Pulsed light measurement method, pulsed light measurement program, and optical spectrum analyzer
The optical spectrum analyzer optimizes pulsed light measurement by adjusting wavelength overlap and delay times, addressing the trade-off between measurement time and waveform quality, thus improving user convenience and analysis efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- YOKOGAWA ELECTRIC CORP
- Filing Date
- 2024-02-14
- Publication Date
- 2026-06-25
AI Technical Summary
Existing optical spectrum analyzers face a trade-off between measurement time and waveform quality when measuring pulsed light, as they cannot measure optical spectra during the off periods of pulsed light, requiring multiple sweeps to compensate for waveform defects, which prolongs measurement time.
An optical spectrum analyzer that adjusts the overlap width of wavelengths and delay times for multiple sweeps, allowing for improved waveform quality by compensating for missing data and reducing measurement time through intuitive user settings.
The method enhances user convenience by optimizing the balance between measurement time and waveform quality, ensuring efficient and high-quality optical spectrum analysis.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a pulse light measurement method, a pulse light measurement program, and an optical spectrum analyzer.
Background Art
[0002] As described in Patent Document 1, an optical spectrum analyzer using a grating is known.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] When measuring the optical spectrum of pulsed light by performing a sweep, the optical spectrum data is obtained at the timing when the pulsed light is emitting, that is, at the timing when the gate signal synchronized with the pulsed light is HI, as shown in FIGS. 1A and 1B, but is not obtained at the timing when the pulsed light is not emitting, that is, at the timing when the gate signal is LO.
[0005]
[0006] Therefore, in order to complete the acquisition of optical spectral data for all wavelengths within the measurement wavelength range, multiple measurements are performed by shifting the phase of the pulse signal, thereby acquiring spectral data for the pulse period. The smaller the phase shift, i.e., the more measurements are taken, the greater the overlap of the waveforms obtained from each measurement. The greater the overlap of the waveforms, the better the quality of the measured optical spectrum waveform.
[0007] On the other hand, the more measurements taken, the longer the measurement time for the optical spectrum becomes. In other words, there is a trade-off between the length of the measurement time and the quality of the waveform of the measured optical spectrum. It is necessary to improve user convenience by shortening the measurement time while ensuring the quality of the waveform of the optical spectrum.
[0008] This disclosure is made in view of the above-mentioned points and aims to provide a pulsed light measurement method, a pulsed light measurement program, and an optical spectrum analyzer that can improve user convenience. [Means for solving the problem]
[0009] (1) A pulsed light measurement method according to several embodiments is a method for measuring the optical spectrum of pulsed light. The pulsed light measurement method includes setting an overlap width of wavelengths for which light intensity is to be measured in each of a plurality of sweeps performed in the measurement wavelength range of the optical spectrum, detecting a trigger for a gate signal synchronized with the pulsed light, and then starting each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed, and synthesizing and displaying the optical spectrum from a plurality of waveforms obtained by performing the plurality of sweeps.
[0010] By allowing the wavelength overlap width to be set during multiple sweeps, both the quality of the optical spectrum waveform and the measurement time can be reduced. As a result, user convenience is improved.
[0011] (2) In the pulse light measurement method described in (1) above according to one embodiment, when synthesizing the optical spectrum from the plurality of waveforms, the light intensity of the wavelengths that overlap with each other in the plurality of waveforms may be the intensity detected during the period in which the waveform data is not missing data. By doing so, missing data is eliminated in the synthesized waveform. As a result, the quality of the waveform is improved.
[0012] (3) In the pulse light measurement method described in (1) above according to one embodiment, when the delay time is increased in the order in which the multiple sweeps are performed, when synthesizing the optical spectrum from the multiple waveforms, the value obtained by performing a later sweep may be used as the light intensity of wavelengths that overlap with each other in the multiple waveforms. In this way, the waveforms obtained in the previously performed sweep do not need to be saved. As a result, the process of synthesizing the waveforms becomes simpler.
[0013] (4) In the pulse light measurement method described in (1) above according to one embodiment, when the delay time is increased in the order in which the multiple sweeps are performed, when synthesizing the optical spectrum from the multiple waveforms, the intensity of the wavelengths that overlap with each other in the multiple waveforms may be the intensity detected in the sweep performed later, from among the intensities detected during the period in which the waveform data is not missing data.
[0014] In one embodiment, (5) the pulsed light measurement method described in (1) above, when synthesizing the light spectrum from the plurality of waveforms, the larger value may be adopted as the light intensity of the wavelengths that overlap with each other in the plurality of waveforms.
[0015] In one embodiment, (6) the pulse light measurement method described in (1) above, when synthesizing the light spectrum from the plurality of waveforms, the larger of the intensities detected during the period in which the waveform data is not missing data may be adopted as the light intensity of the wavelengths that overlap with each other in the plurality of waveforms.
[0016] (7) A pulse light measurement method according to any one of (1) to (6) above according to one embodiment may further include setting the overlap width as a ratio to the pulse width of the pulse light. By setting the overlap width as a ratio to the pulse width, the user can easily understand the overlap width intuitively. As a result, user convenience is improved.
[0017] (8) The pulse light measurement method described in (7) above according to one embodiment may further include determining the number of times the sweep is performed based on the pulse width and the overlap width. This makes the measurement time easier to understand.
[0018] (9) The pulse light measurement method described in any one of (1) to (8) above according to one embodiment may further include displaying the waveforms obtained in each of the multiple sweeps in a distinguishable manner. Displaying the waveforms obtained in each sweep in a distinguishable manner makes it easier for the user to decide how to set the overlap width. As a result, user convenience is improved.
