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.
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