JP2006250849A - Optical image measuring method using light coherence tomography apparatus and optical image measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical image measuring method using a light coherence tomography apparatus of extracting an image only of an interference signal component by removing the component due to background noise light by applying the inter-pixel operation of an image, which contains a spatial interference fringe, automatically formed by predetermined spatial frequency only by acquiring one spatial interference image without requiring a detailed movable mirror by an electrostatic method without relying on mechanical operation, and also to provide an optical image measuring device. <P>SOLUTION: In an interference optical system using a light source with a wide band wavelength range, a reference light wave is passed through a diffraction grating 9 and a diffracted light wave, which is delayed in dependence on the incident position of the diffraction grating 9 and has a spatial delay correlation wave front contributing to the interference with a matter light wave, which forms an angle with respect to the equal phase front of diffracted light, is formed to be combined with and allowed to interfere with the reference light wave so as to form a predetermined angle with respect to the matter light wave. Optical array sensor elements 12 are arranged at every appropriate phase position of the spatial cycle of the spatial interference fringe due to these two luminous fluxes and the signals at every phase from the optical array sensor elements 12 are detected and mutually operated to draw the interference signal intensity distribution or phase distribution of two luminous fluxes in a real time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical image measurement method using an optical coherence tomography apparatus and an apparatus therefor.

  An optical coherence tomography apparatus using a light source having a wide wavelength range has been developed, is currently put into practical use, is used in the medical field, and is widely used (for example, Patent Document 1 and Non-Patent Document 1 below). In a conventional optical coherence tomography apparatus (for example, Patent Document 2 below) based on a one-dimensional tomographic distribution measurement method using generation of a spatial correlation wave by a diffraction grating, the reference light and the object light are coaxially caused to interfere with each other. In this method, the optical path length is displaced by about the wavelength, an image is acquired each time, and then a normal phase shift method is applied to remove the DC component due to the background noise light component to extract the interference signal image. .

  FIG. 5 is a schematic diagram of a conventional coaxial spatial light coherence tomographic image measurement apparatus using a spatial correlation wave by a diffraction grating.

In this figure, 101 is a broadband wavelength light source (for example, an SLD (super luminescent diode) light source), 102 is a light beam magnifying lens, 103 is a half mirror, 104 is a mirror, 105 is an objective lens, 106 is an object to be measured, 107 Is a half mirror, 108 is a movable mirror, 109 is a diffraction grating, 110 is a lens, 111 is a half mirror, and 112 is an optical array sensor.
Patent No. 20110042 Japanese Patent Application No. 2004-249545 Optics, Vol. 28, No. 3, 1999 pp. 116-125

  However, in the conventional coaxial spatial coherence tomographic image measuring apparatus described above, the movable mirror 108 is mechanically moved in the optical axis direction by about 1/2 to 1/4 of the light wavelength of the light source, and the image distribution is changed each time. After observing and storing in an image recording medium, for example, between three images, a phase shift image calculation by this mechanical optical path length change is performed to remove a component due to background noise light, and only an interference signal component is obtained. The image had to be extracted.

  In addition, it takes time to acquire an image, and the object to be measured needs to be stationary while recording each of the three images, and precise mechanical control of the movable mirror at the optical wavelength level is required. There was a problem such as need.

  In view of the above situation, the present invention is not limited to mechanical operation, is a static electrical method, does not require a fine movable mirror, and only acquires a single spatial interference image. Using an optical coherence tomography device that removes the component due to background noise light and extracts only the interference signal component by performing inter-pixel calculation on the image including the spatial interference fringes automatically generated at the spatial frequency of It is an object of the present invention to provide an optical image measurement method and apparatus.

In order to achieve the above object, the present invention provides
[1] In an optical image measurement method using an optical coherence tomography apparatus, in an interference optical system using a light source with a wide wavelength range, a reference light wave is delayed through a diffraction grating depending on the incident position of the diffraction grating. A diffracted light wave having a spatially delayed correlation wave front that contributes to interference with the object light wave that forms an angle with the equiphase surface of the diffracted light is generated, and is combined with the object light wave at a predetermined angle to cause interference. An optical array sensor element is arranged for each appropriate phase position of the spatial period of the spatial interference fringes, and a signal for each phase from each optical array sensor element is detected and calculated mutually, whereby the interference signal of the two light fluxes It is characterized by drawing intensity distribution and phase distribution.

  [2] In an optical coherence tomography apparatus, a light source that emits a light wave having a wide wavelength bandwidth, a lens that converts the light emitted from the light source into a parallel light beam, and the parallel light beam through an optical path on which an object to be measured is placed The object light wave to be traced and the reference light wave to be traced along the optical path on which the diffraction grating is arranged are divided into two, the object light wave reflected from the object to be measured, and the diffraction grating through the delay mechanism for adjusting the reference optical path length. An interference optical system that crosses and interferes with a reference light wave having a spatially delayed correlation wavefront at a predetermined angle, and an optical array sensor element disposed at each appropriate phase position of the spatial period of the spatial interference fringes by the two light beams A computing means for mutually computing signals for each phase from the respective optical array sensor elements, and a computer and a display device for imaging the signal intensity distribution and phase distribution from the computing means, Characterized by comprising.

  [3] The optical coherence tomography device according to [2], wherein the calculation means includes a digital calculation electronic circuit.

  [4] In the optical coherence tomography device described in [2], a digital operation program is used as the operation unit.

  [5] The optical coherence tomography device according to [2], further comprising: a lens system that substantially Fourier transforms-inverses Fourier transforms a diffracted light wave from the diffraction grating in the reference light path; Projecting on the array sensor element surface is characterized.

  [6] The optical coherence tomography device according to [2], wherein the interference optical system includes means for scanning a surface perpendicular to the optical axis direction when irradiating an object light wave on an object to be measured. Features.

  According to the present invention, a single spatial interference image can be obtained by a static electrical method and without changing the optical path length that must be controlled in the wavelength order without relying on conventional mechanical operations. By simply acquiring the image, it automatically performs an inter-pixel calculation on the image including the spatial interference fringes that is automatically generated at a predetermined spatial frequency, removes the component due to background noise light, and creates an image with only the interference signal component in real time. Observable. Furthermore, this device can be easily and inexpensively put into practical use, used in many medical settings, and can provide a useful diagnostic effect for doctors and patients.

  An optical coherence tomography apparatus of the present invention includes a light source that emits a light wave having a wide wavelength bandwidth, a lens that converts the light emitted from the light source into a parallel light beam, and the parallel light beam through an optical path on which an object to be measured is disposed. The object light wave to be traced and the reference light wave to be traced on the optical path on which the diffraction grating is arranged are divided into two parts. The object light wave reflected from the object to be measured and the diffraction grating through the delay mechanism for adjusting the reference optical path length. Interferometric optical system that crosses and interferes with a reference light wave having a spatially delayed correlation wavefront at a predetermined angle, and an optical array sensor element arranged at each appropriate phase position of the spatial period of the spatial interference fringes by the two light beams And computing means for mutually computing signals for each phase from the respective optical array sensor elements, and a computer and a display device for imaging the signal intensity distribution and phase distribution from the computing means. To. Therefore, it is possible to perform an electronic inter-pixel calculation of an image including a spatial interference fringe automatically generated at a predetermined spatial frequency, remove a component due to background noise light, and observe an image of only an interference signal component in real time.

Hereinafter, embodiments of the present invention will be described in detail.
[Example 1]
FIG. 1 is a schematic diagram of an optical coherence tomography apparatus based on image measurement according to the present invention.

