Weihua Jia

Microfiber-Based Inline Mach–Zehnder Interferometer for Dual-Parameter Measurement

An approach to realizing simultaneous measurement of refractive index (RI) and temperature based on a microfiber-based dual inline Mach-Zehnder interferometer (MZI) is proposed and demonstrated. Due to different interference mechanisms, as one interference between the core mode and the lower order cladding mode in the sensing single-mode fiber and the other interference between the fundamental mode and the high-order mode in the multimode microfiber, the former interferometer achieves RI sensitivity of -23.67 nm/RIU and temperature sensitivity of 81.2 pm/°C, whereas those of the latter are 3820.23 nm/RIU, and -465.7 pm/°C, respectively. The large sensitivity differences can provide a more accurate demodulation of RI and temperature. The sensor is featured with multiparameters measurement, compact structure, high sensitivity, low cost, and easy fabrication.

Microfiber Fabry–Perot Interferometer for Dual-Parameter Sensing

We propose and demonstrate a microfiber Fabry–Perot interferometer (MFPI) fabricated by taper-drawing microfiber at the center of a uniform fiber Bragg grating (FBG). The MFPI employing the two separated sections of FBG as reflectors and a length of microfiber as its cavity is derived. Theoretic study shows that the reflection spectrum of such MFPI is consisted of two parts – interference fringes induced by multi-beam interference and reflection spectrum envelope induced by FBGs. Temperature affects both interference fringes and reflection wavelength of FBGs while ambient refractive index (RI) only influences the interference fringes, i.e., MFPI has different response to temperature and RI. Therefore, MFPI for simultaneous sensing of RI and temperature is experimentally demonstrated by tracking a reflection peak of interference fringes and the Bragg wavelength of the FBGs, which are respectively assisted by frequency domain processing and Gaussian fitting of the optical spectrum. Consequently, wavelength measurement resolution of 0.5 pm is realized.

Graphene-Assisted Microfiber for Optical-Power-Based Temperature Sensor

Combined the large evanescent field of microfiber with the high thermal conductivity of graphene, a sensitive all-fiber temperature sensor based on graphene-assisted micro-fiber is proposed and experimentally demonstrated. Microfiber can be easily attached with graphene due to the electrostatic force, resulting in an effective interaction between graphene and the evanescent field of microfiber. The change of the ambient temperature has a great influence on the conductivity of graphene, leading to the variation of the effective refractive index of microfiber. Consequently, the optical power transmission will be changed. The temperature sensitivity of 0.1018 dB/°C in the heating process and 0.1052 dB/°C in the cooling process as well as a high resolution of 0.0098 °C is obtained in the experiment. The scheme may have great potential in sensing fields owing to the advantages of high sensitivity, compact size, and low cost.

Wideband Microfiber Fabry–Pérot Filter and Its Application to Multiwavelength Fiber Ring Laser

A microfiber Fabry-Pérot (MFP) filter consisting of two microfiber Sagnac loop mirrors as the reflectors and a section of microfiber as the cavity is proposed and fabricated. Owing to the high coupling efficiency induced by the large evanescent field of the microfiber, a broadband comb spectrum with high extinction ratio and flat amplitude can be obtained. The MFP with the extinction ratio of 15 dB as well as the free spectrum range of 0.18 nm is fabricated by bending and twisting a microfiber tapered from a single mode fiber. Consequently, the MFP is applied to an erbium-doped fiber ring laser as the wavelength filter. Assisted by a section of highly nonlinear fiber to suppress the mode competition, 42-wavelength lasing oscillations are achieved at room temperature.

Highly sensitive temperature sensor based on D-shaped microfiber with high birefringence

A high sensitive temperature sensor based on D-shaped microfiber with high birefringence is proposed and demonstrated. In order to obtain D-shaped microfiber, we polish a single mode fiber (SMF) and then taper down the polished region into micrometer size. By utilizing Sagnac loop interferometer, we achieve high refractive index (RI) sensitivity of 9951nm/RIU. Further, we realize temperature detection assisted by sucrose solution with high thermo-optic coefficient. Experimental results demonstrate high temperature sensitivity up to -0.98921nm/°C within the range of 22°C-60°C. The sensor is featured with high sensitivity, compact structure and easy fabrication.

Microfiber Fabry-Perot filter consisting of two cascaded Sagnac reflectors for multi-wavelength fiber laser

A micro Fabry-Perot (MFP) filter is proposed and fabricated by twisting a section of microfiber into two Sagnac loop mirrors. With the co-operation of this MFP filter and a section of highly nonlinear fiber, we propose and experimentally demonstrate a multi-wavelength Erbium-doped fiber ring laser (EDFRL) based on the inhomogeneous loss mechanism. When the pump current is set at 450mA, 22-lasering wavelengths with the identical wavelength space of 0.22nm and side-mode suppression ratio (SMSR) above 30dB are achieved. Within the period of one hour’s monitoring, the fluctuation of the output power is less than 0.943dB.

Graphene coated microfiber for temperature sensor

A temperature sensor based on graphene coated microfiber is proposed and demonstrated. By depositing graphene onto the microfiber, the transmission optical power changes linearly along the temperature with a sensitivity of 0.03 dB / C°7.

Highly sensitive refractive index sensor based on two cascaded microfiber knots with Vernier effect

A highly sensitive refractive index (RI) sensor based on two cascaded microfiber knots with vernier effect is proposed and demonstrated by theoretical arithmetic. Deriving from high proportional evanescent field of microfiber and sharp spectrum fringes induced by vernier effect, a slight change of ambient RI will cause large variation of effective RI and significant wavelength shift of resonant peaks, indicating high sensitivity and resolution of the proposed compound resonator. Numerical analysis demonstrates a high sensitivity of 10000nm/RIU and a resolution of 5.57×10−5 RIU at the ambient RI around 1.33 for the fiber diameter of 1μm and cavity radii of R1 = 500μm, R2 = 547.62μm

Dual core photonic crystal fiber based Mach-Zehnder interferometer assisted with two tapers for bending measurement

A bending sensor is achieved by employing a singlemode fiber-dual core photonic crystal fiber- singlemode fiber (SDS) structure with two tapers at fusing points. A sensitivity of -4.3421nm/m~ between the transmission spectra shift and curvature is demonstrated.

High sensitivity temperature sensor using microfiber based Mach-Zehnder interferometer

A high sensitive temperature sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. Temperature measurement is achieved by immerging a section of microfiber into the refractive index (RI) liquid with a high thermo-optic coefficient. A slight change of ambient temperature will lead to the enhanced variation of the liquid index. Due to the evanescent field of microfiber, microfiber effective refractive index will be changed, and subsequently the optical length. Thus, by measuring the free spectral range (FSR) of the MZI, the temperature sensor can achieve a high sensitivity of 6.44nm/°C at the temperature of 20.6°C.