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Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 2, Iss. 12 — Dec. 1, 2012
  • pp: 1690–1701
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Fabrication and application of zirconia-erbium doped fibers

H. Ahmad, K. Thambiratnam, M. C. Paul, A. Z. Zulkifli, Z. A. Ghani, and S. W. Harun  »View Author Affiliations


Optical Materials Express, Vol. 2, Issue 12, pp. 1690-1701 (2012)
http://dx.doi.org/10.1364/OME.2.001690


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Abstract

In this work, the fabrication of a Zirconia-Erbium co-Doped Fiber (Zr-EDF) and its application in the generation of non-linear effects as well as use in a compact pulsed fiber laser system is described. The Zr-EDF is fabricated by the Modified Chemical Vapor Deposition (MCVD) technique in combination with solution doping to incorporate the glass modifiers and nucleating agent. The resulting preforms are annealed and drawn into fiber strands with a 125.0 ± 0.5 µm diameter. Two Zr-EDFs, ZEr-A and ZEr-B, are fabricated with erbium ion concentrations of 2800 and 3888 ppm/wt and absorption rates of 14.5 and 18.3 dB/m at 980 nm respectively. Due to its higher erbium dopant concentration, a 4 m long ZEr-B is used to demonstrate the generation of the Four-Wave-Mixing (FWM) effect in the Zr-EDF. The measured FWM power levels agree well with theoretical predictions, giving a maximum FWM power - 45 dBm between 1558 nm to 1565 nm, and the generated sidebands are as predicted. The non-linear coefficient of ZEr-B is measured to be 14 W−1km−1, with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km respectively. The ZEr-B is also used together with a graphene based saturable absorber to create a compact, passively Q-switched fiber laser. Short pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz are generated at a pump power of 121.8 mW, with a maximum average output power of 161.35 µW and maximum pulse energy value of 17.64 nJ. The fabricated Zr-EDF has many potential applications in multi-wavelength generation as well as in the development of compact, pulsed laser sources.

© 2012 OSA

1. Introduction

The advent of the in-line optical amplifier in the later part of the 20th century acted as a catalyst for the exponential growth of optical communications around the world. In-line optical amplifiers or Fiber Optical Amplifiers (FOAs) were instrumental in overcoming the constraints inherent in electronic regenerators and allowed for the amplification of multiple signals simultaneously, thereby making possible the commercial communications networks that span the globe today [1

1. G. E. Keiser, “A review of WDM technology and applications,” Opt. Fiber Technol. 5(1), 3–39 (1999). [CrossRef]

3

3. M. Wasfi, “Optical fiber amplifiers – review,” Int. J. Commun. Netw. Inf. Secur. 1, 42–47 (2009).

]. Furthermore, recent technological advances have also opened up a variety of new prospects for FOAs, such as the generation of single and multi-wavelength fiber lasers [4

4. D. Richardson, J. Nilsson, and W. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B 27(11), B63–B92 (2010). [CrossRef]

,5

5. H. Ahmad, M. Z. Zulkifli, A. A. Latif, K. Thambiratnam, and S. W. Harun, “17-channels S band multiwavelength brillouin/erbium fiber laser co-pump with Raman source,” Laser Phys. 19(12), 2188–2193 (2009). [CrossRef]

], wavelength converters [6

6. K. Inoue and H. Toba, “Wavelength conversion experiment using fiber four-wave mixing,” IEEE Photon. Technol. Lett. 4(1), 69–72 (1992). [CrossRef]

] and wide-band spectral sources [7

7. E. Yahel and A. Hardy, “Amplified spontaneous emission in high-power, Er3+/Yb3+ codoped fiber amplifiers for wavelength-division-multiplexing applications,” J. Opt. Soc. Am. B 20(6), 1198–1203 (2003). [CrossRef]

], thus making the FOA a focal point of research and development.

The Erbium Doped Fiber Amplifier (EDFA) has long been the dominant technology for the development of FOAs due to its relatively low-cost per wavelength, low complexity and high stability [1

1. G. E. Keiser, “A review of WDM technology and applications,” Opt. Fiber Technol. 5(1), 3–39 (1999). [CrossRef]

,8

8. M. J. Yadlowsky, E. M. Deliso, and V. L. Da Silva, “Optical fibers and amplifiers for WDM systems,” Proc. IEEE 85(11), 1765–1779 (1997). [CrossRef]

]. However, the EDFA does have its limitations; most notably is that the concentration of erbium ions, the active medium of the FOA, cannot be increased significantly without encountering detrimental effects such as concentration quenching [9

9. E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glass,” Opt. Mater. 5(3), 159–167 (1996). [CrossRef]

] and cluster formation [10

10. D. M. Gill, L. McCaughan, and J. C. Wright, “Spectroscopic site determinations in erbium-doped lithium niobate,” Phys. Rev. B Condens. Matter 53(5), 2334–2344 (1996). [CrossRef] [PubMed]

]. In order to overcome this problem, and to address the rising need for compact and lower cost FOAs, research has now turned towards the exploration of new materials to act as hosts or co-dopants for the purpose of creating highly-doped EDFAs. In this regard, the element zirconium is a highly promising candidate towards achieving this goal. Zirconium ions co-doped in a silica host matrix demonstrate a high refractive index of over 1.45 in the visible and near infrared spectrum [11

11. M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Wideband EDFA based on erbium doped crystalline zirconia yttria alumino silicate fiber,” J. Lightwave Technol. 28(20), 2919–2924 (2010). [CrossRef]

