  The need for highly accurate, labor-intensive optical alignment has been a
major hurdle in our ability to leverage the power of complex photonic
integrated circuits. There is a strong need for tolerant and passive alignment
methods that enable interrogation at any point in a photonic circuit. Various
promising and scalable photonic packaging techniques have been under
development, but few methods compatible with low-temperature operation have
been reported. Here, we demonstrate alignment-free $25\%$ coupling efficiency
from an optical fiber to a silicon optomechanical crystal at 7 mK in a dilution
refrigerator. Our coupling scheme uses angle-polished fibers glued to the
surface of the chip. The technique paves the way for scalable integration of
optical technologies at low temperatures, circumventing the need for optical
alignment in a highly constrained cryogenic environment. The technique is
broadly applicable to studies of low-temperature optical physics and to
emerging quantum photonic technologies.
