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Approaches that are, to our knowledge, novel, are proposed in this paper to improve the accurancy performance of self-mixing interferometruy (SMI). First the characteristics associated with signals observed in SMI systems are studied, based on which a new procedure is proposed for achieving accurate estimation of the laser phase.

Abstract-A review of recent experimental and theoretical results about laser diode self-mixing velocimetry is presented, showing that this technique can be deployed to measure velocity and vibration of solid targets with an extremely simple optical setup. This technique reduces optical alignment problems and achieves results comparable to those obtained by the conventional laser Doppler velocimetry (LDV) approach. It is demonstrated that the self-mixing signal can be processed to recover the target velocity and vibration by applying the same analysis method used for LDV. An optimal signal processing method is then proposed to recover the target velocity with good accuracy, also in the presence of relevant speckle disturbance. Application to the measurement of sub-micron vibrations is also demonstrated, using a self-mixing vibrometer instrument capable of 5-nm accuracy. As an example, the characterization of response and hysteresis of piezoceramic transducers (PZTs) is carried out. These results illustrate the effectiveness of the self-mixing technique in the field of laser velocimetry, opening the way to new applications where compactness and low cost of the measuring apparatus are essential.Index Terms-Doppler frequency estimation, optical feedback interferometry, piezoceramics, self-mixing, speckle pattern, vibration and velocity measurement.

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In a recent published work we proposed a technique to recover the absolute phase maps of two fringe patterns with different spatial frequencies. It is demonstrated that a number of selected frequency pairs can be used for the proposed approach, but the published work did not provide a guideline for frequency selection. In addition, the performance of the proposed technique in terms of its anti-noise capability is not addressed. In this paper, the rules for selecting the two frequencies are presented based on theoretical analysis of the proposed technique. Also, when the two frequencies are given, the anti-noise capability of technique is formulated and evaluated. These theoretical conclusions are verified by experimental results.

Feedback parameter (the C factor) is an important parameter for a semiconductor laser operating in the regime of external optical feedback. Self-mixing interferometry (SMI) has been proposed for the measurement of the parameter, based on the time-domain analysis of the output power waveforms (called SMI signals) in presence of feedback. However, the existing approaches only work for a limited range of C, below about 3.5. This paper presents a new method to measure C based on analysis of the phase signal of SMI signals in the frequency domain. The proposed method covers a large range of C values, up to about 10. Simulations and experimental results are presented for verification of the proposed method. Abstract: Feedback parameter (the C factor) is an important parameter for a semiconductor laser operating in the regime of external optical feedback. Selfmixing interferometry (SMI) has been proposed for the measurement of the parameter, based on the time-domain analysis of the output power waveforms (called SMI signals) in presence of feedback. However, the existing approaches only work for a limited range of C, below about 3.5. This paper presents a new method to measure C based on analysis of the phase signal of SMI signals in the frequency domain. The proposed method covers a large range of C values, up to about 10. Simulations and experimental results are presented for verification of the proposed method. Disciplines Physical Sciences and Mathematics

T. (2007). Toward automatic measurement of the linewidth-enhancement factor using optical feedback self-mixing interferometry with weak optical feedback. IEEE Journal of Quantum Electronics, 43 (7), 527-534.Toward automatic measurement of the linewidth-enhancement factor using optical feedback self-mixing interferometry with weak optical feedback Abstract This paper proposes an approach for automatically measuring the linewidth-enhancement factor (LEF) of semiconductor lasers using optical feedback self-mixing interferometry (OFSMI), which works in weak optical feedback regime and where the external target is subject to simple harmonic vibration with unknown vibration frequency and magnitude. According to well-known Lang-Kobayashi theory the waveform of the modulated optical output power from the OFSMI system is influenced by multiple parameters, including the LEF, the optical feedback level factor, and the parameters related to the movement of external target. In order to estimate LEF, other parameters must also be considered and, hence, a multiple parameter estimation strategy is required. We propose a solution for this multiple parameter estimation problem based on the principle of data-to-theoretical model match. In particular, a strategy for minimizing a cost function in order to achieve the best fitting is proposed with which all the unknown parameters can be estimated. The performance of the proposed approach is tested using experimental data in comparison with other two approaches. It is seen that, over different experimental signals, the standard deviation for estimated LEF is less than 4.58% on average, which shows that results have excellent consistency. Moreover, the proposed approach also provides a solution for vibration measurement (that is, vibration frequency and magnitude). Disciplines Physical Sciences and Mathematics Publication DetailsYu, Y., Xi, J., Chicharo, J. F. & Bosch, T. (2007). Toward automatic measurement of the linewidthenhancement factor using optical feedback self-mixing interferometry with weak optical feedback. IEEE Journal of Quantum Electronics, 43 (7), 527-534. Abstract-This paper proposes an approach for automatically measuring the linewidth-enhancement factor (LEF) of semiconductor lasers using optical feedback self-mixing interferometry (OFSMI), which works in weak optical feedback regime and where the external target is subject to simple harmonic vibration with unknown vibration frequency and magnitude. According to well-known Lang-Kobayashi theory the waveform of the modulated optical output power from the OFSMI system is influenced by multiple parameters, including the LEF, the optical feedback level factor, and the parameters related to the movement of external target. In order to estimate LEF, other parameters must also be considered and, hence, a multiple parameter estimation strategy is required. We propose a solution for this multiple parameter estimation problem based on the principle of data-to-theoretical model match. In particular, a strategy for minimizing a...

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