Optical transmission system and optical receiving device

Abstract

This application discloses an optical transmission system and an optical receiving device, relating to the field of optical communication technology. The optical transmission system includes an optical transmitting device and an optical receiving device. The optical transmitting device includes a light source component and a filtering component. The light source component outputs an optical double-sideband modulated signal. The filtering component receives the optical double-sideband modulated signal, filters it, and outputs a vestigial sideband signal. The optical receiving device includes a photoelectric conversion component and a signal processing component. The photoelectric conversion component receives the vestigial sideband signal, converts it into an analog electrical signal, and converts it into a digital electrical signal. The signal processing component receives the digital electrical signal and performs linear equalization and nonlinear equalization processing on it to compensate for linear and nonlinear impairments caused by dispersion in the vestigial sideband signal. Using the above optical transmission system can increase the transmission distance of optical signals in optical fibers.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to optical transmission systems and optical receiving devices. Background Technology

[0002] With the rapid development of the artificial intelligence and big data industries, the demand for high-speed fiber optic interconnects is becoming increasingly urgent. Considering cost and power consumption, short-distance optical interconnects between data centers primarily utilize direct-modulation, direct-detection optical transmission systems.

[0003] However, direct-modulation direct-detection optical transmission systems use a single photoelectric detector (PD) at the receiving end to complete photoelectric conversion. The square-law detection of the PD causes the received electrical signal to lose phase information. As a result, dispersion in the optical fiber link leads to a significant power fading in the spectrum of the received signal, which greatly limits the transmission distance of the optical signal in the optical fiber.

[0004] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this application is to provide an optical transmission system and an optical receiving device, which aim to increase the transmission distance of optical signals in optical fibers.

[0006] To achieve the above objectives, in a first aspect, this application provides an optical transmission system, comprising: an optical transmitting device and an optical receiving device;

[0007] The optical transmitting device includes a light source component and a filtering component. The light source component is used to output an optical double-sideband modulated signal. The filtering component is used to receive the optical double-sideband modulated signal, filter the optical double-sideband modulated signal, and output an optical vestigial sideband signal.

[0008] The optical receiving device includes a photoelectric conversion component and a signal processing component. The photoelectric conversion component is used to receive the optical vestigial sideband signal, convert the optical vestigial sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal. The signal processing component is used to receive the digital electrical signal and perform linear equalization and nonlinear equalization processing on the digital electrical signal to compensate for the linear and nonlinear damage caused by dispersion in the optical vestigial sideband signal.

[0009] In the aforementioned optical transmission system, at the transmitting end, the light source component outputs a double-sideband modulated optical signal. The filtering component can filter out either the left or right sideband of the double-sideband modulated signal, generating a vestigial sideband signal. This allows some phase information of the signal to be retained after photoelectric conversion at the receiving end. The signal processing component can then perform linear equalization on the digital electrical signal converted from the vestigial sideband signal, compensating for the linear impairment caused by dispersion. Furthermore, the residual sidebands in the vestigial sideband signal also introduce nonlinear impairment. The signal processing component can also perform nonlinear equalization on the digital electrical signal converted from the vestigial sideband signal, compensating for the nonlinear impairment caused by dispersion. Therefore, the optical transmission system of this embodiment can compensate for the linear and nonlinear impairments caused by dispersion in the vestigial sideband signal, thereby reducing the negative impact of dispersion on the received signal and reducing the limitation of optical signal transmission distance in optical fiber caused by dispersion, ultimately increasing the transmission distance of the optical signal in optical fiber.

[0010] In one embodiment, the light source assembly includes:

[0011] A digital signal processor, the digital signal processor being used to generate digitally modulated signals;

[0012] A digital-to-analog converter, wherein the input terminal of the digital-to-analog converter is connected to the output terminal of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal;

[0013] An electrical amplifier, the input of which is connected to the output of the digital-to-analog converter, is used to amplify the analog signal;

[0014] Laser, used to generate laser light;

[0015] A modulator, the input of which is connected to the output of the electrical amplifier, is used to receive the laser and modulate the laser based on the amplified analog signal to output the optical double-sideband modulated signal.

[0016] In one embodiment, the filtering component includes an optical filter that filters the optical double-sideband modulation signal and outputs the optical residual sideband signal.

[0017] In one embodiment, the photoelectric conversion component includes:

[0018] A photodetector is used to receive the optical vestigial sideband signal and convert the optical vestigial sideband signal into the analog electrical signal;

[0019] A transimpedance amplifier, the input of which is connected to the output of the photodetector, is used to amplify the analog electrical signal.