[0019] (10) The pulse light measurement method according to any one of (1) to (9) above according to one embodiment may further include receiving input for setting the overlap width while performing the multiple sweeps. By receiving input for setting the overlap width while performing the multiple sweeps, the user can immediately see how the overlap width setting changes the composite waveform and makes it easier to decide how to set the overlap width. As a result, user convenience is improved.
[0020] (11) The pulse light measurement method according to any one of (1) to (10) above according to one embodiment may further include receiving input for setting the overlap width while the waveform of the light spectrum is being displayed. By receiving input for setting the overlap width while the waveform is being displayed, it becomes easier for the user to decide how to set the overlap width. As a result, user convenience is improved.
[0021] The (12) pulse light measurement program according to some embodiments causes a spectral analyzer that measures the optical spectrum of pulse light to set a wavelength overlap width for measuring the optical intensity in each of a plurality of sweeps executed within the measurement wavelength range of the optical spectrum, start each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed after detecting a trigger of a gate signal synchronized with the pulse light, and synthesize and display the optical spectrum from a plurality of waveforms obtained by executing the plurality of sweeps.
[0022] The (13) spectral analyzer according to some embodiments includes a measurement unit that measures the optical spectrum of pulse light and a photodetection unit that detects the optical intensity of each wavelength of the pulse light. The measurement unit sets a wavelength overlap width for measuring the optical intensity in each of a plurality of sweeps executed within the measurement wavelength range of the optical spectrum. The photodetection unit starts each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed after detecting a trigger of a gate signal synchronized with the pulse light. The measurement unit synthesizes and displays the optical spectrum from a plurality of waveforms obtained by executing the plurality of sweeps.
Advantages of the Invention
[0023] According to the pulse light measurement method, the pulse light measurement program, and the spectral analyzer according to the present disclosure, the convenience for the user is improved.
Brief Description of the Drawings
[0024] [Figure 1A] It is a timing chart of the first sweep of the measurement method according to the comparative example. [Figure 1B] It is the waveform of the data measured by the sweep of FIG. 1A. [Figure 2A] It is a timing chart of the second sweep of the measurement method according to the comparative example. [Figure 2B] It is the waveform of the data measured by the sweep of FIG. 2A. [Figure 3]This waveform is a composite of the waveforms in Figure 2A and Figure 2B. [Figure 4] This is a block diagram showing an example configuration of an optical spectrum analyzer according to one embodiment of the present disclosure. [Figure 5] This flowchart shows an example procedure for the pulsed light measurement method related to this disclosure. [Figure 6A] This is a timing chart for the first sweep of the measurement method related to this disclosure. [Figure 6B] Figure 6A shows the waveform of the data measured by the sweep. [Figure 7A] This is a timing chart for the second sweep of the measurement method related to this disclosure. [Figure 7B] Figure 7A shows the waveform of the data measured by the sweep. [Figure 8A] This is a timing chart for the third sweep of the measurement method related to this disclosure. [Figure 8B] Figure 8A shows the waveform of the data measured by the sweep. [Figure 9A] This is a timing chart for the fourth sweep of the measurement method related to this disclosure. [Figure 9B] Figure 9A shows the waveform of the data measured by the sweep. [Figure 10] This waveform is a composite of the waveforms in Figure 6B, Figure 7B, Figure 8B, and Figure 9B. [Figure 11] This figure shows an example of the settings screen for waveform overlap width. [Figure 12] This figure shows an example of displaying data measured in each sweep separately. [Modes for carrying out the invention]
[0025] This disclosure relates to an optical spectrum analyzer for measuring the optical spectrum of pulsed light. In this disclosure, a grating method is employed as the measurement method. When measuring the optical spectrum of pulsed light, a grating method optical spectrum analyzer rotates a grating at an angle corresponding to each wavelength from the start wavelength to the end wavelength of the measurement wavelength range, and measures the optical spectrum, which is the optical intensity for each wavelength. The operation of rotating the grating at an angle corresponding to each wavelength to measure the optical spectrum is also called sweeping.
[0026] When measuring pulsed light, an optical spectrum analyzer can measure the optical spectrum of wavelengths corresponding to the period when the pulsed light is on, but it cannot measure the optical spectrum of wavelengths corresponding to the period when the pulsed light is off. Here, both the on and off periods of the pulsed light are included in a single sweep. Multiple sweeps are required to measure the optical intensity of all wavelengths within the wavelength measurement range.
[0027] When measuring pulsed light, an optical spectrum analyzer performs multiple sweeps, phase-shifted relative to a signal synchronized with the pulsed light, so that the pulsed light is on for at least one period during each sweep across all wavelengths in the measurement wavelength range. The phase shift during each sweep is controlled by delaying the start of each sweep relative to the timing of detecting the trigger of the signal synchronized with the pulsed light. The optical spectrum analyzer measures the optical spectrum across the entire measurement wavelength range by combining the measurement data obtained from each sweep.
[0028] The optical spectrum analyzer shifts the phase of each sweep according to the duty cycle of the pulsed light, so that for all wavelengths in the measurement wavelength range, the pulsed light is on for at least one period during each sweep. Here, the amount of phase shift during each sweep affects the measurement result of the optical spectrum.
[0029] Specifically, the smaller the phase shift in each sweep, the greater the overlap of wavelengths over which intensity can be obtained in each sweep. A larger overlap of wavelengths improves the quality of the waveform of the measured optical spectrum. On the other hand, if the phase shift is small, the number of measurements required to create a period in which the pulsed light is on for all wavelengths in the measurement wavelength range increases. A larger number of measurements increases the measurement time of the optical spectrum. In other words, there is a trade-off between the length of the measurement time and the quality of the waveform of the measured optical spectrum. It is necessary to adjust the balance between the measurement time of the optical spectrum and the quality of the measured waveform.
