WO2023073385A1 - Interféromètre et procédé d'interférométrie - Google Patents

Interféromètre et procédé d'interférométrie Download PDF

Info

Publication number
WO2023073385A1
WO2023073385A1 PCT/GB2022/052755 GB2022052755W WO2023073385A1 WO 2023073385 A1 WO2023073385 A1 WO 2023073385A1 GB 2022052755 W GB2022052755 W GB 2022052755W WO 2023073385 A1 WO2023073385 A1 WO 2023073385A1
Authority
WO
WIPO (PCT)
Prior art keywords
frequency
sum
interferometer
time
length
Prior art date
Application number
PCT/GB2022/052755
Other languages
English (en)
Inventor
Nigel Joseph Copner
Bethan Rose COPNER
Edward Benjamin Hughes
Michael Aloysius CAMPBELL
Kang Li
Dun QIAO
Original Assignee
Usw Commercial Services Ltd
Npl Management Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Usw Commercial Services Ltd, Npl Management Limited filed Critical Usw Commercial Services Ltd
Publication of WO2023073385A1 publication Critical patent/WO2023073385A1/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02007—Two or more frequencies or sources used for interferometric measurement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G01B9/02087—Combining two or more images of the same region

Definitions

  • the present invention relates to an interferometer and an interferometry method.
  • FSI frequency scanning interferometry
  • FSI tuneable lasers that sweep at 100kHz or even 1MHz with tuning ranges over lOOnm would generate a beat frequency over 120GHz at a distance of 10m.
  • Such analogue-to-digital (A/D) converters capable of sampling such frequencies may be difficult to source with high dynamic range or low cost. For reasonable costs, A/D speeds need to be limited to range below 10GHz or less.
  • significant processing is required to be performed on the detected signal to create an output spectrum with sufficient resolution, i.e. using a Fast Fourier Transform (FFT), making real time feedback control of automated equipment problematic.
  • FFT Fast Fourier Transform
  • an interferometer comprising: a continuous-wave beam generator for generating a first beam and a second beam, each having a respective frequency which varies with time; wherein the interferometer is arranged such that, in use, the first beam is transmitted along a target path having a length to be measured and the second beam is transmitted along a reference path having a reference length; a sum-frequency generator for receiving the first beam and the second beam following their respective transmissions along the target path and the reference path and for generating a sum-frequency beam from the first beam and the second beam, the sum-frequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam; and an analyser for analysing the sum-frequency beam to determine the length of the target path.
  • the frequency of one of the first beam and the second beam increases with time while the frequency of the other of the first beam and the second beam decreases with time.
  • the frequencies of the first beam and the second beam vary synchronously with one another and vary symmetrically with respect to one another about a central frequency.
  • the analyser comprises: a spectral filter configured to receive the sum-frequency beam and provide an output when the frequency of sumfrequency beam is at a given frequency; and a detector configured to detect the output from the spectral filter, wherein the output of the spectral filter is indicative of the length of the target path.
  • the spectral filter comprises an etalon, an atomic line filter or an atomic absorption filter.
  • the first beam and the second beam each have a frequency which varies non-linearly with time.
  • the first beam and the second beam are such that the relationship between the frequency of the sum-frequency beam and time is linear.
  • the analyser is arranged to determine the length of the target path based on a relationship between a frequency of the sum-frequency beam and time.
  • the analyser is configured to determine the length of the target path based on a time at which the frequency of the sum-frequency beam reaches a or the given frequency. In some embodiments, the analyser is configured to determine the time at which the frequency of the sum-frequency reaches the given frequency by determining a time at which the output from the spectral filter is detected by the detector.
  • the continuous-wave beam generator is configured to adjust a scanning frequency range of the first beam and the second beam based on a measurement of the time at which the frequency of the sum-frequency beam reaches the given frequency and the analyser is configured to determine one or more further measurements of the time at which the frequency of the sum-frequency beam reaches the given frequency based on the adjusted scanning frequency range.
  • the analyser is configured to determine the length of the target path based on a rate of change of the frequency of the sum-frequency beam with respect to time.
  • the analyser is configured to: adjust a parameter value of the continuous-wave beam generator such that the rate of change of the frequency of the sum-frequency beam has a pre-determined value; and determine the length of the target path based on the parameter value.
  • the parameter value is a value setting the rate of the nonlinear variation with time of the frequency of the first beam and/or second beam.
  • the analyser is configured to detect that the rate of change of the frequency of the sum-frequency beam has the pre-determined value by determining when the frequency of the sum-frequency beam matches an atomic transition resonance frequency.
  • the frequencies of the first beam and the second beam vary linearly with time.
  • the analyser is configured to determine the length of the target path based on a frequency of the sum-frequency beam.
  • the analyser is configured to: adjust a parameter value of the continuous-wave beam generator such that the magnitude of the frequency of the sum-frequency beam matches an atomic transition resonance frequency.
  • the interferometer is arranged such that, in use, the first beam is transmitted along a third path having a given length and the second beam is transmitted along a fourth path having a given length;
  • the interferometer comprises a second sum-frequency generator for receiving the first beam and the second beam following their respective transmissions along the third path and the fourth path and for generating a second sum-frequency beam from the received first beam and the second beam, the second sum-frequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam;
  • the analyser is configured to determine the length of the target path based on an analysis of the sumfrequency beam and the second sum-frequency beam.
  • the analyser is configured to determine the length of the target path by comparing a rate of change of frequency of the sum-frequency beam and a rate of change of frequency of the second sum-frequency beam.
  • the comparing comprises determining a ratio of the rate of change of frequency of the sum-frequency beam and the rate of change of frequency of the second sum-frequency beam, wherein the ratio is indicative of the length of the target path given determined lengths for the third path, the fourth path and the reference path.
  • the sum-frequency generator comprises at least one nonlinear crystal. In some embodiments, the continuous-wave beam generator comprises at least one optical source.
  • the at least one optical source comprises at least one continuous-wave laser.
  • the continuous-wave beam generator comprises a mixing apparatus configured to generate the first beam and the second beam from a first input beam having a frequency which varies with time and a second input beam having a substantially constant frequency.
  • the mixing apparatus comprises a four-wave mixing apparatus or a difference-frequency mixing apparatus.
