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WO1995033970A1 - Came rotative pour systemes optiques - Google Patents

Came rotative pour systemes optiques Download PDF

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Publication number
WO1995033970A1
WO1995033970A1 PCT/US1995/006071 US9506071W WO9533970A1 WO 1995033970 A1 WO1995033970 A1 WO 1995033970A1 US 9506071 W US9506071 W US 9506071W WO 9533970 A1 WO9533970 A1 WO 9533970A1
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WO
WIPO (PCT)
Prior art keywords
radiation
cam
scattered
cam disk
measuring
Prior art date
Application number
PCT/US1995/006071
Other languages
English (en)
Inventor
Eric A. Swanson
Allen D. Pillsbury
James G. Fujimoto
Carmen A. Puliafito
Charles P. Lin
Joel S. Schuman
David Huang
Original Assignee
Massachusetts Institute Of Technology
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 Massachusetts Institute Of Technology filed Critical Massachusetts Institute Of Technology
Publication of WO1995033970A1 publication Critical patent/WO1995033970A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A61B1/00174—Optical arrangements characterised by the viewing angles
    • A61B1/00183—Optical arrangements characterised by the viewing angles for variable viewing angles
    • 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
    • A61B3/1005—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for measuring distances inside the eye, e.g. thickness of the cornea
    • 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
    • A61B3/12—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for looking at the eye fundus, e.g. ophthalmoscopes
    • A61B3/1225—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for looking at the eye fundus, e.g. ophthalmoscopes using coherent radiation
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0062—Arrangements for scanning
    • A61B5/0066—Optical coherence imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
    • 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
    • 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
    • G01B9/0209—Low-coherence interferometers
    • 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
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/02—Catoptric systems, e.g. image erecting and reversing system
    • G02B17/023—Catoptric systems, e.g. image erecting and reversing system for extending or folding an optical path, e.g. delay lines
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1828—Diffraction gratings having means for producing variable diffraction
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/44—Detecting, measuring or recording for evaluating the integumentary system, e.g. skin, hair or nails
    • A61B5/441—Skin evaluation, e.g. for skin disorder diagnosis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/35—Mechanical variable delay line
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/45—Multiple detectors for detecting interferometer signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/70—Using polarization in the interferometer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon

Definitions

  • This invention relates generally to an apparatus and method for introducing path length variations and periodic
  • This latter apparatus and method involves optically performing precision measurements such as distance and thickness measurements, on biological and other samples.
  • Translational scanning systems are often used to introduce optical path length variations and frequency shifts by utilizing a scattering or reflecting surface attached to a translation stage. Such scanning systems are used, for example, in autocorrelators, wavemeters, interferometers, and
  • optical measuring systems are used for performing high resolution measurements and in particular for optically performing such measurements, which improved technique does not require contact with the body being measured, which maintains substantially constant high resolution over a scanning depth of interest, regardless of available apertures size and which is relatively compact and inexpensive to manufacture.
  • Such systems are also capable of providing differentiation between sample layers, identification of layer material or of selected properties thereof, and can provide one, two and three-dimensional images of a scanned body.
  • the systems also provide measurements at rapid enough rates for use in biological and other applications where the sample being measured changes over relatively short time intervals. In fact, they can even provide information concerning the birefringence property and spectral properties of the sample.
  • optical measuring systems include two optical arms, a measuring arm and a reference arm.
  • the translation stage and reflecting surface are located in the reference arm of the measuring systems.
  • the translation stage typically driven by some type of actuator motor, would be coupled to the actuator via some type of gear mechanism.
  • the translation stage would move the scattering surface toward and away from the direction of the incident radiation.
  • the reflecting surface travels in the same direction as the radiation travels, the radiation undergoes a negative Doppler shift of 2V/ ⁇ .
  • the reflecting surface is scanned in one direction at a velocity V, and then rapidly returned to its initial position, the scan having a generally ramp or sawtooth profile.
  • Doppler shift which the incident radiation undergoes which must be filtered out or compensated for by, e.g., focussing the radiation to a smaller beam when incident on the reflecting surface, or utilizing a specific reflecting mechanism such as a corner cube.
  • One object of the invention is to provide a scanning cam with nearly a 100% duty cycle.
  • Another object of the invention is to provide a scanning cam which can scan through cycles at very high rates while avoiding excessive wobble.
  • Another object of the invention is to provide a scanning cam for use in autocorrelators, wavemeters, interferometers, and optical coherence domain reflectometers.
  • Another object of the invention is to provide an optical measuring device which incorporates the optical cam in its reference arm.
  • One advantage of the invention is that the scanning cam has only one moving part.
  • Another advantage of the invention is that it can scan at high rates while avoiding excessive wobble. Another advantage of the invention is that its peripheral face when viewed in a fixed direction can operate to provide high scanning rate linear translations.
  • Another advantage of the invention is that it can be inexpensively made using injection molding, surface duplication or diamond milling techniques which are easily adaptable to mass production techniques.
  • One feature of the invention is that it has a cam disk with a peripheral face which receives the optical radiation. Another feature of the invention is that it has a cam disk with a peripheral face.
  • the peripheral face has a high reflecting surface.
  • Another feature of the invention is that it utilizes a motor for rotating the cam disk.
  • Another feature of the invention is that the peripheral face can be helical.
  • cam disk can be weighted to balance at a center about which the disk rotates.
  • peripheral face can be polished to achieve desired optical properties.
  • the peripheral face can have a thin strip mirrored surface affixed thereto.
  • the peripheral face can be made using diamond machining techniques.
  • a cam including: a cam disk having a center about which the cam disk rotates, an outline and a peripheral scattering face for receiving radiation from a source and scattering the radiation as scattered radiation; and a motor mechanically coupled to the cam disk such that the motor rotates the cam disk about the center, wherein the scattered radiation undergoes periodic delay variations, and each of the delay variations is determined by the outline of the cam disk.
  • a measuring apparatus including: a source for outputting radiation with a short coherence length; a splitter for splitting the radiation into reference radiation and measuring radiation; radiation directing means for receiving the measuring radiation and directing the measuring radiation toward an object and for collecting a portion of the measuring radiation scattered off of the object; a cam for receiving the reference radiation and scattering a portion of the reference radiation as scattered reference radiation; and detecting means for detecting intensity resulting from a part of the portion of measuring radiation which coherently interfere with the scattered reference radiation, wherein the intensity provides information with respect to the object.
  • a method of measuring properties of an object comprising the steps of: outputting radiation with a short coherence length; splitting the radiation into reference radiation and measuring radiation; directing the measuring radiation toward the object and collecting a portion of the measuring radiation scattered off of the object; directing the reference radiation toward a cam and scattering a portion of the reference radiation off of a peripheral surface of the cam as scattered reference radiation; and detecting intensity resulting from a part of the portion of measuring radiation which coherently interferes with the scattered reference radiation, wherein the intensity contains information relating to the properties of the object.
  • Figure 1A shows an optical cam according to one embodiment of the invention.
  • Figure IB shows a top and tilted view of the cam with a motor and axle which fits into the center of the cam disk.
  • Figure IC shows Rz(t), as shown in Figure 1A, as a linear function of time t which repeats every cycle T resulting in a sawtooth type function.
  • Figure 2A is a schematic block diagram of a first fiber optic embodiment of the invention using an embodiment of the cam.
  • Figure 2B is a schematic block diagram of a second fiber optic embodiment of the invention using an embodiment of the cam.
  • Figure 3 is a schematic block diagram of a bulk optic embodiment of the invention illustrating the use of two separate wavelengths to enhance resolution.
  • Figure 4 is a diagram of the envelope of a scan output which might be obtained utilizing the embodiments of Figures 1-3.
  • Figure 5A is an enlarged diagram of a portion of a detector output from a system such as that shown in Figure 3, illustrating the modulation frequency on which such envelope is superimposed.
  • Figure 5B is a diagram of the waveform of Figure 5A after demodulation.
  • Figure 6 is a schematic block diagram of a third fiber optic embodiment of the invention utilizing polarized light to detect birefringence.
  • Figure 1A shows an optical cam 100a according to one embodiment of the invention.
  • Figure 1A shows cam 100a with cam disk 101a.
  • Cam disk 101a has a peripheral scattering face 104a and a center 108a about which cam 100a rotates at an instantaneous frequency F(t) cycles/second, where t represents an instant in time.
  • Cam disk 101a is preferably weighted such that its moment of inertia is balanced about center 108a.
  • Cam 100a receives optical radiation from a fiber 112a as follows.
  • Optical radiation 109a is output from tip Ilia of fiber 112a and is collimated by a collimating lens 116a (which can be regular or cylindrical lens) into collimated optical radiation 117a. This could be done with a single lens for some applications.
  • Optical radiation 117a is then focussed by a focusing lens 120a as a spot 124a (or ellipse if focussing lens 120a is a cylindrical lens) onto peripheral face 104a.
  • Figure 1A shows cam 100a receiving optical radiation from fiber 112a, cam 100a can receive any type of radiation from any type of radiation directing guide or free space radiation directed toward cam 100a.
  • cam disk 101a is not perfectly circular, radiation 117a should be directed to peripheral face 104a slightly off axis (off the z direction) in order to increase coupling of reflected radiation back into fiber 112a. Also, radiation 117a can be directed toward face 104a so far off the z axis (dashed lines in Figure 1A) that a reflector 123' must be used to redirect radiation scattered off face 104a back to face 104a and then back towards fiber 112a. In this double pass embodiment, the radiation undergoes twice the Doppler shift of a single pass which could be useful in some applications.
  • Figure IB shows a tope and tilted view of cam 100a with a motor 150a and axle 152a which fits into center 108a of cam disk 101a.
  • Motor 150a can be either synchronous or asynchronous.
  • Figure IB also shows a timing mark 160a and an optoelectronic sensor 164a.
  • Sensor 162a outputs a once in a revolution signal for each revolution of cam disk 101a at output 166a to whatever optical system cam 100a is being used.
  • Timing mark 160a can be a metal tab and optoelectronic sensor 164a can be an LED photodiode combination known in the art.
  • distance d is defined to be the distance from focusing lens 120a to spot 124a and distance D is the distance from focusing lens 120a to center 108a.
  • the distance from center 108a to peripheral face 104a is defined as radius R.
  • Radius R varies from a smallest value R(0) to a largest value R(2 ⁇ ) where peripheral face 104a has a step transition 130a as indicated in Figure 1A.
  • R(_) can vary in any arbitrary manner. i.e., can both increase and decrease multiple times as ⁇ varies from 0 to 2 ⁇ r, e.g., R( ⁇ ) can have multiple local maxima and minima as ⁇ varies from 0 to 2 ⁇ .
  • the outline or shape of peripheral face 104a is determined by the function R( ⁇ ) .
  • ⁇ generally relates to the rotation rate F(t) as
  • Distance D remains fixed (in one embodiment of the invention) and the rotation of cam 100a about center 108a is translated into transverse motion, and in particular, into a variation of distance d.
  • distance d varies with time t and will be referred to as d(t) .
  • Rz Defining the radius Rz to be the distance from center 108a to spot 124a along the z direction makes Rz a function of time and hence will be referred to as Rz(t).
  • the confocal parameter of the focal spot should be approximately equal to the step size as a compromise between sensitivity to angular misalignment and loss due to focal error.
  • a second and possibly the preferred approach is to select focusing lens 120a which has a focal length f approximately equal to D and lens 120a is a cylindrical lens.
  • the wavefronts of optical radiation output from lens 120a approximately conform to the face 104a of cam 101a. This conformity may further reduce effects of wobble of cam 101a and improve coupling of scattered radiation back into fiber 112a. This improved coupling should result even in the presence of local surface imperfections on face 104a provided cylindrical lens 120a has a focal length approximately equal to distance D.
  • V(t) is made to be a constant V 0 .
  • the duty cycle is nearly 100%. That is, there is almost no translational fly back time as required for any traditional linear scanners, and instead cam disk 101a provides a linear change in Rz for the entire cycle T.
  • One way to make Rz(t) a linear function is time over period T is to fix the rotation rate F(t) to be a constant F 0 with respect to time. In that case, since
  • V 0 dRzz/dt
  • R(0) 30mm
  • Cam disk 101a can be made out of any rigid material and preferably a material which leads itself to techniques such as injection molding, surface duplication or diamond milling. In addition, a mirror strip can be adhesively attached to face 104a. If cam disk 101a is made out of a single material having a single density and if cam disk 101a has a smoothly varying shape or outline, disk 101a will have a center of gravity and is such cases, center 108a about which cam disk 101a rotates, should be located at that center of gravity. However, for any shape or outline having a step transition 130a (e.g., the helical outline discussed above) cam disk 101a will not have such a center of gravity.
  • a step transition 130a e.g., the helical outline discussed above
  • cam disk 101a can be modified so that its center of gravity corresponds approximately to center 108a.
  • One way is to add counter weights to and/or lighten the weight (e.g., drill or remove portions) of disk 101a.
  • Cam disk 101a can also be manufactured to have a varying density and its density must vary in such a manner that a resulting center of gravity can serve as center 108a.
  • Cam 100a can be used in any one of the systems disclosed in U.S. Patent Application Ser. No. 08/033,194 as will be discussed below.
  • the above discussed helical outline R( ⁇ ) is particularly useful in any of the systems disclosed in that application since such an outline provides a fixed Doppler shift over nearly an entire period T for a fixed frequency rate F.
  • the manner in which those systems can be modified to incorporate cam 100a will be discussed below.
  • Figure 2A shows one fiber optic optical coherence domain reflectometer (OCDR) 10.1 in which cam 100a can be used.
  • ODR optical coherence domain reflectometer
  • the output from a short coherence length optical source 12 is coupled as one input to an optical coupler 14. Such coupling may be through a fiber optic path 16.
  • Source 12 may, for example, be a light emitting diode (LED) or super luminescent diode (SLD) of suitable wavelength, and preferably has a coherence length of less than 10 micrometers and a single spacial mode.
  • Source 12 might also be a pulsed laser source or an incandescent source; but for most applications an LED or SLD would be preferable, a pulsed laser having higher power, and an incandescent source with a single spatial mode having good resolution but very low power.
  • LED light emitting diode
  • SLD super luminescent diode
  • the other input to coupler 14 is from a laser 18 generating an optically visible output which is applied to the coupler through a fiber optic path 20.
  • laser 18 is utilized only to provide a source of visible light for proper alignment with a sample when the light from source 12 is in the infrared region or is otherwise not visible.
  • all optical fibers utilized for the various embodiments will be assumed to be single mode fibers. These fibers may be polarization maintaining or not, but are preferably polarization maintaining to insure good polarization mode matching.
  • the output from coupler 14 is applied as the input to coupler 22 through fiber optic path 24.
  • the light or optical energy received at coupler 22 is split between a first fiber optic path 26 leading to sample 28 being characterized and a second fiber optic path 30 leading to cam 100a.
  • Fiber optic path 26 is terminated in probe module 34 which includes a lens 36 for focusing the radiation applied to the module on sample 28 and for receiving radiation scattered from object or sample 28 and transmitting the reflections back to the fiber.
  • Path 30 includes fiber 112a, collimating lens 116a and focusing lens 120a as discussed above with reference to Figure 1A.
  • the optical fibers of path 26 may be wrapped around a piezoelectric crystal 40 which vibrates (i.e.
  • the total length of path 26 between coupler 22 and a selected depth point in sample 28 and the total length of path 30 between coupler 22 and peripheral scattering face 104a should be substantially equal for each depth point of the sample during a scan of selected depth range.
  • the lengths of the optical fibers in paths 26 and 30 should also be substantially equal.
  • the group velocity dispersions may be equalized by placing optical materials of known group velocity dispersion and thickness in the light paths to compensate for any inequality.
  • a length of high dispersion material may be included in the reference path. It is also important that the termination of the optical fibers utilized in the system be angle polished and/or anti-reflection coated to minimize reflections.
  • velocity V (which relates to rotation rate F as discussed above) is preferably greater than 1cm/sec. The length or extent or movement is at least slightly greater than the desired scan depth range in sample 28.
  • Radiation received by probe 34 from sample 28 are applied through path 26 to coupler 22 and scattered radiation from cam 100a through lenses 120a and 116a and path 30 to the coupler. Note that one or both of the lenses 116a and 120a can be eliminated depending on the amount of scattered radiation fiber 112a needed to couple back to coupler 22.
  • the scattered radiation received from the sample and the reference are combined in coupler 22, resulting in interference fringes for length matched reflections (i.e., reflections for which the difference in reflection path lengths is less than the source coherence length) and the resulting combined output is coupled onto fiber optic path 40.
  • the optical signal on fiber path 40 is applied to a photodetector 42 which converts the optical combined signal on path 40 to a corresponding current-varying electrical signal.
