1. Definition of optical transceiver module
The integrated optical transceiver module is composed of optoelectronic devices, functional circuits and optical interfaces. The optoelectronic devices include two parts: transmitting and receiving. The transmitting part is: the input electrical signal with a certain code rate is processed by the internal driver chip to drive the semiconductor laser (LD) or light emitting diode (LED) to emit a modulated optical signal of the corresponding rate, and it has an automatic optical power control circuit inside. The output optical signal power remains stable. The receiving part is: the optical signal with a certain code rate is converted into an electrical signal by the light detection diode after being input into the module. After the preamplifier, the electrical signal of the corresponding code rate is output, and the output signal is generally PECL level. At the same time, when the input optical power is less than a certain value, an alarm signal will be output.
2. Classification of optical transceiver modules
According to the rate: 100Base (100M), 1000Base (Gigabit), 10GE for Ethernet applications
155M, 622M, 2.5G, 10G for SDH applications
According to the package: 1×9, SFF, SFP, GBIC, XENPAK, XFP, see the various packages
1×9 package——welding optical module, the general speed is not higher than gigabit, and SC interface is mostly used
SFF package - welding small package optical modules, the general speed is not higher than gigabit, and LC interface is mostly used
GBIC package - hot-swappable Gigabit interface optical module, using SC interface
SFP package - hot-swappable small package module, currently the highest data rate can reach 4G, mostly using LC interface
XENPAK package - used in 10 Gigabit Ethernet, using SC interface
XFP package - 10G optical module, can be used in 10 Gigabit Ethernet, SONET and other systems, mostly using LC interface
According to laser type: LED, VCSEL, FP LD, DFB LD
According to the emission wavelength: 850nm, 1310nm, 1550nm, etc.
According to the way of use: non-hot-pluggable (1×9, SFF), hot-pluggable (GBIC, SFP, XENPAK, XFP)
Fiber Connectors and Optical Modules
3. Classification and main specifications of optical fiber connectors
Optical fiber connectors are installed on both ends of a section of optical fiber, and are mainly used for optical wiring.
According to the type of fiber: single-mode fiber connector (generally G.652 fiber: fiber inner diameter 9um, outer diameter 125um), multimode fiber connector
According to the connector form of the optical fiber connector: FC, SC, ST, LC, MU, MTRJ, etc., currently commonly used are FC, SC, ST, LC,
FC type - first developed by Japanese NTT. The external reinforcement adopts metal sleeve, and the fastening method is turnbuckle. Test equipment chooses this kind of connector more.
SC type - a molded plug-in coupling connector developed by Japan's NTT company. The shell adopts the molding process and is made of molded glass fiber plastic, which is rectangular; the pin is made of precision ceramics, and the coupling sleeve is a metal slotted sleeve structure. The fastening method adopts the plug-in type and does not need to be rotated.
LC type - the outer diameter of the casing is 1.25mm, which is half of the outer diameter of the commonly used FC-SC and ST casings of 2.5mm. Increase the application density of connectors.
According to the end face of the inner pin of the fiber optic connector connector: PC, SPC, UPC, APC
According to the diameter of the optical fiber connector: Φ3, Φ2, Φ0.9
The performance of optical fiber connectors mainly includes optical performance, interchangeability, mechanical performance, environmental performance and life. The most important of these are insertion loss and return loss.
1. Transmission rate of optical transceiver module: 100M, 1000M, 10GE, etc.
2. Transmitting optical power and receiving sensitivity of the integrated optical transceiver module: Transmitting optical power refers to the light intensity of the transmitting end, and receiving sensitivity refers to the detectable light intensity. Both are in dBm and are important parameters that affect the transmission distance. The distance that an optical module can transmit is limited mainly by loss and dispersion. The loss limit can be estimated according to the formula: loss limited distance = (transmitting optical power - receiving sensitivity) / fiber attenuation.
The fiber attenuation is related to the actual selected fiber. Generally, the current G.652 fiber can achieve 0.5dB/km in the 1310nm band and 0.3dB/km in the 1550nm band or even better. 50um multimode fiber is 4dB/km in the 850nm band and 2dB/km in the 1310nm band. For 100M and 1000M optical modules, the dispersion limitation is far greater than the loss limitation, so it can be ignored.
3. The 10GE optical transceiver module follows the 802.3ae standard, and the transmission distance is related to the type of optical fiber selected and the optical performance of the optical module.
4. The saturated optical power value refers to the maximum optical power that can be detected by the receiving end of the optical module, generally -3dBm. When the received optical power is greater than the saturated optical power, bit errors will also occur. Therefore, there will be bit errors in the loopback test without attenuation for the optical module with high transmit optical power.
5. Important reasons for the failure of optical module functions
The failure of the optical module function is divided into the failure of the transmitter and the failure of the receiver. After analyzing the specific reasons, the most common problems are concentrated in the following aspects:
1. Optical port pollution and damage
Due to the pollution and damage of the optical interface, the loss of the optical link increases, resulting in the failure of the optical link. The reasons are:
A. The optical port of the optical transceiver module is exposed to the environment, and the optical port is polluted by dust entering;
B. The end face of the optical fiber connector used has been polluted, and the optical port of the optical module is polluted twice;
C. Improper use of the end face of the optical connector with pigtails, scratches on the end face, etc.;
D. Use inferior fiber optic connectors;
