Passive optical network system

Abstract

This disclosure provides a passive optical network system, relating to access network technology, comprising: a central office and a first optical network system connected via single-mode optical fiber; the central office includes an old optical line terminal (OLT), a downlink wavelength complemented data transmitter, and a first wavelength division multiplexer (WDM); the first optical network system includes a first remote node, an old optical network unit, and a new optical network unit; the old OLT transmits old optical network signals; the downlink wavelength complemented data transmitter transmits new optical network signals and complemented signals; the amplitude of the complemented signal is the inverse sum of multiple new optical network signals; the first WDM combines the signals into a target optical network signal; the first remote node divides the target optical network signal into two parts, one part is transmitted to the old optical network unit for demodulation, and the other part is transmitted to the new optical network unit. This scheme utilizes unused wavelengths to carry complemented signals, ensuring a constant amplitude after the complemented signal and the new optical network signal are combined, thereby reducing crosstalk to the old optical network signal.

Description

Technical Field

[0001] This disclosure relates to access network technology, and more particularly to a passive optical network system. Background Technology

[0002] Passive Optical Networks (PONs) have become the most attractive solution for addressing access network bottlenecks. Existing PONs typically offer downlink speeds of 1.25Gb / s and 2.5Gb / s. Due to rapidly increasing bandwidth demands, upgrading existing PONs to 10Gb / s or higher downlink speeds is an urgent issue that needs to be addressed.

[0003] In existing technologies, upgrades from existing PONs to next-generation PONs, such as time-division wavelength-division multiplexing passive optical networks (TWDM-PONs), can utilize time-division multiplexing technology to increase bandwidth capacity. Generally, the next-generation PON is added to an existing optical distribution network (ODN) to reuse existing infrastructure. When adding a new PON, the existing PON is still in use; therefore, the new PON link should coexist with the existing PON link until all existing PON users upgrade to the new PON link. To reduce crosstalk between the new PON signal and the old PON signal, spectrum shaping line coding technology can be used to apply line codes to the new PON signal to suppress its low-frequency components, thereby reducing crosstalk to the low-speed old PON signal.

[0004] However, spectrum-shaping line coding technology only works when the bit rate of the old PON signal is much lower than that of the new PON signal. As the bit rates of the two signals become closer, crosstalk increases rapidly. This means the performance of the upgraded PON needs further improvement. Summary of the Invention

[0005] This disclosure provides a passive optical network system to solve the problem of large crosstalk between old and new PON signals in the prior art, thereby improving the performance of the upgraded PON.

[0006] According to a first aspect of this disclosure, a passive optical network system is provided, comprising:

[0007] A central office and a first optical network system are connected via single-mode optical fiber; wherein, the central office includes: an old optical line terminal, a downlink wavelength complement data transmitter, and a first wavelength division multiplexer; the first optical network system includes: a first remote node, multiple old optical network units, and multiple new optical network units;

[0008] The old optical line terminal is used to process the received first input electrical signal, generate and send the old optical network signal to the first wavelength division multiplexer.

[0009] The downlink wavelength complement data transmitter is used to process the received second input electrical signal, generate and send multiple new optical network signals and a complement signal to the first wavelength division multiplexer; each new optical network signal and the complement signal have a different wavelength; the amplitude of the complement signal is the inverse sum of the multiple new optical network signals;

[0010] The first wavelength division multiplexer is used to combine the old optical network signal, the plurality of new optical network signals, and the complement signal into a target optical network signal; the target optical network signal is transmitted to the first remote node through the single-mode optical fiber;

[0011] The first remote node is used to divide the target optical network signal into two parts. One part is transmitted to the old optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal; the other part is transmitted to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal.

[0012] In one possible implementation, the downlink wavelength complement data transmitter includes M-1 first optical line terminals and 1 second optical line terminal; where M is a positive integer greater than 1.

[0013] Each of the first optical line terminals includes: a first non-return-to-zero (NRZ) coded data terminal, a first light source, and a first optical amplitude modulator; the first NRZ coded data terminal is connected to a first terminal of the first optical amplitude modulator; the first light source is connected to a second terminal of the first optical amplitude modulator; the first NRZ coded data terminal is used to process the received third input electrical signal to obtain a first optical signal; the first light source is used to generate a first carrier wave; the first optical amplitude modulator is used to modulate the first optical signal onto the first carrier wave to obtain a new optical network signal;

[0014] The second optical line terminal includes: a second non-return-to-zero (NRZ) encoded data terminal, a second light source, a four-level pulse amplitude modulation encoder, and a second optical amplitude modulator; the second NRZ encoded data terminal, the four-level pulse amplitude modulation encoder, and the second optical amplitude modulator are connected in sequence; the second light source is connected to the second optical amplitude modulator; the second NRZ encoded data terminal is used to process the received fourth input electrical signal to obtain a second optical signal; the four-level pulse amplitude modulation encoder is used to encode the second optical signal to obtain a third optical signal; the second light source is used to generate a second carrier wave; the second optical amplitude modulator is used to modulate the third optical signal onto the second carrier wave to obtain a complement signal.

