1. Photosensitivity and Refractive-index Modification of Glass: Optical Fiber Applications Narin Nuttavut Physics Department, Faculty of Science Mahidol University

2. Physics Department, Faculty of Science, Mahidol University 2 Outline Photosensitivity Application for Bragg gratings Refractive-index modification Applications Future work and direction

3. Physics Department, Faculty of Science, Mahidol University 3 Photosensitivity Refractive index changed by light exposure (UV band) Photo-induced refractivity due to impurities Refractive index Intensity  time n o +  n (~0. 1%) nono UV light Glass

4. Physics Department, Faculty of Science, Mahidol University 4 Bragg gratings

5. Physics Department, Faculty of Science, Mahidol University 5 Bragg gratings Fabrication

6. Physics Department, Faculty of Science, Mahidol University 6 Common characteristics A large number of layers resulting in a strong and narrow bandwidth which can satisfy rigorous dense-wavelength telecommunication requirements. Sensitivity to environmental parameters, e.g. strain and temperature. A compact and passive device

7. Physics Department, Faculty of Science, Mahidol University 7 Refractive-index modification: something deeper Refractive index modification can be achieved by several techniques such as heat treatment, strain treatment, and chemical processes (or even a combination of these).

8. Physics Department, Faculty of Science, Mahidol University 8 An example Mirage effect: Atmospheric optical illusion in which an observer sees a nonexistent body of water or an image of some object, resulting from distortion of light by alternate layers of hot and cool air Hot air Cool air Light path

9. Physics Department, Faculty of Science, Mahidol University 9 Applications Lenses without curve surfaces Optical component fabrication

10. Physics Department, Faculty of Science, Mahidol University 10 Optical lenses What is a lens?

11. Physics Department, Faculty of Science, Mahidol University 11 GRIN lens Rather than varying thickness of the medium, the refractive index is changed as a function of the diameter of the lens. GRIN lens = GRaded INdex lens

12. Physics Department, Faculty of Science, Mahidol University 12 A Melles Griot’s drawing

13. Physics Department, Faculty of Science, Mahidol University 13 Collimator (GRIN lens design) Collimators A Melles Griot’s drawing

14. Physics Department, Faculty of Science, Mahidol University 14 Future work and direction Investigation of refractive-index modification for commercial interest Investigation of refractive-index modification of glass and polymer Enhancement processes for refractive- index modification

15. Physics Department, Faculty of Science, Mahidol University 15 Recommended references K O Hill, et al. Applied Physics Letters, 32:647–649, 1978. K O Hill, et al. Journal of Lightwave Technology, 15(8):1263-76, 1997. D K W Lam, et al. Applied Optics, 20(3):440-5, 1981. Y J Rao. Measurement Science and Technology, 8(4):355-375, 1997.

16. Physics Department, Faculty of Science, Mahidol University 16 Acknowledgements The author would like to thank –Staffs of Physics Department, Mahidol University for internal discussion and their encouragement. –The parents/friends for their great understanding of having a son/friend who is a researcher.

17. Physics Department, Faculty of Science, Mahidol University 17 Appendix Early setup of Bragg gratings recorded in fiber (Hill, 1978).