JP2008304314A - Optical coherence tomography system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical coherence tomography system having high measurement resolution in a depth direction. <P>SOLUTION: The system includes: a light source 114 that emits an irradiating light; a first semitransparent mirror 41 that divides the irradiating light to a first reference light and a test light, and passes the test light toward the fault surface 195 of a sample 190; a second semitransparent mirror 42 that divides the irradiating light to a second reference light and a standard light; a standard reflection mirror 43 that is disposed facing the second semitransparent mirror 42 and reflects the standard light; an interference pattern detection device 153 that detects a composite interference pattern of the first interference pattern between the first reference light and the test light which goes through the measurement light path length irradiated by the fault surface 195 of the sample 190, and the second interference pattern between the second reference light and the standard light which goes through the standard light path length reflected by the standard reflecting mirror 43; an extraction module 310 that extracts an interference pattern component which is variable according to the difference of the light path length between the measuring light path length and standard light path length; and a calculating module 330 that calculates the location of the fault surface 195 of the sample 190 relative to the first semitransparent mirror. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to measurement technology, and more particularly to an optical coherence tomography apparatus.

In order to elucidate the functions of biological organs such as muscles, organs, and eyeballs, development of systems capable of observing biological organs in vivo is in progress. In recent years, optical coherence tomography (OCT: Optical Coherence Tomography) apparatuses have attracted attention (see, for example, Patent Document 1). In the OCT apparatus, a semi-transparent mirror is arranged to face the sample. When light is irradiated toward the semi-transparent mirror, a part of the light is reflected by the semi-transparent mirror as reference light, and a part of the light is transmitted through the semi-transparent mirror as inspection light. After the inspection light is reflected by the sample, it passes through the semi-transparent mirror again and interferes with the reference light. When the optical path length of the inspection light reciprocating between the semi-transparent mirror and the sample is F _P , the interference intensity S _P (ν) is given by the following equation (1).

S _P (ν) = Y + Z × cos {(2πν / c) × F _P }… (1)
Y is a DC component, Z is a constant, ν is the frequency of light, and c is the speed of light. In conventional OCT apparatus, it was calculated (1) obtains the value of the optical path length F _P from the measured waveform by the photo diode of the interference fringes having the interference intensity given by equation surface shape of the sample. However interval of peaks and peaks of an interference fringe optical path length F _P is increased becomes narrow, that determine the value of the optical path length F _P has been difficult from the interference fringes. Therefore in order to obtain the value of optical path length F _P with high resolution, it has been studied to increase the wavelength resolution of the OCT apparatus. In order to increase the wavelength resolution, for example, there are means such as increasing the number of photodiodes assigned to one wavelength component, decreasing the photodiode element size, expanding the beam diameter, or increasing the aperture. However, when a means for increasing the wavelength resolution is adopted, the light output voltage from one photodiode is lowered, and there is a problem that the SN ratio with respect to noise such as dark current is lowered.
JP 2004-340581 A

  An object of the present invention is to provide an optical coherence tomography apparatus having a high measurement resolution in the depth direction.

  The features of the present invention are (a) a light source that emits irradiation light, and (b) a first semi-transparent mirror that divides the irradiation light into first reference light and inspection light and transmits the inspection light toward the tomographic plane of the sample; (C) a second semi-transparent mirror that divides the irradiated light into a second reference light and a reference light; and (d) a reference reflector that reflects the reference light and is disposed opposite the second semi-transparent mirror; E) The first interference fringe between the first reference light and the inspection light irradiated on the tomographic plane of the sample and advanced through the measurement optical path length, and the reference reflected by the second reference light and the reference reflector and advanced through the reference optical path length Interference fringe components that vary according to the optical path difference between the measurement optical path length and the reference optical path length are extracted from the interference fringe detection element that detects the synthetic interference fringe with the second interference fringe with light and (f) the synthetic interference fringe. Calculate the measurement optical path length value based on the extraction module, (g) the interference fringe component and the reference optical path length value, and calculate the position of the tomographic plane of the sample relative to the first semi-transparent The gist of the present invention is an optical coherence tomography device including a calculation module.

  According to the present invention, it is possible to provide an optical coherence tomography apparatus having a high measurement resolution in the depth direction.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
As shown in FIG. 1, the optical coherence tomography device according to the first embodiment divides the irradiation light into the first reference light and the inspection light and emits the irradiation light on the tomographic plane 195 of the sample 190. The first semi-transparent mirror 41 that transmits the inspection light toward the second semi-reflective mirror 42 that divides the irradiation light into the second reference light and the reference light, and the reference light that is disposed facing the second semi-transparent mirror 42 is reflected. Reflection by the reference reflector 43, the first interference fringes of the first reference light and the inspection light irradiated on the tomographic plane 195 of the sample 190 and proceeding the measurement optical path length, and the second reference light and the reference reflector 43 And an interference fringe detecting element 153 that detects a combined interference fringe with the second interference fringe with the reference light that has traveled the reference optical path length. Further, the optical coherence tomography apparatus includes a stage 400 on which a sample 190 is arranged and movable in the horizontal direction.

  The optical coherence tomography apparatus further includes a central processing unit (CPU) 300. The CPU 300 extracts an interference fringe component that varies according to the optical path difference between the measurement optical path length and the reference optical path length from the combined interference fringe, and the measurement optical path length based on the interference fringe component and the reference optical path length value. A calculation module 330 that calculates a value and calculates the position of the tomographic plane 195 of the sample 190 with respect to the first semi-transparent mirror 41 is provided.

As the light source 114, a multi-wavelength light source such as a xenon lamp, a light emitting diode, a super luminescent diode, or a multimode laser diode capable of supporting a continuous spectrum from the ultraviolet region to the infrared region (185 nm to 2,000 nm) can be used. . The irradiation light intensity S ₀ (λ), which is the light intensity of the irradiation light, is expressed by the following equation (2), for example. :
S ₀ (λ) = D × exp {-(λ-λ _CS / Δλ _S ) ² }… (2)
In Equation (2), D represents a constant, λ _CS represents the irradiation light center wavelength of the irradiation light emitted from the light source 114, and Δλ _S represents the emission bandwidth of the light source 114.

A collimating lens 44 is disposed below the light source 114. The collimating lens 44 converts the irradiation light emitted from the light source 114 into parallel light. The surface of the collimating lens 44 is subjected to, for example, antireflection treatment. A wavelength tunable filter 23 is disposed on the optical axis of the collimating lens 44 below the collimating lens 44. The wavelength tunable filter 23 includes, for example, a birefringent crystal. An oscillator 24 is connected to the wavelength tunable filter 23. The oscillator 24 applies ultrasonic waves to the wavelength tunable filter 23. In response to the given ultrasonic wave, the wavelength variable filter 23 transmits an arbitrary wavelength component of the irradiation light. The wavelength tunable filter 23 and the oscillator 24 constitute the spectrometer 3. As shown in FIG. 2, the oscillator 24 scans the wavelength λ of the wavelength component that can transmit the irradiation light according to the time t. When the wavelength resolution of the spectrometer 3 is Δλ _R , the frequency resolution Δν of the spectrometer 3 is given by the following equation (3).