  • an interferometry method comprising: generating, using a continuous-wave beam generator, a first beam and a second beam, each having a respective frequency which varies with time; transmitting the first beam along a target path having a length to be measured; transmitting the second beam along a reference path having a reference length; receiving, at a sum-frequency generator, the first beam and the second beam following their respective transmissions along the target path and the reference path; generating, by the sum-frequency generator, a sum-frequency beam from the received first beam and the received second beam, the sum-frequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam; and analysing the sum-frequency beam to determine the length of the target path.
  • the frequency of one of the first beam and the second beam increases with time while the frequency of the other of the first beam and the second beam decreases with time.
  • the frequencies of the first beam and the second beam vary synchronously with one another and vary symmetrically with respect to one another about a central frequency.
  • the analysing comprises: filtering the sum-frequency beam with a spectral filter configured to receive the sum-frequency beam and provide an output when the frequency of sum-frequency beam is at a given frequency; and detecting the output from the spectral filter, wherein the output from the spectral filter is indicative of the length of the target path.
  • the spectral filter comprises an etalon, an atomic line filter or an atomic absorption filter.
  • the first beam and the second beam each have a frequency which varies non-linearly with time.
  • the first beam and the second beam are such that the relationship between the frequency of the sum-frequency beam and time is linear.
  • the analysing comprises determining the length of the target path based on a relationship between a frequency of the sum-frequency beam and time.
  • the analyser is configured to determine the length of the target path based on a time at which the frequency of the sum-frequency beam reaches a or the given frequency.
  • the analyser is configured to determine the time at which the frequency of the sum-frequency reaches the given frequency by determining a time at which the output from the spectral filter is detected by the detector.
  • the method comprises adjusting a scanning frequency range of the first beam and the second beam based on a measurement of the time at which the frequency of the sum-frequency beam reaches the given frequency; and determining one or more further measurements of the time at which the frequency of the sum-frequency beam reaches the given frequency based on the adjusted scanning frequency range.
  • the method comprises determining the length of the target path based on a rate of change of the frequency of the sum-frequency beam with respect to time.
  • the method comprises adjusting a parameter value of the continuous-wave beam generator such that the rate of change of the frequency of the sum-frequency beam has a pre-determined value; and determining the length of the target path based on the parameter value.
  • the parameter value is a value setting the rate of the nonlinear variation with time of the frequency of the first beam and/or second beam.
  • the analyser is configured to detect that the rate of change of the frequency of the sum-frequency beam has the pre-determined value by determining when the frequency of the sum-frequency beam matches an atomic transition resonance frequency.
  • the frequencies of the first beam and the second beam vary linearly with time.
  • the analyser is configured to determine the length of the target path based on a frequency of the sum-frequency beam. In some embodiments, the analyser is configured to: adjust a parameter value of the continuous-wave beam generator such that the magnitude of the frequency of the sum-frequency beam matches an atomic transition resonance frequency.
  • the method comprises transmitting the first beam along a third path having a given length; transmitting the second beam along a fourth path having a given length; receiving, at a second sum-frequency generator, the first beam and the second beam following their respective transmissions along the third path and the fourth path; generating, at the second sum-frequency generator, a second sumfrequency beam from the received first beam and the received second beam, the sumfrequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam; and determining the length of the target path based on an analysis of the sum-frequency beam and the second sum-frequency beam.
  • the method comprises determining the length of the target path by comparing a rate of change of frequency of the sum-frequency beam and a rate of change of frequency of the second sum-frequency beam.
  • the comparing comprises determining a ratio of the rate of change of frequency of the sum-frequency beam and the rate of change of frequency of the second sum-frequency beam, wherein the ratio is indicative of the length of the target path given determined lengths for the third path, the fourth path and the reference path.
  • the sum-frequency generator comprises at least one nonlinear crystal.
  • the continuous-wave beam generator comprises at least one optical source.
  • the at least one optical source comprises at least one continuous-wave laser.
  • the continuous-wave beam generator comprises a mixing apparatus configured to generate the first beam and the second beam from a first input beam having a frequency which varies with time and a second input beam having a substantially constant frequency.
  • the mixing apparatus comprises a four-wave mixing apparatus or a difference-frequency mixing apparatus.
  • an interferometer comprising: a beam generator for generating a first beam and a second beam, each having a respective frequency which varies non-linearly with time; wherein the interferometer is arranged such that, in use, the first beam is transmitted along a target path having a length to be measured and the second beam is transmitted along a reference path having a reference length; a sum-frequency generator for receiving the first beam and the second beam following their respective transmissions along the target path and the reference path and for generating a sum-frequency beam from the first beam and the second beam, the sum-frequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam; and an analyser for analysing the sum-frequency beam to determine the length of the target path.
  • an interferometer comprising: a beam generator configured to generate a first beam and a second beam, each having a respective frequency which varies non-linearly with time and direct the first and second beams along respective target and reference paths; a sumfrequency generator to receive the first beam and the second beam following their respective transmissions along the target path and the reference path and generate a sum-frequency beam from the first beam and the second beam, the sum-frequency beam having a frequency which is a sum of the respective frequencies of the first beam and the second beam; and, an analyser for analysing the sum-frequency beam to determine the length of the target path relative to the reference path.
  • Figure 1 shows a schematic representation of an embodiment of an interferometer
  • Figures 2 to 4 show schematic representations of sum-frequency beams generated in an embodiment of an interferometer
  • Figure 5 shows a schematic representation of factors which affect the gradient of sum-frequency beams generated in an embodiment of an interferometer
  • Figure 6 illustrates aspects of a time-based measurement technique in an embodiment of an interferometer
  • Figure 7 illustrates schematically the detection of a target frequency in an embodiment of an interferometer
