An optical access system and method supporting optical interconnection between WDM-PON subnets

Abstract

An optical access system and method supporting optical interconnection between WDM-PON subnets. The remote node structure and colorless optical network unit design in WDM-PON are important research topics in optical access networks. This invention proposes an optical access system and communication method supporting optical interconnection between WDM-PON subnets. This scheme achieves the following three functions with relatively low device costs: 1. Conventional uplink and downlink communication between the OLT and the WDM-PON ONUs; 2. Dividing all ONUs into two subnets, with physical wavelength isolation between the subnets; 3. Supporting inter-subnet communication. In this invention, the receivers or transmitters of the two subnets can be entirely colorless, or only partially colorless within a subnet, but each subnet has its own characteristics, especially the tunable laser portion, which can be colored depending on the subnet. This design balances the increased manpower maintenance costs associated with colored ONUs during operation and maintenance, while also considering the increased technical difficulty and cost brought by the wide wavelength range tunability of the tunable laser, and simultaneously adds the function of inter-subnet communication.

Description

Technical Field

[0001] This invention relates to optical communication and optical network technologies, and particularly to wavelength division multiplexing (WDM) passive optical network technology. Background Technology

[0002] Time Division Multiplexing-Passive Optical Network (TDM-PON) and Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) are two important technologies in the field of optical access. During the evolution of optical access network rates from 10 Gbit / s to 40 Gbit / s, and even 100 Gbit / s, TDM-PON was considered an effective solution that combined performance and cost-effectiveness. However, with the increase in the number of users and the improvement in access rates per user, WDM-PON technology has gained industry attention and is considered the most important technology solution in next-generation optical access networks.

[0003] Wavelength Division Multiplexing (WDM) technology applied to PON facilitates the expansion of wavelength resources, and allows different users to use different wavelengths, resulting in better security. A typical WDM-PON structure is shown below. Figure 1 The 1It consists of an optical line terminal (OLT) on the central office side, optical network units (ONUs) or optical network terminals (ONTs) on the user side, and an optical distribution network (ODN). Current technologies generally use an uplink from the OLT to the ONU or ONT, and a downlink from the ONU or ONT to the OLT. WDM-PON ODNs typically include three types: 1. To ensure compatibility with existing ODNs, ODNs often only use optical beam splitters to divide the backbone fiber link into multiple branch fiber links, thus saving fiber resources. Each user can receive signals from the OLT and send signals to the OLT. In this structure, the splitter loss increases with the number of users. PON designs based on this structure must have a high link optical power budget. 2. ODN uses wavelength division multiplexing (WDM) devices to demultiplex different wavelengths and transmit them to different users. Each user connected to the output of a WDM (demultiplexer) can be considered a subnet. This scheme physically isolates different users into independent subnets. In this structure, the loss of the WDM (demultiplexer) only changes slightly with the increase in the number of users. Based on this structure, the optical power budget of the link is significantly reduced compared to the first scheme. 3. ODN uses wavelength selective switches to connect different users. Each port of the wavelength selective switch can independently select any wavelength, but the device loss is relatively high, and it cannot be completely passive. The application of this scheme in practical WDM-PON is currently only in the exploratory stage. Of the three schemes above, the first WDM-PON has the same structure as TWDM-PON. In terms of network structure, it inherits the original TDM-PON technologies such as XG-PON to the greatest extent, with changes concentrated only at the OLT and ONU ends. The second type, WDM-PON, completely changes the original TDM-PON ODN, requiring redeployment in practice. The third type, WDM-PON, is the most flexible, but suffers from high wavelength selective switching losses and is costly. Some research has also attempted to improve the design by combining the requirements of the second and third types, resulting in... Figure 2 The composite remote node shown 2 In this architecture, the wavelength allocated to each ONU can be selected, and the wavelength spacing is not a constant value like in a cyclic arrayed waveguide grating (AWG). Google has also designed remote nodes for WDM-PON to enhance subnet functionality. 3 .

