Dear Arjun,
you need to identify the type of the input and output ports of the Matlab component as desired. This can be set in the component properties window (scroll down on Signal type (output 1). However, you need to set first the number of input and output ports.
I think you are generating an electrical signal that you need to modulate a laser with it. This means that the output signal should be electrical. You need to identify the type of signal for the input port.
Regards,
Ahmad