  • Figures 8 and 9 show a simulation result and parameters for a time-based measurement technique in an embodiment of an interferometer
  • Figure 10 illustrates aspects of a tuning-based measurement technique in an embodiment of an interferometer
  • Figures 11 and 12 show a simulation result and parameters for a tuning-based measurement technique in an embodiment of an interferometer
  • Figure 13 shows a schematic representation of another embodiment of an interferometer
  • Figure 14 shows a schematic representation of a further embodiment of an interferometer
  • Figure 15 illustrates schematically aspects of a ratiometric measurement technique in the embodiment shown in Figure 14;
  • Figures 16 to 18 show schematic representations of examples methods of generating a first beam and a second beam for use in certain embodiments described herein;
  • Figure 19 shows illustrates schematically aspects of a measurement technique used by an embodiment of an interferometer which uses a first beam and a second beam with linearly-varying frequency
  • Figure 20 shows a flowchart representation of an embodiment of an interferometry method.
  • a preferred embodiment of the present invention is directed to an interferometer wherein a sum-frequency, generated from a first beam and a second beam each having a frequency which varies with time, is analysed to determine an optical path difference measurement.
  • the first beam and the second beam may, for example, be, linear or nonlinear, oppositely-chirped beams.
  • the first beam and the second beam may, in certain embodiments, be produced by one or more continuous-wave sources, such as one or more tunable continuous-wave lasers. In other embodiments, the first beam and/or the second beam may not be continuous.
  • the first beam and/or the second beam may be a pulsed beam.
  • Certain embodiments allow an optical path difference measurement to be made in a manner which reduces or avoids significant post-processing which is done in certain conventional interferometers. For example, generating a sum -frequency beam and analysing, e.g. by use of a spectral filter and a detector, the sum-frequency beam allows for the processing to obtain a distance measurement to be performed in the optical domain. This means that a distance measurement may be obtained without, as is done in certain conventional interferometers, performing digital processing such as that involved in performing an FFT. This may mitigate the effects of noise induced in conventional interferometers. Moreover, in certain embodiments, an interferometer may also be low cost since it may mitigate the need for costly high-bandwidth A/D converters.
  • Certain embodiments may allow an absolute distance measurement to be obtained in an accurate and robust manner. Moreover, in some embodiments, the impacts of decoherence or partial decoherence on system performance may be reduced. Furthermore, certain embodiments seek to provide an interferometry technique which provides improved distance resolution while being based on an all-optical processing technique.
  • FIG 1 shows an embodiment of an interferometer 100.
  • the interferometer 100 comprises a continuous-wave beam generator 102.
  • the continuous-wave beam generator 102 is configured to generate a first beam 104 and a second beam 106.
  • the first beam 104 and the second beam 106 each have a frequency which varies with time.
  • the frequencies of the first beam 104 and the second beam 106 vary non-linearly with time.
  • the frequencies of the first beam 104 and the second beam 106 may vary linearly with time.
  • the continuous-wave beam generator 102 is configured to operate continuously to generate the first beam 104 and the second beam 106.
  • operating continuously can be defined as operating to produce the beams 104, 106 over an uninterrupted duration of at least Ins.
  • the continuous-wave beam generator 102 may comprise one or more optical sources, for example one or more lasers.
  • the continuous-wave beam generator 102 may comprise an optical source for generating each of the beams 104, 106.
  • the first beam 104 and the second beam 106 may, for example, have a wavelength in the optical range.
  • the first beam 104 and the second beam 106 may have a wavelength of around lOOnm to 1mm.
  • the first beam and the second beam may have a central frequency of around 1550nm.
  • the continuous-wave beam generator may comprise a mixing apparatus, (not shown in Figure 1), such as a four- wave mixing apparatus or a difference-frequency mixing apparatus, examples of which will be described below with reference to Figures 16 to 18.
  • a mixing apparatus may be configured to take an input from one or more optical sources and output the first beam 104 and the second beam 106.
  • the interferometer 100 comprises a beam splitter 108 which directs the beams 104, 106 along a reference arm and a target arm.
  • the reference arm defines a reference path having a pre-determined length while the target arm defines a target path having a length which is to be measured.
  • the reference path comprises a reference mirror 110 at a pre-determined position and a first filter 109 which filters the second beam 106 from the reference path such that only the first beam 104 is incident on and reflected from the mirror 110.
  • the target path comprises a target 112 at a position to be determined and a second filter 113 which filters the first beam 104 from the target path such that only the second beam 106 is incident on and reflected from the target 112.
  • the first beam 104 is the up-chirp while the second beam 106 is the down-chirp
  • the first beam 104 may be the down-chirp and the second beam 106 may be the up-chirp
  • the reference arm and the target arm may comprise different components for directing the beams than those shown in the schematic representation of Figure 1.
  • the reference mirror 110 may be omitted.
  • the first beam 104 and the second beam 106 are directed, in this embodiment by a second mirror 114, to a sum -frequency generator 116.
  • the sum-frequency generator 116 is configured to receive the first beam 104 and the second beam 106 with a temporal difference between them which is dependent on the difference between the optical path lengths of the reference path and the target path.
  • the sum-frequency generator 116 is configured to generate a sum-frequency beam 117 from the first beam 104 and the second beam 106.
  • the sum-frequency generator 116 may, for example, comprise a nonlinear crystal.
  • the non-linear crystal may comprise any non-linear crystal which allows for correct phase matching between the optical inputs and the sum-frequency output, such as periodically poled lithium niobite (PPLN).
  • the sum-frequency generator 116 may comprise a non-linear crystal which has a %2 effect, which is a nonlinear effect that is typically deployed in optical frequency doubling.
  • An analyser 118 is arranged to analyse the sum-frequency beam 117.
  • the analyser 118 may comprise any suitable apparatus for analysing the sum-frequency beam 117, e.g. measuring the frequency or the wavelength of the sum-frequency beam 117.
  • Figures 2 to 4 illustrate how the frequency of the sum-frequency beam which is generated by the sum-frequency generator 116 depends on the temporal difference between the first beam 104 and the second beam 106 on their arrival at the sum- frequency generator 116.
  • f and f 2 are respective starting frequencies of the first beam 104 and the second beam 106; f c is a central frequency of the first beam 104 and the second beam f +f
  • f c “T P is a second-order coefficient which sets the rate at which the frequencies f up and fdown vary with respect to time t; and t deiay is the temporal difference between the first beam and the second beam on arrival at the sum-frequency generator 116.
  • the frequency f sum of the sum-frequency beam can be described by the following expression.
