  Direct current (DC) converters play an essential role in electronic circuits.
Conventional high-efficiency DC voltage converters, especially step-up type,
rely on switch-mode operation, where energy is periodically stored within and
released from inductors and/or capacitors connected in a variety of circuit
topologies. However, since these energy storage components, especially
inductors, are difficult to scale down, miniaturization of switching converters
for on-chip or in-package electronics faces fundamental challenges.
Furthermore, the resulting switching currents produce electromagnetic noise,
which can cause interference problems in nearby circuits, and even acoustic
noise and mechanical vibrations that deteriorate the environment. In order to
overcome the limitations of switch-mode converters, photonic transformers,
where voltage conversion is achieved through the use of light emission and
detection processes, have been demonstrated. However, the demonstrated
efficiency is significantly below that of the switch-mode converter. Here we
perform a theoretical analysis based on detailed balance, which shows that with
a monolithically integrated design that enables efficient photon transport, the
photonic transformer can operate with a near-unity conversion efficiency and
high voltage conversion ratio. We validate the theoretical analysis with an
experiment on a transformer constructed with off-the-shelf discrete components.
Our experiment showcases near noiseless operation, as well as a voltage
conversion ratio that is significantly higher than obtained in previous
photonic transformer works. Our finding points to a high-performance optical
solution to miniaturizing DC power converters for electronics and improving the
electromagnetic compatibility and quality of electrical power.
