Measuring device, measuring method, and program

Abstract

This enables more precise measurement of the optical spectrum of pulsed light. [Solution] A measuring device 10 comprising a spectrometer 11 that extracts a specific wavelength component from incident light, a photodetector 13 that outputs a signal corresponding to the intensity of the extracted wavelength component, and a processor 16, wherein the processor 16 acquires a first signal output from the photodetector in a light-shielded state and a second signal output from the photodetector in a light-unshielded state according to the intensity of the incident light for each of a plurality of wavelength sections that divide the wavelength range of the object to be measured, and outputs the difference between the second signal and the first signal as the optical spectrum of the wavelength section.

Description

Technical Field

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[0001] The present disclosure relates to a measuring device, a measuring method, and a program.

Background Art

[0002] An optical spectrum analyzer (OSA) is a device that measures the wavelength spectrum of incident light within a certain wavelength range. Patent Document 1 describes a spectrum analyzer that measures the spectrum of incident light chopped by a chopper.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In this way, the measuring device divides the wavelength range of the object to be measured into multiple wavelength intervals, measures the incident light in both a light-shielded and light-unshielded state for each wavelength interval, and outputs the difference in the signals involved in the measurement as the optical spectrum of the wavelength interval. Therefore, the measuring device can suppress the effects of drift in the measured value caused by dark current and measure the optical spectrum of pulsed light with higher accuracy.

[0008] In one embodiment, (2) In the measuring device of (1), The length of each of the plurality of wavelength intervals may be determined according to the magnitude of the variation in the measured value caused by the dark current in the photodetector while measuring the optical spectrum in that wavelength interval.

[0009] Thus, since the length of each wavelength interval is determined according to the magnitude of the fluctuation in the measured value caused by the dark current in the photodetector, the measuring device can effectively reduce the effect of drift in the measured value caused by the dark current.

[0010] In one embodiment, (3) In the measuring device of (1) or (2), The processor may divide the wavelength range of the object to be measured by defining the interval set by the operator via the control unit as the wavelength interval.

[0011] Thus, the measuring device divides the wavelength range of the object to be measured into wavelength intervals based on settings received from the operator. Therefore, the operator can set a desired wavelength interval according to the characteristics of the photodetector and have the optical spectrum measured.

[0012] In one embodiment, (4) In any of the measuring devices described in (1) to (3), The aforementioned processor, The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light may be averaged for each of the time-averaging intervals to obtain the first signal, and the signal output from the photodetector while not shielded from light may be averaged for each of the time-averaging intervals to obtain the second signal.

[0013] In this way, the measuring device accepts the setting of the time-averaging interval from the operator and acquires the optical spectrum for each wavelength interval based on the signal averaged for each time-averaging interval. Therefore, the operator can have the optical spectrum measured at the desired sampling rate.

[0014] In one embodiment, (5) In any of the measuring devices described in (1) to (4), The processor may, for each of the plurality of wavelength intervals, acquire the first signal output from the photodetector while it is shielded from light, and then acquire the second signal output from the photodetector while it is not shielded from light.

[0015] Thus, the measuring device performs measurements in a light-shielded state first, followed by measurements in an unshielded state. Therefore, the temperature of the photodetector rises when light enters it, and the drift caused by the dark current is minimized.

[0016] In one embodiment, (6) In any of the measuring devices described in (1) to (5), The photodetector is further equipped with an optical chopper capable of blocking light. The aforementioned processor, For each of the plurality of wavelength intervals, a signal output from the photodetector in a state shielded by the optical chopper may be acquired as the first signal, and a signal output from the photodetector in a state not shielded by the optical chopper may be acquired as the second signal.

[0017] In this way, the measuring device can easily switch between the shielded state and the non-shielded state by the optical chopper.

[0018] A measurement method according to some embodiments is (7) a spectroscope that extracts a specific wavelength component from incident light, a photodetector that outputs a signal corresponding to the intensity of the extracted wavelength component, a processor, and a measurement method of a measuring device including: where the processor for each of a plurality of wavelength intervals that divide the wavelength range of the measurement target, acquires a first signal output from the photodetector in a shielded state and a second signal output from the photodetector according to the intensity of the incident light in a non-shielded state, and outputs the difference between the second signal and the first signal as the optical spectrum of the wavelength interval. including.

[0019] In this way, the measurement method divides the wavelength range of the measurement target into a plurality of wavelength intervals, measures the incident light in the shielded state and the non-shielded state for each wavelength interval, and outputs the difference of the signals related to the measurement as the optical spectrum of the wavelength interval. Therefore, according to the measurement method, the influence of the drift of the measurement value caused by the dark current can be suppressed, and the optical spectrum of the pulsed light can be measured with higher accuracy.

[0020] In one embodiment (8) In the measurement method of (7), the length of each of the plurality of wavelength intervals may be determined according to the magnitude of the variation in the measurement value caused by the dark current in the photodetector during the measurement of the optical spectrum in the wavelength interval.

