JP3700914B2 - Differential spectrum sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a differential spectrum sensor that simply detects a change in a spectral spectrum of an object to be measured, that is, a differential spectrum, using a variable wavelength interference filter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a device that analyzes a spectral spectrum of an object to be measured and extracts features, for example, a large and complicated device represented by remote sensing has been used.
[0003]
Further, in the spectral image analysis apparatus using the wavelength tunable interference filter, by changing the substrate interval of the wavelength tunable interference filter, the distribution of a plurality of transmission peak spectra is changed, and two images obtained by changing the distribution of the transmission peak spectra are obtained. A differential spectrum image is generated by calculating the difference between them and displayed in color (Japanese Patent Laid-Open No. 8-285688).
[0004]
That is, this spectral image analysis apparatus uses a color imaging means such as a CCD in which three light receiving cells each having R, G, and B filters corresponding to one pixel are arranged, and a variable wavelength interference filter and a photographing lens. R, G, B image data obtained by changing the substrate interval of the wavelength tunable interference filter in two stages for the object image formed by the system is stored in the memory, and the difference between the two images is calculated to obtain R, G and B differential spectrum images are generated and displayed in color. According to such an apparatus for generating a differential spectrum image, by analyzing the generated differential spectrum image, it is possible to determine where there is a characteristic spectrum change in the wavelength spectrum of the object. Furthermore, according to the color display of the differential spectrum image, it is possible to easily read which band of the spectrum has the characteristics.
[0005]
[Problems to be solved by the invention]
However, in the conventional spectral analysis in remote sensing or the like, the spectral image is analyzed after storing the color image or infrared image captured by the image sensor in the memory, and the image has redundant information amount. Spectral analysis software processing is complicated and takes time.
[0006]
In addition, even in a spectral image analyzer using a wavelength tunable interference filter, an image obtained by changing the distribution of different transmission peak spectra by switching the substrate interval of the wavelength tunable interference filter is stored in a memory, and then a difference in pixel units. Since the differential spectrum image is obtained by calculation, the processing load of software image analysis is large, and there is a problem that a high-performance and large-sized apparatus is required when performing image processing in real time.
[0007]
The present invention has been made in view of such conventional problems, and an object thereof is to provide a differential spectrum sensor in which differential spectrum information of an object to be measured can be directly obtained by the sensor itself.
[0008]
[Means for Solving the Problems]
In order to achieve this object, the differential spectrum sensor of the present invention changes spectral distance between a pair of optical substrates in which a reflective film is formed on the opposing surfaces arranged at a minute interval, thereby changing the spectral light of the characteristic portion in the spectral spectrum. a variable wavelength interference filter for transmitting only a driving voltage source to alternating current varying the pair of substrate gap of the tunable filter is disposed at the rear of the variable wavelength interference filter, AC of light transmitted through the wavelength-tunable interference filter And a pyroelectric element that directly outputs a received light signal corresponding to the amount of change , and the sensor itself outputs a detection signal indicating a characteristic point of the spectrum of the target object.
For this reason, the differential spectrum sensor of the present invention is capable of detecting characteristic information in the spectral spectrum and detecting differential information indicating a change in the amount of light in the characteristic spectrum, thereby reducing information that hinders spectral analysis. Remaining valuable information, the amount of information necessary for the spectral analysis of the sensor detection signal by the image processing apparatus or the like can be drastically reduced, and the processing load of the spectral analysis based on the sensor detection signal can be greatly reduced.
[0010]
In another embodiment of the present invention, in order to realize an image sensor for directly obtaining a differential spectrum image, a wavelength variable interference filter, a drive voltage source for alternatingly changing a pair of substrate intervals of the wavelength variable filter, An imaging lens that forms an image of the light beam from the target object that has passed through the tunable interference filter, and light reception that is arranged at the imaging position of the imaging lens and that corresponds to the AC variation of the light that has passed through the tunable interference filter A plurality of pyroelectric elements that directly output signals are constituted by pyroelectric imaging elements that are two-dimensionally arranged as light receiving pixels, and the sensor itself outputs an imaging signal of a differential spectrum image that indicates a characteristic point of the spectral spectrum of the target object.
