Direct detection method, device and system for complex-valued double-sideband signal

Abstract

The invention provides a direct detection method, device and system for a complex-valued double-sideband signal, and the method employs a frequency selective phase shifter to apply a single-side phase shift to a left sideband signal or a right sideband signal of an information bearing signal. Even if the frequency of the carrier signal drifts to one side without phase shift relative to the frequency at the zero point of the phase filter, the detection result is not influenced, so that the working wavelength (equivalent to the frequency of the carrier signal) of the transmitting end laser does not need to be accurately aligned with the wavelength (the frequency at the zero point of the phase filter) at the phase abrupt change position of the phase filter; meanwhile, due to the fact that unilateral phase shift instead of bilateral phase shift is applied to the frequency-selective phase shifter, the number of times of phase abrupt change needing to be completed is reduced from two times to one time, the physical implementation difficulty of the frequency-selective phase shifter is reduced, and the frequency-selective phase shifter can be applied to the frequency-selective phase shifter. And more choices are provided for physical implementation of the frequency selective phase shifter.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a method, device and system for directly detecting a complex-valued double-sideband signal. Background Art

[0002] In recent years, various emerging broadband services have emerged, such as the Metaverse, 5G technology, large-scale computing networks, and ultra-high-definition video. The emergence of new applications has led to a continuous increase in traffic in metropolitan area networks and data centers, which has promoted the development of optical communication systems.

[0003] Currently, direct detection receiving devices are very sensitive to carrier wavelength drift in complex-valued double-sideband signals and require very stable laser sources or precise temperature control systems, which greatly increases system costs. In addition, the frequency-selective phase shifter of the direct detection receiving device needs to complete two phase mutations within a smaller frequency range, which makes physical implementation difficult. Summary of the invention

[0004] The present application provides a method, device and system for direct detection of complex-valued double-sideband signals, which improves the tolerance to carrier wavelength drift in the complex-valued double-sideband signals and reduces the difficulty of physical implementation of frequency selective phase shifters, thereby providing more options for the physical implementation of frequency selective phase shifters.

[0005] In order to achieve the above purpose, this application adopts the following technical solutions: In a first aspect, a direct detection method for a complex-valued double-sideband signal is provided. First, the complex-valued double-sideband signal to be tested is divided into two paths, the complex-valued double-sideband signal to be tested includes a carrier and an information-bearing signal, the information-bearing signal includes a left-band signal and a right-band signal, and in the frequency domain, the carrier is located between the left-band signal and the right-band signal; then, one of the complex-valued double-sideband signals to be tested is passed through a first photodetector and a first analog-to-digital converter to obtain a first digital signal of the complex-valued double-sideband signal to be tested; the other complex-valued double-sideband signal to be tested first applies a phase shift to the left-band signal or the right-band signal of the information-bearing signal through a frequency selective phase shifter, and then passes through a second photodetector and a second analog-to-digital converter to obtain a second digital signal of the complex-valued double-sideband signal to be tested after the phase shift; finally, the reconstructed information-bearing signal is obtained according to the first digital signal and the second digital signal.

[0006] Based on the above technical solution, the direct detection method of the complex-valued double-sideband signal provided in the embodiment of the present application uses a frequency-selective phase shifter to apply a unilateral phase shift to the left-band signal or the right-band signal of the information-bearing signal. In this way, even if the frequency of the carrier signal drifts toward the side where the phase shift is not applied relative to the frequency at the zero point of the phase filter, it will not affect the detection result. Therefore, there is no need to accurately align the operating wavelength of the transmitting laser (equivalent to the frequency of the carrier signal) with the wavelength at the phase mutation point of the phase filter (the frequency at the zero point of the phase filter), thereby improving the tolerance to the carrier wavelength drift in the complex-valued double-sideband signal. At the same time, since the frequency-selective phase shifter applies a unilateral phase shift rather than a bilateral phase shift, the number of phase mutations that need to be completed is reduced from two to one, thereby reducing the difficulty of physical implementation of the frequency-selective phase shifter and providing more options for the physical implementation of the frequency-selective phase shifter.

[0007] In a possible implementation of the first aspect, the transfer function of the frequency selective phase shifter is amplitude full-pass, and the phase response of the frequency selective phase shifter is to apply an adjustable unilateral phase shift to the left band signal or the right band signal of the information-bearing signal.

[0008] In a possible implementation of the first aspect, the phase response of the frequency selective phase shifter is to apply an optimal phase shift angle to the left band signal or the right band signal of the information carrying signal, wherein the optimal phase shift angle is obtained by continuously changing the phase shift angle to obtain a corresponding bit error rate, and when the bit error rate is minimized, the corresponding phase shift angle is the optimal phase shift angle.

[0009] In a possible implementation manner of the first aspect, a protection interval is reserved between the left band and the right band.

[0010] In a second aspect, a direct detection device for a complex-valued double-sideband signal is provided, the device comprising: a first optical coupler, a first photodetector and a first analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence; a frequency selective phase shifter, a second photodetector and a second analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence, and a digital signal processing module connected to the output end of the first analog-to-digital converter and the output end of the second analog-to-digital converter; The first optical coupler is used to divide the input complex-valued double-sideband signal to be measured into two paths, the complex-valued double-sideband signal to be measured includes a carrier and an information-bearing signal, the information-bearing signal includes a left-side band signal and a right-side band signal, and in the frequency domain, the carrier is located between the left-side band signal and the right-side band signal; The first photodetector is used to obtain and convert one of the complex-valued double-sideband signals to be measured into a first electrical signal, and the first analog-to-digital converter is used to convert the first electrical signal into a first digital signal; The frequency selective phase shifter is used to apply a phase shift to the left band signal or the right band signal of the information-bearing signal in the other channel of the complex-valued double-sideband signal to be measured, the second photodetector is used to convert the other channel of the complex-valued double-sideband signal to be measured after the phase shift is applied to a second electrical signal, and the second analog-to-digital converter is used to convert the second electrical signal into a second digital signal; The digital signal processing module is used to obtain a reconstructed information bearing signal according to the first digital signal and the second digital signal.

