  Optical gratings are a key component in many spectroscopy, communications,
and imaging systems. While initially static elements, advances in optical
materials have enabled dynamically tunable gratings to be designed. One common
tuning strategy is relying on mechanical deformation of the grating pitch to
modify the diffraction pattern. To date, most mechanically adaptive optical
gratings consist of a hybrid system where rigid moieties are patterned on an
elastomeric substrate. In the present work, we demonstrate an all-polymer
tunable grating that is fabricated using replica molding from the poly(acrylic
acid) (PAA)/polyethylene oxide (PEO) polymer stereocomplex. PAA/PEO pristine
films exhibit excellent optical transmittance at or above 80% from 500 nm to
1400 nm and stretchability over 800% strain. The experimental studies on the
changes of diffraction mode distances with respect to the applied strains agree
well with the finite-difference time-domain (FDTD) theoretical modeling.