  • the current-varying electrical signal on output line 44 from photodetector 42 is preferably converted to a voltage varying signal by a transimpedance amplifier (TIA) 43 or other suitable means, the TIA output being applied as an input to a demodulator 46.
  • TIA transimpedance amplifier
  • demodulator 46 may consist of a bandpass filter 78 centered around the modulation frequency of the combined output signal and an envelope detector.
  • the filter assures that only the signal of interest is looked at and removes noise from the output. This enhances the signal-to-noise ratio of the system and thus system sensitivity.
  • the filtered signal is then applied to the envelope detector.
  • the envelope detector in demodulator 46 may consist of a rectifier 82 and a subsequent low pass filter 84.
  • the rectifier output would be proportional to the square root of the sample reflectivity.
  • the second filter removes any high frequency components from what is basically a base band signal.
  • the demodulator preferably also includes a logarithmic amplifier 86, strong reflections from boundaries would either be off scale or weaker reflections would not be visible. Alternatively, logarithmic limiting detectors such as Analog Devices 606 may be used.
  • the exemplary demodulator described above is one type of heterodyne demodulator. However, a variety of other demodulation techniques know in the art may also be utilized to perform the demodulator function.
  • the demodulated output from demodulator 46 is the envelope of the interferometric signal of interest.
  • a suitable printer 48 may be utilized to obtain a visual record of this * analog signal which may be utilized by a doctor, engineer or other person for various purposes.
  • the analog output from demodulator 46 is applied, either in addition to or instead of to printer 48, through an analog-to-digital converter 50 to a suitable computer 52 which is programmed to perform desired analyses thereon, computer 52 may, for example, control the display of the demodulated signal on a suitable display device 54, such as a cathode ray tube monitor, or may control a suitable printer to generate a digital record.
  • computer 52 may detect various point of interest in the demodulated envelope signal and may perform measurements or make other useful determinations based on such detectors.
  • Computer 52 may be a suitably programmed standard processor or a special purpose processor may be provided for performing some or all of the required functions.
  • the embodiment shown in Figure 2A would be utilized where cam disk 101a rotates at a frequency F which translates into a uniform but intermediate velocity V(t) .
  • intermediate velocity V(t) is considered one at which the Doppler frequency shift causes by the rotation frequency F of cam disk 101a is not negligible, but is low enough to fall within the predominant low frequency noise for the system.
  • the noise spectrum includes noises arising from fluctuations in light source 12, mechanical components and electrical circuits, and are larger at lower frequencies, typically below 10 kHz. •
  • the Doppler shift frequency f D results from the rotation F of cam disks 101a and is given by the equation:
  • V(t) is the instantaneous velocity as discussed above at a given time t and ⁇ is the wavelength of source 12 at which the peak intensity is output.
  • additional modulation is needed to shift the modulation frequency above the predominant noise spectrum.
  • this is achieved by introducing sinusoidal phase modulation by use of piezoelectric transducer 40. While in Figure 2A the additional modulation is introduced by the use of the oscillator or transducer in path 26, such modulation could also be provided in path 30.
  • the small movement required for this supplemental modulation may be achieved using electromagnetic, electrostatic, or other elements known in the art for providing small generally sinewave movements. Alternatively, this supplemental modulation can be achieved by passing light in the reference arm and/or sample arm through acousto-optic modulators.
  • the supplemental modulation from transducer 40 or other suitable means which modulate the optical path length at a frequency F M and the oscillation amplitude of this modulator is adjusted so that the peak-to-peak oscillating movement or optical delay change is approximately one-half of the wavelength ⁇ of source 12.
  • the combined effect of the supplemental modulation and the Doppler shift frequency causes the output envelope to be on modulating frequencies of f D , f M + f D , f M - f D and at higher harmonics.
  • f M is normally chosen to be higher than the predominant noise spectrum.
  • Demodulation of the output from photodetector 42 is normally at f M + f D and/or f M - f D .
  • demodulation is at f M + f D .
  • the center frequency for bandpass filter 78 is thus set for the frequency (f M + f D ) .
  • the bandwidth for filter 78 should be approximately two to three times the full-width- half-maximum (FWHM) bandwidth of the received signal to avoid signal broadening and distortion. This bandwidth is given by the quotation - _ 4 (to_) V V
  • V 0 F o [R(2 ⁇ )-R(0)] (6)
  • the detection electronics would be the same as those discussed above in conjunction with Figure 2A, except that the center frequency for bandpass filter 78 would be set to Doppler shift frequency F D .
  • the bandwidth of the signal -fpw HM also increases, resulting in corresponding increases in the bandwidth of filters 78 and 84. This leads to a loss of detection sensitivity, an inevitable result of high speed scan.
  • cam 100a has an outline R(_) and instantaneous frequency F(t) yields an instantaneous velocity V(t) which is not constant, e.g., sinusoidal, the
  • Doppler shift frequency f D is no longer constant, and the demodulator 46 much be adapted for this carrier frequency variations. There are at least two methods for accomplishing this objective. In both cases, as illustrated for system
  • an output line 87a is provided from cam
  • line 87 outputs a signal from which V(t) and Rz("-) can *> e determined using digital or analog electronics 210a.
  • Electronics 210a has two outputs, line 87 which corresponds to velocity V(t) and line 89 which corresponds to position R z (t) . If electronics 210a provides a digital output, then line 87 may be connected to computer 52 without going through A/D converter 50'. Also, if the signal output from TIA 43 is digitally sampled, then all subsequent processing can be done digitally in software.
  • the signal on line 87 is required when velocity V(t) is not constant so that intensity and other inputs received at computer 52 may be correlated with R z (t) . This correlation is not required with a linear scan where position can be determined from the time an input is received.
