Enhancement Of Optical Power Research Articles

Enhancement of Optical Output Power of Light-Emitting Diodes with Photonic Crystals in InGaN/GaN Multiple Quantum Wells by Sulfide Passivation

We investigate blue light-emitting diodes (LEDs) containing photonic crystals (PhCs) that are fabricated in InGaN/GaN multiple quantum wells by plasma etching. Sulfide passivation of the etched surfaces in the LEDs using thioacetamide/ammonium solution effectively reduces the content of surface defects that induce defect-related recombination and the reverse leakage current through the sidewall surface of PhCs. Sulfide passivation enhances the optical output power of the PhC LEDs by 71% at 20 mA compared with that of planar LEDs. The large enhancement of optical power is attributed to out-coupling of confined light by the PhCs and the effective recovery of internal quantum efficiency by sulfide passivation.

Modeling of laser interactions with composite materials

We develop models of laser interactions with composite materials consisting of fibers embedded within a matrix. A ray-trace model is shown to determine the absorptivity, absorption depth, and optical power enhancement within the material, as well as the angular distribution of the reflected light. We also develop a macroscopic model, which provides physical insight and overall results. We show that the parameters in this model can be determined from the ray trace model.

Sub-Doppler mid-infrared spectroscopy of molecular ions

The technique of velocity modulation spectroscopy has recently been combined with cavity enhancement and frequency modulation methods into a technique called noise-immune cavity-enhanced optical heterodyne velocity modulation spectroscopy (NICE-OHVMS). We have implemented NICE-OHVMS with a cw-optical parametric oscillator (OPO) tunable from 3.2 to 3.9μm, and used it to record spectra of the R(1,0) and R(1,1)u transitions of the ν2 fundamental band of H3+. The high optical power and cavity enhancement enable saturation of rovibrational transitions, which allows for line center frequencies to be measured with a precision of 70kHz.

Comparison of two-dimensional periodic arrays of convex and concave nanostructures for efficient SERS templates

We describe the optical power enhancement on the surface of the 2D (two-dimensional) periodic arrays of convex and concave gold nanostructures for comparing the characteristics of the nanostructures for surface-enhanced Raman spectroscopy (SERS) templates. The optical power enhancement is due to the surface plasmon polaritons, which is calculated by the Finite-Difference Time-Domain (FDTD) method at commercially-available 532 nm pump light. A periodic array of closely-packed gold particles is defined as convex nanostructure, while a periodic array of hemispherical holes, or voids, on gold substrate is defined as concave nanostructure. The peak power enhancement factor, the average power enhancement factor and the activity rate of each structure were compared. The convex nanostructures show a strong enhancement factor in localized hotspots, while the concave nanostructures show not only the peak power enhancement factor comparable to that of convex nanostructures, but also higher spatially-averaged power enhancement factors and activity rates than those observed on the convex nanostructures, meaning that the highly enhanced near-field zone distributes densely on the substrate. We also revealed the dependence of the void diameter on the inter-void distance for the power enhancement in the concave nanostructures system, providing a guideline for the fabrication of the efficient SERS template, which shows a strong power enhancement factor with a high area density.

Enhanced light extraction in light-emitting diodes with photonic crystal structure selectively grown on p-GaN

We report on the properties of green light-emitting diodes (LEDs) with a photonic crystal (PC) structure on p-GaN. A PC structure was fabricated by the selective area epitaxy of p-GaN using SiO2 nanopillars. The electrical characteristics of LEDs with PC were not degraded and the optical output power of green LEDs with PC was increased by 70% at 20 mA of injection current compared with that of conventional LEDs without PC. This enhancement of optical output power was attributed to the improvement in light extraction efficiency by the SiO2/p-GaN PC layer on p-GaN.

Surface plasmon-enhanced light-emitting diodes using silver nanoparticles embedded inp-GaN

We demonstrate the surface plasmon-enhanced blue light-emitting diodes (LEDs) using Agnanoparticles embedded in p-GaN. A large increase in optical output power of 38% isachieved at an injection current of 20 mA due to an improved internal quantum efficiency ofthe LEDs. The enhancement of optical output power is dependent on the density of the Agnanoparticles. This improvement can be attributed to an increase in the spontaneousemission rate through resonance coupling between the excitons in multiple quantumwells and localized surface plasmons in Ag nanoparticles embedded in p-GaN.

Characterizations of GaN-Based LEDs Encompassed With Self-Aligned Nanorod Arrays of Various Distribution Densities

We designed and fabricated GaN-based light emitting diodes encompassed with self-aligned nanorod arrays of three different distribution densities. The radiation profiles show that the device with less dense nanorod distribution has the highest optical power enhancement factor. By regarding the nanorod arrays as sidewall reflectors, the enhancement is due to the light diffraction of the laterally guided mode to radiative modes in the surface normal direction. As for the densest nanorods in our experiment, the radiation profile shows a better emission directionality as the guided modes are phase matched to the radiation modes. However, they show less optical output enhancement since some of the laterally propagated light is diffracted back to p-mesa by the first several columns of nanorods.

Near-Field Optical Coupling and Enhancement in Surface Plasmon Assisted Media for Heat Assisted Magnetic Recording

As a new structure of heat assisted magnetic recording (HAMR) media, the “surface plasmon assisted HAMR (SPAH) media” was studied to increase the near-field optical power in magnetic media with the aid of the surface plasmon effect at the metal/dielectric interface. Since the near-field light penetrating a nano-slit aperture is coupled at the metal/dielectric interface of the SPAH media, surface plasmon polaritons are excited in the SPAH media, resulting in the enhancement of near-field optical power for HAMR applications. From finite differential time domain (FDTD) simulations, we found that the near-field optical intensity through the nano-slit aperture shows a value 5 times higher at the surface of SPAH media than that shown with conventional discrete track media. In addition, the spot size can be reduced by this near-field optical coupling in the SPAH media. The geometric variables of SPAH media as well as the tolerance of the head and media location were also studied to understand the optimum structure of SPAH media in consideration of the fabrication process.

Enhancement of Light Extraction Efficiency of Gallium Nitride Flip-Chip Light-Emitting Diode With Silicon Oxide Hemispherical Microlens on its Back

Silicon oxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) hemispherical microlens with the density of 8.2 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> has been formed on a sapphire substrate of gallium nitride (GaN) light-emitting diode (LED) by liquid phase deposition to enhance the light extraction efficiency. For flip-chip LED, the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> microlens exhibits 1.25 times enhancement of optical output power. In comparison of the conventional LED, there is 61% enhancement for flip-chip LED with a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> microlens.

Optical Output Power Enhancement of Gallium Nitride Light-Emitting Diodes with Microlens Array on p-GaN Layer and Wave-Patterned Sidewalls by Gas-Assisted Focused Ion Beam Etching

By using iodine gas-assisted focused ion beam etching, a gallium nitride light-emitting diode with wave-patterned sidewalls and a microlens array on a p-GaN layer was successfully fabricated without an additional lithography process. The gallium nitride light-emitting diode after gas-assisted focused ion beam etching on the sidewalls and p-GaN layer shows 24% enhancement from the sidewalls and 53% from the top surface in optical output power with an operating voltage increase of 0.06 V at 20 mA.

Trench 구조를 이용한 단일모드형 고휘도 발광소자의 광출력 증가

기저준위의 중심 피크가 <TEX>$1.3\;{\mu}m$</TEX>인 다층 양자점 구조를 사용하여 트렌치 구조를 가진 J-형태의 고휘도 발광소자 (superluminescent diodes)를 제작하였다. 도파로와 트렌치 구조 사이의 간격이 좁아지면서 광출력이 최대 20배까지 증가하였음을 확인하였다. 전류의 증가에 의한 EL 피크 측정결과 트렌치 구조를 가진 경우에 여기준위의 피크가 기저준위의 피크보다 수 십배 증가하는 것을 확인하였고, 이로부터 트렌치 증가에 의한 광출력의 증가는 양자점의 여기준위에 의한 것으로 판단하였다. J-shaped superluminescent diodes (SLD) utilizing trench structure have been fabricated on the multiple quantum dots epi-structure with its ground state energy wavelength of <TEX>$1.3\;{\mu}m$</TEX>. It was observed that optical power was drastically increased up to 20 times in comparison with that of SLD without trench structure, The electroluminescence characteristics showed that the peak intensity of excited state was several ten times higher in the SLD with trench than without trench structure. It is explained that the optical power enhancement of J-shaped SLD with trench structure resulted from the drastic increase of peak intensity of excited state.