[0020] An analog-to-digital converter is connected to the output of the transimpedance amplifier. The analog-to-digital converter is used to convert the amplified analog electrical signal into a digital electrical signal.

[0021] In one embodiment, the signal processing component includes:

[0022] A linear equalizer, wherein the linear equalizer is used to perform linear equalization processing on the digital electrical signal;

[0023] A nonlinear equalizer is used to perform nonlinear equalization processing on the digital electrical signal.

[0024] In one embodiment, the linear equalizer includes a feedforward equalizer, the number of taps of which is positively correlated with the degree of inter-symbol interference caused by dispersion.

[0025] In one embodiment, the nonlinear equalizer includes a second-order Volterra equalizer.

[0026] Secondly, this application also provides an optical receiving device, which includes: a filtering component, a photoelectric conversion component, and a signal processing component;

[0027] The filtering component is used to receive the optical double-sideband modulation signal sent by the optical transmitting device, and to filter the optical double-sideband modulation signal to output the optical residual sideband signal.

[0028] The photoelectric conversion component is used to receive the optical vestigial sideband signal, convert the optical vestigial sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal;

[0029] The signal processing component is used to receive the digital electrical signal and perform linear equalization and nonlinear equalization processing on the digital electrical signal to compensate for the linear and nonlinear damage caused by dispersion in the optical vestigial sideband signal.

[0030] In the aforementioned optical receiving device, after receiving the optical double-sideband modulated signal transmitted by the optical transmitting device, the filtering component can filter out the left or right sideband signals of the optical double-sideband modulated signal, generating a vestigial sideband signal. After the photoelectric conversion component completes the photoelectric conversion of the vestigial sideband signal, some phase information of the signal can still be retained. Therefore, the signal processing component can perform linear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the linear impairment caused by dispersion. Furthermore, the residual sidebands in the vestigial sideband signal also introduce certain nonlinear impairments. The signal processing component can also perform nonlinear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the nonlinear impairment caused by dispersion. Therefore, the optical receiving device of this embodiment can compensate for the linear and nonlinear impairments caused by dispersion in the vestigial sideband signal, thereby reducing the negative impact of dispersion on the received signal, reducing the limitation of dispersion on the transmission distance of the optical signal in the optical fiber, and ultimately increasing the transmission distance of the optical signal in the optical fiber.

[0031] Thirdly, this application also provides an optical transmission system, which includes an optical transmitting device and an optical receiving device as described in the second aspect. The optical transmitting device is used to generate the optical double-sideband modulation signal and transmit the optical double-sideband modulation signal to the optical receiving device.

[0032] The advantages of the aforementioned optical transmission system relative to the relevant technology are the same as those of the aforementioned optical receiving device relative to the relevant technology, and will not be repeated here.

[0033] In one embodiment, the light transmitting device includes a light source assembly; the light source assembly includes:

[0034] A digital signal processor, the digital signal processor being used to generate digitally modulated signals;

[0035] A digital-to-analog converter, wherein the input terminal of the digital-to-analog converter is connected to the output terminal of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal;

[0036] An electrical amplifier, the input of which is connected to the output of the digital-to-analog converter, is used to amplify the analog signal;

[0037] Laser, used to generate laser light;

[0038] A modulator, the input of which is connected to the output of the electrical amplifier, is used to receive the laser and modulate the laser based on the amplified analog signal to output the optical double-sideband modulated signal. Attached Figure Description

[0039] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0040] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a schematic diagram of the structure of an optical transmission system in one embodiment of this application;

[0042] Figure 2 This is a schematic diagram of the spectrum of an optical double-sideband modulated signal;

[0043] Figure 3 This is a schematic diagram of the spectrum of an optical single-sideband signal;

[0044] Figure 4 This is a schematic diagram of the spectrum of the optical vestigial sideband signal;

[0045] Figure 5 A schematic diagram of the power fading spectrum caused by dispersion after the DSB signal completes photoelectric conversion;

[0046] Figure 6 This is a schematic diagram of the optical transmission system in another embodiment of this application;

[0047] Figure 7 This is a schematic diagram of the optical transmission system in another embodiment of this application;

[0048] Figure 8 This is a schematic diagram of the structure of a five-tap feedforward equalizer in another embodiment of this application;

[0049] Figure 9 This is a schematic diagram of the structure of an optical receiving device in one embodiment of this application;

[0050] Figure 10 This is a schematic diagram of the structure of an optical transmission system in another embodiment of this application.

