CN103576399B - A kind of liquid crystal optical phased array antenna implementation method - Google Patents

Abstract

The invention discloses a method for realizing a liquid crystal optical phased array antenna. The liquid crystal optical phased array antenna includes a common electrode and a grating electrode, and the common electrode is designed as a high-impedance liquid crystal light wedge electrode; Two electrodes are designed at both ends of the electrode, and voltages with different voltage values are loaded respectively to generate a slope phase distribution, which is equivalent to a liquid crystal prism with adjustable slope slope, which can continuously deflect the incident beam; at the same time, on the grating electrode Loading the quantization voltage can realize the step deflection control of the incident beam.

Description

A Realization Method of Liquid Crystal Optical Phased Array Antenna

technical field

The invention relates to a method for realizing a liquid crystal optical phased array antenna, and belongs to the technical fields of satellite laser communication and laser radar.

Background technique

In recent years, laser communication technology has developed rapidly. With the development of satellite laser communication technology, it is necessary to establish a satellite laser communication network to realize communication between one satellite and multiple satellites, that is, multi-user access technology. At present, the laser communication system researched at home and abroad is a point-to-point single-link data transmission system, which adopts mechanical capture and tracking mechanism and traditional capture and tracking strategy. Due to the long distance of the satellite laser communication link and the limited laser emission power, the divergence angle of the laser beam needs to be as close as possible to the diffraction limit. Limited by the divergence angle of the laser beam, the mechanical scanning mechanism can only realize point-to-point laser communication. If multi-point laser communication is to be realized, multiple optical antennas need to be mounted on one platform, which is difficult to meet the size, weight and power consumption requirements of the satellite platform. Require. This requires the use of new optical phased array antennas to realize multi-user access technology for satellite optical communications.

Due to the narrow beam divergence angle of the satellite laser communication system, in order to ensure the robustness of the inter-satellite and satellite-ground laser communication system and the performance of the laser communication system, the beam control accuracy of the new liquid crystal optical phased array antenna is required to be higher. As shown in Figure 1, the core device of the existing liquid crystal optical phased array antenna is the liquid crystal cell. By changing the refractive index of the liquid crystal cell, the wavefront of the incident beam is changed to realize the deflection control of the incident beam. At present, the liquid crystal optical phased array antenna researched abroad mainly adopts two types of designs: periodic grating and non-periodic grating. Due to its nature, it cannot effectively scan the scanning area continuously.

Contents of the invention

The technical problem to be solved by the present invention is: Aiming at the technical characteristics of discontinuous scanning of liquid crystal optical phased array beams and the development requirements of quasi-continuous deflection control of beams, a method for realizing liquid crystal optical phased array antennas is provided, which solves the problem of satellite optical communication on beams. Quasi-continuous, high-precision deflection control requirements ensure the performance of the satellite laser communication system.

The technical solution of the present invention is: a liquid crystal optical phased array antenna implementation method, the liquid crystal optical phased array antenna includes a common electrode and a grating electrode, and the common electrode is designed as a high-impedance liquid crystal wedge electrode; Two electrodes are designed at both ends of the liquid crystal wedge electrode, and voltages with different voltage values are loaded respectively to generate a slope phase distribution, which is equivalent to a liquid crystal prism with adjustable slope slope, which can continuously deflect the incident beam. The grating electrode The quantization voltage is applied to the upper, and the step deflection control of the incident beam can be realized.

The advantage of the present invention compared with prior art is:

The implementation method of the liquid crystal optical phased array antenna of the present invention mainly adopts the continuous beam deflection control technology of the liquid crystal optical wedge and the design technology of the liquid crystal optical phased array control electrode, and the low impedance common electrode of the existing liquid crystal optical phased array is designed as a high impedance electrodes to form liquid crystal wedge electrodes. Simultaneously load the control voltage on the liquid crystal optical phased array grating electrode and the optical wedge electrode, the continuous deflection control of the liquid crystal optical wedge electrode voltage and the step deflection control of the liquid crystal grating electrode voltage can realize the quasi-continuous deflection control of the incident beam. It solves the requirements of satellite optical communication for quasi-continuous and high-precision deflection control of the beam, and ensures the performance of the satellite laser communication system.

Description of drawings

Figure 1 Schematic diagram of liquid crystal optical phased array beam deflection

Fig. 2 is the structure schematic diagram of liquid crystal optical phased array antenna of the present invention;

Figure 3 shows the simulation verification results (the deflection angle is 1.2 degrees).

detailed description

As shown in FIG. 2 , the liquid crystal optical phased array antenna of the present invention includes glass substrates 21 and 27 , liquid crystal 24 , alignment layers 23 and 25 , common electrode 26 , and grating electrode 22 . The liquid crystal optical phased array antenna adopts pure phase modulation to achieve the effect similar to the transmission blazed grating, and the working performance of the liquid crystal blazed grating is largely determined by the control ability of the parallel electrodes. The total width of multiple electrodes in the periodic unit of the liquid crystal blazed grating is equivalent to the grating constant, and the grating constant is changed by changing the number of electrodes of the grating electrode 22 to realize the change of the diffraction angle, and then by adjusting the voltage distribution in the periodic unit, a certain The light of the order is shining. The diffraction angle of a blazed grating is determined by the grating equation dsinθ=mλ. Where d is the grating constant, d=N·d′. d' is the electrode period, N is the number of electrodes in a grating unit, and the drive circuit can generate different voltage values to load on the electrodes, so that the liquid crystal molecules can generate different deflection voltage values, that is, the maximum value of N; θ is the blaze angle , m is the blaze order, and λ is the wavelength of the incident light. The grating constant d can be changed by changing the number N of electrodes in a grating unit, and the blaze angle θ can be changed for the m-order blaze of the incident light of wavelength λ, so as to realize inertialess scanning of the beam.

