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
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02027—Two or more interferometric channels or interferometers
  • G01B9/02028—Two or more reference or object arms in one interferometer
• • 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
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
  • G01B9/02021—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations contacting different faces of object, e.g. opposite faces
• • 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
  • G01B9/02034—Interferometers characterised by particularly shaped beams or wavefronts
  • G01B9/02035—Shaping the focal point, e.g. elongated focus
• • 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
  • G01B9/02075—Reduction or prevention of errors; Testing; Calibration of particular errors
  • G01B9/02078—Caused by ambiguity
  • G01B9/02079—Quadrature detection, i.e. detecting relatively phase-shifted signals
  • G01B9/02081—Quadrature detection, i.e. detecting relatively phase-shifted signals simultaneous quadrature detection, e.g. by spatial phase shifting
• • 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
• • 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
  • A61B3/113—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining or recording eye movement
• • 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
  • 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

Definitions

• the invention relates to a short-coherence interferometer arrangement for measuring a plurality of axially spaced regions of a sample, in particular of the eye, which min.
• the invention further relates to a short-coherence interferometer arrangement for measuring a plurality of axially spaced regions of a sample, in particular of the eye, which min.
• Such short-coherence interferometer arrangements are known for optical imaging by means of optical coherence tomography, for example from WO 2007/065670 A1.
• they use an interference of several measuring beams, each with a separate reference beam, the second-mentioned variant superimposed several individual measuring beams in pairs, which is also referred to as a so-called “dual beam” interferometer.
• Optical coherence domain reflectometry is used to determine the location and size of
• optical coherence tomography in particular in the form of the FD-OCDR, is the fixed combination of measuring range and measuring resolution.
• the state of the art knows many documents, which include the measurement of objects in areas that are geometrically larger than the desired resolution by several orders of magnitude.
• An example of such a measuring task is the measurement of areas on the human eye, e.g. the detection of structures both in the anterior region of the eye, for example on the cornea, and on the retina.
• Interferometeran an inch, each of which is composed of its own reference and an associated arm. By different coordination of these multiple combined in a device, stand-alone interferometer can be measured simultaneously at different locations in the eye.
• the document describes various approaches to differentiate the radiations in the combined interferometers, for example with regard to the polarization of the radiation or its
• the object of the invention is to provide a short-coherence interferometer arrangement which can detect a plurality of axially spaced regions of a sample, wherein the regions may be further apart than the parameters of the OCDR variant, such as the spectral Resolution in the FD-OCDR, allow resulting range, and further where a particularly high sensitivity is given, so even weak backscattering points in the sample can be detected.
• a short-coherence interferometer arrangement of the type mentioned, in which the superposition has multiple outputs, each of which a detector is arranged, wherein the superimposing unit receives the same reference radiation for the superposition, at each output a mixture of several superimposed with the reference radiation Single measuring beams emits, each mixture contains several of the individual measuring beams, superimposed with the reference radiation in different phase position.
• the invention uses only one reference arm in the interferometer. This not only results in an advantageous structural simplification. You can also reach a high
• the reference light component substantially or mainly contributes, such as shot noise.
• the spurious noise is the largest noise source (shot noise limited operation) and thus the measurement signal is small compared to the reference signal
• the signal / noise ratio usually corresponds to the number of detected Meßungsphotonen, since the signal component corresponds to the product of the numbers of interfering measuring and reference light photons during the Noise is proportional to the number of reference light photons.
• the noise component increases corresponding to the sum of the reference photons contained in the reference light components.
• the signal share still only corresponds to the product of measuring light photons with the photons of a single tuned reference light component. This means that the signal-to-noise ratio for the individual measuring signals decreases.
• the solution according to the invention with a plurality of measuring signals matched to only one reference arm, allows limiting the noise to the contribution caused by only the one reference light component for the same signal variables.
• the shot noise-limited signal-to-noise ratio is worse by a factor of 2 or 3 dB compared with the use of only one reference signal the two measuring signals are tuned individually.
• the object is further achieved by a short-coherence interferometer arrangement for measuring a plurality of axially spaced regions of a sample, in particular of the eye, which min.
• a Meßstrahlengang through which several individual measuring beams fall on the sample, wherein the individual -Measurements are axially offset upon incidence on the sample by an amount that is matched to the axial spacing, and the interferometer at least two of the individual measuring beams interfere interfered with each other, the interferometer superimposed on each of the two individual measuring beams interfering with each other and then directed to an associated own detector.
