We report here an optically pumped deep UV edge emitting laser with AlGaN MQWs active region grown on AlN substrate by low pressure organometallic vapor phase epitaxy (LP-OMVPE) in a high-temperature reactor. The 21- period Al0.53Ga0.47N/Al0.7Ga0.3N MQWs laser structure was optically pumped using 193 nm deep UV Excimer laser source. A laser peak was achieved from the cleaved facets at 280.3 nm with linewidth of 0.08 nm at room temperature with threshold power density of 320 kW/cm2. The emission is predominantly TE polarized with a polarization suppression ratio of 24 dB. The side mode suppression ration (SMSR) is measured to be around 14 dB at 465 kW/cm2.
Over the last few years, significant progresses have been made on photonic crystal based surface-emitting lasers on silicon. Both membrane-reflector VCSELs (MR-VCSELs) and bandedge effect based PCSELs have been reported with silicon based photonic crystal cavities and hybrid integrated compound semiconductor gain materials. In this talk, we will report recent advances in these laser structures. Lasing characteristics will be reported considering different coupling efficiencies for both low and room temperature operations. The lateral cavity size effect will also be discussed in making low threshold lasers with small cavity sizes. Finally the integration of other coupling structures will be discussed for beam routing in-plane.
Work is supported by ARO, AFOSR, and NSF.
A portable imager developed for real-time imaging of cutaneous wounds in research settings is described. The imager consists of a high-resolution near-infrared CCD camera capable of detecting both bioluminescence and fluorescence illuminated by an LED ring with a rotatable filter wheel. All external components are integrated into a compact camera attachment. The device is demonstrated to have competitive performance with a commercial animal imaging enclosure box setup in beam uniformity and sensitivity. Specifically, the device was used to visualize the bioluminescence associated with increased reactive oxygen species activity during the wound healing process in a cutaneous wound inflammation model. In addition, this device was employed to observe the fluorescence associated with the activity of matrix metalloproteinases in a mouse lipopolysaccharide-induced infection model. Our results support the use of the portable imager design as a noninvasive and real-time imaging tool to assess the extent of wound inflammation and infection.
We report a novel bi-layer photonic crystal slab (PCS) Fano modulator via a coupled double-layer Si nanomembrane (SiNM) capacitor like structure. Surface normal incident light intensity modulation near 1500nm was achieved by carrier accumulation induced resonance spectral shifting. Device performance simulation suggests the opportunity for high speed modulation exceeding GHz with 20μm × 20μm device size.
Here we report the demonstration of a Si/InAlGaAs/InP PIN cavity enhanced LED around 1.5 um by using membrane
transfer method. The silicon layer is acting not only as the optical guiding layer but also the hole injection layer. The
new hybrid integrated LED could be further developed as laser source for silicon photonics.
We investigated numerically an all-dielectric semiconductor-based circular polarizer consisting of silicon helix on glass substrate. Only three turns of the dielectric helix structure provides extremely high polarization suppression ratio above 2,300:1 with almost 100% transmission. Transmission efficiency greater than 85% for one circularly polarized light is maintained for incident angles as high as 300. The influence of the various helix lattice parameters on the polarization gap and the circular dichroism is also presented.
Based on Fano resonance principles in photonic crystals, high performance broadband reflectors can be realized with 100% reflection. Applying an innovative magnetic field guided metal-assisted chemical etching (MacEtch) process, we report here high performance membrane reflectors on SOI with controlled sidewall etching and high reflection around 1550 nm. This work represents the first demonstration of magnetically guided MacEtch (h-MacEtch) of periodic arrays of discrete nanoholes of sub-micron dimensions. Such an innovative process can lead to facile formation of large area 2D and 3D nanoscale-structures, for high performance photonic crystal membrane reflectors, filters, and metamaterials.
On-chip laser beam tracking finds innumerable applications. Popularly adopted quadrant photodiodes can only detect
laser beam's angle variation up to 0.2° reliably. In this paper, a novel angle detector is designed based on grating
coupling. It consists of a grating layer on top of a silicon-on-insulator slab waveguide. The incident light is coupled into
guided modes within the waveguide via the grating layer, and then, the incident light's angle can be determined by
reading the outputs of light detectors within the waveguide. Performance of the laser angle detector in this paper is
demonstrated by full-wave finite-difference-time-domain simulations. Numerical results show that, the detectable angle
range can be adjusted by several design parameters and can reach [-4°, 4°]. The device structure in this paper can be
straightforwardly extended to two-dimensional photonic crystal configurations.
We report the detailed analysis on the phase discontinuity, field distribution, penetration depth and photon lifetime
in 1D and 2D PC mirrors. Compared to classical distributed Bragg reflectors (DBRs), these new types of PC mirrors
exhibit different phase discontinuties and slower phase changes over the high reflection bands for surface-normal
incident beams. Fabry-Perot (FP) cavity designs were carried out based on these three types of dielectric reflectors. In
PC mirror based FP cavities, we observed penetration depth of 2~4μm, which is related to the large phase discontinuity.
On the other hand, due to the tight field confinement, the energy penetration depths were ~ 0.1μm in PC mirror based FP
cavities, much lower than that in DBR based FP cavities. We will also report on the distinctively different field
distribution behaviors in these cavities, which are critical in the design of various active optoelectronic devices.
We report the design and optimization of plasmonic thin film photovoltaics (TFPV) based on single crystalline Si
nanomembranes, transferred onto ITO/plastic solar cells. Due to the presence of Fabry-Perot (FP) interferences, both
near and far field plasmonic field enhancements are modulated by thin film thicknesses. The placement of absorption
region (junction location and/or quantum well location) is critical in TFPV efficiency improvement. For TFPV thin film
thickness between 200-500 nm, we obtained field enhancement up to 100%, and cell efficiency improvement up to 35%,
assuming the standard test one sun AM1.5 radiation conditions. The efficiency enhancement for 200 nm silver particles
decreases rapidly with the increase of thin film thicknesses, while we observed less change in cell efficiency
enhancement for smaller 100 nm silver particles. Additionally, we observed a relatively large process tolerance window
for the size, shape, and placement of Ag nanoparticles, formed by the annealing of ultra-thin Ag thin films.
Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and
manufacturable, offer unprecedented opportunities for unique and novel device applications. We report here
nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic
crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with
unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on
the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration
and inorganic flexible photonics.
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