JPH0749306A - Light wave echotomography apparatus - Google Patents

Abstract

PURPOSE:To enable the extraction of positional information of points of an interface layer with higher resolutions by making a multi-mode laser oscillation light irradiate to perform a heterodyne detection of a beat component between reflected light from points in depth of a scattering object and a reference light. CONSTITUTION:Multi-mode laser light from a light source 1 is divided in two 3 and one part thereof is used as reference light wave while the other part thereof is made to irradiate an object 4 to be measured and is scattered at each boundary of layers with different refractive indexes while partially turning to reflected light wave. Phases of multiple modes of reflected light wave are delayed according to the position of the boundary. The reflected light wave is introduced to a light spectrum analyzer 7a together with the reference light wave and the reflected light analyzed spectrally at each mode and the reference light shifted in frequency are emitted therefrom to be introduced to a photodetector 7b. Here, the reflected light is subjected to a heterodyne detection at high efficiency only confined to the component along matching a plane wave component of the reference light wave with higher spatial coherence. The signal subjected to an A/D conversion 8c of a spectrum output of each mode undergoes a Fourier inverse transform with a computer 9 and the results are stored 10 in a time series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a multimode laser oscillator as a light source to irradiate an object to be measured, such as a tissue structure of a living body, and detects a reflection distance and a reflection intensity of a reflected light wave from the object to be measured. The present invention relates to an apparatus, and more particularly, to an optical echography apparatus (light wave reflection image measuring apparatus) using a heterodyne detection light receiving system or a highly directional light receiving system and an interferometer.

[0002]

2. Description of the Related Art There is a method of obtaining a tomographic image by irradiating a laser beam instead of an X-ray source and detecting transmitted light with high sensitivity by an optical heterodyne method. For example, Japanese Patent Application No. 1-250036,
Alternatively, the IEICE Transactions C-1 Vol. J7
4-C-1 No. 4 pp. 137-150 199
See April 1st. Japanese Patent Application No. 2-300169 discloses a method for obtaining a tomographic image from a surface to a certain depth by using heterodyne detection for backscattered light using spar luminescence light instead of using these transmitted light. . By the same method as this method, tomographic imaging near the surface of the human retina or the blood vessel wall is performed by M. I. T. (Science, 254, pp. 1178).
~ 1181, 1991). Since this method uses spar luminescence as a light source, the wavefront matching condition of partial coherence determines the beat component of heterodyne detection, and determines the distance resolution of the reflected light from each point in the depth direction of the scattering object. However, since the light source is partially coherent, on the contrary, alignment for wavefront matching is very difficult, and a movable reflecting mirror is always required as a reference light generating means to generate a beat signal. There are problems such as being

On the other hand, as a method for remotely measuring the position information of the measuring object, an optical interferometer is used to sweep the frequency of the laser light linearly or stepwise to sweep the reflected signal light. There is a method of detecting a phase delay and converting it into position information.

Lasers used for these purposes have been required to be narrow-band single-mode lasers capable of sweeping in a wide band in order to increase spatial resolution and observe signals with a good SN ratio. However, the multi-mode laser oscillation phenomenon is essentially present in the laser oscillator, and is a factor that hinders wideband sweeping in the current technology. That is, due to these restrictions, there is a limit to improving spatial distance resolution. Moreover, in order to apply these methods to a light wave echography to obtain a light wave reflection image based on the reflection distance and the reflection intensity by applying the method to a biological sample, the influence of the scattering component peculiar to the biological sample is removed, and the refractive index It is necessary to selectively detect the reflected light from different points.

[0005]

The present invention has been made in view of such a situation, and an object thereof is to refract in an object to be measured in which the influence of a scattering component peculiar to a biological sample is removed. An object of the present invention is to provide a light wave echography apparatus (light wave reflection image measuring apparatus) that obtains position information of boundary surfaces having different rates with high resolution.

[0006]

In order to solve the above-mentioned problems, the present invention provides a multimode oscillation laser beam as irradiation light,
Irradiation means for irradiating a scattering object composed of layers having different refractive indexes, generating means for generating reference light with the frequency of the irradiation light shifted, and reflection from a point having a different refractive index in the depth direction inside the scattering object. Combining means for combining light and reference light, spectroscopic means for spectrally separating the combined light for each mode, and conversion for photoelectrically converting the combined light in each mode output from the spectroscopic means Means, means for storing the magnitude of the beat component output from this photoelectric conversion means for each mode, and inverse Fourier transform of the distribution of the component for each mode to obtain the depthwise refractive index of the scattering object. The means for obtaining the reflection information at different points and the means for scanning the multimode laser light or the sample so that the positions of the scattering object, which is the multimode laser light, and the sample relatively change, are scanned to obtain the light wave And measuring the over tomography (light wave reflected image).

The light wave echography apparatus (light wave reflection image measuring apparatus) of the present invention includes an irradiation means for irradiating a scattering object composed of layers having different refractive indexes as irradiation light with multimode laser light, and one of the irradiation light. A high directivity that removes random backscattered light from the scattering object and generates only reference light that is transmitted from a point having a different refractive index in the depth direction. Light receiving system means, means for combining reflected light and reference light emitted from the highly directional light receiving system means, spectroscopic means for separating the combined light into each mode, and output from the spectroscopic means. Conversion means for photoelectrically converting the combined light, means for storing the magnitude output from this photoelectric conversion means for each mode, and inverse Fourier transform of the distribution of the components of each mode Means for obtaining reflection information at points having different refractive indexes for directions, and means for scanning the multimode laser light or the sample so that the positions of the multimode laser light and the scattering object which is the sample to be measured are relatively changed And scanning by the scanning means to measure light wave echography (light wave reflection image) of the scattering object.

[0008]

The present invention irradiates a scattering object such as a living body containing many scattering components with multimode laser oscillation light from one direction of the scattering object, and the scattering components reflected from each point in the depth direction of the scattering object. The reflected light containing a lot of, by the heterodyne detection of the beat component of the reference light with the frequency of the multimode laser light shifted, or the reference light obtained by dividing a part of the irradiation light, and from each of the points The reflected component of the reflected light is interfered with the light that has passed through the highly directional light receiving system, and the spectral distribution spectrally separated for each mode is inversely Fourier transformed to reliably remove the scattered component and to increase the depth of the scattering object. Only the reflection information can be reliably extracted from each point of the boundary layer having a different refractive index in the direction.

Further, according to the present invention, since the reflection information can be obtained from each point in the depth direction of the scattering object by irradiating the scattering object with the multimode laser oscillation light from one direction, the omnidirectional direction of the scattering object can be obtained. It is possible to identify the information of each point inside the scattering object without irradiating light from. In other words, the multi-mode multi-delayed phase-reflected light as the reflected light from each point inside the scattering object is reproduced as a time-series electric signal by performing an inverse Fourier transform, and it is relatively easy with a spatial resolution of several tens of microns or less. With this algorithm, it is possible to measure the reflected light from each point in the depth direction of the scattering object in a short time. Therefore, the number of times of light irradiation can be reduced as compared with the transmission type optical tomography apparatus.

[00010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the light emitting element 1 is a multi-mode laser oscillator, and is composed of, for example, a semiconductor laser. A condenser lens 2, a beam splitter 3, and an object to be measured 4 are sequentially arranged on the optical axis of a light beam generated from the multimode laser oscillator 1. The measured object 4 is mounted on a movable table 5 which is movable in the X, Y, and Z axis directions, for example. Further, among the light beams generated from the multimode laser oscillator 1, a reflection mirror 6a and a photoacoustic modulator 6b are provided as a frequency shift 6 on the optical axis of the light beam split by the beam splitter 3. There is.

On the other hand, of the light beams reflected from the object 4 to be measured, on the optical axis of the light beam split by the beam splitter 3, as a spectroscopic means for splitting the multimode laser light into each mode. An optical spectrum analyzer 7 is provided. Reference numeral 7a is a spectroscope using a diffraction grating, and 7b is a photodetector as a photoelectric converter. A signal processor 8 is connected to the output terminal of the detector 7b.
The signal processor 8 includes, for example, an amplifier (AMP) 8a for amplifying a signal output from the photodetector 7b, and this amplifier 8
A bandpass filter (BPF) 8b for extracting a beat signal for heterodyne detection of the beat signal from the signal amplified by a, and the bandpass filter 8b.
The magnitude of the signal taken out by the square-law detection is obtained, and the value is converted into a digital signal by an A / D converter 8c. The digital signal output from the A / D converter 8c is supplied to the computer 9. The computer 9 is connected with a memory 10 for performing inverse Fourier transform of the signal output from the signal processor 8 and storing it as a signal of a time series, and a display device 11 for displaying various information.