[0021] Thus, since the length of each wavelength interval is determined according to the magnitude of the fluctuation in the measured value caused by the dark current in the photodetector, the measurement method can effectively reduce the effect of drift in the measured value caused by the dark current.

[0022] In one embodiment, In the measurement method of (9), (7), or (8), The processor may divide the wavelength range of the object to be measured by defining the interval set by the operator via the control unit as the wavelength interval.

[0023] Thus, the measurement method divides the wavelength range of the target to be measured by setting intervals from the operator as wavelength intervals. Therefore, the operator can set the desired wavelength interval according to the characteristics of the photodetector and have the optical spectrum measured.

[0024] In one embodiment, In any of the measurement methods (10)(7) to (9), The aforementioned processor, The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light may be averaged for each of the time-averaging intervals to obtain the first signal, and the signal output from the photodetector while not shielded from light may be averaged for each of the time-averaging intervals to obtain the second signal.

[0025] Thus, the measurement method accepts the operator's setting of time-averaging intervals and acquires optical spectra for each wavelength interval based on the signal averaged for each time-averaging interval. Therefore, the operator can have the optical spectrum measured at the desired sampling rate.

[0026] In one embodiment, In any of the measurement methods (11)(7) to (10), The processor may, for each of the plurality of wavelength intervals, acquire the first signal output from the photodetector while it is shielded from light, and then acquire the second signal output from the photodetector while it is not shielded from light.

[0027] Thus, the measurement method involves performing measurements in a light-shielded state first, followed by measurements in an unshielded state. Therefore, it is possible to minimize the effects of drift caused by dark current, which results from the temperature of the photodetector rising when light is incident on it.

[0028] In one embodiment, In any of the measurement methods (12)(7) to (11), The measuring device further includes an optical chopper capable of blocking light incident on the photodetector. The aforementioned processor, For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded by the optical chopper may be acquired as the first signal, and the signal output from the photodetector while not shielded by the optical chopper may be acquired as the second signal.

[0029] Thus, the measurement method allows for easy switching between a light-shielded state and an unshielded state using an optical chopper.

[0030] In some embodiments, the program is: (13) A spectrometer that extracts specific wavelength components from incident light, A photodetector that outputs a signal corresponding to the intensity of the extracted wavelength component, Processor and A program for controlling a measuring device equipped with the following features: A procedure for obtaining, for each of a plurality of wavelength intervals that divide the wavelength range to be measured, a first signal output from the photodetector while it is shielded from light, and a second signal output from the photodetector according to the intensity of the incident light while it is not shielded from light, and outputting the difference between the second signal and the first signal as the optical spectrum of that wavelength interval. The measuring device is controlled to perform the following action.

[0031] In this way, the program divides the wavelength range of the object to be measured into multiple wavelength intervals, measures the incident light in both shielded and unshielded states for each wavelength interval, and outputs the difference in the measured signals as the optical spectrum of the wavelength interval. Therefore, according to the program, the effect of drift in the measured value caused by dark current can be suppressed, and the optical spectrum of pulsed light can be measured with higher accuracy.

[0032] In one embodiment, In the program of (14)(13), The length of each of the plurality of wavelength intervals may be determined according to the magnitude of the variation in the measured value caused by the dark current in the photodetector while measuring the optical spectrum in that wavelength interval.

[0033] Thus, since the length of each wavelength interval is determined according to the magnitude of the variation in the measured value caused by the dark current in the photodetector, the program can effectively reduce the effect of drift in the measured value caused by the dark current.

[0034] In one embodiment, In the program of (15), (13), or (14), The wavelength range of the measurement target may be divided into wavelength intervals, where the interval set by the operator via the control unit is defined as the wavelength interval.

[0035] In this way, the program divides the wavelength range of the object to be measured into wavelength intervals based on the intervals set by the operator. Therefore, the operator can set the desired wavelength interval according to the characteristics of the photodetector and have the optical spectrum measured.

[0036] In one embodiment, In any of the programs from (16)(13) to (15), The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light may be averaged for each of the time-averaging intervals to obtain the first signal, and the signal output from the photodetector while not shielded from light may be averaged for each of the time-averaging intervals to obtain the second signal.

[0037] In this way, the program accepts the setting of time-averaging intervals from the operator and acquires optical spectra for each wavelength interval based on the signal averaged for each time-averaging interval. Therefore, the operator can have the optical spectrum measured at the desired sampling rate.

[0038] In one embodiment, In any of the programs (17)(13) through (16), For each of the plurality of wavelength intervals, the first signal output from the photodetector may be acquired while the light is blocked, and then the second signal output from the photodetector may be acquired while the light is not blocked.

[0039] Thus, the program performs measurements in a light-shielded state first, followed by measurements in an unshielded state. Therefore, the temperature of the photodetector rises when light enters it, and the drift caused by the dark current is minimized.

