As I know multi-mode fibers suffer from bad dispersion property. However I have seen that several companies sell multi-mode fibers. I wonder what application these fibers are used for.
Note that I am not talking about plastic optical fibers. Indeed I mean the glass fibers with diameters of 50, 62.5 or 125 micrometers.
Though multi-mode fibers have higher dispersion losses but their larger diameter and larger NA makes them suitable for a lot of applications. They are used for studying the mode coupling characteristics, for short-distance communication applications, collimated laser with GRIN, and they are used to transmit/receive light in medical applications.
Indeed there are many applications for multi-mode fibers, such as plain optical energy transport. As Amardeep mentioned, they are widely used for short distance (
Though MM fibers have higher intermodal dispersion, still they are very useful in short distance communication.
MM fibers with a high diameter of e.g. 600 µm are often very robust. They are used for
applications where a lot of mechanicals stress is. Think on sensing in chemical
processes. They are very useful for several applications.
Further, MM fibers with gradient refractive index profile are produced nowdays, and this technology reduces modal dispersion greatly, so this influence is reduced even for very high transmission speed. Of course, as use of optical fibers in LANs and MANs growing rapidly, technology is evolving as well and for communication purposes you can have MM fiber suitable for 10Gbit/s over 2000 meters.
Thank you all for your replies.
Through your comments I realized that it is possible to guide a high power light by a MMF. But I assume that a suitable MMF for this application is POF with diameter of 1mm or more. If this conclusion is correct, what is the usage of MM 50 um glass fibers?
So the traditional answer is:
POF will have very high scattering losses per unit distance (we're talking >25 dB/km vs
Thank you dear Luke Rumbaugh. Your answer clearly explained what I needed to know.
Nowadays, many research group in optical fiber communications, around the world, are considering the use of multimode silica fiber, and plastic optical fiber in Radio of Fiber (RoF) systems. Remenber that VCSELs lasers, in 500 to 850 nm of wavelenght, with an emitting power around 1 - 10 mW, are in the market with a low price. Then, the easy connection of multimode fibers in a link, and optoelectronic components no expensive, make the use of these fibers very interesting.
Continuing
The application is for length link no more than 50 - 200 m (GPOF), and 500 - 1000 m (GMMF). The modal noise, due a bad connections, and a coherent optical source, is an important noise to be considered in the power budget calculation . Modal dispersion may not be a problem, if you use gradual fibers (GF).
Hi Mojtaba
Look this link
http://opli.net/opli_magazine/optical_network/2015/going-beyond-the-limits-of-optical-fibers-apr-news/
in short distance communication multimode fiber is suitable one. for the 500m or 1km fiber, a very small amount of dispersion only accumulated. and also the huge amount of power can coupled by the multimode mode fiber(each mode carrying some power) compare to the singlemode fiber. so, in short distance communication such as Air craft , medical , and inter building communication mutimode fiber exhibits superior performance at low cost
optogenetics, and in-vivo applications use even 200um silica fibers for tranfering light to an animal.
it's also useful if you wnat power transmission, rather than data.