Optical transmission system and optical receiving device

Abstract

The invention discloses an optical transmission system and an optical receiving device, and relates to the technical field of optical communication. The optical transmission system comprises an optical transmitting device and an optical receiving device. The light sending device comprises a light source assembly and a filtering assembly. The light source assembly is used for outputting a light double-sideband modulation signal. The filtering assembly is used for receiving the optical double-sideband modulation signal, filtering the optical double-sideband modulation signal and outputting an optical residual sideband signal; the light receiving device comprises a photoelectric conversion assembly and a signal processing assembly, and the photoelectric conversion assembly is used for receiving the light residual sideband signal, converting the light residual sideband signal into an analog electric signal and converting the analog electric signal into a digital electric signal; and the signal processing assembly is used for receiving the digital electric signal and carrying out linear equalization processing and nonlinear equalization processing on the digital electric signal so as to compensate linear and nonlinear damage caused by dispersion in the light residual sideband signal. By adopting the optical transmission system, the transmission distance of the optical signal in the optical fiber can be increased.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to an optical transmission system and an optical receiving device. Background Art

[0002] With the rapid development of artificial intelligence and big data industries, the demand for high-speed fiber optic interconnection is becoming increasingly urgent. Due to cost and power consumption considerations, the optical interconnection between short distances in data centers mainly adopts direct modulation and direct detection optical transmission systems.

[0003] However, the direct modulation and direct detection optical transmission system uses a single photoelectric detector (PD) at the receiving end to complete the photoelectric conversion. The square-law detection of the PD causes the received electrical signal to lose phase information. Therefore, the dispersion in the optical fiber link will cause the spectrum of the received signal to have a large power attenuation, which greatly limits the transmission distance of the optical signal in the optical fiber.

[0004] The above contents are only used to assist in understanding the technical solution of the present application and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the present application is to provide an optical transmission system and an optical receiving device, aiming to increase the transmission distance of optical signals in optical fibers.

[0006] To achieve the above-mentioned object, in a first aspect, the present application provides an optical transmission system, including: an optical transmitting device and an optical receiving device;

[0007] The optical transmitting device comprises a light source component and a filter component, wherein the light source component is used to output an optical double-sideband modulated signal; the filter component is used to receive the optical double-sideband modulated signal, filter the optical double-sideband modulated signal, and output an optical residual sideband signal;

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

[0009] In the above optical transmission system, at the transmitting end, the light source component outputs an optical double-sideband modulated signal, and the filtering component can filter out the left band or right band signal of the optical double-sideband modulated signal to generate an optical residual sideband signal, so that after the photoelectric conversion is completed by the photoelectric conversion component at the receiving end, part of the phase information of the signal can still be retained, so that the digital electrical signal converted from the optical residual sideband signal can be linearly balanced by the signal processing component to compensate for the linear damage caused by dispersion. In addition, the residual sideband in the optical residual sideband signal will also bring certain nonlinear damage, and the signal processing component can also perform nonlinear equalization on the digital electrical signal converted from the optical residual sideband signal to compensate for the nonlinear damage caused by dispersion. Therefore, the optical transmission system of this embodiment can 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, 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.

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

[0011] A digital signal processor, the digital signal processor is used to generate a digital modulation signal;

[0012] A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end 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 electric amplifier, the input end of the electric amplifier being connected to the output end of the digital-to-analog converter, and the electric amplifier being used to amplify the analog signal;

[0014] A laser for generating laser light;

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

[0016] In one embodiment, the filtering component includes: an optical filter, which performs filtering processing on the optical double-sideband modulated signal and outputs the optical residual sideband signal.

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

[0018] A photodetector, configured to receive the optical residual sideband signal and convert the optical residual sideband signal into the analog electrical signal;

[0019] A transimpedance amplifier, wherein the input end of the transimpedance amplifier is connected to the output end of the photodetector, and the transimpedance amplifier is used to amplify the analog electrical signal;

[0020] An analog-to-digital converter is connected to the output end of the transimpedance amplifier, and 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 comprises a feedforward equalizer, and the number of taps of the feedforward equalizer is positively correlated with the degree of inter-symbol interference caused by dispersion.

