JP2006064610A - Coaxial-type spatial light interference tomographic image measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coaxial type spatial light interference tomographic image measuring instrument, utilizing a spatially correlated wave capable of effectively performing parallel detection of depth detection data due to space interference, using a low coherent light source at a high speed, using a simple constitution. <P>SOLUTION: In the coaxial-type spatial light interference tomographic image measuring instrument, a diffraction lattice 9 is arranged in the optical path of a reference light wave of an interferometer and a coaxial-type spatial light interferometer for combining the diffracted light waves, having a correlation wave front forming an angle with respect to a phase wave front with a signal light wave on the same axis, is constituted and a spatial interference signal is detected in parallel by an optical array sensor 12 to acquire the tomographic image of a target of inspection 6. The correlation wave fronts of the reference light wave and the signal light wave interfere with each other, and the form information in the deep direction of the inspection target are projected in the lateral direction on the detection surface of the optical array sensor 12. Since the shape wave fronts are parallel, the spatial cycle of the spatial interference fringe becomes infinite and the envelope of the interference signal can be detected directly. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention irradiates a subject, particularly a light scattering medium having an inhomogeneous structure, with a light wave beam, and optically measures a tomographic image of the subject using light reflected from the surface or the inside of the subject. The present invention relates to a coaxial spatial light coherence tomographic image measurement apparatus.

  Since the invention of the laser in the 1960s and the practical use of optical fibers in the 1970s, research on measurement methods using various light waves has been underway. Measurement methods using light waves basically have features such as high sensitivity, high resolution, high accuracy, and high-speed detection, and various measurement techniques using light waves have been developed, and many measurement devices are commercially available. In addition, light waves that can be non-contact and non-invasive are also suitable for living body measurements, and near-infrared light that is close to the visible range among light waves is relatively easy to pass through the living body, so image diagnostic technology using light waves Is used in this wavelength range. However, although the light in this wavelength range is relatively easy to pass through the living body, the fact that the living tissue having a non-uniform and complicated microstructure is a high scattering medium is the realization of a diagnostic device using light waves. It was a big obstacle.

  From the latter half of the 1980s, research on measuring the propagation characteristics of light waves in a living body has been actively conducted in order to open the way to biological image diagnosis using light waves, and accordingly, various measurement methods using light waves. Was devised. Among these measurement methods, there is an optical coherence tomography (OCT) method using interference of a low-coherent light source having a wide wavelength band as one of the measurement methods that have been attracting high interest in recent years ( For example, see Patent Document 1 and Non-Patent Document 1 below). This measurement method uses a low coherent light source as a probe and measures the form inside the living body with a spatial resolution of micron order by utilizing the incoherence of the low coherent light source having a wide wavelength band. In addition, the backscattered light is selectively detected by the optical heterodyne method from the light that is scattered and diffused components reflected from the inside of the living body, and the position and amplitude information of the interference signal is converted into a tomographic image. It is.

  Optical coherence tomographic imaging uses a low coherent light source, for example, in a Michelson interferometer. The basic configuration is shown in FIG. The light wave beam from the low-coherent light source 81 is divided into a reference light wave and a signal light wave by a semi-transparent mirror 82. The reference light wave is applied to the reflecting mirror 83 and reflected. On the other hand, the signal light wave is applied to the subject 84, and the backscattered light from the surface or inside of the subject 84 is combined again by the reference light wave and the semitransparent mirror 82 and detected by the point light sensor 85. When the difference between the optical path lengths of the reference light wave and the signal light wave is less than or equal to the coherent length of the light source (the coherent length of the low coherent light source is several tens of μm), only correlated components interfere with each other. Therefore, by scanning the position of the reflecting mirror 83 in the optical axis direction and changing the optical path length of the reference light, it is possible to detect the reflection intensity profile having the shape information of the subject 84 at the signal light wave irradiation position. Furthermore, a two-dimensional tomographic image can be measured by scanning the signal light wave in the horizontal direction.

  However, since the two-dimensional tomographic image measurement as described above requires scanning of the reflecting mirror in the optical axis direction and horizontal scanning of the signal light wave beam, there is a limitation in shortening the measurement time. In order to perform image measurement at a higher speed, it is desirable not to have a mechanical scanning mechanism, and for this, a method of spatially detecting two-dimensional tomographic images in parallel using a two-dimensional array sensor such as a CCD camera. Is effective.

As one of the spatial parallel detection methods, there is an off-axis interferometer using a low-coherent light source (for example, see Non-Patent Document 2 below). In the off-axis interferometer shown in FIG. 11, the reference light wave _er and the signal light wave _es are incident on the center position O of the optical array sensor 91 from the left and right at an angle θ. The phase wavefront perpendicular to the light propagation direction and the correlated wavefront contributing to the interference of the two lightwaves are equal, and the light intensity detected at the detection surface where the two lightwaves intersect is

で与えられる。ただし、ｚは光アレイセンサ９１の検出面上の位置、Ｅ_r 、Ｅ_s はそれぞれ参照光波と信号光波の電界振幅、ｆは光周波数、ｃは光速、Δｚは参照光波と信号光波の光路長差である。

Given in. Where z is the position on the detection surface of the optical array sensor 91, E _r and E _s are the electric field amplitudes of the reference light wave and the signal light wave, f is the optical frequency, c is the speed of light, and Δz is the optical path length of the reference light wave and the signal light wave. It is a difference.

The above equation (1) represents the light intensity in a light wave having a single frequency f, and the detected light intensity when a low coherent (wide frequency band) light source is used can be expressed by the equation (1) in the frequency distribution of the light source. It can be obtained by integrating. For convenience of calculation, assuming that the frequency distribution function of the light source is a Gaussian type, the detected interference component uses the center wavelength λ ₀ and the wavelength width Δλ of the light source,

となる。

It becomes.

