A transmission system

Abstract

The application discloses a transmission system, comprising: an optical line terminal, comprising: at least one first optical module, the first optical module being used for generating first signal light and receiving second single sideband signal light from an optical network terminal; a first filter, connected with the at least one first optical module respectively, and used for filtering out the single sideband of the first signal light to generate first single sideband signal light; and an optical network terminal, connected with the optical line terminal, comprising: a second optical module, used for receiving the first single sideband signal light from the optical line terminal and generating second signal light; and a second filter, connected with the second optical module, and used for filtering out the single sideband of the second signal light to generate second single sideband signal light. The application can improve the problem that the existing passive optical network system is easily affected by dispersion to cause power fading during long-distance transmission, and it is difficult to meet the power budget requirement of the long-distance scene.

Description

Technical Field

[0001] This invention relates to the field of communications, and in particular to a transmission system. Background Technology

[0002] The emergence of new services such as virtual reality interaction and 8K / 16K streaming media has driven an explosive growth in bandwidth demand in the access network industry, continuously promoting large-scale fiber-to-the-home (FTTH) deployments.

[0003] Passive optical networks (PONs) have attracted widespread attention due to their low-cost broadband access, flexibility, and adaptability. As an outstanding candidate for high-capacity, low-latency 5G pre-transmission networks, PONs are one of the most economical means of providing broadband optical connections between networks, especially wavelength division multiplexing (WDM) PONs.

[0004] Traditional passive optical network (PON) systems employ a uniform peak data rate allocation mechanism, resulting in the network performance of each optical network unit (ONU) being limited by the terminal device with the worst channel conditions. Furthermore, while traditional PONs utilize Intensity Modulation Direct Detection (IM-DD) schemes, which offer advantages such as low cost, low complexity, and ease of integration, their transmission capacity is limited. As PONs evolve towards higher transmission capacities, IM-DD technology struggles to meet power budget requirements in high-speed systems due to factors such as poor receiver sensitivity and power fading caused by dispersion at high speeds and long transmission distances. Summary of the Invention

[0005] The purpose of this invention is to provide a transmission system that can improve the problem that existing passive optical network systems are prone to power fading due to dispersion during long-distance transmission, making it difficult to meet the power budget requirements of long-distance scenarios.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A transmission system, comprising: Optical line terminals, including: At least one first optical module, the first optical module being used to generate a first signal light and to receive a second single-sideband signal light from an optical network terminal; A first filter is connected to the at least one first optical module and is used to filter out the single-sideband of the first signal light to generate the first single-sideband signal light. The optical network terminal, connected to the optical line terminal, includes: The second optical module is used to receive the first single-sideband signal light from the optical line terminal and to generate the second signal light. The second filter, connected to the second optical module, is used to filter out the single-sideband of the second signal light to generate the second single-sideband signal light.

[0007] Optionally, the carrier frequency of the first single-sideband signal light is the same as the carrier frequency of the second single-sideband signal light.

[0008] Optionally, the at least one first optical module includes two or more first optical modules, and the carrier frequencies of the first signal light generated by the at least one first optical module are different.

[0009] Optionally, the first filter is used to filter out the single-sideband of the first signal light output by the at least one first optical module.

[0010] Optionally, the optical line terminal further includes: The wavelength division multiplexer is connected to the at least one first optical module and is used to divide the second single-sideband signal light received by the optical line terminal, so that the second single-sideband signal light is transmitted to the first optical module corresponding to the carrier frequency of the second single-sideband signal light.

[0011] Optionally, the optical line terminal further includes: A first circulator, connected to the first filter, is used to transmit the first single-sideband signal light from the first filter and to transmit the second single-sideband signal light received by the optical line terminal to the first optical module.

[0012] Optionally, the optical network terminal further includes: The second circulator is connected to the second optical module and the second filter respectively, and is used to transmit the first single-sideband signal light received by the optical network terminal to the second optical module, and to transmit the second single-sideband signal light from the second filter.

[0013] Optionally, the first optical module includes: The first light source is used to generate the first carrier wave; A first digital signal processor is used to process the first data to be transmitted into a first digital waveform; A first digital-to-analog converter, connected to the first digital signal processor, is used to convert the first digital waveform into a first analog electric drive signal; The first modulator is connected to the first digital-to-analog converter and the first light source respectively, and is used to modulate the first carrier according to the received first analog electric drive signal to generate the first signal light; A first optoelectronic device is used to convert the received second single-sideband signal light into a first analog current signal; A second digital signal processor, connected to the first optoelectronic device, is used to recover the transmission data based on the first analog current signal; Or / and, the second optical module includes: A second light source is used to generate a second carrier wave; The third digital signal processor is used to process the second data to be transmitted into a second digital waveform; A second digital-to-analog converter, connected to the third digital signal processor, is used to convert the second digital waveform into a second analog electric drive signal; The second modulator, connected to the second digital-to-analog converter and the second light source respectively, is used to modulate the second carrier wave according to the received second analog electric drive signal to generate the second signal light; The second optoelectronic device is used to convert the received first single-sideband signal light into a second analog current signal; A fourth digital signal processor, connected to the second optoelectronic device, is used to recover the transmission data based on the second analog current signal.

