a potential application for an optical switch in the local environment is likely in the 1990 39 s since broadband isdn b isdn is likely to become a reality in the early or mid 1990 39 s such a system requires individual video channels with a minimum data rate of 45 mb s for present tv signals and data rates as large as 400 mb s are expected for high definition tv hdtv signals it is likely that a rate of about 140 mb s will be used as a common rate for both the usa and europe these systems will use switches that may require approximately 100 inputs to be competitive with catv systems further it is likely that an enhanced level of tv quality preferably high definition quality if the cost is not too high will be required to show product improvement for b isdn over the present catv these inputs should be switched to hundreds and perhaps thousands of outputs customers if 16 channels are cd multiplexed together on the input of a switch illustrated in fig4 and six wavelengths are used in the wd multiplexer the switch can accept 96 input channels these inputs can be sent to any of hundreds and potentially thousands of outputs if the fanout capability of the technology used will permit instead of making one code switch that will accept 96 inputs and require processing at 96 times the data rate of the input channels as high as 96 u00d7 140 mb s 13 4 gb s the resultant upper limit for data rate is.