Fundamental research of the optical logic gates in a sub-teraherz frequency range

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The goal of this fundamental research project was to achieve a proof of principle and to establish a frequency-response model of the optical logic gate in a frequency range from 200 through 400 GHz. The outlines of the research results are summarized from (1)through (3), as follows :(1)to analytically diagnose and experimentally verify the possible output waveform distortion, under the ultrahigh-frequency operation.First, we analytically discovered, according to our original gate model, that the gate output can inherently contain weak sub-pulse components, for the first time to the investigator's best knowledge. Second, we experimentally verified the analytical discovery. Because the inherent factors which generate the sub-pulse components are supposed to exist in the recent, famous demonstration experiments done by NEC (2000-2001), Lucent Technology (2001-2002), and Technical Univ. of Eindhoven (2005-2006), respectively, their output waveforms are supposed to contain a particular amou … More nt of the distortion (i.e., the sub-pulse components). We speculate that this distortion was one of the sources of their relatively high noise level. [Now we are trying to re-design the gate structure, for significantly reducing the intensity ratio of the sub-pulse components.](2)to access the potential impacts of the secondary relaxation time constantIn contrast to the conventional speculation in the corresponding researcher's community, we discovered that the impacts of the secondary relaxation time constant of the optical logic gate can suppress (instead of enlarge) the output distortion components, depending upon the spectral filtering conditions for the output optical component. After the discovery, we designed and experimentally verified the spectral filtering conditions. [This research result (which was published in January 2006) was referred to very soon in a conference digest paper (which was published more recently in March 2006) in which the Technical University of Eindhoven renewed the record-high error-free-operation bitrate of the optical logic gate from 160 Gb/s (first achieved in 2000 by authors including the present investigator) to 320-Gb/s.](3)Ultrahigh-frequency mode-locked pulse generation with the optical logic gateInstead of directly studying the optical logic gate in a ultrahigh frequency range, we can alternatively study its spontaneous pulse generation when feedbacking the output of the optical logic gate to its input port, as the present investigator theoretically proposed in 2000. In this research project, we have made a significant progress in this research direction, as well ; we achieved 2-ps, 40-GHz mode-locked pulse generation with using the optical logic gate and the feedback loop. The value of the experimentally generated 2-ps, 40-GHz pulses is nearly equivalent to optically multiplexed 160-GHz clock signal, because the pulse width is short enough for such optical multiplexing. Based on the successful mode-locked pulse generation, we have alternatively studied several new, characteristic properties of the optical logic gate in an equivalent frequency range from 10 GHz to 160 GHz, and in a time-constant range from 2 ps to approximately 10 ps. We presented this beautiful research result to CLEO/QELS 2006 and to an industrial newspaper in May 2006. Less