By embedding NaYF 4 :Yb 3+ ,Tm 3+ nanocrystals into the top cladding layer of a resonant waveguide grating structure, we demonstrate that the upconversion fluorescence of Tm 3+ ions can be greatly enhanced, by a factor of up to 10 4 . The resonant waveguide grating structure consists of an SU8 bottom layer with sinusoidal grating morphology coated with a thin TiO 2 waveguide layer and then covered with a poly(methyl methacrylate) cladding layer doped with NaYF 4 :Yb 3+ ,Tm 3+ nanocrystals. The giant enhancement of the upconversion fluorescence is achieved first by coupling the excitation light with a guided mode of the resonant waveguide grating structure and then the fluorescent light with a second guided mode. Our numerical simulation results obtained by rigorous coupled-wave analysis indicate that the electric field of the incident light is strongly enhanced near the interface of the TiO 2 layer and the poly(methyl methacrylate) layer at guided mode resonance, and this is the major effect of the observed enhancement of the upconversion fluorescence of the nanocrystals. The resonance between the fluorescent emission and the waveguide structure further enhances the intensities of the fluorescent signal. We also find that the lifetime of upconversion fluorescence at 480 nm wavelength from the rare-earth nanocrystals is reduced about 1.34-fold when both excitation and extraction resonance occurs in the waveguide structure.

Guided-mode resonances enhanced excitation and extraction of two-photon photoluminescence (TPP) is demonstrated with a one-dimensional resonant waveguide grating (RWG) with a layer of fluorescent polymer (polyfluorene, PFO) on top. In this work, we design and fabricate a PFO RWG, in which two dispersive resonant modes in TE-polarization were measured. By aligning the red-shifting resonant mode with excitation wavelength in the infrared range, and the blue-shifting resonant mode with TPP spectrum in the visible range, the intensity of TPP can be enhanced up to 300-fold compared with that from a flat film with the same thickness coated on a glass slide. Such high enhancement results from firstly the strong evanescent local field in the waveguide layer due to the resonance between the incident light and the waveguide structure according to the results of rigorous coupled-wave analysis calculation, and secondly the enhanced extraction of the emission light which also resonates with the waveguide structure.

Guided mode resonance (GMR) enhanced second- and third-harmonic generation (SHG and THG) is demonstrated in an azo-polymer resonant waveguide grating (RWG), comprised of a poled azo-polymer layer on top of a textured SU8 substrate with a thin intervening layer of TiO2. Strong SHG and THG outputs are observed by matching either in-coming fundamental- or out-going harmonic-wavelength to the GMR wavelengths of the azo-polymer RWG. Without the azo-polymer coating, pure TiO2 RWGs, do not generate any detectable SHG using a fundamental beam peak intensity of 2 MW/cm(2). Without the textured TiO2 layer, a planar poled azo-polymer layer results in 3650 times less SHG than the full nonlinear RWG structure under identical excitation conditions. Rigorous coupled-wave analysis calculations confirm that this enhancement of the nonlinear conversion is due to strong local electric fields that are generated at the interfaces of the TiO2 and azo-polymer layers when the RWG is excited at resonant wavelengths associated with both SHG and THG conversion processes.

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