Giora Griffel

Excitation of resonances of microspheres on an optical fiber

Morphology-dependent resonances (MDRs) of solid microspheres are excited by using an optical fiber coupler. The narrowest measured MDR linewidths are limited by the excitation laser linewidth (<0.025 nm). Only MDRs, with an on-resonance to off-resonance intensity ratio of 10(4), contribute to scattering. The intensity of various resonance orders is understood by the localization principle and the recently developed generalized Lorentz-Mie theory. The microsphere fiber system has potential for becoming a building block in dispersive microphotonics. The basic physics underlying our approach may be considered a harbinger for the coupling of active photonic microstructures such as microdisk lasers.

Enhanced Coupling to Microsphere Resonances with Optical Fibers

Morphology-dependent resonances (MDRs) of polystyrene microspheres were excited by an optical fiber coupler. For optical elimination of the air–cladding interface at the optical fiber coupler surface, the microsphere was immersed in an index-matching oil. MDRs were observed, even though the relative refractive index between the microsphere and the oil was only 1.09. The observed MDR spectra are in good agreement with the generalized Lorenz–Mie theory and the localization principle. The scattering efficiency into each MDR is estimated as a function of the impact parameter by means of generalized Lorenz–Mie theory.

Morphology-dependent resonances of a microsphere–optical fiber system

Morphology-dependent resonances of microspheres sitting upon an index-matched single-mode fiber half-coupler are excited by a tunable 753-nm distributed-feedback laser. Resonance peaks in the scattering spectra and associated dips in the transmission spectra for the TE and TM modes are observed. We present a new model that describes this interaction in terms of the fiber-sphere coupling coefficient and the microspheres intrinsic quality factor Q(0). This model enables us to obtain expressions for the finesse and the Q factor of the composite particle-fiber system, the resonance width, and the depth of the dips measured in the transmission spectra. Our model shows that index matching improves the coupling efficiency by more than a factor of 2 compared with that of a non-index-matched system.

Microring resonators vertically coupled to buried heterostructure bus waveguides

The authors demonstrate all epitaxial semiconductor microring resonators vertically coupled to buried heterostructure (BH) bus waveguides for the first time. Planar vertically stacked waveguides are successfully grown on BH mesas by conducting a two-step regrowth process. This approach is potentially important for any buried waveguide technology where subsequent surface planarity is required. The measured transmission spectra show resonance dips (1.55/spl sim/1.60) /spl mu/m with quality factors, extinction ratios, and free spectral ranges of 2500-3.5 dB, and /spl sim/11 nm, respectively, for 10-/spl mu/m-radii microrings.

Coupled mode formulation for directional couplers with longitudinal perturbation

A grating-assisted directional coupler is investigated using an improved coupled-mode formulation for multi-waveguide systems with longitudinal perturbation. This approach is capable of handling three-dimensional structures as well as a complex index of refraction and nonisotropic media. The case of two coupled channel waveguides is closely examined, and a numerical analysis is carried out for several cases of slab structures. >

Frequency response and tunability of grating-assisted directional couplers

The spectral properties of grating-assisted directional couplers are studied using an improved coupled mode formulation. Key parameters for the design of these structures, such as the grating period, the coupling length, and other structural parameters, are calculated. The frequency response, the filter bandwidth, and the tuning range are analyzed. The technique is used to examine a specific case of InGaAsP-InP tunable filters, and the results are compared to a prior experiment. >

Monolithic integration of a resonant tunneling diode and a quantum well semiconductor laser

A monolithic integration of a double barrier AlAs/GaAs resonant tunneling diode and a GaAs/AlGaAs quantum well laser is reported. Negative differential resistance and negative differential optical response are observed at room temperature. The device displays bistable electrical and optical characteristics which are voltage controlled. Operation as a two‐state optical memory is demonstrated.

Optically controlled resonant tunneling in a double‐barrier diode

The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double‐barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current‐voltage characteristic of a double‐barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak‐to‐valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three‐layer model.

Two-section gain-levered tunable distributed feedback laser with active tuning section

A composite cavity semiconductor laser structure that consists of two active (gain) sections is analyzed. One of the sections has a grating corrugation, while the other is flat. The operation of the device is enhanced by utilizing the gain-lever effect. A round-trip analysis is combined with the rate equations pertinent for this structure to study the characteristics of the device. The performance of the device is compared to that of a similar case without the gain lever. It is shown that, utilizing the gain-lever effect, improved operation in terms of tuning range, modulation efficiency, and output power control can be obtained. >

Single‐mode very wide tunability in laterally coupled semiconductor lasers with electrically controlled reflectivities

Tunable, single longitudinal mode spectrum of a novel monolithic, laterally coupled semiconductor stripe laser has been demonstrated. A tuning range of 14.2 nm, which is the widest observed so far in a monolithic device, has been achieved.