Characteristics of a doubly clad optical fiber with a low-index inner cladding

This paper investigates a novel type of optical fiber which is composed of three portions: the core, inner cladding, and outer cladding. It is assumed that the core has the largest refractive index of the three, and the outer cladding index is the next largest. When the index difference between the core and the inner cladding is much larger than that between the outer cladding and the inner, the new fiber has a stronger confinement property than a usual singly clad fiber in the single-mode region. It is also assumed that the inner-cladding thickness is larger than or comparable with the core radius. This confinement is the origin of the following three properties of potential importance in single-mode optical communication. 1) As compared with a singly clad fiber, the largest core area for single-mode operation is roughly twice. 2) The group delay arising from waveguide characteristics has an opposite sign against that of typical glass dispersion. (Singly clad fiber has a dispersion of the same sign.) 3) The field is much more tightly confined within the core as compared with a singly clad fiber. This minimizes extra attenuation due to absorption in the cladding.     

Propagation characteristics of a single-polarization optical fiber with an elliptic core and triple-clad

This paper gives the propagation characteristics of a single-polarization optical fiber with an elliptic core and triple-clad. This fiber is designed so as to satisfy the zero total dispersion at the operating wavelength of 1.55 /spl mu/m in the single-polarization region. Thus far, we had studied the n propagation characteristics of single-polarization optical fibers with pits between an elliptic core and the outer cladding (Type-1) and with pits alongside the major axis of an elliptic core (Type-2). In this paper, it is found that a single-polarization optical fiber with an elliptic core and triple-clad has better propagation characteristics compared with Type-1 and Type-2. When the relative index difference between the core and the outer cladding is 0.5%, the main comparison results are as follows: 1) The minimum wavelength sensitivity of the total dispersion can be reduced by approximately 1/3 of those for Type-1 and Type-2, and 2) the single-polarization bandwidth is 2.2 times larger than those of Type-1 and Type-2.     

Propagation in Doubly Clad Single-Mode Fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.     

双包层手征光纤的色散特性

在对双包层手征光纤(W型)进行解析求解的基础上，用数值计算方法研究了纤芯和内外包层的手征参数和内包层厚度对模式色散特性的影响，给出了双包层手征光纤中基模的归一化传播常数b、群延迟d(Vb)／dV和波导色散Vd2(V6)／dV2随纤芯和内外包层的手征参数和内包层厚度的变化关系曲线。结果表明在双包层光纤的纤芯和内外包层中引入手征，可以极大地改变光纤中基模的色散特性，特别是内包层厚度不同时，色散特性也极为不同．     

Dispersion of pure GeO2 glass core and f-doped GeO2 glass cladding single-mode optical fibre

The letter investigates the dispersion of GeO2 glass core and F-doped GeO2 glass cladding single-mode optical fibre. It is estimated that the total dispersion goes to zero at about ? = 1.77 ?m. The material dispersions of these glasses are also measured. Material dispersion of GeO2 glass, which contains fluorine of 0.41 wt%, vanished at ? = 1.722?m. This occurs at ? = 1.734 ?m for pure GeO2 glass.     

基于组合包层的微结构光纤的色散特性

为了获得微结构光纤的平坦色散特性,设计了一种圆形排列的微结构光纤,其包层由周期分布的空气孔构成,通过有限元数值分析法对该微结构光纤基模的色散特性进行了数值仿真,研究了色散和纤芯圆孔尺寸以及波长的关系。结果表明:内外空气孔间距和直径对微结构光纤的色散曲线都有影响,但内包层大孔间距和第一圈小空气孔的直径对色散曲线的走向起决定作用。在内圈空气孔直径为3.1μm,其他空气孔直径为1.0μm,内圈空气孔中心间距为5μm,其他空气孔中心间距为4μm时,光纤在1.3μm波长的色散为19.5ps/(nm·km),在1.6μm波长的色散为26.5ps/(nm·km),在1.3～1.6μm波长范围内,其色散值变化范围为7ps/(nm·km)。     

Analysis of Brillouin frequency shift and longitudinal acoustic wave in a silica optical fiber with a triple-layered structure

We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO/sub 2/-doped core, P/sub 2/O/sub 5/, and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 /spl mu/m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.     

太赫兹波段反谐振光纤偏振分束器设计

偏振分束器是在光传感和集成光学等领域中非常重要的光学元器件,太赫兹波段被认为是未来大容量无线通信的载体.而双芯空芯反谐振光纤结构设计更加多变,对包层结构没有严格要求,能实现较高的性能以满足人们更多样化的需求,以双芯空芯反谐振光纤为基础设计适用于太赫兹波段的偏振分束器越来越值得深入研究.提出一种以环烯烃聚合物为基底材料的...     

Low-loss polarisation-maintaining optical fibre with low crosstalk

A low-loss polarisation-maintaining optical fibre with low crosstalk is presented. The minimum transmission loss is 0.35 dB/km at 1.54 ?m and crosstalk is ?32 dB at 1.56 ?m in a 1 km length. The relative refractive index difference between core and cladding is 0.3%, and the modal birefringence is 2.8 × 10?4.     

