JP2008275547A - Optical sampling device and optical signal quality monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sample optical signals with high sampling efficiency with simple low-cost constitution and to stably obtain waveform information of high-speed optical signals. <P>SOLUTION: A carbon nanotube 23 is used as a sampling element of an optical sampling device 22, and the optical signal Px to be monitored is made incident to one optical terminal 23a. Sampling optical pulse Ps emitted from an optical pulse generator 21 for sampling pulse is made incident to the other optical terminal 23b of the carbon nanotube element 23 through an optical coupler 25, and an absorption factor to the optical signal Px is lowered by supersaturated absorption characteristics generated at the incidence of the sampling optical pulse Ps to carry out emission from the other optical terminal 23b for sampling. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for constructing an apparatus for sampling an optical signal at a low cost and accurately monitoring the quality of an optical signal modulated with a high-speed data signal.

  For example, when configuring a network using optical signals modulated with data signals, it is necessary to monitor the quality of the optical signals propagating on the network.

  In general, a signal monitor acquires waveform information of a signal on a transmission line, calculates a value indicating signal quality from the waveform information, and outputs the calculation result. However, the signal monitor is extremely high as several tens of Gb / s. It is extremely difficult to directly receive an optical signal modulated with a bit rate data signal by a photoreceiver and obtain waveform information thereof.

  In order to obtain such high-speed signal waveform information, an equivalent time sampling method has been conventionally used.

  That is, the optical signal P having the same waveform repeated in the cycle Ta as shown in FIG. 17A is slightly smaller than N times the cycle Ta (N is an integer) as shown in FIG. Sampling is performed with a sampling pulse S having a period Ts = N · Ta + ΔT that is longer by a certain time ΔT, and an instantaneous amplitude value (instantaneous intensity) at a position that differs by ΔT in the repetitive waveform of the optical signal P as shown in FIG. To get. The waveform P ′ drawn by the envelope connecting the acquired values is obtained by enlarging the waveform of the optical signal P by Ts / ΔT times on the time axis, and retains the characteristics of the waveform of the original optical signal P. .

  Therefore, for the waveform information obtained by this sampling, for example, a probability distribution of an amplitude representing one of the binary levels and an amplitude representing the other is obtained, and a standard deviation thereof is calculated, thereby calculating a Q value representing the signal quality. Can be obtained.

  A technique for performing equivalent time sampling on an optical signal as described above and calculating a Q value representing signal quality from the obtained waveform information is disclosed in Patent Document 1 below.

Japanese Patent No. 3796357

  In Patent Document 1, a bulk nonlinear optical material is used as an element for sampling an optical signal. However, this bulk nonlinear optical material generally has poor sampling efficiency (sampling efficiency using a wavelength conversion phenomenon is low). Since the wavelength conversion efficiency is −20 dB or less), waveform information of a strong optical signal can be obtained at a high S / N, but sufficient S / N cannot be obtained for waveform information of a weak optical signal.

  In view of this, it is conceivable to use an electroabsorption optical modulator that has significantly less transmission loss than a bulk nonlinear optical material, in other words, high sampling efficiency.

  This electroabsorption optical modulator has a characteristic that the absorptance with respect to light passing through the optical path changes according to the magnitude of the electric field applied to the optical path connecting the two optical terminals. An optical signal is incident, an electrical pulse signal for sampling is given to the power supply terminal, and only when the electrical pulse signal for sampling is input, the absorption rate for the optical signal is reduced and emitted from the other optical terminal. Sampling for optical signals.

  A technique for sampling an optical signal by giving a sampling electrical pulse signal to the power supply terminal of the electroabsorption optical modulator in this way is disclosed in, for example, the following Patent Document 2.

JP 2004-222252 A

  However, the electro-absorption optical modulator is expensive and requires a DC power source, which complicates the apparatus. Also, since it is difficult to match the impedance of a high frequency with an electrical sampling pulse signal, it is extremely difficult to stably narrow the pulse width, and the waveform information of the optical signal modulated at several tens of Gb / s as described above. There is a problem that it is not possible to obtain the image with sufficient resolution and accuracy.

  As another problem of the optical signal quality monitor using the above equivalent time sampling method, an eye pattern is generated by superimposing the acquired waveforms by a predetermined number of bits, and quality calculation processing is performed on the eye pattern. In this case, if the sampling period Ts is not exactly equal to N · Tc + ΔT, the time axis of the waveform to be superimposed is gradually shifted, resulting in a problem that the quality calculation cannot be performed accurately.

