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Views: 399 Author: Anna Publish Time: 2024-07-03 Origin: Site
SFP (Small Form Factor Pluggable) is a compact, hot-swappable transceiver module that converts electrical signals into optical signals (and vice versa), enabling long-distance communication between devices. One of the main advantages of SFP modules is their hot-swappable nature, which allows them to be inserted or removed without powering down network devices.
In networking, SFP stands for Small Form Factor Pluggable. It refers to a compact, hot-swappable transceiver module used to provide data transmission over various media, such as fiber-optic cables or copper cables.
SFP modules support different data rates (e.g., 1Gbps, 10Gbps) and can handle a range of transmission distances, from short-distance multimode fiber to long-distance single-mode fiber.
The sending optical port inputs an electrical signal with a certain bit rate. After being processed by the internal driver chip, the driver's semiconductor laser diode (LD) or light-emitting diode (LED) emits a modulated optical signal with the corresponding bit rate. When the optical signal reaches the receiving optical port through the optical fiber, it is converted back into an electrical signal by the photodetection diode and output at the corresponding bit rate after passing through the preamplifier.
Figure 1-1 Working principle of an SFP module
There are many types of SFP modules, and their appearance and structure are different. However, the basic structure of an SFP module includes some common components, as shown in Figure 1-2.
Figure 1-2 Appearance and structure of an SFP modul
Table 1-1 Structure of an SFP module
Component | Description |
1.Dust plug | Protects optical fiber connectors, optical fiber adapters, optical bores of optical modules, and ports of other devices from extemal polltion and damage. |
2.Spring | Ensures a proper connection between the optical module and the optical port of the device. lt exists only on an SFP optical module. |
3.Label | Displays key parameters and vendor information of an optical module |
4.Connector | Connects the optical module to a board for transmiting signals and supplying power to the optical module. |
5.Shell | Protects internal components. There are two types of shells. 1*9 shell and SFP shell. |
6.Receive optical bore (Rx) | Receives optical signals. |
7.Transmit optical bore (Tx) | Ransmits optical signals |
8.Latch | Used to remove or insert an optical module. For easy identification, the color of the latch varies according to the band. |
We can measure the performance of SFP modules through their key indicators. These key indicators are introduced below for your better understanding.
Average transmit power refers to the optical power output by the light source at the transmitter end of the SFP module under normal working conditions, which can be understood as luminous intensity. The transmit power is related to the proportion of signal 1 in the transmitted data signal. The more signal 1s, the greater the optical power. When the transmitter sends a pseudo-random sequence signal, the number of signal 1s is approximately equal to the number of signal 0s. The power obtained by the test at this time is the average transmit power, in units of W, mW or dBm. W and mW are linear units, dBm is a logarithmic unit, and dBm is usually used to represent optical power in communications.
The extinction ratio refers to the minimum ratio of the average optical power when the laser sends all 1s (luminous) to the average optical power when the sent signal is all 0 (non-luminous) in full modulation mode. The extinction ratio combines these two parameters to express the ability to identify signal 0 and signal 1. Therefore, the extinction ratio can be regarded as a measure of the working efficiency of the laser. The typical minimum extinction ratio is between 8.2dB and 10dB. As shown in Figure 1-3, the laser at the transmitting end of the optical module converts the electrical signal into an optical signal according to the bit rate of the input electrical signal.
Figure 1-3 Working principle of a laser
The central wavelength is the wavelength measured at the midpoint of the half-amplitude line in the emission spectrum. Different types of lasers or two lasers of the same type may have different central wavelengths due to factors such as process and production process. Even for the same type of laser, the central wavelength may be different under different conditions. Generally, optical device and optical module manufacturers will provide central wavelength parameters, and their values are generally a range. There are currently three commonly used central wavelengths of optical modules: 850nm, 1310nm, and 1550nm.
Why are these three bands defined? This is related to the optical fiber loss of the optical signal transmission medium. After continuous research and experiments, it was found that as the wavelength increases, the optical fiber loss may decrease. The optical fiber loss at a wavelength of 850nm is small, while the loss at a wavelength of 900~1300nm increases. The optical fiber loss begins to decrease at a wavelength of 1310nm, is the lowest at a wavelength of 1550nm, and has a tendency to increase at wavelengths of 1650nm and above. Therefore, 850nm is a short wavelength window, and 1310nm and 1550nm are long wavelength windows.
Overload optical power, also known as saturated optical power, refers to the maximum average input optical power that can be received by the receiver of an SFP module under a certain bit error rate (BER, which is usually 10-12). The unit is dBm.
