Strong Optical Coupling Research Articles

Optical directional coupler based on Si-wire waveguides

We fabricated optical directional couplers with Si-wire waveguides and demonstrated their fundamental characteristics. Their coupling-length was extremely short, several micrometers, because of strong optical coupling between the waveguide cores. Wavelength demultiplexing functions were also demonstrated for devices with a long coupled waveguide. Optical output from a device 800 μm long changed reciprocally with 2.5-nm wavelength spacing between the parallel and cross ports.

Strong optical transitions via surface states on Si(001)2×1:H ultrathin films: A theoretical study

Optical transitions via localized surface states on Si(001) ultrathin films terminated by monohydride dimers on both surfaces with 2×1 periodicity are studied by use of the extended Hückel-type nonorthogonal tight-binding method. The calculated oscillator strength between the bottom of the empty surface states and the valence-band maximum is much larger than that for direct band-to-band transitions in films with an ideal dihydride termination on both surfaces. An analysis shows that this strong optical coupling is attributed to a significant s-like character introduced into the surface-state bottom by the formation of the monohydride dimers on the film surface.

Metal Films Prepared by Stepwise Assembly. 2. Construction and Characterization of Colloidal Au and Ag Multilayers

This manuscript describes the stepwise, ligand-directed assembly, characterization, and prospective applications of three-dimensional Au and Ag nanoparticle, multlilayered films. Films were prepared by successive treatments of a Au nanoparticle monolayer with a bifunctional cross-linker and colloidal Au or Ag solutions. Changes in film electrical and optical properties are reported for a series of bifunctional cross-linkers of varying molecular lengths. Interestingly, these films exhibit Beer's law behavior despite the presence of strong interparticle optical coupling. Multilayer films with greater than six exposures to 2-mercaptoethylamine and Au colloid were highly conductive and resembled bulk Au in appearance. In contrast, films of similar particle coverage generated using a longer cross-linker (1,6-hexanedithiol) exhibited higher transmission in the near-infrared region and exhibited a reduced conductivity. Measurement of the multilayer morphology with atomic force microscopy , electrostatic force mi...

Mechanisms of optical confinement in phase-locked laser arrays

The nature of optical confinement in phase-locked laser arrays (PLLAs) with a mesa-stripe structure (MSS) has been studied. Two main mechanisms are distinguished, which are based on the variation of the waveguide effective refractive index due to MSS formation and on the refractive index modulation induced by the heating of the structure. Stable operation was achieved when either weak or strong optical coupling was realized in the PLLA. A phase-locked regime of radiation was obtained only for laser diodes with strong optical coupling. In the latter case the angle divergency was not greater than for the antisymmetric supermode emission from the PLLA.

Type-II quantum-well lasers for the mid-wavelength infrared

We discuss an improved mid-wave infrared diode laser structure based on InAs-Ga1−xInxSb- InAs-Ga1−xAlxSb Type-II multiple quantum wells. The proposed design combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate, and excellent electrical and optical confinement.

Spatiospectral and picosecond spatiotemporal properties of a broad area operating channeled-substrate-planar laser array

Spatiospectral and spatiotemporal properties of an eight-element channeled-substrate-planar laser array are investigated in both cw and pulsed operating conditions. The closely spaced CSP array with strong optical coupling between array elements is characterized by a broad area laserlike operation determined by its spatial mode spectra. The spatiotemporal evolution of the near and far field exhibits complex dynamic behavior in the picosecond to nanosecond domain. Operating parameters for the laser device have been experimentally determined. These results provide important information for the evaluation of the dynamic behavior of coherent semiconductor laser arrays.

Tuned-port twin biconical-taper fiber splitters: fabrication from dissimilar low-mode-number fibers

Fused biconical-fiber splitters have been fabricated from dissimilar low-mode-number optical fibers. Through selective etching of the cladding diameters of the two fibers forming the splitter, the amount of energy transferred between the fibers can be controlled. A tuned condition characterized by low insertion loss and strong optical coupling between modes of the fibers forming the splitter has been demonstrated. In the detuned condition an asymmetry in the coupling between fibers has been observed.

High-power phase-locked arrays of index-guided diode lasers

A nine-unit phase-locked array of index-guided channel-substrate-planar large-optical-cavity AlGaAs diode lasers is fabricated by one-step liquid phase epitaxial growth over a 5-μm period sawtooth grating etched into a GaAs substrate. Two-lobed, 180° phase shift operation is achieved to 75-mW cw power and to 400-mW peak pulsed power. Strong coherent optical coupling between the array units provides single-longitudinal-mode array operation to 80-mW cw output power. The cw and pulsed threshold currents are in the 250–400-mA range. Single-lobe, 0° phase shift operation, with the single beam peaked at 0°, is achieved to 200-mW peak power.

Strong electron-phonon interaction effects in modulated transient reflectance spectra of Ga.50In.50P

Time-resolved modulated reflection spectrum near the fundamental edge of MBE-grown direct-gap GaxIn1−xP (x = 0.5) has been studied by using sensitive picosecond excite-probe methods. The spectrum at 77K shows considerable structure in comparison with steady-state photoluminescence data. In particular, a strong optical phonon coupling effect has been observed in the transient spectra, suggestive of impurity intermediated bound polaron behavior.

Strong electron-phonon interaction effects in modulated transient reflectance spectra of Ga .50In .50P

Time-resolved modulated reflection spectrum below the fundamental edge of MBE-grown direct-gap Ga xIn 1-xP (x = 0.5) has been studied by using sensitive picosecond excite-probe methods. The spectrum at 77K shows considerable structure in comparison with previous steady-state photoluminescence data. In particular, a strong optical phonon coupling effect has been observed in the excitation spectrum, suggestive of an acceptor bound polaron.

Influence of the spectrum of external illumination on transient and self-modulation processes in an injection laser

An experimental study was made of the process of quenching and buildup of relaxation and self-modulation oscillations of the output radiation of an injection laser by external illumination under strong optical coupling conditions. The influence of external illumination (provided by a second laser) was manifested even in the superradiance regime. Periodic increase and reduction in the depth of relaxation oscillations was observed when the pump current through the laser providing external illumination was increased. This was due to the shift of the spectrum of the external illumination because of heating of the laser providing it. Measurements indicated that the range in which the buildup changed to quenching corresponded to a shift of the external illumination by half the mode spacing of the laser providing it.

Two-resonator quantum-optical systems

Trigger systems (flip-flops) with double and single inputs, laser multivibrator, and a laser univibrator (single-shot multivibrator) were investigated experimentally. These systems were based on a two-resonator semiconductor laser with strong optical coupling.

Restricted Sum Rules for Optical Absorption of Metals

A concept of a sum rule applied to the conduction electron subsystem in metals is discussed in connection with the optical conductivity and the Nozieres-Pines sum rules, with the emphasis on an essential role of the Pauli-forbidden transitions of a conduction electron to occupied core states. Obtained restricted sum rules are useful means of optical analysis for metals with strong conduction-core optical coupling, and are applied to the absorption data for alkali metals. The experimental fact that the saturated values of the effective number of electrons per atom contributing to conduction electron absorption exceed the valence is interpreted satisfactorily in terms of a contribution of the Pauli-forbidden transition to the outermost p -core state.