Fiber Optic Tutorials

This is a continuation from the previous tutorial - emission characteristics of semiconductor lasers.   Introduction The next few tutorials discuss the electron-hole recombination mechanisms in a direct-band-gap semiconductor. Recombination mechanisms can in general be classified into two groups, radiative and nonradiative. Radiative recombination occurs when an electron in the conduction band recombines with a hole in the valence band and the excess energy is emitted in the form of a photon. Radiative recombination is thus the radiative transition of an electron in the conduction band to an empty state (hole) in the valence band. The optical processes associated with...

This is a continuation from the previous tutorial - waveguide modes in semiconductor lasers.   Previous tutorials have discussed such basic concepts as gain-loss considerations and characteristics of the longitudinal, transverse, and lateral modes supported by the semiconductor cavity. We now consider the emission characteristics used to characterize the performance of a semiconductor laser. They can be classified into several groups: (i) light-current, (ii) spatial-mode, (iii) spectral, and (iv) transient or dynamic characteristics. In the following discussion we consider each group separately.     Light-Current Characteristics The light emitted by one facet of a semiconductor laser is measured as a...

This is a continuation from the previous tutorial - gain and stimulated emission in semiconductor lasers.   The discussions in the gain and stimulated emission in semiconductor lasers tutorial is based on the plane-wave solutions of the wave equation (2-2-19) [refer to the Maxwell's equations for semiconductor lasers tutorial].   However, the light emitted by a laser has finite transverse dimensions, since it should be confined in the vicinity of the thin active region, which provides gain for stimulated emission. In semiconductor lasers the output is in the form of a narrow beam with an elliptic cross section. Depending on...

This is a continuation from the previous tutorial - threshold condition and longitudinal modes of semiconductor lasers.   In the semiclassical laser theory the medium response is governed by the polarization \(\pmb{\mathscr{P}}\) induced by the optical field \(\pmb{\mathscr{E}}\) and leads to the susceptibility \(\boldsymbol{\chi}\), as defined in Equation (2-2-17) [refer to the Maxwell's equations for semiconductor lasers tutorial]. In terms of the density-matrix operation \(\rho\), the induced polarization is given by \[\tag{2-4-1}\pmb{\mathscr{P}}=\text{Tr}(\rho\mathbf{p})=\sum_{c,v}(\rho_{cv}\mathbf{p}_{vc}+\rho_{vc}\mathbf{p}_{cv})\] where \(\mathbf{p}\) is the dipole-moment operator and the sum is over all the energy states per unit volume in the conduction and valence bands. The dynamic evolution of...

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...