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What is a Fiber Transceiver? Many users believe that the idea of ​​upgrading a network to a fiber network requires the removal of an existing copper infrastructure. It is a misconception that it prevents many users from upgrading to fiber networks. With fiber optic transceivers that convert signals on copper cables into signals that travel over the fiber, users do not need to make additional settings to introduce the fiber into the network.
A fiber optic transceiver is an Ethernet transmission media conversion unit that exchanges short-distance twisted-pair electrical signals and long-distance optical signals. It is also called a photoelectric converter or fiber converter in many places. . To ensure full compatibility with network devices such as network cards, repeaters, hubs, and switches, fiber transceiver products strictly comply with Ethernet standards such as 10Base-T, 100Base-TX, 100Base-FX, IEEE802.3, and IEEE802.3u.
Fiber-optic transceivers are generally used in the actual network environment where Ethernet cables cannot cover and must use optical fiber to extend the transmission distance. At the same time, they also play a huge role in helping to connect the last mile of optical fiber to the metropolitan area network and the outer network. The role. With fiber-optic transceivers, users who need to upgrade systems from copper to fiber, but lack the funds, labor, or time, offer a cheap solution.
The fiber optic transceivers are classified according to the rate, and the fiber transceivers can be divided into single 10M, 100M fiber transceivers, 10/100M adaptive fiber transceivers, and 1000M fiber transceivers.
The 10M and 100M transceiver products work at the physical layer, and the transceiver products working at this layer are bit-by-bit forwarding data. The forwarding method has the advantages of fast forwarding speed, high transparent rate, low delay, etc., and has better compatibility and stability, and is suitable for being applied to fixed-rate links. The 10/100M optical transceiver is working at the data link layer. At this layer, the optical transceiver uses a store-and-forward mechanism. In this way, the forwarding mechanism must read its source MAC address and destination for every received packet. The MAC address and data payload are not forwarded until the CRC cyclic redundancy check is completed. The benefits of store and forward can prevent some wrong frames from propagating in the network and occupy valuable network resources. It can also prevent data packet loss caused by network congestion. When the data link is saturated, store and forward can not The forwarded data is first placed in the buffer of the transceiver and is forwarded when the network is idle. This not only reduces the possibility of data collisions but also guarantees the reliability of data transmission. Therefore, a 10/100M fiber transceiver is suitable for operating on a link with a non-fixed rate.
According to the structure, it can be divided into desktop (stand-alone) fiber optic transceivers and rack-type fiber optic transceivers. Desktop fiber optic transceivers are suitable for individual users, such as meeting the uplink of a single switch in a corridor. Rack-mount fiber transceivers are suitable for multi-user aggregation. For example, the center room of a cell must meet the uplink of all the switches in the cell. The use of a rack facilitates the unified management and unified power supply of all modular fiber transceivers.
Divided by optical fiber, can be divided into multimode fiber optic transceivers and single mode fiber optic transceivers. Because of the different fibers used, the distances that the transceivers can transmit are not the same. Multi-mode transceivers typically have transmission distances between 2 and 5 kilometers, while single-mode transceivers can cover distances from 20 to 120 kilometers. It should be pointed out that due to the difference in transmission distance, the transmit power, receiving sensitivity, and the use wavelength of the optical fiber transceiver itself will also be different. The transmission power of a 5 km optical fiber transceiver is generally between -20 to -14 db, the receiving sensitivity is -30 db, and the wavelength of 1310 nm is used; while the transmitting power of a 120 km optical fiber transceiver is mostly between -5 and 0 dB, and the receiving sensitivity is -38dB using a wavelength of 1550nm.
According to the number of optical fibers, they can be divided into single-fiber optical transceivers and dual-fiber optical transceivers. As the name suggests, a single-fiber device can save half of the fiber, that is, the data can be received and transmitted on one fiber, which is very suitable for fiber optic resources. This kind of product adopts wavelength division multiplexing technology, the used wavelength is mostly 1310nm and 1550nm. However, due to the lack of unified international standards for single-fiber transceiver products, there may be incompatibility between different manufacturers' products when they are interconnected. In addition, due to the use of wavelength division multiplexing, single-fiber transceivers generally suffer from large signal loss. Currently, fiber optic transceivers on the market are mostly double-fiber products. Such products are relatively mature and stable.
According to the network management, it can be divided into network management optical transceivers and non-network management optical transceivers. With the development of the network in the direction of operations and management, most operators hope that all devices in their networks can achieve remote network management, and optical transceiver products will gradually develop in the same direction as switches and routers. At present, most vendors' network management systems are developed based on SNMP network protocols and support various management methods including Web, Telnet, and CLI. The management content includes configuring the operating mode of the fiber transceiver, monitoring the module type, working status, chassis temperature, power supply status, output voltage, and output optical power of the optical transceiver. With the increasing demand for network management by operators, it is believed that the network management of optical transceivers will become increasingly practical and intelligent.
Fiber optic transceivers break the 100-meter limitation of Ethernet cables in data transmission, and rely on high-performance switching chips and large-capacity caches to provide real-time non-blocking transmission switching performance while also providing balanced traffic and isolation conflicts. Detect errors and other functions to ensure high security and stability in data transmission. Therefore, fiber transceiver products will remain an indispensable part of the actual network formation for a long period of time. It is believed that future fiber transceivers will continue to develop in the direction of high intelligence, high stability, network management, and low cost.
The development of fiber optic transceivers With the dramatic increase in demand for network capacity, the variety and complexity of optical transceivers are developing at an alarming rate. The IEEE has approved four optical interfaces for future 10G Ethernet standards; the Optical Network Forum has also adopted four optical interfaces for the OC-192 VSR standard (maybe there will eventually be a fifth); the National Information Technology Standards Committee of the United States responsible for fiber networks The T11 specifies 5 optical interfaces for its proposed 10G standard. Moreover, there are a variety of solutions for special optical backplane products. The dramatic increase in optical transceiver applications has led to diversity and the need to continuously develop related technologies to meet this application requirement.
In the late 1990s, copper-based data communications in LANs began to stagnate. With the development of G-class Ethernet networks, this trend is even more pronounced. Due to technical difficulties, the copper version standard was put on hold while the fiber version was passed. As a result, optical transceivers were first applied to LANs on a large scale, and in the proposed 10G Ethernet standard, the IEEE did not specifically include any copper interfaces. Therefore, optical interconnection has become the technology of choice for backbone LANs.
At the same time, the rapidly increasing demand for network capacity has led to the development of switches and routers that are larger than Tb. Typically used in multi-rack links, the links between racks can be as many as several thousand, and each link is no smaller than 10Gb. /s. Copper technology cannot accomplish this task and a new family of optical transceivers needs to be designed to accommodate this application.
Due to the reduction in the cost of fiber optic technology and the increase in capacity requirements, many telecommunications companies, local governments, and even large enterprise groups have begun to apply fiber optic technology to urban area network (MAN) applications. Therefore, optical link technologies that were once limited to long-distance and high-end backbone networks are now available everywhere in the network infrastructure. However, the rapid increase in the number of fiber link applications has also led to a wide variety of optical transceivers, sometimes even contradictory.
The need for a long-range transceiver lies in the long distance. The transceiver must be able to operate 100Km without an amplifier. If there is an amplifier, it should be farther. This type of transceiver generally operates in the 1550 nm band (1530 to 1565 nm), where light energy loss is low and light amplification is relatively easy, so this band is preferred. Remote transceivers also require a narrower linewidth (less than 0.04nm) to reduce dispersion (pulse widening due to different wavelength propagation speeds), and dispersion limits the transmission distance during high-rate data transmission. To meet the above requirements, it is necessary to use remote transceivers with distributed-feed-back Bragg lasers and external modulators to reduce chirp (chirp, laser wavelength change due to laser modulation current).
The MAN transceiver generally operates at a short distance (up to 40Km), so fiber loss is not important, and optical amplification is not required. This broadens the laser wavelength range (1300nm is usable) and reduces the laser source limitation (linewidth can be Relax to 2nm). For links less than 10Km away, external modulation is also not important. MAN transceivers are much cheaper than remote transceivers, but because they are applied to conversion equipment that is sensitive to channel density and power consumption, they should be smaller and have lower power consumption than remote transceivers.
LAN transceivers operate on links that are closer together, usually within a building or between different buildings on a university campus. The maximum distance requirement is typically 2 Km. In this environment, the distance between most links is less than 100m, and multi-mode fiber links are needed, so LAN transceivers can be used with inexpensive 850nm lasers. Since LAN transceivers are a large part of user port devices, these devices must be low-cost, compact, and low-power. Moreover, they are mainly used to design the ports that the user card can access, and should be as small as possible and reduce electromagnetic interference (EMI). LAN transceivers must also be plug-and-play, different from the various transceivers mentioned above.
The backplane transceiver must operate within a short distance (less than 100m) and has the same requirements as the LAN transceiver except for two important differences. Because backplane transceivers are used for proprietary internal links, multiple sources are also important for a particular transceiver, but do not require a standard. Backplane transceivers must have an absolutely large bandwidth density (the transceiver data rate divided by the bandwidth), which is especially important for optical backplane applications because the user bandwidth is limited by the backplane transceiver link bandwidth and the backplane bandwidth is usually The edge of the user card is determined by the space left by the backplane transceiver.
