JP4991797B2 - Sampling waveform measuring device - Google Patents

Description

  The present invention relates to a sampling waveform measuring apparatus that performs high-resolution equivalent sampling.

  Optical sampling using the mutual absorption saturation characteristic of an electroabsorption optical modulator has been proposed (see, for example, Patent Document 1). FIG. 7 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus. The sampling waveform measuring apparatus shown in FIG. 7 includes an optical pulse generator 11 that generates an optical pulse Ps having a constant period, and an electroabsorption optical modulation that receives an optical signal Px and an optical pulse Ps and outputs an optical signal Py. , A reverse bias voltage generator 13 for inputting a reverse bias voltage to the electroabsorption optical modulator 12, and a photoreceiver 15 for photoelectrically converting the sampled optical signal Py emitted from the electroabsorption optical modulator 12. And having. By sampling the optical signal to be measured Px using the optical gate operation due to the mutual absorption saturation of the electroabsorption optical modulator 12 when the optical pulse Ps is input, and observing the electric signal Dy from the light receiver 15. The optical signal Px to be measured is measured / evaluated by the equivalent sampling method.

International Publication 2008/088709

As shown in FIG. 8, the extinction characteristic of the electro-absorption optical modulator 12 having the multiple quantum well structure is such that the light transmittance decreases as the reverse bias voltage increases, but the transmittance increases at a certain voltage or higher. To do. In the optical sampling using the mutual absorption saturation of the electroabsorption optical modulator 12, when the transmittance of the optical signal under measurement increases when there is no optical pulse, the leakage of the optical signal under measurement other than during sampling increases and noise increases. To do. In order to increase the S / N ratio of the waveform of the measurement result, it is necessary to reduce the transmittance of the optical signal to be measured when there is no optical pulse. For this reason, from the viewpoint of the S / N ratio, the reverse bias voltage V _{A at the} point A at which the transmittance is minimum is suitable.

On the other hand, as shown in FIG. 9, the relationship between the reverse bias voltage and the time width of the optical gate operation is such that the gate width decreases monotonously as the reverse bias voltage increases. For this reason, from the viewpoint of time resolution, the reverse bias voltage V _{B at} the point B at which the gate width is minimum, that is, the maximum reverse bias voltage V _B that can be applied to the electroabsorption optical modulator is desirable. Therefore, there is a problem that a high S / N ratio and a short gate width are not compatible.

  Therefore, an object of the present invention is to achieve both a high S / N ratio and a short gate width in optical sampling using an electroabsorption optical modulator having a multi-quantum well structure.

  In order to achieve the above object, the sampling waveform measuring apparatus of the present invention is a sampling waveform measuring apparatus that performs optical sampling using an electroabsorption optical modulator having a multi-quantum well structure, at least while the optical gate is open. Bias adjustment means for increasing the reverse bias voltage is provided.

  Specifically, the sampling waveform measuring apparatus of the present invention includes an optical pulse generator (11) that generates an optical pulse, an electroabsorption optical modulator (12) that receives an optical signal to be measured and the optical pulse, and A light receiver (15) that converts an optical signal output from the electroabsorption optical modulator into an electrical signal, and mutual absorption saturation of the electroabsorption optical modulator when the optical pulse is input In the sampling waveform measuring apparatus (101) for sampling the optical signal to be measured using the optical gate operation of the optical signal and measuring the waveform of the optical signal to be measured by an equivalent sampling method, the reverse bias of the electroabsorption optical modulator is measured. Bias adjustment means (16) for inputting a bias adjustment electric pulse for increasing the voltage to the electroabsorption optical modulator at least while the optical gate is open. That.

  By providing the bias adjusting means (16), while the optical gate is closed, the transmittance of the optical signal to be measured is lowered to prevent the S / N ratio from decreasing, and at least when the optical gate is open, the electric field is absorbed. The gate width can be reduced by increasing the reverse bias voltage of the optical modulator. Thus, the sampling waveform measuring apparatus of the present invention can achieve both a high S / N ratio and a short gate width in optical sampling using an electroabsorption optical modulator having a multi-quantum well structure.

  In the sampling waveform measuring apparatus of the present invention, the bias adjusting means has an electric pulse generator (21) for generating a bias adjusting electric pulse synchronized with the optical pulse, and at least while the optical gate is open. Preferably, the electric pulse for bias adjustment from the electric pulse generator is input to the electroabsorption optical modulator.