[0004] From a physical layer perspective, WDM-PON directly allocates wavelength resources to users (Optical Network Units, ONUs), eliminating the need for traditional time slot allocation. Just as in TDM-PON, each user needs to receive optical signals from all time slots and also has the ability to transmit optical signals from any time slot. Therefore, in WDM-PON, both uplink and downlink wavelengths need to be covered. For the ONU, a tunable optical filter is required to cover all downlink wavelengths, and a tunable laser is required to cover all uplink wavelengths; that is, the ONU must meet the requirement of being colorless. The colorless requirement poses a significant challenge to photonic devices. Among all photonic devices, the industrialization of high-volume, low-cost tunable lasers has been a major focus since 2012, but the large tuning range means that the industrialization of tunable lasers in WDM-PON is still some distance away.

[0005] In existing WDM-PON optical access network architectures, the change in ODN and the colorless requirement at the ONU end are mismatched. If the second approach is used, each wavelength division multiplexing device outputs only one wavelength, such as a conventional arrayed waveguide grating (AWG), or several wavelengths at fixed intervals, such as a cyclic AWG. However, to output a single wavelength actually needed, the ONU must significantly expand its tuning range, some of which is unnecessary for a user at a fixed location. For example, the ONU connected to AWG port 1 will not need the wavelength of AWG port 2, and for strict colorless operation, each ONU's tunable laser must be able to cover the output wavelengths of all AWG ports. Furthermore, in existing WDM-PONs, direct communication between end users is lacking, which is crucial for future applications requiring low latency. While some ONU-to-ONU direct communication solutions exist in TDM-PONs, such solutions are still relatively rare in WDM-PONs requiring colorless ONUs.

[0006] In conclusion, the design of the basic system architecture still needs further research in the current WDM-PON design, which can enable more powerful functions, including the design of remote nodes.

[0007] References:

[0008] 1. ITU-T Standardization Document G.989.2 Annex A

[0009] 2. Huawei Technologies Co., Ltd., Patent Title: Passive Optical Network Supporting Multicast Services, Multiplexer / Demultiplexer and Method

[0010] Application number: 200610001979.X; application date: 2006-01-23; already authorized.

[0011] 3. Google, Patent title: Increasing the capacity of WDM-PON by using wavelength reuse, Application number: 200610001979.X. Summary of the Invention:

[0012] To address the shortcomings of the prior art, this invention proposes an optical access system supporting optical interconnection between WDM-PON subnets and provides a communication method based on this structure. The optical access system proposed in this invention is as follows: Figure 3 and 4 As shown, this system not only supports conventional uplink and downlink communication between ONUs and OLTs, but also divides all users into two subnets. These two subnets are independent in wavelength usage; that is, the wavelength of subnet 1 (subnet 2) cannot be used by subnet 2 (subnet 1) when communicating with the OLT. Because Figure 3 and Figure 4 These are two similar structures, differing only in the connection relationship between the subnet wavelength division multiplexer (10) and the 2×2 optical beam splitter (20). This structure uses only one subnet wavelength division multiplexer (10) and one 2×2 optical beam splitter (20), achieving the following three functions with lower device costs: 1. Conventional uplink and downlink communication between the OLT and the ONUs of the WDM-PON; 2. Dividing all ONUs into two subnets, with physical wavelength isolation between the subnets; 3. Supporting communication between the subnets.

[0013] according to Figure 3 The system is described as follows: a subnet wavelength division multiplexer (10) adapted to connect to an OLT (40) of WDM-PON via a W1 port (101), capable of providing wavelength division for WDM-PON, dividing all wavelengths into A-band and B-band, with no common wavelength between the A-band and B-band, wherein the A-band is output from the W2 port (102) and the B-band is output from the W3 port (103), the W2 port (102) is connected to the C1 port (201) of the 2×2 optical beam splitter (20), and the W3 port (103) is connected to the C3 port (203) of the 2×2 optical beam splitter (20).

