JP3286151B2 - Optical sampling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sampling device, and more particularly, to a method of sampling an optical signal under measurement with an optical pulse.
The present invention relates to an optical sampling device used for ultra-high-speed optical pulse observation with improved time resolution.

[0002]

2. Description of the Related Art In a conventional optical sampling apparatus, a sampling pulse is generated at a repetition frequency of a sum or a difference between an electric synchronizing signal pulse and a sweep signal with a constant sampling pulse width.

FIG. 9 is a block diagram showing a configuration example of a conventional optical sampling device. In this figure, 111 is an optical pulse generator, 112 is a multiplexer, 113 is a sampler head, 114 is a photodetector, 115 is a processing unit, 116 is a display, 117 is an adder, and 118 is a sweep signal. 19A is an input terminal to which the optical signal under measurement P is applied, 1
9B is an input terminal to which the electric synchronization signal pulse Q is applied.

FIG. 10 shows the operation of the optical sampling device shown in FIG.
This will be described with reference to FIG.

[0005] As the electric synchronization signal pulse Q applied to the input terminal 119B, when the sweep signal 118 is applied to the adder 117, an optical pulse Q 'whose repetition period T0 becomes longer is obtained. Since the optical pulse Q ′ and the optical signal under measurement P enter the multiplexer 112, the sampler head 113
Provides an output signal like R in FIG. The photodetector 114 detects the peak value, sends the peak value to the processing unit 115, and performs processing to cause the measured optical signal P to appear on the display 116.

According to this method, the minimum time resolution of sampling is the optical pulse Q generated by the optical pulse generator 111.
'Depends on the pulse width. The pulse width of an optical pulse that can be generated at present is about 1 to 2 ps.

[0007]

SUMMARY OF THE INVENTION An optical pulse generator 111
Although the light pulse width of the light pulse generated is 1 to 2 ps, it is actually necessary to use a larger-scale configuration than the example shown in FIG. This will be described with reference to FIG.

FIG. 11 is a block diagram showing another example of a conventional optical pulse generator for generating short optical pulses. In this figure, 121 is a ring laser oscillator (hereinafter simply referred to as a ring laser), 122 is an optical amplifier, 123 is a nonlinear optical element, and 124 is a dispersive medium.

Next, the operation will be described. The ring laser 121 oscillates in response to the input of a pulse-like electric signal having a predetermined repetition frequency, and outputs an optical pulse having a pulse width of about 5 ps. This is amplified by the optical amplifier 122 to a level at which the third-order nonlinear optical effect occurs in the nonlinear optical element 123, and is input to the next-stage nonlinear optical element 123.
In the nonlinear optical element 123, the spectrum width of the light pulse is expanded by self-phase modulation. The optical pulse whose spectral width has widened has a state in which the dispersion changes linearly with respect to the wavelength, and the pulse width can be reduced by compensating for the dispersion. In the dispersive medium 124, an optical pulse having a widened spectrum width is narrowed along the time axis by dispersion compensation, and is output as an optical pulse having a pulse width of 1 to 2 ps.

Further, it is difficult to generate an optical pulse having a width of 1 ps or less even with this configuration, and a larger device configuration has to be used, such as by using a collision pulse mode locking method.

As described above, there is a limit even if the pulse width of the light pulse generated by the light pulse generator is reduced. However, it is not so difficult to generate an optical pulse having a pulse width of about 5 ps with a ring laser oscillator.
The oscillation threshold is determined by the configuration of the ring laser. Normalization with the peak value as 1 results in about 0.9. The pulse width of the ring laser is determined by the width a in FIG. Therefore, to obtain a narrow pulse width, a high frequency having a high repetition frequency may be input to the optical modulator.

However, the frequency band of the optical modulator is currently limited to about 70 GHz. When a sine wave of 70 GHz is input, the pulse width is obtained by equation (1).

[0013]

(Equation 1) Therefore, the pulse output has a half value width of 2.5 ps according to the equation (1). In the current ring laser, this is the limit of the output pulse width.

As described above, in the conventional ring laser, the pulse width of the optical output depends on the frequency of the drive signal. To obtain an output with a short pulse width, the frequency of the drive signal must be increased. The pulse repetition frequency determined by the frequency of the signal was changing.

It is an object of the present invention to change the pulse width of a sampling pulse, sample an optical signal, and extract the difference between the output of a photodetector according to the sampling width, thereby achieving optical sampling with a shorter time resolution than before. To provide an optical sampling device for performing the following.

