Jonathan R. Pugh

Design centering of a GaN photonic crystal nanobeam

It is well known that structures containing photonic crystal cavities produce cavity modes with extremely large Q-factors. This type of structure can be hyper sensitive to both design and manufacturing processes. Each parameter, be it structural or material will have a tolerance associated with it and the purpose of design centering is to obtain a final design that will achieve the highest yield while maintaining, not the maximum cavity Q factor available, but a value close to it. In this paper, we show how the cavity Q-factor of a photonic crystal nanobeam varies with some structural parameters using both two and three dimensional Lumerical FDTD s1.

Slot-grating flat lens for telecom wavelengths

We present a stand-alone beam-focusing flat lens for use in the telecommunications wavelength range. Light incident on the back surface of the lens propagates through a subwavelength aperture and is heavily diffracted on exit and partially couples into a surface plasmon polariton and a surface wave propagating along the surface of the lens. Interference between the diffracted wave and re-emission from a grating patterned on the surface produces a highly collimated beam. We show for the first time a geometry at which a lens of this type can be used at telecommunication wavelengths (λ=1.55 μm) and identify the light coupling and re-emission mechanisms involved. Measured beam profile results at varying incident wavelengths show excellent agreement with Lumerical FDTD simulation results.

A thermo-optically tunable flat-lens from visible to near-infrared wavelengths

We present a beam focusing flat lens for use in the mid-infrared wavelength range. The layer structure used is a 360 nm thick amorphous silicon layer on 200 nm thick aluminium on a 300 μm thick Borosilicate Glass Substrate. An aperture through the Al and a-Si layers is used to excite and enhance the coupling efficiency of a hybrid-surface plasmon polariton/waveguide mode. A second-order grating structure in the surface of the a-Si layer then scatters the propagating hybrid mode to constructively interfere in the far-field with the diffracted light from the narrow aperture to produce a narrow beam. The high dn/dT of amorphous silicon has the potential to enable thermo-optic focusing and steering.

Tunable flat lenses in the infrared

We present a beam focusing flat lens for use in the mid-infrared wavelength range. An aperture and second-order grating structure in thin gold and silicon layers is used to excite and then scatter a propagating surface plasmon polariton (SPP) to constructively interfere in the far-field to produce a narrow beam. The silicon layer acts as a mechanism for enhancing the surface plasmon polariton coupling efficiency and as a material whose refractive index can be increased by heating. We have shown through heating the silicon layer to 900 ºC, we can tune the beaming angle of the lens through −7º to 7º.

Tunable flat lenses in the mid-infrared

We present a stand-alone beam focusing flat lens for use in the mid-infrared wavelength range. An aperture and second-order grating structure in a thin gold layer is used to excite and then scatter a propagating surface plasmon polariton (SPP) to constructively interfere in the far-field to produce a narrow beam. A rapidly tunable optical parametric oscillator source is used to demonstrate how changing the wavelength of the incident light from 3.8 - 4.2 μm produces two interfering beams in the far-field caused by the scattering of the propagating SPP interfering with the incident light diffracted by the narrow (sub λ/2) aperture. We identify measured farfield patterns for varying wavelengths using the razor blade edge beam profiling method. The agreement between Finite-Difference Time-Domain (FDTD) modelled and measured results will allow the aperture/grating structures to be integrated directly onto the facets of edge-emitting lasers to dramatically reduce their beam divergence. As edge-emitting lasers have a fixed wavelength, the addition of a thin layer of material such as Silicon or Barium Strontium Titanate to the facets allows tuning by altering the SPP wavelength.

Photonic crystal defect cavity Q-factor optimization using slab thickness

Three mechanisms are studied which give rise to a high-Q L3 cavity mode in a 2D photonic crystal slab where the in-plane photonic bandgap is closed due to increased slab thickness.

Plasmonic Beam Shaping in the Mid-infrared

Simulation results, fabrication details and measurements are presented for a one-dimensional aperture and grating array for the purpose of plasmonic beam shaping of the λ=3.99μm output of an optically pumped semiconductor laser.

Design and Fabrication Techniques for a Midinfrared Photonic Crystal Defect Cavity in Indium Antimonide

Simulation results and fabrication details are presented for a two-dimensional AlxGayIn1-x-ySb photonic crystal membrane defect cavity. Peak emission is predicted at ?=3.372?m with a Q factor of 26233 for an optimized membrane thickness of 1000nm.

Design and fabrication of a mid infra-red photonic crystal defect laser in indium antimonide

This paper presents 2D FDTD modelling and prototype fabrication of a mid-infrared photonic crystal defect laser. The device is fabricated using a two stage focused ion beam process which results in improved hole profiles.