WO2009059406A1 - Tomographie en cohérence optique avec interféromètre en tandem - Google Patents

Tomographie en cohérence optique avec interféromètre en tandem Download PDF

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Publication number
WO2009059406A1
WO2009059406A1 PCT/CA2008/001944 CA2008001944W WO2009059406A1 WO 2009059406 A1 WO2009059406 A1 WO 2009059406A1 CA 2008001944 W CA2008001944 W CA 2008001944W WO 2009059406 A1 WO2009059406 A1 WO 2009059406A1
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WO
WIPO (PCT)
Prior art keywords
interferometer
coherence tomography
arm
optical coherence
tomography apparatus
Prior art date
Application number
PCT/CA2008/001944
Other languages
English (en)
Inventor
Mark Hathaway
John A. Rogers
Original Assignee
Oti Ophthalmic Technologies Inc.
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 Oti Ophthalmic Technologies Inc. filed Critical Oti Ophthalmic Technologies Inc.
Publication of WO2009059406A1 publication Critical patent/WO2009059406A1/fr

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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
    • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
    • G01B9/02044—Imaging in the frequency domain, e.g. by using a spectrometer
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • 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
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02062—Active error reduction, i.e. varying with time
    • G01B9/02064—Active error reduction, i.e. varying with time by particular adjustment of coherence gate, i.e. adjusting position of zero path difference in low coherence interferometry
    • G01B9/02065—Active error reduction, i.e. varying with time by particular adjustment of coherence gate, i.e. adjusting position of zero path difference in low coherence interferometry using a second interferometer before or after measuring interferometer
    • 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
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4795—Scattering, i.e. diffuse reflection spatially resolved investigating of object in scattering medium
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N2021/178—Methods for obtaining spatial resolution of the property being measured
    • G01N2021/1785—Three dimensional
    • G01N2021/1787—Tomographic, i.e. computerised reconstruction from projective measurements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers

Definitions

  • This invention relates to the field of optical coherence tomography (OCT), and in particular to OCT imaging apparatus employing a tandem interferometer.
  • OCT optical coherence tomography
  • OCT uses interferometery to extract depth information from the sample, and thus permit the construction of a three dimensional image.
  • OCT can operate in either the time domain or the frequency domain (spectral OCT).
  • a time domain system is described in US Patent No. 6,769,769, the contents of which are herein incorporated by reference.
  • a frequency domain system is described in DE 4309056, the contents of which are also incorporated by reference.
  • an entire line of data in the z direction can be derived at once by analyzing the spectrum of the returned signal.
  • the light source can either be a broadband source containing multiple frequencies, or alternatively it can be a tunable single frequency source that whose frequency is swept of the wavelength range of interest.
  • the detector can be a simple photodetector. The frequency of the source varies with time as the source frequency is swept through the range of interest.
  • tandem interferometers in sensing applications as illustrated, for example, in for example, US published application no. 20060061768.
  • US U.S. Patent No. 7259862 also describes a low-coherence interferometery optical sensor using a single wedge polarization readout interferometer.
  • the readout interferometer compensates the optical path length differences in the sensing interferometer within a given depth interval, but in this case the object is scanned with the first interferometer.
  • an optical coherence tomography apparatus is implemented using a tandem interferometer arrangement instead of a single interferometer.
  • optical coherence tomography (OCT)apparatus comprising a light source; a first interferometer receiving light from said source and having a first arm and a second arm, said first interferometer producing an output beam, and there being an optical path difference between said first and second arms; a second interferometer coupled to said first interferometer in tandem, said second interferometer producing an output beam and having a third arm and a fourth arm, there being an optical path difference between said third and fourth arms; wherein one of said interferometers forms a sensing interferometer, and one of the arms in the sensing interferometer forms an object beam; a scanner for scanning an object with the object beam and returning light scattered from the object along the arm forming the object beam; and a detector for detecting a signal in one of said output beams; and wherein the optical path difference in said first interferometer is matched to the optical path difference in said second interferometer to produce said signal.
  • OCT optical coherence tomography
  • the object arm is in the second interferometer, with an adjustable mirror in one of the arms of the first interferometer to match the optical path length differences, although it is also possible to put the object in the first interferometer, and place the adjustable mirror for matching the optical path lengths in the second interferometer.
  • the interferometers can operate in either the time domain or the frequency domain, in which latter case the detector may be a spectrometer.
  • the source could be a broadband source, or alternatively it is possible to implement spectral OCT using a swept frequency source.
  • spectral OCT instead of analyzing the spectrum with a spectrometer, it is possible to rapidly sweep the frequency and look at the response at each frequency. The two methods are equivalent, and permit a line of depth information to be obtained using spectral analysis.
  • Tandem interferometry refers to two interferometers connected together so that low coherence light passes through one then the other.
  • One interferometer is normally called the processing interferometer and the other is called the sensing interferometer.
  • the interferometer that includes the patient's eye would be called the sensing interferometer.
  • the invention provides a method of performing an optical coherence tomography (OCT) scan of an object, comprising passing a light beam from a broadband source through a first interferometer having a first optical path difference between first and second arms thereof to produce a first output beam; launching the output beam of the first interferometer into a second interferometer in tandem with the first interferometer and having a third arm and a fourth arm; one of said arms providing an object beam; scanning a sample with said object beam; and returning light from the object beam through the interferometer to a detector; and matching the optical path length difference between the first and second arms of the first interferometer with the optical path length difference between the reference and object arms of the second interferometer in order to obtain a signal at said detector.
  • OCT optical coherence tomography
  • Figure 1 is a block diagram of a first embodiment of the invention
  • Figure 2 is a block diagram of a second embodiment of the invention.
  • a broadband light source 10 such as a super-luminescent diode (SLD) directs light via optical fiber 11 through a collimator 12 into a reference interferometer 20 comprising a beam splitter 13, which divides the light into a reference beam 14 terminating in mirror 15, and an object beam 16 terminating in mirror 17.
  • SLD super-luminescent diode
  • Dispersion compensation unit 18 is inserted in the object beam 16 to compensate for additional components in the object interferometer descried below.
  • Mirror 17 is displaceable along the axis of the object arm 16. In a single interferometer, no interference fringes will be observed if the OPD between the reference arm 14 and object arm 16 exceeds the coherence length of the light. However, in the case of interferometer 20, which is used in tandem with the interferometer 30, the OPD can greatly exceed the coherence length, and, for example, be in the order of 30 cms.
  • the output of the first interferometer 20 is input through an optical fiber 21 into a second interferometer 30, comprising beam splitter 22, reference arm 23, and mirror 24, and object arm 25, XY scanner 26, and objective 27 including lenses Ll and L2, of which lens L2 is adjustable.
  • the objective 27 projects the object beam onto the eye of the patient, and movable lens L2 can be used to focus the object beam within the eye. Returned light scattered from the eye is directed back along the object path and combined with the light traversing the reference arm 23 in beam splitter/combiner 22.
  • the beam splitter/combiner 22 of the second interferometer 30 produces an output beam, which is directed to spectrometer 32 preferably over an optical fiber 31, although the beam can be also directed using bulk components.
  • the path difference between the reference arm 23 and the object arm 25, is significantly greater than the coherence length of the light so that if the second interferometer were directly supplied by light from the light source 10, no interference fringes would be observed.
  • the first interferometer will compensate for the path difference in the second interferometer, and as a result interference fringes will be observed despite the large OPD in each of the interferometers.
  • the OPD in the each of the interferometers is 30 cms, acting alone, neither would produce interference fringes, but when the output light output from the first interferometer is used as an input to the second interferometer, interference fringes are observed at the output of the second interferometer as if the OPD of the second interferometer was within the coherence length of the light source.
  • the output of the beam splitter 22 is fed over an optical fiber 31 to spectrometer 32, from which OCT data can be extracted in a known manner.
  • spectrometer 32 For each x, y point on the object, a line of data in the z direction (A scan) is obtained using spectral OCT methods.
  • a scan spectral OCT methods.
  • the second interferometer 30 can be mounted on a common platform 50 with the scanner 26 providing the actual moveable head of the equipment that is brought up to the patient's eye, whereas the first interferometer 20 and other components can be located anywhere and connected to the second interferometer 30 via the optical fiber 21.
  • the length of reference arm 23 can be made very small, and in practice the mirror 24 can be placed right up against the output of the beam splitter 22, or actually deposited on its surface. This makes arrangement the active head of the equipment much more compact and robust than would be the case if the two arms in the second interferometer were required to be of substantially the same length, as would be the case for a single interferometer.
  • the source 10 can be a tunable laser, for example, whose frequency is swept over a defined range of frequencies during each data capture in the z direction.
  • the spectrometer 32 can be replaced by a simple photodetector because by sweeping the source frequency the spectral response of the sample is still obtained.
  • Figure 2 works in a similar manner to Figure 1 except the first interferometer is formed by beam splitter/combiner 40 and mirror 41, and the second interferometer is formed by beam splitter/combiner 43 and the eye 28.
  • one arm is formed by the path between beam splitter 40 and mirror 41 and the other arm is formed by the light reflected off the backside of beam splitter/combiner 40.
  • This is combined with the light returned from the first arm and in effect the beam splitter/combiner 43 of the second interferometer 30 sees light coming from an interferometer with two arms of greatly unequal path length.
  • the second interferometer 30, which forms an object path between beam splitter/combiner 43 and the eye 28, and a reference path by the light reflected off the backside of beam splitter/combiner 43.
  • the returned light exiting the beam splitter/combiner 43 is directed through collimator 45 into single mode fiber 46, single mode fused fiber coupler 47, and single mode fiber 48 to spectrometer 32, which as in the first embodiment can be replaced by a photodetector if a frequency swept source, such as a tunable laser, is used instead of the SLD 10.
  • a frequency swept source such as a tunable laser
  • the spectrometer sees the second interferometer as having two arms of greatly unequal length, but of course by supplying the input of the second interferometer with the output of the first interferometer, and adjusting the position of the mirror 41, the large optical path differences of the two interferometers can be canceled out.
  • the source 10 supplies light through the single mode fiber 49, single mode fused fiber coupler 50 and single mode fiber 51 to collimator52.
  • the fused fiber couplers 47 and 50 are interconnected by single mode fiber 53.
  • Angle polished fiber ends 54, 55 permit the output power of the apparatus to be monitored. This is particularly important when the equipment is used for scanning the eye.
  • Light returning from the second Interferometer is fed to the spectrometer 32.
  • the returned light is analyzed in a conventional manner to permit the construction of three dimensional images of the eye, for example, by collecting A-scans to form B-scans, and collecting B- scans to form a complete three dimensional image.
  • the data and image processing can be done in a standard computer with a display.
  • the optical path difference of the first interferometer is roughly matched to the optical path difference of the second interferometer to produce a signal.
  • the object in the example, is placed in one of the arms of the second or downstream interferometer. It will be appreciated, however, that the object could also be placed in the first interferometer, for example, at the location of mirror 17 in Figure 1. In this case, the eye 28 would be replaced by an adjustable mirror, and this mirror would be displaced to match the optical path length differences of the two interferometers.
  • the fiber does not need to be part of the arms of either interferometer. This means that polarization issues, which arise when fiber is used within the interferometers, can be easily controlled or removed. Without fiber forming part of the interferometers, it is also easier to implement ultra broadband systems.
  • the two interferometers can be separated by any distance and can be linked be fiber to provide an easy connection between them.
  • the fiber connection between the interferometers does not cause polarization/dispersion problems because of the nature of a tandem interferometer setup.
  • the nature of the fiber components is not critical as there are no tolerance issues with a custom array. Instead, off the shelf couplers and patch cords can be used.
  • the first interferometer can be of fixed length, and only the sensing interferometer need be moved back and forth on the equipment head. This arrangement significantly reduces the complexity and cost of this part compared to the reference arm of current designs
  • the only components that need to be in the optical head are the scanners, interface lenses, and the fiber. All the other components (spectrometer, processing interferometer, SLD, and SLD driver etc..) can be located anywhere, even in a separate cart. This results in a substantial reduction in the size of the equipment head.
  • tandem design is very modular, and the individual components will be simple to make and test before they are assembled into a system. This will reduce manufacturing costs.