[0016]

An optical sampling apparatus according to the present invention receives an electric synchronizing signal pulse synchronized with a period of an optical signal to be measured and a sweep signal, and generates an optical pulse having a pulse width corresponding to the sweep signal. A variable pulse width optical pulse generator (1), an output of the variable pulse width optical pulse generator, and a multiplexer (2) that receives and combines the measured optical signal;
A sampler head (3) for receiving, as an optical pulse, an output of the pulse width variable optical pulse generator and an output of the multiplexer as an optical pulse, and receiving an output of the sampler head; A photodetector (4) for outputting an electric signal according to the average value of the pulse output power, and a difference processing unit (4) for taking a difference between a previous value and a current value of the output of the photodetector according to a sweep signal and outputting the result. 5) a display (6) that receives the output of the difference processing unit and the sweep signal and displays the optical signal to be measured, and a sweep signal generation unit that receives the input of the electric synchronization signal pulse and generates the sweep signal (7).

Further, a frequency divider (9) for dividing the frequency of the electric synchronization signal pulse is provided in the preceding stage of the pulse width variable optical pulse generator.

[0018]

According to the present invention, the width of the generated light pulse is changed, and the output of the photodetector is input to a difference processing section for obtaining a difference according to the sweep signal, so that only the portion where the width of the sampling pulse is changed is obtained. Get output. Then, the optical pulse generator and the difference processing unit are operated in synchronization with the sweep signal to change the sampling pulse width at 1 ps or less and perform optical sampling.

Further, since the frequency of the electric synchronization signal pulse is divided by the frequency divider, the variable range of the pulse width can be widened.

In the conventional optical sampling apparatus, the sampling pulse width has the minimum time resolution, but in the present invention, the sampling pulse width is changed, and the change becomes the minimum time resolution. Even if the width of the sampling pulse is about 5 ps, the amount of change takes a smaller value, and control can be performed at 1 ps or less.

[0021]

FIG. 1 is a block diagram showing an embodiment of the present invention. In this figure, reference numeral 1 denotes a variable pulse width optical pulse generator, the details of which will be described later. 2 is a multiplexer, 3 is a sampler head, and uses a nonlinear optical crystal or the like having a function of sum frequency generation (SFG). A photodetector 4 uses a photodiode or the like. Reference numeral 5 denotes a difference processing unit, the details of which will be described later.
Reference numeral 6 denotes a display unit. Reference numeral 7 denotes a sweep signal generation unit which generates a signal corresponding to the pulse width of the optical pulse generator (that is, the display unit 6 corresponds to the time axis) in synchronization with the input of the electric synchronization signal pulse. 8A and 8B indicate input terminals.

Next, details of the variable pulse width optical pulse generator 1 will be described. FIG. 2 is a block diagram showing the details of the configuration of the pulse width variable optical pulse generator 1.

In FIG. 2, reference numeral 11 denotes a pulse generator for generating two synchronized electric pulse signals, 12 denotes a fixed delay device which symbolically generates a fixed delay in the electric signal by a cable or the like, and 13 denotes an electric signal. Is a first optical modulator that constitutes a ring laser. The electric pulse signal B from the variable delay unit 13 is converted into a high-frequency component. The light input is light-intensity-modulated together with the bias (not shown) and output. Reference numeral 15 denotes a second optical modulator which constitutes a ring laser. The electric pulse signal A from the fixed delay unit 12 is used as a high frequency component, and a DC bias component (not shown) is combined with the optical input signal to modulate the light input. And output. Reference numeral 16 denotes an optical amplifier constituting a ring laser, and an erbium-doped fiber amplifier or the like is used. Reference numeral 17 denotes an optical band-pass filter constituting the ring laser, and sets an oscillation wavelength of the ring laser as a transmission intermediate wavelength. Reference numeral 18 denotes an optical coupler constituting a ring laser, which branches an optical output signal from the ring laser. Reference numeral 19 denotes a variable optical delay unit for adjusting the ring length so that the ring laser operates stably. Each of the parts 14 to 19 is connected in a ring shape to form a ring laser.

Next, the operation of the variable pulse width optical pulse generator 1 of FIG. 2 will be described with reference to FIGS.

FIG. 3 is a diagram showing the principle of operation. As shown in FIG. 3A, when a driving electric pulse signal A having a pulse width tw is input to the second optical modulator 15, an optical output corresponding to the driving electric pulse signal A is output. Exits from the second optical modulator 15. As shown in FIG. 3B, when an electric pulse signal B whose phase is delayed by Δt from the electric pulse signal A is input to the first optical modulator 14, the first optical modulator 1
4, the optical output has a phase that is delayed from the optical output from the second optical modulator 15 by Δt. Therefore, as shown in FIG.
Considering an optical modulator (equivalent block) obtained by combining (b), it is equivalent to inputting an electric pulse signal for driving having a width tw−Δt in which the driving signals A and B overlap each other. An optical signal is obtained. The pulse width decreases as Δt increases.

FIG. 4 is a block diagram showing a main part of the configuration of the variable pulse width optical pulse generator 1 shown in FIG. 2 using the above principle. In this figure, the delay time T obtained by the fixed delay unit 12 is generated by a cable or the like, but is shown as the fixed delay unit 12 for convenience of explanation. Therefore, the delay time T naturally occurs on the variable delay unit 13 side.
In short, the variable delay unit 13 is used to provide a phase difference between the driving electric pulse signals A and B input to the first and second optical modulators 14 and 15. In the first optical modulator 14, the optical input is modulated in the first optical modulator 14 by an electric pulse signal B (Δt is variable) given a delay time of T + Δt by the variable delay unit 13, and the pulse width tw is obtained. Then, the optical input is modulated into an optical pulse delayed by t = T + Δt with respect to the reference time t = 0. The optical signal modulated by the first optical modulator 14 is again modulated by the second optical modulator 15 at the next stage, and has a pulse width tw-Δ as described in the principle diagram of FIG.
An optical signal of t is obtained. The optical signal thus obtained is output from the output terminal C of the optical coupler 18. The optical signal obtained from the output terminal D in FIG. 2 is used again as an optical input in the ring laser.

The minimum value of the actual pulse width is determined by the modulation bands of the first and second optical modulators 14 and 15 and the electric pulse signals B and A.
Of determined by the rise time _{t r} and fall time _{t f.} Therefore, a pulse shorter than that when a doubler or the like is used is not always generated, but the pulse width can be swept. Therefore, the present invention uses the pulse width changing portion.

As described above, when the electric pulse signal having the pulse width tw is shifted by Δt and applied to the first optical modulator 14, the optical output passing through the two optical modulators 14 and 15 becomes tw−Δ
By changing Δt, light modulation of an arbitrary pulse width between 0 and tw can be performed. As a result, the optical pulse output also changes according to equation (1).

Next, the difference processing section 5 in the embodiment of FIG. 1 will be described with reference to FIG. In FIG. 5, reference numeral 51 denotes a control unit, 52 denotes a holding circuit, 53 denotes a previous value holding circuit, and 54 denotes a difference unit.

The operation will be described. When a sweep signal is applied to the controller 51, the output of the photodetector 4 shown in FIG.
Transfer to 3. Then, the holding circuit 52 and the previous value holding circuit 53
The difference is extracted from the value held in each of them by the difference unit 54 to obtain an output.

Next, the overall operation of the embodiment of FIG. 1 will be described with reference to FIG.
This will be described with reference to FIG. FIG. 6 shows waveforms of main parts for explaining the operation of the embodiment of FIG.

When the pulse width of the sampling light pulse generated by the pulse width variable light pulse generator 1 is sequentially increased by the sweep signal, the output R of the sampler head 3 becomes equal to the light signal P to be measured and the light sampling as shown in FIG. The overlapped portion of the pulse Q 'is extracted. This is obtained by accumulating the difference from the previous value for each sampling. This is detected by the photodetector 4 as an average value and input to the difference processing unit 5.
The difference processing unit 5 performs the processing described with reference to FIG. 5, calculates the difference between the average values, inputs the difference to the display unit 6, and displays the waveform of the optical signal P to be measured.

FIG. 7 shows another embodiment of the present invention. Reference numeral 9 denotes a frequency divider provided before the pulse width variable optical pulse generator 1 for dividing the frequency of the electric synchronization signal. FIG.
FIG. 3 is a waveform diagram for explaining the operation of the embodiment. Thus, by placing the divider 9, the variable range of the pulse width of the optical sampling pulse Q'for 1 cycle observing the optical signal to be measured P is _{T 0 + (N-1)} t~T 0 + Nt (N: frequency dividing ratio of frequency divider, t: optical signal repetition period, T ₀ : initial pulse width of optical pulse generator). To increase the sampling time resolution, it is necessary to finely sweep the width of the optical sampling over the optical signal repetition period t. If the initial pulse width T ₀ is smaller than the optical signal repetition period t, it is difficult to operate stably within the entire sweep range, and the pulse width can be swept stably with respect to the initial pulse width T ₀ . The range is limited. Even in the case where the variable range of the pulse width cannot be made large as described above, the operation can be stably performed within this range by inserting the frequency divider 9.

