Optimization method of a combined equalizer and 20km long-distance 5g front-haul system
By optimizing the optical path structure of the combiner and decomposer and the placement of dispersion compensation devices, the problems of uneven fiber loss and limited dispersion tolerance in the 5G fronthaul system were solved, achieving stable transmission over a long distance of 20km and reducing the impact of cost and temperature on the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WUXI TACLINK OPTOELECTRONICS TECH CO LTD
- Filing Date
- 2022-09-28
- Publication Date
- 2026-06-16
Smart Images
Figure CN115589260B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical communication technology, and in particular to an optimization method for a combiner / decomposer and a 20km long-distance 5G fronthaul system. Background Technology
[0002] With the global rollout of 5G deployment in 2020, fiber optic resources for base stations are becoming increasingly scarce. The primary transmission solution for 5G fronthaul systems utilizes wavelength division multiplexing (WDM) technology. Currently, the WDM scheme in 5G fronthaul systems mainly uses CWDM wavelengths, employing six wavelengths: 1271nm, 1291nm, 1311nm, 1331nm, 1351nm, and 1371nm. This six-wavelength scheme offers low cost, good stability, and high fiber core utilization. However, due to the dispersion factors of the transmission fiber, particularly the relatively large dispersion coefficients at 1371nm and 1351nm, and based on the current technological level, and considering the inverse relationship between dispersion tolerance and the square of the modulation rate, the maximum transmission distance under DML (Directly Modulated Laser) modulation is only about 13km.
[0003] As 5G deployment enters its second phase, coverage is required to reach distances of up to 20km. However, due to dispersion issues, the current 6-wavelength CWDM solution cannot directly meet the requirements of long-distance fronthaul systems. Within the 1271-1371nm range, the fiber loss coefficient differs by more than 0.1dB / km. For example, for a 20km system, the fiber loss difference between 1271nm and 1371nm can exceed 2dB. While increasing transmit power and reducing receive power, such as with avalanche photodiode-based solutions, can mitigate some of the high loss issues, this method becomes ineffective when the system reaches dispersion tolerance. Extending the network using two short-distance splicing solutions would lead to a multiple or even exponential increase in the number of central office base stations, whose construction costs and power consumption account for a very large proportion of the total 5G cost.
[0004] Patent CN112187365A describes a 5G fronthaul system that uses dispersion-managed fiber or a combination of dispersion-managed fiber and G652 fiber as the transmission fiber, thereby reducing the impact of line dispersion and achieving a maximum transmission distance of 20km. However, the basic fiber optic network layout in current transmission trunk lines is already largely complete, using almost entirely G652 fiber. Unless new lines are built, the possibility of laying new fiber is virtually zero. Alternatively, external modulation techniques such as EML can be used to improve the chirp characteristics of the light source itself, thus solving the 20km dispersion tolerance problem. However, this solution would increase the cost of the light source by several to ten times, and the industry's production chain is not yet mature. Summary of the Invention
[0005] To address the issues of uneven fiber transmission loss distribution with wavelength and limited dispersion tolerance in long-distance optical fibers in existing power lines, the inventors have proposed an optimization method for a combiner / decomposer and a 20km long-distance 5G fronthaul system. The technical solution of this invention is as follows:
[0006] In a first aspect, this application provides an optimization method for a combiner / decomposer, comprising the following steps:
[0007] Obtain the theoretical value of the total loss of the combiner / decomposer for each wavelength;
[0008] Based on the theoretical value of the total loss of the combiner / decomposer for each wavelength, design the actual value of the total loss of the combiner / decomposer for each wavelength that satisfies the second condition.
[0009] Based on the actual value of the total loss of the combiner and descanner corresponding to each wavelength, adjust the optical path structure inside the combiner and descanner in the fronthaul system to match the changes in fiber transmission loss with wavelength and the changes in the loss of dispersion compensation device with wavelength.
[0010] The dispersion compensation device is placed on the optical trunk of the multiplexer or demultiplexer and connected to the common terminal of the multiplexer or demultiplexer. Full-wave dispersion compensation is performed through the dispersion compensation device to optimize the dispersion cost.
[0011] The second condition includes that the actual value of the total loss of the combiner for each wavelength is equal to the theoretical value of the total loss of the combiner for the same wavelength, and that the changing trend of the actual value of the total loss of the combiner arranged in wavelength order is the same as the changing trend of the theoretical value of the total loss of the combiner arranged in the same order.
