Fiber Optic Tutorials

This is a continuation from the previous tutorial - broad-area lasers.   Most injection lasers intended for commercial applications have a built-in feature that restricts current injection to a small region along the junction plane. This restriction serves several purposes: It allows continuous-wave (CW) operation with reasonably low threshold currents (10-100 mA) compared with an unacceptably high value (~ 1 A) for broad-area lasers; It can allow fundamental-mode operation along the junction plane, which is necessary for applications where the light is coupled into an optical fiber The requirements for heat sinking are considerably less severe than those for a...

This is continuation from the previous tutorial - what is strained-layer epitaxy.   Introduction Semiconductor lasers operating in the wavelength range of 1.1-1.65 μm can be fabricated using the InGaAsP quaternary material which has been grown lattice-matched on an InP substrate. Room-temperature continuous operation of InGaAsP-InP double-heterostructure lasers was first reported in 1976. Since then, a large number of laser structures have been developed guided by the performance requirements of specific applications. The next few tutorials discuss different InGaAsP laser structures with particular emphasis on their performance in terms of the light-current characteristics, the threshold current, and the threshold current's temperature...

This is a continuation from the previous tutorial - material parameters of InGaAsP quaternary alloy grown on InP.   Although the growth of lattice-matched layers is very important for the fabrication of reliable semiconductor lasers, it is possible to make high-quality semiconductor lasers using materials with a small degree of lattice mismatch among them. This lattice mismatch introduces strain on the epitaxial layers, altering the semiconductor band structure. Typical values of tolerable strain (\(\Delta{a}/a\), where \(a\) is the lattice constant of the substrate and \(\Delta{a}\) is the difference in lattice constants between the substrate and the epitaxial layer) are less...

This is a continuation from the previous tutorial - lattice-mismatch effects on semiconductor epitaxial growth.   This tutorial describes the numerical values of various material parameters of InGaAsP quaternary alloy grown lattice-matched on InP. A knowledge of the band-structure parameters, such as the band gap and the effective masses of the conduction and valence bands, is necessary to calculate the radiative and nonradiative Auger recombination rates. The low-field minority carrier mobilities are also useful for calculating the diffusion coefficient that plays an important role in device performance. Tables 4-1 to 4-3 list the band gap, the lattice constant, the effective...

This is a continuation from the previous tutorial - what is molecular-beam epitaxy (MBE)?   A defect-free epitaxial growth of one crystal lattice over another takes place if the lattice constants of the two materials are nearly identical. In the presence of a small lattice mismatch (less than 0.1%), growth occurs with an approximate match of the lattice sites in the interface region of two lattices. This approximate match is possible if there is an elastic strain at the interface, that is, each atom is slightly displaced from its original position at the boundary layer. Although a small amount of...