Spectral Manipulation Research Articles

Spectral manipulation improves elevation perception with non-individualized head-related transfer functions.

Spatially rendering sounds using head-related transfer functions (HRTFs) is an important part of creating immersive audio experiences for virtual reality applications. However, elevation perception remains challenging when generic, non-personalized HRTFs are used. This study investigated whether digital audio effects applied to a generic set of HRTFs could improve sound localization in the vertical plane. Several of the tested effects significantly improved elevation judgment, and trial-by-trial variability in spectral energy between 2 and 10 kHz correlated strongly with perceived elevation. Digital audio effects may therefore be a promising strategy to improve elevation perception where personalized HRTFs are not available.

Large-scale spectral bandwidth compression by complex electro-optic temporal phase modulation.

Spectral-temporal shaping of quantum light has important applications in quantum communications and photonic quantum information processing. Electro-optic temporal lenses have recently been recognized as a tool for noise-free, efficient spectral bandwidth manipulation of single-photon wavepackets. However, standard electro-optic time lenses based on single-tone modulation exhibit, limited bandwidth modification factors due to material limitations on phase modulation amplitude. Here we numerically investigate the use of complex electro-optic temporal phase modulation patterns for bandwidth compression of light over multiple orders of magnitude and show the feasibility of their use in photonic interfaces for quantum network applications.

Spectral manipulation and tunable optical frequency ruler using liquid crystal’s birefringence

The polarization control method using a birefringent solid crystal produces only fixed optical frequency rulers and complementary spectra. A configuration using liquid crystal (LC) improves and extends above method’s ability to control incident polychromatic light spectra. It is shown that, by adjusting the voltage applied to the LC module, the induced birefringence and phase shift can be controlled in a wide range; consequently, this scheme can be employed to realize tunable optical frequency ruler, spectral switches, and spectrum compression. Compared with the previous one, this work provides an easier, and more powerful way to manipulate polychromatic light, which benefits its future applications, such as optics communication, spectra control, etc.

Comparison of artificial-dissipation and solution-filtering stabilization schemes for time-accurate simulations

The current study investigates the use of solution filtering and artificial dissipation as stabilization methods for time-accurate computations, notably focusing on how the decoupling of dissipation from integration impacts simulation error. Rewriting solution filtering in an effective artificial-dissipation form explicitly reveals the issue of temporal inconsistency, which is addressed by a proposed CFL re-scaling. In addition, expressing symmetric discrete filters as difference operators inspires the derivation of a “filter-based” artificial-dissipation formulation that provides the opportunity for direct spectral manipulation by utilizing known filter stencil specifications; this furthermore facilitates the creation of Padé-type artificial dissipation terms with spectrally tunable and scale-discriminant properties. Damping characteristics of the schemes are assessed through von Neumann analysis and are confirmed via simulations of the one-dimensional advection equation (wave-packet transport) as well as the three-dimensional compressible Navier–Stokes system (Taylor–Green vortex), where the impact of time step size on accuracy of the respective stabilization techniques is inspected.

Simultaneous distance measurement at multiple wavelengths using the intermode beats from a coherent supercontinuum

Advances in ultrashort pulse lasers and spectral manipulation enable new approaches to metrological problems in various fields. Dimensional metrology may benefit particularly from this progress, including applications like long distance measurement and 3D laser scanning. Using the intermode beat notes obtained by direct photodetection of a mode-locked femtosecond laser has been demonstrated as a promising alternative to solutions based on actively modulated signals. In this work, we extend the approach to ultra-broadband sources derived from femtosecond lasers, aiming at investigating their potential as a technological basis for multiwavelength distance metrology. We have developed a short-distance experimental set-up for displacement measurement operating simultaneously at two wavelength ranges on both extremes of a 500 nm coherent supercontinuum. The results derived from the phases of the 1 GHz intermode beat notes show that the internal coherence of the source is sufficient to derive distances with an accuracy better than 50 μm. This is a promising first step for the prospective application of this method to develop spectrally-versatile solutions, which is of interest to provide surface material probing capabilities in laser scanning and to increase the accuracy of long distance measurement though dispersion-based refractivity compensation.

Spectrum-agile hundred-watt-level high-power random fiber laser enabled by watt-level tunable optical filter

Through high-fidelity numerical modeling and careful system-parameter design, we demonstrate the spectral manipulation of a hundred-watt-level high-power random fiber laser (RFL) by employing a watt-level tunable optical filter. Consequently, a >100-W RFL with the spectrum-agile property is achieved. The central wavelength can be continuously tuned with a range of ∼20 nm, and the tuning range of the full width at half maximum linewidth, which is closely related to the central wavelength, covers ∼1.1 to ∼2.7 times of the minimum linewidth.

Flexible spectral manipulation property of a high power linearly polarized random fiber laser

Fiber lasers with flexible spectral manipulation property could provide a flexible tool for scenes where the temporal coherence property accounts, for example, coherent sensing/communication and nonlinear frequency conversion. Due to the good laser performance and relative simplicity of implementation, random fiber lasers (RFLs) based on random distributed feedback and Raman gain have earned more and more attention in the past few years, and a variety of RFLs with substantially different spectral properties have been developed. In this presentation, we demonstrate a high power linearly polarized RFL with flexible spectral manipulation property, in which the central wavelength and the linewidth of the spectrum can be tuned independently through a bandwidth-adjustable tunable optical filter (BA-TOF). The central wavelength of the RFL can be continuously tuned from 1095 to 1115 nm, while the full width at half-maximum (FWHM) linewidth has a maximal tuning range from ~0.6 to more than 2 nm. Moreover, the output power of 1102.5–1112.5 nm reaches ~23 W with polarization extinction ratio (PER) value > 20 dB. To the best of our knowledge, this is the first demonstration of a powerful linearly polarized RFL with both wavelength and linewidth tunability.

In-band pumping avenue based high power superfluorescent fiber source with record power and near-diffraction-limited beam quality

High power superfluorescent fiber sources (SFSs), which could find wide applications in many fields such as middle infrared laser generation, Raman fiber laser pumping and spectral beam combination, have experienced a flourishing time in recent years for its unique properties, such as short coherence length and high temporal stability. The challenge for performance scalability of powerful SFS mainly lies on the physical issues including parasitic laser oscillation and modal instability (MI). In this contribution, by employing in-band pumping avenue and high-order transverse-mode management, we explore a high power SFS with record power, near-diffraction-limited beam quality and spectral manipulation flexibility. An ultimate output power of 3.14 kW can be obtained with high temporal stability and a beam quality of $M^{2}=1.59$ for the amplified light. Furthermore, the dynamics of spectral evolutions, including red-shifting of central wavelength and unsymmetrical broadening in spectral wings, of the main amplifier with different seed linewidths are investigated contrastively. Benefiting from the unique high pump brightness and high MI threshold of in-band pumping scheme, the demonstrated system also manifests promising performance scaling potential.

Heralded Single Photons Based on Spectral Multiplexing and Feed-Forward Control.

We propose and experimentally demonstrate a novel approach to a heralded single-photon source based on spectral multiplexing (SMUX) and feed-forward-based spectral manipulation of photons created by means of spontaneous parametric down-conversion in a periodically poled LiNbO_{3} crystal. As a proof of principle, we show that our three-mode SMUX increases the heralded single-photon rate compared to that of the individual modes without compromising the quality of the emitted single photons. We project that by adding further modes, our approach can lead to a deterministic single-photon source.

Multiple night-time light-emitting diode lighting strategies impact grassland invertebrate assemblages.

