A strictly non-blocking wavelength-selective photonic crystal (PC) router for mesh-based optical networks-on-chip (ONoC) that employs a novel crossed-waveguide structure as the routing basic unit is designed. The proposed router only consists of eight crossed-waveguides without the need for a ring resonator, and its entire structure is symmetrically distributed on the top, bottom, left, and right. When implementing the non-blocking routing function, the signal-to-noise ratio is 17.84 to 20.06 dB, and the insertion loss and crosstalk are 0.36 to 0.88 dB and (−50.3) − (−8.03) dB, respectively, when implementing the wavelength-selective routing function. Compared with existing non-blocking wavelength-selective PC routers used in ONoCs, this router not only exhibits strict non-blocking routing transmission characteristics but also has prominent features of a simple structure and easy implementation due to the absence of ring resonators. Furthermore, the proposed structure possesses good scalability and can be easily expanded to realize higher radix non-blocking optical routing systems, which have broad application prospects in ONoC.
Laser heat-mode lithography is very useful for the fabrication of micro/nanostructure-based optical elements. In laser heat-mode lithography, the pattern structures need to be transferred to the substrates by wet-etching or dry-etching method. In this work, a lift-off method for the pattern transfer in laser heat-mode lithography was proposed and studied. A desirable undercut profile was obtained by manipulating the thermal field profile of laser heat-mode exposure, and a lift-off of Cr layer with a thickness of 80 nm on a quartz glass substrate was achieved. The results indicated that laser heat-mode lithography with lift-off process is an effective method to transfer the pattern structures to Cr layer and generate a Cr-based hard mask, which is useful for the fabrication of micro/nanostructure-based optical elements.
The GeSbTe (GST) thin films are usually used as optical and electronic data recording materials. In this work, the GST thin films were used as both negative and positive resists, and the positive and negative tone pattern structures were fabricated on the GST thin films, accordingly. The GST films were first deposited on the substrate, then the laser exposures were conducted through a focused laser beam spot. For negative resist, a Tetramethyl ammonium hydroxide (TMAH) was used as developing solution. For positive resist, (NH4)2S was used as developing solution. The structure heights of positive and negative resists are 53 nm and 180 nm were obtained, respectively. This work provides an effective method for fabricating the micro/nanostructures of optical and electronic elements.
The thermal transmission process induced by single-shot femtosecond laser pulses in Sb70Te30 phase change thin films with or without a Ag thermal-conductive layer was studied numerically with a two-temperature model. The distribution of electron and lattice temperatures was calculated by a one-dimensional finite difference method. The different temperature evolution characteristics on different time scales (from several picoseconds, to tens of picoseconds and to several nanoseconds) are discussed based on the electron-phonon coupling theory. The influence of a special point in the lattice temperature evolution curves on the crystallization time of phase change thin films is analyzed. The results will be helpful to the deeper understanding of the ultrafast phase transition mechanism of phase change memory materials.
The Femtosecond laser pulse induced phase transition dynamics of Cr-doped Sb2Te1 films was studied by real-time reflectivity measurements with a pump-probe system. It was found that crystallization of the as-deposited CrxSb2Te1 phase-change thin films exhibits a multi-stage process lasting for about 40ns.The time required for the multi-stage process seems to be not related to the contents of Cr element. The durations of the crystallization and amorphization processes are approximately the same. Doping Cr into Sb2Te1 thin film can improve its photo-thermal stability without obvious change in the crystallization rate. Optical images and image intensity cross sections are used to visualize the transformed regions. This work may provide further insight into the phase-change mechanism of CrxSb2Te1 under extra-non-equilibrium conditions and aid to develop new ultrafast phase-change memory materials.
Laser thermal lithography has been proposed for a few years, which has the advantages of breaking through the optical diffraction limit, operation in far-field and in air, and low production cost. In this paper, a new hydrazone metal complex is used as the laser thermal lithography material due to its feature of the one-step fabrication of micro/nano structure without mask and wet-etching process. Based on the laser thermal lithography method, super resolution nano-information pits are directly written on the surface of hydrazone metal complex thin films. Pits with a minimum feature size of about 79 nm are successfully obtained, which is only about 1/7 of the writing spot size. Moreover, the reactive ion etching method can be applied to transfer the pits onto a silica substrate. These results suggest the potential applications of the new material in high density optical data storage and semiconductor industries.
As the demand for ultrahigh density information storage continues to grow, recording mark size of several tens nanometer which is smaller than the optical diffraction limit is required in optical memory. Functional film super-resolution technique is one of practical approaches to overcome the optical diffraction limit. Optical constants are important parameters to optical films as super-resolution masks. In this paper, the influence of film thickness on optical constants of antimony-based bismuth-doped super-resolution mask layer is investigated. The structure of the samples with different thickness was studied by X-ray diffraction. The transmission spectrum was measured by spectrophotometry. The optical constants of the films in the range of 300-800 nm were measured by spectroscopic ellipsometry. The results show that the structure of the film transforms from amorphous state to crystal state when the thickness increases from 7 nm to 300 nm. In the range of 300-800 nm, the refractive index and extinction coefficient increase with increasing wavelength. The transmission decreases rapidly when the thickness increases from 7 nm to 30 nm. The influences of film thickness on optical constants are more significant in the thickness range of 7-50 nm than that in the thickness above 50 nm.
KEYWORDS: Silver, Nanoparticles, Near field, Near field optics, Diffraction, Finite-difference time-domain method, Surface plasmons, Super resolution, Optical resolution, Optical storage
Super-resolution near-field structure (super-RENS) is a functional structure which can overcome the optical diffraction limit and play an important role in nano scale optical data storage. The resolution enhancement of the scatter-type super- RENS optical disk is related to the localized surface plasmon of silver particles dissociated from the AgOx layer and its near-field interaction with the recording pits in the phase change layer. Recently, a new method for optically synthesizing silver nanoparticles in a phase change matrix has been proposed by our group [Mater. Chem. Phys. 135, 467-473(2012)], which provides a potential approach to forming a more simple plasmonic recording structure than the traditional AgOx-type structure. In this paper, field distribution of silver-nanoparticles-embedded Ge2Sb2Te5 phase change recording pits is numerically analyzed by the finite-difference time-domain (FDTD) method. The optical contrast enhancement capability is confirmed for the optimized recording structures when the pit size is smaller than the optical diffraction limit.
The crystallization properties of as-deposited amorphous AgInSbTe thin films irradiated by single-shot picosecond laser pulses were studied using in-situ transient optical reflectance and electrical resistance measurements with nanosecond resolution. It was found that the real-time optical and electrical signal responses were different under the same pumping conditions. The optical signals showed a multistage crystallization process with a total time of approximately 150 ns, while the electrical signals showed a negative exponential trend decreasing to the final stable state within about several microseconds. A resistor–capacitor model was constructed to explain this delayed electrical response. The fluencedependent evolution dynamics maybe implied a non-fully crystallization process under ultra-short pulse stimulation.
Crystallization dynamics of as-deposited amorphous AgInSbTe and SiSb thin films induced by picosecond laser pulses
with different fluences were studied using time-resolved reflectivity measurements. The transient phase change process
during crystallization was discussed and compared.
KEYWORDS: Near field, Super resolution, Optical discs, Near field optics, Thin films, Binary data, Laser irradiation, Refractive index, Solids, Nanophotonics
Functional nano-heterostructures are of great interests in nano-photonics applications. A new strategy to obtain
local nano-heterostucture formed by laser-induced eutectic transition is proposed in this paper. Numerical
simulations demonstrate that periodic eutectic microstructures formed on binary eutectic alloy thin film during
irradiation of a laser beam can result in a prominent near-field enhancement. Results can help to understand the
microscopic mechanism of eutectic-binary-alloy-type super-RENS disk from a near-field optics view.
KEYWORDS: Bismuth, Super resolution, Antimony, Near field, Data storage, Optical storage, Gallium nitride, Current controlled current source, Sputter deposition, Silver indium antimony tellurium
Super-resolution near-field structures (super-RENS) with antimony bismuth mask layer (Sb1-xBix, X =0, 0.1, 0.2 and 0.9) were fabricated by magnetron sputtering. AgInSbTe and ZnS-SiO2 were used as recording layer and dielectric layer respectively. Static recording tests with and without super-RENS were carried out using static recording tester whose laser wavelength is 406.7 and numerical aperture is 0.8. The recorded marks were observed by atomic force microscopy (AFM). The influences of Bi proportion in the films on the super-resolution recording properties were investigated.
