JP3592475B2 - Pulse picker - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pulse picker for extracting an optical pulse having a repetition cycle that is an integral multiple of an optical pulse having a predetermined repetition cycle.
[0002]
[Prior art]
There is a pulse picker as a device for extracting a pulse train having a predetermined repetition cycle from a light pulse train having a specific repetition cycle emitted from a pulse laser or the like.
[0003]
FIG. 16 shows a configuration example of a conventional pulse picker. The pulse picker includes an ultrasonic light modulator (AOM) 51 for modulating light, an optical modulator stage 52 for adjusting the position of the AOM 51, an input mirror 53 for guiding an input light pulse to the AOM 51, and an output light for the AOM 51. An output mirror 54 for guiding to the output side, and a beam stopper 55 for blocking unnecessary light pulses among light pulses emitted from the output mirror are provided.
[0004]
FIG. 17 shows a configuration diagram of the AOM 51. There are two types of AOMs, one using the Raman Nurse diffraction shown in FIG. 17A and the other using the Bragg diffraction shown in FIG. 17B. Both of them use the ultrasonic medium 62 as the transducer 61 and the ultrasonic absorber 63. It has a laminated structure sandwiched between. Due to the driving electric signal applied to the transducer 61, the generated ultrasonic waves cause light diffraction in the ultrasonic medium 62. The incident light is incident from the side surface of the ultrasonic medium 62 so as to be substantially parallel to these stacked surfaces.
[0005]
FIG. 18 is a block diagram of a driving unit that applies a driving signal to the AOM 51. The drive unit 70 is configured such that a balanced modulator 72 is connected to both a carrier oscillator 71 and a drive pulse signal generator 74, and a high-frequency amplifier 73 is connected to the balanced modulator 72. The high frequency amplifier 73 is connected to the transducer 61 of the AOM 51.
[0006]
Next, the operation of this conventional example will be described with reference to FIGS. FIG. 19 is a schematic diagram of an optical path inside the pulse picker. FIG. 19 (a) is a diagram viewed from the top as in FIG. 16, and FIG. 19 (b) is a diagram viewed from the side.
[0007]
The incident light pulse to the pulse picker is condensed by the incident mirror 53 and guided to the AOM 51 as shown in FIGS. On the other hand, as shown in FIG. 18, a drive electric signal generated by the drive unit 70 is applied to the transducer 61 of the AOM 51. The driving electric signal is generated by mixing the driving pulse signal generated by the driving pulse signal generator 74 and the oscillation signal of the carrier oscillator 71 with the balanced modulator 72 and amplifying the mixed signal with the high frequency amplifier 73.
[0008]
When the drive electric signal is applied, ultrasonic waves are emitted from the transducer 61, and the generated ultrasonic waves reach the ultrasonic absorber 63 via the ultrasonic medium 62 and are absorbed. That is, the ultrasonic waves in the ultrasonic medium 62 travel in only one direction. In the ultrasonic medium 62, diffraction of an optical pulse passing therethrough occurs due to the acousto-optic effect based on the ultrasonic waves, and as shown in FIG. appear. The diffracted light passes through the optical path indicated by the solid line in FIG. 19, and is emitted from the pulse picker via the output mirror 55.
[0009]
On the other hand, when the driving electric signal is not applied to the AOM 51, since the ultrasonic wave does not propagate inside the ultrasonic medium 62, the diffraction of the light pulse due to the acousto-optic effect does not occur, and the output light becomes 0 as shown in FIG. Only the second-order diffracted light is obtained. This 0th-order diffracted light passes through the optical path shown by the broken line in FIG. 19, passes through the output mirror 55, and is blocked by the beam stopper 54, so that it does not come out of the pulse picker. Therefore, by controlling the drive electric signal to be applied only when the input optical pulse to be extracted passes through the AOM 51, it is possible to extract only a desired optical pulse from the input optical pulses.
[0010]
[Problems to be solved by the invention]
In the pulse picker as in this example, in order to efficiently extract an optical pulse having a predetermined period from an optical pulse having a specific period, a drive electric signal is transmitted to the AOM 51 at the time when the extracted input optical pulse passes through the AOM 51. The phase of the drive electrical signal must be precisely adjusted to be applied. In the past, however, this adjustment had to be performed manually, and the phase of the input optical pulse and the drive electric signal were shifted, which caused the output of the extracted optical pulse to fluctuate or the optical pulse to fail There was a problem that it could not be taken out. In addition, the timing of the drive electric signal is also shifted due to a change in the temperature of the drive unit or the like. For this reason, it is necessary to reset this timing during operation, and it has been difficult to continuously perform stable operation for a long time.
[0011]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a pulse picker that does not need to adjust the timing of extracting an optical pulse and can operate stably for a long time.
[0012]
[Means for Solving the Problems]
According to the present invention, there is provided a pulse picker for extracting and outputting an optical pulse having a repetition cycle that is an integral multiple thereof from an input optical pulse having a predetermined repetition cycle. A drive unit that generates a drive signal pulse that is an integral multiple of a predetermined repetition period of the pulse and has a pulse width including a single pulse of the input optical pulse; and (2) an input optical pulse is input. At the same time, according to the presence or absence of a drive signal pulse, an optical modulator for transmitting and blocking an input optical pulse to the output side, and (3) a part of each optical pulse output from the optical modulator is branched and extracted. An optical branching unit, (4) a measuring unit for measuring a temporal change of the extracted output optical pulse intensity, and (5) an output optical pulse intensity becomes maximum based on the measured temporal change of the output optical pulse intensity. Yo Characterized in that it comprises a control unit which adjusts the output timing of the control to drive signal pulse driving portion.
[0013]
Thus, by applying a drive signal pulse having a cycle that is an integral multiple of the repetition cycle of the input optical pulse train to the optical modulator, an output optical pulse train having the same repetition cycle as the drive signal pulse is extracted from the input optical pulse train. Further, a part of each of the output light pulses is branched and taken out, and the time change of the intensity of the output light pulse is measured. Based on the measured change, the control unit performs feedback control of the generation timing of the drive signal pulse in the drive unit. Therefore, extraction of the optical pulse train is optimized.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of this embodiment.
[0015]
The pulse spicker 10 includes a driving unit 1 that generates a driving signal pulse, an optical modulation unit 2 that is connected to the driving unit 1 and transmits and blocks an input optical pulse depending on the presence or absence of the driving signal pulse. A beam splitter 3 for branching a part of the output, a photodetector 4 for detecting light split by the beam splitter 3, an output level measuring unit 5 connected to the output side of the photodetector 4, and a measuring unit 5 and a control unit 6 connected to the drive unit 1.
[0016]
Among them, the light modulator 2 may be composed of the AOM 51, the mirrors 53 and 55, and the beam stop 54, as in the conventional example of FIG. 16, or may be composed of an electro-optic crystal.
[0017]
FIG. 2 shows an example of the light modulator 2 using an electro-optic crystal. The light modulator 2 of this example is configured by arranging a polarizer 11 for extracting linearly polarized light having a specific angle in incident light from the incident light side, an electro-optic crystal 12, and an analyzer 13 for transmitting light of a specific phase. Have been. A driving electric signal is applied between the upper and lower surfaces of the electro-optic crystal 12 (Z direction in the figure), and the polarization state of light transmitted through the inside of the electro-optic crystal 12 changes according to the driving electric signal. . The incident light becomes linearly polarized light inclined by 45 ° with respect to the Z axis as viewed from the incident side by the polarizer 11 as shown in the figure. This incident light is incident on the electro-optic crystal. When the light passes through the electro-optic crystal 12, its polarization state changes according to the driving electric signal as described above, and elliptically polarized light is output. Of the light, the analyzer 13 extracts a component of linearly polarized light orthogonal to the incident polarized light (a component changed by −45 ° with respect to the Z axis as viewed from the incident side), so that output light corresponding to the driving voltage signal is output. Is obtained.
[0018]
As the light modulation unit 2, various types of light modulators that can obtain output light corresponding to the driving electric signal can be used.
[0019]
Next, the operation of the present embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing the operation timing of the present embodiment. 3 (b) to 3 (e) indicate the operation timing when the timing of the input pulse and the drive signal pulse are synchronized, and the broken line indicates the operation timing when the respective timings are shifted. ing. (A) 'to (c)' are diagrams in which the time axes of (a) to (c) are respectively magnified 10 times.
[0020]
Here, when the pulse repetition period of the input light pulse is T as shown in FIG. 3A, the repetition period of the drive signal pulse generated by the drive unit 1 is nT (n) as shown in FIG. Must be a positive integer). The pulse width of the drive signal pulse is such that only one input light pulse is reliably cut out during one repetition period. The waveform of the drive signal pulse is ideally desirably a square wave, but is actually a trapezoidal wave signal as illustrated. The length of time during which the driving signal pulse corresponding to the top of the trapezoid has the maximum value is t ₁ , The length of the duration (pulse width) when the drive signal pulse corresponding to the bottom of the trapezoid is on is t ₀ Then t ₁ Is sufficiently longer than the pulse width of the input light pulse and t ₀ Is preferably shorter than the pulse interval of the input light pulse.
[0021]
As shown in FIG. 1, the light pulse shown in FIG. The drive signal shown in FIG. 2B generated by the drive unit 1 is applied to the light modulation unit 2. As described above, when the drive signal pulse of the drive unit 1 is on, the light modulation unit 2 transmits the input light pulse, and when the drive signal pulse is off, the light modulation unit 2 blocks the input light pulse. As a result, the output light pulse shown in FIG. This output light pulse has the same repetition period (nT) as the drive signal.
[0022]
The output light intensity of the light modulator 2 depends on the intensity of the drive signal pulse. As shown by the solid line in FIG. 3B, when the timing of the input light pulse and the timing of the driving signal pulse match, the time at which the driving signal pulse is maximum (range t) ₁ The input light pulse passes through the light modulating unit 2 during (). Therefore, as shown by the solid line in FIG. 10C, the input light pulse is extracted from the output light pulse with almost no loss.
[0023]
On the other hand, when the timing of the input light pulse and the drive signal pulse are shifted from each other as shown by the broken line in FIG. Pass through. That is, when the voltage of the drive signal is not the maximum, the input light pulse passes through the light modulation unit 2, so that only an output light pulse weaker than the intensity of the input light pulse can be obtained as shown by the broken line in FIG.
[0024]
As is clear from FIG. 9C, when the timing of the input light pulse and the timing of the drive signal pulse are shifted, the intensity of the output light pulse becomes smaller than when the timing is matched. In other words, the intensity of the output light pulse is maximized when the timing of the input pulse light and the timing of the drive signal pulse match.
[0025]
A part (for example, 1%) of the output light pulse thus obtained is split by the beam splitter 3 shown in FIG. 1 and extracted. The extracted light pulse is guided to the light detector 4, and the light detector 4 outputs an electric signal corresponding to the light pulse intensity (see FIG. 3D). This output electric signal is a temporally intermittent signal corresponding to the point in time when the output light pulse is generated. This signal is sent to the output level measuring unit 4 in FIG. 1 and converted into a DC output level signal corresponding to the peak intensity (see FIG. 3E). This output level signal is sent to the control unit 5 in FIG. 1, and feedback control is performed to control the drive unit so as to maximize the signal intensity and correct the generation timing of the drive signal pulse.
[0026]
Various methods can be used for this feedback control. For example, the following method can be used. Here, it is assumed that the drive signal is given based on a reference signal having the same frequency as the repetition frequency. The reference signal may be generated inside the pulse picker or may be supplied from outside. Then, the output level signal of the n-th extracted optical pulse is V _n Δt is the difference between the drive signal and the reference signal when the light pulse is extracted. _n And This V _n To the previous V _n-1 Δt that determines the next generation timing of the drive signal based on the comparison result _{n + 1} Is determined. FIG. 4 shows a control flow chart of this example.
[0027]
V _n Is sent to the control unit 4, the control unit 4 first _n Is checked whether is not 0 (S1). V _n Is 0 (less than or equal to the measurement error), it means that the input light pulse has not passed through the light modulator 2 within the pulse duration of the drive signal. Therefore, the generation timing of the next drive signal is set to the predetermined time Δt _a (S2). Where Δt _a Is the t ₁ Preferably smaller. This is because if the shift width is too large, the point corresponding to the input pulse is skipped. Next, V _n To the previous V _n-1 And (S3). As a result of comparison, V _n And V _n-1 Is smaller than the measurement error of the detector, the output level is at the maximum, it is determined that the timing of the input light pulse and the timing of the drive signal are compatible, and the next timing generation timing Δt _{n + 1} Is Δt _n Is maintained (S4).
[0028]
On the other hand, V _n And V _n-1 If there is a difference between the two, it is determined that the drive signal generation timing is shifted with respect to the input light pulse. Therefore, an operation for shifting the generation timing is performed.
[0029]
First, Δt _n It is checked whether or not was changed last time (S5). Δt _n Is changed, then V _n Is V _n-1 It is checked whether it is larger (S6). If it is larger than the previous time, it is determined that the direction for shifting the timing is correct, and the generation timing Δt of the drive signal is further changed in the same direction. _{n + 1} Is shifted (S7). Specifically, Δt _{n + 1} = (1 + α) Δt _n -ΑΔt _n-1 Set to. Here, α is a preset convergence coefficient, and 0 <α <1. If the output level signal is smaller than the previous time, the correct timing is Δt _n And Δt _n-1 And Δt _{n + 1} Is set in the meantime (S8). Specifically, Δt _{n + 1} = (1−α) Δt _n + ΑΔt _n-1 And
[0030]
On the other hand, Δt _n Is not changed, it is determined that the reference signal itself is shifted with respect to the input light pulse, and Δt is determined. _n Is a predetermined offset width Δt _b (S9). This Δt _b Is the aforementioned Δt _a Is preferably small enough. This is because the deviation of the reference signal itself is not considered to be large as compared with the repetition period of the normal pulse.
[0031]
By repeating the above every time the pulse output is performed, the generation timing of the drive signal is automatically feedback-controlled so that the output pulse light is maximized. For the timing feedback control, various control methods such as monitoring the polarization state of the output pulse and changing the generation timing of the drive signal can be used.
[0032]
Subsequently, some examples (applied examples) of apparatuses to which this embodiment is applied are shown together with corresponding conventional examples.
[0033]
First, an example in which this embodiment is applied to a synchronization device of an EO sampling device will be described. The EO sampling device measures an electric signal waveform inside a device under test using an optical pulse and an electro-optic crystal. FIG. 5 is a configuration diagram of a typical EO sampling device.
[0034]
The pulse light emitted from the laser light source 101 is split by the beam splitter 102 into synchronous light and probe light. The synchronization light is sent to the synchronization system 103, and a drive voltage synchronized with the laser light source 101 is applied to the circuit under test 104. On the other hand, in the probe light, only a specific polarization component is extracted by the polarizer 105 and is incident on the electro-optic crystal 106. The circuit under test 104 is electrically connected to the electro-optic crystal 106, and the voltage inside the circuit under test 104 is a driving electric signal of the electro-optic crystal 106. Therefore, the polarization state of the probe light passing through the electro-optic crystal 106 is modulated according to the voltage waveform inside the circuit under test 104. Only the modulated phase component is extracted by the analyzer 107, converted into an electric signal by the photodetector 108, amplified by the amplifier 109, and then displayed on the display device 110 with the waveform of the electric signal. The waveform of this electric signal is the same as the internal voltage waveform of the circuit under test 104. In this case, since the circuit under test 104 and the measurement system are electrically separated, the internal voltage waveform of the circuit under test 104 can be accurately measured.
[0035]
At the time of this measurement, in order to perform a measurement with high time resolution, the synchronization system 103 and the laser light emitted from the laser light source 101 need to be synchronized. It becomes a factor to decrease.
[0036]
As a device for synchronizing a synchronization system and a laser beam, Kurt J. et al. Weingarten, et al., "Picosecond Optical Sampling of GaAs Integrated Circuits" (IEEE Journal of Quantum Electronics, Inc., pp. 198-220). 1). The configuration of the synchronous system 103 of the first conventional example is as shown in FIG. In the following, in order to facilitate comparison between the conventional example and the application example using the present embodiment, the description of the common portions will be omitted using the common reference numerals.
[0037]
A Nd: YAG mode-locked laser having a repetition frequency of 82 MHz is used as the laser light source 101 of the first conventional example, and the laser oscillation is controlled by the synchronization system 103. The synchronization system 103 includes an 82 MHz high-frequency synthesizer 123 for synchronizing laser oscillation, and a microwave synthesizer 124 for driving the circuit under test 104 with a drive voltage of 0 to 40 GHz. The two synthesizers 123 and 124 are both driven by the same reference signal of 10 MHz and are electrically synchronized.
[0038]
The synchronous light split by the beam splitter 102 is converted into an electric signal by a photodetector 121, and a phase difference from an output of the high-frequency synthesizer 123 is detected by a phase detector 122. This phase difference signal is transferred to the phase shifter 127 via the gain compensator 126. The 82 MHz output of the high frequency synthesizer 123 is converted to a 41 MHz signal by the frequency halver 125 and then sent to the phase shifter 127. The phase shifter 127 generates a synchronization signal for oscillation of the laser light source 101 based on these two signals. Therefore, the laser oscillation of the laser light source 101 and the output signal of the microwave synthesizer 124 can be synchronized.
