Spectral Manipulation And Characteristics Of Periodical Micro-Nano Photonic Devices

Because of the large demands for large-capacity-data communication, the development of optical communication technology has been promoted greatly. Photonics devices, which are considered as the fundamental of the optical information system, have also received a lot of interests. To take the advantages of low insertion loss and easily coupling with fiber, fiber Bragg gratings (FBGs) play an important role in the optical communication area. Series of research theories and experiment demonstrations for FBG devices have been obtained, such as dispersion/dispersion-slope compensation, multi-channel filtering, gain equalizing, and so on. However, there are still many challenges for FBGs because of the development of optical signal processing technology. Besides, surface plasmon polaritons (SPPs), which have been considered as one of the most promising solutions to overcome the diffraction limit of optical devices, are therefore attracted lots of attentions. According to SPPs, researchers have studied and designed various novel optical devices with nano scale. Against such a deep background of the micro-nano devices, in this dissertation we will study the spectral manipulation and characteristics of periodical micro-nano photonics devices, including analysis on the filtering characteristics of sampled FBGs (SFBGs), design of filters based on FBG; design of SPPs waveguide filters; study on the spectral physical phenomena in the nano-size structure, and so on.According to the Fourier series expansion (FSE) method, the refractive index modulation of SFBG has been analyzed. The simulation results demonstrate that the distribution of the bandwidth performs as a Sine function. The maximum value arises in the0-order reflective peak, and the bandwidths of channels in both sides will decrease. However, the bandwidth of the k-th order peak is larger than that of the-k-th order one. Furthermore, multiple SFBGs with different Bragg wavelengths have been cascaded in a sampling period, so called super-structured SFBG (SSFBG). According to the multiple phase shift (MPS) technology, a high-channel-count filter with identical reflectivity is achieved. The wavelength range, channel spacing and channel count can be controlled by adjusting the sub-gratings count in a period, the duty cycle, and the MPS dense factor. The center wavelength for each peak of the SSFBG filter can be predicted accurately by the FSE method. The analytical results are in high accordance with the simulated ones based on transfer matrix (TM) method. Besides, an en/decoding SSFBG is designed based on the gold sequence. There will be a π phase shift in a sampling period when the adjacent codes are different. A2-channel,4-channel and8-channel en/decoders are designed in a single SFBG with optimized performance for their auto-correlation peak over the maximum wing level ratios and peak over the maximum cross-correlation level ratios being larger than17dB, respectively.The reflective spectrum of weak FBGs might be regarded as the spatial Fourier transform (FT) of the refractive index modulation when the reflection is low. Therefore, the normalized amplitude and the phase, which are obtained from the inverse FT of the expected reflection shape, are the significant factors for designing the intensity and phase modulation of the index change, respectively. By carefully incorporating and designing the intensity and the phase modulations, we obtain FBGs with arbitrary reflective spectra including cosine/sine, triangle, sawtooth, trapezium and upside-down triangle shapes, whose reflections are much lower than1. Moreover, their bandwidths can be modulated by adjusting the FBG parameters. Simulation results based on the TM method further confirm the proposed method.Spectral characteristics of surface plasmon polaritons (SPPs) in metal-insulator-metal (MIM) waveguides with a rectangular-or V-groove are analyzed. Theoretical and simulation results indicate that both schemes can achieve wavelength filtering functionality with the center wavelength possessing a linear relationship with the length of the groove. We further consider the plasmonic MIM waveguide with a tilted groove whose effects can be equivalently described by a function of the height. Characteristics of such waveguides are further investigated numerically by the finite-different time-domain (FDTD) method. The center wavelength of such structure has a nonlinear relationship with the height of the groove. Specifically, the wavelength will decrease firstly and then increase when the height increases. Furthermore, the electromagnetically induced transparency-(EIT) like transmission phenomenon in the MIM waveguide is studied. A plasmonic bus waveguide with a side-coupled T-shaped (TS) or a reverse T-shaped (RTS) resonator, which consists of a parallel and a perpendicular cavity, is proposed. This compact system can be performed as a wavelength de-multiplexing device as a forbidden band is achieved when the resonators are symmetrical. By shifting one cavity away from the center of the resonator, the scheme exhibits EIT like transmission at the wavelength of the former forbidden band. The electromagnetic responses of the structure can be flexible handled by changing the asymmetry degree of the TS or RTS resonator. In these cases, similar performances for two proposed structures can be obtained except for the center wavelength which are determined by both cavities for the RTS resonator or only determined by the cavity parallel to bus waveguide for the TS resonator. Besides, a π phase shift will arise in the transparency window, which will introduce dispersion in the transmission channel.Morevoer, the propagation characteristics of the surface plasmon waves supported inside the MIM waveguide, which are considered as a FP cavity, are studied. The resonance wavelengths are significantly related to the effective index of the mode in the slit and the length of the slit. After estimating the resonance wavelength, three slot cavities which perform as the drop waveguides can be designed in the MIM waveguide with the positions of half of the resonance wavelengths. The lst-order,2nd-oder and3rd-oder resonance wavelengths can be coupled out from the corresponding slot cavities, and all the transmittances are larger than0.1. The limitations for this device are the low transmittance and the limited channel count. To overcome these disadvantages, series of slot cavities have been proposed to array on both sides of the MIM slit. SPPs are captured into the cavities resulting in multiple resonance modes. Two drop waveguides lay on the middle and a quarter of the each cavity, and then the first and the second resonance wavelengths can be coupled out from the corresponding exports, respectively. A2-,4-, and8-channel filters have been designed and numerically demonstrated by2D finite FDTD method. The transmittances are larger than0.5for all the cases. Compared to the previous scheme, the channel count and the transmittance have been improved greatly.A subwavelength plasmonic comb-like filter is proposed by using dual symmetric slot cavities which are placed between two parallel MIM structure waveguides. The structure can be considered as a resonance loop which consists of slot-cavity resonators and MIM-waveguide resonators. As the waveguides and the cavities are not connected directly, the SPPs modes supported inside them are not completely identical. SPPs modes with zero magnetic field intensity in the waveguides can not be coupled into the cavities and will be reflected in the input waveguide. On the contrary, those captured into the cavities can pass through the output waveguide. The reflective wavelength range and channel spacing are determined by the lengths of slot cavities and MIM waveguides, respectively.3-,4-,5-reflective channels with high reflection are achieved in a small wavelength range. Higher channel count can be available by increasing the length or the real part of effective index of the MIM waveguides.Based on MIM waveguides, a plasmonic intersection structure is proposed. An open loop consists of four resonance cavities, in the center of which a drop waveguide is laid. Then two parallel waveguides provide to be a pair of input/output port. There is only one transmission peak whose center wavelength is determined by the length of the cavity. After defining L=300nm and400nm, simulation results based on FDTD method demonstrate that cross propagation for SPPs in this structure is achieved. The transmittance and the isolation degree are higher than0.6and14dB, respectively. Moreover, a MIM-based four-port quasi-circulator consisting of four bus waveguides and eight narrow inside/outside slits is proposed without using nonreciprocity. The phase difference of SPPs at the exports of two slits should satisfy0.5π. Simulation results based on FDTD method demonstrate that the transmittance at the center wavelength437.6nm of the appropriate output port can reach0.4while the extinction ratios of the other two output ports are larger than20dB. Therefore, we can consider that once the input port is defined, only a specific output port is available. Through adjusting the parameters of the waveguides and slits, the center wavelength can be changed.In conclusion, the above researches can develop the applications of the nano-micro devices, such as multi-channel filter, special optical signal generation, parameter sensing, dispersion compensation, and so on.