We perform a structural and optical characterization of InAs1-xNx epilayers grown by molecular beam epitaxy on InAs substrates (x less than or similar to 2.2%). High-resolution x-ray diffraction (HRXRD) is used to obtain information about the crystal quality and the strain state of the samples and to determine the N content of the films. The composition of two of the samples investigated is also obtained with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measurements. The combined analysis of the HRXRD and ToF-SIMS data suggests that the lattice parameter of InAsN might significantly deviate from Vegard's law. Raman scattering and far-infrared reflectivity measurements have been carried out to investigate the incorporation of N into the InAsN alloy. N-related local vibrational modes are detected in the samples with higher N content. The origin of the observed features is discussed. We study the compositional dependence of the room-temperature band gap energy of the InAsN alloy. For this purpose, photoluminescence and optical absorption measurements are presented. The results are analyzed in terms of the band-anticrossing (BAC) model. We find that the room-temperature coupling parameter for InAsN within the BAC model is C-NM=2.0 +/- 0.1 eV. (C) 2010 American Institute of Physics.