TAILIEUCHUNG - Semiconductor Technologies Part 13

Tham khảo tài liệu 'semiconductor technologies part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | All-optical flip-flops based on semiconductor technologies 353 advantage of both the band-gap effect and the highly dispersive property of PCs and the high-density of state and high nonlinear property of QDs. Fig. 8. Schematic diagram of the PC-FF. A Mach Zehnder-type all-optical flip-flop developed by combining GaAs-based twodimensional photonic crystal 2DPC slab waveguides and InAs-based optical nonlinear QDs has been proposed in Azakawa 2007 . The photonic crystal-based flip-flop PC-FF schematic is shown in Fig. 8 and is based on two photonic-crystal-based Symmetric Mach Zehnder PC-SMZ switches. The principle of the PC-SMZ is based on the time-differential phase modulation caused by the nonlinear-induced refractive index change in one arm of the two interferometers. 2DPC waveguides are composed of single missing line defects while nonlinear-induced phase shift arms are selectively embedded with QDs. The mechanism of the third-order nonlinear property is an absorption saturation of the QD caused by a control pump pulse. A resultant refractive index change produces a phase shift for the signal probe pulse. A wavelength of the control pulse is set to the absorption peak of the QD while a wavelength of the signal pulse is set in the high transmission range in the 2DPC waveguide with the QD. A single PC-SMZ switch would operate as a pseudoflip-flop meaning that the on-state is limited by the carrier relaxation time in the nonlinear material 100ps in the experiment . In order to change the pseudo FF into the normal FF operation the scheme of Fig. 8 was proposed. An output signal of the PC-SMZ impinges into an optical AND element which is another PC-SMZ switch via a feedback loop where another input pulse . a clock pulse impinges. An output of the AND element is combined to the set pulse as shown in the figure. The clock pulse serves as a refresh pulse to expand the on-state period against the relaxation of the carrier while the feedback signal restricts the clock .

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