EDFA Tutorial

[Music] so let's get started good morning welcome to one more session of introduction to photonics so what we want to do during this week is identify the fundamental principles of lasers and quantify their performance characteristics so that's that's what we want to get to and and we do understand that laser is essentially an amplifier

with feedback so we'd been spending a lot of time are trying to understand amplifiers understand the process of amplification and we have some unfinished business from that perspective so the last lecture we were trying to address a problem related to the design of an IBM doe fiber amplifier so we said bm2 fiber amplifier

construction is typically like this where you excite the erbium doped fiber from one of the ends of the fiber because this lateral excitation is not it's not practical and when we do that we started looking at how the pump power is getting absorbed along the length of the fiber and also how the signal power

evolves along the length of the fiber and we needed to quantify how the signal power evolves so in order to do that we were defining the signal power along the length as bps over DZ which was essentially dependent on this gain coefficient now this gain coefficient itself one thing that we rely it's n2 x sigma e as it's mentioned over

here it's n2 x sigma e minus n1 multiplied by sigma a previously we had made a rough approximation saying sigma e is equal to sigma a right but if you actually write it out the gain coefficient would would depend on this this factor in the square brackets and what that tells us is that it is not

necessary that n2 is greater than N 1 so we looked at specific conditions where if Sigma E is greater than Sigma a ok then n 2 need not be greater than N 1 and conversely we said if Sigma E is less than Sigma a you if you have sufficiently high n2 over n1 you can