Method and system for sending and recovering half-bandwidth single-sideband optical signal

Abstract

The invention provides a method and a system for transmitting and recovering a half-bandwidth single-sideband optical signal. The system comprises a signal generation and construction module which constructs a single side band signal by using an intensity modulation optical transmitter and a laser for transmitting an unmodulated signal so as to avoid the problem of power fading caused by interaction of optical fiber dispersion and square law detection. According to the signal receiving and processing module, optical signals are limited by device bandwidth when subjected to photoelectric conversion, the relation between output electric signals and correspondingly input single-side-band optical signals can be destroyed, a new digital signal processing method is designed for the situation, and by reconstructing intensity modulation signals in the original single-side-band optical signals, the single-side-band optical signals can be converted into the single-side-band optical signals, and the single-side-band optical signals can be converted into the single-side-band optical signals. And the original signal is recovered. The invention discloses a method and a system for accurately recovering a single side band signal by utilizing a low-bandwidth device incapable of completely receiving an optical signal spectrum and a recovery algorithm of a half-bandwidth single side band signal, and relates to optimization of the whole process from signal generation and construction to receiving processing.

Description

Technical Field

[0001] The present invention relates to the field of optical communication transmission technology, and in particular to a method and system for sending and recovering a half-bandwidth single-sideband optical signal. Background Art

[0002] Recently, intensity modulated direct detection systems have been widely used in short-distance optical communication scenarios due to their low cost advantages. With the increase in the amount of transmitted data and the diversification of transmission scenarios, people's requirements for the baud rate and transmission distance of short-distance optical communication systems continue to increase. However, when the signal baud rate and transmission distance increase, the dispersion power fading problem introduced by the optical fiber becomes more and more prominent in the direct detection system, seriously affecting the accurate reception of the signal. Therefore, how to use low-cost devices and systems to overcome the dispersion power fading in the intensity modulated direct detection system becomes the key.

[0003] Due to its spectrum asymmetry, the single-sideband system naturally has the ability to overcome dispersion power fading. There are currently two main ways to generate single-sideband signals. One is to add a carrier in the digital domain outside the signal spectrum. This method requires the use of a complex signal modulator to generate a carrier at a high frequency to generate a single-sideband signal. The carrier power and protection interval of the single-sideband signal formed can be flexibly set in the digital signal processing at the transmitting end to obtain the optimal single-sideband signal. However, in order to meet the requirements of the single-sideband signal recovery algorithm, the loaded digital domain carrier power is often large, which will cause the quantization accuracy of the digital-to-analog converter to be wasted by the digital domain carrier during digital-to-analog conversion, making the accuracy of the actual signal worse. If the signal accuracy requirements are to be met, the number of quantization bits of the digital-to-analog converter needs to be increased, and the complex signal modulator will increase the hardware complexity.

[0004] The other method is to add a carrier in the optical domain outside the signal spectrum. This method uses an additional laser to generate a carrier in the optical domain outside the signal spectrum to form a single-sideband signal. This solution can avoid the problem of precision being wasted in digital-to-analog conversion, and can flexibly adjust the carrier power by adjusting the laser power to meet the requirements of the single-sideband signal recovery algorithm, but it requires a complex signal modulator, which has higher hardware costs.

[0005] By searching the patent literature, it is found that the invention patent with the publication number of CN106533573A discloses an asymmetric twin single-sideband modulation and demodulation method and system. The transmitting end of the patent includes: a Nyquist filter module at the transmitting end, which is used to filter the left band and the right band; an up-conversion module, which is used to up-convert the signal respectively, wherein after the up-conversion, the baud rate of one sideband of the left band and the right band is less than or equal to the bandwidth of the transmitting end device, and the baud rate of the other sideband is less than or equal to the bandwidth of the transmitting end device minus the protection interval; a Hilbert filter module, which is used to filter the signal processed by the up-conversion module to obtain an asymmetric twin single-sideband signal; the receiving end includes: an optical filter module, for the left band: completely filter out the right band through optical filtering; for the right band: basically filter out the left band through optical filtering, and ensure that the residual left band width is less than the protection interval; a down-conversion module, which is used to down-convert the signal; and a Nyquist filter module at the receiving end, which is used to perform Nyquist filtering on the signal. This patent does not fully solve problems such as dispersion and bit error rate, and requires a complex signal modulator, so its application scenarios are less targeted.

