Center Wavelength Shift Research Articles

100-km-reach, 40 Gb/s/λ downstream and 10 Gb/s/λ upstream, channel-reuse WDM-PON employing tunable laser with back-reflection optical signal detection-based self wavelength management

We experimentally demonstrate a 100-km-reach, channel-reuse wavelength-division-multiplexing passive optical network (WDM-PON) with 40 Gb/s/λ downstream and 10 Gb/s/λ upstream transmission and a back-reflection optical signal detection-based automatic wavelength control method for a tunable laser used in a colorless optical network unit. Channel-reuse, full-duplex, 40 Gb/s/λ downstream and 10 Gb/s/λ upstream transmission on a 100 GHz WDM grid with 100 km reach was achieved. The transmission performance was measured using different optical signal to back-reflection optical signal ratios, optical signal to Rayleigh backscattering noise ratios, and different central wavelength shifts between the upstream and downstream signals in the channel-reuse system.

Enhanced spatial near-infrared modulation of graphene-loaded perfect absorbers using plasmonic nanoslits.

Modulating spatial near-infrared light for ultra-compact electro-optic devices is a critical issue in optical communication and imaging applications. To date, spatial near-infrared modulators based on graphene have been reported, but they showed limited modulation effects due to the relatively weak light-graphene interaction. In combination with graphene and metallic nanoslits, we design a kind of ultrathin near-infrared perfect absorber with enhanced spatial modulation effects and independence on a wide range of incident angles. The modulated spectral shift of central wavelength is up to 258.2 nm in the near-infrared range, which is more promising in applications than state-of-the-art devices. The modulation enhancement is attributed to the plasmonic nanoslit mode, in which the optical electric field is highly concentrated in the deep subwavelength scale and the light-graphene interaction is significantly strengthened. The physical insight is deeply revealed by a combination of equivalent circuit and electromagnetic field analysis. The design principles are not only crucial for spatial near-infrared modulators, but also provide a key guide for developing active near-infrared patch nanoantennas based on graphene.

Twin-Core Fiber-Based Erbium-Doped Fiber Laser Sensor for Decoupling Measurement of Temperature and Strain

In this paper, a novel all-fiber laser sensing configuration for decoupling measurement of strain and temperature based on the twin-core fiber (TCF) with an in-line embedded fiber Bragg grating (FBG) is proposed and experimentally demonstrated. An erbium doped fiber ring laser is built, with an optical signal-to-noise ratio higher than 40 dB and a power instability of 6.75 $\mu \text{W}$ in 1 h. Due to the different spectrum responses of the TCF and FBG to the uniform variation of strain and temperature, the decoupling measurement for these two measurands could be achieved by real-time monitoring both the center wavelength shift and the peak power variation.

Enhancing the output bandwidth of a chirped-pulse Ti:S multipass amplifier via optical rotatory dispersion

In this paper, we present theoretically a simple and passive method to modulate the output spectrum of a broadband multi-pass Ti:S amplifier by means of polarization-dependent gain and optical rotator dispersion (ORD). By choosing the ORD and two π-polarization wavelengths, we can shape the effective gain section flexibly in order to suppress spectral narrowing and red-shift effects. Our simulations show the amplifier we have designed can scale a 0.4nJ, 10fs seed pulse up to 3.31mJ almost without spectral narrowing and central wavelength-shift. Increasing the difference of the two π-polarization wavelengths can result in the saddle output spectrum with a span of about 149nm, which is very helpful for further laser amplification to avoid spectral narrowing.

Out-of-plane nano-electro-mechanical tuning of the Fano resonance in photonic crystal split-beam nanocavity

We propose and experimentally demonstrate the use of Fano resonance as a means to improve the Quality factor of photonic crystal split-beam nanocavities. The Fano resonance is triggered by the interference between the second-order quasi-transverse electric resonant mode and the leaky high-order quasi-transverse electric propagation mode of the optimized photonic crystal split-beam nanocavity. Compared with a similar photonic crystal split-beam nanocavity without asymmetric Fano lineshape, the Q-factor is increased up to 3-fold: from 1.99×104 to 5.95×104. Additionally, out-of-plane tuning of the Fano resonance is investigated by means of a Nano-Electro-Mechanical Systems based actuator. The maximum centre wavelength shift of the Fano resonance reached 116.69 pm, which is more than 4.5 times the original quasi-Full Width at Half Magnitude.

