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Mid-infrared Quantum-cascade Laser Based Key Problems Research Of Carbon Monoxide Monitoring System

Posted on:2017-04-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:M LvFull Text:PDF
GTID:1108330482991877Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
Mining work under complicated geological conditions of coal-bed can easily cause methane leaks result in spontaneous combustion of coal dust. The spontaneous combustion of coal-bed methane will produce large amounts of carbon monoxide gas. Carbon monoxide gas and air mixture is easy to causing explosive accident, and carbon monoxide gas itself is one of risk factors which endanger the safety of workers at the mine. Therefore, provide an accurately detection of carbon monoxide gas in the mine have great practical significance. Carbon monoxide gas effective monitoring, will not only greatly reduce the probability of coal mine production safety accidents, will also protect the safety of coal miners in a great extent.Application of infrared absorption techniques to identify toxic gas concentration measurements are the main trends of the current development. Compared with conventional electrochemical methods, IR absorption spectrometry to identify gas molecules is much stronger, has wider measurement range, high accuracy, hard to poisoning detection device and has a strong anti-electromagnetic interference capability and anti-explosion. Although the IR absorption spectrometry has many advantages, but there are many problems which affecting the application in practice of the mine. These problems include: light intensity and stability of the output optical power of the infrared light source which plays a decisive influence on the instrument’s detection performance. In this project, our application was mid-infrared quantum cascade laser light source which compared with common electroluminescent device has essential difference. Experiments show that if we want to get the desired effect of the light source drive, we need to design a complex drive circuit. Secondly, laser pulse driver performance a very narrow spike pulses at the photodetector. To distinguish the short pulses, we must design a higher vertical resolution signal processing circuit with a higher bandwidth.Research work of this paper mainly focuses on the following key issues:1. Infrared carbon monoxide gas detector light source driving stability and reliability issues. Experiments have shown that the application of a variety of semiconductor materials prepared quantum cascade lasers which work in different wavelengths has very extensive electrical and optical properties. Electrical threshold characteristics of QCLs only in accordance with its exhibits and the corresponding design based on the optical center wavelength of quantum cascade laser is a very rough design. This rough design brings laser output power and emission wavelength jitter, this jitter play the negative part in the instrument’s performance. More sophisticated drive circuit design requires more in-depth understanding of the quantum cascade laser’s work principle. Firstly, the basic structure of the quantum cascade laser and energy level model, the realization of the physical properties of quantum cascade laser simulation model by constructing quantum mechanics Quantum cascade laser modeling work provided the theoretical foundation for the follow-up work.2. The paper theoretical derivation of the quantum cascade laser which proved the best drive mode would be the constant power drive mode. This constant power driver design allows the laser light output power remains stable. Operating temperature is a major factor to influence the laser emission wavelength, in order to stabilize the emission wavelength of quantum cascade laser, we design the laser temperature control circuit. Temperature controller consists of two temperature acquisition system and temperature control system, with built-in laser package thermal resistance and TEC to achieve batter temperature measurement and control.3. Infrared detector output signal amplification meet the requirements both the accuracy and speed. The input impedance must be controlled at a very low level and higher operating bandwidth. While the amplifier output signal acquisition also need to ensure that in the case of digital bandwidth in order to maximize accuracy. In this paper, we designed a high-speed parallel sampling circuit using two pairs of channel high-speed ADC realized 1GSPS acquisition accuracy of sampling rate and vertical resolution of 12 bit. The final link in this signal chain is FPGA data processing circuit, data stream from ADC flow into FPGA processor, with the help of denoising algorithms FPGA packaged and processed thses data and send them to the host computer.This innovation is summarized as follows:1. We building the physical modeling of quantum cascade lasers. Then, we bring the chaos genetic algorithm into the quantum cascade laser model, which provide optimization of quantum cascade lasers’ design parameters. Based on this, we explore the effects that the changing of external magnetic field have a significant impact on laser light-emitting properties. After that we also analyzing the impact of longitudinal optical phonon scattering and rough interface scattering of the quantum cascade laser optical gain and total relaxation rate.2. We designed light source control system of carbon monoxide detector.The optimal driving method of the quantum cascade laser was determined as the constant power driving method through theory deduction. The nanosecond level constant power driving module was designed and developed with the adjustable output pulse width and duty cycle. The peak driving current is up to 10 A and the pulse rise/fall time is less than 10 ns. The constant power driving was achieved by the control of real time feedback current. Applying the quantum cascade laser at 4.65 μm, which was provided by Institute of Semiconductors, Chinese Academy of Sciences(ISCAS), driving performance of the power supply was experimentally demonstrated. The results show that the output laser power is stable without overshooting or ringing during a period of time longer than 5 hours. Then, working temperature is also a key factor impacts on the laser output. In this paper, laser temperature controller was developed in order to stabilize the laser output wavelength. The temperature controller contents two part includes the temperature detecting module and the temperature controlling module. The latest PID algorithm is adopted by the temperature controller and measurement results show that the initializing overshooting can be restrained and the temperature fluctuation of the laser is limited in the range of ±0.2℃.3. We designed photoelectric signal acquisition system of carbon monoxide detector. According to the characteristics of the Hg Cd Te photodetector output signal, we designed preamplifier circuit with high speed and precision. Based on this, we designed analog to digital conversion system based on the principle of parallel alternately sample. We designed a high-speed parallel sampling circuit using two pairs of channel high-speed ADC realized 1GSPS acquisition accuracy of sampling rate and vertical resolution of 12 bit. Farrow filters and CORDIC algorithm were used in the digital signal processing circuit for de-noising and error correction. When the input signal frequency is less than 400 MHz, the signal to noise ratio of the digital signal processing circuit up to 65 d B, the spurious-free dynamic range is up to 70 d B.
Keywords/Search Tags:quantum cascade laser modeling, carbon monoxide detector, constant power nanosecond pulse driver, advanced PID temperature controller, higher speed data sampling system
PDF Full Text Request
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