Grating Devices Research Articles

Overcoming the Switching Bottlenecks in Wavelength-Routing, Multicast-Enabled Architectures

Modular optical switch architectures combining wavelength routing based on arrayed waveguide grating (AWG) devices and multicasting based on star couplers hold promise for flexibly addressing the exponentially growing traffic demands in a cost- and power-efficient fashion. In a default switching scenario, an input port of the AWG is connected to an output port via a single wavelength. This can severely limit the capacity between broadcast domains, resulting in interdomain traffic switching bottlenecks. An unexplored solution to this issue is to exploit multiple AWG free spectral ranges (FSRs), i.e., to set up multiple parallel connections between each pair of broadcast domains. In this paper, we study, for the first time, the influence of the FSR count on the throughput of a multistage switching architecture and propose a generic and novel analytical framework to estimate the blocking probability. We assess the accuracy of our analytical results via Monte Carlo simulations. Our study points to significant improvements with a moderate increase in the number of FSRs. We show that an FSR count beyond four results in diminishing returns. Furthermore, to investigate the tradeoffs between the network- and physical-layer effects, we conduct a cross-layer analysis, taking into account pulse amplitude modulation and rate-adaptive forward error correction. We illustrate how the effective bit rate per port increases with an increase in the number of FSRs.

Latest Achievements in Polymer Optical Fiber Gratings: Fabrication and Applications

Grating devices in polymer optical fibers (POFs) have attracted huge interest for many potential applications in recent years. This paper presents the state of the art regarding the fabrication of different types of POF gratings, such as uniform, phase-shifted, tilted, chirped, and long period gratings, and explores potential application scenarios, such as biosensing and optical communications.

Optimization of 1D Silver Grating Devices for Extraordinary Optical Transmission

This paper reports the behavior of extraordinary optical transmission (EOT) through 1D plasmonic nanostructure devices when thickness and periodicity of silver film simulated on glass substrate are fixed and only slit width is varied. Transverse magnetic (TM) polarized photon incident normally at the grating structure and zero-order transmission spectra has been extracted. Fano-resonance associate with the excitation of the surface plasmon polaritons (SPPs) has been evaluated carefully to calculate EOT. Excited plasmons along with the Febry-Perot mode have contributed toward the EOT through the periodic slits in the grating device. It has been found that its numerical value of EOT is maximum at a particular slit width, i.e., 409 nm, which is greater than one half and less than two third of periodicity, when wavelength of light is comparable with periodicity. This unique behavior is associated with the maximum incident energy coupled to the excited plasmon due to fundamental plasmonic mode being the most efficient. Such optimal devices find many applications in real world, e.g., light-emitting diodes (LEDs), biosensing, and SERs.

Analytic method for fast design of aperiodic fiber Bragg grating devices

An analytic method for fast design of aperiodic fiber Bragg grating (AFBG) devices by use of Fourier mode coupling (FMC) theory is presented. AFBG devices, which are often used in practice, include the superstructure, phase-shifted FBG, and the apodized FBGs with Gauss, cosine, raised-cosine, Hamming, or Blackman windows, and include the in-fiber Fabry–Perot cavities formed by two AFBGs. The analytic solutions to the reflectivities of these AFBG devices are obtained on the basis of FMC theory, from which closed-form expressions for the relation between the AFBG structure parameters and their reflection properties are derived. According to these expressions, an analytic algorithm is established to quickly design AFBG devices with the desired reflection properties, which has linear complexity. The design of each AFBG device was achieved in ∼50 ms on a general PC, and the reflection properties of the designed AFBG device were confirmed by using the transfer matrix method. This indicates that the analytic design methods proposed are highly efficient and sufficiently accurate.

An Optimal Au Grating Structure for Light Absorption in Amorphous Silicon Thin Film Solar Cell

Effect of different gold (Au) grating structures on light absorption in solar cell is investigated by finite elemental analysis using COMSOL multiphysics-RF module. The geometry of the solar cell consists of a 50-nm Au film on the substrate of amorphous silicon (a-Si). An optimum value of the slit width (w) of the Au grating has been obtained whereas periodicity of the grating structure remained the same. The periodicity in the grating device was chosen in such a way that the excitation of the surface plasmon polritons (SPPs) lies in the IR or NIR region where most of the spectrometers work well in practical life. Far-field transmission spectra were extracted from the grating device when illuminating with p-polarized light through the substrate side. Near-field plots of the Fano resonance (dip) associated with the excitation of the surface plasmon polritons (SPPs) were carefully examined to understand the underlying physics. It was deduced from the results that a grating device with slit width of 250–350 nm is the most efficient which reveals the fact that such device offers intermediate scattering from the grating structure and supports fundamental plasmonic mode. Hence, such devices absorb more light being most efficiently and find application in solar cell.

