JP6487253B2 - Optical device and optical device measurement method - Google Patents

Description

  The present invention relates to an optical device and an optical device measurement method.

As infrared sensors that detect long-wavelength infrared rays having minute energy, pyroelectric sensors, thermopile sensors, and bolometer sensors, which are thermal sensors, are generally known. As other sensors, quantum (photovoltaic) infrared sensors such as photodiodes and photoconductors are expected. As a specific example, a quantum infrared sensor having a photodiode structure using a narrow band gap semiconductor material such as InSb, InAlSb, or InAsSb for a light absorption layer can be given.
Specific examples of applications of infrared sensors using these materials include human sensors, non-contact thermometers, non-dispersive infrared (NDIR) gas sensors, and the like. In any of these applications, since the output signal from the light to be detected is weak, a highly sensitive infrared sensor is required.

Infrared sensors using semiconductor materials such as InSb, InAlSb, and InAsSb have a small band gap. Therefore, when operated at a general environmental temperature (for example, around 25 ° C.), the sensitivity of the infrared sensor increases due to ambient temperature fluctuations. fluctuate. Accordingly, the output signal of the infrared sensor fluctuates even when the same level of detection light is incident. Accordingly, there is a demand for an infrared sensor having high sensitivity and excellent temperature characteristics.
However, the sensitivity of a sensor such as a photodiode made of a narrow gap semiconductor is small and easily affected by a temperature change. Therefore, when measuring a weak optical signal, it is difficult to obtain a highly accurate output. Therefore, in many applications, it is necessary to correct the temperature of the output signal from the detected light detected by the infrared sensor.

As the simplest method for performing temperature correction, there is a method in which a thermometer (for example, a thermistor) is provided in the vicinity of the sensor, and the temperature correction of the output signal is performed at a later stage while measuring the ambient temperature.
As another means, there is a method of using temperature information of the internal resistance of the sensor. In this case, as the simplest means, when a switching circuit such as a relay or a switch is provided between the sensor and the input terminal of the first stage amplifier, and when measuring the internal resistance of the sensor from the output signal of the sensor, When a sensor is connected to a resistance measurement circuit and an optical signal is measured from an output signal of the sensor, a method of connecting the output of the sensor to an amplification amplifier at the first stage is also disclosed (for example, see Patent Document 1).

WO2007 / 125873

In the prior art, the resistance measurement means using the switching circuit and the resistance measurement circuit not only increases the number of parts, but also cannot measure the optical signal while measuring the internal resistance of the sensor, There is a problem that a signal body noise ratio (hereinafter also referred to as S / N ratio: Signal to Noise ratio) is lowered.
When temperature information is acquired using a thermometer such as a thermistor, the temperature around the sensor can be measured, but the temperature may be different from the temperature of the sensor core (for example, the PN junction of the photodiode). In addition, since the temperature change timing of the sensor core and the temperature change timing of the thermistor are generally different, temperature correction of the optical signal with high accuracy and high speed is difficult.
The present invention has been made paying attention to the above-described problems, and an object thereof is to provide an optical device and an optical device measurement method capable of further improving the detection accuracy of detected light.

An optical device according to an aspect of the present invention includes a light detection unit that outputs a detection signal corresponding to a signal corresponding to incident light to be detected , an applied bias signal, and a current modulated at a first frequency. A bias unit that applies a signal or a voltage signal as the bias signal to the light detection unit, a first output unit that receives the detection signal and extracts the first frequency component from the detection signal, and the detection signal And a second output unit that extracts a frequency component excluding the first frequency from the detection signal.

An optical device measurement method according to another aspect of the present invention is an optical device measurement method including a light detection unit on which light to be detected is incident, and is a current signal or voltage signal modulated at a first frequency. Is applied to the light detection unit as a bias signal, and the component of the first frequency and the frequency component excluding the first frequency are individually extracted from the detection signal output from the light detection unit, and the extracted first The temperature of the light detection unit is estimated from a component of one frequency, and the frequency component excluding the first frequency is corrected as a signal corresponding to the incident detected light based on the estimated temperature. .

  According to one aspect of the present invention, it is possible to measure a signal corresponding to light to be detected incident on a light detection unit without using a thermometer such as a thermistor, and at the same time, according to the temperature of the light detection unit. Resistance information can be measured. By detecting the temperature of the signal corresponding to the detected light using these measurement results, the detection accuracy of the detected light can be further improved.

It is a block diagram which shows an example of the optical device in 1st embodiment of this invention. It is a block diagram which shows an example of the optical device in 2nd embodiment of this invention. It is a block diagram which shows an example of the optical device in 3rd embodiment of this invention. It is a block diagram which shows an example of the optical device in 4th embodiment of this invention. It is a block diagram which shows an example of the optical device in 5th embodiment of this invention. 1 is a configuration diagram illustrating an example of an optical device in Embodiment 1. FIG. It is a block diagram which shows an example of a lock-in amplifier. In Example 1, it is a characteristic view which shows an example of the measurement result of photocurrent Ip and internal resistance R0 with progress of time. In Example 1, it is a characteristic view which shows an example of the photocurrent Ip1 after temperature correction with progress of time. 6 is a configuration diagram illustrating an example of an optical device in Comparative Example 1. FIG. FIG. 10 is a characteristic diagram illustrating an example of a photocurrent Ip1 after temperature correction with the passage of time in Comparative Example 1. 10 is a configuration diagram showing an example of an optical device in Comparative Example 2. FIG. FIG. 10 is a characteristic diagram illustrating an example of a photocurrent Ip1 after temperature correction with the passage of time in Comparative Example 2.

