Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 10

Years: MAY 2013

Requirements of good fiber connector are as follows:

1. Low coupling losses:

The connector assembly must maintain stringent alignment tolerances to assure low mating losses. These low losses must not change significantly during operation or after numerous connects and disconnects.

1. Interchangeability:

Connectors of the same type must be compatible from one manufacturer to another.

1. Ease of assembly:

A service technician should readily be able to install the connector in a field environment; that is, in a location other than the connector factory. The connector loss should also be fairly insensitive to the assembly skill of the technician.

1. Low environment sensitivity:

Connector such as temperature, dust and moisture should have a small effect on connector loss variations.

1. Low cost and reliable construction:

The connector must have a precision suitable to the application, but its cost must not be a major factor in the fiber system.

1. High strength:

The connection should not degrade due to forces on the connector body of tension on fiber cables.

1. Ease of connection:

Generally one should be able to mate and unmate the connector, simply by hand.

Lensing Schemes

• The source to fiber power launching analysis proves that if the source-emitting area is larger than the fiber-core area, then maximum optical power is coupled into the fiber.

• However, if the emitting area of the source is smaller than the core-area, a miniature lens may be placed between the source and the fiber to improve the power-coupling efficiency.

• The function of microlens is to magnify the emitting area of the source to exactly match the core area of the fiber end face.

• If the emitting area is increased by a magnification factor M, the solid angle within which optical power is coupled to the fiber from source is also increased by the same factor.

• Several possible lensing schemes are shown in the figure below:

Figure 1.25

• These include a rounded end fiber, a small glass sphere (nonimaging microsphere) in contact with both the fiber and the source, a larger spherical lens used to image the source on the core area of the fiber end, a cylindrical lens generally formed from a short section of fiber, a system consisting of a spherical-surfaced LED and a spherical-ended fiber, and a taper-ended fiber.

• Nonimaging microsphere is the most efficient lensing method used to increase power coupling efficiency.

• The theoretical coupling efficiency that can be achieved is based on energy and radiance conservation principles. The efficiency is usually determined by the size of the fiber.

• Although these techniques can improve the source-to-fiber coupling efficiency, they also create additional complexities. One problem is that the lens size is similar to the source and the fiber-core dimensions, which introduces fabrication and handling difficulties.

• In the case of taper-ended fiber, the mechanical alignment must be carried out with greater precision since the coupling efficiency becomes a more sharply peaked function of the spatial alignment. However, alignment tolerances are increased for other types of lensing system.