1.6 μm emission from Pr 3+ :( 3 F 3 , 3 F 4 )→ 3 H 4 transition in Pr 3+ - and Pr 3+ /Er 3+-doped selenide glassesYong Gyu Choi, Kyong Hon Kim, Bong Je Park, and Jong Heo Citation: Applied Physics Letters 78, 1249 (2001); doi: 10.1063/1.1350958 View online: http://dx.doi.org/10.1063/1.1350958 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/78/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Photoluminescence measurements of Er-doped chalcogenide glasses J. Vac. Sci. Technol. A 22, 921 (2004); 10.1116/1.1648673 Energy transfer between Er 3+ and Pr 3+ in chalcogenide glasses for dual-wavelength fiber-optic amplifiers J. Appl. Phys. 91, 9072 (2002); 10.1063/1.1476965 Comparative study of energy transfers from Er 3+ to Ce 3+ in tellurite and sulfide glasses under 980 nmexcitation J. Appl. Phys. 88, 3832 (2000); 10.1063/1.1309054 1.3 μm Fluorescence quenching in Pr-doped glasses J. Appl. Phys. 84, 1800 (1998); 10.1063/1.368336 Nonradiative decay processes and mechanisms of frequency upconversion of Er3+ in ZrF4–BaF2–LaF3 glass J. Appl. Phys. 81, 2940 (1997); 10.1063/1.364324

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1.6 mm emission from Pr 3¿: „3F3 ,3F4…\3H4 transition

in Pr 3¿- and Pr 3¿ÕEr3¿-doped selenide glassesYong Gyu Choia) and Kyong Hon KimTelecommunication Basic Research Laboratory, Electronics and Telecommunications Research Institute,Yusong P.O. Box 106, Taejon 305-600, Republic of Korea

Bong Je Park and Jong HeoDepartment of Materials Science and Engineering, Pohang University of Science and Technology, San 31,Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, Republic of Korea

~Received 31 July 2000; accepted for publication 21 December 2000!

1.6 mm emission originated from Pr31: (3F3 ,3F4)→3H4 transition in Pr31- and Pr31/Er31-dopedselenide glasses were investigated under an optical pump of a conventional 1480 nm laser diode.The measured peak wavelength and full width at half maximum of the fluorescent emission were;1650 and.100 nm, respectively. A moderate lifetime of the thermally coupled upper manifolds(;21265 ms) together with a high stimulated emission cross section of;(361)310220cm2

promises to be useful for 1.6mm band fiber-optic amplifier that can be pumped with an existinghigh-power laser diode. Codoping of Er31 significantly enhanced the emission intensity by way ofa nonradiative Er31: 4I 13/2→Pr31: (3F3 ,3F4) energy transfer. ©2001 American Institute ofPhysics. @DOI: 10.1063/1.1350958#

Optical communication bandwidths are largely limitedby the clarity of the transmission window in the SiO2-basedoptical fiber. By virtue of recent development of elaboratedprocessing technologies, a mass production of OH2-freesilica optical fibers which have transparent characteristics inthe entire spectrum from;1200 to ;1700 nm becamepossible.1 Thus, in order to fully utilize the whole transparentregion of the dry fibers for large capacity optical communi-cation systems of several tens Tb/s, optical amplifiers cover-ing the wavelengths from lower than 1300 to about 1700 nmare necessary.

