Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Fabrication and Characteristics of a Fused
Silica-Based Optical Waveguide with Femtosecond
Fiber Laser Pulses
Ting-Chou Chang 1 , Chien-Hsing Chen 2 , Wei-Hung Shih 3 , Jian-Neng Wang 4 , Chai-Yu Lee 1 , Jaw-Luen Tang 2 , Shau-Chun
Wang 1 , Lai-Kwan Chau 1 , Wei-Te Wu 5*
1 Department of Chemistry and Biochemistry, National Chung Cheng University
168 University Road, Minhsiung, Chiayi 621, Taiwan
2 Department of Physics, National Chung Cheng University
168 University Road, Minhsiung, Chiayi 621, Taiwan
3 Department of Mechanical Engineering, National Chung Cheng University
168 University Road, Minhsiung, Chiayi 621, Taiwan
4 Department of Construction Engineering, National Yunlin University of Science and Technology,
123 University Road, Section 3, Douliou, Yunlin 640, Taiwan
5* Department of Biomechatronics Engineering, National Pingtung University of Science and Technology
1, Shuefu Road, Neipu, Pingtung 912, Taiwan
Tel: +886-8-770-3202 Ext. 7599; Fax: + 886-8-774-0420; weite@mail.npust.edu.tw
Abstract
This study investigates the fabrication characteristics
of a femtosecond fiber laser on a fused-silica-based optical
waveguide. The wavelength and repetition rate of the
femtosecond fiber laser are 532 nm and 1 MHz,
respectively. We selected three main fabrication
parameters for systematic adjustment: laser power (E),
scanning speed ( v s
) and focus depth (d = 0 at the surface
of substrate). We succeeded in fabricating a waveguide
layer inside the silica subtracts. By analyzing the light
translation path and the net fluence in the waveguide, the
range of fabrication energy of the waveguide on the fused
silica was kept within 0.973 - 1.438 KJ/cm 2 .
I. Introduction
Recently, developments in nanotechnology have led to
a proliferation of electro-optic system applications. To
minimize system size, industries including communications,
construction and biomedical detection have widely applied
optical waveguides such as photonic crystal fibers [1], fiber
interferometers [2], surface plasma resonance (SPR) sensors
[3], localized plasma resonance (LPR) sensors [4] and
guided-mode resonance (GMR) sensors [5].
Waveguide device are fabricated through techniques
including ion bombardment, laser machining,
photolithography, and mechanical stamping [6], commonly
using fused silica as a substrate. Laser machining is a low cost,
high speed and high yield method for the localized heat
treatment of fused silica. However the linear absorption of
fused silica depends on the laser source. Using an ultraviolet
laser requires a process to bind oxygen to the fused silica to
increase light sensitivity [7]. Using CO 2 laser [8] results in a
greatly increased linear absorption of the fused silica which
makes precise machining more difficult and can cause
damage around the machining area. High-power density
femtosecond fiber lasers with a pulse of 10 -15 seconds are an
appropriate tool for the fabrication of optical waveguides due
to their independence in the linear absorbing effect of fused
silica.
This study investigates the fabrication characteristics of
femtosecond fiber lasers on fused-silica-based optical
waveguides. We selected three main fabrication parameters,
laser power (E), scanning speed ( v s
) and focus depth (d = 0 at
the surface of substrate) which are systematically adjusted to
investigate the differences of post-machining light waveguide
characteristics, transmission loss rate and the relation
between the net influence and light waveguide.
II. Experimental section
1. Waveguide principles
As shown in Fig. 1, the light waveguide is composed of
a layer of Media 1 (i.e. a media different from the substrate)
sandwiched between two layers of Media 2 (i.e. the
substrate).
One of two application phenomena of light waveguides
is the refraction within these media with different refraction
indices. Based on the Snell’s law, the refraction angle, φ , is
smaller than the incident angle, θ , as light is incident into
Media 1. The other application phenomenon is total reflection
for keeping and transmitting all laser energy within the Media
1 layer. This means that Snell’s law requires the refraction
index of Media 1, n 1 , to be larger than that of Media 2.
The numerical aperture (NA), (i.e., the maximum
acceptable energy of light wave guide), is defined as.
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