Novel component to approximate steady-state mode power distribution in graded-index fibres

A new method for approximating steady-state mode power distribution (SMPD) in graded-index fibres is described. It has been shown that a biconical taper is a very simple and effective means to launch SMPD in short lengths of fibres. Prefabricated tapers can be directly used as component between the source and the test fibre. Experimental results are presented.     

Analysis of ring launching scheme using hollow optical fibre mode converter for 10 Gbps multimode fibre communication

A ring launching scheme using a mode converter based on hollow optical fibre (HOF) is theoretically investigated for the purpose of increasing bandwidth for multimode Gigabit Ethernet communication. The mode converter based on HOF transforms the fundamental mode of a single-mode fibre (SMF) to a ring-shaped mode. It has the characteristic to improve the bandwidth by exciting higher-order modes of the multimode fibre (MMF) selectively. The HOF launch is studied under various aspects such as induced coupling efficiency, mode power distribution, and bandwidth-length product and is compared to centre and offset launching schemes. It is shown that the ring launching scheme is expected to support 10-Gb Ethernet applications using conventional multimode fibres.     

Baseband-frequency-response measurement of graded-index fibre using step-index fibre as an exciter

For measuring reproducibily the baseband frequency response of a graded-index fibre, a mode exciter utilising an ordinary step-index multimode fibre has been proposed. The input mode power distribution and the frequency response of the fibre with the exciter are altered very little for axis offset. Input mode distribution excited indicates that excitation of nearly all modes takes place.     

Power loss caused by random mode coupling in a multimode optical fibre

A method is presented for calculating the effects of random mode coupling in a multimode optical fibre. The calculated results are in good agreement with the experiment, and the relative error in the steady-state power loss is about 1%.     

Compact all-fibre on-line power monitor via core-to-cladding modecoupling

An on-line all-fibre power monitor is demonstrated in which light from the core mode is first coupled to the cladding mode using an acoustooptic tunable filter, and then coupled to an InGaAs pin detector bonded to the fibre. Detection efficiency for different cladding modes and fibre cladding diameters are presented     

Two-dimensional optical power distribution of side-out-coupled radiation from tilted FBGs in multimode fibre

Two-dimensional optical power distribution of the out-coupled radiation from UV-inscribed tilted fibre Bragg gratings (TFBGs) in multimode fibre (MMF) has been side-detected with high spatial/spectral resolution, showing a near-identical radiation mode profile to that measured from the fibre-end detection method. A comparative investigation of the radiation characteristics of TFBGs fabricated in singlemode fibre (SMF) and MMF clearly indicates that the radiation out-coupling is stronger and spatially more confined in MMF. The unique spatial-to-spectral encoding property of the coupling mechanism offers potential application in low-cost WDM devices.     

Radiation from bent optical waveguides

A simple method is presented for determining the radiation losses due to the bending of an optical waveguide. This method circumvents the use of continuous modes and reduces the problem to elementary antenna theory in which radiation is found from a known surface-current distribution. Practical results are given for the bent fibre of circular cross-section. i.e. a toroidal geometry, both for the HE11 mode and for rays in an overmoded fibre.     

Excitation of steady-state power distribution in parabolic-index fibres by Gaussian TEM00-beam

At z = 0 a power distribution may be excited by a Gaussian TEM00 beam in a parabolic-index fibre in which each group of modes with a given propagation constant carries the same power as prescribed by Olshansky's steady-state distribution. This power distribution, however, still depends on both mode numbers ?, ?. Such an excitation may be advantageous for measuring losses in fibres and coupling elements.     

Mode power distribution in optical fibres with fluctuation in physical parameters and application to backscattering signal analysis

The evolution of mode power distribution in fibres with fluctuations of physical parameters is investigated. The analysis is applied to the interpretation of backscattering trace. Rigorous expressions of backscattering power in the presence of fluctuations of fibre core radius and maximum NA are provided in many common cases.     

Leaky optical fibre for large mode area singlemode operation

A novel optical fibre structure is introduced for large mode area singlemode operation. The fibre consists of a cladding index profile that increases monotonically in the radial direction. It is shown that the fibre can introduce exceedingly high leakage losses to the high-order modes, while maintaining a low loss to the fundamental mode. Numerical results are presented for power-law index profiles.     

