Summary form only given. Asymmetric multiple-quantum-well (AMQW) InGaAsP lasers have been designed and fabricated which exhibit broad gain profiles and a significantly increased tuning range due to equal contributions to the gain from the various QWs in the active region. The device structure is a Fabry-Perot (FP) ridge waveguide with 3 /spl mu/m ridge width, and no facet coatings. The active region consists of two 50 /spl Aring/ and two 100 /spl Aring/ QWs separated by 30 /spl Aring/ barriers. A diffractive optical element (DOE) was used in an external cavity to tune the output wavelength of the AMQW lasers. The DOE was designed to replace the combination of a grating and lens in the Littrow configuration and is a reflective Fresnel phase element which provides a strong wavelength dependent focal length. This tunable laser system was used experimentally as a broadband absorption spectrometer. Sensitive detection of trace-gas spectra was performed.