Difference between simplex and dual simplex?

Answer 1

Simplex is usually used to describe a single strand of Fiber Optic cable. This is sometimes used when a signal only needs to go in one direction, like a simple video feed from a security camera.

Duplex (sometimes called "zipcord") is two strands of Fiber Optic cable joined by a thin connection between the two jackets.

This is much more commonly used than simplex as with two fibers you can get synchronous communication between devices. Duplex cables are often labeled with A and B to determine which is the transmit and which is the receive.