What Is Single Mode Fiber?

It is obvious that the fiber-optics are steadily replacing copper wire in telecommunications. The main difference between fiber optic systems and copper wire systems is how they transmit information. Fiber optic cable transmit signals by using light pulses instead of electronic pluses. The light pulses enable fiber optic cable to transmit more data with further distance and fewer signal loss. So fiber optical cables are now widely used for television services, university campuses, office buildings or other long-distance applications. Here will depict one kind of optical fiber: single mode fiber.

Introduction to Single Mode Fiber

Single mode fiber is one kind of fiber which is a single stand of glass fiber deigned to carry light only directly down the transverse mode. Its core diameter is 8.3 to 10 microns. Compared to multimode fiber whose diameter is 50 to 100 microns, single mode fiber has a smaller core, which allows fewer signals to be transmitted simultaneously on a fiber. So the light can only travel on a single path not multimode patch. With only one mode of transmission, single mode fiber has no intermodal dispersion. Multimode fiber transmit signals through multimode paths for its larger core. Those multimode fiber can cause signal distortion at the receiving end in long-distance transmission, making signals unclear and incomplete. In addition, the index of refraction between the core and cladding of single mode changes less than it does for multimode fiber, creating little dispersion.


Conditions for Launching Light to Single Mode Fiber

As one type of optical fiber, single mode fiber carry lights to transmit information. But what should we take care of when launching light into single mode fiber?

Efficiently launching light into a single mode fiber requires the transverse complex amplitude profile of that light at the fiber’s input ends matches that of the guided mode. This means the light source have a high beam quality and a focus at the fiber’s input end and the light should be precisely aligned. A light into a single mode fiber needs well designed mechanical conditions. Taking lasers for example, the laser beam should has the correct size, allowing to precisely align and keep the fixed the focusing lens. It is usually easy to align correctly at the target position, but angular alignment is more critical.

Applications of Single Mode Fiber

Single mode fiber can achieve a high beam quality of the output together with WDM technology and optical amplifiers. In the optical links, single mode fiber can be used to connect different components such as connectors by fusion splicing. Due to little signal dispersion, single mode fiber is widely used for long-distance transmission. Optical media converters are used to do the fiber to fiber conversion to connect two different transmission modes, making single mode fiber efficient in long-distance transmission.

LC-LC Single-mode Fiber Patch Cable

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