JP2019020213A - Wavelength modulation spectroscopic system, error information generation system, and wavelength modulation spectroscopy - Google Patents

Abstract

Provided is a wavelength modulation spectroscopic system capable of more easily and accurately evaluating the characteristics of an object to be measured. A wavelength modulation spectroscopic system includes a wavelength tunable laser and a wavelength tunable laser driving device that modulates the wavelength of laser light emitted from the wavelength tunable laser with a modulation frequency and sweeps the modulation center wavelength. The tunable laser driving apparatus includes an oscillator 102, a voltage sweep power supply 103, a voltage addition circuit 104, and a voltage-current conversion circuit 105, and generates an injection current to the tunable laser 101. The wavelength modulation spectroscopic system includes a 2f component detector 108 that detects a frequency component that is twice the modulation frequency included in the laser light emitted from the wavelength tunable laser and transmitted through the object 106 to be measured, and a frequency that is twice the modulation center frequency. It has a spectrum measuring device 111 that measures a wavelength spectrum that represents the magnitude of a frequency component, and a storage device 113 that stores error information of the wavelength spectrum measured by the spectrum measuring device. [Selection] Figure 1

Description

The present invention relates to a wavelength modulation spectroscopy system, an error information generation system, and a wavelength modulation spectroscopy method.

  Conventionally, laser spectroscopy has been known in which the wavelength of laser light is temporally swept and input to the object to be measured, and the dependence of the intensity of light output from the object to be measured on the wavelength is observed. It is used as an effective method for identifying objects and measuring concentrations.

  Among conventional laser spectroscopy, double frequency (2f) detection wavelength modulation spectroscopy is known as a method with higher measurement sensitivity of an object to be measured. In the conventional 2f detection wavelength modulation spectroscopy, the wavelength of the laser light is modulated with a very small amplitude using a specific frequency, and the modulation center wavelength is swept. And the intensity | strength of the harmonic component twice the frequency of a laser beam is detected from the optical intensity of the laser beam which permeate | transmitted the to-be-measured object.

  FIG. 5 is a block diagram illustrating a configuration example of a conventional 2f detection wavelength modulation spectroscopy system 500. The 2f detection wavelength modulation spectroscopy system 500 includes an oscillator 502, a voltage sweep power supply 503, a voltage addition circuit 504 that adds voltages output from the oscillator 502 and the voltage sweep power supply 503, a voltage-current conversion circuit 505, and a wavelength variable. A laser 501, an object to be measured 506, a light intensity measuring device 507, a 2f component detector 508, a voltage-wavelength converter 509, and a spectrum display device that displays the output value of the 2f component detector 508 with respect to the wavelength as a spectrum 510.

  The oscillator 502 outputs a minute sine wave voltage having a frequency f [Hz] to the voltage-current conversion circuit 505. A small sinusoidal current is superimposed on the current output from the voltage-current conversion circuit 505 and input to the wavelength tunable laser 501 as an injection current. Since the wavelength-modulated laser 501 is injected with a current that is minutely modulated at the frequency f, the wavelength of the output light of the wavelength-tunable laser 501 always changes slightly at the frequency f (hereinafter, this “frequency f”). Is sometimes referred to as “modulation frequency”.)

  When the device under test 506 exhibits an extreme response near a specific wavelength, if the wavelength of the laser beam that has passed through the device under test 506 is minutely modulated at the frequency f around that wavelength, the device under test 506 The response from 506 includes a frequency component of 2f [Hz] (hereinafter referred to as “2f component”) that is the second harmonic of the frequency f.

  Therefore, by measuring the signal intensity of the 2f component detected by the 2f component detector 508, the characteristic unique to the device under test 506 can be obtained. Further, the conventional 2f detection wavelength modulation spectroscopic system 500 has an advantage that it can selectively detect only the response component with respect to the output light of the wavelength tunable laser 501, such as noise light other than the output light of the wavelength tunable laser 501. Light that is not modulated at frequency f can be excluded.