In the above structure, the multimode laser light generated from the light source 1 is collimated by the lens 2 and split into two by the beam splitter 3. One of the light beams becomes a reference light wave whose frequency is shifted by inserting the photoacoustic modulator 6b between the reflecting mirror 6a and the beam splitter 3. Alternatively, the reflected light may be generated by a movable mirror. This reflected light becomes a reference light wave whose frequency undergoes Doppler shift and has a phase delay corresponding to the moving distance of the movable mirror.

The other light beam split by the beam splitter 3 is irradiated from a point determined by the beam size of the object 4 to be measured on the Y-axis coordinate, and propagates through the object. A light beam propagating in an object to be measured composed of an optical layer structure, that is, a multi-layered material having different refractive indexes is scattered at each boundary of this layer, and part of the light beam returns in the direction of the incident light beam to form a reflected light wave. To do. The phase of each of the multiple modes of the reflected light wave is delayed according to the position of the boundary in the depth direction (Z-axis direction) from the incident position of the incident light beam. Furthermore, the amplitude of each of the reflected light waves depends on the reflectance and absorptance of the boundary layer, which is determined by the optical layer structure and physical properties.

The reflected light wave from the object to be measured 4 is guided to the optical spectrum analyzer 7a as the spectroscopic means through the beam splitter 3 together with the reference light wave. Sweeps the wavelength by rotating the diffraction grating of the optical spectrum analyzer, or a multi-wavelength simultaneous observation spectroscope using an array detector, or a Fabry-Perot interferometer type spectroscope compatible with multi-mode laser light The reflected light is spectrally separated for each mode. From the exit slit of the optical spectrum analyzer, the reflected light spectrally separated for each mode and the frequency-shifted reference light are emitted, and the photodetector 7b
Then, in the photodetector 7b, the combined and interfered light waves are subjected to optical heterodyne detection. In general, the reflected light from the measured object 4 has many spatial Fourier spectrum components. However, in this reflected light, only the component matching the plane wave component of the reference light wave having a high spatial coherence degree is highly efficiently heterodyne detected. Therefore, by utilizing this, the reflected light from the reflecting surface in the depth direction of the measured object 4 is selectively detected. The computer 9 outputs the A / D converted signal of the spectrum output for each mode.
Fourier inverse transform is performed by and stored as a time series signal.

As shown in FIG. 2, the reflected signal light from the measured object has a refractive index n0 of the measured object 4 such as an atmosphere.
In the scattering layer (0 layer) of the medium to be measured, and inside the object to be measured 4, medium layers (1 to ₁ having the thicknesses Z ₁ , Z ₂ and Z ₃ in the Z-axis direction are formed.
Layers, 2 layers, 3 layers), and the refractive indices of these layers are n1, n
In the case of 2 and n3, when the measured object 4 is irradiated with incident light, the incident light is attenuated by each layer, reflected at the boundary of each layer, and output from the measured object 4. The reflected light from each layer is exponentially absorbed and attenuated corresponding to the distance that the light propagates in the medium, and due to scattering, is attenuated in inverse proportion to the square of the distance.

That is, the reflected light from each layer, which is reflected by the measured object 4 shown in FIG. 2, is represented as follows. The reflected light intensity I _R01 from the surface of the measured object 4 is

[Formula 1] The reflected light intensity I _R12 from the first and second layers is

[Formula 2] The reflected light intensity I _R23 from the second and third layers is

[Formula 3] The reflected light intensity I _R34 from the third and fourth layers is

[Formula 4] However, T ₀₁ , T ₁₀ , T ₁₂ , T ₂₁ , T ₂₃ , T
₃₂ , ..., 0 to 1 layer, 1 to 0 layer, 1 to 2
Intensity transmittance of light incident on the layers, 2 to 1 layer, 2 to 3 layers, 3 to 2 layers. R ₁₂ , R ₂₃ , R ₃₄ , ...
Light intensity reflectance in the 1st and 2nd layers, the 2nd and 3rd layers, and the 3rd and 4th layers. α
1, α2, α3, ... Are attenuation factors in each layer. Z ₁ , Z
₂ , Z ₃ , ... Represent the thickness of each layer.

Generally, the reflected light from the measured object 4 is
It consists of random scattered light from the inside of the medium layer and reflected light reflected at the boundary of each layer. this house,
Random scattered light can be removed by performing heterodyne detection or by receiving light with a highly directional light receiving system. This principle is described in Japanese Patent Application No. 1-62898, Japanese Patent Application No. 1-250034, Japanese Patent Application No. 1-250036 and Japanese Patent Application No. 2-77690. Therefore, regarding the reflected signal light from the measured object, only the component reflected at the boundary of each layer may be considered without considering the random scattered light.

That is, in the present embodiment, multimode laser light is used as a light source, and the light of each mode is frequency-shifted by a frequency smaller than the mode interval to be the reference light, which is emitted from the boundary of each layer inside the object to be measured. The reflected light is used as the signal light, and both light waves of the reference light and the signal light are spectrally separated by the spectroscope for each mode. By heterodyne detection of signal light and reference light in the same mode but with slightly different frequencies, the effect of random scattered light is removed and only straight-ahead back-reflected light is detected.
By obtaining the heterodyne output distribution for each mode and performing the inverse Fourier transform of the distribution, the boundary surface of each layer is detected on the measured object.

The principle of obtaining the reflection point by inverse Fourier transforming the spectral distribution spectrally separated for each mode will be described. The optical electric field Er (t, z) of the reference light from the multimode laser oscillator 1 has M as the total number of modes of the multimode laser and fm = fo as the frequency of the mth mode electric field Em.
+ MΔf, fo: mode end frequency, Δf: mode interval frequency (Δf = v / 2nL, v: light velocity, L: laser resonator length, n: refractive index) fa is a frequency shift by the photoacoustic modulator, and a beam splitter Reference light reflector 6 from 3
It is expressed by the following equation using the distance Zr to a.

[Equation 5]

The distance to the reflection surface of the object to be measured 4 is Zk
= Zo + KΔZ. Here, Zo is a reference distance, K is an integer, and ΔZ is a decomposition distance. Reflected signal light electric field Es
(T, z) is the distribution function of the reflection coefficient of the electric field on the reflecting surface, which is S
It is represented by the following equation as k. However, in the case of including an effect of exponentially decaying according to the distance propagated in the medium and an effect of decaying in inverse proportion to the square of the distance, Sk = Sk
It may be exp (2αkZk) / Zk. In the following, for the sake of clarity, it will be handled as Sk.

[Equation 6]

Using the relational expression of resolution 2MΔfΔz / v = 1 and the total mode bandwidth ΔfL = MΔf, the equation 6 can be expressed as follows.

[Equation 7]

Here, the following definition is made and Equation 7 is replaced.

[Equation 8]

[Equation 9]

[Equation 10]

By a spectrum analyzer using a spectroscope, there are m-th modes Emr and Ems which have reference light represented by Equation 5 and reflected signal light represented by Equation 10, respectively.
Is spectrally separated into two and square-law detected by the photodetector 7b. For the sake of simplicity, it is essentially the same even if the distance Zr in Equation 5 is set to ZO, so that instead of Emz and Ems,
It becomes like this.

[Equation 11]

[Equation 12]

Consider heterodyne detection of the reference light that has undergone the frequency shift expressed by Expression 11 and the reflected signal light expressed by Expression 12. In general, two light waves V
₁ and V ₂ are expressed as follows.

[Equation 13]

[Equation 14] When these two light waves V ₁ and V ₂ are superposed and detected, the detection signal S can be expressed by the following equation due to the square-law detection characteristic of the photoelectric converter.

[Equation 15] By the way, each term in the above equation can be expressed as follows.

[Equation 16]

[Equation 17]

[Equation 18]

[Formula 19] Therefore, the detection signal S can be expressed as follows.

[Equation 20] In heterodyne detection, ω ₂ = ω ₁ −Δω, φ ₁
Since = φ ₂ can be written, the detection signal S becomes as follows.

[Equation 21] The first term and the second term in the above equation are components that do not vary with time, and the third term is a component observed as a beat signal. The third term is detected by the band-pass filter by separating the component having the magnitude from the first term and the second term.

When the reference light of Expression 11 and the signal light of Expression 12 are detected, the detection signal is as shown in the following expression.

[Equation 22] The first term and the second term are components that do not vary with time. The third term is the beat component that changes with time at the frequency fa. Even if it is replaced with t−2ZO / v = t ′, since it is the same only with time transition, the beat component S _B of the third term is
It becomes the following formula.

[Equation 23] Here, Hm is given by Expression 9, and is the sum of several things having different phases, which is given by just the discrete Fourier transform of hk. Therefore, the beat component detected by the heterodyne detection is detected, Hm for each mode is observed, and its distribution {H
The distribution hk is obtained by calculating m} and applying the discrete inverse Fourier transform for each mode. Here, since hk has a relationship with the distribution function Sk of the reflection surface of the measured object by Equation 8,
Sk is obtained from k.

Next, the image creation and process for obtaining tomography will be described. First, the spatial resolution and depth resolution of the light wave echo image are determined as follows. That is, the spatial resolution (ΔZ) in the depth direction, that is, the Z-axis direction is determined by the spectral width. The spatial resolution (ΔY × ΔX) of the incident cross section is substantially determined by the diameter of the incident light and the optical heterodyne detection aperture angle.

The time-sequential signal waveform including the data in the depth direction of the object to be measured, which is obtained by inverse Fourier transforming the spectral distribution of each mode, is stored in the memory 10 via the computer 9 line by line. . After this movable table 5
Is moved along the Y-axis by the cross-sectional diameter of the incident light, and the same measurement is performed. Further, sequential measurement is performed over the entire range of the measured object 4 in the Y-axis direction.

As described above, the digital data stored in the memory 10 is read out by the computer 9, and by the well-known image processing technique, the spatial resolution (ΔY × ΔZ) of the measured object 4 is divided into sections. It is processed into a grayscale image or a color-based image according to the digital amount. The processed grayscale image or color-based image is supplied to the display device 11 and displayed. In this way, the measured object 4
By displaying the data of the entire ZY plane on the display device 11, a high-resolution tomographic image including the data in the depth direction can be obtained despite the unilateral measurement from the uniaxial direction.

If the above measurement is performed also in the X-axis direction, it is possible to obtain a multi-layered tomographic image of the object 4 to be measured. Therefore, when the measurement is performed also in the X-axis direction as described above, the data in the three-dimensional depth direction of the object 4 to be measured is stored in the memory 10, and therefore, by changing the reading direction of the memory 10, It is possible to generate a tomographic image of the measurement object 4 that is cut from any direction.

Next, another embodiment of the present invention will be described. FIG. 3 shows a second embodiment of the present invention. In the present embodiment, instead of frequency-shifting the reference light wave, instead of performing the heterodyne detection with the reflected signal light from the measured object 4, the reflected light from the reflecting mirror 6a is superposed and put into the spectroscope 7a for each mode. Detects by spectral separation. In heterodyne detection, randomly scattered light is removed by the wavefront matching condition, and only back-reflected light is selected. In this embodiment, instead of performing the heterodyne detection, the highly directional light receiving system 12 is used to remove the random scattered light to receive the light, and the interferometer detects the interference with the reference light and the signal light in each mode. Since the signal processing unit does not detect the beat signal, the bandpass filter (BPF) 8b is not used, and the signal of the amplifier (AMP) 8a is directly A / D-converted.
Convert. Others are the same as those in the first embodiment. The principle and configuration of the highly directional light receiving system have already been described in Japanese Patent Application No. 1-62898.
And Japanese Patent Application No. 2-77690. Use the same one.

These operation principles will be described below using mathematical expressions. It is assumed that the same symbols as those in the embodiment based on heterodyne detection are used. By replacing the distance Zr from the beam splitter 3 to the reflecting mirror 6a with the standard distance Zo for simplification, the reference light Er (t, z) is expressed by the following equation.

[Equation 24] Among them, the multimode is spectrally separated by the spectrum analyzer 7, and the light Emr (t,
Only z) is incident on the detector. Emr (t, z) is
It is expressed as

[Equation 25]

On the other hand, the reflected signal light Es (t, z) is expressed by
Given by the formula. Of these, spectrum analyzer 7
Causes the light Ems (t, z) of the mth mode to enter the detector. Ems (t, z) is expressed by the following equation.

[Equation 26] The reference light Emr of the m-th mode that can be expressed by Equation 25,
The signal light Ems of the m-th mode that can be expressed by Expression 26 is square-law detected by the detector. The output of the detector becomes the same as that of Expression 15, and when Expression 25 and Expression 26 are substituted and rewritten, the following expression is obtained.

