JP2007327909A - Optical tomography apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-resolution optical tomography apparatus by a light source generating low coherence light in the optimum wavelength zone to heightening of resolution from a light absorbing characteristic, a diffusion characteristic or a dispersion characteristic of a living tissue. <P>SOLUTION: Low coherence light having a central frequency λc of 1.1 μm and a spectrum full width at half maximum Δλ of 90 nm is emitted from a light source unit 210. The low coherence light has wavelength characteristics suited for the light absorbing characteristic, the diffusion characteristic, and the dispersion characteristic of an optical living tissue. A light dividing means 3 divides the low coherence light into measuring light, which is irradiated onto a measuring target Sb via an optical probe, and reference light that propagates to the direction of an optical path length adjusting means 220. A multiplexing means 4 multiplexes reflected light reflected at a predetermined depth of the measuring target Sb with reference light. An interference light detection means 240 detects the optical intensity of the multiplexed interference light L4. An image obtaining means 250 performs image processes, and displays an optical tomographic image on a display apparatus 260. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical tomographic imaging apparatus for obtaining a tomographic image of a measurement target by irradiating the measurement target, which is low-coherence light, to the measurement target. The present invention relates to an optical tomographic imaging apparatus for imaging.

  Conventionally, as one method for acquiring a tomographic image of a measurement target such as a biological tissue, a method for acquiring an optical tomographic image by OCT (Optical Coherence Tomography) measurement has been proposed. As one of the OCT measurements, for example, a method of acquiring an optical tomographic image by TD-OCT (Time domain Optical Coherence Tomography) measurement as shown in Patent Document 1 or Patent Document 2 has been proposed. This TD-OCT measurement is a kind of optical interference measurement, in which optical interference is detected only when the optical path lengths of the divided light, that is, the measurement light and the reference light are within the coherence length of the light source. It is a measurement method using what is done. That is, in this method, the low coherent light emitted from the light source is divided into measurement light and reference light, the measurement light is irradiated onto the measurement object, and the reflected light from the measurement object is guided to the multiplexing means.

  In TD-OCT measurement, the measurement position (measurement depth) with respect to the measurement object is changed by changing the optical path length of the reference light or measurement light, and a one-dimensional tomographic image in the optical axis direction is acquired. Yes. For example, an optical path length adjustment mechanism of a TD-OCT apparatus described in Patent Document 1 has an optical system that reflects reference light emitted from an optical fiber to a mirror, and moves the mirror in the optical axis direction of the reference light. The optical path length is adjusted. Further, a tomographic image having a two-dimensional light reflection intensity can be obtained by scanning the irradiation position of the measurement light applied to the measurement object in a direction perpendicular to the optical axis. Furthermore, a tomographic image having a three-dimensional light reflection intensity can be obtained by scanning the irradiation position of the measurement light over a two-dimensional direction perpendicular to the optical axis direction.

  As another OCT measurement method, for example, a method of acquiring an optical tomographic image by SD-OCT (Spectral domain Optical Coherence Tomography) measurement as shown in Patent Document 3 has been proposed. In this SD-OCT apparatus, broadband low-coherent light divided into measurement light and reference light is caused to interfere with the optical path length being almost equal, and then the interference light is decomposed into optical frequency components by a spectroscopic means. By measuring the interference light intensity for each optical frequency component with a photodetector and Fourier-transforming the spectral interference waveform obtained here with a computer, the optical path length can be changed without physically changing the optical path length. One-dimensional tomographic image original data is acquired. By scanning the measurement light irradiation position in a direction perpendicular to the optical axis, a two-dimensional or three-dimensional tomographic image can be obtained.

  In addition, instead of low-coherence light, coherence light whose frequency changes with time is emitted to detect interference light, and the reflection intensity at the depth position of a predetermined measurement target is determined from the interferogram in the optical frequency domain. A method of acquiring an optical tomographic image by SS-OCT (Swept Source Optical Coherence Tomography) measurement that detects and generates a tomographic image using this is also proposed. (For example, see Patent Document 4).

  Such an OCT apparatus is first developed as an ophthalmic apparatus and put into practical use. Currently, following practical application in the field of ophthalmology, further research and development is being carried out with the aim of applying to endoscopes. At the beginning of development, the 0.8 μm band has been mainly used as the light source wavelength of the OCT apparatus (see, for example, Non-Patent Document 1). This is the wavelength selected as a result of considering the absorption characteristics in the living body. FIG. 1 (a) shows the light absorption coefficient of water, blood, melanin, and epidermis, and FIG. 1 (b) shows the water absorption coefficient in the wavelength band from 0.7 μm to 1.6 μm. is there. From FIG. 1B, it can be seen that there are water absorption peaks at 0.98 μm and 1.2 μm. Moreover, the broken line in FIG. 2 shows the absorption loss of the living body obtained based on these absorption coefficients. As can be seen from FIG. 2, in the living body, light in the 0.8 μm band has the smallest absorption loss. From this, at the beginning of development, 0.8 μm band light was considered to be most suitable for the OCT apparatus because of its high biological transmittance and deep measurement depth.

  However, in recent years, it has been clarified that in the OCT apparatus, the scattering characteristics also regulate the measurement depth in order to detect the backscattered reflected light inside the living body. The main scattering in living tissue is Rayleigh scattering. In Rayleigh scattering, the scattering intensity is inversely proportional to the fourth power of the wavelength. The dotted line in FIG. 2 shows the scattering loss in the living body. The total loss when acquiring the OCT signal is the sum of the absorption loss and the scattering loss, and this total loss is indicated by a solid line in FIG.

  It can be seen from FIG. 2 that the wavelength band that minimizes the total loss is the 1.3 μm band. For this reason, after an ophthalmic OCT apparatus is put to practical use, research and development is being carried out using a 1.3 μm band light as a light source wavelength in an endoscope-applied OCT apparatus that requires a greater imaging depth. (For example, refer nonpatent literature 2).

  On the other hand, the purpose of applying the OCT apparatus to an endoscope is in-vivo definitive diagnosis and cancer invasion diagnosis of discrimination between mucosal cancer (m cancer) and submucosal cancer (sm cancer). The procedure for endoscopic diagnosis of cancer will be briefly described below. First, a lesion is detected from a normal observation image to identify whether it is cancer or other disease. This primary diagnosis is a diagnosis based on the experience of a doctor. A tissue at a site estimated to be cancer is collected and a definitive diagnosis is performed by a pathological examination. For this reason, at present, definitive diagnosis during endoscopy is difficult. When a definitive diagnosis of cancer is made, in order to determine a subsequent treatment policy again, a cancer depth is diagnosed by endoscopy. In general, cancer originates from the mucosal epidermis and spreads in the depth direction while spreading laterally as it progresses. As shown in FIG. 3, the structure of the stomach wall is composed of five layers from the surface: a mucosal layer (m layer), a mucosal muscular plate (MM), a submucosal layer (sm layer), a muscular layer, and a schizophrenia. Cancer that remains only in the mucosal layer is called m cancer, and cancer that invades the submucosal layer is called sm cancer. Treatment is different for m cancer and sm cancer. Since the lymphatic system and vascular system are present in the submucosal layer, the possibility of metastasis cannot be denied in sm cancer, so it is indicated for surgery. On the other hand, in the case of m cancer, since there is no metastasis, the cancer is removed under an endoscope. For this reason, it is important to identify m cancer or sm cancer. Specifically, it is important to be able to evaluate as an image whether the mucosal muscle plate (MM layer) has a layer structure or is destroyed. At present, the application of ultrasound is being studied with the aim of diagnosing this depth of penetration. However, since the ultrasonic resolution is about 100 μm, the MM layer cannot be drawn sufficiently. In m cancer having a high degree of progression, lymphoid follicles are formed under the MM layer, and the cancer site and lymphoid follicle are imaged together, so that m cancer is misdiagnosed as sm cancer. For this reason, an imaging method with an axial resolution of 10 μm or less is eagerly desired for accurate depth measurement.

  On the other hand, in the TD-OCT apparatus and the SD-OCT apparatus, the resolution in the optical axis direction is defined by the coherence length of the light source, that is, normally a resolution shorter than the coherence length of the light source cannot be obtained. For this reason, in order to realize a high resolution of 10 μm or less in the optical axis direction, light having a coherence length of 10 μm or less is required. The coherence length Δz of the low-coherence light is proportional to the square of the center frequency and half proportional to the spectrum width, and can be expressed by the following equation when the center wavelength λc and the spectrum width Δλ are assumed.

Δz = 2ln2 / π · (λc ² / Δλ)
For this reason, in order to shorten the coherence length, the spectral width Δλ must be increased. On the other hand, it has been found that if the spectral width Δλ of the coherence light is widened, it is necessary to consider the influence of dispersion (see Non-Patent Document 3).

In the Michelson interferometer, when light propagates through the sample, a phase shift occurs, and as a result, the interference signal waveform changes. If the interference signal waveform is φ (ω) and the spectrum waveform of the light source is Gaussian, the autocorrelation function is

It is expressed. Where σt is the 1 / e ^1/2 width of the autocorrelation function, σt0 is the 1 / e ^1/2 width of the autocorrelation function when D = 0, σw is the light spectrum 1 / e ^1/2 width, and ω0 is The center frequency of the optical spectrum, K, is a broadening ratio due to the influence of dispersion.

  FIG. 4 shows the calculation result (solid line) and the actual measurement result (▲) of the above equation (3) using water as a sample. It can be seen that while the dispersion D is zero (zero dispersion) at a wavelength of 1.0 μm, the influence of dispersion increases as the wavelength goes away from 1.0 μm.

  Fig. 5 shows the underwater propagation distance (water thickness) and broadening ratio (degradation degree) when low-coherent light having a wavelength of 1.32 µm (spectrum width of 76 nm) and a wavelength of 0.94 µm (spectrum width of 75 nm) propagates in water. FIG. 6 is a diagram illustrating an actual measurement value and a simulation result of a relationship with ().

  In the said nonpatent literature 3, when the coherence length of low coherence light is short, it concludes that it is preferable to use low coherence light with a center wavelength of 1.0 micrometer in an OCT apparatus.

Also in the SS-OCT apparatus, the optical axis direction resolution is defined by the wavelength sweep width Δλ of coherence light emitted from the light source. For this reason, in order to increase the resolution in the optical axis direction, the wavelength sweep width Δλ of the coherence light must be increased. On the other hand, if the wavelength sweep width Δλ of the coherence light is widened, it is necessary to consider the influence of dispersion as described above.
JP-A-6-165784 JP 2003-139688 A JP 11-325849 A US 5,956,355 publication Optics Letters Vol.24, No17,1999, P1221-1223 by W.Drexler et.al Optics Letters Vol.26, No9,2001, P608-610, 2001 by I. Hartl et.al Optics Express Vol.11, No12,2003, P14111417, 2003 by Yimin Wang et.al

  However, when acquiring an optical tomographic image of a living body using an OCT apparatus that uses measuring light that is low-coherence light or coherence light whose frequency changes with time, the wavelength band of the measuring light is light absorption of the living body. When a large wavelength band is included, the spectral shape of the measurement light (reflected light) is deformed due to light absorption by the living body, and as a result, sidebands or sideropes appear in the autocorrelation function, resulting in the generation of pseudo signals. There is a problem that the S / N of the optical tomographic image is lowered. As shown in FIG. 1B, water, which is a main constituent of the living body, has absorption coefficient peaks at 0.98 μm and 1.2 μm near a wavelength of 1 μm.

  FIG. 6 is a simulation result assuming a case where light having a Gaussian distribution with a center wavelength of 1.0 μm and a wavelength bandwidth of 100 nm propagates in water. FIG. 6A shows changes in the spectrum shape, and FIG. 6B shows the Fourier transform waveform of each spectrum waveform. Note that the solid line is a waveform that does not pass through water, the one-dot broken line is the waveform that passes through 2 mm thick water, the two-dot broken line is the waveform that passes through 4 mm thick water, and the dotted line is thick. The waveform when 8 mm of water is transmitted is shown. From FIG. 6, it can be seen that when the measurement light having a wavelength of 1 μm and a wavelength bandwidth of 100 nm is transmitted through water, the spectrum shape is greatly deformed due to the absorption at 0.98 μm. As a result, a side band appears in the autocorrelation waveform, a pseudo signal is generated, and the image quality of the optical tomographic image is degraded.

  In Non-Patent Document 3, an optical tomographic image is acquired using low coherence light having a center wavelength of 1.1 μm and a spectral width of 372 nm. In this case, not only 0.98 μm but also absorption at 1.2 μm is obtained. It will also be affected by the peak, and the degradation of image quality due to the occurrence of sidebands will be even greater.

Non-Patent Document 3 describes that when an optical tomographic image is acquired using low-coherence light having a coherence length of approximately 10 μm (λc ² / Δλ is 23), it is affected by dispersion. In addition, when the value of λc ² / Δλ is small and affected by dispersion, it is described that the center wavelength of the low coherence light is preferably near 1.0 μm, but 0.98 μm and 1.2 μm are described. No mention is made of the center wavelength λc and the wavelength bandwidth Δλ that are not affected by the absorption in FIG.

  The present invention has been made in view of these problems. In an optical tomographic imaging apparatus using measurement light that is low-coherence light or coherence light whose frequency changes with time, light absorption characteristics, scattering characteristics, dispersion of biological tissue Clarification of the existence of the optimal wavelength characteristics of measurement light for high resolution from the characteristics, and the acquisition of high-resolution and high-quality optical tomographic images using the measurement light having the optimal wavelength characteristics It aims at realizing.

A first optical tomographic imaging apparatus of the present invention includes a light source unit that emits low-coherence light,
Splitting means for splitting the low-coherence light into measurement light and reference light;
An irradiation optical system for irradiating the measurement object with the measurement light;
An optical path length changing means for changing an optical path length of the reference light or the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement object is irradiated with the measurement light;
The plurality of measurement targets, wherein the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially coincide with each other based on the light intensity of the combined reflected light and the interference light of the reference light In an optical tomographic imaging apparatus comprising: an image acquisition unit that detects the intensity of reflected light at each depth position and acquires a tomographic image of a measurement object based on the intensity at each depth position;
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
It is characterized by satisfying.

A second optical tomographic imaging apparatus of the present invention includes a light source unit that emits low-coherence light,
A light splitting means for splitting the low-coherence light into measurement light and reference light;
An irradiation optical system for irradiating the measurement object with the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement object is irradiated with the measurement light;
Based on the characteristics of the combined interference light of the reflected light and the reference light, the intensity of the reflected light at a plurality of depth positions of the measurement target is calculated, and the measurement is performed based on the intensity at each of these depth positions. In an optical tomographic imaging apparatus comprising an image acquisition means for acquiring a tomographic image of a target,
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
It is characterized by satisfying.

  Further, the image acquisition means detects the light intensity for each frequency of the interference light, and calculates the intensity of the reflected light at a plurality of depth positions of the measurement target from the light intensity for each frequency of the detected interference light. You may do.

  Here, “reflected light from the measurement target” means light reflected by the measurement target, light back-scattered by the measurement target, or light reflected and back-scattered by the measurement target.

  The reference light and the reflected light may have substantially the same center wavelength and the same spectrum full width at half maximum. Note that “substantially the same” means that they are the same to the extent that they do not hinder the measurement of the light intensity of the interference light.

  The light source unit may have a super luminescent diode. The super luminescent diode is formed on a GaAs substrate having a first conductivity, and is disposed on an optical waveguide composed of an InGaAs active layer and on the rear emission end face side of the optical waveguide, and has energy higher than that of the active layer. The gap is large, the refractive index is small, the second conductivity is opposite to the first conductivity, and the lattice constant does not include Al that lattice matches with the lattice constant of GaAs within ± 0.1%. It may have a window region layer made of an original or ternary semiconductor material. The semiconductor layer forming the window region layer may be made of GaAs or InGaP.

  The light source unit may have a light emitter containing a near-infrared fluorescent dye.

  Furthermore, the light source unit may include a Yb pulse laser, an Nd pulse laser, or a Ti pulse laser. As the Yb pulse laser, a Yb: YAG laser, Yb: Glass laser, Yb fiber laser or the like can be used. As the Nd-based pulse laser, an Nd: YAG laser, an Nd: Glass laser, an Nd-based fiber laser, or the like can be used.

  Further, the optical tomographic imaging apparatus may include a Gaussian distribution shaping filter. In the case where the optical tomographic imaging apparatus is provided with a Gaussian distribution shaping filter, if the low coherence light after passing through the Gaussian distribution shaping filter is within a range satisfying the above conditions, a light source The center wavelength and the full width at half maximum of the low-coherence light emitted from itself may be anything.

A third optical tomographic imaging apparatus of the present invention includes a light source that emits laser light while sweeping a wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object of the measurement light and the reference light;
Interference light detection means for detecting the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light combined by the multiplexing means; ,
In an optical tomographic imaging apparatus comprising: an image acquisition unit that acquires a tomographic image of the measurement object using the intensity of the reflected light at each depth position detected by the interference light detection unit;
The laser beam sweep center wavelength λsc and wavelength sweep width Δλs are:
λsc ² / Δλs ≦ 15
λsc + (Δλs / 2) ≦ 1.2 μm
λsc− (Δλs / 2) ≧ 0.98 μm
It may satisfy.

  The interference light detection means may include an InGaAs-based photodetector.

As described above, water, which is a main constituent material of a living body, has light absorption coefficient peaks at 0.98 μm and 1.2 μm near a wavelength of 1 μm. For this reason, when acquiring an optical tomographic image using light near 1.1 μm with good transmittance, the sideband appears in the autocorrelation waveform due to the influence of the light absorption peaks at 0.98 μm and 1.2 μm. Appears, a pseudo signal is generated, and the image quality of the optical tomographic image is lowered. Therefore, the center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light do not overlap at least within the range of the full width at half maximum Δλ with the light absorption peaks at which the reference light and the reflected light are present at 0.98 μm and 1.2 μm. The following formula λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Is introduced.

That is, the first optical tomographic imaging apparatus of the present invention includes a light source unit that emits low-coherence light, a dividing unit that divides the low-coherence light into measurement light and reference light, and irradiates the measurement light with the measurement light. An irradiating optical system, an optical path length changing means for changing an optical path length of the reference light or the measuring light, reflected light from the measuring object and the reference light when the measuring object is irradiated with the measuring light Based on the intensity of the reflected light and the interference light of the reference light, the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially coincide with each other, In an optical tomographic imaging apparatus comprising: an image acquisition unit that detects the intensity of reflected light at a plurality of depth positions of a measurement target and acquires a tomographic image of the measurement target based on the intensity at each depth position ,
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Therefore, the light transmittance is good, and the influence of light absorption peaks existing at 0.98 μm and 1.2 μm is reduced, so that a high-resolution and high-quality optical tomographic image can be obtained. FIG. 7 is a graph showing the center wavelength λc and the full width at half maximum Δλ satisfying the above expression.

Further, when λc ² / Δλ is large, that is, when the coherence length is long and the spectrum full width at half maximum Δλ is narrow, there is almost no influence of dispersion by water, but when λc ² / Δλ is small, the influence of dispersion by water is reduced. It cannot be ignored.

  From the results shown in FIG. 5, it can be seen that when an optical tomographic image is acquired using low coherence light having a center wavelength λc of around 1.32 μm and a spectral width Δλ of around 76 nm, it is affected by dispersion. To compare with the influence of dispersion that occurs when an optical tomographic image is acquired using low-coherence light having a wavelength λc of 1.1 μm, two parameters of the center wavelength λc and the spectral width Δλ must be considered. It is difficult.

Therefore, the present inventor uses the coherence length of low-coherence light, that is, the influence of dispersion that occurs when an optical tomographic image is acquired using low-coherence light with a central wavelength (λc) of 1.3 μm as a parameter, λc ² / Δλ. And the influence of dispersion that occurs when an optical tomographic image is acquired using low-coherence light with a center wavelength (λc) of 1.1 μm.

When the center wavelength λc = 1.32 μm and the spectral width Δλ = 76 nm, that is, λc ² / Δλ = 23, disclosed in FIG. 5, the broadening ratio (degradation degree) at an underwater propagation distance of 2 mm is 1. 03, the broadening ratio (degradation degree) at an underwater propagation distance of 4 mm is 1.15, and the broadening ratio (degradation degree) at an underwater propagation distance of 10 mm is 1.65.

FIG. 8B shows low-coherence light having a center wavelength λc = 1.32 μm and a spectral half-width λλ = 115 nm, that is, λc ² / Δλ = 15 (the spectrum is shown in FIG. 8A). ) Is used to show the results of actually measuring the degree of degradation of the optical axis direction resolution when propagating through water of thickness 2 mm, 4 mm and 10 mm. As shown in FIG. 8B, the degree of deterioration at an underwater propagation distance of 2 mm is 18.2 / 15.2 = 1.2, the degree of deterioration at an underwater propagation distance of 4 mm is 1.4, and the underwater propagation distance of 10 mm. Degradation level at 1.97 is 1.97, and the degradation of the resolution in the optical axis direction is remarkable.

Further, at λc ² / Δλ = 15 where the resolution degradation is noticeable at the center wavelength λc = 1.32 μm, the degree of degradation in the optical axis direction at the center wavelength λc = 1.15 μm was measured. FIG. 8D shows a low coherence light having a center wavelength λc = 1.15 μm and a spectral half-width Δλ = 90 nm, that is, λc ² /Δλ=14.7 (the spectrum is shown in FIG. 8C). ) Is used to show the results of actually measuring the degree of degradation of the optical axis direction resolution when propagating through water of thickness 2 mm, 4 mm and 10 mm. As shown in FIG. 8D, the degree of deterioration at an underwater propagation distance of 2 mm is 1, the degree of deterioration at an underwater propagation distance of 4 mm is 1, and the degree of deterioration at an underwater propagation distance of 10 mm is 1.14. There is no degradation of directional resolution.

From the above, the range of λc ² / Δλ ≦ 15 is a region in which resolution degradation appears remarkably in the central wavelength λc = 1.32 μm band, but resolution degradation does not occur in the central wavelength λc = 1.1 μm band. From this, the range in which the center wavelength of 1.0 μm band is particularly superior to the center wavelength of 1.3 μm band is
λc ² / Δλ ≦ 15
Can be defined.

  Further, by using a super luminescent diode as a light source for the present optical tomographic imaging apparatus, an inexpensive and easy-to-handle apparatus can be realized. The inventors of the present invention have focused on a superluminescent diode having a window structure on the end face of an optical waveguide as a light source for the optical tomographic imaging apparatus, and have started trial production. The desired device lifetime could not be obtained with the structure of the cent diode. The inventors have found through experiments that there are several important conditions that must be considered in addition to the previously known window region layer material conditions.

  First, when an InGaAs active layer is used as the material of the active layer in order to obtain SL light having a center wavelength of 0.98 μm or more and 1.2 μm or less, InGaAs deteriorates at a temperature of 650 ° C. or higher. The step after the formation is preferably performed in an environment of 650 ° C. or lower. As described above, in a superluminescent diode having a window structure, AlGaAs is often used as a material for forming a window. However, it is known that when a semiconductor layer is formed from a material containing Al, it is preferable to form the semiconductor layer in a high temperature environment. This is because when the ambient temperature is low, a large amount of oxygen is taken up (F. Bugge et al J. Cryustal Grouwh Vol. 272 (2004) P531-537).

  When the window region layer is made of an Al-containing material such as AlGaAs at a temperature of 650 ° C. or less by experiment, a large amount of oxygen is taken into the window region layer, thereby increasing non-radiative recombination centers and It has been found that it is difficult to obtain a desired device lifetime.

  In general, the active layer has a thickness of about 100 mm, but the window region layer needs to grow a film having a thickness of several hundred nm or more. Experiments have shown that when a window region layer film is grown using a material that is not lattice-matched to the GaAs substrate, the crystalline film quality deteriorates and it is difficult to obtain a desired device lifetime. For example, when the window region layer is formed using InGaAs having an In composition lower than that of InGaAs forming the active layer, InGaAs does not lattice match with the GaAs substrate, so that an InGaAs layer having a good crystalline film quality is not formed. The desired device life could not be obtained.

  A material having a larger energy gap than the InGaAs layer forming the active layer and lattice-matched with the GaAs substrate is InGaAsP. However, if such a quaternary semiconductor material is used as a material of a layer to be laminated on various crystal planes such as a window region layer by experiment, the balance of the quaternary material ratio is liable to be lost and the crystal film quality is deteriorated. I understood. It was also found that growth at an ambient temperature of 650 ° C. or lower caused an increase in hillocks and deterioration of the crystalline film quality, and further lowered the reliability of the device.

  Accordingly, the superluminescent diode is formed on the GaAs substrate having the first conductivity, and is disposed on the rear emission end face side of the optical waveguide formed of the InGaAs active layer and the optical waveguide. Has a large refractive index and a low refractive index, has a second conductivity opposite to the first conductivity, and does not contain Al that has a lattice constant within ± 0.1% of the lattice constant of GaAs. Alternatively, if a ternary semiconductor material such as one having a window region layer made of GaAs or InGaP is used, low-coherence light having a distortion-free beam cross-sectional shape can be used easily and at low cost. Further, by using the light source unit having such a superluminescent diode, the reliability of the light source unit is improved, and as a result, the reliability of the entire optical tomographic imaging apparatus is also improved.

  Moreover, if the said light source part has the light-emitting body containing a near-infrared fluorescent pigment | dye, the low coherence light of a desired wavelength band can be used.

  If the light source unit has a Yb-based pulse laser, an Nd-based pulse laser, or a Ti-based pulse laser, high-output, low-coherence light can be easily used.

  In addition, as long as the optical tomographic imaging apparatus includes a Gaussian distribution shaping filter, the center frequency and the full width at half maximum of the spectrum of the low-coherence light emitted from the light source itself may be anything. Spread. In addition, the spectral shape of the low-coherence light after passing through the Gaussian distribution shaping filter becomes a Gaussian distribution type, and an optical tomographic image with higher image quality can be acquired.

A second optical tomographic imaging apparatus of the present invention includes a light source unit that emits low-coherence light,
A light splitting means for splitting the low-coherence light into measurement light and reference light;
An irradiation optical system for irradiating the measurement object with the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement object is irradiated with the measurement light;
Based on the characteristics of the combined interference light of the reflected light and the reference light, the intensity of the reflected light at a plurality of depth positions of the measurement target is calculated, and the measurement is performed based on the intensity at each of these depth positions. In an optical tomographic imaging apparatus comprising an image acquisition means for acquiring a tomographic image of a target,
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Therefore, the light transmittance is good, and the influence of light absorption peaks existing at 0.98 μm and 1.2 μm is reduced, so that a high-resolution and high-quality optical tomographic image can be obtained. Further, the range of λc ² / Δλ ≦ 15 is a region in which the resolution degradation is noticeable in the central wavelength λc = 1.32 μm band, but the resolution is not degraded in the central wavelength λc = 1.1 μm band, and the central wavelength is 1.0 μm band. Is particularly advantageous for the center wavelength band of 1.3 μm.

The third optical tomographic imaging apparatus of the present invention is a light source that emits laser light while sweeping the wavelength at a constant period, and light that divides the laser light emitted from the light source into measurement light and reference light Dividing means, irradiating means for irradiating the measurement light to the measurement object, combining means for combining the reflected light of the measurement light from the measurement object and the reference light, and combining by the combining means Further, based on the frequency and intensity of interference light between the reflected light and the reference light, interference light detection means for detecting the intensity of the reflected light at each depth position of the measurement object, and detection by the interference light detection means In an optical tomographic imaging apparatus having image acquisition means for acquiring the tomographic image of the measurement object using the intensity of the reflected light at each of the depth positions, the sweep center wavelength λsc and the wavelength sweep width of the laser light Δλs is
λsc ² / Δλs ≦ 15
λsc + (Δλs / 2) ≦ 1.2 μm
λsc− (Δλs / 2) ≧ 0.98 μm
Therefore, the light transmittance is good, and the influence of light absorption peaks existing at 0.98 μm and 1.2 μm is reduced, so that a high-resolution and high-quality optical tomographic image can be obtained. In the range of λsc ² / Δλs ≦ 15, light with a sweep center wavelength of 1.0 μm is particularly superior to light with a sweep center wavelength of 1.3 μm.

  The optical tomographic imaging apparatus according to the first embodiment of the present invention will be described below with reference to FIG. FIG. 9 is a schematic configuration diagram of the optical tomographic imaging apparatus according to the first embodiment of the present invention.

  An optical tomographic imaging apparatus 200 shown in FIG. 9 acquires a tomographic image to be measured by the above-described TD-OCT measurement, and includes a light source unit 210 including a light source 10 and a condenser lens 11 that emit a laser beam La. And a light splitting means 2 for splitting the laser light La emitted from the light source unit 210 and propagating through the optical fiber FB1, and a light splitting means 3 for splitting the laser light La passing therethrough into the measurement light L1 and the reference light L2. The optical path length adjusting means 220 for adjusting the optical path length of the reference light L2 split by the light splitting means 3 and propagated through the optical fiber FB3, and the measurement light L1 split by the light splitting means 3 and propagated through the optical fiber FB2 An optical probe 230 that irradiates the measurement target Sb, and a multiplexing means 4 that combines the reflected light L3 and the reference light L2 from the measurement target when the measurement target Sb is irradiated from the optical probe 230. light And an interference light detection means 240 that detects the interference light L4 of the reflected light L3 and the reference light L2 that is multiplexed by the multiplexing means 4.

  The light source unit 210 has an SLD (Super Luminescent Diode) 10 that emits low-coherent light La having a center wavelength (λc) of 1.1 μm and a full width at half maximum of 90 nm, and the light emitted from the light source 10 enters the optical fiber FB1. And an optical system 11 for the purpose. The detailed configuration of the SLD 10 will be described later.

  The optical path length adjusting means 220 is a mirror that is movable in the direction of arrow A in the figure so as to change the distance between the collimator lens 21 that collimates the reference light L2 emitted from the optical fiber FB3 and the collimator lens 21. 23 and mirror moving means 24 for moving the mirror 23, and has a function of changing the optical path length of the reference light L2 in order to change the measurement position in the measurement object Sb in the depth direction. . The reference light L 2 whose optical path length has been changed by the optical path length adjusting means 220 is guided to the multiplexing means 4.

  The optical probe 230 includes a cylindrical probe outer cylinder 15 having a closed tip, and one optical fiber 13 disposed in an inner space of the probe outer cylinder 15 so as to extend in the axial direction of the outer cylinder 15. A prism mirror 17 that deflects the light L emitted from the tip of the optical fiber 13 in the circumferential direction of the probe outer cylinder 15, and the light L emitted from the tip of the optical fiber 13 is arranged on the outer circumference of the probe outer cylinder 15. A rod lens 18 that condenses light to converge on the measurement target Sb as a scanning object, and a motor 14 that rotates the prism mirror 17 about the axis of the optical fiber 13 as a rotation axis are provided.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light La guided from the light source unit 210 through the optical fiber FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively. The measurement light L1 is guided through the optical fiber FB2, and the reference light L2 is guided through the optical fiber FB3. The light splitting means 3 in this example also functions as the multiplexing means 4.

  An optical probe 230 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 230. The optical probe 230 is inserted into a body cavity from a forceps opening through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 31.

  Further, the multiplexing means 4 is composed of a 2 × 2 optical fiber coupler as described above, the reference light L2 that has been subjected to frequency shift and change of the optical path length by the optical path length adjusting means 230, and the reflected light L3 from the measurement target Sb. Are combined and emitted to the interference light detection means 240 side via the optical fiber FB4.

  The interference light detection means 240 detects the light intensity of the interference light L4. The light detectors 40a and 40b that measure the light intensity of the interference light L4, the detection value of the light detector 40a, and the light detector 40b And an arithmetic unit 41 that performs balance detection by adjusting the input balance of the detection values. Specifically, when the difference between the total optical path length of the measuring light L1 and the reflected light L3 reflected or backscattered at a certain point of the measurement target Sb and the optical path length of the reference light L2 is shorter than the coherence length of the light source Only an interference signal with an amplitude proportional to the amount of reflected light is detected. By scanning the optical path length by the optical path length adjusting means 220, the reflection point position (depth) of the measurement target Sb from which the interference signal is obtained changes, and the interference light detection means 240 reflects the reflection at each measurement position of the measurement target Sb. A rate signal is detected. The information on the measurement position is output from the optical path length adjustment unit 220 to the image acquisition unit 250. Based on the information of the measurement position in the mirror moving unit 24 and the signal detected by the interference light detection unit 240, the image acquisition unit 250 obtains the reflected light intensity distribution information in the depth direction of the measurement target Sb.

  The operation of the optical tomographic imaging apparatus 1 having the above configuration will be described below. When acquiring a tomographic image, the optical path length is adjusted so that the measurement target Sb is positioned within the measurable region by first moving the mirror 23 in the direction of arrow A. Thereafter, light La is emitted from the light source unit 210, and this light La is split by the light splitting means 3 into the measurement light L1 and the reference light L2. The measurement light L1 is emitted from the optical probe 230 toward the body cavity and irradiated on the measurement target Sb.

  Then, the reflected light L3 from the measurement object Sb is combined with the reference light L2 reflected by the reflecting mirror 22 to generate interference light L4.

  The interference light L4 is split by the light splitting means 3 (multiplexing means 4), one is input to the photodetector 40a, and the other is input to the photodetector 40a.

  The interference light detection means 240 adjusts the input balance between the detection value of the light detector 40a and the detection value of the light detector 40b to perform balance detection, detects the light intensity of the interference light L4, and sends it to the image acquisition means 250. Output.

  Based on the detected light intensity of the interference light L4, the image acquisition means 250 obtains reflected light intensity information at a predetermined depth of the measurement object Sb. Next, the optical path length adjusting means 330 changes the optical path length of the reference light L2, similarly detects the light intensity of the interference light L4, and acquires reflected light intensity information at different predetermined depths. By repeating such an operation, the reflected light intensity information in the depth direction (one-dimensional) of the measuring object Sb can be acquired.

  If the measurement light L1 is scanned on the measurement target Sb by rotating the prism mirror 17 by the motor 14 of the optical probe 230, the depth direction of the measurement target Sb is measured at each portion along the scanning direction. Since information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measurement object Lb to scan the measurement light L1 in a second direction orthogonal to the scanning direction, this second It is also possible to obtain a tomographic image of a tomographic plane including the direction.

  The tomographic image acquired in this way is displayed on the display device 260. For example, by moving the optical probe 230 in the left-right direction in FIG. 9 and causing the measurement object Lb to scan the measurement light L1 in a second direction orthogonal to the scanning direction, this second It is also possible to obtain a tomographic image of a tomographic plane including the direction.

For example, if the light having the center wavelength (λc) of 1.1 μm and the spectrum full width at half maximum (Δλ) of 90 nm is used as the low coherence light La, the measurement light L1, the reference light L2, and the reflected light L3 have the center wavelength (λc) of 1.1. Since μm and the full width at half maximum (Δλ) of 90 nm, λc ² / Δλ of the reference light L2 and the reflected light L3 are 13.9, and considering the influence of dispersion, the central wavelength is 1.0 μm from the central wavelength 1.3 μm band. The belt is particularly advantageous. Further, the center wavelength λc and the full width at half maximum Δλ are
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Therefore, the measurement light L1 has good transmittance in the measurement object Sb, and the reflected light L3 is less affected by light absorption peaks of water present at 0.98 μm and 1.2 μm. A high-quality optical tomographic image can be acquired.

Next, the SLD 10 of the light source unit 210 will be described with reference to FIG. The SLD 10 is a superluminescent diode having an SBR structure formed by crystal growth using a metal organic chemical vapor deposition (MOCVD) method. FIG. 10 shows a cross-sectional view of the structure of the SLD 10. As a raw material gas of metal organic chemical vapor deposition (MOCVD), TEG (triethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), is used AsH ₃ (arsine), PH ₃ (phosphine), or the like. Further, SiH ₄ (silane) and DEZ (diethyl zinc) are used as dopants.

