標準號：IEC 60793-1-49-2006
中文標準名稱：光學纖維.第1-49部分:測量方法和試驗程序.差分模延遲
英文標準名稱：Optical fibres - Part 1-49: Measurement methods and test procedures - Differential mode delay
標準類型：M33
發布日期：1999/12/31 12:00:00
實施日期：1999/12/31 12:00:00
中國標準分類號：M33
國際標準分類號：33.180.10
適用范圍：This part of IEC 60793 applies only to multimode, graded-index glass-core (category A1)fibres. The test method is commonly used in production and research facilities, but is noteasily accomplished in the field.This standard describes a method for characterizing the modal structure of a graded-indexmultimode fibre. This information is useful for assessing the bandwidth performance of a fibreespecially when the fibre is intended to support a variety of launch conditions such as thoseproduced by standardized laser transmitters.With this method, the output from a fibre that is single-mode at the test wavelength excitesthe multimode fibre under test. The probe spot is scanned across the endface of the fibreunder test, and the optical pulse delay is determined at specified offset positions.Two results can be produced from the same data. First, the difference in optical pulse delaytime between the fastest and slowest mode groups of the fibre under test can be determined.The user specifies the upper and lower limits of radial offset positions over which the probefibre is scanned in order to specify desired limits of modal structure. The DMD data is thencompared to DMD specifications that have been determined by modeling and experimentationto correspond to a minimum EMB for a range of transmitters. Second, the optical pulseshapes can be combined using specific weights to determine a calculated effective modalbandwidth (EMBc), and by calculating a sequence of EMBc values with different sets ofweights, a minimum EMBc can be calculated, corresponding to a range of transmitters.The test quantifies the effects of interactions of the fibre modal structure and the sourcemodal characteristics excluding the source spectral interactions with fibre chromaticdispersion. Adding the effects of chromatic dispersion and source spectral width will reducethe overall transmission bandwidth, but this is a separate calculation in most transmissionmodels. In this test, the effects of non-zero spectral width are minimized but any residualeffects will tend to increase the DMD value and decrease the EMBc value.