Group Delay Spectrum Research Articles

Group delay and alpha -parameter measurement of 1.3 mu m semiconductor traveling-wave optical amplifier using the interferometric method

The group delay dispersion and the linewidth broadening factor ( alpha -parameter) are measured for a 1.3- mu m semiconductor traveling-wave optical amplifier (TWA) using a newly developed interferometric method. By Fourier transforming an interferometric cross-correlation signal, both the optical phase and the gain are simultaneously obtained in the entire gain bandwidth. The group delay spectrum is evaluated from the frequency derivative of the phase, and by selecting an appropriate interval for the interferometer scan, a refractive index dispersion of approximately 3.2 fs/nm is separated from the dispersion caused by Fabry-Perot resonance. From the phase and gain change with injection current, the alpha -parameter spectrum is evaluated, and the results indicate a strong dependence on wavelength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of smoothed group delay spectrum distance measure in speaker-independent speech recognition

The smoothed group delay spectrum distance (SGDS) measure is evaluated in speaker-independent recognition experiments. First, the appropriate level of smoothing of the group delay spectrum (GDS) is investigated by adding noise, etc., to the input speech. Then a comparison with the speaker-dependent case is made. An experiment is reported in which, for low amplitude parts of speech (e.g., unvoiced speech), the standard (LPC) distance measure is used in the interframe distance calculation instead of the SGDS distance measure. This method prevents a loss of recognition accuracy due to too strong an emphasis on certain spectral elements and a consistently high recognition accuracy can be achieved. Finally, evaluate the SGDS distance measure is evaluated where the GDS is represented in the spectral domain as a discrete Fourier transform (DFT) of the LPC coefficients. In comparison to the SGDS which was calculated by weighting the LPC cepstrum co-efficients, computation time and memory space can be reduced without loss of recognition accuracy. Furthermore, a low bit quantization of the GDS is reported and a high recognition rate is achieved with only 32 bits per frame.

Evaluation of the smoothed group delay spectrum distance measure for speaker‐dependent speech recognition

AbstractThis paper evaluates first the smoothed group delay spectrum (SGDS) distance measure through the isolated work speech recognition experiment by specified speakers. The experiment was performed for the following three cases, considering the speech recognition in the actual environment: 1) the case where the channels have difference characteristics; 2) the case where a white noise is added to the input speech; and 3) the case where the telephone speech is used as the input.In all three cases, the recognition rate is improved drastically compared to the traditional LPC cepstrum distance measure. An improvement of the recognition rate by 16 percent was realized under the noise of segmental SN ratio 20 dB. Then the distance measure is evaluated for the case where the FFT cepstrum is converted into the group delay spectrum.The proposed method gives a better recognition rate compared to the conventional FFT cepstrum distance measure, but the result is worse than the SGDA measure by approximately 3 percent since the higher‐order FFT cepstrum coefficient has a larger variance on the time axis.Finally, the SGDS distance measure is evaluated by the isolated word speech recognition system with the monosyllable as the registered speech. The vowel recognition rate is improved, which improved the recognition rates for the syllable and the word by 2 percent or more on a relative scale.

Interferometric measurements of chromatic and polarisation mode dispersion in highly birefringent single-mode fibres

Interferometric measurements on highly birefringent single-mode fibres have been performed. The group delay spectrum of each polarisation mode is independently measured over the whole 1.0–1.73μm spectral range. The polarisation mode dispersion is obtained by direct subtraction of the group delay spectra.

Comparing the chromatic dispersions of two single-mode silica fibres with pure F and pure GeO 2 doping, respectively

The refractive-index profile and the group-delay spectrum of a purely F-doped silica fibre were measured. This fibre&apos;s chromatic dispersion behaves considerably differently from that of a purely GeO2-doped fibre having the same profile function and V-parameter at λ = 0.633 μm.