Optical antennas have high photoelectric transformation efficiency, and show great potential in various fields. However, it is very difficult to realize accurate fabrication even via the electron beam lithography because the size of an optical antenna is usually very small. Since it is difficult for the displacement current to flow in a low-epsilon material, the titanium oxide (TiOx) films with low-epsilon characteristics are fabricated for infrared detection via strictly controlling the oxygen content during the film deposition. The low-epsilon TiOx/Au bow-tie antenna with length of 3.7 μm is built, coupled with TiOx/TiO2/Au tunneling diode via in situ oxidation of TiOx that is covered by Au film. The rectifying antenna can convert an optical wave to direct current at about 900 nm. This work provides a new idea to surmount the small size limit of a noble metal optical antenna whose permittivity is heavily negative.