Wavelength division multiplexing system

Abstract

The application provides a wavelength division multiplexing system, which comprises: a first optical module installed at an active antenna unit (AAU) end or a radio remote unit (RRU) end; a second optical module installed at a baseband processing unit (BBU) end or a distribution unit (DU) end; a first multiplexer / demultiplexer installed at the AAU end or the RRU end and connected with the first optical module, wherein the central wavelength of each channel of the first multiplexer / demultiplexer comprises 12 first preset wavelengths of an O band, and the adjacent wavelength interval of each channel is 800 GHz; and a second multiplexer / demultiplexer installed at the BBU end or the DU end and connected with the second optical module, wherein the first multiplexer / demultiplexer is connected with the second multiplexer / demultiplexer, the central wavelength of each channel of the second multiplexer / demultiplexer comprises 12 first preset wavelengths of the O band, and the adjacent wavelength interval of each channel is 800 GHz. The application can reduce the transmission cost to a certain extent under the optical communication front transmission scene in a long distance.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, specifically to a wavelength division multiplexing system. Background Technology

[0002] In the development of 5G technology, the primary wavelength division multiplexing (WDM) scheme used in the fronthaul network is Coarse Wavelength Division Multiplexing (CWDM). This is because the wide wavelength spacing eliminates the need for temperature control devices, meeting industrial-grade temperature requirements (-40℃ to 85℃) and offering a cost advantage. However, wavelengths of 1351nm and 1371nm exhibit significant dispersion, leading to performance degradation over long distances. Current power budgets barely allow for transmission over 10km. For even longer distances, expensive optical transmitting and receiving devices are required. Therefore, the aforementioned approach remains costly for transmission scenarios exceeding 10km. Summary of the Invention

[0003] One objective of this application is to propose a wavelength division multiplexing system to reduce transmission costs in optical communication to a certain extent.

[0004] According to one aspect of the embodiments of this application, a wavelength division multiplexing (WDM) system is disclosed, the WDM system comprising:

[0005] The first optical module is installed at the active antenna unit (AAU) or the radio frequency remote unit (RRU).

[0006] The second optical module is installed at the baseband processing unit (BBU) or the distribution unit (DU).

[0007] The first multiplexer / demultiplexer is installed at the AAU or RRU end and connected to the first optical module. The center wavelength of each channel of the first multiplexer / demultiplexer includes 12 first preset wavelengths in the O band, and the adjacent wavelength interval of each channel is 800 GHz.

[0008] The second multiplexer / demultiplexer is installed at the BBU or DU end and connected to the second optical module. The first multiplexer / demultiplexer is connected to the second multiplexer / demultiplexer. The center wavelength of each channel of the second multiplexer / demultiplexer includes 12 first preset wavelengths of the O-band, and the adjacent wavelengths of each channel are spaced at 800 GHz.

[0009] As an optional implementation, both the first and second multiplexers / demultiplexers are based on a cascaded three-port filter configuration, and the cascading order of each channel of the first multiplexer / demultiplexer is the reverse of the cascading order of each channel of the second multiplexer / demultiplexer.

[0010] As an optional implementation, the cascading order of each channel of the first multiplexer / demultiplexer is from the channel with the largest first preset wavelength to the channel with the smallest first preset wavelength, and the cascading order of each channel of the second multiplexer / demultiplexer is from the channel with the smallest first preset wavelength to the channel with the largest first preset wavelength.

[0011] As an optional implementation, the number of trunk ports of both the first multiplexer and the second multiplexer is 1, and the number of branch ports of both the first multiplexer and the second multiplexer is 12; furthermore,

[0012] The receiving end of each first optical module corresponds to the channels corresponding to the maximum 6 first preset wavelengths, and the transmitting end of each first optical module corresponds to the channels corresponding to the minimum 6 first preset wavelengths.

[0013] The receiving end of each second optical module corresponds to the minimum 6 channels corresponding to the first preset wavelength, and the transmitting end of each second optical module corresponds to the maximum 6 channels corresponding to the first preset wavelength.

[0014] As an optional implementation, the link connection between the first multiplexer and the second multiplexer / demultiplexer can be a single-fiber bidirectional connection or a dual-fiber bidirectional connection.