[0051] Explanation of icon numbers:

[0052] 1-Optical transmitting device, 11-Light source assembly, 111-Digital signal processor, 112-Digital-to-analog converter, 113-Electrical amplifier, 114-Laser, 115-Modulator, 12-Filtering assembly, 121-Optical filter, 2-Optical receiving device, 21-Photoelectric conversion assembly, 211-Photodetector, 212-Transimpedance amplifier, 213-Analog-to-digital converter, 22-Signal processing assembly, 221-Linear equalizer, 222-Nonlinear equalizer, 3-Optical receiving device, 31-Filtering assembly, 32-Photoelectric conversion assembly, 33-Signal processing assembly, 4-Optical transmitting device.

[0053] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0054] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0055] To better understand the technical solutions of this application, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0056] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0057] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0058] With the rapid development of the artificial intelligence and big data industries, the demand for high-speed fiber optic interconnects is becoming increasingly urgent. Considering cost and power consumption, short-distance optical interconnects between data centers primarily utilize direct-modulation, direct-detection optical transmission systems.

[0059] However, direct-modulation direct-detection optical transmission systems use a single photoelectric detector (PD) at the receiving end for photoelectric conversion. The square-law detection of the PD causes the received electrical signal to lose phase information. Consequently, dispersion in the fiber optic link leads to a significant power attenuation in the received signal's spectrum, severely limiting the transmission distance of the optical signal in the fiber. The O-band has relatively low dispersion, so current direct-modulation direct-detection optical modules operate in the O-band. However, when the single-wavelength rate is ≥200Gb / s, even using the O-band, the dispersion of edge wavelengths in commonly used coarse wavelength division multiplexing systems begins to affect the direct-modulation direct-detection optical signal, limiting its transmission distance to within 10km, making it difficult to meet the needs of long-distance optical transmission. As the single-wavelength rate continues to increase, it is foreseeable that its transmission distance will continue to shorten, limiting long-distance application scenarios. Therefore, a direct-modulation direct-detection optical transmission system implementation scheme that can achieve dispersion compensation is needed to improve the transmission distance based on single-wavelength 200Gb / s and above optical modules, expanding the application scenarios of this type of high-speed optical module.

[0060] Based on this, such as Figure 1 As shown in the figure, this application provides an optical transmission system, including an optical transmitting device 1 and an optical receiving device 2. The optical transmitting device 1 is located at the optical transmitting end, and the optical receiving device 2 is located at the optical receiving end.

[0061] The optical transmitting device 1 includes a light source assembly 11 and a filtering assembly 12. The light source assembly 11 is used to output an optical double-sideband modulated signal; the filtering assembly 12 is used to receive the optical double-sideband modulated signal, filter the optical double-sideband modulated signal, and output an optical vestigial sideband signal. A schematic diagram of the spectrum of the optical double-sideband modulated signal is shown below. Figure 2 As shown, the optical double-sideband modulated signal is an optical signal containing two sidebands output by the light source component 11 through a specific modulation method. During the modulation process, certain characteristics of the light source (such as light intensity and frequency) change with the input electrical signal, thereby loading the information carried by the electrical signal onto the optical signal, forming an optical double-sideband modulated signal containing rich information. The filtering component 12 is an important part of the optical transmitting device 1 for further signal processing. The filtering component 12 filters the optical double-sideband modulated signal, aiming to filter out one sideband of the optical modulation signal while retaining the other sideband (i.e., filtering out the left or right sideband signal of the optical double-sideband modulated signal), such as... Figure 3 As shown, ideally, the generated spectrum would be as follows: Figure 3 The image shows a single-sideband optical signal. However, it is practically difficult to completely filter out one sideband while retaining the other. Therefore, the filter component 12 will output a residual optical sideband signal, such as... Figure 4 As shown, Figure 4This is a schematic diagram of the spectrum of the optical residual sideband signal.

[0062] The optical receiving device 2 includes a photoelectric conversion component 21 and a signal processing component 22. The photoelectric conversion component 21 is used to receive optical vestigial sideband signals, convert the optical vestigial sideband signals into analog electrical signals, and convert the analog electrical signals into digital electrical signals. The signal processing component 22 is used to receive digital electrical signals and perform linear equalization and nonlinear equalization processing on the digital electrical signals to compensate for the linear and nonlinear damage caused by dispersion in the optical vestigial sideband signals.

