Optical phased array technology is a new type of beam deflection control technology, which has the advantages of flexibility, high speed and high precision.

At present, most researches are on the optical phased array of liquid crystal, optical waveguide, and microelectromechanicalsystem (MEMS). What we bring to you today is the related principles of the optical phased array of optical waveguide.

The optical waveguide phased array mainly uses the electro-optical effect or thermo-optical effect of the dielectric material to make the light beam deflect after passing through the material.

Optical Waveguide Phased Array Based on Electro-Optical Effect

The electro-optical effect of the crystal is to apply an external electric field to the crystal, so that the light beam passing through the crystal produces a phase delay related to the external electric field. Based on the primary electro-optical effect of the crystal, the phase delay caused by the electric field is proportional to the applied voltage, and the phase delay of the light beam passing through the optical waveguide core can be changed by controlling the voltage on the electrode layer of each optical waveguide core. For the phased array of optical waveguides with N-layer waveguide, the principle is shown in Figure 1: the transmission of light beams in each core layer can be independently controlled, and its periodic diffraction light field distribution characteristics can be explained by grating diffraction theory. By controlling the applied voltage on the core layer according to a certain rule to obtain the corresponding phase difference distribution, we can control the interference distribution of light intensity in the far field. The result of the interference is a high-intensity light beam in a certain direction, while the light waves emitted from the phase control units in other directions cancel each other out, so as to realize the deflection scanning of the light beam.

Fig. 1 Principles of grating based on the Electro-Optical effect of phased array of optical waveguide

Optical Waveguide Phased Array Based on Thermo-Optical Effect

Crystal’s thermo-optical effect refers to the phenomenon that the crystal’s molecular arrangement is changed by heating or cooling the crystal, which causes the optical properties of the crystal to change with the change of temperature. Due to the anisotropy of the crystal, the thermo-optical effect has various manifestations, which may be the change of the semi-axis length of the indicatrix, or the change of the optical axis angle, the conversion of the optical axis plane, the rotation of the indicatrix, and so on. Like the electro-optical effect, the thermo-optical effect makes similar influence on the deflection of the beam. By changing the heating power to change the effective refractive index of the waveguide, the angle deflection in the other direction can be achieved. Figure 2 is a schematic diagram of an optical waveguide phased array based on the thermo-optical effect. The phased array is non-uniformly arranged and integrated on a 300mm CMOS device to achieve high-performance scanning deflection.

Fig. 2 Principles of the phased array of optical waveguide based on the Thermo-Optical effect