Spectral Phase Reconstruction Research Articles

Spectral phase reconstruction of femtosecond laser pulse from interferometric autocorrelation and evolutionary algorithm

We report on the complete temporal characterization of femtosecond laser pulses from second-order interferometric autocorrelation and laser spectrum measurements. The method exploits a newly developed autocorrelator based on a two photon-absorption signal produced directly within a camera sensor so as to provide a single-shot interferometric autocorrelation of great reliability and robustness. Interferometric autocorrelation trace and laser spectrum are exploited for a spectral phase retrieval via an evolutionary algorithm. The quality of the reconstruction for highly modulated spectral phases imprinted by a pulse shaper confirms the reliability of the method. The autocorrelator is compact, robust and easy to use. Possible improvements are discussed.

Robust spectral phase reconstruction of time-frequency entangled bi-photon states

Exploitation of time-frequency properties of SPDC photon pairs has recently found application in many endeavors. Complete characterization and control over the states in this degree of freedom is of paramount importance for the development of optical quantum technologies. This is achieved by accessing information both on the joint spectral amplitude and the joint spectral phase. Here we propose a novel scheme based on the MICE algorithm, which aims at reconstructing the joint spectral phase by adopting a multi-shear approach, making the technique suitable for noisy environments. We report on simulations for the phase reconstruction and propose an experiment using a Franson modified interferometer.

Singing voice synthesizer with non-filter waveform generation using spectral phase reconstruction

This paper discusses a singing voice synthesis system based on non-filter waveform generation using spectral phase reconstruction as an alternative method to replace the conventional source-filter model. Source-filter model has been considered as an essential technique in the long history of speech synthesis as it simulates the human process of speech production consisting of excitation and resonances, even after hidden Markov model was introduced in the 90s toward statistically trainable speech synthesis. Filter (particularly, recursive filter), however, may cause serious problems in undesired amplitude and long time decay when sharp resonances in recursive filter match harmonics of F0 of the excitation. As the ultimate purpose of usage of filter is to transfer the spectrogram designed in the TTS system to the listener’s hearing organs, an alternative solution can be brought from “phase reconstruction” without using filters. We propose a spectral phase reconstruction, instead of using filter, to generate...

Exposing speech tampering via spectral phase analysis

Audio recordings serve as important evidence in law enforcement context. The most crucial problem in practical scenarios is to determine whether the audio recording is an authentic one or not. For this task, blind audio tampering detection is typically performed based on electric network frequency (ENF) artifacts. In case there is a high level of noise, ENF analysis would become invalid. In this paper, we present a novel approach to detect and locate tampering in uncompressed audio tracks by analyzing the spectral phase across the Short Time Fourier Transform (STFT) sub-bands. Spectral phase reconstruction is employed to counteract the impact of noise. Also, a new feature based on higher order statistics of the spectral phase residual and the spectral baseband phase correlation between two adjacent voiced segments is proposed to allow for an automated authentication. Experimental results show that a significant increase in detection accuracy can be achieved compared to the conventional ENF-based method when the audio recording is exposed to a high level of noise. We also testify that the proposed method remains robust under various noisy conditions.

Spectrographic phase-retrieval algorithm for femtosecond and attosecond pulses with frequency gaps

We present a phase-reconstruction algorithm for a self-referenced spectrographic pulse characterization technique called “very advanced method for phase and intensity retrieval of e-fields” (VAMPIRE). This technique permits a spectral phase reconstruction of pulses with separated frequency components. The algorithm uses the particular characteristics of VAMPIRE spectrograms. It is a locally structured algorithm which is fast, robust, and it allows us to master stagnation problems. The algorithm is tested by use of both simulated and measured data.

Simple and highly sensitive optical pulse-characterization method based on electro-optic spectral signal differentiation

A very simple self-referenced, linear pulse-characterization technique based on spectral phase reconstruction by frequency-domain signal differentiation is introduced. This technique can be implemented using electro-optic intensity modulation of the pulse under test with a synchronized RF sinusoid. The pulse spectral phase profile can be accurately and unambiguously reconstructed from only two measured energy spectra, i.e., at the input and at the output of the modulator, using a direct analytic equation. The method is experimentally demonstrated by precisely characterizing microwatt-power picosecond pulses after linear dispersion through short sections (50-700 m) of conventional single-mode fiber.

The amplitude and phase measurements of femtosecond pulses using fringe-free SPIDER

A developed method of fringe free spectral phase interferometry reconstruction (FF-SPIDER) for femtosecond pulse measurement is demonstrated with theoretical simulation and experimental measurements. FF-SPIDER overcomes the disadvantages of the traditional SPIDER in which the time delay measured pulse replica results in fringes in the interference spectrum and complicates the spectral phase reconstruction. The measurement results show that FF-SPIDER reconstructs the amplitude and phase of the measured pulses with higher efficiency, higher accurate and lower requirements on measurement apparatus.

Effects of noise on spectral phase reconstruction with wavelet analysis

We have investigated the accuracy of wavelet analysis of spectral shearing inter ferometry signal with noisy data. Specifically, we have examined at the effects of additive noise, multiplicative noise, and quantization of the interferogram o n the reconstruction of the spectral phase, and revealed that the wavelet transf orm is a robust technique to retrieve spectral phase from the noise background. We also show that the phase of a femtosecond pulse can be identified from the tr ace of wavelet transform.