Research On Digital Receiver Of Fiber-optic Methane Gas Sensor Based On All-optical Buffer

Methane is a common explosive gas and the main component of marsh gas, accounting for about 83%～89%. The accident caused by marsh gas has been the first killer of coal mine safety and caused a great loss to the national economy and the safety of miners, so strengthening the gas supervision is top priority of coal mine safety production. Optical fiber sensor with advantages of high sensitivity, simple structure, anti-electromagnetic interference, corrosion resistance, good electrical insulation, facilitating remote network component, small size, light weight, low power consumption and so on, is drawing more attention and being applicated widely by domestic and abroad. Now the fiber-optic methane gas sensors are still in the laboratory stage in domestic, a long distance from practical application. Moreover, stability, sensitivity and monitoring points are yet to be improved.In this paper, a digital receiver of fiber-optic methane gas sensor system based on all-optical buffer is proposed, which can work with the analog receiver part to achieve the purpose of multi-point monitoring. Because digital burst signal's wavelength is 1665nm, bandwidth is 155Mb/s, and every packet includes three frames, the design of the digital receiver consists of five modules: photoelectric conversion, the main amplification, digit restoration, serial to parallel conversion, and address recognition. In this paper, the principle and the design of every unit are described in detail. The design of photoelectric conversion adopts differential structure, and the key part of the digital receiver is PIN, which directly determines the characteristics of bandwidth and noise of received signal. In the main amplification design, differential three amplifiers with advantages of high input impedance and high common-mode rejection ratio are used innovatively, which can reduce the requirements of the amplifier. This article includes not only detailed descriptions of performance indications of the components of every unit, but also drawing and debugging of the circuit board of the digital receiver, and achieves function of parts of circuit. We can conclude signal bandwidth by observing the signal rise time. This paper also designs signals of multi-address light source, gives design of packet frame format and coding theory, and designs and simulates the address identification unit with QuartusII based on Verilog HDL and FPGA in order to achieve frame header address sequence detection and give a signal to control analog receiver the interception of data information part of the frame corresponding to frame header to achieve the purpose of multi-point monitoring in the same optical path.