[0015] In one possible implementation, the legacy optical line terminal includes: a third non-return-to-zero coded data terminal, a third light source, and a third optical amplitude modulator; the third non-return-to-zero coded data terminal is connected to a first terminal of the third optical amplitude modulator; the third light source is connected to a second terminal of the third optical amplitude modulator.

[0016] The third non-return-to-zero coded data terminal is used to process the received first input electrical signal to obtain a fourth optical signal; the third light source is used to generate a third carrier wave; the third optical amplitude modulator is used to modulate the fourth optical signal onto the third carrier wave to obtain an old optical network signal.

[0017] In one possible implementation, the new optical network unit includes: an optical filter, a first photodetector, a first low-pass filter, and a first signal receiver connected in sequence;

[0018] The optical filter is used to filter the target optical network signal to obtain a fifth optical signal of the required wavelength.

[0019] The first photodetector is used to demodulate the detected fifth optical signal to obtain a first electrical signal;

[0020] The first low-pass filter is used to filter the first electrical signal to obtain a second target signal corresponding to the second input electrical signal;

[0021] The first signal receiver is used to receive the second target signal.

[0022] In one possible implementation, the legacy optical network unit includes: a second photodetector, a second low-pass filter, and a second signal receiver connected in sequence;

[0023] The second photodetector is used to demodulate the detected target optical network signal to obtain a second electrical signal;

[0024] The second low-pass filter is used to filter the second electrical signal to obtain a first target signal corresponding to the first input electrical signal;

[0025] The signal receiver is used to receive the first target signal.

[0026] In one possible implementation, the first optical amplitude modulator, the second optical amplitude modulator, and the third optical amplitude modulator are all Mach-Zehnder modulators;

[0027] The Mach-Zehnder modulator employs amplitude shift keying (APS) modulation.

[0028] In one possible implementation, a second wavelength division multiplexer is also included;

[0029] The downlink wavelength complement data transmitter, the second wavelength division multiplexer, and the first wavelength division multiplexer are connected in sequence; the second wavelength division multiplexer is used to combine the plurality of new optical network signals and the complement signal into a first optical network signal;

[0030] The first wavelength division multiplexer is specifically used to combine the first optical network signal and the old optical network signal into a target optical network signal.

[0031] In one possible implementation, M is 4.

[0032] In one possible implementation, the first remote node is a beam splitter.

[0033] In one possible implementation, the system further includes: a plurality of second remote nodes, which are used to connect remote nodes in the system to legacy network units, or to connect remote nodes in the system to new optical network units; the second remote nodes are used to expand the number of legacy optical network units or the number of new optical network units in the system.

[0034] The passive optical network system disclosed herein includes: a central office and a first optical network system connected via single-mode optical fiber; wherein, the central office includes: an old optical line terminal, a downlink wavelength complement data transmitter, and a first wavelength division multiplexer; the first optical network system includes: a first remote node, multiple old optical network units, and multiple new optical network units; the old optical line terminal is used to process the received first input electrical signal, generate and transmit the old optical network signal to the first wavelength division multiplexer; the downlink wavelength complement data transmitter is used to process the received second input electrical signal, generate and transmit multiple new optical network signals and one complement signal to the first wavelength division multiplexer; each Each new optical network signal and its complement signal has a different wavelength; the amplitude of the complement signal is the inverse sum of the multiple new optical network signals; a first wavelength division multiplexer combines the old optical network signal, the multiple new optical network signals, and the complement signal into a target optical network signal; the target optical network signal is transmitted to a first remote node via single-mode fiber; the first remote node divides the target optical network signal into two parts, one part is transmitted to the old optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal; the other part is transmitted to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal. In the passive optical network system provided by this solution, unused wavelengths can be used to carry the complement signal, ensuring a constant amplitude after the complement signal and the new optical network signal are combined. This minimizes crosstalk to the old optical network signal caused by the combined signal, improving the performance of the upgraded passive optical network system. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this disclosure 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 this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram illustrating the structure of a passive optical network system according to an exemplary embodiment of the present disclosure;

[0037] Figure 2 This is a schematic diagram illustrating the process of generating a target optical network signal, as shown in an exemplary embodiment of the present disclosure.

