High-speed And Long-distance Optical Fiber Transmission System And The Hardware Development For High-temperature Environment

Optical fiber transmission technology has been widely used for diverse communications and sensing. Firstly, the low loss and the broad bandwidth of optical fiber enable a long-distance and high-capacity transmission. Moreover, the optical fiber is robust to the electromagnetic interference. However, conventional optical fiber transmission system (especially optical transceiver modules) always work at room temperature or below 85 ℃, which makes it difficult to be used in high-temperature environment (e.g., oil well logging). Thus, an optical communication system working under a high temperature of 110℃ is designed and developed, which can support a duplex communication with a bandwidth of 2 MHz in a transmission distance of 2km.Firstly, the overall system is designed. A bidirectional optical fiber link between the asymmetric structure of optoelectronic transceiver modules under normal and high temperature is established. The master sends command to the slave machine via downlink optical fiber, and the slave immediately collects corresponding data parameters back to the master by the uplink (asymmetric photoelectric modules complete electro-optical and photoelectric conversion), subsequently, the command and data interaction are completed between master and slave machine. Furthermore, decomposition and implementation step by step for tasks of the system scheme are conducted according to the modules and functions. STM32F407 chips, one of the ARM Cortex-M4 core family, are chose as the primary MCU; PCB hardware and circuits are then designed, of which the function is to drive the light emitting diode and to improve the photodiode by following high-temperature characteristics, such as preamplifier, main amplifier and so on; moreover, by selecting the appropriate operational amplifier and improving amplifier circuit, the bandwidth of the normal photodetector can reach up to 2MHz. Finally, the system functions are defined (i.e., camera, audio, temperature modules), including chip selection and the peripheral circuit design. Besides, related softwares are developed:according to the characteristics of the STM32 series and existing embedded operating systems, the μ C/OS-Ⅱ operating system is selected; the master and the slave communication protocol interpretation are then defined; afterwards, an analysis of the various modules of software tasks is given, including design ideas, development process, and relevant documents and functions. The last is system testing and debugging case, including softwares and hardwares tests, to verify the feasibility of the system, basic communication and system application functions are performed under different conditions. Test results show that under the 2km distance, low-speed temperature and audio signal can be transmitted at 125℃ environment, while high-speed video signal transmission can be transmitted at 110℃ environment, to ensure that the entire optical fiber transmission system can run at 110 ℃ high-temperature environment.In conclusion, the designed and developed optical fiber transmission system, which is comprised of the asymmetric structure with room-temperature and high-temperature optical transceiver modules, the uplink/downlink optic fiber as signal transmission channel. By combining the hardwares and the softwares based on the ARM Cortex-M4 series microcontroller and the μC/OS- Ⅱ embedded operating system respectively, the designed system can satisfy the requirement on high-speed communications and applications under high-temperature environment, such as real-time environment parameters transmission, audio and video information collection and transmission, etc. The system and the results will be a valuable reference for the industrial control (e.g., the oil logging, coal mining) where high-reliability, real-time performance and high-capacity are needed.