Wavelength Monitoring Research Articles

Photoluminescence and optical absorption caused by the F+ centresin anodic alumina membranes

Anodic alumina membranes (AAMs) with highly ordered nanochannel arrays wereprepared by anodizing aluminum in acid solutions. X-ray diffraction revealsthe amorphous nature of AAMs. The photoluminescence (PL) excitation spectraof AAMs consist of a broad band centred at 235 nm and a narrow band peakingaround 360 nm under a monitoring wavelength of 470 nm. There are fiveprominent absorption bands (or edges) at 370, 294, 254, 220 and204 nm in the absorption spectra of AAMs prepared in oxalic solution. Withthe increase of the annealing temperature, the intensities of PL andabsorption bands increase first, then decrease, and a blue-shift is found.The photoluminescence and optical absorption in the wavelength range of200 nm to 500 nm are caused by the F+ centres in AAMs. The energy levelsof F+ centres in AAMs are split and a new energy level of 3.35 eVappears due to the amorphous nature of AAMs.

Tunable silicon etalon for simultaneous spectral filtering and wavelength monitoring of a DWDM transmitter

A temperature-tunable Fabry-Perot filter made of silicon has been developed and applied for simultaneous spectral filtering and wavelength monitoring of a directly modulated DFB laser. This novel device decreases the dispersion penalty of a cost-effective dense wavelength-division-multiplexing (DWDM) transmitter in a long-haul transmission link. Moreover, it allows the operating wavelength of the transmitter to be accurately monitored in real time.

Impact of Internal Electric Field and Localization Effect on Quantum Well Excitons in AlGaN/GaN/InGaN Light Emitting Diodes

Strained InxGa1—xN quantum wells (QWs) on thick GaN base layers were investigated to verify the importance of localized QW excitons in their spontaneous emission mechanisms. A strength of the internal piezoelectric field (FPZ) across the QW increases with increasing x up to 1.4 MV/cm for x = 0.25, since the in-plain strain increases. For the QWs with the well thickness L greater than 3 nm, FPZ dominates the emission peak energy due to the quantum-confined Stark effect. Absorption spectra of both hexagonal and cubic InGaN QWs exhibited a broad band-tail regardless of the presence of FPZ normal to the QW plane. The luminescence peak energy of the 3 nm thick QWs was higher than the bandgap energy of the unstrained bulk crystal for x < 0.15, showing that doping of Si in barriers or injection of carriers effectively screens the field. The emission lifetime increased with increasing monitoring wavelength. Also, a temperature-induced change in the luminescence peak energy decreased with increasing x. The real-space variation of the luminescence peak energy was confirmed by the spatially-resolved monochromatic cathodoluminescence mapping method. The localization depth increases with increasing x. The carrier localization is confirmed to originate from the effective bandgap inhomogeneity due to a fluctuation of the local InN mole fraction, which is enhanced by the large and composition-dependent bowing parameter of InGaN material.

Precision-tuning wavelength addressable laser for reconfigurable WDM networks

In this letter, we demonstrate a precision wavelength addressable laser with a rapid wavelength setting function for reconfigurable wavelength routed wavelength-division-multiplexing networks using a broad-band tunable laser combined with a phased-array waveguide-grating-based integrated real time multichannel wavelength monitoring circuit. The addressable laser could be set to four International Telecommunication Union wavelengths with 0.8-nm (100-GHz) channel spacing, limited by its tuning range, and the wavelength resolution is better than 0.02 nm. The tunable laser also supports self-contained and self-learning functions.

Wavelength monitor based on two single-quantum-well absorbers sampling a standing wave pattern

We demonstrate a wavelength monitor and a two-wavelength detector based on two single-quantum-well absorbers that sample a standing wave created by a distributed Bragg reflector. As a wavelength monitor, our device is power independent over a 15 dB range. Wavelength discrimination is linear over a 12 nm range.

Wavelength monitoring with low cost laser diodesfor DWDM applications

A simple wavelength monitoring technique based on the transparency detection of low-cost laser diodes and very simple circuitry is demonstrated. The wavelength sensor can be operated at either fixed bias or in a sweeping mode. Wavelength monitoring using the proposed approach has been demonstrated to have sub-angstrom resolution and good stability.

Ligand luminescence and photoinduced charge separation in bis(naphthalene) substituted fourteen-membered tetraazamacrocyclic complexes of CuII and NiII

Deaerated solutions of complexes of NiII and CuII of a bis(naphthalene) substituted fourteen-membered tetraazamacrocycle exhibited medium-dependent luminescence when they were irradiated at 351 or 337 nm. The addition of Cu(CH3CN)62+ in increasing concentrations resulted in the formation of a ground state adduct and led to displacements of the emission spectrum toward shorter wavelengths and to a progressive quenching of the luminescence. The rate of the luminescence decay was also dependent on the medium and on the monitoring wavelength and was fitted by single or multiple exponentials with lifetimes shorter than 30 ns. Steady state irradiations of the complexes at 370 nm induced a minor conversion among tautomeric forms. Transient photochemical products with lifetimes of several hundred ns were observed via flash photolysis and assigned as metal–ligand radical species. A mechanism for the formation of such intermediates and various ground and excited state species is proposed.

