FEATURED ARTICLE
The Magic of Nonlinear Laser Processing:
Shaping Multi-Functional Lab-in-Fiber BY MOEZ HAQUE AND PETER R. HERMAN
The manipulation of femtosecond laser light inside transparent media can be directed on varying interaction pathways of micro- explosions, photochemistry and self-focusing filamentation to open new directions in creating dense memory storage, three- dimensional (3D) optical circuits, 3D microfluidic networks, and high-speed scribing tracks[1-3]
these fundamental and nonlinear interactions to control femtosecond laser processes in transparent coreless and single- mode optical fibers (SMFs) and thereby form highly functional and compact fiber devices that may seamlessly integrate with microelectronic chips. Such optical fibers are currently deployed over a billion kilometers of worldwide networks and can also reach into challenging environments such as advanced aircraft structures or cardiovascular systems.
The concept of developing ubiquitous sensing networks relies on the development of novel miniaturized and integrated in-fiber microsystems. Following the miniaturization and integration of chemical and biological devices with optical components for multifunctional lab-on-chip (LOC) microsystems, femtosecond laser processing has enabled us to create a new optofluidic lab- in-fiber platform[4]
for environmental, mechanical and analytical
sensing that may be widely distributed into fiber networks or inside flexible biomedical probes that is otherwise not possible with more traditional LOC-based technologies.
An essential component for the lab-in-fiber is the laser-formed optical tap that predictably couples light into and out of the light-guiding core of SMFs for connecting with optical probing sensors that have been written in the surrounding fiber cladding. To enable such a novel concept of “fiber cladding photonics”[5,6]
, . Our group has been following
Figure 1 shows three traditional approaches developed to partially redirect light from the core waveguide into the laser- written cladding waveguide: (1) A “X-coupler” (Figure 1a) that crosses the center waveguide at a discrete angle, (2) an “S-bend” coupler (Figure 1b) that forms an “S” shaped waveguide to emerge from the SMF core, and (3) a “directional coupler” (Figure 1c) that runs offset and parallel with the SMF core. Our group has demonstrated an unprecedented flexibility in tuning the coupling ratio to values as high as 99 percent while also controlling the light polarization and spectral bandwidth[5,6]
.
A wide variety of photonic cladding sensing circuits is now available within general types of glass fibers. For example, the formation of helical waveguides to define an in-fiber Mach- Zehnder interferometer has offered unambiguous sensing of fiber torsion[7]
fiber-optic 3D shape and temperature sensor shown in Figure 2 that was written in a single laser exposure step[8] Oil-immersion focusing into the buffer-stripped optical fiber
. Alternatively, we showcase the distributed .
Figure 2. (a) Schematic of a temperature-compensated 3D fiber shape sensor, coupled to single-mode fiber (SMF), and laser-written in coreless fused silica fiber[8]
Figure 1. A waveguide (a) X-coupler, (b) S-bend coupler and (c) directional coupler are formed in a single-mode fiber (SMF) by femtosecond laser focusing through index- matching oil[9]
and connected to the SMF core waveguide[5]
with permission, from Fig. 4.5 of Grenier et al.[5] [
http://dx.doi.org/10.1007/978-1-4939-1179-0_4]
14 . The figure is reproduced, © 2015 Springer LIATODAY FOCUS: SCIENCE & RESEARCH SEPTEMBER/OCTOBER 2016
wavelengths represent nine different Bragg resonances for waveguide gratings distributed along three laser-written and parallel waveguide tracks. Micrographs of the fiber cross section (125 µm diameter) at the (b) coupling and (c) sensor regions show the arrangement of the internal laser-written waveguides. The figure is reproduced, with permission, from Fig. 1 of Lee et al.[8]
to λ9 . The λ1 © 2013 OSA [
http://dx.doi.org/10.1364/OE.21.024076].
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