| 摘要 |
An arrayed waveguide grating (WDG) comprises I/O slabs (53a, 53b) interconnected by a grating region (51). The grating region (51) comprises many, e.g. at least 25 and preferably 50 to 500 individual cores (61, 62, 63 ) which have different lengths so as to provide wavelength selectivity by causing phase changes in light conveyed between the I/O slabs (53a, 53b). There are bends (64) for providing the different lengths and, to improve optical guidance round the bends, empty (R.I. = 1) grooves (71) are located adjacent to the inside (71.1) and outside radii (71.2) so that the evanescen t fields extend into the grooves (71). In order to keep the dimensions small, which improves the optical accuracy, tight bends (preferred radii of curvatu re of less than 2 mm and especially less then 500 .mu.m are desirable. The grooves conveniently have tapered ends and they extend into straight portion s adjacent to the bends. The WDG is preferably implemented in silica glass wit h dopants to adjust the refractive index and/or the melting point. |
