While designing an external cavity diode laser for low linewidth and low backscattering loss, what are the losses that needs to be taken into consideration ?
Not exactly. What I meant was simple SOA coupled to an optical fiber to form a laser.
Dear Vincent,
Sorry for such an abstract question. Let me make myself a bit specific.
I wish to build an external fiber cavity ring laser with the two ends of a SOA joined by a fiber forming a ring cavity and a output coupler to couple out useful light for detection. Now, I want to know what are the prominent losses that I must take into account so as to make a fine-working ring laser?
I think that Vincent has named a very important loss mechanism, namely coupling loss between fiber and SOA cavity. If the fibers are lensed to match the dissimilar SOA and fiber modes, then the loss can be minimized but it will still be significant at both ends of the SOA. There are numerical tools, e.g., FIMMWAVE, that can do an accurate job of modeling the loss -- or you can make approximations to do a rough calculation. In the end, you will have to make up this coupling loss with SOA gain. Of course, your out-coupler will be another source of cavity loss, albeit intentional. Linewidth will depend on some difficult-to-control factors, especially with a relatively long fiber ring. But that is an answer for a different question.
Suppose if I take a fiber pig-tailed SOA and fusion splice it to the external fiber forming a ring cavity, will the coupling loss still be high ?
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