,12

12. M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers,” Opt. Lett. 35(17), 2882–2884 (2010). [CrossRef] [PubMed]

], thereby displaying wider emission and absorption bandwidths and allowing more channels to be amplified as compared to materials with a lower refractive index. This behavior is in accordance with the Fuchtbauer–Ladenberg relationship [13

13. J. R. Armitage, “Spectral dependence of the small-signal gain around 1.5 μm in erbium doped silica fiber amplifiers,” IEEE J. Quantum Electron. 26(3), 423–425 (1990). [CrossRef]

,14

14. B. Pedersen, A. Bjarklev, J. H. Povlsen, K. Dybdal, and C. C. Larsen, “The design of erbium-doped fiber amplifiers,” J. Lightwave Technol. 9(9), 1105–1112 (1991). [CrossRef]

] and Judd–Ofelt theory [15

15. J. Yang, S. Dai, Y. Zhou, L. Wen, L. Hu, and Z. Jiang, “Spectroscopic properties and thermal stability of erbium-doped bismuth-based glass for optical amplifier,” J. Appl. Phys. 93(2), 977–983 (2003). [CrossRef]

,16

16. P. Peterka, B. Faure, W. Blanc, M. Karásek, and B. Dussardier, “Theoretical modeling of S-band thulium-doped silica fiber amplifiers,” Opt. Quantum Electron. 36(1-3), 201–212 (2004). [CrossRef]

]. Additionally, silica fibers co-doped with zirconium ions possess significant mechanical strength, are not hygroscopic and are able to resist to chemical corrosion. They also demonstrate excellent compatibility with conventional silica based optical fibers, thus making them useful for real-world applications.

Furthermore, zirconium co-doped fibers have demonstrated substantial non-linear characteristics. While detrimental towards high data-rate optical communications [17

17. R.-J. Essiambre, B. Mikkelsen, and G. Raybon, “Intra-channel cross phase modulation and four-wave-mixing in high speed TDM systems,” Electron. Lett. 35(18), 1576–1578 (1999). [CrossRef]

19

19. N. Kashyap, P. H. Siegel, and A. Vardy, “Coding for the optical channel: the ghost-pulse constraint,” IEEE Trans. Inf. Theory 52(1), 64–77 (2006). [CrossRef]

], non-linear phenomenon such as Four-Wave Mixing (FWM) and Self-Phase Modulation (SPM) have tremendous potential for the development of new, cost-effective applications such as multi-wavelength sources, wavelength converters and supercontinuum sources [20

20. S. Harun, R. Parvizi, S. Shahi, and H. Ahmad, “Multi-wavelength erbium-doped fiber laser assisted by four-wave mixing effect,” Laser Phys. Lett. 6(11), 813–815 (2009). [CrossRef]

,21

21. X. F. Yang, X. Dong, S. Zhang, F. Lu, X. Zhou, and C. Lu, “Multi-wavelength erbium doped fiber laser with 0.8 nm spacing using sampled Bragg grating and photonic crystal fiber,” IEEE Photon. Technol. Lett. 17(12), 2538–2540 (2005). [CrossRef]

]. The FWM effect is of significant interest, due to its tremendous prospective in the development of stable and low cost multi-wavelength sources with channel spacings that are suitable for Dense Wavelength Division Multiplexing (DWDM) applications. However, generating the FWM effect is challenging due to the need to maintain phase matching between the propagating wavelengths, and the long lengths of fiber needed to generate the FWM effect make maintaining phase matching difficult. In this regard, the zirconium co-doped fiber is a promising candidate for generating the FWM effect, exhibiting non-linear behavior in only short fiber lengths [22

22. H. Ahmad, M. C. Paul, N. A. Awang, S. W. Harun, M. Pal, and K. Thambiratnam, “Four-wave-mixing in zirconia-yttria-aluminum erbium codoped silica fiber,” J. Eur. Opt. Soc. Rapid Publ. 7, 12011 (2012). [CrossRef]

] and therefore able to overcome the complexities of phase matching.

2. Fabrication

The fabrication of the Zr-EDF is a three-stage process. The process begins with the fabrication of a conventional silica preform using the Modified Chemical Vapor Deposition (MCVD) technique. Figure 1(a)
Fig. 1 (a) Setup of the MCVD system and (b) the formation of the silica preform.
shows the setup of the MCVD system, while Fig. 1(b) shows the actual system. The fiber preform is fabricated by passing SiCl4 and POCl3 vapors through a slowly rotating silica tube. An external flame source moves along the length of the tube as it rotates, heating the tube and its contents to a temperature of between 1350°C and 1400°C. This high temperature causes the chloride vapors to oxidize, and results in the deposition of a porous phospho-silica layer along the inner diameter of the silica tube.Once an even phospho-silica layer is obtained along the inner wall of the silica tube, the second stage of the fabrication process begins. In this stage, the silica tube with the porous phospho-silica layer on its inner wall undergoes a solution doping process where the glass modifiers ZrO2, Y2O3, Al2O3 and Er2O3 are added. These modifiers are first mixed with an alcohol and water solution at a 1:5 ratio to form the complex ions ZrOCl2.8H2O, YCl3.6H2O, AlCl3.6H2O and ErCl3.6H2O that is then incorporated into the glass matrix of the silica tube by solution doping. At this stage also, small quantities of Y2O3 and P2O5 are added to the glass matrix to function as nucleating agents as well as to increase the phase separation of the Er2O3 doped micro-crystallites that form in the core matrix of the optical fiber preform. The concentration of the dopant constituents is optimized so as to give a fiber with a Numerical Aperture (NA) of 0.17 to 0.20. The addition of Y2O3 also serves a secondary purpose, which is to slow down or eliminate changes in the ZrO2 crystal structure. This is because in a bulk glass matrix, pure zirconium can exist in three distinct crystalline phases, depending on the temperature range. At temperatures of above 2350°C, the ZrO2 crystallites take on a cubic structure, while at lower temperatures of between 1170 and 2350°C they form a tetragonal structure instead and at temperatures of below 1170°C form a mono-clinic structure. The detrimental effect of these changes arises during the shift from the tetragonal to monoclinic phases, which is very fast and accompanied by an increase in volume of between 3 to 5%. This rapid increase causes significant cracking in the developed fiber during the cooling process (observed primarily in the core region, as this is where the concentration of ZrO2 crystallites is the highest) and destroys the mechanical properties of the fiber. Adding a small amount of Y2O3, or oxides such as MgO, CaO can slow or stop down the changes in the crystalline structure, thereby preserving the mechanical strength and integrity of the fiber.