Phase transition kinetics of Sb2Te3 phase change thin films was investigated in this paper. Sb2Te3 thin films, with
thickness of ~100nm, were deposited on K9 glass substrates by DC magnetron sputtering with an alloy target. The
crystallization kinetics of Sb2Te3 thin films under isothermal and non-isothermal annealing was analyzed by a
home-made in situ temperature-dependent reflectivity tester. From the heating rate dependences of phase transition
temperatures, the activation energy was derived. The obtained values of the Avrami indexes indicate that a two
dimension growth crystallization mechanism is responsible for the amorphous-crystalline transformation of Sb2Te3
phase change thin films. Although phase transition of Sb2Te3 thin film is confirmed to be continuous in a larger
temperature range, but short laser pulse can easily trigger its crystallization process and form clear and confined
crystalline marks.
Sb-rich SiSb thin film was recently reported as a promising phase change meromy material. In this paper, optical and
structural properties of as-deposited amouphous and laser-annealed crystalline Sb-rich SiSb thin films are studied and
compared with pure Sb thin film. Sb and Si15Sb85 thin films were deposited on polycarbonate substrates by magnetron
sputtering. Laser initialization in pure Sb and Si15Sb85 thin films were performed with phase-change optical disc
initializer. Reflectivity Spectrum and XRD analysis were performed on as-deposited and initialized Sb and Si15Sb85 thin
films. The influence of Si doping on its optical and structural properties are discussed and qualitatively explained by a
distorted structure model.
Super-resolution read-only optical disks using different mask materials and stack structures were prepared by using rf sputtering method, and then dynamic readout properties were measured, our results show that by using Si as the mask material the signal-to-noise ratio can reach about 35dB, and the density can be increased both in the linear direction and in the track direction, while by using AgInSbTe as the mask material the optimum signal-to-noise ratio is about 40dB, which is very close to the practical application level.
To break through the diffraction limit by optical super-resolution thin films is very attractive for the applications in optical and photonic devices. Large optical nonlinearities, such as optic-thermal nonlinearity and the third order optical nonlinearity, of optical thin film materials are very critical to super resolution optical storage, imaging, lithography, and the enhancement of the throughput of the optical near-field nano-aperture. The super-resolution effect in optical thin films or film structures under laser irradiation is focused in this paper. And its applications, especially in super high density optical storage are analyzed and discussed.
Static recording characteristics of super-resolution near-field structure with bismuth (Bi) mask layer and antimony (Sb) mask layer were investigated and compared. The experimental results show that Bi mask layer can also concentrate energy into the center of a laser beam at a low laser energy input similar to Sb, which may be because that Bi film exhibits giant nonlinearity at low laser intensity. The direct observation of laser-recording marks may help better understand the working mechanism of the super-RENS, super-resolution ablation, and other nonlinear switching phenomena.
According to the change of refractive index of Sb thin film with temperature and the radial distribution of temperature within the spot, we can consider the spot irradiated by a Gaussian beam as a phase-modulated screen. Based on Fresnel-kirchhoff diffraction theory, a Gaussian diffraction model which can compute the intensity from far field has been set up. Using this model we can study the nonlinear change of mask layer samples induced by different reasons. A numerical calculation of the transmittance through an Sb-type super-resolution near-field structure was carried out as an example. The Gaussian diffraction model, which is similar to the far field detection process in the optical disk system, is very useful for analyzing the photothermal-induced local structure change of thin films in phase-change and super-resolution optical disks.
Two novel read-only memory (ROM) disks, one with an AgOx mask layer and the other with an AgInSbTe mask layer, are proposed and studied. The AgOx and the AgInSbTe films sputtered on the premastered substrates with pit depths of 50 nm and pit lengths (space) of 380 nm are studied by atomic force microscopy. Disk readout measurement is carried out using a dynamic setup with a laser wavelength of 632.8 nm and an object lens numerical aperture (NA) of 0.40. Results show that the superresolution effect happens only at a suitable oxygen flow ratio for the AgOx ROM disk. The best superresolution readout effect is achieved at an oxygen flow ratio of 0.5 with the smoothest film surface. Compared with the AgOx ROM disk, the AgInSbTe ROM disk has a much smoother film surface and better superresolution effect. A carrier-to-noise ratio (CNR) of above 40 dB can be obtained at an appropriate readout power and readout velocity. The readout CNR of both the AgOx and AgInSbTe ROM disks have a nonlinear dependence on the readout power. The superresolution readout mechanisms for these ROM disks are analyzed and compared as well.