[0063] It is understandable that in transmission media such as optical fibers, light of different frequencies travels at different speeds, which is the phenomenon of dispersion. Optical VSB (vestigial sideband) signals contain a certain frequency range. Due to dispersion, the light components of different frequencies in the signal travel at different speeds during transmission, causing the signal pulses to broaden in time. As the transmission distance increases, this broadening effect gradually accumulates, leading to pulse overlap and thus ISI (Inter-symbol interference), i.e., linear impairment. After receiving the optical vestigial sideband signal, the photoelectric conversion component 21 can convert it into an analog electrical signal and then into a digital electrical signal. The signal processing component 22 can perform linear equalization on the digital electrical signal, thereby compensating for the linear impairment.

[0064] like Figure 5 As shown, if the optical transmitting device 1 transmits a DSB (double sideband) signal, the square-law detection of the photoelectric conversion component 21 will cause the received electrical signal to lose phase information. Therefore, the dispersion in the optical fiber link will cause a significant power fading in the spectrum of the received signal, resulting in substantial nonlinear impairment. Similarly, when using an optical VSB signal, the residual sideband will also cause some nonlinear impairment. After receiving the optical residual sideband signal, the photoelectric conversion component 21 can convert the optical residual sideband signal into an analog electrical signal, and then convert the analog electrical signal into a digital electrical signal. The signal processing component 22 can perform nonlinear equalization processing on the digital electrical signal, thereby compensating for the nonlinear impairment.

[0065] In the aforementioned optical transmission system, at the transmitting end, the light source component 11 outputs a double-sideband modulated optical signal. The filtering component 12 can filter out the left or right sideband signals of the double-sideband modulated optical signal, generating a vestigial sideband signal. This allows some phase information of the signal to be retained after photoelectric conversion by the photoelectric conversion component 21 at the receiving end. The signal processing component 22 can then perform linear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the linear impairment caused by dispersion. Furthermore, the residual sidebands in the vestigial sideband signal also introduce nonlinear impairment. The signal processing component 22 can also perform nonlinear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the nonlinear impairment caused by dispersion. Therefore, the optical transmission system of this embodiment can compensate for the linear and nonlinear impairments caused by dispersion in the vestigial sideband signal, thereby reducing the negative impact of dispersion on the received signal and reducing the limitation of optical signal transmission distance in optical fiber caused by dispersion, thus increasing the transmission distance of optical signal in optical fiber.

[0066] In one embodiment, such as Figure 6 As shown, the light source assembly 11 includes: a digital signal processor 111, a digital-to-analog converter 112, an electric amplifier 113, a laser 114, and a modulator 115.

[0067] Digital signal processor 111 generates a digitally modulated signal. The input of digital-to-analog converter 112 is connected to the output of digital signal processor 111, and digital-to-analog converter 112 converts the digitally modulated signal into an analog signal. The input of electrical amplifier 113 is connected to the output of digital-to-analog converter 112, and electrical amplifier 113 amplifies the analog signal. Laser 114 generates laser light. The input of modulator 115 is connected to the output of electrical amplifier 113, and modulator 115 receives the laser light and modulates it based on the amplified analog signal, outputting a double-sideband modulated optical signal.

[0068] The digital signal processor 111 can generate a digitally modulated signal by sequentially performing operations such as bit mapping, pulse shaping, and resampling. The laser 114 can be a continuous wave laser, such as a DFB (distributed feedback laser) laser.

[0069] It is understood that the digital-to-analog converter 112, having a digital-to-analog conversion function, can convert the received digital modulation signal into an analog signal. Subsequently, the amplifier 113 amplifies the input analog signal, increasing its amplitude and power to meet the requirements of subsequent modulation. The amplified analog signal has stronger driving capability. Simultaneously, the laser 114 continuously generates laser light. As a high-energy, highly directional light source, the laser provides a carrier wave for the modulation process. The modulator 115 receives the laser light from the laser 114 and, based on the amplified analog signal, modulates the laser light, loading the information from the analog signal onto the laser light, ultimately outputting an optical double-sideband modulated signal. This optical double-sideband modulated signal can be efficiently transmitted through transmission media such as optical fibers, thereby enabling long-distance information transmission.

[0070] In one embodiment, such as Figure 6 As shown, the filtering component 12 includes an optical filter 121. The optical filter 121 filters the optical double-sideband modulated signal and outputs the optical residual sideband signal.

[0071] In this optical double-sideband modulation signal, which contains two sidebands, by precisely setting the center frequency of the optical filter 121, the optical filter 121 can retain the other sideband while filtering out one of the sidebands of the optical double-sideband modulation signal.

