Research on the optical fiber gas flowmeters based on intermodal interference

• A self-heating type optical fiber flowmeter with high sensitivity was proposed.
• The intermodal interference between the two parts of light happened when cladding modes were coupled back into core layer.
• The high power laser was also introduced into fiber to heat the silver film coated on the surface of the cladding layer.
• The experimental results showed the resolution of the proposed sensor was 2×10−2 m/s in the region of 0–8 m/s.
• The highest sensitivity could achieve 1537 pm/(m/s).

In this work, a self-heating type optical fiber flowmeter with high sensitivity was proposed. The core-offset fiber structures were employed to couple a part of signal light into the fiber cladding layer, and the other part of light still propagated in the core layer. The intermodal interference between the two parts of light happened when the cladding modes were coupled back into core layer. Meanwhile, the high power laser was also introduced into fiber to heat the silver film coated on the surface of the cladding layer. When the cool gas flow passed, the temperature of the sensor probe decreased due to the heat transfer process. Because of the thermo-optic effect in the fiber, interference spectrum could be shifted when the temperature was changed. The experimental results showed the resolution of the proposed sensor was 2×10−2 m/s in the region of 0–8 m/s. The highest sensitivity could achieve 1537 pm/(m/s).