App Notes

Multi-Mode versus Single-Mode Fiber

How do I know what type of fiber I need?
This is based on transmission distance to be covered as well as the overall budget allowed. If the distance is less than a couple of miles, multimode fiber will work well and transmission system costs (transmitter and receiver) will be in the $500 to $800 range. If the distance to be covered is more than 3-5 miles, single mode fiber is the choice. Transmission systems designed for use with this fiber will typically cost more than $1000 (due to the increased cost of the laser diode).

What is the difference between multimode and single mode fiber?
Multimode fiber has a relatively large light carrying core, usually 62.5 microns or larger in diameter. It is usually used for short distance transmissions with LED based fiber optic equipment. Single-mode fiber has a small light carrying core of 8 to 10 microns in diameter. It is normally used for long distance transmissions with laser diode based fiber optic transmission equipment.

Should I install single-mode or multimode fiber?
This depends on the application. Multimode fiber will allow transmission distances of up to about 10 miles and will allow the use of relatively inexpensive fiber optic transmitters and receivers. There will be bandwidth limitations of a few hundred MHz per Km of length.  Consequently, a 10 mile link will be limited to about 10 to 30 MHz. For CCTV this will be fine but for high speed data transmission it may not be.

Single-mode fiber on the other hand will be useful for distances well in excess of 10 miles but will require the use of single-mode transmitters (which normally use solid-state laser diodes). The higher cost of these optical emitters mean that single-mode equipment can be anywhere from 2 to 4 times as expensive as multimode equipment.

What is the maximum distance fiber optic transmitters can operate at?
It depends on which Luxlink model you purchase. Normal transmission distances can vary from a fraction of a mile to 40 miles (60 Kilometers) or more. The maximum transmission distance depends on output optical power of the transmitter, the optical wavelength utilized, the quality of the fiber optic cable and the sensitivity of the optical receiver. In general single-mode based systems operate over longer distances than multimode systems. The approximate transmission distances for Luxlink systems are indicated in the table below.

-No. Wavelength Fiber Type Connector

Transmission Distance covered**

-1 850 nm multimode ST up to   2 miles (3 Km)
-3 1310 nm multimode ST up to   6 miles (10 Km)
-7 1310 nm single-mode FCPC up to 20 miles (30 Km)
-8* 1310 nm single-mode ST up to 20 miles (30 Km)
-9 1550 nm single-mode FCPC up to 40 miles (60 Km)

** The transmission distances are only approximate and will depend on the loss of the actual fiber.
* ST connectors are not recommended for single mode applications, however they can be provided for legacy applications.

The cost of the required optics increase as the maximum transmission distance increases. So to be cost effective, you want to choose the appropriate model for your specific application. If you need to go distances greater than 50 to 60 Km you should contact the factory for systems utilizing special high power emitters. It is important to note that Luxlink systems have been produced that will transmit over distances of greater than 100Km.

I already have single-mode fiber installed, but I am only going a short distance. Can I use lower cost multimode equipment?
No. Multimode equipment will not launch (inject) enough light into a single-mode fiber since the light carrying core of this fiber is only 9 microns in diameter compared to 62.5 microns in diameter for multimode fiber. Unfortunately you must use single-mode equipment. If the fiber distance is short however, the cost for replacing the single-mode fiber with multimode fiber may be more economical than the higher cost for the single-mode electronics.


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