Light intensity modulation device and waveform compression device

Abstract

The present invention is provided with: an optical distributor (2) for branching pulsed light; a light detector (3) that converts the one pulsed light branched by the light distributor (2) into an electric signal; an ADC (4) that converts the electrical signal converted by the photodetector (3) from an analog signal to a digital signal; a corrected superimposed waveform calculation unit (5) that, on the basis of the superimposed waveform data and the electrical signal converted by the ADC (4), calculates corrected superimposed waveform data, which is waveform data that corrects distortion due to temporal variation in intensity of the pulsed light; a DAC (6) that converts the corrected superimposed waveform data calculated by the corrected superimposed waveform calculation unit (5) from a digital signal to an analog signal; and a light intensity modulator (7) that obtains intensity-modulated light by superimposing the corrected superimposed waveform data converted by the DAC (6) on the other pulsed light branched by the light distributor (2).

Description

Technical Field

[0001] The present disclosure relates to a light intensity modulation device for modulating the intensity of pulsed light and a waveform compression device having the light intensity modulation device. Background Art

[0002] Conventionally, there is known a device for compressing pulsed light (see, for example, Patent Document 1).

[0003] In the device disclosed in Patent Document 1, first, an optical pulse shaping unit shapes the light intensity waveform of a pulse light outputted from a light source unit, and then a compression unit compresses the pulse light shaped by the optical pulse shaping unit using dispersion to obtain compressed pulse light.

[0004] In addition, in this device, the calculation control unit monitors the pulse light shaped by the optical pulse shaping unit, compares it with the target waveform, and calculates the target value for shaping. In addition, in this device, the calculation result of the calculation control unit is input to the optical pulse shaping unit to perform modulation control, thereby obtaining the target compressed pulse light.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-178374 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, Patent Document 1 does not mention the function and purpose of superimposing an arbitrary superimposed waveform on compressed pulse light.

[0010] In addition, the intensity waveform of pulse light may not have an ideal shape within the pulse and may vary with time. In this case, when an arbitrary superimposed waveform is superimposed on the pulse light, the modulated waveform is distorted.

[0011] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a light intensity modulation device which can suppress distortion in a modulation waveform even when the intensity waveform of pulse light varies in time compared to the related art.

[0012] Means for solving problems

[0013] The light intensity modulation device disclosed in the present invention is characterized in that the light intensity modulation device comprises: an optical distributor, which branches pulse light; a light detector, which converts a pulse light branched from the optical distributor into an electrical signal; an analog-to-digital converter, which converts the electrical signal converted by the optical detector from an analog signal to a digital signal; a correction superimposed waveform operation unit, which calculates waveform data, i.e., correction superimposed waveform data, for correcting distortion caused by temporal intensity variation of the pulse light based on the superimposed waveform data and the electrical signal converted by the analog-to-digital converter; a digital-to-analog converter, which converts the correction superimposed waveform data calculated by the correction superimposed waveform operation unit from a digital signal to an analog signal; and a light intensity modulator, which superimposes the correction superimposed waveform data converted by the digital-to-analog converter on another pulse light branched from the optical distributor, thereby obtaining intensity modulated light.

[0014] Effects of the Invention

[0015] According to the present disclosure, since it is configured as described above, even when the intensity waveform of pulse light varies with time, it is possible to suppress distortion in the modulation waveform compared to the related art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] [ Figure 1 ] is a diagram showing a structural example of a waveform compression device according to embodiment 1.

[0017] [ Figure 2 ] is a diagram showing a specific structural example of the waveform compression device of embodiment 1.

[0018] [ Figure 3 ] is a flowchart showing an operation example of the waveform compression device of embodiment 1.

[0019] [ Figure 4 ] Figure 4 A~ Figure 4 C is a diagram showing an example of the operation of the waveform compression device according to the first embodiment. Figure 4 A is a diagram showing an example of pulse light input to an MZM and pulse light biased by the MZM. Figure 4 B is a diagram showing an example of the modulation characteristics of MZM. Figure 4 C is a diagram showing an example of pulse light after intensity modulation by MZM.

[0020] [ Figure 5 ] is a diagram showing another structural example of the waveform compression device of embodiment 1. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

[0022] Implementation Method 1

[0023] Figure 1 : is a diagram showing a configuration example of a waveform compression device according to Embodiment 1. Figure 2 This is a diagram showing a specific configuration example of the waveform compression device according to the first embodiment.

[0024] like Figure 1 As shown, the waveform compression device has a pulse light source unit 1, an optical distributor 2, a light detector 3, an ADC (analog-to-digital converter) 4, a correction superposition waveform calculation unit 5, a DAC (digital-to-analog converter) 6, a light intensity modulator 7, a pulse light compression unit 8 and a light detector (a second light detector) 9.