  Since the current output from the voltage-current conversion circuit 505 is changed by the voltage sweep power source 503 at a cycle slower than the frequency f, the output light of the wavelength tunable laser 501 is swept at the modulation center wavelength with a minute modulation. The Then, a wavelength modulation spectrum (hereinafter referred to as “2f wavelength modulation spectrum”) representing the magnitude of the 2f component with respect to the modulation center wavelength is obtained over the wavelength range to be swept.

  For example, Non-Patent Document 1 discloses a technique for measuring a 2f wavelength modulation spectrum of methane gas by a conventional 2f detection wavelength modulation spectroscopy. More specifically, in Non-Patent Document 1, while applying weak modulation at a frequency f [Hz], the modulation center wavelength of the output light of the wavelength tunable laser is swept in time, transmitted through methane gas, and detected by a photodetector. A 2f [Hz] component is extracted from the measured signal intensity to measure a 2f wavelength modulation spectrum of methane gas.

  In the conventional 2f detection wavelength spectroscopy system, the change in the wavelength of the laser beam emitted from the wavelength tunable laser is not constant depending on the optical characteristics and electrical characteristics of the laser with respect to the change in the current injected into the wavelength tunable laser. There was a thing. Therefore, in the conventional 2f detection wavelength spectroscopic system, an error is included in the 2f wavelength modulation spectroscopic spectrum of the laser light transmitted through the object to be measured, and the accuracy in identifying the object to be measured may be deteriorated.

  Here, FIG. 6 shows the relationship between the injection current and the wavelength of the output light in a distributed reflection type laser generally used as a conventional wavelength tunable laser. As shown in FIG. 6, in the long wavelength band of the output light of the distributed reflection type laser, the change in the wavelength of the output light with respect to the change in the injection current is small, and the change in the wavelength becomes larger as the wavelength becomes shorter. As described above, the wavelength change of the output light with respect to the change of the injection current of the wavelength tunable laser is not constant and has nonlinear characteristics.

Here, if the 2f component at the wavelength λ inherent to the object to be measured is P _2f (λ), the actually measured value of the 2f component is A (λ) P _2f (λ). A (λ) is an error coefficient (hereinafter referred to as “2f error coefficient”). Further, an error corresponding to 2f error coefficient A (λ) is superimposed on the 2f wavelength modulation spectrum obtained from the actually measured 2f component A (λ) P _2f (λ).

  As described above, in the conventional 2f detection wavelength spectroscopy system, the peak position and peak width of the actually measured 2f wavelength modulation spectrum show the change in the wavelength of the output light with respect to the change in the current injected into the wavelength tunable laser. Includes errors due to nonlinear characteristics. Therefore, in the wavelength modulation spectroscopy system using the conventional 2f detection wavelength modulation spectroscopy, there is a problem that the accuracy of the identification of the type of the object to be measured and the estimation of the concentration deteriorates.

  In order to solve this problem, an error included in the 2f component is compensated by using an exponential function circuit by a semiconductor junction, and the nonlinear characteristic of the wavelength change of the output light with respect to the change of the injection current of the wavelength tunable laser is removed. Technology has been reported. For example, Non-Patent Document 2 discloses a technique for generating a substantially linear wavelength of output light by an exponential function circuit configured using transistors.

  However, in the conventional method of compensating for an error included in the 2f component using an exponential function circuit, not only the circuit configuration is complicated, but also according to the characteristics of each circuit and the characteristics of each wavelength tunable laser, There was a problem that complicated adjustment was required for each circuit.

Shinhei Kano et al., “Supersensitivity of Methane Gas Remote Absorption Sensor”, 31st Laser Sensing Symposium, E-3, September 21, 2013 Masataka Gobara et al., “Improvement of wavelength sweep linearity of DBR laser by nonlinear current sweep circuit”, IEICE General Conference 2017, C-4-3, March 22, 2017

  An object of this invention is to provide the wavelength modulation spectroscopy system which can perform the characteristic evaluation of a to-be-measured object more simply and correctly.

