in optical reflection resulting from optomechanically induced transparency effects. The peak height exceeds one due to converter gain (see supplement). The optical reflection peak is suppressed when $\Gamma_\mathrm{e} \approx \Gamma_\mathrm{o}$, constituting electromechanically induced optical absorption, which, to our knowledge, has not been previously reported.

To further explore the converter box’s performance, the efficiency is extracted from peak transmission for a range of $\Gamma_\mathrm{e}$ with $\Gamma_\mathrm{o} = 2 \pi \times 725~\mathrm{Hz}$ fixed (Fig. \[sparam\]b). For fixed optical cavity parameters, efficiency is maximized when damping rates are matched ($\Gamma_\mathrm{e} = \Gamma_\mathrm{o}$, $\Gamma_\mathrm{T} = 2\pi \times 1.45 ~\mathrm{kHz}$). The conversion efficiency is fit to [@andrews_bidirectional_2014] $$\label{eq:etam}
\eta = \frac{ 4 \Gamma_\mathrm{e} \Gamma_\mathrm{o} }{ (\Gamma_\mathrm{e} + \Gamma_\mathrm{o} + \gamma_\mathrm{m})^2 } \eta_\mathrm{M} = 
\frac{ 4 (\Gamma_\mathrm{T} - \Gamma_\mathrm{o} - \gamma_\mathrm{m})  \Gamma_\mathrm{o} }{ \Gamma_\mathrm{T}^2 } \eta_\mathrm{M},$$ where $\gamma_\mathrm{m}$ and $\Gamma_\mathrm{o}$ are fixed from independent measurements and $\eta_\mathrm{M}$ is the only fit parameter. For our converter $\Gamma_\mathrm{e},\Gamma_\mathrm{o} \gg \gamma_\mathrm{m}$, and thus $\eta=\eta_\mathrm{M}$ when the converter is matched. Therefore we refer to $\eta_M$ as the matched efficiency. In this low mechanical dissipation regime, there is negligible energy loss in the electro-optic transduction process itself, but some energy is absorbed in each electromagnetic resonator, and the spatial profile of 