A Study of Wavefront Measurement Applied to the Coupling between Lasers and Fibers
| Autor: | Yu-Kuan Lu, 呂昱寬 |
|---|---|
| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 We have proposed and demonstrated a technique for the measurement of the wavefront of a diode laser beam with a large dynamic range. Our technique is a modified version of Hartmann and Shack-Hartmann wavefront sensor. The modified version is capable of providing a large dynamic range (180 degrees). The wavefront measurement exhibits a precision of ( 0.02 degrees), subject to a standard deviation governed by the diffraction limit (~λ/d). Using the physical measurement of the wavefront, we are able to reconstruct the electric fields of a diode laser beam at any location, including the far-field and near-field. The reconstructed electric fields were computed form the data of the intensity and the phase distribution by means of Fourier transform. The information about the electric field can be very useful in the design of microlens for the efficient coupling of light source into optical components. The results indicate that the wavefront sensor with large dynamic range can provide a reliable method for measuring the wavefront distributions of diode lasers with large divergence angles. However, the numerical near-field intensity is 150% deviated from the measured near-field intensity because of the inherent inaccuracy in the wavefront measurement. In this study, we have measured the near field intensity distribution directly with an objective and a CCD camera. We found that the distribution of the mode field was symmetric at a distance of 8μm from a diode laser and the mode field diameter was 4.75μm. Using the phase retrieval algorithms, the radii of the near-field wavefront in the vertical axis and the horizontal axis were 8μm and 41μm, respectively. Through the geometrical optics, the optimum curvatures of elliptic-cone-shaped lensed fiber for efficient coupling in the vertical axis and the horizontal axis were 4μm and 20.5μm individually. Once we know the optimum curvatures of elliptic-cone- shaped lensed fiber, we can fabricate it using grinding and fusing. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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