Study of microwave optical multibeam generation based on spatial light modulator

Backgrounds

With the development of mobile communication business, the 6th generation mobile communication technology (6G) has become a research hotspot. 6G communication network has high transmission rate, large channel capacity, small transmission delay, high spectrum efficiency and strong reliability, etc. More importantly, 6G realizes large-scale intelligent connection between people and things, i.e., “Everything is deeply connected! “. In order to realize the many excellent characteristics of 6G communication network, how to realize multi-beam generation with ultra-large-scale antenna array has become the current research hotspot.

With the rapid development of digital technology, the program of generating multiple beams by digital method is more and more researchers' attention and in-depth study. Compared with the traditional analog method of generating multiple beams, the advantages of the digital method of generating multiple beams lie in the flexibility of beam configuration, less susceptible to interference, and simple hardware system.

Principle of beam generation

Regarding array signal, it refers to a collection of several signals arranged in a certain pattern. Array signal processing refers to the processing of signals received or transmitted by an array of multiple sensors at different locations in space.

Beam generation is a very important direction in array signal processing, which refers to the enhancement of the signal in the target direction by adjusting the parameters of the array unit, while attenuating or suppressing the signals in other interfering directions.

The basic idea of transmit beam generation is that by adjusting the amplitude and phase of the signals emitted by each array element, so that they are weighted accordingly, and after being emitted by the antenna array element, the beam can be obtained in the desired direction.

Based on the digital phase matching method to realize the multi-beam transmission is mainly through the array at the same time to add a number of sets of phase weight vectors, its phase weighting, each set of weight vectors corresponds to the generation of a number of different directions of the beam.

Experimental realization

This experiment is based on the common aperture digital phasing method, using the spatial light modulator as the phase control unit of the optical carrier, the spatial light is phase modulated, the modulated optical carrier is received and demodulated by the photodetector into an electrical signal, and the phase is read out by the vector network analyzer, and then brought into the matlab software, and then the generated beams are obtained in the end.

Flowchart of microwave optical beam generation experiment based on spatial light modulator

In the experiment, the light from the laser is divided into two paths through a 50:50 optical coupler. In 1 way, the vector network analyzer works in S21 mode, from its P1 port can output a certain frequency RF signal into the intensity modulator, after electro-optical modulation is loaded onto the optical carrier, the modulated light at the end of the optical fiber through the collimator's self-focusing lens into a parallel spatial light is shot into the beam combiner.

In 2-channel, the local oscillating light is collimated and shot to the reflective spatial light modulator, and after phase modulation, it is shot into the beam combiner, which is bundled with the photosynthesis of the 1-channel, and then detected by the photodetector and demodulated into an electric signal. The other end of the photodetector is connected to the P2 end of the vector network analyzer, and then the phase-frequency curves of the corresponding signals can be observed on the vector network analyzer, and the final generated beam pattern can be obtained by recording the phases corresponding to the same frequency of multiple phase-frequency curves at different spatial positions, and then bringing them into the matlab software.

The Role of Spatial Light Modulators for Major Optoelectronic Devices

In this experiment, the liquid crystal spatial light modulator plays a very important role, it is a programmable phase modulation device, has the advantages of small size, light weight, easy to operate, etc. In the experiment, through the setup and adjustment of the liquid crystal spatial light modulator to control the phase of the optical carrier. The liquid crystal spatial light modulator selected for this experiment is our FSLM-2K55-P04, and its main parameters are as follows:

Summary and outlook

In this experiment, a beam generation and its control scheme based on electro-optical modulator and liquid crystal spatial light modulator is proposed. The innovation of this scheme is that the phase of light is regulated in space, and the phase change of light is realized by controlling the phase modulation unit of liquid crystal spatial light modulator by means of loading the gray scale map, and this scheme has the advantage of good tunability as compared with the traditional devices such as phase shifter.

In the future, it has good application prospects in performing high-frequency microwave signal modulation and two-dimensional beam deflection.