The optical switch with double - heterostructure gaas / gaalas has low switching - voltage and light loss . and the boa - type optical switch utilizes maximum modal dispersion ( a p ) , does not require a specific fabrication length or length range to operate , has simple structure , and can exhibit very high extinction - ration from its two output ports ; so it is suitable for a 2 x 2 unit of optical switch array 而boa型結構(或稱為零間隙定向耦合型)光開關利用了最大的模色散( ) ,不需要嚴格控制特殊的制造長度或制造范圍,結構簡單,從其兩個輸出端可以得到很高的消光比,是一種很好的2 2波導型光開關單元,同時也是光開關陣列的一種較好的選擇。