[0015] As an optional implementation, the link connection method is a single-fiber bidirectional connection, and the first multiplexer / demultiplexer is connected to up to 6 first optical modules, and the second multiplexer / demultiplexer is connected to up to 6 second optical modules.

[0016] As an optional implementation, the link connection method is a dual-fiber bidirectional connection, and the first multiplexer / demultiplexer is connected to up to 12 first optical modules, and the second multiplexer / demultiplexer is connected to up to 12 second optical modules.

[0017] As an optional implementation, both the first optical module and the second optical module include a distributed feedback DFB laser and a PIN receiver.

[0018] As an optional implementation, the nominal center wavelength range of all the first preset wavelengths is from 1269.23 nm to 1318.35 nm.

[0019] As an optional implementation, the center wavelength of each channel of the first multiplexer and the second multiplexer further includes a second preset wavelength in the O band, and the wavelength range of the second preset wavelength is different from the wavelength range of any of the first preset wavelengths.

[0020] In this application, the center wavelength of each channel of the first and second multiplexers / demultiplexers includes 12 first preset wavelengths in the O-band, and the adjacent wavelength spacing of each channel is 800 GHz. Due to the low dispersion cost, the corresponding optical module can still achieve optical communication over longer distances, such as 15km to 20km, while using low-cost devices, thereby reducing the transmission cost in optical communication to a certain extent.

[0021] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0022] It should be understood that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0023] The above and other objectives, features and advantages of this application will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0024] Figure 1 A schematic diagram of the architecture of a wavelength division multiplexing system according to Embodiment 1 of this application is shown;

[0025] Figure 2 A schematic diagram of the architecture of a wavelength division multiplexing system according to Embodiment 2 of this application is shown;

[0026] Figure 3 A schematic diagram of the architecture of a wavelength division multiplexing system according to Embodiment 3 of this application is shown. Detailed Implementation

[0027] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided to make the description of this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The drawings are merely illustrative of this application and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0028] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more exemplary embodiments. Numerous specific details are provided in the following description to give a full understanding of exemplary embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced with one or more of the specific details omitted, or other methods, components, steps, etc., can be employed. In other instances, well-known structures, methods, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0029] Currently, with the development of 5G technology, the wavelength division multiplexing (WDM) scheme mainly used in 5G fronthaul network architecture is CWDM. In transmission scenarios within 10km, low-cost optical transmitters and receivers can ensure relatively good performance. However, for longer transmission distances, more expensive optical transmitters and receivers are required. Therefore, there is an urgent need to propose a lower-cost WDM scheme for longer distances.

[0030] Example 1

[0031] Reference Figure 1 , Figure 1 A schematic diagram of the wavelength division multiplexing system according to Embodiment 1 is shown. The wavelength division multiplexing system includes:

[0032] The first optical module is installed at the active antenna unit (AAU) or the radio frequency remote unit (RRU).

[0033] The second optical module is installed at the baseband processing unit (BBU) or the distribution unit (DU).

[0034] The first multiplexer / demultiplexer is installed at the AAU or RRU end and connected to the first optical module. The center wavelength of each channel of the first multiplexer / demultiplexer includes 12 first preset wavelengths in the O band, and the adjacent wavelength interval of each channel is 800 GHz.

[0035] The second multiplexer / demultiplexer is installed at the BBU or DU end and connected to the second optical module. The first multiplexer / demultiplexer is connected to the second multiplexer / demultiplexer. The center wavelength of each channel of the second multiplexer / demultiplexer includes 12 first preset wavelengths of the O-band, and the adjacent wavelengths of each channel are spaced at 800 GHz.

[0036] In 5G fronthaul networking solutions, the baseband processing unit (BBU) and distribution unit (DU) are uniformly placed in the operator's integrated service access room. This allows for simultaneous connection to remote radio units (RRUs) and active antenna units (AAUs) on multiple remote base stations. By reducing the number of equipment rooms required, costs can be significantly reduced. In this embodiment, the first optical module is installed at the AAU or RRU, the second optical module is installed at the BBU or DU, the first multiplexer / demultiplexer is installed at the AAU or RRU, and the second multiplexer / demultiplexer is installed at the BBU or DU to reduce related costs, such as operating expenses (OPEX) and capital asset costs (CAPEX).

