Dispersive Element Research Articles

Ultra-compact silicon photonics highly dispersive elements for low-latency signal processing.

On-chip optical group-velocity dispersion (GVD) is highly desired for a wide range of signal processing applications, including low-latency and low-power-consumption dispersion compensation of telecommunication data signals. However, present technologies, such as linearly chirped waveguide Bragg gratings (LCWBGs), employ spectral phase accumulation along the frequency spectrum. To achieve the needed specifications in most applications, this strategy requires device lengths that are not compatible with on-chip integration while incurring in relatively long processing latencies. Here, we demonstrate a novel design strategy that utilizes a discretized and bounded spectral phase filtering process to emulate the continuous spectral phase variation of a target GVD line. This leads to a significant reduction of the resulting device length, enabling on-chip integration and ultra-low latencies. In experiments, we show GVD compensation of both NRZ and PAM4 data signals with baud rates up to 24 GBd over a 31.12-km fibre-optic link using a 4.1-mm WBG-based on-chip phase filter in a silicon-on-insulator (SOI) platform, at least 5× shorter compared to an equivalent LCWBG, reducing the processing latency down to ∼ 100 ps. The bandwidth of the mm-long device can be further extended to the THz range by employing a simple and highly efficient phase-only sampling of the grating profile. The proposed solution provides a promising route toward a true on-chip realization of a host of GVD-based all-optical analog signal processing functionalities.

Enhanced Compensation of Nonlinear Signal Distortion by Optical Phase Conjugation in Step-Parameter Profiled Fiber Links

Improving the efficacy of optical phase conjugation (OPC) for compensating nonlinear signal distortion in long distance optical fiber links from the Kerr effect is demonstrated. This is based on tailoring the link spans as step-parameter profiled fiber (SPF) for progressively increasing nonlinearity and decreasing dispersion with distance to mitigate the impact of propagation loss on unbalancing the phase distortion induced before and after OPC. With addition of a dispersion element after OPC, the SPF design also targets compensation in a shorter subsection of spans where induced nonlinear distortion is strongest. This enables performance benefit with less required parameter change in spans comprising just two or three segments of different regular fibers as 2-SPF and 3-SPF, respectively. Numerical simulations of 5 channel WDM dual polarization (DP) 32 Gbaud 64-QAM signals in a 12 × 130 km fiber link shows use of OPC and a 58 km 3-SPF in spans achieves 2.1 dB higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q²</i> -factor at 5 dB higher launch power than without. Similarly, measurements of 5 channel WDM DP 12 Gbaud 16-QAM signals in a 2 × 155 km link shows use of OPC and a 41 km 2-SPF in spans achieves 1.2 dB higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q²</i> -factor at 6 dB higher launch power and with low bit error rate compared to without. The improvements highlight the OPC advancements achievable by link design with regular fibers.

High-Speed Two-Dimensional Spectral-Scanning Coherent LiDAR System Based on Tunable VCSEL

Non-mechanical LiDAR systems have attracted extensive research interests due to their advantages of robustness and high beam-steering speed. Recently, spectral scanning has emerged as a promising solid-state beam-steering method, which combines dispersive elements with frequency-swept laser sources to perform ultrafast beam-steering. However, swept light sources used in LiDAR systems, such as semiconductor lasers and supercontinuum sources, are usually suffering from low sweep rate, bulky and high-cost that severely hinder the development of spectral-scanning LiDAR. Here, we propose a non-mechanical spectral-scanning frequency-modulated continuous-wave (FMCW) LiDAR system based on a simple compact tunable vertical-cavity surface-emitting laser (VCSEL). The fast-swept VCSEL together with wavelength division multiplexing (WDM) technology is employed for high-speed beam-steering. Millimeter-level ranging accuracy and a lateral resolution of 0.286° with an overall depth voxel acquisition rate of 128 kHz are achieved experimentally.

Frequency-selectable microwave generation based on on-chip switchable spectral shaping and wavelength-to-time mapping.

