Wavelength Switching Research Articles

Dynamic wavelength switching of a remote nitrogen or air laser with chirped femtosecond laser pulses

We experimentally investigate the influence of the chirp of 800 nm Ti:sapphire pump laser pulses on the lasing behaviors of N2+ ions for the transitions between the excited electronic B2∑u+ state (v′ = 0) and the ground X2∑g+ state (v = 0,1) at wavelengths of 391 and 428 nm. We found that as the chirp of the pump laser pulses varies from negative to positive, the intensities of the lasing signals at 391 and 428 nm show different chirp-dependent behaviors. Namely, the coherent emission at 391 nm reaches the maximum when the chirp of the pump pulse is transform-limited; whereas the 428 nm emission becomes strongest when the pump pulse is negatively chirped. This observation is ascribed to different self-generated seed sources produced in the plasma channel, which is verified by introducing an external seed for a pump–probe measurement. Our finding enables switching of wavelengths of remote lasing emissions of N2+ by manipulating the chirp of the pump laser pulses.

All-optical quaternary logic gates – An extension of binary logic gates

Abstract All optical multivalued logic processors are of paramount importance in optical computing and signal processing. In this communication, the author proposes a new method of developing all-optical quaternary logic gates which are the extension of binary logic gates. To develop the quaternary logic gate the authors first coverts the quaternary frequency encoded data into equivalent binary intensity encoded data; then binary logic operations are done among the equivalent binary data, and finally the intensity encoded data outputs are converted into frequency encoded quaternary logic output. Simulation result supports the feasibility of the proposed scheme. Novelty of the scheme is that the same optical circuit is dedicated to implement any two-input quaternary logic operation only by changing two basic switches functioning as binary logic gates. Finally, the authors have cascaded these logic gates using “1×2” all-optical switches to develop quaternary logic unit by means of which any kind of quaternary logic operation as proposed in this scheme can be performed. Dense wavelength division demultiplexers (DMUX) are used here for wavelength routing purpose, and switching and frequency conversion characters of semiconductor optical amplifiers are exploited to develop very fast and secure quaternary logic unit.

Simultaneous determination of triple therapy for Helicobacter pylori in human plasma by reversed phase chromatography with online wavelength switching

The infection of gastric mucosa by Helicobacter pylori (HP) is an essential cofactor in the aetiology of gastroduodenal ulcer and gastric carcinoma. Because of the bacterial resistance, combination therapy containing omeprazole (OME), tinidazole (TNZ) and clarithromycin (CLA) is commonly used for eradication of HP. However, the simultaneous determination of the triple therapy in human plasma was not reported. A simple, reproducible, and selective HPLC method was developed for the simultaneous determination of the triple therapy mixture used for management of HP infections in human plasma. An HPLC procedure based on a liquid–liquid extraction, enrichment of the analytes and subsequent reversed-phase chromatography with UV detection was used. To enable sensitive and selective detection, the method involved the use of online wavelength switching detection, with two different detection wavelengths; 280nm for detection of OME and TNZ and 210nm for detection of CLA. Separations were performed on C18 analytical column with acetonitrile–10mM phosphate buffer of pH=3.0 at flow rate of 1.0mLmin−1. The linear ranges in human plasma were 0.05–10μgmL−1 with correlation coefficients >0.9990. The detection limits in human plasma were 0.02–0.07μgmL−1. Validation parameters were assessed in compliance with US-FDA guidelines. The method proved to be valuable for the therapeutic drug monitoring after oral administration of triple therapy tablets.

Application of isoabsorption plots generated by high-performance liquid chromatography with diode array detection to the development of multicomponent quantitative analysis of traditional herbal medicines.