[0038] Figure 3 A schematic diagram illustrating the structure of a passive optical network system as shown in another exemplary embodiment of this disclosure;

[0039] Figure 4 This is a schematic diagram of the structure of a downlink wavelength complement data transmitter shown in an exemplary embodiment of the present disclosure;

[0040] Figure 5 This is a structural diagram of a downlink non-return-to-zero coded data transmitter, illustrating an exemplary embodiment of the present disclosure. Detailed Implementation

[0041] PON has become the most attractive solution to address access network bottlenecks. Existing PONs typically offer downlink rates of 1.25Gb / s and 2.5Gb / s. Due to rapidly increasing bandwidth demands, upgrading existing PONs to 10Gb / s or higher downlink rates is a pressing issue. The upgrade from existing PONs to next-generation PONs should be smooth, as passive optical networks are cost-sensitive, and the primary cost comes from building the ODN. Rebuilding a new ODN is too expensive; therefore, next-generation PONs are expected to be added to the already deployed ODN to reuse existing infrastructure. Simultaneously, existing PONs should still be in use when new PONs are added; therefore, new PON links should coexist with existing PON links until all existing PON users upgrade to the new PON links. For coexistence, new PONs typically use different wavelengths than older PONs, allowing for signal separation via optical filters. Such filters can be equipped when installing new PON links. However, older PON links lack such optical filters because their coexistence requirement was not known at deployment. Adding optical filters to widely distributed Optical Network Units (ONUs) is very costly. Ideally, the added filters should be located at the fiber optic line termination, where access is likely easier. Therefore, crosstalk in coexistence occurs from the new PON downlink signal interfering with the old PON downlink signal.

[0042] To eliminate coexistence crosstalk, synchronous pulse interleaving, electrical stacking modulation, and subcarrier modulation were proposed to provide time-domain / amplitude-domain / frequency-domain coexistence of the old and new PON signals in the downlink direction, respectively. However, the proposed methods require expensive devices (such as high-speed electromultipliers and pulse transmitters) or sacrifice the quality of the new PON signal, and no further research has been conducted.

[0043] A promising technology for smooth upgrades is spectrum-shaping line coding. This technique applies line codes to the new PON signal to suppress its low-frequency components, thereby reducing crosstalk to the slower, older PON signal. Spectrum-shaping line coding is software-operated and requires no additional components. The coding can be turned off after the upgrade, making the upgrade "seamless." Furthermore, it does not degrade the quality of the new PON downlink signal. The main drawback of spectrum-shaping line coding is reduced coding efficiency; the effective bit rate of the line-coded signal is lower than the transmission rate. Spectrum-shaping line coding only works when the bit rate of the old PON signal is significantly lower than that of the new PON signal. As the bit rates of the two signals become closer, crosstalk increases rapidly.

[0044] New PON signals using quadrature modulation, such as differential phase-shift keying (DPS), polarization-shift keying (PSK), and wavelength-shift keying (WPSK), have constant amplitudes and produce very little crosstalk to older PON signals modulated by amplitude shift keying (APS). However, quadrature modulation introduces additional operational complexity and is not recommended in PON specifications.

[0045] To address the aforementioned technical issues, the solution provided in this disclosure utilizes unused wavelengths to carry complement signals, ensuring that the amplitude of the complement signal remains constant after being combined with the new optical network signal. This results in minimal crosstalk between the combined signal and the old optical network signal, improving the performance of the upgraded passive optical network system without introducing additional operational complexity and making it easy to implement.

[0046] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this disclosure are all information and data authorized by the user or fully authorized by all parties. Furthermore, the collection, use and processing of the relevant data must comply with the relevant laws, regulations and standards of the relevant countries and regions, and corresponding operation portals are provided for users to choose to authorize or refuse.

[0047] The technical solutions of this disclosure and how they solve the aforementioned technical problems will be described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of this disclosure will now be described with reference to the accompanying drawings.

[0048] Figure 1 This is a schematic diagram illustrating the structure of a passive optical network system as an exemplary embodiment of the present disclosure.

[0049] like Figure 1As shown, the passive optical network system provided in this embodiment includes: a central office and a first optical network system connected by a single-mode optical fiber; wherein, the central office includes: an old optical line terminal, a downlink wavelength complement data transmitter, and a first wavelength division multiplexer; the first optical network system includes: a first remote node, multiple old optical network units, and multiple new optical network units.

[0050] The legacy optical line terminal is used to process the received first input electrical signal, generate and send legacy optical network signals to the first wavelength division multiplexer.

[0051] The downlink wavelength complement data transmitter processes the received second input electrical signal to generate and transmit multiple new optical network signals and a complement signal to the first wavelength division multiplexer; each new optical network signal and the complement signal have a different wavelength; the amplitude of the complement signal is the inverse sum of multiple new optical network signals.

[0052] The first wavelength division multiplexer is used to combine the old optical network signal, multiple new optical network signals, and the complement signal into a target optical network signal; the target optical network signal is transmitted to the first remote node through a single-mode optical fiber.

[0053] The first remote node is used to divide the target optical network signal into two parts. One part is transmitted to the old optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal; the other part is transmitted to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal.

[0054] Specifically, the passive optical network system may include a central office and a first optical network system connected via single-mode optical fiber. The central office may include a legacy optical line terminal (OLT), a downlink wavelength complement data transmitter, and a first wavelength division multiplexer (WDM). The first optical network system may include a first remote node, multiple legacy optical network units (ROUs), and multiple new optical network units (NEUs). Specifically, the first WDM is connected to the legacy OLT, the downlink wavelength complement data transmitter, and one end of the single-mode optical fiber. The other end of the single-mode optical fiber is connected to the first end of the first remote node. The second end of the first remote node is connected to the multiple legacy optical network units and the multiple new optical network units.

[0055] Specifically, the transmission rate of the old optical network signal emitted by the old optical line terminal can be 1.25Gb / s and 2.5Gb / s. Specifically, the transmission speed of the new optical network signal emitted by the downlink wavelength complement data transmitter can reach 10Gb / s.

[0056] Specifically, the legacy optical line terminal can receive a first input electrical signal that needs to be transmitted for data, process the received first input electrical signal, generate and send a legacy optical network signal to the first wavelength division multiplexer. The legacy optical network signal carries the useful signal that needs to be transmitted for data.

[0057] Specifically, the downlink wavelength complement data transmitter can receive multiple second input electrical signals, process these signals, and generate and transmit multiple new optical network signals and one complement signal. The new optical network signals carry the useful signals required for data transmission. The complement signal does not carry the useful signals required for data transmission.

[0058] Specifically, the wavelengths of the old optical network signal, multiple new optical network signals, and the complement signal are all different. For example, the wavelength of the old optical network signal can be 1490nm; the wavelengths of multiple new optical network signals and the complement signal can be 1596.34nm, 1597.19nm, 1598.04nm, and 1598.89nm, respectively.

[0059] Specifically, a preset encoding method can be used to make the amplitude of the complement signal the inverse sum of multiple new optical network signals. For example, the amplitude of the complement signal can be [3 - the sum of the amplitudes of multiple new optical network signals]. Therefore, the amplitude of the signal after combining multiple new optical network signals with the complement signal is constant. For example, as... Figure 2 As shown, the multiple new optical network signals are new PON signal 1, new PON signal 2, and new PON signal 3; new PON signal 1 is 01010101; new PON signal 2 is 00101100; new PON signal 3 is 01100101; then the complement code signal is: 31122031; the combined signal (i.e., the TWDM-PON combined signal) is 33333333.

[0060] Specifically, the first wavelength division multiplexer can combine the old optical network signal, multiple new optical network signals, and the complement signal into a target optical network signal. Then, the generated target optical network signal can be transmitted to the first optical network system via single-mode fiber. For example... Figure 2 As shown, the old optical network signal (i.e., the old PON signal) can be 01; combined with multiple new optical network signals and complement signals, the combined signal 33333333 is obtained to obtain the target optical network signal (i.e., the coexistence signal).

[0061] Specifically, the target optical network signal can be transmitted to the first remote node via single-mode optical fiber; the first remote node can connect to multiple legacy optical network units and multiple new optical network units. The first remote node can be used to divide the target optical network signal into multiple parts, transmit part of it to the legacy optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal, and transmit part of it to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal.

[0062] Specifically, the new optical network unit can receive the target signal corresponding to the complement signal without demodulation.

[0063] The passive optical network system disclosed herein includes: a central office and a first optical network system connected via single-mode optical fiber; wherein, the central office includes: an old optical line terminal, a downlink wavelength complement data transmitter, and a first wavelength division multiplexer; the first optical network system includes: a first remote node, multiple old optical network units, and multiple new optical network units; the old optical line terminal is used to process the received first input electrical signal, generate and transmit the old optical network signal to the first wavelength division multiplexer; the downlink wavelength complement data transmitter is used to process the received second input electrical signal, generate and transmit multiple new optical network signals and one complement signal to the first wavelength division multiplexer; each Each new optical network signal and its complement signal has a different wavelength; the amplitude of the complement signal is the inverse sum of the multiple new optical network signals; a first wavelength division multiplexer combines the old optical network signal, the multiple new optical network signals, and the complement signal into a target optical network signal; the target optical network signal is transmitted to a first remote node via single-mode fiber; the first remote node divides the target optical network signal into two parts, one part is transmitted to the old optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal; the other part is transmitted to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal. In the passive optical network system provided by this solution, unused wavelengths can be used to carry the complement signal, ensuring a constant amplitude after the complement signal and the new optical network signal are combined. This results in minimal crosstalk between the combined signal and the old optical network signal, improving the performance of the upgraded passive optical network system. Furthermore, it does not introduce additional operational complexity and is easy to implement.

[0064] Figure 3 This is a schematic diagram illustrating the structure of a passive optical network system, which is another exemplary embodiment of this disclosure.