[0014] A 2×2 optical beam splitter (20) has two input ports: C1 port (201) and C2 port (202), and two output ports: C3 port (203) and C4 port (204). C1 port (201) is connected to W2 port (102), C2 port (202) is connected to WDM-PON subnet 2 (32), C3 port (203) is connected to W3 port (103), and C4 port (204) is connected to WDM-PON subnet 1 (32). 1); The 2×2 optical beam splitter (20) is a conventional optical coupler, which performs optical coupling according to the following rules: if the light wave is input from port C1 (201) or port C2 (202), it will be output from port C3 (203) and port C4 (204) in a certain proportion, and there will be no light wave output from other ports.

[0015] WDM-PON subnet 1 (31), wherein the subnet 31 contains one or more users (optical network units), has uplink and downlink communication functions between the WDMPON OLT (40) and WDM-PON subnet 1 (31), uses wavelength resources of the A-band, and also has inter-subnet communication functions between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32).

[0016] WDM-PON subnet 2 (32), wherein the subnet 32 ​​contains one or more users (optical network units), has uplink and downlink communication functions between the WDMPON OLT (40) and WDM-PON subnet 2 (32), uses B-band wavelength resources, and also has inter-subnet communication functions between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32).

[0017] The OLT (40) of WDM-PON is the optical line terminal of the entire WDM-PON, used to provide wavelength resources for WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32).

[0018] according to Figure 4 The system is described as follows: a subnet wavelength division multiplexer (10) adapted to connect to an OLT (40) of WDM-PON via a W1 port (101), capable of providing wavelength division of WDM-PON, dividing all wavelengths into A-band and B-band, with no common wavelength between the A-band and B-band, wherein the A-band is output from the W2 port (102) and the B-band is output from the W3 port (103), the W2 port (102) is connected to the C4 port (204) of the 2×2 optical beam splitter (20), and the W3 port (103) is connected to the C1 port (201) of the 2×2 optical beam splitter (20);

[0019] A 2×2 optical beam splitter (20) has two input ports: C1 port (201) and C2 port (202), and two output ports: C3 port (203) and C4 port (204). C1 port (201) is connected to W3 port (103), C2 port (202) is connected to WDM-PON subnet 2 (32), C3 port (203) is connected to WDM-PON subnet 1 (31), and C4 port (204) is connected to W2 port (103). 2); The 2×2 optical beam splitter (20) is a conventional optical coupler, and optical coupling is performed according to the following rules: if the light wave is input from port C1 (201) or port C2 (202), it will be output from port C3 (203) and port C4 (204) in a certain proportion, and there will be no light wave output from other ports; if the light wave is input from port C3 (203) and port C4 (204), it will be output from port C1 (201) or port C2 (202) in a certain proportion, and there will be no light wave output from other ports.

[0020] WDM-PON subnet 1 (31), wherein the subnet 31 contains one or more users (optical network units), has uplink and downlink communication functions between the WDMPON OLT (40) and WDM-PON subnet 1 (31), uses B-band wavelength resources, and also has inter-subnet communication functions between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32);

[0021] WDM-PON subnet 2 (32), wherein the subnet 32 ​​contains one or more users (optical network units), has uplink and downlink communication functions between the WDMPON OLT (40) and WDM-PON subnet 2 (32), uses wavelength resources of the A-band, and has inter-subnet communication functions between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32);

[0022] The OLT (40) of WDM-PON is the optical line terminal of the entire WDM-PON, used to provide wavelength resources for WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32).

[0023] In this invention, the division of the A-band and B-band can be achieved using the following devices: the sub-band wavelength division (demultiplexer) (10) is a coarse wavelength division multiplexer, in which case the wavelengths of the A-band appear first in the spectrum, followed by the wavelengths of the B-band. Alternatively, the division of the A-band and B-band can be achieved using the following devices: the sub-band wavelength division (demultiplexer) (10) is a cyclic arrayed waveguide grating or a wavelength interleaver, in which case the wavelengths of the A-band and B-band appear alternately in the spectrum.

