JP6501296B2 - Refractive index measuring device - Google Patents

Description

  The present invention relates to a refractive index measurement apparatus.

  The measurement of refractive index is expected to be applied in various fields such as agriculture, chemistry, biology and medicine. As a technique of measuring a refractive index, the measuring apparatus and measuring method of the refractive index which utilized waveguide mode resonance and surface plasmon resonance in patent documents 1-3 are described.

  Patent Document 1 describes a refractometer that easily and accurately determines the refractive index of a sample. When measuring the refractive index using this refractometer, the measurement light is introduced to the end face of the waveguide layer of the waveguide mode resonance filter, and the emitted light diffracted by the grating of the waveguide mode resonance filter at this time is Detected by a detector. The emission angle of the measurement light is scanned within a predetermined angle range by moving the position of the detector, and the resonance emission angle corresponding to the refractive index is obtained.

  Patent Document 2 describes a surface plasmon resonance sensor chip that has a diffraction grating and is suitable for miniaturization. The diffraction grating is formed on an elastically deformable elastic film. When the refractive index is measured using this chip, light is incident on the diffraction grating in a state where the sample is disposed in the vicinity of the diffraction grating surface. In the conventional surface plasmon resonance sensor chip, the incident angle of incident light is scanned to measure the intensity of diffracted light, but in this chip, the elastic film is bulged instead of scanning the incident angle of incident light. By dynamically changing the grating pitch of the diffraction grating surface, the resonant pitch corresponding to the refractive index is determined.

  Patent Document 3 describes a surface plasmon resonance sensor. This sensor has a waveguide core layer for receiving light for measurement, a metal thin film, a dielectric film, and a sample layer for providing a sample for measurement formed on the dielectric film. . When measuring the refractive index using this sensor, a sample is provided in the sample layer, light is incident on the waveguide core layer, and the wavelength spectrum or incident angle spectrum of the light transmitted through the waveguide core layer is measured. .

Unexamined-Japanese-Patent No. 2010-210384 JP, 2009-168469, A JP, 2004-170095, A

  In the refractive index measurement devices described in Patent Documents 1 to 3, the resonance angle giving resonance peak, the resonance wavelength or the resonance pitch is measured based on the intensity of light emitted from the resonance filter, and the refractive index is determined from the measurement result Is calculated. However, according to these methods, in order to detect the intensity of light emitted from the resonance filter, a photodetector separate from the resonance filter is required, and the apparatus configuration becomes complicated. Moreover, since the photodetector is a separate body, the utilization efficiency of the reflected light emitted from the resonance filter is lowered, and the detection accuracy of the light intensity is deteriorated, so that the measurement accuracy of the refractive index tends to be deteriorated. . Moreover, in these refractive index measuring devices, it is difficult to maintain the measurement accuracy against the intensity fluctuation of the measuring light.

  Therefore, an object of the present invention is to provide a refractive index measurement device that can simplify the device configuration and improve the measurement accuracy of the refractive index.

  In the refractive index measurement device according to the present invention, a first semiconductor light receiving element portion that outputs a signal corresponding to incident light, and a linear groove disposed on the light incident side on the first semiconductor light receiving element portion A first diffraction grating portion formed with a plurality of predetermined pitches, a second semiconductor light receiving element portion that outputs a signal corresponding to light, and a straight line disposed on the light incident side on the second semiconductor light receiving element portion A second diffraction grating portion in which a plurality of grooves are formed at a pitch different from a predetermined pitch, and a light source for emitting light of a predetermined wavelength toward the first and second diffraction grating portions A logarithmic conversion circuit for logarithmically converting and outputting the respective intensities of the signal output from the first semiconductor light receiving element unit and the signal output from the second semiconductor light receiving element unit; Differential amplification circuit that amplifies the difference between the respective intensities , The refractive index measuring device comprising a.

  According to this refractive index measurement apparatus, the first semiconductor light receiving element portion provided on the light incident side with the first diffraction grating portion in which the linear groove portions are formed at the predetermined pitch, and the linear diffraction portion is the first diffraction Light from the light source can be made incident on a second semiconductor light receiving element portion provided on the light incident side with a second diffraction grating portion formed at a pitch different from that of the grating portion. After the intensities of the two signals output from the first and second semiconductor light receiving element sections are logarithmically converted by the logarithmic conversion circuit in response to the incidence of light, the differences between them are amplified by the differential amplifier circuit. Output. By using this output, even when the intensity of the output light of the light source fluctuates or the intensity of the output light of the light source is weak, it is possible to accurately measure the refractive index of the substance disposed on the photodiode. Further, since the refractive index can be measured without using a separate photodetector, the apparatus configuration can be simplified. Furthermore, the detection efficiency of the light intensity is further improved by improving the utilization efficiency of the light incident on the photodiode. As a result, the apparatus configuration can be simplified and the measurement accuracy of the refractive index can be improved.

  Here, the light source may modulate and emit light at a predetermined frequency, and lock-in detection of each intensity output from the logarithmic conversion circuit may be performed at the predetermined frequency. In this case, the detection accuracy of the refractive index can be further enhanced by reducing the influence of a direct current component such as dark current and noise in a wide frequency band such as shot noise included in the output of the photodiode.

  Further, the first diffraction grating portion and the second diffraction grating portion are configured such that the formation directions of the grooves are parallel to each other, and the light source is a formation direction of the grooves of the first diffraction grating portion, and The light may be emitted from a direction inclined with respect to the direction perpendicular to the surfaces of the first and second semiconductor light receiving element portions in a plane perpendicular to the direction in which the grooves of the diffraction grating portion are formed. In this case, the rate of change in the difference between the output of the first semiconductor light receiving element and the output of the second semiconductor light receiving element with respect to the change in the refractive index of the substance disposed on the photodiode becomes high. Detection accuracy can be further enhanced.

  According to the present invention, the apparatus configuration can be simplified and the measurement accuracy of the refractive index can be improved.

It is a perspective view showing the refractive index measuring device concerning one preferred embodiment of the present invention. It is principal part sectional drawing of the photodiode of FIG. It is a figure which shows the relationship of the phase matching conditions of measurement light and a waveguide mode. It is a graph which shows the relationship between a refractive index, a peak wavelength, and a peak value. It is a graph which shows the relationship between the wavelength of the measurement light in the photodiode of FIG. 2, and the magnitude | size of the photoelectric current which each of two semiconductor light receiving element parts produces | generates. It is a graph which shows the relationship between the refractive index difference and the photocurrent difference in the photodiode of FIG. It is a block diagram which shows the structure of the refractive index calculation process part of FIG. It is a circuit diagram which shows the detailed structure of the logarithmic transformation circuit unit of FIG. It is a graph which shows the relationship between the output of the semiconductor light receiving element part of FIG. 2, and the output of the logarithmic conversion circuit part of FIG. It is a graph which shows the relationship between the refractive index difference regarding the refractive index of the to-be-measured object M, and the output equivalent value of the differential amplifier circuit of FIG. It is a block diagram which shows the structure of the refractive index calculation process part which concerns on the modification of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

  FIG. 1 is a perspective view showing a refractive index measurement apparatus according to a preferred embodiment of the present invention, and FIG. 2 is a cross-sectional view of an essential part of a photodiode used in the refractive index measurement apparatus. The refractive index measuring apparatus 1 according to the present embodiment is an apparatus for detecting the refractive index n of the object to be measured M by irradiating the object to be measured M with the measuring light (light) L as shown in FIG. . The refractive index measuring apparatus 1 includes a photodiode 3 that outputs an electric signal according to the refractive index n and the like of the disposed object M by irradiation of the measuring light L, and a light source device (light source) that emits the measuring light L 2 and. Furthermore, the refractive index measurement device 1 includes a refractive index calculation processing unit 5 that processes and detects an electric signal output from the photodiode 3.

  The light source device 2 emits measurement light L of a specific wavelength included in a predetermined band. Further, the light source device 2 can adjust the incident angle of the measurement light L to the photodiode 3, and the light source device 2 of this embodiment directs the measurement light L to the diffraction grating portions 6 A and 6 B on the photodiode 3. In order to make the light incident obliquely, in detail, the light is incident from a direction perpendicular to the direction perpendicular to the surface of the photodiode 3 in a plane perpendicular to the formation direction of the grooves of the diffraction grating portions 6A and 6B described later. Is located in

  The photodiode 3 includes two semiconductor light receiving element units 3A and 3B that respectively generate two electric signals corresponding to the light intensity of the measurement light L, and two diffractions provided on the respective semiconductor light receiving element units 3A and 3B. The grids 6A and 6B are provided. In the following description, the lamination direction of each layer constituting the photodiode 3 is taken as the Z-axis direction, and the arrangement direction of the plurality of linear groove portions 6Aa and 6Ba formed in each of the diffraction grating portions 6A and 6B described later. Is the Y-axis direction, and the forming direction of the grooves 6Aa and 6Ba is the X-axis direction, and the respective axes are orthogonal to each other.

