InGaAsP/InP slab-type coupled waveguides consisting of two dissimilar waveguides were experimentally studied as potential dispersion compensators. A narrowing of the autocorrelation signals from the coupled waveguides was experimentally observed and the smallest narrowing factor was 0.233. The narrowing agrees well with the calculated narrowing obtained by a theoretical model based on group- velocity dispersions (GVDs) associated with supermodes. This agreement strongly indicates that the observed narrowing is attributed to pulse compression by dispersion compensation by using the GVDs of the supermodes. Furthermore, controllability of the GVDs of the coupled waveguide was preliminarily demonstrated by changing the spacing between the dissimilar waveguides: pulse-broadening and pulse- compression experiments showed that the GVDs of two coupled waveguides with different spacings are significantly different. In other words, the GVDs of a coupled waveguide increase with increasing spacing. this result is consistent with the theoretically predicted increase in the GVDs.