[0024] In the optical access system supporting WDM-PON subnet optical interconnection provided by this invention, namely Figure 3 In this context, the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) can be performed as follows:

[0025] a) Optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses the A-band, and optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses the B-band. To support this method, the transmitter of the ONU of WDM-PON subnet 1 (31) must contain a tunable laser with a wavelength covering the entire A-band, and the transmitter of the ONU of WDM-PON subnet 2 (32) must contain a tunable laser with a wavelength covering the entire B-band. Therefore, the receivers of the ONU of WDM-PON subnet 1 (31) and the ONU of WDM-PON subnet 2 (32) must contain tunable optical filters with a tunable range covering the entire A-band and B-band.

[0026] b) Optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses the B-band, and optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses the A-band. To support this method, the receiver of the ONU of WDM-PON subnet 1 (31) must contain a tunable optical filter with a wavelength covering the entire A-band, and the receiver of the ONU of WDM-PON subnet 2 (32) must contain a tunable optical filter with a wavelength covering the entire B-band. Therefore, the transmitters of the ONUs of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) must contain tunable lasers with a tunable range covering the entire A-band and B-band.

[0027] c) If the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) both use the A-band, the tunable optical filter of the receiver and the tunable laser of the transmitter in the ONU of WDM-PON subnet 2 (32) must cover the entire A-band and B-band.

[0028] d) If the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) both use the B-band, the tunable optical filter of the receiver and the tunable laser of the transmitter in the ONU of WDM-PON subnet 1 (31) must cover the entire A-band and B-band.

[0029] In the optical access system supporting WDM-PON subnet optical interconnection described in this invention, namely Figure 4In this context, the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) can be performed as follows:

[0030] a) Optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses the A-band, and optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses the B-band. To support this method, the receiver of the ONU of WDM-PON subnet 2 (32) must contain a tunable optical filter with a wavelength covering the entire A-band, and the receiver of the ONU of WDM-PON subnet 1 (31) must contain a tunable optical filter with a wavelength covering the entire B-band. Therefore, the transmitters of the ONUs of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) must contain tunable lasers with a tunable range covering the entire A-band and B-band.

[0031] b) Optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses the B-band, and optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses the A-band. To support this method, the transmitter of the ONU of WDM-PON subnet 1 (31) must contain a tunable laser with a wavelength covering the entire B-band, and the transmitter of the ONU of WDM-PON subnet 2 (32) must contain a tunable laser with a wavelength covering the entire A-band. Therefore, the receivers of the ONUs of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) must contain tunable optical filters with a tunable range covering the entire A-band and B-band.

[0032] c) If the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) both use the A-band, the tunable optical filter of the receiver and the tunable laser of the transmitter in the ONU of WDM-PON subnet 1 (31) must cover the entire A-band and B-band.

[0033] d) If the communication function between WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) both use the B-band, the tunable optical filter of the receiver and the tunable laser of the transmitter in the ONU of WDM-PON subnet 2 (32) must cover the entire A-band and B-band.

[0034] Furthermore, in the optical access system that supports optical interconnection between WDM-PON subnets, WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) can use optical beam splitters as secondary remote nodes, and the branches of the optical beam splitters can connect to various users.

[0035] In the above communication method design, the ONU of WDM-PON subnet 1 (31) and the ONU of WDM-PON subnet 2 (32) can adopt the above-mentioned colorless design within the subnet, while the design between subnets is not colorless. Therefore, it is not possible to completely achieve the colorless design between subnets.

[0036] Furthermore, the present invention can also adopt a colorless design in which all optical network units in the two subnets are the same, that is, satisfying that the tunable optical filters of the receivers in WDM-PON subnet 1 (31) ONU and WDM-PON subnet 2 (32) ONU, as well as the tunable lasers of the transmitters, must cover the entire A-band and B-band.

[0037] Therefore, if we want all ONUs to be colorless, we will place higher demands on the tunable range of both the receiver's tunable optical filter and the transmitter's tunable laser.

[0038] These structures together constitute the basic hardware of the WDM-PON optical access network proposed in this invention, making this invention fundamentally different from existing technologies in terms of network structure and equipment composition. Due to the change in the physical layer structure, this invention also involves some changes in the communication methods. These methods require differences in the device structures of the ONUs of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32).

[0039] Based on the above system structure and communication method, this invention achieves the following three functions with low device cost (i.e., the core remote node only includes a subnet wavelength division multiplexer (10) and a 2×2 optical beam splitter (20)): 1. Conventional uplink and downlink communication between the OLT and the WDM-PON ONU; this function is implemented using the structure of this invention and employing... Figure 1The second conventional structure described above has very little difference; this invention only increases the optical power budget by 3.5dB. 2. All ONUs are divided into two subnets, which are physically isolated by wavelength. That is, different subnets use different wavelengths. For example, the OLT has eight wavelengths: λ1 to λ8, the wavelengths of WDM-PON subnet 1 (31) are λ1 to λ4, and the wavelengths of WDM-PON subnet 2 (32) are λ5 to λ8. The structure within each subnet can be designed according to the situation. For example, the far-end node of WDM-PON subnet 1 (31) can use a 1-to-4 optical beam splitter; while the far-end node of WDM-PON subnet 2 (32) can use a wavelength division multiplexer. The devices in the ONUs of each subnet can be designed according to these requirements. 3. Support for inter-subnet communication is provided. This function is implemented on the basis of the access network structure provided by this invention, especially on the basis of the far-end node structure. It depends on the wavelength resources of each subnet itself or on the wavelength resources of other subnets, without adding any additional wavelength resources. Since this invention focuses on basic structures and basic communication methods, wavelength allocation schemes based on this invention can be further studied. Attached Figure Description

[0040] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments taken in conjunction with the accompanying drawings, in which:

[0041] Figure 1 It is currently recognized by the optical communication industry as a typical structure of WDM-PON.

[0042] Figure 2 This is a typical structure for a remote node in WDM-PON, in which the wavelength allocated to each ONU can be selected.

[0043] Figure 3 This is a basic structural diagram of an optical access system that supports optical interconnection between WDM-PON subnets, as proposed in this invention.

[0044] Figure 4 This is a basic structural diagram of another optical access system supporting optical interconnection between WDM-PON subnets proposed in this invention. Note: (The last sentence appears to be incomplete and possibly contains errors.) Figure 3 The only difference lies in the connection relationship between the subnet wavelength division multiplexer (10) and the 2×2 optical beam splitter (20).

[0045] Figure 5 This is a schematic diagram of the A and B band division in the subnet wavelength division multiplexer (10), a key module of the remote node proposed in this invention. Detailed Implementation

[0046] 1. An embodiment of a subnet wavelength division (demultiplexer):

[0047] The structural diagram of this embodiment is as follows: Figure 5 As shown,

[0048] The subnet wavelength division multiplexer (10) is a cyclic arrayed waveguide grating. In this case, the wavelengths of the A-band and B-band appear alternately in the spectrum. The A-band includes: λ1, λ3, λ5, and λ7. The B-band includes: λ2, λ4, λ6, and λ8. The wavelengths for uplink and downlink communication can be selected in the A-band. For example, uplink: λ1, λ5, downlink: λ3, λ7, or uplink: λ1, λ3, downlink: λ5, λ7. To achieve these selections, only the corresponding design needs to be made in the remote node of the WDM-PON subnet 1 (31) and the OLT (40) of the WDM-PON.

[0049] 2. An embodiment of a remote node:

[0050] Will Figure 5 Placed in Figure 3 or Figure 4 Two types of remote nodes can be obtained from this.