Δν = cΔλ _R / λ _CS ² (3)
In the formula (3), c represents the speed of light. The coherence length L _C of the irradiation light is given by the following equation (4).
L _C = c / Δν (4)
Below the tunable filter 23 shown in FIG. 1, a splitter 21 that divides the irradiation light in two directions is disposed on the optical axis of the collimating lens 44. A half mirror or the like can be used for the splitter 21. The splitter 21 divides the irradiation light into the optical axis direction of the collimating lens 44 and the direction perpendicular to the optical axis direction.

A first semi-transparent mirror 41 is disposed on the optical axis of the collimating lens 44 below the splitter 21. Here, the optical path length between the splitter 21 and the first half mirror 41 and L _R1. A part of the irradiation light is reflected by the first semi-transparent mirror 41 as the first reference light, and another part of the irradiation light is transmitted through the first semi-transmission mirror 41 as the inspection light.

A second semi-transparent mirror 42 is arranged in the lateral direction of the splitter 21. Here, the optical path length between the splitter 21 and the second half mirror 42 and L _R2. The optical path length L _R2 is set to be longer than the optical path length L _R1 by the detour optical path length L _F given by the following equation (5), which is longer than half of the coherence length L _C.

L _F >> (L _C / 2)… (5)
A condensing lens 45 is disposed on the optical axis of the collimating lens 44 below the first semi-transparent mirror 41. The condensing lens 45 condenses the inspection light transmitted through the first semi-transparent mirror 41 to increase the density of the inspection light and focus it on the focus. For example, the surface of the condenser lens 45 is subjected to antireflection treatment.

The first half mirror 41 is arranged at a measurement distance L _T1 in a direction perpendicular to the inside of the fault surface 195 of the sample 190. The inspection light transmitted through the first semi-transparent mirror is reflected by the tomographic plane 195 inside the sample 190 and returns to the first semi-transparent mirror 41. Therefore inspection light, between the first half mirror 41 and the slice plane 195, the process proceeds to the measurement optical path length F ₁ given by the following equation (6) is the length of twice the measurement distance L _T1. As shown in the following equations (6) and (7), the measurement distance L _T1 is set to be shorter than half of the coherence length L _C , so the measurement optical path length F ₁ is shorter than the coherence length L _C. . :
F ₁ = 2L _T1 (6)
2L _T1 <L _C (7)
Part of the inspection light that has returned to the first semi-transparent mirror 41 passes through the first semi-transparent mirror 41 and travels toward the splitter 21. In addition, part of the inspection light that has returned to the first semi-transparent mirror 41 is reflected by the first semi-transparent mirror 41 and travels again toward the tomographic plane 195 inside the sample 190. At this time, the wavelength component of the inspection light traveling from the tomographic plane 195 inside the sample 190 to the first semi-transparent mirror 41, and the wavelength component of the inspection light traveling from the first semi-transparent mirror 41 to the tomographic plane 195 inside the sample 190 When the phases are aligned, the light intensity of the wavelength component is not attenuated. However, the wavelength component of the inspection light traveling from the tomographic plane 195 inside the sample 190 to the first semi-transparent mirror 41 and the wavelength component of the inspection light traveling from the first semi-transparent 41 to the tomographic plane 195 inside the sample 190 When the phases are not aligned, the light intensity of the wavelength component is attenuated. Accordingly, in the inspection light, the light intensity in the wavelength band in which the phases are not uniform is attenuated when multiple reflection is performed between the first semi-transparent mirror 41 and the tomographic plane 195 inside the sample 190.

As shown in the above equations (6) and (7), the measurement optical path length F ₁ is shorter than the coherence length L _C. Therefore, the first reference light reflected by the first semi-transparent mirror 41 due to the optical path difference corresponding to the measurement optical path length F ₁ is reflected by the tomographic plane 195 inside the sample 190 and transmitted again through the first semi-transparent mirror 41. Interfere with. The first light intensity ratio R _S1 , which is the ratio of the interference intensity between the first reference light traveling toward the splitter 21 and the inspection light with respect to the light intensity of the irradiation light traveling toward the first semi-transparent mirror 41, is as follows: It is given by equation (8). :
R _S1 = {R _1Ra + η _a R _2Ra -2 (η _a R _1Ra R _2Ra ) ^1/2 cos2φ _a } / {1 + η _a R _1Ra R _2Ra -2 (η _a R _1Ra R _2Ra ) ^1/2 cos2φ _a }… (8)
Here, R _1Ra represents the reflectance of the first semi- _transparent mirror 41, and R _2Ra represents the reflectance of the tomographic plane 195 inside the sample 190. η _a represents the optical loss between the first semi-transparent mirror 41 and the tomographic plane 195 inside the sample 190, and is given by the following equation (9). Φ _a represents _a phase and is given by the following equation (10). In equation (9), q represents the beam diameter of the irradiation light. :
η _a = 1 / {1 + (λ × F ₁ ) / (2πq ² )} ² … (9)
φ _a = πF ₁ / λ (10)
In the following, for simplification, A is a constant representing the coherence between the first semi-transparent mirror 41 and the tomographic plane 195 inside the sample 190, and the first light intensity ratio R _S1 is expressed by the following equation (11). give.

R _S1 = 1 + A cos {2π × F ₁ / λ} (11)
The first reference light and the inspection light are reflected by the splitter 21 in the direction opposite to the direction in which the second semi-transparent mirror 42 is disposed.

Further, a part of the irradiation light reflected laterally by the splitter 21 is reflected as the second reference light by the second semi-transparent mirror 42, and another part of the irradiation light is transmitted through the second semi-transmission mirror 42 as the reference light. . Reference retroreflector 43 is arranged at a reference distance L _T2 for the second half mirror 42. The optical axis of the reference light emitted from the second semi-transparent mirror 42 is perpendicular to the reference reflecting mirror 43. The reference light is reflected by the reference reflecting mirror 43 and returns to the second semi-transparent mirror 42. Thus the reference light, between the second half mirror 42 and the reference reflector 43, travels the reference distance L reference optical path length is given by the following equation (12) is a length of 2 times the _T2 F _2. As shown in the following equations (12) and (13), the reference distance L _T2 is set to be shorter than half of the coherence length L _C , so the reference optical path length F ₂ is shorter than the coherence length L _C. . :
F ₂ = 2L _T2 (12)
2L _T2 <L _C … (13)
By the optical path difference corresponding to the reference optical path length F _2, the second reference light reflected by the second half mirror 42 interferes with the reference light transmitted through the second half mirror 42 again and is reflected by the reference reflecting mirror 43. The second light intensity ratio R _S2 , which is the ratio of the interference intensity between the second reference light traveling toward the splitter 21 and the reference light with respect to the light intensity of the irradiation light traveling toward the second semi-transparent mirror 42, is as follows: It is given by equation (14). :
R _S2 = {R _1Rb + η _b R _2Rb -2 (η _b R _1Rb R _2Rb ) ^1/2 _{cos2φ b} } / {1 + η _b R _1Rb R _2Rb -2 (η _b R _1Rb R _2Rb ) ^1/2 cos2φ _b }… (14)
Here, R _1Rb represents the _reflectance of the second semi- _transmissive mirror 42, and R _2Rb represents the reflectance of the reference reflecting mirror 43. η _b represents the optical loss between the second semi-transparent mirror 42 and the reference reflecting mirror 43, and is given by the following equation (15). Φ _b represents a phase and is given by the following equation (16). :
η _b = 1 / {1 + (λ × F ₂ ) / (2πq ² )} ² … (15)
φ _b = πF ₂ / λ (16)
Hereinafter, for simplification, the second light intensity ratio R _S2 is given by the following equation (17), where B is a constant representing the coherence between the second semi-transparent mirror 42 and the reference reflecting mirror 43.

