Pulsed light measurement method, pulsed light measurement program, and optical spectrum analyzer

Abstract

To provide a pulsed light measurement method, a pulsed light measurement program, and an optical spectrum analyzer capable of adjusting the balance between measurement time of an optical spectrum and quality of a measured waveform.SOLUTION: A pulsed light measurement method for measuring an optical spectrum of pulsed light includes: setting of overlapping width of a waveform for measuring light intensity in each of multiple times of sweeping executed in a measurement wavelength range of an optical spectrum; starting of each of multiple times of sweeping at a lapse of delay time determined based on overlapping width after detecting the trigger of a gate signal synchronized with pulsed light; and composition and display of an optical spectrum from multiple waveforms obtained by executing multiple times of sweeping.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a pulsed light measurement method, a pulsed light measurement program, and an optical spectrum analyzer. [Background technology]

[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] Patent No. 5339027 Summary of the Invention [Problem to be solved by the invention]

[0004] When an optical spectrum analyzer measures an optical spectrum using a grating, it rotates the grating by 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 light intensity for each wavelength. The operation of measuring the optical spectrum by rotating the grating by an angle corresponding to each wavelength is also called sweeping.

[0005] When measuring the optical spectrum of pulsed light by performing a sweep, optical spectrum data is obtained when the pulsed light is emitted, i.e., when the gate signal synchronized with the pulsed light is HI, as shown in Figures 1A and 1B, but not when the pulsed light is not emitted, i.e., when the gate signal is LO.

[0006] Therefore, to complete the acquisition of optical spectrum data for all wavelengths within the measurement wavelength range, multiple measurements are performed with the phase of the pulse signal shifted, thereby acquiring spectrum data for the entire pulse period. The smaller the phase shift, i.e., the more measurements are performed, the greater the overlap width of the waveforms obtained in each measurement. The greater the overlap width of the waveforms, the better the quality of the measured optical spectrum waveforms.

[0007] On the other hand, the more measurements are performed, the longer the optical spectrum measurement time becomes. In other words, there is a trade-off between the length of measurement time and the quality of the measured optical spectrum waveform. It is necessary to improve user convenience by shortening the measurement time while maintaining the quality of the optical spectrum waveform.

[0008] The present disclosure has been 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] According to some embodiments, a pulsed light measurement method (1) is a method for measuring an optical spectrum of pulsed light, the pulsed light measurement method including: setting an overlap width of wavelengths whose optical intensity is measured in each of a plurality of sweeps performed in a measurement wavelength range of the optical spectrum; starting each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed since detecting a trigger of a gate signal synchronized with the pulsed light; and synthesizing and displaying the optical spectrum from a plurality of waveforms obtained by performing the plurality of sweeps.

[0010] The ability to set the wavelength overlap width when performing multiple sweeps ensures both the quality of the optical spectrum waveform and shortens the measurement time, thereby improving user convenience.

[0011] In one embodiment (2) of the pulsed light measurement method described in (1) above, when synthesizing the optical spectrum from the plurality of waveforms, the intensities detected during a period in which the waveform data is not missing may be used as the optical intensities of wavelengths that overlap each other in the plurality of waveforms. This eliminates missing data in the synthesized waveform. As a result, the quality of the waveform is improved.

[0012] (3) In one embodiment of the pulsed light measurement method described in (1) above, when the delay time is increased in order of execution of the multiple sweeps, when synthesizing the optical spectrum from the multiple waveforms, a value obtained by executing a sweep executed later may be used as the optical intensity of wavelengths that overlap each other in the multiple waveforms. In this way, it is not necessary to store waveforms acquired by sweeps executed earlier. As a result, the process of synthesizing waveforms is simplified.

[0013] (4) In one embodiment of the pulsed light measurement method described in (1) above, 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 sweep performed later may be used as the optical intensity of wavelengths that overlap each other in the multiple waveforms, among the intensities detected during a period in which waveform data is not missing data.

[0014] (5) In one embodiment of the pulsed light measurement method described in (1) above, when synthesizing the optical spectrum from the plurality of waveforms, a larger value may be adopted as the optical intensity of wavelengths that overlap each other in the plurality of waveforms.

[0015] (6) In one embodiment of the pulsed light measurement method described in (1) above, when synthesizing the optical spectrum from the plurality of waveforms, the largest value of the intensities detected during a period in which the waveform data is not missing may be used as the optical intensity of the wavelengths that overlap each other in the plurality of waveforms.

[0016] (7) According to one embodiment, the pulsed light measurement method described in any one of (1) to (6) above may further include setting the overlap width as a ratio to the pulse width of the pulsed 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) According to one embodiment, the pulsed light measurement method described in (7) above may further include determining the number of times to perform the sweep based on the pulse width and the overlap width. This makes it easier to understand the measurement time.

[0018] (9) According to one embodiment, the pulsed light measurement method described in any one of (1) to (8) above may further include displaying the waveforms obtained by each of the multiple sweeps in a distinguishable manner. By displaying the waveforms obtained by each sweep in a distinguishable manner, the user can easily determine how to set the overlap width. As a result, user convenience is improved.

[0019] (10) According to one embodiment, the pulsed light measurement method described in any one of (1) to (9) above may further include receiving an input for setting the overlap width while the multiple sweeps are being performed. By receiving an input for setting the overlap width while the multiple sweeps are being performed, the user can immediately check how the overlap width setting changes the composite waveform, making it easier to determine how to set the overlap width. As a result, user convenience is improved.

[0020] (11) According to one embodiment, the pulsed light measurement method described in any one of (1) to (10) above may further include receiving an input for setting the overlap width while the waveform of the optical spectrum is displayed. By receiving an input for setting the overlap width while the waveform is displayed, the user can easily determine how to set the overlap width. As a result, user convenience is improved.

[0021] (12) A pulsed light measurement program according to some embodiments causes an optical spectrum analyzer that measures the optical spectrum of pulsed light to set an overlap width of wavelengths at which light intensity is measured in each of a plurality of sweeps performed in a measurement wavelength range of the optical spectrum, to start each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed since detecting a trigger of a gate signal synchronized with the pulsed light, and to synthesize and display the optical spectrum from a plurality of waveforms obtained by performing the plurality of sweeps.

[0022] According to some embodiments (13), an optical spectrum analyzer includes a measurement unit that measures the optical spectrum of pulsed light and a photodetector that detects the optical intensity of each wavelength of the pulsed light. The measurement unit sets an overlap width of wavelengths whose optical intensity is measured in each of multiple sweeps performed in the measurement wavelength range of the optical spectrum. The photodetector starts each of the multiple sweeps after detecting a trigger of a gate signal synchronized with the pulsed light and a delay time determined based on the overlap width has elapsed. The measurement unit synthesizes and displays the optical spectrum from multiple waveforms obtained by performing the multiple sweeps. [Effects of the Invention]

[0023] The pulsed light measurement method, pulsed light measurement program, and optical spectrum analyzer according to the present disclosure improve user convenience. [Brief explanation of the drawings]

[0024] [Figure 1A] 10 is a timing chart of a first sweep in a measurement method according to a comparative example. [Figure 1B] 1B is a waveform of the data measured by the sweep of FIG. 1A. [Figure 2A] 10 is a timing chart of a second sweep in a measurement method according to a comparative example. [Figure 2B] 2B is a waveform of the data measured by the sweep of FIG. 2A. [Figure 3]This is a waveform obtained by combining the waveforms in FIG. 2A and FIG. 2B. [Figure 4] FIG. 1 is a block diagram illustrating an example configuration of an optical spectrum analyzer according to an embodiment of the present disclosure. [Figure 5] 1 is a flowchart illustrating an example of a procedure for a pulsed light measurement method according to the present disclosure. [Figure 6A] 10 is a timing chart of the first sweep of the measurement method according to the present disclosure. [Figure 6B] 6B is a waveform of the data measured by the sweep of FIG. 6A. [Figure 7A] 10 is a timing chart of a second sweep in the measurement method according to the present disclosure. [Figure 7B] 7B is a waveform of the data measured by the sweep of FIG. 7A. [Figure 8A] 10 is a timing chart of the third sweep of the measurement method according to the present disclosure. [Figure 8B] 8B is a waveform of the data measured by the sweep of FIG. 8A. [Figure 9A] 10 is a timing chart of the fourth sweep of the measurement method according to the present disclosure. [Figure 9B] 9B is a waveform of the data measured by the sweep of FIG. 9A. [Figure 10] This waveform is a combination of the waveforms in FIG. 6B, 7B, 8B, and 9B. [Figure 11] FIG. 10 is a diagram showing an example of a screen for setting the overlap width of waveforms. [Figure 12] FIG. 10 is a diagram showing an example of displaying data measured in each sweep in a distinguishable manner. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present disclosure relates to an optical spectrum analyzer that measures the optical spectrum of pulsed light. In this disclosure, a grating-based measurement method is adopted. When measuring the optical spectrum of pulsed light, a grating-based optical spectrum analyzer rotates a grating by an angle corresponding to each wavelength from the start wavelength to the end wavelength of a measurement wavelength range, and measures the optical spectrum, which is the light intensity for each wavelength. The operation of measuring the optical spectrum by rotating the grating by an angle corresponding to each wavelength is also referred to as sweeping.

[0026] When measuring pulsed light, an optical spectrum analyzer can measure the optical spectrum of wavelengths corresponding to the periods when the pulsed light is on, but cannot measure the optical spectrum of wavelengths corresponding to the periods when the pulsed light is off. Here, a single sweep includes both periods when the pulsed light is on and periods when the pulsed light is off. To measure the optical intensity of all wavelengths in the wavelength measurement range, multiple sweeps must be performed.

[0027] When measuring pulsed light, an optical spectrum analyzer performs multiple sweeps with phase shifts relative to a signal synchronized with the pulsed light so that the period when the pulsed light is on occurs for all wavelengths in the measurement wavelength range in at least one sweep. The phase shift when performing each sweep is controlled by delaying the start of each sweep relative to the timing when the trigger of the signal synchronized with the pulsed light is detected. The optical spectrum analyzer measures the optical spectrum over the entire measurement wavelength range by combining the measurement data obtained from each sweep.

