Fiber Optic Tutorials

This is a continuation from the previous tutorial - coupled-mode theory. In most applications, we are interested in the coupling between two modes. This includes coupling between two modes in the same waveguide, such as that in a periodic waveguide, or coupling between two parallel waveguides, such as that in a directional coupler. For coupling between two modes, the coupled-mode equations can be written in a simple form that can be solved analytically. In this tutorial, we consider the general formulation and general solutions for this important case of two-mode coupling. The characteristics of specific couplers are discussed in later...

This is a continuation from the previous tutorial - coupled-wave theory. Coupled-mode theory deals with the coupling of spatial modes of different spatial distributions or different polarizations, or both. Although the theory described in this tutorial is formulated specifically in terms of the coupling of waveguide modes, it can be easily extended to other kind of spatial modes, such as Gaussian spatial modes. The mode fields in a lossless waveguide can be expressed in the forms of (1) and (2) [refer to the waveguide modes tutorial], which satisfy Maxwell's equations in (8) and (9) [refer to the optical waveguide field...

This is a continuation from the previous tutorial - Dispersion in Fibers. The principles of many photonics devices are based on the coupling between optical fields of different frequencies or different spatial modes. In general, the coupling mechanism can be described by a polarization ΔP on top of a background polarization representing the property of the medium in the absence of the coupling mechanism. In this tutorial, we present the general coupled-wave and coupled-mode formalisms, which provide the foundation for understanding the functions of many devices. The coupled-wave formalism deals with the coupling of optical waves of different frequencies, whereas coupled-mode...

This is a continuation from the previous tutorial - Attenuation in Fibers. Dispersion is the primary cause of limitation on the bandwidth of the transmission of optical signals through an optical fiber. There are waveguide and modal dispersions in an optical waveguide in addition to material dispersion.  Both material dispersion and waveguide dispersion are examples of chromatic dispersion because both are frequency dependent. Waveguide dispersion is caused by frequency dependence of the propagation constant β of a specific mode due to the waveguiding effect. The combined effect of material and waveguide dispersions for a particular mode alone is called intramode dispersion. Modal...

This is a continuation from the previous tutorial - graded-index fibers. Several factors contribute to attenuation of the power of an optical wave propagating in an optical fiber. As discussed in the propagation in an isotropic medium tutorial, when an optical wave propagates in a lossy medium with an attenuation coefficient \(\alpha\), its intensity decays exponentially with distance according to (103) [refer to the tutorial]. Since the power of an optical wave in a fiber is simply the integration of its intensity over the cross section of the fiber, the attenuation of optical power over a propagation distance l in a...