Hundreds or thousands of these optical fibers are arranged in bundles in optical cables. The bundles are protected by the cable's outer covering, called a jacket.
Optical fibers come in two types:
• Single-mode fibers
• Multi-mode fibers

CONCAVE and CONVEX MIRRORS

Terms and Definition:

1. If a concave mirror is thought of as being a slice of a sphere, then there would be a line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror. This line is known as the principal axis.

2. The point in the center of sphere from which the mirror was sliced is known as the center of curvature and is denoted by the letter C in the diagram.
3. The point on the mirror's surface where the principal axis meets the mirror is known as the vertex and is denoted by the letter A in the diagram.
4. Midway between the vertex and the center of curvature is a point known as the focal point; the focal point is denoted by the letter F in the diagram.
5. The distance from the vertex to the center of curvature is known as the radius of curvature (abbreviated by "R").
6. The distance from the mirror to the focal point is known as the focal length (abbreviated by "f").

CONCAVE:
The simpler method relies on two simple rules of reflection for concave mirrors.
They are:
•Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection.
•Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

CONVEX:

A convex mirror is sometimes referred to as a diverging mirror due to its ability to take light from a point and diverge it. These four rays will each reflect according to the law of reflection. After reflection, the light rays diverge; subsequently they will never intersect on the object side of the mirror. For this reason, convex mirrors produce virtual images which are located somewhere behind the mirror.

Any incident ray traveling parallel to the principal axis on the way to a convex mirror will reflect in a manner that its extension will pass through the focal point.

Any incident ray traveling towards a convex mirror such that its extension passes through the focal point will reflect and travel parallel to the principal axis.

These two rules will be used to construct ray diagrams. A ray diagram is a tool used to determine the location, size, orientation, and type of image formed by a mirror.

Convex Lenses Characteristics:

•Distance from center of lens to focal point = focal length.
•Point is known as focal point.
•Example of a convex lens is a magnifier.
•The thicker the middle of the lens the shorter the focal length.
•Image can be seen without actually looking through the lens. This type of image is known as a real image.
•When held close to objects, inside of its focal length, it produces an image known as a virtual image. To see a virtual image you must look through the lens.

Concave Lenses Characteristics:
•Light rays come apart. It is also known as divergence.
•Always forms a virtual image.

Lens is a device that causes light to either converge and concentrate or to diverge. It is usually formed from a piece of shaped glass or plastic. Analogous devices used with other types of electromagnetic radiation are also called lenses: for instance, a microwave lens can be made from paraffin wax.

Types of lenses: