The present invention relates to a method of adjusting spectroscopic imaging device and a spectroscopic imaging system.
A spectroscopic imaging device includes a collimating lens that collimates input light, a diffraction grating to which light collimated by the collimating lens is inputted and which outputs the light in a different direction according to a wavelength, a condensing lens that condenses the light outputted from the diffraction grating at a different position according to the wavelength, and an array type light receiving part that receives the light condensed by the condensing lens with any of a plurality of light receiving sensors arrayed along a predetermined line. The spectroscopic imaging device can measure a spectrum of input light.
For instance, by measuring an absorption spectrum of a substance, the spectroscopic imaging device can analyze components of the substance. Also, by measuring a spectrum of interference fringes formed by object light and reference light, the spectroscopic imaging device can obtain the thickness of the object and a relative distance. Further, by measuring the spectrum of the interference fringes formed by the object light from a measurement object and the reference light by the spectroscopic imaging device and Fourier-transforming the interference spectrum, an FD-OCT (Fourier Domain Optical Coherence Tomography) can acquire an optical tomographic image in the depth direction of the measurement object in a noninvasive manner (See Patent Literature 1).
In order to measure the spectrum of light with a high wavelength resolution by the spectroscopic imaging device, a condensing point of the light of respective wavelengths condensed by the condensing lens also needs to be positioned on the above-mentioned predetermined line. However, in the spectroscopic imaging device, the relative arrangement relationship among respective components sometimes varies due to an impact from the outside and loosening with time or the like. In this case, when the condensing point of the light of the respective wavelengths condensed by the condensing lens gets out of the above-mentioned predetermined line, the wavelength resolution and detection efficiency of the spectrum to be measured decline. Also, in the FD-OCT, when the condensing point of the light of the respective wavelengths condensed by the condensing lens in the spectroscopic imaging device gets out of the above-mentioned predetermined line, the intensity of the object light reflected at a long distance declines and sensitivity declines.
In order to solve such problems, when monochromatic light is inputted to the spectroscopic imaging device, the size of a condensing area on the plurality of light receiving sensors of the array type light receiving part is obtained, and the relative arrangement relationship of respective optical components of the spectroscopic imaging device is adjusted so as to make the condensing area small, the decline of the wavelength resolution and detection efficiency of the spectrum to be measured can be evaded.
However, in such an adjusting method, since the size of the condensing area on the plurality of light receiving sensors of the array type light receiving part needs to be at least about several times as large as the size of the respective light receiving sensors, it is difficult to accurately obtain the size of the condensing area under the condition. Also, when the plurality of monochromatic lights are inputted to the spectroscopic imaging device, since the respective size of the condensing area of each of the plurality of monochromatic lights in the array type light receiving part needs to be checked, the time required for adjustment becomes longer, and there is the possibility of erroneously determining noise as the condensing area.
The present invention has been made in order to solve the above-mentioned problems, and has an object to provide a spectroscopic imaging device adjusting method capable of easily adjusting the relative arrangement relationship among the respective components in the spectroscopic imaging device, and a spectroscopic imaging system to which such a spectroscopic imaging device adjusting method is applicable.
One aspect of the present invention relates to a spectroscopic imaging device adjusting method. The spectroscopic imaging device adjusting method is a method of adjusting a spectroscopic imaging device comprising a collimating lens which collimates input light, a diffraction grating which inputs the light collimated by the collimating lens and outputs the light in a different direction according to a wavelength, a condensing lens which condenses the light outputted from the diffraction grating at a different position according to the wavelength, and an array type light receiving part which receives the light condensed by the condensing lens with any of a plurality of light receiving sensors P1 to PN arrayed along a predetermined line. A relative arrangement relationship among the collimating lens, the diffraction grating, the condensing lens and the array type light receiving part is adjusted so as to maximize a value of the following expression (1) for output values ƒn from the respective light receiving sensors Pn when monochromatic light is inputted to the spectroscopic imaging device. Provided that n is each integer equal to or larger than 1 and equal to or smaller than N. Also, in the spectroscopic imaging device adjusting method, the full width at half maximum of the spectrum of the monochromatic light may be smaller than a wavelength resolution of the array type light receiving part.
