Volume 98, Issue 6, 15 September 2005
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2005); http://dx.doi.org/10.1063/1.2058182View Description Hide Description
The study of degradation process in high-power laser diodes, in particular, high-power laser bars, has become increasingly important as the output power of these devices continues to rise. We present a “by-emitter” degradation analysis technique, which examines degradation processes at both the bar and emitter levels. This technique focuses on understanding the dynamic mechanisms by which packaging-induced strain and operating conditions lead to the formation of defects and subsequent emitter and bar degradations. In the example presented, we examine a highly compressively strained bar, where thermally induced current runaway is found to be an important factor in the bar degradation and eventual device failure.
98(2005); http://dx.doi.org/10.1063/1.2058190View Description Hide Description
The focusing properties of a photonic-crystal (PC) slab consisting of a square lattice of rectangular dielectric rods in the air background are studied theoretically. We employ the finite-difference time-domain method to investigate the field patterns of a point source placed in the vicinity of the PC slab and find that an image can form in the opposite side of the slab in a frequency window located slightly below the fundamental band gap. We change the orientation of the rectangular rods and find that when the rods are arranged asymmetrically with respect to the surface normal of the slab, the image spot can show a vertical shift relative to the point source. The influence of the PC slab thickness on the quality of the image is also analyzed. From these simulation results and the equifrequency-surface contour analysis, we find that the dominant physical mechanism that shapes the focusing behavior of these rectangular-rod PC slabs in the ground photonic band is the self-collimation effect instead of the negative refraction effect.
Nonlinear AlGaAs waveguide for the generation of counterpropagating twin photons in the telecom range98(2005); http://dx.doi.org/10.1063/1.2058197View Description Hide Description
We have designed and fabricated a set of AlGaAs multilayer waveguides, which can serve as a source of entangled photons at through parametric fluorescence. In our scheme two counterpropagating, orthogonally polarized signal/idler modes are nonlinearly generated by a pump wave impinging on the upper surface of the waveguide. To check the compliance with design specifications on phase-matching wavelength and parametric gain, we have systematically measured effective indices and surface-emitting second-harmonic generation, respectively. This characterization allowed us to single out a nominal sample with optimum performances, which we numerically modeled for counterpropagating parametric fluorescence. We predict a pair generation efficiency (signal photons per pump photon). For a (peak), pump pulse at normal incidence, this corresponds to about 14 photons per dark count with state-of-the-art avalanche photodiodes.
Effect of structural variation on the photonic band gap in woodpile photonic crystal with body-centered-cubic symmetry98(2005); http://dx.doi.org/10.1063/1.2058171View Description Hide Description
A woodpile photonic crystal template with body-centered-cubic symmetry can be fabricated by exposing the photoresist to a four-beam interference pattern or a pattern generated through a diffractive optical element. We present detailed photonic band-gap calculations for photonicstructures obtained under various possible fabrication conditions. The woodpile photonic crystal has a full photonic band gap up to 19% of the gap center frequency when the photoresist template is converted into silicon. The tolerance of the band gap to deviations of the structural parameters from their optimum values indicates great flexibility of the holographicfabrication process.
98(2005); http://dx.doi.org/10.1063/1.2058179View Description Hide Description
We have studied the electric-field distribution in the photonic crystal(PC) concave mirror. This was done numerically and was verified in experiment. The field mapping in our experiments was performed using the Slater’s perturbation technique which was modified for nonresonant structures. The PC consists of a planar array of dielectric rods with a trapezoidal depression that forms the concave mirror. At the midgap frequency of the first stopband of the underlying photonic crystal, the mirror allows focusing to a subwavelength spot size of . The intensity is enhanced by 16 times at the focal point, as compared with the incident wave.