The above equation (2) represents a Gaussian function modulated by a sine function having a spatial period λ ₀ / (2 sin θ), and the profile of the Gaussian function corresponds to the envelope of the interference signal. Further, the peak (Δz−2zsin θ = 0) of the Gaussian function corresponds to the optical path length difference Δz of the two light waves. From the equation (2), when a low-coherent light source is used, the position where the correlation component of the reference light wave taking another optical path and the signal light wave reflected from each part inside the subject overlaps, that is, the optical path length of the two light waves is Interference occurs locally at the matching position, and information on the depth direction of the subject is projected in the horizontal direction on the detection surface of the optical array sensor 91 and detected in parallel.
Japanese Examined Patent Publication No. 6-35946 “Optics”, Vol. 28, No. 3, 1999, p. 116 “Optics Letters” vol. 18, 1993, p. 2129

  However, since the interference signal given by the above equation (2) has a spatial period as short as the wavelength order, it is difficult to detect the profile of this interference signal in actual size, and an optical array sensor with high spatial resolution is required. is there. For example, if a low coherent light source with a center wavelength of 840 nm is used and the incident angle of light to the optical array sensor is 45 °, the spatial period of the detected interference signal is about 600 nm, and in order to detect the interference signal From the Nyquist sampling theorem, an optical array sensor having a spatial resolution of at least 300 nm is required. Further, in order to obtain a two-dimensional tomographic image from the detected interference signal, complicated calculation such as Fourier transformation is required. The necessity of this calculation makes it difficult to increase the speed of measurement by an off-axis interferometer using a low-coherent light source.

  In view of the above circumstances, the present invention provides a coaxial spatial optical interference using a spatial correlation wave that can perform parallel detection of depth direction information by spatial interference using a low-coherent light source with a simple configuration and at high speed. An object is to provide a tomographic image measuring apparatus.

In order to achieve the above object, the present invention provides
[1] In a coaxial spatial optical coherence tomographic image measurement apparatus, in a tomographic image measurement interference optical system using a light source having a wide wavelength range, a reference light wave is made to enter the diffraction grating through the diffraction grating. A diffracted light wave having a correlation wavefront that contributes to interference with the signal light wave that forms an angle with the equiphase surface of the diffracted light that is delayed depending on the position is generated, and the diffracted light wave is caused to interfere with the signal light wave substantially coaxially, A spatial interference signal localized at a position depending on the delay is generated, and a coaxial interference system is configured.

  [2] In a coaxial spatial light coherence tomographic image measurement apparatus, a light source that emits a light wave having a wide wavelength bandwidth, a lens that expands the beam diameter of the light wave emitted from the light source, and converts it into a parallel light beam, and the parallel light beam The signal light wave that follows the optical path in which the subject is arranged and the reference light wave that follows the optical path in which the diffraction grating is arranged, which are different from the optical path that passes through the subject, are irradiated to the subject, A signal light wave that scatters backward from the inside or a signal light wave that scatters forward, a delay mechanism using a translucent mirror and a reflecting mirror for adjusting the optical path length of the reference light wave, and a reference light wave that passes through the delay mechanism further includes a diffraction grating. By passing, the spatial delay correlation wavefront that contributes to interference with the signal lightwave that forms an angle with the phase wavefront is provided, and the reference lightwave having the spatial delay correlation wavefront and the signal lightwave are combined substantially coaxially. Sky Interference optical system for generating a general interference signal, an optical array sensor in which a large number of light receiving elements are arranged in space to detect and detect interference light generated by the interference optical system, and a large number of light receiving elements of the optical array sensor And a signal processing system that integrates and processes the optical interference signals detected in step (1), and forms morphological information on the surface or inside of the subject at the position irradiated with the signal light wave.

  [3] In the coaxial spatial optical coherence tomographic image measurement device according to [1], the wavelength dispersion of diffracted light generated by the reference light wave passing through the diffraction grating on the reference light wave side of the interference optical system. In order to correct, the diffracted light from the diffraction grating is projected onto the optical array sensor by a lens system.

  [4] In the coaxial spatial light coherence tomographic image measurement apparatus according to [1] or [2], the interference optical system irradiates a light wave incident on the subject through a lens system on the signal light wave side. The signal light wave from the subject is condensed using a lens system, and further projected onto the detection surface of the optical array sensor using a cylindrical lens system.

  [5] In the coaxial spatial optical coherence tomographic image measuring device according to [1], the interference optical system is configured to cause the light wave incident on the subject to be incident on the signal light wave side in a vertical direction perpendicular to the incident direction of the light wave. A cylindrical lens and a condensing lens for condensing into a linear shape, condensing the signal light wave from the subject using a lens system, and further using the cylindrical lens on the detection surface of the optical array sensor It is characterized by projecting.

  [6] The coaxial spatial light coherence tomographic image measuring apparatus according to [4] or [5], wherein a mechanism for deflecting and scanning light waves incident on the subject is provided.

  [7] In the coaxial spatial optical coherence tomographic image measurement device according to [4], the optical array sensor is a light array in which light receiving elements are spatially linearly arranged and spatial interference signals can be detected independently and in parallel. The detection surface of the optical array sensor is arranged on the surface on which the reference light wave from the diffraction grating and the signal light wave from the subject are projected, and is detected by light receiving elements arranged in one direction of the optical array sensor. The obtained optical interference signal is used to construct the form information of the propagation direction at the signal light wave irradiation position of the subject by integration and processing, and the signal light wave irradiation position is sequentially moved by the deflection scanning to thereby generate the signal light wave. A two-dimensional tomographic image is constructed by detecting, integrating, and processing.

