| 摘要 |
<p>Optical fiber transmission filters and methods of producing the filters with preselected transmission spectra are disclosed. The transmission filters include a long-period grating (LPG) having a first grating section and a second grating section spaced from the first section by a phase gap. The presence of a phase gap in the LPG introduces a phase shift wherein the amplitude of the electromagnetic radiation passing through the first section adds vectorially to the amplitude of the light passing through the second section with an angle phi related to the phase gap. When the gap length DELTA equals to a half grating period a (a= LAMBDA /2), a pi phase shift is introduced between the light transmitted through the two parts. By carefully selecting the length L1, the period of the two sections and the gap DELTA to give a preselected phase shift, the transmission loss peak can be designed to meet preselected specifications. Transmission filters for gain flattening of erbium-doped fiber amplifiers, notch filters, filters for suppression of amplified spontaneous emission and the like have been produced. Also disclosed are filters including chirped cascaded long-period gratings that exhibit multiple loss peaks over a wavelength band as broad as 240 nm. <IMAGE></p> |
