Wavelength Monitoring Research Articles

Optical-isolator-based modules for monitoring DWDM tunable lasers

Feature Issue on Optical Performance Monitoring (OPM). Simultaneous monitoring of power, wavelength, and channel number for a tunable laser is demonstrated by use of a combination of an optical isolator, an etalon, a polarizer, and photodiodes. The mode hopping and incomplete-tuning problems that might arise in tuning the laser can be detected with the proposed approach. The spectral response of the monitoring module can be adjusted to match the wavelength-tuning range. The spectral adjustment can be performed by rotating the input polarization or the output polarizer. It can also be tuned by rotating the second stage if a two-stage isolator is used. We demonstrate experimentally the feasibility of this approach by use of discrete fiber-pigtailed components.

Passive wavelength monitor based on multimode interference waveguide

A new wavelength monitor based on a multimode interference waveguide is proposed for multiwavelength communication applications. The device characteristics are studied using the beam propagation method. By adjusting the waveguide's geometric length, different wavelength ranges can be addressed. Each device can monitor up to a 50-nm range and has accuracy <5 A.

Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber bragg grating

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.

Dynamics of Solvation of the Fluorescent State of Some Electron Donor−Acceptor Molecules in Room Temperature Ionic Liquids, [BMIM][(CF3SO2)2N] and [EMIM][(CF3SO2)2N

Room temperature ionic liquids, particularly those based on the imidazolium salts, have emerged in recent years as highly promising “green” media suitable for carrying out various reactions. In this paper, picosecond time-resolved fluorescence decay behavior of three electron donor−acceptor (EDA) molecules, coumarin-153 (C153), 6-propionyl-2-dimethylaminonaphthalene (PRODAN), and 4-aminophthalimide (AP), in two room temperature ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][(CF3SO2)2N]) and 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([BMIM][(CF3SO2)2N]), has been reported. The steady-state fluorescence behavior of the EDA molecules suggests that the polarity of the two ionic liquids in the ET(30) scale is around 47.6 for [EMIM][(CF3SO2)2N] and 47.1 for [BMIM][(CF3SO2)2N]. The fluorescence decay behavior of the systems in these media has been found to be dependent on the monitoring wavelength, suggesting solvent-induced relaxation of the fluoresce...

Characteristics of humic substances in the Kuji River waters as determined by high-performance size exclusion chromatography with fluorescence detection

Direct measurement by high-performance size exclusion chromatography with fluorescence detection was applied to the characterization of humic substances in river waters from the Kuji River system, which runs through forest hills and an agricultural plain in Japan. The monitoring wavelength of excitation 320 nm and emission 430 nm corresponds to the fluorescence maxima for aquatic fulvic acid. Chromatograms of the river waters showed four peaks; each peak position was in good agreement among these samples. Peak height ratios for the samples from the upstream Kuji River and its tributaries were different from those of the midstream and downstream sections of the Kuji River, which may reflect differences in the characteristics of humic substances and other organic materials supplied from soil to river.

Adding OSNR and wavelength monitoring functionalities on a double-resolution-AWG-based power monitoring circuit

We propose and demonstrate an improved optical signal-to-noise ratio monitoring scheme based on a double-resolution arrayed-waveguide grating-based power monitoring circuit concatenating with a tunable periodic notch filter. This device, which can be implemented in an integrated power line carrier, exhibits much higher extinction ratio and dynamic range than current available schemes. It is also less sensitive to spectrum shape of the signal.

A high-sensitivity in situ optical diagnostic technique for laser cleaning of transparent substrates

A differential optical transmission technique has been used to monitor in situ the efficiency of laser cleaning for the removal of sub-micrometer-sized particles on substrates transparent at the monitoring wavelength. This technique has been applied to the removal of sub-micrometer polystyrene particles on polyimide substrates using laser pulses of 30 ps duration at 292 nm while probing the material transmission at 633 nm. The sensitivity achieved -1/104 for the transmission changes induced upon single-pulse laser exposure – allows us to monitor the removal of just a few sub-micron-sized particles from the probed region inside the irradiated area.

25-GHz-spacing wavelength-monitor integrated DFB laser module for DWDM applications

For the first time, a 25-GHz-spacing wavelength monitor is successfully integrated into an industry standard 14-pin butterfly laser module through the use of a unique configuration. The temperature-induced wavelength drift of these wavelength-monitor integrated laser modules for a case temperature ranging from -5/spl deg/C to 70/spl deg/C is less than /spl plusmn/10 pm.

Factors influencing fetal pulse oximetry performance.

Fetal pulse oximetry shares many problems with traditional pulse oximetry, but also poses unique challenges that may compromise accurate SpO2 determination and data availability. The purpose of this review is to characterize the factors that may influence fetal pulse oximetry and their relationship to sensor design. A review of the literature of pulse oximetry identifies the factors that have been shown to influence fetal pulse oximetry performance, as well as other factors from traditional pulse oximetry that may also be expected to have an effect. Sensor design choices, including monitoring site, wavelength, and configuration, are related to the incidence and mitigation of these factors. Sensor designs may be characterized by monitoring site, means of retention, and operating mode (reflectance versus transmission). The factors influencing fetal pulse oximetry may be categorized as follows: fetal physiology, tissue characteristics at the monitoring site, sensor-tissue interface, and external influences. Monitoring site selection is of paramount importance in reducing the impact of interfering factors on fetal pulse oximetry performance. Many factors of importance in traditional pulse oximetry have yet to be characterized as far as their potential for interference in fetal pulse oximetry.

Wavelength demultiplexer using waveguide technology with built-in grating structure for multichannel optical wavelength monitor

A wavelength demultiplexer structure using a channel waveguide grating embedded in a planar waveguide is demonstrated. A segmented waveguide structure is used as a built-in grating fabricated simultaneously with the channel waveguide to simplify the fabrication process. The wavelength peak heights are almost constant and a spatial dispersion value of 6×105 was obtained.

Modelling of high temperature optical constants and surface roughness evolution during MOVPE growth of GaN using in-situ spectral reflectometry

An investigation of in-situ optical monitoring during metalorganic vapour phase epitaxy (MOVPE) growth of GaN is reported. We describe the modelling of experimental optical data to determine the important properties of the GaN films such as the high temperature optical constants, the evolving surface roughness during coalescence and the film growth rate. Real time spectral reflectometry has been implemented as a routine tool for quantitative and qualitative monitoring during GaN MOVPE growth across the wavelength range 300–750 nm. The technique allows rapid material optimisation for device performance and tracking of run to run variation. Two multilayer optical modelling techniques have been investigated to simulate the time-dependent reflectance signatures. A virtual interface method where the simulation must begin after a smooth surface has been achieved, and an enhanced modelling routine, developed in-house, to include the evolving surface roughness during coalescence. It is shown that the high temperature optical constants are in close agreement with the limited published literature values, and the growth rate is consistent with post-growth thickness measurements. Using atomic force microscopy (AFM) and spectroscopic ellipsometry to study the surfaces of interrupted GaN growth runs, we show for the first time that the surface topography of a GaN film during coalescence contains components of both macroscopic and microscopic roughness with respect to the optical monitoring wavelengths. Additionally, we obtain very good agreement between values of RMS roughness determined by in-situ spectral reflectometry and spectroscopic ellipsometry compared with AFM.

Wavelength and power monitoring of DWDM systems using scanning F–P filter calibrated with a F–P laser

A novel technique to overcome the long-term drift and hysteresis of a scanning Fabry–Perot filter was developed and applied to wavelength and power monitoring of DWDM system. By using the comb peaks generated by a temperature-stabilized, near threshold-biased Fabry–Perot diode laser as wavelength reference for the scanning Fabry–Perot filter, wavelength and power measurement accuracy of better than ±10 pm and 0.2 dB, respectively, were achieved.