[0051] 3. Implementation example of a communication method based on structures 1 and 2:

[0052] Using Figure 5 Placed in Figure 3 In the structure, communication can be performed using the following methods:

[0053] 1) For WDM-PON subnet 1 (31): the uplink and downlink communication function between WDM-PON and OLT (40) uses the wavelength resources of the A-band; at this time, the A-band signal from C3 port (203) to W3 port (103) is suppressed, that is, it cannot be returned to WDM-PON OLT (40) through W3 port (103).

[0054] 2) For WDM-PON subnet 2 (32): the uplink and downlink communication function between WDM-PON and OLT (40) uses the wavelength resources of B-band; at this time, the B-band signal from port C1 (201) to port W2 (102) is suppressed, that is, it cannot return to OLT (40) of WDM-PON through port W2 (102).

[0055] 3) Optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses the A-band, and optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses the B-band. To support this method, the transmitter of the ONU of WDM-PON subnet 1 (31) must contain a tunable laser with a wavelength covering the entire A-band, and the transmitter of the ONU of WDM-PON subnet 2 (32) must contain a tunable laser with a wavelength covering the entire B-band. Therefore, the receivers of the ONUs of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) must contain tunable optical filters with a tunable range covering the entire A-band and B-band.

[0056] In this architecture, the receivers in both subnets are colorless, but the transmitters, especially the tunable lasers, are colored, following the pattern of the subnets. This design balances the increased manpower costs associated with the colored ONUs during operation and maintenance, while also taking into account the increased technical difficulty and cost due to the wide wavelength range tunability of the tunable lasers. Furthermore, it enhances the inter-subnet communication capabilities.

[0057] Of course, the remote node design in this invention may have other various embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. An optical access system supporting inter-subnetwork optical interconnection of WDM-PON, comprising: a subnetwork wavelength division multiplexer (10) adapted to connect an OLT (40) of a WDM-PON through a Wl port (101), capable of providing wavelength division of the WDM-PON, dividing all wavelengths into an A wavelength band and a B wavelength band, and the A wavelength band and the B wavelength band having no common wavelength, wherein the A wavelength band is output from a W2 port (102), the B wavelength band is output from a W3 port (103), the W2 port (102) is connected to a Cl port (201) of a 2x2 optical beam splitter (20), the W3 port (103) is connected to a C3 port (203) of the 2x2 optical beam splitter (20); the 2x2 optical beam splitter (20) has two input ports: the Cl port (201) and a C2 port (202), and has two output ports: the C3 port (203) and a C4 port (204), wherein the Cl port (201) is connected to the W2 port (102), the C2 port (202) is connected to a WDM-PON subnetwork 2 (32), the C3 port (203) is connected to the W3 port (103), and the C4 port (204) is connected to a WDM-PON subnetwork 1 (31); the 2x2 optical beam splitter (20) is a regular optical coupler, and the optical coupling is performed according to the following rules: when light waves are input from the Cl port (201) or the C2 port (202), the light waves are output from the C3 port (203) and the C4 port (204) in a certain proportion, and no light waves are output from the other ports, and when light waves are input from the C3 port (203) and the C4 port (204), the light waves are output from the Cl port (201) or the C2 port (202) in a certain proportion, and no light waves are output from the other ports; the WDM-PON subnetwork 1 (31) has one or more user optical network units, has uplink and downlink communication functions between the OLT (40) of the WDM-PON and the WDM-PON subnetwork 1 (31), uses wavelength resources of the A wavelength band, and has inter-subnetwork communication functions between the WDM-PON subnetwork 1 (31) and the WDM-PON subnetwork 2 (32); the WDM-PON subnetwork 2 (32) has one or more user optical network units, has uplink and downlink communication functions between the OLT (40) of the WDM-PON and the WDM-PON subnetwork 2 (32), uses wavelength resources of the B wavelength band, and has inter-subnetwork communication functions between the WDM-PON subnetwork 1 (31) and the WDM-PON subnetwork 2 (32); and the OLT (40) of the WDM-PON is an optical line terminal of the entire WDM-PON, and is used to provide wavelength resources for the WDM-PON subnetwork 1 (31) and the WDM-PON subnetwork 2 (32).