  • the frequency f sum of the sum-frequency beam therefore has a value of (2f c — 4 d 2 B 4nd ?
  • f up fi + t 2 p
  • f d0W n fi ⁇ t 2 P
  • Figures 3 and 4 show examples where the path difference d and therefore the value of t deiay between the first beam 104 and the second beam 106 is non-zero.
  • Figure 4 represents an example with a larger value of the path difference d, and therefore a larger gradient of the frequency f sum , than the example shown in Figure 3.
  • Figure 5 illustrates how a sweep time t s for the frequency f sum of the sumfrequency beam to reach a target frequency f t varies based on the values of f and d.
  • d For equal values of d, higher values of (3 result in a larger gradient and therefore a smaller sweep time t s .
  • higher values of d result in a larger gradient and therefore a smaller sweep time t s .
  • these properties may be used in various ways to determine a value of the path difference d.
  • Figure 6 shows an example wherein a first sum frequency f suml and a second sum frequency f sum2 are produced with equal value of 3 but different values d r and d 2 of path difference d.
  • Figure 6 shows that the sum frequencies f suml and f sum2 reach the target frequency f t at different respective times t s l and t s 2 •
  • the different times t s l and t s 2 can be measured and are indicative of the different values d r and d 2 of path difference d for the sum-frequency beams f suml and f sum2 .
  • Figure 7 shows an example of how the time at which a frequency of a sumfrequency beam reaches a target frequency can be measured, according to certain embodiments.
  • the dotted line represents the spectral output response of a spectral filter, in this example a high-finesse etalon.
  • the output response of the filter is centred on the target frequency f t .
  • the etalon provides an output, which may be measured by a detector, at times t S;1 and t s 2 , corresponding to the times when the first and the second sum-frequency beams reach the target frequency f t .
  • the time of detection of an output from the etalon therefore indicates a given value of the path difference d.
  • the analyser 118 may comprise the spectral filter and additionally a detector, such as a photodiode, configured to determine a time at which a frequency of the sum -frequency beam 117 is output from the spectral filter.
  • the term ct may typically be far greater than the term 2nd.
  • the term ct may have a magnitude on the 10 5 — 10 6 level while the term 2nd may typically not exceed the 10 2 level. Accordingly, if the term 2nd is ignored, the At along d can be expressed as which means that
  • an A/D converter may be used which provides resolution in time on the order of one nanosecond.
  • the system can detect a Ippm change in path difference d.
  • the total sweeping time should remain at millisecond level for an achievable laser tuning range.
  • lower sweeping times may be used provided that the first beam and the second beam are continuous for a minimum period to allow a measurement to be made on the sumfrequency beam.
  • the first beam and the second beam should have an uninterrupted duration of at least Ins.
  • first beam and the second beam are continuous-wave beams
  • limitations which may be present if short pulses e.g. pulses of duration on the order of hundreds of femtoseconds
  • the use of short pulses may present limitations due to the spectral breadth of such short pulses or the short duration of a central frequency for the pulses.
  • limitations may arise when using short pulses due to the resolution limits of components in the system.
  • a continuous-wave source may mitigate such limitations while also being lower cost than a source for producing short pulses.
  • a 1GHz A/D converted may break this 1ms into Ins steps i.e. a Ins resolution of this 1ms scan time will be provided. This breaks the 1ms scan period into 10 6 steps, allowing for a Ippm accuracy in measurements of the time. This, in turn, leads to a Ippm accuracy in the distance measurement.
  • a 1GHz A/D provides the same Ins time resolution but over a longer scan period of Is. This provides a Ippb accuracy.
  • the continuous-wave beam generator may be configured to continuously cycle from a starting frequency up to a maximum frequency, for example, once per given time period.
  • another up-chirp may begin.
  • the second beam may similarly sweep to a minimum frequency f ci0W n throughout a downchirp before returning to the starting frequency f 2 and beginning another down-chirp.
  • the frequency of the first beam and the second beam may return to the respective starting frequencies and f 2 in a step-like manner.
  • the frequency may begin to sweep in an opposite direction.
  • the first beam may begin to sweep downwards from the maximum frequency f max according to f max — t 2 [3 while the second beam may begin to sweep upwards from the minimum frequency f min according to f min + t 2 p.
  • measurements may be taken during the period when the first beam is sweeping up and the second beam is sweeping down and also during the period when the first beam is sweeping back down and the second beam is sweeping back up.
  • the tuning of the continuous-wave beam generator may be adjusted such that it zooms in to a timing range.
  • the target position may then be sampled more than once in one scan. For example, in an embodiment as described above where the first beam and second beam continuously sweep up and then sweep down, the target position may be sampled on the frequency up scan or the frequency down scan or both.
  • the continuous-wave beam generator could be programmed such that the first beam and the second beam are cycle tuned 0.5ps, or less or more, before or after this known temporal position by tuning the first beam and the second beam appropriately.
  • a data rate for the target of at least 10 6 may be obtained by such a technique. Zooming the tuning around the target sum frequency f t , but tuning at the same rate and zoom cycling 1MHz, allows for a Ippb accuracy with a data update rate of 10 6 .
  • Selected embodiments of the present invention seek to provide an interferometer for which the linewidth and hence the coherence of the source is less important to accuracy than in standard FSI.
  • the interferometer can be configured such that the sum-frequency is on the order of 10 14 Hz or higher, for example where the first beam and the second beam are each at around 1550nm.
  • measuring the sum-frequency to an accuracy of Ippm requires measuring the frequency with a resolution of 100MHz.
  • a resolution can be achieved in 10ns.
  • the frequency need only be measured to a resolution of 100MHz, a linewidth of up to 100MHz in the source, e.g.
  • a laser used to produce the first beam and/or the second beam would not affect the ability of the interferometer to make measurements to an accuracy of Ippm. This applies even if the source is incoherent when measuring long delays. If the source has a linewidth of 1MHz, an accuracy of lOppm would be achieved even when the first beam and the second beam are incoherent with respect to each other. This relaxation of the source linewidth may allow for much broader linewidth light sources to be used. For example, depending on the desired accuracy of the distance measurements, LEDs or other light sources with linewidths generally larger than those of lasers may be used. In standard FSI, a 1GHz beat frequency requires observation for 1ms to generate a 1kHz resolution, i.e.
  • the frequency can be observed for a far shorter time to achieve the same measurement accuracy. For example, for a sum-frequency at 10 14 Hz, the frequency may need to only be observed for 10ns to achieve a 100MHz resolution, and therefore a Ippm accuracy. Since, as described above, in some embodiments, a source with a linewidth of around 100MHz may be used, on-chip tuning of semiconductor lasers may be used. However, it is also viable that this relaxed linewidth requirement may allow for much faster tuning of the wavelength via injection current or on-chip phase element instead of using the much slower thermal tuning.
