. . . "Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As2S3) rib waveguide with a group index change ranging from ??????44 to +130, which results in a maximum delay of ???23???ns at a relatively low gain of ???23???dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array an" . .