Gershon Rosenblum

Adiabatic mode multiplexer for evanescent-coupling-insensitive optical switching

A novel adiabatic mode multiplexer enables a 2 x 2 optical switch whose operation does not depend on accumulated phase due to evanescent coupling between waveguides. The adiabatic mode multiplexer has a negligible insertion loss over C+L bands and modal cross talk better than -40 dB for any polarization state. Mode multiplexing is achieved by adiabatic transition from the fundamental mode of the single-mode waveguide to the higher mode of the multimode waveguide. Experimental measurement results for a device realized in silica-on-silicon technology are presented. By directly measuring the nonadiabatic transition probability, we show that the adiabatic mode multiplexer operates in the Landau-Zener regime.

ELECTRONIC ENERGY TRANSFER IN SUPERSONIC JET EXPANDED NAPHTHALENE-(CH2) N-ANTHRACENE BICHROMOPHORIC MOLECULES

Abstract A study of intramolecular electronic energy transfer (Intra-EET) has provided evidence, for the first time, of a dramatic difference in Intra-EET efficiency results obtained under jet cooled and room temperature solution conditions. This was observed with anthracene-(CH 2 ) n -naphthalene bichromophoric molecules, A1N ( n = 1) and A3N ( n = 3). The rich fluorescence excitation spectrum of the naphthalene moiety in A1N indicates an inefficient EET process whose rate constant is substantially slower than that of the naphthalene moiety fluorescence. It was shown that the EET rate depends on a specific vibronic excitation that affects the molecular conformation, and was found to be at least two orders of magnitude slower in A1N molecule compared to A3N .

Calculation of intermolecular interaction in aromatic molecular clusters from direction dependent atom‐pair potentials

An expression for the interaction potential between two anisotropic molecules is derived. This expression is suitable for describing the van der Waals interaction between two chromophores within a bichromophoric molecular cluster. For the anthracene–naphthalene cluster the calculation predicts the existence of two isomers, in agreement with experimental observations. The model is also successfully applied to other clusters yielding better results than those obtained by alternative methods which do not take into account the anisotropy of molecular polarizability.

Controlled mode interaction based wide-band and robust optical switching unit in silica-on-silicon

We present a novel wide band and robust planar lightwave circuit (PLC) switching unit having two switching states with low cross talk. The CMI based SU does not require post fabrication trimming and can be used as a normally dark VOA.

Optical switching based on the adiabatic temperature induced mode localization

We present optical switching device that combines two ideas: thermally induced waveguides and adiabatic mode transition in a slowly widening taper. We explain conditions for the optimal operation and present experimental results for 1 /spl times/ 2 switch.

Photophysics of the naphthalene—anthracene bichromophoric molecular system in a supersonic jet expansion

Abstract Intramolecular electronic energy transfer (intra-EET) was investigated in an isolated bichromophoric naphthalene (N) and anthracene (A) 1:1 molecular cluster. Investigation of the spectroscopic properties of these chromophores, separately and loosely bound in a van der Waals complex, helps to understand the dependence of the EET rate on the initially excited vibronic level and on the clusters interchromophoric orientation. Measurement of fluorescence excitation spectra of anthracene, at different anthracene pressures shows bands that can be assigned to dimers of anthracene. From measurement of the anthracene excitation spectrum at increasing naphthalene pressures one can identify other spectral features, characterized by different spectral shifts from excitations of the bare molecule. Some transitions are probably due to a 13.5 cm −1 progression associated with an interchromophore cluster bond. Pressure dependence of fluorescence intensity gives evidence for 1:1 cluster composition, and for a slow intra-EET rate that is associated with an unfavoured orientation of the two chromophores in one of the two possible conformers of the A–N cluster, as supported by a calculation of the cluster geometry and by comparison with a recent study of intra-EET in the A-(CH 2 ) n -N bichromophoric molecules.

Solution and supersonic jet studies of the intramolecular exciplex of dinaphthyl propanes

The newly synthesized dinaphthyl propanes: 1,3-di-(2-naphthyl)-propane and 1-(1-naphthyl), 3-(2-naphthyl)-propane were studied spectroscopically under supersonic jet conditions and in solution. Under supersonic jet conditions, both molecules exhibit a broad, structureless fluorescence excitation spectrum and relatively short non-exponential decay of the highly red shifted fluorescence, consistent with strong interchromophore coupling in the excited state, resulting in, at least, partial excitation directly into an exciplex-like state. These observations are in contrast to the observed spectra and fluorescence decay of all other dinaphthalene bichromophoric molecules. Solution studies support these findings. The optimal flexible sandwich type geometry of both molecules is probably responsible for the observed exciplex state stabilization.

CALCULATION OF THE INTERACTION POTENTIAL FOR BICHROMOPHORIC HETERO-MOLECULAR CLUSTERS

An expression for the interaction potential between two anisotropic molecules is derived. This expression is suitable for describing the van der Waals interaction between two chromophores within a bichromophoric molecular cluster. For the anthracene-naphthalene and for the benzene-biacetyl clusters the calculation predicts the existence of two isomers, in agreement with experimental observations. The model is also successfully applied to other clusters yielding better results than those obtained by alternative methods which do not take into account the anisotropy of molecular polarizability.

Tapping light from waveguides by high-order mode excitation and demultiplexing

A novel high-performance optical tap with low wavelength-dependent loss(WDL), polarization-dependent loss (PDL), and excess loss is described. The tap is based on exciting a high-order mode by an abrupt change in the waveguide profile, and then tapping the optical power in the high-order mode by using a modal-demultiplexer. The tap can be designed to give a tapping ratio in the range of -30 to -10 dB over a wavelength range of 1510-1640 nm. In addition, it is shown that the tapping ratio is tolerant to process variations, repeatable and predictable, enabling the design to be implemented in a single process run, with no need for additional fine-tuning iterations, while achieving a high process yield. We show that measurements are in good agreement with simulated results. In the tap channel we measured 0.3 dB WDL and 0.2-dB PDL over the C- and L- bands, while the signal in the main channel was virtually uncontaminated relative to a plain single-mode reference waveguide.

Controlling coupling of guided to radiating modes using adiabatic transitions between waveguides of different curvature

A simple method for designing adiabatic transitions between straight and curved waveguides is presented. This method results in lower coupling from guided to radiating modes than conventional methods based on introducing an abrupt offset at the junction point. With the new adiabatic transition design, a decrease of 5 to 10 dB in the low-level radiating light cone is found compared with the traditional method.