  By providing an independent electric pulse generator, an electric pulse for bias adjustment having an arbitrary shape can be generated with an arbitrary amplitude voltage. Thus, at least while the optical gate is open, the maximum reverse bias voltage that can be applied to the electroabsorption optical modulator can be applied to achieve both a high S / N ratio and the shortest gate width.

  In the sampling waveform measuring apparatus of the present invention, the bias adjusting means has a second light receiver (31) that receives the optical pulse and outputs an electrical pulse for bias adjustment, and at least while the optical gate is open. It is preferable that the bias adjusting electric pulse from the second light receiver is input to the electroabsorption optical modulator.

  By providing the second light receiver, it is possible to generate a bias adjusting electric pulse with little timing jitter at a timing synchronized with the optical pulse. As a result, even when the pulse width of the electrical pulse for bias adjustment is short, the maximum reverse bias voltage that can be applied to the electroabsorption optical modulator can be applied at least while the optical gate is open, and a high S / N ratio can be obtained. The shortest gate width can be achieved at the same time. Further, a bias adjusting electric pulse having a large amplitude can be generated by using a second light receiving device having a high conversion efficiency or by inserting an electric amplifier into the output of the second light receiving device.

  In the sampling waveform measuring apparatus according to the present invention, the bias adjusting means inverts the polarity of an electric pulse generated at the electrode of the electroabsorption optical modulator when the sampling optical pulse is input, and a predetermined delay time. It is preferable to input the bias adjusting electric pulse to the electroabsorption optical modulator at least while the optical gate is opened by returning to the electrode of the electroabsorption optical modulator later.

  Since the electric pulse generated at the electrode of the electroabsorption optical modulator is used, the S / N ratio and the gate width of the electroabsorption optical modulator are adjusted without providing a separate means for generating an electric pulse for bias adjustment. be able to. Thereby, the sampling waveform measuring apparatus according to the present invention can be configured with a simple configuration.

  In the sampling waveform measuring apparatus according to the present invention, the bias adjusting means is provided at one end of the coaxial cable (41) connected to the electrode of the electroabsorption optical modulator and the coaxial cable, and the electroabsorption optical modulation A DC blocking capacitor (42) for cutting off a DC bias voltage applied to the device, and a short circuit (43) connected to the other end of the coaxial cable, and generated at the electrode of the electroabsorption optical modulator. After propagating the electric pulse to the coaxial cable, it is preferable that the polarity of the electric pulse is reversed and reflected by the short circuit, and returned to the electrode of the electroabsorption optical modulator as the electric pulse for bias adjustment.

  Since the bias adjusting means includes a coaxial cable, a short circuit, and a DC cutoff capacitor, the sampling waveform measuring apparatus according to the present invention can be configured with a simple configuration.

  The above inventions can be combined as much as possible.

  According to the present invention, the sampling waveform measuring apparatus of the present invention can achieve both a high S / N ratio and a short gate width in optical sampling using an electroabsorption optical modulator having a multi-quantum well structure.

1 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus according to Embodiment 1. FIG. It is an example of the relationship between the electric pulse for bias adjustment and the pulse shape of an optical signal, (a) shows the electric pulse Vpm for negative bias adjustment, (b) is transmission of the electroabsorption optical modulator by the optical pulse Ps. Shows rate change. FIG. 6 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus according to a second embodiment. FIG. 10 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus according to a third embodiment. FIG. 6 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus according to a fourth embodiment. It is an example of setting the round-trip delay time of a coaxial cable, (a) shows an electric pulse Vpp generated in the electroabsorption optical modulator, and (b) shows an electric pulse Vpm for bias adjustment returned to the electroabsorption optical modulator. (C) shows the change in transmittance of the electroabsorption optical modulator due to the light pulse Ps. It is a composition schematic diagram showing an example of a sampling waveform measuring device. An example of the extinction characteristic of an electroabsorption optical modulator having a multiple quantum well structure is shown. An example of the relationship between a reverse bias voltage and the time width of optical gate operation is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram illustrating an example of a sampling waveform measuring apparatus according to the present embodiment. The sampling waveform measuring apparatus 101 according to the present embodiment includes an optical pulse generator 11, an electroabsorption optical modulator 12, a reverse bias voltage generator 13, an optical coupler 14, a light receiver 15, and a bias adjusting unit 16. Is provided.

  The measured optical signal Px is incident on the electroabsorption optical modulator 12. The optical pulse generator 11 generates an optical pulse Ps. The reverse bias voltage generator 13 applies a DC reverse bias voltage to the electroabsorption optical modulator 12. The electroabsorption optical modulator 12 receives the measured optical signal Px and the optical pulse Ps, and outputs an optical signal Py. The optical signal to be measured Px is sampled by using the optical gate operation by the mutual absorption saturation of the electroabsorption optical modulator 12 when the optical pulse Ps is input, and the waveform of the optical signal to be measured Px is measured by the equivalent sampling method. To do.

  The sampled optical signal Py is emitted from the electroabsorption optical modulator 12 and enters the light receiver 15. The light receiver 15 converts the optical signal Py output from the electroabsorption optical modulator 12 into an electrical signal and outputs an electrical signal Dy. By observing the electric signal Dy, the waveform of the measured optical signal Px can be evaluated by the equivalent sampling method.

  The bias adjusting means 16 generates a bias adjusting electric pulse Vpm that increases the reverse bias voltage of the electroabsorption optical modulator 12, and the bias adjusting electric pulse Vpm is generated at least while the optical gate is open. Input to the modulator 12. FIG. 2 shows an example of the relationship between the electrical pulse for bias adjustment and the pulse shape of the optical signal, where (a) shows the negative bias adjustment electrical pulse Vpm, and (b) shows the electroabsorption light by the optical pulse Ps. The change in transmittance of the modulator is shown.

The reverse bias voltage generator 13 shown in FIG. 1 is set to the reverse bias voltage V _A at the point A in FIG. 8 where the S / N ratio is maximized. A negative bias adjusting electric pulse Vpm synchronized with the optical pulse Ps is generated by the bias adjusting means 16 and input to the electroabsorption optical modulator 12. The pulse width of the electrical pulse Vpm for bias adjustment is made wider than the pulse width of the transmittance change by the optical pulse Ps, and the optical gate operation time by the optical pulse Ps is within the electrical pulse Vpm for bias adjustment as shown in FIG. In this case, the reverse bias voltage increases during the optical gate operation by the optical pulse Ps, and the gate width is shortened.

When the sum of the voltage of the DC reverse bias voltage V _A and the negative bias adjusting electric pulse Vpm becomes the maximum reverse bias voltage V _B that can be applied to the electroabsorption optical modulator 12, B shown in FIG. This is the minimum gate width at a point. When a negative bias adjusting electric pulse Vpm is input, the transmittance of the electroabsorption optical modulator 12 temporarily increases. The pulse width of the bias adjusting electric pulse Vpm is greater than the time width of the impulse response of the light receiver 15. However, the influence of the increase in leakage of the optical signal to be measured Px due to the bias adjusting electric pulse Vpm is small in the output of the light receiver 15. Therefore, the S / N ratio is not significantly lowered by the bias adjusting electric pulse Vpm, and both a high S / N ratio and a short gate width can be achieved.

(Embodiment 2)
FIG. 3 is a schematic configuration diagram illustrating an example of the sampling waveform measuring apparatus according to the present embodiment. In the sampling waveform measuring apparatus 102 according to the present embodiment, the bias adjusting unit 16 includes an electric pulse generator 21 that generates a bias adjusting electric pulse Vpm synchronized with the optical pulse Ps, and at least the electroabsorption optical modulator 12. While the optical gate is open, the bias adjusting electric pulse Vpm from the electric pulse generator 21 is input to the electrode of the electroabsorption optical modulator 12.

  Here, the synchronization of the bias adjusting electric pulse Vpm and the optical pulse Ps is performed when the synchronizing signal is input from the optical pulse generator 11 to the electric pulse generator 21 and when the synchronizing signal is generated from the electric pulse generator 21. Either the case of inputting to the generator 11 or the case of inputting a synchronizing signal from a separately provided synchronizing signal generator (not shown) to both the optical pulse generator 11 and the electric pulse generator 21 may be used.

  Further, if necessary, the variable delay device 22 is inserted into the output of the electric pulse generator 21, the output of the optical pulse generator 11, or the output of a synchronization signal generator (not shown) to The relative timing of the electrical pulse Vpm for bias adjustment can be adjusted.

