A Novel Short-Cavity Laser with Deep-Grating Distributed Bragg Reflectors

Abstract

We have proposed a novel short-cavity laser with deep-grating distributed Bragg reflectors (DBRs). We monolithically fabricated a 0.98 µm InGaAs/AlGaAs device and 1.55 µm GaInAsP/InP device using electron beam lithography and a reactive ion beam etching technique. The lasing operation of both devices was achieved at room temperature. From a comparison of the threshold current from the experimental result with that from the theoretical result, the reflectivity of formed DBRs was estimated to be less than 30%. The theory also predicts that the ideal DBR exhibits a high reflectivity over 97% even with 3 periods of grating. It achieves lasing operation with a threshold current less than 100 µA using a cavity shorter than 10 µm. This high performance is realized by reducing the surface roughness and damage to etched sidewalls and improving the reflectivity of the DBR.

Photonic microstructures as laser mirrors

“…8 corresponds to the high reflection found here, which emphasizes the fact that these high-contrast structures have low losses when designed properly. Secondly, the other reported work on such deeply etched Bragg mirrors 3,4 uses ''standard'' laser material with a top cladding in excess of 1-m thickness, so the demands on the dry-etch process are considerably greater. Furthermore, and more importantly, Bragg mirrors with a high air fraction were used, so only a small part of the microstructure consists of waveguiding material.…”

“…The top, p-type contacts ͑Ni-Au͒ were defined first, followed by the sputter deposition of a 200-nm-thick layer of SiO 2 . The high-resolution pattern was then defined in 70-nm-thick electron-beam resist and transferred into the SiO 2 by reactive ion etching ͑RIE͒ using CHF 3 . Transfer of the pattern into the semiconductor was achieved by chemically assisted ion beam etching ͑CAIBE͒ using Cl 2 as the reactive gas and a beam voltage of 1500 V. Finally, the n-type contact ͑Au-Ge-Ni͒ was deposited on the back of the substrate.…”

“…1 Our semiconductor-air grating can also be regarded as the simplest realization of a photonic bandgap ͑PBG͒ structure 2 ͑or ''photonic crystal''͒, because it fulfills the requirements of high refractive index contrast and small (Ͻ100 nm) feature size that are essential for PBGs in two and three dimensions. Furthermore, this is one of the few examples [3][4][5][6] where a photonic microstructure has been created and successfully used in an active laser material. Ultimately, it will be possible to realize light-emitting devices where the active area is totally enclosed in a photonic crystal and will therefore have its emission characteristic radically altered; the high-reflectivity mirror described here is only a first, albeit very important, step towards this goal.…”

Photonic crystals in the optical regime — past, present and future

“…The best measured mirror refelectivities are around 95% [112] and the shortest lasers of this type yet realised are 42 m long, amongst the shortest edge-emitters demonstrated to date. Projected threshold currents are below 100 A and therefore as low as that of the best VCSELs [111,113].…”

“…Other types of laser that employ periodic structures for feedback are the`horizontala VCSELs that have now also been demonstrated, i.e. edge-emitting lasers with short high-re#ectivity mirror stacks [111,112]. The mirrors rely on the same principles as waveguide-based photonic microstructures, i.e.…”