Fig. 1 Schematic of an individual pixel of the optical phased array. The Al_0.6Ga_0.4As HCG and 22 pairs of GaAs/Al_0.9Ga_0.1As DBR serve as the top and bottom reflector of the Fabry-Perot etalon. The incident light is surface normal to the etalon, and polarized in parallel to the grating bar. Λ, HCG period; s, grating bar width; t_g, HCG thickness; d, air gap between HCG and DBR. We design Λ = 1150 nm, s = 700 nm, t_g = 450 nm, and d = 700 nm.

Fig. 2 (a) SEM image of an 8x8 optical phased array. Each pixel is an HCG-APF, which can be individually electrically addressed by the fanned-out metal contacts. The pitch of the HCG mirror is ~33.5 μm. (b) Zoom-in view of the HCG mirror in a single pixel. The HCG mirror size (without the MEMS) is 20 μm by 20 μm.

Fig. 3 (a) Reflection spectrum of an HCG-APF with different actuation voltages. As the reversed bias voltage increases, the cavity length decreases, resulting in a blue-shift of the resonance wavelength. (b) Reflection phase shift versus applied voltage on a single HCG-APF of the phased array. ~1.7 π phase shift is achieved within 10 V actuation voltage range at a wavelength of 1550 nm; this corresponds to a displacement of ~50 nm of the HCG. The measured results are curve fitted to extract the reflectivity of the DBR and HCG.

Fig. 4 (a) Laser Doppler velocimetry measurement to characterize the mechanical resonance frequency of the HCG MEMS mirror. (b) Time resolved phase measurement of the HCG APF with a step voltage actuation signal. The blue dots are recorded in the experiment, and red traces are the simulated fitting curve from the second harmonic oscillator model.

Fig. 5 Comparison of the ringing between a single step and two step voltage control. In the two step voltage control case, the time interval between the two different steps is 1 μs, corresponding to half of the ringing period. The individual ringing from these two separate steps would have destructive interference, leading to an overall reduced ringing.

Fig. 6 Beam steering experiment. (a) Near-field phase pattern created by the HCG-APF optical phased array. (b) The corresponding far-field pattern calculated by Fourier optics. (c) Experimentally measured far-field pattern, in reasonably good agreement with the calculation. The strong zeroth order beam is due to the relatively low filling factor of the phased array (~36%). The light that does not hit on the HCG-APF gets reflected with a fixed phase shift, contributing strongly to the zeroth order beam. The field of view of the image windows is 13° x 13°. The box in dashed line in (c) indicates the TFOV of the phased array (9.14° x 9.14°).

Fig. 7 (a) SEM image of the two-dimensional HCG mirror for HCG-AFP array. (b) Beam steering experiment of the optical phased array using two-dimensional HCG as the top mirrors of the APF. Top panel, near-field phase pattern created by the HCG-APF optical phased array. Middle panel, the corresponding far-field pattern calculated by Fourier optics. Bottom panel, experimentally measured far-field pattern, in good agreement with the calculation.