**Hongsik Jung**

Department of Electronic and Electrical Fusion Engineering, Hongik University, Sejong 30016, Korea; hsjung@hongik.ac.kr; Tel.: +82-44-860-2532

Received: 29 July 2019; Accepted: 31 August 2019; Published: 2 September 2019

**Abstract:** We studied photonic electric-field sensors using a 1 × 2 YBB-MZI modulator composed of two complementary outputs and a 3 dB directional coupler based on the electro-optic effect and titanium diffused lithium–niobate optical waveguides. The measured DC switching voltage and extinction ratio at the wavelength 1.3 μm were ~16.6 V and ~14.7 dB, respectively. The minimum detectable fields were ~1.12 V/m and ~3.3 V/m, corresponding to the ~22 dB and ~18 dB dynamic ranges of ~10 MHz and 50 MHz, respectively, for an rf power of 20 dBm. The sensor shows an almost linear response to the applied electric-field strength within the range of 0.29 V/m to 29.8 V/m.

**Keywords:** photonic electric-field sensor; titanium diffused optical channel waveguide; lithium–niobate electro-optic effect; Y-fed balanced-bridge Mach-Zehnder interferometer (YBB-MZI)