Other factors driving drastic growth in transceivers include various technologies for fiber optic transceivers. There are currently three different types of lasers used: Fabry-Perot (FP), DFB and vertical-cavity surface-emitting-lasers (VCSELS), three wavelength ranges (850 nm, 1300 nm, and 1550 nm), two Fiber types (single-mode and multi-mode), four different transmission technologies (serial, parallel, DWDM, and CWDM). If you consider various combinations, 72 different transceivers are possible without the differences caused by fiber link types and form factors.
FP lasers are easier to fabricate than DFB, but due to the relatively large line width (greater than 1 nm) and temperature drift (0.5 nm/°C), they are not suitable for high speed or long distance applications. The DFB laser has the advantages of narrow linewidth (less than 0.04nm) and small wavelength drift with temperature (0.1nm/°C), which is entirely suitable for high-performance communication applications. However, DFB lasers also have limitations. First, lasers operating in the 1500 nm band are very sensitive to chirp and usually require an external modulator (this limitation is not particularly noticeable at 1300 nm). Second, producing DFB lasers is more difficult than FP lasers or VCSELs. Lastly, DFB lasers require more current. These characteristics make DFB lasers unsuitable for many LAN applications and most optical backplane applications. VCSELs have a relatively narrow linewidth (0.35nm) and a very low wavelength drift (0.06nm/°C). The low current threshold (1mA) is more efficient than the FP and DFB lasers at the same output power and is not as DFB lasers. High buzz. Therefore, VCSELs can be directly modulated even at 10 Gb/s. Finally, it is easier to make and align collimated VCSELs than other lasers, which enables the production of low-cost VCSEL-based transceivers. These features seem to be enough to make VCSELs an ideal solution for high-performance communications applications. However, it still has two significant weaknesses. First, it has been proven by practice that it is very difficult to produce VCSELs that can operate at an appropriate power level in the 1300-1500 nm band, which limits the application of VCSELs to multimode fibers. Second, even though they are more effective than DFB lasers, the problem is that they cannot produce as much power as DFB lasers. These weaknesses and wavelength limitations make VCSELs currently only applicable to short-range LAN applications and optical backplane applications.
The 850nm band (770-860nm) is clearly characterized by large attenuation (3.75dB/Km in older optical fibers), high modality and dispersion in multimode fibers, and laser safety concerns if there is no open fiber Control to -4dBm or higher limits the use of maximum laser power. Transceivers operating at 850 nm cannot be used for single mode fiber (standard 9mm single mode fiber does not support single mode below 1260 nm). These limitations can reduce the working distance of the 850nm band transceiver to 10mb/s to less than 30m, depending on the fiber type. However, because of its low cost, 850nm transceivers are still common in optical backplanes and LAN applications.
The 1300 nm band (1270 to 1355 nm) is clearly characterized by lower attenuation (1.5 dB/Km in multimode fiber, 0.5 dB/Km in single mode fiber), and less dispersion (zero dispersion for standard fiber) Wavelengths range from 1295 to 1365 nm, depending on the fiber type) and lower laser safety concerns (up to 2 dB for first-order operation). In addition, the 1300nm transceiver can be used with standard single-mode fiber, so even when using the worst-case multimode fiber, the 1300nm transceiver operates at distances up to 85m at 10Gb/s and up to 10Km with single-mode fiber. . Therefore, the 1300nm transceiver can be ideally applied to many LANs and some MANs.
The 1500 nm band (1530 to 1565 nm) has the lowest light attenuation (0.36 dB/Km in single-mode fiber), and the optical amplification can also significantly increase the working distance in this band, so the band can be used well for long distances. Application and more distant MAN. However, in general, this band is not used for optical backplanes and LANs, because this range of lasers is extremely expensive to operate.
Single mode fiber is the preferred type for all communication applications larger than 500 meters. Single-mode fiber can more easily support high data rates than multi-mode fiber, but it cannot be assumed that single-mode fiber is suitable for all fiber applications. The single-mode technique requires more precise alignment (less than 1 mm) in the transceiver, which makes its production extremely difficult. And single-mode transceivers cannot use low-cost 850-nm VCSELs because these devices cannot run single-mode fibers. Therefore, in the future when replacing networks, if the fiber cost is lower than expensive single-mode transceivers, multi-mode fiber will have a lot of promise.
For many LAN operators, multimode fiber is still the first choice due to the fact that there are already established networks and that it is easier to operate than single mode fiber. Moreover, most backbone links are very close to the data center, and 10Gb/s is also within the capacity of the multimode fiber, so this kind of low-cost multimode for data center links and fully supports existing network facilities.
About ten years ago, serial transmission was the only optical fiber communication technology with the advantages of simple optics (a light source at one end, a detector at the other end, no need for optical multiplexing and demultiplexing), and simple electronics. But when the bandwidth needs to increase, the two limitations of this technology are very obvious. First, the data flow of each fiber cannot fully utilize the actual capacity of the fiber; second, at high data rates, the required optoelectronic components are difficult to design and manufacture products with higher cost performance.
Using multiple wavelengths, DWDM allows multiple data streams (one wavelength corresponds to one data stream) to be transmitted in a single fiber. The wavelength is compressed in the range of 1530 to 1565 nm to meet the needs of optical amplifiers. More than 100 wavelengths have been compressed. In this range, each wavelength operates at 10 Gb/s, so that DWDM can transmit more than 1 Tb of information in a single fiber. However, this capability requires a specific wavelength laser with a very narrow line width. Moreover, this laser must be able to control the temperature to eliminate wavelength drift. DWDM requires an externally modulated laser to eliminate the chirp and an accurate filtering technique to select the wavelength of the receiver. An optical amplifier and a dispersion compensator are required for extremely long distance transmission. Therefore, in a DWDM system, the single channel (wavelength) cost can be up to 20,000 US dollars. This high cost makes DWDM systems and transceivers generally limited to long-distance systems. In such applications, the cost, difficulty, and time for laying fiber optic cables can easily exceed the cost of DWDM equipment.
With multiple wavelengths, CWDM (Coarse WDM) can also transmit multiple data streams within a single fiber. However, the interval between wavelengths is 10 to 25 nm. Such a large wavelength interval allows a single fiber to accommodate only 8 wavelengths. However, the large wavelength spacing simplifies the design of the optical system because it eliminates the need for a laser that precisely adjusts both wavelength and temperature. Simple optical filtering is sufficient. Due to the limited number of channels, CWDM transceivers can use simple optical systems to fit into a small package. Finally, since CWDM transceivers are typically used for short-range links (up to 10Km), inexpensive, directly modulated lasers, including VCSELs, can be used. All of these features make the 4- to 8-wavelength CWDM transceiver market less than $1,000. In addition, CWDM transceivers can also be packaged in the same size for serial transceivers or transponders.
Parallel optical transceivers transmit data over 12 fibers that form a smaller cable than conventional dual fiber cables, each of which constitutes a data channel. Therefore, for each optical fiber, a 2.5Gb/s parallel optical transceiver operates with an integrated data transmission rate of 30Gb/s. Due to the small size of parallel fiber optic cables and linkers, their transceivers are smaller than traditional transceivers operating at 10 Gb/s. Therefore, parallel optical transceivers have become an optional technology for building optical backplanes.
The main disadvantages of parallel optical fiber technology are the high cost of fiber and linker, parallel optical fiber is about 4-5 US dollars / m, terminal cost is 70 US dollars / end (a single bundle of fiber is about 30 cents / m, the terminal cost is 10- $12 per end). In addition, parallel optical fibers are difficult to set up in the field. Therefore, parallel optical fiber transceivers are generally limited to optical backplane applications, where the bandwidth density is critical, the optical fiber length is relatively short, and it is relatively fixed.
Transceivers currently being developed combine CWDM and parallel fiber technologies, and use parallel fibers to achieve 120Gb/s transmission rates in a single link. The main technology is to use CWDM to multiplex four wavelength lasers onto each of the 12 fibers. This structure enables the system to transmit 48 channels of data at the same time. Each channel has a data transmission rate of 2.5 Gb/s. Up to 120Gb/s. If the data transfer rate is increased to 10 Gb/s and the number of wavelengths per fiber is increased to eight, this multiplexing technique can transmit data over a single parallel fiber at rates up to 960 Gb/s. It is very clear that the combination of these technologies can increase the performance of optical backplanes while reducing the number of required fiber links.
This hybrid technology already has a place in the market, making applications that were previously impossible or extremely expensive. With the application of fiber optic technology to more fields, unique application requirements have led to an increase in the number of transceivers. But the key is to clarify the capacity of the new transceiver and then match the corresponding usage requirements.
What is a fiber optic transceiver and what is it used?
With the rapid development of information construction, people are increasingly demanding for multimedia communications such as data, voice, and images, and Ethernet broadband access has been mentioned to an increasingly important position. However, the traditional Category 5 cable can only transmit 100 meters of Ethernet electrical signals, which can no longer meet the needs of the actual network environment in terms of transmission distance and coverage. At the same time, optical fiber communication has been widely used in large-scale networks such as wide area networks due to its advantages of large information capacity, good confidentiality, light weight, small size, no relay, long transmission distance, and the like. In some large-scale enterprises, when the network is built, the optical fiber is directly used to establish the backbone network for the transmission medium. The transmission medium of the internal LAN is generally a copper line. How to connect the LAN to the fiber backbone network? This requires switching between different ports, different lines, and different fibers and guarantees link quality. The emergence of fiber optic transceivers converts twisted pair electrical signals and optical signals to ensure smooth transmission of data packets between two networks. At the same time it extends the network's transmission distance from 100 meters to 100 kilometers (single-mode fiber).