CN112311468A - Non-pulse signal based linear optical sampling method and system - Google Patents

Non-pulse signal based linear optical sampling method and system Download PDF

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CN112311468A
CN112311468A CN201910705767.7A CN201910705767A CN112311468A CN 112311468 A CN112311468 A CN 112311468A CN 201910705767 A CN201910705767 A CN 201910705767A CN 112311468 A CN112311468 A CN 112311468A
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signal
sampling
frequency
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何祖源
樊昕昱
徐炳鑫
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/54—Intensity modulation
    • H04B10/541—Digital intensity or amplitude modulation

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
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Abstract

A non-pulse signal based linear optical sampling method and system, interference sampling is carried out on sampled optical signal by non-pulse sampling optical signal to obtain original sampling result with radio frequency carrier, Fourier transform is carried out on original sampling result to obtain complex number of finite frequency component higher than noise threshold
Figure DDA0002152066640000011
With corresponding compensation signals generated on the basis of the predicted quantities
Figure DDA0002152066640000012
Multiplying to replace points on the frequency spectrum position of the original sampling result to obtain frequency domain representation of the demodulation result, and obtaining time domain complex representation of the demodulation result after Fourier inversion: firstly, recovering the intensity of the sampled signal after envelope taking, and/or secondly, recovering the phase after carrier wave removal, namely the sampled signalThe phase of the sign. The invention takes the electro-optical comb generated by electro-optical modulation as a sampling signal, can remarkably improve the dynamic range and the signal-to-noise ratio of measurement while getting rid of the limitation of a mode-locked laser and a pulse type sampling signal, has far lower cost than the mode-locked laser and has higher practical value.

