Complex double sideband signal direct detection method and system based on optical band reject filter

Abstract

The application provides a kind of based on optical band-stop filter complex double sideband signal direct detection method and system, the method and system are based on optical band-stop filter receiver in receiving end setting, the receiver is divided into two categories according to structure, one kind is based on optical band-stop filter and 90 degree mixer receiver, one kind is based on optical band-stop filter and 2x2 coupler receiver.The application is realized by setting optical band-stop filter to help complex double sideband signal optical field recovery, then square law detection is carried out using photoelectric detector to estimate SSBI, finally subtracts the estimated SSBI from the reconstructed complex signal.By the receiver, the SSBI caused by direct detection can be effectively suppressed, thereby realizing optical field recovery under low CSPR.Compared with the existing double sideband self-coherent method, the required CSPR is significantly reduced, and the OSNR sensitivity of the system is also significantly improved.

Description

Technical Field

[0001] This invention relates to the field of short-distance optical fiber communication technology, and in particular to a method and system for direct detection of complex double-sideband signals based on an optical bandstop filter. Background Technology

[0002] Driven by applications such as video-on-demand, cloud computing, embedded security, machine learning, and virtual reality, achieving high-speed transmission at low cost and low power consumption is receiving increasing attention and importance for data center interconnects and metropolitan area networks. Coherent detection has attracted widespread attention from researchers due to its excellent optical field recovery capabilities. Compared with traditional intensity modulation and direct detection schemes, optical field recovery can achieve higher spectral efficiency and sensitivity. Furthermore, by utilizing signal field information, digital signal processing (DSP) can mitigate various types of impairments during signal transmission. However, for cost-sensitive short-distance optical transmission, direct detection has a significant cost advantage. Therefore, direct detection technology with optical field recovery capabilities has received extensive research attention.

[0003] Self-coherent detection schemes, as a direct detection method capable of recovering the optical field of a signal with low complexity, have attracted widespread research attention. They primarily involve feeding a strong carrier wave and the information-bearing signal together into an optical fiber at the transmitting end, and then obtaining the desired signal through detection by a photodiode (PD) at the receiving end. Compared to coherent detection, it eliminates the need for an expensive local oscillator laser. Furthermore, since the carrier and signal originate from the same laser, the carrier / phase recovery stage in a digital signal processing unit (DSP) can be simplified. Based on the carrier's position relative to the information-bearing signal, self-coherent schemes can be divided into single-sideband self-coherent and double-sideband self-coherent schemes. Among them, double-sideband self-coherent schemes have received increasing research attention due to their ability to fully utilize bandwidth resources.

[0004] Over the past decade, researchers have proposed various double-sideband self-coherent detection schemes, including carrier-assisted differential detection, carrier-free phase reconstruction, asymmetric self-coherent detection, deep learning direct detection schemes, and carrier-assisted phase reconstruction. Compared with single-sideband self-coherent detection, these schemes have significantly improved spectral efficiency, but they also face new challenges. For example, carrier-assisted differential detection receivers have complex hardware structures and require a high carrier-to-signal power ratio (CSPR). For carrier-free phase reconstruction schemes, carrier-free detection necessitates thousands of iterations and the use of pilot symbols to reconstruct the phase. For asymmetric self-coherent detection, an even higher CSPR is required to reconstruct and eliminate signal-signal beat interference (SSBI). Deep learning direct detection schemes require machine learning for phase reconstruction, which is undesirable for cost-sensitive short-range optical transmission. For carrier-assisted phase reconstruction schemes, although the required CSPR is reduced, it is still greater than 0 dB. A lower CSPR implies a higher signal power ratio, resulting in better noise tolerance and improved optical signal-to-noise ratio (OSNR) sensitivity of the transmission system. Therefore, there is a great need for a double-sideband self-coherent detection scheme that can achieve signal optical field recovery at low CSPR and low cost. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method and system for direct detection of complex double-sideband signals based on an optical bandstop filter. This method utilizes an optical bandstop filter in the receiver to aid in the optical field recovery of the complex double-sideband signal. The primary function of the optical bandstop filter is to extract the complex double-sideband signal from the self-coherent signal (composed of a carrier wave and the complex double-sideband signal). A photodetector is then used for square-law detection to estimate the SSBI (Square-Side Bias Detection). Finally, the estimated SSBI is subtracted from the reconstructed complex signal. This receiver effectively suppresses SSBI caused by direct detection, thereby achieving optical field recovery at low CSPR (Cost Per Response Rate).