• the invention uses individual measuring beams which are axially individually delayed so that an interference signal occurs at the associated detector after the superimposition device.
• the separated individual measuring beams can simultaneously detect axially spaced regions of the sample whose spacing is much greater than the axial measuring range for one of the individual measuring beams.
• the measuring radiation preferably originates from a beam source which is designed to carry out the SS-OCDR, that is to say can be tuned.
• a beam source which is designed to carry out the SS-OCDR, that is to say can be tuned.
• the invention is quite fundamentally also possible and achievable for the SD-OCDR (that is to say with spectral analysis of non-tuned radiation) or the TD-OCDR (with tuning of the interference condition in the interferometer, for example adjustment of the length of a reference beam path).
• the division of the individual measuring beams can be effected from a common measuring beam, ie after the superimposing device has separated the measuring beam path and the reference beam path from an original beam provided by the beam source.
• a radiation source providing a measuring radiation which emits an original beam
• the superimposition device divides certain intensity components of the original beam into the measuring beam path and the reference beam.
• a lens device which separates the measuring radiation into the individual measuring beams, these axially offset (delayed) against each other and at the same time focused with different focal lengths on the sample.
• a particularly compact lens device is obtained when it provides the individual measuring beams by means of a pupil division, wherein each individual measuring beam is assigned a separate pupil area of the lens device and the optical path lengths and possibly also the imaging properties of the pupil areas are different.
• Such a lens device is also possible independently of the short-coherence interferometer arrangement described, so that it can be provided as an independent invention, a lens device which separates a supplied beam into individual beam bundles, which delays individual beam bundles against each other and possibly also gives different focuses, wherein the lens device has a divided pupil, a separate pupil region is assigned to each individual beam bundle, and the optical path lengths, dispersions and possibly also the imaging properties of the lens device in the separate pupil regions are different.
• Particularly expedient is a (of course also in the context of the short-coherence interferometer arrangement possible) development in which the lens device has a glass body with two lens surfaces and on a lens side along the optical axis extending into the glass body bore is formed.
• the depth of the bore is then responsible for the mutual retardation of the single beams, as this results in a different optical path length through the glass body for the individual beams.
• the optical properties of the bore bottom and the lens surface in which the bore is introduced, may also differ. Any differences affect the different focussing of the individual rays.
• the delay and the focusing of the individual beams are thus independently set or selected when designing the lens device.
• the cavity in the vitreous body in whole or in part with a material having different optical properties compared with the rest of the vitreous body, i. especially refractive index and dispersion, to achieve the desired optical retardation and / or dispersion ratios.
• An alternative to generating the single measuring beams from a common measuring beam, i. after separation of the reference beam path lies in the fact that the superimposition device divides the individual measuring beams directly directly from the original beam.
• a polarization separation is also regularly limited to a maximum of two separated beams, whereas an intensity distribution, as is possible for example with fiber couplers, can also generate more than two separated beams. It is therefore preferred in a development of the invention that the measuring beam path has different lengths of individual measuring beam paths for the individual measuring beams and the superimposing device divides certain intensity components of the original beam into the individual measuring beam paths. Optionally, the superimposition device can also divide a certain intensity component of the original beam in the reference beam path.
• the separation of the original beam into the individual measuring beams and (if not worked in the dual-beam version) the reference beam can be done after intensity levels particularly easy with a 3x3 fiber coupler or two combined 2x2 fiber coupler, as for example in the above mentioned US 2006/0109477 A1 with the cooperation of the inventor of the present application have already been described.
• the disclosure of this document is expressly incorporated here in terms of the mode of action, the structure and the possibilities of such fiber couplers.
• the superimposing device outputs at the outputs in each case a mixture of at least two individual measuring beams, which are each superimposed with the reference beam, wherein the reference beam at the superposition for each individual measuring beams an individual phase difference is effected, which causes the individual measuring beams to the reference beam experience a different relative phase in the superposition.
• the phase difference is for example 180 °, which makes it particularly advantageous to realize a balanced detection, as already mentioned.
• Each detector thus receives a mixture of several individual measuring beams, each superimposed with the reference beam with different relative phase angle.
• the individual measuring beams may have substantially equal proportions, but also an asymmetric composition in the mixture is possible in which one of the individual measuring beams in the mixture has a disproportionate share, in particular over 90%. Of course, this increase in share is at the expense of the other single measuring beam or the other single measuring beams.
• the simultaneous detection of the measuring range signals enables a compensation of position errors as a result of axial sample movement in distance measurements.
