Manufacturing techniques using femtosecond lasers in transparent materials
Date
2019-12-20
Authors
Cho, Yonghyun
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Abstract
Femtosecond laser direct writing in transparent materials such as glass and optical
fibers has been used as a versatile tool in order to fabricate various 3-D photonic
structures such as active and passive waveguides, couplers, gratings and diffractive
optical elements (DOEs). This capability of patterning and refractive index modification
in the bulk of transparent materials depends on the nonlinear absorption phenomenon.
This practical technique has the potential to be used for cost effective and simplified
manufacturing in various applications. This thesis examines three advanced
manufacturing techniques that use ultrashort pulse filamentary propagation induced by
nonlinear absorption in the transparent materials. First, a new gradient index lens
fabrication method using femtosecond laser direct writing is introduced. Light that passes
through the lens with refractive index change resulting from localized energy deposition is
focused using a beam profiler. Second, wide welding area of glass samples are used to
fabricate microfluidic devices with long channels by adopting customized fixture. The fixture
making artificial pressure helps the two glass samples have wide optical contact area and the
highly intensive pulse filamentation strongly joins glass slides. As an example of a more
specific application, microfluidic samples with long grooves sealed by femtosecond laser
welding were successfully fabricated as part of this project. Finally, a screw-shaped, long period grating sensor was fabricated by rotating the optical fiber. This technique enables the
fiber core to have asymmetric refractive index change, resulting in higher sensitivity
compared to conventional long period grating sensors. Also, a new long-period grating sensor
with reverse bending effect has been demonstrated by producing complex pitches of
refractive index change.
Description
Keywords
Femtosecond laser, Transparent Material, Glass welding, Long period grating, Gradient index lens