熔融拉锥技术在光纤耦合传输中的应用

为了实现光纤激光器和放大器系统中不同参量光纤的低损耦合,采用光纤拉锥方法来实现光纤连接。经过理论分析,在大数值孔径光纤传输到小数值孔径光纤时,采用光纤拉锥技术可以有效地提高传输功率。采用改造的大模光纤熔接机进行拉锥实验研究,精确控制拉锥时间、放电功率、步进量和步进速率可以获得不同的拉锥形状。采用光纤拉锥元件对标准单模光纤和大模场光纤进行耦合实验,得到纤芯内传输的耦合输出效率由之前的50%提高到85%,获得了低损连接效果。结果表明,熔融拉锥技术为不同光纤之间的耦合提供了一种简单实用的方式。     

Er3+-doped cladding fibres and their taper componentapplications

A biconical taper amplifier utilizing an Er³⁺-doped cladding fiber is discussed. A maximum gain of 0.6 dB in a 2.4-Gb/s optical transmission experiment was obtained with a taper about 40 mm long. This result shows the potential of a new structure for Er³⁺ -doped coupling and amplifying components     

High-coupling tapered hyperbolic fiber microlens and taper asymmetry effect

This paper proposes a new scheme of a tapered hyperbolic-end fiber (THEF) microlens for efficient coupling between laser diode and single-mode fiber. The THEFs were fabricated by symmetrically tapering the fiber during the etching process and hyperbolically lensing the tip during the fusing process. The hyperbolic microlenses of the THEFs have demonstrated up to 82% coupling efficiency for a laser with an aspect ratio of 1:1.5. The influence of tapering asymmetry on the coupling has also been investigated experimentally and theoretically. The axially symmetrical tapered microlenses of the THEFs showed far-field profiles well approximated by a Gaussian profile, while the asymmetric taper deviated significantly from a Gaussian profile. The coupling efficiency for both symmetrical and asymmetrical microlenses were calculated based on the Fresnel diffraction theory and the results were in good agreement with the measurements. This study makes it possible to fabricate the hyperbolic microlenses using unique etching and fusion techniques that result in a more than 2 dB improvement in coupling efficiency when compared to the currently available hemispherical microlenses.     

倒锥透镜型光纤端的出射光场性质

倒锥透镜型光纤端系经过特殊技术加工而成。本文用二阶统计相关函数,采用单色相干光源,计算了倒锥透镜型光纤端的光场分布及其统计相关性质,并与平端的情况作了对比。在实验上,用He-Ne激光作为单色相干光源,对理论进行了验证。     

高能激光注入光纤导光锥耦合性能实验研究

提出了测试光纤导光锥耦合效率的试验方法,通过试验验证了光纤导光锥实现激光传导的可行性,同时在光纤入射角度为1°～5°、运动状态为静止及甩动的条件下,对光纤导光锥的耦合效率进行了实验研究。研究结果表明,光纤导光锥在入射角为1°～5°、光斑直径约为2mm时的激光耦合传输效率大于60%,入射光损伤耐受力低于100mJ。利用光纤导光锥实现高能激光的耦合导光,对于开展光电对抗内场仿真试验具有重要意义。     

Single-photon imaging system with a fiber optic taper

We report a time-of-flight photon-counting imaging system in conjunction with a single-photon detector mounted with a fiber optic taper, which equivalently enlarges the active area of the single-photon detector by 100 times. The field of view of the imaging system is extended from ±0.57° to ±7° by using the fiber optic taper to collect the scattered photons. Since only a single avalanche photodiode is used, the noise level of the system is maintained at a low level. We demonstrate the scanning of the targets at a stand-off distance of 28 m with a centimeter depth resolution.     

