The 4 Ports 1310nm Singlemode Polarization Insensitive Optical Circulator is a high-performance non-reciprocal passive device that routes light sequentially from Port 1 → Port 2 → Port 3 → Port 4, ensuring precise and unidirectional signal transmission in singlemode fiber systems. Designed to operate at 1310 nm, it features low insertion loss, high isolation, and excellent return loss, providing reliable performance for optical communication and testing applications.