Probably your employer has patent rights in your invention during your employment course under the employed-to-invent doctrine that you were hired for this mission, also, your contract might include bonuses for your invention if it proves its value.
In case there is no employment agreement or employed-to-invent doctrine applies, the employer might still have shop rights in your invention, which means that he owns patent rights without paying you an additional fee, and this right arises when you use the employers’ resources during your invention.