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Optics Express

  • Editor: Michael Duncan
  • Vol. 14, Iss. 9 — May. 1, 2006
  • pp: 3763–3766

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Long-period gratings in chalcogenide fibers

Dominik Pudo, Eric C. Mägi, and Benjamin J. Eggleton  »View Author Affiliations


Optics Express, Vol. 14, Issue 9, pp. 3763-3766 (2006)
http://dx.doi.org/10.1364/OE.14.003763


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Abstract

We report the first demonstration of long period gratings in single mode As2Se3 chalcogenide glass fiber. The grating is implemented by pressing a threaded rod against a short piece of fiber. Its strength can be tuned over a 25 dB range, has high repeatability, and is fully reversible.

© 2006 Optical Society of America

1. Introduction

Chalcogenide glass optical fibers are of major interest due to their transparency in the near and mid-infrared region where they have been used both for transmission and sensing applications [1

T. Kanamori, Y. Terunuma, S. Takahashi, and T. Miyashita, “Chalcogenide glass fibers for mid-infrared transmission,” J. Lightwave Technol. 2, 607 (1984). [CrossRef]

, 2

J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel, “Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers,” Appl. Opt. 30, 3944–3951 (1991). [CrossRef] [PubMed]

]. Recently, they have also attracted great interest in the telecommunication wavelengths, as they offer the advantage of a large Kerr nonlinearity (up to 1000 x silica glass [3

R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21, 1146–1155 (2004). [CrossRef]

]), low two-photon absorption, and an intrinsic response time below 100 fs [3

R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21, 1146–1155 (2004). [CrossRef]

]. As a result, they are an excellent candidate to investigate both as a novel basis for various well-known fiber optic devices, as well as a nonlinear medium.

Long period gratings (LPGs) are considered to be a very versatile fiber device, both within the context of nonlinear optics, and sensing applications. Indeed, they constitute an elegant embodiment of a nonlinear periodic structure where the nonlinear refractive index is used to detune the coupling in between distinct spatial modes [4

H. G. Winful, J. H. Marburger, and E. Garmire, “Theory of bistability in nonlinear distributed feedback structures,” Appl. Phys. Lett. 35, 379–381 (1979). [CrossRef]

], resulting in intensity-dependent transmission and all-optical switching. Using this principle, optical switching was already demonstrated in silica-based LPGs [5

B. J. Eggleton, R. E. Slusher, J. B. Judkins, J. B. Stark, and A. M. Vengsarkar, “All-optical switching in long-period fiber gratings,” Opt. Lett. 22, 883–885 (1997). [CrossRef] [PubMed]

]. In addition, long period gratings, inherently sensitive to refractive index variations, are an excellent structure for a vast array of sensing applications.

In this paper, we report the first demonstration of resonant coupling in single-mode chalcogenide LPGs. We describe the grating design, characterizing its transmission, polarization dependence, and thermal sensitivity.

2. Principle of operation

We use a single-mode As39Se61 chalcogenide glass fiber with a core diameter of 6 μm, a core/cladding refractive index of 2.8, and a numerical aperture at 1550 nm of 0.18. The dispersion and nonlinear index were measured to be, respectively, D=-504 ps/nm/km and n2=1.1 × 10-13 cm2/W [6

K. S. Abedin, “Observation of strong stimulated Brillouin scattering in single-mode As2Se3 chalcogenide fiber,” Opt. Express 13, 10266–10271 (2005). [CrossRef] [PubMed]

, 7

L. B. Fu, M. Rochette, V. G. Ta’eed, D. J. Moss, and B. J. Eggleton, “Investigation of self-phase modulation based optical regeneration in single mode As2Se3 chalcogenide glass fiber,” Opt. Express 13, 7637 (2005). [CrossRef] [PubMed]

]. The source was butt-coupled into the chalcogenide fiber using a short segment of high numerical aperture (Hi-NA) fiber and index-matching oil to reduce the losses. Overall coupling and propagation losses were measured to be approximately 6 dB, with the chalcogenide fiber having an attenuation coefficient of 1 dB/m.

Fig. 1. Side view of a mechanically-induced LPG

Figure 1 depicts the experimental setup. In a LPG the core mode is coupled to forward-propagating cladding modes for wavelengths λm satisfying: λm=Λ (ncore - n cl m) where Λ is the grating period, ncore and n cl m are the effective indices of, respectively, the core and the cladding and m is the cladding mode order. The grating period is typically on the order of hundreds of micrometers, so it is possible to induce such gratings mechanically, which has the advantage of being very simple, and potentially tunable [8

S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, “Tunable mechanically induced long-period fiber gratings,” Opt. Lett. 25, 710–712 (2000). [CrossRef]

]. The As2Se3 fiber was placed in between an aluminum plate and a 50 mm long threaded steel rod with a period length of 0.7 mm and a groove depth of 0.4 mm. We did not remove the fiber jacket, as induced microbends would have deteriorated the spectral response in addition to compromising the fiber protection. The rod was pressed onto the fiber using an upper clamp, inducing a periodic refractive index modulation along the fiber due to a combination of the photelastic effect [9