[0030] Therefore, according to this disclosure, in an optical spectrum analyzer, the overlap width of wavelengths over which intensity can be obtained in each sweep is set. The user can set the overlap width of wavelengths while viewing the measured waveform. As a result, the balance between the measurement time of the optical spectrum and the quality of the measured waveform is adjusted.
[0031] The embodiments relating to this disclosure will be described below in comparison with comparative examples.
[0032] (Comparative example) In the comparative example, the duty cycle of the pulsed light measured by the optical spectrum analyzer is assumed to be 50%. Furthermore, the intensity of each wavelength of the pulsed light is assumed to be uniform.
[0033] The optical spectrum analyzer initiates a sweep triggered by a gate signal synchronized with the pulsed light. As shown in the timing chart in Figure 1A, the gate signal is represented by two signal levels: HI and LO. The gate signal level is assumed to be HI when the pulsed light is ON, and LO when the pulsed light is OFF.
[0034] In Figure 1A, the optical spectrum analyzer initiates its first sweep operation triggered by the rising edge of the gate signal. The rising edge of the gate signal means that the signal level of the gate signal changes from LO to HI. During the period in which the optical spectrum analyzer is performing the sweep operation, the signal level of the sweep operation is represented as HI. The time it takes for the optical spectrum analyzer to move the grating to cover the entire measurement wavelength range is represented as T_E.
[0035] By performing a sweep operation at the timings shown in the timing chart of Figure 1A, the waveform shown in Figure 1B is obtained as the optical spectrum of the pulsed light in the measurement wavelength range. The time on the horizontal axis of Figure 1B is represented with 0 as the time when the sweep operation starts. When the duty cycle of the pulsed light is 50%, the intensity of the optical spectrum is obtained in a range of 50% of the measurement wavelength range.
[0036] In the comparative example, the optical spectrum analyzer starts its second sweep operation at a time T_D delayed from time 0, when the gate signal rises, as shown in Figure 2A. T_D is also called the delay time. In Figure 2A, the delay time T_D is set to 100% of the pulse width of the pulsed light, i.e., 100% of the pulse width of the gate signal. The pulse width represents the length of time during which the pulsed light is ON.
[0037] By performing a sweep operation at the timings shown in the timing chart of Figure 2A, the waveform shown in Figure 2B is obtained as the optical spectrum of pulsed light in the measurement wavelength range. The time on the horizontal axis of Figure 2B is represented with 0 as the time when the sweep operation starts. Because the delay time T_D is set to 100% of the pulse width, the range in which the optical spectrum intensity is obtained in Figure 2B complements the range in which the optical spectrum intensity is obtained in Figure 1B. In other words, for wavelengths in which intensity is not obtained in Figure 1B, intensity is obtained in Figure 2B.
[0038] By combining the waveform obtained in the first sweep operation shown in Figure 1B and the waveform obtained in the second sweep operation shown in Figure 2B, the waveform of the pulsed light spectrum is generated, as shown in Figure 3.
[0039] Here, the waveforms of the pulsed light spectra shown in Figures 1B and 2B have a loss at the initial wavelength when the pulse rises. A loss is a state where the measured light intensity is lower than what should be measured. The range in which intensity is obtained in the waveform of Figure 1B corresponds to the range in which intensity is not obtained in the waveform of Figure 2B. Conversely, the range in which intensity is not obtained in the waveform of Figure 1B corresponds to the range in which intensity is obtained in the waveform of Figure 2B. Therefore, the waveforms of Figures 1B and 2B are combined without overlapping. As a result, a loss remains in the waveform shown in Figure 3.
[0040] The quality of the optical spectrum deteriorates due to defects remaining in the waveform. In this case, if a defect exists in a certain waveform, it is conceivable to compensate for the defect by detecting the intensity of the defective range with another sweep. Specifically, this could involve performing multiple sweeps with adjusted delay times to ensure that no defects remain in the waveform.
[0041] In the comparative example, the delay time is determined considering the defects shown in Figures 1B and 2B. However, the length of time from the rise of the pulsed light to the occurrence of defects can vary. When determining the delay time, it is conceivable to set a longer delay time to allow for a margin of error, but the longer the delay time, the longer the measurement time. It is necessary to achieve both the maintenance of the waveform quality of the optical spectrum and the reduction of measurement time.
[0042] Hereinafter, this disclosure describes a pulsed light measurement method, a pulsed light measurement program, and an optical spectrum analyzer 10 (see Figure 4) that can adjust the balance between the measurement time of the optical spectrum and the quality of the measured waveform.
[0043] (Example configuration of optical spectrum analyzer 10) As shown in Figure 4, an optical spectrum analyzer 10 according to one embodiment of the present disclosure comprises an optical input unit 11, an optical detection unit 12, a measurement unit 13, a display unit 14, and an operation unit 15.
[0044] The optical input unit 11 includes an input port. The input port is configured to accept pulsed light to be measured by the optical spectrum analyzer 10.
[0045] The photodetector 12 comprises a spectrometer and a photodetector. The spectrometer separates pulsed light into light of each wavelength and allows light of the wavelength to be detected to pass through. In this disclosure, a grating is used as the spectrometer. The photodetector 12 moves the grating and performs a sweep according to control instructions from the measurement unit 13, and detects the light intensity of each wavelength in the measurement wavelength range.
[0046] The measurement unit 13 controls the timing at which the photodetector 12 starts its sweep operation, causing the photodetector 12 to perform multiple sweep operations. The measurement unit 13 acquires the detection results from the photodetector 12 for each sweep and generates the waveform of the pulsed light spectrum by synthesizing the waveforms of the detection results.
[0047] The measurement unit 13 may be configured to include a processor such as a CPU (Central Processing Unit). The measurement unit 13 may achieve predetermined functions by causing the processor to execute a predetermined program. The measurement unit 13 may be configured to include a dedicated circuit such as an FPGA (Field Programmable Gate Array).
