JP4895436B2 - Method and apparatus for measuring optical characteristics of rejection filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring optical characteristics of a rejection filter, and more particularly to a technique capable of measuring a profile of a rejection filter having a high OD in a narrow band.
[0002]
[Prior art]
When the sample is irradiated with measurement light, and the scattered light is collected by a lens and dispersed by a diffraction grating, Raman scattered light having a different wavelength is included in addition to the Rayleigh scattered light having the same wavelength as the incident light. Raman scattered light is a combination of the frequency of incident light and the frequency of the sample, and its intensity is proportional to the intensity of the incident light and the sample concentration. By spectroscopically analyzing the Raman scattered light, the components in the sample can be identified and quantified.
In general, the Raman scattered light is extremely weak compared to the Rayleigh scattered light. Therefore, in order to detect with high accuracy, it is necessary to extract only the Raman scattered light substantially. In order to efficiently extract only the Raman scattered light, a holographic rejection filter such as a holographic notch filter that removes Rayleigh scattered light is used (see JP 2001-51123 A).
[0003]
This holographic rejection filter is produced by making the object light surface of the laser light and the reference light surface incident in opposite directions with a dry plate in between. That is, interference fringes due to the interference of two light beams for creating a hologram are generated almost in parallel with the surface of the photosensitive layer supported by the support, and the interference fringe spacing is equal to the wavelength of the laser used when the refractive index of the photosensitive layer is n. 1 / 2n. Periodic refractive index modulation can be provided in the photosensitive layer by periodic exposure and development processing. The refractive index magnitude n (x) at the position x in the photosensitive layer can be expressed by the following mathematical formula.
[Expression 1]
n (x) = n _A + (1/2) n _P sin (2πx / P) (1)
However, _{n A} is the mean refractive index _{(n H + n L) /} 2
n _P is the modulation width of the refractive index (n _H −n _L )
P is the period n _H is the maximum refractive index n _L is the minimum refractive index
By the way, it is important how the rejection filter can narrow the region to be rejected and how high the absorbance is in the region to be rejected. For example, it is necessary to inspect the optical characteristics of the rejection filter as described above at the time of creation and use.
For this reason, conventionally, an optical characteristic measurement apparatus includes a white light source, a spectroscope using a diffraction grating, and a photodetector, and a filter is installed between the white light source and the spectroscope. And the white light from a white light source was irradiated to the filter, the transmitted light was disperse | distributed using the spectrometer, and the spectrum was measured with the photodetector.
[0005]
[Problems to be solved by the invention]
By the way, the optical density (hereinafter referred to as OD) of the rejection filter is conventionally about 5, but recently, a rejection filter having a high OD of OD6 or more has been developed.
However, when measuring a rejection filter with a high OD in a narrow band, a spectroscope using a diffraction grating has a very narrow rejection area, so the spectroscope itself generates stray light and takes a bright line. The bottom of the bright line is distorted, and it is difficult to measure at a high OD. For example, in a measurement using a conventional white light source and a spectroscope using a diffraction grating, the OD that can be measured in a narrow band is limited to 5 and a recent OD with a high OD in a narrow band of 6 or more. The measurement filter did not provide sufficient measurement results.
[0006]
For this reason, it is necessary to further increase the resolution and low stray light of the spectrometer, and it is conceivable to manufacture a considerably large spectrometer. However, even if a large spectrometer is manufactured, it has a high OD in a narrow band. Rejection filter profile measurement was practically difficult.
The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a method and apparatus for measuring optical characteristics of a rejection filter that can easily perform profile measurement of a rejection filter having a high OD in a narrow band. There is.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an optical characteristic measurement method for a rejection filter according to the present invention includes a light measurement step and a profile creation step in the optical characteristic measurement method for a rejection filter having a hologram structure. Features.
Here, the light measurement step irradiates the filter with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics, and measures the transmitted light output. This is performed while rotating the rejection wavelength in the shifting direction.
In the profile creation step, the relationship between the filter wavelength and the transmittance is obtained from the relationship between the filter angle and the transmitted light output obtained in the light measurement step.
In the light measurement step, the wavelength at which the transmitted light output rises is measured, and the rejection wavelength region of the filter is evaluated from the relationship between the filter wavelength and the transmittance obtained in the profile creation step.
In order to achieve the above object, an optical characteristic measurement apparatus for a rejection filter according to the present invention is an optical characteristic measurement apparatus for a rejection filter having a hologram structure, in which a monochromatic light source, a rotation means, a light detection means, And a profile creation means.
[0008]
Here, the monochromatic light source irradiates the filter with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating optical characteristics.
The rotating means holds the filter rotatably in a direction in which the rejection wavelength shifts.
