Feature Of The Week 4/4/10: Ce3+:YAG double-clad crystal fiber based optical coherence tomography on fish cornea
Feature Of The Week 4/4/10: With the tremendous success of optical coherence tomography (OCT) in recent years, high resolution and high image fidelity are getting more importance. So far, several approaches have been proposed to achieve high axial resolution, such as multiplexed superluminescent diode, femtosecond laser, continuum generation from photonic crystal fiber, and xenon illuminator. In general, these solutions are either have high cost, exhibit bumpy spectrum, or both. In contrast, spontaneous emission light can generate broadband and near-Gaussian spectrum, but the power level is often very weak. Using waveguide to collect the amplified spontaneous emission (ASE) can improve brightness of the source for OCT system. A proprietary double-clad crystal fiber (DCF) growth technique has been developed by Professon Sheng-Lung Huang's team at the Graduate Institute of Photonics and Optoelectronics, National Taiwan University. Using active medium as the single-crystalline core, the DCF can maintain the high cross section of the crystal environment, and effectively collect the ASE.
With the collaboration between the National Taiwan University and the Academia Sinica, a Ce3+:YAG DCF based visible emission was used as the light source for OCT. The visible emission was produced from a 10-μm-core DCF pumped by a diode laser. The broadband emission and short central wavelength of this light source enabled the realization of 1.5-μm axial resolution in air. The relatively smooth spectrum reduced the side lobe of its point spread function, and therefore, facilitated the generation of a high quality image with less crosstalk between adjacent image pixels. As a demonstration, an Aplocheilus Lineatus Gold fish was experimented on to map out the stroma of its cornea. This visible light based OCT can be utilized for industrial inspection as well as ocular applications. This OCT system may be useful for the detection of early stage cornea disorders, such as Fuch’s and keratoconus dystrophies. The aim of the project is to realize a cellular resolution OCT with less image-pixel cross talk in the hope that early disease detection can be achieved with high fidelity.