  The present invention solves the above-described problems, provides an optical sampling device having a high sampling efficiency at a low cost with a simple configuration, and high-speed optical signal waveform information acquisition, and light capable of stably obtaining an optical signal eye pattern. It aims to provide a signal quality monitor.

In order to achieve the above object, an optical sampling device according to claim 1 of the present invention comprises:
In an optical sampling device (22) that receives an optical signal to be sampled and a sampling optical pulse having a predetermined period, samples the optical signal with the sampling optical pulse, and emits an optical pulse signal obtained by the sampling.
A carbon nanotube element (23) having a characteristic that an absorptance with respect to the incident light changes according to the power of the incident light, and receiving the optical signal and the sampling optical pulse,
The optical signal is emitted with a small absorption rate only when the sampling light pulse is incident on the carbon nanotube element.

The optical sampling device according to claim 2 of the present invention is the optical sampling device according to claim 1,
The optical signal is incident on one optical terminal of the carbon nanotube element,
The sampling optical pulse is incident on the other optical terminal of the carbon nanotube element, and an optical pulse signal emitted from the other optical terminal of the carbon nanotube element is emitted to an optical path different from the incident optical path of the sampling optical pulse. An optical coupler (25) is provided.

The optical sampling device according to claim 3 of the present invention is the optical sampling device according to claim 1,
The wavelength of the sampling optical pulse is set to a wavelength different from the optical signal,
An optical coupler (25 ′) for combining the optical signal and the sampling optical pulse to enter one optical terminal of the carbon nanotube element;
A wavelength filter (29) that selectively emits a wavelength component of the optical signal out of light emitted from the other optical terminal of the carbon nanotube element is provided.

An optical sampling device according to claim 4 of the present invention is the optical sampling device according to claim 1,
A polarization controller (28) for making the polarization directions of the optical signal and the sampling optical pulse orthogonal to each other;
An optical coupler (25 ″) that combines the optical signal having the polarization directions orthogonal to each other and the sampling optical pulse to enter one optical terminal of the carbon nanotube element;
A polarization filter (29 ') that selectively emits a polarization component of the optical signal out of the light emitted from the other optical terminal of the carbon nanotube element is provided.

The optical sampling device according to claim 5 of the present invention is the optical sampling device according to claim 3 or 4,
The carbon nanotube element is characterized in that a plurality of element members (123) on which carbon nanotubes are formed are arranged side by side with the light incident surface inclined with respect to a line perpendicular to the incident optical axis.

The optical sampling device according to claim 6 of the present invention is the optical sampling device according to claim 5,
The element member is a set of two elements arranged symmetrically with respect to a line orthogonal to the incident optical axis.

An optical signal quality monitor according to claim 7 of the present invention is
Sampling light that emits sampling light pulses with a period (Ts) that differs by a predetermined offset time (ΔT) with respect to an integer (N) times the clock period (Tc) of the data signal that is modulating the optical signal to be monitored A pulse generator (21);
An optical sampling device (22) for sampling the optical signal with the sampling optical pulse and outputting the optical pulse signal obtained by the sampling;
A photoelectric converter (30) that receives the light pulse signal and converts it into an electrical signal;
In an optical signal quality monitor having a calculation unit (35, 35 ′) for calculating a value representing the quality of the optical signal to be monitored based on an output signal of the photoelectric converter,
The optical sampling device is the optical sampling device according to any one of claims 1 to 6.

An optical sampling device according to claim 8 of the present invention is the optical sampling device according to claim 7,
Fundamental wave component signal output means (41) for outputting a fundamental wave component signal having a frequency equal to the fundamental wave component of the envelope wave of the output signal of the photoelectric converter;
A comparator (42) for comparing the fundamental component signal with a predetermined threshold;
And a data acquisition control unit (44) for starting acquisition of waveform information for the output signal of the photoelectric converter from a timing when the fundamental wave component signal exceeds the threshold value.

  As described above, the optical sampling apparatus of the present invention uses a carbon nanotube element as a sampling element, makes an optical signal and a sampling optical pulse incident on the carbon nanotube element, and the sampling optical pulse enters. The supersaturated absorption characteristic of the resulting carbon nanotube element lowers the absorptance with respect to the optical signal and emits the light.

For this reason, a narrow-width optical pulse can be used for sampling, and the sampling efficiency for the optical signal can be increased, and a weak optical signal can be sampled.
In addition, the carbon nanotube element can be formed at a much lower cost than the electroabsorption optical modulator, and the bias power supply and the control thereof are unnecessary, so that the optical sampling device can be configured at a low cost.

  In addition, an optical signal monitor using this optical sampling device can obtain waveform information with a simple and inexpensive configuration with high accuracy.

  In addition, an optical signal monitor that extracts a fundamental wave component signal from a signal obtained by sampling an optical signal and starts acquiring waveform information at a timing when the fundamental wave component signal exceeds a threshold value is actually incident. The waveform information acquisition start timing can be synchronized with the data signal that is modulating the optical signal, and the eye pattern can be stably obtained by superimposing a plurality of sets of waveform information obtained at the start timing. be able to.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an optical signal quality monitor 20 having an optical sampling device 22 to which the present invention is applied.

  This optical signal quality monitor 20 is intended for monitoring an optical signal Px modulated with a data signal having a predetermined clock period Tc, and the sampling optical pulse generator 21 is data that modulates the optical signal Px. A sampling optical pulse Ps having a period Ts that differs by a predetermined offset time ΔT with respect to an integer N times the clock period Tc of the signal is generated and made incident on the optical sampling device 22.

  The configuration of the sampling optical pulse generator 21 is arbitrary as long as it can generate a narrow optical pulse with a specified period Ts as described above.

  FIG. 2 shows an example thereof. A stable signal Ra having a period Ts (frequency Fs) designated by a parameter setting unit 36, which will be described later, is generated by a synthesizer-structured reference signal generator 21a and input to a multiplier 21b. The output signal Rb is input to the optical modulator 21c, and the continuous light Pcw emitted from the light source 21d is modulated to generate an optical pulse Pa with a period Ts / M. The pulse width of the light pulse Pa is narrowed to 1 / M compared to the case where the continuous light Pcw is directly modulated with the signal Ra.

  Then, this optical pulse Pa is thinned to 1 / M by the optical gate circuit 21e to generate an optical pulse Pb having a period Ts, which enters the dispersion reducing fiber 21f, further narrows the pulse width, and the sampling optical pulse Ps. To be emitted.

  On the other hand, the optical sampling device 22 samples the optical signal Px to be monitored by the sampling optical pulse Ps emitted from the sampling optical pulse generator 21, and emits the optical pulse signal Py obtained by the sampling.

  The optical sampling device 22 includes a carbon nanotube element (hereinafter referred to as a CNT element) 23 and a circulator type optical coupler 25.

  For the CNT element 23, a CNT material made of a tube-like carbon crystal is applied to, for example, a glass or resin substrate surface, mixed with a polymer solvent and solidified into a plate shape, or the core portion contains the CNT material. It is a saturable absorption device having an extremely fast recovery time using fiber or the like as an element member, and has a characteristic that the absorptance changes according to the power of incident light in a wide wavelength range, for example, as shown in FIG. The optical signal Px is received at one optical terminal 23a, and the absorptance with respect to the optical signal Px is reduced and passed to the optical terminal 23b only when the sampling optical pulse Ps is incident from the other optical terminal 23b, thereby allowing the efficiency to pass. High sampling is performed.

  Note that the sampling efficiency at this time is determined by the insertion loss of the CNT element 23, but the insertion loss of the CNT element 23 is generally very small, several dB or less, compared to the case where an electroabsorption optical modulator is used. It is greatly improved.

  From the optical terminal 23b of the CNT element 23, an optical pulse signal Py having a peak value at a level that is equivalent to the insertion loss of the CNT element 23 is lost from the instantaneous intensity of the optical signal Px when the sampling optical pulse Ps is incident. 25, and is emitted to an optical path different from the incident path of the sampling light pulse Ps.

  Here, when the sampling optical pulse Ps having a wavelength different from that of the optical signal Px is used, not only the circulator type as described above but also a spectral type that distributes the optical path according to the wavelength difference is used as the optical coupler 25. It is also possible.

  The circulator type optical coupler 26 inserted into one optical terminal 23a of the CNT element 23 optically terminates the sampling optical pulse Ps incident on the other optical terminal 23b and emitted from the one optical terminal 23a. It terminates at the unit 27 and prevents it from entering the transmission path of the optical signal Px to be monitored.

  The optical pulse signal Py enters the photoelectric converter 30 via the optical coupler 25 and is converted into an electrical signal Ey.