[0065] exist Figure 1 Based on the illustrated embodiment, in one possible implementation of the passive optical network system provided in this embodiment, the downlink wavelength complement data transmitter (i.e. Figure 3The TWDM new OLT includes M-1 first optical line terminals and 1 second optical line terminal; where M is a positive integer greater than 1. Each first optical line terminal includes: a first non-return-to-zero coded data terminal, a first light source, and a first optical amplitude modulator; the first non-return-to-zero coded data terminal is connected to a first terminal of the first optical amplitude modulator; the first light source is connected to a second terminal of the first optical amplitude modulator; the first non-return-to-zero coded data terminal is used to process the received third input electrical signal to obtain a first optical signal; the first light source is used to generate a first carrier; the first optical amplitude modulator is used to modulate the first optical signal onto the first carrier to obtain a new optical network signal.

[0066] In one possible implementation, M is 4.

[0067] Specifically, each first optical line terminal may include: a first non-return-to-zero (NRZ) coded data terminal, a first light source, and a first optical amplitude modulator. Specifically, the first NRZ coded data terminal may be connected to a first terminal of the first optical amplitude modulator; the first light source may be connected to a second terminal of the first optical amplitude modulator. Specifically, the first NRZ coded data terminal may be used to perform NRZ coded processing on the received third input electrical signal to obtain a first optical signal; the first light source may be used to generate a first carrier wave; and the first optical amplitude modulator may be used to modulate the first optical signal onto the first carrier wave to obtain a new optical network signal.

[0068] like Figure 3 As shown, the wavelengths of the multiple new optical network signals and complement signals can be 1596.34nm, 1597.19nm, 1598.04nm, and 1598.89nm, respectively. The new optical network signals can be represented as new PON signal 1, new PON signal 2, and new PON signal 3, respectively. The first light source can be a semiconductor laser light source (Laser Diode, LD).

[0069] The third input electrical signal can be a useful signal that needs to be transmitted.

[0070] In one possible implementation, the first optical amplitude modulator is a Mach-Zehnder modulator (MZM); the Mach-Zehnder modulator employs amplitude shifting modulation.

[0071] Specifically, the extinction ratio of a Mach-Zehnder modulator can be as common as 14 dB.

[0072] Specifically, the Mach-Zehnder modulator uses amplitude shift keying (APS) modulation, which can be binary APS modulation.

[0073] Specifically, the first optical amplitude modulator can be a Mach-Zehnder modulator; the Mach-Zehnder modulator can employ amplitude shift keying (APS) modulation. Specifically, the Mach-Zehnder modulator can use APS modulation to modulate the first optical signal onto the first carrier wave to obtain a new optical network signal.

[0074] The second optical line terminal includes: a second non-return-to-zero (NRZ) encoded data terminal, a second light source, a four-level pulse amplitude modulation encoder, and a second optical amplitude modulator; the second NRZ encoded data terminal, the four-level pulse amplitude modulation encoder, and the second optical amplitude modulator are connected in sequence; the second light source is connected to the second optical amplitude modulator; the second NRZ encoded data terminal is used to process the received fourth input electrical signal to obtain a second optical signal; the four-level pulse amplitude modulation encoder is used to encode the second optical signal to obtain a third optical signal; the second light source is used to generate a second carrier wave; and the second optical amplitude modulator is used to modulate the third optical signal onto the second carrier wave to obtain a complement signal.

[0075] Specifically, the second optical line terminal (OLT) has an additional four-level pulse amplitude modulation (PAM4) encoder compared to the first OLT. Specifically, the second OLT may include: a second non-return-to-zero (NRZ) encoded data terminal, a second light source, a four-level PAM4 encoder, and a second optical amplitude modulator; and the second NRZ encoded data terminal, the four-level PAM4 encoder, and the second optical amplitude modulator are connected sequentially. The second light source is connected to the second optical amplitude modulator. Specifically, the second NRZ encoded data terminal can be used to perform NRZ encoding processing on the received fourth input electrical signal to obtain a second optical signal; the four-level PAM4 encoder can be used to perform four-level PAM4 modulation encoding on the second optical signal to obtain a third optical signal; the second light source can be used to generate a second carrier wave; and the second optical amplitude modulator is used to modulate the third optical signal onto the second carrier wave to obtain a complement signal.

[0076] Specifically, PAM4 can generate data through mapping. For example, PAM4 can map bit "00" to "0", "01" to "1", "10" to "2", and "11" to "3".

[0077] The fourth input electrical signal can be a useful signal that is not required for data transmission.

[0078] In one possible implementation, the second optical amplitude modulator is a Mach-Zehnder modulator; the Mach-Zehnder modulator employs amplitude shifting modulation.

[0079] Specifically, the second optical amplitude modulator can be a Mach-Zehnder modulator; this Mach-Zehnder modulator can employ amplitude shift keying (APS) modulation. Specifically, the Mach-Zehnder modulator can use APS modulation to modulate the third optical signal onto the second carrier wave to obtain a complement signal.

