Abstract In this work, we have developed ways to model and use extremely short external cavity (ESEC) semiconductor lasers. We have used modeling and experiments to analyze the wavelength tuning and other related optical characteristics of various ESEC laser devices. A brief overview is given on the physics related to semiconductor lasers. A simple phenomenological laser model is presented for the efficient calculation of the multi-mode output spectrum of a Fabry-Perot semiconductor laser. The effective reflectance model is used to simulate the influence of the ESEC on the laser operation. Several ways to calculate the effective reflectance from various kinds of ESEC structures are presented, including the Gaussian beam method, Fourier optics methods, and finite-difference time-domain (FDTD) method. We give an overview of the ESEC laser devices. The wavelength tuning and optical power characteristics of the planar-mirror (PM) ESEC laser are analyzed and compared to the measurements. The wavelength tuning of a laser using a micromachined tunable Fabry-Perot etalon in the ESEC configuration is analyzed. A method of wavelength tuning profilometry in the ESEC laser configuration is introduced, and the proof-of-principle experiments are presented and analyzed. The direct semiconductor laser readout systems for optical data storage are analyzed via modeling. Various types of playback signals are constructed, and a wavelength tuning enhanced readout method is introduced. The performance of a conventional Fabry-Perot laser and a very small aperture laser (VSAL) in the direct semiconductor laser readout system are modeled and compared using the novel FDTD laser-end model.