  The output signal Ey of the photoelectric converter 30 is converted into a digital value by the A / D converter 31 and input to the arithmetic unit 35. The sampling of the A / D converter 31 is performed by the sampling clock Es synchronized with the sampling optical pulse Ps. In this embodiment, the electrical sampling clock Es is also output from the sampling optical pulse generator 21. Shall be.

  The computing unit 35 calculates a value representing the quality of the optical signal Px to be monitored based on the signal Ey converted into a digital value by the A / D converter 31.

  Although this calculation is arbitrary, for example, as described in Patent Document 1, the signal Ey is taken as a sample value for a predetermined time, and compared with a predetermined threshold value, and belongs to the data “1”. Dividing into sample values and sample values belonging to data “0”, the average value and standard deviation of the sample value group for each data are obtained, and the ratio μ / γ of the difference μ between the average values and the sum γ of the standard deviations Is obtained as a quality value Q. Note that the higher the Q value, the higher the signal quality.

  The quality value Q is calculated every predetermined time, for example, and the result is notified to another apparatus at a predetermined timing. The value representing the signal quality is not limited to the above Q value, and may be another statistic.

  The sampling optical pulse Ps output from the sampling optical pulse generator 21 and the cycle Ts of the sampling clock Es are set by the parameter setting unit 36.

The parameter setting unit 36 receives information on the clock period Tc (which may be a bit rate) and the offset time ΔT of the data signal modulating the optical signal Px to be monitored, and sets the sampling period Ts.
Ts = N · Tc + ΔT
And set in the sampling optical pulse generator 21.

  Here, the value of N is determined by the clock cycle Tc of the data signal and the frequency variable range of the signal that can be output by the sampling optical pulse generator 21.

  For example, if ΔT is negligibly small with respect to Ts, Tc is about 0.1 ns (10 GHz), and Ts can be varied in the vicinity of 0.1 μs (10 MHz), the value of N is approximately Ts / Tc. = 1000.

  Next, the relationship between the waveform of the optical signal Px to be monitored and its acquisition timing will be described.

  When the optical signal Px to be monitored is for testing and is repeatedly modulated with a predetermined code string having a predetermined bit length L as shown in FIG. 4A, sampling is performed as shown in FIG. 4B. By making the value of N that determines the period Ts of the optical pulse Ps equal to an integer K times the bit length L, sampling of the repetitive waveform of the optical signal Px is performed every ΔT time as shown in FIG. Can be done in time series. Then, by performing this sampling continuously, for example, U · Tc / ΔT times (U is an integer), U-bit waveform data can be obtained in time series from the sampling start timing.

  The optical signal Px that is actually transmitted on the optical network does not have a repetitive waveform as shown in FIG. However, when the optical signal Px is sampled at a period Ts of N · Tc + ΔT as shown in FIG. 5B, the data every N bits of the optical signal Px is sampled at different timings by ΔT. Therefore, the value obtained by the sampling is the amplitude corresponding to the data “1” and “0” or the amplitude in the transition state between them as shown in FIG. 5C, and is a fixed period of the optical signal Px. It is not a sampling result for a continuous waveform.

  However, the quality value Q can be obtained by performing the sampling continuously for a plurality of bits as described above and obtaining the statistics.

  If the sampling period corresponds accurately to the bit rate of the data signal that is modulating the optical signal (synchronized state), the sampling results for a plurality of bits are superimposed on one bit width, An eye pattern as shown in FIG. 5D may be obtained, and the signal quality may be obtained from this eye pattern.

  In addition, when the sampling period is shifted with respect to the bit rate of the data signal modulating the optical signal (asynchronous state), the observation waveform obtained by superimposing flows and the eye pattern cannot be observed. By performing the sampling for a predetermined period, the statistic can be obtained and the quality value Q can be obtained.

(Second Embodiment)
FIG. 6 shows a configuration example of an optical signal quality monitor 20 ′ that can always maintain the synchronization state.

  The optical pulse generator 21 for sampling, the optical sampling device 22, the photoelectric converter 30, the A / D converter 31, and the parameter setting unit 36 of the optical signal quality monitor 20 ′ are the same as those in the first embodiment. Therefore, the description is omitted.

  In the case of this optical signal quality monitor 20 ′, the output signal Ey of the photoelectric converter 30 is input to the fundamental wave component signal output unit 41.

  The fundamental wave component signal output unit 41 is for outputting a fundamental wave component signal U having a frequency equal to the frequency of the fundamental wave component of the envelope wave of the signal Ey output from the photoelectric converter 30 in a pulse shape. .

