CN105049124A - Double-transmission synchronous-receiving transmission system suitable for DDO-OFDM (Direct-Detection Optical Orthogonal Frequency Division Multiplexing) and transmitting end thereof - Google Patents
Double-transmission synchronous-receiving transmission system suitable for DDO-OFDM (Direct-Detection Optical Orthogonal Frequency Division Multiplexing) and transmitting end thereof Download PDFInfo
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- CN105049124A CN105049124A CN201510456963.7A CN201510456963A CN105049124A CN 105049124 A CN105049124 A CN 105049124A CN 201510456963 A CN201510456963 A CN 201510456963A CN 105049124 A CN105049124 A CN 105049124A
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Abstract
The invention provides a double-transmission synchronous-receiving transmission system suitable for DDO-OFDM (Direct-Detection Optical Orthogonal Frequency Division Multiplexing) and capable of realizing small fading at a receiving end, and a transmitting end thereof. Optical carriers output by an optical carrier generating unit at the transmitting end are two beams of laser with different center frequencies; a photoelectric detector at the receiving end is used for receiving two paths of optical signals with different center frequencies and outputting two paths of electric signals with different frequencies; and a digital signal processor is used for realizing power fading complementation by means of overlapping of two paths of signals output by the photoelectric detector. At the transmitting end, the same OFDM signals are modulated with double wavelengths, and subsequently transmitted in the same optical fiber. At the receiving end, the photoelectric detector is used for performing photoelectric conversion. Since fading of signal power is relevant to the wavelengths of the optical carriers, the received modulated signals of different center wavelengths encounter power fading on different frequency points in order that respective fading positions after fading are complemented. Thus, the overall transmission performance of the system is improved, and frequency selective fading caused by chromatic dispersion is effectively resisted.
Description
Technical field
The present invention relates to optical communication technique, particularly the compensation technique of the frequency selective fading of Received signal strength in fiber optic transmission system.
Background technology
In general, the fibre core relatively thin (9/125) of the monomode fiber used in optical fiber telecommunications system, transmission frequency bandwidth, capacity are large, and transmission range is longer.Along with the increasing of transmission range, the dispersion of accumulation can cause symbol time delay thus cause frequency selective fading.Multimode fiber fibre core thick (50/125 or 62.5/125), multiple pattern is allowed to transmit in a fiber, but inter-modal dispersion limits transmission range and the bandwidth of multimode fiber, and the chromatic dispersion in multimode fiber and inter-modal dispersion can cause symbol time delay equally, then cause frequency selective fading.Orthogonal frequency division multiplex OFDM technology has excellent resisting chromatic dispersion and frequency selective fading ability.
Current fiber optic transmission system proposes the various fiber optic transmission system based on OFDM modulation technology.Wherein, based on the OFDM DDO-OFDM system of Direct-detection Optical, there is the advantage that structural design is simple, cost is low, make it have more wide application, in short distance single mode fiber link and multimode fiber transmission, shown expected effect especially.
In traditional Linear Mapping DDO-OFDM system, the signal spectrum of transmitter output be the OFDM frequency spectrum of double-side band linearly copy an additional light carrier, the double-sideband signal now transmitted in a fiber can bring chromatic dispersion problem equally.After direct detection, the power of double-sideband modulation signal is the cosine function of optical carrier wavelength, dispersion, transmission range etc.Along with the change of optical carrier wavelength, dispersion, transmission range etc., the position of signal power decline point also changes thereupon, causes the Selective intensity of different frequency, as shown in Figure 1.
In order to improve system transfers performance, existing method adds dispersion compensation, as high dispersion compensating fiber technology, chirped fiber gratings technology, dispersion compensating filter and front/rearly put dispersion compensation technology etc.These modes had both added overall system cost, too increased the insertion loss of system, or increased the technical sophistication degree of system.Generally dispersion compensation technology is not adopted in short distance and low cost transmission system.
