Optical technology has seen a revival from the previous decade, in terms of innovations and research, especially relating to optical integrated circuits. Similarly, Photonic Crystals (PCs) are one of the main contenders for the purpose. Therefore, this research work implicates different arrangements of the 3-Dimensional PC units based on the employment of a varying radius PC-cavity and its position i.e., at the beginning and within the middle of the PC-lattice. The effects of these PC-cavities are studied, investigating higher shifting in resonant wavelength, a narrower linewidth around 0.0061 µm and a quality factor of 99.59, comprising of a PC-cavity of radius 0.300 µm using input signal only i.e., coupled into the optical structure using the phenomenon of the Guided-mode-resonances (GMR). The structures are computed using an open-source FDTD platform, employing a stripe-model-based structure utilizing the Periodic Boundary Condition to save time and computational resources and later the PML for the realization of the Finite models. Moreover, the concluded structures based on the position of the PC-cavity, are demonstrated for the design of the all-optical-amplification device, executing a control signal reporting an 8 % of the amplification in the output of the input signal.