  • the acceptance band for bandpass filter 78 and low pass filter 84 are increased to accommodate the variations in the Doppler shift frequency f D . These variations occur because f D varies directly with variations in V as discussed above. This increased demodulator acceptance bandwidth will lead to increased acceptance of noise and thus results in lower detection sensitivity.
  • this technique is simple and can be used in cases where the requirement for detection sensitivity is not critical. Further, this increase in acceptance bandwidth may be relatively small when the signal bandwidth -fpw H is already large relative to f D , this occurring when the coherent length is very small.
  • FIG. 2B illustrates the second technique wherein the demodulation frequency is dynamically tuned to the instantaneous Doppler shift frequency using a superheterodyne system.
  • Electronics 210a provides a velocity dependent voltage on line 89 which is modified by a gain circuit 91 and a bias circuit 93 before being applied to a voltage controlled oscillator 95.
  • the output from oscillator 95 is multiplied in a multiplier 97 with the output from detector 42 via amplifier 43.
  • the gain and bias of the signal applied to VCO 95 are adjusted so that the modulating frequency at the output from multiplier 97 is substantially constant at a desired center frequency which is selected as the center frequency for bandpass filter 78.
  • the bandwidth of filter 78 is set at two or three times the peak signal bandwidth and, except for the need for the output on line 87, the remainder of the detection and processing would be substantially identical to that previously described in conjunction with Figure 2A.
  • Figure 3 shows a system 10.3 which is similar to that of Figure 2A, except that bulk optics are utilized rather than fiber optics and ability to observe spatial properties is enhanced by providing two light sources 12A and 12B whic are at different wavelengths. While the multiple wavelength option is being shown for purposes of illustration in conjunction with a bulk optics embodiment, it is to be understood that multiple wavelengths could also be, and may preferably be, used with the fiber optic embodiments.
  • Sources 12A and 12B could be the same type of light sources designed to operate at different wavelengths or could be different types of light sources.
  • the outputs from sources 12A and 12B are merged in a coupler 60, the optical output from which is applied to a coupler 62.
  • the other input to coupler 62 is the output from a laser 18, for example, a helium neon laser, which again is used only for alignment purposes.
  • Coupler 60 and 62 could, for example, be dichotic beam splitters, polarization beam splitters and normal beam splitters.
  • the output from coupler 62 is applied to beam splitters 64 and 66.
  • Beam splitter 64 applies a portion of its input through lenses 116a and 120a to peripheral scattering surface 104a and also passes optical radiation to beam splitter 66 which applies this radiation through lens 36 to sample 28.
  • Reflections from peripheral scattering surface 104a are applied through lenses 120a and 116a, beam splitter 64 and mirror 68 to interfero etric coupler 70.
  • Peripheral scattering surface 104a and lenses 116a and 120a may be part of a translation stage which is moved by a mechanism such as transnational mechanism 39a. Reflections from sample 28 are applied through lens 36 and beam splitter 66 to the interferometric coupler 70.
  • the output from coupler 70 may be applied to a CCD camera 72 used for alignment purposes and is also applied through a lens 74 to a photodetector 42.
  • the output from the detector 42 is applied through two separate paths.
  • Each path contains a demodulator 46A, 46B containing a bandpass filter 78B having a center frequency which corresponds to the Doppler shift frequency f D for the given source 12 since f D varies inversely as a function of the source wavelength, each demodulator only demodulates signals corresponding to the appropriate source wavelength permitting outputs resulting from the two source wavelengths to be separated.
  • the two outputs After being applied through corresponding A-D converters 50A and 50B, the two outputs are applied to computer 52 where they may be appropriately processed.
  • a detector 42 may be provided corresponding to each source wavelength where each photodetector is preceded by an optical wavelength filter that only transmits the appropriate wavelength with an appropriate pass band.
  • a beam splitter would be provided ahead of the optical wavelength filters, with a demodulator at the detector output. While in Figure 3, and in the discussion above, only two separate radiation wavelengths ⁇ have been shown, this is not a limitation on the invention, and a great number of light sources and detectors (and/or demodulator circuits) may be provided for appropriate applications.
  • the sample 28 is the eye of a human or animal patient.
  • the beam must be aligned with the sample so that it enters the sample at a desired angle. This angle is normally an angle perpendicular to the angle of the eye layers.
  • the beam must be laterally positioned on the sample area of interest. This is a control of the lateral position of the beam.
  • the beam must be focused at the level of interest in the eye. A number of techniques may be utilized for performing each of these alignment functions. In particular, a number of different techniques may be utilized to obtain a desired incidence angle.
  • one simple way to achieve alignment is to adjust the position or angle of the probe of beam splitter 66, or lens 36 and/or of the sample (i.e., the patient's eye) and, with the reference arm blocked, detect reflections from the sample.
  • the alignment at which the power of the detected reflections is maximum would thus be the desired alignment angle. It would normally be possible to locate the desired angle relatively quickly using this technique.
  • a second technique for achieving angular alignment is similar to the first except that the reference arm is not blocked and, with normal readings being taken from the system, alignment is manually adjusted until an alignment which maximizes the output is obtained.
  • a third method is to look at the direction in which the cam is reflected in order to detect beam alignment. Since it is hard to do this directly, particularly when a fiber is utilized, such determination is generally made by providing a beam splitter which directs a portion of the beam reflected form the sample to a device such as CCE camera 72 ( Figure 3) which can measure beam position. This device is initially calibrated with the system so that the spot on which the beam impinges on the camera when the beam is properly aligned with a sample is determined. Then, in operation, the sample and probe can be adjusted until an angle of alignment is achieved where the beam impinges on the CCD camera 72 at the previously determined point.
