  The biological skin enables animals to sense various stimuli. Extensive
efforts have been made recently to develop smart skin-like sensors to extend
the capabilities of biological skins; however, simultaneous sensing of several
types of stimuli in a large area remains challenging because this requires
large-scale sensor integration with numerous wire connections. We propose a
simple, highly sensitive, and multimodal sensing approach, which does not
require integrating multiple sensors. The proposed approach is based on an
optical interference technique, which can encode the information of various
stimuli as a spatial pattern. In contrast to the existing approach, the
proposed approach, combined with a deep neural network, enables us to freely
select the sensing mode according to our purpose. As a key example, we
demonstrate simultaneous sensing mode of three different physical quantities,
contact force, contact location, and temperature, using a single soft material
without requiring complex integration. Another unique property of the proposed
approach is spatially continuous sensing with ultrahigh resolution of few tens
of micrometers, which enables identifying the shape of the object in contact.
Furthermore, we present a haptic soft device for a human-machine interface. The
proposed approach encourages the development of high-performance optical skins.
