Chromatic Effects Research Articles

Transmission of 64-Gb/s Pilot-Assisted PAM-4 Signal Over 1440-km SSMF With Phase Noise Mitigation

We propose a direct detection scheme for pulse amplitude modulation (PAM) signals over long-reach fiber transmission with phase noise mitigation. In this scheme, an optical carrier is transmitted as pilot together with the optical signal, whose frequency is located at the edge of the optical signal. The electrical field of the optical signal can be retrieved via the beating between the pilot and optical signal in one photodetector at the receiver side, which facilitates the digital compensation of chromatic dispersion effect. To enable real value signal processing, digital carrier regeneration is proposed to mitigate the phase noise fluctuation in the proposed scheme. To further improve the performance, the digital signal processing including Kramers-Kronig field reconstruction and Volterra equalizer are applied to reduce the signal-to-signal beat noise and nonlinear distortions after fiber transmission. The experimental results for both 56- and 64-Gb/s PAM-4 signal transmission cases show that the performances can be significantly improvement based on the proposed scheme and DSP methods. Both 56- and 64-Gb/s PAM-4 signal transmissions over 720- and 1440-km standard single mode fiber have been successfully achieved under 7% and 20% forward error correction codes, respectively.

Comparative analysis of capacity oriented Integrated AMI modulation technique for the deployment of radio over fiber system

To improve the spectral efficiency and to reduce non-linear distortion in the optical system, various advanced modulation techniques have been investigated for radio over fiber (RoF) system. The investigation indicates the high data rate distortion less transmission for long-haul RoF system still further investigation is required to improve spectral efficiency and to get the reduction in signal degradation. In this paper, an advanced modulation technique referred as integrated alternate mark inversion modulation technique based upon external modulation (electro-absorption modulator) has been designed and simulated. The results show better performance in terms of performance metrics i.e. Q-factor (25.15) and BER (4e−140) and also enhance the data transmission capabilities up to 100 Gbps covering the long distance of 250 km resulting a reasonable reduction in signal degradation particularly chromatic dispersion effects for long-haul transmissions.

Chromatic Callier Effect and its Repercussions on the Digitization of Early Film Colors

The projection on screen has always been the supreme result of cinematography. Thus the digitization of a motion picture should seek to recreate the visual impression in the cinema. The image-forming particles contained in early color films can generate remarkable differences between a film directly observed with diffuse backlighting and its image projected on screen. In the recent decades this discrepancy has been largely overlooked by the film preservation community (film curators, scanner manufacturers, colorists, etc.). This paper re-establishes the importance of referring to the visual impression in the cinema, and describes the spectral variation of the Callier effect that can significantly alter early film colors when digitized. We have introduced the term “chromatic Callier effect” and described its repercussions on film digitization reporting case studies of tinted and toned film prints. The experimental results highlight that important changes are required in the optical design of film scanners to improve the digitization of motion pictures.

Software compensation for chromatic aberration effects in color photos

Software compensation for chromatic aberration effects in color photos

Using the longitudinal chromatic aberration effect to measure distances from a single color photo

Using the longitudinal chromatic aberration effect to measure distances from a single color photo

Color Perception of the Observer with the Manifestation of the Chromatic Effect of Crispening

This research presents the results of the appearance of chromatic effect of crispening on a designer solution in which the primary stimuli are made in the purple color with the values of 55% RTV and 65% RTV and backgrounds are made in the green-blue color, and their variations are designed in the values of 25% RTV, 50% RTV, 75% RTV and 100% RTV that are placed around the primary stimuli. The test subjects (n=10) that took part in the research had the task to equalize the test primary stimuli with the referential stimuli on a computer screen with the help of the technique of simultaneous binocular harmonization. The strength of the crispening effect was defined and shown in the CIEDE00 system. The conclusion of the conducted tests indicates that the intensity of crispening was stronger on the test primary stimuli 65% RTV, where the differences in the perception of color were more significant.

Vlasov description of the effects of nonlinear chromaticity on transverse coherent beam instabilities

A theoretical analysis of transverse coherent beam instabilities in the presence of nonlinear chromatic effects.