[0012] A further technical solution involves obtaining the theoretical value of the total loss of the combiner / decomposer for each wavelength, including:
[0013] Based on the first condition that the 6-wave CWDM fronthaul system must meet, the total loss of the combiner / decomposer for each wavelength is obtained.
[0014] The total loss of the combiner / decomposer for each wavelength is normalized, and the theoretical value of the total loss of the combiner / decomposer for each wavelength is obtained by combining the background loss of the combiner / decomposer and the loss of the dispersion compensation device.
[0015] The first condition is that the difference between the transmit and receive power at any wavelength of the system is not less than the sum of all losses corresponding to that wavelength, expressed as: (1)
[0016] In the formula: n The total number of wavelengths, TX For transmission power, RX Minimum receiving power for back-to-back connections; FLFor transmission fiber loss, MDL j For the multiplexer and demultiplexer in the fronthaul system j The sum of losses for each wavelength, DCP For the price of dispersion, OL Other losses in the line, including losses at connectors and optical distribution boxes, ML This represents the system margin.
[0017] A further technical solution is to derive the expression for the total loss of the combiner / decomposer corresponding to each wavelength based on equation (1):
[0018] (2)
[0019] Based on equation (2), the theoretical value of the total loss of the combined waveguide for each wavelength is expressed as follows:
[0020] (3)
[0021] Where: min( MDL j () represents the minimum total loss of the combiner / decomposer across all wavelengths; BL j = BL + DCL j ,and BL To account for the inherent loss of the deconstructor, DCL j For the first j The loss of the dispersion compensation device corresponding to each wavelength.
[0022] A further technical solution involves adjusting the optical path structure inside the multiplexer and demultiplexer in the fronthaul system based on the actual total loss of the multiplexer and demultiplexer for each wavelength, including:
[0023] Sort the actual values of the total loss of the combiner / decomposer corresponding to each wavelength in ascending order. Inside the combiner or decomposer, arrange the filters corresponding to the first x actual values of the wavelength in the sequence in ascending order of distance from the common terminal. The arrangement of all filters must satisfy the actual value of the total loss of the combiner / decomposer obtained in the design, so that the total loss of the combiner / decomposer reaches the optimal level.
[0024] A further technical solution is to perform full-wave dispersion compensation using the dispersion compensation device, including:
[0025] The dispersion compensation device performs full-wave dispersion compensation based on the dispersion compensation amount calculated for the wavelength with the highest positive dispersion cost; the optimization amount of the dispersion cost corresponding to the wavelength with the smallest margin in the system is greater than the loss of the dispersion compensation device corresponding to that wavelength, and at this time, other wavelengths meet the system usage requirements.
[0026] The dispersion compensation amount must satisfy [L×DW, L×D], where L is the fiber transmission length, D is the maximum fiber dispersion coefficient within 1271nm~1371nm, and W is the system dispersion tolerance.
[0027] Secondly, this application also provides a 20km long-distance 5G fronthaul system, which realizes single-fiber bidirectional transmission based on 6-wavelength CWDM technology, including 6 optical modules and transmission optical fibers, and also includes:
[0028] A combiner and a demultiplexer are located on the AAU side and the DU side, respectively, one of which is equipped with a dispersion compensation device. The combiner and the demultiplexer are implemented based on the optimized design method of the combiner and demultiplexer as described in the first aspect.
[0029] The six optical modules are evenly distributed on the AAU side and the DU side. Each optical module is connected to the corresponding wavelength port of the multiplexer or demultiplexer on that side. The common terminal of the multiplexer and demultiplexer is connected to both ends of the transmission optical fiber.
[0030] A further technical solution is to place the combiner or demultiplexer with dispersion compensation device on the DU side to reduce the impact of temperature changes on the dispersion compensation device.
[0031] A further technical solution is to place optical modules with wavelengths of 1371nm, 1351nm, and 1271nm on the DU side, and optical modules with wavelengths of 1331nm, 1311nm, and 1291nm on the AAU side, in order to reduce the impact of temperature changes on the emission wavelength of the optical modules.
[0032] The beneficial technical effects of this invention are:
[0033] By flexibly optimizing the design of the combiner / decomposer, the actual total loss values for each wavelength of the combiner / decomposer that meet the design conditions are obtained. This allows for adjustment of the filter positions within the combiner / decomposer. Simultaneously, full-wave dispersion compensation is used to optimize dispersion costs, achieving optimal system performance. Compared to traditional designs where the combiner / decomposer loss for each wavelength is uniformly and symmetrically distributed, the actual loss value designed according to theoretical loss values in this application is no longer uniformly distributed. It separately matches the changes in fiber transmission loss, dispersion costs, and dispersion compensation device losses with wavelength, thus solving the technical problems proposed in this application.
[0034] The fronthaul system proposed in this application, based on existing equipment, utilizes an improved combiner / demultiplexer to maximize the system's margin, and the performance of each wavelength is relatively balanced, making it suitable for both short-distance and long-distance fronthaul systems. By rationally allocating combiners or demultiplexers with dispersion compensation devices, as well as the placement of optical modules for specific wavelengths, the impact of temperature on the 20km long-distance 5G fronthaul system is reduced, further improving the system's reliability. Attached Figure Description
[0035] Figure 1 This is a flowchart of the optimization method for the combined decomposer provided in this application.
[0036] Figure 2 This is a schematic diagram of the optical path structure of the optimized combiner / decomposer provided in this application. Among them, (a) is a schematic diagram of the optical path structure of the decomposer with dispersion compensation device, and (b) is a schematic diagram of the optical path structure of the combiner.
[0037] Figure 3 These are schematic diagrams of the optical path structure of a combiner / decomposer implemented according to traditional design methods. Among them, (a) is a schematic diagram of the optical path structure of the decomposer, and (b) is a schematic diagram of the optical path structure of the combiner.
[0038] Figure 4 This is a diagram of the 20km long-distance 5G fronthaul system provided in this application. Detailed Implementation
[0039] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.
[0040] Example 1:
[0041] like Figure 1 As shown, this application provides an optimization method for a combiner / decomposer, comprising the following steps:
[0042] Step 1: Obtain the theoretical value of the total loss of the combiner / decomposer for each wavelength, specifically including:
[0043] Step 11: Based on the first condition that the 6-wave CWDM fronthaul system must meet, obtain the total loss of the combiner / decomposer for each wavelength.
[0044] The first condition is that the difference between the transmit and receive power at any wavelength of the system is not less than the sum of all losses corresponding to that wavelength, expressed as: (1)
[0045] Based on equation (1), the expression for the total loss of the combiner / decomposer for each wavelength is derived as follows:
[0046] (2)
[0047] In the formula: n The total number of wavelengths, TX For transmission power, RX The minimum received power (i.e., receiver sensitivity) for back-to-back (i.e., fiber-free) optical modules is expressed in dBm and is generally assumed to be a fixed value for mass-produced optical modules. FL The fiber loss is equal to the product of the loss coefficient and the fiber length; that is, when the fiber length is constant, FL It is a fixed value; MDL j For the multiplexer and demultiplexer in the fronthaul system j The sum of losses for each wavelength is essentially a fixed value once the design is finalized. DCP Due to dispersion costs, for mass-produced optical modules, a fixed length of fiber corresponds to... DCP Basically the same; OL Other losses in the line, including those at connectors and optical distribution boxes, are also fixed values; ML This is the system margin, a fixed value, and the larger the better.
[0048] Step 12: Normalize the total loss of the combiner / decomposer for each wavelength (i.e., Equation 2), and combine the base loss of the combiner / decomposer with the loss of the dispersion compensation device to obtain the theoretical value of the total loss of the combiner / decomposer for each wavelength.
[0049] Based on equation (2), the theoretical value of the total loss of the combined waveguide for each wavelength is expressed as follows:
[0050] (3)
[0051] Where: min( MDL j This represents the minimum total loss of the combiner / decomposer across all wavelengths; considering the additional losses introduced by the dispersion compensation device, BL j = BL + DCL j ,and BL To account for the inherent loss of the deconstructor, DCL j For the first j The loss of the dispersion compensation device corresponding to each wavelength.
[0052] Optionally, the optimization of the total loss of the decomposer also includes other wavelength-related costs (such as temperature costs), which can be added to the optimization. BL j In order to compensate for the corresponding cost changes with wavelength.
[0053] Step 2: Based on the theoretical value of the total loss of the combiner / decomposer for each wavelength, design the actual value of the total loss of the combiner / decomposer for each wavelength that satisfies the second condition, in order to optimize system performance. This specifically includes:
[0054] The second condition includes: 1) The actual value of the total loss of the combiner / decomposer for each wavelength is at most equal to the theoretical value of the total loss of the combiner / decomposer for the same wavelength, i.e. MDL j (Actual)≤ MDLj (Theory). 2) It also includes the actual trend of the total loss of the combined and decomposed waveguides arranged in wavelength order, which is the same as the theoretical trend of the total loss of the combined and decomposed waveguides arranged in the same order.
[0055] Taking a 10km fronthaul system as an example, due to the short fiber length, the loss deviation caused by the fiber is small, and dispersion compensation is not required. BL j = BL The results obtained according to steps 1 and 2 above MDL j , MDL j (theory) and MDL j (Actual) As shown in Table 1.
[0056] Table 1. Parameter List of 10km Front Gear System
[0057]
[0058] Taking a 20km fronthaul system as an example, assume the original system's dispersion tolerance corresponds to a distance of 10km. Due to the long fiber length, dispersion compensation devices must be added to compensate for the system's dispersion tolerance. This introduces additional losses due to the dispersion compensation devices, and these losses also vary with wavelength. BL j = BL + DCL j The fiber transmission loss deviation, dispersion cost deviation, and dispersion compensation device loss at different wavelengths have a significant impact on the system. This is based on steps 1 and 2 above. MDL j , MDL j (theory) and MDL j (Actual) As shown in Table 2, at this time MDL j (In reality) the second condition is met, where the dispersion compensation is 50 ps / nm, corresponding to... DCL As shown in Table 2.
[0059] Table 2. Parameter List of 20km Front Drive System
[0060]
[0061] Step 3: Based on the actual total loss of the combiner and despinner for each wavelength, adjust the optical path structure inside the combiner and despinner in the fronthaul system, including:
[0062] Sort the actual values of the total loss of the combiner / decomposer corresponding to each wavelength in ascending order. Inside the combiner or decomposer, arrange the filters corresponding to the first x actual values of the wavelength in the sequence in ascending order of distance from the common terminal COM. The arrangement of all filters must satisfy the actual value of the total loss of the combiner / decomposer obtained in the design, so that the total loss of the combiner / decomposer reaches the optimum, that is, the system performance is optimal.
[0063] As shown in Table 1 MDL j (Theoretical) changing trends, and optimal design of the internal optical path of the combiner / decomposer to match a 10km fronthaul system, including the following: MDL j The actual wavelengths ranked first, second, and third are 1371nm, 1351nm, and 1331nm, respectively, with losses being roughly the same for wavelengths from 1311nm to 1271nm. Therefore, the internal filters corresponding to these three wavelengths are placed close to the common terminal (COM) of the combiner / decomposer. The internal filters provided in this example use a 3-port device for optical path design, as shown in the diagram below. Figure 2 As shown in (a) and (b), where MDL j (In reality) it can be fully satisfied. MDL j (Theoretical) requirements. In traditional designs, the loss of the combiner / decomposer for each wavelength is uniformly and symmetrically distributed, such as... Figure 3 As shown in (a) and (b), by comparison, it can be seen that the actual loss value designed according to the theoretical loss value of this application is no longer uniformly distributed. The changes of fiber transmission loss, dispersion cost and dispersion compensation device loss with wavelength are matched respectively, which solves the technical problems of uneven distribution of fiber transmission loss with wavelength, different dispersion costs at different wavelengths and uneven distribution of dispersion compensation device loss with wavelength.
[0064] It should be noted that, Figure 2 This application only illustrates one optical path structure for a combiner and a demultiplexer. In practice, the optical paths of the combiner and the demultiplexer can be interchanged, or other optical path structures that meet the second condition can be used. This application does not impose any restrictions on this.
[0065] Step 4: Place the dispersion compensation device on the optical trunk of the multiplexer or demultiplexer and connect it to the common terminal COM of the multiplexer or demultiplexer. Perform full-wave dispersion compensation through the dispersion compensation device to optimize dispersion cost.
[0066] Among them, full-wave dispersion compensation using dispersion compensation devices must meet two principles:
[0067] Principle 1: Dispersion compensation devices should perform full-wave dispersion compensation based on the dispersion compensation amount calculated at the wavelength with the greatest positive dispersion cost.
