Tapered single-mode optical fiber evanescent coupling

We describe the results of a numerical and experimental investigation of how a point source of radiation couples light to the HE ₁₁ mode of a tapered single-mode fiber. Specifically, we have investigated two different geometries of nonadiabatic, tapered single-mode optical fiber. The motivation for this study is the characterization of a single-mode tapered optical fiber biosensor. In such a device light is collected from fluorescent sources located along the cladding surface of the tapered fiber. Taper-to-taper coupling measurements and fiber mode calculations indicate the device sensitivity decreases exponentially as sources are moved away from the tip of the tapered fiber     

Radiation Fields of a Tapered Film and a Novel Film-to-Fiber Coupler

Light in a tapered thin-film optical waveguide radiates into the substrate because the waveguide mode in the taper becomes cut off. Our measurement of the radiation pattern shows that the light emerges from the taper as a narrow beam with an angular width of only 2/spl deg/-4/spl deg/. We have studied the problem based on ray optics and based on a wave theory of radiation modes. We also have demonstrated a film-to-fiber coupler in which an optical fiber collects all the light emerging from the taper.     

多模锥形光纤耦合与出光特性的研究

从理论和实验两方面研究了多模锥形光纤锥端的特性。用射线理论分析了不同锥角大小条件下锥端光线传输特性,推导出了锥角大小与锥端孔径角及出光发散角的关系。按照理论指导制备了不同锥角的银行光纤,通过激光二极管与锥形光纤耦合等实验验证了理论的正确性。     

Design of a single-mode tapered waveguide for low-losschip-to-fiber coupling

The novel waveguide structures described in this paper have nonlinearly tapered shapes that result in low radiation losses despite their relatively short lengths. The core at the waveguide endface connected with the fiber has a very small cross section and an expanded mode field with a non-Gaussian shape. The taper structures are analyzed by using an improved step-transition method. This method is a based on the theory of enclosing a waveguide within electrical walls and that can therefore treat the radiation modes in a tapered waveguide as discrete mode spectra. Analyzing the relationships between the lengths and shapes of the tapers and the radiation loss due to the tapers show that appropriately tapered semiconductor waveguides operating at an optical wavelength of 1.55 μm and having a taper length of less than 0.7 mm can have a radiation loss of only 0.1 dB and a coupling loss with a conventional single-mode fiber of less than 0.5 dB     

半导体激光器与单模光纤的耦合—理论与实验研究

本文介绍半导体激光器与单模光纤耦合的理论与实验研究.采用拉锥光纤,实验测量的高功率大辐射角半导体激光器与单模光纤之间的耦合效率为44％.     

有双包层结构的楔变脊型光斑转换器的设计

为了提高硅基上单模波导器件与单模光纤的耦合效率和工艺容差,设计了一种实用新型光斑转换器,它由水平和垂直双向楔变的波导芯区和双内包层构成.分析了内包层折射率与其厚度对耦合效率的影响,发现通过优化内包层的参数可以加强对扩展光场的限制.针对在硅基上制作垂直楔变结构的波导还很困难的情况,提出了一种低成本、简单可行的制作方法.     

有双包层结构的楔变脊型光斑转换器的设计

为了提高硅基上单模波导器件与单模光纤的耦合效率和工艺容差,设计了一种实用新型光斑转换器,它由水平和垂直双向楔变的波导芯区和双内包层构成.分析了内包层折射率与其厚度对耦合效率的影响,发现通过优化内包层的参数可以加强对扩展光场的限制.针对在硅基上制作垂直楔变结构的波导还很困难的情况,提出了一种低成本、简单可行的制作方法     

Realization of Tapered Waveguide by Stretching the Rod Waveguide

By stretching the rod waveguide with different velocities in opposite directions, the tapered waveguide can be fabricated. In condition of taking no account of volume expansion caused by heating and under the assumptions of volume conservation,the rod waveguide can be stretched freely in the heated region without being stretched outside of the heated region. A model,which shows the relation of the transition shape and the two factors, that is the ratio of two velocity and the heated region length, is presented for the shape of the taper transition through mathematic deduction. Based on this model, a desired tapered waveguide can be fabricated. The tapered waveguide are widely used for fabricating tapered fiber couplers and sensors. In addition, the conclusion can be used for fabricating fused fiber coupler.     