[0025] In one embodiment, the non-linear equalizer comprises a second order Volterra equalizer.

[0026] In a second aspect, the present application further provides a light receiving device, the light receiving device comprising: a filtering component, a photoelectric conversion component and a signal processing component;

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

[0028] The optoelectronic conversion component is used to receive the optical residual sideband signal, convert the optical residual 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 processing and nonlinear equalization processing on the digital electrical signal to compensate for linear and nonlinear damage caused by dispersion in the optical residual sideband signal.

[0030] In the above optical receiving device, after receiving the optical double-sideband modulated signal sent by the optical transmitting device, the filtering component can filter out the left band or right band signal of the optical double-sideband modulated signal to generate an optical residual sideband signal. After the photoelectric conversion component completes the photoelectric conversion of the optical residual sideband signal, part of the phase information of the signal can still be retained, so that the digital electrical signal converted from the optical residual sideband signal can be linearly equalized by the signal processing component to compensate for the linear damage caused by dispersion. In addition, the residual sideband in the optical residual sideband signal will also cause certain nonlinear damage, and the signal processing component can also perform nonlinear equalization on the digital electrical signal converted from the optical residual sideband signal to compensate for the nonlinear damage caused by dispersion. Therefore, the optical receiving device of this embodiment can 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, 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.

[0031] In a third aspect, the present application also provides an optical transmission system, which includes an optical transmitting device and an optical receiving device as described in the second aspect, wherein the optical transmitting device is used to generate the optical double-sideband modulated signal and send the optical double-sideband modulated signal to the optical receiving device.

[0032] The advantages of the above optical transmission system over related technologies are the same as the advantages of the above optical receiving device over related technologies, which will not be repeated here.

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

[0034] A digital signal processor, the digital signal processor is used to generate a digital modulation signal;

[0035] A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end 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 electric amplifier, the input end of the electric amplifier being connected to the output end of the digital-to-analog converter, and the electric amplifier being used to amplify the analog signal;

[0037] A laser for generating laser light;

[0038] A modulator, wherein the input end of the modulator is connected to the output end of the electrical amplifier, and the modulator is used to receive the laser, and modulate the laser based on the analog signal after amplification, and output the optical double-sideband modulated signal. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

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

[0042] Figure 2 Schematic diagram of spectrum of optical double-sideband modulation signal;

[0043] Figure 3 Schematic diagram of the spectrum of an optical single sideband signal;

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

[0045] Figure 5 This is a schematic diagram of the power attenuation spectrum caused by dispersion after the DSB signal completes the photoelectric conversion;

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

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

[0048] Figure 8 This is a structural diagram of a five-tap feedforward equalizer in yet another embodiment of the present application;

[0049] Fig. 9 This is a schematic diagram of the structure of a light receiving device in one embodiment of the present application;

[0050] Fig.10 It is a structural schematic diagram of an optical transmission system in another embodiment of the present application.

[0051] Description of Figure Numbers:

[0052] 1-optical transmitting device, 11-light source component, 111-digital signal processor, 112-digital-to-analog converter, 113-electric amplifier, 114-laser, 115-modulator, 12-filter component, 121-optical filter, 2-optical receiving device, 21-photoelectric conversion component, 211-photodetector, 212-transimpedance amplifier, 213-analog-to-digital converter, 22-signal processing component, 221-linear equalizer, 222-nonlinear equalizer, 3-optical receiving device, 31-filter component, 32-photoelectric conversion component, 33-signal processing component, 4-optical transmitting device.

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

[0054] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0055] In order to better understand the technical solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

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

[0057] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0058] With the rapid development of artificial intelligence and big data industries, the demand for high-speed fiber optic interconnection is becoming increasingly urgent. Due to cost and power consumption considerations, the optical interconnection between short distances in data centers mainly adopts direct modulation and direct detection optical transmission systems.