[0011] In a possible implementation manner of the second aspect, the frequency selective phase shifter is one of a waveform shaper, a silicon photonic integrated high-resolution all-pass phase filter, and a high-quality factor silicon nitride microring resonator.

[0012] In a possible implementation of the second aspect, the transfer function of the frequency selective phase shifter is amplitude full-pass, and the phase response of the frequency selective phase shifter is to apply an adjustable unilateral phase shift to the left band signal or the right band signal of the information-bearing signal.

[0013] In a possible implementation of the second aspect, the phase response of the frequency selective phase shifter is to apply an optimal phase shift angle to the left band signal or the right band signal of the information carrying signal, wherein the optimal phase shift angle is obtained by continuously changing the phase shift angle to obtain a corresponding bit error rate, and when the bit error rate is minimized, the corresponding phase shift angle is the optimal phase shift angle.

[0014] According to a third aspect, a signal detection system is provided, characterized in that it comprises: a transmitter for transmitting a complex-valued double-sideband signal to be tested, wherein the complex-valued double-sideband signal to be tested comprises a carrier and an information-bearing signal; and a direct detection device for the complex-valued double-sideband signal as described in the second aspect or any possible implementation of the second aspect connected to the transmitter.

[0015] Based on the implementations provided in the above aspects, this application can also be further combined to provide more implementations. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the current direct detection receiving device; Figure 2(a) is Figure 1 The amplitude-frequency response curve of the phase filter shown in; Figure 2(b) is Figure 1 The phase frequency response curve of the phase filter shown in; Figure 3 It is a structural schematic diagram of a direct detection device for complex-valued double-sideband signals provided in an embodiment of the present application; Figure 4(a) is Figure 3 The frequency selective phase shifter shown in FIG. 1 is an amplitude-frequency response curve of a phase shift applied to the right band; Figure 4(b) is Figure 3 A phase-frequency response curve of the frequency selective phase shifter shown in FIG. 1 applying a phase shift to the right band; Figure 4(c) is Figure 3 Another phase-frequency response curve of the frequency selective phase shifter shown in FIG. 1 for applying a phase shift to the right band; Figure 5(a) is Figure 3 The frequency selective phase shifter shown in FIG. 1 is an amplitude-frequency response curve of a phase shift applied to the left band; Figure 5(b) is Figure 3 A phase-frequency response curve of the frequency selective phase shifter shown in FIG. 1 applying a phase shift to the left band; Figure 5(c) is Figure 3 Another phase-frequency response curve of the frequency selective phase shifter shown in FIG. 1 for applying a phase shift to the left band; Figure 6 It is a structural schematic diagram of a direct detection system for complex-valued double-sideband signals provided in an embodiment of the present application; Figure 7 It is a schematic diagram of bit error performance of a direct detection device for complex-valued double-sideband signals provided in an embodiment of the present application; Figure 8 It is a comparison diagram of the tolerance of carrier wavelength drift in a complex-valued double-sideband signal using two schemes, unilateral phase shift and bilateral phase shift, provided by the direct detection device provided in the embodiment of the present application; Fig. 9 It is a flow chart of a direct detection method of a complex-valued double-sideband signal provided in an embodiment of the present application. DETAILED DESCRIPTION

[0017] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0018] In the description of the embodiments of the present application, unless otherwise specified, “ / ” means or. For example, A / B can mean A or B. The “and / or” in this article is merely a way to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0019] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this embodiment, unless otherwise specified, "plurality" means two or more.

[0020] First, the specific terms involved in the embodiments of the present application are explained in a unified manner.

[0021] (1) Complex-valued double-sideband signal Complex-valued Double-Sideband (CV-DSB) signals include a carrier and an information-carrying signal. The carrier is a high-frequency signal, and its frequency is usually much higher than that of the information-carrying signal. The carrier itself does not contain information, but it is a medium for information transmission. The information-carrying signal refers to a signal that contains the information to be transmitted. The information-carrying signal is a complex signal, which includes a real part and an imaginary part. The real part is also called the in-phase component, and the imaginary part is also called the orthogonal component.

[0022] If used x(t) represents a complex-valued double-sideband signal, c Indicates the carrier wave, s(t) represents the information-carrying signal, represents the in-phase component of the information-bearing signal, represents the orthogonal components of the information-carrying signal, then the complex-valued double-sideband signal x(t) It can be expressed as x(t)=c+s(t)=c+ +j ,in, j Is an imaginary unit.

[0023] During the modulation process, the information-carrying signal is loaded onto the carrier. Specifically, during double-sideband modulation, the information-carrying signal generates two sideband signals, a left sideband (LSB) signal and a right sideband (RSB) signal, which correspond to the positive and negative offsets of the carrier frequency, respectively. Indicates the left band signal, The right side band signal is a complex valued double sideband signal x(t) It can also be expressed as The left and right band signals are also complex signals. represents the in-phase component of the left band signal, represents the orthogonal component of the left band signal, then the left band signal = + ; If used represents the in-phase component of the right band signal, represents the orthogonal component of the right band signal, then the right band signal = + .

[0024] The left sideband signal refers to the part of the information-bearing signal whose frequency is lower than the carrier frequency. In this sideband, the frequency of the modulated signal is obtained by subtracting the carrier frequency. For example, if the carrier frequency of a signal is f c , and there is a modulating signal with a frequency of f m , then the frequency of the left band signal will be f c - f m The right sideband signal is the portion of the information-bearing signal that has a higher frequency than the carrier frequency. In this sideband, the frequency of the modulating signal is added to the carrier frequency. Continuing with the above example, the frequency of the right sideband signal would be f c + f m The frequency of the carrier wave is between the frequency of the left band signal and the frequency of the right band signal.