[0037] As an optional implementation, each first preset wavelength is located in the O-band short wavelength region, such as 1269nm to 1319nm. Within this wavelength region, dispersion costs are low. The 12 first preset wavelengths are distinct from each other and are consecutive, with an 800GHz wavelength interval between adjacent channels. For example, the smallest first preset wavelength is 1269.23nm. Thus, the other 11 first preset wavelengths are obtained sequentially according to the 800GHz wavelength interval, ensuring that each first preset wavelength is located in the O-band short wavelength region. Within the O-band short wavelength region, dispersion costs are even lower, thus enabling long-distance optical communication even using low-cost optical receivers and transmitters. Both the first and second optical modules have optical transmitters and receivers, thereby reducing the cost of the optical modules.

[0038] Furthermore, the center wavelengths of both the first and second optical modules are selected from 12 preset wavelengths in the O-band, with a fixed wavelength interval of 800 GHz. The first multiplexer / demultiplexer is installed at the AAU / RRU end, and the second multiplexer / demultiplexer is installed at the BBU / DU side. Both the first and second multiplexers / demultiplexers have multiplexing and demultiplexing functions, i.e., they have multiplexing and demultiplexing capabilities. Both the first and second multiplexers / demultiplexers can be composed of separate independent multiplexers and demultiplexers, or they can be devices that integrate both multiplexing and demultiplexing capabilities simultaneously.

[0039] As an optional implementation, the first multiplexer / demultiplexer can connect to three first optical modules, and the second multiplexer / demultiplexer can connect to three second optical modules. That is, three optical modules are deployed at the AAU / RRU end and the BBU / DU end respectively. This makes it suitable for three-channel transmission scenarios.

[0040] As an optional implementation, the first multiplexer / demultiplexer can connect to six first optical modules, and the second multiplexer / demultiplexer can connect to six second optical modules. That is, six optical modules are deployed at the AAU / RRU end and the BBU / DU end respectively. This makes it suitable for six-channel transmission scenarios.

[0041] As an optional implementation, the first multiplexer / demultiplexer can connect 12 first optical modules, and the second multiplexer / demultiplexer can connect 12 second optical modules. That is, 12 optical modules are deployed at the AAU / RRU end and the BBU / DU end respectively. This makes it suitable for 12-channel transmission scenarios.

[0042] As an optional implementation, the first optical module includes a distributed feedback DFB laser and a PIN receiver, and the second optical module includes a distributed feedback DFB laser and a PIN receiver. Therefore, since the distributed feedback DFB laser and PIN receiver are relatively inexpensive, the overall transmission cost can be reduced.

[0043] As an optional implementation, the nominal center wavelength range formed by all 12 first preset wavelengths is from 1269.23nm to 1318.35nm, that is, the nominal center wavelength range of all the first preset wavelengths is from 1269.23nm to 1318.35nm.

[0044] The specific wavelength schemes are shown in Table 1:

[0045]

[0046] Among them, L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, and L12 are 12 channels, and the 12 channels correspond to 12 different nominal center wavelengths, which are the first preset wavelengths.

[0047] As an optional implementation, the center wavelength of each channel of the first multiplexer / demultiplexer also includes a second preset wavelength in the O-band, and the center wavelength of each channel of the second multiplexer / demultiplexer also includes a second preset wavelength in the O-band. The wavelength range of the second preset wavelength is different from the wavelength range of any first preset wavelength. For example, if both the first and second multiplexers / demultiplexers are used in an 18-channel transmission scenario, then in addition to the channels L1 to L12 mentioned above, there are also six channels: L13, L14, L15, L16, L17, and L18. Each of these six channels corresponds to a second preset wavelength. The second preset wavelengths of L13, L14, L15, L16, L17, and L18 increase sequentially, and the wavelength interval between adjacent wavelengths of each channel is 800 GHz. The wavelength interval between L13 and L12 is also 800 GHz. In the wavelength schemes described above, since each wavelength is located in the short wavelength range of the O-band, it has the characteristic of low dispersion cost, which makes it well adaptable to long-distance transmission. Even low-cost optical transmitting and receiving devices can adapt well to optical transmission, thus making it suitable for low-cost optical communication solutions over longer distances. Furthermore, it can support optical communication in more channel scenarios, improving its applicability to various scenarios.

