This paper presents the optical and mechanical characterization of fully embedded optical links. The flexible optical links consist of ultra thin opto-electronic transceivers, multimode polymer optical waveguides, optical coupling structures and galvanic interconnections, all embedded inside a thin (145 μm) flexible foil. The embedded GaAs transceivers (VCSELs and Photodiodes) are first mechanically thinned down to 20 μm thickness, enabling the unobtrusive embedding inside the foil and allowing the chips to be bent with the foil due to their very low thickness. The embedded links are tested for their flexible behavior by means of several measurements: the optical bending losses of the flexible waveguides, the minimum bending radius before link failure and the bending endurance. The emitted optical modes of the ultra thin VCSEL's were characterized and compared before and after thinning and before and after embedding of the VCSEL's to determine the effect of these actions on the behavior of the VCSEL power and modes. The optical power budget of the complete optical VCSEL-to-Photodiode VCSEL is investigated by simulations and measurements of the different optical loss contributors. Also crosstalk behavior between two neighboring waveguides and links is measured. A proof of principle demonstrator of an embedded optical link on a rigid substrate using standard 50 Ohm test equipment and a basic galvanic lay-out shows a clear open eye diagram at a speed of 1.2 Gb/s. Reliability of the flexible optical link foil was demonstrated with temperature (-40 to 125 degrees Celsius) and humidity (85 rh/85 °C for 1000 hours) fastened aging cycling with good results.