speed and / or long-distance absolute distance measurements.

[0029] The interferometric apparatus can be a frequency-scanning interferometric apparatus. The frequency-scanning interferometric apparatus according to this disclosure is particularly suitable for long-distance, absolute distance measurement.

[0030] The interferometric apparatus can be a swept-source optical coherence tomography (OCT) apparatus. Sweeped-source OCT apparatuses are typically used to measure relatively short distances, for example, on the order of millimeters, for imaging biological tissues such as the retina of the eye and skin cancer. The scan rate in a swept-source OCT apparatus is so high that the teachings of this disclosure can be beneficially applied to such an apparatus.

[0031] A second aspect provides an interferometric measuring apparatus, comprising: a laser source operable to emit a first beam; a beam splitter arranged to split the first beam into an object beam and a reference beam, the object beam propagating along an object beam arm and the reference beam propagating along a reference beam arm; an adaptive delay line located at a distance along the object beam arm, the adaptive delay line being configured to provide one or more length-adjusted object beams in use; a beam splitter arranged to recombine the length-adjusted object beam(s) from the object beam arm and the reference beam from the reference beam arm; and a photodetector operable to detect interference between the length-adjusted object beam(s) and the reference beam(s).

[0032] Compared to devices without adaptive delay lines, the optical path difference between one or more object beams and a reference beam can be adjusted by providing one or more object beams with adjustable lengths. Specifically, the optical path difference between one or more object beams and the reference beam can be reduced. For example, by adjusting the optical path distance of one or more object beams to approximate the optical path distance of a matching reference beam, the frequency of the interference signal can be reduced when measuring the distance to a distant target (e.g., a target 1 meter or more away from the device).

[0033] An adaptive delay line may include a series of N switches, where N ≥ 1, to allow selection of 2. N One of the optical path lengths of the interval, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide an object beam with length adjustment.

[0034] The 2 N The optical path length of each interval can be equal or unequal.

[0035] An adaptive delay line can include any number of switches. An adaptive delay line can include multiple switches. An adaptive delay line can include up to or at least 100 switches, up to or at least 50 switches, up to or at least 20 switches, or up to or at least 10 switches. For example, an adaptive delay line can include one, two, three, four, five, six, seven, eight, nine, or ten switches.

[0036] Each switch in the adaptive delay line may include a rotating half-wave plate and a polarization beam splitter.

[0037] The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, can be adjustable.

[0038] The optical path length selectable by operating each switch within the adaptive delay line can be unique. In other words, the optical path length selectable by operating a given switch within the adaptive delay line can be different from the optical path length selectable by operating any other switch within the adaptive delay line.

[0039] An adaptive delay line can include a series of N splitters to simultaneously provide 2-1 optical path lengths with spacing. N A number of object beams, where N≥1, and including a combiner, thereby enabling the adaptive delay line to operate in use to provide multiple object beams with adjustable lengths.

[0040] The 2 N The optical path length of each interval can be equal or unequal.

[0041] An adaptive delay line may include any number of splitters. An adaptive delay line may include multiple splitters. An adaptive delay line may include up to or at least 100 splitters, up to or at least 50 splitters, up to or at least 20 splitters, or up to or at least 10 splitters. For example, an adaptive delay line may include one, two, three, four, five, six, seven, eight, nine, or ten splitters.

[0042] An adaptive delay line may include one or more etalons, thereby enabling the adaptive delay line to operate in use to provide multiple object beams with adjustable lengths.

[0043] The etalon, or each etalon, can have any suitable free spectral range.

[0044] One or more beamsplitters may include half-wave plates and polarization beamsplitters or 50:50 beamsplitters. Any given beamsplitter may have any suitable beam splitting ratio, such as 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, or 10:90.

[0045] The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, can be the same beam splitter.

[0046] The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, can be different beam splitters.

[0047] In an example implementation, the device may include: a first beam splitter arranged to split a first beam into a target beam and a reference beam; a second beam splitter located at a distance along the arm of the target beam and arranged to separate the target incident beam from the target beam; and a third beam splitter arranged to recombine the target beam and the adapted reference beam.

[0048] The laser source can be a tunable laser source. The laser source can be a VCSEL laser or an FDML laser.

[0049] The device may include a data logger operable to receive and record data from a photodetector. The data logger may include a data acquisition board (DAQ). The sampling rate of the DAQ may not exceed 100 GS / s. -1 Up to 50GS s -1 Up to 20GS s -1 Up to 10GS s -1 Up to 5GS s -1 Up to 2GS s -1 or up to 1GS s -1 .

[0050] The target can include any suitable reflective surface. For example, suitable targets can be metallic, polymeric, or made of composite materials. They can have optically smooth or optically rough surface finishes. Targets can alternatively include weakly scattering media, such as biological tissue.

[0051] The target can be at any distance from the device.

[0052] The apparatus may include a data processing device arranged to receive data from a data logger and process and / or analyze the received data.

[0053] Including an adaptive delay line in the reference beam arm of an interferometric apparatus can make the apparatus particularly suitable for high-speed and / or long-distance absolute distance measurements.

[0054] The interferometric apparatus can be a frequency-scanning interferometric apparatus. The frequency-scanning interferometric apparatus according to this disclosure is particularly suitable for long-distance, absolute distance measurement.

[0055] The interferometric apparatus can be a swept-source optical coherence tomography (OCT) apparatus. Sweeped-source OCT apparatuses are typically used to measure relatively short distances, for example, on the order of millimeters, for imaging biological tissues such as the retina of the eye and skin cancer. The scan rate in a swept-source OCT apparatus is so high that the teachings of this disclosure can be beneficially applied to such an apparatus.

[0056] A third aspect provides an adaptive delay line module suitable for mounting in a reference beam arm of an interferometric apparatus, wherein the adaptive delay line module includes an adaptive delay line configured to provide one or more length-adjustable reference beams during use.

[0057] An adaptive delay line may include a series of N switches, where N ≥ 1, to allow selection of 2. N One of the optical path lengths of the interval, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide a reference beam for length adjustment.

[0058] The 2 N The optical path length of each interval can be equal or unequal.

[0059] An adaptive delay line can include any number of switches. An adaptive delay line can include multiple switches. An adaptive delay line can include up to or at least 100 switches, up to or at least 50 switches, up to or at least 20 switches, or up to or at least 10 switches. For example, an adaptive delay line can include one, two, three, four, five, six, seven, eight, nine, or ten switches.

[0060] Each switch in the adaptive delay line may include a rotating half-wave plate and a polarization beam splitter.

[0061] The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, can be adjustable.

[0062] The optical path length selectable by operating each switch within the adaptive delay line can be unique. In other words, the optical path length selectable by operating a given switch within the adaptive delay line can be different from the optical path length selectable by operating any other switch within the adaptive delay line.

[0063] An adaptive delay line can include a series of N splitters to simultaneously provide 2-1 optical path lengths with spacing. N A reference beam, wherein N≥1, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams.

[0064] The 2 N The optical path length of each interval can be equal or unequal.

[0065] An adaptive delay line may include any number of splitters. An adaptive delay line may include multiple splitters. An adaptive delay line may include up to or at least 100 splitters, up to or at least 50 splitters, up to or at least 20 splitters, or up to or at least 10 splitters. For example, an adaptive delay line may include one, two, three, four, five, six, seven, eight, nine, or ten splitters.

[0066] An adaptive delay line may include one or more etalons, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams.

[0067] The etalon, or each etalon, can have any suitable free spectral range.

[0068] The fourth aspect provides an adaptive delay line module suitable for mounting in the object beam arm of an interferometric apparatus, wherein the adaptive delay line module includes an adaptive delay line configured to provide one or more object beams with adjustable lengths during use.

[0069] An adaptive delay line may include a series of N switches, where N ≥ 1, to allow selection of 2. N One of the optical path lengths of the interval, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide an object beam with length adjustment.

[0070] The 2 N The optical path length of each interval can be equal or unequal.

[0071] An adaptive delay line can include any number of switches. An adaptive delay line can include multiple switches. An adaptive delay line can include up to or at least 100 switches, up to or at least 50 switches, up to or at least 20 switches, or up to or at least 10 switches. For example, an adaptive delay line can include one, two, three, four, five, six, seven, eight, nine, or ten switches.

[0072] Each switch in the adaptive delay line may include a rotating half-wave plate and a polarization beam splitter.

[0073] The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, can be adjustable.

[0074] The optical path length selectable by operating each switch within the adaptive delay line can be unique. In other words, the optical path length selectable by operating a given switch within the adaptive delay line can be different from the optical path length selectable by operating any other switch within the adaptive delay line.

[0075] An adaptive delay line can include a series of N splitters to simultaneously provide 2-1 optical path lengths with spacing. N A reference beam, wherein N≥1, and includes a combiner, thereby enabling the adaptive delay line to operate in use to provide multiple object beams with adjustable lengths.

[0076] The 2 N The optical path length of each interval can be equal or unequal.

[0077] An adaptive delay line may include any number of splitters. An adaptive delay line may include multiple splitters. An adaptive delay line may include up to or at least 100 splitters, up to or at least 50 splitters, up to or at least 20 splitters, or up to or at least 10 splitters. For example, an adaptive delay line may include one, two, three, four, five, six, seven, eight, nine, or ten splitters.

[0078] An adaptive delay line may include one or more etalons, thereby enabling the adaptive delay line to operate in use to provide multiple object beams with adjustable lengths.

[0079] The etalon, or each etalon, can have any suitable free spectral range.

[0080] The interferometric measuring apparatus of any embodiment described herein may be at least partially disposed on or within a chip or photonic integrated circuit. An adaptive delay line or adaptive delay line module may be disposed on or within a chip or photonic integrated circuit.

[0081] The fifth aspect provides the use of an interferometric measuring apparatus according to the first or second aspect to measure the absolute distance to a target or the absolute distance to a structure within a weakly scattering target.

[0082] The target can be located at any distance from the device.

[0083] The target can be located at a distance of 1 meter or more, 5 meters or more, 10 meters or more, or 20 meters or more from the device.

[0084] The target can be located less than 5 meters, less than 1 meter, less than 10 cm, or less than 1 cm away from the device.

[0085] A sixth aspect provides a method for measuring distance using an interferometric apparatus, comprising: operating a laser to provide a first beam; splitting the first beam into an object beam and a reference beam, the object beam being transmitted along an object beam arm of the interferometric apparatus and the reference beam being transmitted along a reference beam arm of the interferometric apparatus; providing an adaptive delay line located at a distance along the reference beam arm, the adaptive delay line being configured to provide one or more length-adjusted reference beams to adjust for optical path differences in the interferometric apparatus; recombining the object beam from the object beam arm and one or more length-adjusted reference beams from the reference beam arm; and detecting interference between the object beam and one or more length-adjusted reference beams.

[0086] A seventh aspect provides a method for measuring distance using an interferometric apparatus, the method comprising: operating a laser to provide a first beam; splitting the first beam into an object beam and a reference beam, the object beam being transmitted along an object beam arm of the interferometric apparatus and the reference beam being transmitted along a reference beam arm of the interferometric apparatus; providing an adaptive delay line located at a distance along the object beam arm, the adaptive delay line being configured to provide one or more length-adjusted object beams thereby adjusting optical path differences in the interferometric apparatus; recombining the length-adjusted object beam(s) from the object beam arm and the reference beam from the reference beam arm; and detecting interference between the length-adjusted object beam(s) and the reference beam(s).

[0087] Those skilled in the art will understand that, unless mutually exclusive, the features or parameters described with respect to any of the foregoing aspects may be applied to any other aspect. Furthermore, unless mutually exclusive, any feature or parameter described herein may be applied to any aspect and / or combined with any other feature or parameter described herein. Attached Figure Description

[0088] An example embodiment will be described with reference to the accompanying drawings, in which:

[0089] Figure 1It is a block diagram of the adaptive delay line of the reference beam arm or the object beam arm of the interferometric measuring device;

[0090] Figure 2 An example of an interferometric measuring device is shown;

[0091] Figure 3 The normalized time signal is shown corresponding to an eight-adaptive delay line configuration for a target approximately 825 mm from the target beam splitter;

[0092] Figure 4 It shows Figure 3 The Fourier transforms of the eight signals shown are presented.

[0093] Figure 5a The frequency detected is shown in the presence of a low-pass filter with a cutoff frequency of 1.8 kHz;

[0094] Figure 5b Showing from Figure 5a Filtered signal;

[0095] Figure 6a The least-squares fit for the frequency-to-distance transformation is shown;

[0096] Figure 6b A comparison of the ranges measured by the frequency-stabilized reference interferometry apparatus and the interferometry apparatus according to an embodiment of the present disclosure is shown, with superimposed best linear fit;

[0097] Figure 7 This is a block diagram of another example of an adaptive delay line for the reference beam arm or object beam arm of an interferometric measuring device;

[0098] Figure 8 This is a block diagram of another example of an adaptive delay line for the reference beam arm or object beam arm of an interferometric measuring device;

[0099] Figure 9 Another example of an interferometric measuring device is shown; and

[0100] Figure 10 Another example of an interferometric measuring device is shown. Detailed Implementation

[0101] The teachings disclosed herein can be applied to measuring distances within any range.

[0102] As used in this article, when used in relation to distance measurement, the term remote can be understood to refer to a distance of 10 meters or more.

[0103] As used herein, when used in connection with distance measurement, the term high speed can be understood as referring to 10 [units per second]. 5One coordinate or a greater speed.

[0104] Due to the extremely high modulation frequencies (typically 100 GHz or higher), frequency scanning interferometry devices are applied to long-range (approximately 10 m) and high-speed (above 10 m) applications. 5 coordinates s -1 Absolute distance measurement is currently impractical at a reasonable cost.

