JPH10233544A - Pulse picker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse picker which does not require manual adjustment of timing for picking up optical pulse and enables stable operation for a long time. SOLUTION: In a pulse picker 10, the repetition cycle is an integral number of input optical pulse repetition cycle in synchronism with input optical pulse. It has a driving part 1 which generates driving signal pulse whose pulse width corresponds to only one pulse of input optical pulse, a light modulation part 2 which transmits and screen input light pulse according to the presence or absence of the driving signal pulse, a beam splinter 3 which branches a part of output of the light modulation part 2, a photodetector 4 which detects the branched light, an output level measuring part 5 which measures output of the photodetector 4 and a control part 6. Since generation timing of a driving signal is subjected to feed back control so that output optical pulse strength is always maximum in this way, stable operation is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. 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]

2. Description of the Related 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.

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.

FIG. 17 shows a configuration diagram of the AOM 51. As shown in FIG. AO
There are two types of M, one using the Raman Nurse diffraction shown in FIG. 17A and the other using the Bragg diffraction shown in FIG. 17B. In both cases, the ultrasonic medium 62 includes the transducer 61 and the ultrasonic absorber 63. It has a laminated structure sandwiched between.
Due to the drive 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.

FIG. 18 is a block diagram of a driving unit for applying a driving signal to the AOM 51. The driving section 70 is configured such that a balanced modulator 72 is connected to both a carrier oscillator 71 and a driving 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.

Next, the operation of this conventional example will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 19 is a schematic diagram of an optical path inside the pulse picker. FIG. 19 (a) is a view from the top as in FIG. 16, and FIG. 19 (b) is a view from the side.

The light pulse incident on the pulse picker is shown in FIG.
6. As shown in FIG. 19, the light is condensed by the incident mirror 53 and guided to the AOM 51. On the other hand, as shown in FIG.
The drive electrical signal generated by the drive unit 70 is applied to the transducer 61 of the OM 51. This drive electric signal is obtained by combining the drive pulse signal generated by the drive pulse signal generator 74 and the oscillation signal of the carrier oscillator 71 with the balanced modulator 7.
2 and are generated by being amplified by the high frequency amplifier 73.

When a 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 wave, and as shown in FIG. 17, multi-order diffracted light in Raman-Nurse diffraction and first-order diffracted light in Bragg diffraction. Occur. 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.

On the other hand, when no drive electric signal is applied to the AOM 51, no ultrasonic wave propagation occurs inside the ultrasonic medium 62, so that light pulse diffraction due to the acousto-optic effect does not occur, and the output light is shown in FIG. Thus, only the zero-order diffracted light is obtained. This zero-order diffracted light passes through the optical path shown by the broken line in FIG.
So it doesn't 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]

In the pulse picker of this example, in order to efficiently extract an optical pulse having a predetermined period from an optical pulse having a specific period, the time at which the input optical pulse to be extracted passes through the AOM 51 is required. AO according to
The phase of the drive electric signal must be accurately adjusted so that the drive electric signal is applied to M51. However, in the past, 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 be reliably output without timing. There was a problem that it could not be taken out.
In addition, the timing of the drive electric signal is 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.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pulse picker which does not need to adjust the timing of extracting light pulses and can operate stably for a long time.

[0012]

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 whose repetition period is an integral multiple of a predetermined repetition period of the input light pulse and whose pulse width is a length including only one pulse of the input light pulse;
(2) an optical modulator that receives an input optical pulse and transmits / blocks the input optical pulse to the output side in accordance with the presence or absence of a drive signal pulse; and (3) an optical modulator output from the optical modulator. Optical branching means for branching and extracting a part of the optical pulse;
(4) a measuring unit for measuring a temporal change in the extracted output light pulse intensity; and (5) a driving unit for maximizing the output light pulse intensity based on the measured temporal change in the output light pulse intensity. And a control unit for controlling the generation timing of the drive signal pulse by controlling.

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 result, 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]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of this embodiment.

The pulse picker 10 includes a driving unit 1 for generating a driving signal pulse, an optical modulation unit 2 connected to the driving unit 1 and transmitting and blocking an input light pulse according to the presence or absence of the driving signal pulse, and an optical modulation unit. A beam splitter 3 for branching a part of the output of the unit 2, a photodetector 4 for detecting light split by the beam splitter 3, and an output level measuring unit 5 connected to the output side of the photodetector 4. , A measuring unit 5 and a control unit 6 connected to the driving unit 1.

