JP2009229196A - Refractive index measuring method using waveguide mode resonance lattice and refractive index measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely calculate the absolute value of the refractive index of an unknown sample even if the structure of a waveguide mode resonance lattice is not as planned. <P>SOLUTION: A plurality of refraction liquids of which the refractive indexes are controlled are prepared (S1) and those refractive indexes are precisely measured (S2). The respective refraction liquids are brought into contact with the waveguide mode resonance lattice and the intensity of refracted light is measured while changing the incident angle of measuring light by a θ-2θ optical system to calculate an angle spectrum while the incident angle of the peak appearing in the angle spectrum is set to a resonance incident angle (S3 and S4). Since a plurality of the relations of a refractive index and the resonance incident angle are clear, fitting using them is performed to be stored as a calibration curve (S5 and S6). The unknown sample is brought into contact with the waveguide mode resonance lattice to measure a resonance incident angle in the same way (S7) and the refractive index is calculated from the resonance incident angle on reference to the calibration curve (S8). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a refractive index measurement method and a refractive index measurement apparatus for measuring the refractive index of a sample that is a dielectric material and an absorbing dielectric material of various phases such as a solid phase, a liquid phase, and a gas phase. The present invention relates to a refractive index measuring method and a refractive index measuring apparatus using a waveguide mode resonance filter.

  Conventionally, various methods have been used and proposed as a method for measuring the refractive index of a substance. For example, as a method of measuring the refractive index of a solid sample, a method of measuring a refraction angle at a flat interface of a dielectric having different refractive indexes, such as a minimum deviation angle method and a critical angle method, or an ellipsometry A method for measuring the reflection characteristics due to the interference effect of a thin film sample is known. As a method for measuring the refractive index of a fluid (gas and liquid) sample, a method for measuring absorption of light propagating through the sample, such as a Michelson Morley interferometer or an absorption spectrum spectroscopy, is generally used.

  However, the various methods as described above have respective disadvantages. In other words, in the minimum deviation method, the sample needs to be made into a prism, and therefore the shape and size of the sample cannot be arbitrarily selected. Therefore, a thin film sample or a miniaturized sample cannot be measured. Similarly, the critical angle method such as Abbe's method and Pullfrich's method cannot sufficiently deal with a thin film sample. This is because in the thin film sample, the boundary of the critical line is not clear due to the interference effect, and high-precision measurement is impossible.

  On the other hand, in the measurement method using ellipsometry, only thin film samples with extremely flat and parallel interfaces formed by epitaxial growth of semiconductor crystals or vapor deposition by sputtering can be measured. Is very big. In addition, the Michelson Morley interferometer and absorption spectrum spectroscopy require a large optical path length, which is not suitable for measuring a minute amount of sample.

  By the way, in recent years, a method of measuring a refractive index using an optical element called a waveguide mode resonance grating, which is different from the conventional principle of measuring a refractive index as described above, has been proposed (see Non-Patent Document 2). . Guided-mode resonant grating (GMRG) is a kind of sub-wavelength diffraction grating first proposed by Maschev et al. In 1985 (see Non-Patent Document 1), and has a refractive index and dimensions of dielectric materials. It is known to have a very sharp narrow band characteristic by making the structure appropriately defined. Utilizing this characteristic, applications to wavelength selective filters, wavelength shifters, and the like are being advanced.

  The optical characteristics of the waveguide mode resonance grating narrowed as described above greatly depend on the refractive index of the dielectric material, the substrate, or the incident space constituting the element, and therefore, a very slight change in the refractive index. Can be detected. Non-Patent Documents 2 and 3 disclose the possibility of a refractive index sensor using this characteristic. Such prior art shows only the measurement of the real part of the complex refractive index using a waveguide mode resonant grating, and does not consider the measurement of the imaginary part of the complex refractive index.

  On the other hand, the inventor of this application proposes a method for measuring not only the real part of the complex refractive index but also the imaginary part by using a guided mode resonance grating according to Non-Patent Document 4. That is, the peak position appearing in the angle spectrum with the incident angle to the waveguide mode resonance filter on the horizontal axis and the reflectance on the vertical axis reflects the real part of the complex refractive index and the intensity reflects the imaginary part. It is shown.

  As pointed out in Non-Patent Document 4, in principle, the waveguide mode resonance grating can narrow the reflection band as much as possible, and the refractive index resolution depends on the angular resolution and wavelength resolution of the measurement system. . If the resonance incident angle and the resonance wavelength are obtained with high accuracy, the values depend on the refractive index of the sample, so that the refractive index can be obtained. Theoretically, the refractive index of the sample can be obtained by calculation from the resonance incident angle and the resonance wavelength.

  However, an actual element structure is not always as designed, and it can be said that a dimensional error of the element structure in manufacturing always occurs. In particular, in the case of a waveguide mode resonance grating, it is still technically difficult to manufacture an element with high dimensional accuracy, and the deviation causes an error in measurement values. Therefore, a refractometer using a waveguide mode resonant grating can measure the difference between the refractive indexes of two different samples, that is, a relative value with high accuracy, but the refractive index of each sample as an absolute value. There is a problem that it is difficult to obtain with high accuracy.