• the otherwise negative effects of axial sample movements on FD-OCT are described, for example, in Yun et al., Opt. Express. 12, 2977 (2004) "Motion artifacts in optical coherence tomography with frequency-domain ranging".
• a particularly high accuracy of detection can be achieved if the superimposition of the individual measuring beams (either with the reference beam or, in the case of the dual-beam variant with at least one other individual measuring beam) results in a loss of less than 50%. In the approaches of the prior art, this feature is not feasible because there, for example, a polarization separation or a spectral separation always causes higher losses.
• the signal quality in the interference depends on the degree of interference which the individual measuring beams brought into interference can have at all.
• the polarization state is significant, since, for example, orthogonal linearly polarized beams can not sometimes interfere. It is therefore preferred that in the Meßstrahlengang an effective for all individual measuring beams polarization controller is provided, which adjusts the polarization states of the individual measuring beams to each other or equal to the polarization state of the reference beam before the superposition of the individual measuring beams (unless with dual beam Version is worked).
• Faraday rotators can be used in the individual measuring beams and in the reference arm to realize an automatic adjustment of polarization states in the superimposition.
• Faraday rotators in the sample and reference arm of an OCT interferometer are described in US7126693.
• a single polarization controller is used to equalize the polarization state of the reference radiation in the superposition with the individual measuring beams.
• the individual measuring beams are separated directly from the original beam
• the described arrangement is of course designed to OCDR by means of tunable radiation source (SS-OCDR), which is why a corresponding embodiment is preferred.
• SS-OCDR tunable radiation source
• the arrangement makes it possible to detect a sample in areas which are more axially spaced than the measuring range allows, e.g. in the case of SS-OCDR, the spectral line width of the tunable radiation source, TD-OCDR by the adjustment path of the reference arm of the interferometer, and SD-OCDR by the spectral resolution of the detection. It is therefore preferred that the axial offset of the individual measuring beams is greater than a given by the tunability of the interferometer arrangement or by the spectral splitting and detection range.
• the variants of the arrangement according to the invention described here can also be designed for the lateral scanning of a sample, in particular for imaging.
• at least one scanning device is provided for scanning the sample by lateral mutual displacement of sample and at least one of the individual measuring beams.
• the scanning device is therefore effective for at least one of the individual measuring beams.
• ocular lens imaging including determination of its shape and position (oblique position of the lens, i.e., angles between the optical axis and visual axis, curvature of the posterior lens surface, curvature of the anterior lens surface), is preferably applied to the eye. Imaging in the area of the retina is also possible, especially in the area of the fovea.
• the scanning device for at least one of the individual measuring beams advantageously also allows a combined measurement, which goes beyond simple distance measurement or topography detection. Missing a moving object, such as the human eye, there is always the problem that eye movements during the measurement process lead to a falsification. This is particularly troublesome in scanning scanning by optical coherence tomography.
• the arrangement according to the invention now makes it possible to use one of the individual measuring beams for detecting the distance of a reference point, for example the corneal vertex or the retina, and out Any changes in distance a measure of the movement of the sample, for example, the eye to win. The movement of the reference point can then be used to correct the measurement data obtained by simultaneous lateral scanning at a different location of the sample.
• the arrangement comprises a corresponding control device which carries out the above-described referencing by detecting the axial position of a reference point by means of a single measuring beam or by detecting the three-dimensional position of a reference point by using a stand-alone scanned single measuring beam and the arrangement controls.
• Fig. 1 is a SS-OCDR interferometer with balanced detection for simultaneous
• FIG. 3 is a schematic representation of an interferometer similar to that of FIG. 2,
• Fig. 4 is a representation similar to that of Fig. 3 with the illustration of the effect of a
• FIG. 5 shows an interferometer representation similar to that of FIG. 4, but in FIG
• FIG. 6 is a schematic view similar to that of FIG. 4, but for an interferometer arrangement with balanced detection
• FIG. 7 shows an interferometer arrangement similar to that of FIG. 6, but with additional lateral scanning of the sample.
• FIG. 8 shows an interferometer arrangement similar to that of FIG. 7, but as a dual-beam
• 9a is a schematic drawing of a beam splitter device in the interferometer of
• FIG. 9b shows a change wheel with different beam splitter devices according to FIG. 9a, FIG.
• 10 - 12 are schematic diagrams of beam splitter devices in the interferometers of
• Fig. 13-15 OCDR interferometer similar to that of Fig. 1, wherein the construction in these figures allow an exact balanced detection, the phase difference between the interference read detectors is exactly 180 °, wherein
• Fig. 14 shows a modification of the construction of Fig. 13 with transmissive
• FIG. 15 is a construction similar to that of FIG. 14, but with a differently configured superposition device and
• Fig. 16 shows a construction similar to that of Fig. 15, but with two independent ones
• Fig. 1 shows schematically an interferometer for SS-OCDR. Radiation from a beam source Q, which is tunable and, for example, a line width of less than 30 pm, preferably from
• the interferometer I serves to detect different partial regions T 1 and T 2 on a sample P, which in the exemplary embodiment is an eye A.
• a sample P which in the exemplary embodiment is an eye A.
• the subregions T 1 and T 2 are shown in points in FIGS. 1 and 2. This is only for clarity.
• the subregions naturally extend over an area that extends along the axis of incidence of the radiation.
• the maximum measuring depth limited in the SS-OCDR by the line width of the tunable radiation source Q is not so great that both the partial area T 1 and the partial area T 2 could be detected in a tuning operation.
• the distance d between the subregions is too far for this.
• scanning depths of about 35.2 mm can be realized, which corresponds only to parts of possible eye lengths, for which reason several axially offset portions are advantageous for use on the eye.
• the radiation of the laser beam source Q is conducted via an optical fiber 1 to a coupler K, which acts as a superposition device and will be explained below.
• the coupler K branches off part of the radiation from the optical fiber 1 into a reference beam path R which is essentially provided by an optical fiber 2, at the end of which a mirror device is provided (for example by end mirroring of the fiber), is realized.
• Another part of the radiation from the optical fiber 1 is fed into the Meßstrahlengang M starting with an optical fiber 4.
• the coupler K causes not only a coupling of the radiation of the laser source Q, which thus provides the source beam for the interferometer I, but also a distribution and
• the thus brought to interference signals are from
• Detectors D 1 and D 2 collected and subsequently amplified by means of a balanced detection with a differential amplifier 13.
• each detector D 1 and D 2 receives a mixture of the measuring beams superimposed with the radiation from the reference beam path, but between the inputs III and IV of the coupler, the individual measuring beams with a relative phase difference in the superposition with the radiation from the reference beam R have experienced. In the mixture, the individual measuring beams are contained in equal proportions.
• the coupler K is thus effective both for the division of the original beam and for the superposition of the reference beam with the measuring radiation.
• the measuring radiation is composed of individual measuring beams (as will be explained).
• the coupler has connections I - VI.
• the coupler K passes, for example, 80% to terminal Il and 20% to terminal IV and 0% to terminal Vl 1 as in the optical fiber 6 coupled radiation in the present structure is not further exploited.
• the radiation which is supplied at terminal Il is conducted to 10% to terminal III, 10% to terminal V and 80% to terminal I.
• the interferometer I of FIG. 1 thus utilizes the radiation from the measuring beam path to a high percentage, but uses the intensity that the laser beam source Q in the Optical fiber 1 feeds, only 20%. This is relatively unproblematic, since it is much easier to use a powerful laser beam source Q, as to compensate for a strong Meßsignallite. Since the composition of the coupler K is a comparatively excessive excess of radiation in the reference beam path R, this radiation can be used otherwise, for example for the spectral calibration of the laser beam source Q or to trigger the signal recording.
• the radiation directed to the sample P in the measuring beam path M is split from the optical fiber 4 by means of a monolithic beam separator 8, which provides the already mentioned individual measuring beams M 1 and M 2 , which are delayed from one another.
• the delay reaches the monolithic beam separator 8, which will be explained later, by different glass paths for the single measuring beams M 1 and M 2 .
• the delay is tuned to the distance d by which the regions T 1 and T 2 (from the coupler to the sample and back) are spaced at the eye A.
• the thus uniform overall length of the measuring beam path M is tuned to the length of the reference beam path R.
• the monolithic beam separator also causes a different focus, ie it ensures that the single measuring beam M 2 is focused in the area T 2 and single measuring beam M 1 in the end in the area T 1 .
• the single measuring beam M 1 or the M 2 to turn off is optional as a blocking element z.
• a movable aperture 24 is provided, which shadows the respective individual measuring beam.
• the diaphragm 24 is thus designed so that it dimmers the pupil area in which the monolithic beam separator 8 provides the single measuring beam M 1 .
• a different or additional aperture 24 is provided, which is designed in the form of a ring diaphragm and can only pass the single measuring beam M 1 .