[0048] The measurement unit 13 may include a storage unit. The storage unit stores various information used for the operation of the optical spectrum analyzer 10, or programs for realizing the functions of the optical spectrum analyzer 10. The storage unit may function as the work memory of the measurement unit 13. The storage unit may be composed of, for example, semiconductor memory. The storage unit may include volatile memory or non-volatile memory. At least a part of the storage unit may be configured as a storage device connected to the outside of the optical spectrum analyzer 10.
[0049] The measurement unit 13 may be implemented as a computer such as a desktop PC (Personal Computer) or notebook PC, connected to the outside of the optical spectrum analyzer 10.
[0050] The display unit 14 may be configured to include various displays, such as a liquid crystal display. The display unit 14 may be configured as a touch panel display that displays a GUI (Graphical User Interface) that functions as the operation unit 15 and accepts input from the user. In other words, the display unit 14 may be configured integrally with the operation unit 15.
[0051] The operation unit 15 may include an input device that receives input from the user. The input device may include, for example, a keyboard or physical keys, or a pointing device such as a touch panel, touch sensor, or mouse. The operation unit 15 may be configured as a touch panel display integrated with the display unit 14, as described above. The operation unit 15 is also simply referred to as the input unit.
[0052] (Example of operation of the optical spectrum analyzer 10) The optical spectrum analyzer 10 generates the waveform of the optical spectrum of pulsed light. By performing a single sweep, the optical spectrum analyzer 10 can acquire the waveform of a portion of the optical spectrum waveforms within the measurement wavelength range of the pulsed light. The optical spectrum analyzer 10 synthesizes the waveforms acquired in each of the multiple sweeps to generate the waveform of the optical spectrum of all wavelengths within the measurement wavelength range of the pulsed light. The waveform obtained by synthesizing the waveforms acquired in each of the multiple sweeps is also called the composite waveform.
[0053] Here, the waveform acquired in a single sweep is the waveform of the wavelength corresponding to the period during which the pulsed light is ON. When the ON period of the pulsed light begins, a loss occurs in the waveform in the initial stage of the pulsed light's rise. This loss degrades the quality of the waveform of the pulsed light's optical spectrum. The wavelength range in which the waveform has a loss is also called the loss range.
[0054] Loss ranges in the waveform acquired in a single sweep are compensated for by acquiring waveforms of the same wavelength range in other sweeps without loss. The optical spectrum analyzer 10 according to this disclosure is configured to allow setting the wavelength overlap of waveforms acquired in each of multiple sweeps so that loss ranges are compensated for by waveforms acquired in other sweeps. By being able to set the wavelength overlap, the user can set the wavelength overlap by looking at the measured waveform. As a result, the balance between the measurement time of the optical spectrum and the quality of the measured waveform is adjusted.
[0055] The following describes a specific example of the operation of the optical spectrum analyzer 10 related to this disclosure.
[0056] The optical spectrum analyzer 10 may perform a pulsed light measurement method, including the steps in the flowchart illustrated in Figure 5. The pulsed light measurement method may be implemented as a pulsed light measurement program to be executed by the optical spectrum analyzer 10. The pulsed light measurement program may be stored on a non-temporary, computer-readable medium.
[0057] The measurement unit 13 sets the overlap width (step S1). The overlap width is expressed as a ratio to the length of the pulse width of the pulsed light. In this disclosure, the overlap width is set to Y%, where Y is set to a value greater than 0% and less than 100%. In this disclosure, Y is set to 50%. The duty cycle of the pulsed light is expressed as X%, and in this disclosure, it is set to 50%. In this case, the overlap width corresponds to 25% of the pulse period. The measurement unit 13 may set the overlap width based on setting input from the user, as will be described later. By setting the overlap width as a ratio to the pulse width, the user can easily understand the overlap width intuitively. As a result, user convenience is improved.
[0058] The measurement unit 13 sets a delay time for the photodetector 12 (step S2). The delay time is the time by which the photodetector 12 delays the start of each sweep from the rising edge of the gate signal synchronized with the pulse light when performing multiple sweeps. By sequentially extending the delay time when performing multiple sweeps, the measurement unit 13 can superimpose the wavelengths of the waveforms acquired in each sweep so that the missing range of the waveform acquired in one sweep is complemented by the waveforms acquired in other sweeps. The measurement unit 13 sets the delay time to zero when performing the first sweep.
[0059] The light detection unit 12 determines whether a gate signal trigger has been detected (step S3). A gate signal trigger is a trigger caused by a change in the signal level of the gate signal. In this disclosure, the gate signal trigger is assumed to occur when the gate signal rises.
[0060] As illustrated in Figure 6A, during the first sweep, a gate signal trigger is considered to have occurred when the signal level of the gate signal changes from LO to HI. The time at which the gate signal trigger occurred is represented by 0.
[0061] If the light detection unit 12 does not detect a gate signal trigger (step S3: NO), it repeats the determination procedure in step S3 until it detects a gate signal trigger.
[0062] If the light detection unit 12 detects a gate signal trigger (step S3: YES), it determines whether a delay time has elapsed since the gate signal trigger was detected (step S4). If the delay time is set to zero, the light detection unit 12 determines that the delay time has elapsed when the gate signal trigger is detected.
[0063] If the delay time has not elapsed (step S4: NO), the light detection unit 12 repeats the determination procedure of step S4 until the delay time has elapsed.
[0064] The photodetector 12 starts sweeping (step S5) when the delay time has elapsed (step S4: YES). As described above, the delay time for the first sweep is set to zero. Therefore, as illustrated in Figure 6A, the photodetector 12 starts the first sweep operation from time 0 when the gate signal trigger occurs. The period during which the sweep operation is performed is represented by the state in which the sweep operation signal level is HI.
[0065] The photodetector 12 determines whether the sweep time has elapsed (step S6). The sweep time is the time required to move the grating so that the intensity of all wavelengths in the measurement wavelength range can be measured. The sweep time is represented by T_E. If the sweep time has not elapsed (step S6: NO), the photodetector 12 repeats the determination procedure in step S6 and continues sweeping across the entire measurement wavelength range until the sweep time has elapsed.
[0066] The photodetector 12 terminates one sweep operation when the sweep time has elapsed (step S6: YES). In the first sweep operation, the photodetector 12 can detect the waveform measured over the wavelength range corresponding to the period during which the pulsed light is turned on, as illustrated in Figure 6B.
[0067] In Figure 6B, the horizontal axis represents time. This time corresponds to each wavelength within the measurement wavelength range. Time 0 corresponds to the minimum wavelength within the measurement wavelength range. Time T_E corresponds to the maximum wavelength within the measurement wavelength range. The vertical axis represents the light intensity for each wavelength, with the maximum value being 1.
[0068] The light detection unit 12 outputs the detected waveform to the measurement unit 13.
[0069] The measurement unit 13 determines whether it has completed acquiring data within the measurement wavelength range after the photodetector 12 has finished one sweep operation (step S7). The measurement unit 13 acquires the waveform detected in one sweep operation from the photodetector 12. The measurement unit 13 determines that it has completed acquiring data within the measurement wavelength range if it has acquired waveforms at all wavelengths within the measurement wavelength range.
[0070] At the end of the first sweep operation, the measurement unit 13 has only acquired waveforms for a portion of the wavelength range. Therefore, the measurement unit 13 determines that it has not completed acquiring data for the measurement wavelength range. If the measurement unit 13 has not completed acquiring data for the measurement wavelength range (step S7: NO), it updates the delay time set for the photodetector 12 in order to perform the next sweep (step S8).
[0071] As described above, the measurement unit 13 sequentially extends the delay time when performing multiple sweeps. In other words, the measurement unit 13 sets the delay time for the next sweep to be the time extended from the delay time set when performing the previous sweep. The time extended from the delay time is calculated as the pulse width of the pulsed light multiplied by (1-Y / 100) when the overlap width of the pulsed light is expressed as Y%. Also, when the duty cycle of the pulsed light is expressed as X%, the pulse width is calculated as the pulse period length multiplied by (X / 100). Therefore, the time extended from the delay time is calculated as the pulse period length of the pulsed light multiplied by (X / 100) × (1-Y / 100). For example, if the pulse period of a pulsed light is 0.1 seconds, the duty cycle (X) of the pulsed light is 25%, and the overlap width (Y) is 10%, the time to be extended from the delay time can be calculated as 0.0225 seconds by calculating 0.1 × (25 / 100) × (1 - 10 / 100).
[0072] In this disclosure, the duty cycle (X) of the pulsed light is assumed to be 50%. The overlap width (Y) is also set to 50% as described above. The measurement unit 13 updates the delay time by a time equal to the length of the pulse width of the pulsed light multiplied by the overlap width set to 50%. In this case, the delay time corresponds to 25% of the pulse period, or 1 / 4 of the length. The updated delay time is denoted by T_D1. After the measurement unit 13 updates the delay time, the procedure returns to step S3, and the photodetector 12 performs a second sweep operation as the next sweep.
[0073] If the photodetector 12 determines in step S3 that it has detected a gate signal trigger and determines in step S4 that the delay time T_D1 has elapsed, it starts the second sweep operation in step S5 from time T_D1, as illustrated in Figure 7A. The period during which the sweep operation is performed is represented by the sweep operation signal level being HI. In step S6, the photodetector 12 continues the second sweep operation until time T_E+T_D1 and then terminates it.
[0074] The photodetector 12 can detect the waveform exemplified in Figure 7B during the second sweep operation. The time on the horizontal axis of Figure 7B is displayed as the time obtained by subtracting T_D1 from the time in Figure 7A, so as to match the relationship between the measurement wavelength range and time in Figure 6B. In other words, the time when the sweep starts is represented as 0, and the time when the sweep ends is represented as T_E. The time 0 on the horizontal axis of Figure 7B corresponds to the minimum wavelength in the measurement wavelength range, and the time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity for each wavelength, and is displayed so that the maximum value is 1.
[0075] In a comparison between the waveform in Figure 7B and the waveform in Figure 6B, the wavelength range detected in the waveform in Figure 7B has shifted to a shorter wavelength side by a length of 1 / 4 of the pulse period, i.e., a phase of 90 degrees, compared to the wavelength range detected in the waveform in Figure 6B. However, even when the waveforms in Figure 6B and Figure 7B are combined, there are still wavelengths within the measurement wavelength range for which waveforms have not been acquired. Therefore, the measurement unit 13 determines that it has not completed acquiring data for the measurement wavelength range and updates the delay time set in the photodetector 12 in the procedure of step S8.
[0076] The measurement unit 13 updates the delay time for the third sweep operation by extending it from the delay time for the second sweep operation by a time equal to 50% of the pulse width of the pulsed light multiplied by the overlap width. The updated delay time is denoted as T_D2. After the measurement unit 13 updates the delay time, the procedure returns to step S3, and the photodetector 12 performs the third sweep operation as the next sweep.
[0077] If the photodetector 12 determines in step S3 that it has detected a gate signal trigger and determines in step S4 that the delay time T_D2 has elapsed, it starts the third sweep operation in step S5 from time T_D2, as illustrated in Figure 8A. The period during which the sweep operation is performed is represented by the sweep operation signal level being HI. In step S6, the photodetector 12 continues the third sweep operation until time T_E+T_D2 and then terminates it.
