Method and system for transmitting and recovering half-bandwidth single-sideband optical signals

Abstract

The present invention provides a method and system for transmitting and recovering half-bandwidth single-sideband optical signals. The system includes a signal generation and construction module, which uses an intensity-modulated optical transmitter and a laser that transmits an unmodulated signal to construct a single-sideband signal to avoid the power fading problem caused by the interaction between optical fiber dispersion and square-law detection. In the signal receiving and processing module, 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 response to 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. The present invention uses a low-bandwidth device that cannot fully receive the optical signal spectrum and a recovery algorithm for half-bandwidth single-sideband signals to accurately recover the single-sideband signal. The method and system involve the optimization of the entire process from signal generation and construction to reception and 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] Intensity-modulated direct detection systems (IMD) have recently gained widespread adoption in short-haul optical communications due to their low cost. With the increasing volume of transmitted data and the diversification of transmission scenarios, the requirements for baud rates and transmission distances in short-haul optical communication systems continue to rise. However, as signal baud rates and transmission distances increase, the problem of chromatic dispersion and power fading introduced by optical fibers becomes increasingly prominent in direct detection systems, seriously impacting accurate signal reception. Therefore, overcoming chromatic dispersion and power fading in IMD DDM systems using low-cost components and systems has become a key issue.

[0003] Due to their spectral asymmetry, single-sideband systems naturally have the ability to overcome dispersion power fading. Currently, there are two main methods for generating single-sideband signals. One is to add a digital domain carrier outside the signal spectrum. This method requires a complex signal modulator to generate a carrier at a high frequency to produce the single-sideband signal. The carrier power and guard interval of the resulting single-sideband signal can be flexibly set in the digital signal processing at the transmitting end to obtain an optimal single-sideband signal. However, to meet the requirements of the single-sideband signal recovery algorithm, the added digital domain carrier power is often large. This results in the quantization accuracy of the digital-to-analog converter being wasted during the digital-domain carrier conversion, resulting in reduced accuracy of the actual signal. To meet the required signal accuracy, the number of quantization bits of the digital-to-analog converter must be increased, and the complex signal modulator increases hardware complexity.

[0004] Another approach involves adding an optical carrier outside the signal spectrum. This method uses an additional laser to generate an optical carrier outside the signal spectrum, thereby forming a single-sideband signal. This solution avoids the loss of precision in digital-to-analog conversion and allows for flexible adjustment of the carrier power by adjusting the laser power to meet the requirements of the single-sideband signal recovery algorithm. However, it requires a complex signal modulator, which increases hardware costs.

[0005] Through searching patent documents, it was found that the invention patent with publication number CN106533573A discloses an asymmetric twin single-sideband modulation and demodulation method and system. The transmitting end of this patent includes: a transmitting end Nyquist filter module, 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 up-conversion, the baud rate of one sideband of the left band and the right band is less than or equal to the transmitting end device bandwidth, and the baud rate of the other sideband is less than or equal to the transmitting end device bandwidth 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 filtering out the right band through optical filtering; for the right band: basically filtering out the left band through optical filtering, ensuring 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 receiving end Nyquist filter module, 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 response to the above-mentioned problems in the prior art, researching a method and system for transmitting and recovering half-bandwidth single-sideband optical signals 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, the present invention aims to provide a method and system for transmitting and recovering a half-bandwidth single-sideband optical signal.

[0008] According to the present invention, a method for transmitting a half-bandwidth single-sideband optical signal 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] In step S3, another laser is used 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. 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.

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

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

[0014] Step S1.2: Take 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: Process the incompletely recovered single sideband signal and strength signal, and reconstruct the strength signal of the single sideband signal using carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm 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, shift the carrier of the incompletely recovered single-sideband signal to zero frequency and filter 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 it from the angle of 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: Take the conjugate square of the single-carrier signal, up-convert it to a certain frequency f2, and take the real part to obtain the signal-signal crosstalk;

