Micromechanical high-Q trampoline resonators from strained crystalline InGaP for integrated free-space optomechanics

Tensile-strained materials have been used to fabricate nano- and micromechanical resonators with ultra-low mechanical dissipation in the kHz to MHz frequency range. These mechanical resonators are of particular interest for force sensing applications and quantum optomechanics at room temperature. Tensile-strained crystalline materials that are compatible with epitaxial growth of heterostructures would thereby allow realizing monolithic free-space optomechanical devices, which benefit from stability, ultra-small mode volumes and scalability. In our work, we demonstrate micromechanical resonators made from tensile-strained InGaP, which is a crystalline material that can be epitaxially grown on III-V heterostructures. The strain of the InGaP layer is defined via its Ga content when grown on (Al,Ga)As. In our case we realize devices with a stress of up to 470\,MPa along the $[1\,1\,0]$ crystal direction. We characterize the mechanical properties of the suspended InGaP devices, such as anisotropic stress, anisotropic yield strength, and intrinsic quality factor. We find that the latter degrades over time. We reach mechanical quality factors surpassing $10^7$ at room temperature with a $Q\cdot f$-product as high as $7\cdot10^{11}$ with trampoline-shaped micromechanical resonators, which exploit strain engineering to dilute mechanical dissipation. The large area of the suspended trampoline resonator allows us to pattern a photonic crystal to engineer its out-of-plane reflectivity in the telecom band, which is desired for efficient signal transduction of mechanical motion to light. Stabilization of the intrinsic quality factor together with a further reduction of mechanical dissipation through hierarchical clamping or machine learning-based optimization methods paves the way for integrated free-space quantum optomechanics at room temperature in a crystalline material platform.Comment: fixed typos, added more material on crystal anisotropy and on fabrication; 15 pages incl. appendix, 13 figure

Integrated microcavity optomechanics with a suspended photonic crystal mirror above a distributed Bragg reflector

Increasing the interaction between light and mechanical resonators is an ongoing endeavor in the field of cavity optomechanics. Optical microcavities allow for boosting the interaction strength through their strong spatial confinement of the optical field. In this work, we follow this approach by realizing a sub-wavelength-long, free-space optomechanical microcavity on-chip fabricated from an (Al,Ga)As heterostructure. A suspended GaAs photonic crystal mirror is acting as a highly reflective mechanical resonator, which together with a distributed Bragg reflector forms an optomechanical microcavity. We demonstrate precise control over the microcavity resonance by change of the photonic crystal parameters. The interplay between the microcavity mode and a guided resonance of the photonic crystal modifies the cavity response and results in a stronger dynamical backaction on the mechanical resonator compared to conventional optomechanical dynamics.Comment: 11 pages, 6 figures + Supplementary Material with 10 pages, 12 figures, 2 table

Double layer photonic crystal membranes in AlGaAs heterostructures for integrated cavity optomechanics

We characterize the opto-mechanical properties of double-layer mechanical devices. These closely spaced photonic crystal membranes can exhibit photonic bound states in the continuum, which could enable the realization of a strongly coupled, integrated optomechanical system

Integrated free-space optomechanics with AlGaAs heterostructures

We fabricated and characterized suspended bi-layered photonic crystal slabs in AlGaAs heterostructures. Our approach allows to create integrated, closely spaced membranes, which can exhibit photonic bound states in the continuum to increase light-matter interaction

Fast Lead-Free Humidity Sensor Based on Hybrid Halide Perovskite

An environmentally friendly analog of the prominent methylammonium lead halide perovskite, methylammonium bismuth bromide (MA3 Bi2 Br9 ), was prepared and investigated in the form of powder, single crystals and nanowires. Complete characterization via synchrotron X-ray diffraction data showed that the bulk crystal does not incorporate water into the structure. At the same time, water is absorbed on the surface of the crystal, and this modification leads to the changes in the resistivity of the material, thus making MA3 Bi2 Br9 an excellent candidate for use as a humidity sensor. The novel sensor was prepared from powder-pressed pellets with attached carbon electrodes and was characterized by being able to detect relative humidity over the full range (0.7–96% RH) at ambient temperature. Compared to commercial and literature values, the response and recovery times are very fast (down to 1.5 s/1.5 s)