We experimentally demonstrated a scheme for the magnetic field measurement based on an in-line Michelson interferometer (MI) and magnetic fluid (MF). The tip packaged technology of a Michelson interferometer is proposed. The sensor is composed of microspherical structure, single-mode fiber (SMF), hollow-core fiber (HCF), quartz tube, and MF. Since the refractive index of the MF will be changed with the intensity of the magnetic field, the effective refractive index (ERI) of the cladding can be changed, which leads to correlative moves of the reflection spectrum. The magnetic field sensitivity of -118.7 pm/mT is obtained in the magnetic range from 1.36 to 11.8mT. We present a sensing structure, compared with other sensors, that has the advantages of simple, compact, and easy integration. The proposed sensor is expected to offer significant potential for detecting weak magnetic fields.
A refractive index (RI) sensor based on three microspheres array (TMSA) Michelson interferometer (MI) is proposed and experimentally demonstrated. The sensor was composed of a TMSA which introduces higher-order cladding mode and a section of silica fiber which is used to transmit light. Due to the flatness and cleanliness requirements of Michelson’s Fresnel reflector, a special packaging method by microtubule was used to protect the end face. The coupling efficiency between the core and the cladding of MI is proved by the coupled mode theory. The results show that the greater the effective refractive index difference (ERID) between different modes, the greater the coupling coefficient can be obtained, and the TMSA achieves the improvement in the ERID between modes. The interference arm of the sensor is 2.7cm, and the size of the microsphere is less than 230 μm. It is discussed in further detail that the order of the excited cladding mode is closely related to the sensitivity of the RI sensing. The experimental results show that the sensitivity of the RI is -56.121nm/RIU. The characteristics of TMSA make it suitable for operation in a variable environment without cross-sensitivity, which may open up new avenues for local temperature sensing.
We propose to introduce a phase shift in each ring of the multi-stage interleavers based on add-drop resonator Mach–Zehnder interferometer to quantitatively measure the wavelength offset of each interleaver, thus a demultiplexer with uniformly segmented multi-channel output can be obtained. It is found that the additional phase of a certain interleaver is equal to the offset value of this stage plus the accumulated offset value of all previous stages. Following this rule, the quantitative cascade rule can be summarized, and theoretically an infinite-channel demultiplexer will be obtained. Combining fine-tuning and thermal tuning machining method, this cascade rule can guide the fabrication of stable and tunable demultiplexers in the integrated silicon photonics technology. Our method will provide a potential application for the fabrication of dense wavelength-division multiplexing systems with ultra-large capacity.
A vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize curvature measurement. Due to the opposite stress direction on the two sides of the neutral plane during bending, the sensor can realize vector measurement of curvature. The curvature sensitivity of the sensor in convex and concave bending is 558.42 pm/m-1 and -818.09 pm/m-1, respectively. This sensor has the advantage of simple structure, low cost, and easy industrial production. It has potential applications in engineering health monitoring and deformation measurement.
A simple composite cavity fiber tip (CCFT) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The composite cavity is composed of an air cavity and a silica cavity. The air cavity is an elliptical air hole embedded in the SMF. The silica cavity is a short section of SMF cascaded to the air cavity. The CCFT FPIs were applied for temperature sensing. To take advantage of the FP’s resonant property, a laser whose wavelength is tuned to the steep slope of one of the FP resonances is used to interrogate the CCFT FPI system. With a laser interrogation, a small wavelength shift caused by a small temperature change will then be translated into a large change in output power, which can be easily detected. Therefore, the temperature sensitivity can be enhanced significantly, and the CCFT FPI can routinely resolve much smaller temperature changes.