Design and Characteristics of Dual-Core Photonic Crystal Fiber Doppler Differential Velocimeter

We present a study on the design and characteristics of laser Doppler differential velocimeter using a dual-core photonic crystal fiber (DC-PCF). First, the transmission modes and mode interference characteristics of the DC-PCF were investigated both theoretically and experimentally. The results show that higher order modes (LP₁₁) of the dual cores and the cladding modes are excited by an input wavelength of 632 .8nm, which can be cut off by bending the DC-PCF. The independent fundamental modes (LP₀₁) of the two cores are clearly obtained. The mode interference near the distal end of the DC-PCF was observed, and the interference process from the independent faculae to the interaction of two core beams is presented as well. The velocimeter demonstrates a good working distance (~30 μm) and a small measuring volume (~273 .4 μm³), which is well suited for flow measurement in micro-scale fluidic channels. The velocity measurement of seeding particle is successfully demonstrated by observing the frequency modulation and the spacing of the fringe projected interference from the proposed DC-PCF Doppler differential velocimeter. The measurements are verified and in good agreement with the results obtained by the light gate sensor.