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Emergence of structural anisotropy in optical glasses treated to support second harmonic generation

Emergence of structural anisotropy in optical glasses treated to support second harmonic generation
Emergence of structural anisotropy in optical glasses treated to support second harmonic generation
Few discoveries have puzzled the optics community more than the emergence of visible (green) light from optical fibers after strong irradiation by an infrared laser. This frequency-doubling phenomenon known as Second Harmonic Generation (SHG) is not expected to take place in a centrosymmetric material such as the amorphous silica fiber-core, which shows no measurable second-order optical susceptibility χ(2). The process to be efficient also requires well defined phase-matching between the interacting waves to allow for constructive interference, and this seems even more difficult to fulfill within the glassy medium. Several plausible explanations about the origin of the phenomenon have been put forward. One of the most widely accepted does not involve structural modifications to accomplish the breakdown of the glass radial symmetry. Rather, it postulates the emergence of a spatially modulated local dc field, E0, which, via a third-order nonlinearity (chi(3)) (finite in isotropic materials), induces a spatially modulated second order nonlinearity ( χ(2) is proportional to χ(3)E0 ) able to double the pump frequency. The achievement of a permanent χ(2) in optical glasses has focused a large research effort, which lead to the discovery of alternative poling techniques. In actual fact, the phenomenon can be produced by application of a high voltage (~5 kV, just below dielectric breakdown) to glass plates at moderate temperatures (~540 - 580 K, compared with ~ 1475 K where the glass melts). This method, known as "thermal" poling provides permanent second-order nonlinear responses comparable to those shown by inorganic crystals. Whether the mechanism(s) leading to the emergence of a second order non-linearity in "thermally-poled" glasses differ from those of photoinduced SHG or not needs to be clarified. At any rate, the relevant point stems from the possibility this method has opened up for developing inexpensive integrated optical frequency converters and electro-optic modulators.
Cabrillo, C.
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García-Fernández, P.
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Bermejo, F.J.
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Pruneri, V.
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Kazansky, P.G.
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Cabrillo, C.
011502de-1453-46f1-85fd-4119841309d7
García-Fernández, P.
fed72f56-d34c-4099-84dc-524d4379c915
Bermejo, F.J.
6e5c6400-6c1d-46d5-8433-bf29fd18e036
Pruneri, V.
0e97eb94-b682-409f-a107-ae6b84763f02
Kazansky, P.G.
a5d123ec-8ea8-408c-8963-4a6d921fd76c

Cabrillo, C., García-Fernández, P., Bermejo, F.J., Pruneri, V. and Kazansky, P.G. (1999) Emergence of structural anisotropy in optical glasses treated to support second harmonic generation. Bragg Gratings, Photosensitivity and Poling in Glass Waveguides (BGPP '99), Stuart, United States. 22 - 24 Sep 1999.

Record type: Conference or Workshop Item (Paper)

Abstract

Few discoveries have puzzled the optics community more than the emergence of visible (green) light from optical fibers after strong irradiation by an infrared laser. This frequency-doubling phenomenon known as Second Harmonic Generation (SHG) is not expected to take place in a centrosymmetric material such as the amorphous silica fiber-core, which shows no measurable second-order optical susceptibility χ(2). The process to be efficient also requires well defined phase-matching between the interacting waves to allow for constructive interference, and this seems even more difficult to fulfill within the glassy medium. Several plausible explanations about the origin of the phenomenon have been put forward. One of the most widely accepted does not involve structural modifications to accomplish the breakdown of the glass radial symmetry. Rather, it postulates the emergence of a spatially modulated local dc field, E0, which, via a third-order nonlinearity (chi(3)) (finite in isotropic materials), induces a spatially modulated second order nonlinearity ( χ(2) is proportional to χ(3)E0 ) able to double the pump frequency. The achievement of a permanent χ(2) in optical glasses has focused a large research effort, which lead to the discovery of alternative poling techniques. In actual fact, the phenomenon can be produced by application of a high voltage (~5 kV, just below dielectric breakdown) to glass plates at moderate temperatures (~540 - 580 K, compared with ~ 1475 K where the glass melts). This method, known as "thermal" poling provides permanent second-order nonlinear responses comparable to those shown by inorganic crystals. Whether the mechanism(s) leading to the emergence of a second order non-linearity in "thermally-poled" glasses differ from those of photoinduced SHG or not needs to be clarified. At any rate, the relevant point stems from the possibility this method has opened up for developing inexpensive integrated optical frequency converters and electro-optic modulators.

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Published date: September 1999
Venue - Dates: Bragg Gratings, Photosensitivity and Poling in Glass Waveguides (BGPP '99), Stuart, United States, 1999-09-22 - 1999-09-24
Organisations: Optoelectronics Research Centre

Identifiers

Local EPrints ID: 76530
URI: http://eprints.soton.ac.uk/id/eprint/76530
PURE UUID: df971288-601d-406a-9fcb-aed01611eefb

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Date deposited: 11 Mar 2010
Last modified: 03 Mar 2020 17:47

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Contributors

Author: C. Cabrillo
Author: P. García-Fernández
Author: F.J. Bermejo
Author: V. Pruneri
Author: P.G. Kazansky

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