Due to the epsilon near zero (ENZ) effect, indium tin oxide (ITO) can be used in optical modulators and reduce the modulator’s size dramatically. The tunability of optical properties and the CMOS compatible capability make ITO more attractive. To study the properties of ITO thin films, several works have been done. Firstly, thin ITO thin films were obtained by magnetron sputtering with different oxygen flow rates ranging from 0 to 50sccm. Secondly, EDS was carried out to investigate the elements' content. It can be found that increasing oxygen flow rate increases the percentage of oxygen atom and Sn atom of ITO thin films. Thirdly, surface profiler was used to measure the stress value of the ITO thin films. We find that the tensile stress of ITO thin films tends to transform into compressive stress when the oxygen flow rate rises, which is worth considering in the design of devices. Fourthly, spectrometer and Hall effect measurement were applied to measure the normal incidence transmittance and electrical properties of the ITO thin films. Larger oxygen flow rate leads to the normal incidence transmittance of ITO thin films becoming larger. Hall effect measurement contributes to the conclusion that the carrier concentration of ITO thin films is able to range from 1019 to 1021 cm-3, and that when the oxygen flow rate is not too large, as the environment oxygen increases, the carrier concentration decreases and the mobility increases. This research can contribute to the design of compact ITO based optical modulators so as to achieve a better performance, which can further the integration of optical modulators.
Based on the epsilon-near-zero (ENZ) effect of indium tin oxide (ITO), we numerically demonstrate a high efficiency ITO phase/intensity modulator by exploiting ultra-thin silicon strip waveguide configuration. Heavily n-doped indium tin oxide is used as the semiconductor together with p-doped silicon and hafnium oxide (HfO2) to form a MOS waveguide. Due to the special feature of the ultra-thin silicon waveguide structure, the propagating transverse electric (TE) mode is less confined to the silicon core and penetrates deeper into the cladding layer, which will enhance the interaction between the active material and the optical mode. The combination of the ultra-thin silicon strip waveguide and ITO material exhibits high modulation efficiency together with broad optical bandwidth. When the modulator operates as a phase modulator, the effective refractive index change can reach the value 8:95x10-3 for the light wavelength λ = 1550 nm when the applied voltage is 6 V. Thus, the phase shifter length which can induce a π phase shift is supposed to be only about 97 µm, giving a corresponding VπL of 0.58 V∙mm. The effective index change even keeps > 7:32 x 10-3 with the wavelength increasing from 1300 nm to 1800 nm, indicating the broad modulation bandwidth. Meanwhile, the modulator can also operate as a variable optical attenuator or an intensity modulator. The modulation depth (MD) is about 0.074 dB/µm at 9 V when the wavelength is 1550 nm. This device confirms electrical phase shifting in ITO enabling its use in applications such as compact phase shifters, sensing, and phased array applications for LiDAR.
A compact polarization demultiplexer (P-DeMux) is proposed and characterized to enable wavelength-divisionmultiplexing and mode-division-multiplexing simultaneously. The proposed structure is composed of a microring resonator in ultrathin waveguide and two bus channels in the novel silicon nitride silica silicon horizontal slot waveguides. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cutoff. The effective index of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation Results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are ∼36.5 and 31.27 dB, and the insertion losses are ∼0.22 and 0.249 dB respectively.
A new doping approach of preparing VO2 film was proposed to significantly tune the transition phase temperature. The heavy Ni-Cr-codoped VO2 film ultra-thin layer was deposited on the pure VO2 film by reactive pulsed magnetron sputtering on the Si substrate followed with annealing. The microstructure, optical and phase transition performance of VO2 films were characterized via X-ray diffraction, UV/VIS/NIR spectrophotometer and thin film phase transition measurement system, respectively. The result indicates that the transition phase temperature of VO2 film can be reduced from 53 ℃ to 30 ℃ by easily controlling different doping time.
Due to the interesting phase transition properties, Vanadium dioxide is a promising materials for smart windows. But phase transition temperature of 68° is high for this application. Doping is an useful method for transition temperature reducing in previous works. In this paper, different thickness VO2 films were prepared by reactive pulsed magnetron sputtering, and a novel doping method was employed to reduce transition temperature. The results of XRD, Raman, transmittance spectra, and thermal hysteresis reveal that the transition temperature of un-doped samples is about 54~58°, and the increasing of phase transition amplitude and optical transmittance in visible decreasing with film thickness was observed. While for doped samples, all the transition temperatures reduced below 37°. For the thin thickness 12.5nm and 25nm, which phase transition performance deteriorated seriously. The thickness 25nm deposited for 1.5 h has the optimal performance of high optical transmittance and high IR adjustment ability.
Single quantum dot-cavity system with a deep confinement potential quantum dot is detailedly investigated, with both s- and p-exciton incoherent pump. Through gradually increasing pump rate (about 10-4=ps ∼ 12=ps), the mean photon number shows a linear-dependence on pump power, the photon probability distribution, characterized by g(2)(0), transforms from antibunching to bunching through Poisson, and the spectra go from the doublet to a singlet, the linewidth shows clear reduction in the lasing region. If we increase pump rate further, the mean photon number decreases monotonically to zero, g(2)(0) reaches its maximum value 2, and all the electrons stack at upper lasing level, indicating thermal light generation. The results show, the deep QD-cavity system under s- and p-exciton pump can generate laser although it is not an ideal coherent light, and with only p-exciton pump considered, in spite of the coherent light generated, this pump method is unreasonable to simulate the experimental conditions for the negligible energy spacing between s-exciton and p-exciton.