Subphthalocyanine (SubPc) thin films exhibit attractive characteristics in high-density optical storage applications. We have realized red-light (632.8 nm) recording on SubPc thin films previously. In this paper, novel subphthalocyanine thin films were developed by vacuum evaporation and spin-coating method. Their static and dynamic green-light (514.5 nm) recording performance were studied using self-developed short-wavelength optical disk testers. Sufficient reflectivity, reflectivity contrast and CNR can also be obtained at 514.5 nm if an appropriate multilayer structure was applied. It spread the dyes' traditional operating wavelength and provided a new clew for double-wavelength (even double short-wavelength) recording/reading and choosing short-wavelength recording materials.
Nickel phthalocyanine thin film was prepared by vacuum deposition, the absorption and transmission spectra, the thermal stability of the film were reported. And the static optical recording properties of the thin film were investigated with a self-developed short-wavelength optical tester with high NA objective lens. The results show that this film occupied suitable absorption and transmission properties for short-wavelength (514.5 nm) optical recording, excellent thermal stability and outstanding thermal decomposition characteristics. And high reflectivity contrast was obtained at low writing power and short writing pulse width using the Ar+ laser (514.5 nm) irradiation. The results indicate that metal phthalocyanine is not only qualified for traditional near infrared optical recording medium of CD-R, but also a promising candidate for the recording medium of green-light DVD-R.
Organometallic photochromic complexes, which are more stable than those traditional pure organic photochromic compounds, have a wide variety of potential applications in high-density optical storage. In this paper, Ag-TCNQ and Cu-TCNQ thin films were prepared by physical vapor deposition method. The proportion dependence of the spectral and optical properties of Ag-TCNQ thin films were studied and discussed. Multilayer film configuration was designed and prepared for optical memory study and its short-wavelength (514.5 nm) photochromic characteristics were reported. A recommendation of application of Metal TCNQ complexes for high-density and super high density optical storage was proposed as well.
KEYWORDS: Optical discs, Reflectivity, Multilayers, Refractive index, Optical design, Near field optics, Crystals, Thin films, Digital video discs, Error analysis
The optical constants of each layer in the optical disk are assumed to be constant regardless of film thickness in conventional optical design and optimization of the multilayer structures. However, this assumption is not valid when the layer becomes very thin for its discontinuity. As we know, very thin layers (< 50 nm) are included in the high-density and super-high density optical disks, such as DVD-RAM, high-density DVD (HD-DVD), and super-resolution near-field structure (Super-RENS). In this paper, the thickness error sensitivity factor for dielectric optical multilayer was derived from the optical matrix, and the change of optical constant of the very thin layers with the film thickness variation is analyzed at the same time. The effect of the thickness error and corresponding refractive index change on the reflectivity or reflectivity contrast of the optical disk multilayer was analyzed with a numerical calculation. As an example, we made a structure optimization for the 4-layer DVD-RAM systems with GeSbTe and AgInSbTe phase-change materials as recording media. These results are significant in improving the accuracy of optical design and thermal simlation of high density and super-high density optical disks.
The film thickness of optical disk multilayer is difficult to be precisely controlled in the actual coating process. The thickness error becomes a main factor influencing the optical characters of the film system. The thickness error sensitivity factor of dielectric optical multilayer is derived from the optical matrix in this paper. The applications to recordable and phase-change optical disk systems are given. The effect of the thickness error on the reflectivity or reflectivity contrast of the optical disk multilayer is analyzed with a computer numerical calculation. The sensitivities to thickness error for different layers or in different film-thickness ranges are compared and discussed. A sketchy method of defining allowable thickness error is given. These results have guidance significance to the design of film layer and the optimization of coating technology in the optical disk systems.
Phthalocyanines (Pcs) are widely investigated compounds for optical storage applications, especially used as recording media of CD-recordable. As a novel class of Pc-related compounds, Subphthalocyanines (SubPcs) share many of the excellent properties of Pcs such as thermal and chemical stability and at the same time have some specific characteristics due to their smaller number of coordinated ring and near-planar cone-shaped geometry. The spectral and optical properties of a new trinitro-substituted SubPc have been studied. Films were prepared either by vacuum evaporation or spin coating from a solution in poly(methylmethacrylate) (PMMA). The UV-vis spectra (absorption, reflection, transmission) and optical constants (refractive index, extinction coefficient) of the sublimed film were measured by a spectrophotometer and an ellipsometer respectively. We also measured the static optical recording performance of this film with a thin Al reflective layer on it. These results demonstrated that SubPc has a strong and broad absorption region near 600 nm and it will be a promising candidate for short-wavelength optical recording (such as DVD-R) if the high-quality films can be got.
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