White light-emitting diodes (LEDs) are rapidly replacing conventional outdoor lighting technologies around the world. Despite rising concerns over their impact on the environment and human health, the flexibility of LEDs has been advocated as a means of mitigating the ecological impacts of globally widespread outdoor night-time lighting through spectral manipulation, dimming and switching lights off during periods of low demand. We conducted a three-year field experiment in which each of these lighting strategies was simulated in a previously artificial light naïve grassland ecosystem. White LEDs both increased the total abundance and changed the assemblage composition of adult spiders and beetles. Dimming LEDs by 50% or manipulating their spectra to reduce ecologically damaging wavelengths partially reduced the number of commoner species affected from seven to four. A combination of dimming by 50% and switching lights off between midnight and 04:00 am showed the most promise for reducing the ecological costs of LEDs, but the abundances of two otherwise common species were still affected. The environmental consequences of using alternative lighting technologies are increasingly well established. These results suggest that while management strategies using LEDs can be an effective means of reducing the number of taxa affected, averting the ecological impacts of night-time lighting may ultimately require avoiding its use altogether.

Spectral manipulation and complementary spectra with birefringence polarization control

A polarization control method using crystal birefringence is suggested to manipulate polychromatic light. This scheme can be used with narrower bandwidth to produce various spectral effects, such as a notch filter, a flat top, and triangle-type, nipple-type, and central-frequency-dominant distributions. A modulated spectrum with greater bandwidth can be used as an optical frequency ruler, and phenomena called complementary spectra are also proposed, where the two spectral distributions, produced by rotating the polarizer, complement each other in the sense that the peaks and valleys in one spectrum are the reverse in the other. These results benefit the controlling of the spectral shape and the measurement of an unknown optical frequency.

Vowel and consonant confusions from spectrally manipulated stimuli designed to simulate poor cochlear implant electrode-neuron interfaces.

Suboptimal interfaces between cochlear implant (CI) electrodes and auditory neurons result in a loss or distortion of spectral information in specific frequency regions, which likely decreases CI users' speech identification performance. This study exploited speech acoustics to model regions of distorted CI frequency transmission to determine the perceptual consequences of suboptimal electrode-neuron interfaces. Normal hearing adults identified naturally spoken vowels and consonants after spectral information was manipulated through a noiseband vocoder: either (1) low-, middle-, or high-frequency regions of information were removed by zeroing the corresponding channel outputs, or (2) the same regions were distorted by splitting filter outputs to neighboring filters. These conditions simulated the detrimental effects of suboptimal CI electrode-neuron interfaces on spectral transmission. Vowel and consonant confusion patterns were analyzed with sequential information transmission, perceptual distance, and perceptual vowel space analyses. Results indicated that both types of spectral manipulation were equally destructive. Loss or distortion of frequency information produced similar effects on phoneme identification performance and confusion patterns. Consonant error patterns were consistently based on place of articulation. Vowel confusions showed that perceptions gravitated away from the degraded frequency region in a predictable manner, indicating that vowels can probe frequency-specific regions of spectral degradations.

Digital generation of wideband chaotic signal with the comb-shaped spectrum for communication systems based on spectral manipulation

An algorithm for the digital generation of broadband chaotic signal with comb-shaped spectrum has been developed on the basis of nonlinear discrete system with delay. The data transmission method using the spectral manipulation technique with digital generation and processing was experimentally implemented. The results obtained can be utilized in the systems of transmitted data security from unauthorized access.

Probe of Multielectron Dynamics in Xenon by Caustics in High-Order Harmonic Generation.

We investigated the giant resonance in xenon by high-order harmonic generation spectroscopy driven by a two-color field. The addition of a nonperturbative second harmonic component parallel to the driving field breaks the symmetry between neighboring subcycles resulting in the appearance of spectral caustics at two distinct cutoff energies. By controlling the phase delay between the two color components it is possible to tailor the harmonic emission in order to amplify and isolate the spectral feature of interest. In this Letter we demonstrate how this control scheme can be used to investigate the role of electron correlations that give birth to the giant resonance in xenon. The collective excitations of the giant dipole resonance in xenon combined with the spectral manipulation associated with the two-color driving field allow us to see features that are normally not accessible and to obtain a good agreement between the experimental results and the theoretical predictions.

