Is it ok to work in Laravel and CodeIgniter side way? Will it kill my learningcurve ?

I think that, in many ways, the two are different enough that, as long as you don't confuse them, you should be able to learn both more or less in parallel. I do find it easier to stick with one thing, especially when I'm learning, but it's still possible to move between things, and you may find methods of working with CI when moving between it and Laravel that aren't as obvious to someone who just works with CI all the time.

On the other hand, I found that I only really started to understand either framework when I spent some time really trying to do some work with it, so you might want to design a basic site that implements a handful of things you think would be necessary for a real site and go through the process of implementing that basic site in each framework (one at a time, rather than constantly moving between the two frameworks).

Finally, if you find something about the way you implemented that basic site in Laravel that you would like to do in CI, but you can't figure out how to do it, this is as good a place as any to ask.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide