Electromagnetic wave propagation in structured metals has attracted strong attention in wide wavelength regions from microwave to visible. We have investigated transmission properties of metal hole arrays and related structures in the terahertz region by using the terahertz time-domain spectroscopy (THz-TDS). We have found a variety of transmission properties depending on the periodic structure of metals, i. e. extraordinary transmission, large polarization conversion, large optical activity, etc. Some of the properties are explained by the surface plasmon-polariton and/or the local structure of holes.
We have experimentally demonstrated ultrashort optical pulse generation from a continuous wave (CW) laser using an external electrooptic deflector (EOD). Highly efficient EOD operating at 16.25 GHz has been realized with periodically domain-inverted LiTaO3 crystal. The shape of domain inversion region has been theoretically designed in consideration of the velocity mismatching between the modulation microwave and the light so as to realize spatially linearly-varying phase shift. The deflected CW Ar laser beam passed the Fourier transform lens, and then optical pulses were picked out at a repetition rate of 32.5 GHz through a narrow slit, which was placed at the focal point of the lens. The pulses were observed by streak camera (Hamamatsu: C5948) and the achieved shortest pulse width was estimated to be 0.9 ± 0.1 ps.
We propose a novel 10-GHz-order frequency shifter using Bragg diffraction in electro-optic traveling phase grating with slant-stripe-typed periodic domain inversion. The principle of frequency shift is same as acousto-optic frequency shifter. However, no electro-optic frequency shifter in 10-GHz-order or less using Bragg diffraction has been developed so far because the wavelength of electromagnetic wave is too long to cause Bragg diffraction. Our new frequency shifter has the feature that spatial period of the phase grating does not depend on not the wavelength of modulating microwave but the period of domain inversion. Therefore, the period of the phase grating small enough to cause Bragg diffraction is possible in the frequency range of over 10 GHz by using our new device. Simulation results from Beam Propagation Method indicates that only the first-order diffraction occurs at the output end of this device, and the optical frequency is shifted by modulating microwave frequency.