Spectral Compensation Research Articles

All-optical and digital non-linear compensation algorithms in flex-coherent grouped and un-grouped contiguous spectrum based networks

We have evaluated that in-line non-linear compensation schemes decrease the complexity of digital backward propagation and enhance the transmission performance of 40/112/224 Gbit/s mixed line rate network. Multiple bit rates, i.e. 40/112/224 Gbit/s and modulation formats (i.e. DP-QPSK and DP-16QAM) are transmitted over 1280 km of Large \(\hbox {A}_{eff}\) Pure-Silica core fiber. Both grouped and un-grouped spectral allocation schemes are investigated. Optical add-drop multiplexers are used to drop the required wavelength for signal processing in the transmission link. Moreover, hybrid mid-link spectral inversion and in-line non-linear compensation methods are also analyzed. This gives us enhanced system performance and DBP step-size of 400 km in WDM 224 Gbit/s DP-16QAM system, significantly reducing the complexity of digital backward propagation.

Compressed sampling reconstruction of hyperspectral images based on spectral prediction

With increasing amounts of hyperspectral images (HSI) and the limitations of the memory requirements, compressive techniques for hyperspectral images have attracted extensive research efforts in recent years. The main difficulty of applying compressed sampling (CS) theory to compression and reconstruction of hyperspectral images lies in using the spatial correlation and spectral correlation of hyperspectral images. In this paper, a reconstruction algorithm of hyperspectral images taking advantage of two‐dimensional compressed sampling (2DCS) and two‐dimensional total variation (2DTV) incorporating spectral prediction (SP) is investigated. In the sampling process, the hyperspectral images are divided into reference bands and common bands, and all bands are sampled using 2DCS independently. In the reconstruction process, the reference bands are reconstructed by 2DTV first. In order to improve the reconstruction quality of common bands, spectral prediction utilizing the spectral correlation between reference bands and common bands is conducted. Then the spectral compensation is computed by using a combination of the prediction value and the initial approximation for the common bands. The residual between the compensation value and the original value is obtained to revise the approximation for the common bands. The algorithm is implemented in an iterative manner to enhance the performance. Experimental results on popular hyperspectral datasets reveal that the proposed algorithm exploiting spectral prediction outperforms the algorithm 2DCS‐2DTV, which does not use spectral correlation, as well as the state‐of‐the‐art algorithms in terms of peak signal‐to‐noise ratio (PSNR). In particular, when the sampling rate of the reference bands is higher than that of the common bands, the proposed algorithm would improve the reconstruction quality dramatically. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Rod- and cone-driven responses in mice expressing human L-cone pigment.

The mouse is commonly used for studying retinal processing, primarily because it is amenable to genetic manipulation. To accurately study photoreceptor driven signals in the healthy and diseased retina, it is of great importance to isolate the responses of single photoreceptor types. This is not easily achieved in mice because of the strong overlap of rod and M-cone absorption spectra (i.e., maxima at 498 and 508 nm, respectively). With a newly developed mouse model (Opn1lw(LIAIS)) expressing a variant of the human L-cone pigment (561 nm) instead of the mouse M-opsin, the absorption spectra are substantially separated, allowing retinal physiology to be studied using silent substitution stimuli. Unlike conventional chromatic isolation methods, this spectral compensation approach can isolate single photoreceptor subtypes without changing the retinal adaptation. We measured flicker electroretinograms in these mutants under ketamine-xylazine sedation with double silent substitution (silent S-cone and either rod or M/L-cones) and obtained robust responses for both rods and (L-)cones. Small signals were yielded in wild-type mice, whereas heterozygotes exhibited responses that were generally intermediate to both. Fundamental response amplitudes and phase behaviors (as a function of temporal frequency) in all genotypes were largely similar. Surprisingly, isolated (L-)cone and rod response properties in the mutant strain were alike. Thus the LIAIS mouse warrants a more comprehensive in vivo assessment of photoreceptor subtype-specific physiology, because it overcomes the hindrance of overlapping spectral sensitivities present in the normal mouse.

