| 摘要 |
<p>In N x N optical couplers, such as are used in local area networks and backplanes of telecommunications and computer equipment, a BRAGG volume diffraction device (101; 801; 1101; 1601) couple light beams between the inputs and outputs. The number of gratings in the diffraction device is reduced by means of so-called 'grating degeneration', whereby one grating can be shared by at least two wave pairs at the same time. In order to achieve this reductin, the directions of light waves in the dielectric slab (or the lateral positions of fibre ends) are suitably arranged. In other embodiments, a reduced number of gratings is achieved by using a 'sandwiched' structure which uses multi-layered dielectric slabs (801A, 801B; 1101A, 1101B). Both embodiments may be combined in the one coupler.</p> |