  The photodiode 3 includes a silicon substrate (substrate) 7, a buried insulating layer 8 disposed on the silicon substrate 7, and two semiconductor light receiving element portions 3A disposed on the buried insulating layer 8 in the Y-axis direction. , And 3B. The semiconductor light receiving element portion 3A includes the semiconductor layers 9, 11A and 12 formed side by side in the X direction, and the gate insulating layer 13A disposed on the semiconductor layers 9, 11A and 12, and the semiconductor light receiving element portion 3B is composed of semiconductor layers 9, 11B and 12 formed side by side in the X direction, and a gate insulating layer 13B disposed on the semiconductor layers 9, 11B and 12. These semiconductor light receiving element portions 3A and 3B, together with the silicon substrate 7 and the buried insulating layer 8, constitute a so-called lateral pn junction diode of a MOS structure. The buried insulating layer 8 is made of silicon oxide, the semiconductor layers 9, 11A, 11B, 12 are made of silicon containing a predetermined impurity, and the gate insulating layers 13A, 13B are made of silicon oxide. Therefore, the photodiode 3 has an SOI (Silicon On Insulator) structure in which the silicon substrate 7 is used as a substrate (support).

The semiconductor layers 9, 11A and 12 of the semiconductor light receiving element portion 3A are provided adjacent to each other in this order along the X-axis direction in a rectangular predetermined region on the buried insulating layer 8. In the semiconductor layer 11A functioning as an optical waveguide and a light absorption layer, most of the depth direction (Z-axis direction) is depleted and a low concentration of silicon is doped with a p-type impurity such as boron or phosphorus or an n-type impurity. It is done. The semiconductor layers 9 and 12 serving as the anode electrode and the cathode electrode are each p ⁺ -type in substantially the same thickness as the semiconductor layer 11A so as to sandwich the semiconductor layer 11A on the embedded insulating layer 8 from the direction along the X axis. The semiconductor layer and the n ⁺ -type semiconductor layer are formed. The p ⁺ -type semiconductor layer 9 and the n ⁺ -type semiconductor layer 12 are each doped with a p-type impurity such as boron and an n-type impurity such as phosphorus at a high concentration (10 ¹⁹ cm ⁻³ or more) with respect to silicon. By being arranged in parallel to the semiconductor layer 11A, it functions as an anode electrode and a cathode electrode. A gate insulating layer 13A is formed on the semiconductor layers 9, 11A, 12 so as to cover the semiconductor layers 9, 11A, 12. The semiconductor light receiving element portion 3B also has the same configuration.

  When the measurement light L is simultaneously detected by such semiconductor light receiving element units 3A and 3B, the gate voltage Vg is applied to the diffraction grating sections 6A and 6B, and the substrate voltage Vsub is applied to the silicon substrate 7. By adjusting the gate voltage Vg and the substrate voltage Vsub, the density of electrons or holes at the upper and lower interfaces of the semiconductor layers 11A and 11B can be controlled in a wide range. In particular, the gate voltage Vg and the substrate voltage Vsub are such that the electron or hole density at the interface of the semiconductor layers 11A and 11B in contact with the gate insulating layers 13A and 13B and the interface of the semiconductor layers 11A and 11B in contact with the buried insulating layer 8 is semiconductor It is preferable to set so as to be sufficiently larger than the intrinsic carrier density of each of the layers 11A and 11B. The gate voltage Vg may be commonly applied to the diffraction grating portions 6A and 6B, or may be independently applied to the diffraction grating portions 6A and 6B so that the respective voltages can be adjusted independently.

  A diffraction grating portion 6A is disposed in a region covering at least the semiconductor layer 11A on the gate insulating layer 13A on the light incident side of the light source device 2. Therefore, the diffraction grating portion 6A covers the semiconductor layer 11A via the gate insulating layer 13A, and is electrically insulated from the semiconductor layers 9, 11A, and 12. The diffraction grating portion 6A is formed of a plurality of linear grooves 6Aa penetrating the metal film, which is a planar conductive member, along the X-axis direction to the surface of the gate insulating layer 13A over the region covering the semiconductor layer 11A. 2) is formed. The plurality of grooves 6Aa are juxtaposed in the Y-axis direction at a constant lattice pitch (period) P1. As a material of such a diffraction grating portion 6A, for example, a conductive metal such as gold (Au), silver (Ag), aluminum (Al) or the like formed on the adhesion strengthening layer of titanium (Ti), or A conductive material such as polycrystalline silicon (poly-Si) to which an n-type or p-type impurity is added at a high concentration is used. The diffraction grating portion 6A has a role of guiding the measurement light L having a predetermined wavelength to the semiconductor layer 11A, a role as a gate electrode, and a role as a placement portion for placing the object to be measured M.

  A diffraction grating portion 6B is disposed in a region covering at least the semiconductor layer 11B on the gate insulating layer 13B on the light incident side of the light source device 2. The diffraction grating portion 6B covers the semiconductor layer 11B via the gate insulating layer 13B, and is electrically insulated from the semiconductor layers 9, 11B and 12. Diffraction grating portion 6B has the same structure as that of diffraction grating portion 6A, and is formed such that the formation direction of groove portion 6Ba of diffraction grating portion 6B is parallel to the formation direction of groove portion 6Aa of diffraction grating portion 6A, The grating pitch P2 in the Y-axis direction of the plurality of groove portions 6Ba is set to be smaller than the grating pitch P1 of the diffraction grating portion 6A (FIG. 2). The diffraction grating portion 6B has a role of guiding the measurement light L having a predetermined wavelength to the semiconductor layer 11B, a role as a gate electrode, and a role as a placement portion for placing the object to be measured M.

  In the photodiode 3, when the measurement light L is simultaneously irradiated to the diffraction grating portions 6A and 6B, the measurement light L having a specific wavelength that satisfies the phase matching condition with the waveguide mode of the semiconductor layers 11A and 11B is most efficient. It is captured by the semiconductor layers 11A and 11B. The measurement light L captured by the semiconductor layers 11A and 11B is absorbed in the semiconductor layers 11A and 11B to generate electron-hole pairs. Then, a photocurrent corresponding to the amount of electrons and holes generated and separated flows from the cathode to the anode in each of the semiconductor light receiving element portions 3A and 3B, so that the semiconductor layers 12 of the respective semiconductor light receiving element portions 3A and 3B. An electrical signal is taken out from.

Propagation wavelength lambda _g of the waveguide mode in the semiconductor layer 11A is represented by the formula (1). Here, λ is the wavelength of the measurement light L, n _s is the refractive index of the semiconductor layer 11A, t _s is the thickness of the semiconductor layer 11A, and n _i is that of the buried insulating layer 8 and the gate insulating layer 13A. It is a refractive index. The TE mode is a mode in which the electric field direction of light propagating in the waveguide (that is, the semiconductor layer 11A) is perpendicular to the propagation direction and in the plane of the waveguide, and similarly to the TM mode, the magnetic field direction is perpendicular to the propagation direction The modes are in the waveguide plane, and equation (1) is different corresponding to each mode.

The phase matching condition will be described. FIG. 3 is a diagram showing the relationship of the phase matching condition between the measurement light and the waveguide mode. As shown in FIG. 3A, when the measurement light L obliquely enters the diffraction grating portion 6A at the incident angle α, an optical path length (per one pitch P (= P1) in the diffraction grating portion 6A ((A)) A phase difference Δ (= P (2πn / λ) sin α) occurs due to P × sin α), the refractive index n, and the wavelength λ. The phase matching condition is a value obtained by adding or subtracting a value (Δ / k _g ) obtained by dividing the phase difference Δ by the wavenumber k _g (= 2π / λ _g ) with respect to the propagation wavelength λ _g of the semiconductor layer 11A (= λ _g ± Δ / k _g ) is shown as being equal to the grating pitch P. FIG. 3B shows the case of addition, and the forward wave propagates to the semiconductor layer 11A. In the case of subtraction, a backward wave propagates. Therefore, Formula (2-1) and Formula (2-2) are obtained. Here, λ is the wavelength of the measurement light L, n is the refractive index of the device under test M, P is the grating pitch, and α is the incident angle of the measurement light L. Further, λ _gf is a propagation wavelength of the forward wave in the semiconductor layer 11A, and λ _gb is a propagation wavelength of the backward wave in the semiconductor layer 11A. The case where the phase matching condition is satisfied is a case where the equations (2-1) and (2-2) are satisfied. According to the equations (2-1) and (2-2), when the phase matching condition is satisfied, the value defined by the grating pitch P, the refractive index n, the wavelength λ of the measurement light L, and the incident angle α is It can also be said that the cases coincide with the propagation wavelengths λ _gf and λ _{gb of the} waveguide mode.

  According to the equations (2-1) and (2-2), the incident angle α of the measurement light L is other than 0 degree, in other words, in a state where the measurement light L is obliquely irradiated to the diffraction grating portion 6A, It can be seen that when the change of the refractive index n occurs, the shift of the wavelength λ of the measurement light L is necessary to satisfy the phase matching condition. Similarly, the phase matching condition in the semiconductor layer 11B is also expressed by the same equation.

The spectral characteristics of the photocurrent will be described. FIG. 4 is a graph showing the relationship between the refractive index and the peak wavelength and peak value. As shown in FIG. 4, the spectral characteristic of the photocurrent is a relationship between the wavelength λ of the measurement light L and the magnitude of the electrical signal output from the photodiode 3 when the measurement light L is irradiated, and the wavelength It shows the magnitude of the electrical signal for each λ. In FIG. 4, the horizontal axis is the wavelength λ of the measurement light L, and the vertical axis is the photocurrent indicating the magnitude of the electrical signal. When the value on the right side of Equations (2-1) and (2-2) approaches the propagation wavelengths λ _gf and λ _gb on the left side, the value of the electrical signal increases and the value on the right side matches the value on the left side. The electrical signal has a maximum value (peak) (when the phase matching condition is satisfied).

  The shift of the peak wavelength λp with the change of the refractive index n will be further described. FIG. 4A shows the spectral characteristics of the photocurrent when the incident angle α of the measurement light L with respect to the diffraction grating 6A in the YZ plane is 10 degrees. FIG. 4B shows the spectral characteristics of the photocurrent when the incident angle α of the measurement light L to the diffraction grating portion 6A is 20 degrees. Furthermore, the graph G1 of FIG. 4A and the graph G3 of FIG. 4B show the spectral characteristics of the photocurrent when the refractive index of the device under test M is n = 1. The graph G1 has two peaks pk1 and pk2, and the graph G3 has peaks pk5 and pk6. Of the two peaks, long wavelength peaks (i.e., pk1, pk3) correspond to backward waves, and short wavelength peaks (i.e., pk2, pk4) correspond to forward waves. Graph G2 of FIG. 4A and graph G4 of FIG. 4B show the spectral characteristics of the photocurrent when the refractive index of the device under test M is n = 1.4933. The graph G2 has two peaks pk3 and pk4, and the graph G4 has peaks pk7 and pk8. Similarly, long wavelength peaks (i.e., pk5, pk7) correspond to backward waves, and short wavelength peaks (i.e., pk6, pk8) correspond to forward waves.

  Here, when the peaks pk1 and pk3 of the reverse wave in FIG. 4A are compared, the peak pk3 of the graph G2 (n = 1.4933) has a peak wavelength with respect to the peak pk1 of the graph G1 (n = 1). It can be seen that λp is shifted to the long wavelength side. In addition, with regard to the peak of the forward wave, the peak wavelength λp of the peak pk4 of the graph G2 (n = 1.4933) is shifted to the short wavelength side with respect to the peak pk2 of the graph G1 (n = 1). I understand. Further, comparing the peaks pk1 and pk3 in FIG. 4A, the peak pk3 of the graph G2 (n = 1.4933) decreases with respect to the peak pk1 of the graph G1 (n = 1). I understand that Further, it can be seen that the peak value of the peak pk4 of the graph G2 (n = 1.4933) also decreases with respect to the peak pk2 of the graph G1 (n = 1).

  Thus, it can be seen that there is a predetermined relationship between the shift amount of the peak wavelength λp and the refractive index n, and there is also a predetermined relationship between the decrease amount of the peak value and the refractive index n. Therefore, in the refractive index measurement device 1 of the present embodiment, the refractive index n is detected using the property that the peak wavelength λp shifts according to the change of the refractive index n. This detection mechanism is further described with reference to FIGS. 5 and 6.

FIG. 5 is a graph showing the relationship between the wavelength of the measurement light L in the photodiode 3 and the magnitudes of the photocurrents I ₁ and I ₂ generated by the semiconductor light receiving element portions 3A and 3B. During the drawing, the solid line characteristics of each photocurrent I _1, I ₂ represents the characteristic when the object to be measured M with a certain reference refractive index n ₀ is positioned, of the optical current I _1, I ₂ The characteristic of the dotted line shows the characteristic when the device under test M having a refractive index n different from the reference refractive index n ₀ is disposed. In the refractive index measurement device 1 of the present embodiment, as shown by the characteristics of the solid line, the measurement is performed with the reference refractive index n ₀ with respect to the wavelength λ _L of the measurement light L emitted from the light source device 2 at the incident angle α. The grating pitch P1 of the diffraction grating portion 6A and the grating pitch P2 of the diffraction grating portion 6B are designed so that the values of the photocurrents I ₁ and I ₂ when the object M is disposed become equal to each other. On the other hand, as shown by the characteristic of the dotted line, in the refractive index measuring device 1, an object under test having a refractive index n with respect to the wavelength λ _L of the measuring light L emitted from the light source device 2 at the incident angle α. When M is disposed, the difference between the _two photocurrents I ₁ and I ₂ occurs with a magnitude corresponding to the amount of change of the refractive index n from n ₀ . Using this property, the refractive index measurement device 1 detects the refractive index n of the object M based on the difference between the _two photocurrents I ₁ and I ₂ .

FIG. 6 is a graph showing the relationship between the difference between the refractive index n of the object to be measured M and the reference refractive index n ₀ in the photodiode 3 and the difference between the two photocurrents I ₁ and I ₂ . In the figure, the characteristic G5 shows the relationship between the refractive index difference n-n ₀ and the photocurrent difference I ₁ -I ₂ with respect to the measurement light L of the predetermined luminous intensity in the refractive index measurement device 1, and the characteristic G6 is the measurement The relationship between the refractive index difference n−n ₀ and the photocurrent difference I ₁ −I ₂ when the light emission intensity of the light L is reduced to 50% is shown, and the characteristic G 7 sets the light emission intensity of the measurement light L to 10%. The relationship between the refractive index difference n−n ₀ and the photocurrent difference I ₁ −I ₂ when decreasing is shown. As shown by these characteristics G5, G6 and G7, the photocurrent difference I ₁ -I ₂ changes almost linearly with the refractive index difference n-n ₀ in each characteristic. As the emission intensity decreases, the rate of change (slope) of the photocurrent difference I ₁ -I ₂ with respect to the refractive index difference n-n ₀ decreases. Therefore, it is assumed that when the light emission intensity of the light source device 2 becomes weak, the detection sensitivity of the refractive index n decreases.

  The refractive index measurement apparatus 1 includes a refractive index calculation processing unit 5 having the following configuration in order to prevent such a decrease in detection sensitivity of the refractive index. That is, as shown in FIG. 7, the refractive index calculation processing unit 5 is a logarithmic conversion circuit unit 21 configured by logarithmic conversion circuits 21A and 21B connected to the outputs of the semiconductor light receiving element units 3A and 3B of the photodiode 3, respectively. And a differential amplifier circuit 22 for differentially amplifying the outputs of the logarithmic conversion circuits 21A and 21B. The refractive index calculation processing unit 5 is manufactured on-chip on the same SOI substrate as the photodiode 3.

  The logarithmic conversion circuit unit 21 is a circuit unit that logarithmically converts the electric signal output from each of the semiconductor light receiving element units 3A and 3B. FIG. 8 is a circuit diagram showing the detailed configuration of the logarithmic conversion circuit unit 21. FIG. 9 is a graph showing the relationship between the outputs of the semiconductor light receiving element units 3A and 3B and the output of the logarithmic conversion circuit unit 21.

