The ability to actively control the perceived color of objects is highly desirable for a variety of applications, such as camouflage, sensing, and displays. We report a completely new flexible, high-contrast metastructure (HCM) whose color can be varied by stretching the membrane. This is accomplished by annihilating the 0th order diffraction while enhancing the-1st order, a new phenomenon made possible with a large index contrast. The color perception of the HCM can thus be changed by varying its period. The structure is fabricated using silicon metastructures embedded in a flexible membrane. We experimentally demonstrate brilliant colors and change the color from green to orange (39 nm wavelength change) with a stretch of 25 nm period change. The same effect can be used for steering a laser beam, with more than 36 resolvable beam spots being demonstrated.
We report an electrically pumped hybrid cavity AlGaInAs-silicon long-wavelength VCSEL using a high contrast grating (HCG) reflector on a silicon-on-insulator (SOI) substrate. The VCSEL operates at silicon transparent wavelengths ~1.57 μm with >1 mW CW power outcoupled from the semiconductor DBR, and single-mode operation up to 65 °C. The thermal resistance of our device is measured to be 1.46 K/mW. We demonstrate >2.5 GHz 3-dB direct modulation bandwidth, and show error-free transmission over 2.5 km single mode fiber under 5 Gb/s direct modulation. We show a theoretical design of SOI-HCG serving both as a VCSEL reflector as well as waveguide coupler for an in-plane SOI waveguide, facilitating integration of VCSEL with in-plane silicon photonic circuits. The novel HCG-VCSEL design, which employs scalable flip-chip eutectic bonding, may enable low cost light sources for integrated optical links.
Optical-fi ber-based, hollow-core waveguides (HCWs) have opened up many new applications in laser surgery, gas sensors, and non-linear optics. Chip-scale HCWs are desirable because they are compact, light-weight and can be integrated with other devices into systems-on-a-chip. However, their progress has been hindered by the lack of a low loss waveguide architecture. Here, a completely new waveguiding concept is demonstrated using two planar, parallel, silicon-on-insulator wafers with high-contrast subwavelength gratings to refl ect light in-between. We report a record low optical loss of 0.37 dB/cm for a 9-µ m waveguide, mode-matched to a single mode fi ber. Two-dimensional light confi nement is experimentally realized without sidewalls in the HCWs, which is promising for ultrafast sensing response with nearly instantaneous fl ow of gases or fl uids. This unique waveguide geometry establishes an entirely new scheme for low-cost chip-scale sensor arrays and lab-on-a-chip applications.Keywords: hollow-core waveguide; high-contrast subwavelength grating; gas-sensing; silicon photonics.Conventional light guiding is achieved in a geometry where a high-refractive-index core is surrounded by a low-refractiveindex cladding. In the past decade, the opposite schemeguiding light through a low-index core surrounded by high-index cladding layers has emerged as a new tool for applications. In particular, hollow-core optical waveguides/fi bers are desirable for gas sensors and gas-based non-linear optics because of the increased lengths for light-matter interaction [1,2] , and for laser surgery to guide light in mid-to far-infrared wavelength regimes that lack low-absorption materials [3,4] . Chip-scale hollow-core waveguides (HCWs) are desirable because they enable cost-effective manufacturing of on-chip systems with the potential to monolithically integrate light sources, detectors and electronics. Chip-scale HCWs have been reported using metal [5] , distributed Bragg refl ectors [6,7] and anti-resonant refl ection layers [8,9] as the guiding refl ectors. However, their use is limited due to large optical losses because of insuffi cient refl ection.A hollow-core waveguide is best understood by the ray optics model, with an optical beam guided by zig-zag refl ections from the guiding walls [6,7,10] . The propagation loss is strongly dependent on the refl ectivity of the walls [6,7,10] due to the large number of refl ections for a given length (the number of refl ections is L λ /2 d 2 , where L is the length of the waveguide, d is the waveguide core height and λ is the wavelength of light used). Low losses can be obtained for HCW with core size in the tens of µ m [7] . However, a core of this size does not lend itself to a low bending loss or effi cient fi ber coupling. High-contrast subwavelength gratings (HCGs) have been found to offer very high refl ection for surface-normal incident light [11 -14] . Recently, we reported numerical simulation results of a one-dimensional (1D) waveguide guided by two parallel layers...
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