Widely Tunable Distributed Bragg Reflectors Integrated into Nanowire Waveguides

Abstract

Periodic structures with dimensions on the order of the wavelength of light can tailor 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 are 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 nitride (GaN) nanowire waveguides. Photonic band 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 reflection coefficients in comparison with the nanowire's 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.

Modal Analysis of β−Ga2O3:Cr Widely Tunable Luminescent Optical Microcavities

“…For parallel polarization, F ¼ 4.8 and R ¼ 53% for the 740-nm peak. These values are notably higher than reflectivity in the unpatterned wire and comparable to those demonstrated in previous reports on nanowires combined with DBR structures [13,53]. It is to be noticed that values of finesse are also shown for peaks above 800 nm in Table I (see Fig.…”

“…As discussed above, x polarization essentially corresponds to E x pq modes, while y polarization essentially corresponds to E y pq modes. Reflectivities up to about 90% are obtained with the simulations in the represented range, similar to other systems based on patterned DBRs on wires [13].…”

“…Some of their functionalities are biosensors [3,5], optical filters, lasers [1], quantum memory [6], or energy harvesting [7]. Since the first fabrication of a photonicband-gap microcavity within a silicon waveguide by x-ray lithography [8], the idea is extended to micro-and nanowires, creating the periodic pattern by techniques such as electron-beam lithography [9][10][11] or focused-ion-beam (FIB) milling [6,12,13]. Optical cavities based on DBRs enhance dramatically the end reflectivity, and allow for higher quality factors and finesse values.…”

“…In this way, the patterned structure would serve at the same time as emitter, gain medium, and resonator. FIB deep etching allows the fabrication of a high-refractive-index contrast DBR, resulting in much shorter device lengths [9] than with two dielectric materials with low-refractive-index contrast [14] or than shallower FIB patterns [12,13]. On the other hand, recent work on microcavities is based many times on single-mode nanowires [1].…”

Perspectives: Nanofibers and nanowires for disordered photonics

“…61 Also, random lasers at single nanowire or nanofiber scale would also serve as highly miniaturized encrypting elements. Technologies to pattern individual light-emitting semiconductor nanowires or polymer nanofibers are already available, such as focused ion beam milling 62 and nanoimprint lithography performed at room temperature, 63 and they can be conveniently addressed to the top-down realization of single-fiber random lasers for encoding and labelling.…”