Advantages and Technologies of All Optical Network

In the existing communication networks based on optical multiplexing, the completion of optical/electrical/optical conversion of each node in the network is still exchanged at the speed of electrical signals processing information. In order to meet the requirements of high speed and large capacity, the electronic components have some disadvantages such as bandwidth limitation, clock offset, serious crosstalk and high power consumption, which brought forth "electronic bottleneck" in communication network. In order to solve this problem, the concept of all-optical network (AON) was put forward. With its good transparency, wavelength routing characteristics, compatibility and scalability, all-optical network has become the first choice of the next generation of high-speed broadband networks.

What is All Optical Network

The all-optical network refers to the whole process of data transmission and exchange from the source node to the end user node are all conducted in the optical domain, that is, end-to-end complete optical path, without the intervention of electrical signals. `

Advantages of All Optical Network

The all-optical communication network based on WDM can enable the communication network to have stronger manageability, flexibility and transparency.  It has the following advantages over the previous communication network and the current optical communication system. 

1. It reduces the use of electronic devices. The flow of optical signal in all-optical network no longer meets the obstacle of photoelectric conversion, which overcomes the difficulty of improving the signal rate of electronic devices on the way, saves a large number of electronic devices, and greatly improves the transmission rate.  

2. It supports multiple protocols. All optical network adopts wavelength division multiplexing technology and selects routing by wavelength, which can provide services of multiple protocols conveniently.

3. It provides high networking flexibility. The all-optical network is very flexible, and a certain wavelength can be extracted or added at any nod

4. It is of high reliability. There is no transformation and storage along the way, and many optical devices in the all-optical network are passive, so it is highly reliable.

Key Technologies in All Optical Network

1. Optical Switching Technology

Optical switching technology can be divided into optical path switching technology and packet switching technology. Optical path switching can be divided into three types, namely, space division (SD), time division (TD) and wave division/frequency division (WD/FD) optical switching, and the combination of these switching forms. In optical packet switching, asynchronous transmission mode is a widely studied mode in recent years.

2. Optical Cross Connection Technology

OXC is a device used in fiber optic network nodes. By cross-connecting optical signals, OXC can flexibly and effectively manage fiber optic transmission networks. It is an important means to achieve reliable network protection/recovery and automatic wiring and monitoring. OXC is mainly composed of optical cross connection matrix, input interface, output interface, management control unit and other modules. To improve OXC reliability, each module has active and standby redundancy structures, and OXC automatically performs active/standby switchover.

3. Optical Add and Drop Multiplexing Technology

In the field of WDM optical networks, more attention is being focused on optical add and drop multiplexers. These devices have the functions of traditional SDH add-and-drop multiplexers (SDHADM) in the time domain in the optical wavelength domain. OADM, in particular, can split a channel from a WDM beam (split function) and generally new information into the optical carrier at the same wavelength ( function). For OADM, there must be a high degree of isolation between the sub-outlet and the insertion port, as well as between the input port and the output port, to minimize the same wavelength interference effect, otherwise the transmission performance will be seriously affected.

4. Fiber Amplifier Technology

Optical amplifier is one of the core technologies for building all-optical communication networks, and also the key element of dense wavelength Division multiplexing (DWDM) systems. The traditional basis of DWDM systems is erbium-doped fiber amplifier (EDFA). The optical fiber has a wide and low loss bandwidth in the 1550 nm window, which can accommodate the optical signals of DWDM to be transmitted on one optical fiber at the same time. After the appearance of EDFA, it quickly replaced the electrical signal regeneration amplifier and greatly simplified the whole optical transmission network.

MUX and DEMUX in WDM

 WDM (Wavelength Division Multiplexing) is to combine a series of optical carrier signals at different wavelengths carrying various information at the transmitter through the Multiplexer and couple them to the same optical fiber for transmission.  At the receiver end, the optical signals are separated from each other by a Demultiplexer. The simultaneous transmission of two or many optical signals of different wavelengths in the same fiber is called Wavelength Division Multiplexing (WDM). WDM technology can double the transmission capacity of a single light, which can easily expand the capacity of existing optical networks. Depending on the direction of the transmitted signal, WDM can be used for multiplexing or demultiplexing.

 

MUX

 

The main function of MUX is to combine multiple signal wavelengths into one optical fiber for transmission. At the transmitter end, N optical transmitters operate at N different wavelengths, which are separated by appropriate intervals. These N light waves are respectively modulated by the signal as carriers and carry the signal. A wave synthesizer combines these different wavelengths of optical carrier signals and couples them into a single-mode fiber. Because the optical carrier signals of different wavelengths can be regarded as independent of each other (without considering the non-linearity of the fiber), the multiplexing transmission of multiple optical signals can be realized in one fiber. Through multiplexing, communication operators can avoid maintaining multiple lines and effectively save operating costs.

 

DEMUX

 

The main function of DEMUX is to separate multiple wavelength signals transmitted in one fiber. At the receiving end, the optical carrier signals of different wavelengths are separated by a demultiplexer, which is further processed by the optical receiver to recover the original signal. A demultiplexer (Demux) is a device that performs reverse processing on a multiplexer.  

 

Performance Parameters of MUX/DEMUX

 

1. Operating Wavelength

 

Multiplexer/demultiplexer operating waveband. For example, 1550 wavelength has three bands: S band (short wavelength band 1460~1528nm), C band (conventional band 1530~1565nm), L band (long wavelength band 1565~1625nm).

 

2. Number of channels & channel spacing

 

Channel number refers to the number of channels that a multiplexer/demultiplexer can combine or separate. This number can range from 4 to 160 to enhance the design by adding more channels. Common channels are 4, 8, 16, 32, 40, 48, etc. Channel spacing is the difference between the nominal carrier frequencies of two adjacent channels and is used to prevent inter-channel interference. According to ITU-T G.692, the channel intervals less than 200GHz(1.6nm) include 100GHz (0.8nm), 50GHz (0.4nm) and 25GHz. Currently, 100GHz and 50GHz channel intervals are preferred.

 

3. Insertion Loss

 

Insertion loss is the attenuation caused by the insertion of WDM in optical transmission system. The attenuation effect of WDM on optical signal directly affects the transmission distance of the system. Generally, the lower the insertion loss, the less signal attenuation.

 

4. Isolation

 

Isolation refers to the isolation degree between signals of each channel. High isolation values can effectively prevent the distortion of transmitted signals caused by crosstalk between signals.

 

5. PDL (Polarization Dependent Loss)

 

PDL refers to the distance between the maximum and minimum loss caused by different polarization states at fixed temperature, wavelength and the same band, namely, the maximum deviation of insertion Loss in all input polarization states.