[0059] However, the direct modulation and direct detection optical transmission system uses a single photoelectric detector (PD) at the receiving end to complete the photoelectric conversion. The square law detection of the PD causes the received electrical signal to lose phase information. Therefore, the dispersion in the optical fiber link will cause the spectrum of the received signal to have a large power attenuation, which greatly limits the transmission distance of the optical signal in the optical fiber. The dispersion of the O band is relatively low, so the current direct modulation and direct detection optical modules all work in the O band. However, when the single-wave rate is ≥200Gb / s, even if the O band is used, the dispersion of the edge wavelengths in the commonly used coarse wavelength division multiplexing system has begun to affect the direct modulation and direct detection optical signal, limiting its transmission distance to within 10km, and it is difficult to meet the needs of long-distance optical transmission. With the continued growth of the single-wave rate, it can be foreseen that its transmission distance will continue to shorten, and the long-distance application scenarios will be limited. Therefore, a direct modulation and direct detection optical transmission system implementation scheme that can achieve dispersion compensation is needed, which can increase the transmission distance based on single-wave 200Gb / s and above optical modules and expand the application scenarios of this type of high-speed optical modules.

[0060] Based on this, Figure 1 As shown, an embodiment of the present 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 an optical transmitting end, and the optical receiving device 2 is located at an optical receiving end.

[0061] The optical transmitting device 1 includes a light source component 11 and a filter component 12. The light source component 11 is used to output an optical double-sideband modulated signal; the filter component 12 is used to receive the optical double-sideband modulated signal, filter the optical double-sideband modulated signal, and output an optical residual sideband signal. The spectrum diagram of the optical double-sideband modulated signal is shown in FIG. Figure 2 As shown, the optical double-sideband modulated signal is a form of 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, frequency, etc.) will 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 filter component 12 is an important part of the optical transmitting device 1 for further processing of the signal. The filter component 12 performs filtering processing on the optical double-sideband modulated signal. The goal is to retain the other sideband (that is, to filter out the left or right sideband signal of the optical double-sideband modulated signal) while filtering out one of the sidebands of the optical modulated signal. Figure 3 As shown, the ideal situation is to produce a spectrum like Figure 3 However, it is difficult to completely filter out one sideband and retain the other sideband in practice, so the filter component 12 will output an optical residual sideband signal, such as Figure 4 As shown, Figure 4Schematic diagram of the spectrum of the optical residual sideband signal.

[0062] The optical receiving device 2 includes an optoelectronic conversion component 21 and a signal processing component 22. The optoelectronic conversion component 21 is used to receive the optical residual sideband signal, convert the optical residual sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal; the signal processing component 22 is used to receive the digital electrical signal and perform linear equalization 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.

[0063] It can be understood that in transmission media such as optical fibers, light of different frequencies has different propagation speeds during transmission, which is the dispersion phenomenon. The optical VSB (vestigial sideband) signal contains a certain frequency range. Due to dispersion, the light of different frequency components in the signal has different propagation speeds during the transmission process, causing the signal pulse to be broadened in time. As the transmission distance increases, this broadening effect will gradually accumulate, causing pulses to overlap with each other, thereby generating ISI (Inter-symbol interference), that is, linear damage. After the optoelectronic conversion component 21 receives the optical vestigial sideband signal, it can 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 22 can perform linear equalization processing on the digital electrical signal to compensate for the linear damage.

[0064] like Figure 5 As shown, if the optical transmitting device 1 sends a DSB (double sideband) signal, the square-law detection of the optoelectronic conversion component 21 will cause the received electrical signal to lose phase information, so the dispersion in the optical fiber link will cause a large power attenuation in the spectrum of the received signal, causing greater nonlinear damage. When using an optical VSB signal, the residual sideband will also cause certain nonlinear damage. Similarly, after receiving the optical residual sideband signal, the optoelectronic conversion component 21 can convert the optical residual sideband signal into an analog electrical signal, and 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 damage.

[0065] In the above optical transmission system, at the transmitting end, the light source component 11 outputs an optical double-sideband modulated signal, and the filter component 12 can filter out the left band or right band signal of the optical double-sideband modulated signal to generate an optical residual sideband signal, so that after the photoelectric conversion is completed by the photoelectric conversion component 21 at the receiving end, part of the phase information of the signal can still be retained, so that the digital electrical signal converted from the optical residual sideband signal can be linearly balanced by the signal processing component 22 to compensate for the linear damage caused by dispersion. In addition, the residual sideband in the optical residual sideband signal will also bring certain nonlinear damage, and the signal processing component 22 can also perform nonlinear equalization on the digital electrical signal converted from the optical residual sideband signal to compensate for the nonlinear damage caused by dispersion. Therefore, the optical transmission system of this embodiment can 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, 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.

