Search

Naphthaldehyde based imine ligands (L1H2 and L2H3) have been designed and synthesized. The coordination of imine ligands with BF2 motif and BPh2 motif lead to the formation of complexes 1–4. Both the ligands and the boron complexes were characterized by multinuclear NMR spectroscopy and mass spectrometry. Boron NMR of the complexes revealed that the boron atom is in tetracoordinate environment. The optical properties of the complexes and the ligands in solution suggest that borylation enhanced the quantum yields of the ligands. The electrochemical studies indicated that diboron complexes (1 & 3) and triboron complexes (2 & 4) exhibit two and three separate reduction waves respectively.

Here, we describe the synthesis and characterization of a silyl protected tetraphenylimidazole monomer and its homo and co-polymer. The requisite monomer was accessed by Suzuki–Miyaura cross-coupling of 2-(1-(4-bromophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol and 4-vinylphenylboronic acid followed by protection of the phenolic group by tert-butyl(chloro)diphenylsilane. The desired polymers were readily synthesized by using free radical polymerization. Both the polymers and monomer were characterized using different analytical techniques including multinuclear NMR, GPC (for polymers), and single crystal X-ray crystallography (for the monomer). By utilizing the greater fluorophilicity of the silyl atom, the polymers were studied as probes for the detection of fluoride ions. The selectivity and sensitivity of the synthesized polymers were investigated in detail.

Novel imidazole based diboron complex (2) was synthesized and characterized by multinuclear NMR and single crystal X-ray analysis. The diboron complex showed red-shifted absorption and fluorescence with significantly higher molar absorption coefficient over our recently reported imidazole based monoboron complex (3).

1-(p-Tolylsulfinyl)-2-(chloromercurio)ferrocene (2) was prepared by direct mercuration of ferrocenylsulfoxide (1). This reaction can be performed at room temperature in open air. Cross-coupling reactions of compound 2 and aryl halides especially aryl iodides resulted in 1,2-disubstituted ferrocene derivatives with moderate to good yields.

Herein we describe the DNA binding properties of two new water-soluble ruthenium complexes; experimental and computational data reveal that both complexes display dual emission from MLCT and LLCT excited states. The interaction of the new complexes with DNA was also investigated. Although one of the complex only binds DNA though groove binding, the second complex has seperate ligands capable of groove binding and intercalation. Nevertheless, it was found that both complexes interact with duplex DNA with high affinity. DNA induced distinctive changes in the emission of the complexes; although the groove binding complex only displays a modest increase in emission on binding, the complex that contains the intercalating RuII(dppz) moiety displays a large increase in MLCT-based emission on DNA binding while emission from LLCT excited state is unaffected. This means that the complex functions as the first ratiometric sensor for DNA.

The synergistic effect of oxygen, light, and photosensitizer (PS) has found applications in medicine for the treatment of cancer through photodynamic therapy (PDT). Induction of apoptosis to cancerous cells will prevent tumor metastasis that spreads cancer cells to the neighboring organs/tissues. Herein, we report the two apoptotic Ru(II)–polypyridyl complexes that are functionalized with pendant amino acid moieties tyrosine (1) and tryptophan (2), respectively. These two water soluble complexes were found to interact strongly (K1a = (1.18 ± 0.28) × 105 M−1 and K2a = (1.57 ± 0.77) × 105 M−1) with CT-DNA. Isothermal titration calorimetry (ITC) studies revealed that these complexes bind to CT-DNA through an entropically driven process. Both the complexes showed photo-induced cytotoxicity and exhibit apoptotic activity under photo-irradiation conditions. The comet assay indicated that these complexes can damage cellular DNA, which is attributed to the significant build-up of 1O2 level even on irradiation with low intensity light (10 J cm−2, λRange 450–480 nm). This photoinduced DNA damage and apoptosis in A549 cells was induced by reactive oxygen species (ROS) and occurred through up-regulation of apoptotic marker caspase-3. Control experiments under dark conditions revealed an insignificant cytotoxicity towards these cells for two photosensitive molecules.\ud \ud

Annealed proton-exchanged wave guides in X-cut LiTaO3 were characterized by infrared reflection and Raman scattering spectroscopy. The measured spectra were related to the multiple crystalline phases of HxLi1−xTaO3 as identified by direct wave guide index profiling. Unique relationships were found to exist between the crystalline phases and corresponding spectra, which thus can be used to identify phase contents in a given wave guide. Vibrational bands of the studied spectra were correlated with the electro-optic properties of HxLi1−xTaO3 phases. Phase-dependent anisotropy of protonic conductivity was predicted based on the observed polarization dependence of OH libration bands. Finally, the electro-optic coefficient r33 was theoretically estimated for all phases and compared with previously reported experimental data.

In this paper, we explore the feasibility of linearizing Y-fed directional couplers. We demonstrate that the linearity of their performance can be enhanced significantly by the appropriate selection of the interaction lengths with respect to the coupling length. The proposed linearization technique brings about the advantage of highly linear performance combined with a simple device design. The single- and two-section embodiments of the Y-fed coupler are compared both in terms of the linearity of the transfer curve and the level of the third-order intermodulation distortion. We show the two-section Y-fed coupler to be the device of choice since it can exhibit high linearity and improved tolerance to fabrication imperfections. We have determined that if the lengths of the two sections are set to 4.1 and 1.05 times the coupling length, respectively, the transfer curve is linear within 1% of the maximum output power over 98% of the entire interval of modulation. Advantageously, a 100% optical modulation depth is achieved at the same time. On the other hand, if these relative lengths are set to 2.3 and 1.05, the third-order intermodulation distortion in the optical output can be significantly suppressed (by more than 100 dB below the carrier). While comparable performance is possible with other linear modulator schemes of more complex designs, practical applications demand simple design with few or no controls. In this regard, the Y-fed modulator is known to benefit from the built-in quadrature point and nearly equal time-averaged power levels in the arms. The former feature can minimize or even eliminate the necessity of using bias voltages, while the latter minimizes potential impact of optical damage on device performance. Furthermore, we also describe a preferred scheme of a two-section Y-fed coupler with a domain reversal in a ferroelectric material. In this case, only a simple uniform electrode structure is utilized which is fully compatible to a single driving source and hence, is convenient for high-speed applications.

LiNbO/sub 3/ waveguides with Si overlays are emerging as a basic building block for a variety of integrated-optic components, including modulators, high-efficiency gratings, and narrowband WDM filters. However, the development and optimization of these devices are, in large part, hindered by the lack of understanding of the specifics of the Si-on-LiNbO/sub 3/ structure which appear to differ dramatically from those of the Si and LiNbO/sub 3/ waveguides, considered separately. In this work, we provide a specific insight into the waveguiding properties of vertically stacked Si-on-LiNbO/sub 3/ waveguides. In particular, we present a detailed theoretical analysis of the effect of the Si film on the modal characteristics (propagation constant and field distribution) of the structure. The vectorial finite element method (VFEM) is used to numerically investigate a step-index and graded-index single-mode channel waveguide in LiNbO/sub 3/, with a Si or Si/SiO/sub 2/ multimode overlay. We show that for /spl sim/70% of all Si thicknesses, in the range from 0 to 1.6 /spl mu/m, the highest order normal mode of the entire structure has more than 99.9% of the total energy confined in the LiNbO/sub 3/ region, i.e., beneath the Si overlay. This fact is quite intriguing given the fact a planar Si layer of submicron thickness on bulk LiNbO/sub 3/ is already multimoded. Furthermore, we show that the effective mode index of the structure is considerably modified compared to that of the LiNbO/sub 3/ waveguide while the propagation loss is, on the other hand, practically unaffected (/spl sim/0.3 dB/cm) even in the presence of the lossy Si film, as confirmed by our previous experimental results. Evidently, large modulation of the effective index and low-loss propagation provide an ideal combination of properties suitable for the fabrication of high-reflectance corrugated waveguide gratings, essential for a number of practical devices, in particular, WDM filters.

