Jianzhong Hao

Simultaneous strain and temperature measurement using a compact photonic crystal fiber inter-modal interferometer and a fiber Bragg grating.

An all-fiber sensor scheme for simultaneous strain and temperature measurement is presented. The sensing head is formed by serially connecting a polarization maintaining photonic-crystal-fiber-based inter-modal interferometer (IMI) with a fiber Bragg grating (FBG). The IMI, exhibiting an opposite strain response as compared to that of the FBG, is highly sensitive to strain, while it is insensitive to temperature. This has potential for improving the strain and temperature measurement resolutions. A sensor resolution of ±8.3 με in strain and ±2 °C in temperature are experimentally achieved within a strain range of 0-957.6 με and a temperature range of 24 °C-64 °C, respectively.

A Pressure Sensor Using Fiber Bragg Grating

A pressure sensor utilizing a fiber Bragg grating (FBG) has been demonstrated. An FBG interrogation system consisting of a fiber Fabry–Perot tunable filter detects the shift in the reflected wavelength when a range of force was applied perpendicularly to a bare FBG, resulting in a nonlinear response. When the FBG was embedded within some carbon fiber material, the test results show an excellent linearity between the wavelength shift and the applied force. Sensing force of up to 60N has been demonstrated without causing deformation to the FBG. The pressure sensor has a sensitivity of 1pm (equivalent to ~0.8 m e ).

Nanotube Q-switched low-threshold linear cavity tunable erbium-doped fiber laser

We demonstrate a novel all-fiber nanotube Q-switched low-threshold linear cavity tunable erbium-doped fiber laser (EDFL). With a compact and low insertion loss carbon nanotube based saturable absorber connected in a linear EDFL cavity, a low pump threshold of 18.57mW is obtained. The pulse repetition rate can be adjusted from 8.12 to 72.2kHz by varying the pump power from 18.57 to 118.8mW. In addition, the emission wavelength can be adjusted from 1545.04 to 1549.99nm by tuning the central wavelength of the fiber Bragg grating, which serves as an end mirror of the laser cavity.

Wide Pulse-Repetition-Rate Range Tunable Nanotube

A novel all-fiber wide pulse-repetition-rate range tunable nanotube Q-switched low threshold erbium-doped fiber (EDF) laser is demonstrated. By connecting a compact and low insertion loss carbon nanotube-based saturable absorber and a section of high concentration EDF in a simple linear laser cavity, Q-switched laser, with a threshold of 29.85 mW, a pulse-repetition-rate tunable range of 14.5-141.4 kHz, and a minimum pulse duration of 330 ns, are achieved. With this laser structure, the self-mode-locking effect on the Q-switch operation can be effectively suppressed.

Q

A novel cladding-mode-resonance-based polarization-maintaining photonic-crystal-fiber Sagnac interferometer (PMPCF-SI) and its application for fiber sensor are demonstrated. By introducing a mode field diameter mismatch at a splicing joint of an inbuilt single-mode fiber (SMF)-PMPCF-SMF structure connected in an SI, an intermodal interference is constructed by the excited cladding modes and the polarization modes of the PMPCF. With such a PMPCF-SI, simultaneous strain and temperature measurements are demonstrated. The SI behaves as a sensor and a filter simultaneously. By measuring the wavelength variation and transmissivity difference between two almost symmetrical resonance peaks in the spectral response of the SI, simultaneous strain and temperature measurements are achieved.

-Switched Low Threshold Erbium-Doped Fiber Laser

We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinal-mode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector.

Cladding-Mode Resonance in Polarization-Maintaining Photonic-Crystal-Fiber-Based Sagnac Interferometer and Its Application for Fiber Sensor

A fiber Bragg grating (FBG) with an inverse-Gaussian apodization function is proposed and fabricated. It is shown that such a FBG possesses dual-wavelength narrow transmission peaks and the wavelength spacing between the two peaks is easily controllable during fabrication. Incorporating such a FBG filter into a fiber laser with a linear cavity, we obtain stable dual-wavelength emission with 0.146 nm wavelength spacing. This arrangement provides a simple and low cost way of achieving dual-wavelength fiber laser operation.

Switchable dual-wavelength single-longitudinal-mode erbium-doped fiber laser using an inverse-Gaussian apodized fiber Bragg grating filter and a low-gain semiconductor optical amplifier

The paper describes the design features and characteristics of an embedded fiber Bragg grating (FBG) pressure sensor that has been developed to measure forces applied in the direction perpendicular to the fiber axis. This FBG-based pressure sensor provides an absolute measurement in terms of wavelength shift, which avoids problems of signal intensity fluctuation often encountered by conventional intensity-modulated or phase-modulated pressure sensors. The initial outcome of our study indicates that direct sensing using bare-FBG is infeasible for real applications due to its non-linearity and limited range of force sensing. However, when the FBG is embedded into some composite material, the sensor exhibits excellent linearity, high stability and reliability over a wider force-sensing range, making it a potentially viable sensing element. When an FBG is embedded into some fiber-reinforced composites, a level of sensing force of up to 60N with a sensitivity of 3.96 pm/N and resolution of 1pm (equivalent to 0.8με) is achievable without causing permanent deformation to the FBG.

Inverse-Gaussian apodized fiber Bragg grating for dual-wavelength lasing

We report a liquid-level variation sensor based on a fiber Bragg grating (FBG) inscribed in a 6.5-μmdiameter microfiber. The proposed microfiber Bragg grating (MFBG) in air has two separated reflection peaks, which are caused by the fundamental mode reflection and the higher-order mode reflection. Each of the two peaks will split into another two adjacent peaks when a fraction of the MFBG sensor immerses into liquid. By measuring the reflectivity difference between the two original peaks and their respective adjacent liquid-induced peaks, the liquid-level variation can be determined.

Realization of an embedded fiber Bragg grating-based pressure sensor in fiber-reinforced composites: embedding techniques and performance characteristics

An erbium-doped fiber ring laser is presented. It consists of an inverse-Gaussian apodized fiber Bragg grating acting as a dual-wavelength passband filter, and an unpumped erbium-doped fiber serving as a saturable absorber. The proposed fiber laser can produce two stable lasing lines in which each of them operates in single-longitudinal-mode (SLM). This dual-wavelength SLM laser can generate a microwave signal at 10.502 GHz by beating the dual wavelengths at a photodetector.