  As a configuration of the fundamental wave component signal output unit 41, a filter method and a PLL (phase lock loop) method can be considered.

  In the case of the filter system, a narrow-band bandpass filter having a center frequency (in the case of the RZ system) equal to the clock frequency Fc of the data signal modulating the optical signal or a center frequency equal to twice that (in the case of the NRZ system). To extract the fundamental wave component signal U of the sine wave.

  In the case of the PLL system, as shown in FIG. 7, the output signal of the narrow bandpass filter 41a and the output signal of the voltage controlled oscillator 41b are input to the phase comparator 41c, and the phase difference is calculated. The oscillation frequency of the voltage controlled oscillator 41b is controlled by the corresponding control signal Vc, the phase of the oscillation output signal is synchronized with the output signal of the band pass filter 41a, and the synchronized sine wave oscillation output signal is converted to the fundamental component signal. Used as U.

  As another example, the output signal Ey of the photoelectric converter 30 is input to the FFT operation unit, the frequency is analyzed, the frequency of the fundamental wave component is obtained, and the fundamental wave component signal U equal to the obtained frequency is obtained as a signal. The structure which produces | generates and outputs with a generator may be sufficient.

  Here, if the clock frequency Fc of the optical signal Px is 10 GHz and the offset time ΔT is 0.1 ps, 1000 times of sampling is necessary to obtain waveform data for one bit of the optical signal Px, and 1000 times Is approximately 0.1 ms, and this time is equal to the period of the fundamental wave component of the envelope wave of the signal Ey, and the frequency is approximately 10 kHz.

  This fundamental wave component signal U is input to the comparator 42, compared with a threshold value Vr set in advance by a threshold value setter 43, and the comparison result is input to the data acquisition control unit 44.

  The data acquisition controller 44 writes the data signal Dy output from the A / D converter 31 in the waveform memory 45 based on the output signal of the comparator 42.

  That is, the writing of the data signal Dy to the waveform memory 45 is started from the timing when the fundamental wave component signal U exceeds the threshold value Vr from the lower side, for example, and after the writing of the predetermined number W of data signals is finished, The operation of waiting until the timing when the wave component signal U is lower than the threshold Vr is repeated H times a predetermined number of times. The predetermined number W of data signals Dy are written in a plurality of different areas of the waveform memory 45 in the order of addresses.

  Similar to the calculation unit 35 of the first embodiment, the calculation unit 35 ′ calculates a value representing the quality of the optical signal Px to be monitored based on the data signal Dy written in the waveform memory 45.

  Next, the relationship between the waveform of the optical signal Px to be monitored according to the second embodiment and the acquisition timing will be described.

  If the optical signal Px to be monitored is for testing, for example, and is repeatedly modulated with a predetermined code string having a predetermined bit length L as shown in FIG. 8A, sampling is performed as shown in FIG. 8B. Sampling is performed in a state where the value of N that determines the period Ts of the optical pulse Ps is equal to an integer K times the bit length L, so that the time axis of the optical signal Px is changed as shown in FIGS. An optical pulse signal Py having an enlarged envelope waveform is obtained, and a sine wave fundamental wave component signal U as shown in FIG. 8E is obtained from the light reception signal Ey of the optical pulse signal Py.

  Then, data acquisition is started as shown in (f) of FIG. 8 from the timing when the fundamental wave component signal U exceeds the threshold value Vr. For example, the data is obtained by sampling J · Tc / ΔT times (U is an integer). Data is acquired. The Q value can be obtained by performing the above calculation on the waveform data for J bits. Note that (d) to (f) in FIG. 8 are shown with the time axis narrowed.

  When obtaining an eye pattern, as shown in FIGS. 8D to 8F, waveform data acquisition is started from the timing when the fundamental wave component signal U exceeds the threshold value Vr. The processing for bits is performed a plurality of times H, and stored in different areas 1 to H of the waveform memory 45 as shown in FIG.

  Then, an eye pattern as shown in FIG. 10 can be obtained by superimposing the waveform data Dy of the plurality of regions in the order of addresses. However, the fundamental wave component signal U has a threshold value Vr as the leading data of these waveform data. Since the value sampled immediately after the timing exceeding is accurately synchronized with the data signal, the time axis of the waveform data is not greatly shifted and superimposed, and the variation in the amplitude of the optical signal is almost exactly Represents.