A narrow-band wavelength filter in InGaAlAs/InP has been modeled, fabricated, and tested. A highly asymmetrical, vertically coupled directional coupler operating near the band-edge is formed by a narrow ridge and a wide strip-loaded waveguide. The results of numerical simulation, performed by employing the spectral index method, effective-index method, and a modified coupled-mode theory, are used to fabricate a filter structure with a prescribed filter response. Operation at a center wavelength around 1.5 /spl mu/m with a bandwidth of 18 /spl Aring/ and transfer efficiency of /spl sim/46-68% is achieved. Excellent agreement between the. Designed and measured bandwidth is demonstrated. A multichannel filter device based on an array of individual filters that is capable of extending the usable spectral range is analyzed.

We have realized broad-band distributed Bragg reflectors with photorefractive gratings recorded at 441.6 nm in channel Ti : Cu : LiNbO/sub 3/ waveguides. Proton-assisted copper exchange is used to enable a high level of copper doping and, thereby, achieve an extremely large modulation of refractive index (/spl ges/ 5/sup */10/sup -4/) within a photorefractive grating. Experimental structures demonstrate reflectivities up to 17% with full-width at half-maximum bandwidths in excess of 1.2 nm at center wavelengths around 1.55 /spl mu/m.

We demonstrate an adiabatic, tapered transition in a multiquantum-well (MQW) and single-quantum-well (SQW) coupled structure. The refractive index of the MQW is tapered by the disordering of the AlGaAs/GaAs layers using z-variant, Zn diffused, impurity-induced layer disordering (IILD). We analyze the tapered structure using the step transition model and multilayer stack theory. Results are in excellent agreement with the measurements, establishing the adiabatic nature of the transition. >

A digital optical switch using a velocity coupler tapered both in dimension and in index, which shows the smallest voltage-length product reported so far for digital optical switches, is presented. Numerical results for the graded-index channel waveguide coupler, which can be applied to all z-variant structures with 2D graded-index profile, are presented. >

The authors consider a tapered velocity coupler (TVC) that meets the adiabatic invariance condition with sufficiently strong coupling between the fundamental modes of individual guides in the middle region of the coupler while permitting individual excitation at the input end and sorting of the modes at the output end. This approach helps reduce the device length considerably by permitting much higher taper angle. A TVC consisting of one tapered and another straight, graded index waveguide is modeled using the normal modes of the entire, composite TVC structure. The analytical results are in excellent agreement with experimental results for a TVC fabricated in Ti:LiNbO/sub 3/. It is shown that the representation of the local normal modes as the superposition of the modes of the uncoupled guides leads to erroneous results. >

A single heterostructure InGaAlAs/InP phase modulator utilizing the quadratic electrooptic effect (QEO) is reported for the first time. The calculated value of the QEO coefficient from the measurements is 3.7*10/sup -19/ m/sup 2//V/sup 2/ at 80 meV below the band edge. In addition, the linear electrooptic effect (LEO) coefficient is estimated to be 1.2*10/sup -12/ m/V, which is comparable to that of GaAs. The propagation loss of a single mode ridge waveguide is in the range of 1.5-1.7 dB/cm, which is better than the previously reported value in this material system. The measured single mode phase shifts are 5.5 and 2.8 degrees /V mm for TE and TM polarizations, respectively. These values are the largest reported so far in an InGaAlAs system. >

A glass waveguide polarization splitter for operation in the 1.3 mu m wavelength region is reported. The device, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K/sup +/-Na/sup +/, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective-index method, the normal mode propagation constants and mode field profiles are calculated to determine the polarization splitting length and the extinction ratio, and the results are compared with the experimental data. It is shown that in a given coupler, the splitting occurs at several wavelengths in the 1.0-1.45 mu m range. A 25 mm-long coupler, fabricated by thermal diffusion of K/sup +/ ions in BK7 glass, exhibits an extinction ratio of 18.2 dB at 1.32 mu m, in excellent agreement with the simulation results. >