We propose and experimentally demonstrate a scheme for the photonic generation of pulsed microwave signals with selectable frequency based on spectral shaping and wavelength-to-time mapping (WTTM) technique. The frequency selectivity is realized by channel switching on an integrated silicon-on-insulator (SOI) spectral shaping chip. The incident signal is spectrally shaped by the asymmetric Mach-Zehnder interferometer (MZI) in the selected channel, and an optical spectrum with uniform free spectral range (FSR) can be generated in a broad bandwidth up to dozens of nanometers, implying large microwave signal duration after WTTM if a pulse light source with matched bandwidth is available. Microwave pulses of frequency from 3.6 GHz to 28.4 GHz with a fixed interval are experimentally generated respectively. The realization of eight microwave frequencies selectable with only one shared dispersive element (DE) required indicates high expansibility in the frequency cover range of our scheme by tuning the dispersion value in WTTM.

Diffraction-limited hyperspectral mid-infrared single-pixel microscopy

In this contribution, we demonstrate a wide-field hyperspectral mid-infrared (MIR) microscope based on multidimensional single-pixel imaging (SPI). The microscope employs a high brightness MIR supercontinuum source for broadband (1.55 upmu hbox {m}–4.5 upmu hbox {m}) sample illumination. Hyperspectral imaging capability is achieved by a single micro-opto-electro-mechanical digital micromirror device (DMD), which provides both spatial and spectral differentiation. For that purpose the operational spectral bandwidth of the DMD was significantly extended into the MIR spectral region. In the presented design, the DMD fulfills two essential tasks. On the one hand, as standard for the SPI approach, the DMD sequentially masks captured scenes enabling diffraction-limited imaging in the tens of millisecond time-regime. On the other hand, the diffraction at the micromirrors leads to dispersion of the projected field and thus allows for wavelength selection without the application of additional dispersive optical elements, such as gratings or prisms. In the experimental part, first of all, the imaging and spectral capabilities of the hyperspectral microscope are characterized. The spatial and spectral resolution is assessed by means of test targets and linear variable filters, respectively. At a wavelength of 4.15 upmu hbox {m} a spatial resolution of 4.92 upmu hbox {m} is achieved with a native spectral resolution better than 118.1 nm. Further, a post-processing method for drastic enhancement of the spectral resolution is proposed and discussed. The performance of the MIR hyperspectral microsopce is demonstrated for label-free chemical imaging and examination of polymer compounds and red blood cells. The acquisition and reconstruction of Hadamard sampled 64 times 64 images is achieved in 450 ms and 162 ms, respectively. Thus, combined with an unprecedented intrinsic flexibiliy gained by a tunable field of view and adjustable spatial resolution, the demonstrated design drastically improves the sample throughput in MIR chemical and biomedical imaging.

Immobilization of Bacillus amyloliquefaciens protease “Neutrase” as hybrid enzyme inorganic nanoflower particles: A new biocatalyst for aldol-type and multicomponent reactions

Organic–inorganic hybrid nanoflowers (hNFs) with commercial protease “Neutrase” is proposed and characterized as efficient and green biocatalysts for promiscuous catalysis in aldol-type and multicomponent reactions. Neutrase hNFs [Neutrase-(Cu/Ca/Co/Mn)3(PO4)2] are straightforwardly prepared through mixing metal ion (Cu2+, Ca2+, Co2+ or Mn2+) aqueous solutions with Neutrase in phosphate buffer (pH 7.4, 10 mM) resulting in precipitation (3 days). The hNFs were characterized by various techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX), element mapping, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In SEM images, the metal-Neutrase complexes revealed flower-like or granular structures after hybridization. The effect of metal ions and enzyme concentrations on the morphology and enzyme activity of the Neutrase-hNFs was examined. The synthesized Neutrase-Mn hNFs showed superior activity and stability compared to free Neutrase. Traditional organic CC coupling reactions such as aldol condensation, decarboxylative aldol, Knoevenagel, Hantzsch-type reactions and synthesis of 4H-pyran derivatives were used to test the generality and scope of Neutrase promiscuity, while optimizing conditions for the Neutrase-Mn hNF biocatalyst. Briefly, Neutrase-Mn3(PO4)2 hNFs showed excellent enzyme activity, stability and reusability, qualifying as effective reusable catalysts for coupling reactions under mild conditions.

Coarray Tensor Completion for DOA Estimation

Sparse array direction-of-arrival (DOA) estimation using tensor model has been developed to handle multi-dimensional sub-Nyquist sampled signals. Furthermore, augmented virtual arrays can be derived for Nyquist-matched coarray tensor processing. However, the partially augmentable sparse array corresponds to a discontinuous virtual array, whereas the existing methods can only utilize its continuous part. Conventional virtual linear array interpolation techniques complete coarray covariance matrices with dispersed missing elements, but fail to complete the coarray tensor with whole missing slices. In this paper, we propose a coarray tensor completion algorithm for two-dimensional DOA estimation, where the coarray tensor statistics can be entirely exploited. In particular, in order to impose an effective low-rank regularization on the slice-missing coarray tensor, we propose shift dimensional augmenting and coarray tensor reshaping approaches to reformulate a structured coarray tensor with sufficiently dispersed missing elements. Furthermore, the shape of the reformulated coarray tensor is optimized by maximizing the dispersion-to-percentage ratio of missing elements. As such, a coarray tensor nuclear norm minimization problem can be designed to optimize the completed coarray tensor corresponding to a filled virtual array, based on which the closed-form DOA estimation is achieved. Meanwhile, the global convergence of the coarray tensor completion is theoretically proved. Simulation results demonstrate the effectiveness of the proposed algorithm compared to other matrix-based and tensor-based methods.

Pulse nonlinear compression generated 71.3 W femtosecond laser

&lt;sec&gt;The power of femtosecond lasers based on Ti: sapphire or Yb-doped gain media has reached a high level by using chirped pulse amplification. The dispersive elements are normally employed in CPA devices, thereby increasing the complexity and cost of the laser system. However, for the Nd-doped laser, its power can be amplified to hundreds of microjoules or even several millijoules directly without CPA technology. So compressing the picosecond pulse to obtain femtosecond laser pulses with hundreds of microjoules pulse energy by post-compression technology becomes meaningful. The pulsed post-compression technology is the combination of nonlinear spectral broadening and dispersion compensation. Currently, the most effective method of nonlinear spectral broadening is achieved through self-phase modulation. The multi-pass cell (MPC) device based on self-phase modulation for broadening spectral bandwidth has been extensively studied, since it was demonstrated. The MPC concept demonstrates significant practical benefits. Essentially, it requires only two curved mirrors and a Kerr medium in between, making it a cost-effective and easily implementable method. Moreover, the MPCs are robust, quite insensitive to beam pointing, and can evendeal with small mode mismatch without transmission losses. These favorable characteristics make MPCs very attractive not only for scientific applications, but also for commercial and facility laser systems where reliability is crucial. The striking progress of the technique in the past six years has made it possible to obtain high average power femtosecond laser.&lt;/sec&gt;&lt;sec&gt;In this work, we demonstrate the generation of a high average power femtosecond laser pulse by nonlinearly compressing the picosecond pulse in the Herriott multi-pass cell device, and the distribution of eigenmode is analyzed. With this efficient and robust scheme, the spectrum is broadened from 0.20 nm to 2.75 nm, with a broadening ratio of 13.75, and the pulse duration of a picosecond amplifier is compressed from 1.25 ps to 780 fs, with a compression factor of 16. The average power before and after pulse compression are 100 W and 71.3 W respectively, so the overall transmission reaches 71.3%. The present scheme offers a viable route to low-cost and simple-configuration high-power femtosecond lasers driven by Nd-doped picosecond amplifiers.&lt;/sec&gt;

Building the capacity of students in creative problem-solving and critical thinking skills: Aesthetic narrative of Ayigya Township, Ghana

The study set out to investigate the environmental aesthetics present in habitual areas, specifically in Ayigya Township, Ashanti Region, focusing on picture-making tendencies for optimal skill development. A total of 346 respondents from various structures were specifically chosen to participate in the study using the Narrative Case Study Design under the qualitative research approach. Semi-structured interviews, observation, and photographic documentation were used for the data collection. The data were analysed using photographic documentary and qualitative narrative analysis. The findings demonstrated how dispersed aesthetic elements are in everyday life and how this appreciation would have a positive impact on the Senior High School student’s capacity for creative problem-solving and critical thinking skills. It is suggested that students develop alternative means of expressing their creativity. The study contends that art teachers must help students to use aesthetics in their environments to develop the tools and materials for their artistic productions.