[0080] Specifically, such as Figure 2 As shown, new PON signal 1, new PON signal 2, new PON signal 3, and the complement signal can form a TWDM-PON combined signal. Due to the nonlinearity of MZM modulation, the level distances of the PAM4 signals are not equal, so the incomplete complement still has some fluctuations. After transmission in single-mode fiber exceeding 25km, the signals become out of sync due to different dispersion, and therefore the TWDM-PON combined signal no longer has a constant amplitude. Therefore, the TWDM-PON combined signal can be pre-delayed after transmission for synchronization, making the TWDM-PON combined signal approach constant amplitude again.

[0081] In one possible implementation, the passive optical network system further includes a second wavelength division multiplexer; a downlink wavelength complement data transmitter, the second wavelength division multiplexer, and a first wavelength division multiplexer are connected in sequence; the second wavelength division multiplexer is used to combine multiple new optical network signals and complement signals into a first optical network signal; the first wavelength division multiplexer is specifically used to combine the first optical network signal and the old optical network signal into a target optical network signal.

[0082] Specifically, such as Figure 3 As shown, the passive optical network system also includes a second wavelength division multiplexer, wherein the downlink wavelength complement data transmitter, the second wavelength division multiplexer, and the first wavelength division multiplexer are connected in sequence. The second wavelength division multiplexer can be used to combine multiple new optical network signals and complement signals into a first optical network signal; then the first wavelength division multiplexer is used to combine the first optical network signal with the old optical network signal into a target optical network signal.

[0083] Specifically, such as Figure 4 As shown, three first optical line terminals, one second optical line terminal, and a wavelength division multiplexer (WDM) can form a downlink wavelength complemented data transmission module. Specifically, the wavelengths corresponding to the three first optical line terminals and the one second optical line terminal can be λ1, λ2, λ3, and λ4, respectively. Each first optical line terminal includes a light source, an NRZ data terminal, and a Mach-Zehnder modulator. The second optical line terminal includes a light source, an NRZ data terminal, a PAM4 encoder, and a Mach-Zehnder modulator.

[0084] In one possible implementation, the legacy optical line terminal includes: a third non-return-to-zero (NRZ) coded data terminal, a third light source, and a third optical amplitude modulator; the third NRZ coded data terminal is connected to a first terminal of the third optical amplitude modulator; the third light source is connected to a second terminal of the third optical amplitude modulator; the third NRZ coded data terminal is used to process the received first input electrical signal to obtain a fourth optical signal; the third light source is used to generate a third carrier wave; and the third optical amplitude modulator is used to modulate the fourth optical signal onto the third carrier wave to obtain a legacy optical network signal.

[0085] Specifically, the legacy optical line terminal may include a third non-return-to-zero (NRZ) coded data terminal, a third light source, and a third optical amplitude modulator. The third NRZ coded data terminal is connected to a first terminal of the third optical amplitude modulator; the third light source is connected to a second terminal of the third optical amplitude modulator. Specifically, the third NRZ coded data terminal can be used to perform NRZ encoding on the received first input electrical signal to obtain a fourth optical signal; the third light source can be used to generate a third carrier wave; and the third optical amplitude modulator can be used to modulate the fourth optical signal onto the third carrier wave, thereby obtaining the legacy optical network signal.

[0086] Specifically, the first input electrical signal can be a useful signal that needs to be transmitted.

[0087] In one possible implementation, the third optical amplitude modulator is a Mach-Zehnder modulator; the Mach-Zehnder modulator employs amplitude shifting modulation.

[0088] Specifically, the third optical amplitude modulator can be a Mach-Zehnder modulator; this Mach-Zehnder modulator can employ amplitude shift keying (APS) modulation. Specifically, the Mach-Zehnder modulator can use APS modulation to modulate the fourth optical signal onto the third carrier wave, obtaining a complement signal.

[0089] Specifically, such as Figure 5 As shown, the old optical line terminal (i.e., the old OLT) can also be called a downlink NRZ data transmitter. The old optical line terminal includes a light source, an NRZ data terminal, and a Mach-Zehnder modulator.

[0090] In one possible implementation, the first remote node (RN) is a splitter.

[0091] In one possible implementation, the passive optical network system may further include: multiple second remote nodes, which are used to connect remote nodes in the system with existing network units, or to connect remote nodes in the system with new optical network units; the second remote nodes are used to expand the number of existing optical network units or the number of new optical network units in the system.

[0092] Specifically, the passive optical network system may also include multiple second remote nodes. Each second remote node can be used to connect the upper-level remote node in the system to an existing network unit, or to connect the upper-level remote node in the system to a new optical network unit; the second remote node can be used to expand the number of existing optical network units or the number of new optical network units in the system.

[0093] Specifically, the second remote node can be the same as the first remote node, both of which can be optical splitters.

