Characteristics of coherent fiber opitcs imaging bundle after high power transmission
This thesis presents a comparative experimental characterization of a coherent fiber optics imaging bundle or coherent fiber bundle (CFB) before and after exposure to high energy density pulses (> 1k J/cm2). A Fujikura FIGH-30-850N ultra-thin imaging fiber with 30,000 individual optical fiber filaments, packed into a 780 μm spot, was selected and tested. Two fiber-coupled laser diodes, operating at a wavelength of 818 nm and 830nm respectively, provided the high power excitation source for the experiments. Precise control of the incident energy density was achieved through a combination of current regulation and pulse width control. The latter technique enabled a pulse-width range from 50 ms to continuous wave (CW) operation at constant repetition rate of one second (1 Hz). The transmitted image through the CFB was observed with an Olympus BH-2 Microscope and recorded with a 2 Megapixel digital microscope still image camera, μCapture.
Post processing of the recorded image was done using software tools, such as, ImageJ (Image Processing and Analysis in JAVA) and MATLAB (MATrix LABoratory). Analysis done using visual inspection and modulation transfer function techniques revealed that the laser induced fiber damage threshold (LIFDT) of the CFB is greater than 11k J/cm2. This high damage threshold is much larger than the accepted levels used for diverse medical procedures, such as, photoepilation. The results indicate that CFBs can be used for precise delivery of lethal doses of optical energy needed to destroy unwanted tissues, in addition to transporting images from remote locations. Through experiments, the results ensure the practicability of using CFB for both imaging and power transmission for the many diverse applications using photoinduced therapies.