JPH068757B2 - Optical pulse measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to a pulse width that changes rapidly in a very short time width and a change in the wavelength of light in each part of the pulse, or a change equivalent in wavelength to the same value. The present invention relates to an optical pulse measuring method for measuring a change in frequency of light.

INDUSTRIAL APPLICABILITY The optical pulse measuring method of the present invention is suitable for use in measuring light emission characteristics, transmission characteristics and other optical characteristics of optical elements.

[Conventional technology]

To measure the characteristics of optical elements used in the field of optical communication and optical signal processing, especially impulse response, it is very fast with a very short time width, especially the response time of existing photodetectors or less. It is necessary to measure the pulse waveform of a short optical pulse that changes in the above manner and the change in the wavelength of light in each part of the pulse, or the change in the frequency of light having the same value as the change in wavelength equivalent thereto.

The present applicant has already applied for a patent for a method of measuring a pulse phase waveform corresponding to a change in the intensity waveform and the instantaneous frequency of a short optical pulse when the short optical pulse is repeated at a constant period (Japanese Patent Application No. 62-73547, hereinafter ""Firstapplication"). In this measuring method, the pulsed light flux to be measured is split into two light fluxes, a relative optical path length difference is given to the optical paths of the two light fluxes, the two light fluxes are combined, and the combined light fluxes are divided into two light fluxes. Second harmonic light is generated by coaxially focusing on a nonlinear crystal having the ability to generate second harmonics, and the intensity of the combined light of the two light fluxes passing through the nonlinear crystal and the second harmonic light is adjusted to their respective intensities. The intensity of the light pulse to be measured is converted into a proportional electrical signal, the intensity change of the combined light and the second harmonic light with respect to the change in the relative optical path length difference is recorded, and the Fourier transform of the recorded measurement value is performed. The waveform and the phase waveform are calculated. Here, the wavelength of the second harmonic light generated by the nonlinear crystal is one half of the wavelength of the incident optical pulse. For the second harmonic light, light whose wavelength has not changed even after passing through the nonlinear crystal is hereinafter referred to as “fundamental light”.

As is well known, in the Fourier transform, there is a fixed relationship between the frequency axis band and the time axis step, and between the time axis band (time width) and the frequency axis step. And when it is intended to widen the band, it is necessary to make the steps finer. Considering a short optical pulse, for example, if the wavelength is 0.6 micron, the frequency is 0.5 PHz, which is a very high frequency, and the time axis step required for this is 1
The fineness is as fine as fs or less. So, in the earlier application method,
Wavelength period of the continuous light source, or the relative optical path difference is always changed at a fine pitch such as an integer division of the wavelength period, the fundamental wave light for the change of the relative optical path difference of the short optical pulse to be measured and The intensity change of the second harmonic light is measured, the measured value is Fourier transformed, and the information on the time axis is converted to the information on the frequency axis.

A short light pulse is a mass of waves commonly called a "wave packet",
A wave that vibrates finely at the frequency of the fundamental wave light draws a pulse-shaped envelope. When this short optical pulse is divided into two, the relative optical path length difference is given, and then they are combined and made incident on some kind of nonlinear crystal, the second harmonic light on the delay time axis corresponding to the relative optical path length difference The intensity change of is superposed by a slow change corresponding to the information of the envelope and a fast change due to the frequency of the light. Therefore, in the prior application method, what kind of phase relation can be realized for the frequency component of the second harmonic light for a slow change, and it is found by iterative calculation with the information on the frequency axis of the fundamental light as a limiting condition.

FIG. 4 is a block diagram of a short optical pulse measuring device that implements the prior application method. This device is an improvement of the device disclosed in the specification and drawings of the prior application so that the intensity waveform and phase waveform of the pulse can be measured for a pulse train that repeats at a relatively low frequency of several tens of kHz or less. .

Beam splitter 1, fixed prism 2 and movable table 4
The movable prism 3 attached to the above constitutes a Michelson interferometer. A short light pulse LB generated in synchronization with the external electric trigger signal ET is incident on the Michelson interferometer.

This short light pulse LB is split by the beam splitter 1, reflected by the fixed prism 2 and the movable prism 3, combined by the beam splitter 1, and passed through the lens 5 to generate a nonlinear second harmonic wave generating function. It is incident on the crystal 7 coaxially. The optical path length difference between the two light beams split by the beam splitter 1 can be changed by moving the movable prism 3. The light that has passed through the nonlinear crystal 7 enters the beam splitter 24 through the lens 6,
The fundamental wave and the second harmonic light generated by the non-linear crystal 7 are divided into two, and the respective wavelength (frequency) components are selected by the optical filters 8 and 30, and the photodetectors 9 and 28 are selected.
Incident on. The detection outputs of the photodetectors 9 and 28 are supplied to the sample and hold circuit 31. The sample and hold circuit 31 holds data in synchronization with the external electric trigger signal ET.

Here, the role of the sample and hold circuit 31 will be briefly described. When the short light pulse repeats at high speed, the next light pulse arrives before the response of the photodetectors 9 and 28 relaxes, and the photodetectors 9 and 28 automatically perform the averaging operation. But,
The repetition cycle of short light pulse measured by this device is at most several
Even if a photodetector with a relatively slow response of 10 kHz is used, the output of the photodetector is relaxed during the interval of the light pulse. Therefore, the sample / hold circuit 31 is used to hold the output of the photodetector at the time when the optical pulse arrives, while timing with the external electrical trigger signal ET.

Next, a method of recording the intensities of the fundamental wave light and the second harmonic light with respect to the relative optical path length difference at an appropriate interval will be described. For this purpose, the light source that emits continuous light with a deceptive wavelength
11.For example, using a continuous wave He-Ne laser, the light from this light source 11 is incident on a Michelson interferometer via a reflecting mirror 12, and is bisected in the same manner as the short optical pulse LB to obtain a relative optical path length difference. After adding, combine. At this time, the 1/8 wavelength plate 19 is inserted in one of the two branched optical paths, and the combined light flux is separated by the polarization beam splitter 20 and is incident on the photodetectors 21 and 22. The photodetectors 21 and 22 receive a signal that changes sinusoidally at the period of the interference fringes as the relative optical path length difference changes. Therefore, when a trigger signal is generated from the trigger signal generating circuit 23 every time the phase of the sinusoidal signal becomes 0, π / 2, ..., The relative optical path length difference is determined by the wavelength cycle of the light source 11 or the wavelength cycle of the light source 11. It can be calibrated with integer divided values. Further, the analog / digital converter 32 is operated at the timing of this trigger signal to convert the output of the sample / hold circuit 31 into a digital signal, and the arithmetic processing unit 33 performs arithmetic processing.

[Problems to be solved by the invention]

However, in this conventional example, since the short optical pulse is measured by the two trigger signals that operate independently, there is a drawback that the measurement can be performed only at an extremely low speed corresponding to the beat cycle of the two trigger signals.

This problem will be described in more detail.

FIG. 5 is a waveform diagram for explaining problems in measurement. Since the intensity of the second harmonic changes with the period of the interference fringes of the second harmonic, it changes as shown in FIG. 5 (a) as the relative optical path length difference is swept. If this wavelength is recorded as it is as data and arithmetic processing can be performed, the measurement error becomes very small. However, even if the relative optical path length difference is slowly changed, the short optical pulse itself also occurs only at a slow repetition period, so that the intensity change that should be measured as a wavelength that naturally changes smoothly is shown in FIG. ), Is smoothly measured as a set of spikes having a wavelength as an envelope. For this wavelength, for example, as shown in FIG. 5 (c), when the peak of the spike is sampled and held, and analog-digital conversion is performed at the timing indicated by the upward arrow,
The measured value at that time becomes a black dot in FIG. 5 (d). That is, the wavelength is largely deviated from the desired wavelength, and a large error is included.

In order to prevent this error from occurring, the relative optical path length difference is swept at a cycle slower than the repetition cycle of the slow short optical pulse. The waveform at that time is such that the envelope curve in the waveform of FIG. 5 (b) is filled with spikes. But this is not realistic. The reason will be described with reference to FIG.

FIG. 6 shows the maximum measurement error with respect to the ratio between the change in relative optical path length difference and the light pulse generation interval. In this figure, the horizontal axis assumes that the relative optical path length difference changes smoothly,
The denominator is the time required for the relative optical path length difference to change by one wavelength of the fundamental wave of the measured light pulse, and the numerator is the light pulse generation interval (time). The vertical axis represents the maximum measurement error. FIG. 6 shows the mutual relationship between the second harmonic and the fundamental wave. The upper diagonal line shows the value of the second harmonic, and the lower diagonal line shows the value of the fundamental wave.

