JP2003004589A - Method and apparatus for measuring optical property of rejection filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for measuring optical property of rejection filter, by which the profile measurement of a rejection filter having a high value of OD in a narrow band can be easily carried out. SOLUTION: The method for measuring optical property of rejection filter with a structure of hologram includes a light measuring step (s10), in which a monochromatic light with a wavelength identical to a wavelength considered as the rejection wavelength of the filter to be evaluated in the optical property is projected to the filter, and the intensity of the light passing therethrough is measured while rotating the filter in such a direction that the rejection wavelength shifts, and a profile creating step (s12), in which the relation between the wavelength and the transmittance of the filter is obtained on the basis of the relation between an angle of the filter and the intensity of passing light measured in the light measuring step (s10).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring optical characteristics of a rejection filter and an apparatus therefor, and more particularly to a method capable of measuring a profile of a rejection filter having a high OD in a narrow band.

[0002]

2. Description of the Related Art When a sample is irradiated with measurement light, and the scattered light is condensed by a lens and dispersed by a diffraction grating, Raleigh scattered light of different wavelength is included in addition to Rayleigh scattered light of the same wavelength as the incident light. . Raman scattered light is a combination of the vibration frequency of the incident light and the vibration frequency of the sample, and its intensity is proportional to the intensity of the incident light and the sample concentration. By spectrally analyzing this Raman scattered light, the components in the sample can be identified and quantified.
Generally, Raman scattered light is extremely weak as compared with Rayleigh scattered light, and therefore, in order to detect it with high accuracy, it is necessary to extract substantially only Raman scattered light. In order to efficiently extract only Raman scattered light, a holographic rejection filter such as a holographic notch filter that removes Rayleigh scattered light is used (Japanese Patent Laid-Open No. 2001-2001).
51123, etc.).

This holographic rejection filter is produced by making the object light surface and the reference light surface of the laser light incident in opposite directions with a dry plate in between. That is, the interference fringes due to the interference of the two light beams for hologram production occur almost parallel to the surface of the photosensitive layer supported by the support, and the interference fringe spacing is the wavelength of the laser used when the refractive index of the photosensitive layer is n. It becomes 1 / 2n. The periodic refractive index modulation can be imparted to the photosensitive layer by the periodic exposure and development processing.
The magnitude of the refractive index n (x) at the position x in this photosensitive layer
Can be expressed by the following formula.

N (x) = n _A + (1/2) n _P sin (2πx / P) (1) where n _A is the average refractive index (n _H + n _L ) / 2 n _P is the refractive index Modulation width (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 for the rejection filter how narrow the rejection region can be and how high the absorbance in the rejection region is. 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 measuring 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.
Then, the filter was irradiated with white light from a white light source, the transmitted light was dispersed by a spectroscope, and the spectrum was measured by a photodetector.

[0005]

The optical density (hereinafter referred to as OD) of the rejection filter has been about 5 in the past, but recently, a rejection filter having a high OD of OD6 or more has been developed. However, when measuring a rejection filter having a high OD in a narrow band, a spectroscope using a diffraction grating has a very narrow rejection area, so that the spectroscope itself generates stray light,
In addition, when the bright line is taken, the tail of the bright line is drawn, and accordingly, high OD measurement is difficult. For example, in the measurement using a conventional white light source and a spectroscope using a diffraction grating, the limit of OD that can be measured in a narrow band is 5, and recent OD has a high OD in a narrow band of 6 or more. Suction filters did not give sufficient measurement results.

Therefore, it is necessary to further improve the resolution of the spectroscope and reduce the stray light, and it is conceivable to manufacture a considerably large-scaled spectroscope, but even if a large-scaled spectroscope is manufactured, it is possible to obtain a high frequency in a narrow band. It was practically difficult to measure the profile of the rejection filter having OD. The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method and an apparatus for measuring optical characteristics of a rejection filter, which can easily measure a profile of a rejection filter having a high OD in a narrow band. Especially.

[0007]

In order to achieve the above object, an optical characteristic measuring method of a rejection filter according to the present invention is a method of measuring an optical characteristic of a rejection filter having a hologram structure, which comprises an optical measuring step, And a profile creating step. Here, in the optical measurement step, monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics is irradiated to the filter, and the transmitted light intensity is measured by the filter. The rotation is performed in the direction in which the rejection wavelength shifts. In the profile creating step, the relationship between the wavelength and the transmittance of the filter is obtained from the relationship between the filter angle and the transmitted light intensity obtained in the light measuring step. Further, in order to achieve the above-mentioned object, the optical characteristic measuring device of the rejection filter according to the present invention is a rejection filter optical characteristic measuring device having a hologram structure, in which a monochromatic light source and a rotating means are provided.
It is characterized by comprising a light detection means and a profile creation means.

Here, the monochromatic light source irradiates the filter with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics.
Further, the rotating means holds the filter rotatably in the direction in which the rejection wavelength shifts. The light detecting means detects the transmitted light intensity of the filter held by the rotating means at a predetermined angle. The profile creating means obtains the relationship between the wavelength and the transmittance of the filter based on the relationship between the angle of the filter detected by the light detecting means and the transmitted light intensity while rotating the filter by the rotating means.

Examples of the rejection filter of the present invention include a holographic notch filter. The optical characteristics of the rejection filter as used herein include whether the region to be rejected is an originally narrow band, and the OD in the region to be rejected is an original high O value.
Whether it is D or not. The present inventors decided to utilize the hologram structure of a rejection filter such as a holographic notch filter for optical evaluation.

That is, since the holographic rejection filter 10 originally rejects a certain wavelength, the refractive index modulation as shown in FIG. 1 is added to the photosensitive layer. Then, in the initial state (angle α = 0 °) in which the filter 10 is installed so that its entrance / exit surface is orthogonal to the optical axis z as shown in FIG. 2A, each modulation layer 12 is
As shown in FIG. 6B, the optical axis z is inclined by an angle θ. The thickness of a certain specific modulation layer 12 in the optical axis direction can be expressed by the thickness d1 = d / sin θ using the thickness d of each modulation layer. Then, 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 is thickness d2 =, as shown in FIG.
Change to d / sin (θ + α). When the filter 10 is tilted in this manner, the thickness of the refractive index modulation layer in the optical axis direction changes, so that the lattice constant changes. The rejection wavelength is shifted to the short wavelength side by that amount, and the intensity change of the transmitted light can be obtained according to the angle of the filter.

Therefore, when the holographic rejection filter is optically evaluated, the hologram structure of the filter is used, that is, while the rejection filter is rotated, the light from the laser having a single wavelength is applied to the filter. By measuring the change in transmitted light intensity depending on the angle of, the profile of the rejection filter having a high OD in a narrow band can be measured without using a spectroscope.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows a schematic configuration of an optical characteristic measuring device 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.
It is to be noted that FIG. 7A is a front view of the filter viewed from the optical axis direction, FIG. 7B is a side view of the filter which is not rotated, and FIG. It is the figure which looked at the state where it was rotated from the side. The optical characteristic measuring device 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.

Here, the laser 22 is composed of, for example, a laser such as a light source of a Raman analyzer, and has the same wavelength as the rejection wavelength of the holographic notch filter (rejection filter) 10 for evaluating optical characteristics. The filter 10 is irradiated with laser light (monochromatic light) 30 having a wavelength λ ₀ . Further, the rotary stage 24 is
A direction in which the rejection wavelength of the filter 10 is shifted by sandwiching the outer peripheral edge portion of the filter 10, as indicated by A in FIG. 5C.
Hold rotatably in any direction. The light detecting means 26 detects the intensity of the transmitted light 32 of the filter 10 held by the rotary stage 24 at a predetermined angle. 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 detecting means 26 while rotating the filter 10 by the rotating stage 24, and stores this relationship in the first storage means 36.
Remember. The CPU 34 then uses the first storage means 36.
The angle information of the filter stored in the table is converted into the wavelength, the transmitted light intensity information is converted into the transmittance, the profile of the relationship between the wavelength and the transmittance of the filter 10 is obtained, and the profile is stored in the second storage means 38. To do.