In the present invention, the low-impedance common electrode 26 of the liquid crystal optical phased array antenna is designed as a high-impedance liquid crystal wedge electrode; the impedance of the high-impedance liquid crystal wedge electrode is greater than 1000Ω; two electrodes are designed at both ends of the high-impedance liquid crystal wedge electrode, The two electrodes are respectively loaded with voltages of different voltage values to generate a slope phase distribution, which is equivalent to a liquid crystal prism with adjustable slope slope, and performs continuous deflection control on the beam. As shown in FIG. 2 , a grating electrode voltage Vi is applied to the grating electrode 22 , and voltages Vcom1 and Vcom2 are respectively applied to the two electrodes of the high-impedance liquid crystal wedge electrode. By applying the grating electrode voltage Vi, the liquid crystal optical phased array step beam deflection control can be realized; by changing the relative value of (Vcom2-Vcom1) and changing the beam deflection angle, the continuous deflection control of the incident beam can be realized.

Suppose the beam deflection angle of the liquid crystal optical phased array antenna is θ _s , then θ _s is composed of the beam deflection angle θ _OPA of the liquid crystal grating and the beam deflection angle θ _wedge of the liquid crystal optical wedge, namely:

θ _s = θ _OPA + θ _wedge (1)

Assuming that no voltage is applied to the grating electrode, that is, the grating electrode does not work, the beam deflection angle of the liquid crystal optical phased array is controlled by the liquid crystal wedge electrode, and the beam deflection angle of the liquid crystal wedge satisfies

${\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; wedge</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; wedge</span>}}}{\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, k is the vacuum wave number, L is the length of the liquid crystal optical phased array antenna, and Δφ _wedge is the phase difference generated by the different voltage drops at both ends formed by the wedge electrode voltages Vcom1 and Vcom2.

Assuming that no voltage is applied to the high-impedance liquid crystal wedge electrode, that is, the high-impedance liquid crystal wedge electrode does not work, the beam deflection angle of the liquid crystal optical phased array is controlled by the liquid crystal grating electrode, and the liquid crystal grating beam deflection angle satisfies

$\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; OPA</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; OPA</span>}}}{\mathrm{<span\; class="notranslate">\; kd</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, d is the grating constant, and Δφ _OPA is the phase transition of adjacent equivalent electrodes.

Assuming that the liquid crystal optical wedge electrode and the liquid crystal grating electrode are applied voltage at the same time, the liquid crystal optical phased array first The phase delay φ _i at the root electrode position should be the sum of the phase delays of the liquid crystal wedge and the liquid crystal grating, expressed as

φ _i = φ _OPA (i) + φ _wedge (i)

Given that the beam deflection angle is θ _s , first determine θ _OPA and θ _wedge according to the deflection accuracy and deflection range of the liquid crystal wedge and liquid crystal grating, and calculate the corresponding θ _OPA and θ _wedge according to formula (2) and formula (3) Phase delay amounts Δφ _OPA and Δφ _wedge . For a liquid crystal wedge, Δφ _wedge =kLθ _wedge , and the phase increases Δφ _wedge from 2π. According to the U-Phi (voltage-phase) relationship curve, the wedge electrode voltages Vcom2 and Vcom1 are obtained, and then the wedge voltage Vcomi corresponding to the i-th grating electrode of the liquid crystal optical phased array is calculated

$\mathrm{<span\; class="notranslate">\; Vcomi</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; Vcom</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Vcom</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Vcom</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

According to the U-Phi relationship curve, determine the voltage drop U _i required to obtain the phase delay of φ _i at the i-th electrode. For different power-on modes of liquid crystal optical multi-beam phased array, different relational formulas of voltage drop U _i and Vi can be obtained. For the PWM (pulse width modulation) AC voltage powering method, the voltage drop U _i is the root mean square value of the difference between the potential V _i and Vcomi on the i-th electrode, namely:

_Ui = RMS(Vi-Vcomi) (5)

According to the formula (5), the grid electrode voltage Vi is calculated.

The method for realizing the liquid crystal optical phased array antenna of the present invention is simulated and verified. Assume that the number of grating electrodes is 1920, and the effective aperture of the liquid crystal optical phased array is 110 mm. The simulation analyzes the beam deflection capability. Assuming that the wedge deflection angle is 1.2 degrees, the beam deflection angle in the far field is shown in Figure 3, and the spot center is 20.942 mrad, the deviation is 1.95μrad, which realizes high-precision deflection control.

The present invention aims at deficiencies in deflection accuracy and scanning range of existing liquid crystal optical phased array antennas, realizes high-precision quasi-continuous deflection control of beams of liquid crystal optical phased arrays, and satisfies the requirements of satellite optical communication optical pair scanning continuity and beam deflection accuracy need.

The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (1)

1. A method for realizing a liquid crystal optical phased array antenna, said liquid crystal optical phased array antenna comprising a common electrode and a grating electrode, characterized in that said common electrode is designed as a high-impedance liquid crystal wedge electrode; a high-impedance liquid crystal light The impedance of the wedge electrode is greater than 1000Ω. Two electrodes are designed at both ends of the high-impedance liquid crystal wedge electrode, and voltages with different voltage values are loaded respectively to generate a slope phase distribution, which is equivalent to a liquid crystal prism with adjustable slope slope. The incident beam is subject to continuous deflection control; the quantized voltage is loaded on the grating electrode to realize the step deflection control of the incident beam.