  The reverse bias voltage generator 13 includes a DC power supply 13a, a bias T13b, and a terminator 13c. The reverse bias voltage generator 13 applies a DC bias voltage to the electroabsorption optical modulator 12, and the bias adjusting electric pulse Vpm from the bias adjusting means 16. The impedance matching is performed so that the electric pulse generated at the electrode of the electroabsorption optical modulator 12 is not reflected by the light pulse Ps.

(Embodiment 3)
FIG. 4 is a schematic configuration diagram illustrating an example of the sampling waveform measuring apparatus according to the present embodiment. In the sampling waveform measuring apparatus 103 according to the present embodiment, the bias adjusting unit 16 includes the second light receiver 31 that receives the optical pulse Ps and outputs the bias adjusting electric pulse Vpm, and at least the electroabsorption optical modulator. While the 12 optical gates are open, the bias adjusting electric pulse Vpm from the second light receiver 31 is input to the electroabsorption optical modulator 12.

  Here, if necessary, the relative delay of the electrical pulse Vpm for bias adjustment with respect to the optical gate can be adjusted by inserting the variable delay device 32 into the input or output of the second light receiver 31. Further, the voltage amplitude of the bias adjusting electric pulse Vpm can be increased by inserting an electric amplifier into the output of the second light receiver 31 as necessary.

(Embodiment 4)
FIG. 5 is a schematic configuration diagram illustrating an example of the sampling waveform measuring apparatus according to the present embodiment. In the sampling waveform measuring apparatus 104 according to the present embodiment, the bias adjusting unit 16 inverts the polarity of the electric pulse Vpp generated at the electrode (not shown) of the electroabsorption optical modulator 12 when the optical pulse Ps is input. The inverted electric pulse is returned as the bias adjusting electric pulse Vpm to the electrode of the electroabsorption optical modulator 12 after a predetermined delay time, so that at least the optical gate of the electroabsorption optical modulator 12 is open. The bias adjusting electric pulse Vpm in which the polarity of the electric pulse Vpp is inverted is input to the electroabsorption optical modulator 12.

  Specifically, in the sampling waveform measuring apparatus 104, the bias adjusting unit 16 is provided on the coaxial cable 41 having one end connected to the electrode of the electroabsorption optical modulator 12 and the coaxial cable 41, and the electroabsorption optical modulation is performed. An electric pulse Vpp generated at the electrode of the electroabsorption optical modulator 12, comprising a DC blocking capacitor 42 for cutting off the DC bias voltage applied to the converter 12, and a short circuit 43 connected to the other end of the coaxial cable 41. Is propagated to the coaxial cable 41, and then the electric pulse Vpp is inverted and reflected by the short circuit 43, and the electric pulse obtained by inverting the polarity of the electric pulse Vpp is used as the bias adjusting electric pulse Vpm. Return to electrode of vessel 12.

  When the optical pulse Ps is input to the electroabsorption optical modulator 12, a positive electric pulse Vpp is generated at the electric input terminal of the electroabsorption optical modulator 12. The positive electric pulse Vpp propagates through the coaxial cable 41, the polarity is reversed by the short circuit 43, and the negative electric pulse propagates backward through the coaxial cable 41 and returns to the electroabsorption optical modulator 12.

  The DC blocking capacitor 42 is for applying a DC bias to the electroabsorption optical modulator 12, and is arranged near the short-circuiting device 43 in FIG. 5, but is arranged near the electroabsorption optical modulator 12. May be. The time from the generation of the electric pulse Vpp to the return of the bias adjusting electric pulse Vpm to the electroabsorption optical modulator 12 is a round trip delay time of the coaxial cable 41 and the DC blocking capacitor 42.

  FIG. 6 shows an example of setting the round trip delay time of the coaxial cable. If the delay time of the coaxial cable 41 is set so that the optical gate operation time by the optical pulse Ps is included in the bias adjusting electric pulse Vpm, an effect of narrowing the gate width is obtained. FIG. 6 shows an example in which the electric pulse Vpp generated by the optical pulse Ps is returned to the electroabsorption optical modulator 12 while the optical gate is opened by the next optical pulse Ps. However, the present invention is limited to this. is not. For example, an electric pulse generated by the electroabsorption optical modulator 12 by a certain optical pulse is delayed so as to match the optical gate operation by the optical pulse after n periods (n is an integer of 1 or more), and the electroabsorption optical modulation is performed. It may be returned to the vessel 12.