The final phase of the fabrication process involves the annealing of the fabricated preform after the solution deposition process. The preform is annealed at a temperature of 1100°C over a duration of 3 hours in a closed furnace, with a heating and cooling rate of 20°C/min so as to create Er2O3 and ZrO2 rich micro-crystallites. Once the preform has been annealed, it is collapsed into a solid rod at a temperature of more than 2000°C and then drawn into a fiber strand with a 125.0 ± 0.5μm diameter through a conventional fiber-drawing tower. The temperature of 2000°C is below the melting temperature of the ZrO2 crystallites but above the melting temperature of glass, thus allowing the ZrO2 crystallites to retain their crystalline structure inside the silica glass matrix. Once the fiber has been drawn, the primary and secondary coatings, Desolite DP-1004 and Desolite DS-2015 is added to the fiber and the coating uniformity is assured by controlling the flow pressure of the inlet gases into the primary and secondary coating resin vessels during the drawing process, as well as the proper alignment of the primary and secondary coating cup units. The fiber diameter is also closely controlled during the drawing process to ensure that a high quality fiber is produced.

3. Optical characteristics of the Zr-EDF

Characterization of the Zr-EDF is carried out at both the preform stage and also using the completed fiber. Using selected preform samples, morphology of the core region was analyzed using a Field-Emission Gun Scanning Electron Microscopy (FEGSEM), while dopant concentration of each sample was determined using Electron Probe Microanalyses (EPMA). Two different preforms were prepared with different Er2O3 and ZrO2 dopant levels by changing the composition of ErCl3.6H2O and ZrOCl2.8H2O during solution doping process, while the Al2O3 content is kept constant for both fiber samples. These preforms, and the resultant fibers drawn from them are designated as ZEr-A and ZEr-B. As the ZrO2 crystallites are able to sustain their crystalline structures at high temperatures, above the temperature required to collapsed the silica rod and draw the fiber from the preform, therefore the existence of some ZrO2 crystallites are expected within the host matrix of the preform. The microstructure of the doping region of ZEr-A and ZEr-B, which are developed without any thermal treatment or annealing, are given in Fig. 2
Fig. 2 The microstructure of the core region of the (a) ZEr-A preform and (b) the ZEr-B preform.
.

The boundaries of the ZrO2 crystallites in the glass matrix of the optical preform can be seen clearly in the figure, and it is observed that the boundaries of the ZrO2 crystallites are larger and better defined in ZEr-B than similar crystallites in ZEr-A. This is attributed to the higher concentration of ZrO2 used in the fabrication of ZrO2. The results of the EPMA analysis of the dopant concentrations for the fabricated fibers are given in Table 1

Table 1. Dopant Concentration within Preform Core Region (ZEr-A and ZEr-B)

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, which shows the Al2O3, ZrO2 and Er2O3 dopant concentrations in ZEr-A and ZEr-B. Both fiber preforms have approximately the same Al2O3 dopant levels of about 24 to 25 mol%. However, the ZEr-B fiber has a much higher ZrO2 dopant concentration, almost quadruple that of ZEr-A, as well as close an Er2O3 dopant concentration almost twice as high as that of ZEr-A.The physical characteristics of ZEr-A and ZEr-B are given in Table 2

Table 2. Physical Characteristics of the Completed Fibers (ZEr-A and ZEr-B)a

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. Both fibers have almost similar characteristics, except for a slightly different NA and effective area (Aeff), with ZEr-A having an NA and Aeff of 0.17 μm and 87 μm2 respectively while ZEr-B has values of 0.20 and 75 respectively. Both fibers are also observed to have significantly higher background losses than standard erbium doped fibers, with ZEr-A and ZEr-B having background losses of 145 dB/km and 175 dB/km respectively at 1300 nm. These losses are much higher than that of standard erbium doped fibers, which have typical values of around 10 to 15 dB/km, and arises due to scattering from the nano-crystalline phases in the fibers.

