UV induced densification during Bragg grating inscription in Ge:SiO2 preforms

doi:10.1016/0925-3467(94)00114-6

Optical Materials

Volume 4, Issue 4, March 1995, Pages 441-449

https://doi.org/10.1016/0925-3467(94)00114-6 Get rights and content

Abstract

The only investigation of a Bragg grating in Ge:SiO₂ in the direct space known to date is a view from an optical microscope. Here, we show surface level modulations associated with the writing of the grating. Our conclusion is that a densification takes place. We estimate the corresponding peak to peak change of the refractive index to be 1.4−1.7 × 10⁻⁴ whether a pulsed or a CW irradiation mode is used. Compared to the refractive index change obtained by optical measurement, this accounts for a non-negligible part (7% for pulsed and 26% for CW irradiation). We discuss the possible application of the observations to fiber and the differences in photo-chemical reactions according to the irradiation mode.

References (31)

W.X. Xie et al.
Optics Comm.
(1993)
P. Cordier et al.
Optics Comm.
(1994)
F.L. Galeener
Solid State Comm.
(1982)
K.O. Hill et al.
Appl. Phys. Lett.
(1978)
G. Meltz et al.
Optics Lett.
(1989)
K.O. Hill et al.
Electron. Lett.
(1990)
B. Malo et al.
Fiber mode converters: point by point fabrication of index gratings, visualisation using thermoluminescence and applications
D.L. Wiliams et al.
Broad bandwidth highly reflecting gratings formed in photosensitive boron codoped fibers
R.M. Atkins et al.
Electron. Letters
(1993)
P.J. Lemaire et al.
Electron. Lett.
(1993)

G.D. Maxwell et al.

Electron. Lett.

(1993)

P. Niay et al.

Optics Comm.

(1994)

R.M. Atkins et al.

Electron. Lett.

(1992)

V. Mizrahi et al.

Electron. Lett.

(1992)

Y. Duval et al.

Appl. Phys. Lett.

(1992)

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The exclusive scientific interest on these glasses, due to the close relationship exists between Ge and Si ions, is resulted to the series of significant differences and peculiarities rather than the conventional borosilicate and phosphosilicate glasses. The loss in transparency of these glasses when they were exposed to UV light leads to the enhancement of the defects in these glass matrix which make them photosensitive [6,7]. Currently, these glasses are being widely used for constructing CW Raman fiber lasers [8].
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UV induced densification during Bragg grating inscription in Ge:SiO2 preforms

Abstract

Optics Comm.

Optics Comm.

Solid State Comm.

Appl. Phys. Lett.

Optics Lett.

Electron. Lett.

Fiber mode converters: point by point fabrication of index gratings, visualisation using thermoluminescence and applications

Broad bandwidth highly reflecting gratings formed in photosensitive boron codoped fibers

Electron. Letters

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Electron. Lett.

Optics Comm.

Electron. Lett.

Electron. Lett.

Appl. Phys. Lett.

UV induced densification during Bragg grating inscription in Ge:SiO₂ preforms