Experimental Parametric Study of a Silicon Photonic Modulator Enabled 112-Gb/s PAM Transmission System With a DAC and ADC

A packaged silicon photonic traveling wave Mach-Zehnder modulator operating at 1310 nm is presented and studied. The modulator is a series push-pull device and requires a bias applied to the common n-doped region. Effects of varying the bias voltage on the modulator's V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> bandwidth, and on chip-insertion loss are studied, and its impact on transmission performance are experimentally investigated for PAM-4 and PAM-8 formats at a throughput of 112 Gb/s, over varying distances of 0, 2, 10, and 20 km. Residual chromatic dispersion is shown to have no impact on performance up to 20 km. The PAM RF driving waveform is generated by an 8-bit digital-to-analog converter, while direct detection is done with a PIN+TIA followed by an 8-bit analog-to-digital converter. This IM/DD system utilizes digital signal processing with transmitter spectral compensation and receiver residual equalization. The performance impact for a varying number of transmitter precompensation taps and receiver equalization taps is studied, which has a direct impact on the transceiver's power consumption. Using PAM-4, a BER below the FEC limit is obtained for either combinations of (transmitter, receiver) tap lengths: (19,19), (7,27), or (35,7), allowing flexibility in power consumption distribution.

Optical retarder system with programmable spectral retardance.

An optical system that works as a retarder waveplate with programmable spectral retardance is proposed. The system is based on a pixelated liquid crystal on silicon (LCoS) spatial light modulator (SLM). The input light beam is spectrally dispersed and different spectral components are projected onto different pixels of the LCoS-SLM. A different retardance is then addressed for each pixel, adapted to the incoming wavelength. Light reflected from the SLM is then recombined by the same setup. In this way a programmable polarization spectrum can be encoded. We illustrate the broadband characterization that is required for proper use of the system. Then several examples are shown, including spectral compensation to yield retarders with constant retardance, retarders with abrupt changes in the spectral retardance function, or bandpass variable retarder filters. The system is also demonstrated to provide programmable light spectrum generation.

Nonquadratic Spectral Phase Aberration With Quadratic Temporal Phase Modulation in an Actively Modulated Ultrafast Laser System

Ultrashort pulses can be generated through active modulation techniques, such as the time-lens technique. To achieve better pulse compression, in the time-lens source, quadratic temporal phase modulation was naturally considered as the ideal modulation. However, it is unknown that whether a quadratic temporal phase modulation (equivalently, a linear chirp) translates into a quadratic spectral phase modulation, which can be easily eliminated using compressors. Here, we study this phase transfer both analytically and numerically. Our results indicate that depending on the pulse shape, nonquadratic spectral phase aberration arises even if the temporal phase modulation is quadratic. Consequently, there is observable difference between the compressed pulses with a flat spectral phase and with quadratic spectral phase compensation only. However, both analytical and numerical analyzes show that as quadratic temporal phase modulation increases, nonquadratic spectral phase modulation decreases, and pulse compression with quadratic spectral phase tends to that with a flat spectral phase.

Comparison of pulse compression methods using only a pulse shaper

Spectral phase compensation is crucial in the production of ultrafast laser pulses. To produce very short pulses, it is necessary to correct higher-order phase terms beyond the typical second-order and third-order corrections. It is helpful to have a pulse shaper to perform the compression, and to use an integrated, deterministic pulse-shaper-only method for pulse compression and characterization. While several algorithms exist for this purpose, it is desirable to know which method is optimal. Using a computer simulation, we investigate the speed of several existing approaches in several typical pulse shaping cases. We also present and demonstrate experimentally a new method named Spectral Phase of Electric field by Analytic Reconstruction (SPEAR), a variant of the Chirp Reversal Technique (CRT). The chirp-scan method, CRT, and SPEAR are found to be the fastest methods to achieve a desired level of accuracy, for the cases investigated.

Spectral Compensation for Linear-Logarithmic Flow Cytometry Acquisitions

Compensating for fluorescence overlap in multiparameter flow cytometry datasets, of which one parameter is linear distributed and at least one parameter is logarithmic distributed, leads usually to extreme high compensation values. We investigated this phenomenon with an adapted flow cytometry model, of which the two parameters can easily be converted from linear to logarithmic and vice versa. With the adapted model, spectral compensation was performed both for linear-logarithmic and linear-linear parameter distribution. The results of the flow cytometry model were validated with a real world example which was also compensated twice. The results of the two experiments show that the compensation values equal to the theoretically expected value when both parameters are linear distributed. However, the compensation value exceeds 100% when one of the two parameters is logarithmic distributed. In addition, we found that spectral compensation of differently distributed parameters leads to deformation of the compensated events. With the adapted flow cytometry model presented in this paper it is shown how to correctly compensate flow cytometry acquisitions with different distributed parameters.

Spectral phase measurement and compensation of femtosecond laser pulse based on multi-photon intra-pulse interference phase scan

In this paper, we develop a system that can be used to measure and compensate spectral phase of femtosecond laser pulses based on the multi-photon intra-pulse interference phase scan (MIIPS). In the system, a liquid crystal spatial light modulator (LC-SLM) is used to impose phase scan on the femtosecond laser pulse, while a spectrometer is used to record the MIIPS trace. Both the LC-SLM and the spectrometer are driven by home-developed LabVIEW programs. By analyzing the MIIPS trace, we obtain the spectral phase of the pre-chirped femtosecond laser pulse with only 3-times iteration. The femtosecond laser pulse is centered at 810 nm and has a repetition of 1 kHz. The accuracy of our measurement is less than ±0.1 rad. The measured phases are compensated by the LC-SLM, then we obtain a femtosecond laser pulse which is almost in the transform limit state. The device will be useful in many fields, for example, multi-photon microscopy, pulse shaping, and femtosecond laser spectroscopy etc.

Advanced multi-contrast Jones matrix optical coherence tomography for Doppler and polarization sensitive imaging

An advanced version of Jones matrix optical coherence tomography (JMT) is demonstrated for Doppler and polarization sensitive imaging of the posterior eye. JMT is capable of providing localized flow tomography by Doppler detection and investigating the birefringence property of tissue through a three-dimensional (3-D) Jones matrix measurement. Owing to an incident polarization multiplexing scheme based on passive optical components, this system is stable, safe in a clinical environment, and cost effective. Since the properties of this version of JMT provide intrinsic compensation for system imperfection, the system is easy to calibrate. Compared with the previous version of JMT, this advanced JMT achieves a sufficiently long depth measurement range for clinical cases of posterior eye disease. Furthermore, a fine spectral shift compensation method based on the cross-correlation of calibration signals was devised for stabilizing the phase of OCT, which enables a high sensitivity Doppler OCT measurement. In addition, a new theory of JMT which integrates the Jones matrix measurement, Doppler measurement, and scattering measurement is presented. This theory enables a sensitivity-enhanced scattering OCT and high-sensitivity Doppler OCT. These new features enable the application of this system to clinical cases. A healthy subject and a geographic atrophy patient were measured in vivo, and simultaneous imaging of choroidal vasculature and birefringence structures are demonstrated.

Suppression of clipping noise in observed speech based on spectral compensation with Gaussian mixture models and reference of clean speech

In recent years, the development of communication system allows people to easily record and distribute their speech. However, in the speech recording, clipping noise degrades sound quality when the level of input signal is excessive for the maximum range of amplifier. In this case, it is necessary to suppress clipping noise in the observed speech for improving its sound quality. Although a linear prediction method has been conventionally proposed for suppressing clipping noise, it has a problem with degradation of the restoration performance by cumulating error when the speech includes a large amount of clipping noise. This paper describes a method for suppression of clipping noise in observed speech based on spectral compensation. In this method, the power spectral envelope of speech on each frame in the lower frequency band is noise suppressed to by using Gaussian Mixture Models (GMM), and the one in the higher frequency band is restored by referring to the clean speech. We carried out evaluation experiments with a speech quality, and confirmed the effectiveness of the proposed method toward the speech, which includes a large amount of clipping noise.