• tunable light sources SS-OCDR have also been described. If, however, a broadband light source such as a superluminescent diode (SLD) is used as the radiation source Q and the detectors D are designed as spectrometers, then an SD-OCDR variant of the short-coherence interferometer arrangement is described which likewise has the described advantages. Interferometer arrangements with several spectrometers for quadrature component determination is known from US 2004/0239943. If the broadband source Q is maintained and the reference arm R is designed such that its optical length can be varied rapidly, then a TD-OCDR variant of the interferometer arrangement is realized. A suitable arrangement for rapidly varying the optical length of reference arms (rapid scanning optical delay line, RSOD) is described, for example, in US Pat. No. 6,654,127.
• RSOD rapid scanning optical delay line
• Fig. 2 offers, if safety-driven limitations of the power of the laser beam source Q or boundary condition, line width, Tuning range and tuning rate show it, so for example would like to work with particularly low power lasers.
• interferometer I of FIG. 2 differs from the construction shown in FIG. 1 essentially in two aspects.
• Meßstrahlengang M The differences in Meßstrahlengang M are due to the fact that the coupler K is the source beam of the laser beam source Q from the optical fiber 1 both in the optical fiber 4 (ie, the terminal IV of the coupler K) and in the optical fiber VI (ie, the terminal VI of the coupler K) ,
• the generation of the individual measuring beams thus does not take place from a previous common measuring beam, but happens directly at the beam splitting device, in this case the coupler K.
• the individual measuring beams M 1 , M 2 then propagate via a polarization controller 7.1 or 7.2, the as already explained for FIG. 1, in the end ensures that that the individual measuring beams have the same direction of polarization after the return from the sample A to one another and above all to the reference beam R.
• Lenses 9.1 and 9.2 ensure that the individual measuring beams are focused on the respective regions T 1 and T 2 of the sample.
• connection IV of coupler K to region T 1 equals the optical path length from connection VI to region T 2 (and both also the optical path length of the reference beam path R).
• this is schematically indicated by different loops in the optical fibers 4, 6.
• the coupling coefficients of the coupler K are now in a preferred embodiment for the interferometer I of FIG. 2 as follows: the distribution of the source beam, supplied at port I is 60% on the terminal Il and 20% each to the terminals IV and VI , The intensity of the source beam, i. The power of the laser radiation source Q, is thus 40% and thus twice as well utilized, as in the interferometer I of FIG. 1st
• the returning at terminal IV single measuring beam M 1 is passed to 80% to terminal III and 20% to terminal I.
• a feedback to 0% takes place.
• 0% between the Terminals IV and V can be realized only with unfavorable effort, a degree of coupling less than or equal to 5% (especially 4%) can be used.
• the degree of coupling between the terminals VI and V then decreases accordingly from 80%.
• the intensity of the individual measuring beams M 1 and M 2 is therefore conducted to 80% to the respective associated detectors D 1 and D 2 .
• connection Il is coupled to 60% with connection I, in each case to 20% with the connections V and VI and in each case to 20% with the connections III and IV.
• the individual detection with the aid of the detectors D 1 and D 2 makes it possible to detect the respective scattering intensity in the area T 1 or T 2 without disturbing influences from the respective other area.
• the energy distribution via the coupler K is particularly advantageous when assuming a laser radiation upper limit on the sample of 2 mW at the wavelength of 1, 05 .mu.m and the source supplies 5 mW. Then the described symmetrical distribution of radiation to the terminals III and V, where the detectors D 1 and D 2 are connected via the optical fibers 3 and 5, optimal.
• Coupler K of FIG. 2 It is therefore also here that is mixed at the output V: the signal at terminal VI superimposed with the signal at terminal Il and the signal at terminal IV superimposed with the signal at terminal II. In the mixture, the signals at both terminals VI and IV superimposed with the reference radiation from the terminal Il in different relative phase.
• the coupler of Fig. 2 causes an asymmetric mixture in which the signal from one of the terminals VI and IV disproportionate share in the mixture, in particular over 90% and 95%.
• the optical fiber 3 which leads predominantly the superimposed signal from the optical fibers 4 and 2.
• Fig. 2 shows an example of a non-uniform composition at the outputs V and III of the coupler K.
• FIG. 3 shows the interferometer structure of FIGS. 1 and 2 in a schematic representation.
• the reference symbol v denotes a delay path
• the reference symbol O an optic
• the reference symbol F a fiber
• the reference symbol A an output.
