Research On Active Intra-cavity Gas Sensor With Photonic Crystal Fiber

In industry, it’s important to detect flammable and explosive gas (like C2H2、NH3and CH4). So, optical fiber sensing technology appears, and it has manyadvantages like smaller volume、the ability of anti-electromagnetic and facility ofdistributed sensor. Active intra-cavity gas sensor with photonic crystal fiber hasbecome a hot area of research because in such a system the area of gas touching opticis largely enhanced; optic can be sufficiently absorbed by gas and detection sensitivityis obviously increased.This thesis is based on active intra-cavity gas sensor with photonic crystal fiber.Main points are as follows:1. We design a new hollow-core photonic crystal fiber, of which the diameter ofsmall ventages is2.4μm, pitch of adjacent ventages is3.8μm, and diameter of core is11μm. Then we set wavelength of the fiber at peak absorption of C2H2and NH3(1530nm and1967nm) to carry out numerical calculation employing COMSOLMultiphysics finite element software, and the relative sensitivity coefficient is above0.95. We also simulate the effect of ventage diameter and efficient mode refractiveindex on relative sensitivity coefficient at wavelength of1530nm and1967nm. Baseon the analysis above, we can conclude that the detection sensitivity of C2H2andNH3can be enormously enhanced using this PCF.2. We simulate the effect of intra-cavity loss on output power at differentcoupling ratio and as well as the effect of pump power on relative sensitivityenhancement coefficient. At last, we get the conclusion that the higher coupling ratiois, the lager relative sensitivity enhancement coefficient is and when laser worksaround the threshold the sensitivity is much higher than other conditions. In addition,we verify the conclusion in experiments and get the good coherence.3. In experiments, we compare the intra-cavity absorption and outside cavityabsorption. When we fill a gas cell in which PCF is tangled with0.2MPa gas, and putthe cell outside cavity, the absorption of gas to optic is3dBm. While we put the samegas cell inner cavity, the absorption of gas to optic is25dBm under the same condition.Thus, we can see that loss of inner cavity is obviously exceeds that of outer cavity,which is also the major reason leading a higher detection sensitivity.