Modal interferometer based on tapering single-mode-multimode-single-mode fiber structure by hydrogen flame

A modal interferometer is experimentally demonstrated based on tapering a single-mode-multimode-singlemode (SMS) fiber structure heated by hydrogen flame.The interference fringe begins to form when tapering length is 19.8 mm,and becomes regular and clear when the tapering length is longer and the tapered waist diameter is smaller.Annealing process is undertaken to achieve a high extension ratio of approximately 17 dB with free spectral range of 1.5 nm when the tapering length is 33 mm and the tapered waist diameter is approximately 5μm.The temperature and axial strain dependences of the tapered SMS structure are characterized,and the measured temperature and strain coefficients are +7 pm/℃and -9.536 pm/με, respectively.     

Low-loss deposition of solgel-derived silica films on tapered fibers

Films of porous silica are deposited on the uniform waists of tapered fibers in minutes by a modified solgel dip coating method, inducing less than 0.2 dB of loss. The coated tapers are an ideal platform for realizing all-fiber devices that exploit evanescent-field interactions with the deposited porous film. As an example we demonstrate structural long-period gratings in which a periodic index variation in the film arises from the porosity variation produced by spatially varying exposure of the waist to a scanned CO2 laser beam. The long period grating is insensitive to temperature up to 800 degrees C.     

Plastic coating of glass fibers and its influence on strength

Abstract

Sodium borosilicate glass fibers pulled from the melt were plastic coated “on-line” to preserve the fiber strength. By the use of tapered nozzles within the coating applicator the coating could be made concentric around the fiber, and a 40-μm concentric coating was found to be sufficient for the fiber to withstand a mild abrasion test with no deterioration in strength. Strength measurements made in ambient conditions showed that the fiber had a uniform breaking strain of 4% elongation. The same fiber measured at liquid nitrogen temperatures had a breaking strain of 14%, even after extensive handling, which is close to the theoretical glass cohesive strength.     

Intensity measurement bend sensors based on periodically tapered soft glass fibers

We demonstrate a technique for tapering periodically an all-solid soft glass fiber, consisting of two types of lead silicate glasses, by the use of a focused CO(2) laser beam and investigate the bend sensing applications of the periodically tapered soft glass fiber. Such a soft glass fiber with periodic microtapers could be used to develop promising bend sensors with a sensitivity of -27.75 μW/m(-1) by means of measuring the bend-induced change of light intensity. The proposed bend sensor exhibits a very low measurement error of down to ±1%.     

锥形光纤间的耦合特性

将通信光纤的末端拉制成锥形,利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤的耦合、连接和分束.用耦合模理论分析了锥形光纤间的传输和耦合性质,给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果.     

Octave spanning supercontinuum in an As₂S₃ taper using ultralow pump pulse energy

An octave spanning spectrum is generated in an As?S? taper via 77 pJ pulses from an ultrafast fiber laser. Using a previously developed tapering method, we construct a 1.3 μm taper that has a zero-dispersion wavelength around 1.4 μm. The low two-photon absorption of sulfide-based chalcogenide fiber allows for higher input powers than previous efforts in selenium-based chalcogenide tapered fibers. This higher power handling capability combined with input pulse chirp compensation allows an octave spanning spectrum to be generated directly from the taper using the unamplified laser output.     

Spectral superbroadening of subnanojoule Cr:Forsterite femtosecond laser pulses in a tapered fiber

Spectral superbroadening of subnanojoule femtosecond Cr:forsterite laser pulses is demonstrated for the first time in experiments with a tapered fiber. Coupling 40-fs 0.6-nJ pulses of 1.25-μm Cr:forsterite laser radiation into a tapered fiber with a taper waist diameter of about 2 μm and a taper waist length of 90 mm, we observed the spectra spanning more than two octaves at the output of the fiber. These experimental results open new horizons for the creation of compact femtosecond systems based on Cr:forsterite lasers and tapered fibers for optical metrology and biomedical applications.     

Characteristics of WDM Couplers Based on 80 μμ m Cladding Fiber

We have fabricated 1310/1550 and 1480/1550nm WDM couplers using a fiber of 80 μm cladding diameter,whose tapering length is shortened by 4～8mm for the identical coupling strength compared to those of 125μm cladding fibers. We also report their splicing loss to conventional single mode fibers.     