The SLD 10 includes an optical waveguide portion 12 and a window portion 13 provided on the side opposite to the light emitting end of the optical waveguide portion 12. The optical waveguide section 12 has an SBR structure in which a ridge-shaped p-type In _0.49 Ga _0.51 P upper second cladding layer 109 formed on the p-type GaAs etching stop layer 108 is used as a light guide.

In the SLD 10, an n-type GaAs buffer layer 102 and an n-type In _0.49 Ga _0.51 P lower cladding layer 103 are sequentially stacked on an n-type GaAs substrate 101. In the optical waveguide section 12, on the n-type In _0.49 Ga _0.51 P lower cladding layer 103, an undoped GaAs lower optical guide layer 104, an InGaAs multiple quantum well active layer 105, an undoped GaAs upper optical guide layer 106, a p-type In _0.49 A Ga _0.51 P upper first cladding layer 107 and a p-type GaAs etching stop layer 108 are sequentially stacked. As a material of the InGaAs multiple quantum well active layer 105, In _x Ga _1-x As having an In ratio X> 0.3 is used.

On the p-type GaAs etching stop layer 108, a ridge-shaped p-type In _0.49 Ga _0.51 P upper second cladding layer 109 is formed. An n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P current blocking layer 113 is formed on the side surface of the ridge (p-type In _0.49 Ga _0.51 P upper second cladding layer 109), and the ridge and n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P p-type GaAs cap layer (0.1 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ^-3 ) 110 on the upper surface of P current blocking layer 113, p-type In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P A third cladding layer 114 and a p-GaAs contact layer 115 are formed.

In the window part 13, on the n-type In _0.49 Ga _0.51 P lower cladding layer 103, a p-type GaAs window region layer 111, an etching stop for window region layer In _0.49 Ga _0.51 P layer 112, n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P current blocking layer 113, p-type In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P upper third cladding layer 114 and p-GaAs contact layer 115 are sequentially stacked.

  In the SLD 10 having such a configuration, light guided through the InGaAs multiple quantum well active layer 105 to the window portion 13 side is emitted and diffused into the p-type GaAs window region layer 111. For this reason, laser oscillation is suppressed and SLD (super luminescent) light having a wide spectrum half width is emitted from the light exit end. The SLD 10 emits SL light having a center wavelength of 1.1 μm, a half-value width of 90 nm, and 30 mW.

  The SLD 10 has a larger energy gap and a lower refractive index than the InGaAs multiple quantum well active layer 105, and the lattice constant is lattice matched with the lattice constant of GaAs within ± 0.1%, and the window region is formed by p-type GaAs containing no Al. Since the layer 111 is formed, the InGaAs active layer 105 without deterioration and the window region layer 111 having a good crystalline film quality are realized, so that the device has a long lifetime, a high output, and a distortion-free beam cross-sectional shape. Super luminescent light can be emitted.

  Since the SLD 10 is not exposed to a temperature environment higher than 650 ° C. after the InGaAs multiple quantum well active layer 105 is formed, the InGaAs multiple quantum well active layer 105 is not deteriorated. The output can be maintained for a long time.

Instead of SLD 10, SLD 10a having window region layer 111a using p-type In _0.49 Ga _0.51 P can also be used. p-type In _0.49 Ga _0.51 P also has a larger energy gap and lower refractive index than InGaAs multiple quantum well active layer 105, lattice constant matches with the lattice constant of GaAs within ± 0.1% range, and does not contain Al SLD10a is also a semiconductor material. Superluminescent light having a wavelength of 1.1 μm and a half-value width of 90 nm and a high-output and distortion-free beam cross-sectional shape can be emitted. Further, when the device was continuously driven at room temperature to evaluate the device life, the output became 90% of the initial value after about 5000 hours had elapsed.

Further, an SLD 10b having an internal stripe structure shown in FIG. 11 can be used instead of the SLD 10. As shown in FIG. 11, the SLD 10 b includes an optical waveguide portion 15 and a window portion 16 provided on the side opposite to the light emitting end of the optical waveguide portion 15. The optical waveguide portion 15 has an internal stripe structure in which the flow of current is narrowed by a stripe structure having a width of 3 mm formed on the p-type GaAs etching stop layer 108. On top of the p-type GaAs window region layer (0.5 μm) 118 is an n-type (Al _0.33 Ga _0.67 ) _0.5 As current blocking layer (0.5 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 119 for the window region layer. Is provided. Other configurations are almost the same as those of the SLD 10. Alternatively, an SLD 10c having a window region layer 118a using p-type In _0.49 Ga _0.51 P can be used.

  By using the light source unit 210 having such an SLD, the reliability of the light source unit 210 is improved, and as a result, the reliability of the optical tomographic imaging apparatus 200 is also improved.

  The SLDs 10 and 10a have an SBR structure, and the SLDs 10b and 10c have an internal stripe structure, but the structure of the SLD is not limited to these structures, and other index guide structures. Or an SLD having a gain guide structure.

Instead of the light source unit 210, a light source unit 410 including a pulse light source unit 141, a pulse compression unit 142, and a spectrum shaping unit 140 using a mode-locked solid-state laser as shown in FIG. It is done. The pulse light source unit 141 includes a mode-locked solid-state laser 143 and a condensing lens 144 that introduces pulsed light emitted from the mode-locked solid-state laser 143 into the pulse compression unit 142. The pulse compression unit 142 is composed of a photonic crystal fiber 145 and an optical connector 146 having negative dispersion characteristics. Since the photonic crystal fiber can select a structural dispersion value, a negative dispersion characteristic can be realized in a desired wavelength band. The spectrum shaping unit 140 includes an optical connector 147, a Gaussian distribution shaping filter 148 that shapes the signal light so that the spectrum shape of the broadband light output from the pulse compression unit 142 has a Gaussian distribution, and the formed low coherence in the fiber. The optical connector 149 is introduced into the FB1. The Gaussian distribution shaping filter 148 has a relationship between the center wavelength λc and the full width at half maximum Δλ.
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
The spectrum of low-coherence light is shaped so as to satisfy the above.

  Further, instead of the light source unit 210, a unit having a light source unit 420 having a light emitter containing a near-infrared fluorescent dye as shown in FIG.

  The light source unit 420 includes a capillary 153 that is a light emitter containing a near-infrared fluorescent dye, a Yb: YAG laser 151 for exciting the capillary 153, an excitation light cut filter 156, and lenses 152, 155, and 157. It is configured. In the capillary 153, a dye that can be excited at 1.0 to 1.2 μm is enclosed together with a solvent. For example, the absorption spectra of dyes 1, 2, and 3 are shown in FIG. This is excited by light having a wavelength of 1.03 μm emitted from the Yb: YAG laser 151. When the concentration of each dye is adjusted so that the fluorescence intensity is almost the same for the three kinds of dyes, fluorescence as shown in FIG. 14 is obtained. The addition of fluorescence from the three types of dyes results in a 1000 nm to 1200 nm band spectrum as shown by the broken line in FIG. The broadband light thus emitted passes through the lens 155, the excitation light cut filter 156, and the lens 157, and is guided to the optical fiber FB1 as low-coherence light L1. The excitation light cut filter 156 prevents the excitation light emitted from the Yb: YAG laser from entering the optical fiber FB1.

  As the fluorescent dye, a pyrylium dye as shown in FIG. 16 can be used. Depending on the combination of dyes, an excitation laser having an optimum wavelength such as an Nd: YLF laser with an oscillation wavelength of 1.04 μm or an Nd: YAG laser with an oscillation wavelength of 1.064 μm may be combined.

  As still another modification of the present embodiment, a light source unit 430 using a Yb pulse laser, Nd pulse laser, or Ti pulse laser as shown in FIG. May be used. As the Yb pulse laser, a Yb: YAG laser, Yb: Glass laser, Yb fiber laser or the like can be used. As the Nd-based pulse laser, an Nd: YAG laser, an Nd: Glass laser, an Nd-based fiber laser, or the like can be used.

  Note that each of the light source units 210, 420, and 430 may include a spectrum shaping unit 140 having a Gaussian distribution shaping filter 148, as with the light source unit 410. Further, the spectrum shaping unit 140 having the Gaussian distribution shaping filter 148 may be disposed at any part of the optical path before the reference light L2 and the reflected light L3 are combined. For example, as shown in FIG. 18, a spectrum shaping unit 140a having an optical connector 147a, a Gaussian distribution shaping filter 148a, and an optical connector 149a is arranged in the optical path of the reference light L2, and in the optical path of the measurement light L2 (reflected light L3). Further, a spectrum shaping unit 140b having an optical connector 147b, a Gaussian distribution shaping filter 148b, and an optical connector 149b may be disposed.

In the case of providing such a Gaussian distribution shaping filter, in the light after passing through the Gaussian distribution shaping filter, the relationship between the center wavelength λc and the full width at half maximum of the spectrum Δλ is
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Anything that satisfies the requirements is acceptable. That is, when a Gaussian distribution shaping filter is provided, if the low coherence light after passing through the Gaussian distribution shaping filter is within the range satisfying the above conditions, for example, SLD, mode-locked solid-state laser, near-infrared fluorescent dye The center wavelength and the full width at half maximum of the light source such as a light-emitting body containing a light source or a pulse laser may be arbitrary. When two Gaussian distribution shaping filters 148a and 148b are provided, the filter characteristics are preferably substantially the same, but the measurement of the light intensity of the interference light L4 is hindered. It may be different as long as it is not.

