G. J. Pearce

Bend loss in all-solid bandgap fibres

Experimental measurements of all-solid photonic bandgap fibres with an array of high-index rods in a low-index background revealed an unexpected variation of bend loss across different bandgaps. This behaviour was confirmed by calculations of photonic band structure, and explained with reference to the differing field distributions of the modes of the cladding rods. Our understanding was confirmed by further experiments, leading to proposals for the improvement of these fibres.

Approximate band structure calculation for photonic bandgap fibres

An approximate method for finding the band structure of simple photonic bandgap fibres is presented. Our simple model is an isolated high-index rod in a circular unit cell with two alternative boundary conditions. Band plots calculated this way are found to correspond closely to calculations using an accurate numerical method.

An improved photonic bandgap fiber based on an array of rings.

We describe the modeling, fabrication and characterization of a silica-core photonic bandgap fiber based on a 2-d array of raised-index cladding rings. The use of rings to form the cladding is shown to re-order the cladding modes in such a way as to broaden the photonic band gaps and reduce bend sensitivity. We compare the performance of the ring fiber with that of a similar fiber made using solid rods.

Solid photonic bandgap fibres and applications

We report on the development of optical fibres which guide light in a solid core using a photonic bandgap effect. The photonic bandgap cladding consists of a two-dimensional array of isolated high-index regions in a lower-index matrix, with a relatively low index contrast. The core is one or more unit cells of the matrix material without the inclusions. The frequency bands for photonic bandgap guidance can be predicted by considering the cut-off frequencies of the guided modes of the high-index rods in the cladding using the weakly-guiding approximation. We demonstrate the basic properties of such fibres and their use as a wavelength-selective element in a fibre laser cavity.

Electromagnetically induced transparency in acetylene molecules with counterpropagating beams in V and Λ schemes

We report on the experimental observation of electromagnetically induced transparency in V and Λ energy level schemes using counterpropagating coupling and probe beam geometry. The observation was achieved using an acetylene photonic microcell. The conditions required for this observation are explored theoretically, and we show that the use of counterpropagating beams in electromagnetically induced transparency may have applications as a spectroscopic technique where velocity discrimination is desirable.

Guidance in Kagome-like photonic crystal fibres I: analysis of an ideal fibre structure

Propagation of light in a square-lattice hollow-core photonic crystal fibre is analysed as a model of guidance in a class of photonic crystal fibres that exhibit broad-band guidance without photonic bandgaps. A scalar governing equation is used and analytic solutions based on transfer matrices are developed for the full set of modes. It is found that an exponentially localised fundamental mode exists for a wide range of frequencies. These analytic solutions of an idealised structure will form the basis for analysis of guidance in a realistic structure in a following paper.

All solid photonic bandgap fiber based on an array of oriented rectangular high index rods

We report the fabrication, characterization and modeling of an all-solid photonic bandgap fiber (PBGF) based on an array of oriented rectangular rods. Observed near-field patterns of cladding modes clearly identify the cut-off rod modes at the bandgap edges. The bend losses in this fiber depend on the bend direction, and can be understood by the directional coupling properties of the different rod modes and the modeled density of cladding states.

EIT with counter-propagating probe-coupling beams in acetylene-filled HC-PCF

We present experimental results demonstrating for the first time to our knowledge the observation of electromagnetically-induced-transparency using a counter-propagating beam configuration in an acetylene filled hollow-core PCF gas-cell, in both ¿ and ¿ energy-level schemes.

Experimental Study Comparing EIT in V and ΛSchemes in Acetylene-Filled HC-PCF

We report detailed experimental and theoretical results comparing electromagnetically- induced-transparency obtained in V and Lambda configurations in acetylene-filled-hollow-core PCF. For the same experimental conditions, the EIT in V-scheme shows a stronger peak but larger linewidth.

Bend loss in all-solid photonic band-gap fibers

We study bend loss in solid photonic bandgap fibers, which is fundamentally different to that in conventional fibers. Our results show that the symmetry of the specific cladding modes has a profound effect on the bend loss.