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] On the one hand, a method for direct detection of complex double-sideband signals based on an optical bandstop filter is provided, including the following steps:

[0008] At the transmitting end, a self-coherent electrical signal composed of a carrier wave and a complex double-sided charged signal is output through the transmitting end digital signal processing module; the self-coherent electrical signal is modulated into a self-coherent optical signal using IQ modulation and sent into a single-mode optical fiber;

[0009] At the receiving end, a receiver equipped with an optical band-stop filter receives the optical signal transmitted through the single-mode fiber, processes it to obtain a constructed complex signal, and demodulates the complex signal through the receiving end digital signal processing module to obtain the final bit sequence.

[0010] The receivers are divided into two categories based on their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler.

[0011] Preferably, the step of outputting a self-coherent electrical signal composed of a carrier wave and complex double-sided charged signals through the digital signal processing module at the transmitting end specifically includes:

[0012] The two independent pseudo-random binary sequences PRBS are mapped to two 16-QAM symbol sequences respectively;

[0013] The two symbol sequences are upsampled, with each symbol sequence being upsampled into eight samples. The pulses are then shaped using a raised cosine root RRC filter with a roll-off factor of 0.01 to obtain two independent shaped signals.

[0014] The two independent signals after shaping are up-converted separately and then merged into one dual single-sideband SSB signal, in which a guard band is reserved in the middle of the signal spectrum through up-conversion;

[0015] After adding a virtual carrier, the output is a self-coherent electrical signal consisting of the carrier and complex double-sided charged signals.

[0016] Preferably, the receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector.

[0017] The first coupler splits the received optical signal into two paths of equal power. The first path uses the first optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the first optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S Complex double-sideband signals S The signal is further split into upper and lower branches by the second coupler. The signal in the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is:

[0018] (1)

[0019] The lower branch signal output from the second coupler and the second signal output from the first coupler are phase-diversified by the 90-degree mixer and then fed into the first balanced photodetector and the second balanced photodetector to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows:

[0020] (2)

[0021] (3)

[0022] in and They represent the real part and the imaginary part, respectively. Indicates conjugate;

[0023] Then the first photocurrent was used. I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1:

[0024] (4)

[0025] Preferably, the receiver based on the optical bandstop filter and the 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector;

[0026] The third coupler splits the received optical signal into two paths with equal power. The first path uses the second optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the second optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is:

[0027] (5)

[0028] The lower branch signal of the fourth coupler and the second branch signal of the third coupler are sent to the third photodetector and the fourth photodetector respectively after passing through the fifth coupler, i.e., the 2×2 coupler, to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows:

[0029] (6)

[0030] (7)

[0031] in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j , 1];

[0032] Then the fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2:

[0033] (8)

[0034] Preferably, the demodulation of the complex signal by the receiving end digital signal processing module specifically includes:

[0035] Compensating for dispersion damage in fiber optic links;

[0036] The compensated complex signal is down-converted and processed by a matched filter to obtain two independent signal sequences.

[0037] The two independent signal sequences are subjected to symbol decision processing to obtain the final binary bit sequence.

[0038] On the other hand, a direct detection system for complex double-sideband signals based on an optical bandstop filter is provided, comprising:

[0039] The transmitting end digital signal processing module is used to output a self-coherent electrical signal composed of a carrier wave and a complex double-sided bandgap signal;

[0040] A modulation module is used to modulate the self-coherent electrical signal into a self-coherent optical signal using IQ modulation and send it into a single-mode optical fiber;

[0041] A receiver equipped with an optical bandstop filter is used to receive the optical signal transmitted through the single-mode optical fiber, process it, and obtain the constructed complex signal.

[0042] The receiving end digital signal processing module is used to demodulate the complex signal to obtain the final bit sequence;

[0043] The receivers are divided into two categories based on their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler.