Also, the spectroscopic imaging device adjusting method as another aspect of the present invention is a method of adjusting a spectroscopic imaging device comprising a collimating lens which collimates input light, a diffraction grating which inputs the light collimated by the collimating lens and outputs the light in a different direction according to a wavelength, a condensing lens which condenses the light outputted from the diffraction grating at a different position according to the wavelength, and an array type light receiving part which receives the light condensed by the condensing lens with any of a plurality of light receiving sensors P1 to PN arrayed along a predetermined line. A plurality of monochromatic lights λ1 to λM having the full width at half maximum of the spectrum of each monochromatic light smaller than the wavelength resolution of the array type light receiving part and having the minimum value of the wavelength interval of two adjacent monochromatic lights larger than the wavelength resolution, are inputted to the spectroscopic imaging device. The plurality of light receiving sensors P1 to PN are divided into M groups G1 to GM so that a group Gm includes the light receiving sensor in a continuous range including the condensing position of the monochromatic light λm among the plurality of light receiving sensors P1 to PN. The relative arrangement relationship among the collimating lens, the diffraction grating, the condensing lens and the array type light receiving part is adjusted so as to maximize the value of the following expression (2) for output values ƒn from the respective light receiving sensors Pn. Provided that n is each integer equal to or larger than 1 and equal to or smaller than N, m is each integer equal to or larger than 1 and equal to or smaller than M. In the spectroscopic imaging device adjusting method, the minimum value of the wavelength interval of the two adjacent monochromatic lights may be at least 10 times as large as the wavelength resolution, and the wavelength bandwidth of the light received by the array type light receiving part may be at least 10 times as large as the maximum value of the wavelength interval of the two adjacent monochromatic lights.
The spectroscopic imaging system as yet another aspect of the present invention comprises a collimating lens which collimates input light, a diffraction grating which inputs the light collimated by the collimating lens and outputs the light in a different direction according to a wavelength, a condensing lens which condenses the light outputted from the diffraction grating at a different position according to the wavelength, an array type light receiving part which receives the light condensed by the condensing lens with any of a plurality of light receiving sensors arrayed along a predetermined line, a monochromatic light supply source arranged on an optical path of the light to be inputted to the collimating lens, the monochromatic light supply source inputting monochromatic light to the collimating lens, and adjusting means which adjusts a relative arrangement relationship among the collimating lens, the diffraction grating, the condensing lens, and the array type light receiving part.
In the spectroscopic imaging system, the full width at half maximum of the spectrum of the monochromatic light may be smaller than a wavelength resolution of the array type light receiving part. Also, the minimum value of the wavelength interval of the two adjacent monochromatic lights may be at least 10 times as large as the wavelength resolution of the array type light receiving part, and the wavelength bandwidth of the light received by the array type light receiving part may be at least 10 times as large as the maximum value of the wavelength interval of the two adjacent monochromatic lights.
According to the present invention, the relative arrangement relationship among the respective components can be easily adjusted in the spectroscopic imaging device.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same symbol is attached to the same element in the descriptions of the drawings and redundant descriptions are omitted.
The light source 10 is capable of outputting wideband continuous light. As the light source 10, for instance, an SC light source, an ASE light source, and an SLD or the like can be suitably used. The interference device 11 is a Michelson type interferometer, inputs light outputted from the light source 10, divides the light into two to attain measurement light and reference light, outputs the measurement light to the irradiating unit 12, then inputs, from the irradiating unit 12, object light which is generated in the measurement object 3 when the measurement object 3 is irradiated with the measurement light by the irradiating unit 12, and outputs interference light by the object light and the reference light to the coupler 21.
