The principle and function of optical transceiver

A fiber optic transceiver is an Ethernet transmission media conversion unit that interchanges short-distance twisted-pair electrical signals with long-distance optical signals, and is also referred to as a photoelectric converter in many places. Enterprises in the information infrastructure, usually pay more attention to routers, switches and even network cards and other network equipment for node data exchange, but often ignore the medium conversion of this non-network core but essential equipment. Especially in some government agencies and enterprises that require high degree of informationization and large data traffic, the network construction needs to be directly connected to the backbone network using optical fiber as the transmission medium, and the transmission medium of the internal LAN of the enterprise is generally copper wire, ensuring A media conversion device in which packets are smoothly transmitted between different networks becomes a necessity.

At present, there are many manufacturers of fiber optic transceivers in foreign and domestic countries, and the product line is also extremely rich. In order to ensure full compatibility with other manufacturers' network devices such as network cards, repeaters, hubs and switches, optical transceiver products must strictly comply with the IEEE802.3 Ethernet standard. In addition, the EMC should comply with FCC in terms of electromagnetic radiation protection. And CE regulations, such as FiberHome's fiber optic transceivers have passed FCC and CE certification. Nowadays, due to the construction of residential networks, campus networks and enterprise networks by major domestic operators, the use of optical transceiver products is also constantly improving to better meet the construction needs of access networks. With the rapid development of informatization construction, people's demand for multimedia communication such as data, voice and image is growing, and the Ethernet broadband access method has been mentioned as an increasingly important position. However, the traditional Category 5 cable can only transmit Ethernet electrical signals by 100 meters, which cannot meet the needs of the actual network environment in terms of transmission distance and coverage. At the same time, fiber-optic communication has been widely used in large-scale networks such as wide area networks because of its large information capacity, good confidentiality, light weight, small size, no relay, and long transmission distance. In some large-scale enterprises, the optical fiber directly uses the optical fiber to establish a backbone network for the transmission medium, and the transmission medium of the internal local area network is generally a copper wire. How to realize the connection between the local area network and the optical fiber backbone network? This requires conversion between different ports, different lines, and different fibers and guarantees link quality. The emergence of fiber optic transceivers converts twisted pair electrical and optical signals to each other, ensuring smooth transmission of data packets between the two networks. At the same time, it extends the transmission distance limit of the network from 100 meters of copper wire to more than 100 kilometers (single mode fiber).

Structure of Optical Transceiver The optical transceiver includes three basic functional modules: an optical medium conversion chip, an optical signal interface (optical transceiver module) and an electrical signal interface (RJ45). If equipped with a network management function, the network management information processing unit is also included.

The main performance indicators of photoelectric dielectric conversion chips are:
1. Network management function Network management is the guarantee of network reliability and is a way to improve network efficiency. The functions of network management, operation, management and maintenance can greatly increase the available time of the network and improve network utilization, network performance, service quality and security. And economic benefits. However, the manpower and material resources required to develop Ethernet fiber optic transceivers with network management functions far exceed the similar products without network management, mainly in:
(1) Hardware investment. The implementation of the Ethernet fiber transceiver network management function requires configuring a network management information processing unit on the transceiver circuit board to process the network management information, and the unit uses the management interface of the medium conversion chip to obtain management information. Management information shares data channels with normal data on the network. Ethernet fiber optic transceivers with network management functions, the types and quantities of components are more than similar products without network management. Correspondingly, the wiring is complicated and the development cycle is long. FiberHome Networks has long been committed to the development of fiber optic transceiver products. In order to optimize product design, make products more stable, and enhance product functions, the company has independently developed fiber-optic transceiver media conversion chips to make products more integrated and effectively reduced. Unstable factors caused by the synergy between multiple chips. The newly developed chip has many practical functions such as online test of fiber line quality, fault location, ACL, etc., which can effectively protect user investment and greatly reduce the maintenance cost of users.
(2) Software investment. In addition to hardware cabling, software programming is more important than network management. The development of network management software is relatively large, including the graphical user interface part, the embedded system part of the network management module, and the information processing unit of the transceiver circuit board. Among them, the network management module embedded system is particularly complicated, and the research and development threshold is high, and it is necessary to use an embedded operating system, such as VxWorks, linux, and the like. Need to complete SNMP agent, telnet, web and other complex software work.
(3) Commissioning work. The debugging of the Ethernet fiber optic transceiver with network management function includes two parts: software debugging and hardware debugging. Any factor in board layout, component performance, component soldering, PCB quality, environmental conditions, and software programming can affect the performance of the Ethernet fiber optic transceiver during debugging. The commissioning personnel must have a comprehensive quality and fully consider the various factors that cause the transceiver to malfunction.
(4) Input of personnel. The design of a normal Ethernet fiber optic transceiver can be done with just one hardware engineer. The design of the Ethernet fiber optic transceiver with network management function requires the hardware engineer to complete the circuit board layout, and also requires many software engineers to complete the network management programming, and requires the hardware and software designers to closely cooperate.

2. compatibility
OEMC should support common network communication standards such as IEEE802 and CISCO ISL to ensure good compatibility of Ethernet fiber transceivers.

3. Environmental requirements
a. Input and output voltage. OEMC's operating voltage is mostly 5 volts or 3.3 volts, but the other important component of the Ethernet fiber optic transceiver - the optical transceiver module operating voltage is mostly 5 volts. If the operating voltages of the two are inconsistent, the complexity of the PCB layout will increase.
b. Operating temperature. When choosing the operating temperature of the OEMC, the developer needs to start from the most unfavorable conditions and leave room for it. For example, the maximum temperature in summer is 40 °C, and the internal parts of the Ethernet fiber optic transceiver chassis are heated due to various components, especially OEMC. Therefore, the upper limit of the operating temperature of the Ethernet fiber transceiver should not be lower than 50 °C.
(1) Hardware investment. The implementation of the Ethernet fiber transceiver network management function requires configuring a network management information processing unit on the transceiver circuit board to process the network management information, and the unit uses the management interface of the medium conversion chip to obtain management information. Management information shares data channels with normal data on the network. Ethernet fiber optic transceivers with network management functions, the types and quantities of components are more than similar products without network management. Correspondingly, the wiring is complicated and the development cycle is long. FiberHome Networks has long been committed to the development of fiber optic transceiver products. In order to optimize product design, make products more stable, and enhance product functions, the company has independently developed fiber-optic transceiver media conversion chips to make products more integrated and effectively reduced. Unstable factors caused by the synergy between multiple chips. The newly developed chip has many practical functions such as online test of fiber line quality, fault location, ACL, etc., which can effectively protect user investment and greatly reduce the maintenance cost of users.
(2) Software investment. In addition to hardware cabling, software programming is more important than network management. The development of network management software is relatively large, including the graphical user interface part, the embedded system part of the network management module, and the information processing unit of the transceiver circuit board. Among them, the network management module embedded system is particularly complicated, and the research and development threshold is high, and it is necessary to use an embedded operating system, such as VxWorks, linux, and the like. Need to complete SNMP agent, telnet, web and other complex software work.
(3) Commissioning work. The debugging of the Ethernet fiber optic transceiver with network management function includes two parts: software debugging and hardware debugging. Any factor in board layout, component performance, component soldering, PCB quality, environmental conditions, and software programming can affect the performance of the Ethernet fiber optic transceiver during debugging. The commissioning personnel must have a comprehensive quality and fully consider the various factors that cause the transceiver to malfunction.
(4) Input of personnel. The design of a normal Ethernet fiber optic transceiver can be done with just one hardware engineer. The design of the Ethernet fiber optic transceiver with network management function requires the hardware engineer to complete the circuit board layout, and also requires many software engineers to complete the network management programming, and requires the hardware and software designers to closely cooperate.

By rate
Can be divided into single 10M, 100M, 1000M fiber optic transceiver, 10/100M adaptive, 10/100/1000M adaptive fiber optic transceiver. Most of the 10M, 100M, and 1000M transceiver products work at the physical layer, and the transceiver products that work at this level are bit-wise to forward data.
The forwarding mode has the advantages of fast forwarding speed and low delay, and is suitable for being applied to a fixed rate link. The 10/100M and 10/100/1000M fiber transceivers work at the data link layer and use the store-and-forward mechanism. The forwarding mechanism reads its source MAC address and destination MAC address for each packet received. The address and data payload, and the packet is forwarded after the CRC cyclic redundancy check is completed.
The advantage of store-and-forward can prevent some erroneous frames from propagating in the network, occupying valuable network resources, and can also prevent packet loss caused by network congestion. When the data link is saturated, store-and-forward can not be used. The forwarded data is first placed in the buffer of the transceiver, and then forwarded when the network is idle. This not only reduces the possibility of data collision but also ensures the reliability of data transmission. Therefore, 10/100M and 10/100/1000M optical transceivers are suitable for working on links with fixed rates.

The development of optical transceivers With the sharp increase in the demand for network capacity, operators are increasingly demanding network management, Ethernet transmission speeds are constantly upgrading, and the types and complexity of optical transceivers are developing at an alarming rate.

Due to the cost reduction of fiber technology and the increase in capacity requirements, many telecom companies, local governments, and even large enterprise groups have begun to apply fiber optic technology to urban area network (MAN) applications. As a result, fiber-optic link technology, once confined to long-haul and high-end backbone networks, is now available in every corner of the network. However, the rapid increase in the number of fiber link applications has also led to a wide variety of fiber optic transceivers, sometimes even contradictory.

The choice of fiber optic transceiver components In the design of Ethernet fiber optic transceivers, the choice of components is important, which determines the performance, life and cost of the product. An optoelectronic media conversion chip (OEMC) is the heart of the entire transceiver. Choosing a media conversion chip is the first step in the design of an Ethernet fiber optic transceiver and is a very important step. Its choice directly affects and determines the choice of other components.

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