[0044] Preferably, the transmitting end digital signal processing module is specifically used for:

[0045] The two independent pseudo-random binary sequences PRBS are mapped to two 16-QAM symbol sequences respectively;

[0046] The two symbol sequences are upsampled, with each symbol sequence being upsampled into eight samples. The pulses are then shaped using a raised cosine root RRC filter with a roll-off factor of 0.01 to obtain two independent shaped signals.

[0047] The two independent signals after shaping are up-converted separately and then merged into one dual single-sideband SSB signal, in which a guard band is reserved in the middle of the signal spectrum through up-conversion;

[0048] After adding a virtual carrier, the output is a self-coherent electrical signal consisting of the carrier and complex double-sided charged signals.

[0049] Preferably, the receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector.

[0050] The first coupler splits the received optical signal into two paths of equal power. The first path uses the first optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the first optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S Complex double-sideband signals S The signal is further split into upper and lower branches by the second coupler. The signal in the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is:

[0051] (1)

[0052] The lower branch signal output from the second coupler and the second signal output from the first coupler are phase-diversified by the 90-degree mixer and then fed into the first balanced photodetector and the second balanced photodetector to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows:

[0053] (2)

[0054] (3)

[0055] in and They represent the real part and the imaginary part, respectively. Indicates conjugate;

[0056] Then the first photocurrent was used. I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1:

[0057] (4)

[0058] Preferably, the receiver based on the optical bandstop filter and the 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector;

[0059] The third coupler splits the received optical signal into two paths with equal power. The first path uses the second optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the second optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is:

[0060] (5)

[0061] The lower branch signal of the fourth coupler and the second branch signal of the third coupler are sent to the third and fourth photodetectors respectively after passing through the fifth coupler, i.e., the 2×2 coupler, to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows:

[0062] (6)

[0063] (7)

[0064] in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j , 1];

[0065] Then the fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2:

[0066] (8)

[0067] Preferably, the receiving end digital signal processing module is specifically used for:

[0068] Compensating for dispersion damage in fiber optic links;

[0069] The compensated complex signal is down-converted and processed by a matched filter to obtain two independent signal sequences.

[0070] The two independent signal sequences are subjected to symbol decision processing to obtain the final binary bit sequence.

[0071] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0072] This invention provides a method and system for direct detection of complex double-sideband signals based on an optical bandstop filter. By using an optical bandstop filter in the receiver to estimate the SSBI, the SSBI caused by direct detection is suppressed. Compared with existing double-sideband self-coherent methods, this invention significantly reduces the required CSPR, and the system's OSNR sensitivity is also significantly improved. Furthermore, the use of an optical bandstop filter and a 2×2 coupler receiver significantly reduces the cost of this invention. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0074] Figure 1 This is a schematic diagram illustrating the principle of the method for direct detection of complex double-sideband signals based on an optical bandstop filter provided in an embodiment of the present invention;

[0075] Figures 2(a) and 2(b) are schematic diagrams of the digital signal processing at the transmitting end and the digital signal processing at the receiving end provided in the embodiments of the present invention;

[0076] Figures 3(a) and 3(b) are schematic diagrams of the receiver based on an optical bandstop filter and a 90-degree mixer and the receiver based on an optical bandstop filter and a 2×2 coupler provided in the embodiments of the present invention.

[0077] Figure 4 This is a graph showing the relationship between OSNR and CSPR required for a complex double-sideband signal direct detection receiver based on an optical bandstop filter to reach the 7% FEC BER threshold after transmitting for 80km, as provided in this embodiment of the invention.

[0078] Figure 5 This is a graph showing the relationship between the bit error rate and the received optical power of a complex double-sideband signal direct detection receiver based on an optical bandstop filter during back-to-back transmission, as provided in an embodiment of the present invention. Detailed Implementation

[0079] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0080] The embodiments of the present invention first provide a method for direct detection of complex double-sideband signals based on an optical bandstop filter. Figure 1 This is a schematic diagram illustrating the principle of the method, which includes the following steps:

[0081] At the transmitting end, a self-coherent electrical signal composed of a carrier wave and a complex double-sided charged signal is output through the transmitting end digital signal processing module; the self-coherent electrical signal is modulated into a self-coherent optical signal using IQ modulation and sent into a single-mode optical fiber;

[0082] At the receiving end, a receiver equipped with an optical band-stop filter receives the optical signal transmitted through the single-mode optical fiber, processes it to obtain a constructed complex signal, and demodulates the complex signal through the receiving end digital signal processing module to obtain the final bit sequence.