[0014] Optionally, the optical line terminal and the optical network terminal are connected via a single optical fiber.

[0015] Optionally, the transmission system includes two or more of the aforementioned optical network terminals; The transmission system also includes: A multiplexer / demultiplexer is connected to the optical line terminal and two or more optical network terminals respectively, and is used to demultiplex the first single-sideband signal light with at least two different carrier frequencies transmitted from the optical line terminal, so that the first single-sideband signal light with any carrier frequency is transmitted to the optical network terminal corresponding to the carrier frequency of the first single-sideband signal light.

[0016] As can be seen from the above technical solution, the transmission system provided by the present invention has a first single-sideband signal light transmitted from the optical line terminal to the optical network terminal in a single-sideband spectrum, and a second single-sideband signal light transmitted from the optical network terminal to the optical line terminal in a single-sideband spectrum. Compared with the existing passive optical network transmission signal light which is double-sideband using intensity modulation direct detection, the single-sideband has a narrower bandwidth than the double-sideband. This can reduce the degree to which different frequencies of light are staggered and superimposed in the time domain due to dispersion, and can reduce the power fading caused by dispersion of the transmitted signal light. Therefore, the transmission system of the present invention can improve the problem that the existing passive optical network system is prone to power fading due to dispersion during long-distance transmission, making it difficult to meet the power budget requirements of long-distance scenarios. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a transmission system provided in one embodiment; Figure 2 This is a schematic diagram of the structure of an optical line terminal of a transmission system provided in one embodiment; Figure 3 This is a schematic diagram of the structure of an optical network terminal of a transmission system provided in one embodiment; Figure 4-1 An optical spectrum diagram of a transmission system provided in one embodiment at point ① of the optical line terminal; Figure 4-2 An optical spectrum diagram of the transmission system provided in one embodiment at point ② of the optical line terminal; Figure 4-3 An optical spectrum diagram of the transmission system provided in one embodiment at point ③ of the optical line terminal; Figure 4-4 The optical spectrum diagram of the transmission system provided in one embodiment at point ④ of the optical line terminal; Figure 4-5 The optical spectrum diagram of the transmission system provided in one embodiment at point ⑤ of the optical line terminal; Figure 5 A schematic diagram of a first optical module of a transmission system provided in one embodiment; Figure 6-1 The optical spectrum diagram of point ① from the first optical network terminal to the Nth optical network terminal of the transmission system provided in one embodiment; Figure 6-2The optical spectrum diagram of point ② from the first optical network terminal to the Nth optical network terminal of the transmission system provided in one embodiment; Figure 6-3 The optical spectrum diagram of point ③ from the first optical network terminal to the Nth optical network terminal of the transmission system provided in one embodiment; Figure 6-4 The optical spectrum diagram of point ④ from the first optical network terminal to the Nth optical network terminal of the transmission system provided in one embodiment; Figure 7 This is a schematic diagram of a second optical module of a transmission system provided in one embodiment.

[0019] The reference numerals in the accompanying drawings include: 1-Optical line terminal, 101-First optical module, 102-Second optical module, 103-Third optical module, 10N-Nth optical module, 110-First filter, 111-Demultiplexer, 112-First optical amplifier, 113-Second optical amplifier, 114-First circulator, 1001-First light source, 1002-First modulator, 1003-First digital-to-analog converter, 1004-First digital signal processor, 1005-First optoelectronic device, 1006-Second digital signal processor; 21-First optical network terminal, 22-Second optical network terminal, 23-Third optical network terminal, 2N-Nth optical network terminal, 201-Second optical module, 211-Second filter, 212-Second circulator, 2001-Second light source, 2002-Second modulator, 2003-Second digital-to-analog converter, 2004-Third digital signal processor, 2005-Second optoelectronic device, 2006-Fourth digital signal processor; 3-Fiber optic cable, 4-Multiplexer / demultiplexer. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0021] For reference Figures 1 to 3 , Figure 1 This is a schematic diagram of a transmission system provided in one embodiment. Figure 2 This is a schematic diagram of the structure of an optical line terminal of a transmission system provided in one embodiment. Figure 3 This is a schematic diagram of the structure of an optical network terminal in a transmission system provided in one embodiment. Figures 1 to 3 As shown, the transmission system provided in this embodiment includes: Optical line terminal 1, comprising: At least one first optical module, the first optical module being used to generate a first signal light and to receive a second single-sideband signal light from an optical network terminal; The first filter 110 is connected to at least one first optical module and is used to filter out the single-sideband of the first signal light to generate the first single-sideband signal light. An optical network terminal, connected to optical line terminal 1, includes: The second optical module 201 is used to receive the first single-sideband signal light from the optical line terminal 1, and to generate the second signal light; The second filter 211 is connected to the second optical module 201 and is used to filter out the single-sideband of the second signal light to generate the second single-sideband signal light.

