Summarize what you understand from this article. Anthony Fu^+d, Hanwei Gao^+8, 1

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Summarize what you understand from this article.

Anthony Fu^+d, Hanwei Gao^+8, 11 Petar Petrov, ^+ and Peidong Yang^8, 'Department of Chemistry and Department of Materials Science and Engineering University of California, Berkeley, California 94720, United States Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States Department of Physics, Florida State University. Tallahasee, Florida 32306, United States Periodic structures with dimensions on the order of the wavelength of light can tail or and improve the performance of optical components, and they can enable the creation of devices with new functionalities. For example, distributed Bragg reflectors (DBRs). which arc created by periodic modulations in a structure's dielectric medium, are essential in dielectric mirrors. vertical cavity surface emitting lasers, fiber Bragg gratings, and single-frequency laser diodes. This work introduces nanoscale DBRs integrated directly into gallium nitiride (GaN) nanowire waveguides. Photonic hand gaps that are tunable across the visible spectrum are demonstrated by precisely controlling the grating's parameters. Numerical simulations indicate that in-wire DBRs have significantly larger rejection coefficients in comparison with the nanowires end facet. By comparing the measured spectra with the Simulated spectra, the index of refraction of the GaN nanowire waveguides was extracted to facilitate the design of photonic coupling structures that are sensitive to phase-matching conditions. This work indicates the potential to design nanowire-based devices with improved performance for optical resonators and optical routing. KEYWORDS: Distributed Bragg Reflectors, nanowire, photonics, gallium nitride, waveguides, selected-area spectroscopy. Semiconductor nanowires have drawn considerable interest as a platform for miniaturized photonics grown bottom-up^1-3. Their one-dimensional geometry mimics conventional photonic platforms that use large-aspect-ratio structures such as waveguides and optical cavities id a highly compact geometry. This resemblance has inspired researchers to explore the use of semiconductor nanowires tor miniaturized lasers, ^4, 5 optical routing^6, 7 and other optoelectronic components.^8-10 Furthermore, there has been considerable effort in nanowire research to control the size^1' shape, ^1' and composition^13-15 of nanowires for photonic applications. In particular, the ability to manipulate the photonic structure of nanowires has enabled the precise control of their optical properties for improved optoelectronic functions. For example, anally coupling nanowire cavities introduces extra degrees of freedom to manipulate the lasing modes in semiconductor nanowires tor single-mode lasing and yields a significant reduction in the lasing threshold at room temperature.^16. Periodic structures arc indispensable tor modem optics and optoelectronics. The optical properties of a film can be precisely controlled through careful selection of its material properties and optical structure, which has enabled innumerable inventions in optics and photonics. The integration of periodic structures, such as DBRs, ^17, 18 into a nanowire can improve the performance and enable additional photonic functionalities in these compact structures.^19, 20 Previously, there have been reports of embedding nanowires into separate periodic structures to achieve a Pure ell enhancement and photonic band gaps in hybrid micro resonator structures^21, 22 Recently, the fabrication of polymer nanofiber-based distributed feedback (DFB) lasers was demonstrated using nanoimprint lithography.^23. The ability to fabricate DBRs in a semiconductor nanostructure is also of considerable interest because inorganic semiconductors generally exhibit favorable transport properties, material stability, and fabrication infrastructure for compact optoelectronics. Tuned properly, these architectures can be used to select specific wavelengths for optical routing single-mode lasing. and potentially lower the lasing threshold of nanowire-based lasers.^17, 18. In this work, the integration of DBR structure into GaN nanowires is demonstrated with photonic stopbands that are broadly tunable across the visible spectrum. Numerical simulations based on finite element methods were used to guide the design of the DBR geometry and to analyze the results from the experimental measurements. These DBR-integrated nanowires are promising for compact photonic devices. A method has also been developed to measure the index of retraction of a GaN nanowire waveguide, which can aid

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Periodic structure (Periodic structure is made of an infinite or finite repetition of a unit cell in one, two or three dimensions) with dimensions on the order of the wavelength of light can tailor (adapt for a particular purpose) are found to improve the performance and also help in introducing new functionalities. These periodic structures are indispensible for modern day optoelectronics. Semiconductor nanowires are one such periodic structure with one-dimensional geometry.

Examples of such structures are distributed Bragg reflectors (DBRs) which are essential in dielectric mirrors, fiber Bragg grating, surface emitting lasers and single frequency laser diodes. The introduction DBRs into a nanowire are found to improve the performance and enable introduction of additional functionalities to compact structures like optical films. Fabrication of DBRs in inorganic semiconductor nanostructure is of considerable interest because of their transport properties, material stability and fabrication infrastructure for compact optoelectronics. Proper tuning of thee architectures can be used to select specific wavelengths of light for optical routing and single mode lasers.

The present article introduces nanoscale DBRs integrated directly into gallium nitride (GaN) nanowire waveguides. Photonic band gaps that are tunable across the visible spectrum are demonstrated by precisely controlling the grating’s parameters. A method has also been developed to measure the index of refraction of a GaN nanowire waveguide. The present article on GaN nanowire waveguides thus indicates the potential to design nanowire-based devices with improved performance for optical resonators and optical routing.

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