[0083] The receivers are divided into two categories based on their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler.

[0084] In this embodiment of the invention, the signal baud rate is 60 Gbaud and the bit rate is 240 bit / s. As shown in Figure 2(a), two independent pseudo-random binary sequences (PRBS) are mapped to two 16-QAM (Quadrature Amplitude Modulation, QAM) orthogonal amplitude modulation symbol sequences. The two symbol sequences are upsampled, with each sequence being upsampled to eight samples. Pulse shaping is then performed using a root raised cosine (RRC) filter with a roll-off factor of 0.01 to obtain two shaped independent signals. These two shaped independent signals are then upconverted and combined into a single-sideband (SSB) signal, with a guard band reserved in the middle of the signal spectrum after upconversion. After adding a virtual carrier, a self-coherent electrical signal composed of a carrier and complex double-sideband electrical signals is output. Finally, IQ modulation is performed to obtain the final self-coherent optical signal, which is then fed into a single-mode optical fiber.

[0085] Optical signals transmitted through a single-mode optical fiber can be represented as... C + S ,in C Indicates carrier wave, S This represents a complex double-sideband signal. In this embodiment of the invention, there are two structures for the receiver based on the optical bandstop filter: the receiver based on the optical bandstop filter and the 90-degree mixer shown in Figure 3(a) and the receiver based on the optical bandstop filter and the 2×2 coupler shown in Figure 3(b).

[0086] As shown in Figure 3(a), the receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector.

[0087] The first coupler splits the received optical signal into two paths of equal power. The first path uses a first optical bandstop filter to obtain the signal. The rectangular optical bandstop filter has a rectangular shape and a bandwidth of 6 GHz. C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after the first optical bandstop filter. When the guard band between the signal and the carrier is large enough, unwanted carrier power is essentially filtered out. ,Signal equal S Complex double-sideband signals S The signal is further split into two branches by the second coupler. The signal from the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is:

[0088] (1)

[0089] The lower branch signal output from the second coupler and the second branch signal output from the first coupler are phase-diversified by a 90-degree mixer and then fed into the first and second balanced photodetectors to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows:

[0090] (2)

[0091] (3)

[0092] in and They represent the real part and the imaginary part, respectively. Indicates conjugate.

[0093] Then the first photocurrent was used. I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1:

[0094] (4)

[0095] As shown in Figure 3(b), the receiver based on the optical bandstop filter and the 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector.

[0096] The third coupler splits the received optical signal into two paths of equal power. Similarly, the first path uses a second optical bandstop filter to obtain a complex double-sideband signal. SThe rectangular optical bandstop filter is rectangular in shape and has a bandwidth of 6 GHz. The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is:

[0097] (5)

[0098] The lower branch signal of the fourth coupler and the second branch signal of the third coupler pass through the fifth coupler, i.e., the 2×2 coupler, and are then sent to the third and fourth photodetectors to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows:

[0099] (6)

[0100] (7)

[0101] in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j , 1).

[0102] Then the fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2:

[0103] (8)

[0104] Furthermore, the two complex signals obtained from the optical bandstop filter receiver are... R 1 or R 2. The signal is fed into the receiving end digital signal processing module, as shown in Figure 2(b). The complex signal is processed by the receiving end digital signal processing module. R 1 or R 2. Demodulation is performed, specifically including:

[0105] Compensate for dispersion impairment in the fiber optic link; perform down-conversion and matched filter processing on the compensated complex signal to obtain two independent signal sequences; perform symbol decision processing on the two independent signal sequences to obtain the final binary bit sequence.