  • This approach could be used particularly effectively in the above-mentioned zooming approach, allowing zoomed cycling of more than 1GHz. This may allow for data rates for one given target in excess of 10 9 . Further, using injection current etc. may allow for easier custom frequency tuning commensurate with this technique. Certain techniques described hereinbelow for generating oppositely-chirped beams are instantaneous and precise and may therefore be advantageously employed in a zooming technique such as that described above.
  • any suitable spectral filter such as an etalon, an atomic absorption filter or an atomic line filter, may be used to provide the output when the target frequency f t is reached.
  • the spectral filter can be designed for any wavelength.
  • the sum-frequency to be analysed may be on the order of 10 14 Hz.
  • achieving a Ippm accuracy (100MHz resolution) requires observing the signal for 10ns.
  • the spectral filter used, e.g. a high-Q etalon, should be consistent with this 10ns and provide a consistent spectral transmission linewidth.
  • Reflection from the etalon and other spectral filters such as dielectric filters, Bragg grating or any interference-type device, used to transmit or reflect the target frequency, could be used.
  • different detectors, different spectral transmission or reflection peaks of a spectral filter may be used to provide additional data samples at different times. This may provide the opportunity of increasing sample data and improving target motion information.
  • the target frequency f t can be determined and locked by atomic transition absorption.
  • an atomic absorption apparatus could be used as a filter with the output of the filter being detected by a detector, in a similar manner to as described in the case where an etalon is used.
  • the sumfrequency beam could be sent into a gas cell filled with atomic gas.
  • a given atomic gas may have a characteristic absorption frequency or frequencies depending on its atomic transition resonance.
  • Absorption peaks could be detected by both photon diode or third harmonic technique which may, for example, offer MHz and kHz level width respectively. Since an atomic transition absorption peak may be ultra-fine, a target frequency may be detected using gas absorption without allowing for the time needed for a signal of sufficient resolution to be built up in an etalon.
  • Figures 8 and 9 shows a simulation result for a time measurement technique such as the example described above in relation to Figure 7.
  • Figure 8 shows a frequency -time plot showing differences A , from a frequency , of a first sum frequency f suml and a second sum frequency f sum2 (where, as above, is the starting frequency of the up chirp).
  • Figure 9 shows a tuning range and parameters of the first beam and the second beam for the frequency-time plot shown in Figure 8.
  • a central wavelength of the beams is 1550nm.
  • a path difference d of 20m is used.
  • the target frequency f t in this example is set 1MHz above the starting frequency of the up chirp.
  • the simulation result shows that a Ippm change in the path difference d results in a change At in the sweep time to reach the target frequency of around 40ns.
  • Figure 10 illustrates another example of how the frequency of a sum-frequency beam may be analysed to determine an path difference d.
  • Figure 10 shows how an increase in path difference by an amount Ad at a given value of J results in a larger gradient for the frequency of a sum-frequency beam, i.e. f sum2 has a larger gradient than f suml .
  • Figure 10 also shows that the change Ad in the path difference can be compensated for by reducing J by an amount A/?. Therefore, as shown in Figure 10, a third sum-frequency beam having a frequency f sum2 (/? — >, d + Ad) has a gradient equal to that of a first sum-frequency beam having a frequency f S umi P> d). Further, fsumi and f sum3 reach an atomic transition resonance frequency fatomic transition at a same time t s .
  • the path difference d may be measured by slightly modulating the value of f and determining the value of f which results in the frequency of the sum-frequency beam reaching the atomic transition frequency fatomic transition at a pre-determined time t s , or, equivalently, results in the frequency of the sum-frequency beam having a pre-determined gradient.
  • f is varied and the value of f which results in a pre-determined sweep time t s or pre-determined gradient is measured.
  • the sumfrequency reaching the atomic transition resonance frequency at the pre-determined time may be detected by detecting repetition of atomic transition resonance frequency from the atomic transition locking apparatus. This may be detected without detecting the actual sweep time t s and thus there may be less dependence on obtaining accurate time measurements.
  • the term ct (10 5 — 10 6 level) may be far greater than the term 2nd. Ignoring the term 2nd and nd, in the above expression, the A ? along d can be expressed as
  • the value of (3 may be measured by any suitable means.
  • the output of the continuous-wave beam generator may be sampled to determine how the wavelength or frequency varies with time.
  • the value of 3 may be measured by analysing the output of the continuous-wave beam generator, e.g. the first beam and/or the second beam, with a Mach-Zehnder interferometer (MZI).
  • MZI Mach-Zehnder interferometer
  • An MZI may allow for the value of (3 to be precisely determined by wavelength sampling and fitting of the output of the continuous-wave beam generator.
  • an additional beam splitter is used to direct a portion of the first beam and/or second beam to an MZI or other apparatus for analysing the first beam and/or second beam to determine the tuning rate of the beams.
  • a beam splitter (not shown) could be positioned between the beam generator 102 and the beam splitter 108 to direct a portion of the first beam and/or the second beam to an MZI.
  • the frequency resolution is same as the distance resolution.
  • v is the frequency to be sampled (for J measurement ⁇ 200THz, for sum frequency ⁇ 400THz)
  • Av is range of the frequency to be sampled (for J measurement -100GHz, for sum frequency ⁇ 10MHz)
  • I is the optical path difference (OPD) on MZI interferometer arm
  • AZ is the fringe distance for measurement.
  • I is the optical path difference (OPD) on MZI interferometer arm
  • AZ is the fringe distance for measurement.
  • 10m OPD could supply around 10 7 sampling points, which is sufficient for detecting a Ippm, i.e. 10' 6 , variation in J .
  • 10m OPD could supply around 10 3 sampling points, which may be sufficient for continuous measurement during throughout frequency sweeping. In examples, this number of sampling points is enough to fit and calculate J and A/?. Since the total number of sampling points N increases with increased tuning range, the tuning range may be increased to improve the accuracy in the calculation of J and A/?.
  • Figure 11 shows a simulation result for the tuning rate measurement technique described above in relation to Figure 10.
  • Figure 12 shows an example tuning range for the tuning rate measurement technique.
  • an path difference d 20m and a value of J of 1 x 10 16 is used.
  • a central frequency of the beams 1550nm.
  • the tuning range of the beams is around 140GHz over a sweep time of around 3.7ms.
  • Figures 11 and 12 show that in this simulation a Ippm change in the path difference d results in a change A ? of around 10 10 .
  • Figure 13 shows an interferometer 1300, according to an embodiment, which is configured for simultaneous measurement of multiple target points.
  • the interferometer 1300 of Figure 13 comprises features of the interferometer 100 of Figure 1, which are labelled with the same figure references as in Figure 1.
  • the interferometer 1300 comprises a lens 1322 configured to direct the second beam 106 towards one or more points on a 3D target 1312 and to focus one or more reflections of the second beam 106 from the one or more points on the target 1312.
  • Each of the reflections of the second beam 106 from the target 1312 may be individually summed with the first beam 104 by the sum-frequency generator 116 to provide a respective sum-frequency beam for each of the points on the target 1312.
  • Each of the sum-frequency beams may be analysed, for example in any of the ways described above, to provide a measurement of a distance to the respective point on the target 1312 to which the given sum-frequency beam corresponds.
  • FIG 14 shows an interferometer 1400, according to another embodiment.
  • the interferometer 1400 comprises a target section 1410 and a reference section 1420.
  • Each of the target section 1410 and the reference section 1420 operates in a similar manner as the interferometer 100 of Figure 1 which has been described above.
  • Components of the target section 1410 and the reference section 1420 which correspond with those of the interferometer of Figure 1 are labelled with like figure references.
  • the interferometer 1400 comprises a continuous-wave beam generator 1402 configured to generate a first beam 1404 and a second beam 1406 as described above in relation to previous embodiments.
  • the first beam 1404 and the second beam 1406 are incident on a first beam splitter 1408 which directs the first beam 1404 and the second beam 1406 to both the target section 1410 and the reference section 1420.
  • a second beam splitter 1418 directs the second beam 1406 along a target path towards a target 1412 while directing the first beam 1404 along a first reference path.
  • no reference mirror (equivalent to the reference mirror 110 of Figure 1) is shown for the first reference path.
  • the same principle applies that the first beam 1404 is transmitted along a reference path of known length before arriving at a sum-frequency generator 1416 while the second beam 1406 is transmitted along a target path having a length to be measured.
  • the sum -frequency generator 1416 generates a sum-frequency beam 1417 from the first beam 1404 and the second beam 1406.
  • the sum-frequency beam 1418 is received by a first analysis section 1418 for analysing.
  • the reference section 1420 comprises equivalent components to the target section 1420. However, in the reference section, in addition to the length of the reference path being pre-determined, the length of the target path is also predetermined.
  • the interferometer 1400 allows for a ratiometric technique for determining an optical path difference measurement to be performed. Since the beams 1404, 1406 are directed to both the target section 1410 and the reference section 1420, two sumfrequency beams 1417, 1427 are generated simultaneously.
  • the two sum-frequency beams 1417, 1427 may have different frequencies, as illustrated in the embodiment shown in Figure 15, depending on the relative optical path differences between the beams in the target section and in the reference section 1420.
  • the frequencies f sumT and f sumR of the sum-frequency beams for, respectively, the target section 1410 and the reference section 1420 are as follows:
  • the gradients Gradient T and Gradient R can be determined by any suitable means.
  • the sum-frequencies f sumT and f sumR may be sampled and the gradient measured based on measurements at two given sample points, e.g. using an MZI as described above.
  • the above-described ratiometric technique allows for the target section and the reference section to be arranged to operate under the same ambient conditions. Accordingly, when the ratio of the gradients is taken, any effect on the refractive index n due to the ambient conditions may be cancelled out.
  • the accuracy of an interferometer operating in air may be limited by measurements of the refractive index of the air in which the interferometer is operating.
  • the refractive index of air may vary with changes temperature, pressure and humidity, as described by the Edlen dispersion formula. This may typically limit the accuracy of optical path difference measurements made by an interferometer to around Ippm. However, the present embodiment allows for these issues to be mitigated. Further, according to this, ratiometric, technique, an optical path difference may be determined without measuring a value for J .
  • This may allow the possibility for reduced error in the calculation of a target distance.
  • it may be possible to continuously measure the gradients and thereby continuously determine the target distance d T .
  • a statistical algorithm may be applied to the multi -gradient results to compensate for errors cause by misalignment of the up- chirp and the down-chirp or system noise.
  • the first beam and the second beam are chirps whose frequency varies parabolically, i.e. as a 2 nd order function with respect to time.
  • the up chirp and down chirp functions are, where, as in previous embodiments, and f 2 are initial frequencies for up and down chirp respectively and are symmetrical about the central frequency f c .
  • the time delay ⁇ deiay due to optical path difference is related to the target distance d and medium refractive index n.
  • the sum frequency f sum is:
  • the chirping function (t) may be expressed with a Power series expansion, as follows
  • the optical path delay is far less than total sweeping time.
  • the frequency sampling in the target section and the reference section is synchronized.
  • the first condition may be generally satisfied when, for example, the target distance remains at ⁇ 10m level ( ⁇ 10' 7 s delay) and sweeping time remains at ms level ( ⁇ 10' 3 s).
  • the continuous-wave beam generator may generally be configured to chirp along a quasi-linear or 2 nd order function. This means that the 1 st and 2 nd order terms in the above equation for /? with arbitrary chirping functions play a more important role for distance measurement than higher order terms. For example, with a time difference of 10' 9 s between sampling on the target arm and the reference arm, for a 3 rd order term, the difference will be 10' 18 level. This is far smaller than the 2 nd order term, and therefore may be ignored without introducing significant errors. Even higher order terms have even lower effects on accuracy.
  • Figures 16 to 18 show schematic representations of methods for generating a first beam and a second beam for use in embodiments herein.
  • Figure 16 illustrates an example of a method of generating an up-chirp and a down-chirp for use in embodiments described herein.
  • a third-order non-linear interaction (%(3) effect) based wavelength conversion is used to achieve up- chirp and the down-chirp.
  • FWM Four Wave Mixing
  • DFWM Degenerative FWM
  • DFWM occurs when there are only two inputs, a first input fl and a second input f2.
  • the first input fl is a fixed laser and the second input f2 is a swept source.
  • the two inputs fl, f2 are input into a mixing apparatus 1603.
  • peaks are generated at frequencies 2fl - f2 and 2f2 - fl. Since f2 is a swept source, the peak generated at 2fl - f2 is a mirrored (about the fl reference) inverted copy of f2. Since the generated sweeping chirp is a perfect copy of the original and is created simultaneously to the original, there are no synchronization issues to resolve. Also, only one swept frequency chirp laser source is required, which reduces the cost and complexity of the system.
  • Figure 17 shows another example method of generating an up-chirp and a downchirp for use in embodiments described herein.
