High sensitivity refractive index sensor based on splicing points tapered SMF-PCF-SMF structure Mach-Zehnder mode interferometer

• The paper proposed and demonstrated a novel splicing points tapered SMF-PCF-SMF structure Mach-Zehnder interferometric refractive index sensor for the first time.
• The paper built a structure model of splicing points tapered SMF-PCF-SMF structure Mach-Zehnder interferometric refractive index sensor to numerically study the refractive index sensing characteristics, and optimizing the structure parameters to improve the sensitivity.
• Experimentally fabricated the splicing points tapered SMF-PCF-SMF structure Mach-Zehnder interferometric refractive index sensor and realized the sensitivity of 260.8 nm/RIU, compared with sensitivity of 224.2 nm/RIU of direct splicing SMF-PCF-SMF Mach-Zehnder mode interferometer with PCF length of 4 cm, the sensitivity increased by 16.3%.

The paper proposed and studied a Mach-Zehnder mode interferometric refractive index sensor, which is based on splicing points tapered SMF-PCF-SMF (SMF, single-mode fiber; PCF, photonic crystal fiber) structure. For the reason that the effective refractive index of photonic crystal fiber cladding high-order modes near fiber core are more sensitive to surrounding refractive index changes, the refractive index measurement sensitivity of splicing points tapered SMF-PCF-SMF Mach-Zehnder mode interferometer can be enhanced further through tapering the splicing points. Relations between refractive index measurement sensitivity and photonic crystal fiber length and taper waist diameter are studied through numerical simulations and experiments. Simulation and experimental results show that sensitivity will be increased with the increase of photonic crystal fiber length and the decrease of taper waist diameter. In the refractive range of 1.3333–1.3737, splicing points tapered SMF-PCF-SMF Mach-Zehnder mode interferometer with PCF length of 4 cm and taper waist diameter of 60.4 μm has refractive index measurement sensitivity of 260.8 nm/RIU, compared with sensitivity of 224.2 nm/RIU of direct splicing SMF-PCF-SMF Mach-Zehnder mode interferometer with PCF length of 4 cm, the sensitivity increased by 16.3%. The research shows that the sensing structure is with good linearity and repeatability.