利用光纖色散提高鎖模雷射高階調變項-頻域光子遷移技術系統中之信噪比

Abstract

基於鎖模雷射高階調變項頻域光子遷移技術是一種非侵入式分析樣品吸收與散射係數的光學檢測方法。此方法是藉由接收物體散射光，並利用光學模型分析出樣品的吸收與散射係數資訊。然而隨著穿透樣品深度的增加，入射光會急遽衰減，進而降低整體系統之訊號雜訊比，而無法量測更深層的組織。因此本論文中我們利用加入不同長度的光纖於頻域光子遷移系統中改善整體訊號雜訊比，因為光纖的色散效應使雷射脈衝寬度增加，進而重新分佈寬頻的光調變能量於較窄的調變頻寬中(~GHz)，等效提升可用範圍分布在每一條頻率上入射光能量強度，讓原本入射的光能穿透更深，反射回來的訊號強度更大。此方法可以進一步提升在某一些調變頻率的能量，未來在深層的生物組織量測中，非常具有應用價值。

Higher-order-harmonic modulations of mode-locked laser for frequency domain photon migration (FDPM) is a non-invasive optical technique that analyzes optical properties (absorption coefficient and reduced scattering coefficient ) from the tissue. The diffused photons were received and the absorption and reduced scattering coefficients were analyzed by optical model. However, the intensity of received photons will be rapidly attenuated when the penetration depth is increased. Thus, the signal-noise ratio (SNR) of FDPM system is rapidly degraded. In this thesis, we propose and demonstrate fiber-dispersion to improve SNR on FDPM system. The fs laser pulses width broadened by the fiber dispersion. And intensity-modulated frequency combs will be redistributed in the narrowed bandwidth. This method is equivalent to raise the modulation intensity in the available bandwidth of the whole systems. Therefore, the incident light can penetrate deeper and reflected signal can be enhanced. In the future, we can use this method to increase higher frequency signal and measure deep biomedical tissue.