Maschev and 1 other, "zero order anomaly of dielectric coated gratings", optical communication, 55, pp.377-380, 1985 Sue Shen and two others, “Strong Resonant Coupling of Surface Plasmon Polaritons to Radiation Mose Through a Thin Metal Slab Deelectric Gratings coupling of surface plasmon polaritons to radiation modes through a thin metal slab with dielectric gratings ”, J. Opt. Soc., Vol. 24, No. 1, pp. 225-230, 2007 Hisao Kikuta and four others, "Refractive index sensor with a guided-mode resonant grating filter", Proceedings of SPIE (Proc. SPIE), Vol. 4416, pp. 219-222, 2001 Satoshi Sato, “Refractive index dependence of guided mode resonance filter”, 36th Electromagnetic Theory Symposium, October 19, 2007, Electromagnetic Theory Research Committee

  The present invention has been made in view of the above problems, and the object of the present invention is to provide a refractive index using a waveguide mode resonance grating that can easily and accurately determine the absolute value of the refractive index of a sample. An object of the present invention is to provide a refractive index measuring method and a refractive index measuring apparatus.

A first invention made to solve the above problems is a waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate. The substrate surface of the waveguide mode resonance grating or the object to be measured in a state where the object to be measured is in contact with the surface opposite to the substrate across the multilayer structure or single layer structure of the waveguide mode resonance grating A light irradiating means for irradiating light on the surface, and a reflected light for the light irradiation by the light irradiating means, and an angle spectrum when the incident angle of the irradiated light is changed or a wavelength spectrum when the wavelength of the irradiated light is changed A refractive index measuring method using a refractive index measuring device that calculates a refractive index of an object to be measured based on a resonance incident angle or a resonance wavelength according to a measurement result of the spectrum measuring means. There,
a) a reference liquid measurement step for measuring a resonance incident angle or a resonance wavelength for each of the plurality of reference liquids having different known refractive indexes, and measuring a resonance incident angle or a resonance wavelength for each refractive index;
b) a calibration curve creating step for creating a calibration curve based on the discrete relationship between the refractive index obtained in the reference liquid measurement step and the resonance incident angle or resonance wavelength;
c) measuring a resonance incident angle or a resonance wavelength with an unknown sample as an object to be measured, referring to the calibration curve, and obtaining a refractive index of the unknown sample from the measurement result; and
It is characterized by performing.

A second invention made to solve the above-mentioned problems is a refractive index measuring apparatus for carrying out the refractive index measuring method according to the first invention,
a) a waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate;
b) The substrate surface of the waveguide mode resonance grating or the measurement object in a state where the object to be measured is in contact with the surface opposite to the substrate across the multilayer structure or single layer structure of the waveguide mode resonance grating A light irradiation means for irradiating the object with light;
c) Resonance that gives a resonance peak by receiving reflected light from the light irradiation means and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed. Spectrum measuring means for determining an incident angle or a resonance wavelength;
d) Using a plurality of reference solutions having different known refractive indexes as objects to be measured, a calibration curve is obtained based on the discrete relationship between the resonance incident angle or the resonance wavelength and the refractive index respectively measured by the spectrum measuring means. A calibration curve creation means to create,
e) an arithmetic processing means for obtaining a refractive index of the unknown sample with reference to the calibration curve from a resonance incident angle or a resonance wavelength measured by the spectrum measuring means with the unknown sample as an object to be measured;
It is characterized by having.

  In the first invention, the second invention, and all other inventions described below, the reference solution may be prepared by the user or the like, but it is convenient to use a commercially available refractive solution with a controlled refractive index. Specifically, contact liquids sold by Shimadzu Corporation (see Internet <URL: http://www.shimadzu.co.jp/products/opt/products/se.html>) and Moritex Corporation Standard refraction liquid made by US Cargill Corporation (see the Internet <URL: http://www.shimadzu.co.jp/products/opt/products/se.html>) and the like can be used. The former is typically available in 0.01 increments with a refractive index in the range of 1.48 to 1.78 at a wavelength of 587.56 nm. The latter is available in a wider refractive index range with a tolerance of ± 0.0002.

  When a commercially available refractive liquid as described above is used as a reference liquid, the refractive index of the refractive liquid is known, but when measurement with high accuracy is required, for example, the minimum deflection angle using a prism cell is used. It is desirable to measure the refractive index of the reference solution by a method such as the method.

  In the refractive index measurement method according to the first aspect of the present invention, in the reference liquid measurement step, a plurality of reference liquids having known refractive indices are respectively measured with a refractive index measurement apparatus using a waveguide mode resonance grating to be calibrated. The resonance incident angle or resonance wavelength is obtained from the position of the peak appearing in the obtained angle spectrum or wavelength spectrum. As a result, a plurality of corresponding points between the refractive index and the resonance incident angle or the resonance wavelength are obtained. In the calibration curve creation step, a calculation formula representing the calibration curve or the calibration curve is calculated using a known method. Here, there are no particular limitations on the known method, but various curve fitting methods such as linear approximation and spline function approximation can be used.

  This calibration curve reflects all deviations in the dimensions of the waveguide mode resonance grating. Usually, different calibration curves are created for each apparatus due to, for example, individual differences in waveguide mode resonance gratings produced in manufacturing. Based on this calibration curve, the refractive index for any resonant incident angle or resonant wavelength can be derived. Therefore, in the sample measurement step, the refractive index is obtained from the resonance incident angle or the resonance wavelength obtained by measuring the unknown sample with reference to the calibration curve. This makes it possible to obtain the absolute value of the refractive index of the unknown sample with high accuracy even if the size of the guided mode resonance grating, such as the spacing and depth, is not designed or ideally manufactured.

  Further, the relationship between the refractive index and the resonance incident angle or the resonance wavelength, in other words, the refractive index dependency (also referred to as “degree of dispersion”) of the resonance incident angle and the resonance wavelength can be analyzed by numerical calculation. However, this calculation does not reflect a shift in the dimensions of the waveguide mode resonance grating. For example, if the resonant grating is close to the intended structure, even if there is a manufacturing deviation as described above, the shape of the curve (including straight lines) showing the refractive index dependence of the resonant incident angle and resonant wavelength, that is, relative Sometimes there is no change in the relationship. Therefore, by measuring only one reference liquid having a known refractive index, the correspondence between the refractive index and the resonance incident angle or the resonance wavelength is determined, and this is used to depend on the refractive index of the resonance incident angle or the resonance wavelength. The absolute value of the curve indicating the sex may be determined.

That is, the third aspect of the invention made to solve the above-described problem is that a waveguide mode resonance in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate. In a state where the object to be measured is in contact with the surface opposite to the substrate across the grating and the multilayer structure or single layer structure of the waveguide mode resonance grating, Light irradiation means for irradiating the object surface with light, and reflected light for light irradiation by the light irradiation means, and when the angle spectrum or the wavelength of the irradiation light is changed when the incident angle of the irradiation light is changed A refractive index measurement using a refractive index measurement device that calculates a refractive index of an object to be measured based on a resonance incident angle or a resonance wavelength according to a measurement result of the spectrum measurement means. A method,
a) measuring a resonance incident angle or a resonance wavelength using a reference liquid having a known refractive index as an object to be measured, and determining a resonance incident angle or a resonance wavelength for at least one refractive index;
b) A dispersion curve curve showing the relationship between the refractive index calculated based on the theoretical value of the design of the waveguide mode resonance grating and the resonance incident angle or the resonance wavelength is a refractive index obtained in the reference liquid measurement step. And a calibration curve acquisition step of acquiring a calibration curve by correcting based on the relationship between the resonance incident angle or the resonance wavelength,
c) measuring a resonance incident angle or a resonance wavelength with an unknown sample as an object to be measured, referring to the calibration curve, and obtaining a refractive index of the unknown sample from the measurement result; and
It is characterized by performing.

A fourth invention made to solve the above-described problem is a refractive index measuring device for carrying out the refractive index measuring method according to the third invention,
a) a waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate;
b) The substrate surface of the waveguide mode resonance grating or the measurement object in a state where the object to be measured is in contact with the surface opposite to the substrate across the multilayer structure or single layer structure of the waveguide mode resonance grating A light irradiation means for irradiating the object with light;
c) Resonance that gives a resonance peak by receiving reflected light from the light irradiation means and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed. Spectrum measuring means for determining an incident angle or a resonance wavelength;
d) Using a reference liquid having a known refractive index as an object to be measured, the waveguide mode resonant grating is designed based on the relationship between the resonant incident angle or resonant wavelength and refractive index measured by the spectral measuring means. A calibration curve acquisition means for acquiring a calibration curve by correcting a dispersion curve curve indicating a relationship between a refractive index calculated based on a theoretical value and a resonance incident angle or a resonance wavelength;
e) an arithmetic processing means for obtaining a refractive index of the unknown sample with reference to the calibration curve from a resonance incident angle or a resonance wavelength measured by the spectrum measuring means with the unknown sample as an object to be measured;
It is characterized by having.

  According to the third and fourth inventions, as in the first and second inventions, the absolute value of the refractive index of the unknown sample can be calculated with high accuracy. The numerical calculation of the refractive index dependency of the resonance incident angle and the resonance wavelength can be performed using commercially available software. For example, GSOLVER (Grating Solver Development), a calculation software based on exact coupled wave analysis (see Internet <URL: http://www.gsolve.com/>), The use of FullWAVE of the Japan Rsoft Design Group, which is analysis and simulation software based on the FDTD method (see the Internet <URL: http://www.rsoftdesign.co.jp/pdfs/fullwave_jpn.pdf>), etc. it can.

  In the refractive index measuring method or the refractive index measuring apparatus according to the first to fourth inventions, the measurement of the reference liquid and the measurement of the unknown sample may be performed in a time-sharing manner using the same waveguide mode resonance grating. The measurement of the reference solution and the measurement of the unknown sample may be performed in parallel using different parts of the same guided mode resonance grating. In the former case, each time measurement is performed with one or more reference liquids in contact with the waveguide mode resonance grating, the contact surface of the resonance grating is cleaned, and the next reference liquid or unknown sample is measured. . In this case, the configuration of the apparatus is simplified.

  On the other hand, in the latter case, the measurement of the reference solution and the measurement of the unknown sample can be performed at substantially the same time and under the same environment (mainly temperature). Therefore, for example, even if the temperature dependence of the refractive index of the reference liquid is large, the refractive index of the unknown sample can be calculated with high accuracy without being substantially affected by this.

  Of course, when the temperature dependence of the refractive index of the reference solution is large, the temperature of each of the reference solution and the unknown sample is measured simultaneously, and the unknown sample is determined based on the difference in temperature and the temperature characteristics of the reference solution. The refractive index may be corrected.

  According to the refractive index measuring method and refractive index measuring apparatus using the waveguide mode resonance grating according to the first to fourth inventions, the refractive index (complex refraction) of samples in various phases such as solid phase, liquid phase, and gas phase. The absolute value of the real part of the rate can be measured with high accuracy.

  First, a refractive index measurement method using a waveguide mode resonance grating will be described. In general, there are several forms of guided mode resonant gratings. FIG. 1 is a schematic cross-sectional view for explaining the structure of a typical guided mode resonance grating. These are relatively easy to produce.

In a guided mode resonant grating 1A shown in FIG. 1A, a waveguide layer 3 having a predetermined thickness is formed on a flat substrate 2, and a rectangular cross section is formed on the waveguide layer 3 in a direction perpendicular to the paper surface. A lattice layer 4 is formed in which lattices 4a extending in the direction are periodically arranged. The refractive index of the substrate 2 is n _s , and the waveguide layer 3 and the grating layer 4 (grating 4a) are made of the same material and have the same refractive index n ₁ . When the waveguide mode resonance grating is used as an optical filter or an optical switch, the space above the grating layer 4 is usually an air layer. Here, the space is a medium layer 5 on which a sample is arranged. To do. The refractive index of the medium layer 5 is n ₀ . A thin film of dielectric material is formed on the substrate 2, and then the grating 4a can be formed so as to leave the waveguide layer 3 by etching.

The fundamental structure of the guided mode resonant grating 1B shown in FIG. 1B is the same as that of FIG. 1A, but the waveguide layer 3 and the grating layer 4 are made of different dielectric materials. Has a refractive index of n ₂ and the latter has a refractive index of n ₁ . The lattice 4a can be formed by laminating two thin films of different dielectric materials on the substrate 2 and etching only the upper layer. For example, when the lattice layer 4 is made of a photoresist material, it is possible to easily achieve the end of etching without eroding the waveguide layer 3.

  In the guided mode resonant grating 1C shown in FIG. 1C, the grating itself also serves as a waveguide layer, and the first grating 6a and the second grating 6b having different refractive indexes are alternately arranged periodically. The lattice layer 6 is formed on the substrate 2.

  The waveguide mode resonance gratings 1A, 1B, and 1C exhibit reciprocal optical characteristics from the upper side (that is, the medium layer 5) and the lower side (that is, the substrate 2). Can be replaced with the substrate 2 on the upper side and the medium layer 5 on the lower side.

  In the following description, a waveguide mode resonance grating in which the waveguide layer 3 and the grating layer 4 are made of the same dielectric material will be considered. FIG. 2 shows a schematic configuration of a measurement system using this guided mode resonance grating. It is assumed that the sample S to be measured covers the lattice layer 4 and is provided so as to penetrate into the space between the adjacent lattices 4a. In this case, the sample S is liquid or gas.

  The measurement light 11 including a component in a predetermined wavelength range emitted from the light source 10 is predetermined on one surface (the lower surface in the drawing) of the substrate 2 opposite to the sample S with the waveguide layer 3 and the grating layer 4 interposed therebetween. Incident at an incident angle. The reflected light 12 from the waveguide mode resonance grating 1 is detected by the detector 13, and a detection signal corresponding to the amount of the reflected light is extracted. The incident angle θ of the measuring light 11 is scanned within a predetermined angle range, and in conjunction with this, the position of the detector 13 is moved so that the outgoing angle of the reflected light 12 incident on the detector 13 is the same as the incident angle. The For example, when the position of the light source 10 is moved to the position 10 'so that the incident angle is changed from θ to θ + Δθ, the position of the detector 13 is also moved to the position 13'. A so-called θ-2θ optical system is used to obtain an intensity spectrum of specular reflection. For this purpose, the light source 10 and the detector 13 may be moved synchronously using a known goniometer or the like.

  As described in Non-Patent Document 4 and the like, the guided mode resonant grating 1 has an infinitely narrow band filtering function in principle. Therefore, a peak appears at a specific incident angle in the angle spectrum in which the reflectance is measured while changing the incident angle, as shown in FIG. Further, the position of this peak shifts to the left and right according to the refractive index of the sample S (the real part of the complex refractive index). Therefore, in principle, the refractive index of the sample S can be obtained from the incident angle at which this peak top appears. Even when the wavelength spectrum is created by scanning the wavelength of the measurement light 11 instead of the incident angle of the measurement light 11, a peak top appears at a wavelength corresponding to the refractive index of the sample S. Therefore, the refractive index of the sample S can also be obtained from the wavelength at which this peak top appears.

  However, the above-described peak wavelength and peak incident angle also change due to structural variations such as the groove depth and spacing of the waveguide mode resonant grating 1. Although it depends on the required accuracy of the refractive index, it is difficult to manufacture the structure of the guided mode resonance grating as designed, and the error of the structure is usually so large that the required accuracy of the refractive index cannot be satisfied. Therefore, the refractive index of the sample S can be calculated with high accuracy even when the structure error of the waveguide mode resonance grating is large by the following characteristic refractive index measurement method. FIG. 4 is a flowchart showing the procedure of this refractive index measurement method.

  First, prior to performing measurement, a plurality of reference liquids having different refractive indexes and controlled in refractive index are prepared (step S1). As the reference liquid, for example, a commercially available refractive liquid as described above may be used. Next, the refractive indexes of the plurality of reference liquids are measured with the accuracy required by the existing refractive index measurement method (for example, the minimum declination method or the Abbe refraction method using a prism cell) (step S2). ). If the refractive index of which the refractive index is controlled as described above is used and the refractive index accuracy (variation) of the refractive liquid satisfies the required accuracy of the calibration curve to be finally obtained, the actual measurement in step S2 is performed. Can be omitted. If the refractive index of the reference liquid has temperature dependency, the temperature dependency may be measured.

  Thereafter, a plurality of reference solutions are sequentially measured with a refractive index measuring device using the above principle, and a resonance incident angle (or resonance wavelength) is measured (step S3). That is, instead of the sample S in FIG. 2, the reference liquid is brought into contact with the waveguide mode resonance grating 1, and the angle spectrum is based on the signal obtained by the detector 13 while changing the incident angle of the measuring light 11 incident thereon. Create Then, a peak appearing in the angle spectrum is extracted, and an incident angle corresponding to the peak top of the peak may be obtained. After the measurement is completed, the reference mode liquid is removed by washing the waveguide mode resonance grating 1 with an organic solvent or the like. If measurement of all the prepared reference solutions has not been completed (NO in step S4), the process returns to step S3 to measure the resonance incident angle (or resonance wavelength) of another reference solution that has not been measured. When the refractive index of the reference liquid has temperature dependence, the temperature at the time of measuring the resonance incident angle is also measured at the same time.

  Since a pair of values of the refractive index (precise measurement value obtained in step S2) and the resonance incident angle is obtained for each reference solution, using the value pairs, various known curve fitting techniques can be used. The most probable curve or straight line is drawn and used as a calibration curve (step S5). A calibration curve can be obtained by linear approximation from a pair of values of at least two refractive indices and the resonant incident angle, but generally the range in which the relationship between the refractive index and the resonant incident angle can be regarded as linear is narrow. In particular, if the value deviates from this range, the error increases. Therefore, it is preferable to perform optimal fitting with a higher-order curve such as a spline function. The calibration curve thus obtained is stored in a storage unit such as a flash ROM (step S6).

  Next, after the waveguide mode resonance grating 1 is cleaned and cleaned with an organic solvent or the like, the sample S to be measured is brought into contact with the waveguide mode resonance grating 1, and the resonance incidence angle is measured in the same manner as in the measurement of the reference liquid. Is measured (step S7). Then, the refractive index is calculated from the obtained resonance incident angle with reference to the calibration curve (step S8). If the refractive index of the reference solution has temperature dependence, the temperature is also measured during the measurement of the resonance incidence angle of this sample, and the difference from the temperature measured during the measurement of the resonance incidence angle of the reference solution is obtained. The refractive index of the sample may be corrected using the measured value of the temperature dependence of the refractive index of the reference solution. The refractive index value thus obtained is output (step S9).

  In the above flowchart, the work procedure is not necessarily in the order of the step numbers. For example, after the measurement of the reference solution and the sample, calculation for obtaining a calibration curve may be executed, and the refractive index may be calculated from the measurement result of the sample using the calibration curve.

  In the measurement method described above, a plurality of reference solutions having different refractive indexes are used, and the measurement result is subjected to arithmetic processing such as curve fitting to obtain a calibration curve. As another method, the shape of the calibration curve is determined by calculating the refractive index dependency of the resonance incident angle by numerical calculation, and the measurement result of one reference solution having a known refractive index is used to determine the calibration curve. A final calibration curve may be obtained by determining the absolute position. In order to analyze the refractive index dependency of the resonance incident angle, it is possible to use various kinds of commercially available software as described above.

  A schematic configuration of an embodiment of a refractive index measuring apparatus for carrying out the above measuring method is shown in FIGS. FIG. 5 shows a configuration in which the measurement of the reference solution and the measurement of the sample are performed in a time-sharing manner, that is, in order. FIG. 6 is a configuration in which the measurement of the reference solution and the measurement of the sample can be performed simultaneously. is there.

  5 and 6, the optical system drive unit 14 including a motor moves the light source 10 and the detector 13 synchronously so as to maintain the relationship of θ−2θ under the control of the control unit 15. is there. Thereby, the incident angle of the measurement light 11 to the waveguide mode resonance grating 1 is scanned. The data processing unit 20 that receives and processes the detection signal of the detector 13 includes an angle spectrum calculation unit 21, a peak extraction unit 22, a calibration curve creation unit 23, a calibration curve storage unit 24, and a refractive index calculation unit 25. The angle spectrum calculation unit 21 is based on detection signals sequentially input as the light source 10 and the detector 13 are moved by the optical system driving unit 14, and the horizontal axis represents the incident angle and the vertical axis represents the reflectance or diffraction efficiency. Create an angular spectrum. The peak extraction unit 22 performs peak detection on the angle spectrum, finds a peak top, and calculates an incident angle corresponding to the peak top, that is, a resonance incident angle. The calibration curve creation unit 23 is based on the refractive index of the reference solution set from the outside and the resonance incident angle obtained by measurement, or by using the numerical calculation of the refractive index dependence of the resonance incident angle. Create The calibration curve storage unit 24 stores the created calibration curve. The refractive index calculation unit 25 refers to the calibration curve stored in the calibration curve storage unit 24 and calculates the refractive index from the measurement result of the sample.