The light modulator 2 may be composed of an AOM 51, mirrors 53 and 55, and a beam stop 54, as in the conventional example shown in FIG. 16, or may be composed of an electro-optic crystal.

FIG. 2 shows an example of the light modulator 2 using an electro-optic crystal. The light modulator 2 of this example includes a polarizer 11 that extracts linearly polarized light having a specific angle in incident light from the incident light side.
, An electro-optic crystal 12 and an analyzer 13 that transmits light of a specific phase. A drive 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 passing through the inside of the electro-optic crystal 12 changes according to the drive electric signal. . The incident light becomes linearly polarized light inclined by 45 ° with respect to the Z axis when 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, the polarization state changes in accordance with the driving electric signal as described above, and elliptically polarized light is output. Of this light, a component of linearly polarized light orthogonal to the incident polarized light by the analyzer 13 (a component changed by −45 ° with respect to the Z axis when viewed from the incident side)
, An output light corresponding to the drive voltage signal is obtained.

As the light modulating unit 2, various types of light modulators that can obtain output light corresponding to the driving electric signal can be used.

Next, the operation of this 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. Also,
(A) 'to (c)' are diagrams in which the time axes of (a) to (c) are respectively magnified 10 times.

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 as shown in FIG. It must be nT (n is 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 drive signal pulse corresponding to the top of the trapezoid has the maximum value is t ₁ , and the length of time (pulse width) when the drive signal pulse corresponding to the bottom of the trapezoid is on is t _0.
In this case, it is preferable that t _{1 be} sufficiently longer than the pulse width of the input light pulse, and t ₀ be shorter than the pulse interval of the input light pulse.

As shown in FIG. 1, the light modulation unit 2
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,
When the drive signal pulse is off, the light modulator 2 blocks the input light pulse. As a result, an output light pulse shown in FIG. This output light pulse has the same repetition period (nT) as the drive signal.

The intensity of the output light from the light modulator 2 depends on the intensity of the drive signal pulse. As shown by the solid line in FIG.
When the timings of the input light pulse and the drive signal pulse match, the input light pulse passes through the light modulator 2 during the time (range t ₁ ) when the drive signal pulse is at its maximum.
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.

On the other hand, when the timing of the input light pulse and that of the drive signal pulse are shifted as shown by the broken line in FIG. The light passes through the modulator 2. 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.

As is apparent from FIG. 3C, 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.

The output light pulse thus obtained is partly branched (for example, 1%) by the beam splitter 3 shown in FIG. 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.

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. this,
The reference signal can be generated inside the pulse picker,
It may be provided from outside. The output level signal of the n-th extracted optical pulse is defined as V _n, and the difference between the drive signal and the reference signal when the optical pulse is extracted is defined as Δt _n . The V _n as compared with the previous V _n-1, based on the comparison result, determining a Delta] t n _{+ 1} for determining the generation timing of the next drive signal. 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, V _n is checked or not 0 (S1). When V _n is 0 (hereinafter measurement error), the input light pulse in the pulse duration of the drive signal means that not passed through the optical modulator 2. Therefore, the generation timing of the next drive signal is shifted by _a predetermined time Δta (S2). Here, Delta] t _a is preferably smaller than t ₁ described above. This is because if the shift width is too large, the point corresponding to the input pulse is skipped. Next, compare the V _n and the previous V _n-1 (S3). As a result of the comparison, if the difference between V _n and V _n-1 is less measurement error of the detector, the output level which is the maximum, determined that the timing of the input light pulse and the drive signal is adapted And the next timing occurrence time Δt _{n + 1} is Δ
t _n is maintained (S4).

On the other hand, when there is a difference between V _n and V _n−1 ,
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.

First, it is checked whether Δt _n has been changed last time (S5). If Δt _n has been changed, V _n
Is greater than V _n-1 (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 _{n + 1} of the drive signal is further shifted in the same direction (S7). Specifically, Δt _{n + 1} = (1 + α) Δt _n -αΔt _n-1 is set. Here, α is a preset convergence coefficient, and 0 <α <1. When the output level signal is smaller than the previous time, the correct timings are Δt _n and Δt
It is determined that it is between _n−1 , and Δt _{n + 1} is set between them (S8). Specifically, Δt _{n + 1} = (1−α) Δt _n + α
_{Let it be} Δt _n-1 .

On the other hand, when Δt _n is not changed,
It is determined that the reference signal itself has shifted from the input light pulse, and Δt _n is shifted by a predetermined offset width Δt _b (S9). It is preferable that Δt _b is sufficiently smaller than Δt _a described above. This is because the deviation of the reference signal itself is not considered to be large compared to the normal pulse repetition period.

By repeating the above every time a 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.

Next, some examples (applied examples) of apparatuses to which this embodiment is applied are shown together with conventional examples corresponding thereto.

First, an example in which the present embodiment is applied to a synchronization device of an EO sampling device will be described. The EO sampling device uses a light pulse and an electro-optic crystal,
It measures the electric signal waveform inside the device under test. FIG. 5 is a configuration diagram of a typical EO sampling device.

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 for 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.

At the time of this measurement, in order to perform a measurement with a high time resolution, the synchronization system 103 and the laser light emitted from the laser light source 101 need to be synchronized. This causes a decrease in time resolution.

As a device for synchronizing a laser beam with a synchronization system, Kurt J. Weingarten et al., "Picosecond Optical Sample"
ing of GaAs Integrated Circuits "(IEEE Journal of
Quantum Electronics, Vol. 24, pp. 198-220, 1988) has a device for driving a pulsed laser by a synthesizer (hereinafter referred to as Conventional Example 1). The configuration of the synchronization system 103 of the first conventional example is as shown in FIG. Hereinafter, in order to facilitate comparison between the conventional example and the application example using the present embodiment, the common parts are denoted by the same reference numerals, and the description is omitted.

As the laser light source 101 of the first conventional example, an Nd: YAG mode-locked laser having a repetition frequency of 82 MHz is used, and the laser oscillation is controlled by a synchronous system 103. The synchronization system 103 synchronizes the laser oscillation.
2 MHz high frequency synthesizer 123 and circuit under test 1
And a microwave synthesizer 124 for driving the driving circuit 04 with a driving 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.

The synchronous light split by the beam splitter 102 is converted into an electric signal by a photodetector 121, and the high-frequency synthesizer 12 is converted by a phase detector 122.
3 is detected. This phase difference signal is
The data is transferred to the phase shifter 127 via the gain compensator 126. The 82 MHz output of the high frequency synthesizer 123 is
After being converted into a 41 MHz signal by the frequency half-life device 125, the signal is 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.

However, in this case, it is difficult to obtain a sufficient time resolution because the oscillation of the laser light source 101 is shifted due to the jitter generated particularly in the gain compensator 126 and the phase shifter 127 serving as a feedback circuit. 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.

On the other hand, as an apparatus applicable to a self-mode-locked laser, JAValdmanis has proposed “Electro-Optic Meas”.
urement Techniques for Picosecond Materials, Devic
es and Integrated Circuits "(Semiconductor and Sem
imetals, Vol.28, pp.135-219, Academic Press Inc.,
1990) which synchronizes the synchronization system 103 with the laser oscillation (hereinafter referred to as Conventional Example 2).

FIG. 7 is a block diagram of the synchronous system 103 of the second conventional example. Repetition frequency of 100 MHz emitted from the laser light source 101 and branched by the beam splitter 102
Is converted by the photodetector 121 into an electric signal having the same frequency of 100 MHz. From this electric signal, the frequency divider 131
Generates a 10 MHz reference signal. 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.

In the case of this apparatus, 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.

FIG. 8 shows an example in which the pulse picker of the present embodiment is applied to the synchronous system 103 (hereinafter, referred to as “pulse picker”).
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. 13
5 and a microwave synthesizer 124 for supplying 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.

Next, the operation of the synchronous 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 beam splitter 102
The synchronous light pulse having a repetition frequency of 100 MHz (see FIG. 9A) branched into the pulse picker 10 is input. The pulse picker 10 has a 10 MH shown in FIG.
10M from this synchronous light pulse based on the drive signal of z.
Hz optical pulses (see FIG. 3C) are extracted and output. This output light pulse enters the high-speed photodetector 121 and is converted into a 10 MHz electric signal (see FIG. 3D). 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 becomes the reference signal of 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.

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.