R. C. Youngquist, “Birefringent fiber polarization coupler,” Opt. Lett. 8, 656–658 (1983). [CrossRef] [PubMed]

] and induced microbends [10

C. B. Probst, A. Bjarklev, and S. B. Andreasen, “Experimental Verification of Microbending Theory using Mode Coupling to Discrete Cladding Modes,” J. Lightwave Technol. 7, 55–60 (1989). [CrossRef]

]. The resonant wavelength can therefore be selected by using rods with different pitches, while the grating strength is controlled through the clamping screw. One advantage of this scheme is the reversibility of the gratings. Once the clamp is removed, the transmission of the fiber returns to its original spectrum, thereby allowing to generate multiple, different gratings using the same piece of fiber and mounting setup.

3. Results and discussion

Fig. 2. LPG grating response for increasing clamp pressure

Figure 2 depicts typical transmission spectra for increasing clamp pressure, measured using an unpolarized broadband LED source. The measured 3 dB and 10 dB bandwidths are, respectively, 25 and 9 nm, with a peak attenuation of 22 dB. The out of band loss of the grating was measured to be less than 0.5 dB, comparable to that of typical silica fiber gratings [8

S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, “Tunable mechanically induced long-period fiber gratings,” Opt. Lett. 25, 710–712 (2000). [CrossRef]

]. The observed spectrum also depicted a second notch in the transmission, corresponding to the resonant coupling into the 2nd cladding mode. As the clamping pressure was increased further, the depth of the 1st resonant notch decreased a characteristic manifestation of the sinc2 like behaviour of LPGs. [8

S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, “Tunable mechanically induced long-period fiber gratings,” Opt. Lett. 25, 710–712 (2000). [CrossRef]

]

Fig. 3. Transmission spectra for two orthogonal linear polarizations

In addition, we analyzed the polarization dependence by placing a linear polarizer immediately before a straight, few cm long section of the coupling fiber. The polarization was subsequently rotated in order to determine the largest shift in the resonant wavelength which was measured to be 1.5 nm, along with a corresponding peak attenuation variation of 3.8 dB, as depicted in Fig. 3. These values, albeit smaller than those one reported in similarly induced LPGs in silica [11

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan, and J. E. Sipe, “Long-period fiber gratings as band-rejection filters,” J. Lightwav. Technol. 14, 58–96 (1996). [CrossRef]

], confirm the inherent birefringent nature of mechanically-induced LPGs [12

J. Y. Cho and K. S. Lee, “A birefringence compensation method for mechanically induced long-period fiber gratings,“ Opt. Commun. 213, 281–284 (2002). [CrossRef]

] .

Fig. 4. Temperature dependence of the LPG resonant wavelength and transmission spectra at 40° and 50° C

Finally, the temperature dependence was analyzed by monitoring the transmission spectrum while heating the grating setup. As shown in Fig. 4 the measured peak wavelength shift was ∆λ ≈ 0.43 nm/°C at 1540 nm, which is about an order of magnitude greater than the values reported for LPGs manufactured using the same technique in silica fiber [8

S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, “Tunable mechanically induced long-period fiber gratings,” Opt. Lett. 25, 710–712 (2000). [CrossRef]

]. The measured transmission spectra for temperatures of 40°C and 50°C are also depicted in Fig. 4. As the steel rod thermal expansion coefficient would account for a shift of only about 0.02 nm /°C, we can attribute the observed wavelength shift to the change in the effective indices within the fiber.

4. Conclusion

We have demonstrated a first mechanically induced long period grating in As2Se3 fiber. The device is simple, reconfigurable, and the operating wavelength can be changed by using an appropriately threaded rod. The resulting grating characteristics, quality of the spectral response, and depth are comparable with those reported for similarly made gratings in silica fiber. Such gratings would constitute an excellent tool to use both within the context of nonlinear optical signal processing, as well as sensing and filtering applications. The grating’s inherent sensitivity to even small changes in the refractive index also allows detecting and analyzing any external factors which would cause such changes, the temperature being one example depicted above.

Acknowledgments

This work has been funded by the Australian Research Council (ARC) and in part by the Canadian Institute for Photonic Innovations. CUDOS (the Centre for Ultrahigh-bandwidth Devices for Optical Systems) is an ARC Centre of Excellence. D. Pudo is visiting from McGill University, Montreal, Quebec, Canada.

References and Links

1.

T. Kanamori, Y. Terunuma, S. Takahashi, and T. Miyashita, “Chalcogenide glass fibers for mid-infrared transmission,” J. Lightwave Technol. 2, 607 (1984). [CrossRef]

2.

J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel, “Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers,” Appl. Opt. 30, 3944–3951 (1991). [CrossRef] [PubMed]

3.

R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, “Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers,” J. Opt. Soc. Am. B 21, 1146–1155 (2004). [CrossRef]

4.

H. G. Winful, J. H. Marburger, and E. Garmire, “Theory of bistability in nonlinear distributed feedback structures,” Appl. Phys. Lett. 35, 379–381 (1979). [CrossRef]

5.