Summary of the invention
Technical problem to be solved by this invention is, the DDO-OFDM transmitting terminal providing a kind of receiving terminal can obtain the Received signal strength of less decline and comprise this transmitting terminal two send out collecting/transmitting system same.
The present invention for solving the problems of the technologies described above adopted technical scheme is, be applicable to the transmitting terminal of DDO-OFDM, comprise OFDM signal generation unit, optical modulator, light carrier generation unit, the output of described ofdm signal generation unit is connected with the modulation signal input of light I/Q modulator, the output of light carrier generation unit is connected with the carrier signal input of light I/Q modulator, and the modulated signal output of light I/Q modulator is connected with optical fiber;
It is characterized in that, the light carrier that described light carrier generation unit exports is two bundle different center frequency laser.
What be applicable to DDO-OFDM two sends out collecting/transmitting system same, and comprise above-mentioned transmitting terminal, receiving terminal, optical fiber, transmitting terminal is connected with receiving terminal by optical fiber; Receiving terminal comprises photodetector, digital signal processor, and the input of photodetector is connected with optical fiber, and the output of photodetector is connected with digital signal processor input, and photodetector carries out direct detection to the light signal received;
The photodetector of described receiving terminal receives the signal of telecommunication of the light signal output two-way different frequency of two-way different center frequency simultaneously, and digital signal processor realizes power fading complementation by the two paths of signals that superimposed light electric explorer exports.
The present invention modulates identical ofdm signal at transmitting terminal dual wavelength, transmits subsequently in same optical fiber, and receiving terminal photodetector carries out opto-electronic conversion.Because the decline of signal power is relevant to optical carrier wavelength, therefore, the different centre wavelength modulation signals received decline at different frequency point place emergent power, decline position respective after superposing is realized complementary, thus the total transmission performance of elevator system, effectively resist the frequency selective fading that dispersion causes.
The invention has the beneficial effects as follows, compared with existing DDO-OFDM system, under additionally not increasing Digital Signal Processing DSP complexity, without the need to dispersion compensation module, realize the performance boost of frequency selective fading lower channel, thus guarantee the Quality of recovery of Received signal strength.
Accompanying drawing explanation
Fig. 1 is existing Single wavelength modulating system received signal power distribution map.
Fig. 2 is invention transmission system transmitting terminal signal spectrum figure.
Fig. 3 is transmission system received signal power distribution map of the present invention.
The system block diagram that Fig. 4 (a), (b) are two kinds of Different Light forms in embodiment.
Embodiment
The present invention is two sends out collecting/transmitting system same, and comprise transmitting terminal, receiving terminal, optical fiber, transmitting terminal is connected with receiving terminal by optical fiber;
Transmitting terminal comprises the orthogonal in the same way I/Q modulator of OFDM signal generation unit, light, light carrier generation unit, the output of described ofdm signal generation unit is connected with the modulation signal input of light I/Q modulator, the output of light carrier generation unit is connected with the carrier signal input of light I/Q modulator, and the modulated signal output of light I/Q modulator is connected with optical fiber; The light carrier that light carrier generation unit exports is two bundle different center frequency laser, and the priori of the frequency selective fading that the frequency interval of 2 wavelength lasers can be tested according to reality is arranged.
Receiving terminal comprises photodetector, and photodetector is connected with optical fiber, and photodetector carries out direct detection to the light signal received.
In dual wavelength modulation transmission system of the present invention, to modulate identical ofdm signal in the transmitting terminal optical wavelength at about 100GHz interval, signal spectrum after modulation as shown in Figure 2, then transmits in same optical fiber, directly carries out opto-electronic conversion with photodetector at receiving terminal.Now, system can be regarded as the superposition of the signal after two single-carrier modulated, because optical carrier wavelength is different, make the signal after modulating not identical at the decline point of high band, realize complementary after superposition on respective decline position, thus promote overall performance, result as shown in Figure 3.Due to dispersion, the signal on different carrier can experience different time delays, can do corresponding compensation deals in the DSP of receiver.And use OFDM modulation, using making these compensation deals become a kind of special circumstances as Multipath Transmission, become simpler.