  In the refractive index measurement apparatus shown in FIG. 5, it is possible to provide means for automatically supplying the sample S to the waveguide mode resonance grating 1 and cleaning after measurement. As a result, the user prepares the sample and one or more reference solutions, and inputs the refractive index value obtained by measuring the reference solution, and performs automatic measurement to obtain the refractive index of the sample from the output unit 26. be able to.

  In the configuration of FIG. 6, the reference solution Sr and the sample Ss are accommodated in different portions separated by the partition wall 100 of one waveguide mode resonance grating 1. The waveguide mode resonance grating 1 can be moved by a moving unit 17 and is configured such that the irradiation position of the measurement light 11 can be switched between the accommodation site for the reference liquid Sr and the accommodation site for the sample Ss. When there are a plurality of reference liquids, it is preferable to provide a storage site for each reference liquid. In this configuration, it is possible to continuously measure one or more reference solutions and the sample without cleaning the waveguide mode resonance grating 1. Therefore, it can be regarded as simultaneous measurement, and there is an advantage that the temperature conditions at the time of measurement can be regarded as the same because the cleaning operation is not sandwiched in particular.

  Note that the light source 10, the detector 13, the optical system drive unit 14 and the like may be moved instead of moving the waveguide mode resonance grating 1, or the measurement light 11 is incident on different parts by switching the optical path of the optical system. However, the reflected light 12 may be introduced into the detector 13.

  5 and 6 uses the refractive index dependency of the resonance incident angle, but can easily be modified to a configuration using the refractive index dependency of the resonance wavelength. In that case, the incident angle of the measurement light 11 and the emission angle of the reflected light 12 are fixed, and the reflected light 12 is introduced into a spectroscopic optical system including a monochromator or a polychromator, and is extracted from the spectroscopic optical system. Wavelength light is introduced into the detector 13. By scanning the wavelength extracted from the spectroscopic optical system within a predetermined range, the wavelength spectrum can be calculated instead of the angle spectrum, and the resonance wavelength can be obtained by extracting a peak on the spectrum.

Hereinafter, it will be clarified by simulation that the refractive index can be accurately obtained by the above-described measurement method when a specific structure of the waveguide mode resonance grating 1 is assumed.
The parameters that determine the structure of the guided mode resonant grating 1 are shown in FIG. That is, the period Λ of the 3600 gratings 4a is 278 nm, the duty ratio f is 0.5, and the groove depth (thickness of the grating layer 4) d2 is 10 nm. The thickness d1 of the waveguide layer 3 is 90 nm. Both the grating layer 4 and the waveguiding layer 3 are aluminum oxide, and the refractive index n ₁ is 1.65 to 1.68. Refractive index n _s of the substrate 2 is 1.52 (assuming the ordinary optical glass, such as the materials such as BK7).

  As the measurement system, the θ-2θ optical system shown in FIG. 2 is assumed. In this optical system, TE polarized light is incident from the substrate 2 side, and the sample is brought into contact with the grating layer 4 and the waveguide layer 3. When the refractive index n of the sample is 1.5, the resonance incident angles with respect to the measurement light having the wavelengths of 486.1 [nm], 587.6 [nm], and 656.3 [nm] are 8.1058 °, 22.7550 ° and 33.4740 °. This resonance incident angle is that in the case where the waveguide mode resonance grating 1 is ideally produced with the above-mentioned dimensions. However, in practice, a dimensional error that occurs in manufacturing is unavoidable, and therefore resonance reflection usually occurs at an incident angle deviated from the above numerical value. Further, depending on the design method, the error in the electromagnetic field calculation used for the design cannot be ignored.

  Therefore, as described above, it is necessary to perform calibration using a reference solution having a known refractive index. The condition that enables the calibration is that the condition of resonance reflection does not disappear even at a position slightly deviated from the target refractive index. The above-described refractive liquid that is commercially available has a refractive index step of 0.01 or less. Therefore, it suffices to show that the resonance condition exists in the refractive index range of 1.5 ± 0.01. If it can be shown, it is possible to measure the resonance angle of incidence when using a reference solution with a known refractive index, and to create a calibration curve that can calculate the refractive index of the sample.