True White Point for Television Screens Across Different Viewing Conditions

This paper proposes the optimal white point settings of consumer televisions observed in different viewing conditions. The ratings from visual experiments were modeled with a bivariate Gaussian distribution to predict the optimal white points. Under dark surround conditions, where there is no effect of lighting chromaticity, the averaged optimal white point was located at a correlated color temperature of 7346 K and a Duv of -0.0015. The optimal white point was shifted toward a higher color temperature compared to the current standards. The results also indicated that current white point settings of major television manufacturers are too bluish. Neither televisions that meet the current standards nor televisions in the market would appear as true white under the viewing conditions employed in this paper. Moreover, the optimal white point depended largely on viewing conditions. Image content and ambient lighting conditions were observed to be important factors that influence the perception of the white point. The research therefore proposed to automatically change the white point of the display based on the image content and the real-time measurements of the surrounding ambient light falling on the screen. Ultimately, this paper might be of interest to the industry as a basis for future deliberations on target white points for consumer televisions designed to provide a better color appearance.

Millimeter-wave band optical single-sideband modulator using array-antenna-electrode and polarization-reversed structures with asymmetric Mach–Zehnder waveguide

The radio-over-fiber (RoF) technology is effective in millimeter-wave (MMW) wireless systems for future broadband massive mobile communication. In constructing MMW RoF systems, a device for converting MMW signals into lightwave signals is important. In particular, a conversion device for optical single-sideband (SSB) modulation is rather attractive since the signal fading caused by the chromatic dispersion effect of an optical fiber does not occur. We have proposed a new optical SSB modulator using array-antenna-electrode and polarization-reversed structures with an asymmetric Mach–Zehnder waveguide for MMW band RoF systems. By introducing polarization-reversed structures in electro-optic modulators, it is possible to control the optical modulation phase arbitrarily. Therefore, by combining with an asymmetric Mach–Zehnder waveguide, we can obtain the SSB optical modulation in the MMW band without an external power supply. In the experiment, SSB modulation characteristics and the switching of enhanced sidebands were successfully demonstrated in the 60 GHz band.

3rd-order spherochromatism surface contribution and its intrinsic and induced aberration parts.

An investigation of the chromatic effects in refracting optical systems naturally shows that all five Seidel aberrations vary in wavelength because they are all dependent on the refractive index. In general, the color variation of spherical aberration is denoted as spherochromatism. Besides the chromatic variation of 1st-order paraxial parameters, e.g.,focal length and magnification, described by axial and lateral color, spherochromatism can also strongly affect the color correction of an optical system. However, to the best of our knowledge, the literature shows no exact analytical formula available, specifying this effect. Actually, a general 3rd-order description based on the chromatic variation of Seidel's surface contribution for spherical aberration has not yet been considered. Therefore, this paper deals with this mentioned analytical gap and provides a description of a 3rd-order surface contribution for spherochromatism. Based on this, the result is analyzed and discussed concerning the differentiating between intrinsic and induced aberration parts. In the case of spherochromatism, its 3rd-order contribution shows induced effects caused by prior summed-up primary color aberrations of the system.

HST imaging of four gravitationally lensed quasars

We present new HST WFPC3 imaging of four gravitationally lensed quasars: MG 0414+0534; RXJ 0911+0551; B 1422+231; WFI J2026-4536. In three of these systems we detect wavelength-dependent microlensing, which we use to place constraints on the sizes and temperature profiles of the accretion discs in each quasar. Accretion disc radius is assumed to vary with wavelength according to the power-law relationship $r\propto \lambda^p$, equivalent to a radial temperature profile of $T\propto r^{-1/p}$. The goal of this work is to search for deviations from standard thin disc theory, which predicts that radius goes as wavelength to the power $p=4/3$. We find a wide range of power-law indices, from $p=1.4^{+0.5}_{-0.4}$ in B 1422+231 to $p=2.3^{+0.5}_{-0.4}$ in WFI J2026-4536. The measured value of $p$ appears to correlate with the strength of the wavelength-dependent microlensing. We explore this issue with mock simulations using a fixed accretion disc with $p=1.5$, and find that cases where wavelength-dependent microlensing is small tend to under-estimate the value of $p$. This casts doubt on previous ensemble single-epoch measurements which have favoured low values using samples of lensed quasars that display only moderate chromatic effects. Using only our systems with strong chromatic microlensing we prefer $p>4/3$, corresponding to shallower temperature profiles than expected from standard thin disc theory.

Pre-Equalizing Electro-Optic Modulator Utilizing Polarization-Reversed Ferro-Electric Crystal Substrate

We have proposed and developed new electro-optic modulators for the pre-equalization of signal distortion caused by the optical fiber chromatic dispersion effect. We found that the synthesis of an almost arbitrary impulse response function is obtainable by utilizing an electro-optic modulator composed of a Mach-Zehnder waveguide and travelling-wave electrodes on a ferro-electric material substrate with polarization-reversed structures. In this paper, the operational principle, design and simulation results of the pre-equalization modulator are presented. Some preliminary experimental results are also shown with future prospects.

Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry atQband (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique atUband (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σlevel betweenUandQbands. With the benefit of quasi-simultaneousUandQband observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.

The modification in the photo–physical properties via transformation of synthetic dihydrated Znq2 to anhydrous (Znq2)4 tetramer by sublimation process

A prominent green emitting anhydrous (Znq2)4 tetramer phosphor has been produced by the sublimation in Ar–atmosphere from dihydrated Znq2. The dihydrated Znq2 was synthesized by the co–precipitation method under normal atmospheric condition. Structural changes which are responsible for change in their photo–physical properties have been confirmed by the XRD, FTIR, NMR analysis and relative stability by the TGA/DTA analysis. The dependence of UV–visible absorption spectrum, in different acidic and basic mediums at different concentrations on the alteration of phase from dihydrated Znq2 to anhydrous (Znq2)4 tetramer leading to the change in the band gap, has been noted. A photoluminescence spectrum of solid and of solution state and structural dependence on emission and excitation wavelength, revealing the modification in the structure, is responsible for a prominent green emission. Solvato–chromatic effect on PL emission leading to blue shift by the addition of acidic solvents and a red shift by basic solvents has also been reported. The structural formation and experimental band gap energy information has been supported by the quantum chemical calculations using DFT Computational study. We conclude from the study that the produced anhydrous (Znq2)4 tetramer phosphor has a potential application as a prominent green dopant in OLEDs including indoor lighting. Additionally, this study gives an insight into the spectroscopy of Zinc (II) quinolate complex.

High-speed demodulation of weak fiber Bragg gratings based on microwave photonics and chromatic dispersion.

A high-speed demodulation technique based on microwave photonics and chromatic dispersion is proposed for distributed weak fiber Bragg gratings (FBGs). A broadband light modulated with a frequency-swept microwave is reflected by FBGs, and the reflected signal mixes with the original microwave to produce a beat frequency. A dispersion compensation fiber (DCF) changes the beat frequency within the FBG wavelength range. With a crossing microwave sweep, all wavelengths of cascade FBGs can be quickly decoded by measuring the change of the beat frequency. The Chirp-Z + Hanning window algorithm helps to analyze the beat frequency in a single cycle. By adopting the single-peak filter as a reference, the DCF thermal drift can be also eliminated. Therefore, the wavelength detection accuracy is improved, and a higher demodulation speed of 40kHz can be realized. We have demonstrated 105FBGs with 0.1% reflectivity and 1m interval, with the achieved accuracy of 8pm.

Calibration of quasi-static aberrations in high-contrast astronomical adaptive optics with a pupil-modulated point-diffraction interferometer.

The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. In order to achieve this, a high-sensitivity wavefront sensor, the pupil-modulated point-diffraction interferometer (m-PDI), is presented. This sensor modulates and retrieves both the phase and the amplitude of an incoming electric field. The theory behind the wavefront reconstruction, the visibility of fringes, chromatic effects and noise propagation are developed. Results show this interferometer has a wide chromatic bandwidth. For a bandwidth of Δλ = 50% in units of central wavelength, the visibility of fringes and the response of the WFS to low and high-order aberrations are almost unaffected with respect to the monochromatic case. The WFS is, in contrast, very sensitive to variations in the size of its pinhole. The size of the pinhole is shown to affect the sensor's linearity, the dynamic range and the amount of noise. Larger pinholes make the sensor less sensitive to low-order aberrations, but in turn also decrease the effects of misalignments.

