Diversity and versatility of characteristics of the organic compounds, including conductivity, semiconductivity, optical absorption and emission as well as optical gain and nonlinearity, have facilitated the utilization of such materials in a broad range of applications, specifically in hybrid photonic and electronic devices. The electronic properties, the electro-optic effect and the optical gain in organic materials are the most attracting features; thus, this research has been devoted to the study of the following four pillars: organic photodetectors, the photocapacitance effect in organic heterostructures, an optical switch based on multimode interference structure using the electro-optic organic polymers and a parity-time symmetric all-optical switch by using the optical gain in organic dyes. Regarding organic photodetectors (OPD), a comprehensive time-domain modeling was presented. This model describes well the bandwidth behavior and the current-voltage characteristics of OPDs according to the reported experimental measurements. Furthermore, based on the implemented simulation framework, the trade-off between the bandwidth and the responsivity was studied and an effective design approach was introduced for improving the performance of OPDs. According to the results, it was found that in a small-area OPD, the bandwidth is most influenced by the carrier transit time which highly depends on the mobility of carriers. The results show that the logarithm of the bandwidth is proportional to the square root of the intensity of the applied electric field, indicating that the bandwidth of OPDs can be improved exponentially by increasing the reversed bias voltage. As an alternative approach to detect optical signals, the photocapacitance effect and its origin in organic heterostructures were investigated and analyzed. The variations of the capacitance by the light exposure is owing to the existence of the traps in the semiconductor; thus, we have shown that at low frequencies the absorption of light leads to decreasing the trapping lifetime. In this respect, several OPDs were fabricated and the photocapacitance effect was measured in the devices. In addition, an analytical model was introduced to justify the frequency dispersion of the photocapacitance effect. The results of the experimental measurements and the analytical model indicate that the existence of traps and the formation of a pn junction are necessary for observation of the photocapacitance effect in organic structures. According to the results, the dominant density of traps in the p-type side of the structure leads to a descending dispersion curve of the photocapacitor. Continuing the research on the organic electro-optic materials, a 1´3 optical switch with the multimode inference (MMI) structure was proposed. In order to simulate such structure, the three-dimensional structure was reduced to a two-dimensional structure by using the effective index method. The results show that the crosstalk between the output ports is less than –17.2 dB and the transmission loss is around 2.1 dB in the proposed MMI-based switch. In addition, and according to the results, the extinction ratio and the insertion loss of this optical switch were 15.1 dB and 1.3 dB respectively. For the fourth pillar of this thesis, by using the optical activity property in dye-doped polymers and utilization of the concept of the parity-time (PT) symmetry, a reflective grating structure was proposed to develop an all-optical switch in which the variations of the gain to the loss ratio was used for controlling the switch. The proposed structure was completely modeled with the aid of the coupled wave theory and the governing equations were analytically derived in form of explicit expressions. As well as to the analytical model, this PT-symmetric switch was simulated with the finite element method in the frequency domain and the validity of the analytical formulas was verified. The results show that by adjusting the gain-loss ratio form unity to 0.42, the extinction ratio better than 40 dB can be achieved in a precise and accurate design. Furthermore, by considering ±5% relative error in the main parameters simultaneously, the extinction ratio more than 25 dB is attainable. Keywords: Organic Semiconductors, Organic Photodetectors, Photocapacitance effect, Electrooptic, Parity-Time Symmetry, Grating, Optical Switch.