By controlling tlic quantum well wtdths and the tunnelling barrier thickness of hcterastructures it i s posrible to create artificial potentials where level separations, dipole matrix dements, lifetimes and seanenng times are dependent on the potential design. This allows us to conceive new materials (mierral by dedgn) where electronic and optical properties cnn h tailored not only far demonstrate new physical effects but also to oplimise device performance. The Quantum Cascade (QC) laser is an excellent example of how quantum engineering can be used to design and develop new laser material in the mid-ir. After the first demonstration of Quantum cascade lasers a strong effort has been done to improve the performance of thi. mid-ir source which is now ready to be exploited into sensing systems for molecular detection in Ihe atmospheric windows (3 5 pm and 8 13 tun). Room temperature operation'.', high peak pow& and DFB lasers4 have been demonstrated, making this laser the first room tempera& mid-ir coherent semiconductor source operating single mode in the 5 .9 pm mnge. The material system m which the QC h a been demonstrated and developed is InGaAs/InAIAs grown lattice matched on InP. There are few advantages related to this IhetemmctuIe namely the higher conduction band discontinuit) (deeper quantum well) and the low refractive index substrate which can be uacd as lower cladding. Nevenheless a strong effort i s underway also in the GaAdAIGaA5 systcm. The la t te~ is the most developed material system (at present represents about 80% of the voiume d the Ill-V market) and can offer more degree of freedom in the quanmiii dasign by vvrying the aluminium concenimtion or hy adding thin GalnA~ strained layers. Recent results on both material systems will be presented with a emphasis on thc new quantum S ~ I U C ~ U I ~ S on GaAslAIGaAs. In conciurion new concepa and experimental results for semiconductor laser waveguide based on surface plasmon at metal-ddearie interface will be discussed.