# Three-Dimensional Broadband Electric Field Sensor Based on Integrated Lithium Niobate on Insulator
## 3 Experimental Results  
Figure 5a presents the photograph of the fabricated 3D sensor and the measurement system. The packaged sensor has a volume of 9.5 cm\({}^{3}\) and is placed into a transverse electromagnetic (TEM) cell. In the TEM cell, a standard and known electric field is produced to achieve measurement and calibration. Three tunable laser sources (Santec TSL-510, Aichi, Japan) are used to guarantee that each sensor chip is biased at its quadrature transmission point. Each modulated light from the sensor chip is detected by using photodetectors (PD, Finisar, XPDV2120R, Sunnyvale, CA, USA). Each electrical signal from the PD is then amplified by using a low-noise amplifier (LNA, Qotana, DBLNA300011800A, Chengdu, China), and is measured by using an electrical spectrum analyzer (ESA, R&S FSU50, Darmstadt, Germany). The measured and simulated transmission optical spectrums of the sensor chip are presented in Figure 5b. The excitation source is an amplified spontaneous emission optical source (Glight OS321498, China), and the measurement device is an optical spectrum analyzer (Yokogawa AQ6370D, Japan). For the next measurements, the tunable laser wavelength is fixed to 1546 nm to guarantee that the sensor chip is biased at its quadrature transmission point.  
Figure 5: (**a**) Photograph of the packaged 3D sensor and the electric field measurement system; (**b**) measurement and simulation transmission optical spectrums of the sensor chip. ESA: electrical spectrum analyzer; PD: photodetector; HPA: high-power amplifier; MS: microwave source; LNA: low-noise amplifier; MPM: microwave power meter.  
The measured amplitude vector \(C_{m}\) is given by  
\[C_{m}=\begin{pmatrix}0.061\text{mV}\\ 0.147\text{mV}\\ 0.119\text{mV}\end{pmatrix} \tag{9}\]  
The measured vector \(B_{max}\) is solved by the vector \(C_{m}\) and the matrix \(A\) is given by  
\[B_{max}=\begin{pmatrix}7.72\text{V/m}\\ 10.82\text{V/m}\\ 7.07\text{V/m}\end{pmatrix} \tag{10}\]  
Therefore, compared with the vector \(B_{thm}\), the absolute error is calculated as  
\[Er_{ab}=\begin{pmatrix}0.37\\ 0.45\\ -0.27\end{pmatrix} \tag{11}\]  
The relative error is calculated as  
\[Er_{re}=\begin{pmatrix}5.1\%\\ 4.3\%\\ -3.7\%\end{pmatrix} \tag{12}\]  
These relative errors indicate that the measurement by the proposed EFS has a high accuracy for electric field recovery.  
Finally, the response of the three sensor chips in the 3D sensor is measured with the bandwidth of 10 MHz to 3 GHz. The measurement system is displayed in Figure 5a with the electric field polarization direction identical to the vector \(B_{1}\) in Equation (3). The measurement results are shown in Figure 6. It can be seen that every sensor chip in the 3D sensor has a relatively flat frequency response up to 3 GHz. Therefore, the response matrix A can be regarded as a constant in this frequency range. The tiny difference in the frequency response among the sensor chips is mainly attributed to the fabrication disorder including the coupled optical insertion loss and the deposited shape of the metal antennas, which can be further calibrated via detailed measurement.  
Figure 6: Frequency response and optical insertion loss of the three sensor chips in the 3D sensor.