Laurence W. Cahill

The study of logarithmic image processing model and its application to image enhancement

Describes a new implementation of Lees (1980) image enhancement algorithm. This approach, based on the logarithmic image processing (LIP) model, can simultaneously enhance the overall contrast and the sharpness of an image. A normalized complement transform has been proposed to simplify the analysis and the implementation of the LIP model-based algorithms. This new implementation has been compared with histogram equalization and Lees original algorithm.

Fabrication, modeling, and direct evanescent field measurement of tapered optical fiber sensors

Tapered optical fibers have been fabricated using a flame elongation technique. The evanescent field distribution surrounding the taper region has been measured directly using a scanning near field optical microscope and results are found to be in good agreement with predictions made using a finite difference beam propagation method.

Retaining and characterising nano-structure within tapered air-silica structured optical fibers.

Air-silica fiber 125m in diameter has been tapered down to ~15m. At this diameter, it is commonly assumed that the nanostructured fiber holes have collapsed. Using an Atomic Force Microscope, we show this assumption to be in error, and demonstrate for the first time that structures several hundred nanometers in diameter are present, and that hole array structures are maintained. The use of Atomic Force Microscopy is shown to be an efficient way of characterising these structures.

Image enhancement using the log-ratio approach

In this paper, we present a new image enhancement algorithm for interactively modifying the contrast and the sharpness of an image. The proposed algorithm aims at solving two basic problems associated with typical image enhancement technique: the enhanced image is usually out of the gray level range of an image, and there are conflicting requirements for image sharpening and noise reduction. A vector space based approach, the log-ratio approach, is employed to solve the first problem and a multiscale approach is used for the second problem. The proposed algorithm has been used successfully to enhance medical images.<<ETX>>

The Modelling of MMI Devices

Multimode interference (MMI) structures have found wide application as low-order couplers, splitters, combiners, switches and multiplexers. Recent advances in MMI devices have led to ultra-short MMI couplers, segmented MMI structures and cascaded MMI switches. This paper reviews the modeling techniques applicable to MMI structures. The paper covers analytical, semi-analytical and numerical approaches to the analysis and design of these newer MMI devices

A new criterion for the evaluation of image restoration quality

The quality of an image depends on the purpose for which the image is intended. The acceptable types and degrees of degradation may be quite different. Both objective quality criteria and subjective evaluation criteria are examined, and a fuzzy criterion is proposed which provides a visually and quantitatively superior performance to the present criteria in image restoration.<<ETX>>

The design of multimode interference couplers with arbitrary power splitting ratios on an SOI platform

A method for obtaining variable power splitting ratios using multimode interference couplers is presented. The method relies on etching the surface on either the top of the MMI coupler or on the linking waveguides. Devices have been designed for the silicon on insulator (SOI) platform. The 3D beam propagation method (3D-BPM) and the full-vectorial finite difference method (FV-FDM) are used to verify the working principle of the devices and to evaluate performance.

The modeling of MMI devices

Couplers based on the multimode interference (MMI) principle form the basis for a variety of integrated optics devices that can achieve routing, switching and other telecommunication functions. Whilst small order MMI couplers show good performance, the imaging properties deteriorate as the order increases. In order to better understand the performance capabilities of these devices there is interest in devising improved analytical models of MMI structures. This paper reviews various approaches to modeling integrated optics devices based on MMI couplers and attempts to highlight the advantages and the pitfalls associated with a number of models, and suggests some avenues for improving these models.

The synthesis of generalised Mach–Zehnder optical switches based on multimode interference (MMI) couplers

The space-division switching properties of a generalised Mach–Zehnder photonic switch are examined in this paper. It is shown for the first time that such an N × N switch can only produce N independent point-to-point switching states. A method that unambiguously identifies these states and thereby provides a synthesis technique for the design of these switches is presented.

The logarithmic image processing model and its applications

This paper presents a summary of operations of the logarithmic image processing (LIP) model and its applications. The LIP model is a mathematical framework which provides a set of generalised version of addition, subtraction, multiplication, convolution and so on, for signal processing. First, we briefly describe the LIP model and point out its distinctive properties for image processing. Then we summarize the current applications of the LIP model. A novel image filtering algorithm and its extension to multiscale processing along with the LIP model based Sobel operator for edge detection are discussed in detail. Finally, we suggest further research area of the LIP model.<<ETX>>