# Multi-Beam Focusing and Deflecting Characteristics of Liquid Crystal Optical Phased Array
## 2 Principles and Methods  
### Structure and Work Principle of LCOPA Device  
We have developed a transmissive-type liquid crystal optical phased array device. The device consists of seven layers, whose cross-sectional diagram is shown in Figure 1. The seven-layer structure includes the upper glass layer, the upper electrode layer, the upper alignment layer, the liquid crystal layer, the lower alignment layer, the lower electrode layer, and the lower glass layer from top to bottom. The two glass substrates are on the outside of the device structure, and the two ITO electrode layers are adjacent to the two glass substrates, respectively. Further inside are two PI alignment layers, each of which is adjacent to an ITO electrode layer. The two PI alignment layers are rubbed to form an anchored orientation control of the liquid crystal molecules. There is a gap of 5 \(\upmu\)m between the two PI alignment layers, which is filled with nematic liquid crystal material of model BHR32100-100 by the capillary effect.  
The upper ITO electrode layer consists of 240 periodically distributed strip electrodes. The center distance between two adjacent electrodes is 30 \(\upmu\)m. The width of the electrodes is  
Figure 1: The sketch of multi-beam fan-out with focusing by liquid crystal optical phased array (LCOPA).  
27 \(\upmu\)m, and the spacing between the electrodes is 3 \(\upmu\)m. The lower ITO electrode layer acts as a common electrode. The effective aperture of the packaged device is 7.2 mm \(\times\) 10 mm. It is determined by the area overlapped by the upper and lower electrode layers, and its transverse dimension depends specifically on the multiplication of the center distance of the electrodes and the number of electrodes, which is 30 \(\upmu\)m \(\times\) 240 = 7.2 mm.  
When a series of driving voltages are imposed on the upper electrodes, a distribution of potential difference relative to the lower electrode layer forms. And the voltage distribution results in a distribution of the refractive index and phase shift, according to the phase-voltage characteristics of the liquid crystal material. Because the driving voltages imposed on upper electrodes are programmable, the phase distribution of the light beam that passes through the LCOPA device can also be modulated programmably. The 240 electrode voltages of the LCOPA device can be independently programmed. In order to meet the frequency requirement of liquid crystal molecules for stable rotation, the frequency of the alternating current (AC) voltage loaded on the liquid crystals is 1 kHz. And the voltage resolution is 256 bits, which is fine enough to drive the LCOPA device.  
The LCOPA device is fabricated using the LCD manufacturing process. Unlike traditional liquid crystal devices, which are controlled by host computer software, this LCOPA device is controlled by a fully- embedded system including a circuit board with a microcontroller and a touch screen. The touch screen communicates with the microcontroller through a serial port, and the microcontroller connects to the LCOPA device through the flexible printed circuit (FPC). The microcontroller's control program and the touch screen human-machine interface allow us to control the liquid crystal device by fully-embedded type, which does not need the host computer and its desktop software.  
We can apply different voltages to each ITO electrode through customized driving circuits. According to the electrically controlled birefringence property of liquid crystal, different near-field phase distributions can be programmably adjusted and created [14; 15; 16].  
In order to realize the composite function of far-field multi-beam fan-out with focusing, we can form a phase distribution of the device in the near-field by means of Gerchberg-Saxton (GS) algorithm superposing with a lens phase.