  • the example shown in Figure 17 uses wavelength conversion based on a second-order nonlinear interaction (%(2) effect).
  • signals fl and f2 are input into a difference-frequency mixer 1703 and the difference-frequency mixed 1703 generates an output at a frequency fl-f2.
  • the signal and output wavelengths are in the 1550nm band, and the pump is near 775nm.
  • the converted down chirp signal frequency is fl/2-A or fl-f2.
  • the converted spectrum is an image of the input spectrum and mirrored around the half pump frequency fl.
  • pump near 775nm may result in simple removal of the pump light from the converted signal in DFG based chirp generation.
  • the chromatic aberration by the difference of the signal and pump wavelengths may cause difficulties in coupling light into a waveguide such as MgO:PPLN. Therefore, the chromatic aberration should be considered to achieve the single-mode conditions for both pump and signal beams if dispersion components like lens and fibre are used in the coupling
  • Figure 18 shows another example method of generating an up-chirp and a downchirp for use in embodiments described herein.
  • Figure 18 shows a cascaded configuration. In this cascaded configuration, second harmonic generation (SHG) of the pump occurs simultaneously with the DFG process, and inputs at frequencies fl and f2 generate an output at frequency 2fl-f2. Since both the pump fl and the chirped signal wavelengths f2 are in the same wavelength range of 1550nm, aberration is negligible for waveguide coupling.
  • SHG second harmonic generation
  • the cascaded %(2) based conversion method has an obvious advantage over the DFG as both single modes can be achieved with higher waveguide-coupling efficiency. Unlike the FWM with unused idler frequency (2f2 - fl in Figure 16), there is no additional photon depletion in the cascaded SHG, therefore, higher efficiency is possible to achieve the mirrored up (f2) and down (2fl-f2) chirp frequency. Furthermore, quasi-phase matched (QPM) LiNbO3 waveguides have demonstrated excellent performances such as low noise, multichannel conversion, broad conversion bandwidth, and relatively-high conversion efficiency.
  • the first beam and the second beam each have a frequency which varies non-linearly with time.
  • one or more of the first beam and the second beam may have a frequency which varies linearly with time.
  • Figure 19 shows aspects of an embodiment where the frequencies of the first beam and the second beam vary linearly with time.
  • Figure 19 shows an example in which the frequencies of the first beam and the second beam vary linearly with time.
  • the frequency of a sum-frequency beam generated from the first beam and the second beam is constant and has a value which is dependent on the temporal difference between the first beam and the second beam when they arrive at the sum-frequency generator.
  • the frequency f own °f the second beam which decreases linearly from the starting frequency f 2 and which arrives at the sum-frequency generator with a time delay of t deiay relative to the first beam, is described by fdown ⁇ fz ⁇ a(t deiay ⁇ Since tdeiay ⁇ 2nd I C , f own ⁇ fz ⁇ a(—2nd/c + t).
  • the frequency of the sum-frequency beam may be measured.
  • a scanning filter such as a scanning etalon, may be used to match and detect the sum frequency.
  • the scanning filter may measure the frequency of the sum-frequency beam by scanning a range of frequencies and detecting the frequency at which the sum-frequency beam has a maximum intensity. The length of the target path may then be determined based on the measured frequency of the sum-frequency beam.
  • a ratiometric approach similar to that described above may also be used in embodiments where the frequencies of the first beam and the second beam vary linearly with time. In this case, however, the ratio of the gradients of the sum-frequency beams for the target section and the reference section is not used. Instead, a ratio of the magnitudes of these sum -frequencies may be used. For example, since the central frequency f c is known, the ratio of the sum frequencies can be expressed as:
  • Figure 20 is a flowchart diagram showing an interferometry method 2000 according to an embodiment.
  • the method 2000 comprises, at block 2002, generating, using a continuous-wave beam generator, a first beam and a second beam, each having a frequency which varies with time.
  • the method comprises transmitting the first beam along a target path having a length to be measured.
  • the method comprises transmitting the second beam along a reference path having a reference length.
  • the method comprises receiving, at a sum-frequency generator, the first beam and the second beam following their respective transmissions along the target path and the reference path.
  • the method comprises generating, at the sum-frequency generator, a sum-frequency beam from the first beam and the second beam following their respective transmissions along the target path and the reference path.
  • the method comprises analysing the sum-frequency beam to determine a length of the target path.
  • the method 2000 may comprise performing any of the steps described above with reference to earlier- described embodiments of an interferometer according to the present invention.
  • atomic absorption is used to determine a rate of change with time of a frequency of a sum-frequency beam.
  • atomic absorption may be used to determine when the frequency of the sum-frequency beam reaches a pre-determined value.
  • Atomic absorption may also be used, in certain embodiments, to determine a rate of change of the first beam and/or the second beam, e.g. linear and/or non-linear chirp coefficients.
  • a gas or combination of gases having an absorption spectrum comprising more than one absorption line may be used to determine a linear or non-linear chirp rate.
  • a portion of the first beam or the second beam may be passed through a gas absorption cell with an optical detector recording the intensity of a signal transmitted from the cell. Sampling this signal synchronously with other signals and fitting the sampled data to the absorption lines of the gas or gases in the absorption cell will allow the co-efficients defining the tuning rate of the beam, given that the absorption lines occur at well-known frequencies.
  • HCN gas in the C-band may be used alone or in combination with one or more other gases as the absorptive gas in the absorption chamber.
  • Iodine gas may be used.
  • another gas or combination of gases may be used.
  • the transmission of one of the first beam and the second beam through one or more etalons, which are of known length or which are long-term stable could be used to determine the tuning rate.
  • a given path such as a reference path
  • the length of a given path may be determined at the time of measurement of the target path.
  • the length of a given path may be determined by passing one or both of the first beam and the second beam through a gas cell, e.g. a gas cell containing HCN or Iodine.
  • a gas cell e.g. a gas cell containing HCN or Iodine.
  • the embodiments above concerned an interferometer having a reference path with a reference length, other implementations are possible. For example, in one embodiment distances are measured relative to a point. In such an arrangement, you do not need to know the second path length at all. Instead, measurements are made from a reference point in the measurement arm (eg.
  • non-linear tuning rate can be determined by various non-distance-related mechanisms, such as use of the above-mentioned gas cell. While the reference length is one way of determining nonlinear tuning rate, as illustrated in the above embodiment, other ways are also possible (and these approaches can also be used in substitution to those highlighted in the above embodiments).

