Eo modulator Series: High speed, low voltage, small size lithium niobate thin film polarization control device
Light waves in free space (as well as electromagnetic waves of other frequencies) are shear waves, and the direction of vibration of its electric and magnetic fields has various possible orientations in the cross section perpendicular to the direction of propagation, which is the polarization property of light. Polarization has important application value in the fields of coherent optical communication, industrial detection, biomedicine, earth remote sensing, modern military, aviation and ocean.
In nature, in order to better navigate, many organisms have evolved visual systems that can distinguish the polarization of light. For example, bees have five eyes (three single eyes, two compound eyes), each of which contains 6,300 small eyes, which help bees to obtain a map of the polarization of light in all directions in the sky. The bee can use the polarization map to locate and accurately lead its own species to the flowers it finds. Human beings do not have physiological organs similar to bees to sense the polarization of light, and need to use artificial equipment to sense and manipulate the polarization of light. A typical example is the use of polarizing glasses to direct light from different images into the left and right eyes in perpendicular polarizations, which is the principle of 3D movies in the cinema.
The development of high performance optical polarization control devices is the key to develop polarized light application technology. Typical polarization control devices include polarization state generator, scrambler, polarization analyzer, polarization controller, etc. In recent years, optical polarization manipulation technology is accelerating progress and deeply integrating into a number of emerging areas of great significance.
Taking optical communication as an example, driven by the demand for massive data transmission in data centers, long-distance coherent optical communication technology is gradually spreading to short-range interconnect applications that are highly sensitive to cost and energy consumption, and the use of polarization manipulation technology can effectively reduce the cost and power consumption of short-range coherent optical communication systems. However, at present, polarization control is mainly realized by discrete optical components, which seriously restricts the improvement of performance and the reduction of cost. With the rapid development of optoelectronic integration technology, integration and chip are important trends in the future development of optical polarization control devices.
However, the optical waveguides prepared in traditional lithium niobate crystals have the disadvantages of small refractive index contrast and weak optical field binding ability. On the one hand, the device size is large, and it is difficult to meet the development needs of integration. On the other hand, the electrooptical interaction is weak, and the driving voltage of the device is high.
In recent years, photonic devices based on lithium niobate thin film materials have made historic progress, achieving higher speeds and lower driving voltages than traditional lithium niobate photonic devices, so they are favored by the industry. In recent research, the integrated optical polarization control chip is realized on the lithium niobate thin film photonic integration platform, including polarization generator, scrambler, polarization analyzer, polarization controller and other main functions. The main parameters of these chips, such as polarization generation speed, polarization extinction ratio, polarization perturbation speed, and measurement speed, have set new world records, and have shown excellent performance in high speed, low cost, no parasitic modulation loss, and low drive voltage. The research results for the first time realize a series of high-performance lithium niobate thin film optical polarization control devices, which are composed of two basic units: 1. Polarization rotation/splitter, 2. Mach-zindel interferometer (explanation >), as shown in Figure 1.
