Bidirectional high sidelobe suppression silicon optical phased array

Abstract

An optical phased array (OPA), the most promising non-mechanical beam steering technique, has great potential for solid-state light detection and ranging systems, holographic imaging, and free-space optical communications. A high quality beam with low sidelobes is crucial for long-distance free-space transmission and detection. However, most previously reported OPAs suffer from high sidelobe levels, and few efforts are devoted to reducing sidelobe levels in both azimuthal ( φ ) and polar ( θ ) directions. To solve this issue, we propose a Y-splitter-assisted cascaded coupling scheme to realize Gaussian power distribution in the azimuthal direction, which overcomes the bottleneck in the conventional cascaded coupling scheme and significantly increases the sidelobe suppression ratio (SLSR) in the φ direction from 20 to 66 dB in theory for a 120-channel OPA. Moreover, we designed an apodized grating emitter to realize Gaussian power distribution in the polar direction to increase the SLSR. Based on both designs, we experimentally demonstrated a 120-channel OPA with dual-Gaussian power distribution in both φ and θ directions. The SLSRs in φ and θ directions are measured to be 15.1 dB and 25 dB , respectively. Furthermore, we steer the beam to the maximum field of view of 25°×13.2° with a periodic 2λ pitch (3.1 μm). The maximum total power consumption is only 0.332 W with a thermo-optic efficiency of 2.7 mW/π .

Integrated optical phased array with on-chip amplification enabling programmable beam shaping

“…The shape of the Gaussian profile was modified by varying its inner to outer arms power ratio; the waist of the Gaussian profile is derived accordingly, assuming a symmetric distribution with respect to the center of the emitter. An increase in the Gaussian distribution power ratio corresponds to an increase in the sidelobe suppression ratio SLSR 18 , as it is shown in Fig. 4.…”

“…For wavelengths that are longer and shorter than 1525 nm (at the gain peak), the booster amplification level is lower, thus moving towards the linear operation regime of the arrayed amplifiers. This results in a larger value of the power ratio between the inner and outer OPA arms, which in turn broadens the far-field beam width 18,44 . This effect was further investigated by running simulations with wavelength-dependent Gaussian power distribution values, which were measured through near-field imaging at different wavelengths [Supplementary Figures S8-S11].…”

Beam Steering Technology of Optical Phased Array Based on Silicon Photonic Integrated Chip

“…According to Equation (2), it is necessary to extend the effective emission length of WGA to reduce the longitudinal divergence angle and improve the beam resolution [ 41 , 53 , 54 , 55 ]. For periodic WGA, the diffraction intensity exhibits an exponential decay, leading to a widening of the divergence angle.…”

“… ( a )The Gaussian distribution design of the output optical power of the grating in the longitudinal dimension. ( b ) The 10 nm shallow etched Si grating [ 55 ]. Photonics Res.…”

Energy-efficient integrated silicon optical phased array

“…We adjust the duty cycle of each unit to form the Gaussian power distribution along the grating. To ensure that the emitting angle of each unit is consistent, we slightly adjust the pitch of each unit (with a maximum adjustment of only 4 nm) [ 62 , 63 ]. Finally, we design 12-dB Gaussian power distribution in both and directions (dual-Gaussian) to obtain the 25 dB SLSR in the far field.…”