[0040] In one embodiment, In any of the programs (18)(13) through (17), The measuring device further comprises an optical chopper capable of blocking light incident on the photodetector, For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded by the optical chopper may be acquired as the first signal, and the signal output from the photodetector while not shielded by the optical chopper may be acquired as the second signal.

[0041] In this way, the program can easily switch between a light-shielded state and an unshielded state using the optical chopper. [Effects of the Invention]

[0042] According to one embodiment of this disclosure, it becomes possible to measure the optical spectrum of pulsed light with higher precision. [Brief explanation of the drawing]

[0043] [Figure 1] This block diagram shows an example configuration of a measuring device according to one embodiment. [Figure 2] This figure schematically shows an example of the configuration of the spectrometer shown in Figure 1. [Figure 3] This flowchart shows an example of operation of a measuring device according to one embodiment. [Figure 4] This is a schematic diagram illustrating an example of operation of a measuring device according to one embodiment. [Figure 5] This is a schematic diagram illustrating an example of operation of a measuring device according to one embodiment. [Figure 6] This figure shows examples of measurement results for the optical spectrum of pulsed light, categorized by measurement method. [Modes for carrying out the invention]

[0044] <Embodiment> Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, parts having the same configuration or function are denoted by the same reference numerals. In the description of this embodiment, redundant descriptions of the same parts may be omitted or simplified as appropriate.

[0045] Figure 1 is a block diagram showing an example configuration of a measuring device 10 according to one embodiment. The measuring device 10 measures the optical spectrum, which is the distribution of intensity for each wavelength of incident light. The measuring device 10 may be provided as an OSA. In this embodiment, the measuring device 10 measures the optical spectrum of pulsed light output from a pulsed laser. The measuring device 10 comprises a spectrometer 11, an optical chopper 12, a photodetector 13, an amplifier 14, an A / D (Analog-to-Digital) converter 15, a processor 16, a memory 17, a display unit 18, and an operation unit 19.

[0046] The spectrometer 11 extracts desired frequency components from the incident light. The spectrometer 11 is composed of, for example, a monochromator (Figure 2), which will be described later, but it may be realized by any instrument that has the function of a spectrometer.

[0047] The optical chopper 12 modulates incident light using a rotating light-shielding plate and a slit. The optical chopper 12 can block incident light by positioning the light-shielding plate in the optical path, or transmit incident light by positioning the slit in the optical path. The measuring device 10 can arbitrarily change the period during which incident light can reach the photodetector 13 by controlling the rotation speed of the optical chopper 12.

[0048] The photodetector 13 outputs an electrical signal according to the intensity of the incident light. The photodetector 13 is implemented using a photoelectric conversion element such as a photodiode. The photodetector 13 is selected to be an element capable of detecting light of the wavelength to be measured.

[0049] As will be described later with reference to Figure 2, in this embodiment, the optical chopper 12 and the photodetector 13 are provided inside the spectrometer 11, but the configuration is not limited to this. For example, the optical chopper 12 may be provided at any position along the optical path from the incident light to the photodetector 13. Alternatively, for example, the optical chopper 12 may be provided before the spectrometer 11.

[0050] The amplifier 14 amplifies the electrical signal output by the photodetector 13 to a predetermined range. The amplifier 14 outputs the amplified electrical signal to the A / D converter 15.

[0051] The A / D converter 15 converts the analog electrical signal amplified by the amplifier 14 into a digital signal. The A / D converter 15 outputs the converted digital electrical signal to the processor 16.

[0052] The processor 16 is comprised of one or more processors or dedicated circuits. In this embodiment, the processor 16 is a general-purpose processor or a dedicated processor specialized for a specific process, but is not limited to these. The dedicated circuit may include, for example, an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The processor 16 is communicated with each component constituting the measuring device 10 and controls the operation of the entire measuring device 10.

[0053] In this embodiment, the processor 16 controls a series of processes, from measuring incident light using the spectrometer 11, optical chopper 12, and photodetector 13, to acquiring the optical spectrum of the incident light based on the measured values. However, the configuration is not limited to this. For example, the process of acquiring the optical spectrum of the incident light based on the measured values ​​may be controlled by a processor or dedicated circuit not built into the measuring device 10, acting as the processor 16.

[0054] Memory 17 stores any information used for the operation of the measuring device 10. Memory 17 includes any storage module such as an SSD (Solid State Drive), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0055] The display unit 18 includes one or more output interfaces for outputting information to the operator and notifying the operator. The display unit 18 may be, for example, a liquid crystal panel display or an organic EL (Electro-Luminescence) display.

[0056] The operation unit 19 includes one or more input interfaces that receive input operations from the operator and acquire input information based on the operator's operations. For example, the operation unit 19 may be, but is not limited to, physical keys, capacitive keys, or a touchscreen integrated with the display of the display unit 18. At least one of the display unit 18 and the operation unit 19 may be configured together with the measuring device 10 or provided as a separate unit.