Comparison of spread spectrum and pulse signal excitation for split spectrum techniques composite imaging

Ultrasonic imaging of composites was investigated. Glass and carbon fiber reinforced plastic produced by resin transfer molding and prepreg forming were analyzed. In some of the samples air bubbles were trapped during RTM (resin transfer molding) process and interlayer gaps were present in prepreg technology samples. One of the most expected techniques to apply in such case is the Split Spectrum processing. On the other hand such signals require specific processing to reliably reconstruct the temporal position of the defect reflection. Correlation processing can be used for signal compression or Wiener filtering can be applied for spectral content equalisation. Pulse signals are simple to generate, but lack the possibility to alter the signal's spectrum shape. Spread spectrum signals offer a powerful tool for signal energy over frequency band increase and resolution enhancement. CW (continuous wave) burst has high energy but lacks the bandwidth needed for SSP (spread spectrum processing). The aim of the investigation was to compare the performance of the above signals in case of composite imaging, when various Split Spectrum Processing techniques are used with preceding Wiener processing for spectral content compensation. Resulting composite signals and images obtained are presented. Structural noise removal performance was evaluated as Receiver Operating Characteristics (ROC).

Flow Cytometry

Flow Cytometry

DWDM Hybrid-Integrated TOSA and ROSA for 10$\,\times\,$10.7-Gb/s Transmission Over 75-km Links

Compact parallel transmitters and receivers with an aggregate capacity of 107 Gb/s are built through hybrid integration of arrays of ten 100-GHz spaced directly modulated lasers, arrays of ten avalanche photodiodes, and high-index contrast silica arrayed waveguide grating multi- and demultiplexers. Unamplified transmission over 75 km of standard single-mode fiber and 155-km amplified links is demonstrated in the C-band, by using a modulation format based on spectral offset filtering and electronic dispersion compensation.

Use of lissamine green before conjunctival impression cytology and flow cytometry in patients with sjögren’s syndrome

AbstractPurpose Lissamine Green (LG) is a vital dye that stains damaged epithelial cells in ocular surface disease. Conjunctival Impression Cytology (CIC) is used with flow cytometry, to examine surface epithelial cells. We were concerned that, if used prior to CIC, cell uptake of LG might affect the fluorescent signal during flow cytometry. We therefore studied whether the use of LG before CIC, could cause fluorescence interference.Methods CIC was performed with two autoclaved Supor semicircular filters applied to the lateral bulbar conjunctiva of 6 patients with Sjögren's Syndrome. LG was eluted from a standard strip with a drop of anaesthetic and delivered into the inferior fornix. Two further filters were applied to the medial bulbar conjunctiva. Cells were recovered by agitation for 1 minute, washed, stained and analysed by flow cytometry.Results When compared with samples taken before LG instillation, cells isolated from all 6 samples taken after LG instillation, and excited at 630nm, showed an increase in fluorescence at 665nm. Some increased fluorescence was also noted at 680nm but was within the limits of spectral compensation. There was no observable effect of LG when cells were excited at 488nm.Conclusion Cell uptake of LG is detected by flow cytometry, predominantly in the 665nm channel when excited at 630nm. This persists despite cell washing. Whilst this excludes the use of fluorochromes that emit within this spectrum, the use of fluorochromes excited or emitting at other wavelengths, is feasible after LG staining.

Imaging of cell surface antigens on tumor lymph-node sections using fluorescence quantum dots

In this work we explored the potential of quantum dots for fluorescent detection of lymphoid surface antigens. To optimize detection with quantum dots, we upgraded a fluorescent microscope that allowed us obtaining multiple images from different quantum dots on a single section. Specimens stained with quantum dots remained stable over two weeks and practically did not bleach under the mercury lamp during scores of minutes. Double staining of frozen sections with direct conjugates of quantum dots with primary mouse monoclonal antibodies demonstrated direct conjugate high specificity and sensitivity. High stability of quantum dots’ fluorescence allows their use in diagnostics to analyze antigen coexpression on lymphoid tissue sections. “Spillover” of fluorescent signals from quantum dots into adjacent fluorescent channels maximally separated by 40 nm did not exceed 8%, which renders spectral compensation unnecessary.