Nanocomposite based on a liquid crystal doped with aluminum nitride nanotubes for optical sensor of sulfur dioxide

AbstractIt has been demonstrated the possibilities of designing the material for optical sensor primary transducer. The nanocomposites based on a cholesteric liquid crystal with aluminum nitride for material of primary transducer of sulfur dioxide optical sensor were studied. The spectral characteristics of studied nanocomposite under the influence of sulfur dioxide were studied. The shift of central wavelength of selective reflection under the sulfur dioxide concentrations was observed.

Femtosecond Laser Ablated FBG Multitrenches for Magnetic Field Sensor Application

Three-dimensional multitrench microstructures, femtosecond laser ablated in fiber Bragg grating (FBG) cladding, TbDyFe sputtered is proposed and demonstrated for magnetic field sensing probe. Parameters such as the number of straight microtrenches, translation speed (feed rate), and laser pulse power of laser beam have been systematically varied and optimized. A 5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick giant Terfenol-D magnetostrictive film is sputtered on to FBG microtrenches, and acts as magnetic sensing transducer. Eight microtrench samples produced the highest central wavelength shift of 120 pm, nearly fivefold more sensitive compared with nonmicrostructured standard FBG. An increase in laser pulse power to 20 mW generated the magnetic sensitivity of 0.58 pm/mT. Interestingly, reduction in translational speed contributed dramatically to the rise in the magnetic sensitivity of the samples. These sensor samples show magnetic response reversibility and have great potential in the magnetic field sensing domain.

Stress sensing characteristics of two-dimensional photonic crystal cross-waveguide geometry

A two-dimensional photonic crystal cross-waveguide consisting of dielectric rods array immersed in air is designed. The optical field pattern and transmission spectra are analyzed by finite difference time domain method. The propagation characteristics and stress sensing behavior of photonic crystal are emphasized through analyzing the linear shift of central wavelength. The results show that optimized cross-waveguide can be used as a high performance dual-channel stress sensing device based on tunable photonic crystal structure.

Bidirectional 40 Gb/s/λ, 100 km-reach, channel-reuse WDM-PON employing tunable optical transceiver with optical intensity detection-based wavelength management

We experimentally demonstrate a channel-reuse, bidirectional 40Gb/s/λ, long-reach wavelength-division-multiplexing passive optical network (WDM-PON) and an optical intensity detection-based wavelength management method for tunable optical transceiver used in colorless optical network unit. A 100km reach, channel-reuse, 40Gb/s/λ transmission on a 100GHz WDM grid is achieved. Transmission performance is also measured with different optical-signal-to-Rayleigh-backscattering-noise ratios (OSRBNRs) and different central wavelength shifts (WSs) between upstream signal and downstream signal in the channel-reuse system. Optimal operating wavelength for the uplink optical signal and effective OSRBNR configurations taking into account AWG pass-band, wavelength instability of the bidirectional optical transmitters are proposed.

Characterization of the Dynamics of Photoluminescence Degradation in Aqueous CdTe/CdS Core-Shell Quantum Dots.

We investigate the effects of the excitation power on the photoluminescence spectra of aqueous CdTe/CdS core-shell quantum dots. We have focused our efforts on nanoparticles that are drop-cast on a silicon nitride substrate and dried out. Under such conditions, the emission intensity of these nanocrystals decreases exponentially and the emission center wavelength shifts with the time under laser excitation, displaying a behavior that depends on the excitation power. In the low-power regime a blueshift occurs, which we attribute to photo-oxidation of the quantum dot core. The blueshift can be suppressed by performing the measurements in a nitrogen atmosphere. Under high-power excitation the nanoparticles thermally expand and aggregate, and a transition to a redshift regime is then observed in the photoluminescence spectra. No spectral changes are observed for nanocrystals dispersed in the solvent. Our results show a procedure that can be used to determine the optimal conditions for the use of a given set of colloidal quantum dots as light emitters for photonic crystal optical cavities.

