Jeong-Ki Hwang

Continuous room-temperature operation of optically pumped two-dimensional photonic crystal lasers at 1.6 /spl mu/m

In this letter continuous operation is realized from two-dimensional slab photonic crystal lasers at room temperature. The laser structure is prepared by wafer fusion of an InGaAsP MQW active layer with an AlAs layer that is wet oxidized into an Al/sub 2/O/sub 3/ layer subsequently. The incident threshold pump power at 0.98 /spl mu/m is 9.2 mW for a /spl sim/10-/spl mu/m-diameter hexagonal cavity lasing at 1.6 /spl mu/m.

Enhancement of light extraction from two-dimensional photonic crystal slab structures

Efficient light extraction from various two-dimensional photonic crystal slab structures is studied. By using the finite-difference time-domain method, effects of finite air-hole depth, and the cladding refractive index on the light extraction efficiency are investigated. The largest extraction efficiency is obtained in the photonic crystal slab with entirely drilled air hole patterns and large index contrast with the bottom cladding. Using InGaAsP quantum wells emitting at 1.5 /spl mu/m large enhancement of photoluminescence is observed from the slab structures with air-hole patterns fully transferred through the active medium and the bottom cladding. The photoluminescence enhancement relative to the as-grown wafer is /spl sim/8 in the oxide-supported slab and /spl sim/13 in the free-standing slab. The large light extraction enhancement results from the coupling to leaky modes above the light line of a band structure. In addition, the extraction behaviors of a triangular lattice and a square lattice are compared, and it is shown that their distinctive extraction characteristics well reflect the features of each band structure.

The smallest possible whispering-gallery-like mode in the square lattice photonic-crystal slab single-defect cavity

The smallest possible whispering-gallery-like mode (WGM) formed in a free-standing square-lattice photonic-crystal slab single-defect cavity is studied by using the three-dimensional finite-difference time-domain method. The WGM is nondegenerate and the only existing resonant mode in the transverse electric mode bandgap of the square lattice. High-quality factors are achieved from this mode by suppressing both the in-plane and the out-of-plane optical losses. By optimizing the structural parameters, a total quality factor of 18 000 and a vertical quality factor of 40 000 are obtained from the WGM. The quality factor does not decrease significantly in the presence of a current flow path at the center of the cavity due to the null of electromagnetic energy at the cavity center, which means this mode is advantageous to achieve electrically pumped photonic-crystal lasers. In addition, by combining the high-quality factor with wavelength-size small-mode volume, very high Purcell factors >8000 are achieved, the largest value ever reported. The WGM of the square-lattice single-defect cavity is promising for both cavity quantum electrodynamics research and the low-threshold microcavity laser.

Effect of nonradiative recombination on light emitting properties of two-dimensional photonic crystal slab structures

InGaAsP-based two-dimensional photonic crystal light emitting structures are fabricated by employing wafer fusion and characterized optically. The structure does not contain defect regions and the whole area of the photonic crystal is used for light generation and extraction. The effect of nonradiative recombination is studied as a function of pump power. The relative contribution of surface recombination can be as low as 10% as pump power increases since carrier recombination is dominated by Auger recombination. In spite of the large surface-to-volume ratio of the photonic crystal pattern, over four-fold enhancement of photoluminescence extraction efficiency is observed.

Resonant modes of two-dimensional photonic bandgap cavities determined by the finite-element method and by use of the anisotropic perfectly matched layer boundary condition

The finite-element approach to the eigenmode analysis of a photonic bandgap cavity by use of an anisotropic perfectly matched layer absorbing boundary is presented. This method rigorously calculates the resonant frequency, the field pattern, and the quality factor of the resonant mode of a finite-sized cavity in free space. The validity of the approach is examined through its application to two-dimensional photonic bandgap cavities. Analyses of numerical error for the resonant frequencies and the quality factor of the cavities demonstrate the accuracy and reliability of our approach, which used nonuniform grids, higher-order elements, and the perfectly matched layer. Far-field patterns of the resonant modes were obtained by simple transformation. Because the perfectly matched layer can represent the real boundary condition well, cavities of any size and shape can be analyzed with the desired accuracy.

Nondegenerate monopole mode of single defect two-dimensional triangular photonic band-gap cavity

The two-dimensional monopole mode is investigated as a candidate for a nondegenerate photonic band-gap (PBG) cavity mode. This monopole mode formed in a single defect triangular PBG cavity is truly nondegenerate and remains nondegenerate in the sense that the introduction of asymmetry does not result in splitting of the mode. Several methods to tune the resonant frequency of the mode are studied. The radii, positions, and shapes of the nearest-neighbor air holes are varied in this analysis using the three-dimensional finite-difference time-domain calculation. The quality factor of the monopole mode formed in a slab waveguide structure is found to be larger than that of the dipole mode when the shape of the nearest-neighbor holes is elliptical.

Conditions of single guided mode in two-dimensional triangular photonic crystal slab waveguides

Photonic band structure analyses are applied to study the effect of slab thickness in two-dimensional photonic crystal slab waveguides. For transverse electric-like modes of a triangular lattice of air holes, the band gap of the asymmetric photonic crystal slab with a drilled low-index cladding do not differ significantly from that of the photonic crystal suspended in air over a wide range of slab thickness. The condition of single guided mode operation is also studied and it is found that the single mode cutoff thickness changes only by a small amount as an air-hole filling ratio varies once the center of the band gap is fixed.

InGaAsP microdisk lasers on Al/sub x/O/sub y/

InGaAsP microdisk lasers are fabricated on Al/sub x/O/sub y/ by wafer fusion. Room-temperature continuous-wave operation with threshold pump power of 1.13 mW has been achieved from a 2.2-/spl mu/m diameter microdisk laser. The lasing wavelength with incident pump power redshifts at a rate of 0.28 nm/mW which shows the improved thermal characteristics due to the high thermal conductivity of Al/sub x/O/sub y/ bottom layer.

Anomalous above-threshold spontaneous emission in gain-guided vertical cavity surface emitting lasers.

Anomalously large decrease in spontaneous emission is observed in gain‐guided vertical‐cavity surface‐emitting lasers after the onset of lasing. By analyzing two‐dimensional profiles of the lasing mode and carrier density, we found that this unexpected phenomenon originates from the contraction of transverse lasing mode size. Under the condition of the constant modal gain, it is explained that the above‐threshold average carrier density could decrease in contradiction to the general understanding. Unless this anomalous effect is taken into account properly, nontrivial errors could occur in determination of the external quantum efficiency.

Computation of resonant modes of open resonators using the FEM and the anisotropic perfectly matched layer boundary condition

Ethe manufacturing of the radiating structure, E the coupling effect in between the matching line and the radiating structure. However, up to 20 GHz, the structure has dimensions which are acceptable for the purposes of incorporating it into a complete system. CONCLUSION The realization of a new surface-mounted antenna type has been shown. A comparison between a conventional structure and this new way of attaching the monopole shows the consistency of the approach. The major advantages and limitations of the concept were described; it is shown that this approach avoids the use of a connector through the ground plane, and that it is mainly suitable for broadband monopole application. We were able to achieve 7 dB of matching through a 3 GHz bandwidth. The only limitations were shown to be the manufacturing limitations if one intends to use it for a frequency higher than 20 GHz.