JP7136854B2 - Pulse-modulated light measurement method, pulse-modulated light measurement program, and optical spectrum analyzer - Google Patents

Description

The present invention relates to a pulse modulated light measurement method, a pulse modulated light measurement program, and an optical spectrum analyzer.

2. Description of the Related Art Conventionally, an optical spectrum analyzer as disclosed in Patent Document 1, for example, has been used to measure wavelength components contained in light to be measured, which is a device under test (DUT).

An optical spectrum analyzer uses an optical filter that has high wavelength selectivity and can change the selected wavelength, selectively receives each wavelength component contained in the light to be measured, and measures the spectral distribution along the wavelength axis. to display the results on the screen.

The optical spectrum analyzer of Patent Document 1 shows a technique for avoiding light loss due to beam splitters in the optical path within the device.

Japanese Patent No. 3986031

By the way, the object to be measured by an optical spectrum analyzer is generally continuous wave (CW) light.
However, when a light source such as a laser diode (LD) module is used to generate continuous emission light, for example, the emission wavelength changes over time due to the effect of temperature changes caused by the continuous flow of current for driving the light source. It is assumed that it will fluctuate with Therefore, in order to suppress the temperature change, in recent years, there is a tendency in various fields to use light that is intermittently emitted in a pulsed manner by performing pulse modulation (periodic on/off of light emission) of the light source. This suppresses temperature changes and stabilizes the emission wavelength.

Further, when pulsed light is emitted from the light source, the state of the object can be detected by measuring the reflected light reflected by the object. For example, LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) technology measures the scattered light from pulsed laser irradiation, and analyzes the distance to a distant target and the characteristics of that target. can.

Therefore, in recent years, the need for measurement of pulsed emitted light (pulse-modulated light) has increased in various fields, unlike conventional applications where continuous emitted light was the main subject. In particular, since technologies such as LiDAR are related to safety, there is an increasing demand for reliability of transmission signals on the light source side.

In other words, for pulse modulated light that repeats on and off, measurement items such as "peak level", "average power", "pulse width", "period", "waveform", "wavelength", and "spectrum width" are measured. must be measured. However, optical spectrum analyzers generally do not have a function to measure changes in optical power in the direction of the time axis. It is necessary to separately prepare a measuring device other than the optical spectrum analyzer.

As a representative example, it is assumed that the output of an O/E converter (optical/electrical converter) is connected to an oscilloscope for measurement. In the case of an oscilloscope, modulation characteristics are measured with respect to the total power obtained by integrating all wavelengths of light input to the O/E converter. Furthermore, in the case of separate measurement for each wavelength, it is necessary to install an expensive optical variable wavelength filter in front of the O/E converter. Therefore, setup of the measurement system is complicated.

When measuring each item of "peak level" and "average power" of pulse-modulated light, it is usually assumed that an optical power meter or an optical spectrum analyzer is used. Also, when the frequency of the pulse-modulated light is higher than the light-receiving bandwidth of the optical power meter, the "peak level" cannot be directly measured, so the "average power" is measured instead. Then, in order to obtain the "peak level", the separately measured values of the "period" and "waveform" are applied to the "average power", and the "peak level" is estimated by calculation.

The optical power meter measures the total power of all input wavelength bands. Therefore, in order to measure the optical power separated for each wavelength, it is necessary to install an expensive optical variable wavelength filter in front of the optical power meter, which complicates the setup of the measurement system.

The present invention has been made in view of the circumstances described above, and its object is to provide a device that is separately used in addition to an optical spectrum analyzer when performing measurement including characteristics in the time axis direction with pulse-modulated light as a measurement target. To provide a pulse-modulated light measurement method, a pulse-modulated light measurement program, and an optical spectrum analyzer capable of reducing the cost associated with measurement and facilitating the measurement system setup work.

In order to achieve the above object, the pulse modulated light measurement method, the pulse modulated light measurement program, and the optical spectrum analyzer according to the present invention are characterized by the following (1) to (5).
(1) A pulse-modulated light measurement method for measuring pulse-modulated light to be measured using an optical spectrum analyzer including an optical variable wavelength filter configured with an optical diffraction grating ,
selecting 0th-order diffracted light by controlling the optical variable wavelength filter;
sampling the selected signal of the 0th order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
Obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data;
controlling the optical variable wavelength filter to select diffracted light of orders other than the 0th order;
determining a sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured to measure the spectrum.
Pulse-modulated light measurement method.

(2) A pulse-modulated light measurement program executable by a given computer for controlling measurement of pulse-modulated light to be measured using an optical spectrum analyzer including an optical variable wavelength filter configured with an optical diffraction grating. hand,
a step of controlling the optical tunable wavelength filter to select 0th-order diffracted light;
a procedure of sampling the selected signal of the 0th-order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured, based on the first data;
a step of controlling the optical variable wavelength filter to select diffracted lights of orders other than the 0th order;
a procedure for determining sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
a procedure of performing sampling during pulse-on of the pulse-modulated light to be measured according to the determined sampling timing to measure the spectrum;
A pulse-modulated optical metrology program including.

(3) An optical spectrum analyzer comprising an optical tunable wavelength filter configured with an optical diffraction grating and a controller for measuring pulse-modulated light to be measured,
The control unit, in a predetermined measurement mode,
selecting 0th-order diffracted light by controlling the optical variable wavelength filter;
sampling the selected signal of the 0th order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
Obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data;
controlling the optical variable wavelength filter to select diffracted light of orders other than the 0th order;
determining a sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured to measure the spectrum.
An optical spectrum analyzer characterized by:

(4) The control unit simultaneously displays on the same screen an optical power level distribution in the time axis direction based on the first data and a spectrum distribution in the frequency axis direction based on the result of the spectrum measurement.
The optical spectrum analyzer according to (3) above.

(5) when the signal level of the light receiver and the measurement range related to the frequency band are variable, the control unit performs measurement to acquire the first data after fixing the measurement range;
The optical spectrum analyzer according to (3) or (4) above.

According to the pulse-modulated light measurement method having the configuration (1) above, by controlling the optical variable wavelength filter that is standardly provided in a normal optical spectrum analyzer, the 0th-order diffracted light of the pulse-modulated light, that is, the total The optical power integrated over the wavelength is incident on the light-receiving sensor and its level is measured. Further, by repeating the sampling of this signal at a constant period, the first data representing the optical power level distribution in the direction of the time axis, that is, the waveform can be obtained. Also, the pulse-on time width (pulse width) and pulse period of the pulse-modulated light to be measured are obtained from the first data. Subsequently, by controlling the optical variable wavelength filter, diffracted lights of orders other than the 0th order are selected. By repeating signal sampling in this state, the light receiving levels of the light receiving sensors can be measured separately for each desired wavelength, so that spectral distribution data of the pulse-modulated light can be obtained. Also, when measuring the spectrum, the sampling timing is determined based on the pulse-on time width and pulse cycle in the waveform of the pulse-modulated light. Sampling can be done. Therefore, more accurate measurement results can be obtained.

By executing the pulse-modulated light measurement program having the configuration (2) above on a predetermined computer and controlling the optical spectrum analyzer, the same results as in the case of the pulse-modulated light measurement method having the configuration (1) above can be obtained. .

According to the optical spectrum analyzer having the configuration (3) above, the controller executes a predetermined measurement mode to obtain the same results as in the case of the pulse modulated light measurement method having the configuration (1) above.

According to the optical spectrum analyzer having the above configuration (4), the user can display the waveform representing the optical power level distribution in the time axis direction and the spectrum distribution in the frequency axis direction of the pulse-modulated light to be measured on the same display screen. be recognized at the same time. Therefore, information useful for understanding the characteristics of the pulse-modulated light to be measured, such as "peak level," "average power," "pulse width," "period," "waveform," "wavelength," and "spectrum width." The user can instantly grasp each measurement item visually.

According to the optical spectrum analyzer having the configuration (5) above, since the measurement range is not switched during measurement, calculation of each measurement item can be easily executed according to the characteristics of the fixed measurement range.

According to the pulse-modulated light measurement method, the pulse-modulated light measurement program, and the optical spectrum analyzer of the present invention, when performing measurement including characteristics in the time axis direction with pulse-modulated light as the measurement target, The equipment used can be reduced, the cost associated with measurement can be reduced, and the measurement system setup work can be facilitated. In other words, by controlling the optical tunable wavelength filter, etc. that is standard in ordinary optical spectrum analyzers, measurement corresponding to pulse-modulated light can be performed with just the optical spectrum analyzer without adding special components. can.