[0105] This disclosure provides a solution based on an adaptive delay line (ADL) architecture, wherein the reference beam passes through a series of N switchable delay lines, each with an exponentially increasing delay. Benefits include a reduction of the required signal sampling rate, the size of the dataset to be processed, and the minimum permissible source coherence length by a factor of 2. N This paves the way for the use of fast scanning lasers (e.g., vertical-cavity surface-emitting lasers (VCSELs) and Fourier domain model-locked (FDML) lasers) in long-range lidar. The effectiveness of this principle has been experimentally demonstrated using a three-switch prototype.

[0106] Interferometric techniques such as frequency-scanning interferometry (FSI) and optical coherence tomography (OCT) involve combining light reflected or scattered from a target with a local reference wave. The mixing of light reflected or scattered from the target surface, or, in the case of a weakly scattering material, from within the target, with the local reference wave at a photodetector produces an electrical signal with a frequency f proportional to the optical path difference Λ between the two waves (i.e., the reflected or scattered wave; and (ii) the local reference wave). For linear frequency ramps and nondispersive media, f is given as follows:

[0107]

[0108] Where f s It is the laser scanning rate or scanning repetition rate, Δλ is the tuning range and λ c It is the center wavelength of Δλ. The resolution of Λ is inversely proportional to Δλ.

[0109] Existing tunable laser sources (e.g., vertical-cavity surface-emitting lasers (VCSELs) and Fourier-domain mode-locked lasers (FDMLs)) can generate scan rates from hundreds of kHz to several MHz, and the Δλ value is within λ c =1.0, 1.3, or 1.5 μm, exceeding 100 nm. Because each scan provides data for one coordinate, and the large Δλ allows for sub-μm resolution measurement of surface position, these sources enable measurements at 10... 5 -10 6 s -1This enables high-precision, long-distance measurements at rates within a given range. These rates offer enormous potential for industrial applications, such as dimensional quality control on production lines, automated assembly, and robot path guidance, and are 2-3 orders of magnitude higher than current FSI-based commercial instruments.

[0110] However, at least four major challenges need to be overcome. The first is the extremely high sampling rate required by the data acquisition board (DAQ). For example, at Δλ = 100 nm, λ c =1.3μm, f s At 100kHz, Equation 1 shows that at a distance z of 1m, f ~ 12GHz (Λ = 2z = 2m in air, for coaxial illumination and viewing direction), and an order of magnitude higher for a range of 10m. The minimum sampling rate is twice these values, resulting in DAQ hardware sampling rate requirements of tens to hundreds of GS. -1 Within that range. Currently, the cost of such hardware is around 1GS. -1 The above is rising rapidly.

[0111] Secondly, processing such high-speed data streams in real time is no easy task.

[0112] Third, the coherence length of these laser sources is not well characterized and may impose limitations on the length Λ.

[0113] Finally, the Fourier domain peak broadening and splitting caused by the imperfect frequency ramp increase significantly with increasing Λ.

[0114] This disclosure may mitigate or resolve one or more of these challenges.

[0115] Specifically, solutions to one or more of these problems can be based on the concept of a so-called adaptive delay line (ADL). The ADL is introduced into either the reference or target beam arm and can reduce the modulation frequency to the standard DAQ (~1 GS s). -1 It can process horizontal points while reducing data throughput, eliminating the need for sources with long coherence lengths, and reducing the peak broadening effect in the Fourier domain.

[0116] Figure 1 This is a block diagram showing the overall adaptive delay line 100, which can be installed in the reference beam arm or object beam arm of the interferometric apparatus according to this disclosure.

[0117] The adaptive delay line 100 includes N switches arranged in an optical order. These N switches allow selection of 2... N One of the equally spaced optical path lengths. Figure 1The diagram shows four switches: 101a, 101b, 101c, and 101d. The first switch 101a can be referred to as S0. The second switch 101b can be referred to as S1. The third switch 101c can be referred to as S2. The fourth switch 101d typically represents the last switch in a series of N switches and is usually referred to as S0. N-1 After the last switch in this series, that is, at switch S... N-1 Subsequently, a combiner (C) 102 is present. During operation, the reference beam or object beam 103 enters the adaptive delay line 100, and through switches 101a, 101b, 101c, 101d and combiner 102, the length-adjusted reference beam or length-adjusted object beam 104 leaves the adaptive delay line 100.

[0118] Each switch 101a, 101b, 101c, 101d can be controlled mechanically, optically, or electronically. Each switch 101a, 101b, 101c, 101d is operable to select one of two optical paths to reach the next switch (or, in the case of the last switch in the series, combiner 102).

[0119] At combiner 102, the last two paths are recombined to form either a length-adjusted reference beam or a length-adjusted object beam 104. The length-adjusted reference beam or the length-adjusted object beam continues through the interferometric measuring device and subsequently interferes with the object beam or the reference beam, respectively.

[0120] Now refer to Figure 1 Describe the general operating principle of an adaptive delay line (e.g., adaptive delay line 100). A reference beam or object beam passes sequentially through N optical switches S0, S1, ..., S... N-1 Each switch (which can be mechanically, optically, or electronically controlled) selects one of two optical paths to reach the next switch. In the final stage, the last two paths are recombined, and the length-adjusted reference beam or the length-adjusted object beam advances into the remainder of the interferometric apparatus, where it interferes with the object beam or the reference beam, respectively.

[0121] The state of the j-th switch can be determined by a single bit b. j The value is specified, where 1 indicates that the longer path was selected, and 0 indicates that the shorter path was selected. This follows an exponential sequence, d, by selecting the path length difference between two possible paths for consecutive switches. j =2 j d0, where d j It is the path difference between the j-th switch and the (j+1)-th switch, and d0 is the path difference of the first switch. It can be selected from a set of 2... NA single Λ of discrete and spaced (e.g., uniformly spaced) Λs with a step size of d0.

[0122] Taking the case of N=10 and d0=10mm as an example. From the bit pattern B=b N-1 b N-2 ...b1 b0 defines the resulting 1024 steps (through which the imbalance between the reference arm and the target arm can be adjusted) covering a range of 0 to ~10m, while reducing the maximum required sampling frequency by 1024×, Λ for 10mm. As a concrete example, for a target Λ = 8.003m, byte B = 1100100000 moves the zero-Λ surface to 8.000m, while the remaining 3mm is detected at a correspondingly much lower frequency. Generally, for a given data acquisition (DAQ) hardware, each additional switch in the chain doubles the maximum range or coordinate acquisition rate. Limitations on source coherence length (l c ≥2 N d0 (which produces the final upper limit of the measurement range) was relaxed by a factor of 2. N , for l c ≥d0.

[0123] The adaptive delay line disclosed in this paper is well-suited for use in absolute distance measurements, especially when used with scanning monochromatic laser sources.

