LD Polarization Orientation

[Photonbeam]

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.

[planters]

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.

[Photonbeam]

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.

[LaNeK779]

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"

[mixedgas]

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

[planters]

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.

[Photonbeam]

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.

[Solarfire]

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.

[planters]

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.