Nanoelectromechanical systems could have applications in fields as diverse as ultrasensitive mass detection and mechanical computation, and can also be used to explore fundamental phenomena such as quantized heat conductance and quantum-limited displacement. Most nanomechanical studies to date have been performed in the frequency domain. However, applications in computation and information storage will require transient excitation and high-speed time-domain operation of nanomechanical systems. Here we show a time-resolved optical approach to the transduction of ultrahigh-frequency nanoelectromechanical systems, and demonstrate that coherent control of nanomechanical oscillation is possible through appropriate pulse programming. A series of cantilevers with resonant frequencies ranging from less than 10 MHz to over 1 GHz are characterized using the same pulse parameters.
We have fabricated and tested planar reflectors exhibiting an omnidirectional stop band centered near 1750 nm wavelength. The reflectors are comprised of multiple layers of Ge33As12Se55 chalcogenide glass and polyamide-imide polymer. Glass layers were deposited by thermal evaporation and polymer layers were deposited by spin-casting. Thin film stacks of up to 13 layers showed good planarity and adhesion, which we attribute to the well-matched thermo-mechanical properties of the materials. The optical properties of the reflectors were tested in both transmission and reflection, and the results are in good agreement with theoretical predictions. Relatively low-temperature processing steps were employed, making these reflectors of interest for integrated optics.
The potential for a dielectric thin-film stack to provide omnidirectional reflection (near unity reflectance for all polarization states and incidence angles, over a finite range of wavelengths) was recognized only recently. [1][2][3] Nevertheless, such one-dimensional omnidirectional dielectric reflectors (ODRs) can provide some of the functionality promised by three-dimensional photonic crystals, while being comparatively simple to fabricate. They have been applied to the construction of low-loss hollow-core fibers [4] and integrated waveguides, [5,6] and to increase the emissivity of light-emitting diodes (LEDs).[7]An ODR is predicated on a pair of compatible dielectric materials that have transparency in the wavelength range of interest and sufficiently different refractive indices. For example, if the lower index material has a refractive index of n ∼ 1.5, an omnidirectional stop band can arise when the higher index material has n ∼ 2.3 or greater. It is an experimental challenge to identify material combinations that satisfy the refractive-index requirement, while also enabling practical implementation of a thermomechanically robust, stable, and uniform multilayer stack. Typical ODRs reported to date [1,2,[8][9][10] have employed a glass or semiconductor substrate as a base. However, ODR-based fibers have also been developed [11,12] and the fabrication of substrateless planar ODR mirrors (for the mid-IR) was reported anecdotally. [13] Of related interest, freestanding polymer-based optical filters were conceived several decades ago.[14] Moreover, efficient wide-angle mirrors based on highly birefringent polymers [15] are commercially available [16] in sheets ca. 50 lm thick. Freestanding optical filters have numerous potential applications, including reflectors for flexible organic LEDs, [17] laminates or wraps for light recycling in displays, [16] membranes in optomechanical light modulators, [18] pellicle-type beam splitters and filters, and sails on spacecraft propelled by radiation pressure. [19] Key to these applications is the flexibility, toughness, and fracture resistance of polymers, even in micrometer-scale thin sheets. These same properties motivate research and development of flexible electronic [20] and photonic [21,22] circuitry, using organic and sufficiently thin inorganic films.In this Communication, we describe a straightforward process for fabricating compliant but mechanically tough freestanding mirrors using commercially available chalcogenide glass and polymer materials. High-refractive-index contrast (Dn ∼ 1) between the materials enables near-unity, omnidirectional reflection from membranes less than 3 lm thick. The reflectors were successfully laminated (using surface-tension forces) on various flat and curved surfaces. Even after handling, bending, and re-lamination, the optical response of the reflectors was in excellent agreement with theoretical predictions. Optical filter response can be customized by manually stacking pieces of the mirror, and optomechanical tuning by stretchi...
We describe the fabrication and characterization of omnidirectional reflectors based on silver-doped chalcogenide glass and polymer. We deposited periodically alternating layers of thermally evaporated Ge33As12Se55 chalcogenide glass, sputtered silver, and spun-cast polyamide-imide polymer. The silver was subsequently dissolved into each adjacent chalcogenide glass layer, either by exposing the multilayer to visible light (photodoping) or by heating the sample. The resultant silver concentration within the chalcogenide glass layers is estimated to be ~20 at. %. Silver doping red-shifts the band edge of the glass, and produces an increase of ~0.3-0.4 in the refractive index. The glass retains good transparency in the near infrared after doping, and the technique enables the omnidirectional bandwidth to be increased from ~100 nm to ~200 nm in the 1550 nm wavelength region.
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