  As a result of intensive studies, the present inventor has made a light detection unit that outputs a detection signal corresponding to a signal corresponding to incident detection light and a bias signal, and a current signal or voltage signal of a first frequency as the bias signal. A bias unit that outputs to the light detection unit, a detection signal is input, a first output unit that extracts a first frequency component from the detection signal, and a frequency from which the detection signal is input and the first frequency is excluded from the detection signal It has been found that the detection accuracy of the detected light can be further improved by providing the optical device with the second output unit for extracting the component.

  In the following detailed description, numerous specific specific configurations are set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be apparent that other embodiments may be practiced without limitation to such specific specific configurations. Further, the following embodiments do not limit the invention according to the claims, but include all combinations of characteristic configurations described in the embodiments.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a conceptual diagram illustrating a configuration example of an optical device 1 according to the first embodiment.
As shown in FIG. 1, the optical device 1 includes a light detection unit 11, a bias unit 12, a first output unit 13, and a second output unit 14.

The light detection unit 11 receives light to be detected from the outside, and a modulation signal including a current or a voltage is supplied from the bias unit 12 as a bias signal Sbias. The light detection unit 11 receives light to be detected. The sum of the signal corresponding to the signal and the signal corresponding to the bias signal Sbias is output to the first output unit 13 and the second output unit 14 as the detection signal S1.
A quantum type photodetecting element such as a photodiode can be applied to the photodetecting unit 11. By outputting a signal corresponding to the light to be detected by the quantum type photodetecting element, it becomes possible to detect light at a higher speed than a thermal type detecting element such as a bolometer.

In one embodiment of the present invention, the quantum type photodetecting element as the photodetecting portion 11 is formed of a narrow band gap compound semiconductor whose light receiving portion includes at least one of indium In and antimony Sb.
By forming the light receiving part of the quantum type photodetecting element from a narrow band gap compound semiconductor containing at least one of In and Sb, the sensitivity of the photodetecting part 11 in the wavelength band including infrared rays is increased, and the S / N ratio is increased. High optical device 1 can be realized.

The quantum type photodetecting element as the photodetecting unit 11 in an embodiment of the present invention is a photodiode having a PN junction or a PIN junction. When a photodiode is used as the light detection unit 11, the detectable wavelength band is determined mainly by the band gap of the material used for the PN junction or PIN junction. For example, when the light to be detected is long-wave infrared light, a material used for the PN junction or the PIN junction includes a narrow band gap semiconductor containing at least one of In or Sb.
For example, in the case of a photodiode including any one of InSb, InAlSb, and InAsSb in the light receiving portion, light having a wavelength of several μm or more and 12 μm or less can be detected. A photodiode made of such a material can receive wavelengths absorbed by environmental pollutant gases such as CO ₂ , CO, NO, and the like, and thus is suitable for measuring the concentration of these gases.

When the optical device 1 is used as a highly accurate sensor that receives radiation from a human body, InSb or InAsSb is used as a light receiving unit of a photodiode in one embodiment of the present invention.
Photodiodes using these semiconductor materials have low resistance at room temperature, and carriers are excited at room temperature by their band gaps, so not only the sensitivity is low, but the sensitivity is often susceptible to the influence of the temperature environment, In many cases, temperature correction is required to achieve highly accurate measurement. In the case of such a material, the internal resistance varies greatly depending on the temperature. For example, in the case of InSb, the internal resistance varies by about 3% per 1 ° C., so that current output may be desirable. When a photodiode using a semiconductor material is used as the light detection unit 11, a current corresponding to the internal resistance can be obtained by applying a weak voltage. Photodiodes using the above materials exhibit a substantially linear current-voltage characteristic at room temperature near no bias (zero voltage). Setting the value of the modulation voltage as the bias signal Sbias in this linear region is preferable because sensitivity to the light to be detected and heat generation can be suppressed.

The bias unit 12 supplies the modulation signal of the first frequency f1 made of current or voltage to the light detection unit 11 as the bias signal Sbias. In an embodiment of the present invention, the bias unit 12 is a voltage power source or a current power source.
In one embodiment of the present invention, the frequency band of the detected light and the frequency (band) f1 of the bias signal Sbias are different.

  The detection signal S1 from the light detection unit 11 is input to the first output unit 13. The detection signal S1 is a signal that is the sum of a signal corresponding to the detected light incident on the light detection unit 11 and a signal corresponding to the bias signal Sbias supplied from the bias unit 12. The first output unit 13 extracts a component of the first frequency f1 from the input detection signal S1. The bias signal Sbias is a modulation signal having the first frequency f1. Therefore, the first output unit 13 extracts a signal corresponding to the bias signal Sbias by extracting the signal of the component of the first frequency f1. Therefore, resistance information of the light detection unit 11 can be obtained from the bias signal Sbias supplied to the light detection unit 11 and the detection signal S1 of the light detection unit 11.

  The detection signal S <b> 1 from the light detection unit 11 is input to the second output unit 14. The second output unit 14 extracts other frequency components excluding the first frequency f1 or a part of the frequency components from the input detection signal S1. Since the bias signal Sbias is a modulation signal of the first frequency f1, the signal of the frequency component excluding the first frequency f1 in the detection signal S1 is a signal corresponding to the detected light. That is, the 2nd output part 14 extracts the signal according to to-be-detected light by extracting the signal of the frequency component except the 1st frequency f1.