[0031] Step M3.5, subtracting the signal-to-signal beat frequency crosstalk from the intensity signal obtained in step M1 to reconstruct the 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: Repeat steps M3.1 to M3.6 in sequence, using the SSB signal obtained in the previous round as input in each cycle. When the number of repetitions reaches the preset number, the obtained SSB signal is used as the accurate SSB 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 frequency f2 is determined by the frequency difference between the carrier and the optical carrier, and is calculated based on the signal bandwidth 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-converts the baseband complex modulated signal to obtain a real-valued signal with a guard interval at zero frequency and conjugate symmetry about zero frequency. The real-valued signal is electro-optically converted through an intensity modulator to generate an optical signal with a certain carrier at zero frequency. Another laser is used to generate a carrier in the optical domain as the carrier of the single-sideband signal, ensuring that the carrier has a guard interval with the optical signal in the spectral position. The carrier in the optical domain is coupled to the optical signal through an optical coupler to form a single-sideband optical signal, which is then sent into the optical fiber for transmission.

[0041] Signal receiving and processing module: Receives the single-sideband optical signal through a photodetector and an analog-to-digital converter to obtain the high-frequency attenuated intensity electrical signal corresponding to the single-sideband optical signal; uses a single-sideband signal recovery algorithm to convert the high-frequency attenuated intensity electrical signal to obtain an incompletely recovered single-sideband signal; processes the incompletely recovered single-sideband signal and the intensity signal, and uses carrier-assisted phase recovery and half-bandwidth single-sideband signal recovery algorithms to reconstruct the intensity signal of the single-sideband signal, 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 uses a carrier in an additional optical domain to form a single-sideband signal, which solves the problem of the signal being affected by dispersion power fading in optical fiber transmission, thereby 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 insufficient bandwidth of the receiving device leading to decreased bit error performance, 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 upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0047] Figure 1 The figure 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 will be described in detail below with reference to specific embodiments. The following examples 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 skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0049] The present invention is aimed at low-cost direct detection systems. At the transmitting end, a single-sideband (SSB) signal is constructed using an intensity-modulated optical transmitter and a laser emitting an unmodulated signal to avoid power fading caused by the interaction between fiber dispersion and square-law detection. At the receiving end, the optical signal undergoes optoelectronic conversion, which is limited by the device bandwidth. This can disrupt the relationship between the output electrical signal and the corresponding input SSB optical signal. To address this issue, the present invention employs a novel digital signal processing method to reconstruct the intensity-modulated signal within the original SSB optical signal to restore the original signal.

[0050] The present invention aims 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 half-bandwidth single-sideband signal recovery algorithm. The method and system involve optimizing the entire process from signal generation and construction (transmission) to reception processing (recovery).

[0051] Example 1:

[0052] Figure 1 The figure 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 transmitting 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 having a guard interval at zero frequency and being conjugate symmetric about the zero frequency.

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

[0056] In step S1.1, a single-carrier complex signal s(t) is generated. The center frequency of the complex signal is shifted to f1 by up-conversion. The up-converted signal has a certain protection bandwidth with 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] In step S1.2, the real part of the up-converted signal is taken to obtain a subcarrier multiplexing signal that is 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 by an intensity modulator to generate an optical signal having a certain carrier at zero frequency.

[0063] In step S3, another laser is used 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. 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.

[0064] Example 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: Process the incompletely recovered single sideband signal and strength signal, and reconstruct the strength signal of the single sideband signal using carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm, thereby obtaining a recovered single carrier signal.

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

[0071] Step M3.1, shift the carrier of the incompletely recovered single-sideband signal to zero frequency and filter 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 it from the angle of 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] In step M3.4, conjugate and square the single-carrier signal, up-convert it to a certain frequency f2, and take the real part to obtain the signal-to-signal crosstalk. The expression of the signal-to-signal crosstalk is as follows:

[0075]

[0076] Wherein, the frequency f2 is determined by the frequency difference between the carrier and the optical carrier, and is calculated using the signal bandwidth and two guard intervals.

[0077] In step M3.5, the intensity signal obtained in step M1 is subtracted from the signal-signal beat frequency crosstalk 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, using 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] Example 3:

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

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

[0085] Signal generation and construction module: Up-convert the baseband complex modulated signal to obtain a real-valued signal with a guard interval at zero frequency and conjugate symmetry about zero frequency; the real-valued signal is electro-optically converted through an intensity modulator to generate an optical signal with a certain carrier at zero frequency; another laser is used 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 in the spectral position; the carrier in the optical domain is coupled to the optical signal through an optical coupler to form a single-sideband optical signal, and then sent into the optical fiber for transmission.

