## 4 Applications in Photonic Devices
### Active Components  
The realm of active photonic components encompasses devices that interact with light through energy conversion or external control, with organic semiconducting polymers playing a crucial role in many applications. Light-emitting devices represent one of the most successful implementations, where polymers like PFO and its derivatives enable efficient electroluminescence across the visible spectrum. The incorporation of electron-transporting units, as demonstrated in FSBT, has led to improved device efficiency and color purity [33; 57]. These materials have found commercial success in display applications, benefiting from solution processing and the ability to achieve large-area devices through printing techniques.  
In the domain of photodetectors, conjugated polymers offer unique advantages for light-sensing applications. P3 HT and its blends with electron-accepting materials have demonstrated high sensitivity and fast response times [41; 42]. More sophisticated systems, such as low-bandgap polymers like PCDTBT, enable broader spectral coverage extending into the near-infrared region [45]. These materials prove particularly valuable in imaging applications and optical communication systems where flexible, large-area detection is required.  
Optical amplifiers based on conjugated polymers exploit their strong stimulated emission properties. MEH-PPV has demonstrated optical gain in waveguide configurations, while more specialized materials like poly(9,9-dioctylfluorene-co-benzothiazole) enable amplification at specific wavelengths through careful molecular design [131; 132]. These systems benefit from high gain coefficients and the ability to integrate directly with polymer waveguide structures, though challenges remain in achieving long-term stability under high-intensity illumination.  
Modulators and switches represent another important category where polymer materials excel through their strong electro-optic and thermo-optic responses. Polymers containing chromophores with large dipole moments, such as DR1-PMMA (Disperse Red 1 functionalized poly(methyl methacrylate)), enable efficient electro-optic modulation [133; 134; 135]. More advanced systems incorporate cross-linkable units to improve stability while maintaining high electro-optic coefficients. Additionally, thermo-optic switches based on conjugated polymers like polyfluorens demonstrate fast switching capabilities with relatively low power consumption.  
The integration of these active components with passive structures has led to increasingly sophisticated photonic circuits. For example, the combination of polymer light-emitting regions with waveguide structures enables integrated light sources, while the incorporation of photodetector sections creates complete optical links [136; 137; 138]. The ability to pattern different polymer materials through solution processing enables the fabrication of complex devices incorporating multiple active functions. Moreover, the development of new materials continues to expand the capabilities of these devices, with recent advances in stability and efficiency pushing toward practical applications in communications, sensing, and computing.  
The success of active polymer photonic components relies heavily on molecular design strategies that optimize both optical and electronic properties while maintaining processability and stability. The continued development of new materials and device architectures, coupled with an improved understanding of structure-property relationships, drives progress toward more efficient and reliable devices for next-generation photonic applications. Table 2 demonstrates the versatility of organic semiconductors in both passive components (waveguides, filters, photonic crystals) and active devices (light-emitting devices, photodetectors, amplifiers, modulators), highlighting their broad applicability in photonic technologies.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline