Dr. Gang Luo Profile

Dr. Gang Luo

at The Chinese Univ of Hong Kong

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Proceedings Article | 13 March 2024 Poster + Paper

Efficient elimination of undesired fringes in quantitative phase measurements

Gang Luo, Yanping He

Proceedings Volume 12857, 128570Q (2024) https://doi.org/10.1117/12.3008556

KEYWORDS: Holographic interferometry, Background noise, Phase measurement, Reflection, Fringe analysis, Cameras, Phase imaging

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Undesired fringes can appear in interferometric phase measurement, leading to a degradation of contrast and resolution in the retrieved quantitative phase of measured cells and materials. Strong fringes can also introduce significant phase discontinuities, thereby increasing the complexity and time required for phase unwrapping. These fringes often originate from factors such as light reflection between material surfaces of optical devices. Addressing this issue typically necessitates more intricate optical designs or advanced devices, but this comes at the cost of extended design periods and increased expenses. Achieving complete elimination of these fringes may be not always feasible. In this context, we propose an efficient method to mitigate their influences and enhance object contrast and resolution. This method involves modeling the fringes and appropriately determining their frequency support. Primarily based on Fourier filtering, this approach has been successfully demonstrated using real-world interferometric data.

Proceedings Article | 1 November 2016 Paper

Short-delayed self-heterodyne interferometer combined with time-frequency analysis for measuring dynamic spectral properties of tunable lasers

Gang Luo, Ying An, Jinyi Li, Zhenhui Du

Proceedings Volume 10157, 1015731 (2016) https://doi.org/10.1117/12.2247245

KEYWORDS: Interferometers, Time-frequency analysis, Tunable lasers, Semiconductor lasers

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The dynamic spectral properties of Continuous Wave (CW) semiconductor lasers during continuous wavelength current tuning process (i.e. slope efficiency, dynamic wavelength current tuning rate and dynamic linewidth) are of utmost significance to high resolution molecular spectroscopy and trace gas detection. In this paper, a system for measuring dynamic spectral properties was setup based on a short-delayed self-heterodyne interferometry with different Optical Path Difference (OPD). And the dynamic spectral properties of different Distributed Feedback (DFB) semiconductor lasers were tested respectively by the system combined with a special time-frequency analysis method. The dynamic slope efficiency unveils nonlinear optical intensity that can’t be neglected in dealing with Residual Amplitude Modulation (RAM). The dynamic wavelength current tuning rate can be used to calibrate laser wavelength. The dynamic linewidth of a laser can be used to evaluate the spectral resolution in gas detecting. The system was demonstrated to simultaneously measure the dynamic spectral properties of different types of tunable lasers with a wavelength range in 2 μm ~ 8 μm during the tuning process. These dynamic spectral properties were distinctly different with the properties while the laser operates at a stable state, which may lay a foundation for deep research and enrichment the highly-precise spectrum database in gas sensing fields.

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