  In the first output unit 13 and the second output unit 14, as means for extracting a predetermined frequency component from the detection signal S1, a band pass filter BPF that allows only a predetermined frequency component of the input detection signal S1 to pass therethrough is used. (Band Pass Filter), a high-pass filter HPF (High Pass Filter) that passes only components higher than a predetermined frequency, or a low-pass filter LPF (Low Pass Filter) that passes only components lower than a predetermined frequency ) Etc. can be used. In addition, the bias signal Sbias from the bias unit 12 is input to the first output unit 13 as a reference signal, and a predetermined frequency component is extracted from the detection signal S1 input to the first output unit 13 based on the reference signal. You may make it do. In this case, as a means for extracting a predetermined frequency component, some demodulation means may be used. For example, a bias signal Sbias is input from the bias unit 12 as a reference signal having the same frequency as the bias signal Sbias, and a lock-in amplifier that selects a signal component having the same frequency and synchronization as the bias signal Sbias is demodulated. It may be used as

  As a specific method for the second output unit 14 to extract the signal of the frequency component excluding the first frequency f1 from the detection signal S1, that is, the signal corresponding to the detected light, as an example, A low-pass filter LPF or the like that selects only components lower than the frequency (band) can be used. For example, when the signal corresponding to the detected light is a signal including a component of 0 [Hz] (DC) to a certain frequency f, the second output unit 14 uses a low-pass filter LPF having a cutoff frequency of f. Can do. In this case, the frequency of the bias signal Sbias needs to be set to a frequency fH higher than f. The first output unit 13 can extract only the frequency fH component from the detection signal S1 and output a signal corresponding to the amplitude. As such an extracting means, a band pass filter BPF having fH as a center transmission frequency can be cited. The amplitude value of the output of the bandpass filter BPF may be inversely proportional to the resistance R0 of the sensor unit in the photodetection unit 11, that is, the quantum photodetection element, for example. Further, the first output unit 13 may output a signal corresponding to the resistance R0 of the quantum photodetecting element.

  In the optical device 1 having such a configuration, the signal component corresponding to the bias signal Sbias applied from the bias unit 12 in the detection signal S1 of the light detection unit 11 varies depending on the resistance of the light detection unit 11. As a specific example of the bias signal Sbias, there is an AC (for example, sine wave) voltage power source having a constant frequency and a constant amplitude. In this case, a detection signal S1 including a current signal corresponding to the amplitude of the bias signal Sbias is output from the light detection unit 11.

  As will be described later, the photodetector 11 formed of a quantum type photodetector composed of a narrow gap semiconductor containing indium or antimony, for example, can be regarded as a resistor in the case of a very small bias. The detection unit 11 outputs a current having a value obtained by dividing the bias signal Sbias composed of the voltage signal applied from the bias unit 12 by its own resistance. Here, the first output unit 13 extracts a predetermined frequency component from the detection signal S1 of the light detection unit 11 based on the frequency of the bias signal Sbias, so that the value of the voltage applied from the bias unit 12, that is, the bias signal is extracted. A current value corresponding to Sbias can be obtained, and the resistance value of the light detection unit 11 can be measured from these values. Further, it is possible to estimate the temperature of the light detection unit 11 based on the obtained resistance value. The estimated temperature information can be used when temperature correction of the photocurrent of the light detection unit 11 is performed.

  The first output unit 13 according to an embodiment of the present invention extracts and outputs a frequency component signal having the frequency of the bias signal Sbias from the bias unit 12 out of the detection signal S1 of the light detection unit 11. That is, a signal corresponding to the bias signal Sbias and corresponding to the internal resistance R0 of the light detection unit 11 is extracted and output as an R0 information signal. Accordingly, in a circuit (not shown) at the subsequent stage of the first output unit 13, based on the R0 information signal corresponding to the internal resistance R0 of the photodetection unit 11 output from the first output unit 13, The temperature can be estimated. For example, when the photodetection unit 11 includes a quantum type photodetection element, since the R0 information signal is a signal corresponding to the internal resistance of the quantum type photodetection element, the temperature of the quantum type photodetection element can be estimated. it can.

In addition, the second output unit 14 according to the embodiment of the present invention is a signal of a frequency component excluding the frequency of the bias signal Sbias in the detection signal S1 of the light detection unit 11, that is, the target input to the light detection unit 11. A signal based on the photocurrent corresponding to the detection light is extracted and output as an Ip information signal.
Since the Ip information signal extracted by the second output unit 14 is a signal representing the intensity of the detected light incident on the light detection unit 11, by using this Ip information signal, human detection or gas concentration can be detected. Arithmetic can be performed.
Further, in one embodiment of the present invention, the second output unit 14 is based on the R0 information signal that is a signal corresponding to the resistance of the quantum photodetecting element as the photodetecting unit 11, and temperature information of the quantum photodetecting element. And the Ip information signal, which is a signal corresponding to the photocurrent generated by the detected light incident on the quantum photodetector, may be corrected based on the temperature information.

  For example, when a circuit for estimating the temperature information of the light detection unit 11 is provided at the subsequent stage of the first output unit 13, the temperature information of the light detection unit 11 estimated by this circuit is input to the second output unit 14, Based on this, the Ip information signal may be corrected, and the R0 information signal from the first output unit 13 is directly input to the second output unit 14. In the second output unit 14, the temperature information of the light detection unit 11 is input. And the Ip information signal may be corrected based on this. Alternatively, a temperature correction circuit for inputting the R0 information signal from the first output unit 13 and the Ip information signal from the second output unit 14 is provided, and in this temperature correction circuit, the temperature information is estimated from the R0 information signal, and the estimation is performed. The Ip information signal may be corrected based on the temperature information, and the corrected Ip information signal may be output as a signal corresponding to the intensity of the detected light that is not affected by the environmental temperature.