[0006] In summary, in view of the above problems of the prior art, studying a method and system for sending and recovering a half-bandwidth single-sideband optical signal has become a key task that needs to be solved urgently. Summary of the invention

[0007] In view of the defects in the prior art, an object of the present invention is to provide a method and system for transmitting and recovering a half-bandwidth single-sideband optical signal.

[0008] A method for transmitting a half-bandwidth single-sideband optical signal according to the present invention comprises the following steps:

[0009] Step S1, up-converting the complex modulated signal of the baseband to obtain a real-valued signal having a guard interval at zero frequency and being conjugate symmetric about zero frequency;

[0010] Step S2, performing electro-optical conversion on the real-valued signal through an intensity modulator to generate an optical signal with a certain carrier at zero frequency;

[0011] Step S3, use another laser to generate a carrier in the optical domain as the carrier of the single sideband signal, so that the carrier has a protection interval with the optical signal at the position of the spectrum, couple the carrier in the optical domain with the optical signal through an optical coupler to form a single sideband optical signal, and send it into the optical fiber for transmission.

[0012] Preferably, step S1 includes the following sub-steps:

[0013] Step S1.1, generating a single-carrier complex signal s(t), and moving the center frequency of the complex signal to f1 by up-conversion to obtain an up-converted signal;

[0014] Step S1.2, taking the real part of the up-converted signal to obtain a subcarrier multiplexed signal that is symmetrical about zero frequency.

[0015] Preferably, in step S1.1, the up-converted signal s1(t) is expressed as follows:

[0016]

[0017] The size of the protection bandwidth is controlled by adjusting the center frequency f1.

[0018] Preferably, in step S1.2, the expression of the subcarrier multiplexing signal is as follows:

[0019]

[0020] The center frequency f1 is greater than the bandwidth of the signal s(t).

[0021] The present invention also provides a method for recovering a half-bandwidth single-sideband optical signal, comprising the following steps:

[0022] Step M1, receiving the single sideband optical signal through a photodetector and an analog-to-digital converter to obtain a high frequency attenuated intensity electrical signal corresponding to the single sideband optical signal;

[0023] Step M2, using a single sideband signal recovery algorithm to convert the high frequency attenuated intensity electrical signal to obtain an incompletely recovered single sideband signal;

[0024] Step M3, processing the incompletely recovered single sideband signal and strength signal, using carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm to reconstruct the strength signal of the single sideband signal to obtain a recovered single carrier signal.

[0025] Preferably, in step M1, the response wavelength range of the photodetector is full-band, and the sampling frequency of the analog-to-digital converter is not less than three times the bandwidth of the single-sideband signal.

[0026] Preferably, step M3 includes the following sub-steps:

[0027] Step M3.1, shifting the carrier in the incompletely recovered single-sideband signal to zero frequency and filtering it through a low-pass filter to obtain the phase noise between the two lasers;

[0028] Step M3.2, conjugate the phase noise to obtain an angle, and then subtract the angle from the incompletely recovered single sideband signal to obtain an incompletely recovered single sideband signal without phase noise;

[0029] Step M3.3, shift the incompletely recovered single-sideband signal without phase noise to zero frequency to obtain an incompletely recovered single carrier signal

[0030] Step M3.4, conjugate and square the single carrier signal, up-convert it to a certain frequency f2, take the real part, and obtain the signal-signal beat frequency crosstalk;

[0031] Step M3.5, subtracting the signal-signal beat frequency crosstalk from the intensity signal obtained in step M1 to reconstruct an intensity signal of the single sideband signal;

[0032] Step M3.6, converting the intensity signal into a single sideband signal using a single sideband signal recovery algorithm;

[0033] Step M3.7, repeating steps M3.1 to M3.6 in sequence, taking the single sideband signal obtained in the previous round as input in each cycle, and when the number of repetitions reaches a preset number, the obtained single sideband signal is taken as an accurate single sideband signal;

[0034] Step M3.8, shift the precise single sideband signal to zero frequency to obtain a recovered single carrier signal.

