JPH09160082A - Optical sampling optical waveform measuring device - Google Patents

Abstract

(57) [Abstract] [Problem] To enable eye pattern measurement with high time resolution. SOLUTION: f ₀ is a measured light repetition frequency, M, N
Is a natural number and Δf is an offset frequency, an oscillator 11 that oscillates at a frequency M (f ₀ −NΔf) is used, and a repetition frequency M is generated based on the output of the oscillator 11.
A pulse light source 1 for generating an optical pulse train of (f ₀ −NΔf)
3, a frequency dividing circuit 12 for dividing the output of the oscillator 11 into 1 / (NM), and an electric pulse generation for generating an electric pulse train having a repetitive frequency f ₀ / N-Δf based on the output of the frequency dividing circuit 12. And a light gate switch 23 that divides the optical pulse train into an optical pulse train having a repetitive frequency f ₀ / N-Δf based on the electric pulse train.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sampling optical waveform measuring device for measuring the waveform of signal light used in optical communication or the like by utilizing a nonlinear optical effect.

[0002]

2. Description of the Related Art Optical sampling optical waveform measurement uses a nonlinear optical effect by introducing an optical pulse to be observed and a sampling optical pulse whose pulse width is sufficiently narrower than the optical pulse into a nonlinear optical material. This is a method of extracting the cross-correlation signal of both. In this optical sampling optical waveform measurement, since the measured light can be sampled in the optical region, it can be expected to realize waveform observation with high time resolution of the ultrafast optical signal.

In the above optical sampling optical waveform measurement,
As the nonlinear optical effect, sum frequency light generation (SFG: Sum Frequency Generati), which is one of the second-order nonlinear optical effects, is used.
on) (Reference [1]: Takara et al., “Ultrafast optical waveform measurement method by optical sampling using sum frequency light generation”, IEICE Transactions, BI, vol.J75-BI, No.8, pp.372-38
0, 1992) and four-wave mixing (FWM), which is a third-order nonlinear optical effect (Reference [2]: P.
A. Andrekson, Electron. Lett. 27, 1440, 1991) is used.

FIG. 6A and FIG. 6B are SFs, respectively.
It shows the relationship between the optical frequency and the optical intensity in the case of G and FWM. In the figure, ν _sam , ν _sin , ν _sfg and ν _fwm are the sampling light frequency, the measured light frequency, the sum frequency light frequency and the FWM light frequency, respectively. P _sam , P _sin , P
_sfg and P _fwm are the sampling light intensity, the measured light intensity, the sum frequency light intensity, and the FWM light intensity, respectively. FIG. 6 (a)
As shown in, when two light waves of the measured light having the optical frequency f _sig and the sampling light having the optical frequency ν _sam are incident on the second-order nonlinear optical material (first nonlinear optical material), the light of the sum of the two is obtained. _{Light of} frequency ν _sfg = ν _sin + ν _sam is generated.
This phenomenon is SFG.

On the other hand, FWM is a phenomenon in which new light (optical frequency ν4 = ν1 + ν2-ν3) is generally generated by three incident lights (optical frequencies ν1, ν2, ν3). However, when applied to optical sampling, the configuration is complicated when three types of light are used, so an FWM in which two light waves are degenerate (ν1 = ν2) is usually used. That is, by inputting the light having the sampling light frequency ν _{sam as} the light having the light frequencies ν 1 and ν 2 and the light having the measured light frequency ν _sig as the light having the light frequency ν 3, as shown in FIG. 6B, Optical frequency ν _fwm (however, ν _fwm = 2ν
_sam −ν _sig ) FWM light is generated. As the first nonlinear optical material, a ferroelectric crystal such as KTP is mainly used in SFG, and a silica optical waveguide such as an optical fiber is used in FWM.

FIG. 7 is a diagram showing an example of the configuration of an optical sampling optical waveform measuring apparatus using these nonlinear optical effects (Reference [3]: Yamabayashi et al., “LiNbO ₃ Waveguide and Ultrashort Optical Pulse”. Optical Sampling Using ", Proc. 1988 IEICE Spring National Conference Proceedings B-671),
In the figure, thick solid lines indicate the flow of optical signals, and thin solid lines indicate the flow of electrical signals.

In FIG. 7, 1 is a light source to be measured as an external device, 2 is a sampling light generator, 3 and 4 are polarization controllers, 5 is a coupler, 6 is a nonlinear optical material, and 7
Is an optical filter, 8 is a detector, 9 is a signal processing unit, and 10 is a display unit. Generally, the conversion efficiency of the nonlinear optical effect of SFG or FWM depends on the polarization state of incident light. Therefore, in the optical sampling optical waveform measuring apparatus shown in FIG. 7, the measured light having the frequency f ₀ from the measured light source 1 and the frequency f ₀ / N−Δ from the sampling light generator 2 are generated.
The sampling lights of f are supplied to the polarization controllers 4 and 3 respectively.
, And the polarization state of each optical pulse is adjusted to the optimum state for the nonlinear optical material 6, and then combined at the coupling section 5.

Further, in the above apparatus, the combined two lights are incident on the nonlinear optical material 6 and the sum frequency light or the FWM light (repetition frequency f ₀ / N-Δ) which is a cross-correlation signal.
f). Here, sum frequency light and FWM
Compared to the level of the optical cross-correlation signal, other background light (light to be measured, sampling light, second harmonic of light to be measured (optical frequency 2ν _sig ), second harmonic of sampling light (light frequency 2ν _sam ), etc.) cannot be ignored, these background lights are removed by using an optical filter (optical bandpass filter) 8 to extract only the cross-correlation signal. Then, the photodetector 8 receives the cross-correlation signal, converts it into an electric signal, performs appropriate signal processing in the signal processing unit 9, and displays an optical waveform on the display unit 10.

FIG. 8 shows a change in relative position with time of the measured optical pulse and the sampling optical pulse in the above-described optical sampling optical waveform measuring method, and a low-speed cross-correlation signal optical waveform obtained by the change. The repetition frequency of the sampling light pulse is Δf [H] rather than an integer fraction (f ₀ / N [Hz]) of the repetition frequency of the measured light pulse.
by lowering (or raising) z], (C)
A correlation signal waveform such as Note that FIG. 8 shows the waveform when N = 1. Further, the envelope of the correlation signal waveform is an enlargement of the measured optical waveform on the time axis, and the repetition frequency is Δf [Hz].

That is, according to this optical sampling optical waveform measuring method, another sampling optical pulse having a pulse width narrower than that of the optical pulse is superposed on the light to be measured and is incident on the nonlinear optical material 7, and this sampling is further performed. When the delay of the optical pulse is swept, the waveform of the cross-correlation signal optical power generated in proportion to the overlapping portion of both optical pulses is displayed on the display unit 1.
The measured light waveform is measured by displaying it on 0. Since the measured optical waveform can be sampled by using the nonlinear optical effect that has an extremely fast response speed of about fsec, and the time axis of the measured optical waveform can be expanded and measured, high-speed light with an extremely high time division capability can be obtained. The pulse waveform can be detected.

By the way, one of the characteristics evaluation of the transmission method is the eye pattern eye pattern measurement. The eye pattern is, as shown in (D) of FIG. 9, a display in which a plurality of sampling waveforms of randomly modulated optical signals are superimposed and displayed.
The characteristics of the optical transmission system can be evaluated by the aperture of this eye pattern and the like. Conventionally, eye pattern measurement was performed using a photoelectric conversion element and a sampling oscilloscope instead of the optical sampling method, but the time resolution was limited to about 10 ps by the band of the photoelectric conversion element.

The principle of eye pattern measurement by optical sampling will be described with reference to FIG. First, a randomly modulated optical signal ((A) in FIG. 9) is sampled at the optical stage by sampling light ((B) in FIG. 9) to obtain a cross-correlation signal optical pulse ((C) in FIG. 9). To be Next, by overlaying and plotting a plurality of waveforms (T1, T2, T3) on the same screen, the eye pattern as shown in (D) of FIG. 9 can be measured.

In order to realize eye pattern measurement by optical sampling, individual sampling values (a in FIG. 9C) are used.
~ P), it is necessary to photoelectrically convert each optical pulse of the cross-correlation signal without interference with an adjacent pulse.
Therefore, the repetition frequency of the cross-correlation signal light pulse (that is, the repetition frequency f0 /
It is necessary to set N−Δf [Hz]) to be equal to or less than the band B of the light receiving system.

Usually, the upper limit of the band B of the light receiving system is about 10 MHz depending on the processing speed of the electric signal processing unit in the subsequent stage. Therefore, in order to perform eye pattern measurement with the optical sampling optical waveform measuring device, it is necessary to generate an ultrashort optical pulse train at a repetition frequency of 10 MHz or less in the sampling light generating section.

[0015]

However, with the sampling light generation method used conventionally, it is difficult to generate an optical pulse train having a low jitter and a narrow pulse width at the low repetition frequency as described above. As a result, there is a problem that the optical waveform measurement with high time division ability cannot be realized.

By the way, FIGS. 10 (a) to 10 (c) are views for explaining a short pulse generating technique which has been mainly used in the related art, and each of them is a ring resonator type mode-locked laser (reference [4]. ]: Takara et al., Electron. Lett., 2
9, p1075 (1993)), Fabry-Perot cavity mode-locked laser and gain switching method of semiconductor laser (reference [5]: Takara et al., J. Lightwave Technol., LT-5, p
p.1525-1533 (1987)).

In FIGS. 10A to 10C, 3
0 is an electric amplifier, 31 is a DC voltage source, 32 is an optical modulator,
34 is an optical delay device, 35 is an optical band pulse filter, 3
Reference numeral 7 is an optical mirror (mirror), 38 is a direct current source, 39 is a semiconductor laser, and 40 is a dispersion medium for pulse compression. By the way, a rare earth-doped optical fiber, a semiconductor laser amplifier, or the like is used as the amplification medium of the mode-locked laser.
The pulse width of the optical pulse output from the mode-locked laser is given by the following equation (1) (reference document [1]).

[Equation 1]

Where fm is the optical modulator drive frequency, and Δf
_a is the band of the optical amplifier. As can be seen from the equation (1), the pulse width ΔT is inversely proportional to the square root of the optical modulator driving frequency f _m . In a normal mode-locked laser, since a sine wave is used as a drive signal for the optical modulator, the optical modulator drive frequency f _m matches the pulse repetition frequency f _rep . Therefore, due to the relationship of the equation (1), the pulse width increases when f _m decreases.

For example, if Δf _a = 500 GHz and f _m = 10 MHz from the speeds of the light receiving system and the electric signal processing system in the above eye pattern measurement, ΔT = 200 p
Therefore, the time resolution of the optical waveform measurement is limited to this pulse width ΔT. On the other hand, the gain switching method uses relaxation oscillation when the semiconductor laser is driven by a short pulse electric signal of about 100 ps, and is therefore 10 MHz.
The following low frequency sine wave drive does not work in principle. That is, it is impossible to generate an optical pulse train with a narrow pulse width by the method of driving a conventional pulse generation technique with a low frequency sine wave.

FIG. 7B is a diagram showing the structure of a conventional sampling light generator. In FIG. 7B, 14-1
Is an optical amplifier that amplifies the peak power of the pulsed light source output,
15-1 is noise light (ASE generated by the optical amplifier 14-1
(Amplified stimulated emission light) etc.). In the sampling light generating section of the conventional optical sampling light waveform device, for the above-mentioned reason, the short light pulse is obtained by driving the pulse light source at a high frequency f ₀ −Δf (Hz) as high as the light to be measured. . However, in that case, since the sampling frequency becomes higher than the band of the light receiving system and the speed (frequency) of the electric signal processing unit, it is impossible to measure individual sampling values and it is impossible to perform eye pattern measurement.

On the other hand, conventionally, as a method of obtaining a short optical pulse at a low repetition frequency, there has been a method of driving an optical modulator of a mode-locked laser or a semiconductor laser of a gain switching method by an electric pulse signal. FIG. 11 is a diagram showing a configuration of a sampling light generator using a conventional electric pulse signal,
FIG. 12 is a diagram for explaining the operation principle. FIG.
In 1, the numeral 22 is an electric pulse generator for generating an electric signal of a short pulse train.