  [8] In the coaxial spatial optical coherence tomographic image measuring apparatus according to [5], the optical array sensor has a light receiving element spatially arranged in a two-dimensional array and can detect spatial interference signals independently and in parallel 2 A two-dimensional optical array sensor, wherein a detection surface of the two-dimensional optical array sensor is disposed on a surface on which a first-order diffraction reference light wave from the diffraction grating and a signal light wave from the subject are projected, and the two-dimensional optical array sensor The optical interference signals detected by the light receiving elements arranged in one direction are constructed and processed to construct morphological information in the propagation direction at the signal light wave irradiation position of the subject, while the two-dimensional optical array sensor The optical interference signal detected by the other light receiving elements arranged in one direction is a signal for constructing vertical morphological information perpendicular to the light propagation direction at the linear signal light wave irradiation position of the subject by integration and processing. With a processing unit And wherein the door.

  [9] In the coaxial spatial light coherence tomographic image measurement device according to [6], the interference optical system according to [8] described above may include a light wave incident on the subject or the subject on the reference light wave side. It is characterized in that it has a function of acquiring three-dimensional shape information of the subject by one-dimensional scanning perpendicular to the light wave propagation direction.

  [10] The coaxial spatial light coherence tomographic image measurement apparatus according to [1], wherein the interference optical system includes a polarizing element that controls a polarization direction of a light wave applied to the subject.

  [11] In the coaxial spatial optical coherence tomographic image measurement device according to [2], the interference optical system may generate a frequency in a spatial interference signal by expanding and contracting an optical path length difference between the reference light wave and the signal light wave by a vibration mechanism. It has a frequency shifter that gives a shift, and has a function of extracting only interference components from background light.

  [12] The coaxial spatial light coherence tomographic image measuring apparatus according to [2], wherein the light source is a superluminescent diode having a coherence distance of 100 μm or less.

  [13] The coaxial spatial light coherence tomographic image measuring apparatus according to [2], wherein the light source is a light emitting diode having a coherence distance of 50 μm or less.

  [14] The coaxial spatial light coherence tomographic image measurement apparatus according to [2], wherein the subject is a light scattering medium.

  [15] The coaxial spatial light coherence tomographic image measuring apparatus according to [2], wherein a delay mechanism for scanning an optical path length difference between the reference light wave and the signal light wave is provided.

  [16] The coaxial spatial light coherence tomographic image measuring apparatus according to [2], wherein the optical array sensor is composed of a CCD or a MOS element.

  [17] The coaxial spatial light coherence tomographic image measurement apparatus according to [2], wherein the optical array sensor is an imaging device with an electron multiplication mechanism.

  According to the present invention, the following effects can be achieved.

  (A) In a low coherent interferometer, a diffraction grating is arranged in the optical path of the reference light wave, a correlation wavefront that forms an angle with the phase wavefront of the diffracted light is used, and wavelength dispersion due to the diffraction grating is detected using a lens. By correcting on the surface, a coaxial spatial interferometer can be constructed.

  (B) Since it is a coaxial interferometer, the phase wavefronts of the reference light wave and the signal light wave are parallel, and an interference signal with an infinitesimal spatial frequency, that is, an envelope of interference fringes can be directly detected.

  (C) Since the two-dimensional tomographic image of the subject can be detected at high speed without scanning, the three-dimensional tomographic image in the subject can be easily drawn by scanning the light irradiation position on the subject in an arbitrary direction. .

  (D) By using a broadband polarization beam splitter and a wave plate, it is possible to control and detect the polarization state of the incident light wave and the reflected light wave on the subject.

  (E) When a phase modulation device using a vibration mechanism is provided on the reference light wave side, an optical interference signal detected by the optical array sensor can be separated from a direct current component due to background light.

  (F) Since only the reference light wave passes through the diffraction grating, a measurement system in which the signal light wave is not limited by the diffraction efficiency can be constructed.

  (G) Since it is a coaxial spatial light interferometer, an apparatus can be easily constructed with a simple configuration.

  (H) A commercially available CCD camera or MOS type camera can be easily used for the optical array sensor, and various imaging devices with a photomultiplier mechanism can be used. An image of a very weak light signal from the deep part of the subject. There is a feature that also enables multiplication detection.

  The present invention relates to a coaxial spatial optical coherence tomographic image measurement apparatus, in an interference optical system for tomographic image measurement by optical interferometry using a light source having a broadband wavelength width, and passing a reference light wave through the diffraction grating, Generates a diffracted light wave that has a correlation wave front that contributes to interference with the signal light wave that forms an angle with the equiphase surface of the diffracted light, which is delayed depending on the incident position, and interferes with the signal light wave substantially coaxially, depending on the delay The present invention is characterized in that a coaxial interference system is configured in spite of generating a spatial interference signal localized at a certain position. Therefore, by arranging a diffraction grating in the optical path of the reference light wave, utilizing the correlation wavefront that forms an angle with the phase wavefront of the diffracted light, and correcting the wavelength dispersion due to the diffraction grating on the detection surface using a lens A coaxial interferometer can be constructed.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a configuration diagram of a coaxial spatial optical coherence tomographic image measurement apparatus using a spatial correlation wave according to a first embodiment of the present invention. In this figure, 1 is a low-coherent light source, 2, 5, 10 are lenses, 3, 7, 11 are translucent mirrors, 4, 8 are reflecting mirrors, 6 is a subject, 9 is a transmission diffraction grating, and 12 is light. It is an array sensor.

