Optical stablized couler

An optical coupler with a stabilized coupling ratio includes at least on first-type delay part having a delay quantity; at least one second-type delay part having a basic delay quantity and an adjustable delay quantity; and multiple optical splitting units. By the optical splitting units, the first-type delay part and the second-type delay part are connected and connected between an input terminal and an output terminal. Wherein, they are, for example, coupled in cascade manner. An effective coupling ratio can be stably obtained. Alternatively, any desired effective coupling ratio can also be stably adjusted out by a set of the adjustable delay quantity.