[0035] Preferably, in step M3.4, the expression of signal-signal beat frequency crosstalk is as follows:

[0036]

[0037] In the formula, the magnitude of frequency f2 is determined by the frequency difference between the carrier and the optical carrier, and is calculated by the bandwidth of the signal and two guard intervals.

[0038] Preferably, in step M3.7, the preset number of times is within 10 times.

[0039] The present invention also provides a half-bandwidth single-sideband optical signal transmission and recovery system, comprising:

[0040] Signal generation and construction module: Up-convert the complex modulated signal of the baseband to obtain a real-valued signal with a guard interval at zero frequency and conjugate symmetry about zero frequency; perform electro-optical conversion on the real-valued signal through an intensity modulator to generate an optical signal with a certain carrier at zero frequency; use another laser to generate a carrier in the optical domain as the carrier of the single-sideband signal, so that the carrier has a guard interval with the optical signal at the position of the spectrum, couple the carrier in the optical domain with the optical signal through an optical coupler to form a single-sideband optical signal, and send it into the optical fiber for transmission;

[0041] Signal receiving and processing module: The single-sideband optical signal is received through a photoelectric detector and an analog-to-digital converter to obtain a high-frequency attenuated intensity electrical signal corresponding to the single-sideband optical signal; the high-frequency attenuated intensity electrical signal is converted using a single-sideband signal recovery algorithm to obtain an incompletely recovered single-sideband signal; the incompletely recovered single-sideband signal and the intensity signal are processed, and the intensity signal of the single-sideband signal is reconstructed using a carrier-assisted phase recovery and a half-bandwidth single-sideband signal recovery algorithm, thereby obtaining a recovered single carrier signal.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention adopts a carrier in an additional optical domain to form a single-sideband signal, which solves the problem that the signal is affected by dispersion power fading in optical fiber transmission, thereby achieving the effect of increasing the transmission distance and bandwidth of the optical signal.

[0044] 2. The present invention adopts a carrier-assisted phase recovery method to solve the problem of phase noise introduced by using different lasers, thereby achieving the effect of reducing the bit error rate of the received signal and reducing the cost of the laser.

[0045] 3. The present invention adopts a half-bandwidth single-sideband signal recovery algorithm to solve the problem of reduced bit error performance caused by insufficient bandwidth of the receiving device, thereby achieving the effect of reducing the bit error rate of the received signal and the cost of the receiving device. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0047] Figure 1 The present invention is a schematic diagram of a method and system for transmitting and recovering a half-bandwidth single-sideband optical signal in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0049] The present invention is directed to a low-cost direct detection system. At the transmitting end, a single-sideband signal is constructed using an intensity modulated optical transmitter and a laser that transmits an unmodulated signal to avoid the power fading problem caused by the interaction between fiber dispersion and square-law detection. At the receiving end, the optical signal is limited by the bandwidth of the device when undergoing photoelectric conversion, which will destroy the relationship between the output electrical signal and the corresponding input single-sideband optical signal. In view of this situation, the present invention designs a new digital signal processing method to restore the original signal by reconstructing the intensity modulated signal in the original single-sideband optical signal.

[0050] The purpose of the present invention is to provide a method and system for accurately recovering single-sideband signals by avoiding dispersion power fading, utilizing a low-bandwidth device that cannot fully receive the optical signal spectrum and a recovery algorithm for a half-bandwidth single-sideband signal, involving the optimization of the entire process from signal generation and construction (sending) to receiving processing (recovery).