[Equation 27]

[Equation 28]

Here, the third term is given by the discrete Fourier transform of hk. The second term is the intensity of the reflected signal light from the measured object, which is weaker than the reference light intensity of the first term and can be ignored.
Therefore, the output Sm is observed for each mode and its distribution {S
If m} is obtained and a discrete inverse Fourier transform is performed for each mode, the component at the origin of k = 0 in the spatial coordinate domain is obtained from the first term, and the distribution hk is obtained from the third term. If hk is obtained, the distribution function Sk of the reflection surface of the measurement object is calculated from Equation 28
Is required.

Compared to the first embodiment using the heterodyne detection, the first term and the second term of the equation 27 are added. However, the inverse Fourier transform component of the first term becomes the origin, the second term can be ignored, and the information of the reflecting surface can be obtained from the inverse Fourier transform of the third term.

An image forming process for obtaining tomography can be performed in the same manner as in the first embodiment.

FIG. 4 shows a third embodiment of the present invention, in which a Fizeau interferometer is used in place of the Michelson interferometer in the second embodiment. The beam splitter 3 in the second embodiment is replaced with a polarizing beam splitter 3'and when the quarter wave plate 13 and the surface of the object to be measured have a small amount of surface reflection, the reference reflector 1 is used as necessary.
4 are provided.

Linear P-polarized light from multimode laser light is
After passing through the quarter-wave plate, it becomes incident circularly polarized light, which is irradiated to the object 4 to be measured. The reflected light from the reflecting surface inside the object to be measured 4 and the reflected light from the reference reflecting surface 14 become circularly polarized reflected light, pass through the quarter-wave plate 13 and become S-polarized light, and the polarization beam splitter 3 ' The light is reflected by and enters the spectrum analyzer 7, and is spectrally separated and detected for each mode. As a result, the reflected signal light wave and the reference light wave from the standard reflection surface interfere very efficiently, and the highly directional light receiving system 1
Random scattered light components that could not be removed in 2 do not interfere, so the influence is removed and detection is performed. The electric signal from the spectrum analyzer 7 is processed in the same manner as in the second embodiment, and the distribution of the reflection surface inside the measured object is detected.

The principle of this embodiment is the same as that of the second embodiment using the Michelson interferometer, and the interference components of the reflected light from the reference reflecting surface 14 and the reflected signal light from the inside of the object 4 to be measured are measured in each mode. Utilizing that the one obtained for each is the one obtained by performing the discrete Fourier transform of the distribution function of the reflecting surface when the intensity of the reflected signal light component is weaker than the reference light and can be ignored.
The reflection surface distribution is obtained by inverse Fourier transforming the spectral distribution for each mode. The present embodiment using the Fizeau interferometer has an advantage that the influence of random scattered light peculiar to a biological sample is small, as compared with the second embodiment using the Michelson interferometer, because interference by polarized light is used. .

The image forming process for obtaining tomography can be performed in exactly the same manner as in the first embodiment.

In the above embodiment, the spectrum analyzer 7 for each mode is used after the reference light wave and the reflected signal light wave are combined. This spectrum analyzer generally observes by spectrally separating each mode by sweeping the wavelength by rotating the diffraction grating. Moreover, since the wavelength sweep is relatively fast, the spectroscope was used for observing that mode by using multimode laser light as the light source, rather than by using it as a means for separating the irradiation laser light into a single mode while maintaining a stable state. It is easier to realize and reliable data can be obtained. If it is possible to oscillate the multimode laser oscillation light in a stable state, select each mode of the multimode laser light at each step with a spectroscope, obtain the spectrum distribution for each mode, and obtain the Fourier distribution. Of course, the reflection distance may be obtained by performing reverse conversion.

In the above embodiment, the object to be measured is moved and scanned by the movable table 5 in order to obtain a reflected image, but a plurality of multimode oscillation laser beams are measured as in ultrasonic echography. By arranging the light emitting elements linearly with respect to the object and sequentially illuminating these light emitting elements by the control means composed of a plurality of switches, the object to be measured can be scanned without moving the object to be measured.

Further, the interferometer of the above embodiment is an optical system in which optical elements such as mirrors are arranged in space, but the invention is not limited to this, and an optical system using optical fibers and optical elements may of course be used. .

It goes without saying that the present invention can be used not only for a tomography apparatus, but also for diagnostic measurement using reflected waves from optical fibers, optical ICs and the like. Further, although the multimode laser is used in the first to third embodiments, various lasers can be used without being limited to the semiconductor laser. Moreover, by using the principle of the present invention, a living body, a crystal, a semiconductor, a composite material, etc., can be used as long as it is a substance that can transmit and propagate these electromagnetic waves not only in lasers such as infrared rays, visible rays and ultraviolet rays but also in the microwave region The multi-layered tomographic image can be rapidly observed non-invasively, and can be applied to medical diagnosis and engineering material structure measurement.