[0078] The photodetector 12 can detect the waveform exemplified in Figure 8B during the third sweep operation. The time on the horizontal axis of Figure 8B is displayed as the time obtained by subtracting T_D2 from the time in Figure 8A, so as to match the relationship between the measurement wavelength range and time in Figures 6B and 7B. In other words, the time when the sweep starts is represented as 0, and the time when the sweep ends is represented as T_E. The time 0 on the horizontal axis of Figure 8B corresponds to the minimum wavelength in the measurement wavelength range, and the time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity for each wavelength, and is displayed so that the maximum value is 1.
[0079] In a comparison between the waveform in Figure 8B and the waveform in Figure 7B, the wavelength range detected in the waveform in Figure 8B is shifted to a shorter wavelength side by a length of 1 / 4 of the pulse period, i.e., a phase of 90 degrees, compared to the wavelength range detected in the waveform in Figure 7B. Here, when the waveforms in Figure 6B, Figure 7B, and Figure 8B are combined, waveforms are acquired for all wavelengths in the measurement wavelength range. However, the missing range in the waveform in Figure 8B does not overlap with the wavelength ranges of the waveforms in Figures 6B and 7B. Therefore, the measurement unit 13 determines that it has not completed acquiring data for the measurement wavelength range and updates the delay time set in the photodetector 12 in the procedure of step S8.
[0080] The measurement unit 13 updates the delay time for the fourth sweep operation by extending it from the delay time for the third sweep operation by a time equal to 50% of the pulse width of the pulsed light multiplied by the overlap width. The updated delay time is represented as T_D3. After the measurement unit 13 updates the delay time, the procedure returns to step S3, and the photodetector 12 performs the fourth sweep operation as the next sweep.
[0081] If the photodetector 12 determines in step S3 that it has detected a gate signal trigger and determines in step S4 that the delay time T_D3 has elapsed, it starts the fourth sweep operation in step S5 from time T_D3, as illustrated in Figure 9A. The period during which the sweep operation is performed is represented by the sweep operation signal level being HI. In step S6, the photodetector 12 continues the fourth sweep operation until time T_E+T_D3 and then terminates it.
[0082] The photodetector 12 can detect the waveform exemplified in Figure 9B during the fourth sweep operation. The time on the horizontal axis of Figure 9B is displayed as the time obtained by subtracting T_D3 from the time in Figure 9A, so as to match the relationship between the measurement wavelength range and time in Figures 6B, 7B, and 8B. In other words, the time when the sweep starts is represented as 0, and the time when the sweep ends is represented as T_E. The time 0 on the horizontal axis of Figure 9B corresponds to the minimum wavelength in the measurement wavelength range, and the time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity for each wavelength, and is displayed so that the maximum value is 1.
[0083] In a comparison between the waveform in Figure 9B and the waveform in Figure 8B, the wavelength range detected in the waveform in Figure 9B is shifted to a shorter wavelength side by a length of 1 / 4 of the pulse period, i.e., a phase of 90 degrees, compared to the wavelength range detected in the waveform in Figure 8B. Here, when the waveforms in Figure 6B, Figure 7B, Figure 8B, and Figure 9B are combined, waveforms are acquired for all wavelengths in the measurement wavelength range. In addition, the missing ranges in each of the waveforms in Figures 6B, 7B, 8B, and 9B overlap with the wavelength range of at least one other waveform. Therefore, the measurement unit 13 determines that it has completed the acquisition of data for the measurement wavelength range.
[0084] When the measurement unit 13 has finished acquiring data within the measurement wavelength range (step S7: YES), it synthesizes the waveform data acquired in each sweep and displays it on the display unit 14 (step S9). The measurement unit 13 may synthesize the waveforms based on the rules shown as (1) and (2) below.
[0085] (1) The wavelength intensity detected by a single sweep is directly used in the composite waveform. (2) In the waveforms detected by two or more sweeps, the light intensity of overlapping wavelengths is used as the intensity detected in each sweep during the period in which the waveform data is not missing data. The period in which the waveform data is not missing data is the period in which the gate signal is on that is after a predetermined time has elapsed since the gate signal was turned on. Conversely, the period in which the waveform data is missing data is the period in which the gate signal is on that is within a predetermined time after the gate signal was turned on.
[0086] The measurement unit 13 may store, in association with the waveform data, at least one of the periods in which the waveform data is not missing or is missing, as used in (2) above, when performing each sweep, and refer to it when synthesizing the waveform data.
[0087] The measurement unit 13 may appropriately set a predetermined time for identifying periods in the waveform data that are not missing or periods that are missing. The measurement unit 13 may accept input from the user to set a predetermined time and set the value entered by the user as the predetermined time. The measurement unit 13 may analyze the waveform in which the intensity of a test signal changes in a step-like manner from LO to HI, and set a predetermined time based on the length of the period from when the intensity of the test signal becomes HI until the intensity of the waveform stabilizes.
[0088] This process eliminates data loss in the synthesized waveform, resulting in improved waveform quality.
[0089] Furthermore, when the measurement unit 13 increases the delay time in the order in which it performs multiple sweeps, it may synthesize waveforms based on the rule shown as (3) below, instead of (2) above.
[0090] (3) In waveforms detected by two or more sweeps, the light intensity of overlapping wavelengths is used in the composite waveform, regardless of whether the waveform data contains missing data. In other words, the intensity of the composite waveform is overwritten by the intensity detected in the later sweep.
[0091] Because the intensity detected in a later sweep overwrites the previous sweep, the waveform acquired in the earlier sweep does not need to be saved. As a result, the process of synthesizing the waveforms becomes simpler. In addition, the memory capacity required to save the waveforms is reduced.
[0092] The measuring unit 13 may synthesize waveforms based on the following rule, which is a combination of (2) and (3), instead of (2) or (3) above.
