熔融拉制微纳光纤耦合器的仿真模拟

为了对微纳光纤耦合器进行研究,采用光束传播法,在不同熔融区长度和不同波长输入光情况下对微纳光纤耦合器的熔融拉制过程进行数值模拟,取得了输出光功率随拉伸长度变化的曲线和光场分布,并分析了耦合器的3个阶段的模场变化和光场特点。结果表明,当拉伸到微纳光纤耦合器失去有效耦合阶段时,两光纤的输出光功率趋于相等且不再随拉伸长度的变化而变化;熔融拉锥耦合器在各个阶段的光场分布特点不同;熔锥型的微纳光纤耦合器失去有效耦合与熔融区的光纤直径直接关联,且此光纤直径与输入光的波长有关,波长越小,熔融区需经拉伸达到的光纤直径越小。这一结果对研究微纳光纤耦合器失去有效耦合的成立条件是有帮助的。     

Wavelength-flattened fused couplers

A technique is reported for the fabrication of fused couplers, which yields devices having splitting ratios substantially independent of wavelength. A low-loss, stable, single-mode 2×2 port coupler has been fabricated using this technique. The coupler has 50/50% coupling at both 1.3 and 1.52 ?m and 50% ± 9% coupling over the wavelength range 1.23 to 1.57 ?m.     

Wavelength-selective fused fiber couplers utilizing fielddifference between core and cladding modes

It is shown that wavelength-selective fused taper couplers can be made by using the large difference in field distribution, between core and cladding modes. It is evident from the calculation results that fibers with a high-index difference and a thin outside diameter are necessary to fabricate the couplers. Fused taper couplers are made of thin fibers with a cladding diameter of 66.0 μm and an index difference of 0.84%. The splitting ratio of the coupler obtained is more than 20 dB in the 1.53-μm region and less than -20 dB in the 0.8 to 1.0-μm region. The loss is less than 0.2 dB and 0.4 dB in the 1.53-μm and the 0.8 to 1.0-μm regions, respectively     

Modelling fused single-mode-fibre couplers

The fused single-mode tapered coupler is successfully modelled by assuming that the neck section of the coupler can be represented by a rectangular dielectric waveguide. Guidance is provided at the glass-to-air (or external medium) boundary and the cores are neglected. The mechanism of field detachment from the cores is outlined and the coupler characteristics are derived from the interference between the two lowest-order modes of the large waveguide.     

Wavelength-insensitive fused polished couplers

Wavelength-insensitive fused polished couplers are fabricated from different fibres and from identical fibres where in the latter case one of the fibres is polished to such an extent that a small portion of its core is removed.<>     

基于强度传输矩阵的保偏光纤耦合器偏振研究

为了描述保偏光纤耦合器的分光比、附加损耗对输入光偏振态较为敏感的问题,提出了强度传输矩阵的概念,利用强度传输矩阵分析方法可以解释分光比和附加损耗随偏振态的变化规律。针对强度传输矩阵的概念,进行了理论分析和实验验证,搭建实验系统测量出耦合器的损耗、分光比以及偏振串音,将测量数据代入到快慢轴的理论方程中进行计算可以得到耦合器的强度传输矩阵参量,并且代入到圆偏振光注入情况下的方程中,进行了相应的实验验证。结果表明,强度传输矩阵参量对于描述保偏光纤耦合器的偏振特性具有重要的参考意义。     

Adiabatic fused tapered couplers

Pre-fattening of one fibre is shown to be a vehicle for achieving wavelength independent adiabatic fused tapered couplers. Compared with the conventional pre-tapered fused tapered coupler, this adiabatic coupler has a significant improvement in its ease of manufacture     

Wavelength dependence of fused couplers

The transmission characteristics of fused couplers are evaluated as a function of the cross-sectional radius and the degree of fusion. The wavelength dependence of the coupling ratio is then examined with a view to minimising the wavelength dependence in wavelength-multiplexed optical networks. The effect of changing the external refractive index is also considered.     

Selective fused couplers consisting of a mismatched twin-core fiberand a standard optical fiber

This paper demonstrates a novel selective fused coupler consisting a mismatched twin-core fiber and an ordinary optical fiber. Selective coupling of over 99% has been achieved between the high NA core of the twin-core fiber and the ordinary optical fiber core with insertion loss as low as 0.04 dB. The coupler can be made easily on a standard fused coupler rig. We also studied the principle of the device. The device opens a variety of applications so far limited by the difficulty in simultaneous accessing the both cores of a mismatched twin-core fiber     

Polarisation analysis of strongly fused and weakly fused tapered couplers

The polarisation properties of both strongly fused and weakly fused single-mode tapered fibre couplers have been analysed. A comparison with experimental results shows excellent agreement with our analysis.     

Back-reflexion from fused biconic couplers

Several theories are investigated to account for the origin of back-reflexions from fused biconic couplers. Amongst the effects causing such variation are those considered in this paper, namely, tapering, surface roughness on the cladding-air interface, fiber bends and twists and, finally, stress arising from bending and packaging. The basic investigative tool is the coupled local mode equations solution for the coupling between the forward- and backward-propagating modes arising in response to these effects. Theoretical analysis shows the stress optic effect to be the most likely reflexion origin and experimental results support this assertion, as well as ruling out tapering and surface roughness as likely causes     

Finite-element analysis for fused couplers

By using the finite-element method we show that the polarisation beam splitting property of realistic fused optical couplers is well modelled by an elliptical cross-section, but differs substantially from a rectangular cross-section.     

Variational analysis of fused tapered couplers

A variational technique is used to evaluate the coupling ratio of a fused coupler. The technique can be used for both strongly and lightly fused couplers. Simple formulas are presented for use in regions of high V-value and are shown to be in agreement with the more lengthy beam propagation calculations. The importance of the fibre core in determining the field shape is highlighted. A realistic coupler model containing a gradual taper is presented and the strong wavelength response of the coupling ratio is confirmed by numerical means.     

Polarization independent narrow channel wavelength divisionmultiplexing fiber couplers for 1.55 μm

A polarization-independent narrow-channel (PINC) wavelength division multiplexing (WDM) coupler for operation at 1.55 μm has been designed based on the birefringent properties of fused single-mode couplers. These couplers are made from both conventional single-mode fiber (SMF) and dispersion shifted fiber (DSF). The couplers are designed so that the coupling-coefficient-length products for the two orthogonal polarizations are π out of phase. As a result of the long coupling lengths required, these couplers have very small cross-sectional dimensions, typically on the order of 10 μm     

Low loss fused D fibre couplers

Low loss fused D fibre couplers are fabricated by a technique simpler than any previously reported. No pre-treatment of the D fibre is required and because of the simplicity of the coupler structure, heat treatment such as core diffusion and tapering, which increase coupling, and annealed twists, which decrease coupling, can be applied without compromising the coupler's excess loss.<>     

Polarization properties of the flint glass fiber

To realize stable characteristics of a current sensor using the Faraday effect in an optical fiber, it is necessary to prevent the influence of birefringent effect on light passing the fiber, which is caused by photo-elastic effect and/or lack of axial symmetry of its structure. The flint glass fiber manufactured from flint glass with very small photo-elastic constant, which has circular core and satisfies the single ode condition,has been developed to solve this problem. This paper reports results of a study to clarify polarization properties of the fiber and to consider a method for highly stabilizing the polarization. From experiments to investigate the relationship between state of polarization of light inserted to the fiber and that emitted from another end, it was confirmed that the birefringence due to the photo-elastic effect and the lack of symmetry are negligibly small. It also became known that the azimuth angle of polarization of the emitted light depends on the shape of the curve of the fiber. Namely, a rotation of the polarization plane is equal to the amount of line integral of the torsional rate along the curve. A countermeasure is necessary for this phenomenon, because characteristics of the current sensor may be influenced if the flint glass fiber coil is deformed by environmental factors. From a consideration of the mechanism of the phenomenon, it is inferred that the problem can be solved by reciprocating light in the fiber to stabilize the polarization. The effect of this method is confirmed experimentally     

熔锥型宽带光纤耦合器的研究

为了探究非对称耦合器的特性, 利用具有折射率差异的两根光纤制作了宽带耦合器。采用数值计算模拟了不同折射率差光纤耦合器的光场分布以及输出光功率随拉伸长度的变化曲线, 并分析了两种宽带耦合器的带宽差异以及熔融度对功率转换比的影响; 采用光束传播法, 通过仿真模拟得到了理论带宽。结果表明, 耦合的功率转换比随两根光纤的不对称情况而变化, 功率转换比调节到耦合器分束比的大小时, 耦合器带宽最宽; 熔融度对宽带耦合器分束比有一定的调节作用; 3dB光纤耦合器在C+L波段波长响应平缓, 带宽范围达到150nm; 分束比3:7和1:9的耦合器带宽范围分别是210nm和330nm; 分束比1:99的耦合器带宽范围是420nm。此研究结果对制作非对称宽带耦合器提供了参考依据。     

Low-loss criterion for fused polarisation-maintaining fibre couplers

A simple low-loss criterion for polarisation-maintaining directional couplers made of fused tapered stress-induced birefringent fibres is proposed and used to explain the loss characteristics of some experimental couplers. It is shown that the very low excess loss of some experimental couplers is due to the combined use of index-matched stress-applying regions and a high core-cladding index difference.<>     

Perturbation analysis of fused tapered single-mode fibre couplers

By treating a fused tapered single-mode fibre coupler as a perturbation of the same coupler with the fibre cores ignored, simple analytical expressions are derived for the coupling coefficients of the coupler. These new expressions highlight the effects of the fibre cores on the characteristics of the coupler.     

Analysis of fused couplers by the effective-index method

Fused couplers of various cross-sections are analysed by the effective-index method. Results show good agreement with those given by an asymptotic analysis. It is also shown that a stadium-shaped coupler which resembles the realistic one has the polarisation beam-splitting property similar to that of a rectangular one.