  In this figure, 1 is a broadband wavelength light source (for example, an SLD (super luminescent diode) light source), 2 is a light beam magnifying lens, 3 is a first half mirror (half mirror for splitting), 4 is a reflection mirror 5 Objective lens, 6 is an object to be measured, 7 is a second half mirror, 8 is a movable mirror, 8a is a drive mechanism for the movable mirror 8, 9 is a diffraction grating (in this embodiment, a transmission type is exemplified), and 10 is a connection An image lens, 11 is a third half mirror, 12 is an optical array sensor, 12a is, for example, a digital arithmetic circuit, and 12b is a computer and a display device.

  The light from the broadband wavelength light source 1 serving as a short coherence light source is expanded into a substantially parallel light beam by the light beam expanding lens 2 and divided into two by the first half mirror 3. The light beam that becomes the reference light is returned by the movable mirror 8 through the second half mirror 7, and the reference optical path length is adjusted by the drive mechanism 8 a of the movable mirror 8 to adjust the length of the reference optical path, and is reflected and diffracted by the second half mirror 7. Incident on the grating 9. The transmitted light from the diffraction grating 9 generates a spatially delayed correlation wavefront and is projected onto the optical array sensor 12 by the lens 10. On the other hand, the light beam that becomes object light is reflected by the reflecting mirror 4 and is irradiated onto the object 6 to be measured by the objective lens 5. Reflected object light from the surface or deep layer of the object to be measured 6 is collected by the objective lens 5, reflected by the third half mirror 11 inclined at a predetermined angle, and incident on the optical array sensor 12. At this time, it intersects with the reference light at a predetermined angle and multiplexes and interferes, and interference fringes are detected by square detection of the optical array sensor.

  In this embodiment, an example is shown in which an SLD is used as a broadband wavelength light source. However, it is obvious that a laser having a wide wavelength width and a short coherence length may be used as the light source.

Figure 2 is an illustration of the state of the interfering wavefronts of the reference beam e _r and the object beam e _s of the present invention.

  The spatial delay correlation wavefront 9a propagates with an inclination with respect to the propagation direction. On the other hand, the object light propagates with a delay of the reflected wavefront 6a from the deep layer. In the wave fronts where the combined interference occurs, the object light interferes with the perpendicularly incident reference light at the crossing angle θ on the sensor surface. When the intersection angle is zero degree, as shown in FIG. 3 of Patent Document 2, for example, one interference intensity distribution of Gaussian distribution is observed at the output of the optical array sensor at the intersection of both. However, in the present embodiment, the spatial interference fringes 12c are observed in the Gaussian distribution by intersecting at a predetermined angle.

This interference fringe becomes a light and dark fringe with a spatial frequency period λ _S (= λ / sin θ, λ: center wavelength of the light source) based on interference. In accordance with this period λ _S , for example, each element of the optical array sensor is arranged every λ _s / 4. If the element spacing of the optical array sensor 12 is a predetermined one, the crossing angle θ is appropriately adjusted to match the cycle. For example, if the central wavelength λ of the light source is 0.8 μm and the period length of one element of the optical array sensor is 10 μm, the crossing angle θ is set to 0.57 degrees, so that the phase is set to every λ _s / 4. It can be output from each element in which outputs every 90 degrees are arranged. Now, assuming that the wave number of the spatial frequency is ks (= 2π / λ _S ), an output In _{n including} an interference term from an element in n rows and m columns of the optical array sensor is expressed as follows. The

I _{n, m} = D _{n, m} + A _{n, m} cos (kz + φ−ksz) (1)
Here, D _{n, m} is a DC component including background noise light, A _{n, m} is an amplitude intensity of an interference component including image information, k is a wave number (= 2π / λ), and z is a depth direction of the measured object. The distance in the m-row direction on the optical array sensor surface proportional to the distance, φ is the initial phase.

  Consider performing the mutual operation of the following expression on the output detected by each element of the optical array sensor 12.