By correcting the temperature of the Ip information signal extracted by the second output unit 14, a photodiode made of a narrow gap semiconductor, etc., which is susceptible to the temperature of the environment, especially in the case of long wavelength applications, the optical signal is weak. Even in the case of this quantum sensor, the accuracy of light detection can be improved.
Thus, in the optical device 1 shown in the first embodiment of the present invention, the Ip information signal corresponding to the detected light is simultaneously output while measuring the resistance value of the light detection unit 11. Therefore, the detected light can be measured at high speed and with high accuracy by correcting the Ip information signal, which is the output signal of the detected light, while estimating the temperature based on the R0 information signal representing the resistance of the light detection unit 11. It can be carried out.

  As an application example of such an optical device 1, there is a detection device for weak long-wavelength infrared light. Specifically, a sensor for detecting radiation from a human body, a gas sensor using infrared rays, such as an NDIR type gas sensor, and the like can be given. A general NDIR type gas sensor is used for measuring the concentration of environmental pollutant gas, but in some cases, it is necessary to detect the concentration with an accuracy of ppm or ppb. In such an application example, the absorption wavelength band of the gas to be detected is several μm to several tens μm. The energy of the light source (for example, LED) used for light in this wavelength band is small, and not only the sensitivity of the sensor used (for example, photodiode) is small, but also the intensity of the output light varies as the system temperature varies, Sensor sensitivity varies greatly. On the other hand, in the measurement of the concentration with the accuracy of ppm and ppb, it is necessary to detect a slight fluctuation of light with high accuracy, but a large error is included in the detected density due to a slight temperature fluctuation of the system.

  That is, in order to realize high-precision gas concentration measurement, high-precision temperature measurement is also required. However, according to the optical device 1 in this embodiment, output by light detection while performing temperature measurement with high precision. A signal can be obtained. Therefore, by correcting the output signal of the detected light based on the measured temperature, it is particularly effective as an optical device for measuring gas concentration with high accuracy.

Next, a second embodiment of the present invention will be described.
FIG. 2 is a configuration diagram illustrating an example of the optical device 1 according to the second embodiment of the present invention.
In addition, the same code | symbol is provided to the same part as the optical device 1 in 1st Embodiment, and the detailed description is abbreviate | omitted.
As shown in FIG. 2, the optical device 1 in the second embodiment includes a light detection unit 11, a bias unit 12, a first output unit 13, and a second output unit 14, and further includes a light source unit 15.
As shown in FIG. 2, the bias unit 12 supplies a modulation signal including a current or voltage signal having the first frequency (f1) to the light detection unit 11 as a bias signal Sbias.

The light source unit 15 outputs light having a second frequency f2 different from the first frequency f1 to the light detection unit 11.
The light detection unit 11 outputs the sum of the signal corresponding to the incident detection light and the signal corresponding to the bias signal Sbias supplied from the bias unit 12 as the detection signal S1.
The detection signal S1 from the light detection unit 11 is input to the first output unit 13, and the first output unit 13 extracts the component of the frequency f1 from the detection signal S1 as the R0 information signal. The R0 information signal extracted by the first output unit 13 represents a signal corresponding to the bias signal Sbias output from the light detection unit 11. Therefore, the resistance information of the light detection unit 11 can be obtained by acquiring the R0 information signal from the bias signal Sbias and the detection signal S1.

The detection signal S <b> 1 is input from the light detection unit 11 to the second output unit 14. The second output unit 14 extracts a frequency f2 component from the detection signal S1. The signal of the component of the frequency f2 extracted by the second output unit 14 represents the intensity of the detected light incident on the light detection unit 11, and this signal is used to estimate object detection and gas concentration. It can be carried out.
By modulating the light output from the light source unit 15 to the light detection unit 11 to a desired frequency, a signal that can be easily demodulated by the second output unit 14, such as a pulsed light signal having a constant frequency, is detected signal S1. Can be output as Therefore, the detection accuracy of the light to be detected can be increased, and as a result, the accuracy of measurement of object detection and gas concentration based on the Ip information signal that is the output signal of the second output unit 14 can be improved. .

Next, a third embodiment of the present invention will be described.
The third embodiment uses a quantum type photodetecting element as the photodetecting portion 11 in the optical device in the first embodiment shown in FIG.
FIG. 3 is a configuration diagram illustrating an example of the optical device 1 according to the third embodiment. The same parts as those of the light detection unit 11 in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
In the optical device 1 according to the third embodiment, the bias signal Sbias output from the bias unit 12 is a voltage signal. In the optical device 1 according to the third embodiment, the bias signal Sbias is connected to an inverted input terminal of an operational amplifier 11b described later.

  The light detection unit 11 according to the third embodiment includes a photodiode 11a as a quantum type light detection element, an operational amplifier 11b, and a resistor 11c. The anode of the photodiode 11a is connected to the inverting input terminal of the operational amplifier 11b, and the cathode of the photodiode 11a is connected to the ground potential GND. The resistor 11c is connected between the output terminal and the inverting input terminal of the operational amplifier 11b. In addition, one end of a voltage power source as the bias unit 12 is connected to the inverted input terminal of the operational amplifier 11b, and the other end is connected to the ground potential GND. The output terminal of the operational amplifier 11 b is connected to the first output unit 13 and the second output unit 14.

In the optical device 1 according to the third embodiment, the light to be detected is incident on the photodiode 11a, and the photocurrent generated by the detection light in the photodiode 11a is converted into a voltage by the current-voltage conversion circuit in the photodiode 11a. And output to the first output unit 13 and the second output unit 14 via the operational amplifier 11b.
3 constitutes an amplifier circuit called a transimpedance amplifier that converts a short-circuit current from the photodiode 11a into a voltage.

For this reason, a voltage signal having the same amplitude and frequency as the short-circuit current from the photodiode 11a is applied from the operational amplifier 11b to the photodiode 11a via the resistor 11c.
In this case, a current corresponding to the internal resistance R0 of the photodiode 11a is converted into a voltage signal by the transimpedance amplifier and output from the operational amplifier 11b. As a result, the output from the photodiode 11a can be read as a voltage value.

In addition to the transimpedance amplifier configuration shown in FIG. 3, a high impedance amplifier that amplifies the release voltage of the photodiode 11a may be used instead of the operational amplifier 11b. In this case, the bias signal Sbias applied to the photodiode 11a may be a current power source connected in parallel with the photodiode 11a.
With the above configuration, the detection signal S1 including a voltage signal corresponding to the sum of the signal (Ip information signal) corresponding to the detected light in the photodiode 11a and the bias signal Sbias is output from the light detection unit 11. Therefore, the first output unit 13 and the second output unit 14 can process the detection signal S1 corresponding to the detection light as a voltage signal.

Next, a fourth embodiment of the present invention will be described.
In the fourth embodiment, the second output unit 14 includes a temperature correction unit 14a in the optical device according to the first embodiment shown in FIG.
FIG. 4 is a configuration diagram illustrating an example of the optical device 1 according to the fourth embodiment. The same parts as those of the light detection unit 11 in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
In the optical device 1 according to the fourth embodiment, the temperature correction unit 14 a of the second output unit 14 estimates temperature information of the light detection unit 11 based on a signal (R0 information signal) corresponding to the resistance of the light detection unit 11. Then, based on the estimated temperature information, a signal (Ip information signal) corresponding to the photocurrent generated by the detected light incident on the light detection unit 11 is corrected.

An example of the correction method in the temperature correction unit 14a is shown below.
(Example of temperature correction method)
Since both the Ip information signal and the R0 information signal correlated with the temperature T have temperature dependence, the Ip information signal can be generally expressed by the following equation (1).
Ip = Ri × Φ
= {A _n (R0) ⁿ + A _n−1 (R0) ⁿ⁻¹ +... + A ₁ (R0) + A ₀ } (1)
However, Ri in the equation (1) is the sensitivity of the light detection unit 11 at a constant temperature T, Φ is the intensity of the optical signal incident on the light detection unit 11, and A _{n to} A ₀ are constants.

In the equation (1), Ip1, which is an Ip information signal that is not affected by the temperature T and the R0 information signal, can be expressed by the following equation (2).
Ip1
= Ip / {A _n (R0) ⁿ + A _n−1 (R0) ⁿ⁻¹ +... + A ₁ (R0) + A ₀ }
(2)

Here, the coefficients A _{n to} A ₀ in {A _n (R 0) ⁿ + A _n−1 (R 0) ⁿ⁻¹ +... A ₁ (R 0) + A ₀ } are the temperatures of the light detection unit 11. It can be obtained by measuring the R0 information signal and the Ip information signal while varying within the range.
Therefore, if the sensitivity Ri at the temperature T and the Ip information signal for the optical signal intensity Φ at the same temperature are known in advance, R0 and Ip at an arbitrary temperature are measured at the same time, and the equation (2) is used. Thus, Ip1, which is an Ip information signal corresponding to the detected light having the intensity Φ of the optical signal, converted (corrected) into an Ip information signal at a predetermined temperature T can be obtained. In other words, from the equation (1), the intensity Φ of the detected light can be obtained from Ip and resistance R0 at an arbitrary temperature.
Thus, even at a temperature other than the predetermined temperature T, by measuring R0 and Ip at that time and performing temperature correction, Ip at the temperature T and the intensity Φ of the detected light (from Equation (1), Φ = Ip1 / Ri) can be obtained, and the accuracy of light detection can be improved even in an environment where the ambient temperature change is large.

Next, a fifth embodiment of the present invention will be described.
In the fifth embodiment, the second output unit 14 includes a temperature correction unit 14a in the optical device according to the third embodiment shown in FIG.
FIG. 5 is a configuration diagram illustrating an example of the optical device 1 according to the fifth embodiment. The same parts as those of the light detection unit 11 in the third embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
In the optical device 1 according to the fifth embodiment, the temperature correction unit 14a of the second output unit 14 includes the photodiode 11a based on a signal (R0 information signal) corresponding to the resistance of the photodiode 11a as the quantum detection element. Temperature information is estimated, and based on the estimated temperature information, a signal (Ip information signal) corresponding to the photocurrent generated by the detected light incident on the photodiode 11a is corrected.

As the correction method, the temperature correction method used in the fourth embodiment can be used.
As described above, by performing temperature correction of a signal (Ip information signal) corresponding to the photocurrent, a sensor having a low sensitivity and being easily affected by the temperature environment, such as a sensor such as a photodiode made of a narrow gap semiconductor. Thus, even when a weak optical signal is measured, the accuracy of light detection can be increased.

