Currently, reversible logic has gained a lot of interest, and it is a reliable solution in optical computing, low-power CMOS, quantum computing, and nanotechnology. Being reversible logic, one-to-one mapping between input and output causes minimal loss of information. In fact, optical Feynman gate (FG), one among many reversible logic gates, is a potential candidate for the realization of low-power photonic computational circuits. We propose and design a reversible optical FG using four titanium indiffused lithium niobate (Ti  :  LiNbO₃) directional couplers. The elaborate design and analysis of uniform Δβ electrodes configuration of directional coupler has been presented preceded by in-depth design details and analysis of single-mode waveguides, fabrication tolerance, and S-type bend waveguides at 1.55-μm transmitting wavelength, using effective-index-based matrix method. Switching voltage of directional coupler, considering z-cut substrate, for a 134-nm-thick SiO₂ buffer layer, is obtained as 24 V. The chip dimension of optical Feynman gate is of 23.8 mm length and 0.63 mm width.