[0051] Embodiment 1:

[0052] Figure 1 The present invention is a schematic diagram of a method and system for transmitting and recovering a half-bandwidth single-sideband optical signal in an embodiment of the present invention.

[0053] like Figure 1 As shown, this embodiment provides a method for sending a half-bandwidth single-sideband optical signal, comprising the following steps:

[0054] Step S1, up-converting the complex modulated signal of the baseband to obtain a real-valued signal with a guard interval at zero frequency and conjugate symmetry about the zero frequency.

[0055] Specifically, step S1 includes the following sub-steps:

[0056] Step S1.1, generate a single-carrier complex signal s(t), and use up-conversion to move the center frequency of the complex signal to f1. The up-converted signal has a certain protection bandwidth with the zero frequency. The up-converted signal s1(t) is expressed as follows:

[0057]

[0058] The size of the protection bandwidth is controlled by adjusting the center frequency f1.

[0059] Step S1.2, taking the real part of the up-converted signal, and obtaining a subcarrier multiplexing signal symmetrical about zero frequency. The expression of the subcarrier multiplexing signal is as follows:

[0060]

[0061] In order to prevent the two subcarrier multiplexed signals from overlapping each other, the center frequency f1 is greater than the bandwidth of the signal s(t).

[0062] Step S2, the real-valued signal is subjected to electro-optical conversion through an intensity modulator to generate an optical signal with a certain carrier at zero frequency.

[0063] Step S3, use another laser to generate a carrier in the optical domain as the carrier of the single sideband signal, so that the carrier has a protection interval with the optical signal at the position of the spectrum, couple the carrier in the optical domain with the optical signal through an optical coupler to form a single sideband optical signal, and send it into the optical fiber for transmission.

[0064] Embodiment 2:

[0065] This embodiment provides a method for recovering a half-bandwidth single-sideband optical signal, comprising the following steps:

[0066] Step M1, receiving the single sideband optical signal through a photodetector and an analog-to-digital converter to obtain a high frequency attenuated intensity electrical signal corresponding to the single sideband optical signal.

[0067] In this embodiment, the response wavelength range of the photodetector is applicable to the entire wavelength band, and the sampling frequency of the analog-to-digital converter is optimal when it is not less than three times the bandwidth of the single-sideband optical signal.

[0068] Step M2: using a single sideband signal recovery algorithm to convert the high frequency attenuated intensity electrical signal to obtain an incompletely recovered single sideband signal.

[0069] Step M3, processing the incompletely recovered single sideband signal and strength signal, using carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm to reconstruct the strength signal of the single sideband signal, thereby obtaining a recovered single carrier signal.

[0070] Specifically, step M3 includes the following sub-steps:

[0071] Step M3.1, shifting the carrier in the incompletely recovered single-sideband signal to zero frequency and filtering it through a low-pass filter to obtain the phase noise between the two lasers;

[0072] Step M3.2, conjugate the phase noise to obtain an angle, and then subtract the angle from the incompletely recovered single sideband signal to obtain an incompletely recovered single sideband signal without phase noise;

[0073] Step M3.3, shift the incompletely recovered single-sideband signal without phase noise to zero frequency to obtain an incompletely recovered single carrier signal

[0074] Step M3.4, conjugate and square the single carrier signal, up-convert it to a certain frequency f2, take the real part, and obtain the signal-signal beat frequency crosstalk. The expression of the signal-signal beat frequency crosstalk is as follows:

[0075]

[0076] In the formula, the magnitude of frequency f2 is determined by the frequency difference between the carrier and the optical carrier, and is calculated by the bandwidth of the signal and the two guard intervals;

[0077] Step M3.5, subtract the signal-signal beat frequency crosstalk from the intensity signal obtained in step M1 to reconstruct the intensity signal of the single sideband signal.

