High performance electro-optic modulator: thin film lithium niobate modulator
An electro-optical modulator (EOM modulator) is a modulator made using the electro-optical effect of certain electro-optical crystals, which can convert high-speed electronic signals in communication devices into optical signals. When the electro-optic crystal is subjected to an applied electric field, the refractive index of the electro-optic crystal will change, and the optical wave characteristics of the crystal will also change accordingly, so as to realize the modulation of the amplitude, phase and polarization state of the optical signal, and convert the high-speed electronic signal in the communication device into an optical signal through modulation.
At present, there are three main types of electro-optic modulators on the market: silicon-based modulators, indium phosphide modulators and thin film lithium niobate modulator. Among them, silicon does not have a direct electro-optical coefficient, the performance is more general, only suitable for the production of short-distance data transmission transceiver module modulator, indium phosphide although suitable for medium-long distance optical communication network transceiver module, but the integration process requirements are extremely high, the cost is relatively high, the application is subject to certain limitations. In contrast, lithium niobate crystal is not only rich in photoelectric effect, set photorefractive effect, nonlinear effect, electro-optical effect, acoustic optical effect, piezoelectric effect and thermoelectric effect are equal to one, and thanks to its lattice structure and rich defect structure, many properties of lithium niobate can be greatly regulated by crystal composition, element doping, valence state control, etc. Achieve superior photoelectric performance, such as the electro-optical coefficient of up to 30.9pm/V, significantly higher than indium phosphide, and has a small chirp effect (chirp effect: refers to the phenomenon that the frequency within the pulse changes with time during the laser pulse transmission process. A larger chirp effect results in a lower signal-to-noise ratio and a nonlinear effect), a good extinction ratio (the average power ratio of the signal’s “on” state to its “off” state), and superior device stability. In addition, the working mechanism of the thin film lithium niobate modulator is different from that of the silicon-based modulator and indium phosphide modulator using nonlinear modulation methods, which uses linear electro-optical effect to load the electrically modulated signal onto the optical carrier, and the modulation rate is mainly determined by the performance of the microwave electrode, so higher modulation speed and linearity as well as lower power consumption can be achieved. Based on the above, lithium niobate has become an ideal choice for the preparation of high-performance electro-optic modulators, which has a wide range of applications in 100G/400G coherent optical communication networks and ultra-high-speed data centers, and can achieve long transmission distances of more than 100 kilometers.
Lithium niobate as a subversive material of the “photon revolution”, although compared with silicon and indium phosphide has many advantages, but it often appears in the form of a bulk material in the device, the light is limited to the plane waveguide formed by ion diffusion or proton exchange, the refractive index difference is usually relatively small (about 0.02), the device size is relatively large. It is difficult to meet the needs of miniaturization and integration of optical devices, and its production line is still different from the actual microelectronics process line, and there is a problem of high cost, so thin film formation is an important development direction for lithium niobate used in electro-optical modulators.
Post time: Dec-24-2024