Next, with reference to FIGS. 10 and 11, an embodiment is described in which the repetition frequency of the laser beam 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. An example (hereinafter, referred to as 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.
Is a diagram showing operation timing.

In the application example 2, as shown in FIG. 10, a pair of non-zero transmittance mirrors 13 between the pulse picker 10 and the beam splitter 102 in the application example 1 (see FIG. 8).
6, a Fabry-Perot (FP) etalon 137 is provided.

In this application example 2, the laser light source 101
The operation will be described in the case where a laser light source that emits a light pulse having a repetition frequency of 75 MHz is used. The light pulse emitted from the laser light source 101 is shown in FIG.
As shown in FIG. 1A, it has a repetition frequency of 75 MHz. Of this light pulse, the beam splitter 102
The synchronous light pulse branched in the step (1) enters the FP etalon 137 and is partially reflected and output to the pulse picker 10 while undergoing multiple reflection between the two mirrors 136. Mirror 1
If the distance between 36 is set to 1 m, FP etalon 137
An output light pulse having a repetition frequency of 150 MHz (see FIG. 11B) is obtained from the surface opposite to the incident surface. This frequency is the required reference signal frequency of 10 MHz.
z and the least common multiple of 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 10 MHz reference signal can be generated by the same operation as that of the application example 1 to synchronize the reference signal and the laser beam.

The FP etalon 137 can adjust the repetition frequency of the output light 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.

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.

The difference between the photo-con sampling device shown in FIG. 12 and the EO sampling device shown in FIG. 5 is the configuration on the probe light side, and the configuration inside the synchronization system 203 is the same as that of the first application shown in FIG. Is the same as the synchronous system 103 of FIG. Therefore, the description of the configuration of the synchronization system 203 will be omitted, and the configuration on the probe light side will be described. An optical delay device 205 is arranged on the optical path of the probe light ahead of the beam splitter 202. This optical delay device 205
Each of the mirrors 212 forms an angle of 45 degrees with the optical path of the probe light, and is disposed at right angles to the two mirrors 212 and a moving stage 213 that moves the mirrors 212 along the optical path.
Consists of 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. On the optical path of the output light of the optical delay device 205, a mirror 206 for further adjusting the optical path and a condenser lens 2 are provided.
07 is arranged.

At the focal point of the condenser lens 207, a photo control switch 214 is provided. Photo control switch 21
Reference numeral 4 denotes an arrangement in which a counter electrode such as a comb-shaped electrode or a parallel electrode is provided on a semiconductor substrate. When light enters between the electrodes, a current flows. One electrode of the photo-control switch 214 is connected to the probe electrode 215 that is in contact with the electrode under measurement of the circuit under measurement 204, and the other electrode is electrically connected to the current detection device 211. The photo control switch 214 and the probe electrode 215 are connected to the probe head 20.
8, the measurement position can be changed by moving the probe head 208 on the circuit under measurement 204. Current detection device 211 and optical delay device 20
5 is connected to the measurement control device 209. The measurement control device 209 is further connected to the display device 210.

The 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.

Here, the above-described E
Similar to the −O sampling device, a drive signal (for example, a frequency of 1 GHz) by a microwave synthesizer is applied. The probe electrode 215 is brought into contact with the electrode to be measured in the circuit to be measured 204, and the
When the probe light condensed by the condenser lens 207 is incident on the photodetector 211, carriers are generated between the opposing electrodes of the photo-control switch 214 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 supplied to the current detection device 211.
Is sent to the measurement control device 209 for processing, and is displayed on the display device 210 as a voltage waveform. Measurement control device 20
9, the optical delay device 205 is moved to change the optical path length of the probe light, whereby it is possible to adjust the drive voltage application to the circuit under test 204 and the timing of the probe light incidence to the photo-control switch 214.

In the present apparatus, as in the case of the above-mentioned EO sampling apparatus, since the synthesizer and the laser pulse are optically synchronized, measurement with high time resolution is possible.

Next, an example in which the pulse picker (see FIG. 1) of Application Example 1 is used for fluorescence measurement by a streak camera will be described with reference to FIG. This measurement system includes a laser light source 301 that emits pulsed light as shown in FIG.
A pulse picker 302 of the present embodiment, a sample 303 for performing fluorescence measurement, a synchro-scan streak camera 304 for performing fluorescence measurement, a controller 305 for controlling the streak camera 304, and a display device for displaying measurement results 306 in combination.