  • Laser 18 is turned on.
  • Source 12 may either be on or off for this operation.
  • Laser 18 provides a narrow beam visual indication of the lateral position on the eye where the beam is striking and the position of either the probe beam or the patient may then be manually adjusted until the beam is striking the desired position. If light from source 12 is in a visible band, laser 18 may not be required and light from source 12 may be used for alignment.
  • the focusing cone angle to be utilized for performing readings is determined by balancing the desirability of having as large a numerical aperture (cone angle) as possible against being able to achieve a desired longitudinal range or depth of field in which back scattered or reflected light is efficiently coupled back to the fiber (or to the other optical path 26 where a fiber is not employed) .
  • a large numerical aperture makes angular alignment for normal incidence o the sample surface less critical and for measurement of back scattering where the returned radiation is spread over wide solid angles, a wider cone angle increases the coupling into the fiber.
  • the large cone angle increases the longitudinal range.
  • the numerical aperture or f number should be selected to correspond to a depth of field that is equal to the longitudinal extent of the area in the eye or other sample on which measurements are to be taken.
  • depth of field is defined as the longitudinal distance from the focal plane at which the back coupling efficiency into the fiber is reduced by one-half.
  • the sample and/or probe are moved relative to each other until the system is focused to a desired point within the sample, i.e., within the eye. Since even with the laser it may be difficult to visually determine the focal point, a preferable way to perform focusing may be to operate the system with, for example, an output being obtained on display 54 ( Figure 2A) . As will be discussed later, certain high amplitude points in such output are indicative of a particular layer or transition in the eye and focus can be adjusted until the transition occurs at a desired point in the scan.
  • the system may be utilized to take desired measurements. To perform such measurements, aiming laser 18 is turned off and source 12 is turned on. Cam 100a and in particular motor 150a is also turned on, if not already on, to cause desired rotation of cam disk 101a.
  • source 12 should have a low coherence length which implies being spectrally wide.
  • coherence length of approximately 10 micrometers
  • spatial separation, and thus resolution, to 10 micrometers can be obtained. This is a far higher resolution than is available than many other currently available devices.
  • Path lengths 26 and 30 are initially equal with the beam focused at a desired initial scan depth in sample 28.
  • peripheral scattering surface 104a moves away from lens 120a, the point in the sample 28 at which the path lengths are equal is scanned to successively greater depths within the sample.
  • reflections occur and light scattering occurs which are a function of the refractive index variation for the material through which the light is passing and of such index boundaries.
  • Interference fringes occur for depth points in the sample (L Su) and the path length to the current mirror location (Lute) differ by less than the coherence length of the light source
  • the coherence length of the light source determines available system resolution.
  • the interferometric output from coupler 22 or 70 is thus indicative of reflections or scattering obtained at a particular depth within the sample.
  • the successive interferometric outputs obtained during a scan form an envelope signal such as that shown in Figure 4, which normally has peaks at optical junctions within the samples where reflections are normally maximum and may have some lesser peaks in a predetermined pattern, depending on the scattering characteristics of the medium at the scan depth.
  • Doppler shift frequency is dependent on the wavelength of source 12.
  • the interferometric output from coupler 70 will contain two separate envelopes which are a function of the difference in absorption and reflection at the different wavelengths, and each interference output will be modulated at a different Doppler shift frequency.
  • the bandpass filter 78A and 78B in each demodulator 46A may be selected to have a center frequency and bandwidth for a different one of the Doppler shift frequencies, or optical filtering with multiple detectors may be utilized, to permit detection and separation of these two signals.
  • the ability to perform the interferometric detection at two or more different wavelengths offers unique advantages. These advantages arise from the fact that the absorption, reflection and other optical characteristics of various sample materials vary with wavelength. Thus, taking measurements at two or more wavelengths permits the spectral characterization of optical properties of the sample such as the wavelength dependent absorption and scattering thereof. In particular, the log rate of attenuation of back scatter is different for different materials and, for a given material, may vary with wavelength. By observing the back scatter pattern at different wavelengths from a substance, and possibly by observing the average rate of back scatter or reflection attenuation from layers of the sample, information concerning the material of the layer or various properties of such material may be obtained.
  • spectral properties may be of interest in themselves and may also be used to distinguish between two sample layers, for example, two tissue layers that it is normally difficult to distinguish with single wavelength measurements because of their similar optical properties.
  • ratios at each of the wavelengths spurious effects such as misalignment are compensated for permitting boundaries to be more easily and accurately identified. Basically, such boundaries are identified by looking at ratios rather than absolute values.
  • FIG. 6 illustrates an alternative embodiment of the invention, system 10.4, utilizing polarized light to detect birefringence.
  • light from light source 12 is polarized in a polarizer 90 sandwiches between a pair of lenses 92 before being applied to a polarization maintaining (high birefringence) fiber 94.
  • polarizer 90 is shown as vertically polarizing light from source 12, vertical polarization being one of the modes of fiber 94.
  • Fiber 94 is connected to a polarization maintaining coupler 96 which outputs the vertically polarized light on polarization maintaining fibers 98 and 100.
  • Fiber 98 terminates in a focusing lens 102, the optical output from which is applied through a quarter wave retardation plate 104 to sample 28.
  • Plate 104 is preferably a zero order or low order plate which is placed and oriented in a manner so that circularly polarized light is incident on sample 28. in the absence of sample birefringence, plate 104 converts reflected light passing therethrough to fiber 98 into horizontal polarization.
  • sample birefringence which causes light to travel at different speeds through the layer depending on polarization
  • the light reflected from sample layers which are in, or deeper than, the birefringent sample structures will in general return to the fiber in elliptical polarization states.