Athermal optical waveguide microring biosensor with intensity interrogation

Abstract The temperature sensitivity of optical waveguide microring (MR) is the critical factor to influence the performance of MR-based biosensor. An athermal MR-based biosensor with intensity interrogation is proposed and analyzed. The integrative biosensor chip is composed of sensing unit MR and interrogation unit Mach–Zehnder interferometer (MZI) with the same temperature sensitivity. The resonant wavelength shift of MR by temperature change is equal to the center wavelength shift of interrogation curve of MZI which cancel with each other during interrogation process. The polymer based integrative biosensor chip is designed and investigated. The simulation results show that the temperature sensitivity of the polymer waveguide biosensor is smaller than 1 pm/K with the temperature change between −10 K to 20 K relative to the reference temperature 20 °C and refractive index change from 0 to 0.05. The intensity interrogation method utilizing the power ratio between the two output ports of MZI has the flexibility of selecting large linear range and high resolution and is immune to output power fluctuations of the light source.

Modeling of spectral changes in bent fiber Bragg gratings.

To better apply fiber Bragg gratings (FBGs) to various bending required situations, good understanding of their bending characteristics is crucial. In this Letter, a theoretical model to describe the changes of spectral properties of an FBG against the bending radius is proposed. This model shows that all the bend-induced spectral changes, the shift of center wavelength, decrease of reflectivity, and reduction of bandwidth, may be explained by the decrease of the effective "dc" refractive index change spatially averaged over one grating period. Experimental results are in agreement with theoretical predictions and confirm the effectiveness of the proposed model.

Pasted type distributed two-dimensional fiber Bragg grating vibration sensor.

A pasted type distributed two-dimensional fiber Bragg grating (FBG) vibration sensor has been proposed and studied in this paper. The optical fiber is directly considered as an elastomer. The two-dimensional vibration can be separated by subtraction/addition of two FBGs' center wavelength shift. The principle of the sensor as well as numerical simulation and experimental analyses are presented. Experimental results show that the resonant frequencies of the sensor x/y main vibration direction are separately 1300/20.51 Hz, which are consistent with the numerical simulation analysis result. The flat frequency range resides in 10-750 Hz and 3-12 Hz, respectively; dynamic range is 28.63 dB; in the x main vibration direction, the sensor's sensitivity is 32.84 pm/g, with linearity 3.91% in the range of 10-60 m/s(2), while in the y main vibration direction, the sensor's sensitivity is 451.3 pm/g, with linearity 1.92% in the range of 1.5-8 m/s(2). The cross sensitivity is 3.91%. Benefitting from the two dimensional sensing properties, it can be used in distributed two-dimensional vibration measurement.

Silicon-based on-chip electrically tunable sidewall Bragg grating Fabry-Perot filter.

We report the design, fabrication, and testing of a silicon-based on-chip electrically tunable sidewall Bragg grating Fabry-Perot filter. Spectral measurement shows that the filter has a narrow notch in reflection of approximately 46 pm, a Q-factor of 33,500, and an extinction ratio of 16.4 dB. DC measurement shows that the average central wavelength shift rates with forward and reverse bias are -1.15 nm/V and 4.2 pm/V, respectively. Due to strong light confinement in the Fabry-Perot cavity, the electro-optic frequency response shows that the filter has a 3-dB modulation bandwidth of ∼5.6 GHz. The performance of using the filter to perform modulation of a 3.5 Gb/s2(7)-1 nonreturn-to-zero pseudorandom binary sequence is evaluated.

Optical Sensor for Steel Corrosion Monitoring Based on Etched Fiber Bragg Grating Sputtered With Iron Film

An optical sensor for steel corrosion monitoring based on etched fiber Bragg grating (FBG) sputtered with iron film is developed. The sensor is fabricated by magnetron sputtering an iron film on an etched FBG, and tested in sodium chloride solution. The chemical composition, structure, and morphology of film are investigated by energy dispersive X-ray analysis, X-ray diffraction, scanning electron microscope, and so on. The central wavelength shift and peak power of the FBG are analyzed with a spectral meter. The experimental results show that the wavelength shift and spectral chirp are related to the corrosion of iron film, and the sensor is able to monitor the status of iron in the corrosion process.

Facile synthesis of optical microcavities by a rationally designed anodization approach: tailoring photonic signals by nanopore structure.

