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You are here: Home › Science Overview › Archive › Index Tailored Optical Fibers for Plasmon Enhanced Scanning Near-field Optical Microscopy and Spectroscopy

Index Tailored Optical Fibers for Plasmon Enhanced Scanning Near-field Optical Microscopy and Spectroscopy

Dec. 20, 2010

Scanning near-field optical microscopy (SNOM) and spectroscopy allow sub-wavelength spatial resolution for gathering a diversity of information typical for optical spectroscopy, e.g. Raman, infrared absorption, and dielectric dispersion. Applications range from fundamental and bio-medical science over material characterization to investigations of fully-functional devices, all on the nanometer length scale.
A tapered optical fiber covered with a thin noble metal coating can potentially be used as highly efficient optical probe in SNOM-based techniques, especially for background-free, internal illumination. In this type of probe, light reaching the fiber tip apex is actively focused by means of propagating surface plasmon polaritons (SPP) to result in a highly confined, extremely intense light source.
However, to efficiently launch the appropriate SPP modes radial or similar states of polarization (SOP) have to be transmitted through the fiber down to the tip. Unfortunately, this is only possible for an unperturbed fiber. Any mechanical stress to the fiber will change the SOP and result in severe losses in field strength and confinement. Here we present index-tailored fibers constructed to maintain complex SOP.
We fabricated such few mode optical fibers and simulated their structure to evaluate the performance. The simulation provided the effective refractive indices and the intensity distributions of respective polarization modes. The index differences where used to construct a suitable mechanical long period fiber grating (mLPG). The mLPGs where used to determine the minimal separation of the effective indices of higher order modes in the fiber. An index spread of 10-4 was found experimentally. The excitation of a selected higher order mode with high efficiency could also be demonstrated.
This fiber can already be used to transmit the higher order modes to the tip of a fiber based apertureless SNOM at IR wavelengths, since mode coupling and polarization changes are strongly reduced. Further work will concentrate on expanding this approach to the visible spectral range, aimed at enhanced fluorescence and Raman spectroscopy.

Original publication:
Zeh C. et al.: Polarization mode preservation in elliptical index tailored optical fibers for apertureless scanning near-field optical microscopy, Applied Physics Letters 97, 103108 (2010).

Please click here to read the poster as a PDF

This poster was presented on NanoBioView, 6-7 October 2010
http://www.nanobioviews.net


Authors:
Christoph Zeh1
Ron Spittel2
Sonja Unger2
Jörg Opitz1
Bernd Köhler1
Johannes Kirchhof2
Hartmut Bartelt2
Lukas M.



Imaging & Microscopy Issue 4 as free epaper or pdf download

 

Eng3

1 Fraunhofer Institute for Non-Destructive Testing, Dresden branch, Maria-Reiche-Straße 2, 01109 Dresden, Germany
2 Institute of Photonic Technology, Albert Einstein Str. 9, 07745 Jena, Germany
3 Institute of Applied Photophysics, Technische Universität Dresden, 01062 Dresden, Germany

Contact:
Chirstoph Zeh
christoph.zeh@izfp-d.fraunhofer.de

 

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Keywords: Christoph Zeh Optical Spectroscopy Poster Scanning Near-field Optical Microscopy SNOM

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