Multicomponent quantitative analysis is one of the mainstream quality control methods of traditional herbal medicines. Since the constituents of traditional herbal medicines samples are complex, the development of high-performance liquid chromatography methods is laborious. In this study, an isoabsorption plot, a chromatographic/spectrometric data image plotted by diode array detection was utilized to facilitate the establishment of a high-performance liquid chromatography method by optimizing and validating the detection conditions off-line. Consequently a simple, reliable and accurate method for simultaneous determination of seven active polyphenolic components (protocatechuic acid, chlorogenic acid, caffeic acid, p-coumaric acid, rosmarinic acid, scutellarin, and apigenin) in Qingfei mixture, a long-used Chinese prescription, was developed. The chromatographic separation was performed on a C18 column with gradient elution of phosphoric acid aqueous solution (0.05%, v/v) and acetonitrile, and a wavelength switch program optimized with isoplot was adopted for detection. The method was validated in terms of linearity, sensitivity, precision, repeatability, and accuracy and was successfully applied to the simultaneous determination of the seven polyphenolic components in different production batches of Qingfei Mixture. These results indicated that isoplot is an effective tool to improve the establishment of multicomponent quantitative analysis methods.

Narrow band wavelength selective filter using grating assisted single ring resonator

This paper illustrates a filter configuration which uses a single ring resonator of larger radius connected to a grating resonator at its drop port to achieve single wavelength selectivity and switching property with spectral features suitable for on-chip wavelength selection applications. The proposed configuration is expected to find applications in silicon photonics devices such as, on-chip external cavity lasers and multi analytic label-free biosensors. The grating resonator has been designed for a high Q-factor, high transmittivity, and minimum loss so that the wavelength selectivity of the device is improved. The proof-of-concept device has been demonstrated on a Silicon-on-Insulator (SOI) platform through electron beam lithography and Reactive Ion Etching (RIE) process. The transmission spectrum shows narrow band single wavelength selection and switching property with a high Free Spectral Range (FSR) ~60 nm and side band rejection ratio >15 dB.

Abstract 430: Impairment of Instant Membrane Resealing by Lipid Raft Clustering in Endothelial Cells: Role in NLRP3 Inflammmasome Activation

Instant membrane resealing importantly contributes to the functional and structural integrity of the endothelial cells (ECs) that are exposed to various physical and chemical stimuli in blood stream. The present study was designed to explore the molecular mechanisms mediating this endothelial membrane resealing with a focus on the role of lipid rafts (LR) clustering. Using high energy Laser gun, a tiny hole was made in cultured EC bathed with FM1-43, and the rapid entry of this FM1-43 to produce fluorescence was used to measure membrane resealing. We demonstrated that ECs exhibited a Ca2+-dependent instant membrane resealing, as shown by a significant reduction of fluorescence appearance within these cells compared to ECs bathed with Ca2+ free solution. This Ca2+-dependent instant membrane resealing was also observed in ECs up stimulation of Lactobacillus casei cell wall fragments (LCWE), which was commonly used to produce arteritis. When ECs were pretreated with LRs clustering stimulators such as C-16 ceramide, ASMase or FasL, EC membrane resealing was substantially abolished and membrane wounding areas are enriched with LR clusters. By dual wavelength high speed wavelength switching microscopy, we found that a small Ca2+ influx (fura-2 fluorescence) was recorded at beginning of LCWE treatment of ECs (about 10 min), but membrane was immediately resealed (no PI fluorescence). However, if the LR stimulator FasL was used to pretreat these ECs, a large flushing of both PI and Ca2+ into ECs was monitored. By calculation of df/dt and time of PI fluorescence reaching the maximum, it was shown that FasL largely increased LCWE-induced PI fluorescence to a level equal to ECs with Ca2+-free solution over a 20-min period (maximum df/dt=1.17 fold/sec±0.22 at 14 min with FasL+Ca2+, 0.87 fold/sec±0.21 at 19 min with Ca2+ free, and 0.03 fold/sec±0.01 at 20 min with Ca2+ in bath). In addition, it was shown that impaired EC membrane resealing significantly enhanced the production of active caspase-1, a marker of NLRP3 inflammasome activation (a ~3-fold increase). These results strongly suggest that ceramide-associated LR clustering impairs the instant membrane resealing in ECs, which may activate EC inflammasomes leading to vascular inflammation and injury.

Wavelength switching of erbium-doped fiber laser by using Mach–Zehnder interferometer and cavity loss control

A new wavelength-switchable erbium-doped fiber laser cavity is proposed and demonstrated. A Mach–Zehnder interferometer with controllable path-length difference was used in the laser cavity to tune the transmission peaks between two output paths of the interferometer. The erbium-doped fiber amplifier used in the laser cavity showed a tilted gain spectrum over the concerned wavelength range. A fiber bending scheme was used to switch the lasing wavelength taking advantage of the gain-tilt characteristics of the spectrum. The experimental result showed a stable four-wavelength lasing for each tuning and bending.

