The Bandwidth and Window of Fiber Optic Cable
For fiber optic cable, theoretically speaking, its bandwidth is infinitely high, transmission capacity is infinitely large and the transmission distance is infinitely far. Besides, optical fiber cable is also light in weight, and all of these features make it an ideal medium for data transmission, which is capable of transmitting unlimited telephone and TV signal. However, in the current application of optical cable, the result is far from the theory. Regardless of the fragile physical properties of silicon, the transmission capability of fiber optic cable has opened a few windows.
In May 2002, the ITU-T organization divided the fiber optical communication system into six bands as O, E, S, C, L and U6. Multi-mode optical fiber at 850nm is known as the first window, single-mode optical fiber at O band is referred to as the second band. C band is called as the third window, L band is the forth window and E band is the fifth window. The following table shows the wavelength bands for both multimode fiber optic cable and single-mode fiber optic cable.
|Frequency band||Window||Wavelength range (nm)||Frequency range (THz)|
|Short wavelength band||/||1460-1530||205.3-195.9|
|Longer wavelength band||4||1565-1625||191.6-184.5|
|Ultralength wavelength band||/||1625-1675||184.5-179.0|
The frequency range in the table above refers to the frequency of light. According to the formula speed = wavelength x frequency, we can easily figure out the frequency of light. Its relation to the transmission loss of fiber optic cable and wavelength has been displayed as follow:
In the early days of fiber optic communication the LED was employed as a light source due to its low price. Multi-mode fiber optic cables that operate at 850nm and 1300nm became the first choice for building small network, while single-mode optical fiber cables, working at 1310nm and 1550nm with laser as the light source , were the foundation for constructing large network. If there were more windows available for single-mode optic cable, one fiber optic cable would achieve ultra high speed transmission by transmitting signals at different wavelength at the same time by employing WDM (wavelength division multiplexing) technology, thus maximizing the potential of single mode fiber. Telephone and network and be using at the same time via ADSL (asymmetric digital subscriber line) modem. That’s because voice and data use different frequency. And this principle is similar with WDM and ADSL technology, which are usually applied in main networks that require higher bandwidth.
For intelligent building, the mainly adopted fiber optic cable are multi-mode optical cable which supports short distance transmission, such as multi-mode optical fiber cable that operates at 850nm or 1300nm with LED as the light source, or multi-mode optical fiber cable working at 850nm with VCSEL laser. Single-mode fiber optic cable is often adopted in buildings that with a longer distance to each other.
Intelligent building applications, fiber optic cable is often close to support multi-mode-based, such as multi-mode fiber optic cable with the emission wavelength of 850nm or 1300nm LED light source, or 850nm VCSEL laser wavelength. Single-mode used in long distance system buildings, single-mode fiber optic cable with emission wavelength 1310nm or 1550nm FP or DFB laser, means that most of the fiber optic cable is only open a window. Single-mode fiber optic cable works together with FP or DFB which transmit wavelength of 1310nm or 1550nm. That’s to say most optical cable only open one window.
Whether the transmission windows of fiber optic cable can be opened or not and how many windows can be opened will be subject to several factors as dispersion, loss, WDM as well as light source and network equipment. In the long term, fiber optic cables that supports multiple windows are bound to have stronger practicability, compatibility and scalability.
Related Article: How to Identify the Fiber Optic Cable Color Code?