[0094] In one possible implementation, the new optical network unit includes: an optical filter, a first photodetector, a first low-pass filter, and a first signal receiver connected in sequence; the optical filter is used to filter the target optical network signal to obtain a fifth optical signal of the required wavelength; the first photodetector is used to demodulate the detected fifth optical signal to obtain a first electrical signal; the first low-pass filter is used to filter the first electrical signal to obtain a second target signal corresponding to the second input electrical signal; and the first signal receiver is used to receive the second target signal.

[0095] Specifically, the new optical network unit (i.e., the new ONU) may include, in sequence, an optical filter, a first photodetector, a first low-pass filter, and a first signal receiver. The optical filter can be used to filter the target optical network signal transmitted through single-mode fiber to obtain a fifth optical signal. Specifically, the optical filter can filter out irrelevant wavelengths from the target optical network signal to obtain the desired wavelength signal, thereby obtaining the first optical signal.

[0096] Next, the first photodetector can be used to demodulate the detected fifth optical signal to obtain the first electrical signal. The demodulation method in the first photodetector can correspond to the modulation method in a Mach-Zehnder modulator.

[0097] Next, a first low-pass filter can be used to filter the first electrical signal to obtain a second target signal corresponding to the second input electrical signal. Specifically, the first low-pass filter can be used to filter out low-frequency interference signals in the first electrical signal. Then, a first signal receiver can be used to receive the second target signal. Specifically, a low-pass filter can be used to simulate a limited receiving bandwidth, and the cutoff frequency can be set to 75% of the received signal bit rate to demodulate the new signal.

[0098] In one possible implementation, the legacy optical network unit (i.e., the legacy ONU) includes: a second photodetector, a second low-pass filter, and a second signal receiver connected in sequence. The second photodetector is used to demodulate the detected target optical network signal to obtain a second electrical signal; the second low-pass filter is used to filter the second electrical signal to obtain a first target signal corresponding to the first input electrical signal; and the signal receiver is used to receive the first target signal.

[0099] Specifically, the legacy optical network unit may include: a second photodetector, a second low-pass filter, and a second signal receiver connected sequentially via single-mode fiber. The second photodetector can be used to demodulate the detected target optical network signal to obtain a second electrical signal. The demodulation method in the second photodetector can correspond to the modulation method in a Mach-Zehnder modulator.

[0100] Next, a second low-pass filter can be used to filter the second electrical signal to obtain a first target signal corresponding to the first input electrical signal. Specifically, since the bandwidth of the selected second filter is limited, it can only receive low-speed signals, while high-speed signals are automatically filtered out, thus enabling the separation of old and new optical network signals in the old optical network unit. Then, the first target signal can be received using a signal receiver.

[0101] Specifically, in older ONUs, because there is no optical filter, the resulting signal is a combination of the old and new signals. However, the combination of the new PON signal and the complement signal can be considered as DC, resulting in very little crosstalk to the traditional PON signal with amplitude shift keying (APS-C). The complement signal is only used to ensure the constancy and amplitude of the new PON signal. PAM is not received in any older ONU, therefore PAM detection is unnecessary; in newer ONUs, because of the presence of optical filters, they can pick up the appropriate wavelength.

[0102] The wavelength complement used in this disclosure can be implemented via software without the need for additional equipment. Modulation and demodulation are both traditional amplitude shift keying (APS) modulation and demodulation, requiring no modification or complex operations, thus reducing upgrade costs.

[0103] Specifically, TWDM-PON can use multiple wavelengths to multiply users and capacity. Typically, as the number of users increases, wavelengths are put into use one after another, thus unused wavelengths can be used to carry complement signals to ensure the amplitude and consistency of the new PON signal and the complement signal. Taking Next Generation Passive Optical Network (NG-PON2) as an example, NG-PON2 uses four wavelengths, so one unused wavelength must remain until the number of users reaches 75% of the maximum. In the final stage of the upgrade, the number of users in the new PON will exceed 75%, so a complement wavelength must be used to carry another new PON signal. In this case, time-division multiplexing (TDM) can be used for the new and old PON signals. If the old PON signal is being transmitted, the complement wavelength is used to carry the complement signal to reduce crosstalk to the old PON signal. If the old PON signal is not being transmitted, the complement wavelength is used to carry the new PON signal. In the final stage, most existing ONUs are upgraded, making the downlink traffic of the old PONs very small, which is feasible using the TDM method. This upgrade does not require modification of existing ONUs, so there are no modification costs. All new PON signals are unencoded, so there is no encoding or decoding process, and the encoding efficiency of each new PON signal is 100%. Complementary code signals do not need to be received. When all existing ONUs are upgraded, another new PON signal can be carried using the complementary code wavelength; the upgrade is "seamless."

[0104] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0105] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A passive optical network system, characterized in that, include: A central office and a first optical network system are connected via single-mode optical fiber; wherein, the central office includes: an old optical line terminal, a downlink wavelength complement data transmitter, and a first wavelength division multiplexer; the first optical network system includes: a first remote node, multiple old optical network units, and multiple new optical network units; The old optical line terminal is used to process the received first input electrical signal, generate and send the old optical network signal to the first wavelength division multiplexer. The downlink wavelength complement data transmitter is used to process the received second input electrical signal, generate and send multiple new optical network signals and a complement signal to the first wavelength division multiplexer; each new optical network signal and the complement signal have a different wavelength; the amplitude of the complement signal is the inverse sum of the multiple new optical network signals; The first wavelength division multiplexer is used to combine the old optical network signal, the plurality of new optical network signals, and the complement signal into a target optical network signal; the target optical network signal is transmitted to the first remote node through the single-mode optical fiber; The first remote node is used to divide the target optical network signal into two parts. One part is transmitted to the old optical network unit for demodulation to obtain and receive the first target signal corresponding to the first input electrical signal; the other part is transmitted to the new optical network unit for demodulation to obtain and receive the second target signal corresponding to the second input electrical signal. The downlink wavelength complemented data transmitter includes M-1 first optical line terminals and 1 second optical line terminal; where M is 4. Each of the first optical line terminals includes: a first non-return-to-zero (NRZ) coded data terminal, a first light source, and a first optical amplitude modulator; the first NRZ coded data terminal is connected to a first terminal of the first optical amplitude modulator; the first light source is connected to a second terminal of the first optical amplitude modulator; the first NRZ coded data terminal is used to process the received third input electrical signal to obtain a first optical signal; the first light source is used to generate a first carrier wave; the first optical amplitude modulator is used to modulate the first optical signal onto the first carrier wave to obtain a new optical network signal; The second optical line terminal includes: a second non-return-to-zero (NRZ) encoded data terminal, a second light source, a four-level pulse amplitude modulation encoder, and a second optical amplitude modulator; the second NRZ encoded data terminal, the four-level pulse amplitude modulation encoder, and the second optical amplitude modulator are connected in sequence; the second light source is connected to the second optical amplitude modulator; the second NRZ encoded data terminal is used to process the received fourth input electrical signal to obtain a second optical signal; the four-level pulse amplitude modulation encoder is used to encode the second optical signal to obtain a third optical signal; the second light source is used to generate a second carrier wave; the second optical amplitude modulator is used to modulate the third optical signal onto the second carrier wave to obtain a complement signal.

2. The system according to claim 1, characterized in that, The old optical line terminal includes: a third non-return-to-zero coded data terminal, a third light source, and a third optical amplitude modulator; the third non-return-to-zero coded data terminal is connected to a first terminal of the third optical amplitude modulator; the third light source is connected to a second terminal of the third optical amplitude modulator; The third non-return-to-zero coded data terminal is used to process the received first input electrical signal to obtain a fourth optical signal; the third light source is used to generate a third carrier wave; the third optical amplitude modulator is used to modulate the fourth optical signal onto the third carrier wave to obtain an old optical network signal.

3. The system according to claim 1, characterized in that, The new optical network unit includes: an optical filter, a first photodetector, a first low-pass filter, and a first signal receiver connected in sequence; The optical filter is used to filter the target optical network signal to obtain a fifth optical signal of the required wavelength. The first photodetector is used to demodulate the detected fifth optical signal to obtain a first electrical signal; The first low-pass filter is used to filter the first electrical signal to obtain a second target signal corresponding to the second input electrical signal; The first signal receiver is used to receive the second target signal.

4. The system according to claim 1, characterized in that, The old optical network unit includes: a second photodetector, a second low-pass filter, and a second signal receiver connected in sequence; The second photodetector is used to demodulate the detected target optical network signal to obtain a second electrical signal; The second low-pass filter is used to filter the second electrical signal to obtain a first target signal corresponding to the first input electrical signal; The second signal receiver is used to receive the first target signal.

5. The system according to claim 2, characterized in that, The first optical amplitude modulator, the second optical amplitude modulator, and the third optical amplitude modulator are all Mach-Zehnder modulators; The Mach-Zehnder modulator employs amplitude shift keying (APS) modulation.

6. The system according to any one of claims 1-5, characterized in that, It also includes a second wavelength division multiplexer; The downlink wavelength complement data transmitter, the second wavelength division multiplexer, and the first wavelength division multiplexer are connected in sequence; the second wavelength division multiplexer is used to combine the plurality of new optical network signals and the complement signal into a first optical network signal; The first wavelength division multiplexer is specifically used to combine the first optical network signal and the old optical network signal into a target optical network signal.

7. The system according to any one of claims 1-5, characterized in that, The first remote node is a beam splitter.

8. The system according to any one of claims 1-5, characterized in that, Also includes: Multiple second remote nodes are used to connect remote nodes in the system to legacy network units, or to connect remote nodes in the system to new optical network units; the second remote nodes are used to expand the number of legacy optical network units or the number of new optical network units in the system.

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