Polarization Effects in Short Length, Single Mode Fibers

The polarization characteristics of "single" mode optical fibers have been the subject of several previous publications. 1,2 An understanding of the polarization sensitivity of such fibers is important in assessing the applicability of polarization dependent optical circuitry. 3 An additional implication of polarization sensitivity is the introduction of delay distortion in "single" mode fibers. In this paper, we present a theoretical model based on the propagation of two orthogonal modes; it is shown that based on the measurement of 635 the ellipticity of the output radiation alone, we cannot distinguish between the following cases: (i) The existence of two orthogonal modes, uncoupled with different propagation constrants. (ii) The existence of two orthogonal modes, with identical propagation constants and uniformly coupled by some means of periodic perturbation (iii) The most general case--two orthogonal modes, uniformly coupled, but with nonidentical propagation constants. The organization of the paper is as follows. In Section II, we summarize the theory, leaving the details to the Appendices. Section III describes the detailed experimental procedure utilized to measure the radiation ellipse as well as details of each of the measurements. In Section IV the experimental data is compared with simple theoretical results developed in Section II. It should be noted that the assumption of synchronous uncoupled modes will not verify our data. An additional finding of importance is that the most general case indicates that for a fiber of any given length, excitation conditions exist at the input that result in linearly polarized output.