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1.
Abstract A comparative study of the fiber-optic evanescent field absorption sensors based on parabolic, linear, and exponential-linear taper profiles has been carried out. The expressions for the effective evanescent absorption coefficient of the fluid have been derived for a diffuse source as well as a collimated source–microscope objective combination. It has been shown that the sensitivity of the sensor depends on the taper profile and the type of the source used in addition to the numerical aperture of the fiber and the refractive index of the fluid. For a given taper profile, the sensitivity is more in the case of the collimated source–microscope objective combination as compared to the diffuse source illumination. Further, the sensor with the exponential-linear taper profile is more sensitive than those having parabolic and linear profiles in the case of both sources. 相似文献
2.
A comparative study of the fiber-optic evanescent field absorption sensors based on parabolic, linear, and exponential-linear taper profiles has been carried out. The expressions for the effective evanescent absorption coefficient of the fluid have been derived for a diffuse source as well as a collimated source-microscope objective combination. It has been shown that the sensitivity of the sensor depends on the taper profile and the type of the source used in addition to the numerical aperture of the fiber and the refractive index of the fluid. For a given taper profile, the sensitivity is more in the case of the collimated source-microscope objective combination as compared to the diffuse source illumination. Further, the sensor with the exponential-linear taper profile is more sensitive than those having parabolic and linear profiles in the case of both sources. 相似文献
3.
C. D. Singh 《Fiber and Integrated Optics》1999,18(4):287-295
A comparative study has been carried out on the detection of gases with the use of attenuated total internal reflection spectroscopy in a multimode step index, based on parabolic, linear, and exponential-linear tapered fibers with porous cladding. Using geometric optics, an expression has been derived for the time dependent evanescent absorbance as the gas diffuses through the cladding. It has been shown that the relative evanescent absorbance depends on the taper profile and taper ratio. For a given taper profile, as the taper ratio increases, the response time of the sensor decreases. Further, the sensor with the exponential-linear taper profile has less response time than those with the parabolic and linear profiles in cases of a particular taper ratio. 相似文献
4.
利用一维变周期谐振腔阵列和非线性缓变边界,可以实现光波从脊波导到光子晶体平面波导 (PCW)的高效耦合.基于平面波展开法(PWE)和时域有限差分法(FDTD),深入分析和讨 论了普通脊波导、2D-PCW结构和本征模以及工作模式、缓变边界形状等对耦合效率的影响, 从而得出光波从脊波导到2D-PCW、再返回脊波导的统一图景.指出考虑模式转换和采用缓变 边界条件可以极大提高PCW与脊波导间的耦合效率.对PC-PW边界采用线性和非线性缓变结构 进行了仿真,讨论了边界缓变程度对耦合效率的影响.结果表明,采用模式耦合和PC-PW余弦 缓变边界时的耦合效率在较宽的带宽内超过了95%.
关键词:
光子晶体波导
脊波导
PWE
FDTD
耦合边界 相似文献
5.
The sucrose concentration measurement and characteristics of light coupling taper structure on sensitivity with various fabrication processes of taper structure for all-fiber Mach–Zehnder interferometer (AFMZI) are presented. Using fusion splicer with electrical discharge, the standard single-mode fiber is employed to be fabricated as conical coupling/decoupling taper structure. The basic two fabrication processes are designed as single fusion-stretching (SFS), multiple fusions without stretching (MF). The third advanced process is composed of SFS and multiple fusions without stretching processes, and called multiple fusions with single stretching (MFSS). Various types of coupling/decoupling taper structures were fabricated based on the three kinds of fabrication processes. The effects of geometry shape including taper waist, taper angle, and sensing length on sensing sensitivity of AFMZIs are estimated. The modifications of fiber core and cladding induced by thermal effect affect the refractive index distributions and shapes of taper structure. The effects of refractive index changes of fiber core and cladding on sensing sensitivity are also discussed. The AFMZI was tested by measuring aqueous sucrose solution of refractive index unit (RIU) from 1.333 to 1.420 RIU. The optical spectrums are measured by a spectrometer. The spectrum dip shifts and sensing sensitivity was measured and calculated, respectively. As shown in results, sensing sensitivities of AFMZIs of taper structure fabricated by MFSS and multiple fusions without stretching processing are generally higher than SFS. The reasons could be aimed on materials modification through thermal effect on blurring fiber core-cladding interface and proper taper angle of taper structure. The more homogeneous refractive index distribution on fiber core-cladding interface, the more detecting light power decoupled through core-cladding interface to interact with exterior environment and enhance the sensing sensitivity. Similarly, an appropriate taper angle also provides a better coupling/decoupling performance. The optimal sensitivities relative to low refractive index, high refractive index, and full refractive index range are 87.62, 133.55, and 104.20 nm/RIU, respectively, and the corresponding sensing length are 30, 50, and 30 mm, respectively, with taper angle of 25° and taper waist of 40 μm. 相似文献
6.
