Vehicle detection is an important topic for advanced driver-assistance systems. This paper proposes an adaptive approach for an embedded system by focusing on monocular vehicle detection in real time, also aiming at being accurate under challenging conditions. Scene classification is accomplished by using a simplified convolution neural network with hypothesis generation by SoftMax regression. The output is consequently taken into account to optimize detection parameters for hypothesis generation and testing. Thus, we offer a sample-reorganization mechanism to improve the performance of vehicle hypothesis verification. A hypothesis leap mechanism is in use to improve the operating efficiency of the on-board system. A practical on-road test is employed to verify vehicle detection (i.e., accuracy) and also the performance of the designed on-board system regarding speed.
Based on the Fraunhofer diffraction theory and the properties of dove prism, the coordinate relationships among the four spatial light modulator (SLM) sections in a vectorial optical field generator (VOF-Gen) are derived and experimentally verified. Taking the coordinate system of the first SLM section as reference, the coordinate displacements between the first SLM section and the subsequent ones are measured through employing the specially designed four-quadrant patterns with varying shifts of the corresponding cross point. Complex optical field could be accurately generated by combining the derived coordinate relationships and pre-compensation of the measured coordinate displacements. A typical complex optical field is generated and the experimental results demonstrate the validity of the proposed transverse alignment method for the VOF-Gen.
We report the realization of precise spatial polarization control of light via a priori optimization of the polarization ratio and retardation modulation in a vectorial optical field generator. For the polarization ratio calibration, we generate 45° linearly polarized light, measure the intensities of the vertical and horizontal components of the output beam and calculate the ratio of them to obtain the modification coefficient. After several iterations, the corresponding coefficient converges to an optimized value based on the criterion that the measured intensities are equal to each other. As for the retardation calibration, circularly polarized light is generated and letting the modulated beam propagate through a circular polarization analyzer. The modification value is adjusted by dichotomy until the detected intensity of the output beam from the circular polarization analyzer approaches extinction. Several typical kinds of vectorial optical beams are generated with the obtained modification parameters and the measured Stokes parameters demonstrate that this method is practicable and beneficial for the performance improvement of the vectorial optical field generator.
Agile beam steering has been previously reported to be one of the unique properties of a liquid crystal optical phased array. We propose a stochastic scanning method using the property of agile beam steering to shorten acquisition time in building a free-space laser communication link. As a specific example, Gaussian stochastic scan enables higher acquisition probability and shorter acquisition time. In addition, there are two factors to influence the results: standard deviation of stochastic scanning angle and the width of the laser beam. Theoretical analysis is presented that the stochastic scanning method is a unique method to speed up the acquisition process in free-space laser communication.
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.
In this paper, by establishing a liquid crystal model of beam steering, a rapid iterative algorithm called Rosenbrock
algorithm is proposed for obtaining wave-control data of liquid crystal phased array (LCPA). The method doesn’t need
wavefront reconstruction, the error is reduced, and the searching direction is adjusted automatically to right space of
solution, thus the algorithm converge rapidly, and the performance of beam steering is optimized at the same time. In this
paper, firstly, a liquid crystal model of beam steering is established. Then, the effectiveness and superiority of this
algorithm is verified compared with Pattern Search algorithm. Finally, we evaluate our algorithm by experiment. The
results show that Rosenbrok algorithm can optimize the efficiency of beam steering rapidly and significantly.
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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