The user or computer 28
Is whether the area to be rejected on the profile stored in the second storage means 38 is the original narrow band,
Optical characteristics such as whether the OD in the rejection area on the profile is originally high OD are evaluated. In addition,
In the present embodiment, the computer 28 has an input means 40 for making settings and the like necessary for evaluating optical characteristics.
And a display unit 42 for externally displaying the evaluation result. Further, in the present embodiment, since only the intensity of the laser beam 30 is reduced without changing the relative spectral distribution of energy, ND which 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 roughly configured as described above, and its operation will be described below with reference to the flowchart of FIG.

First, the light measuring step (s10) is performed. Here, conventionally, a white light source and a spectroscope using a diffraction grating are used for the optical measurement for evaluating the optical characteristics of the rejection filter. Then, it is common to illuminate the filter with white light from a white light source and measure the intensity of the transmitted light using a spectroscope. In the measurement using the conventional white light source and the spectroscope, if the rejection band is wide, a high OD measurement can be performed, but in a narrow band such as 2 to 3 nm, the tail of the bright line is drawn, and OD5 Only satisfactory measurement was possible, and high OD measurement of 6 or more could not be performed. Therefore, in this embodiment, high OD in a narrow band is provided.
In order to perform various measurements, the hologram structure of the holographic notch filter is used for optical measurement of the rejection filter without using a spectroscope. That is,
Originally, the holographic notch filter rejects a certain wavelength, so that the refractive index modulation is provided in the photosensitive layer. Therefore, by tilting the filter, the lattice constant changes, and the rejection wavelength has a property of shifting to the short wavelength side.

In this embodiment, as the light source, the same wavelength λ _{0 as the} wavelength that would be the rejection wavelength of the holographic notch filter 10 for evaluating the optical characteristics.
A laser that emits the laser light is used. Then, the filter is irradiated with laser light from the laser. At this time, the intensity of transmitted light of the filter is measured by the light detecting means while the filter is rotated by the rotating stage in the direction in which the rejection wavelength shifts. In this embodiment, when the filter is rotated by 3 °, for example, the rejection wavelength λ shifts to the short wavelength side by about 2 to 3 nm.
Therefore, as shown in FIG. 7A, in the initial state (angle α = 0 °) in which the filter 10 is installed so that its entrance / exit surface is orthogonal to the optical axis, the rejection wavelength of the filter 10 shifts. Therefore, if the profile of the filter 10 is normal, the wavelength λ ₀ of the laser light 30 and the rejection wavelength of the filter 10 are the same.

Therefore, for example, the laser light 30 from the laser 22 does not pass through the filter 10 and the output of the light detecting means 26 is zero. Then, as shown in FIG. 7 (B), when the filter 10 is gradually rotated in the direction A in the figure, the rejection wavelength of the filter 10 changes from the wavelength λ ₀ in the initial state to the wavelength λ ₀ as shown in FIG. It shifts to the shorter wavelength side in the _i direction. At this time, the laser light 30 does not pass through the filter 10 from the angle α = 0 ° to the angle α ₁ and the output of the light detection means 26 is 0. However, when the angle α is ₁ or more and α ₂ or less, With the increase, the wavelength light of the skirt portion of the laser light 30 is gradually transmitted. Then, the output of the light detecting means 26 rises as shown in FIG.
_{At 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 rejection wavelength λ _i of the filter 10 are completely different. And the output of the light detecting means 26 shows a constant maximum value. As described above, in the present embodiment, by utilizing the hologram structure of the holographic notch filter as described above for the optical measurement of the notch filter 10, a single wavelength laser is irradiated on the filter to change the transmitted light intensity. By rotating the filter for measurement, a high OD measurement of, for example, OD6 or more in a narrow band can be performed without using a spectroscope.

Next, the profile creating step (s12)
Do. That is, the computer obtains the relationship between the angle of the filter and the intensity of the transmitted light of the filter, which is detected by the light detecting means while rotating the filter by the rotating stage. Then, the computer converts the angle information of the filter obtained as described above into a wavelength, converts the transmitted light intensity into a transmittance, and obtains a profile including the relationship between the wavelength of the filter and the transmittance. Then, the user or the computer determines whether or not the rejection area on this profile is the original narrow band, and the OD in the rejection area on the profile is the original high OD.
Evaluate optical characteristics such as whether or not. Then, the computer externally outputs the evaluation result to the display means.