Polarization splitter based on antiresonant reflecting opticalwaveguides

We propose the first polarization splitter based on antiresonant optical waveguides (ARROW's). The three air core structure is built up of two moveable outer cladding layers and two fixed inner cladding layers. The moveability of both outer cladding layers makes micromechanical switching of the polarized light between two output channels possible. The polarization discrimination is realized through thin metal films deposited on the outermost surfaces of the outer cladding layers. The extinction ratios of channels 1 and 3 as a function of the thickness of all cladding layers are calculated. We found that for extinction ratios below -20 dB thickness fluctuations smaller than ±15 mm are allowed     

Perturbation theory of a doubly clad optical fiber with a low-index inner cladding

A doubly clad optical fiber which is composed of the core, inner cladding, and outer cladding is called aW-type fiber when the core has the largest index of refraction of the three and the inner cladding has the lowest. AW-type fiber is known to have several advantages over a conventional singly clad (SC) fiber. This paper presents simple, closed form approximations of aW-type fiber with respect to cutoff, the attenuation constant in the leaky wave region and a rapid change of the group velocity near cutoff, etc. In the approach to be described, aW-type fiber is thought of as a combined system of an SC fiber and an outer perturbing medium.     

Tailoring zero chromatic dispersion into the 1.5?1.6 ?m low-loss spectral region of single-mode fibres

We have designed and fabricated single-mode silica fibres that have zero chromatic dispersion within the 1.5?1.6 ?m low-loss spectral region by controlling their waveguide dispersion and dopant-dependent material dispersion. These fibres have small core diameters and large core-cladding refractive-index differences, ?n = 0.018, corresponding to a 13 mole % GeO2 dopant concentration in the core. The zero-dispersion wavelength was shifted from ?0 = 1.375 ? to ?0 = 1.54 ? by decreasing the fibre core diameter from 7 ?m to 4.8 ?m. This ability to tailor the minimum dispersion wavelength to the ultra-low-loss region near 1.55 ?m is important for designing single-mode fibres for very long distance and very high capacity optical transmission.     

A numerical method for the analysis of single-mode low-dispersion graded-index fibers

A numerical integration method for the calculation of the time dispersion of optical-fiber modes is introduced and used to determine the parameters of single-mode graded-index silica-based fibers for the 1.55-μm band. The method gives an accuracy on the order of 0.001 ps/km/nm, and it was possible to quantify the error in assuming the overall time dispersion to be the sum of the material and waveguide dispersions. The analysis indicates that when large material dispersion is to be neutralized by waveguide dispersion, the outer diameter of the cladding must be increased to avoid higher microbending losses. When the difference between the refractive indices at the center of the core and in the cladding decreases, the ratio between the cladding and core diameters must be increased.     

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     

Design tolerances for dispersion flattened SiO2-cladded single mode fibres

It is shown that the dispersion sensitivity to core diameter and to refractive index of the core of ideal broadband-dispersion-compensated single mode fibres can be accurately extracted from optical properties of the cladding material. In SiO2-cladded dispersion flattened fibres, typical sensitivity coefficients are 1.25 ps/km nm and 0.4?0.8 ps/kmnm per percent change in core diameter and core index, respectively.     

海底光缆用色散均衡光纤

介绍了一种带正色散的单模光纤,用来均衡常用于海底光缆中的非零色散位移光纤的负色散。这种光纤类似于常规单模光纤（Ｇ．６５２光纤）,但具有较低的衰减和较小的宏弯损耗。由于这种光纤应用常规的掺锗纤芯和纯ＳｉＯ２包层,与目前常用的纯ＳｉＯ２纤芯和掺氟包层的色散均衡光纤相比,在成本上具有较大的优越性。     

Fluoride-glass-cladded optical fibres for mid-infra-red ray transmission

Cladded-type fluoride glass fibres with a transmission loss of 0.1 dB/m at 2.5 ?m and 0.3 dB/m at 3.6 ?m, respectively, were fabricated by a novel casting method. Relative refractive-index differences between core and cladding ranging from 0.17% to 0.33% were obtained using BaF2-GdF3-ZrF4-AlF3 glasses as core and cladding components.     

双包层手征光纤中的半漏模

研究了纤芯和内外外层都有手征的双包层手征光纤中的半漏模，给出了单包层和双包层手征光纤中几个低阶模的有效折射率和功率损耗系数随手征参数的变化关系曲线。结果表明，双包层手征光纤中的半漏模特性与半单包层手征光纤中的相比有很大的不同；当只有包层中有手征时，单包层手征光纤中也存在半漏模。     

Design Consideration on Broad-Band W-Type Two-Mode Optical Fibers

Structural design for broad-band W-type two-mode optical fibers is investigated. The optimum parameters are numerically determined as follows: the operating V-value with zero group delay time difference Delta lambda between the LP/sub 01/ and LP/sub 11/ modes is 6.7, the ratio of core radius to inner cladding radius is 0.6, and the index profile parameter is 2.02. then, the core radius is 12.3 µm for Delta=0.3 percent at the operating wavelength of 1.3 µm. The V-value deviation tolerance from the optimum to maintain Delta lambda less than +-20 ps/km is 21 percent, which is 20 times larger than that of the earlier design made on two-layer index profile.     

Large Negative Dispersion in Dual-Core Photonic Crystal Fibers Based on Optional Mode Coupling

Chromatic dispersion of dual-concentric-core photonic crystal fibers (PCFs), which have an inner low-index core and an outer high-index core, is investigated based on a full vector finite-element method. Large negative dispersion can be obtained by introducing avoided crossing between modes of the two asymmetric cores. While increasing the negative dispersion, larger effective mode area is also possible by choosing a higher order mode in the outer core to couple with the fundamental inner core mode. During the analysis, a dual-core PCF with a dispersion peak value of -36 000 ps/(nmldrkm) and effective mode area of 34.8 mum² is presented.