[0072] Assuming the filter edges are steep enough, meaning the transition between the passband and stopband is very rapid, it can precisely filter out the desired frequency components, thoroughly suppress unwanted sidebands, and produce almost no loss for the sidebands that need to be retained. Figure 3 The image shows an example of filtering out the right-sideband and retaining the left-sideband signal. Similarly, by selecting a suitable optical filter 121, the left-sideband can also be filtered out while retaining the right-sideband. In this ideal case, the optical signal processed by optical filter 121 contains only one sideband, thus generating an ideal optical single-sideband (SSB) signal. This optical SSB signal has many advantages in optical communication, such as effectively saving spectrum resources, reducing interference during signal transmission, and improving the efficiency and reliability of the communication system. However, because the edge steepness of the practically usable optical filter 121 is insufficient, filtering will produce something similar to... Figure 4 The residual sideband size depends on the steepness of the edge of the optical filter 121. The steeper the edge of the optical filter 121, the smaller the residual sideband, and the lower the processing complexity of the receiver signal processing component 22.

[0073] In this embodiment, the optical double-sideband modulated signal is filtered by the optical filter 121 to output a residual optical sideband signal. This ensures that after photoelectric conversion by the photoelectric conversion component 21 at the receiving end, some phase information of the signal can still be retained. Therefore, the signal processing component 22 can perform linear and nonlinear equalization to compensate for linear and nonlinear impairments caused by dispersion. Furthermore, this configuration increases the fiber optic transmission distance while reducing the computational complexity of the signal processing component 22 at the receiving end, thereby reducing the power consumption of the signal processing component 22.

[0074] In one embodiment, such as Figure 7 As shown, the photoelectric conversion component 21 includes: a photodetector 211, a transimpedance amplifier 212, and an analog-to-digital converter 213.

[0075] Photodetector 211 receives vestigial sideband signals and converts them into analog electrical signals. The input of transimpedance amplifier 212 is connected to the output of photodetector 211, and it amplifies the analog electrical signals. Analog-to-digital converter 213 is connected to the output of transimpedance amplifier 212, and it converts the amplified analog electrical signals into digital electrical signals.

[0076] In this embodiment, the photodetector 211 functions to convert optical signals into electrical signals. The vestigial optical sideband signal is an optical signal that has undergone special modulation and filtering, carrying specific information. The photodetector 211 operates based on the photoelectric effect principle, converting the vestigial optical sideband signal into an analog electrical signal. The amplitude and variation of this analog electrical signal correspond to the intensity and characteristics of the input vestigial optical sideband signal, thus preserving the information carried by the vestigial optical sideband signal.

[0077] Then, the transimpedance amplifier 212 plays a crucial role in signal amplification throughout the system. Its input is connected to the output of the photodetector 211, and it is responsible for receiving the analog electrical signal converted by the photodetector 211. Since the analog electrical signal output by the photodetector 211 is usually quite weak and difficult to process and analyze directly, the transimpedance amplifier 212 is needed to amplify it. The unique design of the transimpedance amplifier 212 enables it to convert the input current signal (the analog electrical signal output by the photodetector 211 is essentially a current signal) into a voltage signal, and to amplify the signal significantly during the conversion process. By precisely designing the circuit parameters of the transimpedance amplifier 212, it is possible to ensure that while amplifying the signal, it minimizes the introduction of noise, improves the signal quality and stability, and provides an analog electrical signal input of suitable amplitude for the analog-to-digital converter 213.

[0078] The function of the analog-to-digital converter 213 is to convert the analog electrical signal amplified by the transimpedance amplifier 212 into a digital electrical signal, so that the signal processing component 22 can receive the digital electrical signal and perform linear and nonlinear equalization on the digital electrical signal to compensate for the linear and nonlinear damage caused by dispersion in the optical residual sideband signal, thereby reducing the negative impact of dispersion on the received signal and reducing the limitation of dispersion on the transmission distance of the optical signal in the optical fiber, thus increasing the transmission distance of the optical signal in the optical fiber.

[0079] In one embodiment, such as Figure 7 As shown, the signal processing component 22 includes a linear equalizer 221 and a nonlinear equalizer 222.

[0080] Linear equalizer 221 is used to perform linear equalization processing on digital electrical signals. Nonlinear equalizer 222 is used to perform nonlinear equalization processing on digital electrical signals.

[0081] The operations performed by the signal processing component 22 may include resampling, clock recovery, signal synchronization, signal equalization, and demodulation. Signal equalization is performed by a linear equalizer 221 and a nonlinear equalizer 222.