[0022] The transmission system includes optical line terminal 1 and optical network terminal.

[0023] In optical line terminal 1, a first optical module generates a first signal light, and a first filter 110 filters out one sideband of the first signal light to generate a first single-sideband signal light. Optical line terminal 1 transmits the first single-sideband signal light. In optical network terminal, a second optical module 201 receives the first single-sideband signal light from optical line terminal 1, thereby enabling communication from optical line terminal 1 to optical network terminal. By filtering out one sideband of the first signal light through the first filter 110 and retaining the other sideband, the first signal light is formed into a first single-sideband signal light.

[0024] In the optical network terminal, the second optical module 201 generates a second signal light, and the second filter 211 filters out one sideband of the second signal light to generate a second single-sideband signal light. The optical network terminal transmits the second single-sideband signal light. In the optical line terminal 1, the first optical module receives the second single-sideband signal light from the optical network terminal, thereby realizing communication from the optical network terminal to the optical line terminal 1. By filtering out one sideband of the second signal light through the second filter 211 and retaining the other sideband, the second signal light becomes a second single-sideband signal light.

[0025] In this embodiment of the transmission system, the first single-sideband signal light transmitted from the optical line terminal 1 to the optical network terminal is single-sideband in the spectrum, and the second single-sideband signal light transmitted from the optical network terminal to the optical line terminal 1 is also single-sideband in the spectrum. Compared with the existing passive optical network that uses intensity modulation for direct detection and transmits signal light with double-sideband, the single-sideband has a narrower bandwidth than the double-sideband. This can reduce the degree to which different frequencies of light are staggered and superimposed in the time domain due to dispersion, and can reduce the power fading caused by dispersion of the transmitted signal light. Therefore, the transmission system of this embodiment can improve the problem that the existing passive optical network system is prone to power fading due to dispersion during long-distance transmission, making it difficult to meet the power budget requirements of long-distance scenarios.

[0026] In some implementations, the carrier frequency of the first single-sideband (SSB) signal light is the same as that of the second SSB signal light, allowing the optical modules of the optical line terminal 1 and the optical network terminal to use the same wavelength optical carrier. Compared to using optical carriers of different wavelengths, the transmission capacity can be doubled. The frequency bands of the first and second SSB signal lights are located on opposite sides of the carrier frequency, respectively. The frequency band of the first SSB signal light is the upper / lower sideband of the carrier frequency, and the frequency band of the second SSB signal light is the lower / upper sideband of the carrier frequency, which can improve the utilization of spectrum resources. For example, the first SSB signal light uses the upper sideband, and the second SSB signal light uses the lower sideband, or the first SSB signal light uses the lower sideband, and the second SSB signal light uses the upper sideband. The choice between using the upper or lower sideband for the first and second SSB signal lights can be made according to the actual situation, as long as the first and second SSB signal lights do not interfere with each other.

[0027] In some embodiments, at least one first optical module includes two or more first optical modules, and the carrier frequencies of the first signal light generated by at least one first optical module are different. For example, see [reference needed]. Figure 2 As shown, the optical line terminal 1 includes a first optical module 101, a second optical module 102, a third optical module 103, and an Nth optical module 10N. The carrier frequency of the first signal light generated by the first optical module 101 is 1 / λ1, i.e., the carrier wavelength is λ1; the carrier frequency of the first signal light generated by the second optical module 102 is 1 / λ2, i.e., the carrier wavelength is λ2; the carrier frequency of the first signal light generated by the third optical module 103 is 1 / λ3, i.e., the carrier wavelength is λ3; and the carrier frequency of the first signal light generated by the Nth optical module 10N is 1 / λ1. N That is, the carrier wavelength is λ N . Among them λ1, λ2, λ3,…,λ N The differences are as follows: N is a positive integer greater than 1. For example, see [reference needed]. Figure 4-1 , Figure 4-1The optical spectrum diagram of a transmission system provided in one embodiment at point ① of the optical line terminal includes the spectrum of the first signal light generated by the first optical module 101 to the Nth first optical module 10N of the optical line terminal 1.

[0028] Accordingly, the first filter 110 is used to filter out the single-sidebands of the first signal light output by at least one first optical module. The first signal light output by at least one first optical module is transmitted to the first filter 110, and the first filter 110 filters out the single-sidebands of the first signal light output by each of the at least one first optical module. The first signal light output by at least one first optical module is then combined through the first filter 110. For example, see [reference needed]. Figure 4-2 , Figure 4-2 The optical spectrum diagram at point ② of the optical line terminal of the transmission system provided in one embodiment shows that the first signal light generated by the first optical module 101 to the Nth first optical module 10N is filtered out by the first filter 110 after passing through the first single-sideband signal light, and the N first single-sideband signal lights are merged. Figure 4-2 The diagram shows the bottom sideband filtered out while the top sideband is retained. The first filter 110 can be, but is not limited to, a comb filter.