[0025] In some examples, the left sideband signal is also referred to as a lower sideband signal, and the right sideband signal is also referred to as an upper sideband signal.

[0026] (2) Baud Baud is the abbreviation of Baud, a unit of measurement for modulation rate, which indicates the number of times the signal state changes per unit time. 50 GBaud means that the transmitter can modulate 5 billion symbol states per second, which describes the modulation rate of the transmitter.

[0027] (3) 16-QAM Quadrature Amplitude Modulation (QAM) is a modulation technique that modulates amplitude and phase simultaneously.

[0028] Hexadecimal QAM means that the modulation scheme uses 16 different symbol states to represent data. These states are usually represented as points in a constellation diagram, with each point representing a different symbol. In 16-QAM, each symbol can carry 4 bits of information, so the bit rate is the modulation rate (in Baud) multiplied by the number of bits per symbol.

[0029] For a 50 GBaud 16-QAM signal, the bit rate would be 50 GBaud * 4 bits / symbol = 200Gbps (gigabits per second). 50 GBaud describes the modulation rate of the transmitter, and 16-QAM describes the amount of information that can be carried by each modulation symbol. Together, these two parameters define the data transfer rate and efficiency of the communication system.

[0030] (4) Additive Gaussian white noise Additive White Gaussian Noise (AWGN) is a statistical model used to describe the characteristics of noise that is prevalent in many communication systems.

[0031] Additive means that the noise is superimposed on the signal rather than mixed with it in some way. Therefore, the total received signal is the sum of the original signal and the noise.

[0032] Gaussian: The probability density function of the noise follows a Gaussian distribution (also called a normal distribution). This means that the amplitude values ​​of the noise are statistically Gaussian, with most noise values ​​concentrated around the mean and extreme values ​​having a low probability of occurring.

[0033] White noise: This refers to noise that has the same power spectral density at all frequencies, just like white light contains all the frequencies of visible light. Therefore, white noise is flat in the frequency domain and does not contain any specific frequency components.

[0034] In real-world communication systems, noise is inevitable. Adding AWGN to the transmission signal can help simulate the impact of noise in actual communication links and thus evaluate the performance of the system.

[0035] (5) Light field reconstruction Light field reconstruction refers to restoring the complete information of the optical signal, including amplitude and phase, through digital signal processing technology, so that the optical signal at the sending end can be accurately reproduced at the receiving end.

[0036] (6) Bit error rate The bit error rate (BER) refers to the ratio of the number of erroneous bits that occur during data transmission to the total number of transmitted bits within a certain period of time. It is an important indicator for measuring the reliability of a data transmission system.

[0037] The process of calculating the bit error rate is as follows: First, a certain amount of data is transmitted. This usually involves sending a known data sequence and receiving this data at the receiving end. At the receiving end, the received data sequence is compared with the original data sequence sent by the sending end. The number of error bits found during the comparison process is counted.

[0038] The bit error rate BER can be calculated by the following formula: BER = number of error bits / total number of bits, where the number of error bits refers to the number of bits detected by the receiving end that do not match the original data, and the total number of bits refers to the total number of bits sent during the test.

[0039] (7) Optical signal-to-noise ratio Optical Signal-to-Noise Ratio (OSNR) is an important parameter in optical fiber communication, which is used to measure the quality of optical signals. OSNR is defined as the ratio of optical signal power to noise power, OSNR = optical signal power / noise power, and OSNR is usually expressed in decibels (dB). A higher OSNR can reduce the bit error rate and improve the reliability of communication.

[0040] The optical signal power refers to the useful optical signal power, that is, the optical power of the transmitted data signal; the noise power refers to the total power of the noise introduced during the signal transmission process. These noises may include spontaneous emission noise (ASE), shot noise, thermal noise, and other noises generated by nonlinear effects.

[0041] (8) Forward error correction threshold The Forward Error Correction (FEC) threshold defines the minimum signal quality level at which the FEC algorithm can work reliably. Above this threshold, the FEC algorithm can correct enough errors to keep the transmission error rate within an acceptable range. This threshold is usually expressed in terms of the optical signal-to-noise ratio (OSNR) or the bit error rate (BER).

[0042] (9) Square-law detection Square-law detection is a nonlinear detection process in which a photodetector converts an optical signal into an electric current that is proportional to the square of the input optical signal amplitude. In digital communications, square-law detection is often used to recover the amplitude information of a signal because it can convert the phase and amplitude information of a modulated signal into an electrical signal that can be processed by subsequent circuits.

[0043] Next, the technical solutions involved in the embodiments of the present application are described.

[0044] In recent years, various emerging broadband services have emerged, such as the Metaverse, 5G technology, large-scale computing networks, and ultra-high-definition video. The emergence of new applications has led to a continuous increase in traffic in metropolitan area networks and data centers, which has promoted the development of optical communication systems. Receivers in optical communications include two detection methods: coherent detection and direct detection.

[0045] Among them, coherent detection requires a local oscillator light source whose frequency and phase match the optical signal at the transmitting end. The received signal light is mixed with the local oscillator light on a 90-degree optical mixer, and then passes through a photodetector to generate an electrical signal. The electrical signal contains the phase and amplitude information of the signal light; the obtained electrical signal is analyzed by subsequent electronic processing circuits to restore the original transmission data. It can be seen that although coherent detection has superior performance, it requires expensive narrow-linewidth local oscillator lasers to generate local oscillator light, and carrier recovery operations are required to ensure effective mixing between local oscillator light and signal light. Therefore, for medium and short distance transmission scenarios, the system cost is relatively high.