  In order to solve the above-described problem, a wavelength modulation spectroscopic system according to the present invention drives a wavelength tunable laser, the wavelength tunable laser, and sets the wavelength of laser light emitted from the wavelength tunable laser to a predetermined modulation frequency. Tunable laser driving device that modulates and sweeps the modulation center wavelength, and a double frequency that detects a frequency component twice the modulation frequency of the laser light emitted from the tunable laser and transmitted through the object to be measured A component detector, a spectrum measuring device that measures a wavelength spectrum that represents the magnitude of the frequency component that is twice the modulation center wavelength, and a storage device that stores error information relating to the measured wavelength spectrum measured by the spectrum measuring device And a corrected wavelength spectrum obtained by correcting the measured wavelength spectrum based on the error information stored in the storage device. Characterized in that it comprises a correction device for determining the vector.

  Further, in the wavelength modulation spectroscopic system according to the present invention, the error information is information representing a ratio between the size of the measured wavelength spectrum with respect to the wavelength and the size of the theoretical wavelength spectrum, and the correction device includes the measurement wavelength. The corrected wavelength spectrum may be obtained from the spectrum based on the ratio.

  In the wavelength modulation spectroscopic system according to the present invention, the error information includes an error between a peak position of the measured wavelength spectrum and a peak position of a theoretical wavelength spectrum with respect to a wavelength, and the correction device includes the measured wavelength spectrum. From the above, the corrected wavelength spectrum may be obtained based on an error in the peak position of the measured wavelength spectrum.

  An error information generation system according to the present invention drives a wavelength tunable laser and the wavelength tunable laser, modulates the wavelength of the laser light emitted from the wavelength tunable laser at a predetermined modulation frequency, A wavelength tunable laser driving device that sweeps the wavelength, a double frequency component detector that detects a frequency component that is twice the modulation frequency of the laser light emitted from the wavelength tunable laser and transmitted through the wavelength filter, and the modulation center A spectrum measuring device that measures a wavelength spectrum that represents the magnitude of the frequency component that is twice the wavelength, and curve data that interpolates peaks that appear periodically in the measured wavelength spectrum measured by the spectrum measuring device, An error information calculation device that calculates error information relating to a measurement wavelength spectrum and the error information calculation device Is provided with a storage device for storing the error information, it said wavelength filter is characterized in that for selectively transmitting the laser beam emitted from the tunable laser at a predetermined wavelength interval.

  Further, in the error information generation system according to the present invention, the error information calculation device includes the curve data including the error information and the theoretical value curve data obtained by interpolating peaks that periodically appear in the theoretical wavelength spectrum. A ratio may be provided.

  In the error information generation system according to the present invention, the error information calculation device may calculate an error between a peak position of the measured wavelength spectrum with respect to a wavelength and a peak position of the theoretical wavelength spectrum.

  In the error information generation system according to the present invention, the wavelength filter may be an etalon filter or a Mach-Zehnder interferometer filter.

  The wavelength modulation spectroscopic method according to the present invention includes a wavelength variable laser driving step of modulating the wavelength of laser light emitted from a wavelength variable laser at a predetermined modulation frequency and sweeping the modulation center wavelength, and the wavelength variable laser. A double frequency component detecting step of detecting a frequency component twice the modulation frequency of the laser light emitted from the wavelength tunable laser and transmitted through the object to be measured; and the double the frequency with respect to the modulation center wavelength A spectrum measurement step for measuring a wavelength spectrum representing the magnitude of the frequency component of the signal, and correcting the measurement wavelength spectrum based on error information stored in the storage device and related to the measurement wavelength spectrum measured in the spectrum measurement step And a correction step for obtaining the corrected wavelength spectrum.

  According to the present invention, the 2f wavelength modulation spectral spectrum is observed using error information that is stored in advance in a storage device and that is caused by nonlinear characteristics indicated by a change in wavelength of output light with respect to a change in injection current of a wavelength tunable laser. Since the value is corrected, the characteristic evaluation of the object to be measured can be performed more simply and accurately.

FIG. 1 is a block diagram illustrating a configuration example of a wavelength modulation spectroscopy system according to the first embodiment of the present invention. FIG. 2 is a block diagram showing a configuration example of a wavelength modulation spectroscopy system according to the second embodiment of the present invention. FIG. 3 is a flowchart for explaining the operation in the wavelength modulation spectroscopy system according to the second embodiment of the present invention. FIG. 4A is a diagram showing the light transmittance with respect to the wavelength that passes through the wavelength filter measured in the wavelength modulation spectroscopic system according to the second embodiment of the present invention. FIG. 4B is a diagram illustrating a 2f wavelength modulation spectrum of laser light transmitted through the wavelength filter, which is measured in the wavelength modulation spectroscopy system according to the second embodiment of the present invention. FIG. 4C is a diagram showing a measured value curve obtained by interpolating peaks of the 2f wavelength modulation spectrum shown in FIG. 4B and a corresponding theoretical value curve. FIG. 4D is a diagram showing a ratio of measured values to theoretical values of the 2f wavelength modulation spectrum shown in FIG. 4C. FIG. 4E is a diagram illustrating a shift of the peak position in the measured value with respect to the theoretical value of the 2f wavelength modulation spectrum shown in FIG. 4C. FIG. 5 is a diagram showing a configuration of a conventional wavelength modulation spectroscopy system. FIG. 6 is a diagram showing a relationship between an injection current and emitted light of a wavelength tunable laser used in a conventional wavelength modulation spectroscopic system.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4E. Constituent elements common to the drawings are given the same reference numerals.

<First Embodiment>
The wavelength modulation spectroscopic system 1 according to the first embodiment of the present invention modulates the wavelength of the wavelength variable laser 101 and the wavelength of the laser light emitted from the wavelength variable laser 101 with a predetermined modulation frequency f, and sets the modulation center wavelength. And a tunable laser driving device 120 for sweeping. The wavelength tunable laser driving device 120 includes an oscillator 102, a voltage sweep power supply 103, a voltage addition circuit 104, and a voltage-current conversion circuit 105, and generates an injection current that is input to the wavelength tunable laser 101. The wavelength modulation spectroscopic system 1 includes a 2f component detector 108 that detects a frequency (2f) component that is twice the modulation frequency included in the laser light emitted from the wavelength tunable laser 101 and transmitted through the device under test 106. It has a spectrum measuring device 111 that measures a wavelength spectrum that represents the magnitude of a frequency component that is twice the modulation center frequency, and a storage device 113 that stores error information related to the wavelength spectrum measured by the spectrum measuring device 111.

  FIG. 1 is a block diagram showing a configuration example of a wavelength modulation spectroscopy system 1 according to the first embodiment of the present invention. The wavelength modulation spectroscopy system 1 includes a wavelength tunable laser 101, a wavelength tunable laser driving device 120, an object to be measured 106, a light intensity measuring device 107, a 2f component detector 108, a voltage-wavelength converter 109, a spectrum, A spectrum processing device 110 including a measurement device 111 and a correction device 112, a storage device 113, and a display device 114 are provided.

  The wavelength tunable laser 101 is composed of a wavelength tunable semiconductor laser that oscillates in the absorption wavelength band of the object to be measured and outputs laser light. As the wavelength tunable laser 101, a distributed reflection laser or the like can be used. The wavelength tunable laser 101 oscillates upon injection of current from the voltage-current conversion circuit 105 and emits laser light. The wavelength tunable laser 101 can be used as a wavelength tunable light source by controlling the input injection current.

  The wavelength tunable laser driving device 120 includes an oscillator 102, a voltage sweep power supply 103, a voltage addition circuit 104, and a voltage-current conversion circuit 105. The wavelength tunable laser driving device 120 drives the wavelength tunable laser 101, modulates the wavelength of the laser light emitted from the wavelength tunable laser 101 with a predetermined modulation frequency, and sweeps the modulation center wavelength.

  The oscillator 102 outputs a voltage based on a sine wave having a frequency f [Hz] to the voltage addition circuit 104. The sine wave voltage output from the oscillator 102 is a minute voltage.

  The voltage sweep power supply 103 generates a voltage signal for sweeping a predetermined wavelength band near the absorption spectrum of the device under test 106 and outputs the voltage signal to the voltage addition circuit 104. The predetermined frequency band is a wavelength band near the absorption spectrum of the DUT 106.

  The voltage addition circuit 104 adds the minute sine wave voltage output from the oscillator 102 and the voltage output from the voltage sweep power supply 103. The voltage addition circuit 104 outputs a voltage signal on which a minute sine wave voltage is superimposed to the voltage-current conversion circuit 105.

  The voltage-current conversion circuit 105 converts a voltage signal on which a minute sine wave voltage is superimposed into a current signal. The voltage-current conversion circuit 105 inputs a minute sine wave current generated by conversion into the wavelength tunable laser 101 as an injection current, and drives the wavelength tunable laser 101. As a result, the wavelength of the laser light emitted from the wavelength tunable laser 101 is minutely modulated at the modulation frequency f [Hz], and the modulation center wavelength is swept in a predetermined wavelength band.

  The DUT 106 is a substance that is a target of characteristic evaluation by the wavelength modulation spectroscopy system 1. The DUT 106 transmits the laser beam emitted from the wavelength tunable laser 101 and is received by the light intensity measuring device 107.

  The light intensity measuring device 107 includes a photoelectric conversion element such as a photodiode (PD), an amplifier, and the like, receives the laser light transmitted through the object to be measured 106, and converts it into an electric signal indicating the light intensity of the laser light. 2f component detector 108.

  The 2f component detector 108 extracts a frequency component (2f component) that is twice the modulation frequency f of the wavelength tunable laser 101 from the electrical signal indicating the light intensity of the laser beam that has passed through the DUT 106, and a spectrum measuring device. To 111.

  The voltage-wavelength converter 109 receives the voltage of the voltage sweep power supply 103 as an input, and the correspondence relationship between the voltage input from the voltage sweep power supply 103 to the voltage addition circuit 104 and the wavelength of the laser light emitted from the wavelength tunable laser 101. From this, the wavelength (modulation center wavelength) of the laser beam at the time of voltage sweep is obtained and output to the spectrum measuring device 111.

  The spectrum processing device 110 includes a spectrum measurement device 111 and a correction device 112.

  The spectrum measuring apparatus 111 calculates the 2f component from the 2f component signal of the transmitted laser beam detected by the 2f component detector 108 and the wavelength (modulation center wavelength) of the laser beam during voltage sweep from the voltage-wavelength converter 109. The wavelength spectrum (2f wavelength modulation spectrum) is measured. Further, the spectrum measuring device 111 outputs the measured 2f wavelength modulation spectrum to the correcting device 112.

  The correction device 112 reads out error information included in the 2f wavelength modulation spectrum stored in advance in the storage device 113, and obtains a spectrum obtained by removing the error from the 2f wavelength modulation spectrum. Further, the correction device 112 outputs the corrected 2f wavelength modulation spectrum to the display device 114.

  The storage device 113 stores error information of the 2f wavelength modulation spectrum obtained in advance. The error information includes 2f error coefficient A (λ) and information on the error of the peak position of the 2f wavelength modulation spectrum.

  The display device 114 displays the 2f wavelength modulation spectrum corrected by the correction device 112. Further, the display device 114 can display the identification result of the device under test 106 by analyzing the 2f wavelength modulation spectrum.

  Next, correction processing of the 2f wavelength modulation spectrum by the correction device 112 will be described. As described above, the change in the wavelength of the laser light emitted from the wavelength tunable laser 101 with respect to the change in the injection current input to the wavelength tunable laser 101 by the voltage-current conversion circuit 105 has nonlinear characteristics. For this reason, the peak width and peak position in the measurement value of the 2f wavelength modulation spectrum obtained from the laser beam that has passed through the DUT 106 have an error due to this nonlinear characteristic.

Here, the output value of the spectrum measuring apparatus 111 is expressed as A (λ) P _2f (λ). P _2f (λ) is a 2f component at the wavelength λ that the device under test 106 originally has, and A (λ) is a 2f error coefficient.

The correction device 112 reads the 2f error coefficient A (λ) from the storage device 113 and calculates a correction value obtained by dividing the output value A (λ) P _2f (λ) of the spectrum measurement device 111 by the 2f error coefficient. Further, the correction device 112 reads the error information of the peak position from the storage device 113 and corrects the shift amount of the peak position of the measurement value of the 2f wavelength modulation spectrum.

  Further, the correction device 112 outputs to the display device 114 a spectrum obtained by correcting the peak width (peak size) and peak position error for the measurement value of the 2f wavelength modulation spectral spectrum.

  As described above, in the wavelength modulation spectroscopy system 1 according to the present embodiment, the correction device 112 corrects the measured 2f wavelength modulation spectrum based on the error information stored in the storage device 113 in advance. The wavelength modulation spectroscopic system 1 can perform the characteristic evaluation of the DUT 106 more simply and accurately by analyzing the 2f wavelength modulation spectroscopic spectrum from which the error is removed.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a configuration example of a wavelength modulation spectroscopy system 1a (error information generation system) according to the second embodiment. In the following description, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted.

  In the first embodiment, a case has been described in which the correction device 112 corrects the 2f wavelength modulation spectrum of the laser light that has passed through the DUT 106 based on the error information stored in the storage device 113 in advance. . On the other hand, in the second embodiment, the error information calculation device 115 measures error information included in the 2f component of the laser light transmitted through the wavelength filter 116 and stores it in the storage device 113.

  Based on the 2f wavelength modulation spectrum measured from the laser light transmitted through the wavelength filter 116, the error information calculation device 115 obtains 2f error coefficient A (λ) and information on the error of the peak position of the 2f wavelength modulation spectrum. Including error information is calculated. Further, the error information calculation device 115 stores the calculated error information in the storage device 113.

  The wavelength filter 116 is a filter whose light transmittance periodically changes with the wavelength change of the laser light emitted from the wavelength tunable laser 101. For example, an etalon filter or a Mach-Zehnder interferometer is used. Also good. As the wavelength filter 116, for example, a filter that transmits a wavelength specific to a known substance such as methane can be used.

  Next, the operation of the wavelength modulation spectroscopy system 1a will be described. FIG. 3 is a flowchart for explaining the operation of the wavelength modulation spectroscopy system 1a according to the second embodiment.

  First, a minute sine wave current having a frequency f is input to the wavelength tunable laser 101, and laser light modulated by this current is emitted from the wavelength tunable laser 101. The laser light passes through the wavelength filter 116 and is received by the light intensity measuring device 107, and the light intensity measuring device 107 measures the light transmittance, which is the signal intensity of the received laser light (step S11).

  FIG. 4A is a diagram showing the light transmittance with respect to the wavelength of the laser light transmitted through the wavelength filter 116 measured by the light intensity measuring device 107. As shown in FIG. 4A, the light transmittance of the laser light transmitted through the wavelength filter 116 changes periodically with respect to the change in the wavelength of the laser light. Further, the light transmittance data measured by the light intensity measuring device 117 is stored in the storage device 113.

  Next, the 2f component detector 108 extracts the 2f component from the light transmittance of the laser light transmitted through the wavelength filter 116 measured by the light intensity measuring device 107 and outputs the 2f component to the spectrum measuring device 111. The spectrum measuring device 111 obtains a 2f wavelength modulation spectrum from the 2f component signal and the wavelength information of the laser light emitted from the wavelength tunable laser 101 at the time of voltage sweep obtained from the voltage-wavelength converter 109 (step S12).

  Note that the wavelength (modulation center wavelength) of the laser light at the time of voltage sweep is information obtained by using the correspondence between the voltage of the voltage sweep power supply 103 and the wavelength of the wavelength tunable laser measured in advance by the voltage-wavelength converter 109. It is.

  FIG. 4B is a diagram showing a 2f wavelength modulation spectrum of the laser light transmitted through the wavelength filter 116 measured by the spectrum measuring apparatus 111. In FIG. 4B, the curve indicated by the dotted line is the 2f component extracted from the light transmittance of the laser light that has passed through the wavelength filter 116. A curve indicated by a solid line is a 2f wavelength modulation spectrum measured based on the 2f component (dotted line).

  The 2f wavelength modulation spectrum of the laser light that has passed through the wavelength filter 116 obtained by the spectrum measuring device 111 is stored in the storage device 113. Further, the spectrum measuring apparatus 111 outputs 2f wavelength modulation spectrum data to the error information calculating apparatus 115.

  Next, the error information calculation device 115 calculates the error coefficient A (λ) based on the 2f wavelength modulation spectrum measured by the spectrum measurement device 111 and the theoretical value of the 2f wavelength modulation spectrum (step S13). ).

