Introduction
In the optical communication products, optical module occupies has a very important position. Optical transceiver module as one of the key technologies of optical fiber communication network, is widely used in synchronous optical network SONET) and Synchronous Digital Hierarchy SDH), Asynchronous Transfer Mode (ATM), Fiber Distributed Data Interface (FDDI), as well as Fast Ethernet and thousands Gigabit Ethernet and other systems.
In the present optical communication products, fiber optic transceiver module has been more popular than others, SFP GBIC module module volume ratio reduced by half, but also supports hot-swap capabilities, has been widely used. Meanwhile, in the various existing networks needed optical transceiver module types, more and more requirements are also increasing. To meet the ever increasing performance requirements of the system,Optical module continues to develop intelligent, fast and high-density interconnect direction.
Intelligent SFP optical modules, namely USES the fiber optic sfp module of digital diagnosis function, will become a new generation of optical transceiver module integrated in the window.It can realize network management unit real-time monitoring the temperature of the transceiver module, power supply voltage, bias current, as well as the transmitting and receiving optical power.Through monitoring of these parameters, we can help system administrators predict the life of the light module, fault isolation system and authentication module in the installation of compatibility, etc.
A smart SFP optical module system design
1.1
Transmitting section
The main role of the light-emitting process in the optical transmission module is to convert the optical signal into an electrical pulse signal is a pulse, the electrical signal is input, the output optical signal. Transmitter module, mainly by the laser driving circuit and the TOSA. Which TOSA backlit by the laser diode LD and PD components. LD is used in vertical cavity surface emitting laser VCSEL.
First electrical modulation of the laser drive lasers to meet the input digital fiber optic communications system required drive signal, the drive signal from the bias current Ibias And the modulation current Imod composition, the laser emits an optical signal corresponding to the driving of the driving signal, the optical signal is coupled into the optical fiber and transmitted to the receiving end. In this scenario, the laser driver selection MAX3286.
Laser driver with the functions of automatic power control (APC), APC circuit using the backlight diode in the TOSA, monitoring laser the size of the backlight.When the optical power is less than one rating, through increase the drive current feedback circuit, laser output power increases as the rated power value.Conversely, if the optical power is greater than a certain rating, is through feedback circuit reduce drive current, laser power output is less.APC circuit can dynamically adjust the laser power, therefore, the size of the bias current, can automatically compensate laser due to the change of ambient temperature or aging caused by the change of the output optical power, keep the output optical power range is relatively stable.
Receiving part
The main role of the receiver module is attenuated after
deformation weak optical fiber cable transmission signal to a pulse electric pulse signal by photoelectric conversion, and give sufficient amplification, a standard reduction of the digital pulse signal. Optical receiver module schematic shown mainly by the photodiode PD, a preamplifier, a limiting amplifier and other components. Which photodiode and preamp integrated package together constitute ROSA.
A photodiode is a core device of a digital optical receiver, an optical pulse signal will be the electrical pulse signal by photoelectric conversion, commonly used are PIN photodiodes and avalanche photodiode APD. Optical signal from the optical interface enters the photodiode PD, is converted into a weak current, the current through the pre-amplifier and converted into a voltage level is amplified to an appropriate level.
Effect limiting amplifier output of the preamplifier is the magnitude of different amplitude analog signal into a digital signal, these signals can be amplified. To photoelectric detectors with a good match and get the low-noise and wide-band preamplifier gain is not too high, the preamplifier output voltage amplitude is usually from a few millivolts to tens of millivolts, such small signals can not be directly output optical module is therefore necessary to further enlarge the signal; the other hand, the photodetector detects the light signal from the amplitude of the current signal in a defined tolerance level, the tolerance limits of the capacity of the fiber considered Poor, splice loss and the parameter fluctuations caused by temperature and aging, however, the data for further processing, the signal amplitude is preferably a constant value.
Therefore, limiting amplifier requires a certain dynamic range, which usually requires a dynamic range of more than 20dB.
1.3
Digital Diagnostics DDM part
Digital diagnostics mainly composed of MCU to complete. By temperature MCU, the network management unit may receive real-time monitoring module, the power supply voltage, laser bias current and the light emitting and receiving power. By measuring these parameters, the management unit can quickly identify the specific location of fiber link failure occurs, simplify maintenance, improve system reliability.
Five DDM parameter acquisition circuit for acquisition by the first conversion, the inputs to the ADC, ADC five circuit analog voltage into a digital signal sent by the decoder circuit is stored in a memory support DDM corresponding address bit . Transmission of information via a two-wire serial interface (SCL clock line and data line SDA) to achieve.
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