  The relationship between the position in the bit and the quality is obtained on this eye pattern. For example, as shown in FIG. 10, the Q value is calculated based on the sample value at the intermediate point L (1-bit intermediate point) between the two cross points, and the Q for the whole data unrelated to the above-described position is calculated. Along with the value, it is notified to other devices via a communication means (not shown).

  In addition, the optical signal Px actually transmitted on the optical network does not have a repetitive waveform as shown in FIG. 11A, but the optical signal Px is as shown in FIG. 11B. When sampling is performed at a period Ts of N · Tc + ΔT, sampling is performed at different timings by ΔT for data every N bits of the optical signal Px, and the peak value of the optical pulse signal Py obtained by the sampling is obtained. Becomes an amplitude corresponding to data “1” and “0” or an amplitude in a transition state between them as shown in (c) of FIG. 11 and (d) in which the time axis is narrowed, and the optical signal Px However, the envelope wave containing the fundamental wave component of the data signal modulating the optical signal Px is included in the envelope wave. A fundamental wave component signal U is obtained as shown in FIG.

  Similarly to the above, data acquisition is started as shown in (f) of FIG. 11 from the timing when the fundamental wave component signal U exceeds the threshold value Vr. For example, J · Tc / ΔT times (U is an integer). Data obtained by sampling is acquired. The Q value can be obtained by performing the above calculation on the waveform data for J bits. Note that (d) to (f) in FIG. 11 are shown with the time axis narrowed.

  Although it can be said that the waveform data for J bits itself represents an eye pattern, in the case of obtaining an eye pattern that more accurately represents the quality of an optical signal using more sample values, the waveform data shown in FIG. As shown in (d) to (f), a process of starting waveform data acquisition from the timing when the fundamental wave component signal U exceeds the threshold value Vr and performing J bits a plurality of times is performed a plurality of times. An accurate eye pattern can be obtained by storing each in different areas 1 to H of the waveform memory 45 and overlaying them in the order of addresses.

  Even in this case, the leading data of each waveform data is a value sampled immediately after the timing when the fundamental wave component signal U exceeds the threshold value Vr, and is accurately synchronized with the data signal. Are not greatly deviated and superimposed, and the variation in the amplitude of the optical signal is represented almost accurately.

  The optical sampling device 22 used in the optical signal quality monitors 20 and 20 ′ of the above-described embodiments uses a CNT element 23 as a sampling element, and the optical signal Px to be monitored is incident on the CNT element 23. The sampling optical pulse Ps is made incident through the optical coupler 25, and when the sampling optical pulse Ps is made incident, the absorptance with respect to the optical signal Px is lowered, thereby sampling the optical signal.

  For this reason, an optical pulse having a narrow width can be used for sampling, the sampling efficiency for the optical signal can be improved, and waveform information can be obtained with high accuracy even for a weak optical signal. Further, the CNT element 23 is extremely inexpensive as compared with the electroabsorption optical modulator, and does not require a power source and its control, so that it can be configured simply and inexpensively as an optical sampling device.

  Further, in the case where the fundamental wave component signal U is obtained from the signal obtained by sampling and the waveform acquisition start timing is synchronized as in the optical signal quality monitor 20 ′ of the second embodiment, it is different in different periods. Even if the acquired data signals Dy are superimposed, there is no fear that the time axis is largely shifted, and the eye pattern of the optical signal can be obtained stably.

  In the above-described embodiment, the quality value and the eye pattern are obtained by the computing unit 35 ′. However, the computing unit 35 ′ is omitted, and data written in each area of the waveform memory 45 is transmitted via communication means (not shown). May be transmitted to another external device, and the quality calculation processing and eye pattern may be displayed on the other device side.

  The optical sampling device 22 used in the optical signal quality monitors 20 and 20 ′ of the above embodiment makes the optical signal Px incident on one optical terminal 23a of the CNT element 23, and the sampling optical pulse Ps is supplied to the circulator type optical coupler 25. Through the other optical terminal 23b, sampling is performed, and an optical pulse signal Py obtained by the sampling is emitted through the optical coupler 25.

  Therefore, sampling is possible even when the wavelengths of the optical signal Px and the sampling optical pulse Ps are equal.

  The optical coupler 25 is of a circulator type, but can be constructed at a lower cost by using a dichroic coupler that transmits light incident from one side and reflects light incident from the opposite side. Can do.