Ultraviolet laser delivery using an uncoated hollow taper

We demonstrate a simple grazing-incidence-based method for ultraviolet (UV) laser delivery and direct laser-to-taper coupling using an uncoated glass hollow taper. The taper serves as a mode homogenizer that converts the strongly multimode distribution of the input laser emission into a high-quality smooth profile at the taper output. An uncoated pyrex-glass hollow taper is used for direct launching, without any intermediate focusing elements, of UV laser emission from the third harmonic ( 355 nm) of a Q-switched Nd:YAG laser into the taper. The linear hollow taper provides a laser-to-taper coupling efficiency exceeding 70%     

移动温区光纤熔融拉锥锥区形貌研究

光纤拉锥是光纤器件制作中的一项重要技术,为了研究快速往复移动温区熔融拉锥系统中锥区形貌与各拉锥参数的关系,基于体积不变原理,建立了往复运动温区熔融拉锥系统在满足温区运动速度大于光纤拉伸速度条件下的理论模型,详细描绘锥区形貌形成过程,推导出锥区直径、锥区平坦区长度与温区运动次数、温区运动速度、光纤拉伸速度、温区往复运动距离以及温区宽度与光纤初始直径之间的定量关系,并进行验证,实验结果与理论分析一致。     

熔融拉锥过程中的偏振调制效应及应用

对光纤熔锥耦合器拉制过程中的偏振调制效应作了定性的理论分析,耦合区内的几何双折射和应力双折射导致的对称模和反对称模在x偏振方向和y偏振方向上的传播常数差不一致,从而引起两个方向的偏振光耦合的空间周期不同,存在相位差别,当相差正好达到π时实现偏振分离.在此基础上制作了熔锥型偏振分束器,消光比达到了16.5dB.     

Temperature-independent accelerometer using a fiber Bragg grating incorporating a biconical taper

An intensity-modulated optical fiber accelerometer is proposed and experimentally demonstrated by using a fiber Bragg grating (FBG) incorporating a biconical fiber taper. Acceleration-induced microbending of the fiber taper region introduces various attenuation to the light, so that acceleration can be measured from changes of the optical power of the reflected light from the FBG. This power detection method reduces the cost and complexity of the sensor setup since only photodetector is required for the signal detection. In the static measurement, a relatively large range of 5g (g is gravity, equals to 9.8 m/s²) with sensitivity of 4.85 nW/g is achieved. Vibration measurements have also been carried out with a frequency up to 20 Hz. The proposed accelerometer is nearly independent of temperature because the reflected optical power of the FBG is insensitive to temperature.     

Fiber loop polarizers using a fused taper coupler

All-fiber polarizers using a fused taper coupler are presented. The polarizers are fabricated by constructing a fiber loop joining the output ports of a fused taper coupler. Input light splits into two linearly polarized modes which are reflected and transmitted by the polarizers, respectively. The transmitted and the reflected lights become linearly polarized. The demonstrated polarizer shows an extinction ratio of -20.0 dB     

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     

Analysis of the enhanced coupling efficiency for different profile curves of special optical taper

For enhancing the coupling efficiency between the beam and the photodiode, a special optical taper is proposed for receiving optical signal. Based on the circular symmetric structure of special optical taper, the profile curve equations of it are deduced, including the trigonometric function type, parabolic type and exponential type. Moreover, the coupling efficiencies for special optical tapers with different profile curves are studied. The relationships of incident position, incident angle and coupling efficiency are analyzed. Finally, the comparison of coupling efficiency analytical results is also given.     

开槽深度和坡度对高频高阶模带宽和中心频移的影响

为对构建太赫兹频率下高阶单模工作的同轴布喇格谐振腔提供理论依据,基于模式耦合理论,比较研究了不同开槽深度和不同开槽坡度形状及坡度角对工作在太赫兹频率高频高阶耦合模式下工作模式和竞争模式带宽、中心频率偏移特性的影响. 结果表明:工作模式和竞争模式的带宽随着开槽深度的加深都变宽,但中心谐振频率点几乎没有偏移,槽深加深,带隙重叠现象会恶化,不利于模式选择;正圆锥形坡度方式时随着坡度角的增加,工作模式的中心频率点没有发生偏移,竞争模式中心频率点靠近工作模式中心频率点,不利于带隙重叠现象的抑制;倒圆锥形坡度方式时,随着坡度角的增大,竞争模式的中心频率点远离工作模式中心频率点,很好地抑制了带隙重叠;正圆锥形坡度和倒圆锥形坡度对带宽的影响都不大. 这些特性有利于拓展同轴布喇格结构作为反射器和滤波器的性能.     