Hereinafter, examples of the optical device according to one embodiment of the present invention will be described. It goes without saying that the present invention is not limited to the following examples and can be modified without departing from the scope of the invention.
<Example 1>
FIG. 6 is a configuration diagram illustrating an example of the optical device 1 according to the first embodiment.
As shown in FIG. 6, a photodiode 11a is used as the light detection unit 11, and an operational amplifier 11b and a resistor 11c are provided to constitute an amplifier circuit called a transimpedance amplifier. A black body furnace was used as the light source unit 15.

An InSb PIN photodiode was used as the photodiode 11a. As a specific configuration of the photodiode 11a, 400 PIN photodiodes were formed on a 0.7 mm square gallium arsenide GaAs substrate and connected in series with each other. The incident surface of the light to be detected was the surface opposite to the surface on which the photodiode of the substrate was formed. In order to increase the sensitivity at room temperature, a barrier layer for suppressing electron diffusion was inserted between the P layer and the I layer of the photodiode 11a. In this case, the resistance in the vicinity of no bias is about 150 kΩ at room temperature.
Here, a high S / N ratio can be realized by connecting a large number of photodiodes in series. The frequency of the detected light is 90 Hz. The frequency of the bias signal Sbias output from the bias unit 12 was set to 390 Hz and the amplitude was set to 5 mV.

  The first output unit 13 includes a lock-in amplifier (the lock-in amplifier 1 in FIG. 6) that extracts a signal component of 390 Hz, which is the same as the frequency of the bias signal Sbias, as a reference signal from the detection signal S1 from the light detection unit 11. Using. As a result, an output signal corresponding to the internal resistance of the photodiode 11a of the light detection unit 11, that is, an R0 information signal is obtained from the first output unit 13. The second output unit 14 includes a lock-in amplifier (the lock-in amplifier 2 in FIG. 6) that extracts a signal component of 90 Hz, which is the same as the frequency of the detected light, from the detection signal S1 from the light detection unit 11 as a reference signal. Using. Thereby, the signal component according to the to-be-detected light which injected into the photodiode 11a from the 2nd output part 14 is obtained.

  As described above, the optical device 1 according to the first embodiment can simultaneously output the detection signal corresponding to the detected light (for example, radiation from the black body furnace) and the detection signal corresponding to the environmental temperature of the photodiode 11a. . Therefore, even if the sensor 11 is heated by radiation from the light source unit 15 or other disturbance heat source, the resistance R0 near the zero bias of the photodiode 11a varies due to the temperature change. Then, by correcting the detection signal based on the detected light, it is possible to easily correct the detection error due to the temperature characteristic included in the detection signal based on the detected light.

<Operation principle of lock-in amplifier>
Here, the operation principle of the lock-in amplifier will be described.
FIG. 7 shows a basic circuit of the lock-in amplifier.
As shown in FIG. 7, the lock-in amplifier synchronizes based on the preamplifier 101 that amplifies the input signal to a size suitable for subsequent processing, the input signal Vin amplified by the preamplifier 101, and the reference signal Vref. A mixer 102 that converts the frequency by performing detection, a low-pass filter LPF 103 that extracts only a predetermined frequency component from the frequency-converted output signal Vpsd output from the mixer 102, and outputs it as an output of the lock-in amplifier, and a reference signal , The trigger generation circuit 104 that outputs a signal having the same frequency and constant amplitude as the reference signal (reference signal), and the phase difference between the signal output from the trigger generation circuit 104 and the input signal Vin is Adjust the phase so that it becomes zero, and the reference signal Vre after the phase adjustment The includes a phase adjustment circuit 105 to be output to the mixer 102.

Here, it is assumed that the input signal to the lock-in amplifier is a cosine wave as shown by the following equation (3).
Vin = Acos (2πft) (3)
However, A in (3) Formula is an amplitude, t is time, and f is a frequency.
Since the reference signal as the reference signal has the same frequency as the input signal, it can be expressed by the following equation (4).
Vref = Bcos (2πft + θ) (4)
However, B in the equation (4) indicates the amplitude. Θ represents the phase difference between the input signal Vin and the reference signal Vref, and the phase difference θ is adjusted by the phase adjustment circuit 105 provided in the lock-in amplifier.

The mixer 102 receives the input signal Vin amplified by the preamplifier 101 and the reference signal Vref after the phase adjustment is performed by the phase adjustment circuit 105. The output signal Vpsd of the mixer 102 can be expressed by the following equation (5).
Vpsd = Vin × Vref
= (1/2) × ABcos (θ) + (1/2) ABcos (4πft + θ) (5)
Here, if the low-pass filter (LPF) 103 removes components excluding the f component and makes the amplitude B constant, the output signal of the lock-in amplifier is proportional to the amplitude A and cos (θ). It becomes a DC signal.
That is, the frequency signal excluding the f component is removed, and only the f component signal is extracted and output. Further, the lower the cutoff frequency of the low-pass filter 103, the higher the S / N ratio can be obtained.

<Demonstration of temperature correction>
In Example 1, temperature correction was demonstrated using the optical device 1 shown in FIG.
First, for a certain optical signal when the temperature T of the photodiode 11a is 25 ° C., the output current of the photodiode 11a as the light detection unit 11 was measured. Here, an optical signal when a black body furnace having a temperature of 227 ° C. is used as the light source unit 15, the aperture diameter φ is 22.2 mm, the distance from the black body furnace to the photodiode 11a is 100 mm, and light is chopped at a frequency of 90 Hz. Was output. When this optical signal was measured by the photodiode 11a, the output signal (Ip information signal) of the photodiode 11a was an effective value of 5.8 nArms. This effective value 5.8 nArms was obtained by calculating the ratio of the output of the operational amplifier 11b to the resistance value R1 of the resistor 11c.
A sine wave voltage power source having a frequency of 390 Hz and an amplitude of 5 mVrms was used as the bias unit 12.

