WDM Technologies for 5G Carrying Network

 5G Application Scenarios

The development of 5G networks starting in 2019 is generally believed to bring changes not limited to people’s daily life. It will support the evolution of Internet from mobile internet to intelligent internet, which will influence the industrial-ecology deeply.

The international standard organization 3GPP defined the three main application scenarios of 5G: eMBB (Enhance Mobile Broadband), uRLLC (Ultra-Reliable Low Latency Communications), mMTC (Massive Machine Type Communication). eMBB requires the bandwidth experienced by the customers to be more than 1Gbps supporting mobile broadband surfaces such as 3D and ultra-high definition video. uRLLC requires the transmitting delay to be <1ms supporting real time applications such as self-driving cars, industrial automation, and remote surgery. mMTC means application in massive internet of things (IOT) which requires high density terminal connection of more than one million per square kilometer.

Structure of the 5G Carrying Network
Build the carrying network before commercial application of 5G. In order to support the aforementioned three application scenarios, the carrying network based on optical fiber is required to be reconstructed. Fig.1 shows a typical structure for 5G carrying network, which usually consists of metro access network, metro aggregation network, metro core network and inter-province backbone network. Considering investigation and operating cost, the radio access network (RAN) of 4G usually employs D-RAN (distributed wireless access) structure based on function division of RRU+BBU, while the 5G system employs C-RAN (centralized or clouded wireless access) structure based on function division of AAU+DU+CU.

Fig.1 Structure of 5G carrying network

The interconnection between the nodes of 5G carrying network is realized through optical transceiver modules and optical fibers. The interconnection between the wireless base station and DU is defined as front-haul. The interconnection between DU and CU is defined as mid-haul. The interconnection between CU and the metro core network is defined as back-haul. The front-haul distance is usually <10/20km and the bit rate of the data interface is 10/25/100Gbps. The mid-haul distance is usually <40km and the bit rate is 25/50/100Gbps. The back-haul distance is usually 40-80km and the bit rate is usually 100/N×100Gbps. The transmitting span of the trans-provincial backbone network is usually hundreds of kilometers and the bit rate is N×100/200/400Gbps.

Fig.2 The front-haul, mid-haul and back-haul link of the 5G carrying network

Comparing to the 4G network, the frequency of 5G signal is higher and thus the coverage of a single base station is less. Thus the base stations needed by 5G network is 2-3 times of those by 4G network. C-RAN structure is preferred in the front-haul and mid-haul of 5G network, instead of D-RAN in 4G. There are mainly three advantages for C-RAN. Firstly, the required number of terminal equipment rooms and transmitting equipments is reduced. Thus the cost for station address acquisition, equipment room renting, and data transmission is reduced. Theoretically, the more is the DUs concentrated, the cost down is more. Secondly, the concentrated deployment of DUs facilitates the maintenance. Thus the cost for equipment room construction, equipment maintenance, and power rate is much lower than D-RAN. Thus C-RAN is regarded as the main deployment mode of 5G front-haul network. Thirdly, the DUs are grouped and deployed in a DU pool, or in clouded deployment. Thus the baseband resources can be shared and service cooperation between stations is realized.

Consideration for the Choice of Transmitting Technologies
Optical fiber transmission is widely employed in telecom backbone network and data centers. In order to improve the transmission capacity, WDM technologies are commonly used. However, the concrete transmission technologies are diverse facing different application scenarios. The main factors influencing the choice are power loss and chromatic dispersion of the fiber link. The laser sources (with modulators included) and photon detectors (PDs) are important for the cost of the transmission system and should be considered in choice of proposals. What’s more, the heritage of industrial chain also influence the cost and is one of the factors to be considered.