高功率大芯径光纤锥的特性研究

对高功率脉冲激光系统中光纤锥的结构、透过率及损伤阈值特性进行了理论研究和实验分析。研究结果表明：光纤锥的几何结构、数值孔径、熔接损耗等都会影响其透过率,通过合理设计光纤锥的几何尺寸,合理选择光纤数值孔径,有效降低熔接损耗,改进拉锥工艺等措施,可以提高光纤锥的透过率;光纤端面的杂质缺陷是造成光纤抗激光损伤能力下降的重要原因,通过改善光纤端面质量,可较大程度地提高光纤锥传输激光的能量。     

锥形光纤的结构与特性

通过理论分析和仿真试验,研究了锥形光纤的几何形状对锥形光纤的传输损耗和耦合效率的影响.用几何光学的分析方法,说明了光信号在锥形光纤中的传输损耗远低于同类型的圆柱形光纤;仿真试验研究了光源与光纤的相对位置、锥形光纤的尖端半径、锥形光纤的锥角大小对锥形光纤耦合效率的影响.     

指数渐变TEM喇叭辐射脉冲波形畸变分析

指数渐变TEM喇叭沿主轴方向长度一定时,主射方向上辐射脉冲峰峰值随口径高度递增,当辐射脉冲峰峰值到达最大值后,辐射脉冲峰峰值随着口径高度递减,并且辐射脉冲波形发生畸变。为了分析响应波形畸变原因,基于等效开路传输线模型给出指数渐变TEM喇叭脉冲响应的近似表达式,并且结合指数渐变TEM喇叭内部的电磁能量流动过程修正辐射脉冲表达式。理论分析表明,指数渐变TEM喇叭辐射脉冲由两个分量叠加而成,并且这分量之间存在的相对时延与高度渐变线的相对变化率正相关,过大的相对时延会使辐射脉冲的波形发生畸变,从而导致辐射脉冲峰峰值小于同尺寸线性渐变TEM喇叭的辐射脉冲峰峰值。利用电磁仿真软件得到相同尺寸的指数渐变TEM喇叭与线性渐变TEM喇叭的辐射脉冲波形,通过二者之间的对比验证理论分析的正确性。     

An implantable optrode composed of fiber and flexible thin-film electrode

An implantable optrode composed of fiber and multi-channel flexible thin-film electrode is developed. The flexible recording electrode is made from polyimide and is wrapped around the optical fiber. The front end of the fiber is tapered by wet etching. With the tapered shape, the light can leak from the sidewall of the fiber, and the tapered tip makes it easy to be implanted. The flexible electrode is attached with its recording sites aligning to the tapered part on the fiber. With this method, the fiber acts as an optical waveguide, as well as a support probe for flexible thin-film electrode. This novel device simplifies the fabrication process and decreases the size of the optrode. The device works well in vivo and the optical caused spike can be recorded with signal-to-noise ratio of 6:1.     

Coupling between angled-facet amplifiers and tapered lens-endedfibers

The coupling between angled facet amplifiers and tapered lens-ended fibers is investigated theoretically and experimentally. The theoretical investigation is based on a three-dimensional plane wave model which accounts for the phase differences introduced by the angled facets. The coupling is investigated with respect to the beam parameters of the amplifier waveguide and the tapered lens-ended fiber, and with respect to the fiber position. The excess coupling losses due to the facet angle and to the variation of the fiber lens radius are investigated theoretically and found to be in good agreement with experimental results. For optimized lens radii, the excess loss for a 10° facet angle is found to be less than 0.5 dB compared to a normal facet amplifier     

组合锥型光纤SERS探针的理论设计与优化

对组合锥型光纤表面增强拉曼（SERS）探针的结构参数进行了设计与优化。通过建立描述消逝波激发组合锥光纤探针表面纳米颗粒的激发光衰减系数模型,结合激发光经渐变锥段的全反射传输、探针平直段与激发光纤间的模式匹配原理,给出了组合锥型光纤SERS探针的结构参数设计与优化方法。利用该设计与优化方法,在给定的光纤和纳米颗粒结构以及周围环境和激发光功率下,进行了光纤SERS探针结构参数的模拟设计。     

Simulation of radiation generation in an active double-clad optical tapered fiber

A model of radiation generation process in active tapered double-clad optical fibers based on rate equations in the adiabatic approximation is developed. The generation process in active tapered fibers with different geometric profiles and mirrors at both ends alloyed with ytterbium is numerically simulated. The advantages of tapered fibers over cylindrical fibers are demonstrated; these advantages include low power density, high output power, higher power slope efficiency, and smaller length required for achieving similar output power.     

