This dissertation deals with the fabrication of various polymer-based photonic structures (PSs) and their applications in nonlinear optics.

In the first part, we have demonstrated the fabrication of desired PSs by interference lithography technique. The two-beam interference method is theoretically and experimentally demonstrated as a best choice for fabrication of all kinds of PSs with large and uniform area. Desired 1D, 2D, and 3D, periodic and quasi-periodic PSs are successfully fabricated on SU8 photoresist. We also demonstrated a way to overcome the material's absorption effect, which imposes a limitation of PSs thickness. By adding one more exposure of a uniform laser beam in opposite direction of two interfering beams, the fabricated PSs became more uniform and their thickness increased to 25 um. A tentative of using low one-photon absorption technique was also realized showing the possibility to obtain a PS with a thickness upto 600 um. Furthermore, by using the interference technique combined with mass transport effect, we have demonstrated the fabrication of desired surface relief grating structures, with a controllable depth, on passive polymer (SU8) and active polymer (DR1/PMMA).

In the second part, we applied these fabricated structures for enhancement of nonlinearity of polymer materials by two different ways: quasi-phase-matching (QPM) and waveguide resonance grating (WRG). Both theoretical calculation and experimental realization of these techniques have been investigated. The QPM structures allowed to overcome the phase mismatch of fundamental and harmonic waves, thus increasing the conversion efficiency. The second-harmonic generation (SHG), one of the most important applications of frequency conversion, is significantly enhanced thanks to the QPM condition. Besides, the WRG structures allowed to increase the intensity of fundamental wave, thus enhancing the SHG signal by a factor of 25.