[0106] The feasibility of the proposed method is verified below using the optical communication simulation software VPI transmission Makers 11.1 and MATLAB. Figure 4 This paper presents the relationship between the optical signal-to-noise ratio (OSNR) and CSPR required for the complex double-sideband signal direct detection receiver based on the optical bandstop filter to achieve a 7% forward error correction (FEC) bit error rate (BER) threshold. Factors such as insertion loss are not considered here. Figure 4 It can be observed that the performance of the two receivers is comparable. The optimal CSPR of the system is -5dB, and the OSNR can still reach the 7% FEC BER threshold (3.8e-3) when it is as low as 21.45 dB. Figure 5 This diagram illustrates the relationship between bit error rate and received optical power in back-to-back transmission, considering the additional losses of a 90-degree mixer and a 2×2 coupler. The additional loss of the 90-degree mixer is set to 1 dB, and that of the 2×2 coupler to 0.1 dB. Figure 5 It can be seen that the receiver based on the optical bandstop filter and the 2×2 coupler has better power sensitivity than the receiver based on the optical bandstop filter and the 90-degree mixer.

[0107] Accordingly, embodiments of the present invention also provide a system for direct detection of complex double-sideband signals based on an optical bandstop filter, the system comprising:

[0108] The transmitting end digital signal processing module is used to output a self-coherent electrical signal composed of a carrier wave and a complex double-sided bandgap signal;

[0109] A modulation module is used to modulate the self-coherent electrical signal into a self-coherent optical signal using IQ modulation and send it into a single-mode optical fiber;

[0110] A receiver equipped with an optical bandstop filter is used to receive the optical signal transmitted through the single-mode optical fiber, process it, and obtain the constructed complex signal.

[0111] The receiving end digital signal processing module is used to demodulate the complex signal to obtain the final bit sequence;

[0112] The receivers are divided into two categories based on their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler.

[0113] Furthermore, the transmitting end digital signal processing module is specifically used for:

[0114] Two independent pseudo-random binary sequences (PRBS) are mapped to two 16-QAM symbol sequences. The two symbol sequences are upsampled, with each sequence upsampled to eight samples. Pulse shaping is then performed using a raised cosine root RRC filter with a roll-off factor of 0.01, resulting in two shaped independent signals. These two shaped independent signals are then upconverted and merged into a single dual single-sideband (SSB) signal, with a guard band reserved in the middle of the signal spectrum after upconversion. After adding a virtual carrier, a self-coherent electrical signal consisting of the carrier and a complex double-sideband signal is output.

[0115] Furthermore, the receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector;

[0116] The first coupler splits the received optical signal into two paths of equal power. The first path uses the first optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the first optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S Complex double-sideband signals S The signal is further split into upper and lower branches by the second coupler. The signal in the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is:

[0117] (1)

[0118] The lower branch signal output from the second coupler and the second signal output from the first coupler are phase-diversified by the 90-degree mixer and then fed into the first balanced photodetector and the second balanced photodetector to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows:

[0119] (2)

[0120] (3)

[0121] in and They represent the real part and the imaginary part, respectively. Indicate conjugate; then use the first photocurrent.I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1:

[0122] (4)

[0123] The receiver based on the optical bandstop filter and 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector;

[0124] The third coupler splits the received optical signal into two paths of equal power. The first path uses the second optical bandstop filter to obtain a complex double-sideband signal. S The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is:

[0125] (5)

[0126] The lower branch signal of the fourth coupler and the second branch signal of the third coupler are sent to the third and fourth photodetectors respectively after passing through the fifth coupler, i.e., the 2×2 coupler, to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows:

[0127] (6)

[0128] (7)

[0129] in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j [1]; then a fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2:

[0130] (8)

[0131] Furthermore, the receiving end digital signal processing module is specifically used for:

[0132] Compensate for dispersion impairment in the fiber optic link; perform down-conversion and matched filter processing on the compensated complex signal to obtain two independent signal sequences; perform symbol decision processing on the two independent signal sequences to obtain the final binary bit sequence.

[0133] In summary, the method and system for direct detection of complex double-sideband signals based on an optical bandstop filter provided by this invention suppresses SSBI caused by direct detection by estimating SSBI using an optical bandstop filter in the receiver. Compared to existing double-sideband self-coherent schemes, this invention significantly reduces the required CSPR, and the system's OSNR sensitivity is also significantly improved. Furthermore, the introduction of an optical bandstop filter and a 2×2 coupler receiver significantly reduces the cost of this invention.

