The OPTEL3 is usually used to extend a two wire telephone line using optical fibers. The OPTEL3-SL connects to a plain old telephone, and the OPTEL3-CO connects to a CO or PBX at the other end of the link.
It is available with either a 1×9 or SFP optical transceiver. The optical fiber pair which connects the two may be multimode or singlemode depending on the selected transceiver. In addition, it has an RS232 data port.
A dedicated voice link (order-wire) can be created by having an-SL at both ends of the link. Lifting the handset at one end causes the other end to ring.
Another version, the OPTEL3-ASL, is an analog two wire modem which transmits and receives analog signals in the 200 to 3400 Hz range. It can be used as a clear channel for PSK, FSK, DTMF, or other signals.
Fiber optic transmission offers information security, electrical isolation, lightning protection, and EMI/RFI immunity. Since the voice is digitally encoded, the quality does not degrade with distance.