When two counter-traveling modes produce a standing wave pattern in a semiconductor ring laser, population inversion grating is formed which couples one mode to another, leading in unidirectional operation. How is then bidirectional operation still possible?
Dear Arpit! I guess that general solution your task can be reach by decoupling clock /anti-clock ring modes by polarization. If Your diode active media supports both orthogonal light polarization there is possibility to test in ring cavity two Brewster plates with orthogonal orientation. Second decoupling solution is possible if to shift a little oscillation modes on wavelengths. The problem and its solutions can be found in proceeding devoted to laser gyro. I hope my hints occur to be useful in your work.
Warmly greeting,
Eugene A. Tikhonov
Dear Eugene,
Thank you for your answer. But I was asking about how is bidirectional operation possible without the use of any decoupling mechanism, as many people have reported it experimentally.
Dear Arpit,
Its due to the clockwise and counterclockwise light propagations in the ring. The original is due to the ASE emission from amplifier is non-directional.
Basically if you don't deliberately suppress it, it will always be bidirectional. Some people has achieved unidirectional operation, by forcing one of the direction into the other.
Yuqing
Dear Yuqing,
Due to phenomena such as non-linear coupling and mode competition, won't the clockwise and counterclockwise waves couple to each other with one suppressing the other?
Dear Arpit,
It is likely to have coupling between two directions, due to non-linear effects in the SOA. But most of them have same effects on both directions.
If you want to suppress one, then you need to build up an effect which is only strongly effective for one direction.
Gain of one mode becoming larger than the other modes is a normal way of mode suppression. Hence this highest gain mode to come out as a laser beam is well known.Since amplified stimulated emission is non-directional, perhaps,in a ring laser, the polarization is the same for both the clockwise and counter-clockwise beams, and hence transmission is possible in both directions.
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