Use of a single-mode fiber coupler for second-harmonic-generation microscopy

We present a compact second-harmonic-generation (SHG) microscope based on a three-port single-mode fiber coupler. The fiber coupler is used to deliver a near-infrared ultrashort-pulsed laser beam as well as to collect the SHG signal in the visible wavelength range. The SHG microscope exhibits an axial resolution of 1.8 microm, which shows a slight enhancement of the optical sectioning effect compared with that for two-photon excitation at the same excitation wavelength. It is also demonstrated that SHG and two-photon fluorescence images under parallel and perpendicular laser excitation polarization can be simultaneously obtained.     

Two-photon fluorescence endoscopy with a micro-optic scanning head

A major obstacle in the race to develop two-photon fluorescence endoscopy is the use of complicated bulk optics to transmit an ultrashort-pulsed laser beam and return the emitted fluorescence signal. We describe an all-fiber two-photon fluorescence microendoscope based on a single-mode optical fiber coupler, a microprism, and a gradient-index rod lens. It is found that the new endoscope exhibits an axial resolution of 3.2 microm and is capable of imaging transverse cross sections of internal cylindrical structures as small as approximately 3.0 mm in diameter. This device demonstrates the potential for developing a real-time diagnostic tool for biomedical research without the need for surgical biopsy and may find applications in photodynamic therapy, microsurgery, and early cancer detection.     

Double-clad photonic crystal fiber coupler for compact nonlinear optical microscopy imaging

A 1 x 2 double-clad photonic crystal fiber coupler is fabricated by the fused tapered method, showing a low excess loss of 1.1 dB and a splitting ratio of 97/3 over the entire visible and near-infrared wavelength range. In addition to the property of splitting the laser power, the double-clad feature of the coupler facilitates the separation of a near-infrared single-mode beam from a visible multimode beam, which is ideal for nonlinear optical microscopy imaging. In conjunction with a gradient-index lens, this coupler is used to construct a miniaturized microscope based on two-photon fluorescence and second-harmonic generation. Three-dimensional nonlinear optical images demonstrate potential applications of the coupler to compact all-fiber and nonlinear optical microscopy and endoscopy.     

Biosensing based on two-photon fluorescence measurements through optical fibers

We have performed two-photon fluorescence detection in a new scheme in which femtosecond laser pulses were delivered thorugh an optical fiber for nonlinear excitation and the emitted fluorescence was collected through the same fiber. Single-mode fibers were determined to give higher detection efficiency than multimode fibers, consistent with theoretical considerations. The utility of fiber-optic sensing based on two-photon fluorescence detection was proved by an experiment that measured the uptake of a targeted drug delivery agent into cultured cancer cells.     

A fiber-based single-unit dual-mode optical Imaging system: Swept source optical coherence tomography and fluorescence spectroscopy

We propose a fiber optic single-unit but dual-mode optical imaging system that can provide fast cross-sectional imaging capabilities of swept-source optical coherence tomography (SS-OCT) and functional capabilities of fluorescence spectroscopy (FS). By adopting a fiber optic FS system into a fiber-based SS-OCT system, a compact and effective multimodal single-unit SSOCT-FS system is achieved. Here, the key element of the proposed multimodal imaging system is a specially designed fiber coupler based on double-clad fiber (DCF), which has only cladding-mode coupling capability. The DCF couplers are fabricated with home-drawn DCF by several fabrication methods; a twisting method, a side-polishing method and a fused biconical tapered (FBT) method. Experimentally, the FBT method provides rather flat cladding mode coupling efficiency over 40% in a wide wavelength range. With this specially designed DCF coupler, the OCT signal and the fluorescence signal is measured independently but with a single-unit system. The performance of the SSOCT-FS system is confirmed by measuring the cross-sectional image and the fluorescence signal of a photosensitizer chlorin e6 injected in-vivo rat tumor model.     

Potential of two-photon-excited fluorescence for distributed fiber sensing

The design and operating parameters of a new class of continuously distributed optical fiber sensor are described. By use of counterpropagating pulses, two-photon excitation of fluorescence from ions doped into the fiber enables any position to be monitored. By this means temperature and also strain may be sensed with high spatial and temporal resolution. As the doped fiber is transparent for single-photon absorption at the wavelength of the light pulses, attenuation does not set an upper limit to its length.     

一种实现光纤耦合器分光比微调的新方法

随着光纤通信技术的不断发展,光纤通信中至关重要的光无源器件——光纤耦合器,其使用量正在不断的增加。如何提高光纤耦合器的成品率已成为一个很重要的问题。通过对具有一定分光比的未封装的窄带光纤耦合器的一端进行固定和在另一端进行扭转,可以实现耦合器分光比的微调。实验表明,对耦合器施加扭转力矩会使耦合器的分光比发生一定的变化,并且在扭转的过程中附加损耗的变动很小。利用这一特性可以对偏离预定分光比的耦合器的分光比实现微调,从而可得到更符合要求的分光比,提高了成品率。     

Fabrication of an optical fiber reflective notch coupler

A method of fabricating a reflective notch coupler in an optical fiber has been developed. The coupler consists of a 45° microprism that penetrates into the core of a multimode optical fiber. One face, at 90° to the fiber axis, is nonreflective, and one face, at 45° to the fiber axis, is reflective. Our method of fabricating a notch and selectively mirroring only the 45° face is low-cost, precise, and easily scalable. The coupler allows near-100% coupling of light into an optical fiber from the side, while allowing coupling of any desired fraction of light out from the core at a 90° angle on the opposite side of the fiber.     

Simulation and experimental research on polymer fiber mode selection polished coupler

Multimode dispersion is the main obstacle for high bandwidth in multimode optical fiber （MMF） communication system. Mode selection is an effective method to oppress multimode dispersion. We propose and investigate a kind of polymer optical fiber polished coupler. Beam propagation method （BPM） is employed to calculate the coupling coefficient of transmission modes in MMF coupler, and an output pattern from coupling branch is obtained. Analysis and experiment show that this coupler can select certain modes by changing polished depth, contact area, and intersection angle of two branches, which means that the device can be employed both as a mode selector and a sensor. In addition, simulation shows that five times bandwidth enhancement may be realized by selecting modes with the polymer fiber polished coupler.     

Multiple-Output Fiber-Ring Lasers and Amplifiers in a Hybrid CATV and ADSL Broadcasting Optical Fiber Communication System

In this article we propose two kinds of new fiber ring structure with a semiconductor optical amplifier. The first structure is a one-fiber-ring amplifier with an 8 × 8 fiber coupler and a semiconductor optical amplifier (SOA). The second fiber ring structure is a two-fiber-ring laser including an 8 × 8 fiber coupler, a 2 × 2 E/O modulator, and an SOA. The 14-output spectra of the fiber laser are measured. The gain coefficients of each port of the multiple-output-fiber-ring amplifiers are also measured. We apply these two kinds of fiber ring structures in a hybrid CATV and ADSL broadcasting optical fiber communication system. This application can develop a broadcasting system with large coverage area without using many laser diodes and optical amplifiers. The performance of such a system is also analyzed in this article.     

KCl晶体瞬态辐射谱时间分辨多道测量研究

报道了采用多通道光纤延迟和光学多道分析技术采集KCl晶体瞬态冲击辐射时间分辨光谱的新方法。多光纤延时耦合器由5条长度不等的光纤组成,光纤长度差决定延时时差,光纤出射光由透镜耦合进入多色仪,经色散后在面阵探测器上形成与信号光纤一一对应的光谱图形,经计算机处理获得该信号光的空间一时间分辨光谱。建立了实验装置,实现了KCl晶体冲击辐射谱时间分辨多道测量,时间分辨率达到20ns,谱强度分辨率1／18bit。     

Multiple-Output Fiber-Ring Lasers and Amplifiers in a Hybrid CATV and ADSL Broadcasting Optical Fiber Communication System

In this article we propose two kinds of new fiber ring structure with a semiconductor optical amplifier. The first structure is a one-fiber-ring amplifier with an 8 × 8 fiber coupler and a semiconductor optical amplifier (SOA). The second fiber ring structure is a two-fiber-ring laser including an 8 × 8 fiber coupler, a 2 × 2 E/O modulator, and an SOA. The 14-output spectra of the fiber laser are measured. The gain coefficients of each port of the multiple-output-fiber-ring amplifiers are also measured. We apply these two kinds of fiber ring structures in a hybrid CATV and ADSL broadcasting optical fiber communication system. This application can develop a broadcasting system with large coverage area without using many laser diodes and optical amplifiers. The performance of such a system is also analyzed in this article.     

新型1×4塑料光纤功率耦合器的研制

提出了一种新型的塑料光纤功率耦合器 ,该耦合器与传统的拉锥型和混合棒塑料光纤耦合器不同。理论分析了它的损耗特性。该耦合器基于塑料光纤本身的热特性 ,分别将塑料光纤进行拉锥和热缩构成耦合器的两端 ,结构简单 ,制作容易 ,实验结果表明其性能也可满足塑料光纤短距离通信网的要求     

Optical irradiation method for fiber coupler fabrications

An optical irradiation method for high-speed fiber coupler fabrications without contamination is proposed. In optical fiber taper fabrications we found an interesting effect that fiber elongation is self-arrested although laser irradiation is continued. This is a typical effect in the optical irradiation method, but is not seen in the flame method or the thermal heating method. The “self-controlled fiber taper shape effect” is theoretically explained by considering thermal energy flows, and optical fiber couplers are fabricated using this effect. From our experiments, we show that optical fiber coupler fabrications at high-speed without contamination are possible using the optical irradiation method.     

小鼠卵母细胞染色体三维双光子荧光图像的轴向衰减

双光子荧光显微镜作为一种高分辨光学仪器,已经被广泛应用于生物样品的非侵入式三维光学成像中。相比共聚焦显微镜,双光子荧光显微镜拥有更深的探测深度。然而,即便如此,在对较厚的生物样品进行非侵入式光学三维成像时,样品的成像质量也往往会随着探测深度的增加而下降。在临床和生物学领域对研究母性遗传起重要作用的小鼠卵母细胞拥有较大的直径(80～100 μm),吸收和散射效应较为明显。本文研究小鼠卵母细胞染色体的三维双光子荧光图像随探测深度增加图像质量的衰减程度。通过对所得图像进行轴向衰减矫正,利用体积作为参数,将矫正前后小鼠卵母细胞内染色体三维双光子荧光图像进行对比。结果表明,由于吸收和散射效应,卵母细胞存在较严重的光学轴向衰减问题,因此,对用双光子荧光三维成像手段获得的小鼠卵母细胞图像进行衰减矫正是有必要的。这为进一步精确定量的研究卵母细胞内染色体的三维构像打下良好的基础。     

Dynamic analysis of an optical fiber coupler in telecommunications

This paper studies the vibration of an optical fiber coupler which is used in telecommunications subjected to a half sine shock. The emphasis is focused on analyzing the vibration response of the optical fibers inside the coupler and examining the influence of various coupler parameters on the vibration of the optical fibers, since their dynamic behavior is a critical factor in optical fiber communications. A simplified model of the optical fiber coupler is proposed, which consists of a beam and a string representing the substrate and the bundle of the optical fibers of the coupler, respectively. The beam and the string are bonded at four points using adhesive material, and therefore the boundary conditions for their equations of motion are coupled, which increases the complexity of the problem. For the string, two models are developed— the linear model assumes that the tension in the string is constant, while the non-linear one takes into account large transverse deflection and tension variation. With each model, both analytical study and numerical simulations for the vibration of the system under a half shock are carried out. Furthermore, numerical results are compared between the two models. Finally, parametric study leads to conclusions which are of practical importance to the design of optical fiber couplers.     

熔锥型宽带耦合器的研制

介绍了全光纤熔融拉锥型3dB宽带耦合器的理论设计，根据理论设计制作了样品。应用耦合模理论分析了全光纤非对称熔融拉锥型耦合器的宽带特性；提出了3dB宽带耦合器的制作方案，在此基础上制作了样品；对样品进行测试，样品带宽大约为300nm(在1300nm～1600nm波长之间)，附加损耗小于0.5dB，完全达到了实用化的要求。     

Y型熔锥光纤耦合器的应变响应

本文对已广泛应用于光纤通信或作为光纤传感系统中处理元件的Y型单模熔锥光纤耦合器对应变的响应进行了研究.在悬臂梁上进行的应变实验表明,该型耦合器的耦合比不但对应变敏感,而且有单调性.其中,值得注意的是Y型耦合器的应变响应灵敏度高于结构检测中常用的电阻应变片对应变的响应灵敏度.     

单模与多模光纤耦合器的光束合波

现有的光纤耦合器在作为分波器使用时具有较低的插入损耗,在作为合波器时插入损耗较大,为实现低损耗合波目的,提出一种由单模与多模光纤共同构成的混合型光纤耦合器。利用耦合波方程理论分析其工作原理,计算机模拟其耦合过程。采用熔锥法制作工艺,完成单模与多模光纤耦合器的制作,实验结果与理论模拟相吻合;该器件单模到多模光纤的耦合效率、多模到多模光纤的耦合效率均在90％以上,实现了两路光束的功率合波。作为低插入损耗合波器件可广泛应用于光通信以及双包层光纤激光器抽运光的注入。