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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 11, Iss. 13 — Jun. 30, 2003
  • pp: 1585–1589
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UV lamp hypersensitisation of hydrogen-loaded optical fibres

Albert Canagasabey and John Canning  »View Author Affiliations


Optics Express, Vol. 11, Issue 13, pp. 1585-1589 (2003)
http://dx.doi.org/10.1364/OE.11.001585


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Abstract

Strong Bragg grating fabrication in cheap, low power (rated 15W - intensity ~0.054Jcm-2) UV-lamp hypersensitised optical fibres is demonstrated. No optics has been used. Comparable results with recent 355nm laser hypersensitisation are obtained.

© 2003 Optical Society of America

1. Introduction

Hypersensitisation, a technique by which photosensitivity is enhanced in optical fibres and waveguides, has been demonstrated both photolytically and thermally [1

1. J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

7

7. A. Canagasabey, J. Canning, and N. Groothoff, “355nm hypersensitisation of optical fibres,” Opt Lett. In press.

]. It is underpinned by the need to reduce the undesirable component of photosensitivity associated with differences in the photosensitive response between core and core/cladding regions [1

1. J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

,2

2. J. Canning, “Contemporary Thoughts on Glass Photosensitivity and their Practical Application,” Materials Forum 25, 60–87 (2001)

]. The basic two-step mechanism of the core index change involves a complex set of catalytic hydrogen reactions, some of which give additional changes at the core-cladding interface [1

1. J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

,4

4. N. Viswanathan and J. Brennan, “Indication of re-circulating catalyst in photosensitive reactions with H2-saturation”, Optical Fiber Communications Conference (OFC 2002), Anaheim, USA, paper TuQ1, (2002)

]. As well as photo-hypersensitisation, thermal hypersensitisation is possible [1

1. J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

,5

5. J. Canning and P-F. Hu, “Low temperature hypersensitisation of phosphosilicate waveguides in hydrogen”, Opt. Lett. 26, 1230–1232, (2001) [CrossRef]

]. It is characterised by the treatment of optical fibres at low temperatures during hydrogen loading or grating writing. However, to date most photolytic processing has involved laser exposure with UV wavelengths (e.g., from 157nm to 355nm). Multi-photon access of the same pathways is possible using longer wavelengths. The significantly improved properties of gratings prepared this way and the ability to hypersensitise through the polymer coating [7

7. A. Canagasabey, J. Canning, and N. Groothoff, “355nm hypersensitisation of optical fibres,” Opt Lett. In press.

] has seen growing interest. Further, the possibility of low energy hypersensitisation at longer wavelengths suggests that very low power and relatively cheap UV lamps can be employed to carry out this step. In this paper we demonstrate hypersensitisation with extremely cheap low power UV lamps used to sterilise medical equipment. Although the cumulative fluence requires long exposure times, UV lamps of considerably more power are available for relative low costs - the need for high intensity pulsed exciplex lamps of the type previously suggested [1

1. J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

,2

2. J. Canning, “Contemporary Thoughts on Glass Photosensitivity and their Practical Application,” Materials Forum 25, 60–87 (2001)

], such as KrF, ArF, XeCl, F2 and others, can be avoided.

2. Experiment

UV lamp hypersensitisation experiments were carried out with readily available gas filled fluorescent tubes (Philips G15 T8) with just 15W power spread over a relatively wide range of wavelengths, the bulk of the light covering 200–400nm. The broadband intensity at the surface of these lamps is estimated to be just ~0.054J/cm2. These particular lamp sources are commercially available low-cost germicidal lamps commonly used for sterilisation of instruments, mainly within medical and food industries. These lamps are thus designed to have a spectral peak at approximately 254nm, the most effective wavelength for germicidal treatment. For more optimal performance more specific lamps with higher power and relative costs (both purchase and running) still well below that of a UV laser are readily available.

The experiments were carried out with boron co-doped germanosilicate fibre (12 mol% GeO2) as was used in the 355nm hypersensitisation experiments previously reported [7

7. A. Canagasabey, J. Canning, and N. Groothoff, “355nm hypersensitisation of optical fibres,” Opt Lett. In press.

]. A number of fibres were hydrogen-loaded at 373K at 100 atm pressure for a period of 24 hours, then stripped of the polymer coating and placed in a UV steriliser oven containing the 15W lamp source. For maximum knowledge of the sensitisation fluence, the fibres were placed at the surface of the lamp. If lamps centred at longer wavelengths are used it is not necessary to strip the coating. The fibres were allowed to remain in the oven for a 5 day exposure (total cumulative fluence ~22kJ/cm2) - this exposure time can be reduced substantially by employing high power UV lamps and appropriate optics to collect and focus the light. For the purposes of this paper we demonstrate hypersensitisation is possible even at very low intensities. Further, in this case the fibres have been over-sensitised to ensure that sensitisation did take place. Despite out-diffusion of a substantial amount of the hydrogen over the exposure period the process remains effective indicating that not much hydrogen is required in the catalysed two-step hypersensitisation process.

Gratings were written conventionally through an optical phase mask once all the hydrogen is allowed to out-diffuse using 244nm from a frequency-doubled Ar+ laser. A writing speed of 0.5mm/min and 244nm fluence intensity of 1.3kJcm-2 over the hypersensitised region was maintained for all the fibres with the grating length kept at a constant 10mm. Gratings were also prepared under identical conditions in 355nm laser hypersensitised optical fibres for direct comparison. The characteristic growth curves shown in Fig. 1 were derived from the reflection and transmission profiles recorded in between each grating writing pass.

Fig. 1. (a) Natural log plots of grating growth for standard boron co-doped germanosilicate fibres hypersensitised with a UV lamp and 355nm laser and pristine fibre. (b) Fringe contrast plots for lamp and laser hypersensitised and pristine fibres.

3. Results and discussion

Figure 2 shows the transmission profile of the grating fabricated in a lamp hypersensitised fibre. The grating profile is uniform and symmetric about the Bragg wavelength. Further, the total insertion loss remain <0.1dB, consistent with similar gratings produced using conventional CW 244nm grating writing. It can be concluded that the lamp exposure was therefore also highly uniform and the photosensitive response identical in all parts of the grating. Thus it is likely that hypersensitisation with this UV lamp excites both these bands simultaneously with photolytic creation of a strong photosensitivity response in the fibre. By using such low power lamps the role of direct background heating may be considered negligible since such lamps produce very little heat. The low intensities also suggest that local heating through absorption is not large.

Fig. 2. Transmission profile of a grating fabricated using a 244nm frequency tripled argon ion laser in UV tube lamp hypersensitised fibre.

4. Conclusions

Acknowledgements

This work was funded by an Australian Research Council (ARC) Large Grant.

References and links

1.

J. Canning, “Hydrogen and Photosensitivity,” Proceedings of White Nights’ Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger and E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002)

2.

J. Canning, “Contemporary Thoughts on Glass Photosensitivity and their Practical Application,” Materials Forum 25, 60–87 (2001)

3.

J. Canning, “Photosensitisation and photostabilisation of laser-induced index changes in optical fibres”, Opt. Fibre. Tech. 6, 275–289, (2000) [CrossRef]

4.

N. Viswanathan and J. Brennan, “Indication of re-circulating catalyst in photosensitive reactions with H2-saturation”, Optical Fiber Communications Conference (OFC 2002), Anaheim, USA, paper TuQ1, (2002)

5.

J. Canning and P-F. Hu, “Low temperature hypersensitisation of phosphosilicate waveguides in hydrogen”, Opt. Lett. 26, 1230–1232, (2001) [CrossRef]

6.

K.P. Chen, P.R. Herman, and R. Tam, “Stronger fibre Bragg grating fabrication by hybrid 157nm and 248nm laser exposure”, IEEE Photon Technol. Lett. 14, 71, (2002) [CrossRef]

7.

A. Canagasabey, J. Canning, and N. Groothoff, “355nm hypersensitisation of optical fibres,” Opt Lett. In press.

OCIS Codes
(050.2770) Diffraction and gratings : Gratings
(140.3390) Lasers and laser optics : Laser materials processing
(230.1150) Optical devices : All-optical devices

ToC Category:
Research Papers

History
Original Manuscript: May 21, 2003
Revised Manuscript: June 23, 2003
Published: June 30, 2003

Citation
Albert Canagasabey and John Canning, "UV lamp hypersensitisation of hydrogen-loaded optical fibres," Opt. Express 11, 1585-1589 (2003)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-11-13-1585


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References

  1. J. Canning, �??Hydrogen and Photosensitivity,�?? Proceedings of White Nights�?? Summer School on Photosensitivity in Optical Waveguides and Glasses (eds. H. Limberger, E. Dianov, Fiber Optics Research Centre, Moscow), St Petersburg, Russia, Lecture 8, (2002).
  2. J. Canning, �??Contemporary Thoughts on Glass Photosensitivity and their Practical Application,�?? Materials Forum 25, 60-87, (2001).
  3. J. Canning, �??Photosensitisation and photostabilisation of laser-induced index changes in optical fibres�??, Opt. Fibre. Tech. 6, 275-289, (2000). [CrossRef]
  4. N. Viswanathan, J. Brennan, �??Indication of re-circulating catalyst in photosensitive reactions with H2-saturation�??, Optical Fiber Communications Conference (OFC 2002), Anaheim, USA, paper TuQ1, (2002).
  5. J. Canning, P-F. Hu, �??Low temperature hypersensitisation of phosphosilicate waveguides in hydrogen�??, Opt. Lett. 26, 1230-1232, (2001). [CrossRef]
  6. K.P. Chen, P.R. Herman, R. Tam, �??Stronger fibre Bragg grating fabrication by hybrid 157nm and 248nm laser exposure�??, IEEE Photon Technol. Lett. 14, 71, (2002). [CrossRef]
  7. A. Canagasabey, J. Canning, N. Groothoff, �??355nm hypersensitisation of optical fibres,�?? Opt Lett. In press.

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