Answer to Question #181372 in Optics for Asif

Question

With the aid of simple sketches outline the major categories of multiport optical fiber coupler. Describe two common methods used in the fabrication of three- and four-port fiber couplers.

Answer 1

There are three main types of optical fibers.

(1) Single-mode optical fiber

(2) Multi mode optical fiber with stepped index

(3) Multi mode optical fiber with graded-index

$\bigstar$ Several methods are used to fabricate three- and four-port optical fiber couplers.

The lateral offset method

$\bull$ This method relies on the overlapping of the fiber end faces.

And Light from the input fiber is coupled to the output fibers according to the degree of overlap.

$\bull$ Hence , the input power can be distributed in a well defined proportion by appropriate control of the amount of lateral offset between the fibers.

The semitransparent mirror method 

$\bull$ This method provides an ingenious way to accomplish such a fiber coupler, as shown in Figure below.

$\bull$ A partially reflecting surface can be applied directly to the fiber end face cut at an angle of 45° to form a thin-film beam splitter.