An Introduction To Simplex And Duplex Fiber Optic Cable

It is known to all that fiber optic cable is made of glass or plastic that mainly used for transmitting information. Fiber optic cable can be divided into many types according to different classification principles, such as source, mode, usages... In this text, we would mainly introduce simplex and duplex fiber optic cable as well as their differences.

Simplex Fiber Optic Cable

A simplex fiber only consists one single strand of glass of plastic fiber. Simplex signals are sent in one direction. It is much like what we said “one-way-street”. If a signal is transmitted from device A to device B over a simplex fiber optic cable, it cannot return from device B through the same cable. For example, we receive signals from radio station but never send signals to it. Thus, it is used for applications that only require one-way data transfer.

Simplex fiber is most often used where only a single transmit and receiver line is required between devices or when as multiplex data signal is used. Digital data readouts, interstate highway sensor relays, and automated speed and boundary sensors (for sports application) are all great uses of simplex fiber optic cable. Simplex fiber is available in single-mode and multimode. For example, an an interstate trunking scale that sends the weight of the trunk to a monitoring station or an oil online monitor that sends data about oil flow to a central location.

Duplex Fiber Optic Cable

A duplex fiber cable consists of two strand fibers of glass or plastic, and it can be seen as two simplex cables. Generally, the construction format of it is a “zipcord” (side-by-side). Being different from simplex fiber optic cable, this cable is bi-directional and simultaneous when it transmits data. The transmission principle just like this, one fiber transmits data one direction while the other fiber transmits data in the opposite direction.

Therefore, this cable is most often used for duplex communication between devices where a separate transmit transmit and receive are required. Duplex fiber is available in single-mode and multimode. Use duplex multimode or single-mode fiber optic cable for applications that require simultaneous, bi-directional data transfer. Workstations, fiber switches and servers, fiber modems, and similar hardware require duplex fiber cable.

Most commonly, there are two types duplex fibers:
Half-duplex: Data may only be transmitted in one direction at a time.
Full-duplex: Data is transferred in two directions simultaneously.

Half-duplex

Data can be transmitted in two directions but not at a same time in half duplex mode. It can be regarded as a simplex channel whose transmission direction can be switched. To speak more specifically, data can be transmitted from Device A to Device B, but it can be returned only when Device B received data from Device A. Once Device B has been received data, it can send data back to Device A. Just take walkie-talkie for an example, it has a “push-to-talk” button which can be used to turn on the transmitter but turn off the receiver. In this way, you cannot hear the person you are talking to but your partner can hear you once you push the button. This single track is cheaper than the double tracks for the reason of less material.

Full-duplex

Data can be transmitted in both directions on a signal carrier at the same time in full-duplex mode. Being different from half-mode, it uses a pair of simplex links instead of a single simplex link to transmit. Under this condition, bidirectional and simultaneous transmission can be achieved. That is to say, data is transmitted from Device A to Device B or Device B to Device A at the same time. Take telephone for an instance, we can talk and hear other’s voice at the same time because there are bi-directional communication tracks between us. In this way, the communication efficiency has been greatly enhanced by using this full-duplex mode.

Simplex Fiber Optic Cable Vs. Duplex Fiber Optic Cable

• Source—Simplex fiber optic cable uses only single one strand of fiber while duplex fiber cable uses a pair of fiber.
• Transmission Direction—Simplex fiber optic cable is one-way transmission mode while duplex fiber cable is bi-directional transmission mode.
• Cost—For the sake of using less source material, simplex fiber optic cable is cheaper than duplex optic cable.

You can the differences in the following picture more clearly. They are simplex fiber optic cable (left) and duplex fiber optic cable (right).

  

Summary

Simplex fiber optic cable and duplex fiber optic cable both have single-mode and multimode cable type. They are different from source, transmission direction and cost. If you need a fiber optic cable for one-way transmission, and then simplex fiber optic cable is a good choice. When you are looking for a bi-directional fiber optic cable, duplex fiber optic cable is highly recommended.