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  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Pathology (AREA)
  • Biomedical Technology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Immunology (AREA)
  • Optics & Photonics (AREA)
  • Biophysics (AREA)
  • Ophthalmology & Optometry (AREA)
  • Engineering & Computer Science (AREA)
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  • Heart & Thoracic Surgery (AREA)
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  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

L'invention porte sur un appareil de tomographie en cohérence optique (OCT) qui comprend un premier interféromètre recevant la lumière provenant d'une source et ayant des premier et second bras. La lumière provenant des premier et second bras est combinée pour produire un premier faisceau de sortie, avec une différence de trajet optique entre les premier et second bras. Un second interféromètre en tandem avec le premier reçoit en tant qu'entrée le faisceau de sortie provenant du premier interféromètre. Le second interféromètre a un bras de référence et un bras objet. La lumière provenant des bras de référence et objet est combinée pour produire un second faisceau de sortie, avec une différence de trajet optique entre lesdits bras de référence et objet. La différence de trajet optique dans ledit premier interféromètre est mise en concordance avec la différence de trajet optique dans le second interféromètre pour produire un signal de sortie. En variante, le bras objet peut être dans le premier interféromètre.
PCT/CA2008/001944 2007-11-06 2008-11-06 Tomographie en cohérence optique avec interféromètre en tandem WO2009059406A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US98569707P 2007-11-06 2007-11-06
US60/985,697 2007-11-06

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WO2009059406A1 true WO2009059406A1 (fr) 2009-05-14

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013000866A1 (fr) * 2011-06-27 2013-01-03 Hexagon Technology Center Gmbh Procédé de mesure de distance par interférométrie pour le mesurage de surface et agencement de mesure correspondant

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5721615A (en) * 1993-07-12 1998-02-24 The Secretary Of State For Defense In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Sensor system for measurement of temperature or strain

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5721615A (en) * 1993-07-12 1998-02-24 The Secretary Of State For Defense In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Sensor system for measurement of temperature or strain

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HIRAI A. ET AL.: "Low-coherence tandem interferometer for measurement of group refractive index without knowledge of the thickness of the test sample", OPTICS LETTERS, vol. 28, no. 21, 1 November 2003 (2003-11-01) *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013000866A1 (fr) * 2011-06-27 2013-01-03 Hexagon Technology Center Gmbh Procédé de mesure de distance par interférométrie pour le mesurage de surface et agencement de mesure correspondant
KR20140010458A (ko) * 2011-06-27 2014-01-24 헥사곤 테크놀로지 센터 게엠베하 표면 측정을 위한 간섭계 거리 측정 방법, 및 상기 측정 구조
CN103635775A (zh) * 2011-06-27 2014-03-12 赫克斯冈技术中心 用于测量表面的干涉距离测量方法以及这样的测量装置
KR101645274B1 (ko) * 2011-06-27 2016-08-12 헥사곤 테크놀로지 센터 게엠베하 표면 측정을 위한 간섭계 거리 측정 방법, 및 상기 측정 구조
US9677870B2 (en) 2011-06-27 2017-06-13 Hexagon Technology Center Gmbh Interferometric distance measuring method for measuring surfaces, and such a measuring arrangement

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