Experimental Study On Modulation Characteristics Of Lithium Niobate Based Surface Plasmon Resonance

Surface Plasmon Resonance(Surface Plasmon Resonance,SPR) can provide strong field confinement,which opens up new possibilities for reducing device size and reducing energy consumption.Plasma-active components with electro-optic modulation have attracted more and more research interest.In this paper,the modulation characteristics of a plasma-active components based on an electro-optic material lithium niobate(LN)as the substrate and a gold nano-layer with a thickness of about 80 nm are experimentally studied,including the modulation characteristics,polarization characteristics and frequency response characteristics which are related to the field distribution of the electrodes under different laser irradiation.Firstly,the spectrum of LN plasmon resonance was simulated by using FDTD(Finite Difference Time Domain),the results indicate the resonance wavelength was 582 nm.The simulation on electric field distribution of the gold nanolayer electrode was carried out using the finite element method.According to the simulation results,we divided the electrode with size of50um*50um into 9 regions,and marked the three regions on the diagonal line as regions 1,2 and 3,respectively.The corresponding normalized electric field strengths are respectively 0.09,0.27,1.Then,the prism coupling structure was used to excite the SPR,and the super-continuum source(450?2400nm) was used to study the electrical modulation characteristics of the plasmon resonance.The 532 nm and 661 nm lasers were used for amplitude modulation research.The modulation of the SPR spectrum is different when the input light is focused to different areas of the electrode.Wavelength modulations of 8.17 nm/V,10.85 nm/V,and 36.33 nm/V in the regions1,2,and 3 are achieved under the super-continuum source,respectively.Amplitude modulation of 1.22 dB/V,3.17 dB/V,and 5.43 dB/V in regions 1,2,and 3 are obtained under 532 nm laser,respectively.Amplitude modulation of 1.81 dB/V,1.94 dB/V,and 2.72 dB/V in regions 1,2,and 3,are achieved under the 661 nm laser,respectively.Experimental results demonstrate the modulation characteristics associated with the field distribution of the electrodes.The polarization characteristics of the LN plasmonic resonance device were then investigated using lasers with different wavelengths.The experimental results show that the polarization extinction ratio of the device is 8.0dB and 6.8dB under the 532 nm and 661 nmlaser,respectively.This confirms the TM polarization excitation characteristics of the SPR with incident light.Finally,the modulation response characteristics of LN plasmonic resonance devices under lasers with wavelengths are studied.The experimental results show that the larger the external modulation voltage,the deeper the response of the device under the same laser.And the device has a fast modulation response speed under different laser.With a 532 nm laser,the average response time of the device is approximately 40 ms.With a 661 nm laser,the average response time of the device is approximately 30 ms.So far we have demonstrated that LN SPR devices can perform field modulation-related electrical modulation at low DC voltages(1.2 V).In the experimental study,we obtained the SPR modulation characteristics of electro-optical LN with structural electrodes based on amplitude modulation characteristics,polarization characteristics,and modulation response characteristics under single-wavelength(532 nm,661 nm)lasers.This achievement provides a valuable reference for potential applications such as optoelectronic interconnection,electric field sensing,and SPR modulation.The innovations of the paper are as follows:1.It is proposed to combine the LN with the microstructured gold film electrode to modulate the SPR.The LN plasmonic resonance device based on the gold microstructure electrode has a strong field effect,which can realize electro-optic modulation of the device under a low DC voltage(1.2 V),thereby realizing low voltage modulation.2.The microstructured gold film on LN acts as both a structure for exciting SPR and as an electrode for connecting a modulation voltage.Experiments have demonstrated the SPR electrical modulation characteristics associated with the field distribution of the electrodes under different lasers.