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

[0067] The digital signal processor 111 is used to generate a digital modulation signal. The input end of the digital-to-analog converter 112 is connected to the output end of the digital signal processor 111, and the digital-to-analog converter 112 is used to convert the digital modulation signal into an analog signal. The input end of the electric amplifier 113 is connected to the output end of the digital-to-analog converter 112, and the electric amplifier 113 is used to amplify the analog signal. The laser 114 is used to generate laser light. The input end of the modulator 115 is connected to the output end of the electric amplifier 113, and the modulator 115 is used to receive the laser light, and modulate the laser light based on the amplified analog signal, and output an optical double-sideband modulated signal.

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

[0069] It can be understood that the digital-to-analog converter 112 has a digital-to-analog conversion function, and the digital-to-analog converter 112 can convert the received digital modulation signal into an analog signal. Subsequently, the electrical amplifier 113 amplifies the input analog signal to increase the amplitude and power of the signal to meet the needs of subsequent modulation. The amplified analog signal has a stronger driving ability. At the same time, the laser 114 continues to generate laser light. As a high-energy, highly directional light source, the laser provides a carrier for the modulation process. The modulator 115 can receive the laser from the laser 114, and based on the analog signal after amplification, modulate the laser, load the information of the analog signal onto the laser, and finally output an optical double-sideband modulated signal. This optical double-sideband modulated signal can be efficiently transmitted in a transmission medium such as an optical fiber, thereby realizing long-distance transmission of information.

[0070] In one embodiment, Figure 6 As shown, the filter assembly 12 includes an optical filter 121. The optical filter 121 performs filtering processing on the optical double sideband modulated signal and outputs an optical residual sideband signal.

[0071] The optical double-sideband modulation signal includes two sidebands. By accurately setting the center frequency of the optical filter 121 , the optical filter 121 can filter out one sideband of the optical double-sideband modulation signal and retain the other sideband.

[0072] Assuming that the edge of the filter is steep enough, that is, the transition between the passband and the stopband of the filter is very fast, it can screen out the required frequency components extremely accurately, completely suppress the unnecessary sidebands, and produce almost no loss on the sidebands that need to be retained. Figure 3 The figure 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 be filtered out and the right sideband can be retained. In this ideal case, the optical signal processed by the optical filter 121 contains only one sideband, thereby generating an ideal optical single sideband (SSB) signal. This optical SSB signal has many advantages in optical communications, such as effectively saving spectrum resources, reducing interference during signal transmission, and improving the efficiency and reliability of communication systems. However, because the edge steepness of the optical filter 121 that can actually be used is not enough, after filtering, it will produce something like Figure 4 The size of the residual sideband depends on the edge steepness of the optical filter 121. The steeper the edge of the optical filter 121, the smaller the residual sideband, and the lower the complexity of the signal processing component 22 at the receiving end.

[0073] In this embodiment, the optical double-sideband modulated signal is filtered by the optical filter 121, and the optical residual sideband signal is output, so that after the photoelectric conversion is completed by the photoelectric conversion component 21 at the receiving end, part of the phase information of the signal can still be retained, so that the signal processing component 22 can be used to perform linear equalization and nonlinear equalization to compensate for the linear damage and nonlinear damage caused by dispersion. In addition, through the above settings, the calculation complexity of the signal processing component 22 at the receiving end can be reduced while increasing the optical fiber transmission distance, thereby reducing the power consumption of the signal processing component 22.

[0074] In one embodiment, 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] The photodetector 211 is used to receive the optical residual sideband signal and convert the optical residual sideband signal into an analog electrical signal. The input end of the transimpedance amplifier 212 is connected to the output end of the photodetector 211, and the transimpedance amplifier 212 is used to amplify the analog electrical signal. The analog-to-digital converter 213 is connected to the output end of the transimpedance amplifier 212, and the analog-to-digital converter 213 is used to convert the amplified analog electrical signal into a digital electrical signal.