  FIG. 8 is a diagram showing a reflection spectrum when the refractive index of the sample (reference solution) is 1.5 and 1.5 ± 0.01 with respect to TE polarized light having a wavelength of 486.1 [nm]. . FIG. 9 is a diagram showing a reflection spectrum when the refractive index of the sample (reference solution) is 1.5 and 1.5 ± 0.01 with respect to TE polarized light having a wavelength of 587.6 [nm]. . FIG. 10 is a diagram showing a reflection spectrum when the refractive index of the sample (reference solution) is 1.5 and 1.5 ± 0.01 with respect to TE polarized light having a wavelength of 656.3 [nm]. . In all cases, a clear peak appears, indicating that a resonance condition exists. Further, the reflectance at the peak top is almost 100%. That is, when the refractive index of the sample is near 1.5, the resonance angle of incidence can be measured using a refractive liquid having a refractive index close to this value, and it can be seen that this is suitable as a reference liquid.

  FIG. 11 shows the deviation from the resonant incident angle when the refractive index is around 1.5. R, G, and B are the wavelengths shown in FIGS. It has negative dispersion characteristics (in this case, the resonance incident angle decreases as the refractive index increases) at any wavelength of R, G, and B. For example, in the case of abnormal dispersion such as discontinuous dispersion or dispersion with poles, It can be seen that the dispersion is almost linear. Thereby, a calibration curve can be created and the refractive index with respect to the resonance incident angle of the sample can be obtained.

The results of FIGS. 8 to 10 are summarized in FIG. Thus, in the refractive index measurement method according to the present invention,
(1) Resonance conditions are maintained within the refractive index controllable range of the refractive liquid;
(2) The dispersion is normal in the refractive index range (the above-mentioned anomalous dispersion is not seen),
By setting the incident condition (incident angle range) satisfying the two conditions and the waveguide mode resonance grating structure, it can be said that the absolute measurement of the refractive index based on a commercially available refractive liquid is possible. Further, when the refractive index of the refracting liquid has temperature dependency, it can be easily corrected by quantifying the characteristics in advance.

The schematic sectional drawing for demonstrating the structure of the typical waveguide mode resonance grating utilized for the refractive index measuring apparatus which concerns on this invention. The schematic block diagram of the measurement system using the waveguide mode resonance grating shown to Fig.1 (a). The figure which shows an example of the angle spectrum obtained when the incident angle of measurement light is scanned with the measurement system of FIG. The flowchart which shows the procedure of the refractive index measuring method which concerns on this invention. The schematic block diagram of one Example of the refractive index measuring apparatus for enforcing the refractive index measuring method which concerns on this invention. The schematic block diagram of the other Example of the refractive index measuring apparatus for enforcing the refractive index measuring method which concerns on this invention. The figure which shows the parameter which determines the structure of the waveguide mode resonance grating assumed for simulation. The figure which shows the reflection spectrum in case the refractive index of a sample is 1.5 and 1.5 +/- 0.01 with respect to TE polarized light whose wavelength is 486.1 [nm]. The figure which shows the reflection spectrum in case the refractive index of a sample is 1.5 and 1.5 +/- 0.01 with respect to TE polarized light whose wavelength is 587.6 [nm]. The figure which shows the reflection spectrum in case the refractive index of a sample is 1.5 and 1.5 +/- 0.01 with respect to TE polarized light whose wavelength is 656.3 [nm]. The figure which shows the deviation from the resonant incident angle in the refractive index of 1.5 vicinity. The figure which summarized the result of FIGS. 8-10.

Explanation of symbols

1, 1A, 1B, 1C ... guide mode resonance grating 2 ... substrate 3 ... waveguide layer 4, 6 ... lattice layer 4a ... lattice 5 ... media layer 6a ... first grating 6b ... second grating Sr ... reference solution S, Ss ... sample 100 ... partition wall 10 ... light source 11 ... measurement light 12 ... reflected light 13 ... detector 14 ... optical system drive unit 15 ... control unit 17 ... moving unit 20 ... data processing unit 21 ... angle spectrum calculation unit 22 ... peak extraction Unit 23 ... calibration curve creation unit 24 ... calibration curve storage unit 25 ... refractive index calculation unit 26 ... output unit

Claims (12)

A waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate, and a multilayer structure or a single layer of the waveguide mode resonance grating A light irradiating means for irradiating light to the substrate surface or the surface of the object to be measured of the waveguide mode resonance grating in a state where the object to be measured is in contact with the surface opposite to the substrate across the structure; A spectrum measuring means for receiving the reflected light with respect to the light irradiation and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed, and measuring the spectrum. A refractive index measurement method using a refractive index measuring device that calculates a refractive index of an object to be measured based on a resonance incident angle or a resonance wavelength according to a measurement result of a means,
a) a reference liquid measurement step for measuring a resonance incident angle or a resonance wavelength for each of the plurality of reference liquids having different known refractive indexes, and measuring a resonance incident angle or a resonance wavelength for each refractive index;
b) a calibration curve creating step for creating a calibration curve based on the discrete relationship between the refractive index obtained in the reference liquid measurement step and the resonance incident angle or resonance wavelength;
c) measuring a resonance incident angle or a resonance wavelength with an unknown sample as an object to be measured, referring to the calibration curve, and obtaining a refractive index of the unknown sample from the measurement result; and
A refractive index measurement method using a guided mode resonance grating. A waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate, and a multilayer structure or a single layer of the waveguide mode resonance grating A light irradiating means for irradiating light to the substrate surface or the surface of the object to be measured of the waveguide mode resonance grating in a state where the object to be measured is in contact with the surface opposite to the substrate across the structure; A spectrum measuring means for receiving the reflected light with respect to the light irradiation and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed, and measuring the spectrum. A refractive index measurement method using a refractive index measuring device that calculates a refractive index of an object to be measured based on a resonance incident angle or a resonance wavelength according to a measurement result of a means,
a) measuring a resonance incident angle or a resonance wavelength using a reference liquid having a known refractive index as an object to be measured, and determining a resonance incident angle or a resonance wavelength for at least one refractive index;
b) A dispersion curve curve showing the relationship between the refractive index calculated based on the theoretical value of the design of the waveguide mode resonance grating and the resonance incident angle or the resonance wavelength is a refractive index obtained in the reference liquid measurement step. And a calibration curve acquisition step of acquiring a calibration curve by correcting based on the relationship between the resonance incident angle or the resonance wavelength,
c) measuring a resonance incident angle or a resonance wavelength with an unknown sample as an object to be measured, referring to the calibration curve, and obtaining a refractive index of the unknown sample from the measurement result; and
A refractive index measurement method using a guided mode resonance grating.   3. The refractive index measuring method according to claim 1, wherein the measurement of the reference solution and the measurement of the unknown sample are performed in a time-sharing manner using the same guided mode resonance grating. Refractive index measurement method using a resonant grating.   3. The refractive index measurement method according to claim 1, wherein the measurement of the reference solution and the measurement of the unknown sample are simultaneously performed using different parts of the same guided mode resonance grating. A refractive index measurement method using a waveguide mode resonance grating.   5. The refractive index measuring method according to claim 1, wherein the reference liquid is a commercially available refractive liquid with a controlled refractive index. Rate measurement method.   The refractive index measurement method according to any one of claims 1 to 5, wherein each temperature is measured simultaneously when measuring the reference liquid and the unknown sample, and based on the difference in temperature and the temperature characteristics of the reference liquid, A method for measuring a refractive index using a guided mode resonance grating, wherein the refractive index of an unknown sample is corrected. a) a waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate;
b) The substrate surface of the waveguide mode resonance grating or the measurement object in a state where the object to be measured is in contact with the surface opposite to the substrate across the multilayer structure or single layer structure of the waveguide mode resonance grating A light irradiation means for irradiating the object with light;
c) Resonance that gives a resonance peak by receiving reflected light from the light irradiation means and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed. Spectrum measuring means for determining an incident angle or a resonance wavelength;
d) Using a plurality of reference solutions having different known refractive indexes as objects to be measured, a calibration curve is obtained based on the discrete relationship between the resonance incident angle or the resonance wavelength and the refractive index respectively measured by the spectrum measuring means. A calibration curve creation means to create,
e) an arithmetic processing means for obtaining a refractive index of the unknown sample with reference to the calibration curve from a resonance incident angle or a resonance wavelength measured by the spectrum measuring means with the unknown sample as an object to be measured;
A refractive index measuring apparatus using a guided mode resonance grating. a) a waveguide mode resonance grating in which a multilayer structure of a grating layer and a waveguide layer or a single layer structure having both functions is formed on a substrate;
b) The substrate surface of the waveguide mode resonance grating or the measurement object in a state where the object to be measured is in contact with the surface opposite to the substrate across the multilayer structure or single layer structure of the waveguide mode resonance grating A light irradiation means for irradiating the object with light;
c) Resonance that gives a resonance peak by receiving reflected light from the light irradiation means and measuring the angle spectrum when the incident angle of the irradiation light is changed or the wavelength spectrum when the wavelength of the irradiation light is changed. Spectrum measuring means for determining an incident angle or a resonance wavelength;
d) Using a reference liquid having a known refractive index as an object to be measured, the waveguide mode resonant grating is designed based on the relationship between the resonant incident angle or resonant wavelength and refractive index measured by the spectral measuring means. A calibration curve acquisition means for acquiring a calibration curve by correcting a dispersion curve curve indicating a relationship between a refractive index calculated based on a theoretical value and a resonance incident angle or a resonance wavelength;
e) an arithmetic processing means for obtaining a refractive index of the unknown sample with reference to the calibration curve from a resonance incident angle or a resonance wavelength measured by the spectrum measuring means with the unknown sample as an object to be measured;
A refractive index measuring apparatus using a guided mode resonance grating.   9. The refractive index measurement apparatus according to claim 7, wherein the reference liquid measurement and the unknown sample measurement are performed in a time-sharing manner using the same waveguide mode resonance grating. A refractive index measuring device using a resonant grating.   9. The refractive index measurement method according to claim 7, wherein the measurement of the reference liquid and the measurement of the unknown sample are simultaneously performed using different parts of the same waveguide mode resonance grating. A refractive index measurement device using a waveguide mode resonance grating.   The refractive index measuring apparatus according to claim 7, wherein the reference liquid is a commercially available refractive liquid with a controlled refractive index. Rate measuring device.   The refractive index measuring apparatus according to any one of claims 7 to 11, further comprising temperature detecting means for measuring respective temperatures simultaneously when measuring the reference liquid and the unknown sample, wherein the temperature difference and the temperature of the reference liquid are measured. A refractive index measuring apparatus using a waveguide mode resonance grating, wherein the refractive index of an unknown sample is corrected based on the characteristics.

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