A Novel Isotropic Electric Field Sensing System Using Integrated Optical Waveguides

With the rapid development of information and communication technology, the communication system and equipment can be influenced in complicated electromagnetic environment, dramatically. So measurement of electric field plays an important role in electromagnetic compatibility. Traditional measurement methods of electric field have some disadvantages in applications. Thus, integrated optical waveguide electric field sensor using advance integrated optics technology can be adopted, which makes the whole measurement system super-small, steady and reliable, is characteristic of broad bandwidth, immunity to electromagnetics and tiny perturbation. They can be interconnected by optical fiber so that remote control and monitoring can be realized. At present, the electric field sensor is the one of research focus using integrated optics technology based on LiNbO₃ substrate. Therefore, integrated optical waveguide electric field sensor and sensing system are developed in this paper.I. Principle and model of electric field sensor and sensing systemThis paper gives theoretical basis, fundamental parameters and structures of integrated optical modulator, and emphatically introduces analysis method of optical waveguide and microwave electrode. Then, the performance of optical modulator is optimized on the premise of electric field sensor using integrated optical waveguide. Based on fundamental structures of electric field sensor using integrated optical waveguide, this paper points out common concept of electric field sensor using optical waveguide, gives its fundamental parameters and model. According to model of traditional analog optical fiber communication system, the concept of electric field sensing system with integrated optical waveguide is pointed out, its fundamental structures and principle are analyzed, its parameters are given, and its system model is founded.II. Electric field sensor and sensing system with segmented electrodesThe theoretical analysis and experiment of electric field sensor with segmented electrodes are completed. The simulated results show that the length of single segmented electrode, the total length of electrodes and the segmented number have an important impact on the detection sensitivity. The experimental results show that the half wavelength voltage of electric field sensor is lower than 10 V, and the intrinsic phase difference is lower than 10°. The relation between the frequency response of electric field sensor and the segmented number is analyzed according to the equivalent circuit model of electric field sensor. Using numerical method, the total electrode length, the electrode height and the ratio of the length of segmented electrode to the total electrode length are analyzed, which influence the frequency response and the detection sensitivity. By the analysis of the sensing system based on electric field sensor with segmented electrode, the fundamental equation on the detection sensitivity is obtained, and then loaded resistance, intrinsic phase difference, optical power and relative intensity noise are optimized. On the conditions of a specific structure of electric field sensor with segmented electrode, the sensitivity limit is 19.4 dBμV/m. The sensing system consist of the single electric field sensor with segmented electrode is measured and the data show the measured frequency response, sensitivity and direction pattern are consistent with that of the theoretical analysis.III. Electric field sensor and sensing system with dipole antennaAn electric field sensor with dipole antenna based on the segmented electrode structure is proposed, which is modeled by means of equivalent circuit method. The calculated results show that the voltage gain between segmented electrodes is maximized when the segmented number is seven. Then, another electric field sensor using dipole antenna with a variable length is also proposed in this paper. The more high detection sensitivity or the broader bandwidth can be obtained by adjusting the length of dipole antenna. The sensing system can be measured detailedly based on electric field sensor with the dipole antenna. The measured data show that the frequency response range of this sensing system is from 10 MHz to 6 GHz with the shortest dipole antenna length. The sensing system sensitivity is 60 mV/m when the frequency is 400 MHz, Signal-to-Noise is 6 dB, and the dipole antenna is the shortest. The sensing system sensitivity is 30 mV/m when the frequency is 400 MHz, Signal-to-Noise is 6 dB, and the dipole antenna is the longest. The linear dynamic range can be reach 90 dB when the frequency is 200 MHz.IV. Isotropic electric field sensor using integrated optical waveguide On the basis of traditional isotropic antenna, a new structure of isotropic electric field sensor with segmented electrodes using optical waveguide is proposed and is founded. The sensing system is measured using TEM cell and GTEM cell. Some results can be obtained. The system sensitivity is 20 mV/m when optical power of three laser are 1 mW, 1.4 mW and 1.7 mW, microwave frequency is equal to 250 MHz, RBW is 3 Hz, VBW is 100Hz, Span is 200 Hz, Signal-to-Noise is 6 dB. The frequency response can reach 2.5 GHz in±5 dB range and linear dynamic range can be 70 dB when RBW is 100 Hz, VBW is 1 kHz, Span is 5 kHz. The direction pattern is almost isotropic in 3 dB range.The sensing system using integrated optical waveguide is regard as a novel receiving antenna with new material and physical mechanism based on Pockels' effect of LiNbO₃ substrate, whose frequency response range is from several hundred kHz to several GHz, whose volume is decreased drastically. This sensor can be remote monitoring and arrayed because of its extremely low loss and immunity to electromagnetics. So this sensor can be applied in the domain of electric field measurement, far field and near field direction pattern measurement of antenna and new receiving antenna. Additionally, how to enhance detection sensitivity and bandwidth of the sensing system is next work.