Strain sensors are a key for the development of next-generation soft robots. For such applications, the electronic sensing using flexible electronic materials are continuing to be at the forefront of the sensing technology. Recently, optical-sensing technology have attracted much attention because of high spatiotemporal resolution, high sensitivity and noninvasively. Especially, chiral-nematic liquid-crystalline elastomers have much attention to be applied to optical strain sensors because of the change of selective reflection wavelength in response to the strain. Here, we introduce our recent research on optical strain sensors using chiral-nematic liquid-crystalline elastomers. There is remarkable maturity in the development of numerous stimuli-responsive liquid-crystalline elastomers. However, the control of the recovery process after the removal of the stimuli has remained difficult. Interestingly, our simple materials design concept of “layering the elastomers with other materials” allows us to arbitrary control the recovery process in both macroscopic deformation and microscopic molecular orientation. Based on the concept, we have succeeded to fabricate a mechano-optical sensor with high sensitivity and high spatiotemporal resolution. This concept would open a pathway to control the recovery process in various stimuli-responsive liquid-crystalline elastomers.