  In the above description of the first to fourth embodiments, the case where the signal side which is the polarity of the normal electroabsorption optical modulator 12 is p-type and the ground side is n-type has been described. However, the present invention is not limited to this. The present invention can also be applied to an electroabsorption optical modulator having a reverse polarity. In this case, when the electric pulse generator 21 or the second light receiver 31 is separately used as in the second embodiment or the third embodiment, the electric pulse generator 21 or the second light receiver 31 may be used as the bias adjusting electric pulse. It is necessary to generate a positive electric pulse. In the electroabsorption optical modulator 12 according to the fourth embodiment, a negative electric pulse is generated, the polarity is inverted by the short circuit 43, and the positive electric pulse returns to the electroabsorption optical modulator 12 as a bias adjusting electric pulse.

  In the present embodiment, the configuration in which the optical pulse is input from the back of the electroabsorption optical modulator 12 is shown. However, the present invention is not limited to this, and the present invention can be applied to a configuration in which the optical pulse is input from the front. .

  Since the present invention can perform high-resolution optical sampling, it can be applied to the information communication industry and various industries using light.

11: Optical pulse generator 12: Electroabsorption optical modulator 13: Reverse bias voltage generator 13a: DC power supply 13b: Bias T
13c: Terminator 14: Optical coupler 15: Light receiver 16: Bias adjusting means 41: Coaxial cable 42: DC blocking capacitor 43: Short circuit 21: Electric pulse generator 22: Variable delay device 31: Second light receiver 32: Variable delay devices 101, 102, 103, 104: sampling waveform measuring apparatus

Claims (5)

An optical pulse generator (11) for generating optical pulses;
An electroabsorption optical modulator (12) to which an optical signal to be measured and the optical pulse are input;
A light receiver (15) for converting an optical signal output from the electroabsorption optical modulator into an electric signal,
The optical signal to be measured is sampled using the optical gate operation due to the mutual absorption saturation of the electroabsorption optical modulator when the optical pulse is input, and the waveform of the optical signal to be measured is measured by an equivalent sampling method. In the sampling waveform measuring apparatus (101) to
Bias adjusting means (16) for inputting a bias adjusting electric pulse for increasing a reverse bias voltage of the electroabsorption optical modulator to the electroabsorption optical modulator at least while the optical gate is open. A sampling waveform measuring apparatus characterized by the above. The bias adjusting means includes
An electric pulse generator (21) for generating an electric pulse for bias adjustment synchronized with the optical pulse,
2. The sampling waveform measuring apparatus according to claim 1, wherein the bias adjusting electric pulse from the electric pulse generator is input to the electroabsorption optical modulator at least while the optical gate is open. The bias adjusting means includes
A second light receiver (31) that receives the light pulse and outputs an electric pulse for bias adjustment;
2. The sampling waveform measuring apparatus according to claim 1, wherein the bias adjusting electric pulse from the second light receiver is input to the electroabsorption optical modulator at least while the optical gate is open. . The bias adjusting means includes
By inverting the polarity of the electric pulse generated at the electrode of the electroabsorption optical modulator when the sampling optical pulse is input, and returning it to the electrode of the electroabsorption optical modulator after a predetermined delay time, 2. The sampling waveform measuring apparatus according to claim 1, wherein the bias adjusting electric pulse is input to the electroabsorption optical modulator at least while the optical gate is open. The bias adjusting means includes
A coaxial cable (41) having one end connected to the electrode of the electroabsorption optical modulator;
A DC blocking capacitor (42) provided in the coaxial cable and blocking a DC bias voltage applied to the electroabsorption optical modulator;
A short circuit (43) connected to the other end of the coaxial cable;
After propagating the electric pulse generated at the electrode of the electroabsorption optical modulator to the coaxial cable, the electric pulse is inverted and reflected by the short circuit, and the electric field absorption is performed as the electric pulse for bias adjustment. The sampling waveform measuring apparatus according to claim 4, wherein the sampling waveform measuring apparatus is returned to the electrode of the optical modulator.

Images