Active Beam Steering Research Articles

Tunable beam steering enabled by graphene metamaterials.

We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.

Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films.

We demonstrate active beam steering of terahertz radiation using a photo-excited thin layer of gallium arsenide. A constant gradient of phase discontinuity along the interface is introduced by an spatially inhomogeneous density of free charge carriers that are photo-generated in the GaAs with an optical pump. The optical pump has been spatially modulated to form the shape of a planar blazed grating. The phase gradient leads to an asymmetry between the +1 and -1 transmission diffracted orders of more than a factor two. Optimization of the grating structure can lead to an asymmetry of more than one order of magnitude. Similar to metasurfaces made of plasmonic antennas, the photo-generated grating is a planar structure that can achieve large beam steering efficiency. Moreover, the photo-generation of such structures provides a platform for active THz beam steering.

Study of active beam steering system with a simple method

We develope a simple method to stabilize the beam during propagation. Combination of the self-developed control module and the large diameter mirrors reconstruct the beam stabilization system, and some important procedures are presented, such as calibration and average filter. The results show that the horizontal pointing and vertical pointing are stabilized to within 8.43 and 7.59 μrad, and the beam horizontal position and vertical position are stabilized to within 2.16 and 2.11 μm respectively. The regulating time is within 84 ms. Thus the method presented is effective for the current stabilization system applied in lithography tools.

Metal-dielectric-metal plasmonic resonators for active beam steering in the infrared

Active beam-steering devices near the optical frequencies have long been sought after due to their applications in communication, defense, and display technologies; however, the challenge lies in achieving actively tunable structures near these frequencies. An array of metal-dielectric-metal plasmonic resonators is demonstrated as a dynamic beam-steering device to operate at midinfrared wavelengths. We numerically demonstrate continuous-angle beam steering of 8.75° by making use of tunable properties of silicon as the active dielectric. The proposed device achieves a refractive index insensitive divergence angle and it operates in a 650 nm wide spectral window around 10 μm wavelength. The results of this Letter pave the way to exploiting active beam steering in various applications at midinfrared wavelengths.

IFE Target Injection and Tracking Experiment

An experiment is being conducted at Lawrence Berkeley National Laboratory to investigate and demonstrate the engineering feasibility of accurately • injecting and tracking IFE targets into a vacuum chamber. A helium gas gun is used to inject non-cryogenic, aluminum and delrin (plastic) target-sized projectiles. They are optically tracked at three locations using photodiodes. An essential part of this experiment is tracking each projectile's position and predicting when and where it will arrive close enough to the driver beam focal spot so that with active beam steering, IFE driver beams can accurately hit each target Although the standard deviation in projectile position in each lateral direction is about 2 mm, projectile position measurements 1 m from the gun barrel have been used to predict position measurements at 3 m from the barrel with standard deviation less than 100 μm in the lateral directions. These results are encouraging and meet the expected beam steering distance and target position prediction accuracy requirements for indirect drive IFE power plants. Later this year, we intend to combine this experiment with a focused ion beam experiment and use real time position calculations to steer the beam through a small hole in the projectile.