In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[00044]

In this study, a heterodyne detection or highly directional light receiving system is combined with an interferometer by using a multimode oscillation laser, which has been regarded as unnecessary in the conventional reflection distance measuring apparatus, and a spectrum is obtained for each mode. It is possible to provide a light wave echography apparatus capable of removing random scattered light peculiar to a living body by performing inverse Fourier transform on the separated spectrum distribution and achieving high resolution of the distance of the reflecting surface determined by the spectrum width of the multimode oscillation laser.

Further, since the image in the depth direction of the object to be measured can be obtained like ultrasonic echography by only irradiating the object to be measured with laser light from one direction, the number of scans for obtaining a tomographic image can be increased. Can provide a device that can be reduced compared to a transmission type optical tomography device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of light wave echography using a multimode laser according to the present invention.

FIG. 2 is a diagram showing a relationship between incident light and reflected light with respect to an object to be measured 4 for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a second example using a reference light reflecting mirror and a highly directional light receiving system.
FIG.

FIG. 4 is a third example using a Fizeau interferometer and a highly directional light receiving system.
FIG. 1. ... Multi-mode laser oscillator 2. ... Condensing lens 3. ... Beam splitter 3 '. ..Polarizing beam splitter 4. ... Object to be measured 5. ... Movable platform 6. ... Frequency shifter 6a. ..Reflecting mirror 6b. ..Photoacoustic modulator 7. ... Optical spectrum analyzer 7a. ..Spectroscope 7b. ..Photodetectors 8. ... Signal processor 8a. ..Amplifier 8b. ..Bandpass filters 8c. ..A / D converter 9. ... Computer 10. ..Memory 11. ..Display device 12. ..Highly directional light receiving system 13. .. Quarter-wave plate 14. ..Standard translucent reflectors

Claims (5)

[Claims] 1. An irradiation unit that irradiates a scattering object composed of layers having different refractive indexes with multimode oscillation laser light as irradiation light, and a generation unit that generates reference light whose frequency is shifted from a part of the irradiation light. , Combining means for combining reflected light from a point having a different refractive index in the depth direction inside the scattering object, and reference light; means for spectrally separating the combined light for each mode; Conversion means for photoelectrically converting the combined light of each output mode, means for storing the magnitude of the beat component output from the conversion means for each mode, and inverse distribution of the components for each mode An optical wave echography apparatus comprising means for obtaining points having different refractive indices in the depth direction of a scattering object by performing Fourier transform. 2. A means for irradiating a scattering object composed of layers having different refractive indexes with multimode oscillation laser light as irradiation light, a generation means for dividing a part of the irradiation light to generate reference light, and the scattering. Random backscattered light from an object is removed, and highly directional light receiving system means for transmitting only straight reflected light from points having different refractive indices in the depth direction, and emitted from the highly directional light receiving system means. A combining means for combining the reflected light and the reference light, a means for spectrally separating the combined light for each mode, and a conversion for photoelectrically converting the combined light of each mode output from the dispersing means. Means, means for storing the magnitude output from the converting means for each mode, and means for obtaining points having different refractive indices in the depth direction of the scattering object by performing inverse Fourier transform on the component distribution for each mode. When Lightwave echo tomography apparatus characterized by comprising. 3. A means for scanning the scattering object with respect to the irradiation light by changing the positional relationship between the scattering object and the irradiation light, and obtaining reflection information in the depth direction with respect to the scanning direction to obtain a two-dimensional reflection tomographic image. The lightwave echography apparatus according to claim 1 or 2, further comprising: a means for obtaining. 4. A means for synthesizing the reflected light and the reference light,
The light wave echography apparatus according to claim 2, wherein a Michael interferometer including a reference light reflecting mirror and a beam splitter that splits the irradiation light is configured. 5. A means for combining the reflected light and the reference light,
A Fizeau interferometer that does not require frequency shift of the reference light, using a polarizing beam splitter, a quarter-wave plate, and a semitransparent reflecting mirror placed on or in contact with the scattering object surface as the reference light wave reflector. 3. The method according to claim 2,
The described lightwave echography apparatus.