  More specifically, the error information calculation device 115 reads out from the storage device 113 data on the light transmittance (FIG. 4A) of the laser light that has passed through the wavelength filter 116 measured by the light intensity measuring device 107 in step S11. The error information calculation device 115 obtains the characteristics of the wavelength filter 116 from the light transmittance data, and calculates the theoretical value of the 2f wavelength modulation spectrum. The theoretical value of the 2f wavelength modulation spectrum is an ideal value obtained when it is assumed that the change in the wavelength of the output light with respect to the change in the current injected into the wavelength tunable laser 101 is linear.

  FIG. 4C is a diagram showing a measured value curve of a 2f wavelength modulation spectrum obtained by interpolating peaks of the 2f wavelength modulation spectrum shown in FIG. 4B and a corresponding theoretical value curve. A curve indicated by a solid line is a curve formed by interpolating peaks of theoretical values of the 2f wavelength modulation spectrum. A curve indicated by a broken line is a curve in which peaks of measured values are interpolated in the 2f wavelength modulation spectrum (curve indicated by a dotted line) obtained by the spectrum measuring apparatus 111 in step S12.

  As shown in FIG. 4C, the theoretical value (solid line) and the measured value (broken line) of the 2f wavelength modulation spectrum do not match. This is because the wavelength change of the laser light emitted from the wavelength tunable laser 101 is not proportional to the input voltage to the voltage-current conversion circuit 105 as described above.

  The error information calculation device 115 obtains the ratio of the measured value (broken line) to the theoretical value (solid line) of the 2f wavelength modulation spectrum, that is, the 2f error coefficient A (λ). 4D is a diagram showing a ratio of measured values to theoretical values of the 2f wavelength modulation spectrum shown in FIG. 4C, and the curve shown in FIG. 4D is the 2f error coefficient A (λ).

  Next, the error information calculation device 115 calculates the error of the peak position in the measurement value (broken line) with respect to the theoretical value (solid line) of the 2f wavelength modulation spectrum shown in FIG. 4C (step S14). FIG. 4E is a diagram showing a deviation amount of a peak position in a measured value with respect to a theoretical value of the 2f wavelength modulation spectrum shown in FIG. 4C.

  Then, the error information calculation device 115 stores the 2f error coefficient A (λ) obtained in step S13 and the peak position error information obtained in step S14 in the storage device 113 as error information.

  The wavelength modulation spectroscopic system 1a corrects the measurement value of the 2f wavelength modulation spectroscopic spectrum using the error information database created in this way.

  More specifically, the device under test 106 is installed in place of the wavelength filter 116, and the 2f wavelength modulation spectrum of the laser light transmitted through the device under test 106 is measured. The correction device 112 reads the error information calculated by the error information calculation device 115 and stored in the storage device 113, and corrects the 2f wavelength modulation spectrum.

  As described above, according to the wavelength modulation spectroscopic system 1a in the second embodiment, the nonlinear characteristic of the wavelength change of the emitted light of the wavelength tunable laser 101 with respect to the change of the injection current input to the wavelength tunable laser 101 is obtained. The 2f error coefficient A (λ) caused by the cause is calculated in advance. The wavelength modulation spectroscopic system 1a also calculates in advance a peak position error in the 2f wavelength modulation spectroscopic spectrum and stores error information including the 2f error coefficient A (λ) and the peak position error of the 2f wavelength modulation spectroscopic spectrum. Store in device 113.

  Further, in the wavelength modulation spectroscopic system 1a according to the present embodiment, the 2f wavelength modulation spectroscopic spectrum of the laser light transmitted through the DUT 106 is corrected using the error information stored in the storage device 113 in advance. Further, the wavelength modulation spectroscopic system 1a obtains the original 2f wavelength modulation spectral spectrum from which the error included in the 2f component of the laser light has been removed, and uses this as a target for characteristic evaluation. It is possible to more easily and accurately evaluate the characteristics.

  The embodiments of the wavelength modulation spectroscopic system of the present invention have been described above. However, the present invention is not limited to the described embodiments, and various types that can be assumed by those skilled in the art within the scope of the invention described in the claims. Can be modified.