Integrated acoustic echo and noise suppression in modulation domain

The quality of speech transmission in mobile communication systems deteriorates due to the presence of background noise and acoustic echo. The background noises are the disturbances from the surroundings and acoustic echo is induced due to the reverberation of loudspeaker signal in the near end environment. In conventional acoustic echo suppression setup, the echo path effect is modelled either in time or in frequency domain, and to cancel the echo, a replica of the echo is created by estimating the echo path response adaptively in the corresponding domain. Recently, the modulation domain analysis, which captures the human perceptual properties, is widely being used in speech processing. Modulation domain conveys the temporal variation of the acoustic magnitude spectra which acts as an information bearing signal. In this work, a novel integrated system for acoustic echo and noise suppression in the modulation domain is developed. So far, no work in this context in modulation domain has been found as reported. An efficient method for modelling the echo path and estimating the echo in the modulation domain is introduced and implemented. The effects of echo and noise are suppressed using the modulation spectral manipulation and the performance of the proposed system is found to be better than other conventional integrated systems.

Manipulating waves by distilling frequencies: a tunable shunt-enabled rainbow trap

In this work, we propose and test a strategy for tunable, broadband wave attenuation in electromechanical waveguides with shunted piezoelectric inclusions. Our strategy is built upon the vast pre-existing literature on vibration attenuation and bandgap generation in structures featuring periodic arrays of piezo patches, but distinguishes itself for several key features. First, we demystify the idea that periodicity is a requirement for wave attenuation and bandgap formation. We further embrace the idea of ‘organized disorder’ by tuning the circuits as to resonate at distinct neighboring frequencies. In doing so, we create a tunable ‘rainbow trap’ (Tsakmakidis et al 2007 Nature 450 397–401) capable of attenuating waves with broadband characteristics, by distilling (sequentially) seven frequencies from a traveling wavepacket. Finally, we devote considerable attention to the implications in terms of packet distortion of the spectral manipulation introduced by shunting. This work is also meant to serve as a didactic tool for those approaching the field of shunted piezoelectrics, and attempts to provide a different perspective, with abundant details, on how to successfully design an experimental setup involving resistive-inductive shunts.

Spectral light management for solar energy conversion systems

Abstract Due to the inherent broadband nature of the solar radiation, combined with the narrow spectral sensitivity range of direct solar to electricity devices, there is a massive opportunity to manipulate the solar spectrum to increase the functionality and efficiency of solar energy conversion devices. Spectral splitting or manipulation facilitates the efficient combination of both high-temperature solar thermal systems, which can absorb over the entire solar spectrum to create heat, and photovoltaic cells, which only convert a range of wavelengths to electricity. It has only recently been possible, with the development of nanofabrication techniques, to integrate micro- and nano-photonic structures as spectrum splitters/manipulators into solar energy conversion devices. In this paper, we summarize the recent developments in beam splitting techniques, and highlight some relevant applications including combined PV-thermal collectors and efficient algae production, and suggest paths for future development in this field.

Selective Automated Perimetry Under Photopic, Mesopic, and Scotopic Conditions: Detection Mechanisms and Testing Strategies.

