As the most abundant protein in the human body, collagen has a very important role in vast numbers of bio-medical applications. The unique second order nonlinear properties of fibrillar collagen make it a very important index in nonlinear optical imaging based disease diagnosis of the brain, skin, liver, colon, kidney, bone, heart and other organs in the human body. The second-order nonlinear susceptibility of collagen has been explored at the macroscopic level and was explained as a volume-averaged molecular hyperpolarizability. However, details about the origin of optical second harmonic signals from collagen fibrils at the molecular level are still not clear. Such information is necessary for accurate interpolation of bio-information from nonlinear optical imaging techniques. The later has shown great potential in collagen based disease diagnosis methodologies. In this paper, we report our work using an atomic force microscope (AFM), near field (SNOM) and nonlinear laser scanning microscope (NLSM) to study the structure of collagen fibrils and other pro-collagen structures.
Two-photon fluorescence (TPE) and second harmonic generation (SHG) can been used to extract biological information
from tissues at the molecular level, which is blind to traditional microscopes. Through these two image contrast
mechanisms, a nonlinear laser scanning endoscope (NLSE) is able to image tissue cells and the extra cellular matrix
(ECM) through a special fiber and miniaturized scanner without the requirement of poisonous chemical staining.
Therefore, NLSE reserves high potential for in-vivo pathological study and disease diagnosis. However, the high cost
and bulky size of a NLSE system has become one of the major issues preventing this technology from practical clinical
operation. In this paper, we report a fiber laser based multi-modality NLSE system with compact size and low cost, ideal
for in-vivo applications in clinical environments. The demonstration of the developed NLSE nonlinear imaging
capability on different bio-structures in liver, retina and skin are also presented.
A fiber profilometer is developed to measure hard-to-access areas. This system utilizes low coherence light interferometry technique to detect profiles of internal surfaces of samples. A differentiation method is employed to enhance vertical resolutions of imaging results. An auto-focusing scheme is proposed to obtain an optimized lateral resolution. The performance of the profilometer system is demonstrated by experimental studies.
A dual optical detection scheme is proposed for optical code division multiple-access systems utilizing on-off-keying modulation technique. The proposed detector is developed by combining a correlation detector and a chip-level detector with the logical OR operation. In this way, the merits of two detectors can be fully exploited. Thus the dual detector can achieve the enhanced bit error rate performance in the presence of both multi-user interference and noise.