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
- Điều hướng trang này:
- 6.2.4 Extinction ratio
| 6.2.3
Mean launched power The mean launched power at reference point S is the average power of a pseudo-random data sequence coupled into the fibre by the transmitter. It is given as a range to allow for some cost optimization and to cover allowances for operation under the standard operating conditions, transmitter connector degradations, measurement tolerances, and aging effects. These values allow the calculation of values for the sensitivity and overload point for the receiver at reference point R. The possibility of obtaining cost-effective system designs for long-haul applications by using uncooled lasers with maximum mean launched powers exceeding those of Tables 2 to 4, necessitating external, removable optical attenuators in low-loss sections, is for further study. In the case of fault conditions in the transmit equipment, the launched power and maximum possible exposure time of personnel should be limited for optical fibre/laser safety considerations according to IEC 60825. 6.2.4 Extinction ratio The convention adopted for optical logic level is: – emission of light for a logical "1"; – no emission for a logical "0". The Extinction ratio (EX) is defined as: EX A B = 10 10 log where A is the average optical power level for a logical "1" and B is the average optical power level for a logical "0". Measurement methods for the extinction ratio are under study. Recommendation G.957 (06/99) 11 6.2.5 Eye pattern mask In this Recommendation, general transmitter pulse shape characteristics including rise time, fall time, pulse overshoot, pulse undershoot, and ringing, all of which should be controlled to prevent excessive degradation of the receiver sensitivity, are specified in the form of a mask of the transmitter eye diagram at point S. For the purpose of an assessment of the transmit signal, it is important to consider not only the eye opening, but also the overshoot and undershoot limitations. The parameters specifying the mask of the transmitter eye diagram are shown in Figure 2. Annex B considers measurement set-ups for determining the eye diagram of the optical transmit signal. T1508980-92 0 x 1 1 0 1 x 2 x 3 x 4 – y 1 y 1 y 2 1+y 1 UI x 1 /x 4 x 2 /x 3 y 1 /y 2 y 1 /y 2 x 3 –x 2 STM-1 STM-4 STM-16 0.5 A m pl it ud e Time Mean level of logical "1" Mean level of logical "0" 0.20/0.80 0.35/0.65 0.15/0.85 0.20/0.80 0.40/0.60 0.25/0.75 0.25/0.75 0.2 NOTE – In the case of STM-16, x 2 and x 3 of the rectangular eye mask need not be equidistant with respect to the vertical axes at 0 UI and 1 UI. The extent of this deviation is for further study. In view of the frequencies involved in STM-16 systems and the consequent difficulty of realizing this filter, the parameter values for STM-16 may need slight revision in light of experience. tải về 235.99 Kb. Chia sẻ với bạn bè của bạn:
|