Plasmonics paves the way for controlling electromagnetic waves at the nanoscale by coupling light to coherent electronic excitations(surface plasmon resonances, SPRs)at the interface between dielectric and metallic materials. Plasmonic resonances in metallic nanostructures have drawn increasing attention because of their extensive applications, including waveguides, microscopies, sensors, lasers, and light emitting diodes. The strong confinement of light associated with surface plasmon resonances can give rise to the fast development of different kinds of sub-wavelength photonic components and devices. The photon-electron excitations allow solid confinement of the electromagnetic waves to nanoscale dimensions which may lead to strong field enhancement. To manipulate the plasmonic resonances, diversified designs have been used to modify the features, sizes, and spacing of the metallic structures. In comparison with these physical approaches, varying the separations of optically functional nanoelements is a much more efficient method. Here, we investigate the optical response of plasmonic crystal arrays composed of square-and circle-shaped particles with different separations. Using focused ion beam milling, plasmonic crystal arrays with normal separation(relatively large size)are first fabricated, leading to weak coupling regime between adjacent particles. To minimize redeposition effects and achieve fine patterns, small beam current and parallel milling method are applied. In order to further generate plasmon-enhanced reflection, the separation between neighboring plasmonic crystals is remarkably decreased. As the separation reduces, the coupling effects become stronger, enabling strong coupling regime. It is found the reflection can be significantly enhanced by strong coupling effects and the resonance wavelength redshifts with decreasing separation when the gap size is smaller than 30nm. To verify the experimental results, finite-difference time-domain calculations are carried out. Simulations agree well with the measured data. By combining gold(Au)nanoparticle structures with ATR-FTIR spectroscopy technique, the absorbance of glucose can be effectively enhanced. The plasmonic crystal structures and new findings under investigation in this work may find extensive applications in chemical sensing, detecting and optical waveguiding.