Optical fiber tapers--A novel approach to self-aligned beam expansion and single-mode hardware

We investigate the performance characteristics of single-mode optical fiber tapers. These devices have a standard single-mode fiber geometry at one end and gradually increase in cross section so that the size of the core at the other end is comparable or greater to that of a multimode fiber. These tapers effectively expand the single-mode spot size and are envisioned as basic building blocks in a multitude of optical components. Analytical and experimental studies, atlambda = 0.63 mum, show that the dominant mode is preserved while traveling through the taper, from either direction. The excess coupling loss between two tapers is less than 0.1 dB. The sensitivity of the excess loss to lateral and axial displacements for two coupled tapered sections is greatly reduced compared to that between two single-mode fibers. The sensitivity to angular displacement is increased but is within practical limits. For example, for an excess loss of 0.5 dB, the maximum allowed lateral displacement is 3.1 μm for taper coupling, while only 0.73 μm is allowed in the case of fiber coupling. An axial displacement of 291 μm for taper coupling produces 0.5 dB loss while a displacement of only 16.5 μm produces a 0.5 dB loss for fiber coupling. For the same loss, angular displacements of 0.42° for the tapers and 1.77° for the fiber are allowed.     

Transmission characteristics of wide-aperture optical fiber taper

The transmission characteristics of the wide-aperture optical fiber taper (OFT) have been determined experimentally under diffuse and parallel light excitation. Power transmission efficiency versus the normalized radius of the excited input aperture of the OFT has been obtained in both cases. The OFT forms a specific output intensity distribution provided that a uniform excitation of all the OFT modes is ensured. Power transmission efficiency of more than 50% can be obtained at an appropriate normalized radius of the incident laser beam. The wide-aperture OFT is, independent of or within the cavity-taper output laser (CTOL) concept, a suitable element for launching power laser emission into optical fibers     

Compact modal interferometer built with tapered microstructured optical fiber

A modal interferometer was built with tapered large-mode-area microstructured optical fiber (MOF). The tapering was introduced by slowly stretching the fiber while it was heated with a high temperature flame torch. With this "slow-and-hot" tapering process, the MOF air holes collapse and the taper waist is transformed into a solid unclad multimode fiber. This allows the coupling between the fundamental HE/sub 11/ MOF mode and the HE/sub 1m/ modes of the solid fiber. The beating of the HE/sub 1m/ modes makes the transmission spectra of the taper to exhibit an oscillatory pattern. The influence of the taper geometry and wavelength on the interference pattern is discussed. The interferometer can be used for diverse applications.     

Optical fiber tapers at 1.3 µm for self-aligned beam expansion and single-mode hardware

We have experimentally demonstrated the applicability of optical fiber tapers at 1.3 μm as a simple and practical means of achieving beam expansion in a self-aligned unitary structure. These devices have a standard 8.1-μm core at one end which gradually increases in cross section to the order of 100 μm at the other end. Tapers are envisioned as basic building blocks in a multitude of single-mode optical components. Experiments performed on a batch of eight tapers verified, to experimental accuracy, that no significant amount of mode conversion or beam distortion takes places in the taper. The insertion loss of the taper was found to be under 0.1 dB. The sensitivity of the excess loss between two tapers to lateral and axial displacement is greatly reduced as compared to that between two single-mode fibers. For example, the 0.5-dB loss point of taper coupling corresponds to a 10-μm lateral displacement and a 700-μm axial displacement versus respective 1.6-μm and 36.5-μm displacements for fiber coupling. The increased sensitivity to angular displacement is within practical limits.     

微透镜光纤在半导体激光器中的应用研究

对几种典型的半导体激光器与光纤的耦合特性进行分析,提出提高耦合效率所采用的微透镜光纤的结构.介绍熔拉型、化学蚀刻型、研磨抛光型、切削型、自聚焦光纤型和铸模型等微透镜光纤的制作原理和工艺以及目前达到的指标,并对各种形式的透镜光纤进行了评价.提出了提高耦合效率和失调容差、降低插损的新思路.     

Phase and amplitude comparison between experiment and calculation of ultrabroad-band pulses generated in a taper fiber

Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered.