Two-mode fibre spatial-mode converter using periodic coredeformation

Efficient conversion between the LP₀₁ and LP₁₁ modes in a two-mode fibre is achieved by periodically ablating the fibre surface with a CO₂ laser and then annealing the fibre with an electric arc. The resulting periodic core deformation produces 99% mode conversion over a 37 nm bandwidth around 1540 nm and 0.38 dB insertion loss     

Reducing periodic noise using soft morphology filter

A novel spatial domain method--soft morphology filter is presented for reducing the periodic noise in image processing. The simulation results are presented to demonstrate the effectiveness of the method in comparison with a frequency domain method and other spatial domain filters.     

Reflectively tapped fibre optic transversal filter using in-fibreBragg gratings

A novel optical transversal delay line signal processor based on the use of in-fibre Bragg grating reflectors as tapping elements is presented. The requirements on reflectivity mismatch are analysed, and this is accurately controlled using postprocessing techniques. Results on frequency discriminator filters using reflectively tapped optical transversal filter structures demonstrate uniform and level responses >20 GHz with notch depths >44 dB     

Assorted core air-clad fibre

An optical fibre containing a selection of independently addressable air-clad cores with different dimensions is presented. The intrinsic properties of such an assorted core fibre are studied and potential applications are reviewed. The physical dimensions required for guidance at various wavelengths are explored     

Single pole compact narrow band pass filter using periodic ground defects

In this paper a compact narrow band pass filter has been designed. An H-shape section of microstrip is used to get the smaller band width. The parallel lines are connected to the H section. The periodic slots are made on the ground plane of the microstrip. These defects cause the circuit more compact. The filter has been designed for center frequency 4 GHz and fractional band width 3%. The design methodology has been clearly explained. To verify the proposed technique, a filter has been fabricated and tested. Amoderate matching of the results between the measured and simulated results has been observed due to some imperfection in fabrication.     

Flattening of erbium-doped fibre amplifier gain spectrum using an acousto-optic tunable filter

An acousto-optic tunable filter is employed to flatten the gain spectrum of an erbium-doped fibre amplifier. A relatively flat gain spectrum of 15 nm in bandwidth with variations of less than 1 dB is obtained by simultaneously applying eight closely-spaced RF signals to the acousto-optic tunable filter.<>     

810 W continuous-wave and single-transverse-mode fibre laser using 20 /spl mu/m core Yb-doped double-clad fibre

It is shown that continuous-wave kW-power fibre lasers can be built using double-clad fibres with relatively small cores. 810 W in a single-transverse-mode output (M/sup 2/=1.27) is demonstrated experimentally with 20 /spl mu/m core low-NA (NA=0.06) Yb-doped double-clad fibre. A laser numerical model matches experimental results and predicts scalability of achievable powers into a multi-kW range.     

Single-mode propagation in 2-mode region of optical fibre by using mode filter

The effect of a mode filter using fibre bend has been clearly shown experimentally. The mode filter effectively removes the LP11-mode, and has a negligibly small effect on the attenuation of the LP01-mode. The single-mode propagation was attained at the V-value of 2.8 by using the filter.     

Electrically tunable singlemode fibre Bragg reflective filter

An electrically tunable singlemode fibre Bragg reflective filter (FBR) is demonstrated for the first time by using a large amount of magnetostrictive material in which the fibre is embedded and side-polished. With a reflection bandwidth of ~1.5 nm, the measured tuning range of the FBR filter is 1.3 nm     

Bidirectional erbium-doped fibre amplifier with non-reciprocaloptical filter

A 24 dB gain bidirectional erbium-doped fibre amplifier (EDFA) using a new non-reciprocal optical filter is demonstrated. Using the amplifier 2.5 Gbit/s×8 channel WDM signals were transmitted over 160 km long singlemode fibre. The measured penalty caused by multiple optical reflection was negligible     

Tap multiplexed fibre grating-based optical transversal filter

The authors demonstrate the effectiveness of a tap multiplexing technique that enables the doubling of the number of taps in a photonic transversal filter. This technique has been used to achieve a fibre grating-based optical transversal filter with the equivalent of 16 taps. The authors also demonstrate the technique in combination with apodisation of the photonic transversal filter     

Field deformation in a curved single-mode fibre

Simple formulae are given for the field displacement caused by bending, the change in mode volume and for the mode coupling loss which arises at transitions between straight and curved sections of single-mode optical fibre. These formulae are in good agreement with other, more exact, theories.     

Detection and extraction of periodic noises in audio and biomedical signals using Kalman filter

This paper studies the subject of adaptive noise cancelation using the Kalman filtering technique to achieve high precision and fast convergence. It is shown that the Kalman filter can successfully be designed to detect and extract periodic noises which may be constituted of different sinusoidal components with possibly unknown and/or time-varying frequencies. This highlights the feature of Kalman filter in synthesizing periodic noises in the time-domain which is not possible using Fourier-based methods such as DFT. Usefulness of the method is discussed in the context of two examples: active cancelation of periodic noises from audio waveforms and filtering of electrocardiogram measurements.     

Linear periodic systems and multirate filter design

We present a systematic procedure for the design of filters intended for multirate systems. This procedure Is motivated by viewing the equiripple design of filters in linear time-invariant systems as a process of obtaining optimum minimax filters for a class of bounded energy input signals. The philosophy of designing optimum minimax filters for classes of input signals is extended to multirate systems, which are not time-invariant. We develop a generalized Fourier analysis appropriate for linear periodic systems and use it to derive new error criteria for multirate filter design. Using such criteria yields optimum minimax multirate filters for the input signal class. The utility of our method is demonstrated by using it to analyze several multirate systems. We give numerical results on the design of a multirate implementation of a narrowband filter and compare our work to previous work on multirate filter design. Our numerical analysis is based upon a new formulation of the design as a semi-infinite linear programming problem     

Low splice loss between 34 /spl mu/m core diameter Bragg fibre and G-652 fibre by using micro-optics

The splice loss at 1.55 /spl mu/m between a 34 /spl mu/m core diameter singlemode photonic bandgap fibre and a G-652 fibre has been dramatically reduced from 2.5 to 0.8 dB by using a micro-optics composed of graded-index and coreless pure silica fibres.     

Direct measurement of core profile diffusion and ellipticity infused-taper fibre couplers using atomic force microscopy

The geometrical shape and refractive index profile of the cores of fused-taper fibre couplers made by the heating, fusing and tapering technique have been measured to an accuracy of better than 10 nm. This approach involves precision cleaving, hydrofluoric acid etching and atomic force microscope (AFM) measurement. Results reveal that the core profile and cross-sectional geometry along the taper differ significantly from the normal assumption of scaled circular cores     

Optimum bandpass optical filter synthesis using periodic corrugatedwaveguides with π/2 phase shifts

A graphical method is proposed for the synthesis of optical bandpass filters, using π/2-phase shift sections. Bandpass filters with the desired characteristics, such as central wavelength, bandwidth, ripple factor, selectivity, minimum attenuation etc., can be synthesized by proper choice of corrugation pitch, coupling coefficient, filter length, and the location of π/2-phase shift sections. This method is relatively simple as compared to the previous works. Besides, it allows to optimize certain criteria     

Experimental demonstration of an ultraselective and tunable opticalbandpass filter using a fibre grating and a Fabry-Perot

The authors report on the use of a structure composed of a fibre Fabry-Perot and a fibre grating as an ultraselective and tunable optical bandpass filter. The first experimental demonstration of the filter operation is presented and a range of tuning of several hundreds of gigahertz can be achieved by using the presented techniques     

Miniature low-loss CPW periodic structures for filter applications

Several novel periodic structures for coplanar waveguides are presented. The proposed structures exhibit low insertion loss in the passband, simple fabrication, and slow-wave characteristics. These structures are applied to realize miniature low-pass filters one-tenth the size of conventional filters, with spurious-free response and deep attenuation levels using only three cells     

High-power cascaded Raman fibre laser using phosphosilicate fibre

A 13.2 W second cascade phosphosilicate cascaded Raman fibre using a 450 m phosphosilicate singlemode optical fibre is demonstrated. The lasing wavelength is 1539 nm and the conversion efficiency is 32.5%. This is the highest output power ever reported from a cascaded Raman fibre laser in the 1400-1600 nm range.