The FOM-3901 and FOM-3902 both provide complete electrical isolation for Nortel’s Meridian™ M2000 and M3000 series digital telephones. The FOM- 3901 connects to the digital line card and automatically senses and corrects any improper polarity reversals on the RJ-11. The bidirectional signaling between the digital line card and telephone is then carried across a duplex fiber optic cable. The FOM-3902 reproduces the digital signaling at the isolated end of the fiber optic link and provides power sufficient to operate M2000 and M3000 series digital telephones. The FOM-3902 also provides +42VDC power to auxiliary relays in the M2016S telephone.

The module can be used in areas of high electrical noise or in and out of RF shielded enclosures. The module enhances privacy of communications because fiber can not be tapped without being detected and does not radiate any emissions. The fiber optic cable is not susceptible to interference caused by impulse noise, crosstalk, or EMI. The potential problem of creating ground loops or ground offsets is also eliminated because there is no conductive path through the glass fiber for ground.

In addition, fiber optic cable offers much longer transmission distance than traditional telephone line cord wiring. Nortel’s Meridian™ digital telephones are limited to a maximum distance of 1750 feet (458m) from the PBX to the telephone on 24 gauge wire, but multimode and singlemode optics on the module extend the distance to 2km. A typical link consists of an FOM-3901 at the PBX and an FOM-3902 at the telephone with a duplex fiber optic cable between them.