Programmable localized wrinkling of thin films on shape memory polymers with application in nonuniform optical gratings

Shape memory polymers (SMPs) can remember different shapes and can be recovered to their permanent shapes from temporary shapes with appropriate stimuli, such as heat, humidity, and electrical field. Using programmed thermal responsive SMPs as substrates, we demonstrate a self-assembly fabrication method for programmable surface wrinkling within a highly confined area that is accurately controllable. Different from global wrinkling reported in most of the literature, Joule heating through a heating wire embedded in the SMP substrate leads to temperature increase and thus recovery in a highly confined area of the SMP substrate, inducing localized wrinkling of the stiff thin film on SMPs. The patterns show good sinusoidal profiles, with the wrinkling wavelength and amplitude decreasing gradually with the distance from the heat source. The surface wrinkling area can be accurately tuned by controlling the heat input, such as power and duration. Based on this unique surface wrinkling phenomenon, we demonstrate a nonuniform reflective optical grating device, whose peak wrinkling wavelength and amplitude decrease gradually away from the heat source. This study offers a simple method to fabricate programmable localized wrinkling patterns, with potential applications in surface engineering, advanced manufacturing, optical gratings, and other demanding areas.

硅光子阵列波导光栅器件研究进展

硅光子阵列波导光栅器件研究进展

Analog signal processing in the terahertz communication links using waveguide Bragg gratings: example of dispersion compensation.

We study the possibility of analog signal processing for the upcoming terahertz (THz) high-bitrate communications using as an example the problem of dispersion compensation in the THz communication links. In particular, two Waveguide Bragg Grating devices (WBGs) operating in the transmission mode are detailed. WBGs are designed by introducing periodic corrugation onto the inner surface of the metalized tubes. The resultant devices operate in a single mode regime either in the vicinity of the modal cutoff or in the vicinity of a bandgap edge, featuring large negative group velocity dispersions (GVD). We fabricate the proposed WBGs using 3D stereolithography, and metallize them using wet chemistry. Optical properties of the fabricated WBGs are investigated both theoretically and experimentally. The results confirm single mode guidance, relatively high coupling efficiency, as well as large negative group velocity dispersions in the range of several -100's ps/(THz · cm) in the vicinity of 0.14THz. This makes the short sections of proposed WBGs suitable for compensating positive dispersion incurred in the THz wireless links or fiber-assisted THz interconnects for signals of several-GHz bandwidth. Finally, we comment on the challenges associated with the analog signal processing in the THz spectral range.

Design of temperature insensitive in vivo strain sensor using multilayer single mode optical fiber

Bone strain measurement is a case of interest and demanding task for osteogenic adaption responses. In this paper, a novel biocompatible optical sensor for the bone axial strain measurement was proposed. In case modern multilayer single mode WII type optical fibers are well designed, they exhibit superior characteristics compared to conventional metal strain gauges (SGs). Furthermore, they could be strong competitors for SGs based on fiber Bragg grating (FBG) devices. In this study, mode field diameter (MFD) was selected as the indirect parameter for sensing task, which was totally a new approach. The strain sensitivity of 70.7733 pm/μe was obtained. Moreover, temperature sensitivity was–3.0031 × 10–6 pm/°C, which was negligible and removed the temperature compensation complexity for the sensor structure presented. The satisfactory property achieved for the designed sensor is as a result of multilayer fiber’s complicated structure as well as the design procedure based on evolutionary genetic algorithm (GA). In addition, the sensor demonstrated a reliable performance as its sensitivity was independent of the magnitude of the applied load.