[0028] The optical spectrum analyzer shifts the phase when performing each sweep in accordance with the duty ratio of the pulsed light so that the period when the pulsed light is on occurs in at least one sweep for all wavelengths in the measurement wavelength range. Here, the amount of phase shift when performing each sweep affects the measurement results of the optical spectrum.

[0029] Specifically, the smaller the phase shift in each sweep, the wider the overlap width of wavelengths whose intensity can be obtained in each sweep. The wider the overlap width of wavelengths, the better 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 generate a period in which the pulsed light is on for all wavelengths in the measurement wavelength range increases. The more measurements are made, the longer 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 the present disclosure, the wavelength overlap width that allows the intensity to be acquired in each sweep is set in the optical spectrum analyzer. The user can set the wavelength overlap width 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 can be adjusted.

[0031] Hereinafter, an embodiment according to the present disclosure will be described in comparison with a comparative example.

[0032] (Comparative Example) In the comparative example, it is assumed that the duty ratio of the pulsed light to be measured by the optical spectrum analyzer is 50%, and that the intensity of each wavelength of the pulsed light is uniform.

[0033] The optical spectrum analyzer starts sweeping using a gate signal synchronized with the pulsed light as a trigger. As shown in the timing chart in Figure 1A, the gate signal is represented by two signal levels: HI and LO. Suppose the signal level of the gate signal becomes HI in synchronization with the period when the pulsed light is on. Suppose the signal level of the gate signal becomes LO in synchronization with the period when the pulsed light is off.

[0034] In Figure 1A, the optical spectrum analyzer starts the 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. While the optical spectrum analyzer is performing the sweep operation, the signal level of the sweep operation is represented by HI. The time it takes for the optical spectrum analyzer to move the grating so that it covers the entire measurement wavelength range is represented by T_E.

[0035] By performing the sweep operation at the timing shown in the timing chart of Fig. 1A, the waveform shown in Fig. 1B is obtained as the optical spectrum of the pulsed light in the measurement wavelength range. The time on the horizontal axis of Fig. 1B is expressed with 0 as the time when the sweep operation starts. When the duty ratio of the pulsed light is 50%, the intensity of the optical spectrum is obtained in 50% of the measurement wavelength range.

[0036] In the comparative example, the optical spectrum analyzer starts the second sweep operation at a time T_D delayed from the time 0 when the gate signal rises, as shown in FIG. 2A. T_D is also referred to as the delay time. In FIG. 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 the period during which the pulsed light is on.

[0037] By performing the sweep operation at the timing shown in the timing chart of Fig. 2A, the waveform shown in Fig. 2B is obtained as the optical spectrum of pulsed light in the measurement wavelength range. The time on the horizontal axis of Fig. 2B is represented with 0 as the time when the sweep operation starts. By setting the delay time T_D to 100% of the pulse width, the range in which the optical spectrum intensity is obtained in Fig. 2B complements the range in which the optical spectrum intensity is obtained in Fig. 1B. In other words, for wavelengths for which the intensity is not obtained in Fig. 1B, the intensity is obtained in Fig. 2B.

[0038] By combining the waveform obtained in the first sweep operation shown in FIG. 1B and the waveform obtained in the second sweep operation shown in FIG. 2B, the waveform of the optical spectrum of the pulsed light is generated as shown in FIG. 3.

[0039] Here, the waveforms of the optical spectrum of the pulsed light shown in Figures 1B and 2B have a defect at the initial wavelength when the pulsed light rises. A defect is a state in which the measurement result is lower than the light intensity that 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 with each other. As a result, a defect remains in the waveform shown in Figure 3.

[0040] If a defect remains in the optical spectrum waveform, the quality of the optical spectrum waveform will be reduced. If a defect exists in a waveform, it is possible to compensate for the defect by detecting the intensity in the range where the defect exists with another sweep. Specifically, it is possible to perform multiple sweeps by adjusting the delay time so that the defect does not remain in the waveform.

[0041] In the comparative example, the delay time is determined taking into account the defects shown in Figures 1B and 2B. However, the length of time from the rise of the pulsed light until the defect occurs may vary. When determining the delay time, it is possible to set the delay time to a longer time with some leeway, but the longer the delay time, the longer the measurement time. It is necessary to maintain the quality of the optical spectrum waveform while shortening the measurement time.

[0042] In the present disclosure, a pulsed light measurement method, a pulsed light measurement program, and an optical spectrum analyzer 10 (see FIG. 4) that can adjust the balance between the measurement time for an optical spectrum and the quality of the measured waveform will be described below.

[0043] (Configuration example of optical spectrum analyzer 10) As shown in FIG. 4, an optical spectrum analyzer 10 according to an embodiment of the present disclosure includes 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 that is configured so that pulsed light to be measured by the optical spectrum analyzer 10 can be input to the input port.