  As shown in FIG. 1, light emitted from a low coherent light source 1 having a wide frequency bandwidth is converted into a wide range of parallel light beams by a lens 2. The parallel light beam enters the interferometer, and is divided into a signal light wave and a reference light wave by the translucent mirror 3. The signal light wave is reflected by the reflecting mirror 4, passes through the semi-transparent mirror 11, is condensed at a point by the lens 5, and is irradiated to the subject 6 made of a constituent material that is nonuniform and causes light scattering, for example. The light internally reflected from the subject 6 is collected by the lens 5 and sent to the translucent mirror 11. On the other hand, the reference light wave enters the transmissive diffraction grating 9 via the delay mechanism (7, 8), and the first-order diffracted light is, for example, connected to the detection surface of the optical array sensor 12 by the lens (imaging lens) 10. Image. Here, the delay mechanism is composed of a semi-transparent mirror 7 and a reflecting mirror 8. In this delay mechanism, the reference light wave passes through the semi-transparent mirror 7, is totally reflected by the reflecting mirror 8, and returns to the semi-transparent mirror 7. At this time, by moving the reflecting mirror 8 in the light propagation direction, the optical path length in the interferometer is changed and delayed. The reference light wave and the signal light wave are combined by the translucent mirror 11, and the interference signal is detected by the optical array sensor 12.

  Note that a superluminescent diode having a coherence distance of 100 μm or less can be used as the light source.

  Further, as the above light source, a light emitting diode having a coherence distance of 50 μm or less can be used.

  A conventional measurement apparatus using spatial interference of low-coherent light is configured by applying an off-axis optical interferometer. However, the present invention allows a reference light wave to pass through the transmission diffraction grating 9 in the interferometer and transmit it. Coaxial spatial light that detects a spatial interference signal in a coaxial optical interferometer using a diffracted light wave that has a correlation wavefront that is delayed depending on the light irradiation position on the diffraction grating 9 and contributes to interference with the signal light An interference tomographic image measurement apparatus is provided.

  The operation principle of the coaxial spatial light coherence tomographic image measuring apparatus according to the present invention will be described below.

FIG. 2 shows the principle of generation of the delayed correlation wavefront depending on the light irradiation position on the transmissive diffraction grating. The transmission type diffraction grating 9 was arranged on the Z axis so that the normal line was parallel to the Y direction. The light emitted from the low-coherent light source has a parallel correlation wavefront that contributes to interference between the phase wavefront and the signal lightwave. When wide and low coherent light (reference light e _r ) is incident on the transmissive diffraction grating 9 at an angle θ with respect to the vertical axis of the diffraction grating surface, the diffraction grating equation (sin θ−sin β = mλ ₀ / d, where , M is the order, λ ₀ is the center wavelength of the light source, and d is the grating interval). In the present embodiment, description will be made on the first-order diffracted light, but the same principle can be applied to second-order or higher-order diffracted light. For example, at this time, the normal direction of the phase wavefront of the first-order diffracted light becomes the propagation direction by Huygens' principle.

The relative maximum delay distance based on the spatial delay correlation wavefront, that is, the maximum depth measurable distance Zmax is Zmax = mλ ₀ D / 2d cos θ, where D is the diameter of the beam of the incident wave to the transmissive diffraction grating 9. Given in. As a numerical example, for example, when a first-order diffracted light is targeted, m = 1, a center wavelength λ ₀ = 835 nm, a grating interval d = 1.2 μm, an angle θ = 45 degrees, and a beam diameter D = 10 mm, a depth S = 3.5mm is obtained. In currently used tomographic image observation of the fundus and the like, it is sufficient if the deep part can be observed in a range of about 2 mm. Therefore, the observation depth in the Z-axis direction in the present invention can be provided to practical use.

  When low coherent light (light in a wide frequency band) is incident on the transmissive diffraction grating 9, chromatic dispersion occurs according to the diffraction grating equation. From the above diffraction grating equation, the angular dispersion Δβ in the transmissive diffraction grating 9 is

で与えられる。ただし、ｚは透過型回折格子９上の位置座標、λは任意の光波長、λ₀ は光源の中心波長である。

Given in. However, z is a position coordinate on the transmission type diffraction grating 9, λ is an arbitrary light wavelength, and λ ₀ is a center wavelength of the light source.

  Therefore, the phase difference Δφ of the wavelength-dispersed diffracted light wave is

である。上記式（４）は中心波長λ₀ の光と波長λの光の、中心点Ｏを通過する光に対する任意座標Ｚを通過する光の相関波面の距離的な遅れのずれを表したものである。その透過型回折格子９での波長分散を補正するため、各波長における１次回折光波をレンズ（結像レンズ）１０を使って光アレイセンサ１２の検出面上に投影する必要がある。

It is. The above formula (4) represents the shift in the distance delay of the correlation wavefront of the light passing through the arbitrary coordinate Z with respect to the light passing through the center point O between the light having the center wavelength λ _{0 and} the light having the wavelength λ. . In order to correct the chromatic dispersion in the transmissive diffraction grating 9, it is necessary to project the first-order diffracted light wave at each wavelength onto the detection surface of the optical array sensor 12 using the lens (imaging lens) 10.

  The first-order diffracted reference light wave and the signal light wave are combined by the translucent mirror 11.

FIG. 3 shows chromatic dispersion correction on the reference light wave side and signal light wave multiplexing. The present invention is characterized by constructing a coaxial spatial interferometer as shown in FIG. On the reference light wave _er side, the first-order diffracted light emitted from the over-diffractive grating 9 is projected onto the detection surface of the optical array sensor 12 by the lens 10 having an appropriate focal length for correcting chromatic dispersion. Contributes correlation wavefront interference phase front and the angle theta ₁ [= tan ^-1 (cosθ), θ is the incident angle of the reference light wave e _r of the diffraction grating] form a. On the other hand, in the signal light wave e _s side, the light reflected from the subject 6, which is the light irradiation are collected by the lens 5, are multiplexed by the reference light wave e _r translucent mirror 11 is parallel light flux. Contributes correlation wavefront interference signal lightwave e _s is a continuous phase front and parallel wavefronts from each depth of the subject 6. To use the low coherent light source, the reference light wave e correlation wavefront of _r and the signal lightwave e _s only interference where cross occurs, the signal of each depth in the object 6 on the detection surface of the optical array sensor 12 It is detected at a different position Z.

Thus, although the present invention is a coaxial interferometer, it has an excellent feature capable of detecting a spatial interference signal. Contributes phase front to the spatial frequency of the interference signal is parallel with the reference light wave e _r and the signal lightwave e _s, namely crossing angle is zero, the spatial frequency is infinitesimal. Therefore, the envelope of the interference signal of two light waves can be directly detected.

  The principle of the present invention will be described analytically. Assuming that the phase difference of the two light waves on the detection surface of the optical array sensor is 1, the imaging magnification of the imaging system is 1 on both the reference light wave side and the signal light wave side.

で与えられる。ただし、Δｚは参照光波と信号光波の合波までの光路長差である。検出面で検出される光強度Ｉは次式のように計算される。

Given in. However, Δz is an optical path length difference until the reference light wave and the signal light wave are combined. The light intensity I detected on the detection surface is calculated as follows:

上記式（６）における右辺第２項の干渉項を光源のスペクトル分布がガウス分布と仮定して、中心波長λ₀ 、波長幅Δλとして積分すると、

When the interference term of the second term on the right-hand side in the above equation (6) is integrated with the center wavelength λ ₀ and the wavelength width Δλ assuming that the spectral distribution of the light source is a Gaussian distribution,

と計算される。この干渉項は、荷重として正弦関数が掛けられたガウス関数を表している。

Is calculated. This interference term represents a Gaussian function multiplied by a sine function as a load.

Compared with the above equation (2) representing the detected light intensity in the conventional spatial interference method, the Gaussian function representing the envelope of the interference signal is the same, and the phase of the sine function applied as a load is different. Position z where the correlation wavefront of the signal light wave and the reference light wave intersect and interfere
z = Δλ / sinθ (8)
The interference signal is localized around the center. Similar to the off-axis spatial interferometry described above, the peak position of the interference signal, that is, the center position of the Gaussian function is determined by the optical path length difference Δz of the two light waves, and the interference region where the interference signal is localized is determined by the coherent length of the light source. Dependent. In addition, unlike the spatial interferometry, since the position variable z does not exist in the phase of the sine function, the spatial frequency of the generated interference signal is infinitesimal, that is, the envelope of the interference signal can be directly detected. .

  Even in the spatial interferometry using the off-axis interferometer as shown in FIG. 11, an interference signal is generated at the intersection position of the correlation wavefront of the signal light wave and the reference light wave, and information on the depth direction (light irradiation direction) of the subject. Is projected in the horizontal direction on the detection surface of the optical array sensor 91. In the off-axis interferometer, the phase wavefronts also intersect, and thus high spatial frequency interference fringes that are inversely proportional to the intersection angle are generated. In the coaxial spatial optical coherence tomographic image measuring apparatus according to the present invention, only the correlation wave fronts of the reference light wave and the signal light wave intersect and the phase wave fronts are parallel, so that an interference signal having an infinitely small spatial frequency, that is, an envelope of interference fringes. Only the line can be detected.

  The above is fundamentally different from the conventional spatial interference measurement that obtains the envelope of the interference signal by calculating the detected spatial light interference signal.

  FIG. 4 is an embodiment diagram of an optical axis direction non-scanning tomographic image measuring apparatus according to the present invention. In this figure, 13 is a cylindrical lens, 14 is a linear optical array sensor, 15 and 16 are movable mirrors for scanning the XY plane of the subject 6, for example, galvanometer mirrors. The other elements are the same as in FIG.

  In the present embodiment, in the coaxial spatial light coherence tomographic image measurement apparatus of FIG. 1, the reference light wave of the spatial correlation wavefront from the transmission diffraction grating 9 passes through the lens (imaging lens) 10 and is further linearized by the cylindrical lens 13. The light is condensed linearly on the detection surface of the optical array sensor 14. On the other hand, the signal light wave is condensed and applied to a predetermined position of the subject 6 using the movable mirrors 15 and 16 for XY plane scanning. The reflected signal light wave from the surface or deep part of the subject 6 is collected by the lens 5, reflected by the translucent mirror 11 through the movable mirrors 16 and 15 for XY plane scanning, and similarly to the reference light wave by the cylindrical lens 13. It is linear, combined with the reference light wave, and projected onto the linear light array sensor 14 as interference light. As a result, as described in the above principle, the internal reflection information of the subject 6 becomes a normal line of interference, and an output that can be drawn from the linear optical array sensor 14 as one-dimensional position and reflection intensity distribution information is obtained. Further, the movable mirrors 15 and 16 are moved to control the deflection of the signal light wave irradiation point and move and scan in a desired direction to obtain a temporary reflection intensity distribution and observe a two-dimensional tomographic image through a signal integration / processing system. be able to.

  In this embodiment, in a conventional tomographic imaging technique (for example, see Non-Patent Document 1 above), the reference light wave is delayed in the direction of the optical axis (here, the Z axis) at high speed. Delayed scanning performed by mechanical scanning using a rotating prism or the like provides an unnecessary technique. In other words, since the generation of the spatially delayed correlation wavefront plays a role of delayed scanning, the reflected signal intensity in the Z-axis direction is collectively detected without requiring any mechanical scanning. Since the detection speed of the one-dimensional linear optical array sensor 14 is usually several tens of MHz, if the moving scanning speed of the irradiation point is several tens KHz using, for example, a galvano mirror, the latter determines the sampling speed, and the conventional Compared to the A-scan maximum speed of 1000 Hz, a speed increase of several tens of times is realized. The delay mechanism composed of the translucent mirror 7 and the reflecting mirror 8 is used to determine the scanning start position for tomographic detection on the Z axis.

  FIG. 5 shows the coaxial spatial optical coherence tomographic image measurement apparatus of FIG. 1 according to the present invention, which is provided with a cylindrical lens only on the signal light wave side and irradiates the subject with light waves collected in a linear form and connected to the signal light wave side. This is an embodiment in which an image optical system is introduced to enable measurement of a two-dimensional tomographic image without mechanical operation. In this figure, 12 is a two-dimensional optical array sensor (for example, a CCD camera or MOS camera, and various imaging devices with an electron multiplying mechanism), 13 is a cylindrical lens, 17 and 19 are Fourier transform lenses, and 18 is an aperture. . The other elements are the same as in FIG.

  In FIG. 5, the signal light wave is converged linearly in the vertical direction perpendicular to the light irradiation direction by the cylindrical lens 13 and the lens 5, and is irradiated onto the subject 6 made of, for example, a non-uniform constituent material. The light internally reflected from the subject 6 is collected by the lens 5 and projected onto the detection surface of the optical array sensor 12 via the cylindrical lens 13 and the semitransparent mirror 11.

FIG. 6 depicts the transmission of light on the signal light wave side with respect to the XZ plane and the YZ plane with reference to the orthogonal axes in the figure. In FIG. 6, the irradiation of the signal light onto the subject 6 and the capture of the internally reflected light from the subject 6 are illustrated continuously from the left to the right in the figure. The cylindrical lens 13 having the focal length f ₁ and the lens 5 having the object-side focal length f _2b and the image-side focal length f _2f not only irradiate the object 6 with the linear convergent beam but also the linear convergent beam irradiation position. These images are arranged on the detection surface of the optical array sensor 12. On the other hand, as shown in FIG. 5, the reference light wave enters the diffraction grating 9 via the delay mechanism (7, 8), and the first-order diffracted light is incident on the optical array sensor 12 by the imaging lens system (17, 19). An image is formed on the detection surface. The reference light wave and the signal light wave are combined by the translucent mirror 11 and interfered and detected on the two-dimensional optical array sensor 12. In one direction of the two-dimensional light receiving elements of the two-dimensional optical array sensor 12, an interference signal of a deep tomographic reflected light distribution corresponding to the light irradiation axis direction of the subject 6, that is, the Z-axis direction, is present in the other direction. Interference signals corresponding to the direction in which the linear light wave is irradiated are projected, and these interference signals are detected in parallel by the respective light receiving elements with two-dimensional coordinates.

  In this embodiment, as described above, the two-dimensional tomographic image of the subject 6 can be detected in parallel at high speed without scanning. The delay mechanism composed of the semitransparent mirror 7 and the reflecting mirror 8 is used to determine the scanning start position for tomographic detection on the Z axis. Furthermore, by moving the subject 6 in the Z-axis direction, measurement can be performed even if the examination position is controlled in the same manner.

  Further, in the embodiment of FIG. 5, the imaging optical system between the reference light wave side of FIG. 1 according to the present invention and the detection surface of the diffraction grating 9 and the optical array sensor 12 is changed to a 4f optical system (17, 19). is there. By arranging an opening 18 having an appropriate diameter on the Fourier transform surface side of the lens 17, it has an effect of removing scattered light other than the first-order diffracted light wave from the diffraction grating 9.

  FIG. 7 shows an embodiment in which a subject incident point scanning mechanism is provided in the coaxial spatial optical coherence tomographic image measuring apparatus of FIG. 5 of the present invention. In FIG. 7, reference numerals 15 and 16 may be composed of deflection control movable mirrors (for example, galvano mirrors). For example, when linear irradiation is performed on the subject 6 in the Y-axis direction as shown in FIG. 6, the movable mirror 15 or 16 is tilted, and the irradiation position is deflected to sequentially move the irradiation point and scan. Then, 3D tomographic image information can be acquired, and these signals can be integrated and processed to display a 3D tomographic image at an arbitrary angle.

  FIG. 8 shows an embodiment based on polarization control using a band polarization beam splitter in the coaxial spatial optical coherence tomographic image measuring apparatus of FIG. 5 according to the present invention.

  In FIG. 8, 20 is a broadband polarization beam splitter (PBS), 21 is a translucent reflecting mirror, and 22 is a λ / 4 wavelength plate. The other elements are the same as in FIG. Reference numeral 44 denotes a reflecting mirror.

  The output of a low coherent light source such as an SLD or LED is generally non-polarized, i.e., does not have a specific electric field vector direction component, i.e. linear polarization. In FIG. 8, the light from the low-coherent light source 1 is divided into an S-polarized component and a P-polarized component by the PBS 20 so that the reference light wave has an S-polarized component and the signal light wave has a P-polarized component. The signal light wave of the linear P-polarized component passes through the λ / 4 wavelength plate 22 and is converted into circularly polarized light, and is condensed into a linear shape by the cylindrical lens 13 and the lens 5 and enters the subject 6.

