Handbook for Sound Engineers

Transmission Techniques: Fiber Optics 471

four main causes of loss that a connector or splice

must control are:

1. Lateral displacement.


2. End separation.


3. Angular misalignment.


4. Surface roughness.

15.9.3 Fiber Optic Connectors

A fiber optic connector (FOC) is a device designed to
simply and easily permit coupling, decoupling, and
recoupling of optical signals or power from each optical
fiber in a cable to corresponding fibers in another cable,
usually without the use of tools. The connector usually
consists of two mateable and demateable parts, one

attached to each end of a cable or to a piece of equip-

ment, for the purpose of providing connection and dis-

connection of fiber optic cables. When selecting FOCs

one should look for:

1. Minimum insertion loss.


2. Consistent loss characteristics with little change
   after many connect/disconnect cycles.


3. Easy installation without expensive tools and
   special training.


4. Reliability of connection (ruggedness).


5. Low cost.

There are many different types of FOCs being used

and newer types are emerging rapidly. We cannot even

attempt to cover them all, but will discuss the following

popular types in wide use in the communications

industry, see Fig. 15-31:

1. Biconic.


2. SMA.


3. FC/PC.


4. ST (preferred for audio applications).


5. SC.


6. D4.


7. FDDI (used in audio for duplex operations).


8. Small form factor connectors:
   LC.
   MT-RJ.

15.9.3.1 Biconic Connector

The biconic connector was invented by AT&T Bell Lab-

oratories. The latest in precision molding techniques are

incorporated to yield fractional dB losses. It employs a

conic ferrule and has a precision taper on one end that

mates to a free-floating precision molded alignment

sleeve within the coupling adaptor. While the biconic is

still around, it has lost its popularity for the most part.

15.9.3.2 SMA Connector

The SMA was developed by Amphenol Corporation

and is the oldest of all FOCs. It is similar to the SMA

connector used for microwave applications. The SMA

employs a ceramic ferrule and requires preparation of

the fiber end for mounting. There are different versions

of the SMA by other manufacturers called FSMA.

15.9.3.3 FC/PC Connector

The FC was developed by NTT Nippon Telegraph and

Telephone Corp. It has a flat endface on the ferrule that

Figure 15-29. Intrinsic fiber optic losses.

Figure 15-30. Extrinsic fiber optic losses.

A. NA mismatch B. Core diameter mismatch

C. Cladding diameter

mismatch

D. Concentricity

E. Ellipicity

Core 1

Core 2

Core

Cladding

A. Lateral displacement B. End separation

C. Angular misalignment