Modal properties and modal control in vertically emitting annular Bragg lasers

The modal properties, including the resonant vertical radiation, of a type of laser structures based on the annular Bragg resonance (ABR) are studied in detail. The modal threshold gains and the resonance frequencies of such lasers are obtained from the derived governing characteristic equation. Two kinds of ABR lasers, one with a π/2 phase shift in the outer grating and the other without, are analyzed. It is numerically demonstrated that, it’s possible to get a large-area, high-efficiency, single defect mode lasing in ABR lasers if we choose the kind without a π/2 phase shift in the outer grating and also a device size smaller than a critical value

A Comparative Study of Modal Properties of Surface-Emitting Circular Bragg Micro-Lasers

Modal properties of two types of surface-emitting circular Bragg micro-lasers (CBMLs) are compared. Disk CBMLs are suitable for low-threshold, high-efficiency, ultracompact laser design, while ring CBMLs are an excellent candiadate for high-efficiency, large-area, high-power applications

Supermode Si/III-V hybrid lasers, optical amplifiers and modulators: A proposal and analysis

We describe a hybrid laser structure which consists of an amplifying III-V waveguide proximity-coupled to a passive Si waveguide. By operating near the synchronism point (where the phase velocities of the individual waveguides are equal), we can cause the optical power to be confined to any of the two waveguides. This is accomplished by control of waveguides’ geometry. In the portion of the supermode resonator where amplification takes place, the mode is confined nearly completely to III-V guide thus realizing a near maximal gain. Near the output facet, the mode power is confined to the Si waveguide thus optimizing the output coupling. This is to be contrasted with approaches which depend on evanescent field penetration into the III-V medium to obtain gain

A unified theory for surface emitting chirped circular grating lasers

We develop a unified theory to analyze the modal properties of surface emitting chirped circular grating lasers. Based on solving the resonance conditions which involve two types of reflectivities of chirped circular gratings, this theory is both easy to understand and convenient to apply to different configurations of circular grating lasers. Though in a more concise format, this approach is shown to be in agreement with previous derivations which use the characteristic equations. With this unified analysis, the modal properties of circular DFB, disk-, and ring- Bragg resonator lasers are obtained and compared

Supermode Control in Integrated Hybrid Si/III-V Optoelectronic Circuits for Modal Gain Enhancement

We propose using supermode control to enhance the modal gain in integrated hybrid Si/III–V optoelectronic circuits. Numerical simulations predict that a 4-fold enhancement in modal gain can be achieved with optimal design

Surface-emitting circular DFB, disk-, and ring-Bragg resonator lasers with chirped gratings. III: gain saturation effects and above-threshold analysis

As Part III of this series, this paper focuses on an above-threshold modal analysis which includes gain saturation effects in the surface-emitting chirped circular grating lasers. We derive an exact energy relation which states that, in steady state, the net power generated in the gain medium is equal to the sum of peripheral leakage power and vertical emission power. This relation is particularly useful in checking the accuracy of numerical mode solving. Numerical simulations demonstrate the dependence of required pump level on the vertical emission power and compare the laser threshold and energy conversion efficiency under uniform, Gaussian, and annular pump profiles. A larger overlap between the pump profile and modal intensity distribution leads to a lower threshold and a higher energy conversion efficiency. Finally the dependence of required pump level on device sizes offers us new design guidelines of these lasers for single-mode, high-efficiency, high-power applications

Rational design and syntheses of 4-phosphino-catechol hybrid ligands for mixed -metal clusters

Based on the concepts of Incommensurate Symmetry-Driven Cluster Formation, an approach to mixed-metal cluster formation has been proposed and realized by using the incommensurate symmetry requirements at two different metal centers bridged by a hybrid ligand. Critical to this strategy is the proper design and synthesis of hybrid ligands with coordination sites selective towards each metal. 4-Phosphino-Catechol hybrid ligands with both hard catecholate and soft phosphine donor sites have been shown to serve such a role. Three new ligands; 4-PPh2-Catechol (H2L), 4-PH2-Catechol (H2 2) and 4-P(CH2OH)2-Catechol (H23) as well as their precursors 4-PPh2-Veratrole and 4-PH2-Veratrole have been synthesized and characterized. Several phosphine-coordinated soft-metal [Pd(II), Pt(II), Ru(II), Cr(0)] complexes of 4-PPh2-Veratrole and 4-PH2-Veratrole have been synthesized and spectrally characterized to have 2-fold, Mold or 4-fold symmetry. The 3:1 catecholate complexes of H2L, H22 and H2 3 with several trivalent and tetravalent metal cations [M(III) = Fe, Ga; M(IV) = Ti, Sn] have also been prepared and characterized as potential precursors with C3 symmetry for the stepwise aufbau of heterometallic clusters. While the X-ray structure of the Cs2TiL3 salt revealed a C 1-mer-configuration in the solid-state, room temperature and variable-temperature solution NMR studies of this and other complexes are consistent with either exclusive formation of the C 3-fac-isomer with all phosphine donor sites syn to each other, or facile fac/mer isomerization. While attempts to synthesize mixed-metal clusters from ligand 4-PH2-Catechol (H22) and 4-P(CH2OH)2-Catechol (H23) via either aufbau or self-assembly processes failed because of side reactions and/or the poor solubility of intermediates (or products), aufbau of pentametallic [M2 L6Pd3Br6]4- (M = Ti, Sn) clusters have been successful through coordination of the [M IVL3]2- (M = Ti, Sn) metalla-ligands via their soft P donor sites to C2-symmetric PdBr2 units. These clusters have been fully characterized by spectral and X-ray structural data to be C3h mesocates with Cs+ or protonated 1,4-diazabicyclo[2.2.2]octane (DABCO-H +) cations incorporated into deep molecular clefts. In addition to this aufbau approach, self-assembly of several of these [M 2L6Pd3Br6]4- (M = Ti, Sn) clusters from their eleven components (two M(IV), three PdBr2, six L) can also be accomplished under appropriate reaction conditions. Exclusive formation of this type of supramolecular species is sensitive to the nature of counterions. Alkali cations like Li+ , K+, Rb+, and Cs+ led to high-yield formation of the respective clusters while other countercations such as tetramethylammonium (TMA+), tetra-phenylphosphonium (Ph4P+), and bis(triphenylphosphoranylidene)ammonium (PPN+) gave either a mixture of products or insoluble precipitates. Extension of the aufbau assembly to produce related [M 2L6Pd3Cl6]4- , [M2L6Pd3I6] 4-, CsSn2L6Ag3 and [M2L6Cr3(CO)12] 4- clusters has also been realized

Optimal Design and Reduced Threshold in Vertically Emitting Circular Bragg Disk Resonator Lasers

We derive a comprehensive coupled-mode theory, including resonant vertical emission effects, for the analysis of nonperiodic circular Bragg lasers. We derive the governing characteristic equation for such lasers, yielding the threshold gain level and the resonance frequency. By reducing the threshold gain and maximizing the ratio of “useful signal” to the power leakage, we find optimum conditions for vertically emitting circular Bragg microdisk lasers which indicate that low-threshold operation is possible