In the characterization of the completed optical fibers, the absorption and fluorescence lifetimes of the fabricated fibers are analyzed. The peak absorption of the fibers at 978 nm are determined to be 14.5 and 18.3 dB/m respectively for ZEr-A and ZEr-B, translating to an of erbium ion concentration of 2800 and 3888 ppm/wt for the respective fibers. The fluorescence curves of both the ZEr-A and ZEr-B annealed preforms and drawn fibers are shown in Fig. 3(a)
Fig. 3 (a) Fluorescence curve of ZEr-A and ZEr-B annealed preforms and drawn fibers, and (b) decay curves of ZEr-A (above) and ZEr-B (below). (Figures used with permission (these figures are reproduced and modified with the permission of the publisher of [22].))
, while the fluorescence decay curves of both fibers are given in Fig. 3(b). The fluorescence curves are obtained by laterally pumping the fibers at a 980 nm pump power of 100 mW, and it can be seen that the both the ZEr-A and ZEr-B fibers have fluorescence peaks at 1530 nm, as is expected from as the active medium for both fibers is erbium. The ZEr-B has a slightly higher emission power density as compared to the ZEr-A, which is expected due to the higher Er2O3 dopant concentration of ZEr-B. It is also observed that the spectral broadening of the drawn fibers are larger than that of the preforms; this is attributed to the phase change of the Er2O3 from micro-crystallites in the annealed preform into nano-crystallites as the fiber is drawn. The decay curves of both fibers are approximately the same as expected due to the active medium of both fibers being the same. However, the decay curve of ZEr-B shows that it has a slight shorter fluorescence lifetime. Taking this fact into account, together with the higher doping levels of Er2O3 and ZrO2 in ZEr-B, indicates that the concentration-quenching phenomenon that is typical of erbium ions is strongly reduced through an increase in the doping levels of ZrO2.

Based on the characterization of the Zr-EDF, it can be seen that the addition of zirconium ions into the glass matrix of the Erbium Doped Fiber (EDF) allows for the fabrication of highly doped fibers, which have many potential applications in the development of compact devices. The following sections will examine the applications of the Zr-EDF, in particular its non-linear characteristics and also its usage as a compact medium for the generation of short pulses.

4. Four-wave-mixing in the Zr-EDF

In addition to providing high gain in a short fiber length, the Zr-EDF has also garnered increasing interest due to its significant non-linear characteristics that arise from the addition of zirconium ions into the glass matrix of the EDF [1

1. G. E. Keiser, “A review of WDM technology and applications,” Opt. Fiber Technol. 5(1), 3–39 (1999). [CrossRef]

]. The FWM effect is of particular interest when it comes to the non-linear effects of the Zr-EDF, as it has significant potential for new applications such as multi-wavelength generation and wavelength conversion. The FWM effect is an optical Kerr effect, and occurs when two or more wavelengths propagate simultaneously in non-linear medium. The interaction of these wavelengths results in the scattering of the incident photons, which in turn produces a fourth photon, known as an idler, at a wavelength that does not coincide with the incident wavelengths as given by Eq. (1) [22

22. H. Ahmad, M. C. Paul, N. A. Awang, S. W. Harun, M. Pal, and K. Thambiratnam, “Four-wave-mixing in zirconia-yttria-aluminum erbium codoped silica fiber,” J. Eur. Opt. Soc. Rapid Publ. 7, 12011 (2012). [CrossRef]

]:
λnew_signal=2λpumpλsignal,λnew_signal=2λpump+λsignal
(1)
where λpump andλsignal are the pump and signal wavelengths respectively, while λnew_signalis the wavelength of the signal generated by the FWM process. The power of the generated signal, PFWM can be computed as:
PFWM=ηγ2Pp2PseαLLeff2
(2)
where Pp is the input pump power and Ps is the input signal power. Leffis the effective length of the fiber and is given as Leff=1eαLα, with L being the fiber length and α is the fiber attenuation coefficient. The normalized FWM efficiency η, is given asη=α2α2+Δβ2[1+2eαL(1cos(ΔβL)(1eαL)2], where the phase mismatch,Δβ=2πλ2cDΔf2. The dispersion parameter can be given as D=2πcλ2β2 and β2is the group velocity dispersion parameter. The γ parameter is determined by bi-directional measurements of the FWM power, while the chromatic dispersion is determined from the wavelength detuning of the FWM Power Conversion Efficiency (PCE). Figure 4
Fig. 4 Experimental setup for FWM generation and measurement in the Zr-EDF (a similar configuration as in [22]).
shows the experimental setup used in the generation and measurement of the FWM effect:In the setup, two Tunable Laser Sources (designated TLS1 and TLS2) are used as the pump and signal sources. Each TLS has a tuning range from 1460 nm to 1640 nm and linewidth of 0.015 nm. TLS1 is used to generate the pump beam, Pp, fixed at 1560 nm with an average output power of 12.8 dBm. The signal beam, Ps has an average power 10.8 dBm with wavelengths of between 1552 nm to 1557 nm, and is generated by TLS2. Ppand Ps are combined by a 3 dB coupler with Polarization Controllers (PCs) used to obtain the maximum FWM efficiency. Two Laser Diodes (LDs) pumps at 1460 nm and 1490 nm are used to pump the Zr-EDF through a Wavelength Division Multiplexer (WDM) in order to suppress the erbium ions and allow interaction between the propagating beams and the host medium which contain the zirconium ions. A 4 m long ZEr-B fiber, with the characteristics as described in Tables 1 and 2, is used as the non-linear medium. An Optical Spectrum Analyzer (OSA) with a 0.02 nm resolution bandwidth completes the optical circuit and is used to measure the generated FWM spectrum.

Figure 5(a)
Fig. 5 (a) Theoretical and actual values of PFWM against different Pp wavelengths, and (b) generation of idler wavelengths C and S at different Ps wavelengths. (These figures are reproduced with the permission of the publisher of [22].)
shows both the theoretical as well as the actual value of PFWMfor different Ppwavelengths. It can be seen that the actual values of PFWMagree well with the theoretically predicted values of Eq. (2), with the highest PFWMvalue of about – 45 dBm obtained at a Ppregion of between 1558 nm to 1565 nm. Similarly, the wavelengths of the idlers generated auger well with their predicted values, as shown in Fig. 5(b). With the wavelength of Ppfixed and the wavelength of Psvaried by 1 nm, two sets of idler wavelengths are formed at C and S, with C corresponding to λnew_signal=2λpumpλsignal and Scorresponding to λnew_signal=2λpump+λsignal.From the obtained values of PFWM, Cand S, the non-linear coefficient as well as the chromatic and dispersion slopes can be determined. In the case of the ZEr-B fiber, the obtained non-linear coefficient, chromatic slope and dispersion slope is determined to be 14 W−1km−1, 28.45 ps/nm.km and 3.63 ps/nm2.km respectively. Furthermore, the non-linear coefficient remains constant for all wavelengths propagating in the fiber, thus giving the ZEr-B fiber a very high potential for use in a multitude of applications such wavelength conversion and wavelength generation.

5. Generation of short pulses using the Zr-EDF

In addition to its non-linear characteristics, the high concentration of erbium ions in a short length of fiber also provides the Zr-EDF with a significant advantage in the development of compact pulse fiber lasers. These lasers have recently garnered significant attention, and of particular interest are Q-switched fiber lasers, which provide high-energy pulses for applications such as in medicine, range-finding and sensing [23

23. D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, and A. C. Ferrari, “Graphene Q-switched, tunable fiber laser,” Appl. Phys. Lett. 98(7), 073106 (2011). [CrossRef]

27

27. H. Q. Shangguan, L. W. Casperson, A. Shearin, K. W. Gregory, and S. A. Prahl, “Drug delivery with microsecond laser pulses into gelatin,” Appl. Opt. 35(19), 3347–3357 (1996). [CrossRef] [PubMed]

]. In this regard, a compact passively Q-switched pulse fiber laser can be realized by combining the Zr-EDF with an SA based on graphene, due to its relatively easy fabrication and low-cost [28

28. F. Wang, A. G. Rozhin, V. Scardaci, Z. Sun, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Wideband-tuneable, nanotube mode-locked, fibre laser,” Nat. Nanotechnol. 3(12), 738–742 (2008). [CrossRef] [PubMed]

30

30. T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express 13(20), 8025–8031 (2005). [CrossRef] [PubMed]

].

Figure 6
Fig. 6 (a) Setup of the passively Q-switched ZEr-B fiber ring laser using a graphene based SA, and (b) the setup for the deposition of the graphene layer onto the fiber ferrule.
shows the setup of the fiber laser, using a 3 m long ZEr-B fiber as the linear gain medium together with a graphene based SA as the Q-switching mechanism, as well as the setup used to create the graphene layer that will act as the SA for this work.

As shown in Fig. 6(a), the ZEr-B fiber is pumped by a 980 nm laser diode through a 980 / 1550 nm WDM. The ZEr-B fiber is also connected to an Optical Circulator (OC), which is in turn connected to a Fiber Bragg Grating (FBG) with a center wavelength of 1550 nm and a reflectivity of approximately 98.9% that acts to lock the wavelength propagating in the laser cavity. A 70:30 coupler is used to extract a portion of the signal for analysis, while the graphene based SA is placed within the cavity to generate the desired pulses. The extracted signal passes through a 3 dB coupler, with one half being directed to an OSA and the other half connected to a photodiode and oscilloscope. The graphene based SA is fabricated by depositing an emulsion containing graphene flakes suspended in a N-Methyl Pyrrolidone (NMP) onto the face of Fiber Ferrule 1 as illustrated in Fig. 6(b). A 1550 nm beam, at a high power of about 11 dBm then illuminates the fiber ferrule, causing some of the NMP solution to evaporate and leaving a thick layer of graphene. Fiber Ferrule 1 is then connected to Fiber Ferrule 2 so as to sandwich the graphene layer and the TLS turned on, while the output power is recorded by the Optical Power Meter (OPM). After some time, the TLS is shut off and Fiber Ferrule 2 removed. During this process, a portion of the graphene is transferred between the fiber ferrules, thus making the layer of graphene on Fiber Ferrule 1 thinner. Fiber Ferrule 2 is cleaned and the process repeated until the power of the OPM is 4.1% of the power of the input beam, with the reflection for a single layer of graphene contributing approximately 0.1% [31

31. F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, “Graphene photonics and optoelectronics,” Nat. Photonics 4(9), 611–622 (2010). [CrossRef]

] and Fresnel reflection contributing the remaining 4.0%. Once this power is achieved, the assembly of Fiber Ferrules 1 and 2 now form the SA.

The compact ZEr-B based Q-switch laser performs adequately, generating pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz at a pump power of 121.8 mW. The pulses generated are also stable over time and display minimal noise. Figure 7
Fig. 7 Q-switched pulse width (left) and pulse train (right) obtained at a pump power of 121.8 mW.
provides a snapshot of an individual pulse generated as well as the pulse train obtained at a pump power of 121.8 mW.

