(a) In the scenario described with ideal 3-dB couplers, ideal connectors, and fibers, the total loss in dB from transmitter to receiver can be calculated by adding up the individual losses at each component.
Given that ideal 3-dB couplers and ideal connectors and fibers are used, there is no additional loss from the couplers and connectors. Therefore, the total loss is equal to the loss in the fiber, which is 4 dB.
So, the total loss in dB from transmitter to receiver is 4 dB.
(b) In this case, the excess loss of 1.5 dB for each directional coupler and 0.8 dB loss for each connector are considered, in addition to the 4 dB loss in the fiber.
The total loss in dB from transmitter to receiver can be calculated by summing up the losses at each component:
Total loss = Loss in fiber + Loss from excess coupler losses + Loss from connector losses
Total loss = 4 dB + (1.5 dB × 2) + (0.8 dB × 2)
Total loss = 4 dB + 3 dB + 1.6 dB
Total loss = 8.6 dB
Therefore, the total loss in dB from transmitter to receiver, considering the excess coupler losses and connector losses, is 8.6 dB.