We propose wireless millimeter-wave (MMW) to lightwave (LW) signal converters using a simple planar antenna on LiNbO3 optical crystal. The LiNbO3 crystal is bonded with low-κ dielectric material as the substrate. The simple planar antenna is formed with a rectangular patch antenna with a gap and inserted between the bonded structure. An optical waveguide are fabricated on the LiNbO3 crystal and located between the gap. The LiNbO3 crystal has relatively lower dielectric constant compared with a LiTaO3 crystal. Larger antenna size can be obtained using the LiNbO3 crystal. Additionally, an electro-optic coefficient of the LiNbO3 crystal is larger than the LiTaO3 crystal. Therefore, conversion efficiency enhancement can be achieved using the propose device.