[0076] In this embodiment, the function of the photodetector 211 is to convert the optical signal into an electrical signal. The optical residual sideband signal is an optical signal that has been specially modulated and filtered and carries specific information. The photodetector 211 works based on the principle of the photoelectric effect and can convert the optical residual sideband signal into an analog electrical signal, and the amplitude and variation law of the analog electrical signal correspond to the intensity and characteristics of the input optical residual sideband signal, so the information carried by the optical residual sideband signal is retained.

[0077] Then, the transimpedance amplifier 212 plays a key role in signal amplification in the entire system. Its input end is connected to the output end of the photodetector 211, and 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 weak and difficult to directly perform subsequent processing and analysis, the transimpedance amplifier 212 is required 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 greatly amplify the signal during the conversion process. By accurately designing the circuit parameters of the transimpedance amplifier 212, it can be ensured that while amplifying the signal, the introduction of noise is minimized, the quality and stability of the signal are improved, and an analog electrical signal input with a suitable amplitude is provided to the analog-to-digital converter 213.

[0078] The function of the analog-to-digital converter 213 is to convert the analog electrical signal amplified and processed by the transimpedance amplifier 212 into a digital electrical signal, so that after the signal processing component 22 receives the digital electrical signal, it can perform linear equalization and nonlinear equalization on the digital electrical signal, and 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, 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.

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

[0080] The linear equalizer 221 is used to perform linear equalization processing on the digital electrical signal. The nonlinear equalizer 222 is used to perform nonlinear equalization processing on the digital electrical signal.

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

[0082] It can be understood that the linear equalizer 221 performs linear equalization processing on the digital electrical signal, and can compensate for the linear damage caused by dispersion. Similarly, the nonlinear equalizer 222 is used to perform nonlinear equalization processing on the digital electrical signal, and compensate for the nonlinear damage caused by dispersion. The optical transmitting device 1 is used at the transmitting end to generate a VSB signal, and the linear equalizer 221 and the nonlinear equalizer 222 are used at the receiving end to compensate for the signal damage, so that the dispersion can be compensated, so that the signal sent by the transmitting end can be restored more completely at the receiving end, reducing the limitation of the dispersion on the transmission distance of the optical signal in the optical fiber, and can increase the transmission distance of the optical signal in the optical fiber.

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

[0084] Among them, the feedforward equalizer usually includes multiple tapped delay lines, multipliers and adders. The tapped delay line divides the received signal into multiple samples according to time delay, and each sample corresponds to a tap. Each tap is connected to a multiplier, and the other input of the multiplier is the corresponding weight coefficient. These weight coefficients are adjusted according to the channel characteristics, and they determine the contribution of each tap sample to the final output. The outputs of all multipliers are then summed through the adder to obtain the signal after equalization. By adjusting these weight coefficients, the feedforward equalizer can be adapted to different channel conditions. Corresponding to this embodiment, the greater the dispersion, the more symbols affected by ISI (that is, the greater the linear damage), and the more feedforward equalizer taps are required. Therefore, the digital electrical signal is linearly equalized by the feedforward equalizer, so that the number of taps of the feedforward equalizer is positively correlated with the degree of inter-symbol interference caused by the dispersion, so that the feedforward equalizer can better compensate for the linear damage caused by the dispersion. For example, if Figure 8 As shown, Figure 8 This is a structural diagram of a five-tap feedforward equalizer. It can be seen that the output symbol is generated by the combination of a total of five symbols before and after. The purpose is to eliminate the impact of the ISI of the previous and next symbols on the symbol.

[0085] It can be understood that the VSB signal is generated by the light source component 11 and the filter component 12 at the transmitting end, and the signal damage is compensated at the receiving end in cooperation with the linear equalizer 221 and the nonlinear equalizer 222. According to the different sizes of the residual sidebands of the VSB signal caused by the difference in filtering performance of different filter components 12, the tap setting of the equalizer can be flexibly adjusted at the receiving end to balance the transmission performance with the cost and power consumption, and achieve the best dispersion compensation effect at the lowest cost and power consumption.