[0068] The dispersion compensation amount must satisfy [L×DW, L×D]. L is the fiber transmission length; D is the maximum fiber dispersion coefficient in the range of 1271nm to 1371nm. For G.652 fiber, the dispersion coefficient is the largest at 1371nm, which is about 5~7ps / (nm×km); W is the system dispersion tolerance.
[0069] Optionally, step 4 can also be performed before step 1.
[0070] Taking a 20km fronthaul system as an example, as shown in Table 2, the dispersion cost at 1351nm and 1371nm is so high that the system is unusable and dispersion compensation is necessary. Under the premise of dispersion compensation, the dispersion costs at 1371nm and 1351nm... MDL j (Theoretically) the size needs to be as small as possible, so the corresponding filter should be placed at the front when adjusting the optical path. When full-wave dispersion compensation is selected, i.e., the same amount of dispersion compensation is applied to 1271nm~1371nm, the dispersion compensation device is placed at the common terminal COM of the demodulator, such as... Figure 2 As shown in (a), the dispersion compensation is based on 1371nm (the wavelength with the greatest positive dispersion cost). At this time, 1271nm~1291nm is in the state of dispersion overcompensation. After experimental verification, this compensation method is feasible and applicable to dispersion compensation of 20km CWMD 5G fronthaul system. Taking a certain dispersion fiber (assuming a dispersion coefficient of -70ps / (nm×km)) as an example, dispersion compensation is explained. The dispersion value needs to be compensated from 20km to below 10km (the system dispersion tolerance corresponds to a distance of 10km). That is, the dispersion compensation amount is [(20-10)km×5ps / (nm×km)=50ps / nm, 20km×5ps / (nm×km)=100ps / nm]. The length of the dispersion fiber is controlled to be [50, 100] / 70×1000=[715m, 1430m]. Considering cost and space, the shortest length of about 715m is adopted, and all dispersion compensation devices are concentrated in the multiplexer or demultiplexer.
[0071] Principle 2: The optimization amount of the dispersion cost corresponding to the wavelength with the smallest margin in the system is greater than the loss of the dispersion compensation device corresponding to that wavelength, and at this time, other wavelengths meet the system usage requirements.
[0072] For example, if the loss of the dispersion compensation device is 2dB, and the optimization amount of the dispersion cost is only 1.5dB, the system will deteriorate further. Another example is that the 1271nm originally had a 5dB margin, but the dispersion cost of 1371nm was too high (resulting in a smaller margin) to the point that the system was unusable. After optimization with full-wave dispersion compensation, although the margin of 1271nm is only 4dB, the margin of 1371nm is 2dB, which is optimal from the perspective of the overall system.
[0073] In this embodiment, by flexibly optimizing the design of the combiner / decomposer, the actual values of the total loss corresponding to each wavelength of the combiner / decomposer that meet the design conditions are obtained. The positions of the filters inside the combiner / decomposer are adjusted accordingly. At the same time, the dispersion cost is optimized by combining full-wave dispersion compensation, so as to achieve the optimal system performance.
[0074] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.
[0075] Example 2:
[0076] like Figure 4 As shown, based on the same inventive concept, this application also provides a 20km long-distance 5G fronthaul system, which realizes bidirectional transmission over a single fiber based on 6-wavelength CWDM technology. It includes 6 optical modules, transmission optical fibers, a multiplexer (Mux), and a demultiplexer (Demux). One of the multiplexers / demultiplexers contains a dispersion compensation device. The multiplexer (Mux) and demultiplexer (Demux) are implemented based on the optimized method for the multiplexer / demultiplexer given in Embodiment 1, and will not be described further here.
[0077] The multiplexer (Mux) can be located on the active antenna unit (AAU) side, and the demultiplexer (Demux) on the distribution unit (DU) side (central office), or they can be interchanged. Since the 5G fronthaul system uses a wavelength division multiplexing (WDM) scheme and is a single-fiber bidirectional transmission system, the demultiplexer (Demux) and multiplexer (Mux) are not inherently distinguishable. For ease of explanation, this example specifies that the multiplexer (Mux) is located on the AAU side and the demultiplexer (Demux) is located on the DU side. The six optical modules are evenly distributed between the AAU and DU sides. Each optical module connects to the corresponding wavelength port of the multiplexer (Mux) or demultiplexer (Demux) on that side. The common terminal (COM) of the multiplexer (Mux) and demultiplexer (Demux) are connected to the two ends of the transmission fiber, respectively. For example, the transmit (TX) signal of optical module 1 on the DU side passes through the corresponding wavelength port of the demultiplexer (Demux), then through the common terminal (COM) of the demultiplexer (Demux) to the transmission fiber. After being demultiplexed by the multiplexer (Mux) on the AAU side, it connects to the receive (RX) signal of optical module 2, forming a closed loop. Similarly, the other two sets of optical modules are handled in the same way.