The light detection means detects the transmitted light output of the filter held at a predetermined angle by the rotation means.
The profile generation means, from the relationship between the angle and the transmitted light output of the filter detected by the light detecting means while rotating the filter by said rotating means to obtain the relationship between the wavelength and transmittance of the filter.
Further, the filter is rotated by the rotating means, the wavelength at which the transmitted light output rises is measured by the light detecting means, and the wavelength and transmittance of the filter obtained by the profile creating means are calculated. From the relationship, the rejection wavelength range of the filter is evaluated.
[0009]
Examples of the rejection filter of the present invention include a holographic notch filter.
Here, the optical characteristics of the rejection filter refer to whether the area to be rejected is an original narrow band, whether the OD in the area to be rejected is an original high OD, or the like.
The inventors decided to use the hologram structure of a rejection filter such as a holographic notch filter for optical evaluation.
[0010]
That is, the holographic rejection filter 10 originally has a refractive index modulation as shown in FIG. 1 in the photosensitive layer in order to reject a certain wavelength. In the initial state (angle α = 0 °) in which the filter 10 is installed so that the incident / exit surface thereof is orthogonal to the optical axis z as shown in FIG. As shown in B), it is inclined with respect to the optical axis z by an angle θ. The thickness in the optical axis direction of a specific modulation layer 12 can be expressed as thickness d1 = d / sin θ using the thickness d of each modulation layer.
When the filter 10 is rotated by an angle α in the direction in which the rejection wavelength shifts, the thickness of the specific modulation layer 12 in the optical axis direction changes to a thickness d2 = d / sin (θ + α) as shown in FIG. To do.
When the filter 10 is tilted in this way, the thickness of the refractive index modulation layer in the optical axis direction changes . Accordingly, the rejection wavelength is shifted to the short wavelength side, and the intensity change of the transmitted light is obtained according to the angle of the filter. That is, the rejection wavelength is determined by the relationship between the thickness of the refractive index modulation layer in the optical axis direction and the wavelength.
[0011]
Therefore, when optically evaluating a holographic rejection filter, the hologram structure of the filter is used, that is, the light from a laser having a single wavelength is irradiated while rotating the rejection filter, and the angle of the filter is adjusted. By measuring the corresponding change in transmitted light intensity, it is possible to measure the profile of a rejection filter having a high OD in a narrow band without using a spectroscope.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 4 shows a schematic configuration of an optical characteristic measuring apparatus for a holographic notch filter (rejection filter) according to an embodiment of the present invention. FIG. 5 shows an installed state of the filter held by the rotating means according to the present embodiment. 1A is a front view of the filter viewed from the optical axis direction, FIG. 1B is a side view of the filter not rotated, and FIG. 1C is the filter. It is the figure which looked at the state where was rotated from the side.
The optical characteristic measuring apparatus 20 shown in FIG. 4 includes a monochromatic light source (laser) 22, a rotating stage (rotating means) 24, a light detecting means 26, and a computer (profile creating means) 28.
[0013]
Here, the laser 22 is made of a laser such as a light source of a Raman analyzer, for example, and has the same wavelength λ _{0 as the} wavelength that would be the rejection wavelength of the holographic notch filter (rejection filter) 10 that evaluates optical characteristics. The filter 10 is irradiated with laser light (monochromatic light) 30 having
The rotary stage 24 holds the outer peripheral edge of the filter 10 and holds the filter 10 so as to be rotatable in the direction in which the rejection wavelength shifts, that is, in the direction A in FIG.
The light detection means 26 detects the intensity of the transmitted light 32 of the filter 10 held at a predetermined angle by the rotary stage 24.
The computer 28 includes, for example, a CPU 34, a first storage unit 36, a second storage unit 38, and the like. Then, the CPU 34 obtains the relationship between the angle of the filter 10 and the intensity of the transmitted light 30 detected by the light detection means 26 while rotating the filter 10 by the rotary stage 24, and stores this in the first storage means 36. Then, the CPU 34 converts the angle information of the filter stored in the first storage unit 36 into the wavelength, converts the transmitted light intensity information into the transmittance, and obtains a profile of the relationship between the wavelength of the filter 10 and the transmittance, for example. This is stored in the second storage means 38.
[0014]
Then, the user or the computer 28 determines whether the area to be rejected on the profile stored in the second storage means 38 is the original narrow band, and whether the OD in the area to be rejected on the profile is the original. Evaluate optical properties such as high OD.
In the present embodiment, the computer 28 includes an input unit 40 for performing settings necessary for evaluating the optical characteristics, and a display unit 42 for externally displaying the evaluation result.
In this embodiment, since only the intensity of the laser beam 30 is reduced without changing the relative spectral distribution of energy, ND that does not show any spectral selective absorption on the optical axis between the laser 22 and the notch filter 10. A filter 44 is provided.
