Efficient power coupling using taper-ended multimode optical fibres

Highly efficient power coupling of up to 97% between a d.h. laser and a multimode step-index fibre is demonstrated by employing a tapered fibre launcher. Also, it is shown theoretically that a tapered end increases the effective numerical aperture of a fibre. For a Lambertian emitter, the use of a taper launcher permits the maximum coupling efficiency allowed by the Liouville theorem.     

Polarisation-independent optical circulator coupled with multimode fibres

An experiment on a polarisation-independent optical circulator coupled with graded-index fibres was performed. Insertion losses of 2.5?2.9 dB and isolation ratios of 15?34 dB among nonreciprocal ports were measured, at 1.27 ?m wavelength.     

Current sensing with metal-coated multimode optical fibres

A multimode fibre has been used to detect electrical currents. The optical fibre which serves as the sensor is coated with a thick Al metal jacket. Electromotive forces on a wire in a magnetic field are used to induce differential phase shifts between the fibre modes. Good linearity has been observed in the 5 to 2000 mA current range.     

Multicomponent glass fibres with high numerical aperture

Multicomponent glass is suited for the preparation of high numerical aperture (n.a.) fibres which may be used in short-distance applications. Low loss of 20dB/km fibres have been produced with a n.a. of 0.53. Core glass having high refractive index has been prepared by using the additives of BaO and GeO2 which are hardly harmful to the intrinsic absorption loss.     

Pulse propagation in multimode optical fibres

Coupled mode theory is unnecessary for the analysis of pulse propagation in multimode optic waveguides. Instead, a very simple ray or continuum equation is derived from elementary plane-wave concepts to account for the effects of absorption loss and scattering. The formalism reduces to a diffusion equation for highly forward directed scatterers.     

Pulse broadening in multimode optical fibres with large ?n/n: numerical results

The r.m.s. impulse response width of germania doped fibres having power-law profiles at the carrier wavelength is evaluated with the help of a numerical method and measured values of dn/d?. For ?n/n?0.02, our result exceeds by more than one order of magnitude that obtained from an analytical formula based on the assumption that n dn/d? varies linearly with n2. The optimum profiles are found to differ very significantly from power-law profiles. Our numerical technique is based on scalar-ray optics. It is applicable to any fibre having a large V-number and a smooth profile.     

Bending losses of multimode optical fibres

The bending loss of rays within circular and slab multimode optical waveguides is determined using only Snell's laws, the generalised Fresnel transmission coefficient and the Goos-Haenchen shift. The generalised transmission coefficient accounts for radiation losses, due to curvature, not included in Fresnel's classical laws.     

Far-field profiling of multimode optical fibres

Using a recently published relation between far-field intensity and refractive index profile a monotonically decreasing equivalent profile is calculated from measured far-field data. The resulting smooth function may be fitted to composite or multiple ?-profiles very well.     

Nylon buffering effects in multimode optical fibres

In this letter the effects of nylon buffering in multimode fibres are examined using a method previously reported, and the design criteria for avoiding the additional loss due to the nylon buffering are shown.     

Ray analysis of multimode,optical fibres

A ray analysis of a multimode, step or graded index fibre can be conveniently divided into two complementary sections. Those phenomena associated with the fibre core, such as pulse propagation, source excitation, power absorption, scattering and inhomogeneities are viewed as building blocks on a basis of ray trajectories and ray classes as predicted by Snell’s laws. Cladding phenomena, such as absorption and ray tunnelling are superposable building blocks based on Fresnel’s laws and their generalizations.     

Fabrication of low-loss 3 dB couplers with multimode optical fibres

A 3 dB coupler was fabricated using two partially polished fibres which were in contact with each polished portion. The excess insertion loss and the directivity of this coupler are measured to be 0.36 dB and 47.0 dB, respectively.     

Signal transmission with optical carriers in multimode range of single-mode fibres

Low-cost optical transmission systems consisting of GaAlAs transmitter devices, Si-APD receivers and single-mode fibres with 1.2 ?m cutoff have been investigated. Theoretical and experimental results are presented which demonstrate the potential as well as the limitations of such systems for local network applications.     

Length dependence of joint losses in multimode optical fibres

The dependence of actual joint losses on fibre length is studied in some common cases. Interesting relations with scattering loss are found and a strong dependence on launching conditions is evidenced.     

Observation of tubular modes in multimode graded-index optical fibres

The clean propagation of tubular modes over more than 50 m of a multimode optical fibre has been observed. This observation opens the way to multichannel transmission through multimode optical fibres and provides a new fibre testing method.     

Universal curves for power attenuation in ideal multimode fibres

When a step- or parabolic-index fibre is illuminated by a diffuse source the power attenuation along the fibre depends only on a single dimensionless variable which embraces all the parameters of the problem.     

Role of modal distribution in determining power backscattered from fibres with diameter perturbations

Certain results of a theory of the backscattering process in multimode fibres are discussed. Calculated near-field intensities of backscattered waves are presented. The dependence of the backscattered power on diameter perturbations is calculated and shown to agree with the empirically determined relation.     

New method for precise characterisation of multimode optical fibres

It is shown experimentally that short samples (about 1 m) of multimode optical fibres can be characterised by measuring the times of flight of tubular modes. There is fair agreement between measured and calculated values.     

Optimum operating wavelength for chromatic equalisation in multimode optical fibres

Complete chromatic equalisation is not possible in a graded-index fibre owing to the variation of material properties across the core. We show that it is still possible to choose an operating wavelength which effectively eliminates first-order material dispersion.     

玻璃基多模波导光功分器的研制

利用Ag+-Na+电场辅助玻璃基离子交换技术制作了低损耗的掩埋多模波导,并在此基础上研制了多模波导光功分器.测试分析了多模波导和光功分器的损耗和偏心率特性.所研制的多模直波导传输损耗小于0.1dB/cm,所制作的1×2的多模波导光功分器附加损耗小于1.3 dB.