[0025] in addition, Figure 1 The pulse light source unit 1, optical distributor 2, optical detector 3, ADC 4, correction superimposed waveform calculation unit 5, DAC 6 and optical intensity modulator 7 in the waveform compression device shown constitute an optical intensity modulation device.

[0026] The pulse light source unit 1 generates pulse light. The pulse light generated by the pulse light source unit 1 is output to the optical distributor 2.

[0027] For example Figure 2 As shown, the pulse light source section 1 includes a short pulse light source 101 , a spectrum shaping section 102 , and a wavelength dispersion section 103 .

[0028] The short pulse light source 101 generates broadband short pulse light. The time width of the short pulse light generated by the short pulse light source 101 is, for example, about 100 fs to 1 ps. The short pulse light generated by the short pulse light source 101 is output to the spectrum shaping unit 102 .

[0029] In addition, Figure 2 In FIG. 1 , below the functional block showing the short pulse light source 101, two diagrams are used to show an example of short pulse light based on the short pulse light source 101. Here, the diagram on the upper layer shows the time waveform of the short pulse light based on the short pulse light source 101, with the horizontal axis being time and the vertical axis being intensity. In addition, the diagram on the lower layer shows the spectrum waveform of the short pulse light based on the short pulse light source 101, with the horizontal axis being wavelength and the vertical axis being intensity.

[0030] The spectrum shaping unit 102 performs spectrum shaping on the short pulse light generated by the short pulse light source 101. That is, the spectrum shaping unit 102 adjusts the level of each wavelength component of the short pulse light generated by the short pulse light source 101, and performs spectrum shaping of the wavelength so as to become a substantially rectangular shape, for example. The short pulse light after the spectrum shaping by the spectrum shaping unit 102 is output to the wavelength dispersion unit 103.

[0031] As the spectrum shaping unit 102, for example, a WSS (Wavelength Selective Switch) can be used.

[0032] In addition, Figure 2 , below the functional block of the spectrum shaping unit 102, two diagrams are used to show an example of short pulse light after spectrum shaping by the spectrum shaping unit 102. Here, the upper diagram shows the time waveform of the short pulse light after spectrum shaping by the spectrum shaping unit 102, with the horizontal axis being time and the vertical axis being intensity. In addition, the lower diagram shows the spectrum waveform of the short pulse light after spectrum shaping by the spectrum shaping unit 102, with the horizontal axis being wavelength and the vertical axis being intensity.

[0033] The wavelength dispersion portion 103 performs waveform dispersion on the short pulse light after spectrum shaping by the spectrum shaping portion 102. That is, the wavelength dispersion portion 103 adds a delay amount corresponding to the wavelength to the short pulse light after spectrum shaping by the spectrum shaping portion 102, thereby stretching the pulse light and generating a stretched pulse light having a time waveform substantially the same as the spectrum shape. The stretched pulse light obtained by the wavelength dispersion portion 103 is output to the optical distributor 2. For example, the wavelength dispersion portion 103 adds a delay amount that is larger as the wavelength is larger to the short pulse light after spectrum shaping by the spectrum shaping portion 102, thereby obtaining a stretched pulse light. Alternatively, the wavelength dispersion portion 103 adds a delay amount that is larger as the wavelength is smaller to the short pulse light after spectrum shaping by the spectrum shaping portion 102, thereby obtaining a stretched pulse light.

[0034] As the wavelength dispersion portion 103 , for example, SMF (Single Mode Fiber) can be used.

[0035] In addition, Figure 1 and Figure 2 , after showing the functional blocks of the pulse light source section 1 (wavelength dispersion section 103), a diagram showing an example of pulse light (extended pulse light) based on the pulse light source section 1 (wavelength dispersion section 103) is shown. The diagram shows the time waveform of the pulse light (extended pulse light) based on the pulse light source section 1 (wavelength dispersion section 103), with the horizontal axis representing time and the vertical axis representing intensity.

[0036] Moreover, if Figure 1 and Figure 2 As shown in FIG. 1 , the intensity waveform of the pulse light (extended pulse light) based on the pulse light source section 1 (wavelength dispersion section 103) is not an ideal rectangular waveform due to the spectrum shaping error, but actually becomes a waveform with temporal variation within the pulse. In addition, in the figure showing an example of the pulse light (extended pulse light) based on the pulse light source section 1 (wavelength dispersion section 103), the upper dotted line of the two dotted lines shows the maximum value of the intensity variation, and the lower dotted line shows the minimum value of the intensity variation.

[0037] The optical distributor 2 splits the pulse light generated by the pulse light source unit 1 into two. One of the pulse light split by the optical distributor 2 is output to the photodetector 3, and the other pulse light is output to the light intensity modulator 7.

[0038] As the optical distributor 2, for example Figure 2 As shown, an optocoupler can be used.

[0039] The photodetector 3 converts one pulse light branched by the optical distributor 2 into an electric signal. The electric signal obtained by the photodetector 3 is output to the ADC 4.

[0040] As the photodetector 3, for example Figure 2 As shown, a PD (Photo Diode) can be used.

[0041] The ADC 4 converts the electrical signal obtained by the photodetector 3 from an analog signal into a digital signal, thereby obtaining sampling data of the pulse light. The digital signal obtained by the ADC 4 is output to the correction superimposed waveform calculation unit 5 .

[0042] The correction superimposed waveform calculation unit 5 calculates the correction superimposed waveform data based on the arbitrary superimposed waveform data and the electrical signal converted by the ADC 4. In addition, the superimposed waveform data is represented by x(t). In addition, the correction superimposed waveform data is waveform data for correcting the distortion caused by the temporal intensity variation of the pulse light. The correction superimposed waveform data calculated by the correction superimposed waveform calculation unit 5 is output to the DAC 6.

[0043] As the correction-superimposition waveform calculation unit 5 , for example, a DSP (Digital Signal Processing) composed of an FPGA (Field Programmable Gate Array) can be used.

[0044] In addition, Figure 1 and Figure 2 In FIG. 1 , a diagram showing an example of superimposed waveform data input to the corrected superimposed waveform calculation unit 5 is shown in front of the functional block showing the corrected superimposed waveform calculation unit 5. The diagram shows a time waveform of the superimposed waveform data, with the horizontal axis being time and the vertical axis being voltage. Figure 1 and Figure 2 , as an example, a case where the superimposed waveform data is sinusoidal waveform data is shown.

[0045] For example Figure 1 and Figure 2 As shown, the correction-superimposition waveform calculation section 5 includes a data strobe section 501 , a minimum value detection section 502 , a data recording section 503 , and a waveform calculation section 504 .

[0046] The data selection unit 501 extracts data of a part of the interval from the electrical signal converted by the ADC 4 as pulse waveform data. In addition, the pulse waveform data is represented by a(t). The pulse waveform data extracted by the data selection unit 501 is output to the minimum value detection unit 502 and the data recording unit 503.

[0047] The minimum value detection unit 502 detects the minimum value of the pulse waveform data based on the pulse waveform data taken out by the data selection unit 501. min Indicates the minimum value of the pulse waveform data. Data indicating the minimum value of the pulse waveform data detected by the minimum value detection unit 502 is output to the data recording unit 503.

[0048] The data recording section 503 records the pulse waveform data fetched by the data strobe section 501 and data indicating the minimum value of the pulse waveform data detected by the minimum value detection section 502 .

[0049] In addition, the data recording unit 503 may record one pulse waveform data taken out by the data strobe unit 501 and data indicating the minimum value of the pulse waveform data detected by the minimum value detection unit 502. Alternatively, the data recording unit 503 may update and record the pulse waveform data taken out by the data strobe unit 501 and data indicating the minimum value of the pulse waveform data detected by the minimum value detection unit 502 each time or at a predetermined time. Alternatively, the data recording unit 503 may record the result of averaging a plurality of pulse waveform data taken out by the data strobe unit 501 and data indicating the result of averaging the minimum values ​​of each of the plurality of pulse waveform data detected by the minimum value detection unit 502.

[0050] In addition, the data recording unit 503 may be a nonvolatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), EEPROM (Electrically EPROM), a magnetic disk, a floppy disk, an optical disk, a high-density disk, a mini disk, or a DVD (Digital Versatile Disc).

[0051] The waveform calculation unit 504 calculates the corrected superimposed waveform data based on the arbitrary superimposed waveform data, the pulse waveform data recorded in the data recording unit 503, and the data indicating the minimum value of the pulse waveform data. At this time, it is preferable that the waveform calculation unit 504 calculates the corrected superimposed waveform data based on the modulation characteristics of the light intensity modulator 7. The corrected superimposed waveform data calculated by the waveform calculation unit 504 is output to the DAC 6.

[0052] In addition, Figure 1 and Figure 2 , the data recording unit 503 is provided inside the light intensity modulation device and the waveform compression device. However, the present invention is not limited thereto, and the data recording unit 503 may be provided outside the light intensity modulation device and the waveform compression device.