[0029] In some embodiments, the optical line terminal 1 further includes a first circulator 114 connected to a first filter 110, used to transmit a first single-sideband (SSB) signal light from the first filter 110 and to transmit a second SSB signal light received by the optical line terminal 1 to a first optical module. The first circulator 114 isolates the first SSB signal light transmitted outward by the optical line terminal 1 from the received second SSB signal light, preventing mutual interference when they are transmitted simultaneously. Furthermore, by using the first circulator 114 to isolate bidirectional transmission signal light, the optical line terminal 1 and the optical network terminal can transmit signal light through a single channel, such as through a single optical fiber. For example, see [reference needed]. Figure 4-3 , Figure 4-3 The optical spectrum diagram of the transmission system provided in one embodiment at point ③ of the optical line terminal includes both the first single-sideband signal light and the second single-sideband signal light being transmitted. Figures 4-1 to 4-5 The first single-sideband signal light and the second single-sideband signal light shown in the figure have the same carrier frequency, and their frequency bands are located on both sides of the carrier frequency.

[0030] In some embodiments, the optical line terminal 1 further includes: a first optical amplifier 112, connected to a first filter 110, used to amplify the power of the first single-sideband signal light from the first filter 110, so that the power of the transmitted first single-sideband signal light meets the requirements. (See reference...) Figure 2As shown, one end of the first optical amplifier 112 is connected to the first filter 110, and the other end is connected to the first end of the first circulator 114. The second end of the first circulator 114 is used to connect to the optical network terminal.

[0031] The first optical module generates a first signal light according to actual requirements. The wavelength, power, and modulation format of the first signal light must meet the requirements. For example, refer to... Figure 5 , Figure 5 This is a schematic diagram of a first optical module of a transmission system provided in one embodiment. In some embodiments, the first optical module includes: The first light source 1001 is used to generate the first carrier wave; A first digital signal processor 1004 is used to process the first data to be transmitted into a first digital waveform; A first digital-to-analog converter 1003 is connected to a first digital signal processor 1004 and is used to convert a first digital waveform into a first analog electric drive signal. The first modulator 1002 is connected to the first digital-to-analog converter 1003 and the first light source 1001 respectively, and is used to modulate the first carrier according to the received first analog electric drive signal to generate the first signal light.

[0032] A first light source 1001 generates a stable first carrier wave. A first digital signal processor 1004 processes the first data to be transmitted into a first digital waveform. A first digital-to-analog converter 1003 converts the first digital waveform transmitted from the first digital signal processor 1004 into a first analog electric drive signal, such as an analog voltage signal. A first modulator 1002 modulates the first carrier wave according to the first analog electric drive signal, loading the first data to be transmitted onto the continuous light output from the first light source 1001, thereby outputting a modulated signal light carrying the service data.

[0033] The first optical module is also used to perform signal processing operations based on the received signal light. In some embodiments, the first optical module includes: The first optoelectronic device 1005 is used to convert the received second single-sideband signal light into a first analog current signal; The second digital signal processor 1006 is connected to the first optoelectronic device 1005 and is used to recover the transmission data based on the first analog current signal.

[0034] The first optical module can generate a first signal light using an intensity modulation direct detection method and obtain transmission data based on the received second single-sideband signal light.

[0035] In some embodiments, the transmission system includes two or more optical network terminals each connected to the optical line terminal 1. The two or more optical network terminals may each receive a first single-sideband signal optical at a different carrier frequency. For example, see [reference needed]. Figure 1 As shown, the transmission system includes a first optical network terminal 21, a second optical network terminal 22, a third optical network terminal 23 to an Nth optical network terminal 2N. For example, the first optical network terminal 21 receives a first single-sideband signal light with a carrier wavelength of λ1, the second optical network terminal 22 receives a first single-sideband signal light with a carrier wavelength of λ2, the third optical network terminal 23 receives a first single-sideband signal light with a carrier wavelength of λ3, and the Nth optical network terminal 2N receives a first single-sideband signal light with a carrier wavelength of λ2. N The first single-sideband (SSB) signal light. In some embodiments, the transmission system further includes a multiplexer / demultiplexer 4, connected to the optical line terminal 1 and two or more optical network terminals respectively, for demultiplexing the first SSB signal light transmitted from the optical line terminal 1 with at least two different carrier frequencies, so that the first SSB signal light of any carrier frequency is transmitted to the optical network terminal corresponding to the carrier frequency of the first SSB signal light. The multiplexer / demultiplexer 4 is also used to combine the second SSB signal light transmitted from two or more optical network terminals, and then further transmit the combined light to the optical line terminal 1.