6. Conclusion

The fabrication and characterization of the Zr-EDF is described, as well as its uses in generating the FWM effect and also as a compact, passively Q-switched fiber laser. The Zr-EDF is made by first fabricating a conventional silica preform using the MCVD technique at between 1350°C and 1400°C, following which glass modifiers and nucleating agents such as ZrO2, Y2O3, Al2O3, Er2O3 and P2O5 are added by solution doping. The resulting preform is then collapsed and annealed at a temperature of more than 2000°C to produce an optical fiber with a diameter of 125.0 ± 0.5 µm. Two Zr-EDFs are fabricated, designated ZEr-A and ZEr-B with erbium ion concentrations of 2800 and 3888 ppm/wt and absorption rates of 14.5 and 18.3 dB/m at 978 nm respectively. In the generation of the FWM effect, a 4 m long ZEr-B is used as the non-linear gain medium, and generates an FWM output with a power of - 45 dBm when pumped between 1558 nm to 1565 nm as predicted theoretically. The wavelengths of the generated sidebands also agree well with theoretical predictions, showing stability and potential applications as a multi-wavelength source. The ZEr-B is has a non-linear coefficient of 14 W−1km−1 and chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km. The ZEr-B is also used to create a compact, passively Q-switched fiber laser together with a graphene based saturable absorber, and is capable of generating short pulses with a pulse width of 8.8 µs and repetition rate of 9.15 kHz at a pump power of 121.8 mW. The proposed fiber laser has a maximum average output power of 161.35 µW and maximum pulse energy value of 17.64 nJ, and has significant potential for further development as a compact, pulsed laser source.

Acknowledgments

The authors wish to express their gratitude to MOHE for their funding (UM.C/HIR/MOHE/SC/01) as well as to N. A. Awang of the Faculty of Science, Technology and Human Development, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor Darul Takzim for her assistance and support in this work.

References and links

1.

G. E. Keiser, “A review of WDM technology and applications,” Opt. Fiber Technol. 5(1), 3–39 (1999). [CrossRef]

2.

R. Ramaswami, “Optical fiber communication: from transmission to networking,” IEEE Commun. Mag. 40(5), 138–147 (2002). [CrossRef]

3.

M. Wasfi, “Optical fiber amplifiers – review,” Int. J. Commun. Netw. Inf. Secur. 1, 42–47 (2009).

4.

D. Richardson, J. Nilsson, and W. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B 27(11), B63–B92 (2010). [CrossRef]

5.

H. Ahmad, M. Z. Zulkifli, A. A. Latif, K. Thambiratnam, and S. W. Harun, “17-channels S band multiwavelength brillouin/erbium fiber laser co-pump with Raman source,” Laser Phys. 19(12), 2188–2193 (2009). [CrossRef]

6.

K. Inoue and H. Toba, “Wavelength conversion experiment using fiber four-wave mixing,” IEEE Photon. Technol. Lett. 4(1), 69–72 (1992). [CrossRef]

7.

E. Yahel and A. Hardy, “Amplified spontaneous emission in high-power, Er3+/Yb3+ codoped fiber amplifiers for wavelength-division-multiplexing applications,” J. Opt. Soc. Am. B 20(6), 1198–1203 (2003). [CrossRef]

8.

M. J. Yadlowsky, E. M. Deliso, and V. L. Da Silva, “Optical fibers and amplifiers for WDM systems,” Proc. IEEE 85(11), 1765–1779 (1997). [CrossRef]

9.

E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glass,” Opt. Mater. 5(3), 159–167 (1996). [CrossRef]

10.

D. M. Gill, L. McCaughan, and J. C. Wright, “Spectroscopic site determinations in erbium-doped lithium niobate,” Phys. Rev. B Condens. Matter 53(5), 2334–2344 (1996). [CrossRef] [PubMed]

11.

M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Wideband EDFA based on erbium doped crystalline zirconia yttria alumino silicate fiber,” J. Lightwave Technol. 28(20), 2919–2924 (2010). [CrossRef]

12.

M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers,” Opt. Lett. 35(17), 2882–2884 (2010). [CrossRef] [PubMed]

13.

J. R. Armitage, “Spectral dependence of the small-signal gain around 1.5 μm in erbium doped silica fiber amplifiers,” IEEE J. Quantum Electron. 26(3), 423–425 (1990). [CrossRef]

14.

B. Pedersen, A. Bjarklev, J. H. Povlsen, K. Dybdal, and C. C. Larsen, “The design of erbium-doped fiber amplifiers,” J. Lightwave Technol. 9(9), 1105–1112 (1991). [CrossRef]

15.

J. Yang, S. Dai, Y. Zhou, L. Wen, L. Hu, and Z. Jiang, “Spectroscopic properties and thermal stability of erbium-doped bismuth-based glass for optical amplifier,” J. Appl. Phys. 93(2), 977–983 (2003). [CrossRef]

16.

P. Peterka, B. Faure, W. Blanc, M. Karásek, and B. Dussardier, “Theoretical modeling of S-band thulium-doped silica fiber amplifiers,” Opt. Quantum Electron. 36(1-3), 201–212 (2004). [CrossRef]

17.

R.-J. Essiambre, B. Mikkelsen, and G. Raybon, “Intra-channel cross phase modulation and four-wave-mixing in high speed TDM systems,” Electron. Lett. 35(18), 1576–1578 (1999). [CrossRef]

18.

I. Shake, H. Takara, S. Kawanishi, and Y. Yamabayashi, “Optical signal quality monitoring method based on optical sampling,” Electron. Lett. 34(22), 2152–2154 (1998). [CrossRef]

19.

N. Kashyap, P. H. Siegel, and A. Vardy, “Coding for the optical channel: the ghost-pulse constraint,” IEEE Trans. Inf. Theory 52(1), 64–77 (2006). [CrossRef]

20.

S. Harun, R. Parvizi, S. Shahi, and H. Ahmad, “Multi-wavelength erbium-doped fiber laser assisted by four-wave mixing effect,” Laser Phys. Lett. 6(11), 813–815 (2009). [CrossRef]

21.

X. F. Yang, X. Dong, S. Zhang, F. Lu, X. Zhou, and C. Lu, “Multi-wavelength erbium doped fiber laser with 0.8 nm spacing using sampled Bragg grating and photonic crystal fiber,” IEEE Photon. Technol. Lett. 17(12), 2538–2540 (2005). [CrossRef]

22.

