Erik J. Bochove

FM–AM conversion by material dispersion in an optical fiber

We show that material and guide dispersion may be used effectively in an optical fiber to convert an FM signal to an AM signal after it traverses a certain minimum fiber length. This length depends on material and modal dispersion of the guide. An upper limit to the fiber length is established and is shown to be related to laser linewidth. We also discuss laser-mode selection and conversion in multimode fibers.

Geometrical optics field of general optical systems

Using the stationary phase approximation of the Kirchoff diffraction integral, we derive a general expression for the field in the image space of a point source for an arbitrary optical system. The concept of an “optical path matrix” (OPM), which is the Hessian of the point eiconal, is introduced. Luminosity, caustic surfaces, and evanescent fields are defined in terms of the OPM. Detailed consideration of the single-interface problem yields solutions in terms of the Gaussian, mean, and normal curvatures of the interface. A complete solution of the simple lens is given as an example of a system with two refracting surfaces.

Conversion of a wideband frequency-modulated signal to amplitude modulation through dispersion in an optical fiber

Our calculation shows that, by means of group-velocity dispersion of an optical fiber, a cw frequency-modulated signal evolves into an intense and sharp pulse. The results compare favorably with an earlier analysis of a narrowband FM system. In particular, the minimum fiber length needed for maximum FM-AM conversion may be considerably reduced.

Geometrical characterization of liquid core fibers by measurement of thermally induced mode cutoffs and interference

Transmitted and scattered intensity in liquid core fibers have been measured as a function of temperature and v values of cutoff points obtained which are in good agreement with weakly guiding mode theory. We also report observation of oscillations in the transmitted intensity which we interpret to be caused by interference between modes. We show that measurement of the period of these oscillations can be used to make high-precision nondestructive measurements of core radius and core ellipticity along the fiber length.