[0124] Figure 2 An interferometric measuring apparatus 200 for measuring distance is shown. Apparatus 200 is a proof-of-concept experimental optical device.

[0125] The apparatus 200 includes a tunable laser source 201. The tunable laser source 201 is a scanning monochromatic laser source. In the proof-of-concept experimental optical setup, the tunable laser source used is a SANTEC TSL-510, where Δλ = 100 nm. c ~1.8 to 300m and λ c =1300nm, operating in free mode, and with output power limited to 1mW.

[0126] Laser source 201 communicates optically with first beam splitter 202 via optical cable 211. Optical cable 211 is single-mode polarization-maintaining (SM-PM) fiber. First beam splitter 202 includes an optically cascaded reflector collimator 203, a half-wave plate 204, and a polarization beam splitter 205. Polarization beam splitter 205 is used to split the incident beam from laser source 201 into an object beam 212 and a reference beam. Object beam 212 is transmitted along object beam arm 206. Reference beam is transmitted along reference beam arm 209.

[0127] The target beam arm 206 includes a 50:50 beam splitter 207. The 50:50 beam splitter 207 is arranged to separate the target incident beam 213 from the target beam 212. The target incident beam 213 is reflected back to the 50:50 beam splitter 207 by the target 208, wherein a portion of the target incident beam 213 is reflected from the beam splitter 207 to form the target beam 214 traveling forward along the target beam arm 206.

[0128] In the proof-of-concept optical apparatus, target 208 includes a gold reflector. The distance from the 50:50 beam splitter 207 to target 208 is adjustable. In the proof-of-concept optical apparatus, target 208 is mounted on a track assembly (not shown) that allows target 208 to be manually moved within a range of approximately 1 meter.

[0129] In the proof-of-principle optical setup, the reference beam arm 209 includes an adaptive delay line 210. The adaptive delay line 210 is a three-dimensional adaptive delay line.

[0130] The adaptive delay line 210 includes three switches arranged in optical series: a first switch 215, a second switch 216, and a third switch 217.

[0131] The first switch 215 includes an achromatic half-wave plate 2151 disposed in front of the polarizing beam splitter 2152. In use, mechanical switching is performed by rotating the achromatic half-wave plate 2151 relative to the polarizing beam splitter 2152.

[0132] A first switch 215 selectively separates a reference beam so that the separated reference beam is redirected around a first loop 2153 having a loop optical path length. The first loop 2153 includes four mirrors 2154a, 2154b, 2154c, and 2154d, which are arranged to reflect the redirected reference beam so that, traveling around the first loop 2153, the redirected reference beam enters the side of the polarization beam splitter 2152 opposite to the side where the redirected reference beam exits the polarization beam splitter 2152. The third mirror 2154c and the fourth mirror 2154d are mounted on a translation stage 2155 to allow adjustment of the loop optical path length.

[0133] The second switch 216 includes an achromatic half-wave plate 2161 disposed in front of the polarization beam splitter 2162. In use, mechanical switching is performed by rotating the achromatic half-wave plate 2161 relative to the polarization beam splitter 2162.

[0134] The second switch 216 selectively separates the reference beam so that the separated reference beam is redirected around a second loop 2163 having a loop optical path length. The second loop 2163 includes four mirrors 2164a, 2164b, 2164c, and 2164d, which are arranged to reflect the redirected reference beam so that, traveling around the second loop 2163, the redirected reference beam enters the side of the polarization beam splitter 2162 opposite to the side where the redirected reference beam exits the polarization beam splitter 2162. The third mirror 2164c and the fourth mirror 2164d are mounted on a translation stage 2165 to allow adjustment of the loop optical path length.

[0135] The third switch 217 includes an achromatic half-wave plate 2171 disposed in front of the polarizing beam splitter 2172. In use, mechanical switching is performed by rotating the achromatic half-wave plate 2171 relative to the polarizing beam splitter 2172.

[0136] The third switch 217 selectively separates the reference beam so that the separated reference beam is redirected around a third loop 2173 having a loop optical path length. The third loop 2173 includes four mirrors 2174a, 2174b, 2174c, and 2174d, which are arranged to reflect the redirected reference beam so that, traveling around the third loop 2173, the redirected reference beam enters the side of the polarizing beam splitter 2172 opposite to the side where the redirected reference beam exits the polarizing beam splitter 2172. The third mirror 2174c and the fourth mirror 2174d are mounted on a translation stage 2175 to allow adjustment of the loop optical path length.

[0137] Following the adaptive delay line 210, a mirror 218 is arranged to reflect the length-adjusted reference beam 227 toward the 50:50 beam splitter 226. The target beam 214 and the length-adjusted reference beam 227 enter the 50:50 beam splitter 226 in mutually perpendicular directions.

[0138] Before entering the 50:50 beam splitter 226, the target beam 214 passes through the first linear polarizer 219a. Before entering the 50:50 beam splitter 226, the length-adjusted reference beam 227 passes through the second linear polarizer 219b. The first coupler 220a is arranged on the side of the 50:50 beam splitter 226 opposite to the first linear polarizer 219a. The second coupler 220b is arranged on the side of the 50:50 beam splitter 226 opposite to the second linear polarizer 219b.

[0139] Optical fiber 221 carries light from the first coupler 220a to the automatically balancing photodetector 223. Another optical fiber 222 carries light from the second coupler 220b to the automatically balancing photodetector 223. Each of optical fibers 221 and 222 is a single-mode polarization-maintaining (SMPM) fiber.

[0140] The first linear polarizer 219a and the second linear polarizer 219b ensure that interference between matched polarization states occurs at the automatically balanced photodetector 223. In use, this interference between matched polarization states is detected by the automatically balanced photodetector 223.

[0141] Data logger 224 is operatively connected to autobalanced photodetector 223. The data logger may include a storage oscilloscope. In the proof-of-concept experimental optical setup, the data logger is a storage oscilloscope (Tektronix MSO54, 500MHz, 6.25GS s). -1 ).

[0142] Computer 225 is operatively connected to data logger 224. Computer 225 is configured to process and / or analyze data recorded on the data logger.

[0143] To test this concept, use Figure 2 The optical device shown was used for a proof-of-concept experiment. As described above, the device 200 incorporates a 3-bit adaptive delay line 210, where mechanical switching is performed by rotating an achromatic half-wave plate in front of a polarizing beam splitter. If the incident polarization state of a given half-wave plate is horizontal (S), the beam passes directly through the polarizing beam splitter to the next switch. A 45° rotation of the half-wave plate results in a 90° (P) rotation of the polarization state, thereby guiding the beam around a loop formed by two pairs of beam-folding gold mirrors (2154a-d; 2164a-d; 2174a-d). Translation stages 2155, 2165, and 2175 allow for fine-tuning of the delay length, for example, values ​​d0–240 mm, d1–490 mm, and d3–830 mm.

[0144] The half-wave plate 204 and polarization beam splitter 205 preceding the adaptive delay line 210 serve as a variable ratio beam splitter 202.

[0145] The tunable laser source 201 used is a SANTEC TSL-510, where Δλ = 100 nm, l c ~1.8 to 300m and λ c =1300nm, operating in free-running mode with output power limited to 1mW. The beam is transmitted to the interferometric apparatus via a single-mode polarization-maintaining (SMPM) fiber 211 and is then collimated using a reflective collimator 203 before being split into a reference beam and an object beam 212.

[0146] Two linear polarizers 219a and 219b, located on either side of the 50:50 beam splitter 226, ensure that interference between matched polarization states is detected at the automatically balanced photodetector 223. Light is transmitted to the automatically balanced photodetector 223 via this pair of single-mode polarization-maintaining fibers 221 and 222. The signal from the automatically balanced photodetector 223 is then stored by an oscilloscope (Tektronix MSO54, 500MHz, 6.25GS s). -1 The data is digitized by the data recorder 224. The captured data sequence is transmitted to the computer 225 for subsequent processing. Synchronization is achieved by triggering the oscilloscope with a laser transistor-transistor-logic (TTL) output at the start of each scan.

[0147] Figure 3 The normalized intensity signal, measured as a function of time (t), is shown, corresponding to an eight adaptive delay line configuration of a target at a distance of ~825 mm from beam splitter 207.

[0148] To illustrate the system's ability to reduce the interference signal frequency (f), the target 208 was placed several tens of millimeters beyond the maximum delay length (~780 mm) of the 3-bit adaptive delay line 210, implemented in a 111-bit configuration. The laser scanning parameters were: Δλ = 10 nm, initial wavelength λ1 = 1330 nm, and average tuning rate = 10 nm / s. -1 The sample size was set to 1.25 × 10⁻⁶. 6 9000 points were processed, corresponding to Δλ < 1 nm. Due to the combined effects of dispersion and tuning rate fluctuations over the entire Δλ range, the reduced bandwidth was used to minimize the error in z, which would otherwise be impossible to decouple without proper wavelength reference and linearization techniques.

[0149] Figure 3 The interference intensity signals I(t) for all eight bit modes in the ~7ms scan sub-section are shown. The first interference signal 301 is shown for the first bit mode 000. The second interference signal 302 is shown for the second bit mode 001. The third interference signal 303 is shown for the third bit mode 010. The fourth interference signal 304 is shown for the fourth bit mode 011. The fifth interference signal 305 is shown for the fifth bit mode 100. The sixth interference signal 306 is shown for the sixth bit mode 101. The seventh interference signal 307 is shown for the seventh bit mode 110. The eighth interference signal 308 is shown for the eighth bit mode 111.

[0150] like Figure 3 As shown, the frequency gradually decreases as the path length imbalance between the reference beam arm and the target beam arm is reduced by selecting eight different bit configurations, with the 111-bit configuration providing the expected lowest frequency.

[0151] Figure 4 The Fourier transforms of eight signals are shown. The first peak 401 is the Fourier transform of the first interference signal 301. The second peak 402 is the Fourier transform of the second interference signal 302. The third peak 403 is the Fourier transform of the third interference signal 303. The fourth peak 404 is the Fourier transform of the fourth interference signal 304. The fifth peak 405 is the Fourier transform of the fifth interference signal 305. The sixth peak 406 is the Fourier transform of the sixth interference signal 306. The seventh peak 407 is the Fourier transform of the seventh interference signal 307. The eighth peak 408 is the Fourier transform of the eighth interference signal 308. The frequency at each peak position was estimated to subpixel resolution using a Newton-Raphson iterative process, yielding values ​​of 9.89, 8.21, 6.73, 5.23, 4.84, 3.13, 1.67, and 0.13 kHz for the 000 to 111 bit configurations (i.e., for the first interference signal 301, the second interference signal 302, the third interference signal 303, the fourth interference signal 304, the fifth interference signal 305, the sixth interference signal 306, the seventh interference signal 307, and the eighth interference signal 308), respectively.

[0152] The question now arises as to how to choose the correct bit pattern, i.e., the bit pattern that minimizes Λ and thus minimizes f. First, consider the general case, where the object whose range is to be measured is located at an arbitrary point within the measurement volume. Each bit pattern can be applied sequentially to the ADL. For a source with a short coherence length, the highest signal modulation will occur for the bit pattern with the shortest Λ. In a source with a length l... c In the case of a source, a low-pass filter (LPF) can be introduced at the output of the photodetector, or practically by selecting a photodetector with a low bandwidth. Only the shortest Λ bit configuration will then produce the significant signal, and this will be within the Nyquist constraints of the data acquisition hardware, provided that d0 is chosen to be small enough. All 2 N A configuration can be studied during a single frequency scan, and then configured at the selected fixed bit in subsequent scans. Bv Detailed Λ measurements are performed at this location. For example, for N=10 and a scan rate of 10... 5 In the case of Hz, the switching event should occur every 10ns (1 / 2) N f sThis occurs within the capabilities of fiber optic switches. For cases where quasi-continuous surfaces are not critical, the search can be accelerated by studying only bit patterns near those established for previous measurements, where the system only slows down in the presence of large z-discontinuities. Alternatively, a low-cost time-of-flight LADAR operating in parallel with FSI can be used to determine the integer part of z, thus indicating an adaptive delay line that addresses the more precise portions of the measurement.

[0153] However, there may be an additional source of ambiguity: how to distinguish between positive and negative deviations of Λ from the zero-Λ surface that gives the lowest modulation frequency. In the previous example, a target at z = 8.003 m will produce the same signal frequency as a target at z = 7.997 m. This ambiguity can be resolved by incorporating phase information (e.g., through orthogonal, sometimes called I / Q detection), since the frequencies of the Fourier domain peaks will have opposite signs for both cases. When I / Q detection is unavailable, using the modulation frequency measured with one or both of two adjacent bit configurations will allow overcoming this ambiguity. For example, suppose B... v To minimize the bit configuration of the modulation frequency, denoted here as f Bv B v-1 and B v+1 This involves selecting the bit configuration of the nearest adjacent zero-Λ surface. Assuming that the Λ values ​​are the same between pairs of zero-Λ surfaces, then the symbol s... v It can be restored to:

[0154]

[0155] To illustrate the above, an experiment was conducted in which target 208 was placed at arbitrary locations within the measurement volume, while signals corresponding to eight delays were recorded. Although the high-speed version would require an analog low-pass filter (LPF) before sampling, in this demonstration, a low-speed frequency ramp allows this method to be implemented via a post-sampled digital LPF—by applying a 1.8-kHz wide top-hat window to the Fourier spectrum before the inverse transform. After filtering, as... Figure 5a As shown, only three significant Fourier peaks are retained, corresponding to the three adjacent bit configurations 100, 101, and 110 with the largest signal amplitude. Figure 5b The frequency (f) of these peaks 100 =1.3kHz, f 101 =0.19kHz and f 110 Substituting (=1.7kHz) into Equation 2, we get s 101 =-1, indicating that target 208 is closer to the Λ-surface than target 208 is to target 208 ...

[0156] As with any frequency-scanning interferometry system, calibration is required to convert the measured modulation frequency into distance. However, for frequency-scanning interferometry systems based on N-bit ADL, there is an additional step: determining N additional delay lengths, or equivalently, the frequency shifts introduced by these delays. The latter approach is adopted here: the target 208 is fixed a few mm outside the 111 zero-Λ surface, eight signals corresponding to the eight-bit configuration of the adaptive delay line 210 are recorded, and their frequencies are calculated using the method described above.

[0157]

[0158] This produces an overdetermined linear system of eight equations presented in matrix form in Equation 3. A is an 8×4 matrix whose rows represent the bit patterns activated for each of the eight scans. The columns correspond to the four principal delays that are activated (1) or deactivated (0), and F is a column vector containing the measurement frequencies. Solving Equation (3) for the column vector X in the least-squares sense gives four frequency values ​​proportional to the physical lengths of the four principal delays. The final stage of calibration—that is, determining the metric constant that links the frequencies to Λ—can be done in a variety of ways, such as through the absorption lines of a gas cell or reference cavity of known length. For the current setup, a frequency-stabilized reference interferometer (Renishaw XL-80) is introduced to measure the target position in parallel with the frequency-scanning interferometry (FSI) system (i.e., interferometric device 200). A single delay is selected (001 in this case) and the target 208 is moved to eight different positions. By comparing the measurement frequencies with known distance data z R By performing least-squares line fitting, the transformation factor can be extracted from the gradient of the best-fit line, such as... Figure 6a As shown. The calculation result is 0.01157 kHz mm. -1 Furthermore, the RMS residual is 0.09516 kHz. While the latter is relatively high for an FSI system, it is due to the time variation of the scan rate of the specific laser used, and is still low enough to justify the principle of the proposed method.

[0159] As a final verification of the above methods and data processing procedures, another experiment was conducted to compare the use of... Figure 2 The distance measured by the interferometric measuring device 200 is the same as the distance measured by the Renishaw interferometer. A new set of measurements is performed by placing the target 208 in a set of six positions, independent of the positions used for calibration. Figure 6b A graph showing the range measured by the interferometric measuring device 200 relative to the range measured by the Renishaw interferometer is shown. Figure 6bThe graph in the figure shows a superimposed best-fit line with a gradient of 1.00536 ± 0.01458, demonstrating (within experimental error) the expected 1:1 correspondence between the two systems. The RMS residual of the best-fit line is 3.00 mm.

[0160] The use of adaptive delay lines as disclosed herein allows frequency-scanning interferometers to operate with standard data acquisition hardware (maximum sampling rate ~1 GS s). -1 It is used for very high coordinate measurement rates (10) over long distances (tens of meters). 5 s -1 (Above). The optical system includes an adaptive delay line, which comprises a series of N switchable delay lines with exponentially increasing delays.

[0161] The benefits provided by the teachings of this disclosure may include reducing data acquisition rate, dataset size, and minimum permissible source coherence length by a factor of 2. N The validity of this principle has been demonstrated using a low-speed 3-bit prototype.

[0162] It should be understood that Figure 2 The apparatus shown is merely an example of an apparatus embodying the teachings of this disclosure. Various modifications will be apparent to those skilled in the art without departing from the scope of this disclosure.

[0163] For example, the laser source can be a VCSEL laser or an FDML laser.

[0164] An adaptive delay line can include any number of switches. An adaptive delay line can include multiple switches. An adaptive delay line can include up to or at least 100 switches, up to or at least 50 switches, up to or at least 20 switches, or up to or at least 10 switches. For example, an adaptive delay line can include one, two, three, four, five, six, seven, eight, nine, or ten switches.

[0165] One or more switches in an adaptive delay line may include, for example, a half-wave plate and a polarization beam splitter.

[0166] Adaptive delay lines can employ other types of switches, which can be mechanically controllable, and / or electrically controllable, and / or magnetically controllable, and / or optically controllable.

[0167] For example, one or more switches in an adaptive delay line may include electrically controllable switches. Electrically controllable switches may include Pockels cells and polarization beam splitters. One or more switches in an adaptive delay line may employ microelectromechanical systems (MEMS).

[0168] The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, can be adjustable.

[0169] The data logger may include a data acquisition board (DAQ). The sampling rate of the DAQ may not exceed 100 GS / s. -1 Up to 50GS s -1 Up to 20GS s -1 Up to 10GS s -1 Up to 5GS s -1 Up to 2GS s -1 or up to 1GS s -1 .

[0170] Each of the adaptive delay lines whose switches are mechanically, optically, or electrically controlled (e.g., as in interferometric apparatus 200) can be referred to as an active adaptive delay line.

[0171] In other embodiments, the adaptive delay line can be configured as a so-called passive adaptive delay line.

[0172] Figure 7 This is a block diagram showing the overall adaptive delay line 700, which can be installed in the reference beam arm or object beam arm of the interferometric apparatus according to this disclosure.

[0173] The adaptive delay line 700 includes N splitters arranged in optical order. These N splitters provide 2 N The optical path length of each interval. Figure 7 The diagram shows four splitters 701a, 701b, 701c, and 701d. The first splitter 701a can be referred to as D0. The second splitter 701b can be referred to as D1. The third splitter 701c can be referred to as D2. The fourth splitter 701d typically represents the last splitter in a series of N splitters and is usually referred to as D... N-1 Following the last splitter in this series, i.e., at splitter D... N-1 Subsequently, a combiner (C) 702 is present. During operation, a reference beam 703 enters the adaptive delay line 700 and passes through splitters 701a, 701b, 701c, 701d and combiner 702, thereby causing multiple length-adjusted reference beams 704 to exit the adaptive delay line 700.

[0174] Figure 8 This is a block diagram showing the overall adaptive delay line 800, which can be installed in the reference beam arm or object beam arm of the interferometric apparatus according to this disclosure.

[0175] The adaptive delay line 800 includes an etalon 801. During operation, a reference beam 803 enters the etalon 801, which splits the reference beam 803 into multiple length-adjustable reference beams 804. The passive adaptive delay line including the etalon provides improved traceability because the length scale is determined by the etalon spacing.

[0176] The use of passive adaptive delay lines (e.g., adaptive delay line 700 or adaptive delay line 800) can enable simultaneous tracking of multiple targets.

[0177] Compared to active adaptive delay lines, passive adaptive delay lines can have a relatively simple optical configuration. Furthermore, passive adaptive delay lines do not require any active switching during operation.

[0178] One or more adaptive delay lines can be provided in the module, which can be integrated into an existing optical system to measure distance, such as a frequency-scanning interferometry system, a frequency-modulated continuous wave LiDAR system, a LaDAR system, or an optical coherence tomography (OCT) system.