Fast wavelength switching with tunable distributed amplification distributed feedback laser by feedforward control technique

We proposed a method of accelerating the wavelength switching of a tunable distributed amplification distributed feedback (DFB) laser by feedforward control. From experimental laser responses, we designed and simulated feedforward controllers using MATLAB/Simulink so as to reduce the time for wavelength stabilization. We applied this method to two different cases involving a laser drive circuit with a large output current and a 50 ns rise time, and a laser drive circuit with a moderate output current and a 5 ns rise time. In both cases, we showed that the wavelength switching times were improved from 450 to 150 ns and from 75 to 35 ns, respectively. From these results, the proposed control technique is confirmed to be efficient for possible practical applications.

Modeling of two wavelength switching using a reflective vertical cavity semiconductor saturable absorber

Wavelength switching between two optical signals has been studied numerically utilizing the concept of cross-absorption modulation and partial cross-phase modulation in a reflective vertical cavity semiconductor saturable absorber (R-VCSSA). The switching performance of an R-VCSSA designed with high power impedance-matched top mirror reflectivity is studied by fixing a control beam (CB) at low power cavity resonance wavelength (λres) and a signal beam on the short wavelength side of λres, with a fixed low input power. On gradually increasing the CB input power, the carrier concentration within the cavity increases which modifies the absorption and the refractive index of the saturable absorber. This results in a change in the output power of both the beams. In the analysis we have considered a 40Gb/s input signal. The high intra-cavity power introduces thermal effects within the VCSSA cavity due to which the effective cavity length of the device changes. The change in cavity length leads to a red-shift of the cavity resonance wavelength. This effect has also been incorporated in the model. The advantage of a VCSSA, used for switching is owing to its comparatively small carrier recombination time (~5ps or less), which could be utilized for the high speed optical system.

Optical bistability and four-wave mixing with a single nitrogen-vacancy center coupled to a photonic crystal nanocavity in the weak-coupling regime.

We explore optical bistability and degenerate four-wave mixing of a hybrid optical system composed of a photonic crystal nanocavity, a single nitrogen-vacancy center embedded in the cavity, and a nearby photonic waveguide serving for in- and outcoupling of light into the cavity in the weak-coupling regime. Here the hybrid system is coherently driven by a continuous-wave bichromatic laser field consisting of a strong control field and a weak probe field. We take account of the nonlinear nature of the nitrogen-vacancy center in the Heisenberg-Langevin equations and give an effective perturbation method to deal with such problems in the continuous-wave-operation regime. The results clearly show that the bistability region of the population inversion and the intensity of the generated four-wave mixing field can be well controlled by properly adjusting the system practical parameters. The nanophotonic platform can be used to implement our proposal. This investigation may be useful for gaining further insight into the properties of solid-state cavity quantum electrodynamics system and find applications in all-optical wavelength converter and switch in a photonic crystal platform.

Visualization of endosome dynamics in living nerve terminals with four-dimensional fluorescence imaging.

Four-dimensional (4D) light imaging has been used to study behavior of small structures within motor nerve terminals of the thin transversus abdominis muscle of the garter snake. Raw data comprises time-lapse sequences of 3D z-stacks. Each stack contains 4-20 images acquired with epifluorescence optics at focal planes separated by 400-1,500 nm. Steps in the acquisition of image stacks, such as adjustment of focus, switching of excitation wavelengths, and operation of the digital camera, are automated as much as possible to maximize image rate and minimize tissue damage from light exposure. After acquisition, a set of image stacks is deconvolved to improve spatial resolution, converted to the desired 3D format, and used to create a 4D "movie" that is suitable for variety of computer-based analyses, depending upon the experimental data sought. One application is study of the dynamic behavior of two classes of endosomes found in nerve terminals-macroendosomes (MEs) and acidic endosomes (AEs)-whose sizes (200-800 nm for both types) are at or near the diffraction limit. Access to 3D information at each time point provides several advantages over conventional time-lapse imaging. In particular, size and velocity of movement of structures can be quantified over time without loss of sharp focus. Examples of data from 4D imaging reveal that MEs approach the plasma membrane and disappear, suggesting that they are exocytosed rather than simply moving vertically away from a single plane of focus. Also revealed is putative fusion of MEs and AEs, by visualization of overlap between the two dye-containing structures as viewed in each three orthogonal projections.