[0082] It is understandable that the linear equalizer 221 performs linear equalization processing on the digital electrical signal, compensating for the linear impairment caused by dispersion. Similarly, the nonlinear equalizer 222 is used to perform nonlinear equalization processing on the digital electrical signal, compensating for the nonlinear impairment caused by dispersion. By using the optical transmitting device 1 to generate a VSB signal at the transmitting end, and then using the linear equalizer 221 and the nonlinear equalizer 222 at the receiving end to compensate for signal impairment, dispersion compensation can be achieved. This allows for a more complete recovery of the signal transmitted at the receiving end, reducing the limitation of optical signal transmission distance in optical fiber caused by dispersion and increasing the transmission distance of optical signal in optical fiber.

[0083] In one embodiment, the linear equalizer 221 includes a feedforward equalizer, the number of taps of which is positively correlated with the degree of inter-symbol interference caused by dispersion.

[0084] A feedforward equalizer typically includes multiple tapped delay lines, multipliers, and adders. The tapped delay lines divide the received signal into multiple samples with time delay, each sample corresponding to a tap. Each tap is connected to a multiplier, whose other input is a corresponding weighting coefficient. These weighting coefficients are adjusted according to channel characteristics, determining the contribution of each tap sample to the final output. The outputs of all multipliers are then summed by an adder to obtain the equalized signal. By adjusting these weighting coefficients, the feedforward equalizer can adapt to different channel conditions. In this embodiment, the greater the dispersion, the more symbols affected by ISI (i.e., the greater the linear impairment), and the more feedforward equalizer taps are required. Therefore, by using a feedforward equalizer to perform linear equalization on the digital signal, making the number of feedforward equalizer taps positively correlated with the degree of inter-symbol interference caused by dispersion, the feedforward equalizer can better compensate for the linear impairment caused by dispersion. For example, as shown... Figure 8 As shown, Figure 8 This is a schematic diagram of a five-tap feedforward equalizer. As you can see, the output symbol is generated by combining five symbols from the front and back. The purpose is to eliminate the influence of the ISI of the front and back symbols on the current symbol.

[0085] It is understandable that a VSB signal is generated at the transmitting end using a light source assembly 11 and a filter assembly 12, and at the receiving end, a linear equalizer 221 and a nonlinear equalizer 222 are used to compensate for signal impairments. Based on the different sizes of residual sidebands in the VSB signal caused by the varying filtering performance of different filter assemblies 12, the tap settings of the equalizer at the receiving end can be flexibly adjusted to achieve a balance between transmission performance, cost, and power consumption, thus achieving the best dispersion compensation effect with the lowest cost and power consumption.

[0086] It should be noted that the linear equalizer 221 of this application can also use other types of equalizers, such as the minimum mean square error equalizer.

[0087] In one embodiment, the nonlinear equalizer 222 includes a second-order Volterra equalizer.

[0088] The Volterra equalizer is based on Volterra series theory. Volterra series are a mathematical tool for modeling nonlinear systems, representing the output of the nonlinear system as the sum of convolution integrals of the input signal at various orders. The second-order Volterra equalizer primarily considers the first and second-order terms of the input signal to model and compensate for the nonlinear channel.

[0089] Assuming the input signal of a second-order Volterra equalizer is x(n) and the output signal is y(n), then y(n) can be expressed by the following formula:

[0090]

[0091] Where h(l1) are the first-order kernel coefficients, corresponding to the equalization of linear impairments. h(l1, l2) are the second-order kernel coefficients, corresponding to the equalization of nonlinear impairments. lm is the memory depth of the m-th kernel, and Lm controls the number of equalization tap sequences for the m-th kernel. n in x(n) represents the signal sequence of the input equalizer, and n in y(n) represents the signal sequence of the output equalizer. P represents the interval between taps of the second-order kernels. Adjusting the value of P controls the depth of the second-order kernel, corresponding to the magnitude of the nonlinear impairment.

[0092] It is understandable that nonlinear impairments are compensated for using a second-order Volterra equalizer, with the complexity of the nonlinear equalization flexibly adjusted according to the size of the residual sidebands. This reduces the complexity of the receiver's equalization algorithm while ensuring the stability of the transmitter's basic architecture, and allows directly modulated, directly detected signals to be transmitted over longer distances in single-mode fiber.

[0093] It should be noted that the nonlinear equalizer 222 can also be other types of equalizers, or the signal processing component 22 can perform nonlinear equalization in other ways, such as using an artificial intelligence network for nonlinear equalization.

