Fabrication And Analysis Of GaAs Based Integrated Optical Chip For Fiber Optical Gyroscope

The integrated optical chip is one of the core components of the integrated interferometer fiber optical gyroscope (I-FOG). High resolution FOG is mainly used as navigation of advanced weapon, so the FOG has Strategic Significance. Then it is impossible to buy it from foreign countries. Therefore, it is very important to design and fabricate high resolution FOG independently. Integrated optical chips based on GaAs shows good temperature stability and optical transmission characteristics. With GaAs epitaxial materials, it is also expected to monolithically integrate the active components, such as light sources and photon detectors, with passive ones. So GaAs based integrated optical chip will be widely applied in fiber optical gyroscope.In this paper, a deeply etched waveguide is used to increase the confinement of the guided light, improve the modulation efficiency of the phase modulators, and decrease the size of the whole chip. The integrated optical chip is composed of a 1×2 multimode interference (MMI) power splitter followed by two S-bend waveguides, two phase modulators, and two polarizers. Since the phase modulators are realized through a vertical electric field, the upper metal electrodes are designed on the GaAs waveguides. As we know, the surface plasmonic resonance (SPR) generated by the metal electrodes can be used to introduce much large propagation loss to the TM mode compared to the TE mode. Therefore, the phase modulator is also be used as the polarizer by carefully design the upper electrode.Based on analysis and optimization, the integrated optical chip is designed in this paper. The length of the modulation electrodes is 7.5 mm. Simulation shows that the loss of the splitter is less than 0.1 dB, the absorption of the TE mode arose from the metal is less than 1 dB, the extinction ratio (ER) between the TE and TM modes is more than 100 dB and V_πis 10 V.The chip was fabricated in our lab. The size of the chip is within 15mmx0.5mm. The experimental results shows that the threshold volt of the Al-GaAs Schottky diode is about 0.5 V, the breakthrough volt of the Al-GaAs Schottky diode is 60 ~ 70 V, the V_πis 24 V, the ER of the phase modulator is 28.3 dB, the ER between the TE and TM modes is 29.9 dB and the insertion loss of the TE mode is -44.7 dB. The insertion loss of TE mode is arisen from coupling loss between the fiber and the chip (about 10dB), the loss of the power splitter and the upper electrode (about 1dB), and the layer of Al on the side of the waveguide (about 33.7dB). Through the work in this paper, the design and the fabrication of the GaAs based integrated optical chip made certain achievements, which will be the basis for the development of the practical chip.