Jilin Wei

A novel identification system based on visible light communication

A identification system based on visible light communication using white light emitting diode (LED) of the miners lamp has been proposed and demonstrated, in which the Tag and Reader have been designed and realized. The Manchester encoding is presented to transmit identification number from the Tag to the Reader. The novel identification system could substitute for the in being radio frequency identification system to implement the checking attendance, person position and tracking in coal mine and in other LED illumination case.

Absorption Spectroscopy of (8,1) Band in d3Δ-a3Π System of CS Radical

The CS radical was generated by discharging the mixture gas of CS2 and Helium. The Doppler limited spectra of CS were recorded in the region of 12350–12950 cm−1 using optical heterodyne concentration modulation absorption spectroscopy. Three hundred and twenty-six lines were recorded and assigned to the d3Δ-a3Π (8,1) band, in which eighty-three transitions were first observed. A set of improved molecular constants for the d3Δ(v=8) and a3Π(v=1) levels were determined by a non-linear least-squares fitting of all the lines to the effective Hamiltonian.

A portable low-power integrated current and temperature laser controller for high-sensitivity gas sensor applications

A low-noise, low power, high modulation-bandwidth design integrated laser current and temperature driver with excellent long-term stability is described. The current driver circuit is based on the Hall-Libbrecht design. A high sensitivity and a stable driver current were obtained using a differential amplifier and an integral amplifier. The set-point voltage for the current driver came from an ultra-compact, ultra-low temperature coefficient voltage reference chip or the digital to analog convertor output of a microcontroller or a modulation signal. An integral temperature chip, referred to as ADN8834, was used to drive the thermoelectric cooler controller of the distributed feedback (DFB) laser. The internal amplifier acquired the feedback current of the temperature sensor. The proportional-integral-derivative parameters such as proportion, integration, and derivative were set by external resistors. The short- and long-term stability and linearity of the developed laser driver were tested using a DFB laser with a central wavelength of 6991 cm-1. The laser driver was validated for high-sensitivity gas sensing of CO2 and C2H2 via a laser absorption spectroscopy experiment. The limits of detection were less than 11.5 ppm and 0.124 ppm for CO2 and C2H2, respectively. Direct absorption measurements and the 1-f and 2-f demodulation signals confirmed the capabilities of the proposed laser driver system in high-sensitivity gas sensing applications. The driver unit can readily be accommodated into many portable laser sensing devices for industrial applications.

High-speed multi-pass tunable diode laser absorption spectrometer based on frequency-modulation spectroscopy

We report a multi-pass tunable diode laser absorption spectrometer based on the frequency-modulation spectroscopy (FMS) technique. It has the advantage of high scan speed and is immune to the etalon effect. A multi-pass Herriott-type cell was used in the spectrometer to increase the effective optical length to 17.5 m and compact the physical dimensions of the spectrometer to 60×30×30 cm3. Noise due to low-frequency fluctuation of the laser power and the 1/f noise in the rapid detection are sufficiently reduced by FMS. Interference fringes are effectively suppressed when the modulation frequency equals to integer or half-integer times of their free spectral range (FSR). An absorption line of C2H2 around 1.51 µm was recorded with the spectrometer to demonstrate its capabilities. The response frequency of the spectrometer is up to 100 kHz (10 µs) thanks to the high modulation frequency of FMS. The detection sensitivity of the spectrometer is about 240 ppb (3σ) at 100 kHz measurement repetition rate. The amplitude of the absorption signal is highly linear to the C2H2 concentration in the range of 300 ppb -100 ppm. Based on the Allan variation, the detection limit was determined to be 18 ppb with a detection time of 166 s.

Simultaneous Measurements of CO and CO2 Employing Wavelength Modulation Spectroscopy Using a Signal Averaging Technique at 1.578 μm

A resolved line pair was selected for simultaneous measurement of carbon monoxide (CO) and carbon dioxide (CO2) in the near-infrared (NIR) region. The spectral lines of CO and CO2 at 1.578 µm were measured by wavelength modulation spectroscopy (WMS)-2f and the absorption was enhanced with a multipass absorption cell. The white noise was further reduced by averaging technology. The detection sensitivity (1σ) for the system is estimated at 2.63 × 10−7 cm−1 for direct absorption spectroscopy. The ultimate detection limits of CO2 and CO mixed with pure N2 at 75 Torr are 29 parts per million (ppm) and 47 ppm, respectively. It is demonstrated that the signal is highly linear with the concentration in the range of 100–800 ppm. Based on an Allan variation analysis, the minimum detectable limit of CO2 and CO is 7.5 and 14 ppm, respectively. The response time of the system is about 30 s and a relationship of temperature dependence was obtained. As an example, an in situ measurement of exhaust of alkane combustion emission is presented.

Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell

Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1f and 2f, respectively) agree with the Beer–Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz–1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.