2. An optical access system supporting inter-subnetwork optical interconnection of WDM-PON, comprising: ​ The sub-network wavelength division multiplexer (10) is adapted to connect the OLT (40) of the WDM-PON through the W1 port (101), can provide wavelength division of the WDM-PON, divide all wavelengths into an A waveband and a B waveband, and the A waveband and the B waveband have no common wavelength, wherein the A waveband is output from the W2 port (102), the B waveband is output from the W3 port (103), the W2 port (102) is connected to the C4 port (204) of the 2×2 optical beam splitter (20), and the W3 port (103) is connected to the C1 port (201) of the 2×2 optical beam splitter (20); the 2×2 optical beam splitter (20) has two input ports, the C1 port (201) and the C2 port (202), and has two output ports, the C3 port (203) and the C4 port (204), wherein the C1 port (201) is connected to the W3 port (103), the C2 port (202) is connected to the WDM-PON sub-network 2 (32), the C3 port (203) is connected to the WDM-PON sub-network 1 (31), and the C4 port (204) is connected to the W2 port (102); the 2×2 optical beam splitter (20) is a conventional optical coupler, and the optical coupling is performed according to the following rules: when the optical wave is input from the C1 port (201) or the C2 port (202), the optical wave is output from the C3 port (203) and the C4 port (204) according to a certain proportion, and no optical wave is output from the other ports; when the optical wave is input from the C3 port (203) and the C4 port (204), the optical wave is output from the C1 port (201) or the C2 port (202) according to a certain proportion, and no optical wave is output from the other ports; The WDM-PON sub-network 1 (31) comprises one or more user optical network units, has uplink and downlink communication functions between the OLT (40) of the WDM-PON and the WDM-PON sub-network 1 (31), uses wavelength resources of the B waveband, and simultaneously has inter-sub-network communication functions between the WDM-PON sub-network 1 (31) and the WDM-PON sub-network 2 (32); The WDM-PON sub-network 2 (32) comprises one or more user optical network units, has uplink and downlink communication functions between the OLT (40) of the WDM-PON and the WDM-PON sub-network 2 (32), uses wavelength resources of the A waveband, and simultaneously has inter-sub-network communication functions between the WDM-PON sub-network 1 (31) and the WDM-PON sub-network 2 (32); The OLT (40) of the WDM-PON is an optical line terminal of the entire WDM-PON, and is used to provide wavelength resources for the WDM-PON sub-network 1 (31) and the WDM-PON sub-network 2 (32).

3. The optical access system supporting WDM-PON inter-subnetwork optical interconnection according to claim 1 or claim 2, wherein, The division of the A waveband and the B waveband adopts the following device: the sub-network wavelength division multiplexer (10) is a coarse wavelength division multiplexer, and the wavelength of the A waveband appears first in the spectrum, and then the wavelength of the B waveband appears.

4. The optical access system supporting WDM-PON inter-subnetwork optical interconnection according to claim 1 or claim 2, wherein, The division of the A waveband and the B waveband adopts the following device: the sub-network wavelength division multiplexer (10) is a cyclic arrayed waveguide grating or a wavelength crosser, and the wavelengths of the A waveband and the B waveband appear alternately in the spectrum.