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

L'invention concerne un interféromètre comprenant : un générateur de faisceau à ondes continues pour générer un premier faisceau et un second faisceau, chacun ayant une fréquence respective qui varie dans le temps. L'interféromètre est agencé de manière à ce que, en cours d'utilisation, le premier faisceau soit transmis le long d'une trajectoire cible ayant une longueur à mesurer et que le second faisceau soit transmis le long d'une trajectoire de référence ayant une longueur de référence. L'interféromètre comprend également un générateur de fréquence de la somme pour recevoir le premier faisceau et le second faisceau après leurs transmissions respectives le long de la trajectoire cible et de la trajectoire de référence et pour générer un faisceau de fréquence de la somme à partir du premier faisceau et du second faisceau, la fréquence du faisceau de fréquence de la somme étant une somme des fréquences respectives du premier faisceau et du second faisceau ; et un analyseur pour analyser le faisceau de fréquence de la somme afin de déterminer la longueur de la trajectoire cible. L'invention concerne également un procédé d'interférométrie.
PCT/GB2022/052755 2021-11-01 2022-11-01 Interféromètre et procédé d'interférométrie WO2023073385A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB2115684.9A GB202115684D0 (en) 2021-11-01 2021-11-01 Novel frequency scanning interferometer
GB2115684.9 2021-11-01

Publications (1)

Publication Number Publication Date
WO2023073385A1 true WO2023073385A1 (fr) 2023-05-04

Family

ID=78828320

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2022/052755 WO2023073385A1 (fr) 2021-11-01 2022-11-01 Interféromètre et procédé d'interférométrie

Country Status (2)

Country Link
GB (1) GB202115684D0 (fr)
WO (1) WO2023073385A1 (fr)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8355137B2 (en) * 2007-12-21 2013-01-15 Kevin Resch System and method for chirped pulse interferometry

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8355137B2 (en) * 2007-12-21 2013-01-15 Kevin Resch System and method for chirped pulse interferometry

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
JONATHAN LAVOIE ET AL: ""Quantum-optical coherence tomography" with classical light", ARXIV.ORG, CORNELL UNIVERSITY LIBRARY, 201 OLIN LIBRARY CORNELL UNIVERSITY ITHACA, NY 14853, 4 September 2009 (2009-09-04), XP080364976, DOI: 10.1364/OE.17.003818 *
MARTINEZ JUAN JOSE ET AL: "Dual-Sweep Frequency Scanning Interferometry Using Four Wave Mixing", IEEE PHOTONICS TECHNOLOGY LETTERS, IEEE, USA, vol. 27, no. 7, 1 April 2015 (2015-04-01), pages 733 - 736, XP011574756, ISSN: 1041-1135, [retrieved on 20150305], DOI: 10.1109/LPT.2015.2390779 *
PETER J. DELFYETT ET AL: "Chirped pulse laser sources and applications", PROGRESS IN QUANTUM ELECTRONICS., vol. 36, no. 4-6, 3 November 2012 (2012-11-03), GB, pages 475 - 540, XP055342646, ISSN: 0079-6727, DOI: 10.1016/j.pquantelec.2012.10.001 *

Also Published As

Publication number Publication date
GB202115684D0 (en) 2021-12-15

Similar Documents

Publication Publication Date Title
US11287457B2 (en) System and method for measuring time-frequency characteristic of high-frequency electromagnetic signal
CN110646805B (zh) 一种基于虚拟扫频光源的调频连续波激光测距系统
US9207121B2 (en) Cavity-enhanced frequency comb spectroscopy system employing a prism cavity
AU2017372901B2 (en) Methods for performing dual-comb interferometry
US8917396B2 (en) Fourier transform spectrometer with a frequency comb light source
US11300452B2 (en) Spectral measurement method, spectral measurement system, and broadband pulsed light source unit
CN110749873B (zh) 一种飞秒激光雷达以及气体成分探测方法
Wu et al. Absolute distance measurement with correction of air refractive index by using two-color dispersive interferometry
Lešundák et al. High-accuracy long distance measurements with a mode-filtered frequency comb
CN110274880A (zh) 一种高精度空间分辨的光谱探测方法和系统
CN104236725A (zh) 一种精确测量激光波长的装置及方法
Zhai et al. Underwater distance measurement using frequency comb laser
EP2101161A1 (fr) Procédé indépendant de la largeur de bande et installation pour mesurer et stabiliser le déphasage support-enveloppe de pulsations laser
Šmíd et al. Precise length etalon controlled by stabilized frequency comb
WO2023073385A1 (fr) Interféromètre et procédé d'interférométrie
Lawall Interferometry for accurate displacement metrology
Xiong et al. Influence of spectral resolution on dispersive interferometry of optical frequency comb
Klufts et al. Ultra-high-accuracy chromatic dispersion measurement in optical fibers
Imran et al. Measurement of the group-delay dispersion of femtosecond optics using white-light interferometry
Charczun et al. Broadband and high resolution measurements of cavity loss and dispersion
Kato et al. Fully non-scanning three-dimensional imaging using an all-optical Hilbert transform enabled by an optical frequency comb
Hirth et al. Tunable laser thin film interrogation
RU2020409C1 (ru) Акустооптический способ определения расстояния до объекта
Naftaly Broadband terahertz measurements of optical properties of materials
Kayes et al. Fourier transform spectroscopy via a single electro-optic frequency comb

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22817302

Country of ref document: EP

Kind code of ref document: A1