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 fluorescent light is generated by the streak camera 30
4 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 the controller 3
05 to the display device 306 and displayed.

When an optical pulse is directly incident on the sample 303 from the laser light source 301 without using the pulse picker 302, the repetition period of the optical pulse is 12.5 ns.
If the fluorescence lifetime of the sample is longer, the next light pulse enters the sample 303 while the fluorescence of the previous light pulse remains, so that the lifetime of the fluorescence emitted from the sample 303 cannot be accurately obtained. In the case of this application example,
The pulse picker 302 is connected to the sample 303 and the laser light source 3
By setting the interval between 01 and 01, 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.

It is preferable that the repetition frequency of the laser and the synchro frequency of the streak camera 304 match as described above, but fluorescence measurement can be performed even when they do not match. An example will be described with reference to FIGS. FIG. 14 is a block diagram of a measurement system according to the present embodiment.
FIG. 5 is a diagram showing the principle of image display by the streak camera of this example.

The synchro 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. A 100 MHz electric signal is output from the synthesizer 309, and the streak camera 304 is driven by this. The streak camera 304 repeats the sweep at 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 sweep of the streak camera 304 and the timing of the laser beam do not completely match. However, measurement is possible as follows.

As shown in FIG. 15, the streak camera 3
The streak camera 30 in 10 ns which is the sweep time of 04
The output position on the fluorescent screen of No. 4 goes around once. 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 laser light is synchronized with the streak camera 304, the output by the first response light falls within the observation range (FIG. 1).
A point 5). 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 outside 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. In this manner, 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.

The pulse picker of the present invention can be applied to various other synchronizers.

[0063]

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 generated. Can be taken out. 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 always be taken out in response to the change of the operating condition.

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 showing 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;

FIG. 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 conventional example of an AOM Bragg cell.

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 measuring unit, 6 ... control unit, 10
... Pulse picker, 11 ... Polarizer, 12 ... Electro-optical crystal, 13 ... Analyzer, 51 ... Bragg cell, 52 ... Brag cell stage, 53 ... Incident mirror, 54 ... Output mirror, 55 ... Beam stopper, 61 ... Transducer
62 ... ultrasonic medium, 63 ... ultrasonic absorber, 70 ... drive unit, 71 ... carrier oscillator, 72 ... balanced modulator, 73 ...
High frequency amplifier, 74 ... drive pulse signal generator, 101 ...
Laser light source, 102: beam splitter, 103: synchronous system, 104: circuit to be measured, 105: polarizer, 106: electro-optic crystal, 107: analyzer, 108: photodetector, 10
9 amplifier, 110 display device, 121 photodetector, 1
22: phase detector, 123: high frequency synthesizer, 12
4 ... microwave synthesizer, 125 ... frequency halver,
126: gain compensator, 127: phase shifter, 131: frequency dividing 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 2
05: optical delay device, 206: mirror, 207: condenser lens, 208: probe head, 209: measurement control device,
Reference numeral 210: display device, 211: current detection device, 212: mirror, 213: moving stage, 214: photo-control switch, 215: probe electrode, 301: laser light source, 30
2 pulse picker, 303 sample, 304 streak camera, 305 controller, 306 display device, 307 beam splitter, 308 photodetector, 3
09 ... Synthesizer.

Claims (1)

[Claims] 1. A pulse picker for extracting and outputting an optical pulse having an integral multiple repetition period from an input optical pulse having a predetermined repetition period, wherein the pulse picker is synchronized with the input optical pulse and has a repetition period of the input light pulse. A drive unit that generates a drive signal pulse that is an integral multiple of a predetermined repetition period of a pulse and has a pulse width that is a length including only one pulse of the input light pulse; An optical modulator that transmits and blocks the input optical pulse to the output side according to the presence or absence of the drive signal pulse; and a light that branches and extracts a part of each optical pulse output from the optical modulator. A branching unit, a measuring unit that measures a time change of the output light pulse intensity extracted by the optical branching unit, and a time change of the output light pulse intensity measured by the measuring unit. Based on a pulse picker, characterized in that it comprises a control unit which adjusts the output timing of the drive signal pulses by the output light pulse intensity to control the driving unit so as to maximize.