[0094] This application also provides an optical receiving device 3, such as... Figure 9 As shown, the optical receiving device 3 includes: a filtering component 31, a photoelectric conversion component 32, and a signal processing component 33.

[0095] The filtering component 31 receives the optical double-sideband modulation signal transmitted by the optical transmitting device 4, filters the optical double-sideband modulation signal, and outputs the optical vestigial sideband signal. The photoelectric conversion component 32 receives the optical vestigial sideband signal, converts the optical vestigial sideband signal into an analog electrical signal, and converts the analog electrical signal into a digital electrical signal. The signal processing component 33 receives the digital electrical signal and performs linear equalization and nonlinear equalization processing on the digital electrical signal to compensate for the linear and nonlinear impairments caused by dispersion in the optical vestigial sideband signal.

[0096] It can be observed that in the optical transmission system of the aforementioned embodiment, the filter component 12 is located at the optical transmitting end, while in this embodiment, the filter component 31 is located at the optical receiving end. Therefore, in this embodiment, the optical double-sideband modulation signal transmitted by the optical transmitting device 4 is received at the receiving end through the filter component 31, and the optical double-sideband modulation signal is filtered to output a vestigial optical sideband signal. Then, the photoelectric conversion component 32 performs photoelectric conversion on the vestigial optical sideband signal, and the signal processing component 33 performs linear and nonlinear equalization on the digital electrical signal converted from the vestigial optical sideband signal to compensate for the linear and nonlinear damage caused by dispersion, thereby reducing the negative impact of dispersion on the received signal and reducing the limitation of dispersion on the transmission distance of the optical signal in the optical fiber, thus increasing the transmission distance of the optical signal in the optical fiber.

[0097] It should be noted that the components in the optical transmission system of this application embodiment and the aforementioned embodiment can adopt the same structure, that is, the structure of the filter component 31, the photoelectric conversion component 32 and the signal processing component 33 can be the structure of the aforementioned embodiment, and will not be repeated here.

[0098] After receiving the optical double-sideband modulated signal transmitted by the optical transmitting device 4, the optical receiving device 3 can filter out the left or right sideband signals of the optical double-sideband modulated signal using the filtering component 31, generating a vestigial sideband signal. After the photoelectric conversion component 32 completes the photoelectric conversion of the vestigial sideband signal, some phase information of the signal can still be retained. Therefore, the signal processing component 33 can perform linear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the linear impairment caused by dispersion. Furthermore, the residual sidebands in the vestigial sideband signal also introduce certain nonlinear impairments. The signal processing component 33 can also perform nonlinear equalization on the digital electrical signal converted from the vestigial sideband signal to compensate for the nonlinear impairment caused by dispersion. Therefore, the optical receiving device 3 of this embodiment can compensate for the linear and nonlinear impairments caused by dispersion in the vestigial sideband signal, thereby reducing the negative impact of dispersion on the received signal, reducing the limitation of dispersion on the transmission distance of the optical signal in the optical fiber, and thus increasing the transmission distance of the optical signal in the optical fiber.

[0099] This application also provides an optical transmission system, such as... Figure 10 As shown, the optical transmission system includes an optical transmitting device 4 and an optical receiving device 3 as described in the previous embodiment. The optical transmitting device 4 is used to generate an optical double-sideband modulated signal and send the optical double-sideband modulated signal to the optical receiving device 3.

[0100] The advantages of the optical transmission system relative to the correlation technology described above are the same as the advantages of the optical receiving device 3 relative to the correlation technology in the previous embodiment, and will not be repeated here.

[0101] In one embodiment, the light transmitting device 4 includes a light source assembly. The light source assembly includes a digital signal processor, a digital-to-analog converter, an electrical amplifier, a laser, and a modulator.

[0102] A digital signal processor (DSP) is used to generate digitally modulated signals. The input of a digital-to-analog converter (DAC) is connected to the output of the DSP; the DAC converts the digitally modulated signals into analog signals. An electrical amplifier (EMA) is connected to the output of the DAC; the EMA amplifies the analog signals. A laser is used to generate laser light. The input of a modulator is connected to the output of the EMA; the modulator receives the laser light and modulates it based on the amplified analog signals, outputting a double-sideband modulated optical signal.

