微流道中消逝场激励的荧光光源研究

将石英裸光纤植入聚二甲基硅氧烷(PDMS)基片的微流道中,采用沿光纤轴向光激励、消逝场激励染料分子的方式,在基片微流道中获得均匀的荧光辐射。实验发现,在激励光强确定的条件下,荧光辐射的强度与染料溶液的浓度呈线性正相关关系,而与包层溶液的折射率呈非线性正相关的关系。用消逝波激励荧光的辐射理论,很好地解释了实验结果。     

聚二甲基硅氧烷微流道中光流控荧光共振能量转移激光

将单一折射率的石英裸光纤植入由聚二甲基硅氧烷构成的基片微流道中,以低折射率的罗丹明B(RhB)和吡啶821(LDS821)乙醇溶液构成的供体和受体对作为激光增益介质.采用沿光纤轴向消逝波抽运方式,首先以波长为532nm的连续波激光器作为激励光,对荧光共振能量转移特性参数进行了研究.然后以波长为532nm的脉冲激光器作为抽运光,通过直接激励供体分子RhB,并将其能量转移给临近的受体分子LDS821,在不改变抽运光波长的条件下,实现了较低阈值(1.26μJ/mm~2)的受体LDS821激光辐射.     

消逝波激励的双波段光纤回音壁模式激光辐射

将石英光纤浸入低折射率的染料溶液中后构成圆柱形微腔.采用轴向光抽运消逝波激励激光增益的方式,使增益区域局限在圆柱形微腔回音壁模式的模场区域内,由此显著地提高了抽运效率,增加了沿光纤轴向的增益长度.在一根石英光纤的轴向分段填入浓度同为2×10^-3mol/L的罗丹明6G和罗丹明B乙醇溶液,在567—576nm 和592—600nm的两个波长范围内同时获得回音壁模式的激光辐射;分段填入浓度为8×10^-4和8×10^-3mol/L的罗丹明B乙醇溶液, 关键词： 消逝波激励 圆柱形微腔 回音壁模式 双波段激光辐射     

光纤回音壁模式的三波段激光辐射研究

将石英光纤浸入低折射率的激光染料溶液中构成圆柱形微腔.采用沿光纤轴向光抽运的消逝波激励增益方式,获得了沿光纤轴向长距离的激光染料增益,受激辐射光在圆柱形微腔中回音壁模式的支持下形成激光振荡.在直径为288 μm的同一根光纤外分三段分别填入罗丹明6G、罗丹明610和罗丹明640激光染料乙二醇溶液,实现了波长分别在567～575 nm、605～614 nm和656～666 nm三个不同波段的回音壁模式激光振荡,用一根光纤同时获得了红、橙、黄三种不同颜色的激光辐射.对实验所获得的回音壁模式激光光谱做了模式标定,依据标定的模式数计算了各种模式以及抽运光在光纤截面的强度分布.计算结果表明,激光增益区域总是局限在圆柱形微腔回音壁模式的模场区域内,由此可以显著地提高抽运效率,增加抽运光沿光纤轴向的增益长度.     

光纤回音壁模式激光产生长度的实验与理论研究

采用沿光纤轴向光抽运消逝场激励增益的方式,获得了沿光纤轴向较长范围的回音壁模式激光辐射.研究了这种激光器的激光产生长度与抽运能量间的关系.实验发现:当抽运能量刚超过激光产生阈值时,激光产生长度迅速增长;随抽运能量的继续增加,产生长度的增长趋势变缓;产生长度随抽运能量的变化关系决定于增益包层溶液的染料浓度和溶液折射率.根据抽运光沿光纤轴向以受抑全反射方式传播的物理特性,在抽运能量中引入了遵循比尔吸收定律的指数衰减函数,结合消逝场激励增益的回音壁模式激光理论,在分析系统增益和损耗的基础上由激光阈值条件推导出了 关键词： 回音壁模式 受抑全反射 消逝场 激光产生长度     