From this figure, it can be seen that, for example, in order to set the measurement error to 0.1%, the time ratio shown on the horizontal axis must be set to 2 × 10 ⁻⁴ or less. That is, the measurement for one wavelength is completed only when 5000 optical pulses are generated. When the repetition period of the optical pulse is 1 kHz, the time required to measure one wavelength is 5 seconds. For example, the width of the light pulse is 1
In the case of ps or less, it is necessary to measure 1000 wavelengths, and in that case, 5000 seconds, that is, 1 hour 30 minutes is required for measurement.
The short pulse light source must operate stably during this measurement, and the entire device must be protected so that the measuring device is not affected by mechanical vibration or other external influences. Further, when the pulse repetition cycle is 100 Hz or less, the measurement time becomes enormous and the measurement becomes impossible in reality.

In addition, the measuring method of the conventional example has a drawback that it is impossible to measure a single short light pulse.

The present invention solves the above problems, and the repetition cycle is several tens.
An optical pulse measurement method that can measure the change of the wavelength of light at the pulse waveform and each pulse part, or the change of the frequency of light of the same value for short optical pulses of kHz or less, and for single-shot short optical pulses. The purpose is to

[Means for solving problems]

The optical pulse measurement method of the present invention measures the intensity change of the second harmonic light with respect to the change in the relative optical path length difference between the two light beams, the spectrum of at least one of the two light beams, and the spectrum of the second harmonic light. It is characterized in that the intensity waveform and the phase waveform of the optical pulse to be measured are calculated from these measured values by arithmetic processing.

When the light pulse is a short light pulse that repeats at a substantially constant cycle, the measurement is repeated while changing the relative optical path length difference. In this case, in order to prevent interference by the two light beams, the two light beams are incident on the nonlinear crystal in a non-coaxial relationship,
The spectrum of one of the two light beams that passed through this nonlinear crystal is measured, or the two light beams are combined and incident on the nonlinear crystal, and the intensity of the second harmonic light is oscillated while oscillating the relative optical path length difference. The spectrum of the combined light transmitted through the nonlinear crystal and the spectrum of the second harmonic light are measured.

From these measured values, the Fourier analysis value of the intensity change of the second harmonic light with respect to the relative optical path length difference, the spectrum of the second harmonic light, and the fundamental wave component of the spectrum of at least one of the two light fluxes are used to repeatedly calculate. To do.

The relative optical path length difference between the two light beams can be obtained by the difference in the crossing points due to the spread of the diameters of the two light beams when these two light beams are incident on the nonlinear crystal in a non-coaxial relationship. The intensity of the second harmonic light emitted from the nonlinear crystal is spatially measured. By this method, even a single pulse can be measured.

In this case, it is desirable that the diameter of the light pulse to be measured is enlarged and converted into a parallel light flux before the light pulse to be measured is split into two light fluxes.

As the calculation processing at this time, the Fourier analysis value of the spatial intensity distribution of the secondary harmonic light, the spectrum of the secondary harmonic light, and the fundamental wave component of the spectrum of at least one of the two light fluxes are repeatedly calculated.

[Action]

The optical pulse measuring method of the present invention combines the measurement of the intensity change of the second harmonic light with the spectrum measurement by the spectroscope.

The information on the frequency axis of light corresponds to the information on the wavelength axis of light,
The information is obtained by spectral measurement with a spectroscope. Therefore, by measuring the spectra of the fundamental wave light and the second harmonic light, complicated measurement and Fourier transform can be simplified. However, if the second harmonic light intensity of the short light pulse is not large enough to measure the spectrum, the spectroscope cannot be used. The prior application method had an advantage that even such a weak short light pulse could be measured. However, it is difficult to measure low-speed repetitive short light pulses with this prior application method. Therefore, in the present invention, spectrum measurement is used together as a method complementary to the prior application method. The method of the present invention can measure a short optical pulse whose intensity of the second harmonic light can be spectrally measured.

Further, the method of the present invention can measure a slow intensity change of the second harmonic light and its spectrum with the same optical system for a short optical pulse having a low repetition period, and in the case of a single pulse, the measurement can be performed. Can be done at once.

〔Example〕

FIG. 1 is a block diagram of an optical pulse measuring device according to a first embodiment of the present invention.