[0011]
When a pyroelectric element is used, a band-pass filter that passes the frequency band of the detection signal corresponding to the drive frequency that changes the substrate interval of the variable wavelength interference filter is provided in the output circuit to remove noise.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a differential spectrum sensor according to the present invention, which is a spot-type differential spectrum sensor that collects a light beam from a measurement object and detects a differential component of a wavelength spectrum.
[0013]
In FIG. 1, the spot-type differential spectrum sensor 1 is provided with a variable wavelength interference filter 3 following the opening of the case 2, and then a condenser lens 4 is disposed at a condensing position that becomes a focal point of the condenser lens 4. A sensor chip 5 is arranged. A sensor chip circuit shown in FIG. 2 is mounted on the sensor chip 5. Here, the condensing lens 4 is not necessarily required, and the condensing lens 4 may be omitted.
[0014]
The sensor chip circuit of FIG. 2 includes a pyroelectric element 8 that operates as an infrared detection element. The pyroelectric element 8 has detection sensitivity in the infrared band, and outputs a detection signal corresponding to a change in the amount of received light, that is, a differential signal, when the amount of received infrared light changes. Since the power supply voltage + Vc is applied to the pyroelectric element 8, therefore, when receiving a change in the amount of infrared light, a differential voltage signal corresponding to the change in the amount of light is output as the output of the pyroelectric element 8.
[0015]
The detection signal of the pyroelectric element 8 is amplified by the amplifier 9 and then output as the detection signal Vo through the band pass filter (band pass filter) 10. In general, since the pyroelectric element 8 has a large capacitance of, for example, 4 pF, it is desirable to provide the amplifier 9 on the sensor chip 5. Further, by providing the band pass filter 10, high frequency noise of the signal from the amplifier 9 is removed. The low-frequency cutoff frequency of the band-pass filter 10 is set to a frequency lower than the AC driving frequency for changing the substrate interval of the wavelength variable interference filter 3 in FIG.
[0016]
FIG. 3 shows the structure of the wavelength variable interference filter 3 provided in the spot type differential spectrum sensor 1 of FIG. The tunable interference filter 3 is known as a Fabry-Perot interference filter, and is a translucent film that becomes a reflective film of Au or the like having a thickness of, for example, about 200 to 300 angstroms on the opposing surfaces of the pair of glass substrates 11a and 11b. Metal films 12a and 12b are vapor-deposited, and the glass substrates 11a and 11b are disposed with a piezoelectric element 13 therebetween, and a minute interval X is set therebetween.
[0017]
The piezoelectric element 13 receives the application of two-stage DC voltages V1 and V2 (where V1 <V2) from the pulse drive voltage source 14, and changes the substrate interval X in two stages of X1 and X2.
[0018]
This wavelength tunable interference filter 3 has a plurality of transmission peaks as shown in FIG. 4 due to interference action caused by multiple reflection between the light-transmitting metal films 12b and 12a with respect to incident light from the glass substrate 12b side. The spectrum is distributed and transmits light. In the transmission peak spectrum of FIG. 4, for example, the solid transmission peak spectrum is the case where the voltage V1 is applied from the pulse drive voltage source 14 to set the substrate interval to X1, and the transmission peak spectrum distribution of the broken line is the pulse drive voltage source. This is a case where the pulse voltage of 14 is V2 and the substrate interval is X2.
[0019]
When the tunable interference filter 3 of FIG. 3 that creates such a distribution of a plurality of transmission peak spectra changing in an alternating manner is arranged in the spot type differential spectrum sensor 1 as shown in FIG. 1, a specific wavelength in the infrared band is set. The target monitoring wavelength to be measured is set, and the lower pulse voltage V1 of the substrate interval X1, that is, the pulse voltage of the pulse drive voltage source 14 is set so that one of the solid transmission peak spectra in FIG. Decide.
[0020]
In this way, if the peak spectrum is set at the substrate interval X1 of the pulse voltage V1 with respect to the target monitoring wavelength, the pulse is set so that the transmission peak spectrum exists at a position shifted from the target monitoring wavelength as shown by a broken line in FIG. The substrate interval X2 is determined by the higher pulse voltage V2 of the drive voltage source 14.