The method shown in FIGS. 11 and 12 is a method using an electric pulse signal generator including a comb generator, an avalanche transistor and the like. This electric pulse signal generator can generate a short pulse electric signal having a repetition frequency of MHz order and a pulse width of about 100 ps to 1 ns. When the optical modulator of the mode-locked laser is driven by using this short pulse electric signal, the optical modulator drive frequency f _m can be equivalently increased.
The pulse width can be narrowed.

For example, when an electric signal having a repetition frequency of 10 MHz and a pulse width of 100 ps is used, the repetition frequency of the mode-locked laser output optical pulse is f _rep = 10 MH.
z. The pulse width is equivalent optical modulator drive frequency f _{m (although, f m = 1 / 100ps =} 10GH
z), therefore, ΔT = 6 ps or so from the equation (1). Therefore, according to this method, a short optical pulse train can be generated with low repetition.

However, these pulse electric signal generators have a large jitter of 10 ps or more, and the optical pulse generated as a result has the same degree of jitter. Therefore, the time resolution is limited by this jitter value,
There is a drawback that it is difficult to measure an optical waveform with high time resolution. The present invention has been made in view of such circumstances, and by generating a sampling light pulse train having an ultrashort pulse width and low jitter with low pulse repetition, an optical sampling light that enables high-time-resolution eye pattern measurement. An object is to provide a waveform measuring device.

[0025]

According to the first aspect of the present invention,
A sampling light generator that generates a sampling light pulse train with a narrow pulse width of an optical frequency ν sam based on the measured light that has a repetition of the optical frequency ν _sig , and a polarization controller that controls the polarization of the measured light and the sampling light, respectively. , A coupling unit that combines the measured light and the sampling light, a delay signal generator that sweeps the delay of the sampling light with respect to the measured light, and an optical frequency ν _sfg as a cross-correlation signal between the measured light and the sampling light pulse. (However, ν _sfg = ν _sig + ν _sam )
The first non-linear optical material that generates the four-wave mixed light having the sum frequency light of both lights or the optical frequency ν _fwm (where ν _fwm = 2ν _sam −ν _sig ) and the generated cross-correlation signal light are detected. In an optical sampling waveform measuring device equipped with a photodetector for converting an electrical signal into an electrical signal and an electrical processing system for processing the electrical signal and displaying an optical pulse waveform under measurement, f ₀ is the optical repetition frequency under measurement, M, N Is a natural number and Δf is an offset frequency, an oscillator that oscillates at a frequency M (f ₀ −NΔf) is used as the delay signal generation unit, and the sampling light generation unit is based on the output of the oscillator. A pulse light source that generates an optical pulse train having a repetition frequency M (f ₀ −NΔf), a frequency divider that divides the output of the oscillator into 1 / (NM), and repeat based on the output of the frequency divider. Frequency f
₀ / electrical pulse generator for generating electrical pulses of N-△ f, that composed of the optical gate switch for dividing the optical pulse train of repetition frequency f ₀ / N-△ f the optical pulse train by the electrical pulse train It has a feature.

According to a second aspect of the present invention, in the first aspect, between the pulse light source and the multiplexer, an incident light pulse is converted into a supercontinuum light pulse having a wide band spectrum. Non-linear optical material of
An optical bandpass filter for selecting an optical pulse having a desired center wavelength and a spectral bandwidth from the supercontinuum optical pulse, and a chirping compensator for compensating the chirping of the optical pulse are characterized by being provided. . According to a third aspect of the present invention, in the first or second aspect, at least one optical amplifier is arranged between the pulse light source and the multiplexer.
The invention according to claim 4 is the same as that according to claim 3,
An optical bandpass filter having the same center wavelength as that of the optical pulse amplified by the optical amplifier and having a bandwidth wider than the spectral bandwidth of the amplified optical pulse is disposed in the subsequent stage of the optical amplifier. .

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a sampling light pulse generator of an optical sampling light waveform measuring apparatus according to the first embodiment of the present invention. The optical sampling optical waveform measuring device according to the present embodiment is different from the conventional device only in the sampling optical pulse generator shown in FIG.

