Fiber Optic Tutorials

This is a continuation from the previous tutorial - semiconductor laser characteristics.   Types of Photodetectors A photodetector is a device that converts an optical signal into a signal of another form. Most photodetectors convert optical signals into electrical signals, in the form of either current or voltage, that can be further processed or stored. All photodetectors are square-law detectors that respond to the power or intensity, rather than the field amplitude, of an optical signal. Based on the difference in the conversion mechanisms, there are two classes of photodetectors: photon detectors and thermal detectors. Photon detectors are quantum detectors...

This is a continuation from the previous tutorial - semiconductor lasers.   Similarly to an LED, a semiconductor laser is also a junction diode, which has the general electrical characteristics discussed in the semiconductor junctions tutorial with its voltage-current characteristics shown in Figure 12-12. The difference between a laser and an LED is that the active layer of a laser has to be pumped sufficiently to reach the condition in (13-35) [refer to the optical gain in semiconductors tutorial] for an optical gain. When a junction diode is forward biased with a voltage \(V\), the splitting of its Fermi levels...

This is a continuation from the previous tutorial - semiconductor optical amplifiers (SOAs).   Semiconductor lasers, also called laser diodes or diode lasers, are compact and efficient laser that have found many important application in optical communications, optical data storage, optical signal processing, compact-disk players, laser printers, and medical instruments. High-power semiconductor lasers are also used as highly efficient pump sources for other optically pumped lasers and amplifiers, such as solid-state lasers, optical fiber lasers, and fiber amplifiers. Unlike the light-emitting active region of an LED, which can be made of either a direct-gap or an indirect-gap semiconductor, the active...

This is a continuation from the previous tutorial - light-emitting diodes (LEDs).   An amplifier requires an optical gain for stimulated amplification of an optical signal, but it does not need a resonant cavity. Thus, a semiconductor optical amplifier (SOA), also called a semiconductor laser amplifier, can be made by simply eliminating the optical feedback mechanism of a semiconductor laser. For a solitary SOA as shown in Figure 13-29, the end facets have to be antireflection coated. Meanwhile, no other feedback mechanism, such as a distributed feedback grating, is incorporated into the device structure. In theory, the output coupling loss...

This is a continuation from the previous tutorial - lateral structures of semiconductor junctions.   LEDs are simple, but important, solid-state light sources that have a wide range of applications. LEDs that emit light in the visible spectral region are widely used in displays and in fiber-optic illumination. Infrared LEDs are useful for fiber-optic communications in those systems where the coherence, high power, and high speed of semiconductor lasers are not needed. Recent breakthroughs have resulted in LEDs of very high performance, in terms of efficiency and brightness, and have extended the spectral range of these high-brightness LEDs to the...