[0036] For reference Figure 3 As shown, in some embodiments, the optical network terminal further includes a second circulator 212, connected to the second optical module 201 and the second filter 211 respectively. This circulator transmits the first single-sideband (SSB) signal light received by the optical network terminal to the second optical module 201, and transmits the second SSB signal light from the second filter 211 outwards. The second circulator 212 isolates the second SSB signal light transmitted outwards from the optical network terminal from the first SSB signal light received, preventing mutual interference when they are transmitted simultaneously. Furthermore, by using the second circulator 212 to isolate bidirectional transmission signal light, a single-channel transmission link can be established between the optical network terminal and the optical line terminal 1, such as through a single optical fiber. (See reference...) Figure 3 As shown, the first end of the second circulator 212 is connected to the second optical module 201, the second end is connected to the second filter 211, and the third end is used to connect to the optical line terminal 1.

[0037] For example, refer to Figure 6-1 , Figure 6-1 The optical spectrum diagram of point ① of the transmission system provided in one embodiment is as follows: For example, for the first optical network terminal 21, the optical spectrum of point ① of the first optical network terminal 21 simultaneously includes the transmitted first single-sideband signal light and the second single-sideband signal light. Figure 6-1The first single-sideband (SSB) signal light received by the first optical network terminal 21 and the second SSB signal light transmitted have the same carrier wavelength, λ1, and their frequency bands are located on opposite sides of the carrier frequency. The optical spectrum at point ① of the second optical network terminal 22 simultaneously includes both the transmitted first and second SSB signal lights. They have the same carrier wavelength, λ2, and their frequency bands are located on opposite sides of the carrier frequency 1 / λ2.

[0038] For example, refer to Figure 6-2 , Figure 6-2 The optical spectrum diagram at point ② of a transmission system provided in one embodiment, from the first optical network terminal to the Nth optical network terminal, is shown. Point ② is located between the second circulator 212 and the second optical module 201. The optical spectrum at point ② represents the spectrum of the first single-sideband signal light received by the optical network terminal. For example, for the first optical network terminal 21, the optical spectrum at point ② of the first optical network terminal 21 includes the spectrum of the first single-sideband signal light received by the first optical network terminal 21, with a carrier wavelength of λ1. The optical spectrum at point ② of the second optical network terminal 22 includes the spectrum of the first single-sideband signal light received by the second optical network terminal 22, with a carrier wavelength of λ2.

[0039] For example, refer to Figure 6-3 , Figure 6-3 The optical spectrum diagram at point ③ in a transmission system provided in one embodiment, from the first optical network terminal to the Nth optical network terminal, is shown. Point ③ is located between the second optical module 201 and the second filter 211. The optical spectrum at point ③ represents the spectrum of the second signal light generated by the second optical module 201. For example, refer to... Figure 6-4 , Figure 6-4 The optical spectrum diagram of point ④ of the transmission system provided in one embodiment is shown. Point ④ is located on the optical path of the output light of the second filter 211. The optical spectrum of point ④ represents the spectrum of the second single-sideband signal light generated after the second signal light passes through the second filter 211.

[0040] In some embodiments, the optical line terminal 1 further includes a wavelength division multiplexer 111, connected to at least one first optical module, for wavelength division of the second single-sideband (SSB) signal light received by the optical line terminal 1, so that the second SSB signal light is transmitted to the first optical module corresponding to the carrier frequency of the second SSB signal light. The wavelength division multiplexer 111 may include an input terminal, an arrayed waveguide grating, and at least one output terminal, with each output terminal corresponding to at least one first optical module. The light received by the optical line terminal 1 contains a second SSB signal light with at least one carrier frequency. The received light enters the wavelength division multiplexer from the input terminal, interferes through the arrayed waveguide grating, and the second SSB signal light of any carrier frequency is output from the corresponding output terminal.

[0041] For example, refer to Figure 4-4 , Figure 4-4 The optical spectrum diagram at point ④ of the optical line terminal in a transmission system provided in one embodiment represents the spectrum of light received by the optical line terminal 1, which simultaneously includes the received second single-sideband signal light with n different carrier wavelengths. For example, refer to... Figure 4-5 , Figure 4-5 The optical spectrum diagram at point ⑤ of the transmission system provided in one embodiment is shown. The light received by the optical line terminal 1 is split by the wavelength divider 111 to separate n different carrier wavelengths of second single-sideband signal light, which are then transmitted to the corresponding first optical module.

[0042] In some embodiments, the optical line terminal 1 further includes a second optical amplifier 113, which is connected to at least one first optical module, for amplifying the power of the second single-sideband signal light received by the optical line terminal 1, so that the power of the second single-sideband signal light transmitted to the first optical module meets the requirements. In some embodiments, one end of the second optical amplifier 113 is connected to a demultiplexer 111, and the other end is connected to a first circulator 114, so that the second single-sideband signal light received by the optical line terminal 1 is amplified by the second optical amplifier 113 before being transmitted to the demultiplexer 111.

