ed dark current was assumed are the hybrid-r model capacitances. to have negligible effect on the sensitivity and the value of another Personick integral which equals 0.5 for both NRZ and RZ pulse formats. Laser or LED <Popt +eFBI,Q1 (53.75) The details of the design of optical receivers depend on the applications but as a general guideline low noise operation is achieved by minimising the input capacitance of the receiver. Because of the importance of the optical receivers, there has been a large number of designs aiming at particular requirements. How- ever, since the main use of optical receivers is in the trunk and Figure 53.27 Driver for analogue modulation junction network, where the information capacity is standardised, receivers corresponding to these rates have been introduced. Table 53.6 summarises the current performance of optical receivers using p-i-n detectors and operating in the 1300nm to 1600nm range. APD Table 53.6 Sensitivity of optical receivers using p-i-n detectors. (All parameters are at BER = 10-9; all the receivers are with multimode fibre tails) Bit rate Sensitivity (dBm) 2Mbit/s -56.5 -58.5 16Mbit/s -52.0 -54.0 Current 45Mbit/s -49.0 -51.0 90Mbit/s -46.0 -48.0 160Mbit/s -43.0 -45.5 Modulation 565Mbit/s -36.0 -38.0 680Mbit/s -34.0 -35.5 Figure 53.28 Analogue LED modulation 1200Mbit/s -31.0 -33.0 1600Mbit/s -29.0 -31.0 2400Mbit/s -28.0 -29.0 receivers tend to be in house products and the improvement depends on the details of the design but on average 5db of improvement is expected. Some of the bit rates are not within the digital hierarchy, but in a fast evolving field some of the applications require special bit rates. 53.4.4 Optical transmitters The configuration of an optical transmitter depends first on the signal format and second on the class of the device (LED or laser). The simplest modulation format is that of intensity modulation. In Current this format the information carrying current is injected into the optical source and consequence the intensity, that is the square of the f