[0179] Although the basic principles of this disclosure have been described using the main optical components, it is envisioned that the interferometric measurement device may be provided at least partially on or within a chip or photonic integrated circuit. Specifically, one or more adaptive delay lines may be provided on or within a chip or photonic integrated circuit.

[0180] For example, it is conceivable that adaptive delay lines (or adaptive delay line modules) could be provided on a chip using current standard manufacturing techniques for telecommunications equipment.

[0181] The teachings of this disclosure can be applied to a variety of types of interferometric apparatuses, including, for example, the Mach-Zehnder interferometer or the Michelson interferometer.

[0182] Figure 9 An example of a Mach-Zehnder interferometer 900 is shown. The Mach-Zehnder interferometer 900 includes a laser source 901 operable to emit a first beam 902. A first beam splitter 903 splits the first beam 902 into an object beam 905 and a reference beam 904.

[0183] The target beam 905 is guided by the first target beam reflector 909 to a target 910 at a certain distance from the reflector 909. The target beam 905 is reflected by the target and guided to the second beam splitter 913 through the second target beam reflector 911 and the third target beam reflector 912.

[0184] Reference beam 904 passes through adaptive delay line 906. For example, adaptive delay line 906 can be any adaptive delay line described herein. Adaptive delay line 906 generates length-adjusted reference beam 907 or multiple adapted reference beams, which are guided by reference beam reflector 908 to second beam splitter 913.

[0185] The first photodetector 914 and the second photodetector 915 are arranged to detect interference between the target beam 905 and the length-adjusted reference beam 907 or multiple length-adjusted reference beams.

[0186] Alternatively, the adaptive delay line 906 can be positioned within the object beam arm of the interferometer 900, rather than within the reference beam arm of the interferometer 900. In such an arrangement, the adaptive delay line 906 will produce an adapted length-adjusted object beam or multiple length-adjusted object beams.

[0187] Figure 10 An example of a Michelson interferometer 1000 is shown. The interferometer 1000 includes a laser source 1001 operable to emit a first beam 1002. A beam splitter 1003 splits the first beam 1002 into an object beam 1005 and a reference beam 1004.

[0188] The target beam 1005 is incident on the target 1006 at a certain distance from the beam splitter 1003 and is reflected back to the beam splitter 1003.

[0189] Reference beam 1004 passes through adaptive delay line 1008. For example, adaptive delay line 1008 can be any adaptive delay line described herein. Adaptive delay line 1008 generates length-adjusted reference beam 1007 or multiple length-adjusted reference beams, which are guided back by reference beam reflector 1009 through adaptive delay line 1008 to beam splitter 1003. Upon returning through adaptive delay line 1008, the length-adjusted reference beam or multiple length-adjusted reference beams 1007 constitute a double-length-adjusted reference beam or multiple double-length-adjusted reference beams.

[0190] The photodetector 1010 is arranged to detect the interference between the target beam 1005 and a reference beam or multiple reference beams with double-length adjustment.

[0191] Alternatively, the adaptive delay line 1008 can be positioned within the object beam arm of the interferometer 1000, rather than within the reference beam arm of the interferometer 1000. In such an arrangement, the adaptive delay line 1008 will generate a length-adjusted object beam or multiple length-adjusted object beams.

[0192] The teachings of this disclosure can be used, for example, in the aerospace industry for aligning wing components. Another potential application area could be the automotive industry, for example, collision avoidance for autonomous vehicles. Another potential application area could be the general-purpose machine tool industry. Another potential application area could be the medical diagnostics field, for example, for subsurface retinal imaging. Another application area could be measuring vibration by measuring the phase or frequency of a beam of light reflecting or scattered from a target by measuring its Doppler shift. Another application area could be long-distance measurements for topographic surveying purposes. Many more potential applications are envisioned, for example in the automotive field and quality control, because the teachings of this disclosure can improve measurement speed while maintaining measurement accuracy at the level of tens of micrometers or better.

[0193] For example, by Current commercial systems typically achieve up to 1,000 measurement points per second (coordinates per second). Next-generation VCSEL technology has the potential to achieve 100,000 to 500,000 coordinates per second. A major obstacle to realizing this potential arises because the required sampling rate also increases proportionally, and suitable data acquisition systems capable of sampling rates exceeding 1 billion samples per second are extremely expensive.

[0194] This problem can be overcome by utilizing the adaptive delay line disclosed herein. The adaptive delay line (which can be a module comprising a series of optical switches allowing light (the reference beam) to be routed along a path to closely match the optical paths of the target beam arm and the reference beam arm of the interferometer) is used to reduce the (sampling) frequency to a level that can be measured by more affordable (e.g., low-cost) data acquisition systems. For a given data acquisition system, each additional switch (or splitter or etalon spacing) in the adaptive delay line doubles the maximum coordinate measurement rate achievable by the entire interferometric system.

[0195] Therefore, it will be understood that this disclosure can facilitate the use of advanced laser technologies (e.g., VCSEL or FDML technologies) in interferometric measurement devices for measuring distances.

[0196] Beyond the large-volume metrology applications mentioned in the preceding paragraphs, the teachings of this disclosure can be used for very small-scale measurements using a technique called coherent scanning interferometry (CSI). The use of adaptive delay lines as disclosed herein can, for example, allow the construction of all-solid-state high-speed CSI systems. Such systems would avoid the vibration problems inherent in current mechanical scanning systems.

[0197] The above embodiments are described by way of example only. Many variations are possible without departing from this disclosure.

[0198] It will be understood that this disclosure is not limited to the embodiments described above, and various modifications and improvements can be made without departing from the concepts described herein. Any feature may be used alone or in combination with any other feature unless mutually exclusive, and this disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

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Claims

1. An interferometric measuring device for measuring distance, comprising: A laser source, operable to emit a first beam; A beam splitter is arranged to split the first beam into an object beam and a reference beam, the object beam being transmitted along an object beam arm and the reference beam being transmitted along a reference beam arm. An adaptive delay line, located at a distance along the reference beam arm, is configured to provide one or more reference beams with adjustable lengths during use; A beam splitter is arranged to recombine the object beam from the object beam arm and the one or more length-adjusted reference beams from the reference beam arm; as well as A photodetector, operable to detect interference between the target beam and one or more length-adjusted reference beams. in: The adaptive delay line includes a series of N A splitter to simultaneously provide optical path lengths with spacing. 2 N One reference beam, of which N ≥1, and includes a combiner, wherein the adaptive delay line operates in use to provide multiple length-adjustable reference beams; and / or The adaptive delay line includes one or more etalons, wherein the reference beam enters one of the etalons and is split into multiple length-adjustable reference beams, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams.

2. The interferometric measuring device according to claim 1, wherein, The adaptive delay line includes a series of N There are N switches, where N≥1, to allow selection. 2 N One of the interval optical path lengths, and includes a combiner, whereby the adaptive delay line operates in use to provide a reference beam for length adjustment.

3. The interferometric measuring device according to claim 2, wherein, The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, is adjustable.

4. The interferometric measuring device according to claim 2 or 3, wherein, The optical path length that can be selected by the operation of each switch within the adaptive delay line is unique.

5. The interferometric measuring device according to claim 2 or 3, wherein, The adaptive delay line is configured to cause the reference beam or the object beam to pass through a series of... N A switchable delay line, the N Each switchable delay line has an exponentially increasing delay.

6. The interferometric measuring device according to claim 1, 2 or 3, wherein, The 2 N The optical path length of each interval can be either equally spaced or unequally spaced.

7. An interferometric measuring device for measuring distance, comprising: A laser source, operable to emit a first beam; A beam splitter is arranged to split the first beam into an object beam and a reference beam, the object beam being transmitted along an object beam arm and the reference beam being transmitted along a reference beam arm. An adaptive delay line, located at a distance along the object beam arm, is configured to provide one or more object beams with adjustable lengths during use; A beam splitter is arranged to recombine the one or more length-adjusted object beams from the object beam arm and the reference beam from the reference beam arm; as well as A photodetector capable of detecting interference between the one or more length-adjusted object beams and the reference beam. in: The adaptive delay line includes a series of N A splitter to simultaneously provide optical path lengths with spacing. 2 N A beam of objects, of which N ≥1, and includes a combiner, whereby the adaptive delay line operates in use to provide multiple length-adjustable object beams; and / or The adaptive delay line includes one or more etalons, wherein the object beam enters one of the etalons and is split into multiple length-adjustable object beams, thereby the adaptive delay line operates in use to provide multiple length-adjustable object beams.

8. The interferometric measuring device according to claim 7, wherein, The adaptive delay line includes a series of N One switch, among which N ≥1, to allow selection 2 N One of the interval optical path lengths, and includes a combiner, whereby the adaptive delay line operates in use to provide a length-adjustable object beam.

9. The interferometric measuring device according to claim 8, wherein, The length of one or more optical paths, selectable by the operation of one or more switches within the adaptive delay line, is adjustable.

10. The interferometric measuring apparatus according to claim 8 or 9, wherein, The optical path length that can be selected by the operation of each switch within the adaptive delay line is unique.

11. The interferometric measuring apparatus according to claim 8 or 9, wherein, The adaptive delay line is configured to cause the reference beam or the object beam to pass through a series of... N A switchable delay line, the N Each switchable delay line has an exponentially increasing delay.

12. The interferometric measuring apparatus according to claim 7, 8 or 9, wherein, The 2 N The optical path length of each interval can be either equally spaced or unequally spaced.

13. The interferometric measuring apparatus according to claim 1, 2, 3, 7, 8 or 9, wherein, The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, are the same beam splitter.

14. The interferometric measuring apparatus according to claim 1, 2, 3, 7, 8 or 9, wherein, The beam splitter arranged to split the first beam into an object beam and a reference beam, and the beam splitter arranged to recombine the object beam and the adapted reference beam, are different beam splitters.

15. The interferometric measuring apparatus according to claim 14, comprising: A first beam splitter is configured to split the first beam into a target beam and a reference beam. A second beam splitter is located at a distance along the arm of the object beam, and the second beam splitter is arranged to separate the target incident beam from the object beam. And a third beam splitter is arranged to recombine the object beam and the adapted reference beam.

16. The interferometric measuring apparatus according to claim 1, 2, 3, 7, 8 or 9, wherein, The laser source is a tunable laser source.

17. The interferometric measuring apparatus according to claim 1, 2, 3, 7, 8 or 9, comprising a data logger operable to receive and record data from the photodetector.

18. The interferometric measuring apparatus according to claim 1, 2, 3, 7, 8 or 9, wherein the interferometric measuring apparatus is configured to measure the absolute distance to a target or the absolute distance to a structure within a weakly scattering target.

19. An adaptive delay line module, adapted for mounting in the reference beam arm of an interferometric apparatus for measuring distance, wherein, The adaptive delay line module includes an adaptive delay line configured to provide one or more reference beams with adjustable length during use; Alternatively, an adaptive delay line module is suitable for mounting in the object beam arm of an interferometric apparatus, wherein the adaptive delay line module includes an adaptive delay line configured to provide one or more object beams with adjustable lengths during use. in: The adaptive delay line includes a series of N A splitter to simultaneously provide optical path lengths with spacing. 2 N A reference beam or object beam, wherein N ≥1, and includes a combiner, whereby the adaptive delay line operates in use to provide multiple length-adjustable reference beams or object beams; and / or The adaptive delay line includes one or more etalons, wherein the reference beam or object beam enters one of the etalons and is split into multiple length-adjustable reference beams or object beams, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams or object beams.

20. A method for measuring distance using an interferometric measuring device, the method comprising: Operate the laser to provide the first beam; The first beam is split into an object beam and a reference beam. The object beam is transmitted along the object beam arm of the interferometric measuring device, and the reference beam is transmitted along the reference beam arm of the interferometric measuring device. An adaptive delay line is provided at a distance along the arm of the reference beam, the adaptive delay line being configured to provide one or more reference beams with adjustable lengths, thereby adjusting the optical path difference in the interferometric apparatus; Recombining the object beam from the object beam arm and the one or more length-adjusted reference beams from the reference beam arm; as well as Detect the interference between the object beam and the one or more length-adjusted reference beams. in: The adaptive delay line includes a series of N A splitter to simultaneously provide optical path lengths with spacing. 2 N One reference beam, of which N ≥1, and includes a combiner, wherein the adaptive delay line operates in use to provide multiple length-adjustable reference beams; and / or The adaptive delay line includes one or more etalons, wherein the reference beam enters one of the etalons and is split into multiple length-adjustable reference beams, thereby enabling the adaptive delay line to operate in use to provide multiple length-adjustable reference beams.

21. A method for measuring distance using an interferometric measuring device, comprising: Operate the laser to provide the first beam; The first beam is split into an object beam and a reference beam. The object beam is transmitted along the object beam arm of the interferometric measuring device, and the reference beam is transmitted along the reference beam arm of the interferometric measuring device. An adaptive delay line is provided at a distance along the object beam arm, the adaptive delay line being configured to provide one or more object beams with adjustable lengths, thereby adjusting the optical path difference in the interferometric apparatus; Recombining the one or more length-adjusted object beams from the object beam arm and the reference beam from the reference beam arm; as well as Detect the interference between the one or more length-adjusted object beams and the reference beam. in: The adaptive delay line includes a series of N A splitter to simultaneously provide optical path lengths with spacing. 2 N A beam of objects, of which N ≥1, and includes a combiner, whereby the adaptive delay line operates in use to provide multiple length-adjustable object beams; and / or The adaptive delay line includes one or more etalons, wherein the object beam enters one of the etalons and is split into multiple length-adjustable object beams, thereby the adaptive delay line operates in use to provide multiple length-adjustable object beams.

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