Note that the photodetector will have saturated photocurrent when exposed to strong light. When this occurs, the photodetector needs some time to recover. In this case, the receiver sensitivity decreases, and the received signals may be misjudged, causing bit errors. Simply speaking, if the input optical power exceeds the overload optical power, the device may be damaged. Therefore, avoid direct exposure to strong light to prevent the input optical power from exceeding the overload optical power.
The receiver sensitivity refers to the minimum average input optical power that can be received by the receiver of an SFP module under a certain BER (BER = 10-12). If the transmit optical power refers to the luminous intensity at the transmit end, the receiver sensitivity refers to the luminous intensity that can be detected by the SFP module. The unit is dBm.
Generally, a higher rate indicates poorer receiver sensitivity. That is, a higher minimum receive power means higher requirements on the receiver of an SFP module.
The receive power refers to the average optical power range that can be received by the receiver of an SFP module under a certain BER (BER = 10-12). The unit is dBm. The upper threshold of the receive power is the overload optical power, and the lower threshold is the maximum receiver sensitivity.
In general, when the receive power is lower than the receiver sensitivity, the signals may not be received normally because the optical power is too weak. When the receive power is greater than the overload optical power, signals may fail to be received because of bit errors.
The interface rate is the maximum rate of electrical signals that an optical component can transmit without bit errors. The interface rates defined in Ethernet standards include 125 Mbit/s, 1.25 Gbit/s, 10.3125 Gbit/s, and 41.25 Gbit/s.
The transmission distance of an SFP module is limited by loss and dispersion. The loss of light energy is caused by absorption and dispersion of the medium and the leakage of optical signals when optical signals are transmitted over the optical fiber. This part of energy is dissipated at a certain rate as the transmission distance increases. Dispersion is generated because electromagnetic waves of different wavelengths are transmitted at different speeds in the same medium. As a result, different wavelength components of optical signals arrive at the receive end at different time points due to the accumulation of transmission distances. As a result, pulses are broadened and signal values cannot be identified.
The dispersion-limited distance of the SFP module is far greater than the loss-limited distance. Therefore, the dispersion-limited distance can be ignored. The loss-limited distance can be estimated according to the following formula: Loss-limited distance = (Transmit power – Receiver sensitivity)/Optical fiber attenuation. The attenuation of optical fibers is strongly related to their types.
To meet various transmission rate requirements, modules with different rates are provided, including 10Gb/s、25Gb/s、50Gb/s、100Gb/s、400Gb/s optical modules.
A higher transmission rate depends on a more complex structure. Different form factors in different structures are provided for varying transmission rates. switches support optical modules of the following form factors: Small Form-factor Pluggable (SFP)/Enhanced Small Form-factor Pluggable (eSFP), SFP+, SFP28, Quad Small Form-factor Pluggable Plus (QSFP+), 120 Gb/s eXtended-capability Form Factor Pluggable (CXP), Centum Form-factor Pluggable (CFP), QSFP28, and QSFP-Double Density (QSFP-DD).
Table 1-2 Classification by transmission rate
Form Factor | Description |
SFP/eSFP | An SFP optical module supports LC fiber connectors. An eSFP optical module is an enhanced SFP optical module that supports monitoring of voltage, temperature, bias current, transmit power, and receive power. Currently, eSFP and SFP optical modules are both called SFP optical modules. |
SFP+ | An SFP+ optical module is an SFP optical module with a higher rate. It is more sensitive to electromagnetic interference (EMI) because of a higher rate. To reduce EMI, SFP+ optical modules have more springs than SFP optical modules and the cages for SFP+ modules on a card are tighter. |
SFP28 | Its form factor size is the same as that of an SFP+ optical module. An SFP28 port can use a 25GE SFP28 optical module or 10GE SFP+ optical module. |
QSFP+ | A QSFP+ optical module supports MPO fiber connectors and is larger than an SFP+ optical module. |
CXP | A CXP optical module is a hot-pluggable high-density parallel optical module, which provides 12 channels of traffic in each of the Tx and Rx directions. It applies only to short-distance multimode links. |
CFP | CFP is a new optical module standard that supports high-speed transmission in data communication and telecommunications fields. The dimensions of a CFP optical module are 13.6 mm x 144.75 mm x 82 mm (H x W x D). |
QSFP28 | Its form factor size is the same as that of QSFP+. Currently, 100GE QSFP28 optical modules and 40GE QSFP28 optical modules are available. |
QSFP-DD | A QSFP-DD optical module is a high-speed pluggable module defined by the QSFP-DD MSA group. |
Optical fibers are classified into single-mode and multimode fibers. Therefore, optical modules are also classified into single-mode and multimode modules to support different optical fibers.
