Fiber Optic Tutorials

This is a continuation from the previous tutorial - triplet lenses.   In the early 1840s, it was recognized that lenses that exhibit symmetry afford various benefits to the lens designer. The first aberration acknowledged to be corrected by the symmetry principle was distortion. It can also be shown that coma and lateral color are necessarily corrected by a symmetrical lens construction. Although the principle of symmetry implies that the lens be operated at a magnification of \(-1\), the degree to which the aberrations are upset by utilizing the lens at other conjugates is remarkably small. This principle forms the...

This is a continuation from the previous tutorial - achromatic doublet lenses.   In 1893, a new type of triplet lens for photographic applications was invented by theEnglish designer H. Dennis Taylor. He realized that the power of two lenses in contact of equal, but opposite, power is zero, as is its Petzval sum. As the lenses are separated, the system power becomes positive since the negative lens contributes less power. The Petzval sum remains zero, since it does not depend upon the marginal ray height. In order to overcome the large aberrations of such a configuration, Taylor split the...

This is a continuation from the previous tutorial - two lens systems.   The singlet lens suffers from axial chromatic aberration, which is determined by the Abbe number \(V\) of the lens material and its \(\text{FN}\). A widely used lens form that corrects this aberration is the achromatic doublet as illustrated in Fig. 19.   Figure 19  Typical achromatic doublet lens.   An achromatic lens has equal focal lengths in \(c\) and \(f\) light. This lens comprises two lens elements where one element with a high \(V\)-number (crown glass) has the same power sign as the doublet and the other element...

This is a continuation from the previous tutorial - laser amplification.   Figure 16 illustrates the general imaging problem where an image is formed of an object by two lenses at a specified magnification and object-to-image distance.   Figure 16  General imaging problem where the image is formed by  two separated lenses.   Most imaging problems can be solved by using two equivalent lens elements. An equivalent lens can comprise one lens or multiple lenses and may be represented by the principal planes and power of a single thick lens. All distances are measured from the principal points of each equivalent lens...

This is a continuation from the previous tutorial - fiber attenuation loss.   Using the principles of stimulated emission outlined in the preceding section as a foundation, we next outline briefly how a laser material with an inverted atomic population produces useful laser amplification.   Signal Absorption and Attenuation Suppose first that we send a wave of tunable optical radiation through a collection of absorbing atoms, as illustrated in Figure 1.25, with this radiation tuned to a frequency \(\omega\) near the transition frequency \(\omega_{21}\) between two energy levels \(E_1\) and \(E_2\) of the atoms. Let the populations of these energy...