[0045] The light detection unit 12 includes a spectroscope and a light receiving element. The spectroscope separates the pulsed light into light of each wavelength and passes the light of the wavelength to be detected. In this disclosure, a grating is used as the spectroscope. The light detection unit 12 moves the grating to perform a sweep in response to a control instruction 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 light detection unit 12 starts the sweeping operation, and causes the light detection unit 12 to perform the sweeping operation multiple times. The measurement unit 13 acquires the detection results from the light detection unit 12 in each sweeping operation, and generates the waveform of the optical spectrum of the pulsed light by combining 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 realize a predetermined function 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 in the operation of the optical spectrum analyzer 10, or programs for implementing the functions of the optical spectrum analyzer 10. The storage unit may function as a work memory for the measurement unit 13. The storage unit may be configured, for example, as a semiconductor memory. The storage unit may include a volatile memory or a non-volatile memory. At least a part of the storage unit may be configured as a storage device connected externally to the optical spectrum analyzer 10.

[0049] The measuring unit 13 may be realized as a computer such as a desktop personal computer (PC) or a notebook PC, which is 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 be configured to include an input device that accepts input from a user. The input device may include, for example, a keyboard or physical keys, or may include a touch panel or touch sensor, or a pointing device such as a 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 may also be simply referred to as an input unit.

[0052] (Example of operation of the optical spectrum analyzer 10) The optical spectrum analyzer 10 generates an optical spectrum waveform of pulsed light. By performing a single sweep, the optical spectrum analyzer 10 can acquire an optical spectrum waveform of some wavelengths among the optical spectrum waveforms of all wavelengths in the measurement wavelength range of the pulsed light. The optical spectrum analyzer 10 synthesizes the waveforms acquired in multiple sweeps to generate an optical spectrum waveform of all wavelengths in the measurement wavelength range of the pulsed light. A waveform synthesized from the waveforms acquired in multiple sweeps is also called a composite waveform.

[0053] Here, the waveform acquired in one sweep is a waveform of a wavelength corresponding to the period when the pulsed light is on. When the period when the pulsed light is on begins, a gap occurs in the waveform at the beginning of the rise of the pulsed light. The gap reduces the quality of the waveform of the optical spectrum of the pulsed light. The wavelength range in which the waveform has a gap is also called a gap range.

[0054] A missing range in a waveform acquired in one sweep is complemented by acquiring a waveform in the same wavelength range in another sweep so that the missing range is complemented. The optical spectrum analyzer 10 according to the present disclosure is configured to set the wavelength overlap width of the waveforms acquired in each of multiple sweeps so that the missing range is complemented by the waveforms acquired in the other sweeps. By being able to set the wavelength overlap width, the user can set the wavelength overlap width by viewing the measured waveform. As a result, the balance between the measurement time of the optical spectrum and the quality of the measured waveform can be adjusted.

[0055] A specific example of the operation of the optical spectrum analyzer 10 according to the present disclosure will be described below.

[0056] The optical spectrum analyzer 10 may execute a pulsed light measurement method including the steps of the flowchart illustrated in Fig. 5. The pulsed light measurement method may be realized as a pulsed light measurement program executed by the optical spectrum analyzer 10. The pulsed light measurement program may be stored in a non-transitory computer-readable medium.

[0057] The measurement unit 13 sets the overlap width (step S1). The overlap width is expressed as a percentage of the pulse width of the pulsed light. In the present disclosure, the overlap width is set to Y %. Y is set to a value greater than 0% and less than 100%. In the present disclosure, Y is set to 50%. The duty ratio of the pulsed light is expressed as X %, which is 50% in the present disclosure. In this case, the overlap width corresponds to 25% of the pulse period. The measurement unit 13 may set the overlap width based on a setting input from the user, as described below. Setting the overlap width as a percentage of the pulse width makes it easier for the user to intuitively understand the overlap width. As a result, user convenience is improved.

[0058] The measurement unit 13 sets a delay time in the light detection unit 12 (step S2). The delay time is the time by which the timing of starting each sweep is delayed from the rising edge of a gate signal synchronized with the pulsed light when the light detection unit 12 performs multiple sweeps. By sequentially extending the delay time when performing multiple sweeps, the measurement unit 13 can overlap the wavelengths of the waveforms acquired in each sweep so that missing areas in the waveform acquired in one sweep are complemented by 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 is detected (step S3). A gate signal trigger is a trigger that occurs due to a change in the signal level of a gate signal. In the present disclosure, a gate signal trigger occurs when the gate signal rises.

[0060] 6A, in the first sweep, when the signal level of the gate signal changes from LO to HI, it is considered that a gate signal trigger occurs. The time when the gate signal trigger occurs is represented as 0.

[0061] If the light detection unit 12 does not detect a gate signal trigger (step S3: NO), the light detection unit 12 repeats the determination procedure of step S3 until it detects a gate signal trigger.

[0062] When the light detection unit 12 detects a gate signal trigger (step S3: YES), it determines whether the 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] If the delay time has elapsed (step S4: YES), the photodetector 12 starts sweeping (step S5). As described above, the delay time for the first sweep is set to zero. Therefore, as illustrated in FIG. 6A, the photodetector 12 starts the first sweeping operation from time 0 when the gate signal trigger is generated. The period during which the sweeping operation is performed is represented as a state in which the signal level of the sweeping operation 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 of step S6 to continue sweeping over the entire measurement wavelength range until the sweep time has elapsed.