R _S2 = 1 + B cos {2π × F ₂ / λ} (17)
The second reference light and the reference light are transmitted through the splitter 21. An interference fringe detecting element 153 is arranged opposite the second semi-transparent mirror 42 with the splitter 21 interposed therebetween. The first reference light, the inspection light, the second reference light, and the reference light travel toward the interference fringe detection element 153.

Here, the optical path length L _R2 between the splitter 21 and the second semi-transparent mirror 42 is the optical path length L _R1 between the splitter 21 and the first semi-transparent mirror 41 by the detour optical path length L _F given by the equation (5). long. Therefore splitter 21 and the optical path of the light reciprocating between the first half mirror 41, splitter 21 and the optical path difference between the optical path of the light reciprocates between the second half mirror 42, the second bypass optical path length L _F More than double. For this reason, the optical path difference is longer than the coherence length L _C , so that the first reference light and the second reference light do not interfere with each other.

Also, twice the optical path length L _R1 between the splitter 21 and the first semi-transparent mirror 41 and the sum of the measurement optical path length F ₁ , twice the optical path length L _R2 between the splitter 21 and the second semi-transparent mirror 42, and the absolute value of the difference between the sum of the reference optical path length F ₂ is set to be longer than the coherence length L _C as shown in the following equation (18). Therefore, the inspection light and the reference light do not interfere with each other.

| 2L _R1 + F _1- (2L _R2 + F ₂ ) | ≫ L _C … (18)
Also, twice the optical path length L _R1 between the splitter 21 and the first semi-transparent mirror 41 and the sum of the measurement optical path length F ₁ and twice the optical path length L _R2 between the splitter 21 and the second semi-transparent mirror 42 The absolute value of the difference is set to be longer than the coherence length L _C as shown in the following equation (19). Therefore, the inspection light and the second reference light do not interfere.

_{| 2L R1 + F 1 - 2L} R2 | »L C ... (19)
Also, twice the optical path length L _R1 between the splitter 21 and the first semi-transparent mirror 41, twice the optical path length L _R2 between the splitter 21 and the second semi-transparent mirror 42, and the sum of the reference optical path length F ₂ and The absolute value of the difference is set to be longer than the coherence length L _C as shown in the following equation (20). Therefore, the first reference light and the reference light do not interfere.

| 2L _R1- (2L _R2 + F ₂ ) | >> L _C … (20)
The interference fringe detection element 153 receives the first reference light, the inspection light, the second reference light, and the reference light. As the interference fringe detection element 153, a CCD image sensor such as an area image sensor can be used, and includes a plurality of photodiodes. Here, the inspection light intensity S ₁ (λ), which is the light intensity of the first reference light received by the interference fringe detection element 153 and the first interference fringe formed by the inspection light, is given by the following equation (21).

S ₁ (λ) = (1/4) × S ₀ (λ) × T _L1 (λ) × R _S1 … (21)
In equation (21), 1/4 related to the irradiation light intensity S ₀ (λ) indicates a loss of light intensity due to the irradiation light passing through the splitter 21 a total of two times. T _L1 (λ) indicates the transmittance of the optical path through which the irradiation light, the first reference light, and the inspection light pass until they reach the interference fringe detection element 153.

The reference light intensity S ₂ (λ), which is the light intensity of the second reference light formed by the second reference light and the reference light received by the interference fringe detection element 153, is given by the following equation (22).

S ₂ (λ) = (1/4) × S ₀ (λ) × T _L2 (λ) × R _S2 … (22)
In Expression (22), T _L2 (λ) indicates the transmittance of the optical path through which the irradiation light, the second reference light, and the reference light reach the interference fringe detection element 153. From the equations (21) and (22), the output light intensity S _OUT (λ) that is the light intensity of the combined interference fringe of the first interference fringe and the second interference fringe is given by the following equation (23). Fig. 3 shows an example of the spectrum of the output light intensity S _OUT (λ) when the center wavelength λ _CS is 880 nm, the wavelength resolution Δλ _R is 3.6 nm, the bypass optical path length L _F is 7.2 m, and the coherence length L _C is 200 μm. is there.

S _OUT (λ) = S ₁ (λ) + S ₂ (λ)
= (1/4) × S ₀ (λ) × {T _L1 (λ) × R _S1 + T _L2 (λ) × R _S2 }
= (1/4) × S ₀ (λ) [{T _L1 (λ) + T _L2 (λ)} + T _L1 (λ) × A cos {2π × F ₁ / λ}
+ T _L2 (λ) × B cos {2π × F ₂ / λ}]… (23)
If the variables α and β given by the following equations (24) and (25) are defined, the output light intensity S _OUT (λ) given by the equation (23) is transformed into the following equation (26).

α = T _L1 (λ) × A… (24)
β = T _L2 (λ) × B… (25)
S _OUT (λ) = (1/4) × S ₀ (λ) [{T _L1 (λ) + T _L2 (λ)} +
2αcos {(π / λ) (F _1- F ₂ )} cos {(π / λ) (F ₁ + F ₂ )}
+ (β-α) cos {(2π / λ) × F ₂ }]… (26)
The second term cos {(π / λ) (F ₁ − F ₂ )} appears as a low frequency component of the spectrum of the output light intensity S _OUT (λ). As shown in FIG. 4, the low frequency component is expressed by an envelope of the spectrum of the output light intensity S _OUT (λ). Here, the maximum point or minimum point of the low frequency component appears every 2π period. Therefore the n as an integer of 2 or more, the wavelength giving the n-th maximum point and lambda _n, and the wavelength giving the n-1 th maximum point and lambda _n-1, the following (27) is established.

(π / λ _n ) (F _1- F ₂ )-(π / λ _n-1 ) (F _1- F ₂ ) = 2π… (27)
From the equation (27), the interval between the maximum points of the low frequency component of the output light intensity S _OUT (λ) or the peak interval P that is the interval between the minimum points is given by the following equation (28).

P = 1 / λ _n -1 / λ _n-1
= 2 / (F ₁ -F ₂ )… (28)
If the positions of the first semi-transparent mirror 41, the second semi-transparent mirror 42, and the reference reflecting mirror 43 are fixed, the measurement optical path length and the reference optical path depend only on the height of the tomographic plane 195 inside the sample 190. Optical path difference with length (F _1- F ₂ ) varies, and as a result, the peak interval P of the low-frequency component of the synthetic interference fringe varies. Note that the fluctuation of the peak interval P of the low frequency component is not affected by the difference between the light intensity of the inspection light and the light intensity of the reference light.