臭氧是地球大气中一种重要的痕量气体,在光化学反应和气候变化中都扮演着非常重要的角色。高光谱红外卫星可以观测到较高垂直分辨率的大气臭氧信息,但是由于热红外受大气温度影响较大,臭氧反演精度会有所下降。为此详细讨论和分析了温度对臭氧吸收光谱和权重函数的敏感性,以及对臭氧反演精度的影响。首先利用逐线积分辐射传输模型LBLRTM,分别模拟计算了六种不同标准大气模式下,1K的随机温度误差对大气透过率和辐射值的影响,发现1 K温度随机误差和臭氧浓度5%~6%的变化引起的辐射值变化量一致。接着利用CRTM辐射传输模型,针对搭载于美国对地观测卫星Suomi NPP(National Polar-orbiting Partnership)平台上的CrIS(Cross-track Infrared Sounder)红外高光谱观测数据,计算了1K的随机温度误差对大气臭氧权重函数的影响,并计算了由1K温度误差所导致的热红外高光谱资料大气臭氧廓线反演误差,结果显示CrIS对于臭氧的敏感区位于10~100 hPa之间,且1 K的温度误差和6%的臭氧浓度变化引起的权重函数变化量相当。最后以CrIS作为实验数据,在最优估计法框架下,通过特征向量统计法获取臭氧廓线的先验知识,并将大气温度廓线和大气臭氧廓线都作为未知量,进行同步迭代反演。将反演结果和配对的世界臭氧紫外数据中心WOUDC的站点数据进行比较,发现在反演中加入大气温度廓线进行同步迭代后,反演结果有显著提高,尤其在平流层与真值几乎一致,最大相对误差不超过20%,在对流层反演结果相对较差,最大相对误差不超过50%,优于欧洲中期天气预报中心ECMWF(European Center for Medium-range Weather Forecasting)臭氧模式数据集ERA-Interim。 相似文献
7.
In this paper, the effect of launching condition of light and the geometry of the sensing region in the case of detection of gases using attenuated total internal reflection (ATR) technique in multimode step index tapered fiber has been described. Using ray approach the response time of the sensor in case of parabolic, linear and exponential-linear tapered optical fiber have been carried out. It has been shown that launching condition and geometry of the sensing region effect the sensitivity of the sensor. Out of three designs the sensor having exponential-linear tapered with selected ray launching has maximum sensitivity and low response time of the sensor. 相似文献
8.
Benye Li Lan Jiang Sumei Wang Jinpeng Yang Mengmeng Wang Qianghua Chen 《Optics & Laser Technology》2012,44(3):640-645
This study proposes a simple, cost-effective method to fabricate fiber-based Mach–Zehnder interferometer (MZI) sensors by concatenating two ultra-abrupt fiber tapers together using a fusion splicer. By concatenating, the taper diameter and length ratio is 1:1 that is much greater than that (1:10) by stretching. The refractive index sensitivity is comparable to the MZI sensors based on long-period fiber grating pairs or stretched fiber taper pairs. The MZI fiber claddings are etched to improve the sensitivity of refractive index measurements. The sensitivity is 664.57 nm/RIU (refractive index unit) for the refractive index ranging from 1.3348 to 1.3558, which is 2–6 times greater than those measured by long period fiber gratings (LPFGs) after sensitivity enhancement. 相似文献
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10.
Efficient coupling from the silicon waveguide to the GeSi layer is the key to success in the GeSi electro-absorption (EA) modulator based on evanescent coupling. A lateral taper in the upper GeSi layer has room for increasing the modulating efficiency and alleviating the sensitivity of the extinction ratio (ER) and insertion loss (IL) to the length of the active region. The light behavior and the effect of the taper are explored in detail using the beam propagation method (BPM). After optimization, the light can nearly be totally confined in the GeSi layer without any oscillation. The modulator with the designed taper can achieve low IL and high ER. 相似文献
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12.
At nanometer regime, fabricating the structures with non-overlapped channel and abrupt doping profile is very complicated and sometimes impossible. So, the resultant device experiences some non-ideal effects which have to be predicted and well addressed by simulation before fabrication. In this paper the effects of overlap between gate and source/drain regions on the performance of carbon nanotube field effect transistors have been investigated. The overlapped structure has been simulated with various doping profiles at drain/source and gate region junction tip. The device performance has been investigated in terms of ON current, Off current, ON/Off current ratio, subthreshold swing, delay, and power delay product (PDP). Simulations show that depending on the variations in the effective channel length, the overlap deteriorates some device characteristics and enhances the others. Where the effective channel length decreases (increases), the overlap deteriorates (enhances) the current ratio and subthreshold swing but enhances (deteriorates) the delay and PDP compared to non-overlapped structure. Furthermore, the overlapped structure with graded profile results in lower current ratio and higher subthreshold swing compared to overlapped structure with abrupt profile. At a fixed current ratio, the delay and PDP of overlapped structure with graded profile are more than overlapped structure with abrupt profile but at a fixed channel length, both profiles have approximately equal delay and PDP. 相似文献
13.
