Wei-Lin Ye

Near-Infrared Methane Detection Device Using Wavelength-Modulated Distributed Feedback Diode Laser around 1.654 µm

ABSTRACT By using a wavelength-modulated distributed feedback laser centered at 1.654 µm, a stand-alone near-infrared methane detection device was experimentally proposed based on the tunable diode laser absorption spectroscopy technique. An intelligent temperature controller, a scan and modulation module, and a cost-effective lock-in amplifier were developed to drive the distributed feedback laser and extract the second harmonic signal. Experimental results show that the relative detection error is less than 7% within the detection range of 0–106 ppm, and the limit of detection is about 11 ppm with an absorption length of 0.2 m. Long-term monitoring on two gas samples (103 ppm and 2 × 105 ppm) suggests good stability with the maximum detection errors smaller than 7% and 2.5%, respectively. Due to careful design and integration, the developed near-infrared sensor reveals competitive performances compared with our previously reported sensing devices at the mid-infrared region.

Design and Performances of a Carbon Monoxide Sensor Using Mid-Infrared Absorption Spectroscopy Technique at 4.6 µm

ABSTRACT Based on infrared absorption spectroscopy technique, a carbon monoxide sensor was developed using the fundamental absorption band of carbon monoxide molecule at the wavelength around 4.6 µm. The developed sensor consists of pulse-modulated wideband incandescence, open ellipsoid light-collector gas-cell, dual-channel detector, and control and signal-processing module. With the prepared standard carbon monoxide gas sample, sensing characteristics on carbon monoxide were investigated using the sensor. Experimental results reveal that the limit of detection is about 10 ppm, the relative error at the limit of detection point is less than 14%, and that is less than 7.8% within the low concentration range of 20∼180 ppm. The maximum absolute errors of 50 min long-term measurement on the 0 and 14 ppm CO gas samples are about 3 and 3.17 ppm, respectively, and the standard deviations are as small as 0.18 and 1.25 ppm, respectively. Compared with the reported carbon monoxide detection systems utilizing quantum cascaded lasers and distributed feedback lasers, the proposed sensor shows potential applications in carbon monoxide detection under the circumstances of coal-mine and environmental protection, by virtue of high performance, low cost, simple optical structure, and so on.

A near-infrared carbon dioxide sensor system using a compact folded optical structure for deep-sea natural gas hydrate exploration

The detection of dissolved gas (e.g. carbon dioxide (CO2) and methane (CH4)) in seawater is important for deep-sea natural gas hydrate exploration, which requires that the sensor especially the optical structure should be of compact size and capable of operation in a deep-sea environment. A compact optical structure with a simple beam alignment and tracing method was proposed for tunable laser absorption spectroscopy (TLAS) based gas measurements, in order to minimize the sensor size and ease the beam alignment/tracing procedure for deep-sea operation. A near-infrared CO2 sensor system was developed based on the compact optical structure. A distributed feedback (DFB) laser centered at 6361.3 cm−1 and a multi-pass gas cell (MPGC) with an effective optical path length of 29.8 m were employed. The sensor system was integrated as standalone equipment by customizing an aluminum baseplate for a stable field operation. A series of experiments were carried out to assess the performance of the sensor system. A limit of detection (LoD) of ∼7.1 parts-per-million in volume (ppmv) at a 0.4 s averaging time was obtained, and the LoD was reduced to ∼277 parts-per-billion in volume (ppbv) at an optimum averaging time of 153.6 s. Considering the gas mixing time, the rise and fall times were measured to be ∼290 s and ∼200 s, respectively. The proposed compact sensor structure provides the basis for the further development of a sensor system for dissolved CO2 detection with a LoD of ppbv via the use of a mid-infrared tunable laser.

Development and performances of standalone visible light communication terminals using imitate infrared encoding technique

By introducing the imitate infrared encoding technique and employing a white light emitting diode (WLED), a pair of standalone visible light communication (VLC) terminals, including a transmitter and a receiver, were experimentally demonstrated. The mathematic modelling and formulation were proposed on the WLEDs luminous characteristics and the VLC channel response. The terminals were developed using ARM7-based embedded system, and experiments were carried out to derive their performances. A suitable illuminance of 200 lx (measured before the WLED) is preferred for obtaining a uniform bit error ratio (BER) over the distance of 0–2 m, and the measured BER is <10−4 with a communication data rate of 0.1–10 Mbps. High stability was also confirmed through measuring the BER results over 5 h at the two communication distances of 0.2 and 0.3 m and at 1 Mbps data transmission rate. Owing to the advantages of small size, low cost, and 10 Mbps data rate, this kind of terminals can be adopted in indoor short-distance wireless communication.