In FIG. 1, 14-1 and 14-2 are first and second optical amplifiers, 15-1 and 15-2 are first and second optical filters, and 21 is a frequency of an oscillator output. A frequency divider for dividing 1 / (M / N), 22 is an electric pulse generator, and 23 is an optical gate switch. As the pulse light source 13, the mode-locked laser, the gain switching semiconductor laser, etc. described in the prior art can be used. As the optical amplifiers 14-1 and 14-2, a rare earth-doped optical fiber amplifier, a semiconductor laser amplifier, or a Raman amplifier can be used.

As the electric pulse generator 22, the comb generator or avalanche transistor described in the prior art can be used. As an optical gate switch, LiN
A light intensity modulator using a material having an electro-optical effect such as bO _3, a semiconductor laser amplifier utilizing stimulated emission by current injection of a semiconductor material, and an electroabsorption type utilizing a nonlinear absorption characteristic with respect to an applied voltage of the semiconductor material. An optical modulator or the like can be used.

The optical sampling optical waveform measuring apparatus according to the present embodiment has a function of dividing an optical pulse train generated at an optical repetition frequency into an optical pulse train having a low repetition frequency by using an optical gate switch in a sampling optical pulse generator. Have. Other configurations are similar to those described in the related art. FIG. 2 is a diagram for explaining the operation principle of the sampling light pulse generator shown in FIG. The frequency M (f ₀ −NΔ generated by the oscillator 11
When a part of the sine wave of (f) ((A) of FIG. 2) is branched and the pulse light source 13 is driven, a pulse train of the same repetition frequency is generated ((A) of FIG. 2). From equation (1), the pulse width of the generated optical pulse becomes narrower as the drive frequency is increased.

For example, when the repetition frequency f _{0 of the} measured light is 10 GHz, M = 1 and M (f 0 -N
When a pulsed light source is driven by generating a sine wave of Δf) to 10 GHz, a short light pulse of about 6 ps can be obtained from the equation (1). Further, M = 2, and M (f ₀ −NΔf) ˜2
Driving a pulsed light source with a 0 GHz sine wave results in about 4 ps
A short light pulse of is obtained. The output of the pulse light source is amplified by the first optical amplifier 14-1 and is incident on the optical gate switch 23. On the other hand, the other of the branched oscillator outputs is the frequency dividing circuit 2
The frequency is divided by 1 by 1 / (M · N). By driving the electric pulse generator 22 with the divided electric signal of the low frequency f ₀ −NΔf, an electric pulse train having a repetition frequency f ₀ −NΔf and a pulse width of 100 ps to 1 ns is generated (FIG. 2 (C)).

By driving the optical gate switch 23 at the same timing as the optical pulse train by this electric pulse signal, the optical pulse train having the repetition frequency M (f ₀ −NΔf) has the low repetition frequency f ₀ −NΔf. It is divided into optical pulse trains ((d) in FIG. 2). At this time, the electric pulse signal includes jitter, but by gating the optical pulse near the center of the electric pulse signal as shown in (c) of FIG. You can divide.

After that, the output light of the optical gate switch 23 is amplified by the second optical amplifier 14-2 and used as a sampling light pulse. Here, the optical amplifiers 14-1, 1
If the noise light such as ASE (amplified stimulated emission light) generated in 4-2 is at a level that cannot be ignored, optical filters 15-1 and 15-2 are inserted as shown in FIG. May be. Even if the first optical amplifier 14-1 and / or the second optical amplifier 14-2 or both are not provided, if the sampling light pulse has a peak power sufficient for generating a cross-correlation signal in the subsequent stage, These may be omitted.

As described above, by using the sampling light pulse generator of the optical sampling light waveform measuring apparatus according to the present embodiment, it is possible to obtain an ultrashort sampling light pulse train with low repetition frequency and low jitter. Therefore, by using the optical sampling optical waveform measuring device according to the present embodiment, it is possible to perform eye pattern measurement with high time resolution.

Next, a second embodiment of the present invention will be described. FIG. 3 is a diagram showing the configuration of a sampling light pulse generator of the optical sampling light waveform measuring apparatus according to the second embodiment of the present invention. The optical sampling optical waveform measuring device according to the present embodiment has the same configuration as the conventional technique, except for the sampling optical pulse generator shown in FIG.

In FIG. 3, reference numeral 24 is a nonlinear optical material for generating supercontinuum (hereinafter referred to as SC), 25 is a dispersion compensator, and 26 is an optical bandpass filter for wavelength selection (bandpass filter for wavelength selection).
It is. As the SC generating nonlinear optical material 24, a silica-based optical waveguide such as an optical fiber, a semiconductor waveguide, an organic crystal or an organic waveguide, or the like can be used. In addition, the dispersion compensator 25
As the material, a silica type optical waveguide such as an optical fiber or a planar lightwave circuit (PLC), a semiconductor waveguide, a diffraction grating pair or a prism pair, or a Gires-Tournois interference system can be used.

The pumping light pulse train ((H) in FIG. 4) generated by the pulse light source 13 is amplified by the first optical amplifier 14-1 and then enters the SC generating nonlinear optical material 24. At this time, when the wavelength λ _{pump of the} pumping light and the zero-dispersion wavelength of the nonlinear optical material 24 for SC generation are set close to each other and the peak power of the pumping light pulse is amplified sufficiently high (1 W or more), SC generation occurs. Of pumping light pulse to SC light occurs in the nonlinear optical material 24 (Reference: T. Mori
oka et al., "Nearly penelty-free, 4ps supercontinuum
WDM pulse generation for Tbit / s TDM-WDM network ",
OFC94, PD21, 1994).

The SC light is an optical pulse train having a spectrum width in a wide wavelength range of 200 nm or more as shown in FIG. At this time, if the SC light has chirping (the optical frequency varies temporally within the optical pulse) due to the influence of the dispersion characteristics of the SC generating nonlinear optical material 24, the dispersion compensator 25 is used to By controlling the pinging, the chirping is controlled to form an optical pulse train having no chirping (FIG. 4 (C)). Non-linear optical material for SC generation 2
If SC light without chirping is obtained immediately after 4, the dispersion compensator 25 is unnecessary.

Next, the bandpass filter 26 for wavelength selection is used.
The SC light having a desired wavelength λ _sam (optical frequency f _sam ) is cut off by the optical signal ((SA) in FIG. 4) by the second optical amplifier 14-
Amplified by 2. Thereafter, similarly to the first embodiment described above, SC optical pulse train of repetition frequency M (f0 -N △ f) is the optical gate switch 23, is divided into an optical pulse train of a low repetition frequency f ₀ -N △ f It After that, the output light of the gate switch 23 is amplified by the third optical amplifier 14-3 and used as sampling light.

Here, the optical amplifiers 14-1, 14-2, 1
If the noise light such as ASE (amplified stimulated emission light) generated in 4-3 is at a level that cannot be ignored, the optical filters 15-1, 15-2, 15-3 as shown in FIG. May be inserted. Further, when the output light of the pulse light source 13 has a peak power sufficient to generate the SC light in the latter stage, the first optical amplifier 14-1 can be omitted as a matter of course. Furthermore, if the sampling optical pulse has a sufficient peak power for the mutual signal generation in the subsequent stage even without the second optical amplifier 14-2, the third optical amplifier 14-3, or both, naturally, However, these can be omitted.

The spectral bandwidth of the obtained sampling light pulse is the wavelength selection bandpass filter 2
Determined by a bandwidth of 6. This bandwidth is △
When ν and the optical pulse width are Δt, the product of these (time band width product) is equal to or larger than the Fourier transform limit value. That is,
The following expression (2) is established. △ ν ・ △ t ≧ A …… (2)

In the equation (2), A is a value determined by the shape of the optical pulse. For example, A = 0.44 in the case of Gaussian type and A = 0.31 in the case of sech2 type.
Becomes The optical pulse when the equal sign is satisfied in the equation (2) is particularly called a Fourier transform limit pulse. For SC light as well, if there is no chirping, a Fourier transform limit pulse can be obtained. Therefore, the pulse width ≧ Δt of SC light is Δt = A / Δν (3), and it is understood that an optical pulse having a narrow pulse width can be obtained by increasing the bandwidth Δν. For example, Δν
= 650 GHz (wavelength about 5 nm) and the optical pulse waveform is assumed to be a Gaussian type, compared to the output optical pulse of the sampling light source of the first embodiment,
Ultrashort optical pulse with a pulse width of about 1/10 (Δt = 0.5
ps) is obtained. The jitter of this SC optical pulse (ultra-short optical pulse) is almost the same as that of the optical pulse to be excited.

