Fiber Optic Light Source for Optical Communication Systems

The following very important characteristic of this light source is small spectral linewidth of the source. This significantly affects the dispersion magnitude is directly proportional to the line width of the source. Causing fiber dispersion in signal overlap and significantly reduces system capacity bandwidth.

Although there are many different types of light sources, fiber optic systems communication usually just use either diodes LED (light emitting diodes) or laser (LD) because of the requirements listed above. LEDs and LDs have small size, high efficiency and many other beneficial features.

 Laser diodes (LD)

LASER means Light Amplification by Stimulated Emission of Radiation. Highly monochromatic laser is similar to an electronic oscillator concept. A laser consists of an active medium which is capable of providing optical amplification and an optical resonator that provides the required optical feedback.

The most common laser diode is formed of a pn junction and fed by electric current injected. Is formed by doping a very thin layer on the surface of a glass wafer. The crystal is doped n-type to produce a p-type region, one above the other, resulting in a pn junction.

Laser diodes are available as laser diode modules. Some manufacturers offer a wide selection of laser diode modules ranging from continuous wave, line generator, modular, NIR and more.

Diode lasers microscopic chips used gallium arsenide semiconductor or exotic to generate coherent light in a very small package. The energy level differences between the conduction electrons and valence band are what provide the mechanism of action of the laser.

Diode lasers are high power light emitting more efficient. It can also be used for the diode laser instrumentation gives the user the ability to precisely control the laser diode current and temperature. It can operate in continuous wave mode by selecting a drive current modulated laser or by using a characteristic modulation in most drivers. The laser temperature can be set to the wavelength stabilization required.

The active element is a solid state device is not so different from an LED. LD have some disadvantages besides critical requirement of unity. Optical performance is generally not equal to that of other laser types. In particular, the coherence length and monochromicity some types are likely to be inferior.

 Light Emitting Diodes (LED)

An LED is a pn junction polarized in which EH recombination leads to the generation of optical radiation through the process of spontaneous emission. The LED structure is similar to that of a laser diode, except that there is no feedback cavity. The emission of an LED is due to spontaneous recombination and an LED output differs significantly from that of an LD (laser diode).

LEDs have many advantages such as lower energy consumption, longer life, improved robustness, smaller size and greater reliability. Unlike laser diode, there is no threshold and the output power increases smoothly as a function of current. For large currents the output power is saturated. The total power output of the LEDs can be a few milliwatts.

Due to the random and spontaneous emission is displayed along all directions, the output of an LED is not directional. Output beam angles may be typically in the range of 30 ° perpendicular to the junction, at about 120 ° along the junction.

LEDs are also used in many other applications other than the optical fiber communication, such as aviation, automotive lighting, and traffic signals, etc.