We proposed and fabricated a current-driven phase-change optical gate switch using a Ge2Sb2Te5 (GST225) thin film, an indium–tin-oxide (ITO) heater, and a Si waveguide. Microfabrication technology compatible with CMOS fabrication was used for the fabrication of the Si waveguide. The repetitive phase changing of GST225 was obtained by injecting a current pulse into the ITO heater beneath the GST225 thin film. The switching operation was observed by injecting a 100-ns current pulse of 20 mA into the ITO heater. The average extinction ratio over the wavelength range of 1,525 to 1,625 nm was 1.2 dB.

We report a multi-mode interference-based optical gate switch using a Ge(2)Sb(2)Te(5) thin film with a diameter of only 1 µm. The switching operation was demonstrated by laser pulse irradiation. This switch had a very wide operating wavelength range of 100 nm at around 1575 nm, with an average extinction ratio of 12.6 dB. Repetitive switching over 2,000 irradiation cycles was also successfully demonstrated. In addition, self-holding characteristics were confirmed by observing the dynamic responses, and the rise and fall times were 130 ns and 400 ns, respectively.

The optical diffraction limit is rigidly determined as a simple equation of wavelength λ and lens numerical aperture NA (): λ/2/NA. In this paper, we report that Ag5.8In4.4Sb61.0Te28.8 and Ge2Sb2Te5 chalcogenide thin films, which are typical of optical recording materials used in digital versatile discs (DVDs), enable a resolution of under λ/10 due to their ferroelectric properties. In the Ag5.8In4.4Sb61.0Te28.8 film it was found that this optical super-resolution can be observed between 350 and 400 °C, resulting in a second phase transition from a hexagonal (A7 belonging to ) to a rhombohedral structure of R32 or R3m. In Ge2Sb2Te5, on the other hand, the temperature range is much wider, between 250 and 450 °C, which is also due to a second phase transition from a NaCl-type fcc to a hexagonal structure.

Activation energy is one of the basic parameters used to estimate the physical and chemical features of optical and electrical phase-change (PC) films. However, its origin has not been discussed well because of insufficient understanding of the amorphous structures. In this paper, we reveal the origin of the activation energy using a GeSbTe-superlattice model and ab-initio local density approximation (LDA) calculations. The simulated energy required for transition from amorphous to crystal formation in a 9-atomic system was 2.34 eV; This is in good agreement with experimentally reported values. #

Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass material Ge2Sb2Te5 triggered by ultrashort optical pulses; however, a detailed understanding of the amorphization and damage mechanisms governed by nonthermal processes is still lacking. Here we performed ultrafast time-resolved electron diffraction and single-shot optical pump-probe measurements followed by femtosecond near-ultraviolet pulse irradiation to study the structural dynamics of polycrystalline Ge2Sb2Te5. The experimental results present a nonthermal crystal-to-amorphous phase transition of Ge2Sb2Te5 initiated by the displacements of Ge atoms. Above the fluence threshold, we found that the permanent amorphization caused by multi-displacement effects is accompanied by a partial hexagonal crystallization.

We have measured the temperature dependence of the thermal conductivities of Ge 2 Sb 2 Te 5 (GST) and ZnS-SiO 2 using a nano second thermoreflectance measurement system from room temperature to 500 -600 C. The specific heat capacities of these materials also have been determined from À130 to 500 C for GST and from room temperature to 600 C for ZnS-SiO 2 . The Debye temperature was obtained from specific heat capacity measurement. Using the obtained temperature dependence of the thermal conductivities, a temperature simulation inside a simple structured optical disk with and without considering its temperature dependence was carried out, and the difference in maximum temperature was approximate 80 C.

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Effect of constituent phases of reactively sputtered Ag O x film on recording and readout mechanisms of superresolution near-field structure diskRecording and readout mechanisms of super-resolution near-field structure disk with a silver oxide mask layerWe have simultaneously measured the carrier-to-noise ratio ͑CNR͒ as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure ͑PtO x super-RENS͒ disks. The the reflected and transmitted light intensities were found to decrease and increase, respectively, as the CNR value increased. The phase-change material AgInSbTe ͑AIST͒ used in PtO x super-RENS disks was found to exhibit a strong optical nonlinearity with respect to readout laser power. AIST becomes transparent at higher laser powers. To ascertain whether the presence of Pt nanoparticles is important to the readout mechanism, a super-RENS disk was fabricated in which the PtO x layer was replaced with a metal-free phthalocyanine ͑H 2 Pc͒ layer and the CNR of the H 2 Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtO x , we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, we also investigated the use of Si and the alloy Ge 2 Sb 2 Te 5 in lieu of AIST in a super-RENS disk and simple three layer structure disks. The super-resolution effect was observed for all disk types. Based upon these observations, we discuss the possibility of a thermal origin for the super-resolution effect in all super-resolution disks.