As described above, according to the present invention, it is possible to obtain a sampling light pulse train having a pulse width narrower than that of the first embodiment, in which jitter is extremely small at a low repetition frequency. Therefore, by using the optical sampling optical waveform measuring device of this embodiment, it is possible to perform eye pattern measurement with higher time resolution (femtosecond region).

Next, a third embodiment of the present invention will be described. FIG. 5 is a diagram showing the configuration of a sampling light pulse generator of an optical sampling light waveform measuring apparatus according to the third embodiment of the present invention. The optical sampling optical waveform measuring device according to the present embodiment has the same configuration as the conventional technique, except for the sampling optical pulse generator shown in FIG.

In the optical sampling optical waveform measuring apparatus according to the present embodiment, the output optical pulse train (repetition frequency M (f ₀ −NΔf)) of the pulse light source 13 is supplied to the optical gate switch 23.
After frequency division (repetition frequency f ₀ −NΔf) by
It is converted into SC light by the generating nonlinear optical material 24. Other functions are exactly the same as those of the second embodiment described above. Therefore, the optical sampling optical waveform measuring device according to the present embodiment also enables eye pattern measurement with high time resolution (femtosecond region).

Further, the optical sampling optical waveform measuring device according to the present embodiment has the following advantages. When a long optical fiber is used as the SC generating nonlinear optical material 24, the influence of expansion and contraction of the optical fiber due to temperature fluctuation is large. Therefore, when the optical gate switch 23 is arranged at the subsequent stage of the SC generating nonlinear optical material 24 as in the second embodiment, the optical pulse train and the electric power in the optical gate switch 23 are caused by the expansion and contraction of the optical fiber due to the temperature variation. There is a possibility that the timing with the pulse signal will shift. On the other hand, in the case of this embodiment, the optical gate switch 23 is S
Since it is arranged before the C generating nonlinear optical material 24, there is an advantage that the optical pulse train can be frequency-divided stably without being affected by the expansion and contraction of the optical fiber due to the temperature fluctuation. . Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the scope of the present invention. Also included in the present invention.

[0047]

As described above, according to the present invention, in the sampling optical pulse generator, the optical pulse train generated at the high repetition frequency is divided into the low repetition frequency optical pulse train by using the optical gate switch. Have. Since the optical pulse train obtained by driving the short pulse light source with a high frequency electric signal is used, an ultrashort optical pulse with low jitter can be obtained, and optical waveform measurement with high time resolution becomes possible. Furthermore, the time resolution in the femtosecond region can be realized by converting the short pulse light source into supercontinuum light and using it as a sampling light pulse. Also, by setting the pulse repetition frequency after frequency division to less than the processing speed of the light receiving system band and the electric signal processing unit,
Individual cross-correlation signals can be detected without interference with adjacent pulses. Therefore, it is possible to measure the waveform of the signal light to be measured that is randomly modulated (eye pattern measurement). That is, according to the present invention, it is possible to perform eye pattern measurement with high time resolution.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a sampling light generator of an optical sampling light waveform measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation principle of the sampling light generation unit.

FIG. 3 is a diagram showing a configuration of a sampling light generator of an optical sampling light waveform measuring device according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining supercontinuum light generation.

FIG. 5 is a diagram showing a configuration of a sampling light generator of an optical sampling light waveform measuring apparatus according to a third embodiment of the present invention.

FIG. 6A is a diagram showing sum frequency light generation, and FIG. 6B is a diagram showing input / output light spectra in four-wave mixing.

