Fourier-method beam analysis for coherent vertical cavity surface emitting laser arrays.

Effective engineering and exploitation of coherently coupled vertical cavity surface emitting laser arrays will benefit from simple and fast characterization of the optical coupling and coherence. We propose a Fourier method of analyzing beam profiles as an alternative to the prior beam visibility analysis and show that the mode suppression ratio and phase between a pair of supermodes can be extracted. Our analysis enables fast quantitative determination of the array coherence and supermode characteristics.

Demonstration of enhanced side-mode suppression in metal-filled photonic crystal vertical cavity lasers.

Previously reported simulations have suggested that depositing thin layers of metal over the surface of a single-mode, etched air hole photonic crystal (PhC) vertical-cavity surface-emitting laser (VCSEL) could potentially improve the laser's side-mode suppression ratio by introducing additional losses to the higher-order modes. This work demonstrates the concept by presenting the results of a 30 nm thin film of Cr deposited on the surface of an implant-confined PhC VCSEL. Both experimental measurements and simulation results are in agreement showing that the single-mode operation is improved at the same injection current ratio relative to threshold.

Unusual strategies for using indium gallium nitride grown on silicon (111) for solid-state lighting.

Properties that can now be achieved with advanced, blue indium gallium nitride light emitting diodes (LEDs) lead to their potential as replacements for existing infrastructure in general illumination, with important implications for efficient use of energy. Further advances in this technology will benefit from reexamination of the modes for incorporating this materials technology into lighting modules that manage light conversion, extraction, and distribution, in ways that minimize adverse thermal effects associated with operation, with packages that exploit the unique aspects of these light sources. We present here ideas in anisotropic etching, microscale device assembly/integration, and module configuration that address these challenges in unconventional ways. Various device demonstrations provide examples of the capabilities, including thin, flexible lighting "tapes" based on patterned phosphors and large collections of small light emitters on plastic substrates. Quantitative modeling and experimental evaluation of heat flow in such structures illustrates one particular, important aspect of their operation: small, distributed LEDs can be passively cooled simply by direct thermal transport through thin-film metallization used for electrical interconnect, providing an enhanced and scalable means to integrate these devices in modules for white light generation.

Stochastic coupled mode theory for partially coherent laser arrays.

Partially coherent, transversely coupled laser arrays are investigated within a stochastic coupled mode formalism. Predictions of the coherence or correlation functions in both the spectral and time domains are made. It is demonstrated that the coherence properties of the system in both domains are strongly dependent on the number and intensity of coupled modes. The theory can be useful for the study of semiconductor laser arrays, particularly vertical-cavity surface-emitting laser arrays.

Printed assemblies of inorganic light-emitting diodes for deformable and semitransparent displays.

We have developed methods for creating microscale inorganic light-emitting diodes (LEDs) and for assembling and interconnecting them into unusual display and lighting systems. The LEDs use specialized epitaxial semiconductor layers that allow delineation and release of large collections of ultrathin devices. Diverse shapes are possible, with dimensions from micrometers to millimeters, in either flat or "wavy" configurations. Printing-based assembly methods can deposit these devices on substrates of glass, plastic, or rubber, in arbitrary spatial layouts and over areas that can be much larger than those of the growth wafer. The thin geometries of these LEDs enable them to be interconnected by conventional planar processing techniques. Displays, lighting elements, and related systems formed in this manner can offer interesting mechanical and optical properties.

Partial coherence in coupled photonic crystal vertical cavity laser arrays.

A classical, stochastic, coupled-oscillator model for the emergence of partial coherence in arrays of vertical cavity surface emitting lasers is presented. The spectra of the uncoupled lasers determine the second order coherence properties of the coupled system. Predictions of the resultant radiation and interference patterns are verified experimentally.

Optical properties of photonic crystal heterostructure cavity lasers.

We design, fabricate, and test photonic crystal heterostructure cavity lasers in the InP material system. A heterostructure cavity is formed by interfacing two different photonic crystals such that a dispersion maximum of the inner lattice lies within the band gap of the surrounding lattice. Feedback to slow light modes of the central region results in a lower threshold and single mode operation. The use of a kagome lattice as the inner defect area increases the semiconductor volume as well as the modal overlap with the gain material. We use a simulation technique to verify experimentally observed single mode operation as well as to quantify the effects of the heterostructure cavity formation.

Two-dimensional integration of a vertical-cavity surface-emitting laser and photodetectors for position sensing.

Noncontact long-range position sensing is desirable for a number of applications. We have designed and fabricated a monolithically integrated vertical-cavity surface-emitting laser (VCSEL) and p-type/intrinsic/n-type (PIN) photodetectors for optical position sensing. Calculations using the reflection from a periodic metallic corrugation as a position gauge indicate resolution in the submicron regime. High device uniformity is obtained using novel fabrication techniques. We observe a threshold current of 0.52 mA for the VCSELs and a detector responsivity of 0.38 A/W at 840 nm. The optical cross talk between VCSELs and detectors is also quantified.

Optical AND/OR gates based on monolithically integrated vertical cavity laser with depleted optical thyristor structure.

Latching optical switches and optical logic gates with AND and OR functionality are demonstrated for the first time by the monolithic integration of a vertical cavity lasers with depleted optical thyristor structure. The thyristors have a low threshold current of 0.65 mA and a high on/off contrast ratio of more than 50 dB. By simply changing a reference switching voltage, this single device operates as two logic functions, optical logic AND and OR. The thyristor laser fabricated by using the oxidation process and has achieved high optical output power efficiency and a high sensitivity to the optical input light.