[0134] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0135] The use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0136] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0137] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for direct detection of complex double-sideband signals based on an optical bandstop filter, characterized in that, Includes the following steps: At the transmitting end, a self-coherent electrical signal composed of a carrier wave and a complex double-sided charged signal is output through the transmitting end digital signal processing module; the self-coherent electrical signal is modulated into a self-coherent optical signal using IQ modulation and sent into a single-mode optical fiber; At the receiving end, a receiver equipped with an optical band-stop filter receives the optical signal transmitted through the single-mode fiber, processes it to obtain a constructed complex signal, and demodulates the complex signal through the receiving end digital signal processing module to obtain the final bit sequence. The receivers are divided into two categories according to their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler. The receiver based on the optical bandstop filter and 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector; The third coupler splits the received optical signal into two paths of equal power. The first path uses the second optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the second optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is: (5) The lower branch signal of the fourth coupler and the second branch signal of the third coupler are sent to the third photodetector and the fourth photodetector respectively after passing through the fifth coupler, i.e., the 2×2 coupler, to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows: (6) (7) in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j , 1]; Then the fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2: (8) 。 2. The method for direct detection of complex double-sideband signals based on an optical bandstop filter according to claim 1, characterized in that, The output of a self-coherent electrical signal composed of a carrier wave and complex double-sided bandgap signals via the transmitter's digital signal processing module specifically includes: The two independent pseudo-random binary sequences PRBS are mapped to two 16-QAM symbol sequences respectively; The two symbol sequences are upsampled, with each symbol sequence being upsampled into eight samples. The pulses are then shaped using a raised cosine root RRC filter with a roll-off factor of 0.01 to obtain two independent shaped signals. The two independent signals after shaping are up-converted separately and then merged into one dual single-sideband SSB signal, in which a guard band is reserved in the middle of the signal spectrum through up-conversion; After adding a virtual carrier, the output is a self-coherent electrical signal consisting of the carrier and complex double-sided charged signals.

3. The method for direct detection of complex double-sideband signals based on an optical bandstop filter according to claim 1, characterized in that, The demodulation of the complex signal by the receiving end digital signal processing module specifically includes: Compensating for dispersion damage in fiber optic links; The compensated complex signal is down-converted and processed by a matched filter to obtain two independent signal sequences. The two independent signal sequences are subjected to symbol decision processing to obtain the final binary bit sequence.

4. A method for direct detection of complex double-sideband signals based on an optical bandstop filter, characterized in that, Includes the following steps: At the transmitting end, a self-coherent electrical signal composed of a carrier wave and a complex double-sided charged signal is output through the transmitting end digital signal processing module; the self-coherent electrical signal is modulated into a self-coherent optical signal using IQ modulation and sent into a single-mode optical fiber; At the receiving end, a receiver equipped with an optical band-stop filter receives the optical signal transmitted through the single-mode fiber, processes it to obtain a constructed complex signal, and demodulates the complex signal through the receiving end digital signal processing module to obtain the final bit sequence. The receivers are divided into two categories according to their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler. The receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector. The first coupler splits the received optical signal into two paths of equal power. The first path uses the first optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the first optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S Complex double-sideband signals S The signal is further split into upper and lower branches by the second coupler. The signal in the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is: (1) The lower branch signal output from the second coupler and the second signal output from the first coupler are phase-diversified by the 90-degree mixer and then fed into the first balanced photodetector and the second balanced photodetector to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows: (2) (3) in and They represent the real part and the imaginary part, respectively. Indicates conjugate; Then the first photocurrent was used. I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1: (4) 。 5. A system for direct detection of complex double-sideband signals based on an optical bandstop filter, characterized in that, include: The transmitting end digital signal processing module is used to output a self-coherent electrical signal composed of a carrier wave and a complex double-sided bandgap signal; A modulation module is used to modulate the self-coherent electrical signal into a self-coherent optical signal using IQ modulation and send it into a single-mode optical fiber; A receiver equipped with an optical bandstop filter is used to receive the optical signal transmitted through the single-mode optical fiber, process it, and obtain the constructed complex signal. The receiving end digital signal processing module is used to demodulate the complex signal to obtain the final bit sequence; The receivers are divided into two categories according to their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler. The receiver based on the optical bandstop filter and 2×2 coupler includes: a third coupler, a fourth coupler, a fifth coupler, a second optical bandstop filter, a second photodetector, a third photodetector, and a fourth photodetector; The third coupler splits the received optical signal into two paths of equal power. The first path uses the second optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the second optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S The complex double-sideband signal S is further split into upper and lower branches by the fourth coupler. The upper branch signal passes through the second photodetector to obtain the fourth photocurrent. I 3. The expression is: (5) The lower branch signal of the fourth coupler and the second branch signal of the third coupler are sent to the third and fourth photodetectors respectively after passing through the fifth coupler, i.e., the 2×2 coupler, to obtain the fifth photocurrent. I 4 and the sixth photocurrent I 5. The expression is as follows: (6) (7) in j Represents the imaginary unit. To represent conjugation, the transfer matrix of a 2×2 coupler is: [1, j ; j , 1]; Then the fourth photocurrent was used. I 3. Fifth photocurrent I 4 and the sixth photocurrent I 5. Constructing the second complex signal R 2: (8) 。 6. The complex double-sideband signal direct detection system based on an optical bandstop filter according to claim 5, characterized in that, The transmitting end digital signal processing module is specifically used for: The two independent pseudo-random binary sequences PRBS are mapped to two 16-QAM symbol sequences respectively; The two symbol sequences are upsampled, with each symbol sequence being upsampled into eight samples. The pulses are then shaped using a raised cosine root RRC filter with a roll-off factor of 0.01 to obtain two independent shaped signals. The two independent signals after shaping are up-converted separately and then merged into one dual single-sideband SSB signal, in which a guard band is reserved in the middle of the signal spectrum through up-conversion; After adding a virtual carrier, the output is a self-coherent electrical signal consisting of the carrier and complex double-sided charged signals.

