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. 

What is Optical Circulator in Optical Communication?

Optical circulator is a multi-port optical device with nonreciprocal property. It is based on the nonreciprocal polarization of an optical signal by Faraday effect. When an optical signal is input from any port, it can be output from the next port sequentially with very low loss, and the loss from this port to all other ports is very large, so these ports are not communicating with each other.

That means that optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. If light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3. This is analogous to the operation of an electronic circulator.

 

Fiber-optic circulators are used to separate optical signals that travel in opposite directions in an optical fiber, for example to achieve bi-directional transmission over a single fiber. Because of their high isolation of the input and reflected optical powers and their low insertion loss, optical circulators are widely used in advanced communication systems and fiber-optic sensor applications.

 

Optical circulators are non-reciprocal optics, which means that changes in the properties of light passing through the device are not reversed when the light passes through in the opposite direction. This can only happen when the symmetry of the system is broken, for example by an external magnetic field. A Faraday rotator is another example of a non-reciprocal optical device, and indeed it is possible to construct an optical circulator based on a Faraday rotator.

 

Structure Principle
It consists of a Faraday rotator and two polarizing prisms on both sides. When polarized light passes through a Faraday rotator, its polarization plane can rotate 45°under the action of an external magnetic field. As long as the optical axes of the two polarizing prisms are set at an appropriate angle to each other, the insertion loss of the inter-connected optical paths can be very low and the isolation of the disconnected optical path is very large.

 

The optical circulator can also be formed by utilizing the characteristics of the single-mode fiber will produce the Faraday rotation effect under the action of an external magnetic field. The insertion loss and isolation of the polarization-independent optical circulator are independent of the polarization state of the incident light.

 

Technical Parameters
The technical parameters of optical circulator include insertion loss, isolation, crosstalk, polarization dependent loss(PDL), polarization mode dispersion(PDM) and return loss, etc. The definitions of insertion loss, isolation, polarization dependent loss and polarization mode dispersion of optical circulators are basically the same as those of optical isolators, except that for an optical circulator, it refers to a specific index between two adjacent ports.

What Is Optical Communication?

 Optical communication is any type of communication in which light is used to carry the signal to the remote end, instead of electrical current. The transmitted information is firstly converted into an electrical signal in the transmitting end, and then the electrical signal is modulated onto the laser beam emitted by the light source, so that the light intensity changes with the frequency of electrical signal. Based on the principle of total internal reflection, the light signal is transmitted in optical fiber.

Due to the loss and dispersion of the optical fiber, the optical signal will be attenuated and distorted over a long distance transmission. It is necessary to amplify the attenuated signal at the optical repeater and repair the distorted waveform. At the receiving end, the detector converts the optical signal into an electrical signal after receiving it, the original information will be restored after demodulation. 

 

Advantages of Optical Transmission

• Large Capacity and Long Transmission Distance
• Small Size, Light Weight, Long Life and Low Cost
• High Insulation and High Voltage Resistant
• High Temperature and Anti-corrosion
• Strong Adaptability and High Confidentiality

 

Optical communication consists of a series of optical communication devices. There are active devices and passive devices. Optical active devices are key devices in optical communication systems that convert electrical signals into optical signals or convert optical signals into electrical signals. Optical passive devices mainly include optical fiber patch cables, wavelength division multiplexers(WDM), optical splitters, optical switches, optical circulators and optical isolators, etc.

 

Optical fiber patch cord is a fiber optic cable with connectors at both ends to realize the connection of optical path. The cable with only one connector is called pigtail.

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths. This technique enables bidirectional communications over a single strand of fiber, also called wavelength-division duplexing, as well as multiplication of capacity.

 

A optical splitter is an optical device that splits a beam of light in two or more. There are two types of splitters: FBT couplers and PLC splitters.

 

Optical Switch is a device that switches or amplifies optical signals. It is mainly used to realize the physical switching of optical signal or other logical operation in optical path, and is often used as the key device of optical cross connection (OXC) technology to switch optical path.

An optical circulator is a three- or four-port optical device designed such that light entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3.

 

An optical isolator is an optical component which allows the transmission of light in only one direction. The working principle is based on the non-reciprocity of Faraday rotation. Optical Isolator is typically used to prevent unwanted feedback into an optical oscillator, such as a laser cavity.

Rack Optical Switch, Rackmount Fiber Optical Switches|GlsunMall

GLSUN Rackmounted optical switch is a kind of optical path control and switching device to choose working optical path switch manually with button and also control optical path switch or scan in frequency the optical switch which need to be monitored with RS 232 port and Ethernet port.

GLSUN MEMS 1xN Optical Switch

GLSUN MEMS 1xN optical switch is based on micro-electro-mechanical system, which uses optical micro mirrors or optical micro-mirror arrays to change the propagation direction of light beam to achieve optical path switching. This 1xN MEMS Optical Switch is mainly used for DWDM networks, channel monitor and R&D in laboratory.

All-Optical Switches: MEMS vs Mechanical Switches in Fiber Optical Network

In the optical fiber communication system, the Optical Switch (OS) is mainly used to realize the physical switching of optical signals or other logical operations in the optical path, and is mostly used in the optical cross-connect (OXC) technology as a key device for switching the optical path.

Types of Optical Switches

According to the number of input and output ports of the optical switch, it can be divided into 1x1, 1x2, 1xN , 2x2, 2xN, MxN, etc. Thus optical switch has one or more transmission windows for different uses in different occasions.

Classified from the manufacturing process, optical switches can be divided into mechanical optical switches, thermo-optical switches, acousto-optical switches, electro-optical switches, magneto-optical switches, liquid crystal optical switches and MEMS optical switches, etc. Among them, mechanical optical switches and MEMS optical switches are two widely used optical switches.

Mechanical Optical Switches

The mechanical/optomechanical switch may be regarded as the oldest type of optical switches. The working principle of the mechanical optical switch is to redirect the optical signal by physically moving the optical fiber with the aid of a mechanical device. By moving the prism or the directional coupler, the light at the input end is directed to the required output port. There are three main types of mechanical optical switches: one is to use prism to switch the optical path technology, the other is to use mirror switching technology, and the third is to switch the optical path by moving optical fibers. Read more on All-Optical Switches: MEMS vs Mechanical Switches in Fiber Optical Network.