Modelling and dimensioning of a high-radix datacentre optical packet switch with recirculating optical buffers

Recently, high port-count optical packet switches, based on the Arrayed Waveguide Grating (AWG) device, have been proposed for providing the very high bandwidth and connectivity degree that will be required in future datacentre interconnection networks. A practical, cost-effective realisation of such a switch requires that over-subscription of the AWG cross-connect output ports be allowed, with the resulting packet contention being resolved using a packet buffering facility in the switch. In this paper, we propose an efficient AWG switch architecture of this type that uses a recirculating optical packet buffering scheme and we develop analytic modelling methods to estimate the switch packet blocking probability and packet buffering delay. The analytic model resolves internal traffic flows in the switch as Markov-modulated Poisson Processes (MMPP) and also allows modelling of offered load to the switch as a MMPP process. Taking this model of the switch, we first show its accuracy compared to discrete event simulations and then use it to develop a heuristic optimisation algorithm to dimension the switch hardware components, with the objective of minimising the operating cost by optimally dimensioning the main power consuming components, subject to constraints on the maximum contention probability and average and maximum propagation delays. The resulting optimised switch design demonstrates the proposed architecture to be a promising candidate for future high-port count datacentre switches.

Plasmonic properties of asymmetric dual grating gate plasmonic crystals

We report on numerical study of dispersion properties and frequency dependent absorption characteristics of asymmetric dual grating gate terahertz (THz) plasmonic crystals. The study shows that the dispersion relations of plasmons in a two-dimensional electron gas (2DEG) capped with asymmetric dual grating gates have energy band gaps in the Brillion zones. Depending on the wave vector, the plasmons can have symmetrical, anti-symmetrical, and asymmetrical charge distributions that are different from the ones for uniform gratings case. Plasmons in the studied plasmonic crystal exhibit both tightly confined/weakly coupled behavior and propagating/strongly coupled behavior depending on the plasmonic modes. The responsivity of the plasmonic detector based on asymmetric dual grating gate does not monotonically decrease with the frequency, which is in contrast to the responsivity of uniform grating THz detectors. The cross-section of an asymmetric dual grating gate terahertz plasmonic device under THz illumination is represented, where excited plasmons are shown in red.

Analysis of the Performance of a PAM/PPM/OOK System Operating with OCDMA, under Nonlinear Optical Effects in Optical Fiber Propagation

AbstractIn this article, we present a numerical simulation study of encoding, decoding and propagation performance of short optical pulses and words with modulations OOK, PAM and PPM in OCDMA systems (Optical Code Division Multiple Access). The encoding and decoding of short pulses are obtained through fiber Bragg grating(FBG – FBG optical) devices, where the codes are inserted through discrete jumps in the optical phase (±

Resonant quantum efficiency enhancement of midwave infrared nBn photodetectors using one-dimensional plasmonic gratings

We demonstrate up to 39% resonant enhancement of the quantum efficiency (QE) of a low dark current nBn midwave infrared photodetector with a 0.5 μm InAsSb absorber layer. The enhancement was achieved by using a 1D plasmonic grating to couple incident light into plasmon modes propagating in the plane of the device. The plasmonic grating is composed of stripes of deposited amorphous germanium overlaid with gold. Devices with and without gratings were processed side-by-side for comparison of their QEs and dark currents. The peak external QE for a grating device was 29% compared to 22% for a mirror device when the illumination was polarized perpendicularly to the grating lines. Additional experiments determined the grating coupling efficiency by measuring the reflectance of analogous gratings deposited on bare GaSb substrates.

Optical Load-Balancing Tradeoffs in Wavelength-Routing Cloud Data Centers

Wavelength routing based on arrayed waveguide grating (AWG) devices has been proposed as a disruptive technology for capacity, footprint, and flexibility requirements of cloud data centers. The limited buffering capacity of AWG-based routers, however, affects network throughput and makes them highly susceptible to data center traffic imbalance. A load-balancing stage, capable of evenly distributing the incoming traffic in both space and time, can improve network robustness and remedy congestion penalties. Robustness and scalability due to load balancing come at the cost of physical-layer complexities in terms of added cost, power consumption, and impairments. In this paper, we conduct a novel scalable analysis to study load-balancing tradeoffs between network-layer gains and physical-layer penalties in a multistage routing scenario. Our cross-layer simulations examine the requirements of a wavelength-routing load balancer based on AWG and tunable wavelength converters (TWCs) in order to achieve performance interesting for a data center. Our results point to the critical contribution of Q-factor degradation to load-balancer performance and encourage efforts in the design of novel router architectures, aiming to consolidate routing with scheduling-based load balancing.