双折射单模光纤的保圆耦合

提出了一种利用双折射单模光纤扭转时产生的圆双折射性获得保圆偏振的新方法，该法应用于光纤耦合器的基本思想是通过有效地改变扭转光纤在耦合区域的单位扭转度，从而达到光纤之间实现保圆耦合的目的。同时，用耦合模方程分析了利用该法构成的２×２单模光纤耦合器的耦合行为，结果表明光纤耦合器达到了较好的保圆耦合。     

Coupling to high-index waveguides via tapered microstructured optical fibre

A novel method of coupling to high-index, small mode-field diameter, waveguides using free-standing tapered 'grapefruit' microstructured optical fibre pigtails with mode fields down to 1 /spl mu/m is presented. 0.15 dB mode mismatch loss with chalcogenide rib waveguides is demonstrated, a reduction of more than 5 from high NA fibre, and it is shown that they can be used to butt-couple to silicon nanowires.     

Low pump power photonic crystal fibre amplifiers

Designs of low pump power optical amplifiers, based on photonic crystal fibres are presented. The potential of these fibre amplifiers is investigated, and it is demonstrated that such amplifiers may deliver gains of more than 15 dB at 1550 nm with less than 1 mW of optical pump power. We focus on the design of erbium-doped photonic crystal fibre amplifiers operated at very low pump powers. We achieve this by using PCFs with large air holes and thereby large index contrasts. With such high index contrast fibres, we may obtain very small mode field diameters.     

单模光纤耦合器技术现状及应用

本文扼要介绍了单模光纤耦合器的技术现状和发展动态;概述了我所引进的世界一流水平的美国 Aster 公司单模光纤耦合器制造技术;简单介绍了单模光纤耦合器在光纤通信、光纤传感和尤纤仪器仪表方面的应用。     

High-efficiency, single-longitudinal-mode ring fibre laser

A novel single-longitudinal-mode erbium-doped ring fibre laser is proposed and demonstrated experimentally. It combines a narrow-linewidth fibre Bragg grating (FBG) with several Mach-Zehnder mode filters (MZF) to obtain a single-frequency emission. It yields a power conversion efficiency of 16%. It is shown that the sidemodes are suppressed when one inserts the series of MZFs inside the cavity. At 1547 nm, the output power measures over 15 dBm, with a sidemode suppression ratio of 50 dB and a linewidth of no more than 7 kHz.     

Simultaneous multilevel proof testing of high-strength silica fibre

A technique of simultaneous multilevel proof testing of optical fibre is described and shown to be equivalent to a coarse nondestructive tensile test for the low end of the fibre strength distribution. Yields of silica fibre at four proof-test levels up to 1.9% are presented.     

高功率光子晶体光纤激光器研究进展

光子晶体光纤的出现,为高功率光纤激光器的关键技术-大模区光纤的实现提供了新途径。基于铒镱共掺磷酸盐材料的包层掺杂新结构出现,为实现更加紧凑的光纤激光器提供了可能。常规高功率光纤激光器中的抽运技术,谐振腔技术和相干组束技术也在不断融入高功率光子晶体光纤激光器。高功率光子晶体光纤激光器的调Q和锁模输出也已经实现。     

Direct cavity assessment and mode optimisation technique for DFB fibre laser

A technique for direct real-time assessment of distributed feedback fibre laser cavity conditions during operation is demonstrated and used to provide a cavity mode conditioning feedback mechanism to optimise output performance. Negligible wavelength drift is demonstrated over a 52 mW pump power range.     

Cladding-mode extraction from long-period fibre grating using self-aligned core-mode blocker

A novel method is presented of fabricating a core-mode blocker for use in long-period fibre gratings by forming a self-aligned absorber on the end of the fibre core. The absorber efficiently suppresses the core-mode power and allows the cladding-mode radiation to pass through, thereby resulting in a bandpass output at the resonant wavelengths     

Wavelength-switchable DBR fibre laser with high spectral purity output

A compact, wavelength-switchable, singlemode DBR fibre laser configuration is demonstrated. Stable, high spectral purity single-line or wavelength-switching operations are achieved by controlling the cavities' resonance mode conditions through a simple strain mechanism, without pump power limitations