H. Ahmad, M. C. Paul, N. A. Awang, S. W. Harun, M. Pal, and K. Thambiratnam, “Four-wave-mixing in zirconia-yttria-aluminum erbium codoped silica fiber,” J. Eur. Opt. Soc. Rapid Publ. 7, 12011 (2012). [CrossRef]

23.

D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, and A. C. Ferrari, “Graphene Q-switched, tunable fiber laser,” Appl. Phys. Lett. 98(7), 073106 (2011). [CrossRef]

24.

R. J. Williams, N. Jovanovic, G. D. Marshall, and M. J. Withford, “All-optical, actively Q-switched fiber laser,” Opt. Express 18(8), 7714–7723 (2010). [CrossRef] [PubMed]

25.

W.-J. Cao, H.-Y. Wang, A.-P. Luo, Z.-C. Luo, and W.-C. Xu, “Graphene-based, 50 nm wide-band tunable passively Q-switched fiber laser,” Laser Phys. Lett. 9(1), 54–58 (2012). [CrossRef]

26.

M. L. Siniaeva, M. N. Siniavsky, V. P. Pashinin, A. A. Mamedov, V. I. Konov, and V. V. Kononenko, “Laser ablation of dental materials using microsecond Nd:YAG laser,” Laser Phys. 19(5), 1056–1060 (2009). [CrossRef]

27.

H. Q. Shangguan, L. W. Casperson, A. Shearin, K. W. Gregory, and S. A. Prahl, “Drug delivery with microsecond laser pulses into gelatin,” Appl. Opt. 35(19), 3347–3357 (1996). [CrossRef] [PubMed]

28.

F. Wang, A. G. Rozhin, V. Scardaci, Z. Sun, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Wideband-tuneable, nanotube mode-locked, fibre laser,” Nat. Nanotechnol. 3(12), 738–742 (2008). [CrossRef] [PubMed]

29.

A. G. Rozhin, V. Scardaci, F. Wang, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Generation of ultra-fast laser pulses using nanotube mode-lockers,” Phys. Status Solidi B 243(13), 3551–3555 (2006). [CrossRef]

30.

T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express 13(20), 8025–8031 (2005). [CrossRef] [PubMed]

31.

F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, “Graphene photonics and optoelectronics,” Nat. Photonics 4(9), 611–622 (2010). [CrossRef]

OCIS Codes
(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers
(060.7140) Fiber optics and optical communications : Ultrafast processes in fibers
(140.3500) Lasers and laser optics : Lasers, erbium
(140.3510) Lasers and laser optics : Lasers, fiber
(160.2290) Materials : Fiber materials
(160.4330) Materials : Nonlinear optical materials

ToC Category:
Materials for Fiber Optics

History
Original Manuscript: September 4, 2012
Revised Manuscript: September 23, 2012
Manuscript Accepted: September 23, 2012
Published: October 31, 2012

Virtual Issues
Specialty Optical Fibers (2012) Optical Materials Express

Citation
H. Ahmad, K. Thambiratnam, M. C. Paul, A. Z. Zulkifli, Z. A. Ghani, and S. W. Harun, "Fabrication and application of zirconia-erbium doped fibers," Opt. Mater. Express 2, 1690-1701 (2012)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-2-12-1690


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References

  1. G. E. Keiser, “A review of WDM technology and applications,” Opt. Fiber Technol.5(1), 3–39 (1999). [CrossRef]
  2. R. Ramaswami, “Optical fiber communication: from transmission to networking,” IEEE Commun. Mag.40(5), 138–147 (2002). [CrossRef]
  3. M. Wasfi, “Optical fiber amplifiers – review,” Int. J. Commun. Netw. Inf. Secur.1, 42–47 (2009).
  4. D. Richardson, J. Nilsson, and W. Clarkson, “High power fiber lasers: current status and future perspectives [Invited],” J. Opt. Soc. Am. B27(11), B63–B92 (2010). [CrossRef]
  5. H. Ahmad, M. Z. Zulkifli, A. A. Latif, K. Thambiratnam, and S. W. Harun, “17-channels S band multiwavelength brillouin/erbium fiber laser co-pump with Raman source,” Laser Phys.19(12), 2188–2193 (2009). [CrossRef]
  6. K. Inoue and H. Toba, “Wavelength conversion experiment using fiber four-wave mixing,” IEEE Photon. Technol. Lett.4(1), 69–72 (1992). [CrossRef]
  7. E. Yahel and A. Hardy, “Amplified spontaneous emission in high-power, Er3+/Yb3+ codoped fiber amplifiers for wavelength-division-multiplexing applications,” J. Opt. Soc. Am. B20(6), 1198–1203 (2003). [CrossRef]
  8. M. J. Yadlowsky, E. M. Deliso, and V. L. Da Silva, “Optical fibers and amplifiers for WDM systems,” Proc. IEEE85(11), 1765–1779 (1997). [CrossRef]
  9. E. Snoeks, P. G. Kik, and A. Polman, “Concentration quenching in erbium implanted alkali silicate glass,” Opt. Mater.5(3), 159–167 (1996). [CrossRef]
  10. D. M. Gill, L. McCaughan, and J. C. Wright, “Spectroscopic site determinations in erbium-doped lithium niobate,” Phys. Rev. B Condens. Matter53(5), 2334–2344 (1996). [CrossRef] [PubMed]
  11. M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Wideband EDFA based on erbium doped crystalline zirconia yttria alumino silicate fiber,” J. Lightwave Technol.28(20), 2919–2924 (2010). [CrossRef]
  12. M. C. Paul, S. W. Harun, N. A. D. Huri, A. Hamzah, S. Das, M. Pal, S. K. Bhadra, H. Ahmad, S. Yoo, M. P. Kalita, A. J. Boyland, and J. K. Sahu, “Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers,” Opt. Lett.35(17), 2882–2884 (2010). [CrossRef] [PubMed]
  13. J. R. Armitage, “Spectral dependence of the small-signal gain around 1.5 μm in erbium doped silica fiber amplifiers,” IEEE J. Quantum Electron.26(3), 423–425 (1990). [CrossRef]
  14. B. Pedersen, A. Bjarklev, J. H. Povlsen, K. Dybdal, and C. C. Larsen, “The design of erbium-doped fiber amplifiers,” J. Lightwave Technol.9(9), 1105–1112 (1991). [CrossRef]
  15. J. Yang, S. Dai, Y. Zhou, L. Wen, L. Hu, and Z. Jiang, “Spectroscopic properties and thermal stability of erbium-doped bismuth-based glass for optical amplifier,” J. Appl. Phys.93(2), 977–983 (2003). [CrossRef]
  16. P. Peterka, B. Faure, W. Blanc, M. Karásek, and B. Dussardier, “Theoretical modeling of S-band thulium-doped silica fiber amplifiers,” Opt. Quantum Electron.36(1-3), 201–212 (2004). [CrossRef]
  17. R.-J. Essiambre, B. Mikkelsen, and G. Raybon, “Intra-channel cross phase modulation and four-wave-mixing in high speed TDM systems,” Electron. Lett.35(18), 1576–1578 (1999). [CrossRef]
  18. I. Shake, H. Takara, S. Kawanishi, and Y. Yamabayashi, “Optical signal quality monitoring method based on optical sampling,” Electron. Lett.34(22), 2152–2154 (1998). [CrossRef]
  19. N. Kashyap, P. H. Siegel, and A. Vardy, “Coding for the optical channel: the ghost-pulse constraint,” IEEE Trans. Inf. Theory52(1), 64–77 (2006). [CrossRef]
  20. S. Harun, R. Parvizi, S. Shahi, and H. Ahmad, “Multi-wavelength erbium-doped fiber laser assisted by four-wave mixing effect,” Laser Phys. Lett.6(11), 813–815 (2009). [CrossRef]
  21. X. F. Yang, X. Dong, S. Zhang, F. Lu, X. Zhou, and C. Lu, “Multi-wavelength erbium doped fiber laser with 0.8 nm spacing using sampled Bragg grating and photonic crystal fiber,” IEEE Photon. Technol. Lett.17(12), 2538–2540 (2005). [CrossRef]
  22. H. Ahmad, M. C. Paul, N. A. Awang, S. W. Harun, M. Pal, and K. Thambiratnam, “Four-wave-mixing in zirconia-yttria-aluminum erbium codoped silica fiber,” J. Eur. Opt. Soc. Rapid Publ.7, 12011 (2012). [CrossRef]
  23. D. Popa, Z. Sun, T. Hasan, F. Torrisi, F. Wang, and A. C. Ferrari, “Graphene Q-switched, tunable fiber laser,” Appl. Phys. Lett.98(7), 073106 (2011). [CrossRef]
  24. R. J. Williams, N. Jovanovic, G. D. Marshall, and M. J. Withford, “All-optical, actively Q-switched fiber laser,” Opt. Express18(8), 7714–7723 (2010). [CrossRef] [PubMed]
  25. W.-J. Cao, H.-Y. Wang, A.-P. Luo, Z.-C. Luo, and W.-C. Xu, “Graphene-based, 50 nm wide-band tunable passively Q-switched fiber laser,” Laser Phys. Lett.9(1), 54–58 (2012). [CrossRef]
  26. M. L. Siniaeva, M. N. Siniavsky, V. P. Pashinin, A. A. Mamedov, V. I. Konov, and V. V. Kononenko, “Laser ablation of dental materials using microsecond Nd:YAG laser,” Laser Phys.19(5), 1056–1060 (2009). [CrossRef]
  27. H. Q. Shangguan, L. W. Casperson, A. Shearin, K. W. Gregory, and S. A. Prahl, “Drug delivery with microsecond laser pulses into gelatin,” Appl. Opt.35(19), 3347–3357 (1996). [CrossRef] [PubMed]
  28. F. Wang, A. G. Rozhin, V. Scardaci, Z. Sun, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Wideband-tuneable, nanotube mode-locked, fibre laser,” Nat. Nanotechnol.3(12), 738–742 (2008). [CrossRef] [PubMed]
  29. A. G. Rozhin, V. Scardaci, F. Wang, F. Hennrich, I. H. White, W. I. Milne, and A. C. Ferrari, “Generation of ultra-fast laser pulses using nanotube mode-lockers,” Phys. Status Solidi B243(13), 3551–3555 (2006). [CrossRef]
  30. T. R. Schibli, K. Minoshima, H. Kataura, E. Itoga, N. Minami, S. Kazaoui, K. Miyashita, M. Tokumoto, and Y. Sakakibara, “Ultrashort pulse-generation by saturable absorber mirrors based on polymer-embedded carbon nanotubes,” Opt. Express13(20), 8025–8031 (2005). [CrossRef] [PubMed]
  31. F. Bonaccorso, Z. Sun, T. Hasan, and A. C. Ferrari, “Graphene photonics and optoelectronics,” Nat. Photonics4(9), 611–622 (2010). [CrossRef]

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