一种新型温度自补偿高灵敏度折射率计

基于高频CO2激光脉冲写入的新型超长周期光纤光栅(ULPFG),提出了一种可实现温度自补偿的新型高灵敏度折射率计。理论与实验表明,新型超长周期光纤光栅不同闪耀阶次谐振峰对外界折射率与温度变化的灵敏度各自不同,特别的是,该光栅存在对外界折变不敏感的谐振峰,测量中除了可以利用该峰实现温度同时测量外,还可以补偿另一个测量折变的谐振峰因温度变化带来的测量误差。该折射率计具有制作简单、成本低、强度好,灵敏度高等优点,当外界折射率在1.43~1.45范围内变化时,其折射率测量灵敏度可达每单位折射率240 nm,在实际工业应用中具有较大的潜在实用价值。     

Arbitrary chirped fiber Bragg gratings on application of filtering for optical communications

This paper presents an analysis of how to obtain narrow transmission band in the centre of the spectrum of the arbitrary chirped fiber Bragg grating (ACFBG). Grating chirp coefficient and refractive index profile are the critical parameters in contributing to performance of fiber Bragg grating. The reflection spectra and transmission band were analyzed with different refractive index profile. Apodization techniques are used to get optimized reflection spectra. The simulations are based on solving coupled mode equations by transfer matrix method that describes the interaction of guided modes.     

Bragg gratings in rectangular microfiber for temperature independent refractive index sensing

We present fiber Bragg grating fabricated in rectangular microfiber for temperature-independent refractive index (RI) measurement. The grating has two Bragg peaks due to the high geometrical birefringence of the rectangular microfiber. The two peaks present different RI responses because the modes along the orthogonal polarizations have different energy fractions in terms of evanescent field outside the silica microfiber and hence the light/liquid interaction strength are different. In contrast, they exhibit identical temperature sensitivities because most mode energy is confined in the microfiber and the thermal-optic effect of silica dominantly determines the temperature response. As a result, temperature-independent RI sensing can be realized by monitoring the wavelength separation between the two peaks.     

First-order distributed feedback dye laser effect in reflection pumping geometry

Tunable distributed feedback lasing output based on reflection grating configuration instead of the traditional transmission one was realized from rhodamine 6G (R6G)-doped ethanol and 4-dicyanomethylene-2-methyl-6- (p-dimethylaminostyryl)-4H-pyran-(DCM)-doped methanol. Pure gain coupling and additional index coupling were obtained in R6G-doped ethanol and DCM-doped methanol, respectively. The tuning, which was found to be independent of the refractive index of the lasing media, went through the entire stimulated emission band for the two cases. Dual-peak lasing emission indicative of the existence of an index grating was observed in DCM-doped methanol. The interval between the two peaks increased with pump energy.     

Numerical analysis of a temperature sensor based on the photonic band gap effect in a photonic crystal fiber

In this paper we investigate, by the plane wave expansion method and an analytical model, the temperature effect on the photonic band gap fiber, and we report on a numerical demonstration of a temperature sensor based on the photonic band gap (PBG) shift in a solid core photonic crystal fiber (PCF) infiltrated with a high refractive index oil. The bandwidth and the position of the central wavelength of the band gap are the parameters of interests for our temperature sensing purpose. Simulation results were found to be in excellent agreement with the refractive index scaling law and the highest sensitivity of 3.21?nm/°C was achieved, and it will be even higher than the grating based sensors written in PCFs with similar structure.     

高频CO2激光脉冲写入超长周期光纤光栅特性研究

分析了高频CO₂激光脉冲写入的周期达数毫米的超长周期光纤光栅(ULPFG)的模式耦合特性，并在此基础上，简单分析了这种折射率变化主要在光纤包层，且沿光纤横截面呈非对称分布的ULPFG所具有的温度、应变、扭曲及环境折射率响应特性，并在文末做了实验验证，实验结果表明该ULPFG不同谐振峰具有不同的特性响应灵敏度，这与理论分析符合得较好.这些独特的光学特性将使得这种光纤光栅在光纤通信和光纤传感中具有应用价值. 关键词： 光纤传感 光纤光栅 2激光')" href="#">CO₂激光 超长周期光纤光栅     

一种同时测量液体折射率和温度的方法

由长周期光纤光栅的相位匹配条件与光纤纤芯基模LP01和光纤包层模LP0P的模式方程,利用长周期光纤光栅透射谱的谐振峰随温度与外围介质折射率变化而移动的特性,提出了同时测量水的折射率和温度的方法,并分析了其工作原理.对温度与谐振波长的关系进行了计算机仿真.用该方法进行了实验研究,实验结果与理论研究结果基本吻合.     