[0053] The DAC 6 converts the correction superimposition waveform data obtained by the correction superimposition waveform calculation unit 5 from a digital signal to an analog signal. The correction superimposition waveform data converted by the DAC 6 is output to the light intensity modulator 7 .

[0054] In addition, Figure 1 and Figure 2 , after showing the functional blocks of DAC 6, a diagram showing an example of corrected superimposed waveform data based on DAC 6 is shown. This diagram shows the time waveform of the corrected superimposed waveform data based on DAC 6, with the horizontal axis being time and the vertical axis being voltage.

[0055] The optical intensity modulator 7 superimposes the correction superimposition waveform data converted by the DAC 6 on another pulse light branched from the optical distributor 2 and modulates the pulse light to obtain intensity modulated light. The intensity modulated light obtained by the optical intensity modulator 7 is output to the pulse light compressor 8.

[0056] As the light intensity modulator 7, for example Figure 2 As shown, an MZM (Mach-Zehnder Modulator) can be used. In addition, in the MZM, it is known that harmonic distortion is generated due to overmodulation as a modulation characteristic.

[0057] In addition, Figure 1 and Figure 2 , a diagram showing an example of intensity modulated light by the light intensity modulator 7 is shown above or behind the functional block of the light intensity modulator 7. The diagram shows a time waveform of the intensity modulated light by the light intensity modulator 7, with the horizontal axis being time and the vertical axis being intensity.

[0058] The pulse light compressor 8 compresses the pulse light modulated by the light intensity modulator 7, thereby obtaining compressed pulse light. That is, the pulse light compressor 8 performs wavelength dispersion on the pulse light modulated by the light intensity modulator 7 in the opposite manner to that of the wavelength dispersion unit 103, thereby compressing the pulse light. The compressed pulse light obtained by the pulse light compressor 8 is output to the photodetector 9.

[0059] As the pulse light compression unit 8, for example Figure 2 As shown, a wavelength reverse dispersion portion such as a reverse dispersion optical fiber can be used.

[0060] In addition, Figure 1 and Figure 2 , a diagram showing an example of compressed pulse light by the pulse light compressor 8 is shown above or behind the functional blocks of the pulse light compressor 8. The diagram shows the time waveform of the compressed pulse light by the pulse light compressor 8, with the horizontal axis being time and the vertical axis being intensity.

[0061] The photodetector 9 converts the compressed pulse light obtained by the pulse light compression unit 8 into an electrical signal. Thus, the waveform compression device can obtain an electrical signal with a high frequency and desired compressed pulse waveform. The electrical signal obtained by the photodetector 9 is output to the outside of the waveform compression device.

[0062] As the photodetector 9, for example Figure 2 As shown, PD can be used.

[0063] In addition, Figure 1 and Figure 2 , after showing the functional blocks of the photodetector 9, a diagram showing an example of an electrical signal based on the photodetector 9 is shown. This diagram shows the time waveform of the electrical signal based on the photodetector 9, with the horizontal axis representing time and the vertical axis representing voltage.

[0064] In addition, Figure 1 and Figure 2 , the pulse light source unit 1 is provided inside the waveform compression device and the light intensity modulation device. However, the present invention is not limited thereto, and the pulse light source unit 1 may be provided outside the waveform compression device and the light intensity modulation device.

[0065] Next, refer to Figure 3 right Figure 1 An operation example of the waveform compression device according to the first embodiment shown will be described.

[0066] exist Figure 1 In the example of operation of the waveform compression device of the embodiment 1 shown in FIG. Figure 3As shown, first, the pulse light source unit 1 generates pulse light (step ST301). In addition, the intensity waveform of the pulse light generated by the pulse light source unit 1 is not an ideal rectangular waveform, but actually becomes a waveform with temporal variation within the pulse. The pulse light generated by the pulse light source unit 1 is output to the optical distributor 2.

[0067] Next, the optical distributor 2 splits the pulse light generated by the pulse light source unit 1 into two (step ST302 ). One pulse light split by the optical distributor 2 is output to the photodetector 3 , and the other pulse light is output to the light intensity modulator 7 .

[0068] Next, the photodetector 3 converts the single pulse light branched by the optical distributor 2 into an electric signal (step ST303 ). The electric signal obtained by the photodetector 3 is output to the ADC 4 .

[0069] Next, the ADC 4 converts the electrical signal obtained by the photodetector 3 from an analog signal to a digital signal, thereby obtaining sampling data of the pulse light (step ST304 ). The electrical signal converted by the ADC 4 is output to the correction superimposition waveform calculation unit 5 .