[0039]
However, in this case, the oscillation of the laser light source 101 is shifted due to the jitter generated in the gain compensator 126 and the phase shifter 127 serving as a feedback circuit, so that it is difficult to obtain a sufficient time resolution. Further, this apparatus can use only a pulse laser capable of external mode locking, and cannot use a self-mode locked laser such as a collision pulse mode locked ring laser or a Kerr lens mode locked laser.
[0040]
On the other hand, J. Appl. A. Valdmanis disclosed in “Electro-Optic Measurement Technologies for Picosecond Materials, Devices and Integrated Circuits, Synchronous, Semiconductors, 19th, and 18th. There is a device for causing the following (hereinafter referred to as Conventional Example 2).
[0041]
FIG. 7 shows a block diagram of the synchronous system 103 of the second conventional example. Synchronous light having a repetition frequency of 100 MHz emitted from the laser light source 101 and split by the beam splitter 102 is converted by the photodetector 121 into an electric signal having the same frequency of 100 MHz. A 10 MHz reference signal is generated from the electric signal by the frequency dividing circuit 131. The 10 MHz reference signal drives the microwave synthesizer 124 that drives the circuit under test 104 and the local signal synthesizer 132 that controls the display timing of the display device. The output of the local signal synthesizer 132 is combined with the output signal of the photodetector by the mixer 133 and output as a trigger signal of the display device.
[0042]
In the case of this device, since the reference signal of the microwave synthesizer 124 is generated from the light pulse emitted from the laser light source 101, it can be applied to a self-mode-locked laser. However, when the reference signal is generated from the optical pulse, the frequency division operation is performed by the electric circuit (frequency division circuit 131). Therefore, the jitter generated by the frequency division circuit 131 limits the entire time resolution, and There is a disadvantage that it is not possible to obtain a proper time resolution.
[0043]
On the other hand, an example in which the pulse picker of the present embodiment is applied to the synchronous system 103 is shown in FIG. 8 (hereinafter, referred to as application example 1). In this case, the synchronization system 103 includes the pulse picker 10 of the present embodiment, a high-speed photodetector 121 that converts the output light of the pulse picker into an electric signal, and a filter circuit that adjusts the output electric signal of the high-speed photodetector to a sine wave. 135 and a microwave synthesizer 124 that supplies a drive voltage to the circuit under test 104 described above are connected in series. The filter circuit 135 is a combination of passive elements such as a capacitor, a coil, and a resistor.
[0044]
Next, the operation of the synchronization system 103 will be described with reference to FIGS. FIG. 9 is a timing chart of signals transmitted in the synchronous system 103. As shown in FIG. 8, a synchronous light pulse having a repetition frequency of 100 MHz (see FIG. 9A) emitted from a laser light source 101 and branched by a beam splitter 102 is made incident on a pulse picker 10. The pulse picker 10 extracts a 10-MHz optical pulse (see FIG. 9C) from the synchronous optical pulse and outputs it based on the 10-MHz drive signal shown in FIG. 9B. This output light pulse is incident on the high-speed photodetector 121 and is converted into an electric signal of 10 MHz (see (d) in the figure). Further, a high frequency component is removed from the output signal by the filter circuit 135, and the output signal is adjusted to a 10 MHz sine wave signal (see FIG. 9E). This serves as a reference signal for the microwave synthesizer 124. The output of the microwave synthesizer 124 is applied as a drive signal to the circuit under test 104 shown in FIG.
[0045]
In the first application example, the reference signal is generated from the light pulse of the laser light source 101 as in the second conventional example. However, unlike the conventional example 2, since the frequency dividing operation is performed optically, no jitter occurs at the time of frequency dividing. Since the filter circuit 135 is also a combination of passive elements, jitter does not easily occur, so that stable measurement with high time resolution can be performed.
[0046]
Next, with reference to FIGS. 10 and 11, an embodiment in which the repetition frequency of the laser light emitted from the laser light source 101 in the application example 1 is not an integral multiple of the frequency of the reference signal required by the microwave synthesizer 124 (hereinafter, referred to as an example). , Application Example 2) will be described. FIG. 10 is a configuration diagram of a part of the synchronization system 103 of the application example 2, and FIG. 11 is a diagram illustrating operation timing.
[0047]
In the application example 2, as shown in FIG. 10, a Fabry-Perot (FP) including a pair of non-zero transmittance mirrors 136 between the pulse picker 10 and the beam splitter 102 of the application example 1 (see FIG. 8). Etalon 137 is installed.
[0048]
In this application example 2, the operation of a case where a laser light source that emits a light pulse having a repetition frequency of 75 MHz is used as the laser light source 101 will be described. The light pulse emitted from the laser light source 101 has a repetition frequency of 75 MHz, as shown in FIG. Of these optical pulses, the synchronous optical pulse split by the beam splitter 102 is incident on the FP etalon 137 and is partially reflected in the direction of the pulse picker 10 while being multiply reflected between the two mirrors 136. If the distance between the mirrors 136 is set to 1 m, an output light pulse having a repetition frequency of 150 MHz (see FIG. 11B) can be obtained from the surface opposite to the incident surface of the FP etalon 137. This frequency is the least common multiple of the required reference signal frequency of 10 MHz and the laser frequency of 75 MHz. This light is guided to the pulse picker 10 and a 10 MHz optical pulse (see FIG. 4D) can be extracted by a 10 MHz drive signal (see FIG. 4C). Hereinafter, a reference signal of 10 MHz is generated by the same operation as that of the application example 1, and the reference signal and the laser beam can be synchronized.
[0049]
The FP etalon 137 can adjust the repetition frequency of the output optical pulse by adjusting the interval between the mirrors 136. Therefore, a laser having another repetition frequency can be used as the laser light source. Further, the repetition frequency of the light output from the FP etalon 137 may be an integer multiple of the reference signal.
[0050]
Next, an example in which the pulse picker of the present embodiment is applied to a photo-con sampling device will be described with reference to FIG. The photo-con sampling device is a device for measuring an electric signal waveform on an electrode in a circuit to be measured such as an IC driven by a synthesizer or the like, and has a structure similar to that of the EO sampling device shown in FIG. ing.
[0051]
The difference between the photo-con sampling device shown in FIG. 12 and the EO sampling device shown in FIG. 5 lies in the configuration on the probe light side, and the configuration inside the synchronization system 203 is the same as the synchronization system of the application example 1 shown in FIG. 103 is the same. Therefore, description of the configuration of the synchronization system 203 is omitted, and the configuration on the probe light side will be described. On the optical path of the probe light ahead of the beam splitter 202, an optical delay device 205 is arranged. The optical delay device 205 includes two mirrors 212, each of which forms an angle of 45 degrees with the optical path of the probe light and is arranged orthogonal to each other, and a moving stage 213 that moves the mirrors 212 along the optical path. By adjusting the length of the optical path, the timing of the optical pulse reaching the optical path behind the optical delay device 205 can be adjusted. A mirror 206 and a condenser lens 207 for further adjusting the optical path are arranged on the optical path of the output light of the optical delay device 205.
[0052]
At the focal point of the condenser lens 207, a photo control switch 214 is provided. The photocon switch 214 has a counter electrode such as a comb-shaped electrode or a parallel electrode provided on a semiconductor substrate, and a current flows when light enters between the electrodes. One electrode of the photo-control switch 214 is connected to the probe electrode 215 that is in contact with the electrode to be measured of the circuit to be measured 204, and the other electrode is electrically connected to the current detecting device 211. The photocontrol switch 214 and the probe electrode 215 are housed in the probe head 208, and the measurement position can be changed by moving the probe head 208 on the circuit under measurement 204. The current detection device 211 and the optical delay device 205 are connected to the measurement control device 209. The measurement control device 209 is further connected to the display device 210.
[0053]
Laser light emitted from the laser light source 201 enters the beam splitter 202 and is split into two. The probe light traveling straight is guided to the condenser lens 207 by the optical delay device 205 and the mirror 206.
[0054]
Here, a drive signal (for example, a frequency of 1 GHz) by a microwave synthesizer is applied to the circuit under measurement 204 as in the above-described EO sampling device. When the probe electrode 215 is brought into contact with an electrode to be measured in the circuit to be measured 204 and the probe light condensed by the condenser lens 207 is incident on the photo-control switch 214, the probe electrode Carriers are generated and sent to the current detection device 211. This carrier output is proportional to the voltage of the electrode under measurement of the circuit under measurement 204. The carrier output is further sent from the current detection device 211 to the measurement control device 209, processed, and displayed on the display device 210 as a voltage waveform. The optical delay device 205 is moved by the measurement control device 209 to change the optical path length of the probe light, thereby adjusting the drive voltage application to the circuit under measurement 204 and the timing of the probe light incidence to the photo-control switch 214. Can be.
[0055]
In this apparatus, as in the above-described EO sampling apparatus, since the synthesizer and the laser pulse are optically synchronized, measurement with high time resolution is possible.
[0056]
Next, an example in which the pulse picker (see FIG. 1) of Application Example 1 is used for fluorescence measurement with a streak camera will be described with reference to FIG. As shown in FIG. 13, this measurement system includes a laser light source 301 that emits pulsed light, a pulse picker 302 according to the present embodiment, a sample 303 for performing fluorescence measurement, and a synchro-scan streak camera 304 for performing fluorescence measurement. , A controller 305 that controls the streak camera 304, and a display device 306 that displays the measurement result.
[0057]
Next, the operation of this application example will be described. The pulse light (repetition frequency: 80 MHz) emitted from the laser light source 301 is guided to a pulse picker 302, from which an output light pulse having a repetition frequency of 10 MHz is extracted. When the output light pulse is applied to the sample 303, the sample 303 emits fluorescence using the light pulse as excitation light. This fluorescence is incident on the streak camera 304 and measured. The sync frequency (80 MHz) of the streak camera 304 is synchronized with the repetition frequency of the laser light source 301 by the controller 305. The output of the streak camera 304 is output to the display device 306 via the controller 305 and displayed.
[0058]
When a light pulse is directly incident on the sample 303 from the laser light source 301 without using the pulse picker 302, if the fluorescence lifetime of the sample is longer than 12.5 ns, which is the repetition period of the light pulse, the fluorescence by the previous light pulse is Since the next light pulse is incident on the sample 303 while remaining, the lifetime of the fluorescence emitted from the sample 303 cannot be accurately obtained. In the case of this application example, by placing the pulse picker 302 between the sample 303 and the laser light source 301, the repetition period of the light pulse can be made as long as 100 ns. If the fluorescence lifetime of the sample 303 is less than 100 ns, The fluorescence lifetime can be accurately measured. When the fluorescence life of the sample 303 is longer, the fluorescence life of the sample 303 can be accurately measured by changing the frequency of the driving voltage of the pulse picker 302 to further increase the repetition period of the light pulse.
[0059]
It is preferable that the laser repetition frequency and the synchro frequency of the streak camera 304 match as described above. However, even when they do not match, fluorescence measurement can be performed. An example will be described with reference to FIGS. FIG. 14 is a block diagram of the measurement system of the present example, and FIG. 15 is a diagram showing the principle of image display by the streak camera of the present example.
[0060]
The sync frequency of the streak camera 304 is different from 100 MHz and the repetition frequency of the laser is 80 MHz. Therefore, in order to synchronize the laser with the streak camera 304, a part of the laser light is branched by the beam splitter 307, guided to the pulse picker 302, and an optical pulse of 10 MHz is extracted. This is converted into an electric signal by the photodetector 308 and then applied as a reference signal for driving the synthesizer 309. An electric signal of 100 MHz is output from the synthesizer 309, and the streak camera 304 is driven by this. The streak camera 304 repeats the sweep in 10 ns, but the response light from the sample 303 enters at 80 MHz, so that the response light repeats every 12.5 ns. That is, the timing of the sweep by the streak camera 304 and the timing of the laser beam do not completely match. However, measurement is possible as follows.
[0061]
As shown in FIG. 15, the output position on the fluorescent screen of the streak camera 304 makes one round in 10 ns, which is the sweep time of the streak camera 304. Here, of the sweep time of the streak camera 304, the range in which the output can be actually observed as an image is limited to 2.5 ns or less. Since the streak camera 304 and the laser beam are synchronized, the output of the first response light falls within the observation range (point A in FIG. 15). The output by the second response light after 12.5 ns is output to point B, which is a position that makes one round from point A in FIG. Since this point B is out of the observation range, it is not actually observed (point B in the figure). Subsequently, the output by the third and fourth response lights is not observed similarly (points C and D in the same figure). The output of the fifth response light 50 ns after the first response light is output to the point A, which is a position exactly five times from the first response light, and can be observed. Therefore, it is possible to observe the response light every 50 ns. Thus, the present invention can be applied to a case where the synchro frequency of the streak camera 304 and the repetition frequency of the pulse laser are different.
[0062]
The pulse picker of the present invention can be applied to various other synchronizers.
[0063]
【The invention's effect】
As described above, according to the pulse picker of the present invention, since the timing of extracting the optical pulse is feedback-controlled so that the output of the extracted optical pulse is maximized, a stable optical pulse can be extracted. In particular, even when the operating condition of the optical modulator inside the pulse picker changes due to temperature fluctuation or the like, a stable optical pulse can be always taken out in response to the change of the operating condition.