[0046] Direct detection is the simplest and most commonly used signal detection method in optical communication. Its working principle is as follows: when the optical signal reaches the receiving end through optical fiber transmission, the photodetector at the receiving end converts the optical signal into an electrical signal (such as a current or voltage signal), and the generated electrical signal is then sent to the signal processing circuit for amplification, filtering, and judgment to restore the original transmission data. It can be seen that compared with coherent detection, direct detection does not require complex local oscillator light sources and phase matching technology required for coherent detection, so the system design and implementation are simpler, the optical communication system cost is low, and it is suitable for medium and short distance communications.

[0047] In the complex-valued double-sideband signal direct detection optical communication system, the transmitter generates a quadrature amplitude modulation (QAM) signal similar to homodyne coherent detection and uses a low-cost direct detection method to receive the signal, which fully combines the advantages of both direct detection and coherent detection.

[0048] A structure of a direct detection receiving device is as follows Figure 1 As shown, with the simplest design, the performance approaches that of homodyne coherent detection. Figure 1 After the complex-valued double-sideband signal enters the receiver, it is split into two paths by the optical splitter. One path directly enters the photodetector to detect the in-phase component of the signal. The other path first passes through a phase filter and then enters the photodetector to detect the orthogonal component of the signal. The optimal transfer function of the phase filter is amplitude full pass, see the amplitude-frequency response curve in Figure 2 (a); the phase response is an adjustable double-side phase shift applied to the information-bearing signal, see the phase-frequency response curve in Figure 2 (b).

[0049] because Figure 1The phase response of the phase filter in the receiving device shown is manifested as applying an adjustable bilateral phase shift to the information-bearing signal, thereby introducing a certain phase difference between the carrier and the information-bearing signal, causing the conversion between the in-phase component and the orthogonal component of the information-bearing signal. However, since the bilateral phase shift needs to satisfy the phase difference between the carrier and the left-band signal and the right-band signal of the information-bearing signal at the same time, the frequency of the carrier signal is required to be accurately aligned with the frequency at the zero point of the phase filter, that is, the operating wavelength of the transmitting laser (equivalent to the frequency of the carrier signal) is required to be accurately aligned with the wavelength at the phase filter phase mutation point (the frequency at the zero point of the phase filter), which is very sensitive to the wavelength drift of the transmitting laser and requires a very stable laser source or a precise temperature control system, which greatly increases the system cost. In addition, the phase filter needs to complete two phase mutations within a small frequency range, which is difficult to achieve physically.

[0050] In view of this, the embodiments of the present application provide a method, device and system for direct detection of a complex-valued double-sideband signal. The method for direct detection of a complex-valued double-sideband signal provided in the embodiments of the present application uses a frequency selective phase shifter to apply a unilateral phase shift to the left-band signal or the right-band signal of the information-bearing signal. In this way, even if the frequency of the carrier signal drifts toward the side where the phase shift is not applied relative to the frequency at the zero point of the phase filter, it will not affect the detection result. Therefore, there is no need to accurately align the operating wavelength of the transmitting laser (equivalent to the frequency of the carrier signal) with the wavelength at the phase mutation point of the phase filter (the frequency at the zero point of the phase filter), thereby improving the tolerance to the carrier wavelength drift in the complex-valued double-sideband signal. At the same time, since the frequency selective phase shifter applies a unilateral phase shift rather than a bilateral phase shift, the number of phase mutations that need to be completed is reduced from two to one, thereby reducing the difficulty of physical implementation of the frequency selective phase shifter and providing more options for the physical implementation of the frequency selective phase shifter.

[0051] Figure 3 The direct detection device for complex-valued double-sideband signals provided in the embodiment of the present application is described in detail below.

[0052] The direct detection device of the complex-valued double-sideband signal includes: a first optical coupler, a first photodetector and a first analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence; a frequency selective phase shifter, a second photodetector and a second analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence, and a digital signal processing module connected to the output end of the first analog-to-digital converter and the output end of the second analog-to-digital converter.

[0053] The first optical coupler is used to divide the input complex-valued double-sideband signal to be tested into two paths. The complex-valued double-sideband signal to be tested includes a carrier and an information-bearing signal. The information-bearing signal includes a left-band signal and a right-band signal. In the frequency domain, the carrier is located between the left-band signal and the right-band signal.

[0054] The complex double-sideband signal to be measured is used c + s ( t ) indicates that Indicates the carrier wave, s ( t ) represents an information-carrying signal. Information-carrying signal s ( t ) including left band signal And right side with signal ,Right now s ( t )= + Therefore, the complex-valued double-sideband signal to be measured can be expressed as + + Since the information-carrying signal s ( t ) is a complex signal, including in-phase components and orthogonal components, so the information carrying signal s ( t ) can also be expressed as the in-phase component and the orthogonal components The sum of s ( t ) = + , where j is the imaginary unit.

[0055] Left side with signal And right side with signal Also for complex signals, use represents the in-phase component of the left band signal, represents the orthogonal component of the left band signal, then the left band signal can be expressed as = + ; If used represents the in-phase component of the right band signal, represents the orthogonal component of the right band signal, then the right band signal can be expressed as = + .

[0056] For example, in the frequency domain, the left band signal And right side with signal A small guard interval is reserved between the left and right double-sideband signals, which does not contain any modulated signal. Since the guard interval can separate the left and right band signals, the left and right band signals will not interfere with each other during the modulation process. For example, a 1 Hz guard band can be inserted at the zero frequency of the complex double-sideband signal, that is, −0.5 Hz-0.5 Hz.

[0057] It is feasible that the carrier may be retained in the guard interval, which can also avoid interference between the left-band signal or the right-band signal and the carrier, helping to improve the efficiency and clarity of signal transmission, while also making it easier for the receiver to extract the original information from the received signal.

[0058] The first optical coupler is used to receive the input complex-valued double-sideband signal and split the complex-valued double-sideband signal into two paths. The information carried by the optical signals after being split into two paths (referred to as the first optical signal and the second optical signal in this application) is roughly the same, but the intensity of the optical signals after being split into two paths may be different. c + s ( t ), then the optical signal after being divided into two paths can be expressed as c + s ( t ).

[0059] The first optical signal is input into the first photodetector, the first photodetector is used to convert the first optical signal into a first electrical signal, and the first analog-to-digital converter is used to convert the first electrical signal into a first digital signal.

[0060] Specifically, the first optical signal c + s ( t ) is input into the first photodetector, the first photodetector converts the first optical signal into a first electrical signal through square law detection, and the first electrical signal is used express, , It can also be expressed as formula (1): (1) Afterwards, the first electrical signal Entering the first analog-to-digital converter, the first analog-to-digital converter will simulate the first electrical signal Converted into a first digital signal.

[0061] The second optical signal c + s ( t) input frequency selective phase shifter, the frequency selective phase shifter is used to apply a phase shift to the left band signal or the right band signal of the information carrying signal in the second optical signal, the second photodetector is used to convert the other complex-valued double-sideband signal to be measured after the phase shift is applied into a second electrical signal, and the second analog-to-digital converter is used to convert the second electrical signal into a second digital signal.

[0062] Specifically, the time domain impulse response of the frequency selective phase shifter is h(t) express.

[0063] In one embodiment, the transfer function of the frequency selective phase shifter is amplitude full pass, and the phase response of the frequency selective phase shifter is to apply a single-sided phase shift to the right-hand side signal of the information-bearing signal.

[0064] Its amplitude-frequency response curve is shown in FIG4 (a), and the amplitude-frequency response exhibits amplitude full pass; its phase-frequency response curve is shown in FIG4 (b) or 4 (c), and the phase-frequency response exhibits a unilateral phase shift applied to the right band signal of the information-bearing signal, that is, the frequency selective phase shifter applies a unilateral phase shift to the right band signal of the information-bearing signal.

[0065] Assume that the magnitude of the phase shift of the frequency selective phase shifter is expressed as The frequency response of the frequency selective phase shifter is to apply a unilateral phase shift to the right band signal of the information-bearing signal. Then the second optical signal c+s(t)= , after passing through the frequency selective phase shifter, can be expressed as The optical signal after phase shift The second photodetector converts the phase-shifted second optical signal into a second electrical signal. , the second electrical signal , the second electrical signal It can be expressed as formula (2): (2) In another embodiment, the transfer function of the frequency selective phase shifter is characterized by an amplitude full pass, and the phase response of the frequency selective phase shifter is to apply a single-sided phase shift to the left-hand side signal of the information-bearing signal.

[0066] Its amplitude-frequency response curve is shown in FIG5(a), and the amplitude-frequency response exhibits amplitude full pass; its phase-frequency response curve is shown in FIG5(b) or 5(c), and the phase-frequency response exhibits a unilateral phase shift applied to the left band signal of the information-carrying signal, that is, the frequency selective phase shifter applies a unilateral phase shift to the left band signal of the information-carrying signal.

[0067] Assume that the magnitude of the phase shift of the frequency selective phase shifter is expressed as The frequency response of the frequency selective phase shifter is to apply a unilateral phase shift to the left band signal of the information-bearing signal. Then the second optical signal c+s(t)= , after passing through the frequency selective phase shifter, can be expressed as The optical signal after phase shift The second photodetector converts the phase-shifted second optical signal into a second electrical signal. , the second electrical signal , the second electrical signal It can also be expressed as formula (3): (3) In this embodiment, the frequency selective phase shifter can adopt a frequency selective phase shifter with a step phase shift, and its phase-frequency response curve is shown in FIG4 (b) or 5 (b). At a specific frequency point, the phase shift amount will suddenly jump from one value to another value, and its phase shift process is a sudden change process. Therefore, the physical implementation difficulty of this type of frequency selective phase shifter is relatively large. In order to reduce the physical implementation difficulty of the frequency selective phase shifter, the frequency selective phase shifter can also adopt a frequency selective phase shifter with a continuous phase shift, and its phase-frequency response curve is shown in FIG4 (c) or 5 (c). The phase shift amount changes continuously with the frequency change, and there is no sudden jump. Therefore, the physical implementation difficulty of this type of frequency selective phase shifter is relatively low. In practical applications, different types of frequency selective phase shifters can be selected according to needs to achieve unilateral phase shift.

[0068] It is achievable that the above-mentioned unilateral phase shift is an adjustable unilateral phase shift, and the frequency selective phase shifter can adjust the phase shift magnitude applied to the left band signal or the right band signal as required.

[0069] The phase response of the frequency selective phase shifter can be realized by applying an optimal phase shift angle to the left band signal or the right band signal of the information bearing signal.

[0070] The above optimal phase shift angle is obtained by iterative adjustment based on the actual direct detection device. The optimal phase shift angle is related to the optical signal-to-noise ratio and the carrier signal power ratio. In order to obtain the optimal phase shift angle, the phase shift angle of the frequency selective phase shifter can be continuously changed. , based on the actual direct detection device, the reconstructed optical signal is obtained, and the corresponding bit error rate is calculated according to the reconstructed optical signal and the original optical signal. When the bit error rate is minimum, the corresponding phase shift angle is the optimal phase shift angle.

[0071] The above process of finding the optimal phase shift angle of the frequency selective phase shifter can be carried out during the testing phase of the direct detection device. When the direct detection device is put into use, the phase shift angle of the frequency selective phase shifter in the direct detection device adopts the optimal phase shift angle to ensure that the direct detection device achieves the best detection effect in actual applications.

[0072] Realizable, frequency selective phase shifter can be one of waveform shaper, silicon photonic integrated high-resolution all-pass phase filter, high quality factor silicon nitride microring resonator.

[0073] The first digital signal and the second digital signal are inputted into a digital signal processing module, and the digital signal processing module is used to obtain a reconstructed information bearing signal according to the first digital signal and the second digital signal.