Logarithmic converter 21A of the logarithmic converter circuit 21, a first MOSFET (field effect _{transistor) M 11,} and the 2MOSFETM _12, is configured to include a resistance element _{R L1.} In the logarithmic conversion circuit 21A, the cathode which is the output of the semiconductor light-receiving element portion 3A is connected to a source (current terminals) of the 1MOSFETM _11, the source of the 1MOSFETM ₁₁ is further connected to the gate (control terminal) of the 2MOSFETM ₁₂ with the drain is connected (current terminals) and a gate to the power supply bias voltage of the 1MOSFETM ₁₁ it is applied. Further, the logarithmic transformation circuit 21A, the source of the 2MOSFETM ₁₂ is connected to ground through a resistor _{R L1} is connected to the inverting input terminal of the differential amplifier circuit 22, the drain of the 2MOSFETM ₁₂ is connected to a power supply Bias voltage is applied. Logarithmic converter having the above structure 21A is the intensity of the light current I ₁ of an electric signal output from the semiconductor light-receiving device section 3A is a circuit for outputting the logarithmic conversion.

Similarly, the logarithmic conversion circuit 21B of the logarithmic converter 21, a first MOSFET (field effect _{transistor) M 21,} and the 2MOSFETM _22, is configured to include a resistance element _{R L2,} similar to the logarithmic conversion circuit 21A configured The input terminal is connected to the output of the semiconductor light receiving element 3 B, and the output terminal is connected to the non-inverted input terminal of the differential amplifier circuit 22. The logarithmic converter 21B is a circuit for intensity logarithmically converts the output of the photocurrent I ₂ of the electric signal output from the semiconductor light-receiving element portion 3B.

Figure 9 is a graph showing the relationship between the logarithmic conversion circuit 21A, the light current _I 1 is input to 21B, _{I 2} logarithm and the logarithm conversion circuit 21A, 21B output voltage _{V O1, V O2.} As described above, according to the logarithmic conversion circuits 21A and 21B, in the predetermined range W of the logarithmic values logI ₁ and logI ₂ of the photocurrents I ₁ and I ₂ , the respective pairs of output voltages V _O1 and V _O2 are used. A voltage value proportional to the numerical values logI ₁ and logI ₂ is obtained.

The differential amplifier circuit 22 amplifies and outputs the difference between the intensity of the output voltage V _O1 of the logarithmic conversion circuit 21A and the intensity of the output voltage V _O2 of the logarithmic conversion circuit 21B. FIG. 10 is a graph showing the relationship between the refractive index difference n−n ₀ relating to the refractive index n of the device under test M and the output equivalent value {log I ₁ −log I ₂ } of the differential amplifier circuit 22. Thus, the output of the differential amplifier circuit 22 has a characteristic that linearly changes with respect to the refractive index difference n−n ₀ , and this characteristic is the same as the case of simply detecting the photocurrent difference I ₁ −I ₂ It becomes the characteristic of On the other hand, since the output of the differential amplifier circuit 22 substantially represents the ratio I ₁ / I ₂ of the photocurrent logarithmically converted, it does not depend on the intensity of the light source device 2, and the intensity decreases Even in the case where the sensitivity (inclination) to the refractive index is constant, it has a property different from the case of detecting the photocurrent difference I ₁ -I ₂ .

  According to the refractive index measurement device 1 described above, the semiconductor light receiving element portion 3A provided on the light incident side with the diffraction grating portion 6A in which the linear groove portions 6Aa are formed at the predetermined pitch P1, and the linear groove portion 6Ba is a diffraction grating Light can be made incident from the light source device 2 to the semiconductor light receiving element portion 3B provided on the light incident side with the diffraction grating portion 6B formed at a pitch different from that of the portion 6A. After the intensities of the two signals output from the semiconductor light receiving element sections 3A and 3B are logarithmically converted by the logarithmic conversion circuits 21A and 21B in response to the incidence of light, the differences between them are amplified by the differential amplifier circuit 22. Output. By using this output, even if the output intensity of the light source device 2 fluctuates or the output intensity of the light source device 2 is weak, the refractive index of the object to be measured M disposed on the photodiode 3 can be accurately measured. Can. That is, it is possible to reduce the detection error of the refractive index due to the fluctuation of the output intensity of the light source and the detection error due to the decrease of the SN ratio in the detection signal.

  Further, since the refractive index can be measured without using a separate photodetector, the apparatus configuration can be simplified. Moreover, by improving the utilization efficiency of the light incident on the photodiode 3, the detection accuracy of the light intensity is further improved. As a result, the apparatus configuration can be simplified and the measurement accuracy of the refractive index can be improved. For example, by applying the refractive index measurement device 1, it is possible to realize an optical biosensor chip that can be realized with a simple optical system, including a large number of arrayed sensors. This enables highly sensitive and high-throughput biomedical testing by a simple method that does not use a fluorescent label.