[0043] The second optical module 201 generates a second signal light according to actual requirements. The wavelength, power, and modulation format of the second signal light must meet the requirements. For example, refer to... Figure 7 , Figure 7 A schematic diagram of a second optical module of a transmission system provided in one embodiment. In some embodiments, the second optical module 201 includes: The second light source 2001 is used to generate the second carrier wave; The third digital signal processor 2004 is used to process the second data to be transmitted into a second digital waveform; The second digital-to-analog converter 2003, connected to the third digital signal processor 2004, is used to convert the second digital waveform into a second analog electric drive signal; The second modulator 2002 is connected to the second digital-to-analog converter 2003 and the second light source 2001 respectively, and is used to modulate the second carrier according to the received second analog electric drive signal to generate the second signal light.

[0044] The second light source 2001 generates a stable second carrier wave. The third digital signal processor 2004 processes the second data to be transmitted into a second digital waveform. The second digital-to-analog converter 2003 converts the second digital waveform transmitted from the third digital signal processor 2004 into a second analog electric drive signal, such as an analog voltage signal. The second modulator 2002 modulates the second carrier wave according to the second analog electric drive signal, loading the second data to be transmitted onto the continuous light output from the second light source 2001, thereby outputting a modulated signal light carrying the service data.

[0045] The second optical module 201 is also used to perform signal processing operations based on the received signal light. In some embodiments, the second optical module 201 includes: The second optoelectronic device 2005 is used to convert the received first single-sideband signal light into a second analog current signal; The fourth digital signal processor 2006, connected to the second optoelectronic device 2005, is used to recover the transmission data based on the second analog current signal.

[0046] The second optical module 201 can generate a second signal light using an intensity modulation direct detection method and obtain transmission data based on the received first single-sideband signal light.

[0047] The first light source 1001 and the second light source 2001 may be, but are not limited to, lasers. The first modulator 1002 and the second modulator 2002 may be, but are not limited to, Mach-Zehnder modulators (MZM). The first optoelectronic device 1005 and the second optoelectronic device 2005 may be, but are not limited to, photodiodes.

[0048] The modulation formats of the first signal light and the second signal light are not limited. The same or different direct modulation formats can be used to process the first single-sideband signal light and the second single-sideband signal light according to the actual situation.

[0049] In practical applications, the specific components included in the optical line terminal 1 and the optical network terminal can be changed according to the actual needs of the system. Commonly used components such as amplifiers, attenuators, arbitrary waveform generators and optical filters can be added or removed according to the actual needs of the system. Other network flow monitoring devices can also be added to the optical line terminal 1 to play other roles, such as devices that monitor and analyze transmission link congestion and whether there are transmission anomalies such as packet loss.

[0050] The signal light transmitted from optical line terminal 1 to optical network terminal can be considered as downlink signal light, and the signal light transmitted from optical network terminal to optical line terminal 1 can be considered as uplink signal light.

[0051] In some implementations, the optical line terminal 1 (OLT 1) and the optical network terminal (ONT 1) are connected via a single optical fiber to transmit signal light. Alternatively, the OLT 1 ​​and ONT 1 can be connected via a single-mode optical fiber. This transmission system employs single-fiber bidirectional transmission, which, compared to dual-fiber bidirectional transmission, reduces the amount of optical fiber used, saves cost and space, simplifies the transmission system design, and is more suitable for scenarios with short paging distances, such as mobile fronthaul. It also reduces cabling complexity and minimizes low-order dispersion in the transmission link, ensuring the quality of the transmitted signal.

[0052] A comb filter is used in optical line terminal 1. This device combines the functions of a wavelength division multiplexing (WDM) multiplexer / demultiplexer and a filter. Together with the multiplexer / demultiplexer on the receiver link and the filters in each optical network terminal, it acts on the uplink and downlink signals respectively, allowing the bidirectional signals to be transmitted on different frequency bands. This reduces pulse broadening in single-sideband signals, significantly lowers signal distortion, improves anti-dispersion capability, and further simplifies the signal processing complexity of the optical modules at both ends. Simultaneously, the receiver devices, except for the optical modules, are all passive, simplifying the complexity of the optical network terminal and thus reducing the overall system cost. In this embodiment, the transmission system uses a circulator to construct a single-fiber bidirectional transmission link, resulting in less low-order dispersion during transmission, increasing transmission capacity, and better adapting to future high-speed, high-capacity transmission requirements. By using a comb filter, filter, and multiplexer / demultiplexer in combination, the bidirectional upper and lower sideband signals are transmitted on the same wavelength, increasing system capacity without compromising the system's anti-interference capability.

