Having been widely utilized as the foundation material for CMOS industry, with high refractive index and large spectrum transparency window, silicon has also long been considered as a perfect platform for photonics applications. Optical structures such as microcavities, photonic crystals, interferometers and etc. have already been demonstrated as on-chip silicon photonic devices. Such platforms have already been utilized in different applications such as high speed optical signal processing, optomechanical system demonstration, optical nonlinearity research and etc. Moreover, since the optical property of integrated silicon photonic devices are highly susceptible to the change of the refractive index of the surrounding medium, ultrasensitive optical sensor has also been demonstrated in various fields such as chemical and biological sensing, fiber strain analysis, EM (electromagnetic) field sensing, mechanical motion sensing and etc. However, silicon dioxide, as the material for the buried layer of silicon on insulator (SOI) substrate, which is the most widely adopted silicon photonic device platform, has limited both the optical and mechanical potential for silicon based optical sensor since it possesses a very narrow transparency window and is highly rigid. Within the past decades, flexible electronics based on inorganic material has been successfully demonstrated by using stamp-assisted heterogeneous integration method, which could also be applied to the field of silicon photonics. This thesis has been focusing on utilizing various heterogeneous fabrication methods such as integrating high quality silicon photonic devices onto materials other than silicon dioxide, or applying polymer based materials on top of SOI substrate in order to demonstrate devices with novel applications which are inaccessible with traditional silicon photonic devices. Firstly, a highly sensitive strain sensor is demonstrated by transferring silicon ring resonator and Mach-Zehnder Interferometer (MZI) onto stretchable PDMS substrate. Secondly, fully integrated silicon photonic circuit with grating couplers and ring resonators has been successfully transferred onto thin and flexible plastic substrate. Thirdly, by using a photoresist-pedestal assisted transfer method, a microcavity-enhanced mid-infrared optical chemical sensor is successfully demonstrated by using a silicon-on-calcium difluoride platform. Lastly, by applying a thin layer of polymer on one-dimensional photonic crystal cavity, an ultrasensitive infrared optical chemical sensor is realized.