  The diffraction grating portion 6A and the diffraction grating portion 6B are configured such that the forming directions of the groove portions 6Aa and 6Ba are parallel to each other, and the light source device 2 includes the forming direction of the groove portion 6Aa of the diffraction grating portion 6A and the diffraction grating The light is emitted from a direction inclined with respect to the direction perpendicular to the surfaces of the semiconductor light receiving element portions 3A and 3B in a plane perpendicular to the forming direction of the groove portion 6Ba of the portion 6B. With such a configuration, the rate of change in the difference between the output of the semiconductor light receiving element 3A and the output of the semiconductor light receiving element 3B with respect to the change in the refractive index of the measurement object M disposed on the photodiode 3 becomes high. The detection accuracy of the refractive index can be further enhanced.

  The refractive index measurement device according to the present invention is not limited to the above embodiment. For example, in the above embodiment, the refractive index calculation processing unit 105 having a configuration as shown in FIG. 11 may be employed. The difference from the refractive index calculation processing unit 5 of the refractive index calculation processing unit 105 shown in the figure is the lock-in detection circuit 23A connected between the logarithmic conversion circuit 21A and the non-inverting input of the differential amplification circuit 22. , And a lock-in detection circuit 23B connected between the logarithmic conversion circuit 21B and the inverting input of the differential amplification circuit 22.

  In the modification shown in the figure, the light source device 2 is configured to emit light whose light emission intensity is modulated at a predetermined frequency f. Then, the lock-in detection circuit 23A receives the electric signal output from the logarithmic conversion circuit 21A, and performs lock-in detection of the intensity at the frequency f, thereby extracting only the component of the frequency f of the electric signal to perform differential operation. The signal is output to the amplifier circuit 22. Similarly, the lock-in detection circuit 23B extracts only the component of the frequency f of the electric signal by performing lock-in detection of the strength of the electric signal output from the logarithmic conversion circuit 21B at the frequency f, and the differential amplifier circuit 22 Output to

  With such a configuration, the detection accuracy of the refractive index can be further enhanced by reducing the influence of DC components such as dark current and noise in a wide frequency band such as shot noise included in the output of the photodiode 3. it can.

  DESCRIPTION OF SYMBOLS 1 ... refractive index measuring apparatus, 2 ... light source device, 3 ... photodiode, 3A, 3B ... semiconductor light receiving element part, 5, 105 ... refractive index calculation processing part, 6A, 6B ... diffraction grating part, 6Aa, 6Ba ... groove part, 21: Logarithmic conversion circuit unit, 21A, 21B: Logarithmic conversion circuit, 22: Differential amplifier circuit, 23A, 23B: Lock-in detection circuit, L: Measurement light, M: Measurement object.

Claims (3)

A first semiconductor light receiving element portion for outputting a signal corresponding to the incident light, and a plurality of linear grooves formed at a predetermined pitch, disposed on the light incident side of the first semiconductor light receiving element portion A first diffraction grating portion, a second semiconductor light receiving element portion for outputting a signal corresponding to the light, and a linear groove disposed on the incident side of the light on the second semiconductor light receiving element portion A photodiode having a plurality of second diffraction grating portions formed at a pitch different from the predetermined pitch;
A light source for emitting light of a predetermined wavelength toward the first and second diffraction grating portions;
A logarithmic conversion circuit that logarithmically converts the intensities of the signal output from the first semiconductor light receiving element unit and the signal output from the second semiconductor light receiving element unit;
A differential amplifier circuit for amplifying the difference between the intensities output from the logarithmic conversion circuit;
A refractive index measuring device comprising: The light source modulates and emits the light at a predetermined frequency,
The respective intensities output from the logarithmic converter, lock-in detection at the predetermined frequency,
The refractive index measurement device according to claim 1. The first diffraction grating portion and the second diffraction grating portion are configured such that the formation directions of the grooves are parallel to each other,
The light source is a surface of the first and second semiconductor light receiving element portions in a plane perpendicular to the formation direction of the grooves of the first diffraction grating portion and the formation direction of the grooves of the second diffraction grating portion. Emit the light from a direction inclined with respect to a direction perpendicular to the
The refractive index measurement device according to claim 1.