The single wavelength light source 22 outputs the monochromatic light of a single wavelength. The wavelength of the monochromatic light is the wavelength that can be detected by the spectroscopic imaging device 30. The full width at half maximum of the spectrum of the monochromatic light is smaller than the wavelength resolution of the array type light receiving part 35 (a value for which the bandwidth of the array type light receiving part 35 is divided by the number of light receiving sensors). The coupler 21 inputs the light outputted from the interference device 11 or the monochromatic light with single wavelength outputted from the single wavelength light source 22 to the spectroscopic imaging device 30. The coupler 21 and the single wavelength light source 22 configure a monochromatic light supply source for inputting the monochromatic light with single wavelength to the spectroscopic imaging device 30.
The spectroscopic imaging device 30 measures the spectrum of the light arriving from the coupler 21. The spectroscopic imaging device 30 includes an optical fiber 31, a collimating lens 32, a diffraction grating 33, a condensing lens 34 and an array type light receiving part 35. Also, the spectroscopic imaging device 30 includes adjusting means that adjusts the relative arrangement relationship among the collimating lens 32, the diffraction grating 33, the condensing lens 34, and the array type light receiving part 35.
The optical fiber 31 guides the light outputted from the coupler 21 and outputs the light from an end face. The collimating lens 32 collimates the light outputted from the end face of the optical fiber 31. The diffraction grating 33 inputs the light collimated by the collimating lens 32 and outputs the light in a different direction according to the wavelength. The condensing lens 34 condenses the light outputted from the diffraction grating 33 at a different position according to the wavelength. The array type light receiving part 35 has a plurality of light receiving sensors arrayed at a fixed pitch along a predetermined line and receives the light condensed by the condensing lens 34.
The adjusting means that adjusts the relative arrangement relationship includes means that moves the collimating lens 32, the diffraction grating 33, the condensing lens 34 and the array type light receiving part 35 respectively in parallel and means that changes directions of these components. In particular, the adjusting means includes means that adjusts the position of the collimating lens 32, and means that adjusts a distance between the condensing lens 34 and the array type light receiving part 35. As the adjusting means, a movable stage or the like is used.
The data extracting part 41 receives line data (a row of output data from the respective light receiving sensors) outputted from the plurality of light receiving sensors of the array type light receiving part 35. The tomographic image data generating part 42 Fourier-transforms the line data, and acquires one-dimensional optical tomographic images in a depth direction of the measurement object 3 on the basis of the result of the Fourier transformation. The irradiating unit 12 one-dimensionally or two-dimensionally scans irradiation of the measurement light to the measurement object 3, and the tomographic image data generating part 42 acquires the one-dimensional optical tomographic images in the depth direction of the measurement object 3 at respective irradiating positions during scanning thereof. Then, the imaging part 43 forms and displays the two-dimensional or three-dimensional optical tomographic images of the measurement object 3 by laminating the one-dimensional optical tomographic images acquired by the tomographic image data generating part 42.
The focus score calculating part 44 calculates an evaluation value (focus score) indicating the excellence degree of the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, on the basis of the line data received from the array type light receiving part 35 by the data extracting part 41. The position controlling part 45 controls the adjusting means that adjusts the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, on the basis of the focus score.
In this embodiment, in order to obtain the focus score and adjust the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, the monochromatic light with single wavelength outputted from the single wavelength light source 22 is inputted to the spectroscopic imaging device 30. When the monochromatic light with single wavelength is inputted to the spectroscopic imaging device 30, a light intensity distribution on a light receiving surface of the array type light receiving part 35 has a peak at a position according to the wavelength, and the intensity declines with distance from the position. It is assumed that each of the plurality of light receiving sensors of the array type light receiving part 35 is in a linear relationship that output data is fixed with respect to incident light intensity.
The line data ƒ(x) outputted from the array type light receiving part 35 is expressed by a Gaussian function in the following expression (3). A value a is a positive value and indicates the size of a condensing area on the light receiving surface of the array type light receiving part 35. The line data outputted from the array type light receiving part 35 is actually discrete for a position x, however, is handled here as a function in which the position x is a variable.
[Expression 3]
ƒ(x)=a1/2exp(−ax2) (3)
An integrated value (called “simple sum”, hereinafter) of the line data ƒ(x) is expressed by the following expression (4a). The value of the simple sum is a fixed value regardless of the value a, and is independent of the size of the condensing area. In the meantime, the integrated value of the α-th power (called “α-th power sum”, hereinafter) of the line data ƒ(x) is expressed by the following expression (4b). When it is α>1, as the value a is larger (as the condensing area is narrower), the value of the α-th power sum is larger. From this, the value of the α-th power sum is defined as the focus score, and the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 may be adjusted so as to increase the value.
However, the line data outputted from the array type light receiving part 35 is actually discrete for the position x. Then, the plurality of arrayed light receiving sensors of the array type light receiving part 35 are defined as P1 to PN, the output values from the respective light receiving sensors Pn when the monochromatic light is inputted to the spectroscopic imaging device 30 are defined as ƒn, the value of the following expression (5) is defined as the focus score, and the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 may be adjusted so as to maximize the focus score.
When adjusting the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, the coupler 21 does not input the light from the interference device 11 to the spectroscopic imaging device 30, but inputs the monochromatic light from the single wavelength light source 22 to the spectroscopic imaging device 30. The coupler 21 may be an optical switch for selecting either one of the light outputted from the interference device 11 and the monochromatic light outputted from the single wavelength light source 22 and inputting it to the spectroscopic imaging device 30.
Therefore, when the change of the focus score is checked while adjusting the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, and the relative arrangement relationship in which the focus score becomes the maximum is obtained, the best relative arrangement relationship can be obtained. Also, the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 may be cyclically changed, the fluctuation component of the same cycle in the focus score obtained at the time may be extracted, and the relative arrangement relationship may be adjusted to minimize the component.
In comparison with the configuration of the first embodiment illustrated in
Each single wavelength light source 26m outputs the monochromatic light with a center wavelength λm. The wavelengths λ1 to λM are the wavelengths that can be detected by the spectroscopic imaging device 30, and are different from each other. The full width at half maximum of the spectrum of each monochromatic light is smaller than the wavelength resolution of the array type light receiving part 35. The minimum value of the wavelength interval of the two adjacent monochromatic lights is larger than the wavelength resolution of the array type light receiving part 35. It is suitable that the minimum value of the wavelength interval of the two adjacent monochromatic lights is at least 10 times as large as the wavelength resolution of the array type light receiving part 35, and it is suitable that the wavelength bandwidth of the light received by the array type light receiving part 35 is at least 10 times as large as the maximum value of the wavelength interval of the two adjacent monochromatic lights.
The multiplexer 25 multiplexes the monochromatic lights with the wavelengths λ1 to λM outputted from the plurality of single wavelength light sources 261 to 26M and outputs the multiplexed light to the coupler 21. The coupler 21 inputs the light outputted from the interference device 11 or the monochromatic lights with multiple wavelengths outputted from the multiplexer 25 to the spectroscopic imaging device 30.
In this embodiment, in order to obtain the focus score and adjust the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, the monochromatic lights with the wavelengths λ1 to λM outputted from the plurality of single wavelength light sources 261 to 26M are multiplexed and inputted to the spectroscopic imaging device 30. When the monochromatic lights with the multiple wavelengths are inputted to the spectroscopic imaging device 30, a light intensity distribution on a light receiving surface of the array type light receiving part 35 has a peak at a position according to each wavelength, and the intensity declines with distance from the position.
When the light quantities of the monochromatic lights outputted from the plurality of single wavelength light sources 261 to 26M are fixed, the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 can be adjusted on the basis of the focus score similar to that in the first embodiment. When the light quantities of the monochromatic lights outputted from the plurality of single wavelength light sources 261 to 26M are not fixed, the relative arrangement relationship is adjusted as follows.