5. The optical access system of claim 1, supporting WDM-PON inter-subnet optical interconnection, characterized in that The WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) inter-subnet communication function is performed according to one of the following methods: a) From WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) direction of optical transmission, using A wave band, from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) direction of optical transmission, using B wave band; to support this method, the transmitter of WDM-PON subnet 1 (31) ONU must contain a tunable laser, the laser wavelength covers the entire A wave band, the transmitter of WDM-PON subnet 2 (32) ONU must contain a tunable laser, the laser wavelength covers the entire B wave band, then the receiver of WDM-PON subnet 1 (31) ONU and WDM-PON subnet 2 (32) ONU must contain a tunable optical filter, the tunable range of the filter must cover the entire A wave band and B wave band; b) From WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) direction of optical transmission, using B wave band, from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) direction of optical transmission, using A wave band; to support this method, the receiver of WDM-PON subnet 1 (31) ONU must contain a tunable optical filter, the filter wavelength covers the entire A wave band, the receiver of WDM-PON subnet 2 (32) ONU must contain a tunable optical filter, the filter wavelength covers the entire B wave band, then the transmitter of WDM-PON subnet 1 (31) ONU and WDM-PON subnet 2 (32) ONU must contain a tunable laser, the tunable range of the laser must cover the entire A wave band and B wave band; c) If the WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) inter-subnet communication function uses A wave band, the tunable range of the tunable optical filter of the receiver and the tunable laser of the transmitter in the WDM-PON subnet 2 (32) ONU must cover the entire A wave band and B wave band; d) If the WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) inter-subnet communication function uses B wave band, the tunable range of the tunable optical filter of the receiver and the tunable laser of the transmitter in the WDM-PON subnet 1 (31) ONU must cover the entire A wave band and B wave band.

6. The optical access system supporting WDM-PON inter-subnetwork optical interconnection according to claim 2, wherein the WDM-PON inter-subnetwork optical interconnection is implemented by using a wavelength selective switch (WSS) or a wavelength division multiplexer / demultiplexer (WDM). The WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) inter-subnet communication function is performed according to one of the following methods: a) the optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses A band, the optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses B band; to support this method, the receiver of WDM-PON subnet 2 (32) ONU must contain a tunable optical filter, the filter wavelength covers the entire A band, the receiver of WDM-PON subnet 1 (31) ONU must contain a tunable optical filter, the filter wavelength covers the entire B band, then the transmitter of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) ONU must contain a tunable laser, the tunable range of the laser must cover the entire A band and B band; b) the optical transmission from WDM-PON subnet 1 (31) to WDM-PON subnet 2 (32) uses B band, the optical transmission from WDM-PON subnet 2 (32) to WDM-PON subnet 1 (31) uses A band; to support this method, the transmitter of WDM-PON subnet 1 (31) ONU must contain a tunable laser, the laser wavelength covers the entire B band, the transmitter of WDM-PON subnet 2 (32) ONU must contain a tunable laser, the laser wavelength covers the entire A band, then the receiver of WDM-PON subnet 1 (31) ONU and WDM-PON subnet 2 (32) ONU must contain a tunable optical filter, the tunable range of the filter must cover the entire A band and B band; c) if the inter-subnet communication function of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) uses A band, the tunable range of the tunable optical filter of the receiver in WDM-PON subnet 1 (31) ONU and the tunable laser of the transmitter must cover the entire A band and B band; d) if the inter-subnet communication function of WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) uses B band, the tunable range of the tunable optical filter of the receiver in WDM-PON subnet 2 (32) ONU and the tunable laser of the transmitter must cover the entire A band and B band.

7. The optical access system of claim 1 or claim 2, supporting inter-WDM-PON subnet optical interconnection, characterized in that WDM-PON subnet 1 (31) and WDM-PON subnet 2 (32) use an optical splitter as a secondary remote node, and the branches of the optical splitter are connected to each user.

8. The optical access system of claim 1 or claim 2, supporting inter-WDM-PON subnet optical interconnection, characterized in that All optical network units in the two subnets use the same colorless design, that is, the tunable range of the tunable optical filter of the receiver in WDM-PON subnet 1 (31) ONU and WDM-PON subnet 2 (32) ONU and the tunable laser of the transmitter must cover the entire A band and B band.

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