- 學位論文
多模態光纖內視鏡之探針設計與特性化之研究
Probe design and characterization for a multimode fiber based endomicroscope
摘要
在這篇論文中，我們成功的利用我們所建造的多模態光纖內視鏡得到解析度大於一微米的螢光成像。多模態光纖在很小的光纖直徑內卻具有高度的自由度，並且其高數孔直徑 (numerical aperture, NA) 使其內視鏡具有高度的解析度。然而，多模態光纖最大的問題在於，當光進入多模態光纖後，光激發了不同的模態而它們彼此之間互相干涉，波前因而產生扭曲變形的情形，最後在光纖的出口端形成了類似散斑的圖樣 (speckle pattern)。我們使用數位光學相位共軛 (Digital Phase Conjugation) 技術解決了光波前扭曲變形的情形並成功的在光纖末端產生了高對比度的重建光點。藉由數位技術我們可以動態控制光在多模態光纖中的傳輸並且使其內視鏡能夠在沒有機械式掃描器的情形下掃描光點。為了得到更深層的生物組織影像，我們需要為我們的內視鏡建造一個極細且堅硬的探針。我們成功的利用了醫學用26 gauge 的針頭(外徑450微米) 製成了前視探針 (forward-viewing probe)。我們並且使用此探針成功展示了高於一微米解析度的螢光成像，藉由掃描一微米的螢光珠 (fluorescence beads) 樣本並得到足以區分兩個相鄰螢光珠的螢光影像。我們並設計了高數值孔徑 (NA>0.4) 且極細(D=250 μm) 的側視探針(side-viewing probe)，即利用折射率漸變透鏡 (GRIN lens) 和稜鏡反射鏡 (prism mirror) 加之於光纖末端而完成之設計。藉由ZEMAX軟體模擬此側像探針內視鏡，在光中心波長為832奈米時可以達到0.8微米解析度。我們並且模擬探針的數值孔徑對應其離軸距離 (off-axis distance) 及 工作距離 (working distance) 之關係圖。藉由這些關係圖得到探針的視角 (field of view) 資訊。 總的來說，我們成功展示了高解析度且無需機械式掃描的多模態光纖內視鏡。藉由掃描一微米大小的螢光珠，我們證明了我們製作的前視探針可以達到高於一微米的高解析度。我們並且設計且模擬極細且高數值孔徑的側視探針。
並列摘要
In the presented thesis, we have successfully demonstrated sub-micron fluorescence imaging using our multimode fiber-based endomicroscope. Multimode fibers have a large number of degrees of freedoms in a small diameter, and have high numerical aperture which provides high resolution to an endoscopic system. However, light gets scrambled while propagating through a multimode fiber due to the intermodal coupling of the propagating modes. By using digital phase conjugation, we compensate for the scrambling problem of light propagating through a multimode fiber and generate a high contrast reconstructed focus spot at the distal end of the fiber. The digital implementation enables the dynamic control of light transmission through the multimode fiber and enables the endomicroscope to perform the scanning without mechanical scanners. In order to acquire images deep inside biological tissues, an ultrathin rigid needle probe is required. We have successfully fabricated the forward-viewing needle probe with the 26 gauge clinical needle of which the outer diameter is 450 μm. The sub-micron resolution has been obtained by distinguishing two adjacent 1 μm fluorescence beads with the needle probe. We also designed a high numerical aperture (NA>0.4) ultrathin (D=250 μm) side-viewing imaging probe by attaching GRIN lenses and a prism mirror at the distal end of the multimode fiber. The simulation results shows that with our side-view imaging probe design, the resolution of 0.8 μm could be obtained at 532 nm. The plots of the numerical aperture versus the off-axis distance and working distance of the probe has been shown, giving us the information on the field of view. In conclusion, a high-resolution scanner-free multimode endomicroscope has been presented. Sub-micron resolution has been achieved by imaging 1 μm fluorescence beads with the forward-view needle probe. An ultrathin, high numerical aperture side-viewing probe is also designed.