  Furthermore, as shown in FIG. 19, a phase modulator 440 having a function of giving a slight frequency shift to the reference light L2 may be arranged in the optical path of the reference light L2 (optical fiber FB3). In this case, the interference light detection means 340 can detect the light intensity of the interference light L4 propagated from the multiplexing means 4 through the optical fiber FB2 by, for example, heterodyne detection. Specifically, when the sum of the total optical path length of the measurement light L1 and the total optical path length of the reflected light L3 is equal to the total optical path length of the reference light L2, it is strong and weak at the difference frequency between the reference light L2 and the reflected light L3. A beat signal that repeats is generated. By detecting this beat signal, the light intensity of the interference light L4 can be detected with high accuracy.

  Next, an optical tomographic imaging apparatus that is a specific second embodiment of the present invention will be described with reference to FIG. FIG. 20 is a schematic configuration diagram of an optical tomographic imaging apparatus according to the second embodiment of the present invention. In FIG. 20, the same elements as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted unless particularly necessary.

  The optical tomographic imaging apparatus 500 acquires a tomographic image of a measurement target such as a living tissue or a cell in a body cavity by the above-described SD-OCT measurement, and includes a light source unit 210 that emits low-coherence light La and The light splitting means 53 for splitting the light La emitted from the light source unit 210 into the measuring light L1 and the reference light L2, and the optical path length adjusting means 520 for adjusting the optical path length of the reference light L2 split by the light splitting means 53. And the optical probe 230 that irradiates the measurement object Sb with the measurement light L1 divided by the light dividing means 53, and the reflected light L3 reflected by the measurement object Sb when the measurement light L1 is irradiated onto the measurement object Sb. It has the combining means 54 which combines the light L2, and the interference light detection means 540 which detects the interference light L4 between the combined reflected light L3 and the reference light L2.

  The light splitting means 53 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light La guided from the light source unit 210 through the optical fiber FB51 into the measurement light L1 and the reference light L2. The light splitting means 53 is optically connected to the two optical fibers FB52 and FB53, the measuring light L1 is guided through the optical fiber FB52, and the reference light L2 is guided through the optical fiber FB53. The light splitting means 53 in this example also functions as the multiplexing means 54.

  An optical probe 230 is optically connected to the optical fiber FB52, and the measurement light L1 is guided from the optical fiber FB52 to the optical probe 230.

  On the other hand, optical path length adjusting means 520 is arranged on the side of the optical fiber FB53 where the reference light L2 is emitted. The optical path length adjusting unit 520 changes the optical path length of the reference light L2 in order to adjust the position at which tomographic image acquisition is started, and reflects the reference light L2 emitted from the optical fiber FB53. 522, a first optical lens 521a disposed between the reflection mirror 522 and the optical fiber FB53, and a second optical lens 521b disposed between the first optical lens 521a and the reflection mirror 522. Yes.

  The first optical lens 521a has a function of converting the reference light L2 emitted from the core of the optical fiber FB53 into parallel light and condensing the reference light L2 reflected by the reflection mirror 522 onto the core of the optical fiber FB53. ing. Further, the second optical lens 521b condenses the reference light L2 converted into parallel light by the first optical lens 521a on the reflection mirror 522, and makes the reference light L2 reflected by the reflection mirror 522 into parallel light. have. That is, a confocal optical system is formed by the first optical lens 521a and the second optical lens 521b.

  Therefore, the reference light L2 emitted from the optical fiber FB53 is converted into parallel light by the first optical lens 521a, and is condensed on the reflection mirror 522 by the second optical lens 521b. Thereafter, the reference light L2 reflected by the reflection mirror 522 becomes parallel light by the second optical lens 521b, and is condensed on the core of the optical fiber FB53 by the first optical lens 521a.

  Further, the optical path length adjusting means 520 has a base 23 on which the second optical lens 521b and the reflection mirror 522 are fixed, and a mirror moving means 24 for moving the base 23 in the optical axis direction of the first optical lens 521a. is doing. When the base 23 moves in the direction of arrow A, the optical path length of the reference light L2 can be changed.

  The multiplexing means 54 is composed of a 2 × 2 optical fiber coupler as described above, and combines the reference light L2 whose optical path length has been changed by the optical path length adjusting means 520 and the reflected light L3 from the measuring object Sb. The light is emitted to the interference light detection means 540 side through the optical fiber FB4.

  On the other hand, the interference light detecting means 540 detects the interference light L4 between the reflected light L3 combined by the combining means 54 and the reference light L2, and the interference light L4 emitted from the optical fiber FB4 is converted into parallel light. The collimator lens 541 to be converted, the spectroscopic means 542 for splitting the interference light L4 having a plurality of wavelength bands for each wavelength band, and the light detection means 544 for detecting the interference light L4 of each wavelength band split by the spectroscopic means 542. And have.

  The spectroscopic means 542 is composed of, for example, a diffraction grating element or the like. The spectroscopic interference light L4 incident on the spectroscopic means 542 is split and emitted toward the light detecting means 544. The light detection means 544 is composed of, for example, a CCD array in which light sensors are arranged one-dimensionally or two-dimensionally, and each light sensor detects the interference light L4 dispersed as described above for each wavelength band. It is like that.

  The light detection means 544 is connected to an image acquisition means 550 made up of a computer system such as a personal computer, and this image acquisition means 550 is connected to a display device 560 made up of a CRT or a liquid crystal display device.

  Hereinafter, the operation of the optical tomographic imaging apparatus 500 having the above configuration will be described. When acquiring a tomographic image, the optical path length is adjusted so that the measurement target Sb is positioned within the measurable region by first moving the base 23 in the direction of arrow A. Thereafter, the light La is emitted from the light source unit 210, and the light La is split by the light splitting means 53 into the measurement light L1 and the reference light L2. The measurement light L1 is emitted from the optical probe 230 toward the body cavity and irradiated on the measurement target Sb. At this time, the measurement light L1 emitted from the optical probe 230 operating as described above scans the measurement target Sb in one dimension. Then, the reflected light L3 from the measurement target Sb is combined with the reference light L2 reflected by the reflecting mirror 522, and the interference light L4 between the reflected light L3 and the reference light L2 is detected by the interference light detection means 540. The detected interference light L4 is subjected to appropriate waveform compensation and noise removal in the image acquisition means 550, and then subjected to Fourier transform, thereby obtaining reflected light intensity distribution information in the depth direction of the measurement target Sb.

  If the measurement light L1 is scanned on the measurement target Sb by rotating the prism mirror 17 by the motor 14 of the optical probe 230, the depth direction of the measurement target S in each part along the scanning direction is measured. Since information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the display device 560. For example, by moving the optical probe 230 in the left-right direction in FIG. 20 and causing the measurement object Lb to scan the measurement light L1 in a second direction orthogonal to the scanning direction, this second It is also possible to obtain a tomographic image of a tomographic plane including the direction.

For example, if light having a center wavelength (λc) of 1.1 μm and a spectrum full width at half maximum (Δλ) of 90 nm is used as the low coherence light La, λc ² / Δλ is 13.9. The center wavelength 1.0 μm band is particularly superior to the wavelength 1.3 μm band. Further, the center wavelength λc and the full width at half maximum Δλ are
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
Therefore, the measurement light L1 has a good transmittance in the measurement object Sb, and the reflected light L3 is further less affected by the light absorption peaks of water present at 0.98 μm and 1.2 μm. In addition, a high-quality optical tomographic image can be acquired.

  Also in the present embodiment, as in the first embodiment, instead of the light source unit 210, the pulse light source unit 141, the mode-locked solid-state laser 143, the pulse compression unit 142, and the like shown in FIG. A light source unit 410 composed of a condensing lens 144 for introducing pulsed light emitted from a mode-locked solid-state laser 143, or a light source unit 420 having a light emitter containing a near-infrared fluorescent dye shown in FIG. Can also be used. Alternatively, a light source unit 430 using a Yb pulse laser, an Nd pulse laser, or a Ti pulse laser shown in FIG. As the Yb pulse laser, a Yb: YAG laser, Yb: Glass laser, Yb fiber laser or the like can be used. As the Nd-based pulse laser, an Nd: YAG laser, an Nd: Glass laser, an Nd-based fiber laser, or the like can be used. Further, as shown in FIG. 18, a spectrum shaping unit 140a having an optical connector 147a, a Gaussian distribution shaping filter 148a and an optical connector 149a is arranged in the optical path of the reference light L2, and the optical path of the measurement light L2 (reflected light L3). A spectrum shaping unit 140b having an optical connector 147b, a Gaussian distribution shaping filter 148b, and an optical connector 149b may be disposed therein.

  Hereinafter, an optical tomographic imaging apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 21 is a schematic configuration diagram of an optical tomographic imaging apparatus according to the third embodiment of the present invention. In FIG. 21, the same elements as those in FIG. 20 are denoted by the same reference numerals, and description thereof will be omitted unless particularly necessary.

  An optical tomographic imaging apparatus 600 shown in FIG. 21 acquires a tomographic image to be measured by the above-described SS-OCT measurement, and includes a light source unit 610 that emits light Ls, and light emitted from the light source unit 610. The light is split by the light splitting means 63 for splitting Ls into measurement light Ls1 and reference light Ls2, the optical path length adjusting means 520 for adjusting the optical path length of the reference light Ls2 split by the light splitting means 63, and the light splitting means 63. The optical probe 630 that irradiates the measurement target Sb with the measured light Ls1, and the multiplexing of the reflected light Ls3 and the reference light Ls2 reflected by the measurement target Sb when the measurement target Sb is irradiated with the measurement light Ls1. Means 64 and interference light detection means 640 for detecting interference light Ls4 between the combined reflected light Ls3 and reference light Ls2.

The light source unit 610 emits the laser light Ls while sweeping the frequency at a constant period. As shown in FIG. 22, the frequency f of the laser light Ls is a center frequency fc and is periodically swept within a predetermined frequency sweep width Δf. Therefore, the frequency f sweeps in a sawtooth shape between the frequency f ₀ (fc−Δf / 2) and the frequency fc + Δf / 2.

  For convenience of explanation, the description is made by paying attention to the change in the frequency f of the laser light Ls. However, since the frequency f = the speed of light c / wavelength λ, the frequency f of the laser light Ls is swept at a constant period. Is synonymous with sweeping the wavelength λ of the laser beam Ls at a constant period, and the center frequency fc of the laser beam Ls in FIG. 22 is the center wavelength λsc when the wavelength λ is swept, and the frequency sweep The width Δf is the wavelength sweep width Δλs. Further, although FIG. 22 illustrates the case where the frequency is swept in a sawtooth shape, the frequency may be swept in a wave shape.

The center wavelength λsc and the wavelength sweep width Δλs of the laser light Ls are
λsc ² / Δλs ≦ 15
λsc + (Δλs / 2) ≦ 1.2 μm
λsc− (Δλs / 2) ≧ 0.98 μm
The center frequency fc and the frequency sweep width Δf of the laser light Ls are set so as to satisfy the above.

  The light source unit 610 includes a semiconductor optical amplifier (semiconductor gain medium) 611 and an optical fiber FB70, and the optical fiber FB70 is connected to both ends of the semiconductor optical amplifier 611. The semiconductor optical amplifier 611 has a function of emitting weak emission light to one end side of the optical fiber FB70 by injecting drive current and amplifying light incident from the other end side of the optical fiber FB70. When a drive current is supplied to the semiconductor optical amplifier 611, a sawtooth laser beam Ls is emitted to the optical fiber FB61 by an optical resonator formed by the semiconductor optical amplifier 611 and the optical fiber FB70. .

  Further, an optical branching device 612 is coupled to the optical fiber FB70, and a part of the light guided in the optical fiber FB70 is emitted from the optical branching device 612 to the optical fiber FB71 side. Light emitted from the optical fiber FB71 is reflected by a rotary polygon mirror (polygon mirror) 616 via a collimator lens 613, a diffraction grating 614, and an optical system 615. The reflected light is incident on the optical fiber FB71 again via the optical system 615, the diffraction grating 614, and the collimator lens 613.

  Here, the rotating polygonal mirror 616 rotates in the direction of the arrow R1, and the angle of each reflecting surface changes with respect to the optical axis of the optical system 615. As a result, only the light in a specific frequency region out of the light split by the diffraction grating 614 returns to the optical fiber FB71 again. The frequency of light returning to the optical fiber FB71 is determined by the angle between the optical axis of the optical system 615 and the reflecting surface. Then, light in a specific frequency range incident on the optical fiber FB71 is incident on the optical fiber FB70 from the optical splitter 612, and as a result, laser light Ls in a specific frequency range is emitted to the optical fiber FB61 side. .

  Therefore, when the rotary polygon mirror 616 rotates at a constant speed in the direction of the arrow R1, the wavelength λ of the light incident on the optical fiber FB71 again changes with a constant period as time passes. In this way, the wavelength-swept laser beam Ls is emitted from the light source unit 610 to the optical fiber FB61 side.

  The light splitting means 63 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light Ls guided from the light source unit 610 through the optical fiber FB61 into the measurement light Ls1 and the reference light Ls2. The light splitting means 63 is optically connected to the two optical fibers FB62 and FB63, respectively. The measurement light Ls1 is guided through the optical fiber FB62, and the reference light Ls2 is guided through the optical fiber FB63. The light splitting means 63 in this example also functions as the multiplexing means 64.

  An optical probe 630 is optically connected to the optical fiber FB62, and the measurement light Ls1 is guided from the optical fiber FB62 to the optical probe 630.

  The optical probe 630 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB62 by an optical connector 631. The optical probe 630 includes a cylindrical probe outer cylinder 635 whose tip is closed, and one optical fiber 633 disposed in an inner space of the probe outer cylinder 635 so as to extend in the axial direction of the outer cylinder 635. And a prism mirror 637 that deflects the light Ls emitted from the tip of the optical fiber 633 in the circumferential direction of the probe outer cylinder 635, and the light Ls emitted from the tip of the optical fiber 633 is arranged on the outer circumference of the probe outer cylinder 635. A rod lens 638 that collects light so as to converge on the measurement target Sb as a scanned body and a motor 634 that rotates the optical fiber 633 around the optical axis direction are provided.

  On the other hand, optical path length adjusting means 520 is arranged on the side of the optical fiber FB63 where the reference light Ls2 is emitted. The optical path length adjusting unit 520 changes the optical path length of the reference light Ls2 in order to adjust the position where the tomographic image acquisition is started, and reflects the reference light Ls2 emitted from the optical fiber FB63. 523, a first optical lens 521a disposed between the reflection mirror 523 and the optical fiber FB63, and a second optical lens 521b disposed between the first optical lens 521a and the reflection mirror 523. Yes.

  The first optical lens 521a has a function of converting the reference light Ls2 emitted from the core of the optical fiber FB63 into parallel light and condensing the reference light Ls2 reflected by the reflection mirror 523 onto the core of the optical fiber FB63. ing. Further, the second optical lens 521b condenses the reference light Ls2 converted into parallel light by the first optical lens 521a on the reflection mirror 523, and makes the reference light Ls2 reflected by the reflection mirror 523 parallel light. have. That is, a confocal optical system is formed by the first optical lens 521a and the second optical lens 521b.

  Therefore, the reference light Ls2 emitted from the optical fiber FB63 is converted into parallel light by the first optical lens 521a and is condensed on the reflection mirror 523 by the second optical lens 521b. Thereafter, the reference light Ls2 reflected by the reflecting mirror 523 is converted into parallel light by the second optical lens 521b, and is condensed on the core of the optical fiber FB63 by the first optical lens 521a.

  Further, the optical path length adjusting means 520 has a base 523 to which the second optical lens 521b and the reflecting mirror 523 are fixed, and a mirror moving means 24 for moving the base 523 in the optical axis direction of the first optical lens 521a. is doing. Then, when the base 523 moves in the direction of arrow A, the optical path length of the reference light Ls2 can be changed.

  Further, the multiplexing means 64 is composed of a 2 × 2 optical fiber coupler as described above, the reference light Ls2 that has been subjected to frequency shift and change of the optical path length by the optical path length adjusting means 520, and the reflected light Ls3 from the measurement target Sb. Are combined and emitted to the interference light detection means 640 side via the optical fiber FB64.

  The interference light detection means 640 detects the interference light Ls4 between the reflected light Ls3 and the reference light Ls2 combined by the multiplexing means 64, and an InGaAs-based photodetector that measures the light intensity of the interference light Ls4. 642a and 642b, and a calculation unit 641 that performs balance detection by adjusting the input balance between the detection value of the photodetector 642a and the detection value of the photodetector 642b. The interference light Ls4 is divided into two by the light splitting means 63 and detected by the photodetectors 642a and 642b.

  The image acquisition unit 650 detects the intensity of the reflected light Ls3 at each depth position of the measurement target Sb by performing Fourier transform on the interference light Ls4 detected by the interference light detection unit 640, and obtains a tomographic image of the measurement target Sb. get. The acquired tomographic image is displayed on the display device 660.

  Here, the detection of the interference light Ls4 and the generation of the image in the interference light detection means 640 and the image acquisition means 650 will be briefly described. Details of this point are described in “Mitsuo Takeda,“ Optical Frequency Scanning Spectrum Interference Microscope ”, Optical Technology Contact, 2003, Vol. 41, No. 7, p426-p432”.

When the measurement object Lb is irradiated with the measurement light Ls1, interference fringes with respect to each optical path length difference l when the reflected light Ls3 and the reference light Ls2 from each depth of the measurement object Sb interfere with each other with various optical path length differences. S (l) is the light intensity I (k) detected by the interference light detection means 640,
I (k) = ∫ ₀ ^∞ S (l) [1 + cos (kl)] dl
It is represented by Here, k is the wave number, and l is the optical path length difference. It can be considered that the above equation is given as an interferogram in the optical frequency domain with the wave number k = ω / c as a variable. For this reason, in the image acquisition means 250, the spectral interference fringes detected by the interference light detection means 640 are subjected to Fourier transform, and the light intensity S (l) of the interference light Ls4 is determined, so that from the measurement start position of the measurement object Sb. Distance information and reflection intensity information can be acquired, and a tomographic image can be generated.