[0078] From the perspective of the impact of temperature on the system, the multiplexer (Mux) or demultiplexer (Demux) with dispersion compensation function needs to be located in an environment with minimal temperature variation to reduce the impact of temperature changes on the dispersion compensation device. Therefore, placing it in a DU-side equipment room with air conditioning and a constant temperature is very suitable. Thus, the dispersion compensation device is placed in the demultiplexer (Demux), such as... Figure 2 As shown in (a), this is to reduce the impact of temperature changes on the dispersion compensation device.
[0079] For a 20km 6-wavelength CWMD 5G fronthaul system, the wavelengths at both ends need to be specifically controlled from the perspective of dispersion coefficient. The 1371nm wavelength can drift to a maximum of 1377.5nm, where dispersion degradation is severe, and the fiber loss coefficient increases significantly due to the presence of water peaks. For conventional DCF (Dispersion Compensating Fiber), the water peak loss coefficient degradation is even more severe, exceeding 2dB / km. Therefore, the 1371nm wavelength needs to be controlled below 1372nm, ideally below 1370nm. The dispersion situation at 1351nm is similar to 1371nm (without water peak influence), but the dispersion cost is relatively high. The situation at 1271nm is the opposite of 1371nm, exhibiting a negative dispersion coefficient. The shorter the wavelength, the larger the negative dispersion coefficient and the greater the loss coefficient; therefore, it is also best to control it above 1271nm. Furthermore, from a design and manufacturing process perspective, the wavelengths (shortest and longest wavelengths) of the optical modules on both sides are prone to exceeding requirements. Therefore, in this embodiment, optical modules with wavelengths of 1371nm and 1351nm must be placed on the DU side, and the 1271nm optical module should ideally be placed on the DU side. Optical modules with wavelengths of 1331nm, 1311nm, and 1291nm are placed on the AAU side to reduce the impact of temperature changes on the emission wavelength of the optical modules and mitigate the dispersion degradation caused by wavelength drift.
[0080] In this embodiment, based on existing equipment—that is, without changing the optical modules, multiplexers / demultiplexers, dispersion compensation devices, base stations, and already laid transmission optical fibers (which suffer from uneven loss distribution and limited dispersion tolerance)—an improved multiplexer / demultiplexer maximizes the margin of the fronthaul system. The system achieves relatively balanced performance across all wavelengths, making it suitable for both short-distance and long-distance (0-20km) 6-wavelength CWDM 5G fronthaul systems. By rationally allocating multiplexers or demultiplexers with dispersion compensation devices and optimizing the placement of optical modules at specific wavelengths, and leveraging the relatively stable ambient temperature at the DU (Distribution Unit) headquarters, the wavelength shift of the optical modules with temperature is reduced, minimizing dispersion degradation caused by wavelength drift and further improving system reliability. The same design approach is also applicable to MWDM and other fronthaul systems.
[0081] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.
Claims
1. An optimization method for a combiner / decomposer, characterized in that, The method includes: Obtain the theoretical value of the total loss of the combiner / decomposer for each wavelength; Based on the theoretical value of the total loss of the combiner / decomposer for each wavelength, design the actual value of the total loss of the combiner / decomposer for each wavelength that satisfies the second condition. Based on the actual value of the total loss of the combiner and descanner corresponding to each wavelength, adjust the optical path structure inside the combiner and descanner in the fronthaul system to match the changes in fiber transmission loss with wavelength and the changes in the loss of dispersion compensation device with wavelength. The dispersion compensation device is placed on the optical trunk of the multiplexer or demultiplexer and connected to the common terminal of the multiplexer or demultiplexer. Full-wave dispersion compensation is performed through the dispersion compensation device to optimize the dispersion cost. The second condition includes that the actual value of the total loss of the combiner / decomposer corresponding to each wavelength is equal to the theoretical value of the total loss of the combiner / decomposer corresponding to the same wavelength, and that the changing trend of the actual value of the total loss of the combiner / decomposer arranged in wavelength order is the same as the changing trend of the theoretical value of the total loss of the combiner / decomposer arranged in the same order. The step of performing full-wave dispersion compensation through the dispersion compensation device includes: The dispersion compensation device performs full-wave dispersion compensation based on the dispersion compensation amount calculated for the wavelength with the highest positive dispersion cost; the optimization amount of the dispersion cost corresponding to the wavelength with the smallest margin in the system is greater than the loss of the dispersion compensation device corresponding to that wavelength, and at this time, other wavelengths meet the system usage requirements. The dispersion compensation amount must satisfy [L×DW, L×D], where L is the fiber transmission length, D is the maximum fiber dispersion coefficient within 1271nm~1371nm, and W is the system dispersion tolerance.
