Laser Picoprojector

[Eidetical]

I'm organizing a display case to add items I've built over the years and dug this one out. It's an RGB picoprojector made by my former employer 8 years ago. I did all the assembly and alignment of the system except for the green DPSS laser shown in the box without its cover. They called me "The human Finetech", after the sub-micron assembly tool maker.

The green laser has crossed rod lenses in front of it and the red and blue lasers have one each. Then there's a collimating lens and structured diffuser in each path before the dichroics. The RGB beam reflects off an LCoS display (for despeckling) into an assembly holding a polarizing cube beamsplitter and projection lens. The imaging LCoS display is not shown. The whole thing was only 5mm thick. It's glued to an aluminum block and base for easy handling. Never went into production.

 

[farbe2]

That looks really nice.
Do you have any insights on how the optics where glued and aligned?

I tried many times to glue and align at the same time but I got problems with loosing alignment while the glue set.
Some time ago I even tried with a full 6DOF alignment stage from Thorlabs parts but every time I tried to harden the UV glue I got movement. (I tried many different glues)

 

[Eidetical]

I used a large optical table (for path length), oversized translators (for stability with no backlash), and a couple of cameras with long working distance video microscope lenses (to monitor optic position). The optic was held by a small piece of mounting foam on the bottom end of an 8-32 screw, so I could square it up to the base before lowering it into the tiny glue spot on the base. The glue used was Dymax OP-67-LS, a low-shrinkage UV curable adhesive for precision optical alignment. Hope that helps.

 

[farbe2]

That might really help.
How good did you get the beam alignment in the end? Lets say 10m distance, perfect overlap? 1/2 a mrad off? More off?

I will check some of that glue and see what I can cook up.

 

[paul1598419]

Do you remember the total output power?

 

[Eidetical]

That might really help.
How good did you get the beam alignment in the end? Lets say 10m distance, perfect overlap? 1/2 a mrad off? More off?

I will check some of that glue and see what I can cook up.

I just needed to get the hot spot of each laser centered on their respective diffusers. Collinearity of the beams after the dichroics was probably over a milliradian.

I seem to remember 80mW for the green, so the other colors would be similar I think.