[0048] In this wavelength division multiplexing system, data can be transmitted from the transmitting end of the first optical module and sequentially pass through the first multiplexer and the second multiplexer to the receiving end of the second optical module, or it can be transmitted from the transmitting end of the second optical module and sequentially pass through the second multiplexer and the first multiplexer to the receiving end of the first optical module.

[0049] The first and second multiplexers / demultiplexers are connected via an optical fiber link. As an optional implementation, the link between the first and second multiplexers / demultiplexers can be a single-fiber bidirectional connection or a dual-fiber bidirectional connection. A single-fiber bidirectional connection is less expensive than a dual-fiber bidirectional connection, but it can support more transmission channels.

[0050] Furthermore, since 5G fronthaul primarily uses G.652 fiber, the zero-dispersion region of the fiber is located between 1300nm and 1324nm. The wavelengths defined in this embodiment are mainly in the zero-dispersion and negative-dispersion regions of the fiber. After transmission over 10km or 20km, the dispersion cost is relatively small, allowing for six sets of margins when considering the power budget, thus ensuring the long-term reliability of the wavelength division multiplexing system.

[0051] This embodiment proposes a novel fine wavelength division multiplexing (LWDM) system, which, compared to the traditional CWDM system, enables a low-cost, high-performance 5G fronthaul solution, meeting the growing demands of current 5G network construction.

[0052] In this embodiment, by using 12 wavelengths of the O-band as the center wavelength of the multiplexer and the wavelength spacing is 800 GHz, optical communication of 15 km to 20 km can still be achieved using low-cost optical modules due to the low dispersion cost, thereby reducing the cost of long-distance optical communication.

[0053] Example 2

[0054] Reference Figure 2 As shown, Figure 2 A schematic diagram of the architecture of the wavelength division multiplexing system involved in Embodiment 2 is shown.

[0055] exist Figure 2 In the wavelength division multiplexing system shown, based on Embodiment 1, the link connection between the first and second multiplexers / demultiplexers is further defined as a single-fiber unidirectional connection. A single-fiber bidirectional connection means that there is one fiber optic link between the first and second multiplexers / demultiplexers, and this fiber optic link is used to transmit data in both directions. The first multiplexer / demultiplexer connects to six first optical modules, and the second multiplexer / demultiplexer connects to six second optical modules.

[0056] The first multiplexer / splitter is based on a cascaded configuration of three-port thin-film filters (TFF), and the second multiplexer / splitter is also based on a cascaded configuration of TFF three-port filters. The cascading order of the channels in the first multiplexer / splitter is the reverse of that in the second multiplexer / splitter. Because of the cascaded three-port filter configuration, the inherent loss of each of the 12 tributary ports is different. A tributary port refers to the port where either the first or second multiplexer / splitter connects to the corresponding optical module. Due to the tight power budget in the fronthaul link, the arrangement of the multiplexer / splitter cascades can be designed such that for any wavelength channel, if the insertion loss on the AAU side is low, the insertion loss on the BBU side can be higher. This ensures that the insertion loss of each pair of wavelength channels is not too high, improving transmission performance while reducing fronthaul link costs. Furthermore, it can alleviate nonlinear problems caused by fiber optic transmission, such as four-wave mixing, where longer wavelengths experience higher insertion loss at the transmitting side of the multiplexer / splitter ports, reducing the power supplied to the fiber.

[0057] As an optional implementation, the cascading order of the channels of the first multiplexer / demultiplexer is from the channel with the largest first preset wavelength to the channel with the smallest first preset wavelength, and the cascading order of the channels of the second multiplexer / demultiplexer is from the channel with the smallest first preset wavelength to the channel with the largest first preset wavelength. The channel with the largest first preset wavelength is denoted as L12, and the channel with the smallest first preset wavelength is denoted as L1. Therefore, the cascading order of the multiplexers / demultiplexers on the AAU side is from L12 through L11, L10, L9, L8, L7, L6, L5, L4, L3, L2 to L1, and the cascading order on the BBU side is from L1 through L2, L3, L4, L5, L6, L7, L8, L9, L10, L11 to L12. Thus, the cascading order is reversed. Among these, the four-wave mixing problem tends to occur in the last six bands, which are located at the BBU end. Therefore, the insertion loss at the BBU-end multiplexer / demultiplexer is relatively lower than that of the first six bands, resulting in a lower input optical power after passing through the multiplexer / demultiplexer. The last six bands refer to the six longer first preset wavelengths, while the first six bands refer to the six shorter first preset wavelengths.

