In this paper the new dual principle of designing high-capacity strictly nonblocking optical switches is presented for the first time. The new type of switches with decentralized control based on the dual principle has been developed for the first time too. In accordance with the scheme topology this type of switching system was called as the quasicomplete dual switch. It also is analysed the optical signals minimal transmission time that provide the non-blocking property of the new schemes. For the circuit and link complexity calculations the accurate analytical expressions are obtained for the first time. The numerical investigation shows that the proposed schemes significantly benefit in comparison with the well-known switches, for example, the crossbar and Clos schemes. The results of comparing of the dual switch and other types of self-routing switches throughput show an obvious advantage of the proposed scheme. It also is shown that the offered switch type can be considered as a perspective for high-capacity strictly non-blocking optical systems. Indeed, the strictly nonblocking property, the scalability, high throughput, and the decentralized control are the main advantages of offered switches.