[0057] The functions of the measuring device 10 can be realized by executing a computer program (program) according to this embodiment on a processor included in the processor 16. In other words, the functions of the measuring device 10 can be realized by software. The computer program causes the computer to execute the processing of steps included in the operation of the measuring device 10, thereby realizing the functions corresponding to the processing of each step on the computer. In other words, the computer program is a program that causes the computer to function as the measuring device 10 according to this embodiment.

[0058] Figure 2 is a schematic diagram showing an example of the configuration of the spectrometer 11 shown in Figure 1. Figure 2 shows an example of a spectrometer 11 configured as a monochromator. The spectrometer 11 comprises a collimating mirror 112, a diffraction grating 113, a focusing mirror 114, an exit slit 115, an optical chopper 12, and a photodetector 13. In the example in Figure 2, incident light enters the spectrometer 11 via an optical fiber 111.

[0059] The collimating mirror 112 and the focusing mirror 114 are parabolic mirrors.

[0060] The diffraction grating 113 is constructed by cutting very fine grooves into a mirror. The diffraction grating 113 is an optical element that extracts light of a specific wavelength from light containing a mixture of various wavelengths. When light containing a mixture of various wavelengths is incident on the diffraction grating 113, diffraction occurs at predetermined angles depending on each wavelength. Therefore, the wavelength can be identified based on the diffraction angle from the diffraction grating 113.

[0061] The optical chopper 12 switches between blocking and transmitting (not blocking light) according to the control of the processor 16. The exit slit 115 adjusts the wavelength resolution and light intensity of the spectrometer 11. The photodetector 13 converts the incident light into electrical signals and outputs an electrical signal corresponding to the intensity of the incident light.

[0062] In the spectrometer 11, light incident from the optical fiber 111 is made into parallel rays by the collimating mirror 112 and guided to the diffraction grating 113. The light diffracted by the diffraction grating 113 is then imaged in the dispersion direction around the exit slit 115 by the focusing mirror 114. Therefore, only the light of wavelengths focused on the exit slit 115 in the spectrum is detected by the photodetector 13. The wavelength of the detected light, that is, the center wavelength of the optical bandpass filter, can be changed by rotating the diffraction grating 113. Therefore, the spectrometer 11 can measure the spectrum of the incident light by obtaining the relationship between the angle (tilt) of the diffraction grating 113 corresponding to the wavelength of the incident light and the intensity of the light detected by the photodetector 13.

[0063] In the example shown in Figure 2, an optical chopper 12 is provided in the optical path between the focusing mirror 114 and the exit slit 115. The optical chopper 12 switches between blocking or transmitting incident light based on the control of the processor 16.

[0064] Generally, photoelectric conversion elements such as photodiodes are known to output a current called dark current even when no light is incident on them. As a result, as will be described later, a phenomenon called drift occurs in which the measured value changes little by little over time, and in wavelength ranges where the intensity of incident light is low, it may be difficult to detect light waves with high sensitivity (Graph 52 in Figure 6).

[0065] Regarding this, it is known that the effect of drift caused by dark current can be suppressed by using an optical chopper to measure the electrical signal output from the photoelectric conversion element in both the shielded and unshielded states and taking the difference between the two. However, if the incident light being measured is pulsed light that is intermittently output with a predetermined repetition period, the change in light intensity cannot be accurately captured unless the repetition period of the pulsed light and the period in which the shielded and unshielded states switch are not synchronized. As a result, periodic errors are introduced into the acquired optical spectral data, making it difficult to measure the optical spectrum of the incident light with high accuracy (Graph 53 in Figure 6).

[0066] Therefore, the measuring device 10 according to this embodiment divides the entire wavelength range of the object to be measured into wavelength intervals that are longer than the repetition period of the pulsed light and correspond to a period in which the effect of drift of the photodetector 13 is sufficiently small (see Figure 4). The measuring device 10 measures the optical spectrum in both a light-shielded state and an unshielded state within each wavelength range, and obtains spectral data with the effect of dark current suppressed by subtracting the measured value in the light-shielded state from the measured value in the unshielded state. The measuring device 10 combines these spectral data from each wavelength range to obtain spectral data for the entire wavelength range.

[0067] Thus, the measuring device 10 according to this embodiment can cancel out the effect of dark current by subtracting the light spectrum measured in a light-shielded state from the light spectrum measured in an unshielded state, making it possible to measure the light spectrum with high sensitivity even in wavelength ranges where the signal intensity is weak. Furthermore, by measuring each wavelength section, the measuring device 10 can shorten the measurement time for each measurement and suppress the influence of drift caused by dark current that occurs during measurement on the measured spectrum data.

[0068] An example of the operation of the measuring device 10 will be described with reference to Figures 3 to 5. Figure 3 is a flowchart illustrating an example of the operation of the measuring device 10 according to one embodiment. Figures 4 and 5 are schematic diagrams illustrating an example of the operation of the measuring device 10 according to one embodiment. The operation of the measuring device 10 described with reference to Figures 3 to 5 may correspond to one of the measurement methods of the measuring device 10. The operation of each step in Figure 3 may be performed based on control by the processor 16 of the measuring device 10.

