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Ultra-slow Bright and Dark Optical Solitons in Cold Media

We present a systematic study on the formation of ultra-slow bright and dark optical solitons in highly resonant media. By investigating four life-time broadened atomic systems, i.e., three-state Λ-type and cascade-type schemes, and four-state N-type and cascade-type schemes, we show that the formation of such ultra-slow solitons in cold atomic systems is a fairly universal phenomenon.