Abstract: The capacity of an optical transmission system can in principle be increased by interleaving two bits streams with orthogonal polarisation states. This requires, in the interleaved bit stream, the bits of one component bit stream to be timed to occur close to midway between the bits of the other component bit stream. Achieving this by adjustment of relative optical path lengths upstream of the interleaver requires control of those lengths to ±200 microns for ±1 ps bit interleaving accuracy. Such precision is awkward to achieve using fusion splicing. Instead, the necessary precision of interleaving accuracy is achieved by trimming a length of birefringent fiber inserted downstream of the interleaving, this fiber oriented to have its principal polarisation planes (principal axes) aligned with the polarisation states of the two bit streams. Employing birefringent fiber with a beat length of 2.

Abstract: A method of writing a diffraction grating into a photosensitive optical transmission medium is disclosed, in which a first phase mask is used to generate an interference pattern in a second phase mask substrate and using photolithographic techniques. This produces a second phase mask, which is then use to write a diffraction grating into a photosensitive optical transmission medium. This method enables the line placement in a phase mask to be improved by averaging out the line placement errors.

Abstract: Apparatus is disclosed for aligning optical components. The apparatus may for instance comprise a light source providing an emission, an optical element for receiving the emission from the light source, and at least one of the light source and the optical element being mounted to a gimbal mount. Adjustment of the light source and/or the optical element mounted to the gimbal mount adjusts the angle of incidence of the emission from the light source on the optical element. This adjustment in turn aligns the optical components, A method is disclosed for aligning optical components. The method comprises generating an emission from a light source, adjusting a gimbal mount on at least one of the light source and an optical element, wherein the angle of incidence of the emission from the light source is adjusted on the optical element, and fixing in place the position of the gimbal mount on the light source and/or the optical element.