PurposeAutomated scotopic, mesopic, and photopic perimetry are likely to be important paradigms in the assessment of emerging treatments of retinal diseases, yet our knowledge of the photoreceptor mechanisms detecting targets under these conditions remains largely dependent on simian data. We therefore aimed to establish the photoreceptor/postreceptoral mechanisms detecting perimetric targets in humans under photopic, mesopic, and scotopic conditions and to make recommendations for suitable clinical testing strategies for selective perimetry.MethodsPerimetric sensitivities within 30° of fixation were determined for eight wavelengths (410, 440, 480, 520, 560, 600, 640, and 680 nm) under scotopic, mesopic (1.3 cd.m−2) and photopic (10 cd.m−2) conditions. Data were fitted with vector combinations of rod, S-cone, nonopponent M+L-cone mechanism, and opponent M- versus L-cone mechanism templates.ResultsScotopicperimetric sensitivity was determined by rods peripherally and by a combination of rods and cones at, and immediately around, fixation. Mesopic perimetric sensitivity was mediated by M+L-cones and S-cones centrally and by M+L-cones and rods more peripherally. Photopic perimetric sensitivity was determined by an opponent M- versus L-cone, a nonopponent M+L-cone, and an S-cone mechanism centrally and by a combination of an S-cone and an M+L-cone mechanism peripherally.ConclusionsUnder scotopic conditions, a 480-nm stimulus provides adequate isolation (≥28 dB) of the rod mechanism. Several mechanisms contribute to mesopic sensitivity: this redundancy in detection may cause both insensitivity to broadband white targets and ambiguity in determining which mechanism is being probed with short-wavelength stimuli. M- and L-cone–derived mechanisms are well isolated at 10 cd.m−2: these may be selectively probed by a stimulus at 640 nm (≥ 20 dB isolation).Translation RelevanceIn human observers, multiple mechanisms contribute to the detection of Goldmann size III and size V perimetric targets under scotopic, mesopic, and photopic conditions. The relative contribution of these mechanisms appears to differ from those found previously for macaques. Our results furthermore suggest that caution must be exercised when using microperimetric techniques, which are typically conducted under mesopic conditions and which are likely to be important in the assessment of emerging treatments for retinal disease. This is because mesopic background conditions maximize the redundancy of target detection. Furthermore, our results demonstrate that spectral manipulation of the stimulus alone cannot be used to reliably separate rod from cone responses under these conditions.

Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory.

The spectral manipulation of photons is essential for linking components in a quantum network. Large frequency shifts are needed for conversion between optical and telecommunication frequencies, while smaller shifts are useful for frequency-multiplexing quantum systems, in the same way that wavelength division multiplexing is used in classical communications. Here we demonstrate frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory. Heralded 723.5 nm photons, with 4.1 nm bandwidth, are stored as optical phonons in the diamond via a Raman transition. Upon retrieval from the diamond memory, the spectral shape of the photons is determined by a tunable read pulse through the reverse Raman transition. We report central frequency tunability over 4.2 times the input bandwidth, and bandwidth modulation between 0.5 and 1.9 times the input bandwidth. Our results demonstrate the potential for diamond, and Raman memories in general, as an integrated platform for photon storage and spectral conversion.

Manipulation of light spectral quality disrupts host location and attachment by parasitic plants in the genus Cuscuta

Summary Parasitic plants in the genus Cuscuta (dodders) make their living by extracting resources from other plants. While relatively few dodder species are agricultural pests, those that are can be challenging to control, in part due to their intimate physical and physiological association with host plants. Consequently, dodders remain pervasive and economically damaging pests in a variety of crop systems. The development of improved management strategies would be facilitated by greater understanding of the ecological and environmental factors that influence the establishment and perpetuation of dodder infestations. Light cues play an important role in dodder host location and attachment. To better understand the influence of light conditions on parasite ecology, and potential implications for management, we examined how manipulating the ratio of red to far‐red wavelengths (R:FR), via both passive filtering of natural sunlight and active spectral manipulation using LEDs, affects host location and host attachment by two dodder species (C. campestris on tomato hosts and C. gronovii on jewelweed). For both host–parasite combinations, host location and subsequent attachment by dodder parasites was dramatically reduced in high‐R:FR environments compared to control conditions (with R:FR characteristic of sunlight) and low‐R:FR conditions. Circumnutation by dodder seedlings was also significantly faster under high R:FR. We observed short‐term effects of high R:FR on the height and dry mass of tomato host plants (immediately following 7‐day exposure), as well as changes in tomato volatile emissions. However, preliminary investigation of long‐term effects on host plants suggests that short‐term exposure to high R:FR (i.e. during the critical period when dodder seedlings emerge and attach to hosts) has little or no effect on host plant size or fruit yield at the time of harvest. Synthesis and applications. Our findings suggest that spectral manipulation during the early stages of crop plant growth (e.g. via light‐filtering row covers) may have significant potential to augment existing methods for managing or preventing dodder infestations in agricultural crops. We discuss potential obstacles to the realization of its potential, as well as next steps towards the development and optimization of spectral manipulation methods for use in agroecosystems.