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A fiber sphere-embedded long-period fiber grating (LPFG) sensor has been proposed and fabricated for curvature measurement with high sensitivity. Compared with the normal LPFG, the embedded fiber sphere excites cladding modes and two dips of the output spectrum have been observed. The curvature measurement can be realized by monitoring the shift of the two dips. Experimental results show that the highest curvature sensitivity is up to -104.642 nm/m-1 with the curvature ranging from 0 to 0.71 m-1. The temperature response of the sensor has also been studied and a quadratic linear relationship between the dip shift and the temperature has been observed. The highest temperature sensitivity is 0.36 nm/°C with the temperature range between 20°C and 90°C. [ABSTRACT FROM AUTHOR]

A mode-locked all-fiber laser based on the nonlinear multimode interference (NL-MMI) effect of the graded-index multimode fiber (GIMF) is proposed and demonstrated. The saturable absorber (SA) used in the laser consists of a step-index multimode fiber (SIMF) connected by a GIMF. Compared with the theoretically proposed SMF--GIMF--SMF structure, the introduction of the SIMF eliminates the restriction on the length of the GIMF and provides a more flexible method of making an SA based on the NL-MMI. Through bending the device to a certain state, the modulation depth of the SA was measured to be 3.16%. The mode-locked laser output pulses have the pulse width of ~446 fs, the bandwidth of 4.48 nm, and the fundamental repetition rate of 11.7 3MHz. This versatility and simplicity of the SA device combined with the possibility of scaling the pulse energy in the large-mode-area double-clad fiber laser make it highly attractive in ultrafast photonics. [ABSTRACT FROM AUTHOR]

An optical fiber spherical end face coated with zeolite thin film is used together with a fiber Bragg grating (FBG) for simultaneous measurement of trace organic vapor and temperature. The fiber spherical end face is fabricated by using electrical arc discharge on single mode fiber and then coated with zeolite thin film. The FBG is placed in front of the zeolite film-coated fiber spherical end head. The coated fiber spherical end essentially forms an intrinsic Fabry–Perot (F–P) cavity. The trace chemical vapor concentration is measured by monitoring the interference wavelength shift of the coated optical fiber spherical F–P sensor head, due to the zeolite film adsorption to organic vapor molecules. Meanwhile, temperature is measured by monitoring the Bragg wavelength shift of the FBG. The experimental results show that the proposed trace organic vapor sensor exhibits a high sensitivity, which is 1.199 nm∕ppm for isopropanol within the range from 0 to 20 ppm, and the temperature sensitivity is 10.2 pm∕°C within the range from 30°C to 70°C. Such a sensor has high sensitivity, excellent repeatability, fast response, and real-time monitoring capability. [ABSTRACT FROM AUTHOR]

A novel relative humidity (RH) sensor based on a microfiber loop resonator (MLR) is proposed and experimentally demonstrated. As refractive index of the microfiber in the MLR is modified by environmental humidity, resonant wavelength of the MLR changes with RH level. By detecting this wavelength shift, RH measurement is realized with a linear response sensitivity of 1.8 pm/% RH. The obvious advantage of this technique over others is that no coating of humidity-sensitive material is required. [ABSTRACT FROM AUTHOR]

We describe a novel erbium-doped fiber ring laser utilizing the backward amplified spontaneous emission (ASE) power as a secondary pump source so that it can operate in L-band stably. The output wavelength can be tuned in a wide range of 45 nm, from 1560 to 1605 nm. We also compared this scheme with the condition of not using the ASE as secondary pump source, and found this scheme could improve the performance of the laser when using the same components. [ABSTRACT FROM AUTHOR]

We investigate the modal birefringence behavior of a near-elliptic core index-guiding photonic crystal fiber (PCF) by using the first-order perturbation correction technique of mode analysis combined with semivectorial mode-field convergence method. The algorithm requires simple formulation, yields reasonably accurate results, and is efficient as needed for a design analysis; it is also applicable to any index-guiding regular structure/PCFs. The efficacy of our design tool has been verified with otherwise known solutions. Using this as a design recipe, we have realized PCFs with high birefringence characteristics. [ABSTRACT FROM PUBLISHER]

A novel bandwidth-tunable fiber Bragg grating (FBG) filter with fixed center wavelength is demonstrated. A linear tuning range of 7.8 nm (0.26-8.06 nm) for the 3-dB bandwidth is realized in a 10-cm-long uniform FBG with an original 3-dB bandwidth of 0.26 nm. Reflectivity is maintained at higher than O. 7, even as the FBG filter is tuned to the maximum bandwidth of the range. Variation of the center wavelength is less than 0.2 nm. [ABSTRACT FROM AUTHOR]