The effect of random phase errors on coherent beam combining based on liquid crystal phased array is studied. Utilizing the Fraunhofer propagation principle and probability theory, the analytical expressions of the far-field intensity distribution functions of the output beam are derived. According to these expressions, it can be concluded that as the phase errors increase, the peak intensity of the combined beam in the far-field decreases, the main lobe width widens and the error of deflection angle becomes greater. Considering the influence of random phase errors on the three parameters, a threshold of phase control precision can be designated. When the phase errors are less than the threshold, the performance degradation of the CBC system caused by the phase errors can be accepted. The computer simulations illustrate that the conclusions obtained from analytical expressions are reasonable. In the simulation parameters, the threshold of the phase control precision is λ / 20. The results in this paper can be employed to research methods to reduce the adverse effects of random phase errors and can also be used to determine the phase control precision when using phase-locking algorithms to lock the phase of the beams to be combined in the CBC system.
We present an effective method to realize continuously one-dimensional steering of coherently combined beam in the
field-of-view of PALCOPA. To achieve this purpose, besides the linear phase profiles to steer the incident lasers, extra
phase modulations should be applied to them. These phase offsets depend on both the assigned deflection angle of
combined beam and the parameters of beam combining system. Using the Fraunhofer propagation principle, we derive
the analytical expressions of the far-field intensity distribution of the combined beam. The analytical functions
demonstrate the validity of the proposed method. Finally, we evaluate the proposed technique through computer
simulations and experiments, by considering three main indicators of the combined beam, i.e. deflection accuracy,
mainlobe width and combining gain.
On the basis of Coherent Beam Combination(CBC) based on Array of Liquid Crystal Optical Phased Arrays(LCOPA array), two major contributions are made in this article. Firstly, grating lobes and side lobes of combined beam are analyzed. Furthermore, according to interference theory the methods to suppress grating lobes and side lobes are put forward. Secondly, a new beam quality factor Q(θ0) is proposed to evaluate the beam quality of combined beam and several influence factors are discussed. These analysis results help to obtain combined beam with better beam quality.
Three novel multiple-beam forming methods were proposed in this paper for liquid crystal optical phased array. These three methods called sub-aperture method, array division multiplexing method, iterative Fourier transform pattern approximation method could form multiple beams simultaneously for multi-target tracking in lidar and uninterrupted communication among multiple satellites. Principles of these methods were discussed in this paper. Simulations and experiment results were given to verify the feasibility of these methods.
The grating lobes of the liquid crystal optical-phased array (LCOPA) based on blazed grating theory is studied. Using the Fraunhofer propagation principle, the analytical expressions of the far-field intensity distribution are derived. Subsequently, we can obtain both the locations and the intensities of the grating lobes. The derived analytical functions that provide an insight into single-slit diffraction and multislit interference effect on the grating lobes are discussed. Utilizing the conventional microwave-phased array technique, the intensities of the grating lobes and the main lobe are almost the same. Different from this, the derived analytical functions demonstrate that the intensities of the grating lobes are less than that of the main lobe. The computer simulations and experiments show that the proposed method can correctly estimate the locations and the intensities of the grating lobes for a LCOPA simultaneously.
The limited quantization digit of voltage and the effect of fringing field between adjacent electrodes (phased-array
controlling units) limit the deflection efficiency when a Liquid-Crystal Phased Array (LCPA) is used for beam steering.
In this paper, an optimization algorithm named pattern search is proposed to improve the diffraction efficiency. This
algorithm directly optimizes the step phase slope to obtain high diffraction efficiency, rather than discussing the complex
relationship between the diffraction efficiency and various influence factors. Besides, other optimization algorithms
based on phase retrieval, such as GS, need the entire energy distribution; however, it is hard to obtain in practical. Our
algorithm need only the energy of the target diffraction point and it can be easily realized. Firstly, we construct the model
for beam steering, and point out that the deformation of the phase slope by influence factors is the reason why
conventional method can not realize high diffraction efficiency. Secondly, we construct an optimization model for the
issues and apply the pattern search algorithm to optimize the diffraction efficiency. The simulation results show high
performance of our algorithm comparing with the conventional steering method. Finally, a set of beam steering
experiments were performed with a one-dimensional LCPA being set both according to the un-optimized and the
optimized recipe, and the results were in very good agreement with the theoretical predictions. We show that the
deflection efficiency can be drastically improved.
A novel angular magnification method based on a telescope system is proposed in this paper to achieve liquid crystal optical phased array (LCOPA) wide-angle deflection. The optics transfer matrix of telescope is studied and the angle
magnification effect is derived. The transformation formulas of a Gaussian beam through the telescope system are also
derived by using the ABCD law. Simulation and experiment have been done to magnify the angle that deflected by a
LCOPA. This method is feasible and convenient to obtain wide-angle steering for a LCOPA.
The characteristics of Gaussian beam and the transition function of lens are analyzed in this paper. Based on the principle of liquid crystal optical phased array (LC-OPA) technology, an implementation of controlling the divergence angle of the laser beam is proposed. Through simulation, the transformation graph in which the divergence angle varies with the modulation depth is obtained, and the discretization error is also counted. Experiment have been done to verify the feasibility of this method. This method is convenient and can obtain various value of the angle without changing the structure of the device.
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