What is passive DWDM?

Passive DWDM refers to a system or solution that uses DWDM (Dense Wavelength Division Multiplexing) technology but does not rely on any motor components such as amplifiers or converters. In such a system, all signal processing, multiplexing and demultiplexing are done in the optical domain, and there is no need to convert signals into electrical signals.

Here are some key features of passive DWDM:

1. Multiplexer/Demultiplexer:

 Passive DWDM systems use optical multiplexers to combine multiple optical signals of different wavelengths into a single fiber, and demultiplexers to separate multiple signals of different wavelengths from the optical fiber. .

2. No amplification required:

 Since passive DWDM systems do not have amplifiers, they are typically used over shorter distances, such as inter-data center interconnects or metropolitan area networks, where signal loss can be compensated by providing sufficient initial power.

3. Cost-effectiveness:

Due to the lack of expensive electric components, passive DWDM is generally more economical than active DWDM systems, especially in short-distance transmission.

4. Simplified design and deployment:

 Passive systems are generally simpler and easier to deploy because they do not require power or complex management and monitoring.

However, without electric components such as amplifiers, the transmission distance and capacity of passive DWDM systems may be limited. When longer transmission distances or greater signal capacity are required, active DWDM systems may need to be considered.

What is Active WDM vs. Passive WDM?

WDM technology allows multiple wavelengths of optical signals to be transmitted simultaneously on a single optical fiber. Depending on whether the system requires power supply to drive certain functions, WDM can be divided into active WDM and passive WDM.

1. Active WDM:

     * Contains components that require power supply, such as amplifiers, transponders, and electrical modulators.

     * Can enhance the signal, thereby increasing the transmission distance.

     * Generally used for long distance transmission and high bandwidth applications.

     *Example: Optical amplifiers such as EDFA (Erbium-doped Fiber Amplifier) are used to amplify signals in DWDM systems, and they require power to work.

2. Passive WDM:

     * Does not include any components requiring power.

     * Relying solely on passive devices such as splitters and multiplexers to operate.

     * Typically used in short-range, low-cost and low-maintenance applications such as enterprise networks or short-distance data center interconnects.

     *Example: CWDM (Coarse Wavelength Division Multiplexing) is often passive and uses optical multiplexers and splitters to combine or separate signals at different wavelengths.

Overall, the choice of using active or passive WDM depends on the specific application, distance, budget and required bandwidth.

What are the passive components in WDM?

In WDM (Wavelength Division Multiplexing) systems, passive components refer to devices or components that do not require external power supply and only rely on incident optical signals to work. Here are some common passive components:

1. Multiplexer/Demultiplexer (Mux/Demux):

 These devices can combine multiple signals of different wavelengths into one optical fiber for transmission (multiplexing), or separate signals of multiple wavelengths from one optical fiber. out (demultiplexing).

2. Optical Splitter:

This is a device used to split an optical signal into multiple identical signals. It is often used in fiber-to-the-home (FTTH) or other point-to-multipoint optical communication applications.

3. Optical Attenuator:

 Used to reduce the intensity of optical signals to prevent overloading or other problems at the receiving end.

4. Optical Isolator:

 Allows optical signals to be transmitted in only one direction, preventing reverse propagation of optical signals from interfering with the system.

5. Optical Circulator:

 It allows optical signals to pass through multi-port devices in a clockwise or counterclockwise direction.

6. Wavelength Selective Switch (WSS):

 Although WSS can be active in some applications, it can also be used as a passive device without the need for power to specify a signal path for a specific wavelength. .

7. Optical Cross-Connect (OXC):

 This device can switch input and output optical channels in a fiber-optic network, usually as a node in the network.

The above are only some of the passive components in WDM systems. The actual system design may select and use these components based on needs, applications and technological progress.

1. Wavelength division multiplexing:

At the sending end, the passive wdm  combines optical signals of different wavelengths through optical splitters (such as fiber gratings, optical waveguide arrays, etc.), so that they are transmitted on the same optical fiber . In this way, optical signals of multiple wavelengths can be simultaneously transmitted on the same optical fiber, which improves the utilization rate of the optical fiber.

2. Optical signal attenuation and dispersion during transmission:

During optical signal transmission, due to the loss and dispersion characteristics of the optical fiber itself, optical signals of different wavelengths will be affected to varying degrees during transmission. 

The passive wdm equipment minimizes the attenuation and dispersion of the optical signals of each wavelength during the transmission process by selecting an appropriate optical splitter and adjusting the parameters of the optical fiber.

3. Demultiplexing:

At the receiving end, the passive wdm demultiplexes the received optical signals through another optical splitter, and separates optical signals of different wavelengths.

Then, the optical signal is converted into an electrical signal through a photoelectric converter, and then the signal is demodulated and filtered through the corresponding electrical signal processing technology, and finally the original signal is restored.

Demand for broadband

At present, in the construction of the network transmission system, different transmission technologies are applied.

At this stage, with the continuous innovation of network transmission media, there has been great development both in terms of performance and coverage.

In terms of transmission system access, it is necessary to focus on the continuous improvement of broadband demand in actual transmission, and strengthening the technical transformation of the original broadband transmission system has become an important trend.

Passive WDM equipment is based on passive wavelength division technology.

By improving the transmission capacity and bandwidth of traditional optical fiber broadband, it can solve the transmission and access needs of the network communication system, thereby promoting the improvement of the transmission system.
The broadband access of the transmission system requires the terminal equipment connected to the optical fiber trunk line in the network to establish a technical connection between the network transmission users and the network transmission system, and form a transmission target under the multi-user demand in the equipment.

Traditional optical fiber broadband, in the case of a surge in network transmission demand, it is difficult to use traditional methods to meet the coverage requirements of network traffic.

When building a network transmission system, it is necessary to consider aggregated broadband ports and use more efficient and stable interruption devices to connect The transmission trunk line lays the foundation for the use of passive WDM equipment technology.

Passive WDM technology equipment is not only small in size, but also can be used for multi-port simultaneous network transmission, and has low energy consumption, which enables the optimization of modern broadband transmission systems to be realized.

Business security

When the network transmission system serves a large number of traffic demands, it needs to guarantee a high degree of security and build protection measures for transmission ports.

The terminal equipment connected to the backbone of the broadband transmission system needs to better deal with the transmission security issues that often occur during the network transmission construction in the port connection.

The solution to transmission security is a necessary guarantee for the stability and reliability of network transmission, especially in the case of increasing network transmission services at this stage, it needs to be satisfied by using corresponding technical equipment.

Passive wavelength division technology equipment has obvious advantages in terms of transmission service security.

Passive WDM technology equipment can improve the speed and efficiency of the downshifting of terminal equipment data in the trunk line of the transmission system, and combine with the optical cables in the transmission system to transfer all ports of the transmission system under the passive wavelength division technology mode Carry out aggregation;

By using the unified router equipment of the system to carry out transmission protection, so that the transmission system can improve the protection performance, and the unified routing protection can concentrate the protection resources of the transmission port, reducing the resource consumption of the system when ensuring transmission security, and improving The economic benefit level of the transmission system.

Application of passive WDM equipment in transmission system

Application of passive WDM equipment in system construction

In the practical application of passive wavelength division technology equipment, it has great advantages in improving and perfecting the traditional system structure.

In optical fiber transmission, passive wavelength division technology equipment can be used, and multiple devices can be used in a concentrated manner, so that it can respond to multi-user aggregation network transmission requests in modern broadband transmission.

Especially in a relatively dense network structure system, multiple transmission ports can be connected on the transmission fiber structure of the trunk line.

In the transmission system structure, in order to improve the transmission efficiency, one optical fiber is often used to drive multiple transmission devices.

This requires the use of passive wavelength division technology equipment, and through port aggregation performance, one routing device can serve multiple transmission devices. The purpose of the transport port.

Passive wdm technology equipment can improve the transmission efficiency of access in the port downlink, increase the transmission traffic, and at the same time enhance the aggregation transmission capability in the use of a single terminal device.

Application of passive WDM equipment in long-distance transmission

In the network transmission system, due to the significant expansion of the application range of the LAN, when using passive wavelength division technology equipment, the advantages of point-to-point transmission can be actively used.

In the LAN system, it can better meet the requirements of large traffic and long distance Transport needs.

In the service form of passive WDM equipment, an appropriate transmission method can be selected according to the actual needs of network transmission, such as transmission speed and wavelength, which can greatly improve the original LAN service performance.

Especially in the transmission mode of different speeds, the transmission network can be combined to increase and expand the transmission system.

When expanding the transmission system, under the framework of passive wavelength division technology, the one-way transmission mode can be changed to form a two-way or even multi-way transmission form to meet the actual needs of different transmission ports.

Application of passive WDM equipment in network construction

In modern network construction, the advantages of passive wavelength division technology equipment can be actively used to improve efficient services for multi-task hybrid applications.

In the process of optical cable transmission, passive WDM technology equipment can better respond to the resource requirements of broadband optical fiber users and enhance the performance of data transmission;

especially in areas that need optical fiber transformation and upgrading, they can rely on passive wavelength division technology A device that enables a transport system to simultaneously connect multiple port trunk connection points.

In network construction, passive wavelength division technology equipment can be applied to implement deployment of optical fiber transmission, and form a more reliable transmission guarantee in multi-service and large-scale transmission.

Nowadays, optical fiber access technology based on passive optical network technology has been widely used in various forms around the world.

In order to meet the development needs of higher speed, more transmission wavelengths, and wider coverage of future optical access networks, new FTTx (Fiber To The X: Fiber Access) technologies emerge in an endless stream, and WDM-PON is also one of the key technologies. Next, follow ETU-LINK to see WDM-PON passive wavelength division multiplexing technology.

What is passive WDM technology ?

Let’s first talk about what are PON and WDM technologies? A Passive Optical Network (PON) refers to a type of optical network that uses optical cables, splitting and combining mechanisms between the central office equipment (OLT) and various end-user devices (ONU/ONT).

This connection is facilitated by the Optical Distribution Network (ODN) and its associated components.

Currently, the PON technologies used for broadband access mainly include EPON and GPON. WDM (Wavelength Division Multiplexing) is wavelength division multiplexing, a technology that uses multiple lasers to simultaneously transmit multiple laser beams of different wavelengths on a single optical fiber. 

As an important supplement to the 5G fronthaul solution, its basic idea is to save optical fiber, which is the main way to expand the transmission capacity of optical fiber and increase the speed.

What is WDM-PON ?

WDM-PON is a point-to-point passive optical network using wavelength division multiplexing technology, that is, in the same optical fiber, the number of wavelengths used in both directions is more than 3, and the uplink access can be realized by using wavelength division multiplexing technology.

Increase users’ access to broadband several times or even dozens of times to meet the ultimate needs of users. A typical WDM PON system consists of three parts: Optical Line Terminal (OLT), Optical Wavelength Distribution Network (OWDN) and Optical Network Unit (ONU).

A straightforward WDM-PON approach involves having multiple light sources of varying wavelengths in the OLT. Each ONU utilizes a specific wavelength light source, and every point-to-point link operates based on its predetermined wavelength.

WDM-PON solution

The biggest feature of WDM-PON is that the ODN (Optical Distribution Network) is composed of passive devices such as optical splitters (Splitter), and does not contain any active electronic devices and electronic power supplies.

The reason why WDM-PON can become a 5G fronthaul solution is related to the technical characteristics it embodies, as follows:

1. Long transmission distance: The insertion loss is smaller than that of the optical power splitter in the traditional TDM PON system, and the network coverage is larger.

2. High transmission rate: each ONU uses independent and different wavelength channels, no special MAC protocol is required, and the system complexity is reduced.

3. High bandwidth: Each user exclusively enjoys the bandwidth of one wavelength channel, does not require dynamic allocation of bandwidth, and meets the bandwidth requirements of 25G eCPRI fronthaul signals.

4. High security: All ONUs are physically isolated and will not affect each other.

5. Low cost: The optical modules used by the ONU are exactly the same, which solves the problem of device storage, and the 32-40 waves of a single fiber can be expanded to 80 waves, saving the cost of backbone optical fibers and OSP.

6. Easy maintenance: Due to the application of colorless light source technology in WDM PON, maintenance is more convenient.

WDM-PDM technology solves the problems of transmission efficiency, bandwidth and cost well, and provides favorable support for the realization of fixed-mobile convergence.

Passive WDM technology in 5G fronthaul

With the deployment of 5G networks, wireless fronthaul has become even more critical. Traditional 4G and previous networks typically used CPRI (Common Public Radio Interface)-based fronthaul solutions, while 5G is driving the need for higher bandwidth, lower latency and higher connection density. In this context, optical technology, especially passive WDM (Wavelength Division Multiplexing), plays a key role in 5G fronthaul.

The following are the main applications of passive WDM in 5G fronthaul:

1. Cost saving:

Passive WDM does not require power supply and complex management systems, which can greatly reduce the total cost of ownership (TCO).

2. Bandwidth efficiency:

 Passive WDM can combine multiple wavelengths on a single fiber to provide higher bandwidth and support multiple 5G cells or gNodeB sites.

3. Simplified deployment:

 Since passive WDM does not require power supply and complex configuration, deployment becomes simpler and faster.

4. Increase fiber capacity:

In places where fiber resources are limited, passive WDM can help network operators maximize existing fiber assets, thereby avoiding expensive new fiber laying.

5. Meet multi-site requirements:

5G networks require more cells or sites than previous networks. Using passive WDM technology, multiple sites can be supported on a single fiber, reducing fiber and hardware requirements.

6. Reliability and Stability:

 Passive WDM solutions are generally more reliable and stable due to the lack of moving parts and power requirements.

7. Support C-RAN architecture:

 5G fronthaul solutions are usually based on the centralized radio access network (C-RAN) architecture, in which the remote radio head (RRH or RU) is linked to a centralized baseband unit (BBU) through the fronthaul. Passive WDM is a key technology in this architecture because it can connect multiple RRHs to a pool of BBUs without requiring large amounts of fiber.

Overall, passive WDM technology provides an efficient, reliable and cost-effective solution for 5G fronthaul to support the high bandwidth, low latency and high connection density requirements in 5G networks.