[0064]
Further, when the pulse picker of the present invention is used for generating a reference signal of a synchronizer, a reference signal having a high time resolution can be used, so that accurate synchronization can be achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of the present invention.
FIG. 2 is a configuration diagram of a light modulation unit using an electro-optic crystal.
FIG. 3 is a diagram showing operation timings of the pulse picker according to FIG. 1;
FIG. 4 is a flowchart illustrating an example of feedback control of the embodiment according to FIG. 1;
FIG. 5 is a configuration diagram of a typical EO sampling device.
FIG. 6 is a configuration diagram of a conventional device for synchronizing an EO sampling device and a laser beam.
FIG. 7 is a configuration diagram of a conventional synchronization system for synchronizing an EO sampling device with laser oscillation.
8 is a configuration diagram of a synchronization system of an EO sampling device to which the pulse picker according to FIG. 1 is applied.
FIG. 9 is a diagram showing operation timings of the synchronous system according to FIG. 8;
FIG. 10 is a configuration diagram of an application example of the EO sampling device according to FIG. 8;
11 is a diagram illustrating operation timings of an application example of the EO sampling device according to FIG. 8;
FIG. 12 is a configuration diagram of a photo-con sampling device to which the pulse picker according to FIG. 1 is applied;
13 is a configuration diagram of a fluorescence measurement device using a streak camera to which the pulse picker according to FIG. 1 is applied.
14 is a configuration diagram of an application example of the fluorescence measurement device according to FIG.
FIG. 15 is a diagram showing the principle of image display of the device according to FIG.
FIG. 16 is a configuration diagram of a conventional pulse picker.
FIG. 17 is a configuration diagram of a Bragg cell using a conventional AOM.
FIG. 18 is a block diagram of a driving unit of a conventional example.
FIG. 19 is an optical path diagram inside a conventional pulse picker.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... drive part, 2 ... light modulation part, 3 ... beam splitter, 4 ... photodetector, 5 ... output level measurement part, 6 ... control part, 10 ... pulse picker, 11 ... polarizer, 12 ... electro-optic crystal, Reference numeral 13: analyzer, 51: Bragg cell, 52: Bragg cell stage, 53: incident mirror, 54: output mirror, 55: beam stopper, 61: transducer, 62: ultrasonic medium, 63: ultrasonic absorber, 70: drive Reference numeral 71, a carrier oscillator, 72, a balanced modulator, 73, a high-frequency amplifier, 74, a driving pulse signal generator, 101, a laser light source, 102, a beam splitter, 103, a synchronous system, 104, a circuit under test, 105, polarization. Reference numeral 106: electro-optic crystal, 107: analyzer, 108: photodetector, 109: amplifier, 110: display device, 121: photodetector, 122: phase detector, 1 DESCRIPTION OF SYMBOLS 3 ... High frequency synthesizer, 124 ... Microwave synthesizer, 125 ... Frequency halver, 126 ... Gain compensator, 127 ... Phase shifter, 131 ... Frequency divider circuit, 132 ... Local signal synthesizer, 133 ... Mixer, 135 ... Filter circuit, 136 Mirror 137 FP etalon 201 Laser light source 202 Beam splitter 203 Synchronous system 204 Circuit under test 205 Optical delay device 206 Mirror 207 Condenser lens 208 Probe head 209: Measurement control device, 210: Display device, 211: Current detection device, 212: Mirror, 213: Moving stage, 214: Photocon switch, 215: Probe electrode, 301: Laser light source, 302: Pulse picker, 303: Sample , 304: streak camera, 305: controller, 06 ... display unit, 307 ... beam splitter, 308 ... photodetector, 309 ... synthesizer.

Claims (1)

In a pulse picker that extracts and outputs an optical pulse having a repetition cycle of an integral multiple thereof from an input optical pulse having a predetermined repetition cycle,
A drive signal pulse synchronized with the input light pulse, having a repetition period that is an integral multiple of a predetermined repetition period of the input light pulse, and a pulse width having a length including only one pulse of the input light pulse. A driving unit that generates
An optical modulator that receives the input optical pulse and transmits / blocks the input optical pulse to the output side in accordance with the presence or absence of the drive signal pulse,
Optical branching means for branching and extracting a part of each optical pulse output from the optical modulator,
A measuring unit that measures a time change of the output light pulse intensity extracted by the light branching unit,
A control unit that adjusts the generation timing of the drive signal pulse by controlling the drive unit such that the output light pulse intensity is maximized based on a time change of the output light pulse intensity measured by the measurement unit. When,
A pulse picker comprising:

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