Single-mode optical modules have a typical center wavelength of 1310 nm or 1550 nm, and are used with single-mode fibers. Single-mode fibers support a wide band and large transmission capacity, and are used for long-distance transmission.
Multimode optical modules have a typical center wavelength of 850 nm, and are used with multimode fibers. Multimode fibers have lower transmission performance than single-mode fibers because of modal dispersion, but are more cost-effective. They are used for small-capacity, short-distance transmission.
The operating wavelength of an optical module is a range. To facilitate description, the center wavelength is used, in unit of nm.
To support transmission of optical signals in different optical bands, optical modules with different center wavelengths, such as 850 nm, 1310 nm, and 1550 nm, are provided.
The biggest difference between colored optical modules and other types of optical modules lies in the center wavelength.
Generally, the center wavelength of an optical module can be 850 nm, 1310 nm, or 1550 nm. The center wavelength of an optical module is simple, and the light is called gray light.
A colored optical module carries light with different center wavelengths. This type of light is called colored light.
Colored optical modules are classified into two types: coarse wavelength division multiplexing (CWDM) and dense wavelength division multiplexing (DWDM). Within the same band, DWDM modules are available in more types and use wavelength resources more efficiently than CWDM modules. DWDM and CWDM modules allow lights with different center wavelengths to be transmitted on one fiber without interfering each other. Therefore, a passive multiplexer can be used to combine the lights into one channel, which is then split into multiple channels by a demultiplexer on the remote end. This reduces the optical fibers required. DWDM and CWDM modules are used for long-distance transmission.
Short Reach SFP Modules:SX (Short Wavelength): For MMF, typically supports distances up to 300 meters.
Medium Reach SFP Modules:LX (Long Wavelength): For SMF, typically supports distances up to 10 kilometers.
Long Reach SFP Modules:EX (Extended Wavelength): For SMF, typically supports distances up to 40 kilometers.
ZX (Extended Reach): For SMF, typically supports distances up to 80 kilometers.
CWDM/DWDM SFP Modules: Used in wavelength-division multiplexing (WDM) systems to transmit multiple signals over the same fiber using different wavelengths, suitable for high-bandwidth and long-distance transmission applications.
BiDi (Bi-directional) SFP Modules: Use a single fiber for bidirectional transmission by employing different wavelengths at each end of the same fiber, suitable for scenarios requiring fiber resource savings.
Special Types
Fiber Channel SFP Modules: Used in Fiber Channel storage networks, supporting various speeds such as 2 Gbps, 4 Gbps, 8 Gbps, etc.
PON (Passive Optical Network) SFP Modules: Used in PON systems for Fiber-to-the-Home (FTTH) applications.
These types of SFP modules are chosen based on specific requirements, catering to various network environments and application needs.
Optical modules are classified by their operating temperature ranges into commercial grade and industrial grade. These categories are based on the modules' stable performance and reliability in different environmental temperatures.
Commercial Grade:
Temperature Range: 0°C to 70°C
Applications: Commercial grade optical modules are typically used in data centers, enterprise networks, and telecom rooms where the environment is temperature-controlled.
Features: They operate well in stable temperature environments and are relatively cost-effective.
Industrial Grade:
Temperature Range: -40°C to 85°C
Applications: Industrial grade optical modules are suitable for harsh environments, such as outdoor communication facilities, industrial automation systems, and deployments in extreme climates.
Features: They have stronger resistance to environmental interference and higher reliability, functioning normally under extreme temperature conditions. These modules are generally more expensive.
These different grades of optical modules cater to the needs of various application scenarios. Selection should be based on specific usage environments and performance requirements.
SFP modules are used to interconnect fiber optic cables with network switches and other communication equipment such as industrial Ethernet switches and media converters. This hot-swappable device allows the user to equip the interface port with any suitable type of transceiver, which is usually required for fiber optic connections.
SFP (Small Form Factor Pluggable) optical module is a packaging technology commonly used for high-speed fiber optic communications in computer networks. It is a small, hot-swappable optical transceiver module widely used in data communication operations. There are many types of SFP optical modules, including BIDI-SFP, electrical port SFP, CWDM SFP, DWDM SFP, SFP+ optical modules, etc. These modules support different transmission rates up to 10G (such as SFP+ modules) and commonly use LC interfaces. The main features of SFP modules are portability, flexibility and easy upgrade.