[0078] Step M3.6, converting the intensity signal into a single sideband signal using a single sideband signal recovery algorithm;

[0079] Step M3.7, repeat steps M3.1 to M3.6 in sequence, and use the single sideband signal obtained in the previous round as input in each cycle. When the number of repetitions reaches the preset number, the obtained single sideband signal is used as the accurate single sideband signal.

[0080] In this embodiment, the preset number of times is generally 3 to 7 times for optimal performance, and can be flexibly adjusted within 10 times to achieve performance convergence.

[0081] Step M3.8, shift the precise single sideband signal to zero frequency to obtain a recovered single carrier signal.

[0082] Embodiment 3:

[0083] The present invention also provides a half-bandwidth single-sideband optical signal sending and recovery system. The half-bandwidth single-sideband optical signal sending and recovery system can be implemented by executing the process steps of the half-bandwidth single-sideband optical signal sending method and the half-bandwidth single-sideband optical signal recovery method. That is, those skilled in the art can understand the half-bandwidth single-sideband optical signal sending method and the half-bandwidth single-sideband optical signal recovery method as preferred implementations of the half-bandwidth single-sideband optical signal sending and recovery system.

[0084] The half-bandwidth single-sideband optical signal transmission and recovery system comprises:

[0085] Signal generation and construction module: Up-convert the complex modulated signal of the baseband to obtain a real-valued signal with a protection interval at zero frequency and conjugate symmetry about zero frequency; convert the real-valued signal into light through an intensity modulator to generate an optical signal with a certain carrier at zero frequency; use another laser to generate a carrier in the optical domain as the carrier of the single-sideband signal, so that the carrier has a protection interval with the optical signal at the position of the spectrum, couple the carrier in the optical domain with the optical signal through an optical coupler to form a single-sideband optical signal, and send it into the optical fiber for transmission.

[0086] Signal receiving and processing module: The single-sideband optical signal is received through a photoelectric detector and an analog-to-digital converter to obtain a high-frequency attenuated intensity electrical signal corresponding to the single-sideband optical signal; the high-frequency attenuated intensity electrical signal is converted using a single-sideband signal recovery algorithm to obtain an incompletely recovered single-sideband signal; the incompletely recovered single-sideband signal and the intensity signal are processed, and the intensity signal of the single-sideband signal is reconstructed using a carrier-assisted phase recovery and a half-bandwidth single-sideband signal recovery algorithm, thereby obtaining a recovered single carrier signal.

[0087] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0088] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for transmitting a half-bandwidth single-sideband optical signal, characterized in that: The steps include: Step S1, up-converting the complex modulated signal of the baseband to obtain a real-valued signal having a guard interval at zero frequency and being conjugate symmetric about zero frequency; Step S2, performing electro-optical conversion on the real-valued signal through an intensity modulator to generate an optical signal with a certain carrier at zero frequency; Step S3, using another laser to generate a carrier in the optical domain as the carrier of the single-sideband signal, so that the carrier has a protection interval with the optical signal at the position of the spectrum, and the carrier in the optical domain is coupled with the optical signal through an optical coupler to form a single-sideband optical signal, and is sent into the optical fiber for transmission.

2. The method for transmitting a half-bandwidth single-sideband optical signal according to claim 1, characterized in that: The step S1 includes the following sub-steps: Step S1.1, generating a single-carrier complex signal s(t), and moving the center frequency of the complex signal to f1 by up-conversion to obtain an up-converted signal; Step S1.2, taking the real part of the up-converted signal to obtain a subcarrier multiplexing signal that is symmetrical about zero frequency.

3. The method for transmitting a half-bandwidth single-sideband optical signal according to claim 2, characterized in that: In the step S1.1, the up-converted signal s1(t) is expressed as follows: The size of the protection bandwidth is controlled by adjusting the center frequency f1.

4. The method for transmitting a half-bandwidth single-sideband optical signal according to claim 2, characterized in that: In step S1.2, the expression of the subcarrier multiplexing signal is as follows: The center frequency f1 is greater than the bandwidth of the signal s(t).

5. A method for recovering a half-bandwidth single-sideband optical signal, characterized in that: The steps include: Step M1, receiving the single sideband optical signal through a photodetector and an analog-to-digital converter to obtain a high frequency attenuated intensity electrical signal corresponding to the single sideband optical signal; Step M2, converting the high frequency attenuated strength electrical signal using a single sideband signal recovery algorithm to obtain an incompletely recovered single sideband signal; Step M3, processing the incompletely recovered single sideband signal and the strength signal, using carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm to reconstruct the strength signal of the single sideband signal to obtain a recovered single carrier signal.

6. A method for recovering a half-bandwidth single-sideband optical signal according to claim 5, characterized in that: In the step M1, the response wavelength range of the photodetector is full-band, and the sampling frequency of the analog-to-digital converter is not less than three times the bandwidth of the single-sideband signal.

7. The method for recovering a half-bandwidth single-sideband optical signal according to claim 5, characterized in that: The step M3 includes the following sub-steps: Step M3.1, shifting the carrier in the incompletely recovered single-sideband signal to zero frequency, and filtering it through a low-pass filter to obtain the phase noise between the two lasers; Step M3.2, taking a conjugate angle of the phase noise, and then subtracting it from the angle of the incompletely recovered single sideband signal to obtain an incompletely recovered single sideband signal without phase noise; Step M3.3, shifting the incompletely recovered single sideband signal without phase noise to zero frequency to obtain an incompletely recovered single carrier signal Step M3.4, conjugate and square the single carrier signal, up-convert it to a certain frequency f2, take the real part, and obtain the signal-signal beat frequency crosstalk; Step M3.5, subtracting the signal-signal beat frequency crosstalk from the intensity signal obtained in step M1 to reconstruct an intensity signal of the single sideband signal; Step M3.6, converting the intensity signal into a single sideband signal using a single sideband signal recovery algorithm; Step M3.7, repeating steps M3.1 to M3.6 in sequence, taking the single sideband signal obtained in the previous round as input in each cycle, and when the number of repetitions reaches a preset number, the obtained single sideband signal is taken as an accurate single sideband signal; Step M3.8, shifting the precise single sideband signal to zero frequency to obtain a recovered single carrier signal.

8. A method for recovering a half-bandwidth single-sideband optical signal according to claim 7, characterized in that: In step M3.4, the expression of the signal-signal beat frequency crosstalk is as follows: In the formula, the magnitude of frequency f2 is determined by the frequency difference between the carrier and the optical carrier, and is calculated by the bandwidth of the signal and two guard intervals.

9. The method for recovering a half-bandwidth single-sideband optical signal according to claim 7, characterized in that: In the step M3.7, the preset number of times is within 10.

10. A half-bandwidth single-sideband optical signal transmission and recovery system, characterized in that: include: Signal generation and construction module: Up-convert the complex modulated signal of the baseband to obtain a real-valued signal with a guard interval at zero frequency and conjugate symmetry about zero frequency; The real-valued signal is subjected to electro-optical conversion by an intensity modulator to generate an optical signal having a certain carrier at zero frequency; Using another laser to generate a carrier in the optical domain as a carrier of a single sideband signal, so that the carrier has a protection interval with the optical signal at a position in the spectrum, coupling the carrier in the optical domain with the optical signal through an optical coupler to form a single sideband optical signal, and sending it into an optical fiber for transmission; Signal receiving and processing module: receiving the single-sideband optical signal through a photodetector and an analog-to-digital converter to obtain a high-frequency attenuated intensity electrical signal corresponding to the single-sideband optical signal; converting the high-frequency attenuated intensity electrical signal using a single-sideband signal recovery algorithm to obtain an incompletely recovered single-sideband signal; processing the incompletely recovered single-sideband signal and the intensity signal, reconstructing the intensity signal of the single-sideband signal using a carrier-assisted phase recovery and a half-bandwidth single-sideband signal recovery algorithm, thereby obtaining a recovered single carrier signal.

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