The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading the following detailed description of the invention (hereinafter referred to as "embodiment") with reference to the accompanying drawings. .

FIG. 1 is a block diagram showing an example configuration of an optical spectrum analyzer according to an embodiment of the present invention. FIG. 2 is a flow chart showing an operation example when pulse-modulated light is measured by the optical spectrum analyzer of the embodiment. FIG. 3 is a time chart showing an example of pulse-modulated light. FIG. 4 is a front view showing an example of screen display.

Specific embodiments relating to the present invention will be described below with reference to each drawing.

<Device configuration example>
FIG. 1 shows a configuration example of an optical spectrum analyzer OSA according to an embodiment of the present invention.

The basic structure and operation of the optical spectrum analyzer OSA shown in FIG. 1 are the same as those of a general optical spectrum analyzer, and have components as shown in FIG. 1 of Patent Document 1, for example. However, the optical spectrum analyzer OSA of this embodiment is provided with a special function for measuring pulse-modulated light as an object to be measured.

A pulse-modulated optical DUT to be measured by the optical spectrum analyzer OSA of the present embodiment is one whose optical power is periodically switched on and off, as shown in the waveform shown in FIG. 3, for example. In other words, the optical signal is intermittently generated in a pulse shape. Such a pulse-modulated light DUT suppresses heat generation of the light source and helps stabilize the emission wavelength. Also, when using a pulse-modulated light DUT, it is possible to measure reflected light from an object, which can be used to detect the state of the object.

The pulse modulation frequency of the pulse-modulated light DUT is assumed to be relatively low, on the order of several tens of kHz to several MHz. That is, the optical spectrum analyzer OSA of this embodiment treats signal light pulse-modulated at a low-speed frequency that can follow its operation as a measurement target.

As shown in FIG. 1, the optical spectrum analyzer OSA of this embodiment includes a light incidence section 11, an optical variable wavelength filter 12, an optical attenuator 13, a light receiving sensor 14, a light receiving circuit 15, a control section 16, a display 17, and It has control software 18 .

The light input unit 11 receives a pulse-modulated light DUT introduced from the outside through an optical component such as a predetermined optical fiber, and guides the optical signal SG1 to the input of the optical variable wavelength filter 12 as it is.

The optical variable wavelength filter 12 is composed of, for example, an optical diffraction grating or a collimator. The collimator converts incident light into parallel light and guides it to the incident surface of the optical diffraction grating. The optical diffraction grating generates diffracted light for each output direction of the output surface according to the incident angle of the incident light.

The optical tunable wavelength filter 12 of the present embodiment can selectively switch between the 0th-order diffracted light and the 1st-order diffracted light to enter the light receiving sensor 14 by adjusting the angle of the optical tunable wavelength filter 12, for example. Since the 0th-order diffracted light is straight light and travels straight at all wavelengths, light containing all wavelength components is emitted in the same direction. Since the 1st-order diffracted light has a different diffraction angle for each wavelength, it can be separated for each wavelength and selectively emitted in the direction of the light receiving sensor 14 .

The optical signal SG2 emitted from the optical variable wavelength filter 12 passes through the optical attenuator 13 and enters the light receiving sensor 14 as the optical signal SG3. The light-receiving sensor 14 is an optical-electrical converter, and generates an electrical signal SG4 having a level corresponding to the received optical power.

The electric signal SG4 generated by the light receiving sensor 14 is processed by the light receiving circuit 15 and input to the control section 16 as an electric signal SG5. The light-receiving circuit 15 incorporates, for example, a circuit for adjusting the level and frequency bandwidth of the electric signal, a sampling circuit, an analog-digital converter, and the like. Therefore, the digital signal of the measured value sampled at each time is input to the control section 16 as the electrical signal SG5.

The control unit 16 is a component that controls the entire optical spectrum analyzer OSA, and is composed of a microcomputer in this embodiment. Further, the control unit 16 has an operation unit (not shown) capable of receiving user's operation input.

Control software 18 necessary for the microcomputer of the control unit 16 to operate is held in, for example, a non-volatile memory (not shown). The control software 18 comprises basic software (operating system) and application programs for realizing various functions of the optical spectrum analyzer OSA. It contains a program to implement.

The microcomputer of the control unit 16 can switch the states of the optical variable wavelength filter 12, the optical attenuator 13, and the light receiving circuit 15 as necessary using control signals SG6, SG7, and SG8.

The display 17 has a two-dimensional display screen composed of, for example, a liquid crystal panel, and can display information necessary for operation of measurement, measurement results, and the like in the form of characters, figures, graphs, images, and the like. Actually, the screen display contents of the display 17 are updated under the control of the control unit 16 .

<Operation example>
FIG. 2 shows an operation example when the optical spectrum analyzer OSA of this embodiment measures pulse-modulated light. That is, the microcomputer in the control unit 16 executes a special program included in the control software 18 to implement measurement processing suitable for measuring the pulse-modulated light DUT according to the operation procedure shown in FIG. Of course, it is also possible to replace the operation similar to the function of this special program with dedicated hardware.

When the user selects a special measurement mode prepared for measuring the pulse modulated light DUT, the microcomputer starts the processing of FIG. 2 from step S11. The processing of FIG. 2 will be described below.

The processing shown in FIG. 2 includes a processing S01 for all wavelength bands and a spectrum measurement processing S02. In the first step S11, the light input section 11 of the optical spectrum analyzer OSA inputs the pulse-modulated light DUT from an external optical fiber. Also, in order to avoid input of excessive optical power to the light receiving sensor 14 and the like, the control section 16 controls the optical attenuator 13 with the control signal SG7 and automatically adjusts the amount of attenuation in step S12.

The control unit 16 controls the control signal SG6 in step S13 to adjust the diffraction grating position in the optical variable wavelength filter 12 to a predetermined state. That is, the diffraction grating position is switched so as to select the 0th-order diffracted light. As a result, all the powers of the pulse-modulated light DUT are selected as measurement targets without distinction of wavelength.

In the optical spectrum analyzer OSA of this embodiment, the measurement range of the signal level and frequency band when measuring the light to be measured can be selectively switched from a plurality of ranges. However, if the measurement range is switched during the same measurement process, the calculation process becomes complicated. Therefore, in the present embodiment, the control unit 16 fixes the measurement range in step S14 before starting measurement.

In the next step S16, the control unit 16 repeatedly samples the pulse-modulated light DUT (0th-order diffracted light) detected by the light receiving sensor 14 at a constant period to sequentially acquire optical power measurement values for each time. The sampling frequency in this case is, for example, 1 MHz. That is, the sampling circuit in the light receiving circuit 15 samples the level of the electric signal SG4 every 1 μsec, and the analog-digital converter in the light receiving circuit 15 converts the level to a digital value, which is input to the controller 16 . Therefore, by repeating sampling 1,000 times at a cycle of 1 μsec, for example, the control unit 16 can obtain data D1 of optical power measurement values at 1,000 points along the time axis.

The control unit 16 calculates the following information (1) to (4) in the next step S16 based on the data D1 of the optical power measurement value for each time obtained in step S15.
(1) Pulse-on time of pulse-modulated light: Ton
(2) Pulse period of pulse-modulated light: Tp
(3) Pulsed light peak power in all wavelength bands: Pp
(4) Average power of pulsed light in all wavelength bands: Pm

That is, the data D1 of the optical power measurement value for each time obtained in step S15 represents, for example, the waveform of the pulse-modulated light DUT as shown in FIG. , the pulse period Tp of the pulse-modulated light, the pulsed light peak power Pp in the entire wavelength band, and the pulsed light average power Pm in the entire wavelength band can be calculated.

Subsequently, when performing the spectrum measurement process S02, the control unit 16 first adjusts the position of the diffraction grating in the optical tunable wavelength filter 12 in step S17 to select the first-order diffracted light. As a result, the pulse-modulated light DUT can be measured separately for each wavelength.

In the next step S18, the controller 16 determines the sampling timing tx to be used in the next measurement based on the pulse-on time Ton of the pulse-modulated light and the pulse period Tp of the pulse-modulated light obtained in S16. The sampling timing tx is determined so that sampling is performed only during periods when the pulse of the pulse-modulated light DUT is on. In this case, since the pulse-on time Ton and the pulse period Tp are known, the sampling timing tx can be easily determined.

In the next step S19, the control unit 16 performs sampling at the sampling timing tx for each wavelength of the pulse-modulated light DUT to obtain spectrum measurement, that is, optical power distribution data in the frequency axis direction.

The control unit 16 displays the spectrum waveform obtained in S19 on the screen of the display 17 in S20. When a specific display mode is selected, the waveform of the optical power distribution along the time axis and the waveform of the optical power distribution along the frequency axis are simultaneously displayed on the same screen (see FIG. 4).

In step S21, the control unit 16 acquires the following information (1) to (3) as the result of spectrum measurement in S19.
(1) Optical peak level PLf for each wavelength
(2) Emission wavelength WL of pulse-modulated light
(3) Spectrum width Ws of pulse-modulated light

<Specific example of waveform>
FIG. 3 shows an example of the waveform of the pulse-modulated light DUT.
As shown in FIG. 3, the pulse modulated light DUT appears intermittently and periodically. That is, the optical power measurement value increases only in the section of the pulse-on time Ton, and the optical power measurement value is almost 0 in other sections. The cycle of repeating the ON/OFF is the pulse cycle Tp.

Also, in this waveform in the direction of the time axis, the maximum value of the optical power measurement value is the "pulse light peak power Pp in all wavelength bands". The optical power measurement value obtained by averaging this waveform in the time axis direction is the "pulse light average power Pm in all wavelength bands".

<Screen display example>
FIG. 4 shows an example of screen display in the optical spectrum analyzer OSA of this embodiment.
In the example of FIG. 4, the waveform of the optical power distribution in the time axis direction and the waveform of the optical power distribution in the wavelength axis (frequency axis) direction are simultaneously displayed on the same screen under the control of the control unit 16 (S20). .

In addition to these waveforms, pulse-on time Ton of pulse-modulated light, pulse period Tp of pulse-modulated light, pulsed light peak power Pp in all wavelength bands, pulsed light average power Pm in all wavelength bands, optical peak for each wavelength Numerical data representing the level PLf, the emission wavelength WL of the pulse-modulated light, and the spectral width Ws of the pulse-modulated light can also be displayed on the screen.

As described above, according to the optical spectrum analyzer OSA according to the present embodiment, there is no need to use a special measuring instrument such as an oscilloscope or an optical power meter when measuring a pulse-modulated optical DUT. It is possible to acquire necessary information such as optical power measurement values in the direction of the time axis by using OSA alone without adding a special O/E converter or the like. Also, the optical power distribution waveform in the time axis direction and the spectral distribution waveform in the frequency axis direction can be displayed side by side at the same time.

Further, when using the pulse modulated light measurement method or the pulse modulated light measurement program according to the present embodiment, an optical spectrum analyzer having a general configuration is used to perform the same functions as the optical spectrum analyzer OSA of FIG. realizable.

Here, the features of the pulse-modulated light measurement method, the pulse-modulated light measurement program, and the optical spectrum analyzer according to the embodiments of the present invention described above are briefly listed in [1] to [5] below.
[1] A pulse-modulated light measuring method for measuring a pulse-modulated light (DUT) to be measured using an optical spectrum analyzer including an optical variable wavelength filter (12),
controlling the optical tunable wavelength filter to select 0th-order diffracted light (S13);
sampling the selected signal of the 0th order diffracted light at a constant period to acquire first data (D1) representing the optical power level distribution in the time axis direction (S15);
Obtaining at least the pulse-on time width (Ton) and the pulse period (Tp) of the pulse-modulated light to be measured based on the first data;
controlling the optical variable wavelength filter to select diffracted lights of orders other than the 0th order (S17);
determining a sampling timing (tx) for spectrum measurement based on the pulse-on time width and pulse period (S18);
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured, and spectrum measurement is performed (S19);
Pulse-modulated light measurement method.

[2] A predetermined computer-executable pulse-modulated light measurement program (control software 18 ) and
a step of controlling the optical tunable wavelength filter to select 0th-order diffracted light (S13);
a step of sampling the selected signal of the 0th-order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction (S15);
a step of acquiring at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data (S16);
a step of controlling the optical variable wavelength filter to select diffracted lights of orders other than the 0th order (S17);
a step of determining sampling timing for spectrum measurement based on the pulse-on time width and pulse period (S18);
a step (S19) of performing sampling during pulse-on of the pulse-modulated light to be measured according to the determined sampling timing to measure the spectrum;
A pulse-modulated optical metrology program including.