[0069] In step S1 of Figure 3, the processor 16 receives the setting of the time averaging interval from the operator.

[0070] As mentioned above, the measuring device 10 divides the entire measurement period into short wavelength intervals for measurement (see Figure 4). Therefore, the measuring device 10 accepts from the operator the setting of a time-averaging interval corresponding to the repetition period of the pulsed light that is the incident light.

[0071] The time-averaging interval is the interval used to calculate a single measurement point. The measuring device 10 calculates, for each time-averaging interval, the average value of the light intensity measured by the photodetector 13 in a light-shielded state and the average value of the light intensity measured by the photodetector 13 in an unshielded state. For each time-averaging interval, the measuring device 10 obtains a light intensity measurement that suppresses the effect of dark current by subtracting the average value of the light intensity measured in a light-shielded state from the average value of the light intensity measured in an unshielded state. In other words, the time-averaging interval corresponds to the sampling interval of light intensity.

[0072] The operator sets a time value (msec) larger than the repetition period of the pulsed light as the time-averaging interval. By setting the time-averaging interval to a value sufficiently larger than the repetition period of the pulsed light (for example, more than 5 times the repetition period), the ON / OFF ratio of the pulsed light can be kept approximately the same during measurements in the shielded and unshielded states. However, if the value of the time-averaging interval is too large, the sampling interval becomes large, and the effect of drift caused by the dark current in the photodetector 13 becomes significant. Therefore, the operator sets an appropriate value as the time-averaging interval according to the characteristics of the photodetector 13, the required measurement accuracy, etc.

[0073] In step S2, the processor 16 calculates the size of the wavelength interval from the time-averaged interval set in step S1.

[0074] Specifically, the processor 16 calculates the wavelength interval (number of points) using the following equation (Equation 1). (Formula 1) Wavelength interval (number of points) = Drift tolerance time (msec) / Time-averaging interval (msec)

[0075] Here, the drift tolerance time is the time between measurements in a light-shielded state and measurements in an unshielded state within a divided section. Depending on the characteristics and temperature of the photodetector 13, the time during which the effect of drift caused by dark current in the photodetector 13 can be ignored is pre-set as the drift tolerance time in memory 17. For example, if the drift tolerance time is 1000 msec and the time-averaging interval is 10 msec, the wavelength interval will be 100 points.

[0076] The processor 16 divides the entire range of wavelengths to be measured into n wavelength intervals. Figure 4 shows the wavelength range divided into n wavelength intervals. In Figure 4, the horizontal axis represents wavelength. The vertical axis represents the intensity of the electrical signal output from the photodetector 13 due to incident light. In steps S3 to S6, the processor 16 acquires spectral data with the influence of dark current suppressed by measuring in both a light-shielded state and an unshielded state for each of the n wavelength intervals.

[0077] Hereinafter, for k=1,...,n, the k-th wavelength interval may be referred to as "wavelength interval k". In Figure 4, "Measurement k (shielded)" shows the measurement of the optical spectrum in the shilded state within wavelength interval k. "Measurement k (unshielded)" shows the measurement of the optical spectrum in the unshielded state within wavelength interval k. For both the shilded and unshielded states, the time required to measure one wavelength interval corresponds to the drift tolerance time.

[0078] Figure 5 shows the relationship between the passage of time and the wavelength of the incident light whose intensity is measured. In Figure 5, the horizontal axis represents time, and the vertical axis represents the wavelength of the incident light. Graph 61 shows how the intensity of incident light from wavelengths λ1 to λ2 is measured from time t1 to time t2 in a light-shielded state. Graph 62 shows how the intensity of incident light from wavelengths λ1 to λ2 is measured from time t2 to time t3 in an unshielded state. Graph 63 shows how the intensity of incident light from wavelengths λ2 to λ3 is measured from time t3 to time t4 in a light-shielded state. Graph 64 shows how the intensity of incident light from wavelengths λ2 to λ3 is measured from time t4 to time t5 in an unshielded state.

[0079] In Figure 5, graphs 61 and 62 from time t1 to t3 show measurements in wavelength interval k. Graphs 63 and 64 from time t3 to t5 show measurements in wavelength interval (k+1). Here, time (t2-t1), time (t3-t2), time (t4-t3), and time (t5-t4) correspond to the drift tolerance time, respectively. The measuring device 10 acquires the average value of the measured values ​​in the shaded and unshaded states for each time averaging interval set in step S1 for each wavelength interval, calculates the difference between the two, and obtains spectral data with the influence of dark current suppressed. As a result, the measured values ​​of the number of points of light intensity calculated in step S2 are acquired for each wavelength interval.