2. The optimization method for the combiner / decomposer according to claim 1, characterized in that, The process of obtaining the theoretical value of the total loss of the combiner / decomposer for each wavelength includes: Based on the first condition that the 6-wave CWDM fronthaul system must meet, the total loss of the combiner / decomposer for each wavelength is obtained. The total loss of the combiner / decomposer for each wavelength is normalized, and the theoretical value of the total loss of the combiner / decomposer for each wavelength is obtained by combining the background loss of the combiner / decomposer and the loss of the dispersion compensation device. The first condition is that the difference between the transmit and receive power at any wavelength of the system is not less than the sum of all losses corresponding to that wavelength, expressed as: (1) In the formula: n The total number of wavelengths, TX For transmission power, RX Minimum receiving power for back-to-back connections; FL For transmission fiber loss, MDL j For the multiplexer and demultiplexer in the fronthaul system j The sum of losses for each wavelength, DCP For the price of dispersion, OL Other losses in the line, including losses at connectors and optical distribution boxes, ML This represents the system margin.
3. The optimization method for the combiner / decomposer according to claim 2, characterized in that, Based on equation (1), the expression for the total loss of the combiner for each wavelength is derived as follows: （2） Based on equation (2), the theoretical value of the total loss of the combined waveguide for each wavelength is expressed as follows: （3） Where: min( MDL j () represents the minimum total loss of the combiner / decomposer across all wavelengths; BL j = BL + DCL j ,and BL To account for the inherent loss of the deconstructor, DCL j For the first j The loss of the dispersion compensation device corresponding to each wavelength.
4. The optimization method for the combiner / decomposer according to claim 1, characterized in that, The step of adjusting the optical path structure inside the multiplexer and demultiplexer in the fronthaul system based on the actual value of the total loss of the multiplexer and demultiplexer for each wavelength includes: Sort the actual values of the total loss of the combiner / decomposer corresponding to each wavelength in ascending order. Inside the combiner or decomposer, arrange the filters corresponding to the first x actual values of the wavelength in the sequence in ascending order of distance from the common terminal. The arrangement of all filters must satisfy the actual value of the total loss of the combiner / decomposer obtained in the design, so that the total loss of the combiner / decomposer reaches the optimal level.
5. A 20km long-distance 5G fronthaul system, based on 6-wavelength CWDM technology to achieve bidirectional transmission over a single fiber, comprising 6 optical modules and transmission optical fibers, characterized in that... Also includes: A combiner and a demultiplexer are located on the AAU side and the DU side respectively, one of which is equipped with a dispersion compensation device. The combiner and the demultiplexer are implemented based on the optimized design method of the combiner and demultiplexer as described in any one of claims 1-4. The six optical modules are evenly distributed on the AAU side and the DU side. Each optical module is connected to the corresponding wavelength port of the multiplexer or demultiplexer on that side. The common terminal of the multiplexer and demultiplexer is connected to both ends of the transmission optical fiber.
6. The 20km long-distance 5G fronthaul system according to claim 5, characterized in that, Place the combiner or demultiplexer with dispersion compensation device on the DU side to reduce the impact of temperature changes on the dispersion compensation device.
7. The 20km long-distance 5G fronthaul system according to claim 5, characterized in that, Optical modules with wavelengths of 1371nm, 1351nm, and 1271nm are placed on the DU side, while optical modules with wavelengths of 1331nm, 1311nm, and 1291nm are placed on the AAU side to reduce the impact of temperature changes on the emission wavelength of the optical modules.