The hydrogen epoch of reionization array dish III: measuring chromaticity of prototype element with reflectometry

The experimental efforts to detect the redshifted 21 cm signal from the Epoch of Reionization (EoR) are limited predominantly by the chromatic instrumental systematic effect. The delay spectrum methodology for 21 cm power spectrum measurements brought new attention to the critical impact of an antenna's chromaticity on the viability of making this measurement. This methodology established a straightforward relationship between time-domain response of an instrument and the power spectrum modes accessible to a 21 cm EoR experiment. We examine the performance of a prototype of the Hydrogen Epoch of Reionization Array (HERA) array element that is currently observing in Karoo desert, South Africa. We present a mathematical framework to derive the beam integrated frequency response of a HERA prototype element in reception from the return loss measurements between 100-200 MHz and determined the extent of additional foreground contamination in the delay space. The measurement reveals excess spectral structures in comparison to the simulation studies of the HERA element. Combined with the HERA data analysis pipeline that incorporates inverse covariance weighting in optimal quadratic estimation of power spectrum, we find that in spite of its departure from the simulated response, HERA prototype element satisfies the necessary criteria posed by the foreground attenuation limits and potentially can measure the power spectrum at spatial modes as low as $k_{\parallel} > 0.1h$~Mpc$^{-1}$. The work highlights a straightforward method for directly measuring an instrument response and assessing its impact on 21 cm EoR power spectrum measurements for future experiments that will use reflector-type antenna.

Multifocal diffractive lens generating several fixed foci at different design wavelengths

We propose a method for designing multifocal diffractive lenses generating prescribed sets of foci with fixed positions at several different wavelengths. The method is based on minimizing the difference between the complex amplitudes of the beams generated by the lens microrelief at the design wavelengths, and the functions of the complex transmission of multifocal lenses calculated for these wavelengths. As an example, a zone plate generating three fixed foci at three different wavelengths was designed, fabricated, and experimentally investigated. The proof-of-concept experimental results confirm the formation of foci with fixed positions at the design wavelengths. The obtained results may find applications in the design and fabrication of novel multifocal contact and intraocular lenses with reduced chromatic effects.

The influence of the chromatic effect of crispening on the shift in the manifestation of the color of the observer

The paper presents the results of the research on the manifestation of the chromatic effect crispening, where the primary stimuli are designed as squares in the blue-green color with the values of 55% RTV and 65% RTV, while the secondary stimuli are designed as backgrounds in the purple color and their variations are made in the values of 25% RTV, 50 % RTV, 75% RTV and 100% RTV that surrounds the primary stimuli. Ten respondents of both sexes participated in the research. They had the task to match on a computer screen through the binocular harmonization technique the test primary stimuli with the referential stimuli, so that the test primary stimuli are perceived the same or equal to the referential primary stimuli. The intensity of the effect was determined and presented in the CIEDE00 system. The results of the research show that the intensity of the effect was more pronounced on the test primary stimuli of 65% RTV, where the deviations in the perception of color were more pronounced. The smallest deviation was measured on the primary stimulus of 55% RTV with the background of 75% RTV, which is also a recommendation to the designers when creating a conceptual solution with the combination of pairs presented in this paper.

CWDM DFBLD Transmitter Module for 10-km Interdata Center With Single-Channel 50-Gbit/s PAM-4 and 62-Gbit/s QAM-OFDM

Single-channel 50-Gbit/s 4-level pulse amplitude modulation (PAM-4) and 62-Gbit/s orthogonal frequency division multiplexed quadrature amplitude modulation (QAM-OFDM) direct encoding of an uncooled coarse wavelength division multiplexer (CWDM) 100-Gbit/s distributed feedback laser diodes (DFBLD) transmitter module at 1310-nm transmitter interdata center transmission over 10-km single-mode fiber (SMF) are demonstrated. To enable preleveled 16-QAM OFDM and PAM-4 data transmissions at 62 and 50 Gbit/s, the 1310-nm channel of the DFBLD CWDM transmitter provides modulation bandwidth of 15 GHz, side-mode suppression ratio of 48 dB, and relative intensity noise of −126 dBc/Hz. For encoding the PAM-4 data, the 1310-nm channel of the CWDM DFBLD 100-Gbit/s transmitter achieves transmission capacities of 58 and 50 Gbit/s after BtB and 10-km SMF transmissions, respectively. Instead of supporting the back-to-back 16-QAM OFDM with the transmission at 62 Gbit/s with forward error correction (FEC) certified BER of 3.3 × 10−3, such a CWDM 100-Gbit/s DFBLD transmitter module can still maintain its highest data rate capacity to indicate a receiving power penalty of 0.35 dB even after 10-km SMF propagation. This is mainly attributed to the selected channel wavelength of the narrow-linewidth DFBLD, which suffers from extremely low chromatic dispersion and RF fading effect.