*3.1. Experimental Setup*

To measure the frequency responses and the minimum measurable field strength of the device, frequency tests were performed utilizing a tunable laser at a wavelength of 1.3 μm. The input optical power was about 1.4 mW. A detailed diagram of the measurement setup is shown in Figure 7. The device was tested in a uniform electric-field environment by placing it in a Transverse Electro Magnetic (TEM) cell (Tescom TC-5010A), as shown in Figure 7, where the TEM cell is utilized to generate accurate electro-magnetic (EM) waves over a wide frequency range. EM waves generated in the cell are transmitted in the transverse mode and have similar characteristics to the plane-wave. The optical fibers penetrating through the slanted wall of the TEM cell and were connected to the laser and photodetector using an FC/PC fiber-optic connector. The applied electric-field strength was calculated using the output level and the size of the TEM cell. The −20~+20 dBm (10 μW~100 mW) rf input power to the TEM cell corresponds to the electric-field strength from 0.293 V/m to 23.2 V/m. Due to the high permittivity (ε ≈ 35) of LiNbO3, the substantial electric-field intensity experienced on the sensor substrate (23.2 V/m) corresponds to 0.66 V/m in the TEM cell. The rf power propagates through the TEM cell in the same direction as the light passing through the optical fibers and the sensor [9].

**Figure 7.** Block diagram of the measurement setup for electric-field sensing and the evaluation of the frequency response. TEM and PM are abbreviations for Transverse Electro Magnetic and polarization maintaining, respectively.