In order to the transmitting terminal realizing dual wavelength modulation can use following two kinds of forms:
Scheme one:
As shown in Fig. 4 (a), light carrier generation unit comprises 2 single-mode lasers, couplers, and the output of 2 single-mode lasers is connected with the input of coupler, the laser of the different center frequency of 2 single-mode laser outputs.What single-mode laser here adopted is adjustable single mode band isolation laser device.
Two adjustable single mode band isolation laser devices are as light source, and Output of laser frequency phase-difference is about 100GHz, and Output of laser live width is narrower;
The laser of two adjustable single mode band isolation laser device outputs is coupled through three-dB coupler;
The laser that three-dB coupler exports is connected with light I/Q modulator, and the radiofrequency signal of light I/Q modulator is the OFDM radiofrequency signal that array waveguide grating AWG exports;
Signal after the modulation that light I/Q modulator exports enters single mode/multimode fiber SMF/MMF and transmits;
The other end of single mode/multimode fiber is connected with photoelectric detector, carries out direct-detection;
Photoelectric detector output is connected with digital signal processor, the transfer function such as demodulation, judgement of settling signal.
Scheme two:
As shown in Fig. 4 (b), light carrier generation unit is two-frequency laser.
At present, two-frequency laser is widely used in technical fields such as millimeter wave and optical interference measurements.Conventional two-frequency laser is the He-Ne laser based on longitudinal Zeeman effect, and its frequency difference is less than 3MHz, is called little frequency difference, and birefringence double-frequency laser frequency difference is greater than 40MHz, is called large frequency-difference.Compared with He-Ne laser, Nd: the gain bandwidth of YAG laser is generally 150GHz ~ 180GHz, now becomes study hotspot, and various countries' researcher proposes multiple double frequency Nd in succession: YAG laser research approach.In addition, existing distributed feedback double-bus network double frequency semiconductor laser can obtain the very-large frequency difference of tens GHz to GHz up to a hundred, and frequency difference is tunable, and this makes two-frequency laser be applied to optical fiber communication becomes possibility.
With very-large frequency difference two-frequency laser as light source, two-frequency laser exports the laser of two bundle frequency interval number 100GHz as light carrier, and two bundle laser linewidths of output are narrower;
Two-frequency laser is connected with light I/Q modulator, and the radiofrequency signal of light I/Q modulator is the ofdm signal that AWG exports;
Signal after the modulation that light I/Q modulator exports enters single mode/multimode fiber and transmits;
The other end of single mode/multimode fiber is connected with photoelectric detector, carries out direct-detection;
Photoelectric detector output is connected with digital signal processor, the transfer function such as demodulation, judgement of settling signal.
Claims (8)
1. be applicable to the transmitting terminal of DDO-OFDM, comprise OFDM signal generation unit, optical modulator, light carrier generation unit, the output of described ofdm signal generation unit is connected with the modulation signal input of optical modulator, the output of light carrier generation unit is connected with the carrier signal input of optical modulator, and the modulated signal output of optical modulator is connected with optical fiber;
It is characterized in that, the light carrier that described light carrier generation unit exports is two bundle different center frequency laser.
2. be applicable to the transmitting terminal of DDO-OFDM as claimed in claim 1, it is characterized in that, described light carrier generation unit is two-frequency laser.
3. be applicable to the transmitting terminal of DDO-OFDM as claimed in claim 1, it is characterized in that, described light carrier generation unit comprises 2 single-mode lasers, couplers, and the output of 2 single-mode lasers is connected with the input of coupler, the laser of the different center frequency of 2 single-mode laser outputs.
4. be applicable to the transmitting terminal of DDO-OFDM as claimed in claim 3, it is characterized in that, described single-mode laser is adjustable single mode band isolation laser device.