低阈值光纤激光器稳频特性研究

为了实现低阈值光纤激光器的频率稳定输出,设计了环形腔光纤激光器,以光纤光栅作为波长选择元件,在未泵浦光纤饱和吸收体和其锥形化结构的协同作用下实现激光纵模选择,获得了短光纤饱和吸收体长度下的单纵模激光稳定输出。介绍了未泵浦光纤饱和吸收体选频原理和锥形结构滤波原理,实验研究了不同光纤饱和吸收体长度下激光纵模特性和波长稳定性,以及锥形化光纤饱和吸收体的激光输出特性。实验表明,引入锥形化结构的饱和吸收体后,激光器能够稳定输出1545 nm波长的单纵模激光,并有效降低光纤激光器阈值至7.58 mW,采用延迟自外差方法测得该光纤激光器的线宽小于8 kHz。     

Modeling of Tapered Fiber-Optic Surface Plasmon Resonance Sensor With Enhanced Sensitivity

Theoretical model for surface-plasmon-resonance-based fiber-optic sensor with a metal-coated uniform core sensing region sandwiched between two identical tapered fiber regions is proposed. The effect of taper ratio (TR) on the sensitivity of the sensor is studied. The study shows that the proposed probe geometry with TR lying between 1.5 and 2.0 provides the best performance. The physical reasons behind sensitivity enhancement due to tapered regions are provided.     

熔锥光纤的特性研究

从理论和实验两方面研究了熔锥光纤锥区的传输、耦合、偏振和调制特性。用耦合模 理论分析了光纤锥形区的传输和耦合性质,给出了锥形光纤传输和耦合效率与锥形区结构的关系。实验上测定了实际锥形光纤在不同锥角、不同长度下的偏振特性,得出偏振光经实际锥形光纤传输或耦合后,再传输其终端,得到均是椭圆偏振光的结论。测定了载波光脉冲经过锥形光纤耦合后其脉冲的变化特性,实验表明,光脉冲在经过锥形光纤耦合传输后其形状保持不变。     

Index-and-dimensional taper and its application to photonic devices

A mode-field-converting optical channel waveguide with tapered refractive index and cross-sectional dimensions is proposed. In this waveguide, both the refractive index and cross-sectional dimensions of a core are adiabatically varied along a propagation direction in such a way that the normalized frequency V of the waveguide may be kept constant. Since radiation loss caused by waveguide imperfections is strongly dependent on the V value, the waveguide has good mode-field-converting capability without causing high radiation loss. Layer thickness and index of a core of a silica waveguide were tapered by modulating a raw material gas flow in a flame hydrolysis deposition method, and a channel width taper was formed by a photolithographical technique. In order to confirm the usefulness, taper waveguides have been used (1) to achieve good field matching between a fiber and a guided-wave optical switch, and (2) to fabricate a fiber-compatible monolithic 32×32 star coupler in a small chip     

Optical spot-size converters for low-loss coupling between fibersand optoelectronic semiconductor devices

Structures of spot size converters that allow low loss and easy coupling between an optical semiconductor device and a fiber are proposed and designed theoretically. These spot-size converters have a tapered small core for expanding the mode field. They also have a double cladding region which consists of an n⁺-doped InP substrate as the outer cladding and a p-doped or nondoped InP layer as the inner cladding with a ridge structure. This double cladding utilizes the plasma effect of a carrier which makes the refractive index of highly doped n-InP lower than that of p-doped or nondoped InP. The double-cladding structure can tightly confine an expanded mode field in the inner cladding, and results in low radiation loss at the tapered waveguide, in addition, this structure reforms the mode field shape into a Gaussian-like shape and achieves a low loss coupling of less than 1 dB with a large misalignment tolerance for fiber coupling. These spot-size converters are easily fabricated and applicable to all types of optical semiconductor devices