Gas detection is relative with industry safety, indoor ventilation, medical and health, etc, in which many applications require the detection limitation down to ppb level. That is quite challenges for most of conventional miniature gas sensors in the market. Although some equipment can achieve ppb-level detection accuracy, e.g. gas chromatography and tunable diode laser spectrometry (TDLS), they are too bulky and expensive to be adopted widely . And, they need a big sample gas volume that results of long time consuming and lower accuracy because in real cases the gas concentration always changes as time going on. Here, we demonstrate a new ppb-level detection approach based on photonics waveguides. The detection limitation down to around 200 ppb - level, and the gas volume for one test is less than 1 mL.
Figure 1 shows the schematic of the gas detection system. A low-cost blackbody radiation light source is used to generate a broad-band spectrum (from visible light to long-wavelength infrared) that promises this system can be used as a universal gas detection platform. The output light passes a bandpass filter and is coupled into an optical fiber. At one end of the fiber, a waveguide with a detector is connected. The waveguide exposes in the air to sense the target gas molecules in the surrounding, in which no pump is needed. Insert shows the principle of the gas sensing by use of waveguide.
Figure 2 shows the detection limitation analysis. In the experiment, we use carbon dioxide as a verification gas whose absorption spectrum is around 4.26 µm. The sensitivity of the system is around 15.91 mV/100ppm, while the noise floor is only 0.03 mV. Thus, the detection limitation is around 188 ppb.