B. J. Eggleton, R. E. Slusher, J. B. Judkins, J. B. Stark, and A. M. Vengsarkar, “All-optical switching in long-period fiber gratings,” Opt. Lett. 22, 883–885 (1997). [CrossRef] [PubMed]

6.

K. S. Abedin, “Observation of strong stimulated Brillouin scattering in single-mode As2Se3 chalcogenide fiber,” Opt. Express 13, 10266–10271 (2005). [CrossRef] [PubMed]

7.

L. B. Fu, M. Rochette, V. G. Ta’eed, D. J. Moss, and B. J. Eggleton, “Investigation of self-phase modulation based optical regeneration in single mode As2Se3 chalcogenide glass fiber,” Opt. Express 13, 7637 (2005). [CrossRef] [PubMed]

8.

S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, “Tunable mechanically induced long-period fiber gratings,” Opt. Lett. 25, 710–712 (2000). [CrossRef]

9.

R. C. Youngquist, “Birefringent fiber polarization coupler,” Opt. Lett. 8, 656–658 (1983). [CrossRef] [PubMed]

10.

C. B. Probst, A. Bjarklev, and S. B. Andreasen, “Experimental Verification of Microbending Theory using Mode Coupling to Discrete Cladding Modes,” J. Lightwave Technol. 7, 55–60 (1989). [CrossRef]

11.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan, and J. E. Sipe, “Long-period fiber gratings as band-rejection filters,” J. Lightwav. Technol. 14, 58–96 (1996). [CrossRef]

12.

J. Y. Cho and K. S. Lee, “A birefringence compensation method for mechanically induced long-period fiber gratings,“ Opt. Commun. 213, 281–284 (2002). [CrossRef]

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(350.2770) Other areas of optics : Gratings

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: February 15, 2006
Revised Manuscript: April 3, 2006
Manuscript Accepted: April 23, 2006
Published: May 1, 2006

Citation
Dominik Pudo, Eric C. Mägi, and Benjamin J. Eggleton, "Long-period gratings in chalcogenide fibers," Opt. Express 14, 3763-3766 (2006)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-9-3763


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References

  1. T. Kanamori, Y. Terunuma, S. Takahashi, and T. Miyashita, "Chalcogenide glass fibers for mid-infrared transmission," J. Lightwave Technol. 2,607 (1984). [CrossRef]
  2. J. Heo, M. Rodrigues, S. J. Saggese, and G. H. Sigel, "Remote fiber-optic chemical sensing using evanescent-wave interactions in chalcogenide glass fibers," Appl. Opt. 30,3944-3951 (1991). [CrossRef] [PubMed]
  3. R. E. Slusher, G. Lenz, J. Hodelin, J. Sanghera, L. B. Shaw, and I. D. Aggarwal, "Large Raman gain and nonlinear phase shifts in high-purity As2Se3 chalcogenide fibers," J. Opt. Soc. Am. B 21,1146-1155 (2004). [CrossRef]
  4. H. G. Winful, J. H. Marburger, and E. Garmire, "Theory of bistability in nonlinear distributed feedback structures," Appl. Phys. Lett. 35,379-381 (1979). [CrossRef]
  5. B. J. Eggleton, R. E. Slusher, J. B. Judkins, J. B. Stark, and A. M. Vengsarkar, "All-optical switching in long-period fiber gratings," Opt. Lett. 22,883-885 (1997). [CrossRef] [PubMed]
  6. K. S. Abedin, "Observation of strong stimulated Brillouin scattering in single-mode As2Se3 chalcogenide fiber," Opt. Express 13,10266 - 10271 (2005). [CrossRef] [PubMed]
  7. L. B. Fu, M. Rochette, V. G. Ta'eed, D. J. Moss, and B. J. Eggleton, "Investigation of self-phase modulation based optical regeneration in single mode As2Se3 chalcogenide glass fiber," Opt. Express 13,7637 (2005). [CrossRef] [PubMed]
  8. S. Savin, M. J. F. Difonnet, G.S. Kino, and H.J. Shaw, "Tunable mechanically induced long-period fiber gratings," Opt. Lett. 25,710-712 (2000). [CrossRef]
  9. R. C. Youngquist, "Birefringent fiber polarization coupler," Opt. Lett. 8,656-658 (1983). [CrossRef] [PubMed]
  10. C. B. Probst, A. Bjarklev, and S. B. Andreasen, "Experimental Verification of Microbending Theory using Mode Coupling to Discrete Cladding Modes," J. Lightwave Technol. 7,55-60 (1989). [CrossRef]
  11. A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, T. Erdogan, and J. E. Sipe, "Long-period fiber gratings as band-rejection filters," J. Lightwav. Technol. 14,58-96 (1996). [CrossRef]
  12. J. Y. Cho and K. S. Lee, "A birefringence compensation method for mechanically induced long-period fiber gratings," Opt. Commun. 213,281-284 (2002). [CrossRef]

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