Spectral characteristics of a two-section multilayer long-period fiber grating sensor

A novel long period fiber grating (LPFG) sensor structure is proposed in this paper. It is constituted by coating an over-layer partially on the fiber grating. Then the LPFG has a two-section multilayer transversely distributed refractive index structure. Using coupling mode theory and transfer matrix method, the influences of refractive index, thickness and length of the coating layer on the spectral characteristics of the new type LPFG were analyzed. The simulation results show that the resonant band is split due to the particularity of the LPFG structure, and the wavelength splitting is strongly dependent on the parameters of the coating layer. This LPFG designing may solve the cross sensitive problem and then realize synchronous measurement of temperature, strain and other physical quantities.     

长周期光纤光栅:原理、制备与应用

较全面介绍了长周期光纤光栅。对比Bragg光纤光栅说明了长周期光纤光栅的特点。对其耦合机理进行了分析 ,阐明了波长选择损耗特性。介绍了长周期光纤光栅的制备方法 ,大致分之为基于非形变的制备方法和基于形变的制备方法。详细阐述其在通信、传感领域的应用 ,尤其是新型应用 :带通滤波、光上下路复用、光纤光源、偏振器件、新型传感等。并针对长周期光纤光栅对温度、应力、外部折射率敏感的特性 ,探讨了调谐性以及温度稳定性的方案     

含负折射率缺陷的一维光子晶体的杂质带

利用传输矩阵方法研究了含负折射率缺陷的一维光子晶体的透射谱.以19个周期的1/4波堆存在3个负折射率缺陷的光子晶体为例进行了数值计算.结果表明:如果改变缺陷的折射率,缺陷模之间的耦合作用将发生改变,带隙中形成的杂质带也随之改变; 当这个折射率取适当值时,在禁带中出现多个尖锐的透射峰,与正折射率缺陷构成的杂质带不同.     

Energy band gap and oscillator parameters of Ga4Se3S single crystals

The optical properties of the Bridgman method grown Ga₄Se₃S crystals have been investigated by means of room temperature, transmittance and reflectance spectral analysis. The optical data have revealed an indirect allowed transition band gap of 2.08 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static dielectric constant and static refractive index as 21.08 and 3.85 eV, 6.48 and 2.55, respectively.     

含双负缺陷的一维光子晶体耦合腔的杂质带特性

利用转移矩阵方法研究了含双负缺陷的一维光子晶体耦合腔的透射谱.计算结果表明，如果改变缺陷的折射率，缺陷模之间的耦合作用将发生改变，使得能隙中的杂质带也随之改变.若这个折射率取适当值，则可以在禁带中同时出现几个尖锐的透射峰和较宽的通带，这种结构可同时用于多通道窄带滤波和宽带滤波. 关键词： 光子晶体 缺陷模 杂质带 滤波     

Hybrid FBG–LPG sensor for surrounding refractive index and temperature simultaneous discrimination

In this work, we propose a configuration of a hybrid fiber Bragg grating together with a long period grating sensor used for simultaneously detect surrounding refractive index and temperature to be applied in aqueous environment and to reveal pollution. We present the simulation of such sensor and analyze the reflected wavelength and amplitude variations of the fiber Bragg grating spectrum to obtain the temperature and the external refractive index variations, respectively. The results show that the fiber Bragg grating reflected amplitude change depends on the variation of the long period grating transmission spectrum with the surrounding refractive index modification and the reflected wavelength shift depends on the temperature of the aqueous solution.     

Sampled fiber Bragg grating for simultaneous refractive-index and temperature measurement

We present a novel scheme for simultaneous measurement of temperature and refractive index by use of a single sampled fiber Bragg grating (SFBG). The intrinsic nature of a SFBG that possesses both fiber Bragg grating and long-period grating spectral responses permits the temperature effect to the measured solely from the former, whereas the refractive-index information is extracted from the latter. Using such a dual-parameter sensor, we successfully demonstrated measurement of the dependence on temperature of the refractive index of an aqueous solution of sucrose.     

