Plasmonic nanostructure for photonic integrated circuit

Abstract

The interaction of surface plasmon polaritons on periodic structures is investigated theoretically and experimentally. It is shown that asymmetric T-shaped plasmonic gratings can display plasmon-polariton band structures with wide range of band gaps and tunable group velocities. A structure gap is introduced in the post of T-shaped plasmonic gratings and it is found that the size of this gap plays an important role in controlling the plasmon-polariton band gap and group velocities. We obtained variation of energy band gap ranging from 0.4 eV to 0.0323 eV by changing the size of the structure gap from 0 to 250 nm. We studied the difference between symmetric and asymmetric T-shaped gratings and found that the symmetric structure has a momentum gap in the photonic band structure, which can be avoided in the asymmetric structure. We analyze the structure using Fourier expansion and perform numerical simulation using Rigorous Coupled Wave Analysis (RCWA). A detailed derivation of equations which can be used to control the momentum gap behavior using Fourier transform is given. Furthermore, by varying the post and spacer (made of SiO2) thicknesses we can tune the energy band gap from 0.1 eV to 0.148 eV and from 0.183 eV to 0.19 eV, respectively. In this device, we obtain tunable group velocities ranging from one to several orders of magnitude smaller than the speed of light in the vacuum. We have found that the plasmon mode can be decupled with light when the upper post is displaced by half a period. Thus, such a structure can be used as plasmonic decupler. Furthermore, by displacing the T-shaped post we can tune the plasmon-polariton band gap and group velocity in a non-monotonic manner. This asymmetric T-shaped plasmonic grating is expected to have applications in surface plasmon polariton (SPP) based optical devices, such as filters, waveguides, splitters and lasers, especially for applications requiring large photonic band gap. The reflection and thermal radiation properties of a T-shaped array are investigated. The angular dependent reflectance spectrum shows a clear resonant dip at 0.35eV for full polar angles. No other significant localized resonant mode is found in the investigated spectral range from 0.12eV to 0.64eV. According to the Kirchhoff’s law, the thermal radiation of the T-shaped array can lead to a sharp peak at 3.5m with low sideband emission. We have also found that the T-shaped structure filled with organic material such as PMMA with different thicknesses (10 nm -50 nm) can lead to significant shift of the resonance wavelength. Thus, the T-shaped structure can also be used as a good sensor for organic materials. Also, we have measured the absorbance and reflectance spectra of a T-shaped array by using a Fourier transform infrared (FTIR) spectrometer. This structure can be used as a reflection-type angle-independent band-stop filter. The stop band can also be adjusted by varying the structure geometry. The T-shaped structure is able to offer a single, narrow, angle-independent band stop filter. The plasmon-polariton band structures of metallic disk structure for both TM and TE polarizations have been investigated. It is shown that the metallic disk structure can be used as an efficient narrow-band thermal emitter in the IR region. The absorption spectra of such structure are investigated both theoretically and experimentally. Calculations of thermal radiation properties of the metallic disk show that the metallic disk is a perfect emitter at a specific wavelength, which can be tuned by varying the diameter of the disk. The metallic disk exhibits only one significant localized surface plasmon polariton mode for both TM and TE polarizations simultaneously. The localized surface plasmon polariton (LSPP) mode can be tuned by either varying the disk diameter or the spacer (made of SiO2) Spectroscopic ellipsometry (SE) measurements of the specular and off-specular reflection of 1D-PMMA grating on Au-coated glass substrate has been analyzed with efficient theoretical modeling. We obtained a very good agreement between calculation and experiment for both specular and off-specular results. It is found that the resonance peak of the off-specular reflection is much sharper than specular reflection at a wavelength that matches the condition for exciting the interface mode (surface plasmon) resonance. When different media are used as the ambient, we found that the off-specular reflection can give an order of magnitude improvement in detection sensitivity than the corresponding specular reflection. This study may open a new way in terms of far field application such as biosensing. Furthermore, we developed a method to compute quasi photonic band structures for periodic structures with frequency-dependent complex dielectric constants.