[0070] Next, the correction superimposition waveform calculation unit 5 calculates the correction superimposition waveform data based on the arbitrary superimposition waveform data and the electric signal converted by the ADC 4 (step ST305 ). The correction superimposition waveform data calculated by the correction superimposition waveform calculation unit 5 is output to the DAC 6 .

[0071] At this time, first, the data strobe unit 501 extracts data of a partial interval from the electrical signal converted by the ADC 4 as pulse waveform data.

[0072] Next, the minimum value detection section 502 detects the minimum value of the pulse waveform data based on the pulse waveform data fetched by the data strobe section 501 .

[0073] Next, the data recording section 503 records the pulse waveform data fetched by the data strobe section 501 and data indicating the minimum value of the pulse waveform data detected by the minimum value detection section 502 .

[0074] Next, the waveform calculation unit 504 calculates the corrected superimposed waveform data based on the arbitrary superimposed waveform data, the pulse waveform data recorded in the data recording unit 503, and the data indicating the minimum value of the pulse waveform data. At this time, the waveform calculation unit 504 preferably calculates the corrected superimposed waveform data based on the modulation characteristics of the light intensity modulator 7.

[0075] Next, the DAC 6 converts the correction superimposition waveform data calculated by the correction superimposition waveform calculation unit 5 from a digital signal to an analog signal (step ST306 ). The correction superimposition waveform data converted by the DAC 6 is output to the light intensity modulator 7 .

[0076] Next, the optical intensity modulator 7 superimposes the correction superimposed waveform data converted by the DAC 6 on another pulse light branched from the optical distributor 2 and modulates the pulse light to obtain intensity modulated light (step ST307 ). The intensity modulated light obtained by the optical intensity modulator 7 is output to the pulse light compressor 8 .

[0077] Next, the pulse light compressor 8 compresses the pulse light modulated by the light intensity modulator 7 to obtain compressed pulse light (step ST308 ). The compressed pulse light obtained by the pulse light compressor 8 is output to the photodetector 9 .

[0078] Next, the photodetector 9 converts the compressed pulse light obtained by the pulse light compression unit 8 into an electrical signal (step ST309). Thus, the waveform compression device can obtain a signal with a high frequency and desired compressed pulse waveform. The electrical signal obtained by the photodetector 9 is output to the outside of the waveform compression device.

[0079] Next, refer to Figure 4 A specific example of the operation of the correction superimposed waveform calculation unit 5 will be described. Figure 4 In FIG. 1 , the light intensity modulator 7 is an MZM and the bias point of the MZM is the half value of the maximum intensity of the pulse light input to the MZM. Figure 4 , a case where the superimposed waveform data is sinusoidal waveform data is shown.

[0080] First, in Figure 4 A shows an example of pulse light input to the MZM and pulse light biased by the MZM. Figure 4 In A, reference numeral 41 indicates the pulse light input to the MZM, and reference numeral 42 indicates the pulse light biased by the MZM. Figure 4 In A, the horizontal axis is time and the vertical axis is intensity.

[0081] In addition, Figure 4 In B, an example of the modulation characteristics of MZM is shown. Figure 4 In B, the horizontal axis is the phase difference between the paths (arms) of the interferometer in the MZM, and the vertical axis is the intensity. The phase difference corresponds to the voltage value of the correction superimposed waveform data input to the MZM.

[0082] In addition, Figure 4 C shows an example of intensity modulated light obtained by MZM. Figure 4In C, the horizontal axis is time and the vertical axis is intensity. That is, in MZM, Figure 4 The pulse light input to the MZM shown in A is biased to half the maximum intensity of the pulse light, and then intensity modulated according to the correction superposition waveform data input to the MZM and the modulation characteristics of the MZM, thereby obtaining Figure 4 Intensity modulated light shown in C.

[0083] Here, if Figure 4 As shown in A, the pulse light input to the MZM produces a temporal intensity variation. Therefore, when the pulse light is intensity modulated by the MZM, the range of the modulated waveform that can be expressed is restricted according to the intensity variation. For example, in the waveform shown by reference numeral 41, the point at which the intensity is the maximum value can be modulated within the range up to the maximum value, whereas the point at which the intensity is the minimum value can only be modulated within the range up to the minimum value.

[0084] Therefore, when only arbitrary superimposed waveform data is superimposed on such pulse light, the intensity modulation may not be performed normally in the entire section of the pulse light, and the waveform may be distorted.

[0085] In addition, if Figure 4 As shown in B, in MZM, the modulation characteristic is not linear but a curved characteristic as shown in the following equation (1). Therefore, in MZM, due to the above-mentioned modulation characteristic, the change in voltage is not directly projected into the change in intensity to cause distortion.

