  Optomechanical devices operated at their quantum limit open novel
perspectives for the ultrasensitive determination of mass and displacement, and
also in the broader field of quantum technologies. The access to higher
frequencies implies operation at higher temperatures and stronger immunity to
environmental noise. We propose and demonstrate here a new concept of quantum
well photoelastic comb for the efficient coupling of light to optomechanical
resonances at hundreds of GHz in semiconductor hybrid resonators. A purposely
designed ultra-high resolution Raman spectroscopy set-up is exploited to
evidence the transfer of spectral weight from the mode at 60 GHz to modes at
190-230 GHz, corresponding to the $8^{th}$ and $10^{th}$ overtone of the
fundamental breathing mode of the light-sound cavities. The coupling to
mechanical frequencies two orders of magnitude larger than alternative
approaches is attained without reduction of the optomechanical constant $g_0$.
The wavelength dependence of the optomechanical coupling further proves the
role of resonant photoelastic interaction, highlighting the potentiality to
access strong-coupling regimes. The experimental results show that
electrostrictive forces allow for the design of devices optimized to
selectively couple to specific mechanical modes. Our proposal opens up exciting
opportunities towards the implementation of novel approaches applicable in
quantum and ultra-high frequency information technologies.