新型缓变锥型PCF结构接口耦合损耗特性

提出一种新型的缓变锥型光纤接口器件。该接口器件是一个长度为150mm左右的缓变锥型光子晶体光纤。利用有限元方法对模场直径差别较大的不同光纤进行拼接时的损耗问题进行研究。研究结果表明:在模场直径分别为9μm和10.4μm的光纤之间加入锥型光纤后可以有效降低耦合损耗,并且在不同波长下耦合损耗都维持在一个较低水平。因此,该接口器件能够实现光纤拼接时物理结构的过渡和不同模场直径的转换,从而使拼接损耗降到最低。     

Laser-diode-pumped 1319-nm monolithic non-planar ring single-frequency laser

Single-frequency 1319-nm laser was obtained by using a laser-diode-pumped monolithic Nd:YAG crystal with a non-planar ring oscillator (NPRO). When the NPRO laser was pumped by an 800-μm fiber coupled laser diode, the output power of the single-frequency 1319-nm laser was 220 mW, and the slope efficiency was 16%. With a 100-μm fiber coupled diode laser pumped, 99-mW single-frequency 1319-nm laser was obtained with a slope efficiency of 29%.     

Wideband supercontinuum generation in tapered tellurite microstructured fibers

Enhanced soliton trapping of dispersive waves in a tapered tellurite microstructured fiber pumped by a 1556 nm femtosecond fiber laser is demonstrated. The short wavelength edge of supercontinuum light is extended from 960 to 600 nm after tapering the tellurite microstructured fiber, which is caused by the enhanced soliton trapping of dispersive waves owing to the changing group velocities in tapered fibers. Wide-band supercontinuum light source spanning from 600 to >2400 nm is generated in tapered tellurite micro-structured fibers. Our experimental and simulated results show that short length (several centimeters) zero-dispersion-wave length decreasing highly nonlinear fiber has a potential for generating wideband supercontinuum light source expanding from visible to mid-infrared region.     

Effects of tapering on gyrotron backward-wave oscillators

Computer modeling has been utilized to guide gyrotron backward-wave oscillator (gyro-BWO) experiments at the University of Michigan over a wide range of tapered interaction regions and tapered magnetic fields. E-GUN code is used to examine beam and diode characteristics, while MAGIC is used to analyze the dynamics of the problem, such as particle kinematics and microwave power production. Several innovative techniques are used to create matching boundary conditions for a backward propagating wave. MAGIC simulations predict optimum performance of the gyro-BWO operating in a TE₀₁ mode within a combination of uniform interaction region and a tapered axial magnetic field which increases 7.5% in the direction of beam propagation. Experiments have been performed to investigate the effects of tapering magnetic fields and tapered interaction region radii on the high-power microwave emission from the gyro-BWO over the frequency range from 4.0 to 6.0 GHz. These experiments were performed on the Michigan Electron Long-Pulse Accelerator (MELBA) with parameters: V=-0.7 to -0.9 MV, I_diode=1-10 kA, I_tube=1-4 kA, T_e-beam =0.4-1.0 μs. Tapered interaction regions of 37%, 23%, 9.4%, and 6.4% were built and tested to determine their effect on microwave power, pulselength, and inferred energy compared to the uniform interaction region. Magnetic tapering trim coils with a range of -10.6%<ΔB/B₀<+15.0% were constructed which allow the orientation of the field taper to be changed without breaking the vacuum. The peak microwave power from individual shots was from 30 to 55 MW. Experiments on magnetic field tapering indicate that positive tapered fields improve microwave power and energy output     

超连续谱光纤合束器的数值模拟

设计了一种用于超连续谱合束的光纤合束器,这种合束器通过将多路光子晶体光纤拉锥后对接到一路多模光纤制成。借助有限差分波束传输法对该合束器进行了数值模拟,结果表明拉锥过渡长度和拉锥比例对耦合损耗具有较大影响,当拉锥过渡长度小于拉锥衍射长度时合束器有较大传输损耗,而过渡长度足够大以及拉锥比例较小时,合束器具有较低的耦合损耗以及优良的宽光谱耦合特性。所得出的数值结果为光子晶体光纤拉锥和超连续谱光纤合束器研制提供了一定的参考依据。     

Highly nonlinear chalcogenide glass micro/nanofiber devices: Design, theory, and octave-spanning spectral generation

In this review we consider the basic elements of tapering chalcogenide optical fibers for the generation of extreme spectral broadening through supercontinuum generation. Creating tapered nanofiber devices in chalcogenide fiber, which has an intrinsic nonlinearity that is two orders of magnitude higher than silica, has resulted in the demonstration of octave-spanning spectra using record low power. We first present a brief theoretical understanding of the tapering process that follows from the basic principle of mass conservation, and a geometric construction tool for the visualization of the shape of tapered fibers. This is followed by a theoretical treatment of dispersion engineering and supercontinuum generation in a chalcogenide nanofiber. In the final section, we cover the experimental implementation of the chalcogenide nanofiber and demonstrate an octave-spanning spectrum created with 150 W of peak power.     

High-field electron emission of carbon nanotubes grown on carbon fibers

Carbon nanotubes with uniform density were synthesized on carbon fiber substrate by the floating catalyst method. The morphology and microstructure were characterized by scanning electron microscopy and Raman spectroscopy. The results of field emission showed that the emission current density of carbon nanotubes/carbon fibers was 10 μA/cm² and 1 mA/cm² at the field of 1.25 and 2.25 V/μm, respectively, and the emission current density could be 10 and 81.2 mA/cm² with the field of 4.5 and 7 V/μm, respectively. Using uniform and sparse density distribution of carbon nanotubes on carbon fiber substrate, the tip predominance of carbon nanotubes can be exerted, and simultaneously the effect of screening between adjacent carbon nanotubes on field emission performance can also be effectively decreased. Therefore, the carbon nanotubes/carbon fibers composite should be a good candidate for a cold cathode material.     

Refractive index sensor based on tapered PCF in-line interferometer

A simple and compact refractive index sensor is demonstrated by tapering a photonic crystal fiber (PCF) in-line interferometer. The PCF is spliced between two single-mode fibers and tapered via hydrofluoric acid etching. Its sensitivity in liquid is more than an order of magnitude larger than the untapered one. By optimizing the etching process, we can fabricate more uniformly and thinly tapered PCF interferometers with higher sensitivity in the future.     

Optimum fiber tapers for increasing the power in the blue edge of a supercontinuum-group-acceleration matching

We demonstrate how the gradient of the tapering in a tapered fiber can significantly affect the trapping and blueshift of dispersive waves (DWs) by a soliton. By modeling the propagation of a fundamental 10?fs soliton through tapered fibers with varying gradients, it is shown that the soliton traps and blueshifts an increased fraction of the energy in its DW when the gradient is decreased. This is quantified by the group-acceleration mismatch between the soliton and DW at the entrance of the taper. These findings have direct implications for the achievable power in the blue edge of a supercontinuum generated in a tapered fiber and explain observations of a lack of power in the blue edge.     

一种新型的基于四孔单元光子晶体光纤的设计与分析

设计了一种基于四孔单元的光子晶体光纤,它可以满足光通信系统中高双折射率、负色散和低限制损耗的要求,比起通常的三角结构光纤有着更高的双折射率,并且结构制作也较简单。采用全矢量有限元法和各项异性完美匹配层法对所设计的光纤进行了仿真研究。仿真结果表明:该光纤在1.55μm波长处可获得10~(-2)数量级的双折射率,在较宽广的波段范围具有大的负色散,限制损耗低于10~(-9)dB/m;该光纤在保偏光纤、单极化单模光纤、色散补偿光纤等方面具有重要的应用。     

Plastic coating of glass fibers and its influence on strength

Sodium borosilicate glass fibers pulled from the melt were plastic coated “on-line” to preserve the fiber strength. By the use of tapered nozzles within the coating applicator the coating could be made concentric around the fiber, and a 40-μm concentric coating was found to be sufficient for the fiber to withstand a mild abrasion test with no deterioration in strength. Strength measurements made in ambient conditions showed that the fiber had a uniform breaking strain of 4% elongation. The same fiber measured at liquid nitrogen temperatures had a breaking strain of 14%, even after extensive handling, which is close to the theoretical glass cohesive strength.     

微米光子回路中能量的荧光显示与调节

基于弯曲的罗丹明B(rhodamine B)掺杂聚合物微米线,搭建了Y型分束器、微米线-环形腔耦合结构等典型微米光子回路;采用锥形光纤耦合的方式,将光能量导入回路并在微米线中激发荧光;通过移动锥形光纤增加光的传输距离,分析能量的输出强度与传输长度之间的关系。研究发现,通过激发出的荧光光路强度,可显示回路中的能量沿微米线轴线周期性地衰减振荡,并在微米线弯折处发生相位跃变;回路输出端能量随传输距离的增加呈周期性变化,且在半个周期内,可将Y型分束器分光比从1.3调节到2.4(<2μm),使耦合结构中单个输出端的强度峰谷比达到2.1(<6μm)。利用锥形光纤耦合激发出的荧光,可在远场直接显示回路的能量传输状态,并在传输距离改变时对能量的耦合情况进行实时反映,实现回路输出性能的大范围调节,为复杂微光子器件的搭建及性能调节提供了一种直观、简便的方法。