  When the sampling optical pulse Ps having a wavelength different from that of the optical signal Px is used, the optical signal Px and the sampling optical pulse Ps are combined by the optical coupler 25 'as in the optical sampling device 22 shown in FIG. The wavelength filter 29 selects only the optical pulse signal Py ′ having the wavelength component of the optical signal Px out of the light incident on one optical terminal 23 a of the CNT element 23 and emitted from the other optical terminal 23 b of the CNT element 23. It is also possible to emit light.

  As the optical coupler 25 'in this case, the above-described dichroic coupler and WDM coupler can be used.

  Further, as in the optical sampling device 22 shown in FIG. 13, the optical signal Px is incident on the polarization controller 28, the polarization direction of the optical signal Px is made orthogonal to the polarization direction of the sampling optical pulse Ps, and then the sampling optical pulse. The light is incident on a polarization multiplexing type optical coupler 25 ″ together with Ps and combined, and the combined light is incident on one optical terminal 23 a of the carbon nanotube element 23 and is emitted from the other optical terminal 23 b of the carbon nanotube element 23. Of the emitted light, only the polarization component of the optical signal Px may be selected by the polarization filter 29 '.

  Here, a polarization controller, a polarizing plate, and a polarizing beam splitter can be used as the polarization controller 28, and a polarizing plate, a polarizing beam splitter, and the like can be used as the polarizing filter 29 '.

  In this configuration, sampling is possible even if the wavelengths of the optical signal Px and the sampling optical pulse Ps match.

  Further, when the optical signal and the sampling optical pulse are incident on the same optical terminal of the CNT element 23 as described above, a high extinction ratio is given to the emitted optical pulse signal by making the CNT element 23 multi-element. Can do.

  FIG. 14 shows an example of the configuration. As the CNT element 23, a laminated glass plate 123 as an element member on which carbon nanotubes are formed is inclined with respect to a line whose light incident surface is orthogonal to the incident optical axis. Two or more sheets are lined up.

  Thus, in the case of a structure in which a plurality of laminated glass plates 123 on which carbon nanotubes are formed are arranged, the optical signal Px and the sampling optical pulse Ps travel along the same path at substantially the same speed, so the first laminated glass plate The optical signal Px at the timing when the sampling optical pulse Ps is incident on the sample 123 is sampled, and the optical pulse signal Py1 obtained by the sampling is incident on the second laminated glass plate 123 together with the sampling optical pulse Ps. The process of sampling is repeated, and the extinction ratio of the finally emitted optical pulse signal Py4 is increased.

  Moreover, since the light incident surface of the laminated glass plate 123 is inclined with respect to the incident optical axis, the reflection component R on the surface of each laminated glass plate 123 does not return to the incident side, and the influence can be ignored. it can.

  When the laminated glass plate 123 has a polarization dependency that cannot be ignored, when the plurality of laminated glass plates 123 are arranged in parallel as described above, the polarization characteristics are superimposed and a large polarization dependency appears. In that case, as shown in FIG. 15, a set of two laminated glass plates 123 may be disposed so as to be symmetric with respect to a line orthogonal to the incident optical axis. In this way, even if the polarization state is changed by the first laminated glass plate 123, the change is offset by the second laminated glass plate 123, and almost non-polarization characteristics are obtained, and the polarization dependence is improved. It can be almost eliminated.

  In the optical sampling apparatus 22 described above, the sampling optical pulse Ps is incident on the CNT element 23 via the optical couplers 25 and 25 '. As shown in a simple example in FIG. It is also possible to perform sampling by directly entering the sampling optical pulse Ps with an optical axis having an angle different from the optical axis of the optical signal Px incident on the optical signal Px.

  As described above, the laminated glass plate 123 formed by applying a CNT material to a glass substrate has been described as an example of the element member of the CNT element 32. However, the substrate is made of resin, and the CNT material is mixed with a polymer solvent and solidified. An optical fiber type having a core or a CNT material contained in the core can be employed.

  The optical sampling device 22 described above can be used not only as the optical signal quality monitor 20, 20 'but also as an optical sampling unit of other optical devices.

