Interference Measurement Technology Based On Dual-core Photonic Crystal Fiber

Dual-core photonic crystal fiber is a novel type of microstructure fiber developedin recent years. With a unique structure of double guide core, DC-PCF plays asignificant role in the field of optical fiber sensing. In this paper, the sensing theoryand characteristics of dual-core photonic crystal fiber itself was studied primarily. Onthe basis, we explore the characteristics of DC-PCF in curvature sensing andtemperature sensing experimentally. Lastly, based on self-mixing effect, we researchthe feasibility of DC-PCF applying in the velocity measurement of particles in theflow field.Firstly, the coherent synthesis mechanism of DC-PCF was researched. On thepremise of ensuring that the laser emitted from DC-PCF is single mode, the formingprinciple of interference fringes was analyzed theoretically and experimentally, whoseresult shows that interference effect and diffraction effect both act on emergent lightfrom DC-PCF. Moreover, the further studies in transverse optical coupling of DC-PCFwere carried out. The results indicated that there exists certain transverse couplingbetween the two cores, and the power in two cores is not constant equal.Secondly, because of the peculiar structure of DC-PCF similar to Mach-Zehnderinterferometer, we explored whether DC-PCF could be applied to sensing for variousphysical quantities. In the section, two experiments about curvature sensing andtemperature sensing were conducted. In the experiment of curvature, we obtainedrelation curve between bending angle of fiber and, and the curve linearity reached0.9968, which demonstrate the theoretical analysis, namely, phase variation ofemergent light d corresponding to an arbitrary planar deformation overincremental changes dθ. Afterwards, the characteristics of temperature sensing wasexplored, we conducted heating experiments of straight DC-PCF segment and curvedDC-PCF segment respectively. From the result, we conclude that the reason DC-PCFcould be able to sense the temperature is that the phase difference of two coresgenerated from heat is not equal when the fiber is curved. When the fiber wasring-shaped, the linearity of curve between temperature and phase variation reached to0.9988. And in this circumstance, its temperature sensitivity reached to1.023×104rad/m·℃. Finally, based on self-mixing effect, we developed a new type of measuringparticle velocity detection system. Compared to traditional Laser Doppler Velocitysystem, the interference region of the novel LDV system is unusual, conventionalcontrol body is not applicable to it, so “control surface” is proposed. In order to verifyDC-PCF could be applied in the velocity measurement of particles, we build LDVsystem based on DC-PCF successfully, measuring and calibrating the velocity ofmoving objects. At last, we illustrated the reason why the spectrum broadened in theprocess of increasing velocity of particle. The experimental results show that thevelocity with LDV system is agreeable to that with light gate, and the linearity is up to0.99993. The new LDV system could be well applied to measuring the speed ofpractical moving objects. And the new laser Doppler velocimetry, which provides anew solution for measurement of the particle velocity in MEMS and biomedicalissues, broadens the development direction of photoelectric detection technology.