  DESCRIPTION OF SYMBOLS 1, 1a ... Wavelength modulation spectroscopy system, 101 ... Wavelength variable laser, 102 ... Oscillator, 103 ... Voltage sweep power supply, 104 ... Voltage addition circuit, 105 ... Voltage-current conversion circuit, 106 ... Measurement object, 107 ... Light intensity measurement 108 ... 2f component detector 109 ... Voltage-wavelength converter 110 ... Spectrum processing device 111 ... Spectrum measuring device 112 ... Correction device 113 ... Storage device 114 ... Display device 115 ... Error information calculation device 116 wavelength filter 120 wavelength tunable laser driving device.

Claims (8)

A tunable laser;
A wavelength tunable laser driving device that drives the wavelength tunable laser, modulates the wavelength of the laser light emitted from the wavelength tunable laser at a predetermined modulation frequency, and sweeps the modulation center wavelength;
A double frequency component detector for detecting a frequency component twice the modulation frequency in the laser light emitted from the wavelength tunable laser and transmitted through the object to be measured;
A spectrum measuring device for measuring a wavelength spectrum representing the magnitude of the frequency component twice the modulation center wavelength;
A storage device for storing error information relating to a measurement wavelength spectrum measured by the spectrum measurement device;
Based on the error information stored in the storage device, a correction device for obtaining a correction wavelength spectrum obtained by correcting the measurement wavelength spectrum;
A wavelength modulation spectroscopic system comprising: The error information is information representing the ratio of the size of the measured wavelength spectrum to the wavelength and the size of the theoretical wavelength spectrum,
The wavelength modulation spectroscopy system according to claim 1, wherein the correction device obtains the correction wavelength spectrum from the measurement wavelength spectrum based on the ratio. The error information includes an error between a peak position of the measured wavelength spectrum with respect to a wavelength and a peak position of a theoretical wavelength spectrum,
3. The wavelength modulation spectroscopy system according to claim 1, wherein the correction device obtains the correction wavelength spectrum from the measurement wavelength spectrum based on an error in a peak position of the measurement wavelength spectrum. A tunable laser;
A wavelength tunable laser driving device that drives the wavelength tunable laser, modulates the wavelength of the laser light emitted from the wavelength tunable laser at a predetermined modulation frequency, and sweeps the modulation center wavelength;
A double frequency component detector for detecting a frequency component twice the modulation frequency of the laser light emitted from the wavelength tunable laser and transmitted through the wavelength filter;
A spectrum measuring device for measuring a wavelength spectrum representing the magnitude of the frequency component twice the modulation center wavelength;
An error information calculation device that calculates curve data obtained by interpolating peaks that periodically appear in the measurement wavelength spectrum measured by the spectrum measurement device, as error information related to the measurement wavelength spectrum;
A storage device for storing the error information calculated by the error information calculation device;
With
The wavelength filter selectively transmits laser light emitted from the wavelength tunable laser at a predetermined wavelength interval.   5. The error information calculation device calculates a ratio between the curve data including the error information and theoretical value curve data in which peaks periodically appearing in a theoretical wavelength spectrum are interpolated. The error information generation system described in 1.   6. The error information generation system according to claim 5, wherein the error information calculation device calculates an error between a peak position of the measured wavelength spectrum with respect to a wavelength and a peak position of the theoretical wavelength spectrum.   The error information generating system according to any one of claims 4 to 6, wherein the wavelength filter is an etalon filter or a Mach-Zehnder interferometer filter. A wavelength tunable laser driving step for modulating the wavelength of laser light emitted from the wavelength tunable laser at a predetermined modulation frequency and sweeping the modulation center wavelength;
A second frequency component detecting step of driving the wavelength tunable laser and detecting a frequency component twice the modulation frequency of the laser light emitted from the wavelength tunable laser and transmitted through the object to be measured;
A spectrum measurement step of measuring a wavelength spectrum representing the magnitude of the frequency component twice the modulation center wavelength;
A correction step for obtaining a correction wavelength spectrum obtained by correcting the measurement wavelength spectrum based on error information relating to the measurement wavelength spectrum measured in the spectrum measurement step, stored in a storage device;
A wavelength modulation spectroscopic method comprising:

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