[0053] In some implementations, the operation flow of the transmission system in this embodiment is as follows: First, in the downlink transmission direction, at least one first optical module of the optical line terminal 1 generates a direct-modulation signal light, which is then multiplexed and processed by the first filter 110, outputting a signal light with only the upper sideband. After being amplified by the first optical amplifier 112, the signal light enters the optical fiber 3 for transmission through the first circulator 114. Then, the receiving end performs wavelength division processing on the obtained signal light in the multiplexer / demultiplexer 4 according to different wavelengths. Each type of signal light is transmitted to the second optical module of the corresponding optical network terminal for signal processing and information reading according to its wavelength. Next, in the uplink transmission direction, the second optical module of at least one optical network terminal generates a corresponding double-sideband direct-modulation signal based on the received information. After being filtered by the second filter 211, a signal light with only the lower sideband is generated. After being multiplexed by the second circulator 212 and the multiplexer / demultiplexer 4, the signal light enters the optical fiber 3 for transmission. Finally, the optical line terminal 1 performs wavelength division processing on the multiplexed signal light obtained after amplification by the second optical amplifier 113 in the wavelength divider 111 according to different wavelengths. Each signal light is transmitted to the corresponding first optical module for signal processing and information reading according to its wavelength.

[0054] Existing coherent passive optical network (PON) systems are considered a promising approach, capable of meeting extended transmission distance requirements exceeding 20 km. Simultaneously, coherent schemes can achieve higher receiver sensitivity, greater network flexibility, and higher data rates. In dense wavelength division multiplexing (DWDM) PONs, there are two main motivations for employing coherent detection: first, its fine wavelength selectivity preserves the filterless nature of PONs, indicating cost-effective PON deployment; second, its superior sensitivity is crucial for compensating for insertion loss in optical distribution networks and increasing the power budget of PONs. However, conventional coherent receivers are not only complex but also expensive, significantly more complex than conventional direct-probe receivers, hindering their application in cost-sensitive PONs.

[0055] To meet current transmission capacity requirements, most optical access network solutions employ coherent modulation, which not only improves receiver sensitivity and achieves sufficient power budget at moderate transmit power but also supports more connected users. Coherent passive optical networks (CPONs), with their support for advanced multi-level modulation formats and efficient utilization of digital signal processing algorithms, are better equipped to withstand future capacity demands. Furthermore, coherent detection obtains the corresponding channel by selecting the local oscillator laser wavelength, eliminating the need for any optical filters. While CPONs offer advantages such as high sensitivity, long transmission distance, high capacity, and good wavelength selectivity, traditional coherent receivers are complex and expensive, making them unsuitable for cost-sensitive optical network applications.

[0056] Industry professionals have also proposed flexible passive optical networks (PONs), which achieve breakthroughs in network performance through dynamic adaptive mechanisms. In this system, different wavelengths can be allocated different protocols, have variable access rates, and flexible modulation formats, thereby significantly reducing fiber optic costs and latency. Simultaneously, each optical network terminal uses a different wavelength, meaning each terminal uses an independent wavelength to communicate with the optical line terminal in each direction. However, the use of different wavelengths for uplink and downlink transmission in flexible PONs results in higher spectrum resource consumption and requires further optimization of bandwidth utilization.

[0057] Direct-modulation passive optical networks (CPONs) offer several advantages over coherent passive optical networks (PONs). First, the typical power consumption distribution of the DSP-ASIC digital core logic used in line card applications is evident, with dispersion compensation and forward error correction decoders being the primary power-consuming modules. Compared to other PON solutions, the single-sideband uplink and downlink signals used do not interfere with each other. Furthermore, the dispersion compensation required by the intensity modulation direct detection system is simpler than that of coherent systems, and the simpler modulation format necessitates a simpler signal processing flow. Therefore, the power consumption of this direct-modulation PON system is significantly lower than that of coherent PON systems, providing a larger power budget and making it more suitable for cost-sensitive PON applications. Second, referencing the simplified approach of coherent PONs, each optical network terminal includes essential optical modules as well as passive components such as circulators and filters. While the cost of this solution is slightly higher than some PON systems that only use optical modules, the use of filters allows for single-sideband modulation, reducing system bandwidth consumption and ultimately lowering the overall cost. Third, for access network scenarios within 20km, direct-modulation passive optical networks (PONs) have been widely deployed and commercialized, allowing for a smooth upgrade to PON systems based on intensity modulation direct detection without large-scale modifications to existing optical distribution networks; whereas the high sensitivity and other advantages of coherent PONs cannot be realized. Fourth, direct-modulation PONs have mature chips, optical modules, and an ecosystem, while coherent PONs are still in the research and pilot stages. Furthermore, PON systems can select different modulation formats for uplink and downlink signals based on actual conditions, and in this solution, the two do not interfere with each other, thus allowing for the selection of different direct-modulation modulation formats with significantly different complexities.

