Yinggang Liu

High-Sensitivity Mach–Zehnder Interferometric Curvature Fiber Sensor Based on Thin-Core Fiber

A simple and compact thin-core fiber (TCF)-based Mach-Zehnder interferometer (MZI) is proposed for curvature measurement. The sensor head is composed by a short section of TCF embedded between two single-mode fibers. The MZI works on the basis of interference between the core mode and cladding mode in TCF. The transmission spectrum of the sensor is analyzed by the fast Fourier transform, which indicates that the interference mainly occurs between LP01 and LP018 modes propagating in TCF. The experimental results show that the dip wavelengths in transmission spectrum decrease linearly as the curvature increase with a sensitivity of -13.53 nm/m-1. The high curvature sensitivity makes this sensor a candidate for curvature discrimination and measurement in the field of structural deformation, intelligent artificial limb, and mechanical engineering.

Humidity sensing of microfiber Bragg grating

A humidity sensor based on microfiber Bragg grating is proposed and demonstrated. The microfiber Bragg grating is obtained through chemical etching commercial fiber Bragg grating. The experimental results show that the central wavelength of the microfiber Bragg grating has red shift with humidity increasing, while the power decreases. The relative humidity sensitivity of the microfiber Bragg grating with diameter of 8.9um is 3pm/%RH in the range of 55%-80%RH. Furthermore, the sensor has a linear response to humidity with linear fitting of 0.991. The sensor possesses advantages of easy fabrication and low cost.

In-Fiber Quasi-Michelson Interferometer Based on Waist-Enlarged Fiber Taper for Refractive Index Sensing

A novel refractive-index (RI) Michelson interferometer based on a waist-enlarged taper is achieved. Such a device is fabricated by splicing a section of multimode fiber (MMF) at one end of single-mode fiber (SMF). Due to the fiber bitaper at the coupling point of SMF and MMF, the light is coupled into the MMF from lead in fiber core, and the intermodal interference will occur for the optical path difference between core mode and cladding mode. Then, the light will be reflected at the end of the fiber and recoupled back into the lead out fiber core by the fiber bitaper. When the lights return back to the lead out fiber, the intermodal interference will occur for the optical path difference between core mode and high order mode. The sensor has a linear response to RI with a sensitivity of -178.424 dB/RIU in the range of 1.351-1.4027 RIU. The temperature cross sensitivity is also analyzed, and the influence can be eliminated by simultaneous measurement of RI and temperature through the matrix equation. The proposed sensor features the advantages of easy fabrication, low cost, high mechanical strength, which make it a good candidate for bio-chemical measurement.

Superfluorescent fiber source achieving multisignal power equalization in distributed fiber Bragg grating sensing

In order to achieve multisignal power equalization in a quasidistributed fiber Bragg grating (FBG) sensing system, an erbium-doped fiber (EDF) superfluorescent source with high flatness and broadband spectrum is presented using a three-stage double-pump configuration. The spectral protrusions in the vicinity of 1532 and 1570 nm are flattened, which is achieved by designing a gain flattening filter with a long-period grating. The result shows that the flatness of the output spectrum covering the C and L band, from 1526.52 to 1607.87 nm, is less than 0.76 dBm. The 3 dB bandwidth is 75.68 nm, and the output power of 13.11 mW is achieved in the C and L band. By using the fiber amplified spontaneous emission (ASE) source in FBG sensing system for decreasing multisignals peak power variation, the standard deviation of multisignals peak power is decreased to 1.00 dBm. In a multiplexed FBG sensing system, the high flattening fiber ASE source is beneficial to long-distance transmission, amplification, recognition, and demodulation of FBG sensing signals.

Slow-light effects in microfiber coil resonator

At present, miniaturized, low loss and integrated slow-light elements are the urgent needs for the slow-light technology development. In this paper, we study the slow-ight effects in a compact microfiber coil resonator (MCR) structure and fabricate the compact MCR slow-light element. Furthermore, we test its slow-light properties and find that the optical pulse propagating in the MCR can be delayed about 30 ps. By caculating, we find that the group velocity of the light pulse propagating in the MCR slow-light element can be reduced to about 0.47c (c is the speed of light in vacuum) and the shape of the light pulse passing through the MCR keeps well.

S-band gain-flattened EDFA with two-stage double-pass configuration

A gain-flattened S-band erbium-doped fiber amplifier (EDFA) using standard erbium-doped fiber (EDF) is proposed and experimentally demonstrated. The proposed amplifier with two-stage double-pass configuration employs two C-band suppressing filters to obtain the optical gain in S-band. The amplifier provides a maximum signal gain of 41.6 dB at 1524 nm with the corresponding noise figure of 3.8 dB. Furthermore, with a well-designed short-pass filter as a gain flattening filter (GFF), we are able to develop the S-band EDFA with a flattened gain of more than 20 dB in 1504-1524 nm. In the experiment, the two-stage double-pass amplifier configuration improves performance of gain and noise figure compared with the configuration of single-stage double-pass S-band EDFA.