  • the vertically polarized light in fiber 100 is focused by lens 102 and a quarter-wavelength retardation plate 110 to peripheral scattering surface 104a of optical cam 100a.
  • Plate 110 which is also preferably zero order or low order, is oriented in such a manner that light applied to the mirror is elliptically polarized and some of the radiation scattered from peripheral scattering surface 104a are in linear polarization state with equal horizontal and vertical components.
  • the sample and reference reflections are recombined with approximately interferometric fringes in coupler 96 and applied to a polarization maintaining fiber 112.
  • Fiber 112 terminates in a lens 114 leading to a polarizing beam splitter 116, with horizontally polarized light from the beam splitter being applied to detector 43C and vertically polarized light from the beam splitter being applied to detector 42D.
  • Lens 114 and polarizing beam splitter 116 may be replaced by a fiber polarizing beam splitter.
  • the interferometric signals detected by the two detectors which signals are both at the same Doppler shift frequency, are separately processed in demodulator 46 and A/D converters 50 (the separate demodulator and A/D converters being shown for simplicity as single units in Figure 6) to produce two interferometric signals, a horizontal amplitude component II and a vertical amplitude component 12.
  • demodulator 46 and A/D converters 50 the separate demodulator and A/D converters being shown for simplicity as single units in Figure 6
  • Back scattering from inside the retinal nerve fiver layer can be identified because the refringent retardation of back scattering from inside the RNFL increases, as for other birefringent surfaces, wit depth.
  • the range of depth over which the birefringent retardation is changing is the thickness of the RNFL and the rate of change of birefringent retardation (total retardation divided by the thickness of the RNFL) can provide a measure of the nerve axon density inside the RNFL.
  • the back scattering and reflections from layers deeper than the RNFL will acquire a constant amount of birefringent retardation.
  • a fiber optic probe of the type shown in Figure 2A or Figure 6 could be delivered by use of an endoscope to a desired site to provide high resolution images for use in laser angioplasty and lithotripsy. This would enhance the usability of such procedures by reducing the dangers of unintentional vessel damage and rupture.
  • the beam has been projected along a single axis.
  • the probe and/or beam may after alignment be laterally scanned on a sample area of interest to provide two-dimensional or three-dimensional information or imaging.
  • a display 54 Figure 2A
  • a tomographic image of a sample can be obtained in much the same way that such images are obtained with ultrasonic scanners.

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Abstract

La présente invention concerne une came (100a) constituée d'un disque à came (101a) présentant un centre (108a) autour duquel il tourne, une face périphérique diffusante (104a) épousant le contour. Cette face périphérique reçoit le rayonnement (117a) d'une source et le diffuse, produisant ainsi un rayonnement diffusé (124a). La came (100a) comporte un moteur (150a) faisant tourner le disque à came. Cette rotation soumet le rayonnement diffusé à des variations à décalage périodique respectant le contour du disque à came. Un appareil de mesure (10.1) utilisant la came (100a) est constitué d'une part d'une source (12) produisant un rayonnement caractérisé par une longueur de cohérence courte, d'autre part d'un diviseur (22) divisant le rayonnement en rayonnement de référence et rayonnement de mesure, et enfin d'une unité d'orientation (34) de rayonnement qui reçoit et oriente le rayonnement de mesure en direction d'un objet (28), puis récupère une partie du rayonnement de mesure diffusé en provenance de l'objet. La came (100a) reçoit le rayonnement de référence et diffuse une partie du rayonnement de référence restituant ainsi un rayonnement de référence diffusé. Ledit appareil de mesure (10.1) est ainsi capable de délivrer des informations concernant l'objet car il comporte un détecteur (42) détectant l'intensité résultante de la parite du rayonnement de mesure qui se trouve en interférence cohérente avec le rayonnement de référence diffusé.
PCT/US1995/006071 1994-06-02 1995-05-16 Came rotative pour systemes optiques WO1995033970A1 (fr)

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WO1997032182A1 (fr) * 1996-02-27 1997-09-04 Massachusetts Institute Of Technology Procede et appareil permettant d'effectuer des mesures optiques a l'aide d'un endoscope, un catheter ou un fil de guidage d'imagerie a fibre optique
WO2000045153A1 (fr) * 1999-01-29 2000-08-03 June Iris Medford Microscope a coherence optique et procedes d'utilisation pour assurer la visualisation tridimensionnelle rapide in vivo de fonctions biologiques
WO2000050218A1 (fr) * 1999-02-22 2000-08-31 General Electric Company Commande en boucle fermee des vitesses des cylindres dans des operations d'extrusion de feuilles de plastique
US6191862B1 (en) 1999-01-20 2001-02-20 Lightlab Imaging, Llc Methods and apparatus for high speed longitudinal scanning in imaging systems
WO2002017775A1 (fr) * 2000-08-31 2002-03-07 Carl Zeiss Jena Gmbh Systeme de mesure sans contact de la qualite de reproduction optique d'un oeil
US6501551B1 (en) 1991-04-29 2002-12-31 Massachusetts Institute Of Technology Fiber optic imaging endoscope interferometer with at least one faraday rotator
GB2385417A (en) * 2002-03-14 2003-08-20 Taylor Hobson Ltd Determining surface profile by measurement of interference fringes