[0103] The optical transmitting device 4 in this embodiment differs from the optical transmitting device 1 of the optical transmission system in the aforementioned embodiment in that the optical transmitting device 4 in this embodiment does not include the filtering component 31, which is located at the optical receiving end, while the optical transmitting device 1 of the optical transmission system in the aforementioned embodiment includes the filtering component 12, which is located at the optical transmitting end. Therefore, the optical transmitting device 4 in this embodiment outputs a double-sideband modulated optical signal, rather than a vestigial sideband optical signal. For a description of the light source components, please refer to the description of the light source components in the aforementioned embodiments; it will not be repeated here.

[0104] The above description is only a part of the embodiments of this application and does not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. An optical transmission system, characterized in that, The optical transmission system includes: an optical transmitting device and an optical receiving device; The optical transmitting device includes a light source component and a filtering component. The light source component is used to output an optical double-sideband modulation signal. The filtering component is used to receive the optical double-sideband modulation signal, filter the optical double-sideband modulation signal, and output an optical residual sideband signal that retains some phase information. The optical receiving device includes a photoelectric conversion component and a signal processing component. The photoelectric conversion component is used to receive the optical vestigial sideband signal, convert the optical vestigial sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal. The signal processing component includes a linear equalizer and a nonlinear equalizer. The linear equalizer is used to perform linear equalization processing on the digital electrical signal, and the nonlinear equalizer is used to perform nonlinear equalization processing on the digital electrical signal to compensate for the linear and nonlinear damage caused by dispersion in the optical vestigial sideband signal. The linear equalizer includes a feedforward equalizer, the number of taps of which is positively correlated with the degree of inter-symbol interference caused by dispersion; the nonlinear equalizer includes a second-order Volterra equalizer.

2. The optical transmission system according to claim 1, characterized in that, The light source assembly includes: A digital signal processor, the digital signal processor being used to generate digitally modulated signals; A digital-to-analog converter, wherein the input terminal of the digital-to-analog converter is connected to the output terminal of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal; An electrical amplifier, the input of which is connected to the output of the digital-to-analog converter, is used to amplify the analog signal; Laser, used to generate laser light; A modulator, the input of which is connected to the output of the electrical amplifier, is used to receive the laser and modulate the laser based on the amplified analog signal to output the optical double-sideband modulated signal.

3. The optical transmission system according to claim 1, characterized in that, The filtering component includes an optical filter, which filters the optical double-sideband modulation signal and outputs the optical residual sideband signal.

4. The optical transmission system according to claim 1, characterized in that, The photoelectric conversion component includes: A photodetector is used to receive the optical vestigial sideband signal and convert the optical vestigial sideband signal into the analog electrical signal; A transimpedance amplifier, the input of which is connected to the output of the photodetector, is used to amplify the analog electrical signal. An analog-to-digital converter is connected to the output of the transimpedance amplifier. The analog-to-digital converter is used to convert the amplified analog electrical signal into a digital electrical signal.

5. An optical receiving device, characterized in that, The optical receiving device includes: a filtering component, a photoelectric conversion component, and a signal processing component; The filtering component is used to receive the optical double-sideband modulation signal sent by the optical transmitting device, and to filter the optical double-sideband modulation signal to output the optical residual sideband signal. The photoelectric conversion component is used to receive the optical vestigial sideband signal, convert the optical vestigial sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal; The signal processing component includes a linear equalizer and a nonlinear equalizer. The linear equalizer is used to perform linear equalization processing on the digital electrical signal, and the nonlinear equalizer is used to perform nonlinear equalization processing on the digital electrical signal to compensate for the linear and nonlinear damage caused by dispersion in the optical vestigial sideband signal. The linear equalizer includes a feedforward equalizer, the number of taps of which is positively correlated with the degree of inter-symbol interference caused by dispersion; the nonlinear equalizer includes a second-order Volterra equalizer.

6. An optical transmission system, characterized in that, The optical transmission system includes an optical transmitting device and an optical receiving device as described in claim 5, wherein the optical transmitting device is used to generate an optical double-sideband modulated signal and transmit the optical double-sideband modulated signal to the optical receiving device.

7. The optical transmission system according to claim 6, characterized in that, The optical transmitting device includes a light source assembly; the light source assembly includes: A digital signal processor, the digital signal processor being used to generate digitally modulated signals; A digital-to-analog converter, wherein the input terminal of the digital-to-analog converter is connected to the output terminal of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal; An electrical amplifier, the input of which is connected to the output of the digital-to-analog converter, is used to amplify the analog signal; Laser, used to generate laser light; A modulator, the input of which is connected to the output of the electrical amplifier, is used to receive the laser and modulate the laser based on the amplified analog signal to output the optical double-sideband modulated signal.

Images