Major sensitivity improvements in ion chromatography determinations involving post-column spectrophotometric reaction detectors through elimination of pump noise using a dual wavelength monitoring procedure

A novel dual wavelength procedure is described for the elimination of baseline pump noise in spectrophotometric post-column reaction detection systems in high-performance liquid chromatography. The method is applicable if there is some overlap between the spectrum of the analyte reaction product and the spectrum of the excess reagent. One wavelength is chosen to monitor the analyte reaction product and the other wavelength is set close to the isosbestic point. After simple arithmetic manipulation of the data using commonly available computer software, the pump noise is subtracted from the analyte baseline, allowing much higher sensitivity settings to be used. The two examples shown are taken from the ion chromatography of trace metals using colorimetric post-column reaction detectors, where close to a 20-fold increase in signal to noise ratio was obtained when using the dual wavelength procedure.

A quantum-well waveguide photodetector for high-precision wavelength monitoring about 1.55 μm

A two-segment InGaAsP rib waveguide photodetector is shown to function as a high resolution wavelength monitor in the 1.55-/spl mu/m spectral region. For two in-line detector elements, the ratio of photocurrents produced is a sensitive function of the input wavelength near the material's absorption edge. This ratio varies rapidly with wavelength over a range from 1.53 to 1.565 /spl mu/m and is independent of the optical input power. By utilizing the quantum confined Stark effect, the operating range of the device can be extended to over 50 nm. An average wavelength sensitivity of 3 pm is demonstrated.

Kinetics of the reaction of CH 3O 2 radicals with NO 2

The kinetics of the gas-phase reaction of CH 3O 2 radicals with NO 2 were studied at 295 K in 0.5–14 atm of SF 6 diluent using pulse radiolysis combined with time-resolved UV–VIS spectroscopy. Rate data were obtained by following the loss of CH 3O 2 using a monitoring wavelength of 260 nm. The results were well described using the Troe formula with F c=0.40±0.09, k 0=(1.46±0.50)×10 −30 cm 6 molecule −1 s −1 and k ∞=(1.81±0.25)×10 −11 cm 3 molecule −1 s −1. These results are compared to the previous data and discussed in terms of reactivity trends and the atmospheric chemistry of peroxy radicals.

Variation of band-edge position with errors in the monitoring of layer termination level for long- and short-wave pass filters

Optical monitoring of periodic thin-film stacks by the termination of each layer at the same constant photometric level has certain advantages. One of these principal advantages is the error compensation effect in the vicinity of the monitoring wavelength. In this study, we examine, by simulation, the effect of an error in the knowledge of the absolute value of the photometric termination level on the probable stability in the manufacture of the edge position of a blocked band. The results include equations that allow the determination of the appropriate values of parameters associated with the optimum termination levels to minimize the effects of such errors.

Upper Excited State Photochemistry: Solution and Gas Phase Photochemistry and Photophysics of 2- and 3-Cyclopropylindene1

The cyclopropylcarbinyl radical rearrangement has been used to probe the photochemistry and photophysics of S2 and S1 in 2-cyclopropylindene (2CPI) and 3-cyclopropylindene (3CPI). Studies in solution and the gas phase are described. Population of S2 with 254 nm light excitation in the gas phase produces the anticipated ring expansion products 2,3,3a,8-tetrahydrocyclopenta[a]indene (1, Φ1 = 0.1) and 1,3,3a,8-tetrahydrocyclopenta[a]indene (2, Φ2 = 0.06) from 2CPI and 3CPI, respectively (Scheme 3). Direct excitation into the S2 state (254 nm) of 2CPI in solution also produces compound 1. The efficiency of the solution phase chemistry is a function of excitation wavelength (Φ1 = 0.022 and 0.006 for 254 and 280 nm, respectively). The solution phase excitation spectrum of 2CPI shows an anomalous dependency on monitoring wavelength which is attributed to a conformational equilibrium. The S1 singlet lifetimes of the cyclopropylindenes are quite short (0.39 and 1.0 ns for 2CPI and 3CPI, respectively) relative to t...

An integrated liquid crystal phase modulator for speckle shearing interferometry

A versatile phase-stepping speckle shearing interferometer is described that employed a calibrated liquid crystal as its phase modulator, operating at 514 nm. By implementation of an algorithm upon phase-stepped shearographic images it was possible to create a phase map, that provided quantitative data regarding the derivative of any out-of-plane surface displacement. The use of a liquid crystal phase modulator in an optical arrangement had advantages over alternative methods. However, it is normally limited by spatial non-uniformity of the cells birefringence. The birefringence for a nematic liquid crystal cell was determined in several cross-sectional locations, before the cell was successfully integrated into a Michelson speckle shearing interferometer. Such a scheme offers flexibility in the shearing angle, and a measurement system that may operate over an extended range of monitoring wavelengths.