[0074] In this embodiment, it is assumed that the first digital signal and the first electrical signal The second digital signal is the same as the second electrical signal Taking the same expression formula as an example, the process of reconstructing the information-bearing signal by the digital signal processing module is explained: In one embodiment, the phase response of the frequency selective phase shifter is to apply a single-sided phase shift to the right band signal of the information-bearing signal, and the first digital signal , the second digital signal .

[0075] In order to reconstruct the signal, the digital signal processing module first processes the first digital signal and the second digital signal By subtracting, we can get the following formula (4): (4) because is the intermediate frequency signal, and They are Hilbert transform relations, then It can be expressed as formula (5): (5) Here, Hilbert represents Hilbert transform.

[0076] Combining formulas (4) and (5), we can obtain and .in and is a second-order term and can be eliminated by an iterative algorithm.

[0077] The right side of the reconstructed signal It can be expressed as the following formula (6): (6) According to formula (1), we can get (7) therefore, (8) Then the reconstructed left band signal can be expressed as shown in the following formula (9): (9) Then the reconstructed information carrying signal s` = + .

[0078] In another embodiment, the phase response of the frequency selective phase shifter is to apply a single-sided phase shift to the left band signal of the information-bearing signal, and the first digital signal , the second digital signal .

[0079] In order to reconstruct the signal, the digital signal processing module first processes the first digital signal and the second digital signal By subtracting, we can get the following formula (10): (10) because is the intermediate frequency signal, and They are Hilbert transform relations, then It can be expressed as formula (11): (11) Here, Hilbert represents Hilbert transform.

[0080] Combining formulas (10) and (11), we can obtain and .in and is a second-order term and can be eliminated by an iterative algorithm.

[0081] The left band signal after reconstruction It can be expressed as the following formula (12): (12) According to formula (1), we can get (13) therefore, (14) Then the right side of the reconstruction has a signal It can be expressed as the following formula (15): (15) Then the reconstructed information carrying signal s` = + .

[0082] The digital signal processing module completes the above-mentioned second-order term elimination and signal reconstruction. Specifically, deep learning technology can be used to implement the above-mentioned signal reconstruction process, thereby optimizing system performance.

[0083] Realizable implementation carriers of the digital signal processing module include but are not limited to offline signal processing programs, field programmable gate arrays (FPGA), photonic neural networks, etc.

[0084] The transfer function of the frequency selective phase shifter in the complex-valued double-sideband signal direct detection device provided in the embodiment of the present application is amplitude full-pass, and the frequency selective phase shifter applies a unilateral phase shift to the left-band signal or the right-band signal of the information-bearing signal. In this way, even if the frequency of the carrier signal drifts toward the side where the phase shift is not applied relative to the frequency at the zero point of the phase shifter, it will not affect the detection result. Therefore, there is no need to accurately align the operating wavelength of the transmitting laser (equivalent to the frequency of the carrier signal) with the wavelength at the phase mutation point of the phase shifter (the frequency at the zero point of the phase filter), thereby improving the tolerance to the carrier wavelength drift in the complex-valued double-sideband signal. At the same time, since the frequency selective phase shifter applies a unilateral phase shift rather than a bilateral phase shift, the number of phase mutations that need to be completed is reduced from two to one, thereby reducing the difficulty of physical implementation of the frequency selective phase shifter and providing more options for the physical implementation of the frequency selective phase shifter.

[0085] Figure 6 The direct detection system of the complex-valued double-sideband signal provided in the embodiment of the present application includes a transmitter and the above-mentioned direct detection device. The transmitter and the direct detection device are connected by an optical fiber, and the transmitter is used to send the complex-valued double-sideband signal to be tested, and the complex-valued double-sideband signal to be tested includes a carrier and an information-bearing signal. The direct detection device is used to receive the complex-valued double-sideband signal (optical signal) to be tested and reconstruct the information-bearing signal in the complex-valued double-sideband signal to be tested. The information-bearing signal in the reconstructed complex-valued double-sideband signal is a digital signal, which is convenient for computer equipment to process.

[0086] Realizable, in real-world communication systems, noise is inevitable. Therefore, after the complex double-sideband signal to be tested sent by the transmitter passes through the additive white Gaussian noise channel model, Gaussian white noise will be added to the complex double-sideband signal to be tested to simulate the actual environment of the optical fiber channel.

[0087] It should be noted that the additive white Gaussian noise channel is not an actual physical device, but a mathematical model.

[0088] The following is a specific analysis of the technical effects that can be achieved in this application in combination with the above-mentioned direct detection system.

[0089] The transmitter is set to output a 50 GBaud complex double-sideband 16-QAM (16-QAM) signal. A 1 Hz guard band is inserted at the zero frequency of the complex double-sideband signal, that is, −0.5 Hz -0.5 Hz, and the carrier signal power ratio is set to 3 dB. Additive white Gaussian noise is introduced into the complex double-sideband 16-QAM signal to simulate the optical fiber channel.

[0090] At the receiving end, a complex double-sideband signal direct detection device based on unilateral phase shift is used to convert the optical signal into an electrical signal. A digital signal processing module is used to realize the optical field reconstruction of the signal. Finally, after the bit error rate is calculated, the following is obtained: Figure 7 The system bit error performance diagram is shown in Figure 1. Figure 7 It can be seen that when the optical signal-to-noise ratio is 24.5 dB, the bit error rate can reach the FEC threshold of 20%. Figure 7 The inset in Figure 2 shows the constellation diagram of the recovered signal when the optical signal-to-noise ratio is 36 dB.