This device is a device for measuring a short optical pulse that repeats at a substantially constant period, and includes a beam splitter 1 that splits an optical pulse to be measured into two light beams, and a fixed prism that gives a relative optical path length difference to these two light beams. 2 and a movable prism 3 attached to a movable table 4, and an optical means for injecting two light beams having the relative optical path length difference into a non-linear crystal 7 to generate a second harmonic light, that is, a beam splitter 1. , Fixed prism 2, movable prism 3 and lens 5
And means for measuring at least one of the two light fluxes passing through the nonlinear crystal 7 and the second harmonic light, that is, the lens 6, the optical filters 45 and 46, the slit 42, the wavelength sweeping device 41.
The spectroscope 40, the slit 43, the photodetector 47, the amplifier 48, and the analog-to-digital converter 49 provided with, and the calculation processing for calculating the intensity waveform and the phase waveform of the measured optical pulse by processing the measurement values And a device 33. The measuring means can measure the intensity change of the second harmonic light with respect to the relative optical path length difference between the two light fluxes, the spectrum of at least one of the two light fluxes, and the spectrum of the second harmonic light.

In this measurement and measurement, two light beams are incident on the nonlinear crystal 7 in a non-coaxial relationship, and the spectrum of one of the two light beams that have passed through this nonlinear crystal is measured.

The arithmetic processing unit 33 repeatedly performs an operation based on the Fourier analysis value of the intensity change of the secondary harmonic light with respect to the relative optical path length difference, the spectrum of the secondary harmonic light, and the fundamental wave component of the spectrum of one light flux.

The measuring method by the apparatus of this embodiment will be described in more detail.

The short light pulse LB enters the beam splitter 1 and is split into two light beams. The first light flux passes through the fixed prism 2 and the second light flux passes through the movable prism 3. The movable prism 3 is mounted on a moving table 4, and its position can be variably moved by a motor, and a relative optical path length difference can be given to two light beams. The two light beams further enter the nonlinear crystal 7 non-coaxially via the beam splitter 1 and the lens 5, and are focused within the nonlinear crystal 7. The fundamental wave light that has passed through the nonlinear crystal 7 and the second harmonic light that has been generated by this nonlinear crystal 7 enter the spectroscope 40 through the lens 6.
The spectroscope 40 is provided with a wavelength sweeping device 41 and slits 42 and 43. Further, a filter holder 44 having optical filters 45 and 46 attached is inserted between the lens 6 and the spectroscope 40. The optical filter 45 passes only the wavelength component of the fundamental wave light and blocks the second harmonic light. Further, the optical filter 46 passes only the wavelength component of the second harmonic light and blocks the fundamental wave light. The light passing through the spectroscope 40 is a photodetector 47.
Detected by. The electrical output of the photodetector 47 is an amplifier
Amplified by 48, converted into a digital signal by the analog-digital converter 49, stored in the arithmetic processing unit 33,
Numerically calculated.

First, the measurement of the slow intensity change corresponding to the change in the relative optical path length difference of the second harmonic light will be described.

For this measurement, the filter holder 44 is set at a position where the optical filter 46 transmits light. Then slit
Adjust 42 or 43 to set the wavelength resolution of the spectrometer 40 low. While operating the movable table 4 in this state, the relative optical path length difference is swept and the intensity change of the second harmonic light is detected by the photodetector.
The signal is detected by 47, amplified by the amplifier 48, converted into a digital signal by the analog / digital converter 49, and the arithmetic processing unit 33
To record.

In this measurement, only the slow intensity change of the second harmonic light can be measured. That is, in order to prevent the intensity of the second-harmonic light from changing in the cycle of the interference fringes, two light beams are made to enter the non-linear crystal 7 in a non-coaxial manner, and all light in the wavelength band in which the second-harmonic light exists is transmitted. It is important to lower the wavelength resolution of the spectroscope 40 so that it can be performed. Since it is not necessary to measure the interference fringe cycle at a fine pitch, a normal step motor or the like can be used as a motor for moving the moving table 4, and it is only necessary to sweep slowly compared to the repetition rate of the short light pulse. Good.

Here, when the response speed of the amplifier 48 is faster than the repetition speed of the short optical pulse, the analog-digital converter
It is necessary to operate 49 in synchronization with the trigger signal of short light pulse. In the opposite case, it is not necessary to input a trigger signal from the outside, and the averaging process can be performed by the amplifier 48.