High-performance Liquid Chromatographic Analysis of Sildenafil Citrate and Methyltestosterone Adulterants in a Herbal Medicine

Sildenafil citrate (Viagra) and methyltestosterone were detected in herbal medicine capsules from mainland China by thin layer chromatography (TLC), ultraviolet spectrometry (UV), gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass-mass spectrometry (LC-MS-MS). The sample was further assayed by high-performance liquid chromatography (HPLC). Separation was conducted on an Inertsil ODS-2 reversed-phase column using gradient: elution with acetonitrile and 0.1 % (v/v) phosphoric acid as the mobile phase. Propyl paraben was used as an internal standard and the monitor wavelength was 254 nm. Calibration curves of standard sildenafil citrate and methyltestosterone were constructed in the range of 80-800 and 20-200μ/m L, respectively. The relative standard deviations of sildenafil citrate and methyltestosterone for intra-day and inter-day analyses were 0.54-3.56 % and 1.62-3.75 %, respectively. The recoveries of the synthetic drugs from herbal medicine ranged from 98.0 to 100.4 %. The sildenafil citrate and methyltestosterone content in herbal medicine was 20.0 and 1.6 mg/cap, respectively.

Dynamics of photoinduced changes in birefringence and dichroism in a nematic phase containing an azobenzene as dopant.

Changes in birefringence and dichroism induced by light were monitored after pulse excitation of a nematic phase consisting of a mixture of a low molecular weight liquid crystal (ZLI-1132) and a dopant 4-(N,N-dimethylamino)-azobenzene. After excitation in the UV, large changes in the light transmitted by the sample, placed between polarizers at various angles or in the polarized absorption spectra, could be detected and were monitored as a function of time and temperature in samples with 1-10% w/w of dopant. Birefringence experiments, performed with different monitoring wavelengths and with dopants that degrade all the absorbed energy as heat, demonstrate that all the changes observed are due to the photoisomerization process of the dopant. The recovery of the optical delay in the sample and of the polarized absorption follows the same monoexponential kinetics, indicating that E-Z isomerization of the dopant governs the order of the nematic phase. When samples are irradiated near the clearing point, a photoinduced nematic-isotropic phase change is observed.

Solvation Dynamics of Coumarin-153 in a Room-Temperature Ionic Liquid

Room-temperature ionic liquids are rapidly emerging as a new class of medium that is ideally suited for carrying out chemical reactions and various other applications. In this paper, steady-state and time-resolved fluorescence behavior of coumarin-153 (C153) have been reported in a room-temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate or [BMIM][BF4]. The polarity of the solvent, as estimated from the fluorescence maximum of C153, is found to be 48.9 on the ET(30) polarity scale. The fluorescence decay behavior of C153 in [BMIM][BF4] is found to be dependent on the monitoring wavelength. Although the time dependence of fluorescence in the blue region of the spectrum is represented by a multicomponent decay, that in the red region of the spectrum consists of clear growth followed by decay. The time-dependent evolution of the fluorescence spectrum of C153, constructed from the decay profiles at several wavelengths, indicates biphasic solvation dynamics similar to that observed in the c...

The Relaxation Pathways of CdSe Nanoparticles Monitored with Femtosecond Time-Resolution from the Visible to the IR: Assignment of the Transient Features by Carrier Quenching

The relaxation dynamics of photoexcited CdSe nanoparticles (NPs) were studied with femtosecond pump−probe spectroscopy in the spectral range from 450 nm to 5 μm. Thus, the intraband relaxation of the electron and the hole were monitored with femtosecond time resolution. The transition from delocalized electronic to localized defect states and the slower relaxation through the trapping sites (trap hopping mechanism) were followed by time-resolved emission on time scales from picoseconds to milliseconds in the spectral range from the visible into the mid-infrared. The spectral dynamics in the visible, near-infrared (NIR), and infrared (IR) range give a mechanistic picture about the relaxation pathway of the excited charge carriers in CdSe NPs. In addition, by using electron and hole quenchers to the photoexcited nanoparticles, we could assign the observed dynamics to the electron or the hole. In the visible range, bleach features (negative signals in the differential transient absorption measurements) were observed at early delay times with time components of 2 ps, 30 ps, and a long-lived component of ∼200 ps. Based on the quenching experiments, the bleach could be assigned to contributions from the electron and the hole. In the NIR and IR spectral range, the transient signal for short delay times (<1 ns) were positive (transient absorption). A decay time of 1.2 ps was found for the transient absorption observed in the NIR. With the carrier removal technique, it could be shown that the NIR signal is mainly due to hole transitions. The IR signal with lifetimes of 2 ps, 30 ps, and a long component of ∼200 ps compares directly to the decay times observed in the visible spectral range. It therefore is also composed of contributions from electron and hole. Photoluminescence is observed in the visible range at 570 nm (near band edge recombination), in the NIR at 1000 nm (deep-trap emission), and in the IR region at 4.8 μm (deeper-trap emission) with lifetimes of 43 ns, 250 ns, and 1 μs, respectively. The lifetimes of the emission increased for longer monitoring wavelengths, suggesting that for the investigated sample, the carriers relax from the band edge into shallow traps and from there continue stepwise relaxation into lower energy sites (trap hopping mechanism).