[0091] Figure 8A comparison chart of the tolerance of the carrier wavelength drift in the complex-valued double-sideband signal using the two schemes of single-sided phase shift and double-sided phase shift of the direct detection device is shown. It can be seen that for the double-sided phase shift scheme, at a 20% FEC threshold, the tolerance for the carrier wavelength drift in the complex-valued double-sideband signal is less than 1 Hz, and when the carrier wavelength drifts by 1 Hz in the complex-valued double-sideband signal, the bit error rate is extremely high, and signal reconstruction is completely impossible to achieve; while for the single-sided phase shift scheme in the embodiment of the present application, at a 20% FEC threshold, the tolerance for the carrier wavelength drift in the complex-valued double-sideband signal is greater than 2 GHz, and when the carrier wavelength drifts by 2 GHz in the complex-valued double-sideband signal, the bit error rate is still small, and signal reconstruction can still be achieved. Therefore, it can be seen that in the direct detection device of the embodiment of the present application, the phase response requirement of the frequency selective phase shifter is changed from bilateral phase shift to unilateral phase shift, so that the tolerance of the direct detection device to the carrier wavelength drift in the complex-valued double-sideband signal is increased from 0 Hz to over 2 GHz, which improves the tolerance of the direct detection device to the carrier wavelength drift in the complex-valued double-sideband signal and reduces the performance requirements for the transmitter. At the same time, since the bilateral phase shift is changed to unilateral phase shift, the number of phase mutations that the frequency selective phase shifter needs to complete is reduced from two to one, which reduces the difficulty of physical implementation of the frequency selective phase shifter and provides more options for the physical implementation of the frequency selective phase shifter.

[0092] In summary, the frequency selective phase shifter described in the embodiment of the present application only needs to apply a unilateral phase shift to the left band signal or the right band signal of the signal, and does not need to apply a bilateral phase shift to the left and right bands at the same time. For a forward error correction (FEC) threshold of 20%, the bilateral phase shift scheme has no tolerance for carrier wavelength drift in complex-valued double-sideband signals, while the embodiment of the present application can achieve a tolerance for carrier wavelength drift in complex-valued double-sideband signals greater than 2 GHz. In addition, in the embodiment of the present application, the bilateral phase shift is evolved into a unilateral phase shift, so that the number of phase mutations that need to be completed is reduced from two to one, which reduces the difficulty of physical implementation of the frequency selective phase shifter and provides more options for the physical implementation of the frequency selective phase shifter.

[0093] Fig. 9 A flow chart of a direct detection method for a complex-valued double-sideband signal provided in an embodiment of the present application is provided. The direct detection method is applied to the above-mentioned direct detection device. The direct detection method includes the following steps: Step S101: dividing the complex-valued double-sideband signal to be measured into two paths.

[0094] Step S102: obtaining a first digital signal of the complex-valued double-sideband signal to be measured through a first photodetector and a first analog-to-digital converter.

[0095] Step S103: The other complex-valued double-sideband signal to be measured firstly applies a phase shift to the left band signal or the right band signal of the information-bearing signal through a frequency selective phase shifter.

[0096] Step S104: obtaining a second digital signal of the complex-valued double-sideband signal to be measured after phase shift through a second photodetector and a second analog-to-digital converter.

[0097] Step S105: Obtain a reconstructed information bearing signal according to the first digital signal and the second digital signal.

[0098] The complex-valued double-sideband signal to be measured includes a carrier and an information-bearing signal. The information-bearing signal is a complex signal including an in-phase component and an orthogonal component. The information-bearing signal includes a left-side band signal and a right-side band signal. In the frequency domain, the carrier is located between the left-side band signal and the right-side band signal.

[0099] The first optical coupler receives the input complex-valued double-sideband signal to be measured and divides the complex-valued double-sideband signal to be measured into two paths. The information carried by the optical signal divided into two paths (which may be referred to as the first optical signal and the second optical signal in this application) is roughly the same, but the intensity of the optical signal divided into two paths may be different.

[0100] The first optical signal is input to the first photodetector for square-law detection to convert the first optical signal into a first electrical signal, and the first analog-to-digital converter converts the first electrical signal into a first digital signal.

[0101] The second optical signal is input into the frequency selective phase shifter, and a single-sided phase shift is applied to the left band signal or the right band signal of the information-bearing signal through the frequency selective phase shifter. After that, the other complex-valued double-sideband signal to be measured after the phase shift is converted into a second electrical signal through the second photodetector, and the second analog-to-digital converter converts the second electrical signal into a second digital signal. After that, the digital signal processing module obtains the reconstructed information-bearing signal according to the first digital signal and the second digital signal.

[0102] In the direct detection method of the complex-valued double-sideband signal provided in the embodiment of the present application, a frequency-selective phase shifter is used to apply a unilateral phase shift to the left-band signal or the right-band signal of the information-bearing signal. In this way, even if the frequency of the carrier signal drifts toward the side where the phase shift is not applied relative to the frequency at the zero point of the phase filter, it will not affect the detection result. Therefore, there is no need to accurately align the operating wavelength of the transmitting laser (equivalent to the frequency of the carrier signal) with the wavelength at the phase mutation point of the phase filter (the frequency at the zero point of the phase filter), thereby improving the tolerance to the carrier wavelength drift in the complex-valued double-sideband signal. At the same time, since the frequency-selective phase shifter applies a unilateral phase shift rather than a bilateral phase shift, the number of phase mutations that need to be completed is reduced from two to one, thereby reducing the difficulty of physical implementation of the frequency-selective phase shifter and providing more options for the physical implementation of the frequency-selective phase shifter.

[0103] The transfer function of the frequency selective phase shifter is amplitude full pass, and the phase response of the frequency selective phase shifter is to apply an adjustable unilateral phase shift to the left band signal or the right band signal of the information carrying signal.

[0104] It is achievable that the phase response of the frequency selective phase shifter is to apply an optimal phase shift angle to the left band signal or the right band signal of the information carrying signal, wherein the optimal phase shift angle is obtained by continuously changing the phase shift angle to obtain the corresponding bit error rate, and when the bit error rate is minimized, the corresponding phase shift angle is the optimal phase shift angle.

[0105] It is feasible that a protection interval is reserved between the left band and the right band.