Configuration diagram of the first embodiment of the present invention The figure which shows the structural example of the principal part of embodiment. The figure which shows the example of a characteristic of the principal part of embodiment Operation explanation diagram when optical signal has repetitive waveform Operation explanation diagram when optical signal is not repetitive waveform Configuration diagram of second embodiment of the present invention The figure which shows the structural example of the principal part of 2nd Embodiment. Operation explanation diagram when optical signal has repetitive waveform Diagram of acquired waveform data Eye pattern diagram with superimposed acquired waveform data Operation explanation diagram when optical signal is not repetitive waveform The figure which shows another structure of an optical sampling device The figure which shows another structure of an optical sampling device The figure which shows the structure of the multi-element CNT element used for the structure of FIG. 12, FIG. The figure which shows another structure of the multi-element CNT element used for the structure of FIG. 12, FIG. The figure which shows the structural example which does not use the optical coupler Illustration of equivalent time sampling method

Explanation of symbols

  20, 20 '... Optical signal quality monitor, 21 ... Optical pulse generator for sampling, 22 ... Optical sampling device, 23 ... CNT element, 25, 25', 25 "... Optical coupler, 28 ... Bias Wave controller 29... Wavelength filter, 29 ′ polarization filter, 30 …… photoelectric converter, 31 A / D converter, 35, 35 ′ computing unit 36, parameter setting unit 41 ...... Fundamental component signal output unit, 41a ... Band pass filter, 41b ... Voltage controlled oscillator, 41c ... Phase comparator, 42 ... Comparator, 43 ... Threshold setting unit, 44 ... Data acquisition control 45, waveform memory, 123 ... laminated glass plate

Claims (8)

In an optical sampling device (22) that receives an optical signal to be sampled and a sampling optical pulse having a predetermined period, samples the optical signal with the sampling optical pulse, and emits an optical pulse signal obtained by the sampling.
A carbon nanotube element (23) having a characteristic that an absorptance with respect to the incident light changes according to the power of the incident light, and receiving the optical signal and the sampling optical pulse;
An optical sampling apparatus characterized in that the optical signal is emitted with a small absorption rate only when the sampling optical pulse is incident on the carbon nanotube element. The optical signal is incident on one optical terminal of the carbon nanotube element,
The sampling optical pulse is incident on the other optical terminal of the carbon nanotube element, and an optical pulse signal emitted from the other optical terminal of the carbon nanotube element is emitted to an optical path different from the incident optical path of the sampling optical pulse. The optical sampling device according to claim 1, further comprising an optical coupler (25). The wavelength of the sampling optical pulse is set to a wavelength different from the optical signal,
An optical coupler (25 ′) for combining the optical signal and the sampling optical pulse to enter one optical terminal of the carbon nanotube element;
The optical sampling according to claim 1, further comprising: a wavelength filter (29) that selectively emits a wavelength component of the optical signal out of the light emitted from the other optical terminal of the carbon nanotube element. apparatus. A polarization controller (28) for making the polarization directions of the optical signal and the sampling optical pulse orthogonal to each other;
An optical coupler (25 ″) that combines the optical signal having the polarization directions orthogonal to each other and the sampling optical pulse to enter one optical terminal of the carbon nanotube element;
The light according to claim 1, further comprising a polarizing filter (29 ') that selectively emits a polarization component of the optical signal out of the light emitted from the other optical terminal of the carbon nanotube element. Sampling device.   The carbon nanotube element is characterized in that a plurality of element members (123) on which carbon nanotubes are formed are arranged side by side with the light incident surface inclined with respect to a line perpendicular to the incident optical axis. The optical sampling device according to claim 3 or 4.   6. The optical sampling apparatus according to claim 5, wherein the element member is a set of two elements arranged symmetrically with respect to a line orthogonal to the incident optical axis. Sampling light that emits sampling light pulses with a period (Ts) that differs by a predetermined offset time (ΔT) with respect to an integer (N) times the clock period (Tc) of the data signal that is modulating the optical signal to be monitored A pulse generator (21);
An optical sampling device (22) for sampling the optical signal with the sampling optical pulse and outputting the optical pulse signal obtained by the sampling;
A photoelectric converter (30) that receives the light pulse signal and converts it into an electrical signal;
In an optical signal quality monitor having a calculation unit (35, 35 ′) for calculating a value representing the quality of the optical signal to be monitored based on an output signal of the photoelectric converter,
The optical sampling device according to any one of claims 1 to 6, wherein the optical sampling device is an optical signal quality monitor. Fundamental wave component signal output means (41) for outputting a fundamental wave component signal having a frequency equal to the fundamental wave component of the envelope wave of the output signal of the photoelectric converter;
A comparator (42) for comparing the fundamental component signal with a predetermined threshold;
A data acquisition control unit (44) for starting acquisition of waveform information for the output signal of the photoelectric converter from a timing at which the fundamental wave component signal exceeds the threshold value. Optical signal quality monitor as described.

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