The spectral transmission loss of the common quartz fiber is shown in Fig.3. Its first, second and third transmission windows are centered at 850nm, 1310nm and 1550nm. 850nm is the wavelength selected by the first multimode fiber (MMF) communication system. 1310nm is the zero dispersion wavelength of the conventional single mode fiber (SMF) G.652. As shown in Fig.4(a), the material dispersion and waveguide dispersion counteracts at this wavelength. 1550nm is the wavelength experiencing the lowest loss for quartz fiber. G.655 SMF was developed with its zero dispersion wavelength set with a small shift from 1550nm, as shown in Fig.4(b). Thus low dispersion is obtained at 1550nm-band and non-linear effects, such as four-wave mixing and cross-phase modulation, are avoided.

Fig.3 Spectral transmission loss of quartz fiber

Fig.4 Spectral dispersion of G.652 and G.655 optical fibers

In the engineering applications, the second and third windows in Fig.3 are usually called O-band and C-band, respectively. In order to extend the available transmission band, S-band and L-band are developed neighboring to C-band. What’s more, the water peak around 1385nm (due to OH- absorption) is cut down by further purification of quartz fiber. Thus E-band is developed and the transmission band of quartz fiber is extended to 1260~1620nm. The bandwidth is totally 360nm and the optical fiber is called all-wave fiber.

The optical fiber communication system usually employs semi-conductor lasers as the light source. The emission from a semi-conductor laser is not an ideal monochromatic light. It has a certain linewidth. The different wavelength components transmit in different velocity due to dispersion and thus bit error is introduced in high-speed, long-haul transmission system. Optical signals in different bit rate have different dispersion tolerance, as shown in Table 1.

Table 1. Dispersion tolerance for optical signals in different bit rate

The early transmission system in low bit rate usually employ FP lasers with low cost and broader linewidth. However, DFB lasers are necessary for high-speed transmission systems with bit rate ≥10Gbps. When the transmission distance is not too much, people intend to modulate the DFB lasers directly, which are called DML (Direct Modulated Laser) lasers. Direct modulation on the lasers generates chirp effect and broadens the linewidth, which introduces more chromatic dispersion. In order to avoid broadening the linewidth of the lasers to transmit longer distance, external modulation is employed. An EAM (Electro-absorption Modulation) modulator is cascaded behind the laser. The DFB+EAM combination is called EML laser. In order to transmit ever longer distance, LN (Lithium Niobate) modulator is required, which is an electro-optical modulator with Math-Zehnder (MZ) interferometer structure.

Transmission Proposal for Different Application Scenarios
The focus of 5G investment is development of the front-haul and mid-haul networks. The investment is too much and exceeds the affordability of a single telecom operator. China Unicom and China Telecom decide to develop a 5G front-haul network together, while China Mobile cooperates with China Radio and television network Cooperation. A wireless base station should be equipped with upload/download interfaces for three sectors. Under the co-construction and sharing mode, the bandwidth demand for a single base station is doubled and thus six 25G interfaces are required for a 5G base station. For the deployment scenario where 4G and 5G equipments share a base station, 12 front-haul interfaces are required. In some multi-service access region, bandwidth demand is much higher and 24 front-haul interfaces are required for a single base station. Based on above application scenarios, base stations with 12 interfaces will become the main-stream construction in the 5G front-haul network.

In the 4G front-haul network, BBU is set near to RRU and D-RAN configuration is more adopted. The mostly employed transmission proposal is fiber direct driving. While in the 5G front-haul network, DU is deployed far from AAU. The cost of optical fiber is too much and thus xWDM is popular to save fiber resources. According to the application scenarios and based on the deployed fiber resources, the configurations of 5G front-haul networks can be D-RAN, C-RAN small aggregation and C-RAN massive aggregation, as shown in Fig.5. In the D-RAN deployment, fiber direct driving proposal is selected. BiDi (bi-directional transmission in and single fiber) transmission is suggested to save half of the fiber resources, as shown in Fig.6. In C-RAN small aggregation deployment, six 25G interfaces are required and 6-λ CWDM transmission is proposed, as shown in Fig.7.

