An optically-driven THz-modulator

Abstract

370 / CLE0'99 / THURSDAY MORNING cations of the phenomena; mapping of supercurrent distribution and magnetic-flux trap memory.(a) Two-dimensional mapping of supercurrent distributionSince the amplitude of the THz radiation excited by the fs laser pulses is proportional to the supercurrent density at the laser spot, the two-dimensional supercurrent can be obtained from the THz radiation intensity by scanning the excitation laser beam. Figure 1 shows the distribution of the THz amplitude (root of the intensity) near the bridge of the bow-tie antenna type device under a bias current of 100 mA. It is seen that the supercurrent flows near the edge of the bridge. Until now, the supercurrent distribution is obtained indirectly from the magnetic field measured by a magneto-optical film or Hall sensor. The present method provides a new direct noncontact method for measuring the supercurrent distribution.(b) Magnetic-flux trap memory We found that the THz radiation is emitted into free space from the YBCO films subjected to an external magnetic field and magneticflux trapped state without a bias current. Here, we propose and demonstrate a new type of superconducting optical flux-trap memory using the THz radiation from magnetic-flux trapped states. Figure 2(a) shows the structure of the memory cell and Fig. 2(b) shows the change of the waveform with the bias current and the laser spot position. The cell has a hole in the center of the bridge to trap the magnetic flux. The direction of the magnetic flux trapped in the hole can be changed by the combination of the bias current direction and the laser spot position. The polarity ofthe THz radiation (read-out signal) reflects the direction of the magnetic flux. By integrating this memory cell two-dimensionally, it is possible to make a new type of superconducting optical flux-trap memory.

Modulators for Terahertz Communication: The Current State of the Art

“…of the carrier signal [29]. In recent years, various THz modulators based on different materials and structures [30–32] have been reported to achieve large modulation depth, fast modulation speed, and wide modulation bandwidth [33]. Figure 2 shows a diagram of the elementary THz communication [9].…”