Constant envelope modulations are of vital importance in radio communications due to limitations of electronic components. In practice it is necessary to analyze not only the symbols of a modulation, but also the transitions between them. For example, in a QPSK modulation, all symbols have constant envelope, but there are transitions between them where the […]
The envelope of a bandpass signal represents the signal, typically baseband, that served as the modulator of the carrier frequency. Although the power of the resulting signal may vary with time, its value can be generalized as a function of the envelope amplitude. The following text shows the evolution from the calculation of the power […]
Complex numbers extend the real numbers by adding an additional term called imaginary. This two-dimensionality makes it possible to simplify the understanding and calculations of many mathematical and physical questions. This article explains the basic fundamentals of complex numbers and their main applications for the particular case of electronics [1][2] and communications [3][4]. The table […]
Optical modulators use electrical signals to modify the physical characteristics of materials in such a way that the propagation conditions of light change. This article explains the most common optical modulators that are widely employed in optical communications. Firstly, Electro-Absorption Modulators are briefly describred. Secondly, electro-optic Mach-Zehnder Modulators (MZM) are introduced. Finally, the most relevant […]
Academic books in science and engineering tend to be expensive, both for students and professionals. When it comes to buying a copy of some of the most famous books in the field, prices are much higher than those of a conventional book. This phenomenon is especially relevant in emerging countries, where book prices in local […]
The term laser is used as a noun, but it was originally an acronym for “light amplification by stimulated emission of radiation”. A laser is a fundamental part in any optical transmitter, as it is the generator of the optical carrier. In optical communications, the spectral location of a carrier is often stated in wavelengths […]
This section provides a basic classification of optical networks. The overall network is a complicated system that ensures robust optical communications between exchange information nodes. This high-level system can be divided into typical subnetworks that meet specific geographical and functional requirements: the core network, Metropolitan Area Networks (MAN), access networks and Local Area Networks (LAN). […]
This article shows the relevance of optical communications emphasizing how the introduction of optical devices marked an inflexion point in the performance of guided data links. The development of electro-optical technology allowed to increase simultaneously the distance and capactiy of communications systems. In practice, optical communications have enabled the ever-increasing worldwide data traffic. The table […]
Communication is an essential element in our social, cultural and technical evolution. Especially over recent decades, human habits and technology have influenced each other, but always relying on a growing exchange of information. Optical communications have enabled this development and have become the only mature technology that can satisfy the demand of capacity in wired […]
The complex envelope is a baseband analytic signal. It is obtained by suppressing the negative (or positive) frequencies of a real bandpass signal, and transferring the remaining spectral content to baseband. Due to the complex notation and the spectral efficiency of the resulting signal, the complex envelope is very useful in both linear system simulation […]