The optical characteristic measuring apparatus 20 according to the present embodiment is configured as described above, and the operation thereof will be described below with reference to the flowchart of FIG.
[0015]
First, a light measurement step (s10) is performed.
Here, conventionally, a white light source and a spectroscope using a diffraction grating are used for light measurement for evaluating the optical characteristics of the rejection filter. In general, the filter is irradiated with white light from a white light source, and the transmitted light intensity is measured using a spectroscope. In the measurement using the conventional white light source and the spectroscope, if the band to be rejected is wide, high OD measurement can be performed. However, in the narrow band of 2 to 3 nm, for example, the emission line oscillates and OD5 Only a satisfactory measurement could be performed, and a high OD measurement of 6 or more could not be performed.
Therefore, in the present embodiment, in order to perform high-OD measurement in a narrow band, the hologram structure of the holographic notch filter is used for light measurement of the rejection filter without using a spectroscope.
That is, the holographic notch filter originally has a refractive index modulation in the photosensitive layer in order to reject a certain wavelength. For this reason, when the filter is tilted, the lattice constant is changed, and the rejection wavelength is shifted to the short wavelength side accordingly.
[0016]
In the present embodiment, a laser that emits laser light having the same wavelength λ _{0 as} the wavelength that will be the rejection wavelength of the holographic notch filter 10 that evaluates optical characteristics is used as the light source. Then, the filter is irradiated with laser light from the laser. At this time, the transmitted light intensity of the filter is measured by the light detection means while rotating the filter in the direction in which the rejection wavelength is shifted by the rotating stage.
In this embodiment, when the filter is rotated by 3 °, for example, the rejection wavelength λ is shifted to the short wavelength side by about 2 to 3 nm.
For this reason, as shown in FIG. 7A, in the initial state (angle α = 0 °) in which the filter 10 is installed so that the incident / exit surface thereof is orthogonal to the optical axis, the rejection wavelength of the filter 10 is shifted. Therefore, if the profile of the filter 10 is normal, the wavelength λ ₀ of the laser beam 30 and the rejection wavelength of the filter 10 are the same.
[0017]
Therefore, for example, the laser beam 30 from the laser 22 does not pass through the filter 10 and the output of the light detection means 26 is zero.
When the filter 10 is gradually rotated in the direction A in the figure as shown in FIG. 7B, the rejection wavelength of the filter 10 is changed from the initial wavelength λ ₀ to the wavelength λ ₀ as shown in FIG. Shifts to the short wavelength side in the _i direction. At this time, the angle alpha = 0 ° ~ angle alpha laser light 30 to ₁ without through the filter 10, the output of the light detection means 26 is 0, the angle alpha ₁ or more, with alpha ₂ below, the angle alpha of With the increase, the wavelength light at the skirt portion of the laser light 30 gradually transmits. Then, the output of the light detection means 26 rises as shown in FIG. 9, and at a certain angle α ₂ or more, the rejection wavelength of the filter 10 is also completely shifted to the short wavelength side, and the wavelength λ ₀ of the laser light 30 and the filter 10 since the rejection wavelength lambda _i is completely different, the laser beam 30 is a filter 10 and fully transparent, the output of the light detection means 26 exhibits a certain maximum value.
As described above, in the present embodiment, the optical measurement of the notch filter 10 is performed by using the hologram structure of the holographic notch filter as described above to irradiate the filter with a single wavelength laser and change the transmitted light intensity. By measuring by rotating the filter, a high OD measurement of, for example, OD6 or more in a narrow band can be performed without using a spectroscope.
[0018]
Next, a profile creation step (s12) is performed.
That is, the computer obtains the relationship between the angle of the filter and the intensity of transmitted light of the filter, which is detected by the light detection means while rotating the filter with the rotary stage. Then, the computer converts the angle information of the filter obtained as described above into a wavelength, converts the transmitted light intensity into the transmittance, and obtains a profile formed by the relationship between the wavelength of the filter and the transmittance.
Then, the user or the computer can check the optical characteristics such as whether the area to be rejected on the profile is an original narrow band, and whether the OD in the area to be rejected on the profile is an original high OD. evaluate. Then, the computer externally outputs the evaluation result to the display means.
[0019]
As described above, according to the optical characteristic measuring apparatus 20 according to the present embodiment, the laser light 30 is irradiated onto the holographic notch filter 10, and the intensity change of the transmitted light 32 is measured by rotating the filter 10 with the rotary stage 24. I decided to do it.
As a result, the present embodiment rejects the narrow band to be rejected by the filter without using a general spectroscope using a spectroscopic element, a large spectroscope that takes into account high resolution and low stray light. The profile which consists of the relationship with OD in can be obtained.
Therefore, in the present embodiment, the entire apparatus becomes compact, thereby reducing elements that affect stray light and the like, and it is difficult to perform measurement using a conventional white light source and a spectroscope. Profile measurement of notch filters with high OD can be easily performed.
[0020]
In this embodiment, the laser provided in the Raman analyzer is used as the monochromatic light source, and the photodetector provided in the similar Raman analyzer is used as the light detection means. Therefore, the optical characteristic measurement according to this embodiment is performed. Compared to the parts newly provided separately from the parts provided in the Raman analyzer, the configuration can be simplified.
In the above configuration, an example in which the filter is rotated in the counterclockwise direction A in the figure has been described. However, a similar profile can be obtained by rotating the filter in the counterclockwise direction.
[0021]
【Effect of the invention】
As described above, according to the method for measuring optical characteristics of a rejection filter according to the present invention, the filter is irradiated with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics, and transmitted through the filter. A profile that obtains the relationship between wavelength and transmittance from the relationship between the light measurement step of rotating the filter in the direction in which the rejection wavelength shifts and the angle of the filter and the transmitted light intensity. Since the creation process is provided, it is possible to easily create a profile of a rejection filter having a high OD in a narrow band, which has been extremely difficult in the past.
Further, according to the optical characteristic measuring apparatus for a rejection filter according to the present invention, a monochromatic light source that irradiates the filter with the monochromatic light, and a rotating unit that rotatably holds the filter in a direction in which the rejection wavelength shifts. The wavelength and transmittance of the filter based on the relationship between the light detection means for detecting the transmitted light intensity of the filter and the angle of the filter detected by the light detection means and the transmitted light intensity while rotating the filter by the rotating means. Therefore, it is possible to easily create a profile of a rejection filter having a high OD in a narrow band, which has been extremely difficult in the past.
[Brief description of the drawings]
FIG. 1, FIG. 2 and FIG. 3 are explanatory diagrams of the principle of an optical characteristic measuring method according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram of a schematic configuration of an optical characteristic measuring apparatus according to an embodiment of the present invention.
FIG. 5 is an explanatory view of an installation state of a filter held by a rotating means according to an embodiment of the present invention, in which FIG. 5 (A) is a front view of the filter viewed from the optical axis direction, and FIG. ) Is a view when the filter is not rotated from the side, and FIG. 10C is a view when the filter is rotated from the side.
FIG. 6 is a flowchart showing a processing procedure of an optical characteristic measurement method according to an embodiment of the present invention.
FIG. 7 is an explanatory diagram of an installed state of a filter at the time of measurement by the optical characteristic measurement device according to one embodiment of the present invention.
FIG. 8 is an explanatory diagram showing a shift state of a rejection wavelength when a filter is rotated in the optical characteristic measurement apparatus according to the embodiment of the present invention.
FIG. 9 is an example of the relationship between the filter angle and the transmitted light intensity obtained by the optical characteristic measuring apparatus according to the embodiment of the present invention.
[Explanation of symbols]
10 Holographic notch filter (rejection filter)
20 Optical characteristic measuring device 22 Laser (monochromatic light source)
24 Rotating stage (Rotating means)
26 light detection means 28 computer (profile creation means)

Claims (2)

In a method for measuring optical characteristics of a rejection filter having a hologram structure,
Irradiate the filter with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics, and measure the transmitted light output in the direction in which the rejection wavelength shifts the filter. A light measurement process performed while rotating;
With the relationship between the angle and the transmitted light output of the filter obtained by the light measurement process, a profile creating step of obtaining the relationship between the wavelength and transmittance of the filter, and
In the light measurement step, the wavelength at which the transmitted light output rises is measured, and the rejection wavelength region of the filter is evaluated from the relationship between the filter wavelength and the transmittance obtained in the profile creation step. A method for measuring optical characteristics of a rejection filter. In the optical characteristic measuring device of a rejection filter having a hologram structure,
A monochromatic light source that irradiates the filter with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics;
Rotating means for rotatably holding the filter in a direction in which the rejection wavelength shifts;
A light detecting means for detecting the transmitted light output of the filter held at a predetermined angle by the rotating means;
While rotating the filter by said rotating means comprises the relationship between the angle and the transmitted light output of the filter detected by the light detecting means, and profile creation means for obtaining a relationship between the wavelength and transmittance of the filter, the ,
The filter is rotated by the rotating means, the wavelength at which the transmitted light output rises is measured by the light detecting means, and the relationship between the filter wavelength and the transmittance obtained by the profile creating means is obtained. An apparatus for measuring optical characteristics of a rejection filter, wherein a rejection wavelength range of the filter is evaluated .

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