Next, the R0 information signal and the Ip information signal were measured while changing the temperature of the photodiode 11a in the range of 25 ° C. or more and 50 ° C. or less. Thereby, the correlation as shown in the following equation (6) was obtained between the R0 information signal and the Ip information signal.
Ip
= −5.55 × 10 ⁻³⁹ R0 ⁶ + 3.19 × 10 ⁻³³ R0 ⁵
−7.46 × 10 ⁻²⁸ R0 ⁴ + 9.13 × 10 ⁻²³ R0 ³
−6.24 × 10 ⁻¹⁸ R0 ² + 2.32 × 10 ¹³ R0
+ 1.98 × 10 ⁻⁹ [Arms] (6)

When the ambient temperature of the photodiode 11a changes, the current at the temperature of 25 ° C. can be obtained from the following equation (7) based on the equation (2).
Ip1
= 5.8 × 10 ⁻⁹ /(−5.55×10 ⁻³⁹ R0 ⁶ + 3.19 × 10 ⁻³³ R0 ⁵
−7.46 × 10 ⁻²⁸ R0 ⁴ + 9.13 × 10 ⁻²³ R0 ³
−6.24 × 10 ⁻¹⁸ R0 ² + 2.32 × 10 ¹³ R0
+ 1.98 × 10 ⁻⁹ ) [Arms] (7)
Further, the intensity of the detected light at an arbitrary temperature can be obtained from the relationship of Φ = Ip1 / Ri from the equation (1).
The calculation processing of the output of the lock-in amplifier and the temperature correction thereof were performed by a computer.

<Effect of temperature correction>
In order to verify the effect of temperature correction, hot air was applied to the photodiode 11a so that the temperature of the photodiode 11a was heated to around 70 ° C. FIG. 8 shows the relationship between the Ip information signal, R0 information signal, and time at that time. In FIG. 8, the horizontal axis represents elapsed time, and the vertical axis represents photocurrent Ip (Ip information signal) and internal resistance R0 (R0 information signal).

Here, using the equation (7), a current whose temperature was corrected to be equal to the Ip information signal when the temperature of the photodiode 11a was 25 ° C. was obtained.
The result is shown in FIG. The horizontal axis represents elapsed time, and the vertical axis represents photocurrent Ip1 (Ip information signal) after temperature correction. As can be seen from FIG. 9, even in an environment where the temperature of the photodiode 11a changes due to disturbance such as hot air, the influence of the temperature change is largely canceled, and a stable photocurrent value is obtained. I understand.

<Comparative Example 1>
As shown in FIG. 10 as Comparative Example 1, a photodiode 11a is used as the light detection unit 11, and the output current of the photodiode 11a is input to the lock-in amplifier 2 as the second output unit 14, and is adjacent to the photodiode 11a. The thermistor (platinum resistor) 21 was provided in the sensor, the resistance of the thermistor 21 was measured by the resistance measuring device 22, and the measured resistance value was used as temperature information. The other conditions were the same as in Example 1.

  As in the demonstration experiment of the first embodiment, the Ip information signal output from the photodiode 11a based on the resistance value as the temperature information measured by the resistance measuring device 22 while applying hot air to the photodiode 11a and the thermistor 21. The temperature was corrected. The result is shown in FIG. In FIG. 11, the horizontal axis represents elapsed time, and the vertical axis represents photocurrent Ip1 (Ip information signal) after temperature correction.

  When the temperature of the photodiode 11a is rapidly changed (around the elapsed time of 100 s) due to the influence of hot air applied from the outside, an output fluctuation of about 28% occurs as shown in FIG. This is because the temperature follow-up property of the thermistor 21 is poor, and the temperature information of the photodiode 11a used for the temperature correction is deviated from the accurate temperature, and the accuracy of the temperature correction may be insufficient. Possible cause.

<Comparative example 2>
As Comparative Example 2, an experiment was performed using a circuit as shown in FIG.
That is, as shown in FIG. 12, a photodiode 11 a is used as the light detection unit 11, and both ends of the photodiode 11 a are connected to the lock-in amplifier 2 as the second output unit 14 via the switch SW, and the resistance measurement device 22. I switched to either one of them to connect.
Using the switch SW, a period in which both ends of the photodiode 11a are connected to the resistance measuring device 22 is TR, and a period in which the photodiode 11a is connected to the second output unit 14 including the lock-in amplifier 2 for measuring the Ip information signal is TI. While alternately switching the connection destinations at both ends of the diode 11a, measurement of the Ip information signal by the photodiode 11a and measurement of R0 based on the resistance value of the photodiode 11a were performed. In this measurement, TR was set to 450 ms and TI was set to 150 ms.

Then, as in the demonstration experiment in Example 1, temperature correction was performed on the Ip information signal output from the photodiode 11a based on R0 measured by the resistance measuring device 22 while supplying hot air. The result is shown in FIG.
In FIG. 13, the horizontal axis represents elapsed time, and the vertical axis represents photocurrent Ip1 (Ip information signal) after temperature correction.

  As shown in FIG. 13, the experimental result in Comparative Example 2 shows that the variation in the photocurrent Ip after temperature correction is small when the temperature changes compared to the experimental result in Comparative Example 1 shown in FIG. 9 shows that the S / N ratio is about 1/2 compared to the experimental result in Example 1 shown in FIG. Further, the photocurrent Ip1 after temperature correction when the temperature of the photodiode 11a is rapidly changed (around 100 s) due to the influence of hot air applied from outside has a larger fluctuation than the experimental result shown in FIG. This is because the switch SW is switched and the Ip information signal and the resistance R0 measurement by the resistance measuring device 22 are alternately performed, and therefore there is a period during which the temperature of the photodiode 11a cannot be measured accurately. This is probably because the accuracy of temperature correction has deteriorated as a result of performing temperature correction using.

(Summary)
As described above, the optical device 1 according to the embodiment of the present invention can simultaneously output the Ip information signal corresponding to the detected light and the R0 information signal corresponding to the resistance of the light detection unit 11. Therefore, it is possible to obtain an Ip information signal having a high S / N ratio and based on a photocurrent according to the detected light. Further, by correcting the temperature of the Ip information signal based on the R0 information signal that is output simultaneously with the Ip information signal corresponding to the detected light and that changes according to the resistance of the light detection unit 11, A highly accurate Ip information signal can be obtained, that is, the detection accuracy of the detection light by the optical device 1 and the intensity measurement of the detection light can be improved.
In addition, since resistance information corresponding to the temperature of the light detection unit 11 can be obtained without using a thermometer such as a thermistor, an increase in the number of components is suppressed, and the optical device 1 is reduced in size and thickness. Can do.

  In addition, when using a photo diode as the temperature of the core of the light detection unit 11 instead of the temperature near the light detection unit 11, that is, when the photo detection unit 11 is used, resistance information corresponding to the temperature of the PN junction portion of the photo diode is obtained. Can be obtained. When a thermometer such as a thermistor is used, there is a difference in the position of the core of the light detection unit 11, that is, the PN junction portion of the photodiode, and the arrangement position of the thermometer. Further, since a deviation occurs between the temperature change of the PN junction portion and, for example, the temperature change of the thermistor, it is difficult to obtain the instantaneous temperature of the PN junction portion with high accuracy. However, in one aspect of the present invention, since resistance information is acquired from the detection signal S1 of the light detection unit 11, resistance information that reflects the temperature change of the PN junction portion instantaneously with high accuracy can be obtained. Therefore, the temperature can be estimated with high accuracy by estimating the temperature based on the resistance information.

Therefore, the detection accuracy of the detected light can be further improved by correcting the signal (Ip information signal) corresponding to the detected light based on the temperature of the light detection unit 11 obtained in this way.
Although the embodiments of the present invention have been described so far, it is needless to say that the present invention is not limited to the above-described embodiments, and may be implemented in various forms within the scope of the technical idea.

  In addition, the scope of the present invention is not limited to the illustrated and described exemplary embodiments, and includes all embodiments that provide the same effects as those intended by the present invention. Further, the scope of the invention is not limited to the combinations of features of the invention defined by the claims, but may be defined by any desired combination of specific features among all the disclosed features. .

  The optical device of the present invention can be applied to an NDIR-type gas sensor or the like that requires high-precision measurement for weak infrared rays.

DESCRIPTION OF SYMBOLS 1 Optical device 10 Semiconductor light emitting element 11 Photodetection part 11a Photodiode 11b Operational amplifier 11c Resistor 13 1st output part 14 2nd output part 14a Temperature correction part 15 Light source part 21 Thermistor 22 Resistance measuring apparatus

Claims (9)

A signal corresponding to the detected light incident, and a bias signal applied, a light detection unit that outputs a detection signal according to,
A bias unit that applies a current signal or a voltage signal modulated at a first frequency to the photodetection unit as the bias signal;
A first output unit that receives the detection signal and extracts a component of the first frequency from the detection signal;
An optical device comprising: a second output unit that receives the detection signal and extracts a frequency component excluding the first frequency from the detection signal.   The temperature of the light detection unit is estimated based on the first frequency component extracted by the first output unit, and the frequency component excluding the first frequency extracted by the second output unit based on the estimated temperature is obtained. The optical device according to claim 1, further comprising a temperature correction unit for correcting. The optical device according to claim 1 , wherein the light detection unit includes a quantum-type light detection element. 4. The optical device according to claim 3 , wherein the light receiving portion of the quantum type photodetecting element is formed of a narrow band gap compound semiconductor containing any one of indium and antimony. The light detection unit further includes an operational amplifier and a resistor,
The resistor is connected between an output terminal and an inverting input terminal of the operational amplifier, and the quantum photodetecting element is connected between an inverting input terminal of the operational amplifier and a ground potential, and the output of the bias unit There optical device according to claim 3 or claim 4 is connected to the non-inverting input terminal of said operational amplifier. The optical device according to any one of claims 3 to 5 , wherein the first output unit extracts a signal corresponding to a resistance of the quantum photodetecting element as the component of the first frequency. A light source unit that outputs light having a second frequency different from the first frequency, which is the detected light;
The second output section, said as a component of a second frequency, any one of the claims 6 claim 3 for extracting a signal corresponding to the photocurrent generated by the light to be detected is incident on the quantum photodetection element The optical device according to Item. Optical device according to any one of claims 7 wherein the quantum detection element of claims 3 is a photodiode. A method of measuring an optical device including a light detection unit on which light to be detected is incident,
Applying a current signal or voltage signal modulated at a first frequency to the photodetection unit as a bias signal;
From the detection signal output from the light detection unit, the first frequency component and the frequency component excluding the first frequency are individually extracted,
Estimating the temperature of the light detection unit from the extracted component of the first frequency,
A method for measuring an optical device that corrects a frequency component excluding the first frequency as a signal corresponding to the incident detected light based on the estimated temperature.

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