Fast-Tuning Coherent Burst-Mode Receiver for Metropolitan Networks

We demonstrate a fast wavelength-tunable burst-mode receiver for coherent 28 GBd dual-polarization quadrature phase shift keying signals using a commercially available DS-DBR laser as the local oscillator (LO). We find that the frequency drift and linewidth of the LO must be precisely controlled to prevent bit-error-ratio (BER) penalties when the signal undergoes transmission distances typical of metropolitan-area networks. We demonstrate reduction of the LO frequency drift and linewidth after wavelength switching by compensation using the phase section of the laser and achieve negligible BER penalty with burst-mode reception for single-mode fiber transmission up to 1280 km. We also measure the sensitivity of the receiver to LO detuning when multiple wavelength-division multiplexed channels are received simultaneously as in a broadcast-and-select network architecture.

Core–Shell Heterojunction of Silicon Nanowire Arrays and Carbon Quantum Dots for Photovoltaic Devices and Self-Driven Photodetectors

Silicon nanostructure-based solar cells have lately intrigued intensive interest because of their promising potential in next-generation solar energy conversion devices. Herein, we report a silicon nanowire (SiNW) array/carbon quantum dot (CQD) core-shell heterojunction photovoltaic device by directly coating Ag-assisted chemical-etched SiNW arrays with CQDs. The heterojunction with a barrier height of 0.75 eV exhibited excellent rectifying behavior with a rectification ratio of 10(3) at ±0.8 V in the dark and power conversion efficiency (PCE) as high as 9.10% under AM 1.5G irradiation. It is believed that such a high PCE comes from the improved optical absorption as well as the optimized carrier transfer and collection capability. Furthermore, the heterojunction could function as a high-performance self-driven visible light photodetector operating in a wide switching wavelength with good stability, high sensitivity, and fast response speed. It is expected that the present SiNW array/CQD core-shell heterojunction device could find potential applications in future high-performance optoelectronic devices.

The study of multi-granularity switching based on parallel processing routing technology

A novel parallel processing optical code label-switched paths (PP-OC-LSPs) is proposed to achieve efficient conversion performance for core router and large throughput in optical network, which combines the merits of optical label switching (OLS), optical code-generalized multi-protocol label switching (OC-GMPLS), and optical code division multiplexing-paths (OCDM-paths) technology. In the proposed technology, the smallest switching granularity is an optical code which carries the label information of data packets and would be parallel converted in the core router. In the edge node, the label and payload are separated by using the optical polarity characteristics, and encoded/decoded with two different code series based on OCDM techniques so as to process them in parallel. Compared with the OLS, its switching capability has been extended to support fiber switching, wavelength switching, and OCDM switching. We present simulation results to demonstrate its performance over OCDM-paths technology.

Switchable double wavelength generating vertical external cavity surface-emitting laser

Switchable, double wavelength generation is demonstrated from a single vertical external cavity surface-emitting laser chip. Power of ~0.5 W for two wavelengths λ≈967 nm and 1,018 nm i.e. within the spectral distance of 51 nm were registered. In the semiconductor heterostructure a single set of nominally identical quantum wells was enclosed in a single, two-mode resonant microcavity. The wavelength switching was induced by the change of the pump power. The increase or decrease of the pump power changes the active region temperature and thus tunes spectrally the gain spectrum to the one of two modes.

Wavelength Switching Speed in Semiconductor Ring Lasers With On-Chip Filtered Optical Feedback

We experimentally and numerically characterize the wavelength switching speed of a tunable semiconductor ring laser using filtered optical feedback. The feedback is realized employing two arrayed-waveguide gratings to split/recombine light into different wavelength channels. The wavelength tuning and switching is controlled by changing the currents injected in semiconductor optical amplifiers in the feedback section. A wavelength switching speed of a few nanoseconds is achieved. We investigate also the effect of the feedback parameters and noise strength on the wavelength switching speed.