[0086] It should be noted that the linear equalizer 221 of the present application may also adopt other types of equalizers, such as a minimum mean square error equalizer.

[0087] In one embodiment, non-linear equalizer 222 comprises a second order Volterra equalizer.

[0088] Among them, the Volterra equalizer is constructed based on the Volterra series theory. The Volterra series is a mathematical tool for modeling nonlinear systems. It represents the output of a nonlinear system as the sum of the convolution integrals of each order of the input signal. The second-order Volterra equalizer mainly considers the first-order and second-order terms of the input signal to model and compensate for the nonlinear channel.

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

[0090]

[0091] Among them, h(l1) is the first-order kernel coefficient, corresponding to the equalization of linear damage. h(l1, l2) is the second-order kernel coefficient, corresponding to the equalization of nonlinear damage. lm is the memory depth of the m-th order kernel, and Lm is used to control the number of equalization tap sequences of the m-th order kernel. The n in x(n) represents the signal sequence of the input equalizer, and the n in y(n) represents the signal sequence of the output equalizer. P represents the interval between the number of taps of the second-order kernel. Adjusting the size of P can control the depth of the second-order kernel, corresponding to the size of the nonlinear damage.

[0092] It can be understood that the nonlinear damage is compensated by the second-order Volterra equalizer, and the complexity of the nonlinear equalization is flexibly adjusted according to the size of the residual sideband. While ensuring the stability of the basic architecture of the transmitter, it not only reduces the complexity of the receiver equalization algorithm processing, but also enables the direct modulation and direct detection signal to be transmitted over a longer distance in a single-mode optical fiber.

[0093] It should be noted that the nonlinear equalizer 222 may also adopt other types of equalizers, or the signal processing component 22 may adopt other methods to perform nonlinear equalization, for example, an artificial intelligence network may be used to perform nonlinear equalization.

[0094] The present application also provides a light receiving device 3, such as Fig. 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 filter component 31 is used to receive the optical double-sideband modulated signal sent by the optical transmitting device 4, and filter the optical double-sideband modulated signal to output the optical residual sideband signal. The photoelectric conversion component 32 is used to receive the optical residual sideband signal, convert the optical residual sideband signal into an analog electrical signal, and convert the analog electrical signal into a digital electrical signal. The signal processing component 33 is used to receive the digital electrical signal, and perform linear equalization 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.

[0096] It can be found 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 modulated signal sent by the optical transmitting device 4 is received at the receiving end through the filter component 31, and the optical double-sideband modulated signal is filtered and processed to output the optical residual sideband signal. Then, the optical residual sideband signal is converted into an optical signal by the photoelectric conversion component 32, and the digital electrical signal converted from the optical residual sideband signal is linearly equalized and nonlinearly equalized by the signal processing component 33 to compensate for the linear damage and nonlinear damage caused by dispersion, 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.

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

[0098] In the above-mentioned optical receiving device 3, after receiving the optical double-sideband modulated signal sent by the optical transmitting device 4, the filter component 31 can filter out the left band or right band signal of the optical double-sideband modulated signal to generate an optical residual sideband signal. Then, after the photoelectric conversion component 32 completes the photoelectric conversion of the optical residual sideband signal, part of the phase information of the signal can still be retained, so that the digital electrical signal converted from the optical residual sideband signal can be linearly balanced by the signal processing component 33 to compensate for the linear damage caused by dispersion. In addition, the residual sideband in the optical residual sideband signal will also bring certain nonlinear damage, and the signal processing component 33 can also perform nonlinear equalization on the digital electrical signal converted from the optical residual sideband signal to compensate for the nonlinear damage caused by dispersion. Therefore, the optical receiving device 3 of this embodiment can 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, 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] The present application also provides an optical transmission system. Fig.10 As shown, the optical transmission system includes an optical transmitting device 4 and an optical receiving device 3 as 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 above optical transmission system over the related art are the same as the advantages of the optical receiving device 3 in the previous embodiment over the related art, which will not be repeated here.