• the respective indices arrange these quantities, as already made with reference to FIGS. 1 and 2 for the detectors D and the individual measuring beams M, these quantities to the respective individual measuring beams.
• the regions T 1 , T 2 T N which are detected on the sample P.
• the fiber coupler K which can also be realized by a combination of a plurality of couplers, a part of the laser radiation source Q in the optical fiber 1 is provided
• an individual delay V i, V 2, ..., v N so that the optical path length from the coupler K up to the respective area T 1, T 2, ..., T N of the sample is the same for all individual measuring beams M 1 , M 2 , .... M N.
• Corresponding optics O 1 , O 2 O N in the individual measuring beam paths illuminate the partial areas T 1 , T 2 T N to be detected , receive backscattered light and redirect it to the fibers F and the coupler K.
• the delays v are designated independently of the optics A.
• the order, eg order of delay v and optics O is independent, among other things, the delays can also occur in the optics O.
• different strong delaying and / or different lengths of fibers F can cause the delays v.
• the construction of the measuring beam path M is selected for each individual measuring beam M 1 , M 2 M N SO such that the individual measuring beams returning to the coupler K are capable of interfering with the radiation from the reference beam path R, ie in particular has a sufficiently similar polarization state. Any polarization controllers are not shown in FIG.
• the delay lines are now on the one hand, as already explained with reference to FIGS. 1 and 2, chosen so that the optical path length for each individual measuring beam from the coupler K is equal to the region of the sample to be detected. At the same time, however, they are also chosen (this also applies, of course, to FIGS. 1 and 2) in that the optical path length of individual measuring beams is matched to that of the reference beam in the reference beam path R, because only then an interference of superimposed individual measuring beams and reference beam is possible.
• This superimposition is carried out by the coupler K, and feeds the individual measuring beams M 1 , M 2 ,..., M N superimposed and brought into interference with a portion of the reference beam into the respective outputs A 1 , A 2 A N , where they are recorded by corresponding detectors D, which are read out by an evaluation unit 10. Since the coupler K, of course, in turn superimposed on the outputs A 1 , A 2 ... A N , a mixture of the individual measuring beams, each superimposed in different relative phase with the reference radiation, the mixture here again of equal proportions (and a if appropriate, differential readout for balanced detection) up to far disproportionate proportions of one or more individual measuring beams. As far as certain divisions, proportions or mixture compositions are described below, these are not to be understood as limiting, but purely by way of example.
• the schematic representation of the interferometer I in Fig. 3 illustrates that the taken in Figs. 1 and 2 representation with two individual measuring beams is not limiting. Rather, the number of individual measuring beams can be chosen arbitrarily and the upper limit for N need not be 2.
• one of the delays can be replaced by a correspondingly set distance to the sample P or the length (eg to the mirror S) in the reference beam path.
• a further reduction in the number of delay lines can be achieved by limiting the Distances of the areas T can be achieved in conjunction with an enlarged scanning depth of the laser beam source Q.
• the coupler K is designed so that for all outputs to fibers F a coupling between the original beam, i. the fiber 1 and the respective fiber F is less than 50%.
• the interferometer I for the types described here in that the beam splitting device performs an asymmetrical coupling of original beam into reference / measuring beam path and measuring beam path in detector feed lines.
• the degree of coupling with which the source beam is split into the individual Meßstrahlen réelle be reduced below 50% in return to achieve a coupling between the individual Meßstrahlen réellen and the outputs for the associated detectors of over 50%.
• Fig. 4 shows an example in which solid lines indicate a total degree of coupling of 80% and dot-dashed lines a total degree of coupling of 20%.
• the total degree of coupling is the sum of the degrees of coupling for all at this output, corresponding marked outgoing beams.
• the radiation from the optical fiber 1, leading the original beam is thus coupled to 80% of the optical fiber 2 and to a total degree of coupling to 20% to the optical fibers F.
• Each individual optical fiber F contains an equal fraction of this 20% share.
• the respective coupling between F and A i.
• the passage of the individual measuring beam when superimposed with the reference beam to the respective detector can amount to a maximum of 1 minus the total degree of coupling with which the original beam is distributed to the fibers.
• the individual measuring beams are superimposed with each other and given to the outputs A.
• combined partial area signals can be detected which have different phase relationships between the partial area portions.
• the evaluation device 10 can determine quadrature components, e.g. To reduce mirror artifacts that can occur with Fourier Domain OCT. This applies equally to the construction according to FIG. 4.