In this paper, the effect of various taper profiles on dispersion slope compensation in optical fiber links is studied. Theoretical and numerical investigation of the linear and nonlinear group delays of tapered fiber Bragg grating's (T-FBG) under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equation using transfer matrix method. Our study shows that the linear tapered FBG profile provide the best result than the linear-exponential profile which can compensate up to 500 km. As result, the spectral characteristics of tapered grating allow them to be used efficiently in high bit rates WDM and long-haul optical communication systems for chromatic dispersion of single-mode fiber. 相似文献
14.
提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%. 相似文献
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In this paper we theoretically study the broadband mid-IR supercontinuum generation (SCG) in a lead-silicate microstructured fiber (the glass for simulation is SF57). The total dispersion of the fiber can be tailored by changing the core diameter of the fiber so that dispersion profiles with two zero dispersion wavelengths (ZDWs) can be obtained. Numerical simulations of the SCG process in a 4 cm long SF57 fiber/fiber taper seeded by femto-second pulses at telecommunications wavelength of 1.55 µm are presented. The results show that a fiber taper features a continuous shift of the longer zero dispersion wavelength. This extends the generated continuum to a longer wavelength region compared to fibers with fixed ZDWs. The phase-matching condition (PMC) is continuously modified in the fiber taper and the bandwidth of the generated dispersive waves (DWs) is significantly broadened. 相似文献
17.
利用图像的非接触检测螺纹是一种高效的检测方法。检测中,精准的获取到螺纹图像的牙型边界是检测的关键,而现有的图像处理技术并不能消除由于螺纹旋线对螺纹图像的影响。针对螺纹图像中牙型边界被遮挡的问题,从圆锥螺纹的几何空间关系分析图像产生误差的原因,建立圆锥螺纹数学模型,得到误差的方程。最后再设计了图像检测系统,根据误差方程修正螺纹图像、提取参数,经验证,此方法可以提高螺纹的检测精度,且通用在圆锥螺纹与圆柱螺纹中。 相似文献
18.
Influence of Reflections of the Output Port on Beam-wave Interaction in Gyrotron Traveling Wave Amplifier 总被引:1,自引:0,他引:1
Haiyan Sun Chongqing Jiao Jirun Luo 《International Journal of Infrared and Millimeter Waves》2008,29(7):657-662
Based on the nonlinear self-consistent theory of gyrotron traveling wave amplifier (gyro-TWA), the influence of the reflections
of the output port with the taper on the beam-wave interaction in the gyro-TWA is studied. The simulation results show that
the reflections have great effects on the TE01 mode gyro-TWA operating at the fundamental. The influence of the taper angle and the interaction length on the beam-wave
interaction and the power profile is discussed and the corresponding physical mechanism is analyzed. The saturated output
power keeps same approximately with the increase of the taper angle in the presence of reflection while the saturated gain
decreases obviously. 相似文献
19.
对1.5μm波导型声光TE-TM模式转换光滤波器进行了研究。采用了可降低驱动功率的表面声波导结构。在1.5 ̄1.6μm波段实现了可调滤光,通带宽度小于2nm,达到97¥以上转换率所需的射频驱动功率约80mW(19dBm),器件总插入损耗约9dB。 相似文献
20.
Eiji Okada 《Optical Review》2000,7(5):375-382
Near infrared spectroscopy and imaging have been used in measurements of brain activity. The scatter of light in biological tissue which causes ambiguity in the volume of tissue interrogated with near infrared instruments is a serious problem for near infrared spectroscopy and imaging. The heterogeneity of superficial tissue of the head, especially the presence of non-scattering clear cerebrospinal fluid, affects the light propagation in the brain. In this paper the theoretical results of the effect of superficial tissue on the spatial sensitivity profile in the head for near infrared spectroscopy and imaging are reviewed. Simplified homogeneous and heterogeneous models are used to investigate the effect of the non-scattering clear layer on the spatial sensitivity profile in the head. Time resolved spatial sensitivity profiles reveal the effect of this layer on the early and late detected light. Finally, the author presents the spatial sensitivity profiles in the sophisticated adult and neonate head models to discuss the effect of superficial tissue on the near infrared measure of brain activity bydetecting the two heads. 相似文献