Each of the plurality of photodiodes included in the interference fringe detection element 153 illustrated in FIG. 1 transmits the output light intensity S _OUT (λ) of the combined interference fringe to the CPU 300. The CPU 300 includes a drive module 305. The drive module 305 moves the stage 400 in the xy plane and controls the (x, y) coordinates where the stage 400 is arranged. The correction module 306 of the CPU 300 always receives the output light intensity S _OUT (λ) of the combined interference fringes. The correction module 306 corrects the output light intensity S _OUT (λ) of the combined interference fringe by the moving average method. Here, the “moving average method” will be described. When the spectrum of the output light intensity S _OUT (λ) is obtained as shown in FIG. 4, the correction module 306 shown in FIG. 1 performs the low frequency component cos {(π / λ) (F _1- F ₂ )} is defined as a section having a width of at least one period and less than one period of the spectral distribution of the irradiation light intensity S ₀ (λ). Further, the correction module 306 calculates the average value of the output light intensity S _OUT (λ) in the defined section and plots it at the center of the section. Next, the correction module 306 moves the section in the wavelength direction, calculates the average value of the output light intensity S _OUT (λ) in the moved section, and plots it at the center of the section. Thereafter, the correction module 306 moving average shown in FIG. 5 is a set of moving and repeatedly calculating the average value of the output light intensity S _OUT (λ), the mean value of the calculated output light intensity S _OUT (lambda) of the section Calculate the line.

The spectral distribution of the output light intensity S _OUT (λ) illustrated in FIG. 4 includes the spectral distribution of the irradiated light intensity S ₀ (λ), the low-frequency component cos {(π / λ) (F _1- F ₂ )} spectral distribution, high-frequency component cos {(π / λ) (F ₁ + F ₂ )} included in the second term of equation (26), and third term of equation (26) The spectral distribution of the given reflected light component (β-α) cos {(2π / λ) × F ₂ } is superimposed. Where the low frequency component cos {(π / λ) (F ₁ − F ₂ )} period or more and shorter than the period of the spectral distribution of the irradiation light intensity S ₀ (λ), and calculating the moving average line of the output light intensity S _OUT (λ), the low frequency component cos {(π / λ) (F _1- F ₂ )}, high-frequency component cos {(π / λ) (F ₁ + F ₂ )}, and reflected light component (β-α) cos {(2π / λ) × F ₂ } The spectral distribution is averaged. Therefore, the moving average line shown in FIG. 5 reflects only the spectral distribution of the irradiation light intensity S ₀ (λ).

As shown in the following equation (29), the correction module 306 shown in FIG. 1 divides the output light intensity S _OUT (λ) by the irradiation light intensity S ₀ (λ) approximated by the moving average line to obtain the output light intensity. The spectrum distribution of the irradiated light intensity S ₀ (λ) is removed from the spectrum distribution of S _OUT (λ), and the spectrum distribution of the corrected output light intensity S _{OUT_C} (λ) shown in FIG. 6 is calculated.

S _{OUT_C} (λ) = S _OUT (λ) / S ₀ (λ)
= (1/4) [{T _L1 (λ) + T _L2 (λ)} +
2αcos {(π / λ) (F _1- F ₂ )} cos {(π / λ) (F ₁ + F ₂ )}
+ (β-α) cos {(2π / λ) × F ₂ }]… (29)
Here, the relationship between the light frequency ν, the speed of light c, and the wavelength λ is given by the following equation (30).

ν = c / λ (30)
The conversion module 307 shown in FIG. 1 converts the expression (29), which is a function of the wavelength λ, into a function of the frequency ν shown in FIG. 7 using the expression (30). The corrected output light intensity S _{OUT — C} (ν) expressed as a function of the frequency ν is given by the following equation (31).

S _{OUT_C} (ν) = (1/4) [{T _L1 (c / ν) + T _L2 (c / ν)} +
2αcos {(πν / c) (F _1- F ₂ )} cos {(πν / c) (F ₁ + F ₂ )}
+ (β-α) cos {(2πν / c) × F ₂ }]… (31)
If the frequency that gives the nth local maximum of the low frequency component of the output light intensity S _{OUT_C} (ν) given by Eq. (31) is ν _n and the wavelength that gives the n-1st local maximum is ν _n-1 The following equation (32) is established.

(πν _n / c) (F _1- F ₂ )-(πν _n-1 / c) (F _1- F ₂ ) = 2π… (32)
From the equation (32), the peak interval P of the low frequency component of the output light intensity S _{OUT — C} (ν) is given by the following equation (33).

P = (ν _n -ν _n-1 ) / c
= 2 / (F ₁ -F ₂ )… (33)
Therefore, the peak interval P of the low frequency component of the output light intensity S _{OUT_C} (ν) is also the optical path difference between the measured optical path length and the reference optical path length (F ₁ − It varies depending only on F ₂ ). For example, FIG. 8 shows the optical path difference between the measurement optical path length and the reference optical path length (F ₁ − F ₂ ) increase from the beginning Δ (F _1- This is a spectrum of output light intensity S _{OUT — C} (ν) when F ₂ ) is 0 μm, 9.12 μm, 15.78 μm, and 22.08 μm. Optical path difference between measurement optical path length and reference optical path length (F _1- As F ₂ ) increases, the peak interval P of the low frequency component of the combined interference fringes becomes narrower. The extraction module 310 shown in FIG. 1 extracts the peak interval P of the low frequency component from the output light intensity S _{OUT — C} (ν).

For example, the calculation module 330 calculates the optical path difference (F ₁ − between the measurement optical path length acquired in advance and the reference optical path length shown in FIG. 9. F ₂ ) increase Δ (F ₁ − F ₂ ) and the low frequency component peak interval P using the relationship between the low frequency component peak interval P extracted by the extraction module 310 shown in FIG. 1 and the optical path difference between the measured optical path length and the reference optical path length (F ₁ - F ₂ ) is calculated. Since the reference light path length F ₂ it is known, calculation module 330 calculates the measured distance L _T1 from the calculated optical path difference. The CPU 300 further includes an image generation module 331. Image generation module 331, calculation module 330 based on the respective outputs of the plurality of photodiodes fringe detection element 153 based on the measured distance L _T1 calculated to generate a tomographic image of 195 samples 190.

A data storage device 200 is connected to the CPU 300. The data storage device 200 includes an interference fringe component storage module 201, a relation storage module 202, and a result storage module 203. The interference fringe component storage module 201 stores the peak interval P of the low frequency component of the combined interference fringe extracted by the extraction module 310. The relationship storage module 202 uses the optical path difference (F ₁ − between the measured optical path length and the reference optical path length acquired in advance. The relationship between F ₂ ) and the low frequency component peak interval P is stored. The result storage module 203 stores the measurement distance L _T1 calculated by the calculation module 330 and the image of the tomographic plane 195 of the sample 190 generated by the image generation module 331.

  Next, the optical coherence tomography method according to the first embodiment will be described with reference to FIG.

(a) In step S101, the light source 114 shown in FIG. 1 emits irradiation light having a spectrum of irradiation light intensity S ₀ (λ) given by equation (2). The irradiation light is collimated by the collimating lens 44 and travels toward the spectroscope 3. In step S102, the spectrometer 3 selectively transmits the wavelength component of the irradiation light according to the time t as shown in FIG. The irradiation light transmitted through the spectroscope 3 shown in FIG. In step S103, the irradiation light is split in two directions by the splitter 21. Irradiation light transmitted through the splitter 21 along the optical axis of the collimator lens 44 travels toward the first semi-transparent mirror 41. The irradiation light reflected perpendicularly to the optical axis of the collimator lens 44 by the splitter 21 travels an optical path length L _R2 that is longer than the optical path length L _R1 between the splitter 21 and the first semi-transparent mirror 41 by the detour optical path length L _F2. The second semi-transparent mirror 42 is reached.

