Itu-t rec. G. 957 (06/99) Optical interfaces for equipments and systems relating to the synchronous digital hierarchy
tải về 235.99 Kb. Chế độ xem pdf
|
co so truyen thong soi quang chuong 3 bo phat quang
|
Recommendation G.957 (06/99) 9 The operating wavelength range is the maximum allowable range for source wavelength. Within this range, the source wavelength can be selected for different fibre-related impairments (and different amplifier implementations should they be included). The receiver must have the minimum operating wavelength range that corresponds to the maximum allowable range for the source wavelength. For SDH networks utilizing optical fibre amplifiers, it could be necessary to limit the operating wavelength range. The wavelength regions permitting system operation are partially determined by either the cut-off wavelength values of the fibre or of the fibre cable. For G.652 and G.653 fibres, these values have been chosen to allow single-mode operation of the fibre cable at 1270 nm and above, with values as low as 1260 nm permitted by some Administrations. For G.654 fibre cables, the cut-off wavelength values have been accepted for single-mode operation at 1530 nm and above. The allowable wavelength regions are further defined by the fibre attenuation. Although the intrinsic scattering attenuation generally decreases with increasing wavelength, OH-ion absorption can manifest itself around 1385 nm, and to a smaller extent around 1245 nm. These absorption peaks and the cut-off wavelength therefore define a wavelength region centred around 1310 nm. Dispersion- unshifted fibres complying with Recommendation G.652 are optimized for use in this wavelength region. At longer wavelengths bending attenuation occurs towards 1600 nm or beyond, and infra- red absorption occurs beyond 1600 nm. These attenuations and the 1385 nm water peak therefore define a second operating wavelength region around 1550 nm. Recommendation G.654 for cut-off shifted fibre is limited to this region only. However, both G.652 and dispersion-shifted G.653 fibres may be used in this region. Apart from cut-off wavelength and attenuation that determine the broad operating wavelength regions, the allowable wavelength ranges are determined by the interaction of the fibre dispersion with the spectral characteristics of the transmitter. Parts of this range may lie inside or outside the wavelength range determined by attenuation. The overlap of the two ranges is the permissible wavelength range for system operation. tải về 235.99 Kb. Chia sẻ với bạn bè của bạn:
|