  On the other hand, the circularly polarized signal light wave reflected from the subject 6 passes through the lens 5 and the cylindrical lens 13 again, and then passes through the λ / 4 wavelength plate 22 again to be converted into linear S-polarized light. On the other hand, the reference light wave having linear S-polarized light passes through the transmissive diffraction grating 9, and is combined with the signal light wave having the same linear S-polarized light by the semitransparent mirror 21, and the interference signal is the same as in the case of FIG. Is detected. In this embodiment, by using the broadband polarizing beam splitter 20 and the λ / 4 wavelength plate 22, the polarization direction of the incident light on the subject 6 can be controlled, and the internal structure of the subject 6 can be detected with high efficiency. This is an extremely effective method for detecting that the subject 6 has birefringence characteristics and the like.

  FIG. 9 shows the coaxial spatial optical coherence tomographic image measuring apparatus of FIG. 5 according to the present invention, in which the reflecting mirror 8 in the delay mechanism is arranged on the high-speed vibration mechanism 23 and the frequency of the interference signal is shifted by the operation of the vibration mechanism 23 This is an embodiment having a function of separating an interference component from a direct current component caused by background light.

  In FIG. 9, 23 is a high-speed vibration mechanism, 24 is a reflecting mirror, and 25 is a reflection type diffraction grating. The other elements are the same as in FIG.

  In FIG. 9, the output from the low coherent light source 1 is divided into a reference light wave and a signal light wave by the semi-transparent mirror 3. The reference light wave enters the delay mechanism (7, 8). The reflecting mirror 8 in the delay mechanism is disposed on a high-speed vibration mechanism (for example, a piezo vibrator) 23, and the light returning from the high-speed delay mechanism 23 is subjected to phase modulation by the optical path length being slightly expanded and contracted by the piezo vibrator. The phase-modulated reference light wave is then incident on the reflective diffraction grating 25, and the first-order diffracted light forms an image on the detection surface of the optical array sensor 12 by the 4f optical system (17, 19).

  In this embodiment, by periodically vibrating a high-speed vibration mechanism 23 such as a piezo vibrator, the reference light wave is periodically phase-modulated, and the optical interference signal detected by the optical array sensor 12 is phase-modulated. By selectively detecting this AC signal, only the interference component can be separated and detected from the interference signal in which the background light and the signal component overlap as shown in the above equation (6).

  On the other hand, phase shift detection can also be introduced. By scanning a high-speed vibration mechanism 23 such as a piezo vibrator discretely, a plurality of interference signals having different phases are detected, and by calculating these interference signals, an interference signal in which background light and signal components overlap is detected. Only interference components can be separated and detected.

  Further, the embodiment of FIG. 9 uses the reflective diffraction grating 25 with high diffraction efficiency instead of the transmissive diffraction grating 9 of FIG. 4 according to the present invention, and can obtain the effect of increasing the intensity of the reference light wave and increasing the SN ratio. It is.

  In FIG. 9, the reference light wave returning from the delay mechanism (7, 8) is reflected by the reflecting mirror 24 and is applied to the reflective diffraction grating 25. For example, first-order diffracted light from the reflective diffraction grating 25 is projected onto the detection surface by the two lenses (17, 19), and an interference signal with the signal light wave is detected.

  In addition, this invention is not limited to the said Example, A various deformation | transformation and combination are possible based on the meaning of this invention, These are not excluded from the scope of the invention.

  The coaxial spatial light coherence tomographic image measurement apparatus of the present invention can be used as a tool for biological image diagnosis using light waves.

It is a figure which shows the coaxial optical space coherence tomographic image measuring apparatus using the spatial correlation wave which shows the Example of this invention. It is a figure which shows the principle of generation | occurrence | production of the delayed correlation wave front depending on the light irradiation position to the transmission type diffraction grating concerning this invention. It is a figure which shows the wavelength dispersion correction | amendment by the side of the reference light wave and the multiplexing of a signal light wave which are the principles of this invention. It is an Example figure of the optical axis direction non-scanning tomographic image measuring apparatus of this invention. It is a figure which shows the Example which introduce | transduced the cylindrical lens system for the two-dimensional tomographic image measurement to the signal light wave side of the coaxial optical space coherence tomographic image measuring apparatus of FIG. 1 by this invention. It is a figure shown about the imaging optical system of the coaxial optical space coherence tomographic image measuring apparatus of FIG. 6 shows an embodiment in which a subject incident position scanning mechanism is provided in the coaxial optical space coherence tomographic image measurement apparatus of FIG. 5 of the present invention. It is a figure which shows the Example which used polarization control for the coaxial type optical space coherence tomographic image measuring apparatus of FIG. 5 by this invention. FIG. 6 is a diagram showing an embodiment in which a high-speed vibration mechanism for separating interference components is used on the reference light wave side of the coaxial optical space coherence tomographic image measurement apparatus of FIG. 5 according to the present invention. It is a figure which shows the basic composition of the optical coherence tomographic image measuring apparatus using a Michelson interferometer. It is a figure which shows the basic composition and the principle of the off-axis interferometer using the conventional low coherent light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low coherent light source 2,5,10 Lens 3,7,11,21 Translucent mirror 4,8,24,44 Reflector 6 Subject 9 Transmission type diffraction grating 12,14 Optical array sensor 13 Cylindrical lens 15,16 X -Movable mirror for Y-plane scanning (galvano mirror)
17, 19 Fourier transform lens 18 aperture 20 broadband polarization beam splitter (PBS)
22 λ / 4 wavelength version 23 High-speed vibration mechanism (piezo vibrator)
25 Reflective diffraction grating

Claims (17)

