Fibre-optic Trunk Lengths


Thread Starter

Ranjan Acharya

Dear List,

My supplier has assured me that I can drive four hundred metres (400m / 1312 feet / 437 yards) of plastic fibre optic cable without incident (provided that the plastic cable has a good attenuation specification).

The cable runs between two industrial-grade switches - one in a control room and one in an electronics room.

I would appreciate any thoughts or notes regarding experience in such issues. Naturally, plastic is much easier and cheaper to use than glass. We are also considering a glass-plastic polymer, but I do not have the numbers on that yet.

Thank You


Bob Peterson

I'd be inclined to believe the vender, OTOH, my experience with fiber optic cable leads me to believe that the installation costs (conduit, labor, etc.) generally exceeds the cost of the fiber optic cable. One thing you really should do is run some spare cables just in case, preferably in seperate conduits. The extra cost is well worth it.

BTW - you really don't need conduit for fiber optic cable, it can be routed along the bottom of an existing cable tray if it is out of the way and unlikely to get damaged. Otherwise installing it in conduit (I have seen it run in plastic pipe) is probably a good idea.
The only sure way to know if a particular distance is achievable or not is to do the attenuation db loss calculations. You must know what the loss budget is between the two switches (How much light is output, and how much must be received to insure proper operation, this is given in db) You must also find out what wavelength the switches are using. Then you can find out the losses per meter or 100 meter that the fiber cable has at that wavelength given in db/meter. You must also include losses for every connection/coupling in the system (worst case .5db/connection if a relatively poor job is done, this also gives a little safety margin when estimating.) You can now add up all the losses and if these are less that the optical budget of the switches then you are ok.

Ranjan Acharya

Further to my original posting regarding plastic optical fibre (POF) versus glass optical fibre (GOF). Research on the web has led me to the following conclusions:


Fibre optic cables are classified as either multi-mode (typical applications LAN, backbone up to 1 GHz) or single-mode (long distance and
telecommunications up to 1 THz).

A multi-mode system uses a short-wave laser transceiver with fibre thickness at 62.5 µm (range typically 175 metres, some sources show up to 500 metres; wavelength 850 nm [just visible at the red end of the spectrum] or 1.3 µm / 1300 nm [infra-red]) or 50 µm (range 550 metres).

For Ethernet and Fast Ethernet on multi-mode fibre, the wavelengths used are 850 nm and 1300 nm respectively and practical ranges end up in the 2 km range.

A single-mode system uses a longer wave laser transceiver with typical cable thickness of 8-10 µm (ranges up to 10 kilometres, wavelength 1.3 µm / 1300 nm).

For Ethernet and Fast Ethernet on single-mode fibre, the wavelength is always 1300 nm with practical ranges up to 15 km.

Transmission at 1550 nm is also available with significantly lower losses than the smaller wavelengths for single-mode fibre.

Cable is either glass fibre optic cable (glass optical fibre, GOF) or plastic fibre optic cable (plastic optical fibre, POF).

The wavelengths of 850 nm, 1300 nm and 1500 nm all reflect the transmission properties of GOF. POF uses 650 nm up to 100 metres only. Transmission is either by laser or LED for multi-mode fibre and laser for single-mode fibre.
Multi-mode transmission is hampered in that light is transmitted in rays or “modes” that bounce around the fibre and arrive at the destination at
different times resulting in signal degradation. Single-mode transmission has only one ray or one mode. There is no modal dispersion and much less
signal degradation.


Most of the data I have found gives slightly different numbers (different vendors' cables I assume). No one can quite agree. But I still have not found one site that suggests I can drive more than one hundred metres with POF. The vendor's claims are still in doubt.