Factors That Limit Optical Transmission Distance

Nowadays, fiber optic network is gaining its popularity because it has high speed, high density and high bandwidth, etc. Compared with traditional copper cable, the fiber optic cable could support much further distance although the exact distance is limited by many factors. For the super fast optical communication, transmission distance has already become the most vital issue. The optical signal may become weak over long distance. Thus, many components and methods have been adopted to break the limitations of the optical transmission distance. This article will emphasize the factors that limit optical transmission distance.

Optical Fiber Cable Type

Typically, the dispersion in the fiber optic cable could have a great impact on the transmission distance. There are two types of dispersion—chromatic dispersion and modal dispersion. Chromatic dispersion is the spreading of the signal over time resulting from the different speeds of light rays, while modal dispersion is the spreading of the signal over time resulting from the different propagation mode.

As it is known to all, optical fiber cable could be divided into single-mode fiber cable and multimode fiber cable. For the single-mode fibers, transmission distance is affected by chromatic dispersion, because the core of single-mode fibers is much smaller than that of multimode fibers. And this is the main reason why single-mode fiber can have longer transmission distance than multimode fiber. For the multimode fibers, transmission distance is largely affected by the modal dispersion. Due to the fiber imperfections, the optical signals of multimode fibers cannot arrive simultaneously and there is a delay between the fastest and the slowest modes, which causes the dispersion and limits the performance of multimode fibers (see the following picture).

Light Source of Fiber Optic Transceiver

Fiber optic cable is the path sending the optical signals. However, most of the terminals are electronic based. The conversions between electrical signals and optical signals are necessary. Fiber optic transceivers are widely used in today’s optical network to achieve this purpose. The conversion of signals depends on a LED (light emitting diode) or a laser diode inside the transceiver, which is the light source of fiber optic transceiver. The light source can also affect the transmission distance of a fiber optic link.

LED diode based transceivers can only support short distances and low data rate transmission. Thus, they cannot satisfy the increasing demand for higher data rate and longer transmission distance. For longer and higher transmission data rate, laser diode is used in most of the modern transceivers. The most commonly used laser sources in transceivers are Fabry Perot (FP) laser, Distributed Feedback (DFB) laser and Vertical-Cavity Surface-Emitting (VCSEL) laser. The following chart shows the main characteristics of these light sources.

Frequency of Transmission

As is shown in the above chart, different laser sources support different frequencies. The maximum distance of fiber optic transmission system can support is affected by the frequency at which the fiber optic signal will be transmitted. Generally the higher the frequency, the longer distance the optical system can support. So it is essential to select the right frequency to transmit optical signals. Typically single-mode fibers use frequencies of 1300 nm and 1550 nm, while multimode fibers use frequencies of 850 nm and 1300 nm.

Bandwidth

Another factor influencing the transmission distance is the bandwidth of fiber optic cables. Generally, the transmission distance decreases proportionally, as the bandwidth increases. For example, a fiber that can support 500 MHz bandwidth at a distance of one kilometer will only be able to support 250 MHz at 2 kilometers and 100 MHz at 5 kilometers. Single-mode fibers have an inherently higher bandwidth than multimode fibers due to the way in which light passes through them.

Splices and Connectors

Splices and connectors in most fiber optic system are inevitable. Signal loss can be caused when the optical signal passes through each splice and connector. The total amount of the loss depends on the types, quality and number of connectors and splices.

Conclusion

According to the above statement, the optical transmission distance is affected by various factors including the fiber type, light source of transceiver, frequency of transmission, bandwidth as well as splices and connectors. So it is necessary to consider these factors to minimum the limitations on transmission distance when deploying the fiber optic network.

Article source: www.roarsummit.com/factors-that-limit-optical-transmission-distance-1562133546.html

BiDi Transceiver Overview

For several years ago, when talked about fiber optic transceiver, almost most of people engaged in telecommunication industry would tell that a transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry. Almost all fiber optic transceivers uses two fibers to transmit data between routers and switches. One fiber is devoted to transmitting data to the networking equipment, while the other one is devoted to receiving data from the networking equipment. For recent years, a new kind of fiber optic transceiver has been available — Bi-Directional transceiver (BiDi transceiver).

BiDi Transceiver Basis

BiDi transceiver is a type of fiber optic transceiver which uses WDM (wavelength division multiplexing) bi-directional transmission technology so that it can achieve the transmission of optical channels on a fiber propagating simultaneously in both directions. BiDi transceiver is only with one port which uses an integral bidirectional coupler to transmit and receive signals over a single optical fiber (see the following picture). BiDi transceivers are specifically designed for the high-performance integrated duplex data link over a single optical fiber and used in bi-directional communication applications. The BiDi transceivers interface a network device mother board (for a switch, router or similar device) to a fiber optic or unshielded twisted pair networking cable.

Working Principle of BiDi Transceiver

The difference between BiDi transceivers and the two-fiber optical transceiver mainly lies in that BiDi transceivers are fitted with WDM couplers, also known as diplexers, which help to combine and separate data transmitted over a single fiber based on the wavelengths of the light. So BiDi transceivers are also called WDM transceivers. BiDi transceivers are usually deployed in matched pairs to get the work most efficiently. And the diplexers of BiDi transceivers are tuned to match the expected wavelength of the transmitter and receiver that they will be transmitting data from or to.

As can be seen from the following diagram, the paired BiDi transceivers are being used to connect two devices. Device A is used to get upstream data, and Device B is used to get downstream data. Tx means transmit. Rx means receive. The diplexer in one transceiver (Device A) should have a transmitting wavelength of 1310 nm and have a receiving wavelength of 1550 nm. The diplexer in the other transceiver (Device B) should have a transmitting wavelength of 1550 nm and have a receiving wavelength of 1310 nm.

Advantages of BiDi Transceiver

The decisive advantage of using BiDi transceiver is that it helps to reduce the cost of fiber cabling infrastructure. This is caused by reducing the number of fiber path panel ports as well as reducing the amount of tray space dedicated to fiber management. The deployment of BiDi transceiver enables the bandwidth capacity of the optical fiber to be doubled.

 

Fiberstore BiDi Transceiver Solution

Fiberstore supplies a series of BiDi transceivers with different types such as BiDi SFP. These BiDi SFP transceivers support Fast Ethernet, Gigabit Ethernet, and Fibre Channel, etc. And they can be available for simplex SC or LC connector interface, which is used for data transmitting and receiving. Also, the BiDi SFPs from Fiberstore are able to support a wide range of physical media from copper to long-wave single-mode optical fiber with transmission distance up to hundreds of kilometers. The most typical Tx and Rx wavelength combinations are 1310/1490 nm, 1310/1550 nm and 1490/1550 nm. Fiberstore has a large selection of BiDi transceivers in stock. Choosing a Fiberstore BiDi transceiver can help your fiber optic network to be most economical and efficient.

Originally published: www.fiber-optic-components.com/