With the development of 10 Gbit/s Ethernet technology, traditional 10 Gbit/s optical transceiver modules have been unable to further increase the access density of ports, and the power loss and crosstalk problems brought by this low port density method also affect 10 Gbit/s optical transceiver modules.
The process of marketization of Gbit/s technology. In this case, the new SFP+ SR optical transceiver module provides a more cost-effective 10 Gbit/s solution.
This paper will start from the working principle of the 10G SFP+ SR optical transceiver module, analyze its hardware circuit and software control implementation, and study the APC (automatic power control) of the optical transmitter unit and the intelligent control of the extinction ratio temperature compensation.
Through the test of photoelectric performance, the feasibility of applying a 10 Gbit/s optical transceiver module to a 10 Gbit/s optical transmission network is verified.
10GBASE-SR Optical Transceiver Module System Implementation Scheme
The implementation scheme of 10G SFP+ SR optical transceiver module can be divided into three categories: receiving unit, transmitting unit and control circuit unit
Receiving Part of 10GBASE-SR SFP+
The light receiving unit of 10GBASE-SR uses a photodetector that integrates a PIN and a TIA (transimpedance amplifier) to process the received light signal.
The 10 Gbit/s optical signal is converted into an electrical signal with a signal amplitude of about 450 mVpp after passing through the detector, and then amplified into 10 Gbit with an adjustable amplitude of 600-900 mVpp through a limiting amplifier with a gain coefficient of 40 dB in the latter stage high-speed serial electrical signal output.
The receiving part can also realize the control of the limiting amplifier through the communication interface inside the SFP+ module, and perform pre-emphasis processing on the 10 Gbit/s high-speed electrical signal to increase the channel length of the reliable transmission signal.
Transmitting Part of 10GBASE-SR SFP+
The light emitting unit of 10GBASE-SR is mainly composed of direct modulation DFB-LD (distributed feedback semiconductor laser) and laser driver. 10 Gbit/s electrical signal input by SFI interface.
It is input to the laser driver through a 100Ω differential transmission line, and after output by the laser driver, it is coupled with the front-end DFB laser through a 50Ω differential transmission line by means of AC coupling (AC-Couple). Finally, the 10 Gbit/s electrical signal is converted into an optical signal output by a DFB laser.
Because the slope efficiency (Slope Efficiency) of DFB lasers varies with temperature, APC and extinction ratio compensation circuits are required to achieve the stability of its operation.
The APC Circuit of 10GBASE-SR SFP+
The APC circuit of 10GBASE-SR directly uses the detection of optical power/voltage to realize the compensation of the laser bias current.
First, the value of the photocurrent is detected by the high-side current detection circuit, and then it is converted into a detected voltage value and fed back to the MCU (microcontroller) through the sampling resistor.
The MCU controls the D/A (digital/analog) through the detected feedback value. output, thereby adjusting the magnitude of the bias current to stabilize the value of the output optical power of the laser. The whole process is realized by a closed-loop circuit.
The 10G SFP+ SR optical transceiver module adopts the design of moving the CDR (clock and data recovery) part out of the module, which not only reduces the power consumption of the module, but also saves the cost.
From the experimental results, its optical interface performance index meets the application requirements of 10 Gbit/s Ethernet.
At the same time, in order to adapt to the corresponding optical interface link, the SFI electrical interface has strengthened electromagnetic shielding and signal protection on the circuit, and its performance is also In full compliance with the provisions of the SFF-8431 protocol.
The 10G SFP+ SR optical transceiver module can be industrialized and become a miniaturized, hot-swappable optical transceiver module for a new generation of 10 Gbit/s transmission systems.