Full coverage multichannel wavelength monitoringcircuit using centre-offset phased-array waveguide grating

An integrated multichannel optical wavelength monitoring circuit for wavelength division multiplexing communication systems is presented. Full wavelength coverage of the working range without any blind spot is realised by a centre-offset phased-array waveguide grating design. The monitor exhibits a wavelength resolution of 0.02 nm/dB (200 GHz channel spacing).

Adaptive dispersion equalisationby detecting dispersion fluctuationsusing PM-AM conversion

A novel adaptive dispersion equalisation technique that detects and equalises dispersion fluctuations in transmission fibre during data transmission is proposed. This technique first detects dispersion fluctuations in the fibre by using the PM-AM conversion effect at a monitoring wavelength, and then tunes the data wavelength to equalise the fluctuation. This technique was tested by conducting a 40 Gbit/s, 8.5 ps pulse transmission experiment over 300 km of dispersion-shifted fibre, and was shown to suppress the sensitivity degradation to below 0.2 dB when the temperature of the fibre was varied between 0 and 40/spl deg/C.

Concatenated fiber grating optical monitor

A new optical wavelength-division-multiplexed (WDM) wavelength monitor comprised of concatenated fiber Bragg gratings and an InGaAsP electroabsorption optical modulator is described. Input WDM signals were modulated at 10 kHz with 15-ns-width pulses and the signals reflected from the gratings were detected with an InGaAs p-i-n photodiode and displayed on an oscilloscope as a series of pulses corresponding to each wavelength component.

Tunable sampled-grating DBR lasers with integrated wavelength monitors

We report on the design and development of a wavelength monitor for use with tunable semiconductor lasers. The device is based on two-mode interference in an asymmetrically excited waveguide that is coupled to a Y-branch splitter. The monitoring range of the device is 30 nm. The wavelength monitor is capable of operating over an input power range of 34 dB, and the waveguide detectors do not saturate at photocurrents as high as 1.2 mA. The sensitivity of the monitor is only 1.24 nm for an isolated device, but improves to 0.44 nm when it is integrated on chip with the laser.

The Determination of Creatinine in Human Urine by Capillary Zone Electrophoresis with Photodiode Array Detection

The application of capillary zone electrophoresis (CZE) to the separation and determination of creatinine in human urine with photodiode array detection was described. Optimum conditions for the separation were established. The effect of pH of the background buffer on the existence state of creatinine was investigated. Photodiode array detection permitted the rapid identification of creatinine in the samples analysed. By selecting 234 nm as monitoring wavelength, the interference from urea in urine was eliminated. By selecting a suitable pH, the interferences from other substances in urine were also eliminated. The linear range, detection limit, precision and recovery of the method were investigated.

The effect of the group propagation of waves on the spectral behaviour of a multilayer Ar coating

As the monitoring wavelength detected by an optical monitor (photometer) is inevitably of a considerable spectral width, it should be travelling as a group of waves rather than a monochromatic wave. In addition, the photometer is influenced simultaneously by the waves’ combined effect. The phases of the disturbance of different wavelengths travelling with the group velocity are in good agreement. Therefore, the phase thickness(es) of the monitored layer(s) should be modulated by the group factor. The effect of the new thickness(es) is investigated and the close correlation between theoretically predicted and experimental results is presented.

Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 2. Demonstration of Selectivity in the Presence of Direct Interferences

Three modes of selectivity based on charge-selective partitioning, electrolysis potential, and spectral absorption wavelength were demonstrated simultaneously in a new type of spectroelectrochemical sensor. Operation and performance of the three modes of selectivity for detection of analytes in the presence of direct interferences were investigated using binary mixture systems. These binary mixtures consisted of Fe(CN)(6)(3-) and Ru(bpy)(3)(2+) and of Fe(CN)(6)(4-) and Ru(CN)(6)(4)(-) in aqueous solutions. Results on the Fe(CN)(6)(3-)/Ru(bpy)(3)(2+) binary mixture showed that an anion-exchange coating consisting of PDMDAAC-SiO(2) [where PDMDAAC is poly(dimethyldiallylammonium chloride)] and a cation-exchange coating consisting of Nafion-SiO(2) can trap and preconcentrate analytes with charge selection. At the same time, such coatings exclude interferences carrying the same type of charge as that of the exchange sites in the sensor coating. Using the Fe(CN)(6)(4-)/Ru(CN)(6)(4-) binary mixture, the Fe(CN)(6)(4-) component can be selectively detected by restricting the modulation potential cycled to a range specific to the redox-active Fe(CN)(6)(4-) component and simultaneously monitoring the optical response at the overlapping wavelength of 420 nm. It was also shown that, when the wavelength for optical monitoring was chosen as 500 nm, which is specific to the Ru(CN)(6)(4-) component, interference from the Fe(CN)(6)(4-) component for spectroelectrochemical detection of Ru(CN)(6)(4-) was significantly suppressed, even though the cyclic modulation potential encompassed the redox range for the Fe(CN)(6)(4-) component.