Next, spectrum measurement of the fundamental wave light and the second harmonic light by the same measuring device will be described.

At this time, the moving table 4 is swept to set the relative optical path length difference between the two light fluxes to zero so that the second harmonic light intensity becomes maximum, and the moving table 4 is stopped. In this state, the slit 42 is set so that the wavelength resolution of the spectrometer 40 is sufficiently high.
Or adjust 43. Then, the optical filter 45 is set to transmit light, the wavelength sweeping device 41 is operated, and the fundamental wave light intensity (spectrum) for each wavelength is recorded. Next, the optical filter 46 is moved to the transmission position, and the spectrum of the second harmonic light is recorded in the same manner.

Here, when a diffraction grating is used as the spectroscope 40, the fundamental wave light and the second harmonic light can be diffracted as the first-order diffracted light and the second-order diffracted light at the same grating angle, and the sweep of the wavelength sweeping device 41 can be performed. Calibration becomes easy. When a prism is used as the spectroscope 40, it is necessary to perform wavelength sweep at different positions for the fundamental wave light and the second harmonic light.

As described above, in the present embodiment, the same measurement device is used, and only the wavelength resolution of the spectroscope 40 and the operating condition of the movable table 4 are changed, and the relative optical path length difference of the second harmonic light is corrected. It is possible to measure a slow intensity change waveform, the spectrum of the fundamental wave light, and the spectrum of the second harmonic light. This makes it possible to obtain all the information necessary for determining the waveform of the short optical pulse, and thus it is possible to obtain the change in the waveform and the wavelength in each part of the pulse by arithmetic processing in the same manner as the prior application method and other conventional methods. . Further, it is not necessary to calibrate the relative optical path length difference with the wavelength pitch, and it is not necessary to generate the trigger signal with this pitch, and the measurement time can be greatly reduced.

In the above-described embodiment, the two light beams are incident non-coaxially on the nonlinear crystal 7 having the second harmonic generation capability. However, when the time width of the measured short light pulse is short, the nonlinear crystal 7
The chromatic dispersion of light inside may cause an error. In order to reduce the influence of chromatic dispersion, it is desirable that the two light beams be made coaxial and are incident on the nonlinear crystal 7. However, when the light beams are made incident on the same axis, there is a problem in that the two light beams interfere with each other and the light and dark are superimposed on the measurement light. An embodiment will be described below which solves such a problem and is coaxially incident and is not affected by the interference fringe period.

FIG. 2 is a block diagram of an optical pulse measuring device according to a second embodiment of the present invention.

In this embodiment, two light fluxes are combined and incident on the nonlinear crystal 7, and the intensity of the second harmonic light while oscillating the relative optical path difference, the spectrum of the combined light transmitted through the nonlinear crystal, and the secondary light. The measurement of the spectrum of harmonic light is different from the first embodiment. A micro-vibrator 50 is attached to the movable table 4 in order to vibrate the relative optical path length difference.

By slightly oscillating the relative optical path length difference, it is possible to average the contrast of the interference fringe period. For this purpose, the amplitude of the vibration is set to be as large as the wavelength of light. Therefore,
A micro-vibrator 50 may be provided separately from the motor, and a motor that slowly moves in one direction and micro-vibrates may be used. Then, when measuring the slow intensity change of the second harmonic light corresponding to the change of the relative optical path length difference, and when measuring the spectrum of the fundamental wave light and the second harmonic light, this micro vibrator 50 is always To operate. As a result, even in the case of coaxial incidence, measurement can be performed without being affected by interference fringes.

Thus, according to the second embodiment, as in the first embodiment,
Using the same measuring device, only by changing the wavelength resolution of the spectroscope and the operating conditions of the motor, a slow intensity change waveform with respect to the relative optical path length difference of the second harmonic light, the spectrum of the fundamental light, and the secondary The spectrum of harmonic light can be measured. By this method, all the information necessary for determining the waveform of the short light pulse can be obtained, and the waveform of the short light pulse and the change in the wavelength at each part of the pulse can be obtained by the conventional arithmetic processing. Further, in this measuring method, it is not necessary to calibrate the relative optical path length difference by the wavelength pitch, and therefore, the trigger signal at this pitch is not necessary, and the measuring time can be greatly shortened.

FIG. 3 is a block diagram of an optical pulse measuring device according to a third embodiment of the present invention.

