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What physically determines the polarization orientation of a laser diode? I always thought it was the junction orientation. I noticed that with the fast axis oriented the same, the Mitsu 500mW 638nm and the 9mm 445nm diodes polarization orientation seem to be different - 90 degrees apart.
Funny you brought that up. Just today I was placing the wave plate in a '71 quad that mimics the lay out of a 445 quad and you're right, the red beam appears to be polarized perpendicular to the axis of the near field stripe. I also thought the polarization was due to the asymmetric junction and would be the same for all diodes relative to the fast/slow axis.
Right! I'm building a dual/dual RB module and had planned the layout for the red section to be the same as the blue. But I must place the wave plate in front of the other laser in the red pair for the PBS to work. Why? It's a mystery to me.
I was also troubled by that at first
I would expect to place the waveplate in front of the diode that gets bent 90degrees by the PBS like i do with 445 and LOCs, but with the mitsu 71 the WP needs to be in front of the diode that goes through the PBS
Then, I opened a beer and said "have it your way darling"
Because there is no "Convention" on orienting P-cubes. Each manufacturer does it their own way. There may only be two physical possibilities, but you have to look at the "Cut Sheet" to know what your getting.
Steve
Steve,
You MAY be right, but this finding seems to be widespread and my PBS both come from the same manufacturer( presumably). One easy test; anyone with a broadband PBS should be able to verify this very easily.
I'm using BB PBS, same for red an blue. I can swap them and the results are still the same - the blue and red LD's polarization are 90 degrees apart with the junctions/stripe oriented the same. So it's not the PBS's that are different - it's the diodes.
I can also confirm that the 445nm and the mitsu 638nm have oposit polarization (just built 2 RB modules). That's great if you want to combine the 2 via PBS, saves the WP.
Nice point,but unless I'm building a pocket projector or the diodes climb above 5W each, I'm not going to limit my projects to single diodes.