[0066] If the sweep time has elapsed (step S6: YES), the light detection unit 12 ends one sweep operation. In the first sweep operation, the light detection unit 12 can detect a waveform measured over a wavelength range corresponding to the period when the pulsed light is on, as exemplified in FIG. 6B.

[0067] In Figure 6B, the horizontal axis represents time. This time corresponds to each wavelength in the measured wavelength range. Time 0 corresponds to the minimum wavelength in the measured wavelength range. Time T_E corresponds to the maximum wavelength in the measured wavelength range. The vertical axis represents the light intensity of each wavelength, with the maximum value being 1.

[0068] The light detection unit 12 outputs the detected waveform to the measurement unit 13 .

[0069] After one sweep operation by the light detection unit 12 is completed, the measurement unit 13 determines whether acquisition of data in the measurement wavelength range is complete (step S7). The measurement unit 13 acquires waveforms detected in one sweep operation from the light detection unit 12. The measurement unit 13 determines that acquisition of data in the measurement wavelength range is complete when waveforms have been acquired for all wavelengths in the measurement wavelength range.

[0070] At the end of the first sweep operation, the measurement unit 13 has only acquired waveforms at some wavelengths in the measurement wavelength range. Therefore, the measurement unit 13 determines that acquisition of data in the measurement wavelength range has not been completed. If acquisition of data in the measurement wavelength range has not been completed (step S7: NO), the measurement unit 13 updates the delay time set in the light detection unit 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. That is, the measurement unit 13 sets the delay time when performing the next sweep to be the time extended from the delay time set when performing the previous sweep. When the overlap width of the pulsed light is expressed as Y%, the time extended from the delay time is calculated as the value obtained by multiplying the pulse width of the pulsed light by (1-Y / 100). When the duty ratio of the pulsed light is expressed as X%, the pulse width is calculated as the value obtained by multiplying the pulse period by (X / 100). Therefore, the time extended from the delay time is calculated as the value obtained by multiplying the pulse period of the pulsed light by (X / 100) x (1-Y / 100). For example, if the pulse period of the pulsed light is 0.1 seconds, the duty ratio (X) of the pulsed light is 25%, and the overlap width (Y) is 10%, the time to extend the delay time is calculated as 0.0225 seconds by calculating 0.1 × (25 / 100) × (1 − 10 / 100).

[0072] In the present disclosure, the duty ratio (X) of the pulsed light is assumed to be 50%. The overlap width (Y) is set to 50% as described above. The measurement unit 13 updates the delay time so as to extend it by the time obtained by multiplying the pulse width of the pulsed light by 50%, which is set as the overlap width. In this case, the delay time corresponds to 25% of the pulse period, i.e., 1 / 4 of the length. The updated delay time is assumed to be represented by T_D1. After the measurement unit 13 updates the delay time, the process returns to step S3, and the light detection unit 12 performs a second sweep operation as the next sweep.

[0073] If the photodetector 12 determines in step S3 that a gate signal trigger has been detected and determines in step S4 that the delay time T_D1 has elapsed, the photodetector 12 starts a second sweep operation in step S5 from time T_D1 as illustrated in FIG. 7A. The period during which the sweep operation is performed is represented as a state in which the signal level of the sweep operation is HI. In step S6, the photodetector 12 continues the second sweep operation until time T_E+T_D1 and then ends it.

[0074] During the second sweep operation, the light detection unit 12 can detect the waveform illustrated in FIG. 7B. The time on the horizontal axis of FIG. 7B is displayed as the time in FIG. 7A minus T_D1 so as to match the relationship between the measurement wavelength range and time in FIG. 6B. In other words, the time when the sweep started is represented as 0. The time when the sweep ended is represented as T_E. Time 0 on the horizontal axis of FIG. 7B corresponds to the minimum wavelength in the measurement wavelength range. Time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity of each wavelength, with the maximum value being 1.

[0075] When comparing the waveform of FIG. 7B with the waveform of FIG. 6B, the wavelength range detected in the waveform of FIG. 7B is shifted toward shorter wavelengths than the wavelength range detected in the waveform of FIG. 6B by 1 / 4 of the pulse period, i.e., by a phase difference of 90 degrees. However, even when the waveforms of FIG. 6B and FIG. 7B are combined, there remain wavelengths in the measured wavelength range for which waveforms have not been acquired. Therefore, the measurement unit 13 determines that acquisition of data for the measured wavelength range has not been completed, and updates the delay time set in the light detection unit 12 in step S8.

[0076] The measurement unit 13 updates the delay time when performing the third sweep operation so that it is extended by the time obtained by multiplying the pulse width of the pulsed light by 50% set as the overlap width from the delay time when performing the second sweep operation. The updated delay time is represented as T_D2. After the measurement unit 13 updates the delay time, the process returns to step S3, and the light detection unit 12 performs the third sweep operation as the next sweep.