[0058] The transmission system in this embodiment has the following advantages: 1. Excellent spectrum and bandwidth utilization: It adopts twin single-sideband modulation, and the uplink and downlink can share the same upper and lower sidebands of the same wavelength for transmission, which greatly saves transmission bandwidth and improves spectrum utilization.

[0059] 2. Strong anti-interference capability: Relying on the comb filter and the built-in filtering design of the optical network terminal, it realizes bidirectional transmission of single-mode fiber at the same wavelength without signal interference and isolates uplink and downlink crosstalk.

[0060] 3. Excellent cost control: Based on the IM / DD intensity modulation direct detection architecture, it eliminates the need for expensive and complex coherent receivers, significantly reducing the overall system cost compared to coherent passive optical networks.

[0061] 4. Capacity performance close to coherent solutions: Under the same number of wavelengths, the transmission capacity is very close to that of coherent passive optical networks, balancing the requirements of low cost and high capacity.

[0062] 5. Wide range of applicable scenarios: It retains the low complexity and easy integration characteristics of direct-modulation passive optical networks, while solving the problems of interference and bandwidth waste in bidirectional transmission at the same wavelength, and has good prospects for practical application in optical fiber access networks.

[0063] The transmission system provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. A transmission system, characterized in that, include: Optical line terminals, including: At least one first optical module, the first optical module being used to generate a first signal light and to receive a second single-sideband signal light from an optical network terminal; A first filter is connected to the at least one first optical module and is used to filter out the single-sideband of the first signal light to generate the first single-sideband signal light. The optical network terminal, connected to the optical line terminal, includes: The second optical module is used to receive the first single-sideband signal light from the optical line terminal and to generate the second signal light. The second filter, connected to the second optical module, is used to filter out the single-sideband of the second signal light to generate the second single-sideband signal light.

2. The transmission system according to claim 1, characterized in that, The carrier frequency of the first single-sideband signal light is the same as the carrier frequency of the second single-sideband signal light.

3. The transmission system according to claim 1, characterized in that, The at least one first optical module includes two or more first optical modules, and the carrier frequencies of the first signal light generated by the at least one first optical module are different.

4. The transmission system according to claim 3, characterized in that, The first filter is used to filter out the single-sideband of the first signal light output by the at least one first optical module.

5. The transmission system according to claim 3, characterized in that, The optical line terminal also includes: The wavelength division multiplexer is connected to the at least one first optical module and is used to divide the second single-sideband signal light received by the optical line terminal, so that the second single-sideband signal light is transmitted to the first optical module corresponding to the carrier frequency of the second single-sideband signal light.

6. The transmission system according to claim 1, characterized in that, The optical line terminal also includes: A first circulator, connected to the first filter, is used to transmit the first single-sideband signal light from the first filter and to transmit the second single-sideband signal light received by the optical line terminal to the first optical module.

7. The transmission system according to claim 1, characterized in that, The optical network terminal also includes: The second circulator is connected to the second optical module and the second filter respectively, and is used to transmit the first single-sideband signal light received by the optical network terminal to the second optical module, and to transmit the second single-sideband signal light from the second filter.

8. The transmission system according to claim 1, characterized in that, The first optical module includes: The first light source is used to generate the first carrier wave; A first digital signal processor is used to process the first data to be transmitted into a first digital waveform; A first digital-to-analog converter, connected to the first digital signal processor, is used to convert the first digital waveform into a first analog electric drive signal; The first modulator is connected to the first digital-to-analog converter and the first light source respectively, and is used to modulate the first carrier according to the received first analog electric drive signal to generate the first signal light; A first optoelectronic device is used to convert the received second single-sideband signal light into a first analog current signal; A second digital signal processor, connected to the first optoelectronic device, is used to recover the transmission data based on the first analog current signal; Or / and, the second optical module includes: A second light source is used to generate a second carrier wave; The third digital signal processor is used to process the second data to be transmitted into a second digital waveform; A second digital-to-analog converter, connected to the third digital signal processor, is used to convert the second digital waveform into a second analog electric drive signal; The second modulator, connected to the second digital-to-analog converter and the second light source respectively, is used to modulate the second carrier wave according to the received second analog electric drive signal to generate the second signal light; The second optoelectronic device is used to convert the received first single-sideband signal light into a second analog current signal; A fourth digital signal processor, connected to the second optoelectronic device, is used to recover the transmission data based on the second analog current signal.

9. The transmission system according to any one of claims 1 to 8, characterized in that, The optical line terminal and the optical network terminal are connected by a single optical fiber.

10. The transmission system according to any one of claims 1 to 8, characterized in that, The transmission system includes two or more optical network terminals; The transmission system also includes: A multiplexer / demultiplexer is connected to the optical line terminal and two or more optical network terminals respectively, and is used to demultiplex the first single-sideband signal light with at least two different carrier frequencies transmitted from the optical line terminal, so that the first single-sideband signal light with any carrier frequency is transmitted to the optical network terminal corresponding to the carrier frequency of the first single-sideband signal light.

Images