Heating effects in tip-enhanced optical microscopy

Finite element simulations of laser-induced heating in scanning probe microscopy are presented. The electromagnetic field is first simulated for a variety of tip and substrate materials, and for air and aqueous environments. This electromagnetic field, in the end of the tip and substrate under the tip, produces Joule heating. Using this Joule heat source, steady state thermal simulations are performed. As a result of the large enhancement of optical power by the tip-substrate cavity, predicted temperature rises can be over 3 orders of magnitude higher than the values predicted without a tip present, but the optical signal can be enhanced by over 10 orders. Gold tips and substrates are predicted to give the highest optical signal for a given temperature increase.

Optical dipole trap inside a laser resonator.

We report the first realization, to our knowledge, of an optical dipole trap inside the active resonator of a laser. The concept, which is demonstrated with a CO2 laser (lambda = 10.6 microm), combines the advantages of optical power enhancement (up to 1.3-kW peak power) with the intrinsic stability of laser intensity as a result of the feedback of the active laser medium. Two kinds of trapping geometries are presented: a Gaussian trap in a transverse TEM00 mode and a boxlike transverse confinement in a superposition of transverse modes. In addition, longitudinal superlattices are created by two-frequency operation of the laser. Transfer efficiencies of up to 50% from a cesium magneto-optical trap are achieved. Storage times (7 = 0.3 s) are mainly limited by the background gas pressure. Possible sources of additional loss of atoms are discussed.

Bright, Crack-Free InGaN/GaN Light Emitters on Si(111)

Crack-free, up to 2.8 μm thick GaN-based light emitting diodes were grown by metalorganic chemical vapor deposition on 2-inch Si(111) substrates. Elimination of cracks was achieved by using two ∼12 nm thick low-temperature AlN : Si interlayers for stress reduction. A significant enhancement in optical output power was obtained by an in situ insertion of a SixNy mask. Transmission electron microscopy measurements showed a tenfold reduction in dislocation density to ∼109 cm—2 by the low-temperature AlN and SixNy interlayers, resulting in a significant increase in luminescence intensity. Vertically contacted diodes showed a light output power of 152 <$>\mmu<$>W at a current of 20 mA and a wavelength of 455 nm. Turn-on voltages around 2.8 V and series resistances of 55 Ω were obtained.

Optical dispersion eigencompensators for high-speed long-haul IM/DD lightwave systems: computer simulation

This paper proposes what is believed to be the first linear optical dispersion-compensating technique capable of more effectively compensating for dispersively chirped signal than dispersively chirp-free signal. An effective digital eigen-filter approach is introduced for designing optical dispersion eigencompensators (ODECs) for compensation of the combined effects of laser chirp and fiber chromatic dispersion at 1550 nm in high-speed long-haul intensity-modulation direct-detection (IM/DD) lightwave systems. An integrated-optic synthesis of the ODEC using planar lightwave circuit (PLC) technology is proposed to enable high-speed signal regeneration. The proposed eigencompensating scheme is shown to result in the phenomenon of optical power enhancement: the combined effects of laser chirp, fiber chromatic dispersion and ODEC group delay can re-open the receiver eye further than the ideal eye-opening. The eigencompensating approach is shown to compare favorably with the Chebyshev filter technique in both the frequency and time domains.

Spectrum control and shaping of optical pulses in optical fibre interferometers

This paper discusses the use of single-mode fibre ring interferometers for injection laser line narrowing and for enhancement of optical emission power. The efficient launching into fibre ring interferometers of multi-frequency external cavity injection laser emission, in both the c.w. and mode-locking regime, has been achieved. Matching the optical lengths of the external cavity and fibre interferometer allowed the measurement of mode width of such a laser. A method is proposed for shaping optical pulses in fibre ring interferometers from constant intensity frequency modulated emission. The mode-locking regime of all-fibre external cavity injection lasers has been achieved.