Fig.5 The deployment configurations of 5G front-haul network

Fig. 6 Fiber direct driving proposal for front-haul network

Fig.7 6-λ CWDM proposal for 5G front-haul network

In C-RAN massive aggregation deployment, each wireless base station requires 12 high-speed optical interfaces. China Mobile presented a 12-λ MWDM proposal. The 12 wavelengths are listed in Table 2. Based on the 6-λ CWDM laser chips, the emission wavelengths are shifted by 3.5nm to the left and right through TEC tuning. Thus 12 wavelengths are obtained based on the current industrial chain for data transmission. China Telecom selected the 12-λ LWDM proposal. The channel spacing is 800GHz. The 12 wavelengths are listed in Table 3. TEC is required to stabilize the emission wavelength of the laser sources because the wavelength pitch is only 4.3-4.7nm. The power consumption of the optical transceiver module is about 0.5W higher due to the introduction of TEC module.

Table 2. CWDM/MWDMtransmission wavelengths and proposals

Table 3. LWDM transmission wavelengths and proposals

The different WDM wavelengths and dispersion spectrum of quartz are shown in Fig.8. The latter two wavelengths of 6-λ CWDM is far from the zero-dispersion wavelength 1310nm. In order to compensate for the power loss cost due to dispersion, APD photon detectors are employed which have higher sensitivity. Thus we can see, for the CWDM transmission proposal in Table 2, the laser sources and PDs choose DML+PIN for the former wavelengths, while DML+APD for the latter two wavelengths. For the same reason, the latter four wavelengths of MWDM also employ DML+APD.

Fig. 8 Chromatic dispersion spectrum of optical fiber and WDM proposals for 5G front-haul network

Table 2 and 3 list different WDM transmission proposals for 5G front-haul network, together with the sharing of the current industrial chain in data transmission (for data centers). WDM technologies were first applied in telecom mainly for long-haul transmission in the backbone networks and core networks. DWDM transmission in C-band (1530-1570nm) is preferred because the transmission loss of quartz fiber is the lowest at this band. However, the optical devices for this industrial chain are expensive. With the development of mobile internet and the construction of massive data centers, optical fiber transmission technologies are widely employed, which become the second and ever larger blue-ocean market of optical fiber communication technologies. The transmission distance in data centers are relatively short (comparing to telecom applications), while the data transmission speed is higher. The aim of transmission proposals is focused on solution of dispersion restrictions, which is different from loss restriction in telecom long-haul network.

The current 5G front-haul network is part of the telecom network, while its application scenarios are different from those of telecom long-haul network. It is similar to the applications in data centers. The transmission is characterized by high-speed and short distance, which is mainly restricted by chromatic dispersion. Thus the transmission wavelengths are selected in O-band centered at 1310nm. CWDM4, LWDM transmissions in O-band have been widely deployed in data centers. The industrial chains are mature and the cost is low. 5G front-haul network can share its industrial chain to cut down the investment. For example, for the 6-λ CWDM proposal in 5G front-haul network, the former 4 wavelengths can share the CWDM4 industrial chain of data transmission. For the 12-λ MWDM proposal, the former 8 wavelengths can also share the CWDM4 industrial chain. For the 12-λ LWDM proposal, the 2-5 wavelengths can share the 400G LR8 industrial chain and the 7-10 wavelengths can share the 100G LR4 industrial chain.

Sharing the CWDM4 industrial chain for data transmission is one of the main considerations why China Mobile projected MWDM proposal. The construction of 5G network can be started as soon as possible with the cost under control.

In response to the new needs of 5G fronthaul applications, HYC quickly launched MWDM and LWDM series products to make full use of O-band optical resources, increase band utilization, and increase speed. HYC can provide customers with a full range of WDM wavelength division multiplexing solutions, including CWDM, DWDM, CCWDM, MWDM, LWDM products, etc.

HYC Co., Ltd has 20 years of R&D and manufacturing experience in the optical communication industry, and has a certain influence in the global industry. It focuses on providing customers with one-stop customization of the design, R&D and manufacturing of passive optical devices. HYC has production lines including fiber optic connectors, patch cords, PLC splitters, WDM wavelength division multiplexers, MEMS optical switches and so on. Products are widely used in FTTH, data centers, 5G networks, and telecommunication networks.

MPO/SC/LC Secure Lockable Fiber Connector

 The secure lockable fiber optic connector is mainly used in some private networks with high security level requirements, and improves security by preventing unauthorized modifications in the entire critical network.

MPO Secure Lockable Connector

The MPO secure lockable connector is a secure accessory that can be compatible with conventional MPO connector.  Once the MPO connector with secure accessory insert into the adapter, it will be locked. The connector cannot be pulled out unless remove the secure accessory. MPO connectors equipped with safety locks will not affect the original height and density of the connectors, and are also compatible with conventional adapters and optical modules. The installation is simple and convenient, requires no extra tools. It can effectively prevent releasing the connector by mistake, and to reduce the chance of getting dusty on the connector's surface.

SC Secure Lockable Connector

SC secure lockable connector is designed with unique keying details in the connector body, as long as it is inserted into the adapter, it is locked and the connector cannot be pulled out. The connectors of different colors correspond to the keys of the same color to open the lock and pull out the connector. There are also dust caps with locks that are suitable for SC conventional adapters, which can prevent dust and lock. For some unused fiber ports, it can prevent mistaken insertion.

 

LC secure lockable connector

LC keyed connector is installed with a secure lock accessory on the LC duplex connector. The connector with lock accessory can be locked once insert into the adapter. You need to use the equipped unlocking key to pull out the connector. There is also a dust cap with lock for the LC adapter, which can be unlocked with the same key. Removing the security lock accessory on the connector will not interfere with the LC adapter or cause network performance degradation.

HYC Co., Ltd was founded in 2000, has 20 years experiences in OEM ODM manufacturing of passive optical devices. We focus on providing customers one-stop services of the design, R&D and manufacturing of passive optical communication devices. We have fiber optic connectors, fiber optic jumpers, WDM wavelength division multiplexing, PLC optical splitters, MEMS optical switches and other product lines.

How does fiber optic attenuator work?

 As we all know, too little or too little optical power will cause equipment errors. Too much power will saturate the receiving amplifier, while too little power will interfere with the signal and cause noise problems. An optical fiber attenuator is an optical device that can be used to attenuate the input power to avoid distortion of the optical receiver due to excessive power.

The optical fiber attenuator reduces the optical power through the absorption, reflection, diffusion, scattering, deflection, diffraction and dispersion. How to reduce the power light level? The fiber attenuator is set in a working wavelength range that can absorb light energy. Within this range, it will not reflect light and reduce unnecessary echo reflection. In this way, the optical power attenuation effect is achieved. Usually, the optical attenuator is made by air isolation technology, displacement dislocation technology, attenuation fiber technology, absorption glass method, etc.

The normally attenuation range of the optical attenuator is 0~65dB. The attenuation power of the fixed attenuators on the market is between 1 and 30dB. Fixed fiber attenuator is a type of fiber attenuator, which fixes the attenuation power at an attenuation value. It is commonly used in telecommunication networks, fiber optic test equipment, local area networks (LAN) and cable television (CATV) systems.

There is also a variable optical attenuator. The attenuation level of the variable attenuator can be adjusted, for example, from 0.5 dB to 20 dB, or even 50 dB. Some variable attenuators have very fine resolution, such as 0.1dB or even 0.01dB. Mainly used in: optical distribution frame, optical fiber network system, high-speed optical fiber transmission system, cable television (CATV) system, long-distance trunk line dense wavelength division multiplexing (DWDM) system, optical add/drop multiplexer (OADM).

Among them, the fixed optical attenuator has pigtail type, converter type and so on. It can be made into FC, SC, ST, LC, MU and other interface types, which is convenient to use in daily cabling. Generally, a single optical attenuator has two interfaces, male and female, which can be male-female or female-female. The male connector interface is generally used to plug into the receiver of the device or the adapter on the adapter panel, and the female connector interface is used to connect the fiber jumper. HYC can provide various types of fixed female and male optical fiber attenuators with stable performance and reliable quality, which can meet the requirements of various connector interface types and working wavelength customization of ST, SC, FC, MU, and LC.

