What is the difference between single-fiber and dual-fiber?

The biggest difference between single-fiber and dual-fiber optical terminals lies in the optical modules on their mainboards; everything else is essentially the same.

Single-fiber Optical Terminal: Transmit and receive data over a single fiber.

Dual-fiber Optical Terminal: Transmit and receive data over two separate fibers.

As the name implies, a single-fiber optical terminal can save half of the fiber cable resources, i.e., it enables data transmission and reception over one fiber core, making it highly suitable for scenarios where fiber resources are scarce. A dual-fiber optical terminal, on the other hand, requires two fiber cores—one for transmitting (Tx) and one for receiving (Rx). Single-fiber optical terminals typically use paired wavelengths of 1310nm and 1550nm, where one end operates at 1310nm and the other at 1550nm, allowing both transmission and reception. Dual-fiber optical terminals, however, use a uniform wavelength, meaning both ends of the equipment operate at the same wavelength.

However, since optical terminal products lack a unified international standard, products from different manufacturers may experience compatibility issues when interconnected. Additionally, due to the use of wavelength-division multiplexing, single-fiber optical terminals suffer from signal attenuation, making their stability slightly inferior to that of dual-fiber products. In other words, single-fiber optical terminals place higher demands on optical modules, which is why they are generally more expensive than dual-fiber optical terminals on the market. Currently, most optical terminals on the market are dual-fiber products, which are more mature and stable but require more fiber cable resources.

The transmission distance of an optical terminal mainly depends on its optical module. The most common transmission distances available in the domestic market are: 10km/20km/40km/60km/80km/100km/120km. Generally, single-fiber equipment uses SC optical interfaces, while dual-fiber equipment uses FC optical interfaces. If one end has an FC interface and the other end has an SC interface, a hybrid pigtail—an FC-SC patch cord—can be used to connect them. If both ends have FC interfaces, dual-fiber FC pigtails can be selected.