[0080] The following describes an example of acquiring spectral data in the wavelength interval k in the order of k=1, 2, ..., n. The processor 16 sets the initial value of k to k=1 and executes the process from step S3 onwards.

[0081] In step S3, the processor 16 acquires spectral data in the wavelength interval k while the light is shielded. Specifically, the processor 16 measures the intensity of the incident light while rotating the diffraction grating 113 according to the drift tolerance time and the wavelength range to be measured in the wavelength interval k. The processor 16 averages the measured values ​​for each time averaging interval set in step S1 to acquire the spectrum of the intensity of the incident light measured at intervals of the time averaging interval.

[0082] In step S4, the processor 16 acquires spectral data in the wavelength interval k in an unshielded state. Specifically, similar to step S3, the processor 16 measures the intensity of incident light while rotating the diffraction grating 113 according to the drift tolerance time and the wavelength range to be measured in the wavelength interval k. The processor 16 averages the measured values ​​for each time averaging interval set in step S1 to acquire the spectrum of the intensity of incident light measured at intervals of the time averaging interval.

[0083] In step S5, the processor 16 subtracts the spectral data obtained in step S3 under the light-shielding state from the spectral data obtained in step S4 under the light-shielding state to obtain spectral data in which the effect of dark current in the wavelength interval k is suppressed. Specifically, for each of the incident light intensities measured by averaging for each time-averaging interval, the processor 16 subtracts the measured value under the light-shielding state from the measured value under the light-shielding state to obtain the optical spectrum in the wavelength interval k.

[0084] In step S6, the processor 16 determines whether measurements have been taken for all wavelength intervals. Specifically, the processor 16 determines whether spectral data suppressing the effect of dark current has been obtained for all wavelength intervals from wavelength interval 1 to wavelength interval n. If the processor 16 has measured all wavelength intervals (YES in step S6), it proceeds to step S7; otherwise (YES in step S6), it increments the value of k by 1 and returns to step S3.

[0085] In step S7, the processor 16 concatenates the optical spectral data for each wavelength range measured by the processing in steps S3 to S6 to obtain spectral data for the entire wavelength range.

[0086] In step S8, the processor 16 outputs spectral data for the entire wavelength range acquired in step S7. Specifically, for example, the processor 16 may output the spectral data for the entire wavelength range to memory 17 for storage. The processor 16 may output the spectral data for the entire wavelength range to display unit 18 for display. The processor 16 may also output the spectral data for the entire wavelength range to a storage medium such as a USB (Universal Serial Bus) memory or to another device. After completing the processing in step S8, the processor 16 terminates the processing shown in the flowchart of Figure 3.

[0087] Figure 6 shows an example of the measurement results of the optical spectrum of pulsed light, categorized by measurement method. In Figure 6, the horizontal axis represents wavelength, and the vertical axis represents the intensity of the incident light. In Figure 6, the vertical axis shows the light intensity in decibel-milliwatt (dBm) units, calculated using a logarithmic scale.

[0088] In Figure 6, Graph 51 shows an example of an optical spectrum measured with the measuring device 10 using the same incident light. Graph 52 shows an example of an optical spectrum measured with the same incident light without using the optical chopper 12. Graph 53 shows an example of an optical spectrum when the same incident light is measured with the optical chopper 12 blocking and unblocking the light at a period not synchronized with the pulse repetition period.

[0089] Actual incident light has a complex spectral shape not only in the central frequency region but also in the low-frequency and high-frequency regions. In contrast, Graph 52 has a nearly horizontal shape in the low-frequency and high-frequency regions. This indicates that, as a result of measurements taken without using the optical chopper 12, minute information about the light intensity in the low-frequency and high-frequency regions was buried and lost in errors due to drift caused by dark current. Graph 53 has a shape that is generally similar to the true spectrum of the incident light, but shows an error where the intensity increases and decreases at regular wavelengths. This indicates that periodic errors were introduced into the acquired optical spectral data due to the non-synchronization of the pulsed light repetition period and the switching period between shielding and unshielding.

[0090] In contrast, Graph 51, which is the measurement result from the measuring device 10, has a shape that is generally similar to the true spectrum of the incident light. This is because Graph 51 measures components with low intensity in the low-frequency and high-frequency regions with high sensitivity, while not including periodic errors like those in Graph 53. Therefore, the measuring device 10 can generate highly sensitive measurement spectral data compared to Graph 52. Furthermore, the measuring device 10 can generate more accurate measurement spectral data that does not include periodic errors compared to Graph 53. Thus, the measuring device 10 can measure the optical spectrum of pulsed light with higher precision.

[0091] As described above, the measuring device 10 includes a spectrometer 11 that extracts a specific wavelength component from incident light, a photodetector 13 that outputs a signal corresponding to the intensity of the extracted wavelength component, and a processor 16. For each of the multiple wavelength intervals that divide the wavelength range of the object to be measured, the measuring device 10 acquires a first signal output from the photodetector 13 in a light-shielded state and a second signal output from the photodetector 13 in a light-unshielded state according to the intensity of the incident light. The measuring device 10 outputs the difference between the second signal and the first signal as the optical spectrum of the wavelength interval.

[0092] In this way, the measuring device 10 divides the wavelength range of the object to be measured into multiple wavelength intervals, measures the incident light in both a light-shielded and light-unshielded state for each wavelength interval, and outputs the difference in the signals related to the measurement as the optical spectrum of the wavelength interval. Therefore, the measuring device 10 can suppress the effect of drift in the measured value caused by dark current and measure the optical spectrum of pulsed light with higher accuracy.

[0093] The length of each of the multiple wavelength intervals may be determined according to the magnitude of the fluctuation in the measured value caused by the dark current in the photodetector 13 while measuring the optical spectrum in that wavelength interval.

[0094] Thus, since the length of each wavelength interval is determined according to the magnitude of the fluctuation in the measured value caused by the dark current in the photodetector 13, the measuring device 10 can effectively reduce the effect of drift in the measured value caused by the dark current.

[0095] Alternatively, the measuring device 10 may divide the wavelength range of the target to be measured by defining the interval set by the operator via the operation unit 19 as the wavelength interval.

[0096] In this way, the measuring device 10 divides the wavelength range of the object to be measured into wavelength intervals based on the intervals set by the operator. Therefore, the operator can set a desired wavelength interval according to the characteristics of the photodetector 13 and have the device measure the optical spectrum.

[0097] Furthermore, the measuring device 10 may accept the setting of time-averaging intervals from the operator via the operation unit 19. The measuring device 10 may acquire as a first signal a signal obtained by averaging the signals output from the photodetector 13 in a light-shielded state for each time-averaging interval for each of the multiple wavelength intervals. The measuring device 10 may acquire as a second signal a signal obtained by averaging for each time-averaging interval the signals output from the photodetector 13 in an unshielded state.

[0098] In this way, the measuring device 10 accepts the setting of time-averaging intervals from the operator and acquires optical spectra for each wavelength interval based on the signal averaged for each time-averaging interval. Therefore, the operator can have the optical spectrum measured at a desired sampling rate.

[0099] Alternatively, the measuring device 10 may acquire a first signal output from the photodetector 13 in a light-shielded state for each of the multiple wavelength intervals, and then acquire a second signal output from the photodetector 13 in an unshielded state.

[0100] Thus, the measuring device 10 performs measurements in a light-shielded state first, followed by measurements in an unshielded state. Therefore, it is possible to minimize the effects of drift caused by dark current resulting from the temperature rise of the photodetector due to light incidence on the photodetector. Alternatively, the measuring device 10 may perform measurements in an unshielded state first, followed by measurements in a light-shielded state.

[0101] Furthermore, the measuring device 10 may further include an optical chopper 12 capable of blocking light incident on the photodetector 13. The measuring device 10 may acquire, for each of a plurality of wavelength intervals, the signal output from the photodetector 13 while blocked by the optical chopper 12 as a first signal, and the signal output from the photodetector 13 while not blocked by the optical chopper 12 as a second signal.

[0102] Thus, the measuring device 10 can easily switch between a light-shielded state and an unshielded state using the optical chopper 12.

[0103] As described above, the measuring device 10 can cancel out the effect of dark current by subtracting the measurement data in the light-shielded state from the measurement data in the non-shielded state, and can measure the optical spectrum of incident light with high sensitivity. In addition, by measuring the optical spectrum for each wavelength interval, the measuring device 10 can shorten the measurement time for each measurement and suppress the influence of drift caused by dark current that occurs during measurement on the measured spectral data.

[0104] This disclosure is not limited to the embodiments described above. For example, multiple blocks shown in a block diagram may be combined, or one block may be divided. Multiple steps shown in a flowchart may be performed in parallel or in a different order, depending on the processing capacity of the device performing each step, or as necessary, instead of being performed in chronological order as described. Other modifications are possible without departing from the spirit of this disclosure.

[0105] Furthermore, for example, the configuration and operation of the measuring device 10 may be distributed among multiple computers that can communicate with each other. Also, for example, some or all of the components of the measuring device 10 may be provided on other devices such as a PC (Personal Computer). [Explanation of symbols]

[0106] 10: Measuring device 11: Spectrometer 12: Light Chopper 13: Photodetector 14: Amplifier 15: A / D converter 16: Processor 17: Memory 18: Display section 19:Operation section 111: Fiber optic 112: Collimating mirror 113: Diffraction grating 114: Focusing Mirror 115: Ejection slit 51-53: Graphs 61-64: Graphs

Claims

1. A spectrometer that extracts specific wavelength components from incident light, A photodetector that outputs a signal corresponding to the intensity of the extracted wavelength component, Processor and A measuring device comprising, The aforementioned processor, For each of the multiple wavelength intervals that divide the wavelength range to be measured, a first signal output from the photodetector while it is shielded from light and a second signal output from the photodetector according to the intensity of the incident light while it is not shielded from light are acquired, and the difference between the second signal and the first signal is output as the optical spectrum of that wavelength interval. Measuring device.