[0058] In addition, Figure 2In the wavelength division multiplexing (WDM) system shown, the first multiplexer / demultiplexer has 1 trunk port, and both the first and second multiplexers / demultiplexers have 1 trunk port. The trunk port count refers to the number of ports involved in the connection between the first and second multiplexers / demultiplexers. The first and second multiplexers / demultiplexers each have 12 tributary ports, which represent the number of ports connecting the multiplexers / demultiplexers to the optical modules. Furthermore, the receiving end of each first optical module corresponds to the channels corresponding to the six largest first preset wavelengths, i.e., L7 to L12, and the transmitting end of each first optical module corresponds to the channels corresponding to the six smallest first preset wavelengths, i.e., L1 to L6. Similarly, the receiving end of each second optical module corresponds to the channels corresponding to the six smallest first preset wavelengths, i.e., L1 to L6, and the transmitting end of each second optical module corresponds to the channels corresponding to the six largest first preset wavelengths, i.e., L7 to L12. The last six bands are at the BBU end. Therefore, the insertion loss when passing through the BBU multiplexer is relatively small compared to the first six bands, and the optical power entering the fiber after passing through the multiplexer is relatively small.

[0059] In another embodiment, the cascading order of the channels of the second multiplexer / demultiplexer is from the channel with the largest first preset wavelength to the channel with the smallest first preset wavelength, and the cascading order of the channels of the first multiplexer / demultiplexer is from the channel with the smallest first preset wavelength to the channel with the largest first preset wavelength. This also reduces the input optical power.

[0060] In another embodiment, the number of trunk ports of both the first multiplexer and the second multiplexer is 1, and the number of branch ports of both the first multiplexer and the second multiplexer is 12; furthermore, the channels corresponding to the receiving end of each second optical module are the channels corresponding to the maximum 6 first preset wavelengths, and the channels corresponding to the transmitting end of each second optical module are the channels corresponding to the minimum 6 first preset wavelengths; the channels corresponding to the receiving end of each first optical module are the channels corresponding to the minimum 6 first preset wavelengths, and the channels corresponding to the transmitting end of each first optical module are the channels corresponding to the maximum 6 first preset wavelengths.

[0061] The wavelengths on both sides of the first and second multiplexers / demultiplexers need to be staggered to transmit data in different directions within a single optical fiber. For example, the transmitting ends of the six first optical modules correspond to channels L1 to L6, while the transmitting ends of the six second optical modules correspond to channels L7 to L12. The receiving ends of the six first optical modules correspond to channels L7 to L12, and the receiving ends of the six second optical modules correspond to channels L1 to L6. The first multiplexer / demultiplexer can connect to a maximum of six first optical modules, and the second multiplexer / demultiplexer can connect to a maximum of six second optical modules. Using a single-fiber bidirectional connection can save costs.

[0062] In this embodiment, by reversing the cascading order of the channels of the first multiplexer / demultiplexer compared to the second multiplexer / demultiplexer, for any wavelength channel, if the insertion loss on the AAU side is low, the insertion loss on the BBU side can be higher. This ensures that the insertion loss of each pair of wavelength channels is not too large, improving transmission performance while reducing fronthaul link costs. Furthermore, it can alleviate nonlinear problems caused by fiber optic transmission, such as four-wave mixing, which results in higher insertion loss at the transmitting side of the multiplexer / demultiplexer ports for longer wavelengths, thus reducing input power.

[0063] Example 3

[0064] Reference Figure 3 As shown, Embodiment 3 of this application provides a wavelength division multiplexing system.

[0065] This wavelength division multiplexing (WDM) system differs from the single-fiber bidirectional connection method used in Embodiment 2. Instead, it employs a dual-fiber bidirectional connection to link the first and second multiplexers / demultiplexers. A dual-fiber bidirectional connection means there are two fiber optic links between the first and second multiplexers / demultiplexers, with different data transmission directions. Using this dual-fiber bidirectional connection, the services on each fiber optic link do not interfere with each other, thus eliminating the need to stagger wavelengths. Each fiber optic link can be configured with 12 channels. The first multiplexer / demultiplexer can connect to up to 12 first optical modules, and the second multiplexer / demultiplexer can connect to up to 12 second optical modules. Therefore, this dual-fiber bidirectional connection supports a wider range of transmission channels.

[0066] In this wavelength division multiplexing (WDM) system, the first and second multiplexers / demultiplexers are connected via two optical fiber links. The transmitting channels of the 12 first optical modules are sequentially arranged from L1 to L12, and the receiving channels of the 12 second optical modules are also sequentially arranged from L1 to L12. This approach supports scenarios with more channels, improving the applicability of multi-channel applications.

[0067] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application 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 application are indicated by the appended claims.

Claims

1. A wavelength division multiplexing system, characterized in that, The wavelength division multiplexing system includes: The first optical module is installed at the active antenna unit (AAU) or the radio frequency remote unit (RRU). The receiving end of each first optical module corresponds to the channels corresponding to the maximum six first preset wavelengths, and the transmitting end of each first optical module corresponds to the channels corresponding to the minimum six first preset wavelengths. The second optical module is installed at the baseband processing unit (BBU) or the distribution unit (DU). The receiving end of each second optical module corresponds to the minimum of the six channels corresponding to the first preset wavelength, and the transmitting end of each second optical module corresponds to the maximum of the six channels corresponding to the first preset wavelength. The first multiplexer / demultiplexer is installed at the AAU or RRU end and connected to the first optical module. The center wavelength of each channel of the first multiplexer / demultiplexer includes 12 first preset wavelengths in the O band, and the adjacent wavelength interval of each channel is 800 GHz. The cascading order of each channel of the first multiplexer / demultiplexer is from the channel with the largest first preset wavelength to the channel with the smallest first preset wavelength. The second multiplexer / demultiplexer is installed at the BBU or DU end and connected to the second optical module. The first multiplexer / demultiplexer is connected to the second multiplexer / demultiplexer. The center wavelength of each channel of the second multiplexer / demultiplexer includes 12 first preset wavelengths of the O-band, and the adjacent wavelength interval of each channel is 800 GHz. The cascading order of each channel of the second multiplexer / demultiplexer is from the channel with the smallest first preset wavelength to the channel with the largest first preset wavelength. The first and second multiplexers are both based on a cascaded three-port filter configuration; the number of trunk ports of the first and second multiplexers is 1, and the number of branch ports of the first and second multiplexers is 12.

2. The wavelength division multiplexing system as described in claim 1, characterized in that, The link connection between the first multiplexer and the second multiplexer / demultiplexer is either a single-fiber bidirectional connection or a dual-fiber bidirectional connection.

3. The wavelength division multiplexing system as described in claim 2, characterized in that, The link connection method is a single-fiber bidirectional connection, and the first multiplexer / demultiplexer is connected to up to 6 of the first optical modules, and the second multiplexer / demultiplexer is connected to up to 6 of the second optical modules.

4. The wavelength division multiplexing system as described in claim 2, characterized in that, The link connection method is a dual-fiber bidirectional connection, and the first multiplexer / demultiplexer is connected to up to 12 of the first optical modules, and the second multiplexer / demultiplexer is connected to up to 12 of the second optical modules.

5. The wavelength division multiplexing system as described in claim 1, characterized in that, Both the first optical module and the second optical module include a distributed feedback DFB laser and a PIN receiver.

6. The wavelength division multiplexing system as described in claim 1, characterized in that, The nominal center wavelength range for all the first preset wavelengths is from 1269.23 nm to 1318.35 nm.

7. The wavelength division multiplexing system as described in claim 6, characterized in that, The center wavelength of each channel of the first and second multiplexers and demultiplexers also includes a second preset wavelength in the O-band, and the wavelength range of the second preset wavelength is different from the wavelength range of any of the first preset wavelengths.

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