title: [Laser Tuning Performance Testing and Optimization in TDLAS Oxygen Measuring Systems].
abstract: TDLAS (tunable diode laser absorption spectroscopy) technology, with its unmatched advantages such as high selectivity molecular spectra, fast response, high sensitivity, non-contact measuring, become the preferred scheme for combustion process diagnosis, and can be effectively used for oxygen measuring. DFB (distributed feedback) laser diode with its small size, low power consumption, long service life, narrow linewidth, tunable wavelength has become the main choice of the TDLAS system. Performance of laser tuning characteristics is a key factor restricting TDLAS's measuring performance. According to TDLAS oxygen measuring system's working requirements, a simple experimental method was used to test and analyze tuning characteristics such as wavelength current, power current and wavelength temperature of a 764 nm DFB laser diode in the system. Nonlinear distortion of tuning curves was obvious, which affects oxygen measuring accuracy. The laser spectra's characteristics such as narrow linewidth, high side mode suppression ratio and wide wavelength tuning range are obvious, while its wavelength-current tuning curve with a tuning rate of about 0.023 nm x mA(-1) is not strictly linear. The higher the temperature the greater the threshold current, the PI curve is not strictly linear either. Temperature tuning curve is of good linearity, temperature-wave-length tuning rate keeps constant of about 0.056 nm/DEG C. Temperature tuning nonlinearity can be improved by high temperature control accuracy, and current power nonlinearity can be improved by setting the reference light path. In order to solve the wavelength current tuning nonlinear problems, the method of DA controlling injection current was considered to compensate for non-linear wavelength current tuning according to DFB laser diode tuning mechanism and polynomial fitting of test results. In view of different type of lasers, this method needs only one polynomial fitting process before the system's initial work. The compensation scheme is reasonable and the realization is simple, what's more, it does not affect the measuring process. The experiments prove that XI curve's linear fit residuals are less than 1 μm after compensation, far less than those of before compensation 22 pm, the compensation effect is obvious, which provided a basis for various oxygen parameters' TDLAS measuring and inversion.
authors.forename: Jun-feng
authors.initials: JF
authors.lastname: He
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.forename: Rui-feng
authors.initials: RF
authors.lastname: Kan
authors.forename: Zhen-yu
authors.initials: ZY
authors.lastname: Xu
authors.forename: Tao
authors.initials: T
authors.lastname: Wang