US7385707B2 (en) 2002-03-14 2008-06-10 Taylor Hobson Limited Surface profiling apparatus
EP1962051A1 (fr) * 2007-02-21 2008-08-27 Agfa HealthCare N.V. Système et procédé destinés à la tomographie de cohérence optique
EP1962049A1 (fr) * 2007-02-21 2008-08-27 Agfa HealthCare N.V. Système et procédé destinés à la tomographie de cohérence optique
WO2008101962A1 (fr) * 2007-02-21 2008-08-28 Agfa Healthcare Nv Système et procédé de tomographie par cohérence optique
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US8339610B2 (en) 2007-02-21 2012-12-25 Agfa Healthcare N.V. System and method for optical coherence tomography with spectrally modulated light injected into optical fibre
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US8593639B2 (en) 2007-02-21 2013-11-26 Agfa Healthcare Nv System and method for optical coherence tomography with light or detector modulation
US8928890B2 (en) 2007-02-21 2015-01-06 Agfa Healthcare N.V. System for optical coherence tomography with different optical properties of specimen and reference objectives
US20170343791A1 (en) * 2016-05-30 2017-11-30 Eric Swanson Few-mode fiber endoscope

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Cited By (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6134003A (en) * 1991-04-29 2000-10-17 Massachusetts Institute Of Technology Method and apparatus for performing optical measurements using a fiber optic imaging guidewire, catheter or endoscope
US6501551B1 (en) 1991-04-29 2002-12-31 Massachusetts Institute Of Technology Fiber optic imaging endoscope interferometer with at least one faraday rotator
WO1997032182A1 (fr) * 1996-02-27 1997-09-04 Massachusetts Institute Of Technology Procede et appareil permettant d'effectuer des mesures optiques a l'aide d'un endoscope, un catheter ou un fil de guidage d'imagerie a fibre optique
US6191862B1 (en) 1999-01-20 2001-02-20 Lightlab Imaging, Llc Methods and apparatus for high speed longitudinal scanning in imaging systems
AU779717B2 (en) * 1999-01-29 2005-02-10 Richard Campbell Haskell Optical coherence microscope and methods of use for rapid (in vivo) three-dimensional visualization of biological function
WO2000045153A1 (fr) * 1999-01-29 2000-08-03 June Iris Medford Microscope a coherence optique et procedes d'utilisation pour assurer la visualisation tridimensionnelle rapide in vivo de fonctions biologiques
WO2000050218A1 (fr) * 1999-02-22 2000-08-31 General Electric Company Commande en boucle fermee des vitesses des cylindres dans des operations d'extrusion de feuilles de plastique
US6250904B1 (en) 1999-02-22 2001-06-26 General Electric Company Closed loop control of roll speeds in plastic sheet extrusion
WO2002017775A1 (fr) * 2000-08-31 2002-03-07 Carl Zeiss Jena Gmbh Systeme de mesure sans contact de la qualite de reproduction optique d'un oeil
US7084986B2 (en) 2000-08-31 2006-08-01 Carl Zeiss Jena Gmbh System for measuring the optical image quality of an eye in a contactless manner
GB2385417B (en) * 2002-03-14 2004-01-21 Taylor Hobson Ltd Surface profiling apparatus
GB2385417A (en) * 2002-03-14 2003-08-20 Taylor Hobson Ltd Determining surface profile by measurement of interference fringes
US7385707B2 (en) 2002-03-14 2008-06-10 Taylor Hobson Limited Surface profiling apparatus
US7948634B2 (en) 2002-03-14 2011-05-24 Taylor Hobson Limited Surface profiling apparatus
EP1814443B1 (fr) * 2004-09-21 2012-11-07 Digital Signal Corporation Systeme et procede permettant de controler a distance des fonctions physiologiques
WO2008101961A1 (fr) * 2007-02-21 2008-08-28 Agfa Healthcare Nv Système et procédé de tomographie par cohérence optique
US8593639B2 (en) 2007-02-21 2013-11-26 Agfa Healthcare Nv System and method for optical coherence tomography with light or detector modulation
WO2008101962A1 (fr) * 2007-02-21 2008-08-28 Agfa Healthcare Nv Système et procédé de tomographie par cohérence optique
EP1962049A1 (fr) * 2007-02-21 2008-08-27 Agfa HealthCare N.V. Système et procédé destinés à la tomographie de cohérence optique
US8199327B2 (en) 2007-02-21 2012-06-12 Agfa Healthcare Nv System for optical coherence tomography
EP1962051A1 (fr) * 2007-02-21 2008-08-27 Agfa HealthCare N.V. Système et procédé destinés à la tomographie de cohérence optique
US8330962B2 (en) 2007-02-21 2012-12-11 Agfa Healthcare N.V. System and method for optical coherence tomography with modulated detector sensitivity
US8339610B2 (en) 2007-02-21 2012-12-25 Agfa Healthcare N.V. System and method for optical coherence tomography with spectrally modulated light injected into optical fibre
US8526006B2 (en) 2007-02-21 2013-09-03 Agfa Healthcare Nv System and method for optical coherence tomography and method for calibrating said type of system
WO2008101959A1 (fr) * 2007-02-21 2008-08-28 Agfa Healthcare Nv Système et procédé de tomographie par cohérence optique
US8665449B2 (en) 2007-02-21 2014-03-04 Agfa Healthcare Nv System and method for optical coherence tomography
US8810797B2 (en) 2007-02-21 2014-08-19 Agfa Healthcare Nv System and method for optical coherence tomography
US8908190B2 (en) 2007-02-21 2014-12-09 Agfa Healthcare Nv System and method for focus tracking optical coherence tomography
US8928890B2 (en) 2007-02-21 2015-01-06 Agfa Healthcare N.V. System for optical coherence tomography with different optical properties of specimen and reference objectives
US20170343791A1 (en) * 2016-05-30 2017-11-30 Eric Swanson Few-mode fiber endoscope
US10969571B2 (en) * 2016-05-30 2021-04-06 Eric Swanson Few-mode fiber endoscope
US11774743B2 (en) 2016-05-30 2023-10-03 Eric Swanson Few-mode optical fiber measurement instrument

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