7. The complex double-sideband signal direct detection system based on an optical bandstop filter according to claim 5, characterized in that, The receiving end digital signal processing module is specifically used for: Compensating for dispersion damage in fiber optic links; The compensated complex signal is down-converted and processed by a matched filter to obtain two independent signal sequences. The two independent signal sequences are subjected to symbol decision processing to obtain the final binary bit sequence.

8. A system for direct detection of complex double-sideband signals based on an optical bandstop filter, characterized in that, include: The transmitting end digital signal processing module is used to output a self-coherent electrical signal composed of a carrier wave and a complex double-sided bandgap signal; A modulation module is used to modulate the self-coherent electrical signal into a self-coherent optical signal using IQ modulation and send it into a single-mode optical fiber; A receiver equipped with an optical bandstop filter is used to receive the optical signal transmitted through the single-mode optical fiber, process it, and obtain the constructed complex signal. The receiving end digital signal processing module is used to demodulate the complex signal to obtain the final bit sequence; The receivers are divided into two categories according to their structure: one is a receiver based on an optical bandstop filter and a 90-degree mixer, and the other is a receiver based on an optical bandstop filter and a 2×2 coupler. The receiver based on the optical bandstop filter and the 90-degree mixer includes: a first coupler, a second coupler, a first optical bandstop filter, a 90-degree mixer, a first photodetector, a first balanced photodetector, and a second balanced photodetector. The first coupler splits the received optical signal into two paths of equal power. The first path uses the first optical bandstop filter to obtain the signal. ;in C Indicates carrier wave, S This represents a complex double-sideband signal. This represents the relative amount of carrier power filtered out before and after passing through the first optical bandstop filter; when the guard band between the signal and the carrier is sufficiently large, ,Signal equal S Complex double-sideband signals S The signal is further split into upper and lower branches by the second coupler. The signal in the upper branch passes through the first photodetector to obtain the first photocurrent. I 0, the expression is: (1) The lower branch signal output from the second coupler and the second signal output from the first coupler are phase-diversified by the 90-degree mixer and then fed into the first balanced photodetector and the second balanced photodetector to obtain the second photocurrent, respectively. I 1 and the third photocurrent I 2. The expression is as follows: (2) (3) in and They represent the real part and the imaginary part, respectively. Indicates conjugate; Then the first photocurrent was used. I 0. Second photocurrent I 1 and the third photocurrent I 2. Constructing the first complex signal R 1: (4)。

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