  Hereinafter, the operation of the optical tomographic imaging apparatus 600 having the above configuration will be described. When acquiring a tomographic image, the optical path length is adjusted so that the measurement target Sb is positioned within the measurable region by first moving the base 523 in the direction of arrow A. Thereafter, the light Ls is emitted from the light source unit 610, and the light Ls is split into the measurement light Ls1 and the reference light Ls2 by the light splitting means 63. The measurement light Ls1 is emitted from the optical probe 630 toward the body cavity and irradiated to the measurement target Sb. At this time, the measurement light Ls1 emitted from the optical probe 630 operating as described above scans the measurement object Sb in a one-dimensional manner. Then, the reflected light Ls3 from the measurement target Sb is combined with the reference light Ls2 reflected by the reflecting mirror 523, and the interference light Ls4 between the reflected light Ls3 and the reference light Ls2 is detected by the interference light detection means 640. The detected interference light Ls4 is subjected to appropriate waveform compensation and noise removal in the image acquisition means 250 and then subjected to Fourier transform, thereby obtaining reflected light intensity distribution information in the depth direction of the measurement target Sb.

  Then, by rotating the optical fiber 633 by the motor 634 of the optical probe 630, the measurement light Ls1 is scanned on the measurement target Sb, and the depth direction of the measurement target Sb is measured at each portion along the scanning direction. Since information is obtained, a tomographic image of a tomographic plane including this scanning direction can be acquired. The tomographic image acquired in this way is displayed on the display device 660. For example, by moving the optical probe 630 in the left-right direction in FIG. 21 and causing the measurement light Ls1 to scan the measurement target Sb in a second direction orthogonal to the scanning direction, It is also possible to obtain a tomographic image of a tomographic plane including the direction.

  The tomographic image acquired in this way is displayed on the display device 660. For example, by moving the optical probe 630 in the left-right direction in FIG. 21 and causing the measurement light Ls1 to scan the measurement target Sb in a second direction orthogonal to the scanning direction, It is also possible to obtain a tomographic image of a tomographic plane including the direction.

Further, the center wavelength λsc and the wavelength sweep width Δλs as the laser light Ls are as follows:
λsc ² / Δλs ≦ 15
Since the laser beam satisfying the above is used, the center wavelength of 1.0 μm band is superior to the center wavelength of 1.3 μm band.

Furthermore, λsc + (Δλs / 2) ≦ 1.2 μm
λsc− (Δλs / 2) ≧ 0.98 μm
Therefore, the measurement light Ls1 has a good transmittance in the measurement object Sb, and the reflected light Ls3 is less affected by the light absorption peaks of water present at 0.98 μm and 1.2 μm. A high-quality optical tomographic image can be acquired.

  When the center wavelength λc of the laser light Ls is 0.98 μm or more and 1.2 μm or less, as in the present embodiment, the photodetectors 642a and 642b of the interference light detection means 640 are InGaAs-based photodetectors. Is preferably used. This makes it possible to reliably detect the interference light of the laser light Ls as indicated by the sensitivity characteristics of the InGaAs-based photodetector in FIG.

 The embodiment of the present invention is not limited to the above embodiment. For example, in the optical tomographic imaging apparatus 600 in FIG. 21, the laser light Ls, the measurement light Ls1, the reference light Ls2, the reflected light Ls3, and the interference light Ls4 are illustrated as being propagated through the optical fiber. You may make it propagate in air | atmosphere or a vacuum.

Illustration of absorption characteristics Illustration of loss in living tissue Explanatory diagram of cancer progression in stomach wall Illustration of water dispersion Illustration of relationship between underwater propagation distance and broadening ratio Illustration of spectrum waveform and Fourier transform waveform Illustration of the relationship between center frequency and full width at half maximum of spectrum Illustration of relationship between underwater propagation distance and optical axis resolution 1 is a schematic configuration diagram of an optical tomographic imaging apparatus according to a first embodiment of the present invention. Schematic configuration diagram of SLD Schematic diagram of other SLD Schematic configuration diagram of a variation of the light source unit Schematic configuration diagram of another modification of the light source unit Illustration of absorption spectrum of dye Illustration of fluorescence Illustration of pyrylium pigment Schematic configuration diagram of still another modification of the light source unit Schematic configuration diagram of a modification of the optical tomographic imaging apparatus Schematic configuration diagram of still another modification of the optical tomographic imaging apparatus Schematic configuration diagram of an optical tomographic imaging apparatus according to a second embodiment of the present invention Schematic configuration diagram of an optical tomographic imaging apparatus in the third embodiment of the present invention Illustration of laser light Ls Sensitivity characteristics of InGaAs photo detector

Explanation of symbols

3,53,63 Light splitting means
4,54,64 multiplexing means
10,10a, 10b, 10c SLD
140,140a, 140b Spectral shaping part
148,148a, 148b Gaussian filter
210,410,420,430 Light source unit
230,530 Optical path length adjustment means
230,630 Optical probe
240,540,640 Interference light detection means
250, 550,650 Image acquisition means
260,560,660 Display device

Claims (11)

A light source that emits low coherence light;
Splitting means for splitting the low-coherence light into measurement light and reference light;
An irradiation optical system for irradiating the measurement object with the measurement light;
An optical path length changing means for changing an optical path length of the reference light or the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement object is irradiated with the measurement light;
The plurality of measurement targets, wherein the optical path length of the reference light and the total optical path length of the measurement light and the reflected light substantially coincide with each other based on the light intensity of the combined reflected light and the interference light of the reference light In an optical tomographic imaging apparatus comprising: an image acquisition unit that detects the intensity of reflected light at each depth position and acquires a tomographic image of a measurement object based on the intensity at each depth position;
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
An optical tomographic imaging apparatus characterized by satisfying the above. A light source that emits low coherence light;
A light splitting means for splitting the low-coherence light into measurement light and reference light;
An irradiation optical system for irradiating the measurement object with the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement object is irradiated with the measurement light;
Based on the characteristics of the combined interference light of the reflected light and the reference light, the intensity of the reflected light at a plurality of depth positions of the measurement target is calculated, and the measurement is performed based on the intensity at each of these depth positions. In an optical tomographic imaging apparatus comprising an image acquisition means for acquiring a tomographic image of a target,
The center wavelength λc and the full width at half maximum Δλ of the reference light and the reflected light are
λc ² / Δλ ≦ 15
λc + (Δλ / 2) ≦ 1.2 μm
λc− (Δλ / 2) ≧ 0.98 μm
An optical tomographic imaging apparatus characterized by satisfying the above.   The image acquisition means detects the light intensity for each frequency of the interference light, and calculates the intensity of the reflected light at a plurality of depth positions of the measurement object from the detected light intensity for each frequency of the interference light The optical tomographic imaging apparatus according to claim 2, wherein:   4. The optical tomographic imaging apparatus according to claim 1, wherein the light source unit includes a superluminescent diode. 5.   The superluminescent diode is formed on a GaAs substrate having a first conductivity, and is disposed on an optical waveguide composed of an InGaAs active layer and a rear emission end face side of the optical waveguide, and has an energy gap larger than that of the active layer. A binary material that does not contain Al that is large and has a low refractive index, has a second conductivity opposite to the first conductivity, and has a lattice constant within ± 0.1% of the lattice constant of GaAs. 5. The optical tomographic imaging apparatus according to claim 4, further comprising a window region layer made of a ternary semiconductor material.   6. The optical tomographic imaging apparatus according to claim 5, wherein the semiconductor layer forming the window region layer is made of GaAs or InGaP.   4. The optical tomographic imaging apparatus according to claim 1, wherein the light source unit includes a light emitter containing a near-infrared fluorescent dye. 5.   4. The optical tomographic imaging apparatus according to claim 1, wherein the light source unit includes a Yb pulse laser, an Nd pulse laser, or a Ti pulse laser. 5.   9. The optical tomographic imaging apparatus according to claim 1, further comprising a Gaussian distribution shaping filter. A light source that emits laser light while sweeping the wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
A multiplexing means for multiplexing the reflected light from the measurement object of the measurement light and the reference light;
Interference light detection means for detecting the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light combined by the multiplexing means; ,
In an optical tomographic imaging apparatus comprising: an image acquisition unit that acquires a tomographic image of the measurement object using the intensity of the reflected light at each depth position detected by the interference light detection unit;
The sweep center wavelength λsc and the wavelength sweep width Δsλ of the laser light are as follows:
λsc ² / Δλs ≦ 15
λsc + (Δλs / 2) ≦ 1.2 μm
λsc− (Δλs / 2) ≧ 0.98 μm
An optical tomographic imaging apparatus characterized by satisfying the above. 11. The optical tomographic imaging apparatus according to claim 10, wherein the interference light detection means includes an InGaAs-based photodetector.

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