An On-Chip Photon-Counting Reconstructive Spectrometer with Tailored Cascaded Detector Array

The hybrid integration of superconducting nanowire single-photon detectors (SNSPDs) on various substrates and photonic structures has great potential on developing complicated photonic devices based on single-photon detections, such as photon-counting reconstructive spectrometers for the spectral sensing of single-photon level faint light. In this paper, we introduce the cascaded absorption effect of SNSPDs to develop a photon-counting reconstructive spectrometer. The device includes a Rowland grating as the spatial dispersion element and a tailored cascaded SNSPD array in the focusing region of the grating. The spectral responses of the SNSPDs could be flexibly modulated by their coiled patterns and the cascaded absorption in the array, which are used as the bases for spectral reconstruction. A prototype device was designed and fabricated to demonstrate the principle of the scheme. The experiment results showed the feasibility of the spectral response modulations by the coiled pattern design and the cascaded absorption effect of the SNSPD array. It supports the spectral measurement and reconstruction in the wavelength range of 1,495 to 1,515 nm, with a spectral resolution of 0.4 nm. The proposed scheme achieves the bases for spectral reconstruction only by the design of SNSPDs and without the spectral modulation effects of additional photonic structures. It provides an interesting and promising way to develop devices with high photon utilization.

Enrichment characteristics and its geological significance of dispersed elements within sulfide minerals from the Ⅵ ore belt in the Maoping Pb-Zn deposit, Yunnan Province, China

Enrichment characteristics and its geological significance of dispersed elements within sulfide minerals from the Ⅵ ore belt in the Maoping Pb-Zn deposit, Yunnan Province, China

Detail characterization on the microstructure evolution of nickel-base alloy 600MA via surface mechanical attrition treatment

Microstructure evolution of alloy 600MA was explored after surface mechanical attrition treatment (SMAT) with different durations via scanning electronic microscopy, electron backscattered diffraction, transmission electron microscopy and transmission Kikuchi diffraction. The grain refinement and coarsening occurred gradually as strain accumulated with increasing SMAT time. During grain refinement, the initiation and development of dislocation walls or cells came up at early stage. A strip of dislocation wall led to straight element concentration just prior to the formation of ultrafine-laminated (UFL) structures containing abundant twin boundaries (TB) and low angle grain boundaries (LAGB). The UFL structures with a texture orientation were subdivided by the development of dislocation arrays into ultrafine-grained (UFG) structures with random orientations. Meanwhile, the elements were dispersedly concentrated in a few grains. During grain coarsening, the dispersed element concentration still existed. The fraction of LAGB, TB and dislocation density was significantly reduced while the fraction of high angle grain boundary (HAGB) increased along with grain growth. • The grain refinement and coarsening occurred gradually as strain accumulated with increasing SMAT time. • During grain refinement, the initiation and development of dislocation walls or cells came up at early stage. • A strip of dislocation wall led to straight element concentration just prior to the formation of ultrafine-laminated (UFL) structures containing abundant twin boundaries (TB) and low angle grain boundaries (LAGB). • The UFL structures with a texture orientation were subdivided by the development of dislocation arrays into ultrafine-grained (UFG) structures with random orientations. • During grain coarsening, the fraction of LAGB, TB and dislocation density was significantly reduced while the fraction of high angle grain boundary increased along with grain growth.

