With this paper we present a new developed phase-only LCOS (Liquid Crystal On Silicon) spatial light modulator (SLM) based on an electrically controlled birefringence (ECB) liquid crystal mode for dynamic diffractive optics applications, optical tweezing, wave front control, digital holography and beam/pulse shaping. This device is the first phase-only SLM showing HDTV resolution and a small pixel pitch of only 8μm (87% fill factor) on a digital silicon back plane. Here the LC molecules are aligned parallel to the electrodes and an applied electric field forces them to tilt in the direction of the field. In this way, the refractive index seen by the light is changed for one polarization direction. This leads to a pure phase modulation without any polarization change (<1%) if the incident light is polarized linearly parallel to the director axis of the LC molecules. We have investigated two versions of this new SLM. One version is optimized for the visible wavelength region (420-800nm) and the other one is designed for 2π phase retardation up to 1064nm. We will discuss the optical modulation and show measurements on reflectivity, diffraction efficiency as well as measurements of the surface quality (flatness). With user software one is able to adapt the electro-optical response of the system to different wavelengths and applications. Furthermore, we discuss the optical effect of different sequence encoding for the phase modulation properties.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.