[0021]
Referring again to FIG. 1, filter driving leads 6 a and 6 b are drawn out from the wavelength variable interference filter 3 provided in the case 2. Further, a power supply lead 7 a and an output lead 7 b are drawn out from the sensor chip 5.
[0022]
Next, the operation of the spot type differential spectrum sensor of FIG. 1 will be described. The spot-type differential spectrum sensor 1 of FIG. 1 is used for a flame detector that detects infrared rays emitted from a flame generated by a fire, for example. FIG. 5A shows a spectrum when light is received from the measurement object.
[0023]
With respect to the spectrum to be measured, a plurality of transmission peaks when the substrate interval of the wavelength variable interference filter 3 is changed by X1 and X2 by repeating the pulse voltages V1 and V2 from the pulse drive voltage source 14 as shown in FIG. The pulse drive voltages V1 and V2 are determined so that one of the spectra is located in the characteristic part of the spectrum of the measurement object as shown in FIG.
[0024]
For this reason, when the substrate interval X1 is set by the lower pulse voltage V1, a solid peak spectrum is generated at the wavelength λ1, for example, 3.8 μm, and a broken line peak spectrum is generated at the wavelength λ2, for example, 4.3 μm, at the substrate interval X2 by the pulse voltage V2. .
[0025]
FIG. 6A shows the switching of the substrate interval of the tunable interference filter 3 of FIG. 1, and the substrate interval is set to X1 at a repetition period determined by the predetermined drive frequency f0 by the pulse voltages V1 and V2 from the pulse drive voltage source 14. And X2. At this time, if a light beam having a measurement spectrum is received as shown in FIG. 5A, the peak spectrum of the wavelength λ1 as shown in FIG. 6B is obtained by switching the peak spectrum of the interference filter shown in FIG. The light reception power and the light reception power based on the peak spectrum of the wavelength λ 2 are alternately obtained and condensed on the sensor chip 5.
[0026]
For this reason, the light receiving power (light receiving amount) as shown in FIG. 6B is added to the pyroelectric element 8 of FIG. 2 provided in the sensor chip 5, and the rising change and the rising of the light receiving power as shown in FIG. A sensor output having a differential waveform corresponding to the falling change is output as the detection signal Vo. The detection signal Vo serving as the sensor output is a differential spectrum at a characteristic wavelength representing the amount of change in the wavelengths λ1 and λ2 of the measurement spectrum of FIG.
[0027]
Therefore, when the sensor output as shown in FIG. 6C is obtained, for example, a flame detection can be warned. Of course, when the spectrum having the characteristic as shown in FIG. 5A is not obtained, the received light power obtained by the transmission of the peak spectra of the wavelengths λ1 and λ2 of the tunable interference filter 3 is substantially at the same level. A differential waveform as a sensor output cannot be obtained.
[0028]
In addition, the received light power at each of the measurement wavelengths λ1 and λ2 is substantially the same even when receiving a noise spectrum over the entire measurement spectrum band, and as a result, the influence of the noise spectrum does not appear on the sensor output that is the differential output. , High SN can be secured.
[0029]
Thus, by changing the substrate interval of the wavelength tunable interference filter 3 in an alternating manner, the chopper required in the conventional pyroelectric sensor can be made unnecessary. Can be prevented. Further, a detection signal can be output only when there is a target object having a target feature spectrum.
[0030]
FIG. 7 shows another embodiment of the differential spectrum sensor of the present invention, which is an image type differential spectrum sensor capable of obtaining a differential spectrum image as a two-dimensional image.
[0031]
In FIG. 7, the image type differential spectrum sensor 20 is provided with an imaging lens 21 following the wavelength variable interference filter 3, and an imaging element 22 is disposed at the imaging position of the imaging lens 21. The imaging lens 21 is an example of an inverted optical system that forms an inverted image 24 obtained by inverting the measurement object 23 on the image sensor 22.
[0032]
The wavelength tunable interference filter 3 has the structure shown in FIG. 3, and the substrate spacing is switched between X1 and X2 by applying the voltages V1 and V2 (where V1 <V2) at the drive frequency f0 by the pulse drive voltage source 14 as shown in FIG. The transmission peak spectrum distribution as shown by a solid line and a broken line is switched.
[0033]
FIG. 8 is an embodiment of the image sensor 22 provided in the image type differential spectrum sensor 20 of FIG. The image sensor 22 constitutes an infrared two-dimensional image sensor, and controls a control signal input terminal 26 that receives a control signal including an external timing signal and an address signal, and controls the operation of the image sensor 22 according to the external control signal. A control circuit 28 that outputs signals, a sensor array 31 in which pixel cells 32 are two-dimensionally arranged in a matrix, and a row pulse Sx based on a clock CLK1 from the control circuit 28 to select a row in the sensor array 31 The column selector 30 for performing the selection, the column selector 30 for selecting the column in the sensor array 31 by the output of the column pulse Sy based on the clock CLK2 from the control circuit 28, and provided corresponding to the column of the sensor array. The operational amplifier 33 for amplifying the pixel signal from the pixel cell 32 and the operational amplifier 33 provided corresponding to the column of the sensor array 31. A band-pass filter 34 that removes high-frequency noise contained in these signals, and a multiplexer 40 that selectively controls whether or not pixels are used from the band-pass filter 34 to the output terminal 27 under the control of the control signal SC from the control circuit 28. Is provided.
[0034]
The control circuit 28 in the image pickup device 22 controls the row selector 29, the column selector 30, and the multiplexer 40. The column selector 30 outputs the column pulse Sy of FIG. From FIG. 9, the row pulse Sx of FIG. That is, the column pulse Sy in FIG. 9A outputs a column pulse at a cycle Ty, and during this column pulse cycle Ty, the row pulse Sx in FIG. 10B corresponds to the number of pixel cells 32 in the row direction. Is output only, and this is repeated below.
[0035]
FIG. 10 is a cell circuit diagram showing one of the pixel cells 32 provided in the sensor array 31 of FIG. In the cell circuit of FIG. 10, the pyroelectric element 8 is used as an infrared sensor. The output of the pyroelectric element 8 is amplified by an amplifier 9 and then output as a pixel signal Vo through transistors 35 and 36. The
[0036]
The transistor 35 is turned on in response to the row pulse Sx in FIG. 9B, and the transistor 36 is turned on in response to the column pulse Sy in FIG. Then, the detection signal V0 of the pyroelectric element 8 is output as a pixel signal by the amplifier 9 with both transistors 35 and 36 turned on.
[0037]
The wavelength spectrum of the image of the measurement object formed on the pyroelectric element 8 is 2 by alternately switching the peak spectra of the wavelengths λ1 and λ2 by pulse driving of the wavelength variable interference filter 3 as shown in FIGS. The light reception power of one specific spectrum is incident, and a sensor output as shown in FIG. 6C, that is, a differential spectrum signal is output for each pixel cell 34.
[0038]
As a result, the differential spectrum image signal by the plurality of pixel cells 32 two-dimensionally arranged on the sensor array 31 can be directly output from the multiplexer 40 of the image sensor 22 in FIG. Can be displayed.
[0039]
In addition, by reading the differential spectrum image obtained from the image sensor 22 into an image processing apparatus such as a personal computer, the feature extraction of the differential spectrum image having a characteristic at a specific wavelength can be directly performed, and the differential spectrum image is subjected to a difference calculation. Therefore, the processing load is greatly reduced, and real-time monitoring of the differential spectrum image can be easily realized.
[0040]
In the imaging device 22 of FIG. 8, since the operational amplifier 33 is provided outside the sensor array 31, it is not necessary to provide the pixel built-in amplifier 9 when the pyroelectric element 8 of FIG. 10 is used. Good. Since the band pass filter 34 is provided outside the sensor array 31, it is not necessary to provide a band pass filter independently for each pixel cell 32.
[0041]
Further, as an example of setting the wavelength of infrared rays emitted from the flame as a target wavelength for measurement by the wavelength tunable interference filter 3, an appropriate wavelength is set according to the characteristics of the spectrum of the light beam from the measurement object. A sensor function corresponding to an appropriate object to be measured can be realized by setting the wavelength of the peak spectrum (setting the substrate interval).