Generation of polarization entangled photons using concurrent type-I and type-0 processes in AlGaAs ridge waveguides

A technique to generate polarization entangled photons using concurrent type-I and type-0 second-order nonlinear processes in monolithic Bragg reflection waveguides is presented and analyzed. Concurrent phase matching is achieved by lithographic tuning of the waveguide ridge width. Nearly perfect entanglement is achievable on-chip through appropriate epistructure design without the need of spectral filtering and group velocity compensation. Theoretical calculations predict that a high quantum interference visibility could be experimentally achieved with the pair generation rate of each process being approximately 3.0×10(6) pairs/s/mW/GHz.

Parametric Tunable Dispersion Compensation With Spectrally Noninverting Wavelength Conversion Using Quasi-Phase-Matched Adhered Ridge Waveguide

We develop a highly efficient quasi-phase-matched adhered ridge waveguide (QPM-ARW) in LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as a nonlinear material, and demonstrate tunable wavelength conversion without spectral inversion (SI) and parametric tunable dispersion compensation for a single-mode fiber (SMF) link. The QPM-ARW module with a second harmonic generation efficiency of 700 %/W achieves tunable wavelength conversion with a wavelength-tuning range of at least 25 nm through cascaded sum- and difference-frequency generation (SFG-DFG) process in which the signal and pumps are located symmetrically around the phase matching wavelength. The power penalty of the wavelength conversion is less than 0.6 dB for 43-Gb/s nonreturn-to-zero on-off-keying (NRZ-OOK) signals. We then apply the tunable wavelength conversion without SI to the parametric tunable dispersion compensation scheme, and achieve successful optical tunable dispersion compensation in 43-Gb/s NRZ-OOK transmissions over 53.2-km SMF.

VOICE CONVERSION USING INTERPOLATED SPEECH UNIT START AND END−TIME CONVERSION RULE MATRICES AND SPECTRAL COMPENSATION ON ITS SPECTRAL PARAMETER VECTOR

A voice conversion rule and a rule selection parameter are stored. The voice conversion rule converts a spectral parameter vector of a source speaker to a spectral parameter vector of a target speaker. The rule selection parameter represents the spectral parameter vector of the source speaker. A first voice conversion rule of start time and a second voice conversion rule of end time in a speech unit of the source speaker are selected by the spectral parameter vector of the start time and the end time. An interpolation coefficient corresponding to the spectral parameter vector of each time in the speech unit is calculated by the first voice conversion rule and the second voice conversion rule. A third voice conversion rule corresponding to the spectral parameter vector of each time in the speech unit is calculated by interpolating the first voice conversion rule and the second voice conversion rule with the interpolation coefficient. The spectral parameter vector of each time is converted to a spectral parameter vector of the target speaker by the third voice conversion rule. A spectrum acquired from the spectral parameter vector of the target speaker is compensated by a spectral compensation filter or power ratio. A speech waveform is generated from the compensated spectrum.

A novel rapid method for simultaneous determination of three diagnostically important porphyrins in erythrocytes using hyphenated synchronous fluorescence techniques

The species and concentrations of porphyrins in erythrocytes are of great importance in the clinical screening and diagnosis of porphyrias. However, it is difficult to analyze them simultaneously by conventional spectrofluorimetry. In this paper, we proposed a novel, simple and rapid method for the simultaneous determination of three diagnostically important porphyrins in human erythrocytes, protoporphyrin IX (PP), coproporphyrin III (CP) and zinc protoporphyrin IX (ZnPP), using hyphenated techniques based on derivative matrix isopotential synchronous fluorescence spectrometry and nonlinear variable-angle synchronous fluorescence spectrometry (DMI-NLVASFS). The spectral overlapping problems were well resolved and these three components were determined in one scanning without spectral compensation factors and chromatographic separation. The detection limits were 0.58, 0.21, 0.05nmolL−1 for PP, CP and ZnPP, respectively. Only 30s was needed for a single scanning and the recoveries were from 73% to 105% in erythrocytes. The Bland–Altman analysis indicates no significant difference between the proposed DMI-NLVASFS method and conventional fluorimetry method. The PP level of the erythropoietic protoporphyria (EPP) patients was significantly higher than that of healthy volunteers. This method can determine PP, CP and ZnPP simultaneously in a single scanning, thus providing a potential tool for the clinical analysis of porphyrins in human erythrocytes and the differential diagnosis of porphyrias.