Structural engineering of porous anodic aluminum oxide (AAO) nanostructures by anodization has been extensively studied in the past two decades. However, the transition of this technique into the fabrication of AAO-based one-dimensional photonic crystal is still challenging. Herein, we report for the first time on the fabrication of AAO optical microcavities by a rationally designed anodization approach. In our study, two feasible methods are used to fabricate microcavities with tunable resonance peak across the visible and near-infrared spectra. Distributed Bragg reflector (DBR) nanostructures are first fabricated by pulse anodization approach, in which the anodization voltage was periodically manipulated to achieve pseudosinusoidal modulation of the effective refractive index gradient along the depth of the AAO nanostructures. Microcavities were created by creating a nanoporous layer of constant porosity between two AAO-DBR nanostructures, and by introducing a shift of the phase of the porosity gradient along the depth of AAO. The position of the resonance peak in these microcavities can be linearly tuned by means of the duration of the high voltage anodization. These optical nanostructures are sensitive to alterations of the effective media inside the nanopores. The AAO microcavity shows a central wavelength shift of 2.58 ± 0.37 nm when exposed to water vapor. Our research highlights the feasibility of anodization technique to fabricate AAO-based photonic nanostructures for advanced sensing applications.

Bidirectional 10 Gb/s/λ, channel-reuse, long-reach DWDM-PON employing tunable optical transceiver with optical intensity detection-based wavelength management

We experimentally demonstrate a channel-reuse, bidirectional 10 Gb/s/λ, long-reach dense wavelength-division-multiplexing passive optical network (DWDM-PON) and an optical intensity detection-based wavelength management method for tunable optical transceiver used in colorless optical network unit. A channel-reuse, full-duplex, 42 km/87 km reach without/with optical amplification, 10 Gb/s transmission on a 50 GHz DWDM grid is achieved. Transmission performance is also measured with different optical-signal-to-Rayleigh-backscattering-noise ratios (OSRBNRs) and different central wavelength shifts between upstream signal and downstream signal in the channel-reuse system. Optimal operating wavelength for the uplink optical signal and effective OSRBNR configurations taking into account AWG pass-band, wavelength instability of the downlink optical transmitter and the distance of the feeder fiber are proposed.

Channel-reuse bidirectional transmission at 10 Gb/s/λ in long-reach DWDM-PON employing self wavelength managed tunable laser

We experimentally demonstrate a channel-reuse, bidirectional, 10Gb/s/λ, long-reach dense wavelength-division-multiplexing passive optical network (DWDM-PON) and an optical beat noise-based automatic wavelength control method for a tunable laser used in a colorless optical network unit (ONU). A 42km reach, channel-reuse, full-duplex, 10Gb/s transmission on a 50GHz DWDM grid is achieved. Transmission performance is also measured with different optical-signal-to-Rayleigh-backscattering-noise ratios (OSRBNRs) and different central wavelength shifts (WSs) between upstream signal and downstream signal in the channel-reuse system.

Fifty-five km reach, bidirectional, 400 Gb/s (40 \times 10 Gb/s), channel-reuse DWDM–PON employing a self-wavelength managed tunable laser

We experimentally demonstrate a channel-reuse bidirectional 10 Gb/s/λ long-reach dense wavelength-division multiplexing passive optical network (DWDM-PON) and an optical beat-noise-based automatic wavelength control method for a tunable laser used in a colorless optical network unit (where λ=wavelength). A 55 km, bidirectional, 400 Gb/s (40×10 Gb/s) capacity channel-reuse transmission with 100 GHz channel spacing is achieved. The transmission performance is also measured with different optical signal to Rayleigh backscattering noise ratios and different central wavelength shifts between upstream and downstream in the channel-reuse system.

Method for tuning chirp ratio of fiber gratings without central wavelength shift

A method for tuning the chirp ratio of a fiber grating without the central wavelength shift is proposed by using a two-fixed-end compressive beam, which induces a linear strain distribution along the grating. This technique allows dynamic control of the grating’s chirp ratio by changing the displacement of the translation stage. The 3-dB bandwidth tuning range is from 6.52 to 13.5 nm when the grating is tuned in the broadening way, while the bandwidth tuning range is from 6.52 to 0.95 nm in the compressing way. The proposed method has potential applications for the dynamic dispersion compensation and the sensors of pressure and displacement, etc., by detecting the change of bandwidth information.