Description

Non-pulse signal based linear optical sampling method and system
Technical Field
The invention relates to a technology in the field of optical communication, in particular to a non-pulse signal-based linear optical sampling method and a non-pulse signal-based linear optical sampling system.
Background
The linear optical sampling technology uses ultrashort pulses as a sampling light source, can provide ultrahigh time resolution by utilizing gate function effect of the ultrashort pulses, does not need to rely on a nonlinear process, has no power requirement and is simple in system, and is widely applied to detection of time division multiplexing optical signals, novel modulation format optical signals and wavelength division multiplexing optical signals. However, linear optical sampling techniques rely on high quality sampling pulses, which imposes two limitations on the system. Firstly, a mode-locked laser is needed as a sampling light source, and the price is high; secondly, the peak power of the pulse light is very high, the power must be limited for protecting the detection device, and the dynamic range and the signal-to-noise ratio of the measurement are reduced.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a non-pulse signal-based linear optical sampling method and system, an electro-optical comb generated by electro-optical modulation is used as a sampling signal, the limit of a mode-locked laser and a pulse type sampling signal is eliminated, the dynamic range and the signal-to-noise ratio of measurement can be obviously improved, the cost is far lower than that of the mode-locked laser, and the practical value is higher.
The invention is realized by the following technical scheme:
the invention relates to a sampling method based on a non-pulse signal linear optical system, which comprises the steps of carrying out interference sampling on a sampled optical signal through a non-pulse sampling optical signal to obtain an original sampling result with a radio frequency carrier, carrying out Fourier transform on the original sampling result, and then obtaining a complex number of finite frequency components higher than a noise threshold value
Figure BDA0002152066620000011
With corresponding compensation signals generated on the basis of the predicted quantities
Figure BDA0002152066620000012
Multiplying to replace points on the frequency spectrum position of the original sampling result to obtain frequency domain representation of the demodulation result, and obtaining time domain complex representation of the demodulation result after Fourier inversion: firstly, the intensity of the sampled signal is recovered after envelope taking, and/or secondly, the phase, namely the phase of the sampled signal, is recovered after the carrier wave is removed.
The frequency components of the non-pulse sampling optical signal are as follows:
Figure BDA0002152066620000013
the frequency components of the sampled optical signal are:
Figure BDA0002152066620000014
wherein: f. ofs0And fd0Respectively the center frequency, f, of the optical carriersAnd fdIn order to be able to repeat the frequency,
Figure BDA0002152066620000015
and
Figure BDA0002152066620000016
are complex coefficients of the corresponding frequency components.
The original sampling result with the radio frequency carrier wave is as follows:
Figure BDA0002152066620000017
wherein: Δ f0＝fd0-fs0，Δf＝fd-fsWhich may be considered to be the center frequency and repetition frequency, respectively, of the original sampling result, the bandwidth and repetition frequency of the sampled signal are compressed by a factor of k,
Figure BDA0002152066620000021
when the sampling signal is an ultrashort pulse generated by a mode-locked laser,
Figure BDA0002152066620000022
the sampled signal can be directly recovered as a constant of equal strength and 0 in phase.
The compensation signal is based on a non-pulse sampling optical signalThe traditional linear optical sampling technology of the mode-locked laser is obtained by the following specific steps:
Figure BDA0002152066620000023
the demodulation result is
Figure BDA0002152066620000024
The non-pulse signal linear optical system comprises: the optical sampling module comprises a microwave source, an electric amplifier and a dual-drive Mach-Zehnder modulator, the optical sampling module and a signal to be sampled are subjected to coherent sampling through an 50/50 optical fiber coupler, the output end of the 50/50 optical fiber coupler is provided with a signal recovery module consisting of a balanced photoelectric detector, a data acquisition card and a data processor, and the frequency difference of delta f exists between the repetition frequency of the sampling signal and the repetition frequency of the sampled signal by controlling the output frequency of the microwave source, so that equivalent sampling is performed.
The frequency difference is delta f ═ fd-fsThe difference between the repetition frequency of the non-pulsed sampling optical signal and the repetition frequency of the sampled optical signal is inversely proportional to the equivalent sampling rate and directly proportional to the time actually consumed for sampling. At the repetition frequency f of the sampled signaldUnder certain conditions, the frequency f of the output signal of the microwave source in the optical sampling module can be specifically controlledsAnd (5) controlling.
The signal to be sampled adopts, but is not limited to: the laser, the optical fiber coupler, the signal generator and the electro-optical modulator.
The optical communication waveform generated by the electro-optical modulator and including formats such as on-off keying (OOK), Differential Phase Shift Keying (DPSK), Quadrature Amplitude Modulation (QAM) and the like, or other arbitrary periodic waveforms, can be used as a sampled signal of the system.
The optical sampling module preferably receives a laser carrier from the same source as the signal to be sampled to generate an optical sampling signal.
The homogeneous laser carrier wave divides the single-frequency laser generated by the laser into two paths by the optical fiber coupler, one path enters the electro-optical modulator, and the other path is used as local light used in coherent reception.
The dual-drive Mach-Zehnder modulator modulates local light, is driven by a radio frequency signal output by a microwave source amplified by the electric amplifier, and generates an electro-optical modulation light frequency comb as a sampling light source; the local light may be replaced by another laser output when only intensity modulated.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention;
FIG. 2 is a signal comparison diagram of an embodiment;
in the figure: the device comprises a laser 1, an 50/50 optical fiber coupler 2, an electro-optic modulator 3, a signal generator 4, a dual-drive Mach-Zehnder modulator 5, an electric amplifier 6, a microwave source 7, a 50/50 optical fiber coupler 8, a balanced photoelectric detector 9, a data acquisition card 10 and a data processor 11.
Detailed Description
As shown in fig. 1, the present embodiment includes: the device comprises a signal module to be sampled, an optical sampling module, a coherent receiving module and a signal acquisition and processing module.
The signal module to be sampled comprises: a laser 1, 50/50 fiber coupler 2, an electro-optic modulator 3 and a signal generator 4.
The optical sampling module comprises: dual drive Mach-Zehnder modulator 5, electrical amplifier 6 and microwave source 7
The coherent receiving module comprises: 50/50 fiber coupler 8 and balanced photodetector 9.
The signal acquisition and processing module comprises: a data acquisition card 10 and a data processor 11.
As shown in fig. 1, the single-frequency laser generated by the laser 1 is divided by the fiber coupler 2 into two branches with the same power, and the two branches are respectively output to: firstly, an electro-optical modulator 3 generates a code pattern signal through a signal generator 4 to drive so as to generate an on-off keying signal with the signal code rate of 10Gb/s, and secondly, a dual-drive Mach-Zehnder modulator 5 outputs a driving signal which is output by a microwave source 7 amplified by an electric amplifier 6, and the frequency of the driving signal is 1.001 GHz; the output signals of the two branches interfere through a coherent receiving module 8, are received through a balanced photoelectric detector 9, and are collected by a data acquisition card 10 to obtain an original sampling result. And processed by a data processor 11 to obtain the data of FIG. 2
The original sampling result is processed by the data processor 11, and the specific process is as follows: fourier transform is carried out on the original sampling result, and complex values of finite frequency components are taken
Figure BDA0002152066620000031
And compensation signal
Figure BDA0002152066620000032
Multiplying, obtaining time domain complex representation of a demodulation result after fourier inverse transformation, and obtaining an intensity waveform of a sampled signal time domain by envelope, as shown in fig. 2 (Generalized LOS technique corresponding waveform), compared with a result (LOS technique corresponding waveform) obtained by a traditional mode of sampling with a mode-locked laser, a relative error is less than 5%, and the measurement accuracy is equivalent.
Through a specific practical experiment, linear optical sampling is performed on a 10Gb/s on-off keying signal by using a non-pulse sampling signal in a time domain, specifically an electro-optical comb with a repetition frequency of 1GHz generated by electro-optical modulation, and a demodulation result shown in fig. 2 can be obtained through the demodulation method.
Compared with the linear light sampling result of the traditional mode-locked laser, the sampling result obtained by the method has equivalent measurement accuracy, and the relative error is less than 5 percent; compared with the ultrashort pulse used in the traditional linear optical sampling, the average power of the sampling signal of the method is improved by more than 10 times; compared with the traditional mode-locked laser linear light sampling system, the system used by the method has the advantages that the cost is only about one fifth of the cost, the cost is greatly reduced, and the practicability is enhanced; the method can not only use the electro-optical comb as a sampling light source, but also use other low-cost optical comb light sources as sampling signals, such as gain-switch laser and the like.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (10)

1. A sampling method based on a non-pulse signal linear optical system is characterized in that interference sampling is carried out on a sampled optical signal through a non-pulse sampling optical signal to obtain an original sampling result with a radio frequency carrier, Fourier transform is carried out on the original sampling result, and then a complex number of finite frequency components higher than a noise threshold value is obtained
Figure FDA0002152066610000011
With corresponding compensation signals generated on the basis of the predicted quantities
Figure FDA0002152066610000012
Multiplying to replace points on the frequency spectrum position of the original sampling result to obtain frequency domain representation of the demodulation result, and obtaining time domain complex representation of the demodulation result after Fourier inversion: firstly, the intensity of the sampled signal is recovered after envelope taking, and/or secondly, the phase, namely the phase of the sampled signal, is recovered after the carrier wave is removed.
2. The method of claim 1, wherein the non-pulsed signal linear optical system comprises: the optical sampling module comprises a microwave source, an electric amplifier and a dual-drive Mach-Zehnder modulator, the optical sampling module and a signal to be sampled are subjected to coherent sampling through an 50/50 optical fiber coupler, the output end of the 50/50 optical fiber coupler is provided with a signal recovery module consisting of a balanced photoelectric detector, a data acquisition card and a data processor, and the frequency difference of delta f exists between the repetition frequency of the sampling signal and the repetition frequency of the sampled signal by controlling the output frequency of the microwave source, so that equivalent sampling is performed.
3. The method of claim 1, wherein the frequency components of the non-pulsed sampled optical signal are:
Figure FDA0002152066610000013
the frequency components of the sampled optical signal are:
Figure FDA0002152066610000014
wherein: f. ofs0And fd0Respectively the center frequency, f, of the optical carriersAnd fdIn order to be able to repeat the frequency,
Figure FDA0002152066610000015
and
Figure FDA0002152066610000016
are complex coefficients of the corresponding frequency components.
4. The method of claim 1, wherein the raw sampling result with the radio frequency carrier is:
Figure FDA0002152066610000017
wherein: Δ f0＝fd0-fs0，Δf＝fd-fsWhich may be considered to be the center frequency and repetition frequency, respectively, of the original sampling result, the bandwidth and repetition frequency of the sampled signal are compressed by a factor of k,
Figure FDA0002152066610000018
when the sampling signal is an ultrashort pulse generated by a mode-locked laser,
Figure FDA0002152066610000019
the sampled signal can be directly recovered as a constant of equal strength and 0 in phase.
5. The method of claim 1, wherein the compensation signal is obtained by performing a conventional linear optical sampling technique based on a mode-locked laser on the non-pulse sampled optical signal, and specifically comprises:
Figure FDA00021520666100000110
6. the method of claim 1, wherein the demodulation result is
Figure FDA0002152066610000021
7. The method of claim 2, wherein said frequency difference is Δ f ═ fd-fsThe difference between the repetition frequency of the non-pulse sampling optical signal and the repetition frequency of the sampled optical signal is inversely proportional to the equivalent sampling rate and directly proportional to the time actually consumed by the sampling, and the repetition frequency f of the sampled optical signal isdUnder certain conditions, the frequency f of the output signal of the microwave source in the optical sampling module can be specifically controlledsAnd (5) controlling.
8. The method as claimed in claim 2, wherein the laser carrier of the same source is obtained by dividing the single-frequency laser generated by the laser into two paths by the fiber coupler, one path enters the electro-optical modulator, and the other path is used as the local light for coherent reception.
9. The method as claimed in claim 2, wherein the dual drive mach-zehnder modulator modulates the local light, and is driven by the radio frequency signal output from the microwave source amplified by the electrical amplifier to generate the electro-optically modulated optical frequency comb as the sampling light source.
10. The method of claim 9, wherein the local light uses another laser output when only intensity modulation is performed.
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