Mechanism of Spectrum Moving, Narrowing, Broadening, and Wavelength Switching of Dissipative Solitons in All-Normal-Dispersion Yb-Fiber Lasers

We report experimental observations and numerical simulation results on the spectrum moving, narrowing, broadening, and wavelength switching of dissipative solitons (DSs) in an all-normal-dispersion Yb-fiber laser that is passively mode-locked by using the nonlinear polarization rotation (NPR) technique. We found numerically that the DS spectrum moving, together with spectrum narrowing/broadening, is caused by the effective gain profile change resulted from the moving of the artificial spectral filter. Furthermore, we show that the wavelength switching observed in the laser is a natural consequence of the effective gain switching. The moving of the artificial spectral filter could be originated from either the cavity birefringence change or the polarizer rotation. Due to the broad gain and the artificial birefringent filter introduced by the NPR technique, apart from the central wavelength shifting and bandwidth changing, wavelength switching of DSs could be obtained by simply rotating the polarizer. Numerical simulations well reproduced the experimental observations. Our results suggest that extra effort should be made for wavelength tuning if there is any polarization-dependent component in the cavity as the wavelength switching will interrupt the continuously wavelength shift.

Optimal Wavebanding in WDM Ring Networks

Savings in switching costs of an optical cross-connect can be achieved by grouping together a set of consecutive wavelengths and switching them as a single waveband. This technique is known as waveband switching. While previous work has focused on either uniform band sizes or nonuniform band sizes considering a single node, in this paper we focus on the number of wavebands and their sizes for ring topologies. First, we show that such solutions are inadequate when considering the entire network. We then present a novel framework for optimizing the number of wavebands in a ring network for deterministic traffic. The objective of the Band Minimization Problem is to minimize the number of nonuniform wavebands in the network while using the minimum possible number of wavelengths. We show that the problem is NP-hard and present heuristics for it. We then consider a specific type of traffic, namely all-to-all traffic, and present a construction method for achieving the minimum number of wavebands in the ring. Our results show that the number of ports can be reduced by a large amount using waveband switching compared to wavelength switching, for both all-to-all traffic and random traffic. We also numerically evaluate the performance of our waveband design algorithms under dynamic stochastic traffic.

Fast Wavelength Switching 6 GBd Dual Polarization 16QAM Digital Coherent Burst Mode Receiver

A commercially available digital supermode distributed Bragg reflector tunable laser is employed as a fast wavelength switching local oscillator (LO) in a dual polarization (DP) 16-quadrature amplitude modulation (16QAM) coherent burst mode receiver. A digital coherence enhancement technique is used to compensate both the Lorentzian and non-Lorentzian distributed phase noise of the tunable LO laser. It is shown that differential decoding is not sufficient to overcome the substantial bit errors caused by the LO laser phase noise. However, the coherence enhancement technique enables the reception of low symbol rate DP-16QAM bursts, with an average optical signal to noise ratio penalty of 3.5 dB observed relative to theory at the forward error correction threshold (1.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ).

Bichromatic random laser from a powder of rhodamine-doped sub-micrometer silica particles

We studied the random laser (RL) bichromatic emission (BCE) from a powder consisting of silica particles infiltrated with Rhodamine 640 (Rh640) molecules. The BCE is attributed to Rh640 monomers and dimers. Because of the efficient monomer-dimer energy transfer, we observed RL wavelength switching from ≈ 620 nm to ≈650 nm and the control of the emitted wavelength was made by changing only the excitation laser intensity. None of external parameters such as excitation laser spot size or radiation detector position was changed as in previous experiments. Two laser thresholds associated either to monomers or dimers were clearly observed. Moreover, an effect analog to frequency-pulling among two coupled oscillators was identified measuring the RL spectra as a function of the excitation laser intensity. A wavelength shift, Δλ, was measured between the monomer and dimer resonance wavelengths, changing only the excitation laser intensity. The maximum value of Δλ ≈ 16 cm−1 was obtained for laser pulses of 7 ns with 30 μJ.