With the development of semiconductor Laser Diode (LD), Wavelength modulation spectroscopy (WMS) has evolved as an emerging technology in recent years. Combined with LD’s wavelength tunability and harmonic detection technology, as Dharamsi analyzed in [1], WMS could well realize the high sensitivity detection of specific gases with the apriori knowledge on gases’ absorption spectrum.
Mianyang, China lizhanfeng@
Abstract—Online analysis of carbon monoxide with the highprecision, high-sensitivity is of great significance to control environment pollution and industrial production-line process. The influence of these factors, such as input voltage variation of load and ripple to driver, were analyzed. The hybrid-driven power, with functions of slow-start, constant power laser diode control and over-current protection, was designed by integrating the principles and operation requirement, and the damage mechanism of laser diode. The experimental tests reveal that the tuning performance and the stability of output wavelength are fully guaranteed, and that the designed laser diode drive circuit well meets the requirement of measurement based on TDLAS.
Keyworห้องสมุดไป่ตู้s- laser diode; absorption spectroscopy;power drive
I. INTRODUCTION
On-site analysis of carbon monoxide (CO) gas concentration can effectively monitor the production process, and play an important role in improving production and yields. By most conventional CO detection methods, samples are usually collected by the flue sensors, and then delivered to laboratory for component analysis, the whole process of which is time-consuming and lacks real-time property.
In the CO Tunable Diode Laser Absorption Spectroscopy (TDLAS)-based measurement system, dual-frequency
Liao Xiaochun, Chao wen, Shang Liping
School of Information Engineering Southwest University of Science and Technology
Modulation circuits consist of waveform generator and signal synthesis. The former generates the desired frequency
Fund Project: "863" project (2009AA063002) and the Sichuan Provincial Science and Technology Support Project (2009SZ0118) funded. 978-1-4244-7161-4/10/$26.00 ©2010 IEEE
Mianyang, China liaoxiaochun@
modulation and harmonic detection are adopted to modulate the drive currents, with the reference information expressed by Shimei Wang in [5], so the LD current drive is realized in CP mode.
LD output wavelength is determined by the material’s band gap energy, and affected by temperature and injection current. LD drive is realized by two ways of Constant Current (CC) and Constant Power (CP), as Shushu Liu stated in [3]. In CC mode, through the negative feedback control loop, direct and effective control is implemented over drive current level, to achieve the minimal current deviation and the maximal LD output stability. CC mode with precise temperature control could obtain even better results, also indicated by Xianbing Liao in [4]. While in CP mode, the current is fluctuating. In order to accurately control the output wavelength, the current must be tracked in real time. Generally, photodiodes (PD) are used to detect the LD output optical power for drive current’s real-time control.
Laser Diode Drive Circuit Design for Carbon Monoxide TDLAS Measurement System
Li Zhanfeng
School of Manufacturing Science and Engineering Southwest University of Science and Technology
Overall protection measures for LD include: slow-start, self short circuit in non-work state, and overload protection in work state.
II. LD DRIVE CIRCUIT SCHEME
Optical source drive scheme for CO TDLAS measurement system is illustrated in Fig.1.
DC Signal
Signal Synthesis
Power Supply
DDS Modulation Source
Laser Diode
The life of LD could be quite long at normal use. But if under improper working or storage conditions, as Sliney mentioned in [2], LD will suffer a sharp deterioration in performance, even destruction. Those necessitate perfect protection measures for LD drive system, which could exempt LD from damages in start, working, and closing circuit status. LD damages mainly derive from PN junction breakdown or cleavage plane destruction. Depending on the damage degree, it could be decreased output or zero-output.
and waveform; the latter synthesizes the signal’s amplitude and the bias voltage, to meet LD’s requirements. In working process, a frequency sweep of modulation frequency is required normally so as to acquire maximal detection output value. Therefore, the high resolution of waveform generator usually reaches 0.01-0.1Hz, which is realized by highprecision DDS signal generator chip, controlled by System Control to generate sufficient high-resolution and highprecision sinusoidal voltage signal.