[0042]
【The invention's effect】
As described above, according to the present invention, the sensor itself can directly detect the differential information indicating the extraction of the characteristic portion in the spectral spectrum and the change in the amount of light in the characteristic portion. Therefore, information that hinders the analysis of the spectral spectrum. Is significantly reduced, leaving only effective information, eliminating the need for external spectral analysis and differential analysis, greatly reducing the processing load on the apparatus, and easily detecting the differential spectrum of the measurement object.
[0043]
In particular, in the case of an image sensor type that outputs a differential spectrum image, a differential spectrum image signal for a characteristic wavelength in the spectral spectrum can be obtained directly from the sensor. Monitoring display can be performed, and by reading the differential spectrum image from the sensor with the image processing apparatus, it is possible to easily and quickly perform feature analysis and determination of the measurement target object.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention using a single sensor chip. FIG. 2 is a circuit diagram of the sensor chip of FIG. 1 using a pyroelectric element. FIG. 4 is an explanatory diagram of a plurality of peak spectrum distributions when the substrate interval of the wavelength tunable interference filter of FIG. 3 is changed in two stages. FIG. 5 is a diagram illustrating measured wavelength spectra and wavelength tunable interference in the embodiment of FIG. FIG. 6 is an explanatory diagram of switching of characteristic peak spectrum by a filter. FIG. 6 is an explanatory diagram of switching of a substrate interval of a tunable interference filter, sensor light reception power and sensor detection signal in the embodiment of FIG. FIG. 8 is an explanatory diagram of the image sensor of FIG. 7. FIG. 9 is a time chart of column pulses and row pulses in the image sensor of FIG. 8. FIG. 10 is a circuit diagram of the pixel cell of FIG. Description】
1: Spot type differential spectrum sensor 2: Case 3: Wavelength variable interference filter 4: Condensing lens 5: Sensor chip 6a, 6b: Filter driving lead 7a: Power supply lead 7b: Output lead 8: Pyroelectric element 9: Amplifier 10: Bandpass filters 11a, 11b: Glass substrates 12a, 12b: Metal film 13: Piezoelectric element 14: Pulse drive voltage source 20: Image type differential spectrum sensor 21: Imaging lens 22: Imaging element 24: Inverted image 26: Control Signal input terminal 27: Image signal output terminal 28: Control circuit 29: Row selector 30: Column selector 31: Sensor array 32: Pixel cell 33: Operational amplifier 34: Band pass filter 40: Multiplexer

Claims (3)

A wavelength tunable interference filter that transmits only the spectral light of the characteristic part in the spectral spectrum by changing the substrate interval of the pair of optical substrates in which the reflection films are formed on the opposing surfaces arranged at a minute interval;
A drive voltage source for alternatingly changing the distance between the pair of substrates of the tunable filter;
A pyroelectric element that is disposed at the rear of the wavelength tunable interference filter and directly outputs a received light signal corresponding to an AC change amount of light transmitted through the wavelength tunable interference filter;
A differential spectrum sensor characterized by outputting a detection signal indicating a feature point of a spectrum of a target object by the sensor itself . A wavelength tunable interference filter that transmits only the spectral light of the characteristic part in the spectral spectrum by changing the substrate interval of the pair of optical substrates in which the reflection films are formed on the opposing surfaces arranged at a minute interval;
A drive voltage source for alternatingly changing the distance between the pair of substrates of the tunable filter;
An imaging lens that forms an image of a light beam from a target object that has passed through the variable wavelength interference filter;
A focusing device in which a plurality of pyroelectric elements, which are arranged at the imaging position of the imaging lens and directly output a light receiving signal corresponding to an AC change amount of light transmitted through the wavelength variable interference filter, are two-dimensionally arranged as light receiving pixels. An electric imaging device;
A differential spectrum sensor characterized by outputting an imaging signal of a differential spectrum image indicating a feature point of a spectrum of a target object by the sensor itself . 3. The differential spectrum sensor according to claim 1, wherein the pyroelectric element output circuit passes a frequency band of a detection signal corresponding to a driving frequency that changes a substrate interval of the wavelength variable interference filter. A differential spectrum sensor characterized by comprising:

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