2. The measuring apparatus according to claim 1, wherein the length of each of the plurality of wavelength intervals is determined according to the magnitude of the fluctuation in the measured value caused by the dark current in the photodetector while measuring the optical spectrum in the wavelength interval.

3. The measuring apparatus according to claim 1, wherein the processor divides the wavelength range of the object to be measured by setting an interval from an operator via an operation unit as the wavelength interval.

4. The aforementioned processor, The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light is averaged for each of the time-averaging intervals and obtained as the first signal, and the signal output from the photodetector while not shielded from light is averaged for each of the time-averaging intervals and obtained as the second signal. The measuring device according to claim 1.

5. The measuring apparatus according to claim 1, wherein the processor acquires the first signal output from the photodetector in a light-shielded state for each of the plurality of wavelength intervals, and then acquires the second signal output from the photodetector in an unshielded state.

6. The photodetector is further equipped with an optical chopper capable of blocking light. The aforementioned processor, For each of the plurality of wavelength intervals, the signal output from the photodetector while it is shielded by the optical chopper is acquired as the first signal, and the signal output from the photodetector while it is not shielded by the optical chopper is acquired as the second signal. The measuring device according to any one of claims 1 to 5.

7. A spectrometer that extracts specific wavelength components from incident light, A photodetector that outputs a signal corresponding to the intensity of the extracted wavelength component, Processor and A measuring method for a measuring device equipped with, The aforementioned processor, For each of the multiple wavelength intervals that divide the wavelength range to be measured, a first signal output from the photodetector while it is shielded from light and a second signal output from the photodetector according to the intensity of the incident light while it is not shielded are acquired, and the difference between the second signal and the first signal is output as the optical spectrum of that wavelength interval. Measurement methods, including those mentioned above.

8. The measurement method according to claim 7, wherein the length of each of the plurality of wavelength intervals is determined according to the magnitude of the variation in the measured value caused by the dark current in the photodetector while measuring the optical spectrum in the wavelength interval.

9. The measurement method according to claim 7, wherein the processor divides the wavelength range of the object to be measured by setting an interval from an operator via an operation unit as the wavelength interval.

10. The aforementioned processor, The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light is averaged for each of the time-averaging intervals and obtained as the first signal, and the signal output from the photodetector while not shielded from light is averaged for each of the time-averaging intervals and obtained as the second signal. The measurement method according to claim 7.

11. The measurement method according to claim 7, wherein the processor acquires the first signal output from the photodetector in a light-shielded state for each of the plurality of wavelength intervals, and then acquires the second signal output from the photodetector in an unshielded state.

12. The measuring device further includes an optical chopper capable of blocking light incident on the photodetector. The aforementioned processor, For each of the plurality of wavelength intervals, the signal output from the photodetector while it is shielded by the optical chopper is acquired as the first signal, and the signal output from the photodetector while it is not shielded by the optical chopper is acquired as the second signal. The measurement method according to any one of claims 7 to 11.

13. A spectrometer that extracts specific wavelength components from incident light, A photodetector that outputs a signal corresponding to the intensity of the extracted wavelength component, Processor and A program for controlling a measuring device equipped with the following features: A procedure for obtaining, for each of a plurality of wavelength intervals that divide the wavelength range to be measured, a first signal output from the photodetector in a light-shielded state and a second signal output from the photodetector in a light-unshielded state according to the intensity of the incident light, and outputting the difference between the second signal and the first signal as the optical spectrum of that wavelength interval. A program that controls the measuring device to perform the following actions.

14. The program according to claim 13, wherein the length of each of the plurality of wavelength intervals is determined according to the magnitude of the variation in the measured value due to the dark current in the photodetector while measuring the light spectrum in the wavelength interval.

15. The program according to claim 13, which divides the wavelength range of the object to be measured by setting an interval from the operator via the control unit as the wavelength interval.

16. The operator can set the time average interval via the control unit. For each of the plurality of wavelength intervals, the signal output from the photodetector while shielded from light is averaged for each of the time-averaging intervals and obtained as the first signal, and the signal output from the photodetector while not shielded from light is averaged for each of the time-averaging intervals and obtained as the second signal. The program according to claim 13.

17. The program according to claim 13, wherein for each of the plurality of wavelength intervals, a first signal output from the photodetector in a light-shielded state is acquired, and then a second signal output from the photodetector in an unshielded state is acquired.

18. The measuring device further comprises an optical chopper capable of blocking light incident on the photodetector, For each of the plurality of wavelength intervals, the signal output from the photodetector while it is shielded by the optical chopper is acquired as the first signal, and the signal output from the photodetector while it is not shielded by the optical chopper is acquired as the second signal. The program according to any one of claims 13 to 17.

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