I _ac = (I _{n, m} −1 _{n, m + 1} ) ² + (I _{n, m + l} −I _{n, m + 2} ) ² (2)
Φ = tan ⁻¹ [(I _{n, m + 1} −I _{n, m + 2} ) / (I _{n, m} −I _{n, m + l} )] (3)
As a result, the interference light component 4 (A _{n, m} ) ² from which the direct current component is removed is observed in the output I _ac of the equation (2), and the direct current component is similarly applied to the output Φ of the equation (3). The removed phase distribution Φ is observed. The intensity and phase of each interference component for each pixel can be obtained by performing the above calculation while shifting the output from each element one by one or plural.

  Since such an operation is a linear operation, it is easy to execute with an existing digital arithmetic electronic circuit, and it is also easy to execute with an arithmetic program of a computer. Such a digital arithmetic circuit 12a is provided, and further a computer and a display device 12b are provided to measure the image distribution in the m column direction, and thus in the depth direction of the measured object.

As another calculation method, when the DC component of the background noise varies from element to element, the movable mirror 8 in FIG. 1 is moved by the drive mechanism 8a to shorten the reference optical path length, and at first the object reflected light is reduced. Set to avoid interference. In this way, the DC component D _{n, m} may be observed in advance _, and the calculation of the following equation may be executed.

I _ac = (I _{n, m} −D _{n, m} ) ² + (I _{n, m + 1} −D _{n, m + l} ) ² (4)
Φ = tan ⁻¹ [(I _{n, m + 1} −D _{n, m + 1} ) / (I _{n, m} −D _{n, m} )] (5)
In this case, the element period of the optical array sensor may be detected by setting the period λs / 2 of the spatial frequency.

In the present embodiment, the method of forming the interference fringes by inclining the third half mirror 11 in the XZ plane by θ in the coordinate system shown in FIG. 1 is described. However, the third half mirror 11 is formed in the YZ plane. It is obvious that the same result can be obtained even if the half mirror 11 is inclined by θ to form interference fringes.
[Example 2]
FIG. 3 is a configuration diagram of an optical coherence tomography apparatus based on image measurement in which the Fourier transform reference light of the present invention is arranged.

  In FIG. 3, 13 is a cylindrical lens, 17 is a Fourier transform lens, 18 is a spatial filter, and 19 is a Fourier inverse transform lens. The other components are the same as in FIG.

  With this configuration, the spatially delayed correlation wave from the diffraction grating 9 is Fourier transformed by the Fourier transform lens 17 to form a diffraction image on the focal plane. A spatial filter 18 is disposed on the diffracted image to transmit substantially zero-order diffracted light, and a substantially plane wave is applied to the detection surface of the optical array sensor 12 by the Fourier inverse transform lens 19. As a result, a plane wave having a substantially uniform intensity distribution on the detection surface is obtained as reference light, and ideal interference fringes can be automatically formed in spatial interference with object light.

In the present embodiment, the cylindrical lens 13 is further arranged to irradiate the object in a slit shape with the object light as a strip-shaped intensity cross section. By this irradiation, the tomographic reflection distribution light on the XZ plane of the deep object is projected onto the detection surface of the optical array sensor 12. By using such slit-like object light, a two-dimensional tomographic image of the XZ plane can be obtained in real time without providing another mechanical optical delay device or a one-dimensional scanning mechanism. It is clear that a tomographic image of an arbitrary fracture surface can be observed by appropriately rotating the cylindrical lens 13 with respect to the optical axis.
Example 3
FIG. 4 is a configuration diagram of an optical coherence tomography apparatus based on image measurement in which an XY plane scanning mechanism for determining an object irradiation position according to the present invention is arranged.

  In FIG. 4, 15 is an X-axis scanning mirror, and 16 is a Y-axis scanning mirror, which is constituted by a galvanometer mirror, for example. When the object light is irradiated onto the surface of the object 6 to be measured in the slit shape, it can be used as a plane perpendicular to the optical axis, that is, an XY plane light beam scanning mechanism to determine the position of the fracture surface to be observed. The other components are the same as in FIG.

  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 optical image measurement method and apparatus using the optical coherence tomography apparatus of the present invention can be widely used in the medical field.

It is a schematic diagram of the optical coherence tomography apparatus by the image measurement of this invention. It is a diagram showing a state of interfering wave fronts of the reference beam e _r and the object beam e _s of the present invention. It is a schematic diagram of the optical coherence tomography apparatus by the image measurement which has arrange | positioned the Fourier-transform reference light of this invention. It is a schematic diagram of the optical coherence tomography apparatus by image measurement which has arrange | positioned the XY plane scanning mechanism which determines the object irradiation position of this invention. It is a schematic diagram of a coaxial spatial optical coherence tomographic image measurement apparatus using a spatial correlation wave by a conventional diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Broadband wavelength light source 2 Light beam expansion lens 3 1st half mirror 4 Reflecting mirror 5 Objective lens 6 Object to be measured 7 2nd half mirror 8 Movable mirror 8a Movable mirror drive mechanism 9 Diffraction grating 10 Imaging lens 11 3rd Half mirror 12 Optical array sensor 12a Digital arithmetic circuit 12b Computer and display device 12c Spatial interference fringe 13 Cylindrical lens 15 X axis scanning mirror 16 Y axis scanning mirror 17 Fourier transform lens 18 Spatial filter 19 Fourier inverse transform lens

Claims (6)

  In an interference optical system using a light source with a wide wavelength range, interference with an object light wave that forms an angle with the equiphase surface of the diffracted light, which 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 spatially delayed correlation wavefront that contributes to the light is generated and combined with the object light wave at a predetermined angle to cause interference, and an optical array sensor for each appropriate phase position of the spatial period of the spatial interference fringes by the two light beams An optical coherence tomography characterized in that an element is arranged, and an interference signal intensity distribution and a phase distribution of the two light fluxes are drawn by detecting a signal for each phase from each optical array sensor element and calculating each other. Optical image measurement method using the apparatus. (A) a light source that emits a light wave having a wide wavelength bandwidth;
(B) a lens that converts light emitted from the light source into a parallel light beam;
(C) The parallel light beam is divided into two, an object light wave that follows an optical path in which the object to be measured is arranged and a reference light wave that follows an optical path in which a diffraction grating is arranged, and the object light wave reflected from the object to be measured is referred to An interference optical system that crosses a reference light wave having a spatially delayed correlation wavefront through a diffraction mechanism via a delay mechanism for adjusting an optical path length and intersects at a predetermined angle,
(D) an optical array sensor element disposed at each appropriate phase position of the spatial period of the spatial interference fringes by the two light beams;
(E) computing means for mutually computing signals for each phase from the respective optical array sensor elements;
(F) An optical coherence tomography apparatus based on an optical image measurement method, comprising a computer and a display device for imaging a signal intensity distribution and a phase distribution from the calculation means.   3. An optical coherence tomography apparatus using an optical image measurement method according to claim 2, wherein the arithmetic means comprises a digital arithmetic electronic circuit.   3. An optical coherence tomography apparatus using an optical image measurement method according to claim 2, wherein the calculation means uses a digital calculation program.   3. The optical coherence tomography apparatus according to claim 2, further comprising: a lens system that substantially Fourier transform-Fourier inversely transforms a diffracted light wave from the diffraction grating in the reference light path; and a spatial filter, An optical coherence tomography apparatus based on an optical image measurement method, which projects onto an optical array sensor element surface.   3. An optical coherence tomography apparatus according to the optical image measurement method according to claim 2, wherein said interference optical system comprises means for scanning with a plane perpendicular to the optical axis direction when irradiating an object light wave on an object to be measured. An optical coherence tomography device using an optical image measurement method.

Images