PURE SILICA SINGLE-MODE FIBRE WITH HEXAGONAL PHOTONIC CRYSTAL CLADDING

Pure silica fibres supporting guided modes were first investigated in the 1970's [ 11, the aim being to achieve low transmission losses. The huge success of chemical vapour deposition in producing extremely low loss fibre has largely superseded this early technology. We have recently revisited it in the context of photonic crystals [2], and report here the realisation of a new kind of pure silica microstructured optical fibre which supports a robust single mode. Photonic crystals are periodically microstructured materials with a pitch on the scale of the optical wavelength. They have recently been the subject of much interest because of their unusual optical properties, including their ability to support a full photonic band gap [3]. Severa1 research teams have reported fabricating two-dimensional photonic crystal material out of glasses using selective etching processes [4,5]. However, such a fabrication process results in samples of at most a few millimetres in the third dimension. The photonic crystal fibre described here is formed by creating a hexagonal silica/air preform (including a deliberate defect to guide light) on a macroscopic scale and then reducing its size by several orders of magnitude by pulling it into an optical fibre (see Figure 1).