[0077] If the photodetector 12 determines in step S3 that a gate signal trigger has been detected and determines in step S4 that the delay time T_D2 has elapsed, the photodetector 12 starts a third sweep operation in step S5 from time T_D2 as illustrated in FIG. 8A. The period during which the sweep operation is performed is represented as a state in which the signal level of the sweep operation is HI. In step S6, the photodetector 12 continues the third sweep operation until time T_E+T_D2 and then ends the third sweep operation.

[0078] During the third sweep operation, the light detection unit 12 can detect the waveform illustrated in FIG. 8B. The time on the horizontal axis of FIG. 8B is displayed as the time in FIG. 8A minus T_D2 so as to match the relationship between the measurement wavelength range and time in FIGS. 6B and 7B. In other words, the time when the sweep started is represented as 0. The time when the sweep ended is represented as T_E. Time 0 on the horizontal axis of FIG. 8B corresponds to the minimum wavelength in the measurement wavelength range. Time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity of each wavelength, with the maximum value being 1.

[0079] Comparing the waveform of FIG. 8B with the waveform of FIG. 7B, the wavelength range detected in the waveform of FIG. 8B is shifted toward shorter wavelengths than the wavelength range detected in the waveform of FIG. 7B by 1 / 4 of the pulse period, i.e., by a phase of 90 degrees. Here, when the waveforms of FIG. 6B, FIG. 7B, and FIG. 8B are combined, waveforms are acquired for all wavelengths in the measured wavelength range. However, the missing range in the waveform of FIG. 8B does not overlap with the wavelength ranges of the waveforms of FIG. 6B and FIG. 7B. Therefore, the measurement unit 13 determines that data acquisition for the measured wavelength range has not been completed, and updates the delay time set in the light detection unit 12 in step S8.

[0080] The measurement unit 13 updates the delay time when performing the fourth sweep operation so that it is extended by the time obtained by multiplying the pulse width of the pulsed light by 50% set as the overlap width from the delay time when performing the third sweep operation. The updated delay time is represented as T_D3. After the measurement unit 13 updates the delay time, the process returns to step S3, and the light detection unit 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 a fourth sweep operation in step S5 from time T_D3 as illustrated in FIG. 9A. The period during which the sweep operation is performed is represented as a state in which the signal level of the sweep operation is HI. In step S6, the photodetector 12 continues the fourth sweep operation until time T_E+T_D3 and then ends it.

[0082] During the fourth sweep operation, the light detection unit 12 can detect the waveform illustrated in FIG. 9B. The time on the horizontal axis of FIG. 9B is displayed as the time in FIG. 9A minus T_D3 to match the relationship between the measurement wavelength range and time in FIGS. 6B, 7B, and 8B. In other words, the time when the sweep started is represented as 0. The time when the sweep ended is represented as T_E. Time 0 on the horizontal axis of FIG. 9B corresponds to the minimum wavelength in the measurement wavelength range. Time T_E corresponds to the maximum wavelength in the measurement wavelength range. The vertical axis represents the light intensity of each wavelength, with the maximum value being 1.

[0083] When comparing the waveform of FIG. 9B with the waveform of FIG. 8B, the wavelength range detected in the waveform of FIG. 9B is shifted toward shorter wavelengths than the wavelength range detected in the waveform of FIG. 8B by 1 / 4 of the pulse period, i.e., a phase shift of 90 degrees. Here, when the waveforms of FIG. 6B, FIG. 7B, FIG. 8B, and FIG. 9B are combined, waveforms are acquired for all wavelengths in the measured wavelength range. Furthermore, the missing ranges in each of the waveforms of FIG. 6B, FIG. 7B, FIG. 8B, and FIG. 9B overlap with the wavelength range of at least one other waveform. Therefore, the measurement unit 13 determines that data acquisition for the measured wavelength range has been completed.

[0084] When the measurement unit 13 has completed acquisition of data in 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 following rules (1) and (2).

[0085] (1) The wavelength intensity detected in only one sweep is used as is in the composite waveform. (2) As the optical intensity of wavelengths that overlap in waveforms detected in two or more sweeps, the intensity detected in each sweep during a period in which the waveform data is not missing data is used for the composite waveform. The period in which the waveform data is not missing data is the period after a predetermined time has elapsed since the gate signal was turned on during the period in which the gate signal was turned on. Conversely, the period in which the waveform data is missing data is the period within a predetermined time after the gate signal was turned on during the period in which the gate signal was turned on.

[0086] The measurement unit 13 may store at least one of the periods in which the waveform data is not missing data or the periods in which the waveform data is missing data, as used in (2) above, in association with the waveform data 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 a period during which waveform data is not missing data or a period during which waveform data is missing data. The measurement unit 13 may accept an input from a user to set the predetermined time, and set the value input by the user as the predetermined time. The measurement unit 13 may analyze a waveform in which the intensity of a test signal whose intensity changes stepwise from LO to HI has been detected, and set the predetermined time based on the length of the period from when the intensity of the test signal becomes HI to when the intensity of the waveform stabilizes.

[0088] In this way, the defects are eliminated in the synthesized waveform, resulting in improved waveform quality.

[0089] Furthermore, when the measurement unit 13 increases the delay time in order of executing multiple sweeps, the measurement unit 13 may synthesize waveforms based on the rule shown as the following rule (3) instead of the rule (2) above.