[0086] Therefore, in this MZM, when only arbitrary superimposition waveform data is superimposed on pulse light, harmonic distortion due to overmodulation occurs.

[0087]

[0088] Therefore, in the correction superimposed waveform calculation unit 5 in the first embodiment, first, the data selection unit 501 extracts data of a part of the interval from the electrical signal converted by ADC4 as pulse waveform data. That is, the data selection unit 501 extracts the interval corresponding to the interval where the intensity variation may occur in the pulse light from the electrical signal converted by ADC4. Figure 4 In A, the gating width is roughly set to the pulse width, the time when the intensity of the pulse light rises to half the maximum intensity is set as the starting point of the gating, and then the time when the intensity of the pulse light drops to half the maximum intensity is set as the ending point of the gating. Figure 4 In A, a max Indicates the maximum value of the pulse waveform data.

[0089] Next, the minimum value detection section 502 detects the minimum value of the pulse waveform data based on the pulse waveform data fetched by the data strobe section 501 .

[0090] Then, the waveform calculation unit 504 calculates the corrected superimposed waveform data based on the arbitrary superimposed waveform data, the pulse waveform data taken out by the data selection unit 501, and the minimum value of the pulse waveform data detected by the minimum value detection unit 502. At this time, it is preferable that the waveform calculation unit 504 calculates the corrected superimposed waveform data based on the modulation characteristics of the light intensity modulator 7.

[0091] For example, the waveform calculation unit 504 calculates the waveform data x(t), the pulse waveform data a(t), and the minimum value a of the pulse waveform data. min The modulation characteristics of the MZM shown in equation (1) are used to calculate the corrected superimposed waveform data according to equation (2). In equation (2), V(t) is the corrected superimposed waveform data, V π is the half-wavelength voltage.

[0092] That is, Figure 4 As shown in FIG. 3C, the waveform calculation unit 504 calculates the correction superimposed waveform data so that the minimum value of the pulse light input to the MZM becomes the upper limit value of the full-scale range of the pulse light modulated by the MZM. Furthermore, the waveform calculation unit 504 calculates the correction superimposed waveform data in consideration of the modulation characteristics of the MZM so as to suppress the high-order harmonic distortion generated by overmodulation in the MZM. Figure 4 In the example of C, the MZM can finally obtain the half value of the minimum value of the pulse light input to the MZM, that is, a min / 2 is set as the bias of the intensity modulated light with no distortion of the waveform.

[0093] Thus, in the light intensity modulation device of embodiment 1, by correcting the superimposed waveform data in consideration of the minimum value of the pulse waveform data and the modulation characteristics of the light intensity modulator 7, both the distortion caused by the intensity variation of the pulse light and the harmonic distortion caused by the light intensity modulator 7 can be reduced.

[0094] In addition, the above example shows that the waveform calculation unit 504 uses the ArcSin function to perform calculations. However, the calculation method of the waveform calculation unit 504 is not limited to this, and the waveform calculation unit 504 may not use the ArcSin function, but may use other functional formulas (such as linear approximation or polynomial approximation, etc.) that approximate the modulation characteristics of the light intensity modulator 7 to perform calculations.

[0095] Here, the waveform calculation unit 504 performs calculation using linear approximation, which is substantially equivalent to calculating the corrected superimposed waveform data without considering the modulation characteristics of the light intensity modulator 7 .

[0096] In addition, it is not necessary to obtain the pulse waveform data and the minimum value of the pulse waveform data one by one in the correction superimposed waveform calculation unit 5. For example, in the case where the intensity variation of the pulse light is assumed to be static, the correction superimposed waveform calculation unit 5 does not need to obtain the pulse waveform data and the minimum value of the pulse waveform data one by one, and it is sufficient to obtain the pulse waveform data and the minimum value of the pulse waveform data only once or at a predetermined time.

[0097] On the other hand, the correction superimposed waveform calculation unit 5 repeatedly obtains pulse waveform data and the minimum value of the pulse waveform data, and can respond quickly even when the intensity of the pulse light changes due to, for example, ambient temperature changes or aging of the device.

[0098] In addition, for example, in the case where the intensity variation of the pulse light is assumed to be static, the correction superimposed waveform calculation unit 5 may obtain the pulse waveform data and the minimum value of the pulse waveform data multiple times, record data indicating the result of averaging the multiple pulse waveform data and the result of averaging the multiple minimum values, and use them for calculation of the correction superimposed waveform data. That is, the waveform calculation unit 504 may calculate the correction superimposed waveform data based on the result of averaging the multiple data taken out by the data selection unit 501 and the result of averaging the minimum values ​​of each of the multiple data detected by the minimum value detection unit 502, and the superimposed waveform data. In this way, the correction superimposed waveform calculation unit 5 can improve the data acquisition accuracy.