The optical pulse measurement method described in the first and second embodiments, the light source capable of generating the second harmonic light of sufficient intensity to allow spectrum measurement, the measurement time seems to be too long in the prior art. It is possible to measure short light pulses that are repeated at low speed. However, it is not possible to measure short-lived light pulses. Therefore, in the third embodiment, two light beams are incident on the non-linear crystal in a non-coaxial relationship, and at this time, the difference between the intersections due to the spread of the diameter of the light beams is used as the relative optical path length difference, and the intensity of the second harmonic light is Is measured spatially and a short light pulse is similarly measured.

The one-shot short light pulse LB enters the beam expander 51 and is expanded into a thick light beam having the same light intensity in the radial direction.
The peripheral non-uniform portion is removed by the aperture 52. The thick light beam is split into two light beams by the beam splitter 1, and one light beam ELB1 passes through the prism 2 and is reflected by the beam splitter 1 again, and is incident on the nonlinear crystal 7 having a second harmonic generation capability. The other luminous flux ELB2 is
The light is reflected by the reflecting mirrors 53 and 54 and enters the nonlinear crystal 7. At this time, the center lines of the two light fluxes intersecting each other are nonlinear crystals 7
Are set so that they intersect each other on the surface of and the bisector of the angle formed by the center lines of the two center lines coincides with the normal line of the nonlinear crystal 7. Thus, for example, on the right side of the crystal, the luminous flux EL
B1 reaches the nonlinear crystal 7 before the luminous flux ELB2, the luminous flux ELB1 and the luminous flux ELB2 simultaneously reach at the intersection of the center lines, and the luminous flux ELB2 precedes the luminous flux ELB1 on the left side of the nonlinear crystal 7.

In this way, a relative optical path length difference can be given to the two light beams depending on the incident position of the nonlinear crystal 7. In this case, the intensity of the generated second harmonic light is spatially distributed corresponding to the difference in optical path length depending on the position of the nonlinear crystal 7. The photodetector 58 detects this spatial intensity distribution.
Here, the aperture 55 is for avoiding the incidence of the fundamental wave light on the photodetector 58. Further, as the photodetector 58, it is necessary to be able to measure the position distribution of the light intensity, and as such an example, a photodetector in which photodetection elements are linearly arranged, a camera or the like can be used. .

Next, spectrum measurement of the fundamental wave light and the second harmonic light will be described. The light that has passed through the nonlinear crystal 7 is split by the beam splitter 24. Each of the split light fluxes of the fundamental wave light and the second harmonic light is condensed by the condenser lens 57 and enters the entrance slit 65 of the spectroscope 63. The aperture 56 blocks one of the fundamental wave bundles in order to prevent the interference of the two luminous fluxes of the fundamental wave spectrum in the spectroscope 63. The spectroscope 63 is a Czerny-Turner type spectroscope including a reflecting mirror 66, concave mirrors 67 and 68, a diffraction grating 69, and a reflecting mirror 70.
The reflecting mirror 70 on the emitting side is a semi-transparent mirror. A photodetector 59 that does not have a slit on the exit side and is positionally resolvable at that position
And a position-resolvable photodetector 60 is arranged on the transmission side of the reflecting mirror 70. These two photodetectors 59, 60
Optical filters 61 and 62 are arranged on the front surface of the
To the photodetector 60, only the second-harmonic light enters.

Here, the removal of the exit side slit will be described. In a normal spectroscope, a slit is provided on the emission side in order to extract only a desired wavelength component of light bent at different angles for each wavelength. However, in the case of the present embodiment, the wavelength components collected at different positions and the position-resolvable photodetectors 59 and 60 are simultaneously measured to obtain the spectra.

The outputs of the three photodetectors 58, 59, 60 are converted from analog to digital by the control device 64 and numerically calculated by the arithmetic processing device 33.

By the above-described measurement, the slow change of the second harmonic light intensity with respect to the relative optical path difference, the spectrum of the fundamental light and the spectrum of the second harmonic light are measured. That is, all the information necessary for determining the waveform of the short optical pulse can be obtained, and the wavelength and the change in the wavelength at each part of the pulse can be obtained by the same calculation as the conventional method.

In the case where at least two or more light pulses are continuously generated instead of the short light pulse being generated individually, instead of the optical filter 61 in the third embodiment, the optical of the first embodiment is used. Similar to filters 45 and 46, two optical filters are used to measure the spectrum of the fundamental wave light in the first short light pulse and the spectrum of the second harmonic light in the second short light pulse to detect light. The number of vessels can be reduced by one.