  In an interferometric optical system for tomographic image measurement by optical interferometry using a light source having a wide wavelength width, an equiphase surface of diffracted light that delays the reference light wave through the diffraction grating and depends on the incident position of the diffraction grating A diffracted light wave having a correlation wave front that contributes to interference with the signal light wave that forms an angle with the signal light wave is generated, and the diffracted light wave is interfered substantially coaxially with the signal light wave to generate a spatial interference signal localized at the position depending on the delay. And a coaxial spatial light coherence tomographic image measuring apparatus, characterized in that a coaxial interference system is configured. (A) a light source that emits a light wave having a wide wavelength bandwidth;
(B) a lens that enlarges the beam diameter of the light wave emitted from the light source and converts it into a parallel light beam;
(C) The parallel light beam is divided into a signal light wave that follows an optical path in which the subject is arranged and a reference light wave that is different from an optical path that passes through the subject and that follows an optical path in which a diffraction grating is arranged, and the reference The space that contributes to interference with the signal light wave that forms an angle with the phase wavefront by further passing the reference light wave that has passed through the delay mechanism composed of a translucent mirror and a reflecting mirror for adjusting the optical path length of the light wave, through the diffraction grating A delayed correlation wavefront is provided, and a reference light wave having the spatial delay correlation wavefront and a signal light wave irradiated to the subject and back-scattered from the inside or a signal light wave forward-scattered from the inside thereof are combined in a substantially coaxial manner and spatially combined. An interference optical system for generating a simple interference signal;
(D) an optical array sensor in which a large number of light receiving elements are arranged spatially for receiving and detecting interference light generated by the interference optical system;
(E) a signal processing system that integrates and processes optical interference signals detected by a large number of light receiving elements of the optical array sensor, and forms morphological information on the surface or inside of the subject at the position irradiated with the signal light wave; A coaxial spatial light coherence tomographic image measuring apparatus comprising:   On the reference light wave side of the interference optical system, in order to correct the wavelength dispersion of the diffracted light generated by the reference light wave passing through the diffraction grating, the diffracted light from the diffraction grating is applied to the optical array sensor by the lens system. The coaxial spatial light coherence tomographic image measuring apparatus according to claim 1, wherein the coaxial spatial optical coherence tomographic image measuring apparatus is projected.   The interference optical system irradiates a light wave incident on the subject through a lens system on the signal light wave side, condenses the signal light wave from the subject using the lens system, and further provides a cylindrical lens system. The coaxial spatial optical coherence tomographic image measuring apparatus according to claim 3, wherein the coaxial spatial optical coherence tomographic image measuring apparatus is used to project onto a detection surface of the optical array sensor.   The interference optical system uses, on the signal light wave side, a cylindrical lens and a condensing lens to narrow down a light wave incident on the subject in a vertical direction perpendicular to the incident direction of the light wave, and the subject 4. The coaxial spatial light coherence tomographic image measurement according to claim 3, wherein the signal light wave from the light beam is condensed using a lens system, and further projected onto the detection surface of the optical array sensor using the cylindrical lens. apparatus.   6. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 4, further comprising a mechanism for deflecting and scanning a light wave incident on the subject.   5. The coaxial spatial optical coherence tomographic image measurement apparatus according to claim 4, wherein the optical array sensor is an optical array sensor in which light receiving elements are spatially linearly arranged and spatial interference signals can be detected independently and in parallel. The detection surface of the optical array sensor is disposed on the surface on which the reference light wave from the diffraction grating and the signal light wave from the subject are projected, and the light detected by the light receiving elements arranged in one direction of the optical array sensor. The interference signal is formed by integrating and processing to form morphological information in the propagation direction at the signal light wave irradiation position of the subject. The signal light wave irradiation position is sequentially moved by the deflection scanning to detect the signal light wave. A coaxial spatial light coherence tomographic image measuring apparatus that constructs a two-dimensional tomographic image by integration and processing.   6. The coaxial spatial optical coherence tomographic image measurement apparatus according to claim 5, wherein the optical array sensor is a two-dimensional optical array in which light receiving elements are spatially two-dimensionally arranged and spatial interference signals can be detected independently and in parallel. A detection surface of the two-dimensional optical array sensor is disposed on a surface on which a first-order diffracted reference light wave from the diffraction grating and a signal light wave from the subject are projected, and is in one direction of the two-dimensional optical array sensor The optical interference signals detected by the light receiving elements arranged in a line are integrated and processed to construct form information of the propagation direction at the signal light wave irradiation position of the subject, while the other one of the two-dimensional optical array sensors. The optical interference signals detected by the light receiving elements arranged in the direction are integrated and processed by a signal processing unit that constructs vertical shape information perpendicular to the light propagation direction at the linear signal light wave irradiation position of the subject. Specially provided Coaxial type spatial light interference tomographic image measuring apparatus according to.   9. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 8, wherein the interference optical system is configured to cause a light wave incident on the subject or the subject to be perpendicular to the propagation direction of the light wave on the reference light wave side. A coaxial spatial light coherence tomographic image measuring apparatus having a function of acquiring three-dimensional morphological information of the subject by two-dimensional scanning.   The coaxial spatial light coherence tomographic image measuring apparatus according to claim 1, wherein the interference optical system includes a polarization element that controls a polarization direction of a light wave applied to the subject. Image measuring device.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the interference optical system gives a frequency shift to a spatial interference signal by expanding and contracting an optical path length difference between the reference light wave and the signal light wave by a vibration mechanism. A coaxial spatial light coherence tomographic image measuring apparatus comprising a shifter and having a function of extracting only interference components from background light.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the light source is a super luminescent diode having a coherence distance of 100 [mu] m or less.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the light source is a light emitting diode having a coherence distance of 50 [mu] m or less.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the subject is a light scattering medium.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, further comprising a delay mechanism that scans an optical path length difference between the reference light wave and the signal light wave.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the optical array sensor is constituted by a CCD or a MOS element.   3. The coaxial spatial light coherence tomographic image measurement apparatus according to claim 2, wherein the optical array sensor is an imaging device with an electron multiplication mechanism.

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