回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中,采用沿光纤轴向光抽运消逝波激励染料增益的方式,发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加,对小直径光纤,阈值能量随之增加;对大直径光纤,阈值能量单调缓慢递减;对直径适中的光纤,阈值能量先减后增,存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论,导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线 关键词： 光纤激光器 回音壁模式 激光阈值 消逝波     

偏斜光线抽运下的回音壁模式光纤激光辐射特性

研究了偏斜光线抽运下的回音壁模式光纤激光辐射特性.实验发现,在抽运光以偏斜光线方式沿光纤的近轴向抽运时,回音壁模式的光纤激光辐射中,既存在光电矢量和光纤径向垂直的横电波(TE),也存在光电矢量和光纤径向平行的横磁波(TM);随增益包层染料溶液折射率的增加,径向模式数和角模式数相同的TE波和TM波之间的波长差单调减小,回音壁模式激光辐射的中心波长向短波方向移动,辐射的波长范围变窄.用回音壁模式激光的辐射理论结合激光染料的四能级模型,满意地解释了实验结果.     

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。     

基于光纤腔衰荡技术的液体挥发过程监测法

提出一种基于光纤腔衰荡系统并以一小段包层腐蚀光纤作为传感头的液体挥发测量方法,同时搭建相应的实验装置进行了实验研究.从模式理论出发分析单模光纤传输模场的能量分布,并采用有限元法数值模拟光纤端面能量的分布,结果表明:包层越细的单模光纤对应越大的消光系数,即泄露出来的倏逝波能量越大,从而对外界环境更敏感,但是较细包层的单模光纤存在的损耗更大.综合分析得出腐蚀光纤的最佳直径应为26μm,最佳腐蚀长度为1cm.通过实时监测衰荡谱的衰荡时间变化,得到了30℃恒温环境下,乙醇与丙三醇混合溶液中乙醇浓度随挥发时间的变化曲线.实验结果表明,混合溶液中乙醇的浓度随挥发时间呈单指数规律衰减,该变化规律与理论分析相符.由于液体浓度与其折射率成正比,随着乙醇的挥发,混合溶液的折射率逐渐接近光纤包层的折射率,使其对腐蚀光纤纤芯中泄漏的倏逝波能量的吸收程度逐渐增大,环腔的衰荡时间也相应逐渐减小.此外,该监测方法在常温下具有较低的温度交叉敏感性.     

基于荧光强度比值法可用于现场测量的低成本聚合物光纤温度传感器

基于荧光强度比值法,设计了一种使用两种荧光染料的光纤温度传感器.实验中,罗丹明B和罗丹明110分别为对温度敏感和对温度不敏感的荧光传感物质,利用聚合物光纤来传导激发光及接收荧光.由于两种染料的荧光谱峰相距60 nm,因此容易将二者对应的荧光谱分开.通过确定能代表两种染料的最优荧光光谱范围,获得具有良好线性度的温度-荧光强度标定曲线.实验研究了不同浓度的荧光染料对标定曲线的影响,当染料浓度为0.3 g/L时,可获得0.28℃的最小均方误差及0.0128/℃的灵敏度.此外,该传感器还具备一定的抗光源扰动和抗荧光染料漂白的能力.     

轴向隐失波激励的回音壁模式光纤激光器

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器.在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应.实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽.用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果.低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段.     

Linearly polarised three-colour lasing emission from an evanescent wave pumped and gain coupled fibre laser

A novel Whispering--Gallery--Mode (WGM) fibre laser, emitting linearly polarised three-colour light, is demonstrated by pumping and gain coupling with evanescent waves. The pump light is longitudinally coupled into a bare optical fibre immersed in a dye solution of lower refractive index. The dye molecules around the bare fibre are excited by the evanescent waves of pump light when they propagate along the fibre in a total internal reflection. When the pump beam within the fibre is a meridian beam, the WGM lasing emission from the fibre laser is a linearly polarised transverse electric wave, while it is a mixed wave of the linearly polarised transverse electric and magnetic waves if the pump beam is a skew beam within the fibre. Because the excited molecules are located within the evanescent field of WGM, a good spatial overlap between the dye gain and the evanescent field leads to a high pumping efficiency and a longer gain distance along the fibre. Once the bare fibre is inserted into three glass capillaries filled with Rhodamine 6G, 610 and 640 dye solutions, respectively, WGM laser oscillations at the wavelengths of 567--575, 605--614 and 656--666~nm occur simultaneously, and a linearly polarised three-colour lasing emission is achieved in a single optical fibre.     