[0034]

As described in detail above, the present invention provides
An electric synchronizing signal pulse synchronized with the period of the optical signal to be measured;
A pulse width variable optical pulse generator (1) for receiving a sweep signal and generating an optical pulse having a pulse width corresponding to the sweep signal;
A multiplexer (2) for receiving and combining the output of the variable pulse width optical pulse generator and the optical signal to be measured, and receiving the output of the multiplexer for receiving the output of the variable pulse width optical pulse generator. And a sampler head (3) that outputs an overlapping portion of the output of the multiplexer as an optical pulse, and a photodetector (4) that receives the output of the sampler head and outputs an electric signal according to the average value of the pulse output power. ), A difference processing unit (5) for taking the difference between the previous value and the current value of the output of the photodetector according to the sweep signal and outputting the difference, and receiving the output of the difference processing unit and the sweep signal, and Since a display unit (6) for displaying an optical signal and a sweep signal generating unit (7) for receiving the input of the electric synchronization signal pulse and generating the sweep signal are used, sampling with a narrower optical pulse is performed in the conventional method. High time equivalent to It is possible to perform sampling in capacity.

Further, since the frequency divider (9) for dividing the frequency of the electric synchronization signal pulse is provided at the preceding stage of the pulse width variable optical pulse generator, stable operation can be performed even when the variable range of the pulse width cannot be made large. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a configuration of a pulse width variable optical pulse generator in the embodiment of FIG.

FIG. 3 is a diagram for explaining the operation principle of the pulse width variable optical pulse generator of FIG. 2;

FIG. 4 is a block diagram showing a main part of the variable pulse width optical pulse generator of FIG. 2;

FIG. 5 is a block diagram illustrating an example of a configuration of a difference processing unit in the embodiment of FIG. 1;

FIG. 6 is a waveform chart of a main part for explaining the operation of the embodiment of FIG. 1;

FIG. 7 is a block diagram showing a configuration of another embodiment of the present invention.

8 is a waveform chart of a main part for explaining the operation of the embodiment of FIG. 7;

FIG. 9 is a block diagram illustrating a configuration example of a conventional optical sampling device.

FIG. 10 is a waveform diagram of a main part for explaining the operation concept of the conventional optical sampling device of FIG. 9;

FIG. 11 is a block diagram illustrating a configuration example of a conventional optical pulse generator.

FIG. 12 is a waveform chart for explaining the operation of the conventional device of FIG. 11;

[Explanation of symbols]

 Reference Signs List 1 variable pulse width optical pulse generator 2 multiplexer 3 sampler head 4 photodetector 5 difference processing unit 6 display unit 7 sweep signal generation unit 8A input terminal 8B input terminal 9 frequency divider

Claims (2)

(57) [Claims] A pulse width variable optical pulse generator for receiving an electric synchronizing signal pulse synchronized with a cycle of an optical signal to be measured and a sweep signal and generating an optical pulse having a pulse width corresponding to the sweep signal; A multiplexer (2) for receiving and combining the output of the variable pulse width optical pulse generator and the optical signal to be measured; and receiving the output of the multiplexer for receiving the output of the variable pulse width optical pulse generator. A sampler head (3) for outputting, as an optical pulse, a portion where an output and an output of the multiplexer are overlapped; and a photodetector for receiving an output of the sampler head and outputting an electric signal according to an average value of pulse output power ( 4), a difference processing unit (5) for taking the difference between the previous value and the current value of the output of the photodetector according to the sweep signal and outputting the difference, and receiving the output of the difference processing unit and the sweep signal, A display unit (6) for displaying a measurement light signal; A sweep signal generation unit (7) for receiving the input of the electric synchronization signal pulse and generating the sweep signal. 2. The optical sampling apparatus according to claim 1, wherein a frequency divider for dividing the frequency of the electric synchronization signal pulse is provided at a stage preceding the pulse width variable optical pulse generator.