Дисперсионные элементы зеркального спектрометра на диапазон 7-30 nm

Multilayer interference structures acting as dispersion elements for a mirror spectrometer for a wavelength range of 7-30 nm have been calculated and synthesized. Three elements are implemented: for the range λ=7-12 nm – multilayer structure Mo/B4C (periods N=60; period thickness d=6.50 nm); for the range λ=11-18 nm – Mo/Be (N=50; d=9.83 nm) and for the range λ=17-30 nm – Be/Si/Al (N=40; d=18.2 nm). For the entire spectral range, an efficiency of more than 10% was obtained at a wavelength resolution of 0.15-1.0 nm.

Simultaneous Angle-of-Arrival and Frequency Measurement System Based on Microwave Photonics

A simultaneous angle-of-arrival (AOA) and frequency measurement system based on microwave photonics is proposed and experimentally demonstrated. The measurement of the AOA and the frequency is realized based on the simultaneous AOA-to-power and frequency-to-time mapping. Using optical pulses and optical dispersion elements, the frequencies of the received RF signals will map to the time intervals of the output electrical pulses. At the same time, by introducing a DPMZM, the received RF signals with the AOA-dependent phase differences interfere in the optical domain, mapping the AOA-dependent phase difference to the power of the interfered optical sidebands, which further maps to the output electrical pulse amplitudes. By measuring the time intervals and the normalized amplitudes of the output electrical pulses, the AOA and the frequency can be obtained simultaneously. In addition, the measurement of multiple RF signals can be realized due to the independence of the output mapping signals in the time domain for different RF frequencies. A proof-of-concept experiment is carried out. The AOA measurement from -70º to 70º with a measurement error of ±2.5º, and the frequency measurement from 5 to 15 GHz with a measurement error of ±12 MHz are successfully achieved simultaneously. The measurements of single-tone and multiple RF signals are experimentally achieved.

Quasi-distributed FBG interrogation based on coherent wavelength-to-time mapping using mode-locked laser and pseudo-random barcode

A microwave photonic demodulation scheme for multiplexing fiber Bragg grating (FBG) sensing system based on coherent wavelength-to-time (WTT) mapping is proposed and demonstrated experimentally in this paper. With the help of mode-locked laser (MLL) source and dispersion element, the broadband pseudo-random barcode obtained from fiber random grating can be mapped into time domain to fulfill high-speed interrogation for FBGs. The shifts of FBG center wavelength will be transformed into the variations of filtered pseudo-random barcode, and finally converted into the time location changes of the cross-correlation peaks with narrow full-width half-maximum (FWHM), which is helpful to realize high-accuracy and high-resolution FBG demodulation utilizing oscilloscope. The experiment results exhibit good demodulation linearity and a strain interrogation sensitivity of 0.0302 ns/με in cascaded sensing network with a repetition rate of 20 MHz, corresponding to a strain measurement resolution of 2.05 με. Besides, the impacts of system noises and light source line-shapes on the demodulation performance are studied numerically, and the relevant solutions are proposed and verified respectively.

Soft X-ray grating monochromators as a source of spatial coherence degradation: A wave-optical approach

We present wave-optical simulations and a coherence analysis of the photon beam transported through a soft X-ray beamline, paying particular attention to a focusing varied line spacing (VLS) plane grating monochromator (PGM). We show that this beamline optical element used in several soft X-ray beamlines at synchrotron sources and free-electron lasers can cause a non-negligible spatial coherence degradation. We demonstrate that the origin of this effect arises from the coupling between spatial and spectral properties of the photon beam generated by the grating. The latter implies that space and frequency dependencies are not separable after such a dispersive element. It is shown which parameters are essential for this effect and how they are linked to each other.

Optical frequency combs in dispersion-controlled doubly resonant second-harmonic generation.

We report on the experimental realization and a systematic study of optical frequency comb generation in doubly resonant intracavity second harmonic generation (SHG). The efficiency of intracavity nonlinear processes usually benefits from the increasing number of resonating fields. Yet, achieving the simultaneous resonance of different fields may be technically complicated, all the more when a phase matching condition must be fulfilled as well. In our cavity we can separately control the resonance condition for the fundamental and its second harmonic, by simultaneously acting on an intracavity dispersive element and on a piezo-mounted cavity mirror, without affecting the quasi-phase matching condition. In addition, by finely adjusting the laser-to-cavity detuning, we are able to observe steady comb emission across the whole resonance profile, revealing the multiplicity of comb structures, and the substantial role of thermal effects on their dynamics. Lastly, we report the results of numerical simulations of comb dynamics, which include photothermal effects, finding a good agreement with the experimental observations. Our system provides a framework for exploring the richness of comb dynamics in doubly resonant SHG systems, assisting the design of chip-scale quadratic comb generators.

Compact multichannel spectrometer employed for soft x-ray spectrum diagnostics at the Shenguang-III Laser Facility.

The quantitative measurement of plasma soft x-ray spectra is an important diagnostic problem in indirect-drive laser inertial confinement fusion (ICF). We designed, built, and tested a compact multichannel soft x-ray spectrometer with both spatial and temporal resolution capabilities for the detection of the spatiotemporal distribution of soft x-ray spectra. The spectrometer occupies a small solid angle, and the close measurement angle used for each channel enables the measurement of the angular distribution of emitting soft x-rays in ICF experiments. The spectrometer comprises pinhole, filter, and multilayer flat mirror arrays, and an x-ray streak camera. Its energy range is 0.1 - 3 keV. The dispersive elements of the spectrometer were calibrated at the Beijing Synchrotron Radiation Facility. The accuracy of the calibration was ≤ 5%, and the combined energy resolution (E/ΔE) of the calibrated dispersive elements of each channel was higher than 10. Finally, the instrument was tested at the Shenguang-III Laser Facility. The measurement results of x-ray radiation flux are agreed well with the experimental results of the M-band flat-response x-ray diode, demonstrating the feasibility of the proposed spectrometer configuration.

A CRISPRi-based investigation reveals that multiple promoter elements drive gene expression from the genome of mycobacteriophage D29.

A unique feature found in the genomes of mycobacteriophages such as L5 belonging to the A cluster is the presence of multiple dispersed repeated elements known as stoperators. The phage repressor binds these repeat elements, shutting off transcription globally and thereby promoting lysogeny. Interestingly, the sequence of these stoperators closely matches that of the consensus -35 region of prokaryotic promoters, leading us to propose that they may have a role to play in the initiation of transcription by serving as RNA polymerase binding sites. Mycobacteriophage D29 is closely related to phage L5, and their genome organizations are very similar. As in L5, there are multiple stoperators in the genome of D29. The positions occupied by the stoperators in the two genomes are almost identical. The significant difference between the two phages is that D29 lacks the gene encoding the equivalent of the L5 repressor. Since phage D29 does not produce a repressor, we considered it to be a suitable model for testing our hypothesis that the stoperators function as promoters in the absence of the repressor. To prove our point, we targeted CRISPR guide RNAs against six stoperators. In the case of five out of the six, we found a significant reduction in downstream gene expression and phage growth. Based on this observation and primer extension assays, we conclude that promoting gene expression is likely to be the primary function of stoperators.

Large Dispersion Silicon Bragg Grating for Full-Field 40-GBd QPSK Phase Retrieval Receiver

Optical devices that introduce and compensate for dispersion serve an important role in communication networks, photonic signal processing, and nonlinear optics. In this article, we demonstrate a silicon photonic Bragg grating which simultaneously achieves a large dispersion and wide bandwidth. We measure the grating to have a dispersion of −146 ps/nm over a 171 GHz bandwidth, representing the highest demonstrated grating dispersion over this wide bandwidth in a standard thickness silicon photonics process. Additionally, we show a significant reduction of group delay ripple by tuning the grating using an integrated phase shifter array to address fabrication variations. We further use the silicon grating as a dispersive element in a direct-detection phase retrieval receiver for 40 GBd quadrature phase shift keying (QPSK) signals and achieve a bit error rate (BER) below the 20% forward error correction (FEC) threshold. These results establish the potential for scalable silicon photonic circuits leveraging large dispersion for optical communication and other applications.