[0090] (3) For the optical intensities of wavelengths that overlap in waveforms detected in two or more sweeps, the intensities detected in the later sweep are used in the composite waveform, regardless of whether the waveform data is missing. In other words, the intensities detected in the later sweep overwrite the intensities of the composite waveform.

[0091] By overwriting the intensities detected in later sweeps, waveforms acquired in earlier sweeps do not need to be saved, simplifying the process of synthesizing waveforms and reducing the storage capacity required to store waveforms.

[0092] The measurement unit 13 may synthesize a waveform based on the following rule (4), which is a combination of the above (2) and (3), instead of the above (2) or (3).

[0093] (4) As the optical intensity of wavelengths that overlap in waveforms detected in two or more sweeps, the intensity detected in the later sweep among the intensities detected during the period when the waveform data is not missing data is used for the composite waveform.

[0094] The measuring section 13 may synthesize a waveform based on the following rule (5) instead of the above rules (2) to (4).

[0095] (5) As the optical intensity of wavelengths that overlap in waveforms detected in two or more sweeps, the greater value of the intensity detected in each sweep is adopted for the composite waveform, regardless of whether the waveform data is missing data.

[0096] In this way, the defects are eliminated in the synthesized waveform, resulting in improved waveform quality.

[0097] The measurement section 13 may synthesize a waveform based on the following rule (6), which is a combination of the above (2) and (5), instead of the above (2) to (5).

[0098] (6) As the optical intensity of wavelengths that overlap in waveforms detected in two or more sweeps, the larger value of the intensity detected during the period when the waveform data is not missing data is adopted as the composite waveform.

[0099] The measurement unit 13 displays the composite waveform of the optical spectrum of the pulsed light on the display unit 14, as exemplified in Fig. 10. In the composite waveform, a deficiency remains on the shortest wavelength side of the measurement wavelength range, but is eliminated in other ranges.

[0100] The gap at the shortest wavelength side of 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 optical detection unit 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 be shorter than the minimum value of the measurement wavelength range, the gap at the shortest wavelength side of the measurement wavelength range can be eliminated.

[0101] In the operational example described above, data acquisition for the measurement wavelength range was completed by performing four sweep operations. The number of sweeps required to complete data acquisition for the measurement wavelength range is calculated as (100 / X) × {100 / (1-Y / 100)}, and is calculated as a natural number by rounding up the decimal point of the calculated value. For example, if the duty ratio (X) of the pulsed light (X) is 25% and the overlap width (Y) is 50%, the number of sweeps 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., if the overlap width (Y) is 0%, the required number of sweeps is calculated by dividing X by 100. If the calculation result for the required number of sweeps contains a fraction after the decimal point, the fraction is rounded up. For example, if the duty ratio of the pulsed light is 25%, the required number of sweeps is calculated as 4 by calculating 100 / 25. For example, if the duty ratio of the pulsed light is 30%, the required number of sweeps is calculated as 4 by calculating 100 / 30 and rounding up the fraction. 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 of step S9, the measurement unit 13 ends execution of the procedure of the flowchart of FIG. 5. After executing the procedure of step S9, the measurement unit 13 may restart the procedure of the flowchart of FIG. 5. In this case, the user may set the overlap width in the procedure of step S1 by looking at the composite waveform displayed as a result of the previous operation of the flowchart of FIG. 5. If a gap is observed in the composite waveform, the user may set the overlap width to a larger value so that the gap will disappear when the next operation of the flowchart of FIG. 5 is performed. Conversely, if a gap is not observed 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 of FIG. 5 is performed.

[0104] To enable 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 FIG. 11 . The setting window 143 may be displayed when an operation such as a touch or a click is input to a setting unit 142 that displays the setting value of the overlap width. The setting window 143 may be displayed on the waveform display unit 141 that displays the waveform, or 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 as Y%, which represents the overlap width. For example, the setting window 143 may be configured to allow a value between 1% and 99% to be input.

[0105] The optical spectrum analyzer 10 may accept an input for setting the overlap width from the user in the setting window 143 while the composite waveform is displayed on the waveform display unit 141. Accepting an input for setting the overlap width while the composite waveform is displayed makes it easier for the user to determine how to set the overlap width, thereby improving user convenience.

[0106] The optical spectrum analyzer 10 may accept an input for setting the overlap width from the user in the setting window 143 while multiple sweeps are being performed. By accepting an input for setting the overlap width while multiple sweeps are being performed, the user can immediately check how the overlap width setting changes the composite waveform, making it easier to determine how to set the overlap width. As a result, user convenience is improved.

[0107] The setting window 143 may be configured to allow input of a setting represented as AUTO. When the overlap width is set to AUTO, the measurement unit 13 automatically sets the overlap width. For example, the measurement unit 13 may 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 range is eliminated in the composite waveform.

[0108] Before completing the acquisition of data in the measurement wavelength range, the measurement unit 13 may sequentially combine the waveforms acquired in each sweep and display the combined waveform on the display unit 14 as an intermediate measurement progress.

[0109] As illustrated in FIG. 12, 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. In the example of FIG. 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 so as to be distinguished by line color. The waveforms acquired in each sweep may be displayed in various manners other than the 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 determine how to set the overlap width. As a result, user convenience is improved.

[0110] Although the measurement unit 13 extends the delay time in order as the number of sweeps increases, the delay time may be shortened between multiple sweeps. Also, although the measurement unit 13 sets the delay time so that the difference in delay time between each sweep is equal, the measurement unit 13 may set the delay time so that the difference in delay time between each sweep is different.

[0111] The measurement unit 13 may determine the number of sweeps to be performed based on the pulse width and overlap width. By determining the number of sweeps to be 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 between each sweep is equal in accordance with the determined number of sweeps.

[0112] (summary) As described above, the optical spectrum analyzer 10 according to the present disclosure detects optical spectrum waveforms 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 starting each sweep when performing multiple sweeps. The optical spectrum analyzer 10 generates an optical spectrum waveform of pulsed light by synthesizing the waveforms detected in each sweep so as to eliminate waveform loss that occurs at the initial rise time of the pulsed light. The optical spectrum analyzer 10 is also configured to allow a user to set the overlap width by viewing the optical spectrum waveform. As a result, the balance between the measurement time of the optical spectrum and the quality of the measured waveform is adjusted. User convenience is also improved.

[0113] In the embodiments described above, the overlap width is expressed as a ratio to the length of the pulse width of the pulsed light, but it may be expressed in various other ways, such as a ratio to the length of the pulse period of the pulsed light.

[0114] Although the embodiments of the present 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 the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined or divided into one. [Explanation of symbols]

[0115] 10 Optical Spectrum Analyzer 11 Optical input section 12 Light detection unit 13 Measuring part 14 Display section (141: waveform display section, 142: setting section, 143: setting window) 15 Control section

Claims

1. A pulsed light measurement method for measuring an optical spectrum of pulsed light, comprising: setting an overlap width of wavelengths at which light intensity is measured in each of a plurality of sweeps performed in the measurement wavelength range of the optical spectrum; starting each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed since detecting a trigger of a gate signal synchronized with the pulsed light; synthesizing and displaying the optical spectrum from a plurality of waveforms obtained by executing the plurality of sweeps; A pulsed light measurement method comprising:

2. 2. The pulsed light measurement method according to claim 1, wherein when synthesizing the optical spectrum from the plurality of waveforms, an intensity detected during a period in which waveform data is not missing data is used as the optical intensity of wavelengths that overlap each other in the plurality of waveforms.

3. 2. The pulsed light measurement method according to claim 1, wherein, when the delay time is increased in order of execution of the plurality of sweeps, in synthesizing the optical spectrum from the plurality of waveforms, an intensity detected in a sweep executed later is used as the optical intensity of wavelengths that overlap each other in the plurality of waveforms.

4. 2. The pulsed light measurement method according to claim 1, wherein, when the delay time is increased in order of execution of the plurality of sweeps, in synthesizing the optical spectrum from the plurality of waveforms, an intensity detected in a sweep executed later, among intensities detected during a period in which waveform data is not missing data, is used as the optical intensity of wavelengths that overlap in the plurality of waveforms.

5. 2. The pulsed light measurement method according to claim 1, wherein when synthesizing the optical spectrum from the plurality of waveforms, a larger value is adopted as the optical intensity of wavelengths that overlap each other in the plurality of waveforms.

6. 2. The pulsed light measurement method according to claim 1, wherein, when synthesizing the optical spectrum from the plurality of waveforms, a larger value of intensities detected during a period in which waveform data is not missing is adopted as the optical intensity of wavelengths that overlap in the plurality of waveforms.

7. The pulsed light measurement method according to claim 1 , further comprising: setting the overlap width as a ratio to the pulse width of the pulsed 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 claim 1 , further comprising displaying the waveforms obtained by each of the plurality of sweeps in a distinguishable manner.

10. The pulsed light measurement method according to claim 1 , further comprising: receiving an input of a setting of the overlap width while the plurality of sweeps are being performed.

11. The pulsed light measurement method according to claim 1 , further comprising: receiving an input of a setting for the overlap width while the waveform of the optical spectrum is being displayed.

12. An optical spectrum analyzer that measures the optical spectrum of pulsed light has setting an overlap width of wavelengths at which light intensity is measured in each of a plurality of sweeps performed in the measurement wavelength range of the optical spectrum; starting each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed since detecting a trigger of a gate signal synchronized with the pulsed light; synthesizing and displaying the optical spectrum from a plurality of waveforms obtained by executing the plurality of sweeps; A pulsed light measurement program that executes the above.

13. a measuring unit that measures an optical spectrum of pulsed light, and a light detecting unit that detects the optical intensity of each wavelength of the pulsed light, the measurement unit sets an overlap width of wavelengths at which light intensity is measured in each of a plurality of sweeps executed in the measurement wavelength range of the optical spectrum, the light detection unit starts each of the plurality of sweeps after a delay time determined based on the overlap width has elapsed since detecting a trigger of a gate signal synchronized with the pulsed light, The measurement unit synthesizes and displays the optical spectrum from a plurality of waveforms obtained by executing the plurality of sweeps.

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