FIG. 7A is a diagram showing a configuration of a conventional optical sampling light waveform measuring device, and FIG. 7B is a diagram showing a configuration of a sampling light generating unit used in the device.

FIG. 8 is a time chart showing the relationship among the measured light, the sampling light, and the cross-correlation signal light.

FIG. 9 is a diagram for explaining eye pattern measurement of light under measurement that is randomly modulated.

FIG. 10 is a diagram showing configurations of various pulse light sources,
(A) and (b) show a mode-locked laser, and (c) shows a gain switching semiconductor laser.

FIG. 11 is a diagram showing a configuration of a conventional sampling light generator.

FIG. 12 is a diagram for explaining the operation of the generation unit.

[Explanation of symbols]

1 ... Light source to be measured, 2 ... Sampling light generation unit, 3,
4 ... Polarization controller, 5 ... Coupler, 6 ... Non-linear optical material, 7 ... Optical filter, 8 ... Photodetector, 9 ... Signal processing unit, 10 ... Display unit, 11 ... Oscillator , 12 ... Frequency divider circuit, 13 ... Pulse light source, 14-1 to 14-3, 3
3 ... Optical amplifier, 15-1 to 15-3 ... Optical filter,
22 ... Electric pulse generator, 23 ... Optical gate switch, 24 ... Non-linear optical material for supercontinuum generation, 25 ... Dispersion compensator, 26 ... Optical bandpass filter for wavelength selection (wavelength selection band) Pass filter), 30 ... Electric amplifier, 31 ... DC voltage source, 32
...... Optical modulator, 34 ...... Optical delay device, 35 ...... Optical band pass filter, 37 ...... Optical mirror (mirror), 38 ...
... DC current source, 39 ... semiconductor laser, 40 ... dispersion medium for pulse compression.

Claims (4)

[Claims] 1. A sampling light generation section for generating a sampling light pulse train having a narrow pulse width of an optical frequency ν _sam based on a measured light having a repetition of an optical frequency ν _sig .
A polarization controller that controls the polarization of each of the measured light and the sampling light, a coupling unit that combines the measured light and the sampling light, and a delay signal generation unit that sweeps the delay of the sampling light with respect to the measured light, An optical frequency ν _sfg (where ν _sfg =
ν _sig + ν _sam ) Sum frequency light of both lights or optical frequency ν _fwm (where ν _fwm = 2ν _sam −ν _sig ) The first nonlinear optical material that generates the four-wave mixed light and the generated cross-correlation a photodetector for converting into an electric signal by detecting the signal light, the optical sampling waveform measuring apparatus having an electric processing system for displaying the processed electrical signals measured optical pulse waveform, repeat the f ₀ measured light Frequency, M and N are natural numbers, Δf
Is an offset frequency, an oscillator that oscillates at a frequency M (f ₀ −NΔf) is used as the delay signal generation unit, and the sampling light generation unit generates the repetition frequency M (f _0- NΔf) pulsed light source for generating an optical pulse train, a frequency divider for dividing the output of the oscillator into 1 / (NM), and a repetition frequency f ₀ / N based on the output of the frequency divider. - to △ electrical pulse generator for generating electrical pulses of f, characterized in that the electric pulse train consisting of optical gate switches for dividing the optical pulse train of repetition frequency f ₀ / N-△ f the optical pulse train Optical sampling waveform measuring device. 2. A second non-linear optical material for converting an incident light pulse into a supercontinuum light pulse having a wide band spectrum between the pulse light source and the multiplexer, and from the supercontinuum light pulse. The optical sampling waveform according to claim 1, further comprising: an optical bandpass filter for selecting an optical pulse having a desired center wavelength and a spectral bandwidth, and a chirping compensator for compensating for chirping of the optical pulse. measuring device. 3. At least one optical amplifier is arranged between the pulse light source and the multiplexer.
Alternatively, the optical sampling waveform measuring device described in 2. 4. An optical bandpass filter, which has the same center wavelength as the optical pulse amplified by the optical amplifier and has a wider bandwidth than the spectral bandwidth of the amplified optical pulse, is arranged in the subsequent stage of the optical amplifier. The optical sampling waveform measuring device according to claim 3, wherein