• Fig. 6 shows a construction in which, on the one hand, the coupler K is realized by two single couplers K 1 and K 2 .
• a balanced detection as already described in US 2006/0109477 A1 cited for this aspect for a different type of interferometer.
• the principle of this balanced detection is, inter alia, that paired signal have a phase shift (eg, about 180 °), thus eliminating differential analysis by means of the differential amplifier 13 and 14 any Gleichlichtanteile, eg fluctuations in the intensity of the laser radiation source Q or interference radiation eliminated.
• Fig. 6 shows the example of two measuring beams, of course, a variant with three or more measuring beams is possible. With respect to the coupling factors, Fig.
• Fig. 7 shows a development in which a scanner 12 is provided in the measuring beam path, which deflects laterally, for example, a single measuring beam to detect a three-dimensional area T.
• the combination with another (for example undeflected) single measuring beam thus allows to detect a reference point to which the coordinate system of the three-dimensional deflection of the other sample area can be referred.
• Possible axial movements of the sample P for example of an eye, can thus be compensated and do not lead to a falsification of the three-dimensional scanning.
• the reference point can also be detected three-dimensionally, not only with regard to its axial position, but also through a further independent scanner in the individual measuring beam path of this individual measuring beam, so that three-dimensional movements of the sample in the measuring signals can be compensated for another sampled sample area.
• the construction of Fig. 6 is substantially realized, although the individual measuring beam M 2 and possibly also the single measuring beam M 1 is deflected in each case with an independent scanner 12 (or 15).
• the evaluation unit 10 receives the signals from the corresponding scanner and, taking into account these signals, composes the signals output by the differential amplifiers 13 and 14 into a correspondingly corrected image with respect to movements of the sample.
• this application of the scanner can be used in any of the described Interferometer I.
• This is illustrated schematically in Fig. 8, which shows the use of a scanner in a dual-beam approach.
• the scanning device is therefore effective for at least one of the individual measuring beams.
• This also allows imaging with respect to the eye lens when used on the eye, including determination of its shape (skew of the lens, i.e., angles between the optical axis and visual axis, curvature of the posterior lens surface, curvature of the anterior lens surface). Imaging in the area of the retina is also possible, especially in the area of the fovea.
• Particularly advantageous in measurements on the eye is the use of a static, on the largest corneal reflex-aligned single-measuring beam, while a second single measuring beam is deflected laterally to allow recording the spatial distribution of retinal structures, for example, for imaging (dual-beam OCT ) or to determine the eye length with respect to certain reference points on the retina.
• a simple determination of the frequency distribution of eye lengths during lateral scanning supplies information suitable for characterizing an eye.
• the structure of the monolithic beam separator 8 will be described with reference to FIG. 9a.
• This serves to divide a delivered from an optical fiber 4 beam into two individual beams, which are axially offset from each other with respect to a possible eventual interference and possibly. In different, spaced by a distance foci are focused.
• the beam separator 8 brings the measuring beam paths together again.
• the beam separator 8 receives a beam 18, which emerges at the end of the optical fiber 4, and collimates it by means of a first lens side L 1 , which has a glass body 17 of the beam separator 8.
• the thus collimated radiation then passes through the glass body 17, which has a pupil division on the output side.
• a bore 18 extending along the optical axis is introduced into the opposite lens side L 2 .
• the radiation emerging at the bore bottom 19 passes through a glass path which is smaller by the depth t of the bore 18 than the radiation which exits at the lens side L 2 .
• This causes the delay of the individual beams against each other. The delay thus corresponds to the optical light path of the depth t of the bore 18 in the glass body 17 (of course, any lens-suitable material can be used).
• the individual measuring beams exit in different focus cones 20, 21.
• This different focusing is caused by different diffraction properties of the lens surface L 2 and the bore bottom 19.
• the different diffraction characteristics of the pupil division achieved thereby results in the foci 22, 23 being spaced apart by the distance a. Focus distance and delays can be adjusted independently of each other by lens surface area and hole depth.
• the focusing is of course only to be understood as an example.
• the single jet emerging in this pupil part may also be parallel, or the same as the propagation direction effected by the lens surface L 1 .
• Fig. 9b shows that a change of the beam separator 8 is possible.
• various beam separators 8.1 and 8.2 and 8.3 are mounted on a change wheel W and it is in each case that one beam separator pivoted in the beam path, which is needed.
• the various beam splitters 8.1, 8.2 and 8.3 differ in terms of the delay caused by the optical path of light of depth t.
• an imaging acting beam separator 8 and a non-imaging beam separator can be used when the first and second sides of the glass body 17 are not formed as lens sides but plan.
• FIGS. 10 to 12 show diagrams for the fiber coupler K.
• a 3x3 coupler is shown having terminals I - VI and causes a corresponding coupling of I, III and IV on the one hand with II, IV and VI on the other.
• Fig. 11 shows a modification of the fiber coupler K of Fig. 10, in which now not 3 fibers was partially fused, but twice 2 fibers.
• a 3 ⁇ 3 coupler can be replaced by this.
• a coupler K as shown in FIG. 12, which has a 40% crosstalk between VI ⁇ V and IV ⁇ III, is advantageous.
• the physical embodiment shows in perspective the Fig. 12. The course of the coupling path V ⁇ IV is thus kinked over a plane which is spanned by the routes Il ⁇ IV and I ⁇ Il.
• Fig. 13 shows a construction similar to that of Fig. 1, wherein here now a so-called exact balanced detection can be made, the mixture is thus composed symmetrically or proportionally.
• FIG. 13 On the one hand illustrated by a dashed line box that the optical fiber 4 quite generally a differently designed application module 25 may be arranged downstream, which divides the single Meßstrahlen réelle from the Meßstrahlengang, which begins with the optical fiber 4.
• a third coupler K 3 is used, which takes over the separation and merging of the individual Meßstrahlen réelle.
• the construction shown in the lower box of the application module 25 of FIG. 13 uses the beam splitter of FIG. 9a, but in the variant already described without optical surfaces on the component 8.
• the couplers K 1 and K 2 together realize a coupler K, which in principle that of FIG. 1 corresponds.
• the coupler K 2 is designed as a 50/50 coupler or splitter, whereby it is achieved that the mixtures in the optical fibers 5 and 3 are composed symmetrically, ie in equal proportions the radiation from the measuring beam paths M 1 and M 2 respectively with relative phase shift of 180 ° with respect to the superposition with the reference beam path included. Further, by constructing the coupler K from a 2x2 coupler doublet, it is possible to access a link optical fiber 26 between the couplers K 1 and K 2 . This makes it possible to realize a kind of circulator. If the original radiation from the radiation source Q is linearly polarized and if an MA unit is arranged in the optical fiber 26, circularly polarized radiation passes into the measuring beam path M.
• the source Q returned radiation is polarized as a result perpendicular to the original radiation. This has proved positive for undisturbed and stable operation of the source Q.
• the optional use of a Faraday rotator in the light path 26 is advantageous because an orthogonal polarization state with respect. Of the light coming from the light source in the light path 26 is achieved.
• Fig. 14 shows a modification of the construction of Fig. 13.
• the reference radiation is now through an optical fiber loop, i. reaches a connection of the optical fibers 2 and 6.
• This can be called a transmissive reference.
• the transmissive reference arm may include fixed or variable attenuation elements for purposes of signal adjustment on the detectors or may be designed such that such attenuation is realized. Otherwise applies to the construction of Fig. 14 for the Fig. 13 said analog.
• Fig. 15 corresponds substantially to that of Fig. 14, but the couplers K 2 and K 1 are inverted in their order with respect to the connecting optical fiber 26.
• the original radiation in turn passes first to the coupler K 2 , but from there directly into the Meßstrahlengang and of course in the here again transmissively formed reference beam path.
• Fig. 16 finally shows a construction similar to Fig. 15, but the coupler K 2 is here constructed to a 3x3 coupler, so that it takes over connections IV.1 and IV.2 equal to the separation into the two single Meßstrahlenlandais.
• the individual measuring beam paths are adapted with respect to their optical paths to the distance of the sample areas to be detected.
• a suitable medium is introduced individually into the Meßstrahlen réelle, which influences the dispersion with the same optical delay, the effects of meßstrahlenindividuell irradiated sample areas are compensated.
• the above-described embodiments can basically be designed for SS, SD or TD-OCDR. In the latter case, an adjustment of the effective reference arm length is provided. In the illustrations of FIGS.
• a device for adjusting the propagation time of the radiation in the reference beam path is additionally present in the reference beam path denoted by R, for example the RSOD according to US Pat. No. 6,654,127, cited above a path length adjustment.
• R the reference beam path denoted by R
• An analogous element is provided in Figure 4 and 16 at the terminal of the optical fiber 2.
• VOA variable optical attenuator
• VOA variable optical attenuator

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