Yeah you can, it has to be the whole drive and it has to be compatible for your model and the exact same model of the drive.
I've seen lots of drives on ebay and seen lots of videos on youtube of people showing how to replace them.
Yeah, you can't - either:
1) Get a new laser (same type)
2) Get a new drive , and swap your old BD controller board with the new one, then install the new drive unit (with the old board).
if i cant fix the drive at least i have the option to replace it or replace its parts.