侧边抛磨光子晶体光纤传输特性理论分析

在建立了侧边抛磨光子晶体光纤D型光纤光学模型的基础上,采用三维有限差分光束传输法计算和分析了侧边抛磨光子晶体光纤的光功率衰减、传输模场等与抛磨区几何参数(剩余半径、轴向旋转角、侧边抛磨区长度)的变化关系。结果表明,当剩余半径大于-1.5μm时,侧边抛磨光子晶体光纤的光功率衰减随着剩余半径的减小而增大;光沿着光纤传输时,基模光传输到抛磨区光功率发生衰减,经过抛磨区后,基模光功率出现回升。沿不同的轴向旋转角方向侧边抛磨,剩余半径大于0.5μm时,侧边抛磨光子晶体光纤的光功率衰减随着剩余半径变化的差别较小;剩余半径足够小时,光沿着光纤传输到抛磨区时,会产生高阶模,沿轴向旋转角θ=30°侧边抛磨时基模模场分布分散程度最大,且在抛磨区产生更多的高阶模。剩余半径大于1.5μm时,抛磨光纤长度变化对输出光功率影响很小,剩余半径小于1.5μm时,输出光功率透射率随着光纤抛磨长度的变化呈振荡变化。分析结果可为侧边抛磨光子晶体光纤的器件制作提供理论指导。     

侧边抛磨光纤中传输光功率变化的实验研究

针对轮式光纤侧边抛磨法制备的侧边抛磨光纤,研究了在侧边抛磨区覆盖不同折射率的材料时,侧边抛磨光纤传输光功率随覆盖材料折射率变化的特性.研究表明,侧边抛磨光纤中传输光功率会随抛磨区覆盖材料折射率的变化而改变.当覆盖材料的折射率小于1.437 8时,光功率损耗近似为零；而当覆盖材料的折射率逐渐增大接近1.452 1时,光功率损耗迅速增大至最大值.当覆盖材料的折射率由1.453 2逐渐增大时,光功率损耗由最大值逐渐减小,最终维持在某个确定的值.侧边抛磨光纤并不是抛磨深度越深,损耗就越大.侧边抛磨光纤中传输的光功率存在波长相关损耗(WDL）.实验结果与理论结论符合较好.     

侧边抛磨光纤光栅的数值模拟和实验研究

本文设计并建立侧边抛磨光纤Bragg光栅的光学模型,通过改变剩余包层的厚度以及抛磨区材料的折射率,模拟计算光栅谐振波长的偏移量以及光栅光谱反射率的变化.实验结果表明,当抛磨区材料折射率越接近光纤纤芯折射率,以及抛磨程度越深(3μm以内),抛磨区材料的折射率的微小变化也会引起光栅谐振波长与光栅光谱反射率明显变化.     

基于光纤侧边抛磨技术的醋酸浓度光纤传感器

演示了两种利用光纤侧边抛磨技术制备的用于醋酸浓度检测的光纤传感器.其中一种光纤传感器采用轮式抛磨法对光纤光栅的光栅区包层进行侧边抛磨加工而成,将醋酸溶液覆盖于光纤光栅的抛磨区,利用侧边抛磨光纤光栅反射峰波长的变化对醋酸浓度进行测量;另一种光纤传感器采用轮式抛磨法对普通单模光纤包层进行侧边抛磨加工而成,将醋酸溶液覆盖于光纤抛磨区,利用抛磨光纤插入损耗的变化对醋酸浓度进行测量.两种光纤传感器的实验都表明:光纤包层抛磨表面与纤芯的距离越小,测量分辨率越高.剩余包层厚度为 0 μm 的侧边抛磨光纤光栅传感器测量醋酸溶液浓度分辨率为6.67%;剩余包层厚度为O.5μm 的侧边抛磨光纤传感器测量醋酸溶液浓度分辨率为0.55%.     

