Question: simplifying complex expressions

How do I simplify :

Zin := Rin + omega*L*I + (omega*L)^2/(RL + omega*L*I);
 

so that there are no imaginary terms in the denominator?  

I've tried, 

assum := Rin::real, omega::real, L::real, RL::real, 0 < Rin, 0 < omega, 0 < RL, 0 < L
Zin := Rin + omega*L*I + (omega*L)^2/(RL + omega*L*I);
 
(simplify(Zin) assuming assum);

but this doesn't work.

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