We have measured the surface index change and birefringence in K(+)-Na(+) ion-exchanged waveguides and compared the results with theory. The contribution to the index change caused by the polarizability/volume changes (Deltan(p)) is calculated using two theoretical models which use empirical relations based on the glass composition. In both cases, we encounter large discrepancies between the predicted and measured values which are attributed to the inherent deficiency in the models, which assume free expansion of the glass in calculating the volume changes. Recognizing that the net volume change is much smaller, we accurately measure its value and show that both models can be used to predict Deltan(p) with the same accuracy, provided that the correct volume change is used. We show that the limitation in accuracy is dictated by measurement errors and uncertainties in the values of the ionic radii and polarizabilities. We also present a unique and systematic method for determining the compressive stress generated in the glass resulting from ion exchange.

A thorough and detailed characterization of annealed proton-exchanged (APE) waveguides in Z-cut LiNbO/sub 3/ is described. The mode index measurements in planar waveguides as a function of wavelength and annealing time are reported, including useful analytical relations for the refractive index change, its dispersion, and the depth profile as a function of annealing parameters. Analytical expressions for the mode propagation characteristics are presented and experimentally verified with reasonable accuracy. It is shown that the planar waveguide characterization results can be used to model the channel waveguide characteristics accurately. The model provides closed-form expressions for the mode index and the mode field profile, and the theoretical results are in excellent agreement with the measured data. The technique is used to accurately predict the phase mismatch between the fundamental and second harmonic modes in frequency-doubling experiments using APE channel waveguides. An optimum waveguide geometry for which the phase mismatch is relatively insensitive to the waveguide nonuniformity was predicted and verified experimentally. >

We demonstrated a linearized Y-fed directional coupler modulator in Z-cut LiNbO/sub 3/. The proof-of-concept device employed two electrode sections of opposite polarity whose lengths were chosen based on the results of our previous theoretical modeling. A highly linear modulation characteristic and improved tolerance to fabrication errors were achieved with a simple design, in excellent agreement with the theory. The linearity exceeded 90% over a wavelength range of 45 nm, centered around 1530 nm, with a maximum linearity of 97% at 1510 nm and a maximum modulation depth of 98%. By comparison, the linearity of conventional modulators is typically around 70%. Thus the device was proven to have a high linearity with a wide usable spectral range and relaxed fabrication tolerances.

A deep domain inversion (DI) technique for X-cut LiNbO3 is reported. DI regions as deep as 70 μm, i.e., deep enough for virtually any guided-wave application, were obtained by electric-field poling, with even deeper DI regions possible. As an application of the DI technique, a bandpass traveling-wave Mach–Zehnder modulator is demonstrated with a 15 GHz bandwidth centered at 21 GHz.

The fluorescence spectrum of Er-indiffused LiTaO3 was measured and revealed strong anti-Stokes fluorescence (ASF) with upconverted green and red emissions when the 4F9/2 manifold of an Er3+ ion was pumped by either a 632.8 or a 647 nm laser. Investigation into the dependence of fluorescence intensity on pump intensity and depth profiling of the Stokes and anti-Stokes fluorescences revealed that the ASF is attributed mainly to energy transfer upconversion within Er3+ cluster sites. Postindiffusion processing in molten LiNO3 was found to be effective in suppressing the upconversion via decrease of the cluster site concentration.

A quantitative comparison of the photorefractive effect in proton-exchanged (PE), annealed-proton-exchanged (APE), and Ti-diffused LiNbO(3) waveguides in the visible region is reported. In the low-intensity region, the optically induced index change in PE/APE waveguides is almost 3 orders of magnitude smaller than that of Ti-diffused waveguides for a given intensity, primarily as a result of the increased dark conductivity owing to proton exchange. However, the photorefractive index change at higher intensities is almost the same for all the waveguides. Our results indicate that the optically induced space-charge field is relatively independent of the concentration or the valence state of iron impurities and the waveguide fabrication process.