〔The invention's effect〕

As described above, the optical pulse measuring method of the present invention measures the slow change of the intensity of the second harmonic light with respect to the relative optical path length difference, the spectrum of the fundamental light and the spectrum of the second harmonic light. This makes it possible to determine in detail the intensity waveform and the phase waveform of the short light pulse when the repetition of the short light pulse is a low speed that causes a problem in measurement time and when the short light pulse is generated only once.

INDUSTRIAL APPLICABILITY The present invention has an effect of enabling measurement in a short time when measuring characteristics of an optical element, for example, when measuring emission characteristics of a light emitting element, characteristics of an optical fiber transmission line and other passive elements.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical pulse measuring device according to a first embodiment of the present invention. FIG. 2 is a block diagram of an optical pulse measuring device according to a second embodiment of the present invention. FIG. 3 is a block diagram of an optical pulse measuring device according to a third embodiment of the present invention. FIG. 4 is a block diagram of a conventional optical pulse measuring device. FIG. 5 is a diagram for explaining a measurement problem of the conventional example. FIG. 6 is a diagram showing the relationship between the measurement pitch and the maximum error in the conventional example. 1, 24 ... Beam splitter, 2, 3 ... Prism, 4 ...
Mobile stand 5, 6, ... Lens, 7 ... Non-linear crystal, 8, 30, 4
5, 46, 61, 62 ... Optical filter, 9, 21, 22, 28, 47, 5
8, 59, 60 ... Photodetector, 10, 29 ... Integrating amplifier, 11 ... Light source, 12, 53, 54, 66, 70 ... Reflecting mirror, 19 ... 1/8 wavelength plate, 20 ... Polarizing beam splitter, 23 ... Trigger signal generating circuit, 31 ... Sample and hold circuit, 32, 49 ... Analog-digital converter, 33 ... Arithmetic processing device, 40, 63 ... Spectrometer, 41 ... Wavelength sweeping device, 42, 43 ... Slit, 44 ... Filter holder, 48 ... Amplifier, 50 ... Micro vibrator, 51 ... Beam expander, 52, 55, 56 ... Aperture, 57 ... Focusing lens, 64 ... Control device, 65 ... Incident slit, 67, 68 ... Concave mirror, 69 ... Diffraction grating.

Claims (7)

[Claims] 1. A light pulse to be measured is split into two light beams, a relative optical path length difference is given to the two light beams, and the two light beams having the relative optical path length difference are incident on a nonlinear crystal. Generate the second harmonic light, measure at least one of the two light fluxes that have passed through the nonlinear crystal and the second harmonic light, and calculate the measured values to obtain the intensity waveform and phase waveform of the measured optical pulse. In the optical pulse measuring method to be obtained, the measurement is a change in intensity of the second harmonic light with respect to a relative optical path length difference between the two light fluxes, at least one spectrum of the two light fluxes, and a spectrum of the second harmonic light. An optical pulse measuring method characterized by measuring and. 2. The optical pulse measuring method according to claim 1, wherein the optical pulse is a short optical pulse that repeats at a substantially constant cycle, and the measurement is repeated while changing the relative optical path length difference. 3. The optical pulse measuring method according to claim 2, wherein the two light beams are incident on the nonlinear crystal in a non-coaxial relationship, and the spectrum of one of the two light beams passing through the nonlinear crystal is measured. 4. The intensity of the second harmonic light, the spectrum of the combined light transmitted through the nonlinear crystal, and the second order while the two light beams are combined and incident on the nonlinear crystal while oscillating the relative optical path length difference. The optical pulse measuring method according to claim 2, wherein a spectrum of harmonic light is measured. 5. The relative optical path length difference between the two light beams is given by the difference between the intersections due to the spread of the diameters of the two light beams when these two light beams are incident on the nonlinear crystal in a non-coaxial relationship, The optical pulse measuring method according to claim 1, wherein the intensity of the second harmonic light emitted from the nonlinear crystal is spatially measured. 6. The light pulse is a single pulse.
The optical pulse measurement method described. 7. The optical pulse measuring method according to claim 5, wherein the diameter of the measured optical pulse is enlarged and converted into a parallel luminous flux before the optical pulse is split into two luminous fluxes.