  Advanced electro-optic processing combines electrical control with optical
modulation and detection. For quantum photonic applications these processes
must be carried out at the single photon level with high efficiency and low
noise. Integrated quantum photonics has made great strides achieving single
photon manipulation by combining key components on integrated chips which are
operated by external driving electronics. Nevertheless, electrical
interconnects between driving electronics and the electro-optic components,
some of which require cryogenic operating conditions, can introduce parasitic
effects. Here we show an all-optical interface which simultaneously delivers
the operation power to, and extracts the measurement signal from, an advanced
photonic circuit, namely, bias and readout of a superconducting nanowire single
photon detector (SNSPD) on a single stage in a 1K cryostat. To do so, we supply
all power for the single photon detector, output signal conditioning, and
electro-optic readout using optical interconnects alone, thereby fully
decoupling the cryogenic circuitry from the external environment. This removes
the need to heatsink electrical connections, and potentially offers low-loss,
high-bandwidth signal processing. This method opens the possibility to operate
other advanced electrically decoupled photonic circuits such as optical control
and readout of superconducting circuits, and feedforward for photonic quantum
computing.
