Abstract

An optical fiber coupler fabricated with a mechanical polishing method has the advantages of power splitting tunability and device rigidity.¹ A side view of the device structure is shown in Fig. 1(a) with coupling in the z-direction. To provide a smooth coupling adjustment through the lateral translation of the top substrate on the bottom substrate, a layer of index matching liquid is placed between the substrates in which the fiber cores are buried. The two fibers are curved with typical radius of curvature of the order of tens of centimeters. Figure 1(b) shows one cross section of the device transverse to the z-axis. Coupled-mode theory considering distributed coupling^2,3 has been capable of predicting the general coupling characteristics of such a polished type coupler.¹ As temperature changes, the index of refraction of the matching liquid varies accordingly, causing variations of the coupled power. In the prior modeling,¹ it was assumed that the entire fiber cladding was sensitive to temperature with the same Δn /ΔT coefficient as the matching liquid. Although that analysis explained the general trend of the observed coupler behavior, its numerical result did not fit the experimental data well.

© 1990 Optical Society of America