Fiber Optic Tutorials

This is a continuation from the previous tutorial - Maxwell's equations for semiconductor lasers.   The plane-wave solution, Equation (2-2-21) [refer to the Maxwell's equations for semiconductor lasers tutorial], of the wave equation obtained in the Maxwell's equations for semiconductor lasers tutorial can be used to obtain an estimate of the laser frequency and the optical gain required for the onset of oscillations. It should be kept in mind that the lasing modes are never plane waves; another later tutorial considers the spatial variations of the lasing modes. Nonetheless, the threshold condition derived here is reasonably accurate and is helpful...

This is a continuation from the previous tutorial - operating principles of semiconductor lasers.   Since the mathematical description of all optical phenomena is based on Maxwell's equations, it is appropriate to start our discussion of semiconductor lasers by considering these equations in some detail. In the MKS system of units, the field equations take the following form: \[\tag{2-2-1}\pmb{\nabla}\times\pmb{\mathscr{E}}=-\frac{\partial\pmb{\mathscr{B}}}{\partial{t}}\] \[\tag{2-2-2}\pmb{\nabla}\times\pmb{\mathscr{H}}=\pmb{\mathscr{J}}+\frac{\partial\pmb{\mathscr{D}}}{\partial{t}}\] \[\tag{2-2-3}\pmb{\nabla}\cdot\pmb{\mathscr{D}}=\rho_f\] \[\tag{2-2-4}\pmb{\nabla}\cdot\pmb{\mathscr{B}}=0\] where \(\pmb{\mathscr{E}}\) and \(\pmb{\mathscr{H}}\) are the electric and magnetic field vectors, respectively, and \(\pmb{\mathscr{D}}\) and \(\pmb{\mathscr{B}}\) are the corresponding electric and magnetic flux densities. The current density vector \(\pmb{\mathscr{J}}\) and the free charge density \(\rho_f\) represent the sources...

This is a continuation from the previous tutorial - the history of semiconductor lasers.   This tutorial provides a qualitative understanding of the physics behind the semiconductor laser. Most of the concepts introduced here are discussed in detail in subsequent tutorials. Two things are required to operate a laser: (i) a gain medium that can amplify the electromagnetic radiation propagating inside it and provide the spontaneous-emission noise input and (ii) a feedback mechanism that can confine the electromagnetic field through the well-defined optical modes. As the name itself implies, the gain medium for a semiconductor laser consists of a semiconductor material...

This is a continuation from the previous tutorial - guided-wave photodetectors.   The advent of the laser dates back to 1958, the year in which the seminal paper of Schawlow and Townes appeared. It was followed by the successful operation of a solid-state ruby laser in May 1960 and of an He-Ne gas laser in December 1960. The feasibility of stimulated emission in semiconductor lasers was considered during this period, and in 1962 several groups reported the lasing action in semiconductors. The device consisted of a forward-biased GaAs p-n junction. Electron-hole recombination in the depletion region of the p-n junction...

This is a continuation from the previous tutorial - avalanche photodiodes.   The photodetectors discussed in the previous tutorials are vertically illuminated. In a vertically illuminated photodetector (VIPD), the optical signal propagates in a direction perpendicular to the junction interfaces of the device. This situation leads to a trade-off between the carrier transit time and the quantum efficiency, resulting in a limitation on the bandwidth-efficiency product of the device. Another limitation of a high-speed VIPD arises from the trade-off between its bandwidth and its saturation power. A large bandwidth for a VIPD requires a small absorption volume, which results in...