[0086] Signal receiving and processing module: Receives the single-sideband optical signal through a photodetector and an analog-to-digital converter to obtain the high-frequency attenuated intensity electrical signal corresponding to the single-sideband optical signal; uses a single-sideband signal recovery algorithm to convert the high-frequency attenuated intensity electrical signal to obtain an incompletely recovered single-sideband signal; processes the incompletely recovered single-sideband signal and the intensity signal, and uses carrier-assisted phase recovery and half-bandwidth single-sideband signal recovery algorithms to reconstruct the intensity signal of the single-sideband signal, thereby obtaining a recovered single-carrier signal.

[0087] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention 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 a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0088] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

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; The step S1 includes the following sub-steps: Step S1.1, generate a single-carrier complex signal , using up-conversion to move the center frequency of the complex signal to At, the up-converted signal is obtained, the up-converted signal The expression is as follows: By adjusting the center frequency Control the size of the protection bandwidth; Step S1.2, taking the real part of the up-converted signal to obtain a subcarrier multiplexing signal symmetrical about zero frequency, wherein the expression of the subcarrier multiplexing signal is as follows: Among them, the center frequency Greater than signal bandwidth; 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; In step S3, another laser is used 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 a spectral position. The carrier in the optical domain is coupled with the optical signal through an optical coupler to form a single-sideband optical signal, and the signal is sent into the optical fiber for transmission.

2. A method for recovering a half-bandwidth single-sideband optical signal, for recovering the half-bandwidth single-sideband optical signal according to claim 1, 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 signal corresponding to the single-sideband optical signal; Step M2, converting the high-frequency attenuated intensity signal using a single-sideband signal recovery algorithm to obtain an incompletely recovered single-sideband signal; Step M3: Process the incompletely recovered single sideband signal and the intensity signal, and reconstruct the intensity signal of the single sideband signal using a carrier-assisted phase recovery and half-bandwidth single sideband signal recovery algorithm to obtain a recovered single carrier signal. The step M3 includes the following sub-steps: Step M3.1, shifting the carrier of 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 the conjugate angle of the phase noise and 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: shift 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 and up-convert it to a certain frequency. At , take the real part and get the signal-signal beat frequency crosstalk; Step M3.5, subtracting the signal-to-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: Repeat steps M3.1 to M3.6 in sequence, using the SSB signal obtained in the previous round as input in each cycle. When the number of repetitions reaches the preset number, the obtained SSB signal is used as the accurate SSB signal; Step M3.8: Shift the precise single-sideband signal to zero frequency to obtain a recovered single-carrier signal.

3. The method for recovering a half-bandwidth single-sideband optical signal according to claim 2, wherein: 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.

4. The method for recovering a half-bandwidth single-sideband optical signal according to claim 2, wherein: In step M3.4, the expression of the signal-signal beat frequency crosstalk is as follows: Where, frequency The size of is determined by the frequency difference between the carrier and the optical carrier, and is calculated using the signal bandwidth and two guard intervals.

5. The method for recovering a half-bandwidth single-sideband optical signal according to claim 2, wherein: In step M3.7, the preset number of times is within 10.

6. A half-bandwidth single-sideband optical signal transmission and recovery system, used to implement the half-bandwidth single-sideband optical signal transmission method of claim 1 and the half-bandwidth single-sideband optical signal recovery method of claim 2, characterized in that: include: Signal generation and construction module: Up-converts the baseband complex modulated signal 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 guard interval with the optical signal at a spectral position, 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; The signal receiving and processing module receives the single-sideband optical signal through a photodetector and an analog-to-digital converter to obtain a high-frequency attenuated intensity signal corresponding to the single-sideband optical signal; converts the high-frequency attenuated intensity signal using a single-sideband signal recovery algorithm to obtain an incompletely recovered single-sideband signal; processes the incompletely recovered single-sideband signal and the intensity signal, and reconstructs the intensity signal of the single-sideband signal using a carrier-assisted phase recovery and half-bandwidth single-sideband signal recovery algorithm, thereby obtaining a recovered single-carrier signal.

Images