1. Introduction Controlling the propagation velocity of optical pulses in dispersive media is important both at the level of basic and applied science [1, 2]. Fundamental studies of entanglement [3], information velocity [4], and optical precursors [5] rely on the fact that one can decrease (increase) the group velocity of light v$_{g}$ = c/n$_{g}$ in regions of normal (anomalous) dispersion to produce slow (fast) light (here c is the speed of light in vacuum and n$_{g}$ is the group index). In recent years, a growing number of technological applications of slow-light techniques have been investigated, including all-optical buffering and routing, optical memories, and data synchronization [6,7]. While many slow light approaches make use of optical resonances [8–10] to provide large values of the group delay t$_{D}$ with small absorption, the spectral region over which the slow light occurs is generally narrow. Because the spectral width of the slow light region limits the minimum temporal duration T 0 of a pulse that can be delayed without significant distortion, it sets an upper bound on the maximum achievable data rate and fractional pulse delay ( f$_{D}$ = t$_{D}$/T 0 ) [11]. In addition, some applications require tunable delay lines that can retard the arrival of ultrashort optical pulses ( T 0 ∼ 100 fs) by several hundred fs. Thus, it is important to investigate techniques for realizing ultra-broadband slow light materials where the achievable group delay can greatly exceed the injected pulse width without causing significant pulse distortion. Previous methods for realizing broadband, distortion-free slow-light media include coher- ent control of the optical properties of a material and the design of novel materials. As an example of an approach involving coherent control, Sharping et al. measured f$_{D}$ = 0 . 85 for a 430-fs-long pulse via stimulated Raman scattering [12]. More recently, conversion/dispersion techniques in dispersive optical fibers have demonstrated f$_{D}$ ∼ 20 , 000 for 2.6-ps-long pulses [13] and f$_{D}$ = 10 for 370-fs-long pulses [14]. Using a materials-based approach, Gan et al. [15] employed solid-state dispersion engineering via plasmonic structures to demonstrate fixed slow light delays over several hundred nanometers in the visible range. In this work, we make use of the region of uniform group index between a pair of absorb- 2