[0093] (4) Among the light intensities of wavelengths that overlap in waveforms detected by two or more sweeps, the intensities detected in the later sweep among the intensities detected during the period in which the waveform data is not missing data are adopted as the composite waveform.
[0094] The measurement unit 13 may synthesize waveforms based on the rule shown as (5) below, instead of (2) to (4) above.
[0095] (5) In waveforms detected by two or more sweeps, the larger of the intensities detected in each sweep is used as the light intensity of overlapping wavelengths, regardless of whether the waveform data contains missing data.
[0096] This process eliminates data loss in the synthesized waveform, resulting in improved waveform quality.
[0097] The measuring unit 13 may synthesize waveforms based on the rules shown as (6) below, which combine (2) and (5) above, instead of (2) to (5) above.
[0098] (6) For waveforms detected by two or more sweeps, the larger of the intensities detected during periods when the waveform data is not missing data is adopted as the light intensity of wavelengths that overlap with each other.
[0099] As illustrated in Figure 10, the measurement unit 13 displays the composite waveform of the pulsed light spectrum on the display unit 14. In the composite waveform, the defects remain at the shortest wavelength end of the measurement wavelength range, but are eliminated in the other ranges.
[0100] The shortest wavelength loss in the measurement wavelength range is difficult to eliminate because it corresponds to the rising edge of the pulse in each sweep. In the optical spectrum analyzer 10, the grating of the photodetector 12 may be configured to move from a wavelength shorter than the minimum value of the measurement wavelength range. By setting the wavelength at which the sweep operation starts to a wavelength shorter than the minimum value of the measurement wavelength range, the shortest wavelength loss in the measurement wavelength range can be eliminated.
[0101] In the operation examples described above, data acquisition within the measurement wavelength range was completed by performing four sweep operations. The number of sweep operations required to complete the acquisition of data within the measurement wavelength range is calculated as a natural number obtained by rounding up the decimal part of the value calculated as (100 / X) × {100 / (1-Y / 100)}. For example, if the duty cycle (X) of the pulsed light is 25% and the overlap width (Y) is 50%, the number of sweep operations is calculated as 8 by calculating (100 / 25) × {100 / (1-50 / 100)}.
[0102] If the wavelengths of the waveforms acquired in each sweep do not overlap at all, i.e., the overlap width (Y) is 0%, the required number of sweeps is calculated by calculating 100 / X. If the calculation result of the required number of sweeps results in a fractional part, the decimal part is rounded up. For example, if the duty cycle of the pulsed light is 25%, the required number of sweeps is calculated as 4 by calculating 100 / 25. For example, if the duty cycle of the pulsed light is 30%, the required number of sweeps is calculated as 4 by calculating 100 / 30 and rounding up the decimal part. On the other hand, as will be described later, the required number of sweeps increases as the overlap width increases.
[0103] After executing the procedure in step S9, the measurement unit 13 terminates the execution of the procedure in the flowchart of Figure 5. After executing the procedure in step S9, the measurement unit 13 may restart the procedure in the flowchart of Figure 5. In this case, the user may set the overlap width in step S1 by looking at the composite waveform displayed as a result of the previous operation of the flowchart in Figure 5. If there are missing values in the composite waveform, the user may set the overlap width to a larger value so that there are no missing values when the next operation of the flowchart in Figure 5 is performed. Conversely, if there are no missing values in the composite waveform, the user may set the overlap width to a smaller value so that the measurement time can be shortened when the next operation of the flowchart in Figure 5 is performed.
[0104] To allow the user to set the overlap width, the optical spectrum analyzer 10 may display a setting window 143 on the display unit 14 as a GUI for setting the overlap width, as illustrated in Figure 11. The setting window 143 may be displayed when an operation such as touching or clicking is input to the setting unit 142 that displays the set value for the overlap width. The setting window 143 may be displayed on top of the waveform display unit 141 that displays the waveform, or it may be displayed outside the waveform display unit 141. The setting window 143 may be configured to accept input of a value to be set to Y%, which represents the overlap width. For example, the setting window 143 may be configured to accept values from 1% to 99%.
[0105] The optical spectrum analyzer 10 may accept input from the user for setting the overlap width in the setting window 143 while the composite waveform is displayed on the waveform display unit 141. Accepting input for setting the overlap width while the composite waveform is displayed makes it easier for the user to decide how to set the overlap width. As a result, user convenience is improved.
[0106] The optical spectrum analyzer 10 may accept input from the user for the overlap width setting in the setting window 143 while performing multiple sweeps. By accepting input for the overlap width setting while performing multiple sweeps, the user can immediately see how the overlap width setting changes the composite waveform, making it easier to decide how to set the overlap width. As a result, user convenience is improved.
[0107] The settings window 143 may be configured to allow input of a setting represented as AUTO. If the overlap width is set to AUTO, the measurement unit 13 automatically sets the overlap width. The measurement unit 13 may, for example, set the overlap width to 5%. The measurement unit 13 may analyze the missing range of the waveform acquired in each sweep and automatically set the overlap width so that the missing data is eliminated in the composite waveform.
[0108] Before completing the acquisition of data within the measurement wavelength range, the measurement unit 13 may sequentially synthesize the waveforms acquired in each sweep and display them on the display unit 14 as an intermediate result of the measurement.
[0109] The measurement unit 13 may display the waveforms acquired in each sweep on the display unit 14 in a manner that allows them to be distinguished from one another, as illustrated in Figure 12. In the example in Figure 12, the waveforms acquired in each of the three sweeps are displayed with different line types. The waveforms acquired in each sweep may also be displayed in a manner that allows them to be distinguished by line color. The waveforms acquired in each sweep may be displayed in various other manners, not limited to line type or line color. Displaying the waveforms acquired in each sweep in a manner that allows them to be distinguished from one another makes it easier for the user to decide how to set the overlap width. As a result, user convenience is improved.
[0110] The measurement unit 13 sequentially increased the delay time as the number of sweeps increased, but the delay time may be shortened between repeated sweeps. Also, the measurement unit 13 set the delay time so that the difference in delay time between each sweep was equal, but the delay time may be set so that the difference in delay time between each sweep was different.
[0111] The measurement unit 13 may determine the number of sweeps to perform based on the pulse width and overlap width. By determining the number of sweeps performed by the measurement unit 13, the measurement time becomes easier to understand. The measurement unit 13 may set the delay time so that the difference in delay time in each sweep is equal, in accordance with the determined number of sweeps.
[0112] (summary) As described above, the optical spectrum analyzer 10 according to this disclosure detects the waveform of the optical spectrum of pulsed light in different wavelength ranges in each sweep by setting the overlap width of the waveforms acquired in each sweep and varying the timing of the start of each sweep when performing multiple sweeps. The optical spectrum analyzer 10 generates the waveform of the optical spectrum of pulsed light by synthesizing the waveforms detected in each sweep so as to eliminate waveform loss that occurs in the initial rise of the pulsed light. Furthermore, the optical spectrum analyzer 10 is configured so that the user can set the overlap width by viewing the waveform of the optical spectrum. As a result, the balance between the measurement time of the optical spectrum and the quality of the measured waveform is adjusted. In addition, user convenience is improved.
[0113] In the embodiments described above, the overlap width was expressed as a ratio to the length of the pulse width of the pulsed light, but it may also be expressed in various other ways, such as a ratio to the length of the pulse period of the pulsed light.
[0114] While embodiments relating to this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, the functions included in each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated. [Explanation of Symbols]
[0115] 10. Optical Spectrum Analyzer 11 Optical input section 12. Light detection unit 13 Measuring part 14 Display Unit (141: Waveform Display Unit, 142: Settings Unit, 143: Settings Window) 15 Control section
Claims
1. A pulsed light measurement method for measuring the optical spectrum of pulsed light, Setting the overlap width of the wavelengths for which light intensity is measured in each of the multiple sweeps performed within the measurement wavelength range of the aforementioned optical spectrum, After detecting the trigger of the gate signal synchronized with the pulse light, and after a delay time determined based on the overlap width has elapsed, each of the multiple sweeps is initiated. The optical spectrum is synthesized and displayed from the multiple waveforms obtained by performing the aforementioned multiple sweeps. A pulsed light measurement method, including the above.
2. The pulsed light measurement method according to claim 1, wherein when synthesizing the optical spectrum from the plurality of waveforms, the intensity detected during a period in which the waveform data is not missing is adopted as the light intensity of the wavelengths that overlap with each other in the plurality of waveforms.
3. The pulsed light measurement method according to claim 1, wherein, when the delay time is increased in the order in which the multiple sweeps are performed, when synthesizing the optical spectrum from the multiple waveforms, the intensity detected in the later sweep is adopted as the light intensity of the wavelengths that overlap with each other in the multiple waveforms.
4. The pulsed light measurement method according to claim 1, wherein when the delay time is increased in the order in which the multiple sweeps are performed, when synthesizing the optical spectrum from the multiple waveforms, the intensity detected in a later sweep is adopted as the light intensity of wavelengths that overlap with each other in the multiple waveforms, from among the intensities detected during the period in which the waveform data is not missing data.
5. The pulsed light measurement method according to claim 1, wherein when synthesizing the optical spectrum from the plurality of waveforms, the larger value is adopted as the light intensity of the wavelengths that overlap with each other in the plurality of waveforms.
6. The pulsed light measurement method according to claim 1, wherein when synthesizing the optical spectrum from the plurality of waveforms, the larger value of the intensities detected during the period in which the waveform data is not missing is adopted as the light intensity of the wavelengths that overlap with each other in the plurality of waveforms.
7. The pulse light measurement method according to any one of claims 1 to 6, further comprising setting the overlap width as a ratio to the pulse width of the pulse light.
8. The pulsed light measurement method according to claim 7, further comprising determining the number of times to perform the sweep based on the pulse width and the overlap width.
9. The pulsed light measurement method according to any one of claims 1 to 6, further comprising displaying the waveforms obtained in each of the multiple sweeps in a distinguishable manner.
10. The pulsed light measurement method according to any one of claims 1 to 6, further comprising receiving input for setting the overlap width while performing the aforementioned multiple sweeps.
11. The pulsed light measurement method according to any one of claims 1 to 6, further comprising receiving input for setting the overlap width while the waveform of the light spectrum is being displayed.
12. An optical spectrum analyzer that measures the optical spectrum of pulsed light, Setting the overlap width of the wavelengths for which light intensity is measured in each of the multiple sweeps performed within the measurement wavelength range of the aforementioned optical spectrum, After detecting the trigger of the gate signal synchronized with the pulse light, and after a delay time determined based on the overlap width has elapsed, each of the multiple sweeps is initiated. The optical spectrum is synthesized and displayed from the multiple waveforms obtained by performing the aforementioned multiple sweeps. A pulse light measurement program that performs this operation.
13. It comprises a measuring unit for measuring the optical spectrum of pulsed light and a photodetecting unit for detecting the optical intensity of each wavelength of the pulsed light, The measurement unit sets the overlap width of the wavelengths for which the light intensity is measured in each of the multiple sweeps performed within the measurement wavelength range of the light spectrum. The light detection unit detects the trigger of the gate signal synchronized with the pulse light, and after a delay time determined based on the overlap width has elapsed, it starts each of the multiple sweeps. The measurement unit is an optical spectrum analyzer that synthesizes and displays the optical spectrum from multiple waveforms obtained by performing the multiple sweeps.