光纤型热光可调光衰减器的设计及其衰减分析

提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。     

数字全息成像技术测量侧边抛磨光纤包层剩余厚度

测量侧边抛磨光纤（side polished fiber,SPF）的包层剩余厚度对其应用有重要的指导意义,现今的测量方法均有所不足,现提出一种基于数字全息技术的测量方法。利用单模光纤纤芯折射率比包层折射率高的特点,基于数字全息成像技术,通过角谱传播法对二维全息图进行相位重构,并通过精确最小二乘法解相位包裹,得到侧边抛磨光纤的相位分布图。根据重构的相位分布图,进一步运用相关的边缘提取算法处理得到侧边抛磨光纤包层剩余厚度。实验测量结果与电子扫描电镜（SEM）测量结果相比,测量相对误差小于0.5%。这种测量方法是一种直接测量方法,减小了间接测量法中由于光纤不对称以及SPF轮廓边缘衍射所带来的测量误差,为侧边抛磨光纤包层剩余厚度的无损、在线测量提供了一种新的途径。同时,此方法还可应用于测量其他特种光纤,例如光子晶体光纤、微纳光纤等。     

侧边抛磨区材料折射率对光纤光栅波长的影响

针对轮式光纤侧边抛磨法,研究了在侧边抛磨光纤光栅抛磨区覆盖不同折射率的材料时,侧边抛磨光纤光栅Bragg波长随外界折射率的改变而变化的特性.理论计算与实验结果都表明,侧边抛磨光纤光栅Bragg波长会随抛磨区覆盖材料折射率的增大向长波长方向偏移；侧边抛磨面离光栅区纤芯表面越近,覆盖材料折射率对波长偏移的影响越大.实验指出,当侧边抛磨区覆盖材料的折射率从1.389 7变到1.447 9时,Bragg波长将会发生1.402 nm的偏移.用轮式光纤侧边抛磨法制备的侧边抛磨光纤光栅可应用于光纤光栅的波长调谐或传感器.     

基于侧边抛磨光纤的全光纤在线光功率监测器

应用侧边抛磨光纤的倏逝波原理,用光电探测器对光纤侧边抛磨区出射光能进行监测,根据理论和实验分析光纤侧边抛磨区出射光能分布,将具有特殊U型侧边抛磨形状和适当抛磨深度的侧边抛磨光纤与光电探测器精密微封装,制成基于侧边抛磨光纤的全光纤在线光功率监测器。测试表明:此全光纤在线光功率监测器对光纤传输的光功率响应特性好,监测器光电转换效率可达200 mA/W以上。测试了器件的插入损耗、波长相关损耗、波长相关光电转换效率和偏振相关损耗等。其波长相关损耗和偏振相关损耗分别为0.3 dB(1 520 nm～1 620 nm)和0.07 dB(1 310nm)。此器件具有对光纤纤芯无破坏、光路中无插入元件、可与光纤系统直接熔接等诸多优点。     

侧边抛磨单模光纤表面等离子体传感器的设计和优化

光纤表面等离子体共振传感器具有体积小、抗电磁干扰,可以实现在线实时远距离检测的优点。为提高传感器的性能,建立了侧边抛磨光纤表面等离子体共振传感的物理模型,分别研究了侧边抛磨光纤的剩余厚度、银膜层的厚度对传感器的灵敏度、共振峰的深度和半高全宽等的影响。结果表明：光纤剩余厚度越小,表面等离子体共振现象越强;随银膜层的厚度增大,共振峰的宽度变宽,而传感器的灵敏度呈现非单调变化。通过综合表面等离子体共振传感器的折射率传感灵敏度和共振峰半高全宽,提出了质量因数作为传感器的优化指标,并最终得到最优化的设计方案为光纤剩余厚度为66.5 μm,银膜的厚度为50 nm,此时质量因数达到98.67。     

基于连通器原理的小探头光纤液位传感器研究

介绍了以汞包层光波导为传感探头的光纤液位传感器的原理及信号处理,其工作原理是利用连通器将液位的变化转变为汞包层光波导包层长度的变化。理论分析和实验表明,当光波导直径和光波长一定时,光功率衰减随汞包层光波导长度增加作线性增加。通过对汞包层光波导引起光功率衰减的检测,探头结构的优化设计以及探测器件的选型,可以获得实时性很强的高精度液位测量。实验测得10m液位的最大测量误差为5．2mm,理论分析的相对测量精度可达0．02％。该液位传感器的研制对于油库等易燃、易爆环境中的液位测量具有重要意义。     

基于侧边抛磨光纤传感器的混合液晶薄膜光折变特性研究

利用侧边抛磨光纤(SPF)传感器抛磨区对外界折射率敏感的特性,研究了混合有偶氮苯(AZO)和手征材料(ZLI811)的液晶混合物薄膜在紫外光照射下产生的光折变效应.将液晶、AZO 和 ZLI811 等 3 种材料的混合物涂覆在经过标定的 SPF 传感器的抛磨区上,制备成混合物薄膜.用 UV 光照射光敏薄膜导致 SPF 中传输光功率改变.实验表明:混合物薄膜在 UV 光照射下有光敏特性,会产生折射率变化,其折射率从1.474 变到1.470.这表明此光敏薄膜材料是负光折变材料.这种光敏薄膜材料可应用于制作新型全光纤光控器件和传感器.     

