offers a continuous and distortion-free inscription[9]
, where nine
different Bragg grating waveguides (BGWs) were distributed along three parallel waveguide tracks and interconnected via a 1x3 directional coupler. The instantaneous 3D fiber shape is computed from shifts in the nine BGW wavelengths when probed by a spectrometer as shown in Video 1[10]
, where the
center waveguide was designed for minimal sensitivity to bend- induced strain to permit the simultaneous measurement of the temperature profile along the fiber as shown in Video 2[11]
.
Such a freestanding, flexible and lightweight 3D shape sensor is attractive in wide ranging applications, including the guidance of drug delivery, biomedical catheters and other instruments used in minimally invasive surgeries.
We also exploit the selective hydrofluoric acid etching of laser- modification tracks to enable precise 3D structuring of through and blind holes, reservoirs, microfluidic networks and near- optical quality (12 nm rms) hollow resonators anywhere inside an optical fiber. In this way, existing fiber-optic technology can be elevated from “cladding photonics” into new types of “fiber optofluidics” or MEMS sensors, for example, permitting refractive index and pressure sensing with a fiber-embedded wavefront splitting interferometer[12]
. Figure 3 showcases a higher level
of integration, combining cladding photonics, microfluidics and optical resonators that efficiently connect with the probing
SMF core waveguide[4]
. This multiplexed lab-in-fiber offers
simultaneous probing of an inline BGW and a cladding Fabry Perot resonator either in-core with a laser-formed X-coupler or externally with a total internal reflection mirror. This highly compact lab-in-fiber was spliced to a SMF for real-time sensing of temperature, axial strain, bending strain, gas pressure, fluid or gas refractive index, or analyte fluorescence[4]
.
The overall approach of femtosecond laser structuring in optical fiber extends much further to enable selective formation of through and blind holes, evanescent and plasmonic sensing elements, MEMS, 3D microfluidic networks, reservoirs, micro- optics, inline BGW filters, polarization elements, interferometers, spectrometers and bioprobes. New research tools, commercial products and biomedical devices may now be manufactured to, for example, (1) develop analyte-specific sensors into optical fibers for monitoring oil and gas exploration systems and water supplies, (2) exploit the 3D fiber shape sensing capability for catheter guidance, (3) enable optical coherence tomography probing devices in the human body, and (4) construct micro- to nano-holes for differentiating cells, bacteria, viruses and DNA. University of Toronto spin out company, Incise Photonics Inc. (
www.incisephotonics.com) is now targeting such commercial applications.
Dr. Moez Haque is a postdoctoral researcher developing novel lab-in-fiber sensors for commercial applications. Prof. Peter R. Herman is full professor in the Department of Electrical and Computer Engineering at the University of Toronto.
Figure 3. A multiplexed lab-in-fiber is shown by (a) schematic and (b, c) optical micrographs, integrating: (1) A through-hole crossing the single-mode fiber (SMF) core waveguide for fluorescence detection or absorption spectroscopy, (2) a Fiber Bragg grating (FBG) for strain or temperature sensing, (3) an inline Fabry Perot interferometer (FPI) for refractive index or pressure sensing, and (4) a X-coupler tap and laser-formed waveguide to probe a cladding FPI for refractive index, pressure or bend sensing. Total internal reflecting (TIR) mirrors are used as an alternate probing method by tapping light either into or out of the fiber cladding. The figure is reproduced, with permission, from Figs. 1 and 4 of Haque et al.[4]
© 2014 The Royal Society of Chemistry [
http://dx.doi.org/10.1039/C4LC00648H]
www.lia.org 1.800.34.LASER 15
References [1] S. A. Hosseini, P. R. Herman, “Method of material processing by laser filamentation”, U.S. Patent 20130126573 A1, filed July 24, 2011.
http://www.google.com/patents/ US20130126573 [2] R. Osellame, G. Cerullo, R. Ramponi, Femtosecond laser micromachining: photonic and microfluidic devices in transparent materials, Springer-Verlag Berlin Heidelberg, 2012.
http://dx.doi.org/10.1007/978-3-642-23366-1 [3] K. Sugioka, Y. Cheng, Ultrafast laser processing: from micro- to nanoscale, Pan Stanford, Boca Raton, 2013.
http://dx.doi.org/10.1201/b15030 [4] M. Haque, K. K. C. Lee, S. Ho, L. A. Fernandes, P. R. Herman, “Chemical-assisted femtosecond laser writing of lab-in-fibers”, Lab Chip 14, 3817-3829 (2014).
http://dx.doi. org/10.1039/C4LC00648H [5] J. R. Grenier, M. Haque, L. A. Fernandes, K. K. C. Lee, P. R. Herman, “Femtosecond laser inscription of photonic and optofluidic devices in fiber cladding”, in G. Marowsky (ed.), Planar waveguides and other confined geometries, p. 67, Springer Series in Optical Sciences vol. 189, New York (2015).
http://dx.doi.org/10.1007/978-1-4939-1179-0_4 [6] J. R. Grenier, L. A. Fernandes, P. R. Herman, “Femtosecond laser inscription of asymmetric directional couplers for in-fiber optical taps and fiber cladding photonics”, Opt. Express 23(13), 16760-16771 (2015).
http://dx.doi.org/10.1364/OE.23.016760 [7] L. A. Fernandes, J. R. Grenier, J. S. Aitchison, P. R. Herman, “Fiber optic stress- independent helical torsion sensor”, Opt. Lett. 40(4), 657-660 (2015).
http://dx.doi. org/10.1364/OL.40.000657 [8] K. K. C. Lee, A. Mariampillai, M. Haque, B. A. Standish, V. X. D. Yang, P. R. Herman, “Temperature-compensated fiber-optic 3D shape sensor based on femtosecond laser direct- written Bragg grating waveguides”, Opt. Express 21, 24076-24086 (2013).
http://dx.doi. org/10.1364/OE.21.024076 [9] V. Maselli, P. R. Herman, “Integrated optical circuits in fiber cladding by tightly focused femtosecond laser writing”, Proc. SPIE 7585, 75850F-1-75850F-11 (2010). http://
dx.doi.org/10.1117/12.845431 [10] Video 1: 3D fiber shape sensing by laser-written cladding photonics, from [8], available at
http://www.opticsinfobase.org/oe/viewmedia.cfm?uri=oe-21-20-24076-1 [11] Video 2: 3D fiber shape and distributed temperature sensing, from [8], available at
http://www.opticsinfobase.org/oe/viewmedia.cfm?uri=oe-21-20-24076-2 [12] M. Haque, Y. Shen, A. A. Gawad, and P. R. Herman, ‘’Chemical-assisted femtosecond laser structuring of waveguide-embedded wavefront-splitting interferometers”, J. Lightwave Technol. 33(21), 4478-4487 (2015).
http://dx.doi.org/10.1109/JLT.2015.2473795
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