A study on the biological detection chip through the use of PDMS lens for the reinforcement of fluorescence receiving signal

In this study, MEMS process technology is adopted to produce microfluidic chip and PDMS lens. SU-8 thick film photo resist is coated onto silicon wafer surface in two times of spin coating, then through lithography and mold transfer technology, PDMS chip of minimal line width 100 μm and thickness 200 μm is printed. In fluorescence detection aspect, we use objective lens to couple laser optical source to optical fiber, and then have it incident to excite fluorescence sample, the excited fluorescence then passes through filter and detected by optical detector of experiment group and spectrophotometer of reference group. From the experiment result, the Hex fluorescence detection limit of the system is verified to be 1 pmol/5 μl. In addition, we have integrated PDMS lens into microfluidic chip to make generalized detection experiment, it was found that the signal measured by optical embedded type is higher than that of non-embedded type. Meanwhile, the microfluidic chip with double concave lens (135°) and10 mm PDMS focusing lens can be utilized to obtain optimal fluorescence receiving effect. The fluorescence intensity is raised by 2–3 times, and the measurement limit is lowered to 100 fmol/5 μl.     

Anomalous variation of thermal lens signal with concentration from rhodamine B in methanol solution

Thermal lens signals in solutions of rhodamine B laser dye in methanol are measured using the dual beam pump-probe technique. The nature of variations of signal strength with concentration is found to be different for 514 and 488 nm Ar⁺ laser excitations. However, both the pump wavelengths produce an oscillatory type variation of thermal lens signal amplitude with the concentration of the dye solution. Probable reasons for this peculiar behaviour (which is absent in the case of fluorescent intensity) are mentioned.     

Flow Injection Small-volume Fiber-optic pH Sensor Based on Evanescent Wave Excitation and Fluorescence Determination

A small-volume fiber-optic pH sensor (FOEWS) based on evanescent wave excitation is developed and evaluated. The sensor is simply fabricated by inserting a decladded optical fiber into a transparent capillary tube. A microchannel between the optical fiber and the capillary inner wall was formed and acted as flow cell for solution flowing through. The pH-sensitive fluorophore of fluorescein can be excited by the evanescent wave field produced on the fiber core surface to produce emission fluorescence. pH value was then sensed by its enhancing effect on the emission fluorescence intensity. The response range of the sensor is from pH 2.09 to pH 8.85 and the linear range is from pH 3.25 to 8.85. The proposed sensor has a small detection volume of 2.5 μL and a short response time of 8 s. It has been applied to measure pH values of real water samples and was in good agreement with the results obtained by commercial pH meter.     

Cavity-Q-driven phenomena in an evanescent-wave pumped and gain coupled whispering-gallery-mode fiber laser

We study cavity-Q-driven lasing wavelength shift and line-width widening in an evanescent-wave pumped and gain coupled Whispering-Gallery-Mode (WGM) fiber lasers. A bare optical fiber is immersed in a lower refractive index (RI) dye solution, pumped and gain coupled by evanescence waves, and linearly polarized WGM lasing emission is observed from the rim of the fiber. We find that both lasing wavelengths and line width of WGM peaks are sensitive to the RI of the dye solution and the fiber diameter, with the increase of the RI of the dye solution or decrease of the fiber diameter, a blue shift of the lasing spectrum and a widening on the spectral line width are observed. The observed phenomena have been attributed to the change of quality factor of a circular cavity built in the fiber cross section, the achieved experimental data agree well with the calculated values of the quality factor.