Wideband athermal wavelength monitor integratedwavelength temperature-tunable DFB-LD module

A wavelength temperature-tunable DFB-LD module containing a wideband athermal birefringent filter for a wavelength monitor has been developed. The FSR and the thermal drift of the filter are measured to be 12.7 nm and 0.26 pm/°C, respectively. By temperature wavelength tuning, ten channel selection for 50 GHz spacing and stabilisation with locking accuracy of ±7 pm are also demonstrated.

High-resolution wavelength monitoring using differential/ratio detection of junction voltage across a diode laser

High-resolution, compact, and power-insensitive wavelength monitoring can be realized by using a low-cost diode laser as the wavelength sensor. The wavelength resolution can be improved by more than an order with the help of the Fabry-Perot resonance inside the cavity of a diode laser, as well as by differential or ratio detection. Wavelength resolution of 0.01 nm can he obtained with much relaxed requirement on the detection circuitry. The wavelength monitoring with such resolution ran tolerate up to 15 dB of power variation on the incident light power.

Monitoring light source for CMS lead tungstate crystal calorimeter at LHC

Light monitoring will serve as an intercalibration for Compact Muon Solenoid (CMS) lead tungstate crystals in situ at the Large Hadronic Collider, which is crucial for maintaining crystal calorimeter's subpercent constant term in the energy resolution. This paper presents the design of the CMS electromagnetic calorimeter monitoring light source and high-level distribution system. The correlations between variations of the light output and the transmittance for the CMS choice of yttrium-doped PbWO/sub 4/ crystals were investigated and were used to study monitoring linearity and sensitivity as a function of wavelength. The monitoring wavelength was determined so that a good linearity as well as adequate sensitivity can be achieved. The performance of a custom manufactured tunable laser system is presented. Issues related to monitoring precision are discussed.

Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 8. Selectivity at Poly(vinyl alcohol)-Polyelectrolyte Blend Modified Optically Transparent Electrodes

Poly(vinyl alcohol) (PVA)-based polymer blends show potential utility as polymer films for a newly designed spectroelectrochemical sensor to achieve three modes of selectivity: charge-selective partitioning, electrolysis potential, and spectral absorption wavelength. The polymer blends were formulated by entrapping two polyelectrolytes, poly(vinylbenzyltrimethylammonium chloride) (PVTAC) and poly(acrylic acid) (PAA) into a cross-linked PVA matrix, which was covalently coated onto the surface of ITO glass. Sensing of the analyte is based on the change in attenuation of the light guiding through an optical substrate resulting from an electrochemical reaction of the analyte induced by electromodulation. The signal of the analyte in a competitive binary system is isolated by careful choice of polymer modifying film, potential window and monitoring wavelength. A 10−4 M equimolar binary solution of Ru(BiPy)32+ and Fe(CN)63– was used to study the selectivity of charge-selective partitioning. Cyclic voltammograms clearly demonstrated the exclusion of same charged ions from the selective layer with polymer blend modified sensors. 10−4 M equimolar Ru(CN)64– and Fe(CN)64– was chosen to demonstrate the selectivities of electrolysis potential and spectral absorbance wavelength. The detailed kinetics and associated electrochemical and optical waveforms from the spectroelectrochemical sensors in competitive binary mixtures of analytes are presented.