Numerical ray tracing through a modified cladding fiber optic segment sensors

By using 3-D geometric optics, the effect of a modified cladding on the transmission of light through optical fiber is investigated. Analysis of the light transmission of the optical fiber as function of the modified cladding refraction index and length are presented for various input illumination focused and compared with 3-D ray theory. Applications to chemical sensors are also discussed.The intensity of light signal transmitted through an optical fiber, which its cladding over a finite length is removed, is used as a sensor of refractive of liquids, in which the fiber is immersed. The transmitted light intensity is measured as a function of liquid refractive index for different lengths of the unclad section of the fiber and at each unclad length its sensitivity to change in refractive index of liquid is presented.     

Effect of the Pd-Au thin film thickness uniformity on the performance of an optical fiber hydrogen sensor

Thin alloy film of Pd and Au, formed by simultaneous electron-beam and thermal evaporation techniques, respectively, is used in the design of an optical fiber hydrogen sensor. The sensor consists of a multimode fiber (MMF) in which a short section of single mode fiber (SMF), coated with the Pd-Au thin film, is inserted. Due to core diameter mismatch, the SMF cladding guides light, allowing the interaction between the sensing layer and the guided light. When the sensor is exposed to hydrogen, the Pd-Au layer refractive index diminishes and causes attenuation changes on the transmitted light. Several samples with different layer thickness uniformity were fabricated and tested in a very simple experimental set-up. We have observed that the sensor signal change is dependant on layer thickness uniformity, since the effective interaction length between the evanescent field and the sensing layer is increased. By contrast, such uniformity practically has no influence on the time response of the sensor. The resulting Pd-Au film can detect 4% hydrogen with a response time of 15 s.     

Investigation on characteristics of W-type fiber with an inner cladding made of negative refractive index materials

A doubly clad optical fiber with an inner cladding made of negative refractive index material was proposed and the modes distribution, dispersion and time delay were investigated by fully vectorial numerical method. The results indicate that HE₁₂ mode can be operated as a single mode, the cut-off frequency of modes shifts to low normalized frequency with increasing thickness of inner cladding made of negative index materials, large negative dispersion and time delay can be obtained and tailored by the inner cladding. These results provide theoretical basis for designing novel fibers or optical devices.     

Enhancement of sensitivity in long-period fiber gratings with deposition of low-refractive-index materials

It was proved [Opt. Lett. 30, 720 (2005)] that the deposition of an overlay of higher refractive index than that of the cladding on a long-period fiber grating (LPFG) causes large shifts in the attenuation bands induced by the grating. The result is an enhancement of the sensitivity of the LPFG to variations in the ambient and overlay refractive indices or the overlay thickness. The limitation of the previous design to materials with higher refractive indices than that of the cladding of the LPFG is overcome with a five-layer model. To this purpose, a first overlay of higher refractive index than that of the cladding of the LPFG will enhance the sensitivity of the device to variations in the refractive index of a second overlay of lower refractive index than that of the cladding of the LPFG. Moreover, it is proved that, if the second overlay is thick enough, its behavior resembles that of an infinite layer.     

超细低水峰抗弯损光纤的设计及制作

采用全合成预制棒制造法（VAD＋OVD）和改进的G.652.D光纤拉制法制造光纤.研究了工艺中光纤芯径的大小、第一包层的厚度、芯包折射率差、芯包比等参量与光纤弯曲性能的关系,并据此制作了几种超细低水峰抗弯损光纤.该光纤的裸光纤直径约80 μm,涂覆后成品光纤直径约140 μm,当弯曲半径不小于7.5 mm时,能够在1 260～1 625 nm整个波段内满足DWMD的传输要求.