Browsing by Author "Tseng, Sheng-Hao"

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Higher-order modulations of fs laser pulses for GHz frequency domain photon migration system
(2014-02-24)
Lin, Huang-Yi
;
Cheng, Nanyu
;
Tseng, Sheng-Hao
;
Chan, Ming-Che
;
影像與生醫光電研究所
Except the fundamental modulation frequency, by higher-order-harmonic modulations of mode-locked laser pulses and a simple frequency demodulation circuit, a novel approach to GHz frequency-domain-photon-migration (FDPM) system was reported. With this novel approach, a wide-band modulation frequency comb is available without any external modulation devices and the only electronics to extract the optical attenuation and phase properties at a selected modulation frequency in FDPM systems are good mixers and lock-in devices. This approach greatly expands the frequency range that could be achieved by conventional FDPM systems and suggests that our system could extract much more information from biological tissues than the conventional FDPM systems. Moreover, this demonstration will be beneficial for discerning the minute change of tissue properties. (C) 2014 Optical Society of America
Signal Enhancement by Fiber-Dispersion in Sub-GHz Frequency Domain Biophotonic Diagnosis Systems
(2019-01-01)
Tseng, Sheng-Hao
;
Huang, Tzu-Feng
;
Yeh, Jun-Liang
;
Chan, Ming-Che
;
光電學院
Pulsed lasers can be utilized to generate intensitymodulated light at the fundamental frequency of the laser repetition rate as well as higher order modulation (HOM) frequencies in the recent study. We also demonstrated the feasibility of using pulse lasers and fiber-wavelength-convertors as a light source in multicolor frequency-domain (FD) biophotonic systems. In this paper, we present a novel approach to enhancing the intensity of signals below 1 GHz in HOM-based FD systems simply by employing the fiber dispersion effect. The energy spectrum of HOMs can be redistributed to enhance the intensity of HOMs within the bandwidth of the photo-detector without the need for an external (optical or electrical) amplifier. We also demonstrate that the length of dispersive fiber can be optimized via numerical calculations, the results of which are in good agreement with experimental measurements. Finally, we demonstrate a frequencydomain-photon-migration system employing the fiber dispersion effect to enhance sub-GHz signals at a wavelength of 1.03 pro in order to recover the optical properties of turbid samples. Our measurements results demonstrate the superiority of the proposed FD source over the conventional directly modulated FD light source. Furthermore, the simple configuration of the proposed scheme makes it applicable to a wide range of FD biophotonic systems.
Widely wavelength tunable fast intensity-modulated light source for biophotonic applications
(2017-07-15)
Huang, Tzu-Feng
;
Tseng, Sheng-Hao
;
Wang, Hsien-Yi
;
Chan, Ming-Che
;
光電學院
High modulation depth, fast (megahertz to gigahertz), intensity-modulated light sources of various wavelengths within the 0.7-1.35 mu m bio-penetration window are highly desirable for many biophotonic diagnosis systems. In this Letter, we present a novel scheme of a wavelength tunable, ultra-broadband light source which simply consists of a pump laser, a nonlinear fiber, and demodulation circuits. The working wavelength range of the light source is from 0.7 to 1.35 mu m which covers a vast part of the bio-penetration window, and its modulation frequencies extends from tens of megahertz to gigahertz. The performances of the proposed light source in either working wavelength range or modulation frequency bandwidth are much superior to any typical laser diodes or solid state lasers currently employed in the frequency-domain or other biophotonic utilization. The wide applicability of this novel light source in diverse biophotonic applications can be observed from our carefully designed diffused optical spectroscopy phantom measurement. (C) 2017 Optical Society of America