We have experimentally demonstrated the optical diode performance in a two-layered device consisting of a cholesteric liquid crystal (CLC) film with a right-handed helical structure and a nematic liquid crystal (NLC) layer as a phase retarder of a half wave. Right-circularly polarized (RCP) light of the wavelength the same as the optical pitch of the helix is totally rellected by the CLC film when the light is incident from the CLC film side. On the other hand, if the incidence is made from the NLC side, RCP is transformed to left-circularly polarized (LCP) light and is then passed through the CLC film. Not only such an optical diode performance, i.e., unidirectional propagation (non-reciprocal transmission), but also its electro-tunability was also shown. The transmittance can be essentially tuned between 0% and 100%. (c) 2005 Published by Elsevier B.V.