[3] An optical spectrum analyzer (OSA) comprising an optical variable wavelength filter (12) and a controller (16) for measuring pulse-modulated light to be measured,
The control unit, in a predetermined measurement mode,
controlling the optical tunable wavelength filter to select 0th-order diffracted light (S13);
sampling the selected signal of the 0th-order diffracted light at regular intervals to obtain first data representing the optical power level distribution in the time axis direction (S15);
acquiring at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data (S16);
controlling the optical variable wavelength filter to select diffracted lights of orders other than the 0th order (S17);
determining a sampling timing for spectrum measurement based on the pulse-on time width and pulse period (S18);
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured, and spectrum measurement is performed (S19);
An optical spectrum analyzer characterized by:

[4] The control unit simultaneously displays on the same screen the optical power level distribution in the time axis direction based on the first data and the spectrum distribution in the frequency axis direction based on the result of the spectrum measurement (S20, See Figure 4),
The optical spectrum analyzer according to [3] above.

[5] When the measurement range of the signal level and frequency band of the photodetector is variable, the control unit fixes the measurement range (S14), and then performs measurement to obtain the first data ( S15),
The optical spectrum analyzer according to [3] or [4] above.

11 light incidence part 12 optical variable wavelength filter 13 optical attenuator 14 light receiving sensor 15 light receiving circuit 16 control part 17 display 18 control software DUT pulse modulated light OSA optical spectrum analyzer SG1, SG2, SG3 optical signals SG4, SG5 electrical signals SG6, SG7, SG8 Control signal D1 Optical power measurement value data Ton Pulse-on time of pulse-modulated light Tp Pulse period of pulse-modulated light Pp Pulsed light peak power in all wavelength bands Pm Pulsed light average power in all wavelength bands tx Sampling timing PLf For each wavelength Optical peak level WL Emission wavelength of pulse-modulated light Ws Spectrum width of pulse-modulated light

Claims (5)

A pulse-modulated light measurement method for measuring pulse-modulated light to be measured using an optical spectrum analyzer including an optical variable wavelength filter configured with an optical diffraction grating, comprising:
selecting 0th-order diffracted light by controlling the optical variable wavelength filter;
sampling the selected signal of the 0th order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
Obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data;
controlling the optical variable wavelength filter to select diffracted light of orders other than the 0th order;
determining a sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured to measure the spectrum.
Pulse-modulated light measurement method. A pulse-modulated light measurement program executable by a predetermined computer for controlling measurement of pulse-modulated light to be measured using an optical spectrum analyzer including an optical tunable wavelength filter configured with an optical diffraction grating ,
a step of controlling the optical tunable wavelength filter to select 0th-order diffracted light;
a procedure of sampling the selected signal of the 0th-order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured, based on the first data;
a step of controlling the optical variable wavelength filter to select diffracted lights of orders other than the 0th order;
a procedure for determining sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
a procedure of performing sampling during pulse-on of the pulse-modulated light to be measured according to the determined sampling timing to measure the spectrum;
A pulse-modulated optical metrology program including. An optical spectrum analyzer comprising an optical tunable wavelength filter configured with an optical diffraction grating and a controller for measuring pulse-modulated light to be measured,
The control unit, in a predetermined measurement mode,
selecting 0th-order diffracted light by controlling the optical variable wavelength filter;
sampling the selected signal of the 0th order diffracted light at a constant period to acquire first data representing the optical power level distribution in the time axis direction;
Obtaining at least the pulse-on time width and pulse period of the pulse-modulated light to be measured based on the first data;
controlling the optical variable wavelength filter to select diffracted light of orders other than the 0th order;
determining a sampling timing for spectrum measurement based on the pulse-on time width and pulse period;
According to the determined sampling timing, sampling is performed during pulse-on of the pulse-modulated light to be measured to measure the spectrum.
An optical spectrum analyzer characterized by: The control unit simultaneously displays on the same screen an optical power level distribution in the time axis direction based on the first data and a spectrum distribution in the frequency axis direction based on the result of the spectrum measurement.
An optical spectrum analyzer according to claim 3. When the measurement range of the signal level and frequency band of the photodetector is variable, the control unit performs measurement to obtain the first data after fixing the measurement range.
The optical spectrum analyzer according to claim 3 or 4.

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