Hi Fayiqa,
the working of coupler and fork is different, you can refer to the “Optisystem component library” pdf for this.
A Fork Copies the input signal into two output signals. This tool allows you to duplicate the input signal to the output ports.
It can be used in electrical as well as in optical domain where you need to generate a duplicate copy. there is nothing like power loss in case of coupler.
and you are right about the working of cross coupler it have some loss.
Regards,
Dhiman Kakati