The line data outputted from the array type light receiving part 35 is expressed by the sum of a Gaussian function ƒm(x) in the following expression (6). The Gaussian function ƒm(x) expresses the line data to be outputted from the array type light receiving part 35 when only the monochromatic light with the wavelength λm outputted from the single wavelength light source 26m is inputted to the spectroscopic imaging device 30. A value Am indicates the light quantity of the monochromatic light with the wavelength λm, a value am indicates the size of the condensing area of the monochromatic light with the wavelength λm, and a value x0m, indicates a peak position in the condensing area of the monochromatic light with the wavelength λm.
[Expression 6]
ƒm(x)=Amam1/2exp(−am(x−x0m)2) (6)
The simple sum is expressed by the following expression (7a). The value of the simple sum is a fixed value regardless of the value am, and is independent of the size of the condensing area. In the meantime, the α-th power sum is expressed by the following expression (7b). When it is α>1, as the value am is larger (as the condensing area is narrower), the value of the α-th power sum is larger. However, for the value of the α-th power sum, contribution of the monochromatic light with the wavelength λm having a large light quantity Am is great.
Then, in this embodiment, the plurality of light receiving sensors P1 to PN are divided into M groups G1 to GM so that a group Gm includes the light receiving sensor in a continuous range including the condensing position of the monochromatic light λm among the plurality of light receiving sensors P1 to PN of the array type light receiving part 35. Each group Gm includes the light receiving sensor at the condensing position of the monochromatic light λm, and the light receiving sensor in the vicinity of the light receiving sensor. Then, the ratio of the value of the α-th power of the simple sum and the α-th power sum (the following expression (8)) in each group Gm is obtained, and the total sum of the ratio (the following expression (9)) is defined as a focus score. The focus score is independent of the light quantity Am of each monochromatic light λm. The relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 may be adjusted so as to maximize the focus score.
However, the line data outputted from the array type light receiving part 35 is actually discrete for the position x. Then, the plurality of arrayed light receiving sensors of the array type light receiving part 35 are defined as P1 to PN, the output values from the respective light receiving sensors Pn when the monochromatic lights with multiple wavelengths λ1 to λM are inputted to the spectroscopic imaging device 30 are defined as ƒn, the value of the following expression (10) is defined as the focus score, and the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30 may be adjusted so as to maximize the focus score.
When adjusting the relative arrangement relationship among the respective optical components in the spectroscopic imaging device 30, the coupler 21 does not input the light from the interference device 11 to the spectroscopic imaging device 30, but inputs the monochromatic lights with multiple wavelengths from the multiplexer 25 to the spectroscopic imaging device 30. The coupler 21 may be an optical switch that selects either one of the light outputted from the interference device 11 and the monochromatic lights with multiple wavelengths outputted from the multiplexer 25 and inputs it to the spectroscopic imaging device 30.
According to the present invention, the relative arrangement relationship among the respective components in a spectroscopic imaging device can be easily adjusted.
1, 1A, 1B, 1C, 2, 2A, 2B, 2C . . . Spectroscopic imaging system, 3 . . . Measurement object, 10 . . . Light source, 11 . . . Interference device, 12 . . . Irradiating unit, 21 . . . Coupler, 22 . . . Single wavelength light source, 23 . . . Divider, 24 . . . Single wavelength transmission filter, 25 . . . Multiplexer, 261 to 26M . . . Single wavelength light source, 27 . . . Multiple wavelength transmission filter, 30 . . . Spectroscopic imaging device, 31 . . . Optical fiber, 32 . . . Collimating lens, 33 . . . Diffraction grating, 34 . . . Condensing lens, 35 . . . Array type light receiving part, 41 . . . Data extracting part, 42 . . . Tomographic image data generating part, 43 . . . Imaging part, 44 . . . Focus score calculating part, 45 . . . Position controlling part.
Number | Date | Country | Kind |
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2012-150594 | Jul 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/068266 | 7/3/2013 | WO | 00 |