Fiber optic attenuators are widely used in optical passive devices. The performance indicators to measure the optical attenuator mainly include attenuation, insertion loss, and attenuation accuracy, return loss, etc. High-performance optical attenuators have low insertion loss, and return loss is usually above 40dB.

HYC Co., Ltd was founded in 2000, has 20 years experiences in OEM ODM manufacturing of passive optical devices. We focus on providing customers one-stop services of the design, R&D and manufacturing of passive optical communication devices. We have fiber optic connectors, fiber optic jumpers, WDM wavelength division multiplexing, PLC optical splitters, MEMS optical switches and other product lines.

What is Fiber Array (FA)?

Fiber Array (FA for short) is an array formed by installing a bundle of optical fibers or a fiber ribbon on the substrate at specified intervals by using a V-Groove substrate.

An optical fiber array in optical communication mainly includes a substrate, a pressing plate, and an optical fiber. Usually, a plurality of grooves are cut on the base of the substrate, and the optical fiber is fixed into the groove by the pressure plate. Optical fiber arrays have high requirements on materials and manufacturing processes.

Fiber array is usually located by the precision carved V-shaped grooves. The V-groove requires special cutting process to achieve precise fiber positioning. In order to reduce the connection fiber loss, it’s very important to accurately position the fiber core in the V-groove. After positioning, pressurize with a compactor and fix it with an adhesive to polish the end face of the optical fiber. That is the final fiber array. The substrate material will affect the optical performance of the optical fiber array, and it is necessary to use a material with a small expansion coefficient to ensure that the optical fiber array has no stress, high reliability, and no fiber displacement at high temperatures. Glass and silicon are commonly used materials, in addition to ceramics, conductive substrates and plastic substrates.

Fiber Array

The distance between the grooves of the V-shaped groove, the number of fiber channels, and the grinding angle are all customized according to the needs. The parallelism of the groove length direction between the grooves is usually within ± 0.1 degree. Most of the fibers used in FA are colored ribbon fibers, which have good bending resistance, and the colorful colors can easily distinguish the channels.

Fiber Array

Fiber arrays are usually used in planar optical waveguides, arrayed waveguide gratings, active/passive array fiber devices, micro-electromechanical systems, multi-channel optical modules, etc. Among them, the optical fiber array is one of the important components of the PLC Splitter, which can greatly reduce the loss of optical waveguide devices and optical coupling alignment.

HYC provides a variety of choices of fiber arrays, such as the number of fiber array channels, core spacing and grinding angle can be customized. HYC Co., Ltd has been focusing on the OEM/ODM manufacturing of optical passive devices for 20 years. It has a strong R&D team and production capacity. It can provide customers with one-stop customized production of optical communication passive basic device design, R&D and manufacturing. Product lines mainly include optical fiber connectors, optical fiber jumpers, PLC splitters, wavelength division multiplexers(WDM), MEMS optical switches, etc.
http://www.hyc-system.com

How to prevent unauthorized access in data centers?

In some large data centers or telecommunications rooms with complex management psersonnel or multiple departments, it’s important to ensure that the optical connection is not disconnected by some misoperations.

Lockable fiber optic connectors are products based on this security requirement.On the basis of ordinary fiber optic connectors, the lock connector adds a unique locking and independent unlocking tool, which uses to lock the dedicated fiber port.It can effectively prevent accidental inserting and removing by other personnel and improve the security of the entire network.

How does it work?
Here is two lockable connectors: SC secure lockable connector and LC secure lockable connector.

SC secure lockable connector

Secure-Keyed SC connector has unique keying details and can be locked by simply plugging it into the adapter. Once the connector is locked, only the matching color key can open and release the connector. The security lock sc connector comes in five different colors and can be used in different applications. For fiber ports that are not being used temporarily, dust caps with the same locking function have also been developed. The difference is that the dust cap can be opened with any color key.

The secure locking LC connector was developed from adding a lockable accessory to the traditional duplex connector. The removal of the security lock will not interfere with the LC adapter or cause network performance degradation.

LC secure lockable connector

Both locking LC/SC fiber optic connectors are fully compatible with conventional adapters without the need to use specific cables or adapters. It can be easily installed and removed without affecting adjacent ports.

It is especially suitable for networks with higher security levels such as military, government, finance, education, and medical treatment, which can effectively prevent unauthorized tampering.

About HYC Co., Ltd
HYC has 20 years of OEM/ODM manufacturing experience in optical passive devices in the optical communications industry and is committed to providing high-quality connected products for global data users. At present, HYC has several major product lines such as optical fiber connectors, optical fiber jumpers, PLC optical splitters, WDM wavelength division multiplexers, and MEMS optical switches. The factory has more than 1,000 employees and has strong production capabilities.

What is the IL Value of Ultra Low Loss MPO Fiber Optic Cable?

With the wide application of FTTH, the requirements for data transmission capability and speed have become more and more important in optical fiber communications, which has also led to high requirements for high-density, low-loss optical fiber connectors.

In the previous article, we introduced what are insertion loss and return loss? These two parameters are the most important indicators of fiber optic connectors. The three factors that affect fiber connection loss are the lateral shift of the fiber core, fiber tilt and gap. Among them, lateral offset is the most important factor.

For MPO connectors, the factors that affect the lateral offset are the eccentricity of the fiber hole, the gap between the fiber hole and the fiber, and the gap between the positioning pin hole and the positioning pin. By determining the dimensional tolerances required for MT sleeves, optical fibers and positioning pins, low losses can be achieved. This requires MPO connectors to have low-loss and high-reliability performance during the grinding process, polishing process, and manufacturing process of experimental testing.

So what is low loss? First, let's take a look at the standard typical insertion loss values of MPO fiber connectors.

 Optical performance index of MPO single-mode fiber connector
－The maximum insertion loss of any plug through the standard adapter and standard plug ≤0.75dB (including repeatability); return loss>30dB (MPO/PC),>50dB (MPO/APC)
－The maximum insertion loss of two plugs connected arbitrarily through the adapter ≤1dB; return loss>20dB (MPO/PC),>40dB

 Optical performance index of MPO multimode fiber connector plug
－The maximum insertion loss of any plug through the standard adapter and standard plug ≤0.35dB (including repeatability)
－The maximum insertion loss of two plugs connected arbitrarily through the adapter ≤1dB

Although the IEC standard specifies the maximum insertion loss of the connector, the typical insertion loss of most manufacturers' connectors will be below the standard value. At present, the insertion loss index of 8-core or 12-core multimode MPO connectors in the industry is generally standard loss 0.5dB, and low loss is less than 0.35dB.

MPO/MTP fiber optic connectors are an important part of high-density optical interconnect products in data centers. Today, data center cabling also requires higher-performance, higher-density MPO/MTP fiber optic cables. By improving the connector technology and manufacturing technology, HYC Co., Ltd successfully reduced the loss of the MPO connector SM single-mode 12-core to less than 0.25dB, which is 28% lower than the industry low loss value of 0.35dB; The loss of SM single-mode 24 core is reduced to 0.35dB, which is far below the industry standard and the typical loss value of MPO connectors provided by other manufacturers. It provides high-quality MPO fiber optic cables for data center 400G network construction.

About HYC Co., Ltd
HYC can provide customized high-quality MPO/MTP optical fiber cable according to customer needs. Founded in 2000, HYC has more than 20 years of OEM/ODM manufacturing experience in optical communication devices. The main products include high-density optical connectivity, PLC optical splitters, WDM wavelength division multiplexers, MEMS optical switches and other products, which are widely used in FTTx, telecommunications, 5G networks, data centers and other fields.

What is C band and L band in WDM (Wavelength Division Multiplexing)?

WDM (Wavelength Division Multiplexing) is a transmission technology that uses a single optical fiber to simultaneously transmit multiple optical carriers of different wavelengths in optical fiber communications. When the wavelength of light is different, the transmission loss in the fiber is also different. In order to reduce fiber loss, it’s important to find the most suitable transmission wavelength. After a long period of exploration and testing, light with a wavelength of 1260nm~1625nm has the smallest dispersion signal distortion with low loss, which is the most suitable for transmission in optical fiber.

The fiber loss of different wavelength

The wavelength of fiber can be divided into several bands, each band is used as an independent channel to transmit predetermined wavelength. According to the ITU-T standards, single-mode fiber with the band over 1260nm is divided into O/E/S/C/L/U
six bands.

Different bands

What is O band?
The O band is the original band with wavelenght from 1260 to 1360nm. The O-band is the first wavelength band used in optical communications in history, and the signal distortion (due to dispersion) is minimal.

What is E band?
The E-band (extended wavelength band: 1360-1460 nm) is the least common of these bands. The E-band is mainly used for the expansion of the O-band, but it is rarely used, mainly because many existing optical cables show high attenuation in the E-band and the manufacturing process is very energy-intensive, so the use in optical communication is limited.

What is S band?
The optical fiber loss in the S-band (Short-wavelength Band, 1460-1530 nm) is lower than the loss in the O-band. The S-band is used as many PON (passive optical network) systems.

What is C band?
The C-band (Conventional Band) ranges from 1530 nm to 1565nm and represents the conventional band. Optical fiber shows the lowest loss in the C-band and occupies a large advantage in long-distance transmission systems. It is usually used in many metropolitan areas combined with WDM, long-distance, ultra-long-distance and submarine optical transmission systems and EDFA technology. As the transmission distance becomes longer, and fiber optic amplifiers are used instead of optical-to-electronic-to-optical repeaters, the C-band becomes more and more important. With the advent of DWDM (Dense Wavelength Division Multiplexing) that allows multiple signals to share a single fiber, the use of the C-band has been expanded.

What is L band?
The L-band (Long-wavelength Band, 1565-1625nm) is the second lowest-loss wavelength band and is often used when the C-band is insufficient to meet the bandwidth requirements. With the wide availability of b-doped fiber amplifiers (EDFAs), DWDM systems have expanded upward to the L-band, and were initially used to expand the capacity of terrestrial DWDM optical networks. Now, it has been introduced to submarine cable operators to do the same thing-to expand the total capacity of submarine cables.

Due to its low transmission attenuation loss, C-band and L-band is usually selected to use in the DWDM system. Except for the O-band and L-band, there are two other bands, the 850nm band and the U band (ultra-long band: 1625-1675 nm). The 850nm band is the main wavelength of the multimode optical fiber communication system, which combines VCSEL (Vertical Cavity Surface Emitting Laser). The U frequency band is mainly used for network monitoring.

WDM technology can be divided into WDM, CWDM, DWDM according to different wavelength modes. The wavelength range stipulated by ITU for CWDM (ITU-T G.694.2) is 1271 to 1611nm, but considering the attenuation of the 1270-1470nm band in the application, the band of 1470~1610nm is usually used. The channel space of DWDM is more closeness, so choose the C-band (1530 nm-1565 nm) and L-band (1570 nm-1610 nm) transmission windows. Ordinary WDM generally uses 1310 and 1550nm wavelengths.

The wavelength of CWDM

With the growth of FTTH applications, the C-band and L-band will play an increasingly important role in optical transmission systems.

HYC Co., Ltd has 20 years of OEM/ODM manufacturing experience in the optical communications industry. The WDM devices independently developed and manufactured are fully used in metropolitan area networks and 5G networks. The diversified design and production capabilities meet various application requirements, such as pigtail modules, plug-in The LGX, high-density rack, 6port WDM, CCWDM, non-thermal multi-channel AWG, 5G module, etc., fully contribute to the global 5G deployment and development.