(b) In step S201, the irradiation light that has reached the first semi-transparent mirror 41 is partially reflected as the first reference light and partially transmitted through the first semi-transparent mirror 41 as the inspection light. In step S202, the inspection light is collected by the condenser lens 45, travels toward the tomographic plane 195 inside the sample 190, and is reflected by the tomographic plane 195 inside the sample 190. The inspection light reflected by the tomographic plane 195 inside the sample 190 passes through the first semi-transparent mirror 41 again. When reciprocates between the interior of the fault plane 195 of the first half mirror 41 and the sample 190, the inspection light goes measurement optical path length F _1. In step S203, the first reference light reflected by the first half mirror 41 interferes with the advanced measurement optical path length F ₁ inspection light. Thereafter, the first reference light and the inspection light are reflected by the splitter 21 and travel toward the interference fringe detection element 153.

(c) In step S301, a part of the irradiation light that has reached the second semi-transparent mirror 42 is reflected as the second reference light, and a part thereof is transmitted through the second semi-transparent mirror 42 as the reference light. In step S302, the reference light travels toward the reference reflecting mirror 43 and is reflected by the reference reflecting mirror 43. The reference light reflected by the reference reflecting mirror 43 passes through the second semi-transmissive mirror 42 again. When reciprocates between the second half mirror 42 and the reference reflector 43, the reference light advances to a reference optical path length F _2.

(d) In step S303, the second reference light reflected by the second half mirror 42 interferes with the reference light advances to a reference optical path length F _2. Thereafter, the second reference light and the reference light pass through the splitter 21 and travel toward the interference fringe detection element 153. Note that the progress of steps S301 to S303 is parallel to the progress of steps S201 to S203. Further, Step S103, Step S201 to Step S203, and Step S301 to Step S303 are continuously performed for each wavelength component of the irradiation light that is selectively transmitted according to time t in Step S102.

(e) In step S401, the interference fringe detecting element 153 detects a combined interference fringe of the first interference fringe by the inspection light and the first reference light and the second interference fringe by the reference light and the second reference light. Each of the plurality of photodiodes included in the interference fringe detection element 153 transmits the output light intensity S _OUT (λ) given by the above equation (26) of the combined interference fringe to the CPU 300. In step S402, the correction module 306 of the CPU 300 receives the output light intensity S _OUT (λ) of the combined interference fringe. Next, the correction module 306 calculates a moving average line of the spectrum distribution of the output light intensity S _OUT (λ). Thereafter, the correction module 306 divides the spectral distribution of the output light intensity S _OUT (λ) by the spectral distribution of the irradiation light intensity S ₀ (λ) approximated by the moving average line, and corrects the corrected output given by Equation (29). The light intensity S _{OUT_C} (λ) is calculated. The correction module 306 transmits the output light intensity S _{OUT — C} (λ) to the conversion module 307.

(f) In step S403, the conversion module 307 receives the output light intensity S _{OUT — C} (λ) given by equation (29). Next, the conversion module 307 converts equation (29), which is a function of wavelength λ, into equation (31), which is a function of frequency ν. The conversion module 307 transmits the output light intensity S _{OUT — C} (ν) given by the equation (31) to the extraction module 310. In step S404, the extraction module 310 receives the output light intensity S _{OUT — C} (ν). Next, the extraction module 310 extracts the peak interval P of the low frequency component included in the spectrum of the output light intensity S _{OUT — C} (ν). The extraction module 310 stores the extracted value of the peak interval P of the low frequency component in the interference fringe component storage module 201.

(g) In step S405, the calculation module 330 performs, for example, the optical path difference between the measurement optical path length acquired in advance and the reference optical path length (F ₁ − The relationship between F ₂ ) and the low frequency component peak interval P is read from the relationship storage module 202 shown in FIG. Next, the calculation module 330 calculates the optical path difference between the measurement optical path length and the reference optical path length (F ₁ − F ₂ ) and the peak interval P, and the optical path difference (F ₁ − Approximate with the approximate expression of F ₂ ). Thereafter, the calculation module 330 reads the value of the peak interval P of the low frequency component extracted by the extraction module 310 from the interference fringe component storage module 201. The calculation module 330 substitutes the value of the peak interval P into the approximate expression, and calculates the optical path difference (F ₁ − F ₂ ) is calculated. Further calculation module 330, using known reference optical path length F _2, and calculates the measured distance L _T1 from the optical path difference. Calculation module 330 stores the measured distance L _T1 calculated based on the respective outputs of the plurality of photodiodes fringe detection element 153 in the result storing module 203.

(h) In step S406, the image generation module 331 reads the measurement distance L _T1 calculated based on the outputs of the plurality of photodiodes from the result storage module 203. Next, the image generation module 331 generates a concavo-convex image of the tomographic plane 195 of the sample 190 based on the planar distribution of the measurement distance _LT1 . The image generation module 331 stores the generated image of the tomographic plane 195 of the sample 190 in the result storage module 203, and ends the optical coherence tomography method according to the first embodiment.

Conventional OCT apparatus had analyzes (1) interference intensity S _P ([nu) given by equation 2 Kakari' as a coefficient in the optical path length F _P included in the formula of the interference intensity S _P ([nu) ing. In contrast, the low-frequency component cos (31) below at given output light intensity _{S OUT_C (ν) {(πν} / c) (F 1 - F ₂ )} does not have a coefficient of 2 for the measurement optical path length F ₁ included. Further, the reference optical path length F ₂ is subtracted from the measurement optical path length F ₁ . Therefore, the decrease in the peak interval P illustrated in FIG. 8 caused by the increase in the measurement optical path length F ₁ is suppressed as compared with the conventional OCT apparatus. Therefore, it is possible to increase the measurement resolution of the measurement distance L _T1 without adopting a means for increasing the wavelength resolution, and as a result, it is possible to increase the measurement resolution in the depth direction of the tomographic plane 195 of the sample 190. Further, the optical coherence tomography device according to the first embodiment can also capture images of a plurality of tomographic planes of the sample 190 by changing the focus of the condenser lens 45.

(First modification of the first embodiment)
Cos {(π / λ) (F ₁ − Focusing on F ₂ )}, the first period G _{1 at} an arbitrary first wavelength λ ₁ of the low frequency component of the spectrum of the output light intensity S _OUT (λ) is given by the following equation (34): The second period G ₂ of the low frequency component at the second wavelength λ ₂ different from the wavelength λ ₁ is given by the following equation (35). The difference between the first period G ₁ and the second period G ₂ is given by the following equation (36). Furthermore, from equation (36), the difference between the measurement optical path length F ₁ and the reference optical path length F ₂ (F ₁ − F ₂ ) is given by the following equation (37).

G ₁ = (F _1- F ₂ ) / (2 × λ ₁ )… (34)
G ₂ = (F _1- F ₂ ) / (2 × λ ₂ )… (35)
G ₁ -G ₂ = (F _1- F ₂ ) × {(1 / (2 × λ ₁ ))-(1 / (2 × λ ₂ ))}… (36)
F _1- F ₂ = (G ₁ -G ₂ ) / {(1 / (2 × λ ₁ ))-(1 / (2 × λ ₂ ))}… (37)
Here, the difference (G ₁ -G ₂ ) between the first period G ₁ and the second period G ₂ is the interference of the low frequency component between the first wavelength λ ₁ and the second wavelength λ ₂ Represents the number of stripes. Therefore, if the number of interference fringes due to the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the first wavelength λ ₁ and the second wavelength λ ₂ is known, from the above equation (37), the measurement optical path Difference between length F ₁ and reference optical path length F ₂ (F _1- F ₂ ) can be calculated.

In the first modification that applies the principle described above, the extraction module 310 shown in FIG. 1 uses the spectrum data of the output light intensity S _OUT (λ) of the combined interference fringes to obtain an arbitrary first wavelength λ ₁ and the _first wavelength λ ₁ . Extract the maximum point of the low frequency component between the _two wavelengths λ ₂ . The extraction module 310 calculates the envelope of the spectrum of the output light intensity S _OUT (λ) of the combined interference fringe, and the maximum point of the envelope between any first wavelength λ ₁ and second wavelength λ ₂ May be extracted.

The calculation module 330 counts the number of extracted maximum points. Further, the calculation module 330 substitutes the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the number of extracted maximum points into the above equation (37), and the measurement optical path length F ₁ and the reference optical path Difference from length F ₂ (F _1- F ₂ ) is calculated. In the first modification, the interference fringe component storage module 201 stores the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point extracted by the extraction module 310. The relationship storage module 202 stores the above equation (37).

  Next, an optical coherence tomography method according to the first modification of the first embodiment will be described with reference to FIG.

(a) Steps S101 to S103, Steps S201 to S203, Steps S301 to S303, Step S401, and Step S402 are performed in the same manner as in the first embodiment. Step S403 is omitted. Next, in step S404, the extraction module 310 shown in FIG. 1 performs the maximum point of the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the arbitrary first wavelength λ ₁ and the second wavelength λ _2. Are extracted as interference fringe components that vary according to the optical path difference between the measurement optical path length F ₁ and the reference optical path length F ₂ . The extraction module 310 stores the extracted value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point of the low frequency component in the interference fringe component storage module 201.

(b) In step S405, the calculation module 330 uses the interference fringe component storage module 201 to calculate the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the maximum point of the low frequency component extracted by the extraction module 310. Read from and count the number of local maxima. In addition, the calculation module 330 reads the expression (37) from the relation storage module. Next, the calculation module 330 substitutes the value of the _first wavelength λ ₁ , the value of the second wavelength λ ₂ , and the number of local maximum points into the equation (37), so that the measurement optical path length F ₁ and the reference optical path length Difference from F ₂ (F _1- F ₂ ) is calculated, and then step S406 is performed in the same manner as in the first embodiment, and the optical coherence tomography method according to the first modification of the first embodiment is terminated.

By optical coherence tomography apparatus and an optical coherence tomography method according to a first modification of the first embodiment described above, it is possible to measure the measured optical path length F ₁ with high accuracy. It should be noted that the extraction module 310 determines the number of minimum points of the low frequency component of the spectrum of the output light intensity S _OUT (λ) between the arbitrary first wavelength λ ₁ and the second wavelength λ ₂ or the output light intensity S. The number of local minimum points in the envelope of the spectrum of _OUT (λ) is expressed as the difference between the measured optical path length F ₁ and the reference optical path length F ₂ (F ₁ − It may be extracted as an interference fringe component that varies according to F ₂ ).

(Second modification of the first embodiment)
In the optical coherence tomography device according to the second modification of the first embodiment shown in FIG. 11, an optical waveguide 29 is disposed between the light source 114 and the wavelength tunable filter 23. The optical waveguide 29 propagates the irradiation light irradiated from the light source 114 to the wavelength tunable filter 23. Between the wavelength tunable filter 23 and a splitter 121 such as an optical fiber coupler, an optical waveguide 30 that propagates irradiation light transmitted through the wavelength tunable filter 23 is disposed.

  The splitter 121 is connected to an optical waveguide 31 that propagates one of the divided irradiation lights and an optical waveguide 32 that propagates the other divided irradiation light. A collimating lens 47 is disposed opposite the end of the optical waveguide 31. The collimating lens 47 makes the irradiation light emitted from the end of the optical waveguide 31 parallel light. A part of the irradiation light converted into parallel light is reflected by the first semi-transparent mirror 41 as the first reference light, and a part of the irradiation light is transmitted through the first semi-transparent mirror 41 as the inspection light. The first reference light and the inspection light reflected by the tomographic plane 195 are transmitted again through the collimator lens 47 and propagated toward the splitter 121 through the optical waveguide 31.

The optical path length of the optical waveguide 32 is set (5) bypass optical path length given by the formula L _F only longer than the optical path length of the optical waveguide 31. A collimating lens 46 is disposed facing the end of the optical waveguide 32. The collimating lens 46 converts the irradiation light emitted from the end of the optical waveguide 32 into parallel light. A part of the irradiation light converted into parallel light is reflected by the second semi-transparent mirror 42 as the second reference light, and a part of the irradiation light is transmitted through the second semi-transparent mirror 42 as the reference light. The second reference light and the reference light reflected by the reference reflecting mirror 43 are transmitted again through the collimating lens 46 and propagated toward the splitter 121 through the optical waveguide 32.

  An optical waveguide 33 is further connected to the splitter 121. The optical waveguide 33 propagates inspection light, reference light, first reference light, and second reference light. A collimating lens 48 is disposed facing the end of the optical waveguide 33. The collimating lens 48 collimates the inspection light, the reference light, the first reference light, and the second reference light emitted from the end of the optical waveguide 33. The interference fringe detection element 153 receives the inspection light, the reference light, the first reference light, and the second reference light that are converted into parallel light. For each of the optical waveguides 29, 30, 31, 32, and 33, a single mode optical fiber, a graded index optical fiber, a step index optical fiber, or the like can be used.

  Other components of the optical coherence tomography apparatus shown in FIG. 11 are the same as those in FIG. By using the optical waveguides 29 to 33, it is possible to flexibly set the arrangement positions of the light source 114, the sample 190, the interference fringe detection element 153, and the like.

(Second embodiment)
In the optical coherence tomography apparatus shown in FIG. 1, a collimating lens 44 and a wavelength tunable filter 23 are arranged between a light source 114 and a splitter 21. On the other hand, in the optical coherence tomography device according to the second embodiment, only the collimator lens 44 is disposed between the light source 114 and the splitter 21, as shown in FIG. However, a spectrometer 93 is disposed between the splitter 21 and the interference fringe detection element 153. The spectroscope 93 includes a diffraction grating 54 as shown in FIG. The diffraction grating 54 reflects the inspection light, the first reference light, the reference light, and the second reference light toward the interference fringe detection element 153. Here, the diffraction grating 54 reflects the wavelength components of the inspection light, the first reference light, the reference light, and the second reference light in different directions for each wavelength. Therefore, different wavelength components are incident on each of the plurality of photodiodes of the interference fringe detection element 153. Other components of the optical coherence tomography device according to the second embodiment are the same as those in FIG.

  Next, an optical coherence tomography method according to the second embodiment will be described with reference to FIG.

(a) In step S111, the light source 114 shown in FIG. 12 emits irradiation light having a spectrum of irradiation light intensity S ₀ (λ), and the irradiation light travels toward the splitter 21. Thereafter, step S113, step S211, step S212, step S311 and step S312 are performed in the same manner as step S103, step S201, step S202, step S301 and step S302 in FIG. 10, respectively.

  (b) In step S213 of FIG. 14, the first reference light and the inspection light that interfere with each other are reflected toward the spectroscope 93 by the splitter 21 shown in FIG. In step S313, the second reference light and the reference light that interfere with each other pass through the splitter 21 and travel toward the spectroscope 93.

  (c) In step S410, the spectroscope 93 reflects the wavelength components of the first reference light, the inspection light, the second reference light, and the reference light toward the interference fringe detection element 153 at an angle corresponding to the wavelength. Then, after steps S411 to S416 in FIG. 14 are performed in the same manner as steps S401 to S406 in FIG. 10, the optical coherence tomography method according to the second embodiment is terminated.

  According to the optical coherence tomography device and the optical coherence tomography method according to the second embodiment described above, the spectroscope 93 shown in FIG. 12 can be arranged near the CPU 300. Therefore, the setting of the spectroscope 93 can be easily changed.

(Modification of the second embodiment)
In the optical coherence tomography device according to the second embodiment shown in FIG. 15, an optical waveguide 34 that propagates the irradiation light emitted from the light source 114 is disposed between the light source 114 and the splitter 121. A diffraction grating 54 is disposed so as to face the collimating lens 48. Other components of the optical coherence tomography apparatus shown in FIG. 11 are the same as those in FIG.

(Third embodiment)
Unlike the optical coherence tomography apparatus shown in FIG. 1, the optical coherence tomography apparatus according to the third embodiment includes a modulation drive circuit 115 shown in FIG. As shown in FIG. 17, the modulation drive circuit 115 supplies a drive current that varies with time t to the light source 114 shown in FIG. By supplying a drive current that varies according to time t, the light source 114 such as a semiconductor laser resonator changes the wavelength of irradiation light according to time t as shown in FIG. Since the light source 114 changes the wavelength of irradiation light, the optical coherence tomography apparatus shown in FIG. 16 does not require a spectroscope. The other components of the optical coherence tomography apparatus shown in FIG. 16 are the same as those of the optical coherence tomography apparatus shown in FIG.

  Next, an optical coherence tomography method according to the third embodiment will be described with reference to FIG.

  In step S101, the modulation drive circuit 115 shown in FIG. 16 supplies the light source 114 with a drive current that varies according to time t. The light source 114 supplied with the drive current emits irradiation light whose wavelength changes with time t. Irradiation light travels toward the splitter 21. After step S103, step S201, step S202, step S301, and step S302 are performed in the same manner as in FIG. 10, the first reference light and the inspection light that interfere with each other in step S203 in FIG. Reflected toward the detection element 153. In step S303, the second reference light and the reference light that interfere with each other pass through the splitter 21 and travel toward the interference fringe detection element 153. Then, after steps S401 to S406 are performed in the same manner as in FIG. 10, the optical coherence tomography method according to the third embodiment is terminated.

According to the optical coherence tomography apparatus and the optical coherence tomography method according to the third embodiment described above, the light intensity loss of the irradiation light by the spectroscope is eliminated. Therefore, it is possible to prevent the output light intensity S _OUT (λ) from being reduced. Note that the modulation drive circuit 115 may vary the drive current in a sawtooth shape according to the time t. Further, the irradiation light, the inspection light, the reference light, the first reference light, and the second reference light may be propagated through the optical waveguide.

(Fourth embodiment)
Unlike the optical coherence tomography apparatus shown in FIG. 11, the optical coherence tomography apparatus according to the fourth embodiment has an optical waveguide 34a connected to a light source 114 as shown in FIG. 19, and a splitter 20 is connected to the optical waveguide 34a. It is connected. The irradiation optical waveguide 80a and the optical waveguide 34b are connected to the splitter 20. A wavelength filter 85 is connected to the irradiation optical waveguide 80a. The wavelength filter 85 selectively transmits a part of the wavelength components of the irradiation light propagated through the irradiation optical waveguide 80a. As the wavelength filter 85, a multilayer interference filter, a Fabry-Perot filter, a fiber Bragg grating, or the like can be used. The wavelength filter 85 is connected to an irradiation optical waveguide 80b that propagates the irradiation light transmitted through the wavelength filter 85. An irradiation light receiving element 154 that receives irradiation light is connected to the irradiation optical waveguide 80b. Since the wavelength filter 85 is disposed, the irradiation light receiving element 154 emits the irradiation light with the strongest light intensity when the wavelength of the irradiation light emitted from the light source 114 coincides with the center of the transmission wavelength band of the wavelength filter 85. Receive light. Hereinafter, the drive current when the wavelength of the irradiation light coincides with the center of the transmission wavelength band is referred to as a set drive current.

  When a semiconductor laser resonator or the like is used as the light source 114, the wavelength of irradiation light may change due to a change in ambient temperature even if the drive current is managed by the modulation drive circuit 115. When the light source 114 has a Fabry-Perot structure, mode hopping (wavelength jump) may occur due to a temperature change as shown in FIG. When a surface emitting laser (VCSEL) light source is used as the light source 114, the wavelength of the irradiation light changes almost in proportion to the drive current. However, if the ambient temperature changes, even if the drive current is the same, the wavelength of the irradiation light may change as shown in FIG.

  Therefore, a feedback circuit 116 is connected to the modulation drive circuit 115 and the irradiation light receiving element 154 shown in FIG. The feedback circuit 116 monitors the drive current supplied to the light source 114 by the modulation drive circuit 115 and the light intensity of the irradiation light received by the irradiation light receiving element 154. Further, as shown in FIG. 22, the feedback circuit 116 stores the center wavelength of the transmission wavelength band in the initial state and the set drive current. Here, as shown in FIG. 23, when the driving current when the irradiation light receiving element 154 receives the irradiation light of the center wavelength becomes weaker than the setting driving current due to the temperature change, the feedback driving circuit 116 uses the modulation driving circuit 115 as the light source 114. Is set so that the light source 114 emits irradiation light in the same wavelength range as the initial state. Further, when the driving current when the irradiation light receiving element 154 receives the irradiation light having the center wavelength is increased from the setting driving current due to the temperature change, the feedback circuit 116 scans the driving current supplied to the light source 114 by the modulation driving circuit 115. Is set so that the light source 114 emits irradiation light in the same wavelength range as the initial state.

  Other components of the optical coherence tomography apparatus shown in FIG. 19 are the same as those in FIG. Next, an optical coherence tomography method according to the fourth embodiment will be described with reference to FIG.

  (a) In step S51, the modulation drive circuit 115 shown in FIG. 19 supplies drive current to the light source 114 within the scanning range determined by the initial setting. The feedback circuit 116 monitors the drive current. In step S52, the light source 114 emits irradiation light having a wavelength corresponding to the drive current. The irradiation light propagates through the optical waveguide 34a and is split by the splitter 20 in the direction of the irradiation optical waveguide 80a and the direction of the optical waveguide 34b. The irradiation light divided in the direction of the irradiation optical waveguide 80a is propagated to the wavelength filter 85 through the irradiation optical waveguide 80a.

  (b) In step S53, the wavelength component of the irradiation light in the band equal to the transmission wavelength band of the wavelength filter 85 is transmitted through the wavelength filter 85. The irradiation light transmitted through the wavelength filter 85 is propagated through the irradiation optical waveguide 80b and received by the irradiation light receiving element 154 in step S54. The irradiation light receiving element 154 transmits the light intensity of the received irradiation light to the feedback circuit 116. In step S55, the feedback circuit 116 monitors whether or not the light intensity of the irradiation light received by the irradiation light receiving element 154 is maximum at the set drive current. If the set drive current is not the maximum, the process proceeds to step S56. If the set drive current is the maximum, the process proceeds to step S60.

(c) When the light intensity of the irradiation light received by the irradiation light receiving element 154 is maximum at a driving current weaker than the set driving current, the feedback circuit 116 scans the driving current of the modulation driving circuit 115 in step S56. Shift the range in the negative direction. When the light intensity of the irradiating light received by the irradiating light receiving element 154 is maximized at a driving current stronger than the set driving current, the feedback circuit 116 shifts the scanning current scanning range of the modulation driving circuit 115 in the plus direction. Let In step S60, similarly to the optical coherence tomography method according to the third embodiment calculates the measured optical path length F _1, and terminates the optical coherence tomography method according to the fourth embodiment.

When the wavelength of the irradiation light is modulated with the temperature change, the difference between the measurement optical path length F ₁ and the reference optical path length F ₂ (F ₁ − An error occurs when calculating F ₂ ). On the other hand, according to the optical coherence tomography device and the optical coherence tomography method according to the fourth embodiment, the feedback circuit 116 prevents the wavelength modulation of the irradiation light accompanying the temperature change. Therefore, the difference between the measurement optical path length F ₁ and the reference optical path length F ₂ (F ₁ − F ₂ ) can be calculated.

(Other embodiments)
Although the present invention has been described by the embodiments as described above, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art. For example, when the interference fringe detection element 153 shown in FIG. 1 is a linear image sensor, a two-dimensional image of the tomographic plane 195 of the sample 190 is generated by calculating the measurement distance L _T1 while moving the stage 400 by the drive module 305. May be. Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

1 is a schematic diagram of an optical coherence tomography device according to a first embodiment of the present invention. It is a graph which shows the selection wavelength for every time by the spectrometer which concerns on the 1st Embodiment of this invention. It is a 1st spectrum of the synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 2nd spectrum of the synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a graph which shows the moving average line which concerns on the 1st Embodiment of this invention. It is a 1st example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 2nd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a 3rd example of the spectrum of the corrected synthetic | combination interference fringe which concerns on the 1st Embodiment of this invention. It is a graph which shows the relationship between the optical path difference which concerns on the 1st Embodiment of this invention, and a peak space | interval. It is a flowchart which shows the optical coherence tomography method which concerns on the 1st Embodiment of this invention. It is a schematic diagram of the optical coherence tomography apparatus which concerns on the 2nd modification of the 1st Embodiment of this invention. It is a schematic diagram of the optical coherence tomography apparatus which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows the spectrometer which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the optical coherence tomography method which concerns on the 2nd Embodiment of this invention. It is a schematic diagram of the optical coherence tomography apparatus which concerns on the modification of the 2nd Embodiment of this invention. It is a schematic diagram of the optical coherence tomography apparatus which concerns on the 3rd Embodiment of this invention. It is a graph which shows the drive current for every time by the modulation drive circuit which concerns on the 3rd Embodiment of this invention. It is a flowchart which shows the optical coherence tomography method which concerns on the 3rd Embodiment of this invention. It is a schematic diagram of the optical coherence tomography apparatus which concerns on the 4th Embodiment of this invention. It is a 1st graph which shows the temperature dependence of the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention. It is a 2nd graph which shows the temperature dependence of the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention. It is a 1st graph which shows the relationship between the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention, and a drive current. It is a 2nd graph which shows the relationship between the wavelength of the irradiation light which concerns on the 4th Embodiment of this invention, and a drive current. It is a flowchart which shows the optical coherence tomography method which concerns on the 4th Embodiment of this invention.

Explanation of symbols

3, 93 ... Spectroscope
20, 21, 121 ... Splitter
23… Wavelength tunable filter
24 ... Oscillator
29, 30, 31, 32, 33, 34, 34a, 34b ... optical waveguide
41 ... First semi-transparent mirror
42… Second semi-transparent mirror
43 ... Reflective mirror for reference
44, 46, 47, 48… collimating lens
45 ... Condensing lens
54 ... Diffraction grating
80a, 80b ... Irradiation optical waveguide
85… Wavelength filter
114 ... Light source
115: Modulation drive circuit
116 ... Feedback circuit
153 ... Interference fringe detector
154 ... Irradiation light receiving element
190 ... Sample
195 ... Fault surface
200 ... Data storage device
201 ... Interference fringe component storage module
202 ... Relational memory module
203 ... Result storage module
300 ... CPU
305 ... Drive module
306 ... Correction module
307 ... Conversion module
310 ... Extraction module
330 ... Calculation module
331… Image generation module
400 ... Stage

Claims (10)

A light source that emits irradiation light;
A first semi-transparent mirror that divides the irradiation light into first reference light and inspection light and transmits the inspection light toward a tomographic plane of a sample;
A second semi-transparent mirror that divides the irradiation light into second reference light and reference light;
A reference reflecting mirror that is disposed opposite to the second semi-transmissive mirror and reflects the reference light;
A first interference fringe between the first reference light and the inspection light that has been irradiated on the tomographic plane of the sample and has traveled the measurement optical path length, and reflected by the second reference light and the reference reflecting mirror to obtain a reference optical path length. An interference fringe detecting element for detecting a combined interference fringe with the second interference fringe with the advanced reference light;
An extraction module that extracts an interference fringe component that varies according to an optical path difference between the measurement optical path length and the reference optical path length from the combined interference fringe;
A calculation module that calculates a value of the measurement optical path length based on the interference fringe component and the value of the reference optical path length, and calculates a position of a tomographic plane of the sample with respect to the first semi-transparent mirror. Optical coherence tomography device.
2. The optical coherence tomography apparatus according to claim 1, wherein the first semi-transparent mirror is disposed at a measurement distance shorter than half of the coherence length of the irradiation light with respect to the tomographic plane of the sample. .
3. The optical coherence according to claim 1, wherein the reference reflecting mirror is disposed at a reference distance shorter than half of the coherence length of the irradiation light with respect to the second semi-transparent mirror. Tomography device.
The first semi-transmission mirror and the second semi-transmission mirror are configured such that interference between the inspection light and the reference light, interference between the inspection light and the second reference light, interference between the first reference light and the reference light, and the first 4. The optical coherence tomography apparatus according to claim 1, wherein the optical coherence tomography apparatus is disposed at a position that prevents interference between the reference light and the second reference light. 5.
The optical coherence tomography apparatus according to any one of claims 1 to 4, wherein the extraction module calculates an envelope of a spectrum of the combined interference fringe.
The optical coherence tomography apparatus according to claim 5, wherein the extraction module extracts an interval between extreme points of the envelope.
The optical coherence tomography apparatus according to any one of claims 1 to 6, further comprising a spectrometer that selectively transmits a wavelength component of the irradiation light.
The spectroscope which selectively transmits each wavelength component of the inspection light, the first reference light, the reference light, and the second reference light is further provided. The optical coherence tomography device according to item.
The optical coherence tomography apparatus according to claim 1, wherein the light source changes a wavelength of the irradiation light.
  The optical coherence tomography apparatus according to claim 1, further comprising a correction module that removes the spectrum distribution of the irradiation light from the spectrum distribution of the combined interference fringes.

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