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

[0102] The digital signal processor is used to generate a digital modulation signal. The input end of the digital-to-analog converter is connected to the output end of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal. The input end of the electric amplifier is connected to the output end of the digital-to-analog converter, and the electric amplifier is used to amplify the analog signal. The laser is used to generate laser light. The input end of the modulator is connected to the output end of the electric amplifier, and the modulator is used to receive the laser light and modulate the laser light based on the amplified analog signal to output an optical double-sideband modulated signal.

[0103] Among them, the optical transmitting device 4 of this embodiment is different from the optical transmitting device 1 of the optical transmission system in the aforementioned embodiment. The difference is that the optical transmitting device 4 of this embodiment does not include the filter component 31, and the filter component 31 is located at the optical receiving end, while the optical transmitting device 1 of the optical transmission system in the aforementioned embodiment includes the filter component 12, and the filter component 12 is located at the optical transmitting end. Therefore, the optical transmitting device 4 of this embodiment outputs an optical double-sideband modulated signal instead of an optical residual sideband signal. The description of the light source component can refer to the description of the light source component in the aforementioned embodiment, and will not be repeated here.

[0104] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. An optical transmission system, characterized in that: The optical transmission system comprises: an optical transmitting device and an optical receiving device; The optical transmitting device comprises a light source component and a filter component, wherein the light source component is used to output an optical double-sideband modulated signal; the filter component is used to receive the optical double-sideband modulated signal, filter the optical double-sideband modulated signal, and output an optical residual sideband signal; The optical receiving device includes an optoelectronic conversion component and a signal processing component. The optoelectronic conversion component is used to receive the optical residual sideband signal, convert the optical residual 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 processing and nonlinear equalization processing on the digital electrical signal to compensate for linear and nonlinear damage caused by dispersion in the optical residual sideband signal.

2. The optical transmission system according to claim 1, characterized in that: The light source assembly comprises: A digital signal processor, the digital signal processor is used to generate a digital modulation signal; A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal; an electric amplifier, the input end of the electric amplifier being connected to the output end of the digital-to-analog converter, and the electric amplifier being used to amplify the analog signal; A laser for generating laser light; A modulator, wherein the input end of the modulator is connected to the output end of the electrical amplifier, and the modulator is used to receive the laser, and modulate the laser based on the analog signal after amplification, and 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 performs filtering processing on the optical double-sideband modulated signal and outputs the optical residual sideband signal.

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

5. The optical transmission system according to claim 1, characterized in that: The signal processing component comprises: A linear equalizer, the linear equalizer is used to perform linear equalization processing on the digital electrical signal; A nonlinear equalizer is used to perform nonlinear equalization processing on the digital electrical signal.

6. The optical transmission system according to claim 5, characterized in that: The linear equalizer includes a feedforward equalizer, and the number of taps of the feedforward equalizer is positively correlated with the degree of inter-symbol interference caused by dispersion.

7. The optical transmission system according to claim 5, characterized in that: The nonlinear equalizer comprises a second order Volterra equalizer.

8. A light receiving device, characterized in that: The optical receiving device comprises: a filtering component, a photoelectric conversion component and a signal processing component; The filtering component is used to receive an optical double-sideband modulated signal sent by an optical transmitting device, and filter the optical double-sideband modulated signal to output an optical residual sideband signal; The optoelectronic conversion component is used to receive the optical residual sideband signal, convert the optical residual 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 processing and nonlinear equalization processing on the digital electrical signal to compensate for linear and nonlinear damage caused by dispersion in the optical residual sideband signal.

9. An optical transmission system, characterized in that: The optical transmission system comprises an optical transmitting device and the optical receiving device as claimed in claim 8, 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.

10. The optical transmission system according to claim 9, characterized in that: The light transmitting device comprises a light source assembly; the light source assembly comprises: A digital signal processor, the digital signal processor is used to generate a digital modulation signal; A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end of the digital signal processor, and the digital-to-analog converter is used to convert the digital modulation signal into an analog signal; an electric amplifier, the input end of the electric amplifier being connected to the output end of the digital-to-analog converter, and the electric amplifier being used to amplify the analog signal; A laser for generating laser light; A modulator, wherein the input end of the modulator is connected to the output end of the electrical amplifier, and the modulator is used to receive the laser, and modulate the laser based on the analog signal after amplification, and output the optical double-sideband modulated signal.

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