[0106] It is feasible to obtain the information-bearing signal according to the first digital signal and the second digital signal, including: reconstructing the light field according to the first digital signal and the second digital signal by deep learning technology to obtain the reconstructed information-bearing signal.

[0107] It is worth noting that the direct detection method of the complex-valued double-sideband signal in the embodiment of the present application is applied to the direct detection device of the complex-valued double-sideband signal mentioned above, and the technical details in the direct detection device of the complex-valued double-sideband signal mentioned above can also be applied to the present embodiment. For details, please refer to the contents of the above embodiment, which will not be repeated here.

[0108] It should be understood that the above examples are intended to help those skilled in the art understand the embodiments of the present application, rather than to limit the embodiments of the present application to the specific numerical values ​​or specific scenarios illustrated. Those skilled in the art can obviously make various equivalent modifications or changes based on the above examples, and such modifications or changes also fall within the scope of the embodiments of the present application.

[0109] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0110] In the several embodiments provided in the embodiments of the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0111] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, and may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0112] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0113] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiment of the present application is essentially or the part that contributes to the prior art or the part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a memory (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0114] The above is only a specific implementation of the embodiment of the present application, but the protection scope of the embodiment of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the embodiment of the present application, which should be included in the protection scope of the embodiment of the present application. Therefore, the protection scope of the embodiment of the present application should be based on the protection scope of the claims.

Claims

1. A direct detection method for complex-valued double-sideband signals, characterized in that: The method comprises: Divide the complex-valued double-sideband signal to be measured into two paths, wherein the complex-valued double-sideband signal to be measured includes a carrier and an information-bearing signal, wherein the information-bearing signal includes a left-side band signal and a right-side band signal, and in the frequency domain, the carrier is located between the left-side band signal and the right-side band signal; One of the complex-valued double-sideband signals to be measured is passed through a first photodetector and a first analog-to-digital converter to obtain a first digital signal of the complex-valued double-sideband signal to be measured; The other path of the complex-valued double-sideband signal to be measured first applies a phase shift to the left-side band signal or the right-side band signal of the information-bearing signal through a frequency selective phase shifter, and then passes through a second photodetector and a second analog-to-digital converter to obtain a second digital signal of the complex-valued double-sideband signal to be measured after the phase shift; The reconstructed information bearing signal is obtained according to the first digital signal and the second digital signal.

2. The method according to claim 1, characterized in that The transfer function of the frequency selective phase shifter is amplitude full pass, and the phase response of the frequency selective phase shifter is to apply an adjustable single-sided phase shift to the left band signal or the right band signal of the information-bearing signal.

3. The method according to claim 1 or 2, characterized in that: The phase response of the frequency selective phase shifter is to apply an optimal phase shift angle to the left band signal or the right band signal of the information carrying signal, wherein the optimal phase shift angle is obtained by continuously changing the phase shift angle to obtain a corresponding bit error rate, and when the bit error rate is minimum, the corresponding phase shift angle is the optimal phase shift angle.

4. The method according to claim 1 or 2, characterized in that: A protection interval is reserved between the left band and the right band.

5. The method according to claim 1 or 2, characterized in that: Obtaining the information bearing signal according to the first digital signal and the second digital signal comprises: Light field reconstruction is performed according to the first digital signal and the second digital signal through deep learning technology to obtain the reconstructed information-bearing signal.

6. A direct detection device for complex-valued double-sideband signals, characterized in that: The device comprises: A first optical coupler, a first photodetector and a first analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence; a frequency selective phase shifter, a second photodetector and a second analog-to-digital converter connected to the output end of the first optical coupler and connected in sequence, and a digital signal processing module connected to the output end of the first analog-to-digital converter and the output end of the second analog-to-digital converter; The first optical coupler is used to divide the input complex-valued double-sideband signal to be measured into two paths, the complex-valued double-sideband signal to be measured includes a carrier and an information-bearing signal, the information-bearing signal includes a left-side band signal and a right-side band signal, and in the frequency domain, the carrier is located between the left-side band signal and the right-side band signal; The first photodetector is used to obtain and convert one of the complex-valued double-sideband signals to be measured into a first electrical signal, and the first analog-to-digital converter is used to convert the first electrical signal into a first digital signal; The frequency selective phase shifter is used to apply a phase shift to the left band signal or the right band signal of the information-bearing signal in the other channel of the complex-valued double-sideband signal to be measured, the second photodetector is used to convert the other channel of the complex-valued double-sideband signal to be measured after the phase shift is applied to a second electrical signal, and the second analog-to-digital converter is used to convert the second electrical signal into a second digital signal; The digital signal processing module is used to obtain a reconstructed information bearing signal according to the first digital signal and the second digital signal.

7. The device according to claim 6, characterized in that The frequency selective phase shifter is one of a waveform shaper, a silicon photonic integrated high-resolution all-pass phase filter, and a high-quality factor silicon nitride microring resonator.

8. The device according to any one of claims 6 to 7, characterized in that The transfer function of the frequency selective phase shifter is amplitude full pass, and the phase response of the frequency selective phase shifter is to apply an adjustable single-sided phase shift to the left band signal or the right band signal of the information-bearing signal.

9. The device according to any one of claims 6 to 7, characterized in that The phase response of the frequency selective phase shifter is to apply an optimal phase shift angle to the left band signal or the right band signal of the information carrying signal, wherein the optimal phase shift angle is obtained by continuously changing the phase shift angle to obtain a corresponding bit error rate, and when the bit error rate is minimum, the corresponding phase shift angle is the optimal phase shift angle.

10. A signal detection system, characterized in that: include: A transmitter, used for transmitting a complex-valued double-sideband signal to be measured, wherein the complex-valued double-sideband signal to be measured includes a carrier and an information-bearing signal; A direct detection device for complex-valued double-sideband signals as claimed in any one of claims 6 to 9 connected to the transmitter.

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