Theoretical Analysis and Experimental Investigation of Silicon-Organic Hybrid Integrated Electro-Optic Modulator with Traveling-Wave Electrodes

Objective With the rapid development of communication technology, the coverage area, transmission bandwidth, energy efficiency ratio, and device size of communication networks have higher requirements. Optical communication network using lightwave as the information carrier has become a very competitive technology development direction due to its characteristics of ultra-wide bandwidth, low delay, and low loss. Electro-optic modulator (EOM) is one of the most important optoelectronic devices in optical communication systems and microwave photonic systems, and its characteristics directly affect the performance of optoelectronic information systems. The function of the EOM is to convert the signal from the electrical domain to the optical domain and then to process and transmit the signal. After a period of rapid development of optoelectronic technology, the entire system has gradually developed from discrete optical devices to board-level interconnection and on-chip integration, especially the array and multifunctional integration needs of optoelectronic information systems make highly integrated optoelectronic chips an inevitable trend of technological development. In order to meet the application requirements of a larger range, higher speed, and higher energy efficiency of photoelectric information processing, the development of integrated electro-optic modulators with larger bandwidth, lower half-wave voltage, and smaller volume is one of the important directions of photoelectric integration technology. Methods The silicon-organic hybrid (SOH) integrated EOM with traveling-wave electrode structure is investigated. The mathematical model of an EOM with the traveling-wave electrode is established, and the effects of the group refractive index of lightwave, effective refractive index of microwave, and characteristic impedance of the modulator on the electro-optic modulation response bandwidth are analyzed. Under the guidance of the theoretical model, the traveling-wave electrode structure of the SOH-integrated EOM is optimized, and the fabrication of the silicon optical waveguide device and the on-chip polarization of the electro-optical polymer are completed by the domestic process platform. Results and Discussions According to the theoretical model, the corresponding electro-optical bandwidths under different impedance matching and velocity matching conditions are simulated, and the matching state under the maximum bandwidth condition is that the speed between the lightwave and the microwave is perfectly matched, and the characteristic impedance of the modulator is slightly greater than the system impedance (50 Omega), as shown in Fig. 6 and Fig. 7. The electrode structure of the modulator is simulated and optimized, and the electrical bandwidth is greater than 80 GHz. The effective refractive index of a microwave is about 3. 3, and the characteristic impedance is about 37 Omega. The fabrication and on-chip polarization of the modulator chip are completed (Figs. 10-12), and the electrical tests of the modulator are carried out. The measured electrical bandwidth of the modulator is greater than 60 GHz, and the characteristic impedance of the electrode is calculated to be about 45 Omega, with an effective refractive index of 4. 5 (Fig. 13 and Fig. 14). The final modulation effect of the modulator is tested, and the electro-optic modulation bandwidth greater than 50 GHz is obtained (Fig. 16). Conclusions In this paper, the traveling-wave electrode structure model of SOH-integrated EOM is established, and its working principle is theoretically deduced in detail. The effects of electrode characteristic impedance and microwave effective refractive index on the response bandwidth of electro-optic modulation are analyzed. On this basis, an SOH integrated EOM is designed and fabricated, and the high-performance electro-optic modulation is obtained by exploring the on-chip polarization process of electro-optical polymer material. The experimental system is set up to test and analyze the characteristics of the modulator chip, and the 3 dB electro-optic modulation response bandwidth of 50 GHz is measured. The experimental results are in good agreement with the theoretical calculation results, which verifies the validity of the structure model of the traveling- wave electrode. The theoretical modeling analysis and experimental research work in this paper provide a good foundation for further improving the performance of SOH-integrated EOMs.