is there a way to couple two circuits with minimum loading other than putting a high resistance in between, for example say if i provide a bias to a diode which is a part of an oscillator from a different circuit.
Without knowing exactly what you intend or are attempting to do, I will have to make several assumptions and say yes, use a FET. Since the input impedance of a FET is very high, it will provide very low loading to the previous stage.