5. what be applicable to DDO-OFDM two sends out collecting/transmitting system same, and comprise transmitting terminal, receiving terminal, optical fiber, transmitting terminal is connected with receiving terminal by optical fiber;
Described transmitting terminal comprises OFDM signal generation unit, optical modulator, light carrier generation unit, the output of described ofdm signal generation unit is connected with the modulation signal input of optical modulator, the output of light carrier generation unit is connected with the carrier signal input of optical modulator, and the modulated signal output of optical modulator is connected with optical fiber;
Receiving terminal comprises photodetector, digital signal processor, and the input of photodetector is connected with optical fiber, and the output of photodetector is connected with the output of digital signal processor, and photodetector carries out direct detection to the light signal received;
It is characterized in that, the light carrier that described light carrier generation unit exports is two bundle different center frequency laser;
The photodetector of described receiving terminal receives the signal of telecommunication of the light signal output two-way different frequency of two-way different center frequency simultaneously, and digital signal processor realizes power fading complementation by the two paths of signals that superimposed light electric explorer exports.
6. what be applicable to DDO-OFDM as claimed in claim 5 two sends out collecting/transmitting system same, and it is characterized in that, described light carrier generation unit is two-frequency laser.
7. what be applicable to DDO-OFDM as claimed in claim 5 two sends out collecting/transmitting system same, it is characterized in that, described light carrier generation unit comprises 2 single-mode lasers, couplers, the output of 2 single-mode lasers is connected with the input of coupler, the laser of the different center frequency of 2 single-mode laser outputs.
8. what be applicable to DDO-OFDM as claimed in claim 7 two sends out collecting/transmitting system same, and it is characterized in that, described single-mode laser is adjustable single mode band isolation laser device.
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| CN201510456963.7A CN105049124B (en) | 2015-07-30 | 2015-07-30 | Double hairs suitable for DDO-OFDM are the same as collecting/transmitting system and its transmitting terminal |
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| CN201510456963.7A CN105049124B (en) | 2015-07-30 | 2015-07-30 | Double hairs suitable for DDO-OFDM are the same as collecting/transmitting system and its transmitting terminal |
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Cited By (4)
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| CN106788735A (en) * | 2016-12-12 | 2017-05-31 | 南京理工大学 | Tunable true time delay experimental provision and method based on discrete chirped fiber grating |
| CN111342899A (en) * | 2020-03-23 | 2020-06-26 | 电子科技大学 | Optical fiber conjugate phase-stable transmission method |
| WO2021147957A1 (en) * | 2020-01-23 | 2021-07-29 | 中国移动通信有限公司研究院 | Optical signal transmission method, apparatus, and device |
| CN114296033A (en) * | 2021-12-23 | 2022-04-08 | 中国电子科技集团公司第十四研究所 | Light-operated receiving beam forming method and device |
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Cited By (7)
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| CN106788735A (en) * | 2016-12-12 | 2017-05-31 | 南京理工大学 | Tunable true time delay experimental provision and method based on discrete chirped fiber grating |
| CN106788735B (en) * | 2016-12-12 | 2019-03-05 | 南京理工大学 | Tunable true delay experimental provision and method based on discrete chirped fiber grating |
| WO2021147957A1 (en) * | 2020-01-23 | 2021-07-29 | 中国移动通信有限公司研究院 | Optical signal transmission method, apparatus, and device |
| CN111342899A (en) * | 2020-03-23 | 2020-06-26 | 电子科技大学 | Optical fiber conjugate phase-stable transmission method |
| CN111342899B (en) * | 2020-03-23 | 2022-09-06 | 电子科技大学 | Optical fiber conjugate phase-stable transmission method |
| CN114296033A (en) * | 2021-12-23 | 2022-04-08 | 中国电子科技集团公司第十四研究所 | Light-operated receiving beam forming method and device |
| CN114296033B (en) * | 2021-12-23 | 2024-02-27 | 中国电子科技集团公司第十四研究所 | Light-operated receiving beam forming method and device |
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