柚子型光子晶体光纤啁啾光栅的反射谱特性

利用有限元法和传输矩阵法,对柚子型结构的光子晶体光纤啁啾光栅的反射谱进行了理论分析。得到了啁啾光栅参数和光纤参数对光子晶体光纤啁啾光栅反射谱的影响规律。结果表明随着啁啾系数和折变量的增加,光栅反射谱呈规律变化,当啁啾系数增大到一定程度时几个反射峰会连到一起,形成一个大的反射带宽。光纤的内包层直径和纤芯直径的改变能够影响各反射峰之间的间距。同时研究了切趾变迹对光子晶体光纤啁啾光栅反射谱的影响,研究表明,所用切趾函数会同时对多个峰进行切趾,每个峰的切趾效果都很好。对反射谱波动较大的几个峰相连的啁啾光栅经过柯西切趾后反射谱曲线平滑,适合于实际应用。     

Simultaneous measurement of refractive index and temperature using dual-period grapefruit microstructured fiber grating

By cascading the long period fiber grating (LPFG) and fiber Bragg grating (FBG) in grapefruit microstructured fiber, a novel dual-period fiber grating sensor is proposed. The refractive index and temperature are measured simultaneously by using the different sensitivity of FBG and LPFG. The relationship between dual-period fiber grating transmission spectrum and refractive index, resonant wavelengths and temperature are analyzed theoretically, respectively. The simulation results show that the accuracy of the sensor in measuring refractive index and temperature is estimated to be 2319.6 nm/RIU in a range from 1.33 to 1.36 and 0.017 nm/°C from 0 °C to 100 °C, respectively. Thus, the sensor has high refractive index sensitivity, and can provide the theoretical foundation for the optical fiber biosensor.     

一种新颖的超结构光纤Bragg光栅梳状滤波器的设计

报道一种新颖的用于多波长光纤激光器的超结构光纤Bragg光栅（SFBG）梳状滤波器，其突出特点是仅由单个光栅构成、折射率调制和局部啁啾富于变化、反射峰均匀性好、窄带宽和标准的信道间隔.采用基于LP算法的IS光纤光栅设计技术，将整体加窗切趾法改进为各信道独立加窗切趾，成功地设计出所需的SFBG，同时对SFBG的制作技术也进行了探讨.用传输矩阵法分析反射谱、时延曲线和群时延抖动.结果表明，所设计的SFBG满足各项设计指标要求，在DWDM系统中，这种新颖的SFBG可望成为用于多波长光纤激光器的最理想的高性 能梳 关键词： 超结构光纤Bragg光栅 光栅设计 梳状滤波器     

Influence of slit width on the electromagnetic transmission of a periodic metallic grating

The light transmittance of a periodic metallic grating with varied slit widths has been investigated. The transmission peaks move to the shorter wavelength direction with an increase in the width of slits while keeping the other parameters unchanged. It was demonstrated that the slit width affects the spectral transmittance of the metal grating significantly. It was also found that the effective refractive index and cavity modes in slits are responsible for this phenomenon. Cavity modes play an important role in extraordinary transmission of the sub-wavelength aperture grating. When a complete resonant mode forms in the slits, a high transmission will appear. A wider slit results in a smaller efficient refractive index and thus affects the cavity mode in the slits. These two elements cause the transmission peaks to move to the shorter wavelength direction with widening of slits. The results obtained here may provide a useful guide to design metallic slit grating devices.     

Theoretical analysis of novel fiber grating pair

A novel fiber grating pair that consists of a conventional long-period fiber grating and a fiber Bragg cladding grating (FBCG) is proposed. The FBCG is a new type of fiber grating in which refractive index modulation is formed in the cladding. Through the coupled-mode theory, we accurately calculate the coupling coefficients between modes supported in the fibers. And some other mode coupling features in the fiber cladding gratings are analyzed in detail. The calculation of the modes involved in this paper is based on a model of three-layer step-index fiber geometry. Then, we have investigated the sensitivity characteristics for variation of the modulation strengths of the fiber Bragg cladding gratings’ resonance peaks and the long-period cladding gratings’ (LPCGs) dual resonant peaks. Finally, the modulation strength sensitivity of the grating pair’s three resonant peaks is demonstrated, and the results indicate that these grating pairs may find potential applications in optical fiber sensing.     

一种双段多层长周期光纤光栅光谱特性研究

长周期光纤光栅(LPFG)传感器具有非常广泛的应用价值,而有效解决物理量交叉敏感问题是其实用化的关键。基于LPFG对包层外介质折射率和厚度的敏感性,提出一种双段多层折射率横向分布结构的新型LPFG传感器的设计,并利用耦合模理论和传输矩阵方法分析了镀膜材料折射率、膜层厚度和镀层长度对新型LPFG传感器光谱特性的影响。软件仿真结果证明,这种LPFG由于结构设计上的特殊性,将使LPFG的谐振峰发生分裂,即一个透射峰分裂为两个。由于两个分裂峰对应力和温度的灵敏度不同,利用该结构的LPFG作为传感器,可以实现温度、应力等物理量的同步测量,从而解决LPFG传感器的交叉敏感问题。