Three applications of the interaction of light with periodic dielectric structures are investigated. The first application is large-area spectroscopy, for which we use the mid-field diffraction pattern generated by the light source passing through a transmission grating to determine its spectral composition. By utilizing a large grating size, we are able to achieve resolutions of < 4 nm experimental while having an etendue of roughly 0.033 mm2. Furthermore, since we are sampling the mid-field light pattern as opposed to the farfield, the entire spectrometer can fit within a 10 mm by 10 mm by 5 mm volume. The second application are barcodes based on the wavelength-dependent back-scattering off of a photonic crystal resonant cavity. The challenge is that we want to observe high quality factor resonant peaks while reducing the size of the crystal to less than 10 microns. So far the highest quality factor observed was about 800. The third application is a Fano silicon photonic crystal modulator waveguide device. The resonant cavity of the modulator is a 1D photonic crystal cavity. If we excite the fundamental and first excited mode of the waveguide, we obtain a Fano resonance that can potentially increase modulation depth and efficiency. We investigated how to improve the modulator architecture to reliably design resonators with sharp Fano resonance peaks. Those these applications are still in their early stages, the are promising for furthering each technology.