The 4 Ports 1550nm Singlemode Polarization Insensitive Optical Circulator is a high-performance non-reciprocal passive optical device designed to control the direction of light transmission in singlemode fiber systems. It sequentially routes optical signals from Port 1 → Port 2 → Port 3 → Port 4 with minimal insertion loss and excellent isolation, ensuring reliable and efficient unidirectional signal flow without back reflection.