[0099] Furthermore, in the device disclosed in Patent Document 1, it is necessary to monitor the pulse light shaped by the optical pulse shaping unit every time the target waveform changes.

[0100] In contrast, in the light intensity modulation device of the first embodiment, it is not necessary to monitor the pulse light every time the superimposed waveform data changes. That is, in the light intensity modulation device of the first embodiment, even if the superimposed waveform data changes, the superimposed waveform data can be corrected by using the pulse waveform data acquired in the past and the minimum value of the pulse waveform data.

[0101] In addition, Figure 2 , the case where the spectrum shaping unit 102 is provided in the pulse light source unit 1 is shown. However, the spectrum shaping unit 102 is not an essential structure of the pulse light source unit 1 and may not be provided in the pulse light source unit 1.

[0102] In addition, Figure 2 2 shows a case where an MZM is used as the light intensity modulator 7. However, the light intensity modulator 7 is not limited to this, and as the light intensity modulator 7, for example, an electric field absorption type modulator may be used.

[0103] The wavelength dispersion portion 103 may be any device that can provide different delay amounts for each wavelength component. For example, a chirped fiber Bragg grating can be used as the wavelength dispersion portion 103 .

[0104] Likewise, the pulse light compressor 8 may be any device that can provide different delay amounts for each wavelength component. For example, a chirped fiber Bragg grating may be used as the pulse light compressor 8 .

[0105] In addition, Figure 4 , the following situation is shown: the data selection section 501 sets the selection width to be approximately the pulse width, sets the time when the intensity of the assumed pulse light rises to half the maximum intensity as the starting point of the selection, and then sets the time when the intensity of the assumed pulse light drops to half the maximum intensity as the ending point of the selection. However, this is not limited to the above, and the data selection section 501 sets the selection to extract the range of the intensity variation of the pulse light that can be monitored by the correction superposition waveform calculation section 5. In addition, when the pulse waveform data extracted by the data selection section 501 includes data before the rise of the pulse light or data after the fall of the pulse light, the value before the rise of the pulse light or the value after the fall of the pulse light is detected as the minimum value in the minimum value detection section 502, thereby preventing such data from being included.

[0106] In addition, in the above description, the minimum value detection unit 502 detects the minimum value of the pulse waveform data. However, the minimum value does not need to be strictly the minimum value, and there may be a slight deviation.

[0107] In addition, the above description shows a case where the waveform compression device simultaneously suppresses the distortion caused by the intensity variation of the pulsed light and superimposes any superimposed waveform data on the pulsed light. However, the present invention is not limited thereto, and the waveform compression device may separately suppress the distortion caused by the intensity variation of the pulsed light and superimpose any superimposed waveform data on the pulsed light.

[0108] In this case, for example Figure 5 As shown, the waveform compression device first uses fixed data (fixed value) as superimposed waveform data to suppress distortion caused by intensity variation of the pulse light, and then the light intensity modulator 10 superimposes the pulse light using arbitrary superimposed waveform data. In addition, at this time, the waveform compression device may also correct the superimposed waveform data used in the light intensity modulator 10 according to the modulation characteristics of the light intensity modulator 10 to suppress high-order harmonic distortion, and then superimpose.

[0109] In addition, the above description shows a case where the light intensity modulation device of Embodiment 1 is applied to a waveform compression device. However, the application destination of the light intensity modulation device of Embodiment 1 is not limited to this. For example, the light intensity modulation device of Embodiment 1 can also be applied to a spectroscopic analysis device that performs spectroscopic analysis of pulsed light. In this spectroscopic analysis device, the temporal intensity component of the pulsed light used in the spectroscopic analysis can be shaped into an arbitrary form, thereby enabling high-sensitivity spectroscopic analysis.

[0110] As described above, according to the first embodiment, the light intensity modulation device includes: the optical distributor 2 for branching the pulse light; the optical detector 3 for converting one pulse light branched from the optical distributor 2 into an electric signal; the ADC 4 for converting the electric signal converted by the optical detector 3 from an analog signal to a digital signal; the correction superimposed waveform calculation unit 5 for calculating waveform data for correcting distortion caused by temporal intensity variation of the pulse light, that is, correction superimposed waveform data, based on the superimposed waveform data and the electric signal converted by the ADC 4; the DAC 6 for converting the correction superimposed waveform data calculated by the correction superimposed waveform calculation unit 5 from a digital signal to an analog signal; and the light intensity modulator 7 for superimposing the correction superimposed waveform data converted by the DAC 6 on another pulse light branched from the optical distributor 2, thereby obtaining intensity modulated light. Therefore, in the light intensity modulation device of the first embodiment, even when the intensity waveform of the pulse light varies temporally, the distortion in the modulated waveform can be suppressed compared to the conventional method. Furthermore, the light intensity modulation device of the first embodiment can superimpose an arbitrary waveform.

[0111] Furthermore, any structural elements of the embodiments may be modified or omitted.

[0112] Industrial Applicability

[0113] The light intensity modulation device of the present disclosure can suppress distortion in the modulation waveform even when the intensity waveform of pulse light varies with time, compared with the related art, and is suitable for light intensity modulation devices that modulate the intensity of pulse light.

[0114] Description of symbols

[0115] 1: Pulse light source unit; 2: Optical distributor; 3: Photodetector; 4: ADC (Analog-to-Digital Converter); 5: Correction superposition waveform calculation unit; 6: DAC (Digital-to-Analog Converter); 7: Light intensity modulator; 8: Pulse light compression unit; 9: Photodetector (second photodetector); 101: Short pulse light source; 102: Spectrum shaping unit; 103: Wavelength dispersion unit; 501: Data selection unit; 502: Minimum value detection unit; 503: Data recording unit; 504: Waveform calculation unit.

Claims

1. A light intensity modulation device, the light intensity modulation device comprising: An optical distributor that branches the pulsed light; a light detector that converts a pulse of light branched from the light distributor into an electrical signal; an analog-to-digital converter that converts the electrical signal converted by the photodetector from an analog signal to a digital signal; a correction superimposed waveform calculation unit that calculates waveform data for correcting distortion caused by temporal intensity variation of the pulsed light, that is, correction superimposed waveform data, based on the superimposed waveform data and the electrical signal converted by the analog-to-digital converter; a digital-to-analog converter that converts the correction-superimposition waveform data calculated by the correction-superimposition waveform calculation unit from a digital signal into an analog signal; and A light intensity modulator superimposes the corrected superimposed waveform data converted by the digital-to-analog converter on another pulse light branched from the light distributor, thereby obtaining intensity modulated light.

2. The light intensity modulation device according to claim 1, characterized in that: The correction-superimposition waveform calculation unit calculates correction-superimposition waveform data based on the modulation characteristics of the light intensity modulator.

3. The light intensity modulation device according to claim 1 or 2, characterized in that: The correction superposition waveform calculation unit comprises: A data selection unit for extracting data of a part of the interval from the electrical signal converted by the analog-to-digital converter; a minimum value detection section for detecting a minimum value of the data fetched by the data strobe section; as well as A waveform calculation section calculates and corrects the superimposed waveform data based on the superimposed waveform data, the data fetched by the data selection section, and the minimum value of the data detected by the minimum value detection section.

4. The light intensity modulation device according to claim 3, characterized in that: The data strobe unit extracts data every time the analog-to-digital converter converts the electrical signal.

5. The light intensity modulation device according to claim 3, characterized in that: The data strobe unit retrieves data at once or at a predetermined time.

6. The intensity modulation device according to claim 3, characterized in that: The waveform calculation section calculates corrected superimposed waveform data based on a result of averaging a plurality of data fetched by the data strobe section, a result of averaging the minimum values ​​of the plurality of data detected by the minimum value detection section, and superimposed waveform data.

7. A waveform compression device, the waveform compression device comprising: An optical distributor that branches the pulsed light; a light detector that converts a pulse of light branched from the light distributor into an electrical signal; an analog-to-digital converter that converts the electrical signal converted by the photodetector from an analog signal to a digital signal; a correction superimposed waveform calculation unit that calculates waveform data for correcting distortion caused by temporal intensity variation of the pulsed light, that is, correction superimposed waveform data, based on the superimposed waveform data and the electrical signal converted by the analog-to-digital converter; a digital-to-analog converter that converts the correction-superimposition waveform data calculated by the correction-superimposition waveform calculation unit from a digital signal into an analog signal; an optical intensity modulator that superimposes the corrected superimposed waveform data converted by the digital-to-analog converter on another pulse light branched from the optical distributor, thereby obtaining intensity modulated light; a pulse light compression unit that compresses the intensity modulated light obtained by the light intensity modulator to obtain compressed pulse light; as well as The second photodetector converts the compressed pulse light obtained by the pulse light compression unit into an electrical signal.

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