Hi Elina,

I have polished a lot of waveguide edges when I worked with Silica AWGs.
Always, I used lapping films. You may use free abrasives, but there are
problems associated with that :

a) Conventional polishing requires that as you polish, you have a flow of
water that removes the polished particles from waveguides so that they dont
scratch the edge again. Flowing water helps reduce the scratching on the
edges and need you to polish lesser for attaining a degree of smoothness.
With free abrasives, one would need to keep adding these as we continue
polishing, just because the abrasive material will get removed by the water
flow just like the pieces of silica which are getting removed.

b) For polishing waveguide edges, the best technique is to start with a big
sized lap (say with particle diameters of about 30 um) and go all the way
down (typically 0.1 um). With free abrasives, we need a huge stock of
abrasives with different particle diameters and we need to keep adding them
after thorough cleaning each time. This is not convenient.

c) The reproducibility of well polished surfaces has been proven and is very
clear while one uses a lap. Because the abrasives are almost always evenly
distributed on the film, the reproducibility is very high. With free
abrasives, distribution of the abrasive particle is very difficult to
control.

All the above said, you can definitely try to use free abrasives for
polishing edges, with proper care and patience, they should work. It is just
a matter of convenience that many people use laps.

Thanks,
Ananth Krishnan
Texas, USA


*From: "Kasman, Elina" 
To: 
Date: Tue, 13 Jan 2009 15:34:28 -0600
Subject: [mems-talk] Waveguide polishing

Does anyone have experience with waveguide edge polishing?
I am trying to figure out why mostly lapping films are used. My best
guess is tradition and this is something that people have had on hand.
Are free abrasives used at all? Any reasons not to use free abrasives?

Thanks
Elina*