A new method of measuring the waveguide dispersion factor and the thermo-optic coefficient of long-period fiber gratings

Based on the Mach-Zehnder effect between the core mode and the cladding modes, the interference fringes are formed by a pair of cascaded long-period fiber gratings (CLPFGs). Theoretical analyses show that the spectral spacing and the wavelength of these fringes are functions of the waveguide dispersion factor gamma, which is a characterizing parameter to LPFG and with theoretical and applicational significance. By measuring the characteristics of the transmission spectra of CLPFGs, the absolute value of gamma can be obtained. At the same time, the thermo-optic coefficient of effective refractive index difference between core and cladding modes, p, can also be obtained by measured the temperature sensitivity of these fringes. In the experiments, \gamma\ and mu were measured by this method to be 0.874 and 4.08 x 10(-5) degreesC(-1), respectively, for LPFGs with period of 450 mum and with a HE14 resonant peak at 1554 nm. (C) 2004 Elsevier B.V. All rights reserved.

Tuning the resonant wavelength of long period fiber gratings by etching the fiber's cladding

In this paper the resonant wavelength of a long period fiber grating (LPG) is tuned toward longer wavelength by etching the fiber, For LP04 and LP05 cladding modes', the tuning ranges of 23 and 81 nm are achieved, respectively. Also the dependence of the resonant wavelength on the cladding radius of LPG is theoretically simulated. (C) 2001 Elsevier Science B,V. All rights reserved.

长周期光纤光栅波导色散因子和有效折射率热光系数的测量

对串联的长周期光纤光栅(CLPFG)的透射谱特性进行了理论分析和实验研究。分析表明，长周期光纤光栅中纤芯模和包层模之间的马赫-曾德尔干涉效应导致在长周期光纤光栅谐振峰内的梳状滤波结构特性；其峰值位置和峰间距同串联区光纤的长度以及光纤的波导色散因子有关。测量了长周期光纤光栅的透射谱，并研究了其温度特性。根据测量数据，得到对应于1554nm波长处，所用单模光纤HE14模的波导色散因子γ为0．874；纤芯／包层有效折射率差的热光系数为4．8×10^-5℃^-1。并对这一测试方法和结果，以及长周期光纤光栅的应用进

All-optical switching application of germano-silicate optical fiber incorporated with Ag nanocrystals

银纳米晶体掺杂的高非线性石英光纤的全光转换应用

Temperature and stress tuning characteristics of long-period gratings imprinted in Panda fiber

Temperature and stress tunabilities of long-period Bragg gratings imprinted in Panda fiber are presented in this letter. It is shown that the temperature and strain response of the resonance peaks for fast and slow axes are different not only in their magnitudes but also in the signs of the slope. Furthermore, the characteristics for different order modes are different both in magnitudes and signs. The complicated phenomena are discussed by using a simplified model.

Optical fiber long-period grating with solgel coating for gas sensor

The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity S-n, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection Of C2H5OH was fabricated, and a preliminary gas-sensing test was performed. (c) 2006 Optical Society of America.

长周期莫尔光栅的理论研究

长周期光纤光栅作为一种损耗型的带阻滤波器，在光纤通信和光纤传感器领域有着广泛的应用。结合长周期光纤光栅的传输特性，利用传输矩阵法对多种长周期莫尔光栅的透射谱进行了理论模拟。分析结果表明，莫尔光栅技术在制作高性能的相移长周期光栅和变迹长周期光栅上有着很好的应用前景。

Long period two-dimensional gratings for 8-12 mu m quantum well infrared photodetectors

By considering all possible high order diffracted waves, the authors investigate the spectral response of two-dimensional gratings for quantum well infrared photodetectors (QWIPs). A new method is proposed that using long period gratings may improve grating quality and reduce the resulting cross talk in grating-coupled QWIPs. A sensitivity analysis indicates that the influence of variation of the grating constant on the coupling efficiency is less sensitive for the long period gratings than for the short ones. A large coupling efficiency has been demonstrated for long period gratings. The calculated wide grating response spectra are in good agreement with the experiment result. (C) 1996 American Institute of Physics.

Long period grating for 3-5 mu m quantum-well infra-red photodetectors

By considering all possible high order diffracted waves, the authors calculate the coupling efficiency of long period gratings for 3-5 mu m quantum-well infra-red photodetectors (QWIPs) on the basis of the modal expansion model (MEM). A large coupling efficiency for 3-5 mu m QWIPs has been demonstrated. This greatly reduces the difficulties in fabricating 3-5 mu m grating coupled QWIPs and opens the way to fabricate high performance 3-5 mu m and two colour QWIPs image arrays.

Fiber grating sensors for high-temperature measurement

Two fiber grating sensors for high-temperature measurements are proposed and experimentally demonstrated. The interrogation technologies of the sensor systems are all simple, low cost but effective. In the first sensor system, the sensor head is comprised of one fiber Bragg grating (FBG) and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured based on the wavelength-shifts of the FBG induced by the strain. In the second sensor system, a long-period fiber grating (LPG) is used as the high-temperature sensor head. The LPG is very-high-temperature stable CO2-Aaser-induced grating and has a linear function of wavelength-temperature in the range of 0 - 800 degrees C. A dynamic range of 0 - 800 degrees C and a resolution of 1 degrees C have been obtained by either the first or the second sensor system. The experimental results agree with theoretical analyses. (c) 2007 Elsevier Ltd. All rights reserved.

Optimization of mechanically induced long-period fibre grating transmission spectrum

A new double-layer grating template is designed to reduce the out-of-band loss as much as 1.8dB when the loss of LP03 reaches 10.2 dB. Meanwhile, we propose a method to remove the sidelobes in the transmission spectra by the adjustment of the thickness of pressure plates. The plate-thickness-induced shift of resonant wavelength and the attenuation of loss peak intensity when removing sidelobes can be modified by the fibre distance and contact point on the pressure plates.

室温下稳定的多波长掺铒光纤激光器的研究

通过在线形谐振腔中引入一段缠绕在压电陶瓷上的单模光纤作为正弦相位调制器，使得激射波长的损耗不固定，抑制由于掺铒光纤的均匀展宽效应引起的模式竞争，从而避免了在室温下不稳定的单波长激射，实现了多波长掺铒光纤激光器的稳定输出。为了获得平坦的多波长输出，在谐振腔里使用了一个损耗峰位于1530nm处的长周期光纤光栅，以获得较为平坦的增益谱。通过两个3dB耦合器制成的反射型梳状滤波器的滤波作用，实验中观察到稳定的多波长激射，相邻波长间隔约为0．45nm。中心9个波长的输出功率平坦度为10dB，边模抑制比大于25dB。