Structural Stability of Large-size Grating Tiling Device Based on Dynamic Stiffness

Structural Stability of Large-size Grating Tiling Device Based on Dynamic Stiffness

Infrared waveguide fabrications with an E-beam evaporated chalcogenide glass film

Chalcogenide glasses have a variety of unique optical properties due to the intrinsic structural flexibility and bonds metastability. They are desirable materials for many applications, such as infrared communication sensors, holographic grating, optical imaging, and ultrafast nonlinear optic devices. Here, we introduce a novel electron-beam evaporation process to deposit the good quality arsenic trisulfide (As2S3) films and then the As2S3 films were used to fabricate the As2S3 waveguides with three approaches. The first method is photoresist lift-off. Because of the restriction of thermal budget of photoresist, the As2S3 film must be deposited at the room temperature. The second one is the silicon dioxide lift-off process on sapphire substrates, in which the As2S3 film could be evaporated at a high temperature (>180 °C) for better film quality. The third one is the plasma etching process with a metal protective thin layer in the pattern development process.

Multi-parameter Simultaneously Sensing Based on an Optimized Concatenated FBG with LPG

AbstractWe analyze an optical fiber sensor based on a concatenated fiber Bragg grating (FBG) with long period grating (LPG) with transfer matrix method and experiment. First, we optimize parameters of concatenated structure in the method of simulation and discuss the influence that the lengths, periods and dc induced index changes of FBG and LPG and length of optical fiber between LPG and FBG has to influence reflection spectrum. Second, based on the optimized parameters for concatenated structure, fabricate such structure and use it to monitor concentration and temperature simultaneously. Simulation result proves that increasing the lengths of FBG and LPG properly, and length of optical fiber between LPG and FBG fixed in 20 mm, more clearly reflection spectrum can be obtained. Experiment result shows a novel optical fiber sensor based on a concatenated strong fiber Bragg grating with a weak long period grating (CLBG) device can be used to monitor concentration and temperature simultaneously. The result of research has reference value in multi-parameter simultaneously sensing.

Signal Demodulation of High-Temperature LPFG Strain Sensor Based on Arrayed Waveguide Grating

Among all the kinds of optical fiber sensors, FBG and LPFG become the main current owing to its features and advantages. LPFG sensor is especially suitable in high temperature sensing and stimulates more related research interests. The key point of LPFG sensing is the signal demodulation and processing. In this paper, signal demodulation of the LPFG strain sensor was studied based on Arrayed Waveguide Grating. The fabrication method and high temperature performance of this sensor were presented,and a novel strain signal demodulation method was presented based on Arrayed Waveguide Grating (AWG) device by equi-intensity cantilever beam. The experimental results demonstrated that the signal demodulation technology based on AWG has many advantages, such as simple structure, innovative and reliable performance.

Characterization of Grating Coupled Surface Plasmon Polaritons Using Diffracted Rays Transmittance

A method to sense the excitation of surface plasmon polariton (SPP) on metallic grating device using the transmitted signal will be presented. The grating transmittance signal will be fully characterized varying the light incident angle and azimuthal grating orientation by means of the SPP vector model and rigorous coupled-wave analysis simulation. Simulation results will be compared with experimental measurements obtained with a 635 nm wavelength laser in the transverse magnetic polarization mode. The laser will light grating devices in contact with either air or water through a customized microfluidic chamber. A characterization of the diffracted rays will show the relationship between the grating coupling configuration and the Kretschmann one. In fact, the diffracted ray affected by SPP resonance is transmitted with an output angle which is the same incident angle that should be used to excite SPP in Kretschmann configuration. Lastly, the grating parameters (amplitude and metal thickness) impact on transmittance signal will be analyzed with respect to the order zero reflectance signal.

Application of Fiber Bragg Grating Device in Icing Monitoring System of Transmission Lines

Ice accretion has been a huge threat for the stable operation of transmission line. Icing monitoring devices used presently are active sensors with low working stability. Signals are transmitted in the electrical form, which are easily affected by the electromagnetic interference. In this paper, an online icing monitoring device of transmission line based on fiber bragg grating (FBG) sensor is designed, and is operated as a pilot unit on the 44# tower of 110kV Zhenzou line. Experimental results show that the online icing monitoring device operates stably, and the designed fiber bragg grating sensor has high linearity, good sensitivity and high accuracy.