As described above, according to the optical characteristic measuring apparatus 20 of the present embodiment, the holographic notch filter 10 is irradiated with the laser beam 30 and the change in the intensity of the transmitted light 32 is measured by the rotary stage 24. I decided to do it while rotating. As a result, in the present embodiment, a general spectroscope using a spectroscopic element, high resolution,
Without using a large-scale spectroscope in which low stray light is taken into consideration, it is possible to obtain a profile based on the relationship between the narrow band of rejection of the filter and the OD at the time of rejection. Therefore, in the present embodiment, the entire apparatus is made compact, which can reduce the factors that affect stray light and the like, and narrow band that has been difficult in the measurement using the conventional general white light source and the spectroscope. High OD
It is easy to measure the profile of a notch filter with.

Further, in the present embodiment, since 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 detecting means, the present embodiment is concerned. The configuration of the optical characteristic measuring device can be simplified and the like can be achieved by comparing the components of the optical characteristic measuring device to those newly provided separately from the components provided in the Raman analyzer. In the above configuration, the example in which the filter is rotated in the counterclockwise direction A in the drawing has been described, but the same profile can be obtained by rotating the filter in the counterclockwise direction.

[0021]

As described above, according to the optical characteristic measuring method of the rejection filter of the present invention, the monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristics is used. The measurement of the transmitted light intensity by irradiating the filter with a light measurement step performed while rotating the filter in the direction in which the rejection wavelength shifts, and the relationship between the angle of the filter and the transmitted light intensity, the wavelength and the transmittance. Since a profile creating step for obtaining the relationship of (1) 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 device for a rejection filter according to the present invention, a monochromatic light source for irradiating the filter with the monochromatic light, and a rotating means for rotatably holding the filter in a direction in which the rejection wavelength shifts. , The wavelength of the filter and the 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 while rotating the filter by the rotating means and the transmitted light intensity. Since a profile creating means for obtaining the relationship with 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.

[Brief description of drawings]

[Figure 1]

[Fig. 2]

FIG. 3 is an explanatory diagram of a 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 device according to an embodiment of the present invention.

5A and 5B are explanatory views of an installed state of the filter held by the rotating means according to the embodiment of the present invention, and FIG. 5A is a front view of the filter seen from the optical axis direction, and FIG. ) Is a side view of the state where the filter is not rotated, and FIG. 6C is a side view of the state where the filter is rotated.

FIG. 6 is a flowchart showing a processing procedure of an optical characteristic measuring method according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a filter installation state at the time of measurement by the optical property measuring apparatus according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram of a shift state of the rejection wavelength when the filter is rotated in the optical characteristic measuring device 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 device according to the embodiment of the present invention.

[Explanation of symbols]

10 Holographic Notch Filter (Rejection Filter) 20 Optical Property Measuring Device 22 Laser (Monochromatic Light Source) 24 Rotating Stage (Rotating Means) 26 Light Detecting Means 28 Computer (Profile Creating Means)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiro Kawasaki             5 Japan, 2967 Ishikawacho, Hachioji City, Tokyo             In spectroscopy Co., Ltd. F-term (reference) 2G020 CA02 CB23 CB52 CD13                 2G086 EE05                 2H049 CA01 CA05 CA07 CA24

Claims (2)

[Claims] 1. A method for measuring an optical characteristic of a rejection filter having a hologram structure, wherein the filter is irradiated with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating the optical characteristic. The measurement of the transmitted light intensity, the optical measurement step performed while rotating the filter in the direction in which the rejection wavelength shifts, and the relationship between the angle of the filter and the transmitted light intensity obtained in the optical measurement step, And a profile creating step for obtaining a relationship between the wavelength and the transmittance of the rejection filter. 2. An optical characteristic measuring device for a rejection filter having a hologram structure, wherein the filter is irradiated with monochromatic light having the same wavelength as the rejection wavelength of the filter for evaluating optical characteristics. A light source, a rotation unit that holds the filter rotatably in a direction in which the rejection wavelength shifts, a light detection unit that detects the transmitted light intensity of the filter held at a predetermined angle by the rotation unit, and the rotation unit. Profile rotating means for obtaining the relationship between the wavelength of the filter and the transmittance from the relationship between the angle of the filter detected by the light detecting means and the transmitted light intensity while rotating the filter by the means. A device for measuring the optical characteristics of a characteristic rejection filter.