Recently, a significant technical improvement has beenmade in Raman fiber amplifiers and semiconductor opticalamplifiers as well as rare-earth~RE! doped fiber amplifiers.However, the RE doped fiber amplifiers have several supe-rior characteristics over the Raman and semiconductor am-plifiers. Some of them are possibilities to have a relativelyhigh signal-to-noise ratio, good gain stability, and low signalcrosstalk.2 This letter deals only with fiber materials relatedto new RE doped amplifiers. Erbium ions doped in eithergermano-silicate or tellurite glasses have been well demon-strated to provide signal amplification over the wavelengthregion of 1530–1600 nm.3,4 Praseodymium and dysprosiumions are proven to be useful for amplifiers in the 1.3mmband.5,6 Thulium ions in fluoride glasses amplify optical sig-nals in the wavelengths of 1450–1520 nm7 and of longerthan 1650 nm.8 So far, there has been no RE-host combina-tion optimized for optical amplifiers in wavelength regionsaround 1350–1450 nm where the hydroxyl ions cause anadditional absorption in the conventional silica fibers and1610–1650 nm where the gain-shifted erbium-doped fiberamplifiers can not provide an optical gain. In this letter, wereport measured results of spectroscopic properties of a

Pr31-doped low phonon energy glass which is considered asa possible candidate material for 1.6mm band fiber amplifi-ers. Sensitizing effect of Er31 on the 1.6mm emission fromthe Pr31-doped glass for optical pump at around 1480 nm isalso discussed.

Magnitude of multiphonon relaxation is one of the pa-rameters that govern emission intensity of some radiativeintra-4f -configurational transitions of RE ions in a dielectricmedium. One representative example of such transitions isthe 1.3 mm emission originated from the Pr31: 1G4→3H5

transition.5 The Pr31 ion actually has a luminescence cen-tered at about 1.6mm from (3F3 ,3F4)→3H4 transition, butdue to the tightly spaced energy levels of an energy gap of;1350 cm21, the radiative transition is virtually forbidden inmost glasses, even in sulfide glasses. A lasing action at;1.6mm has been demonstrated by using this transition in aLaCl3 crystal,9 but no detailed spectroscopic data on thistransition from a glass host have been reported yet.10

The multiphonon relaxation process from the (3F3 ,3F4)level can be reduced in glasses having a lower vibrationalphonon energy than the sulfide glasses (;350 cm21). Somegermano-selenide glass systems have a thermal stabilitygood enough to be drawn into a fiber form without anycrystallization,11 and possess the most intense phonon energyat about 200 cm21.12 In this study, we used aGe30–As8–Ga2–Se60 ~mol %! composition, and regarded itas a representative of selenide glasses. Pr31-single-doped andPr31/Er31-codoped glasses were prepared. All the startingmaterials were in an element state with 99.999% purity. Adetailed procedure about batching, melting and annealing isavailable elsewhere.13 Up to 1 mol % praseodymium couldbe solved in the host. Introduction of a small amount ofgallium to the Ge–As–Se system enhanced the RE solubilityas did it in Ge–As–S glasses.14

The 3F3 and 3F4 manifolds are thermally coupled~Fig.1!.15 The Boltzmann distribution predicts that approximatelya!Electronic mail: ygchoi@etri.re.kr

APPLIED PHYSICS LETTERS VOLUME 78, NUMBER 9 26 FEBRUARY 2001

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90% of populations reside in the lower-lying3F3 level in thisselenide glass. Thus, we consider the two manifolds as a(3F3 ,3F4) level. The absorption cross-section peaks at about1585 nm (;2.2310220cm2), while at 1480 nm it is;1.2310220cm2. Three Judd–Ofelt intensity parameters, i.e.,V2 , V4 , andV6 ,16 were calculated to be 1.01, 10.54, and2.53 in 10220cm2, respectively. Uncertainty involved in theanalysis was estimated to be;15%. Estimated branchingratio of the (3F3 ,3F4)→3H4 transition was;77%.

Figure 2~a! shows the emission spectrum originatedfrom the (3F3 ,3F4)→3H4 transition. The peak wavelengthand full width at half maximum are;1650 and.100 nm,respectively. Peak emission cross section is about (361)310220cm2, which is mostly attributed to high refractiveindex of the host (;2.5) at near-infrared wavelengths.Measured lifetimes of the fluorescing level are shown inFig. 3. Up to 0.05 mol % (;1.731019cm23) of Pr31, theupper level lifetime is nearly constant to be;212610ms,whereas the lifetime decreases as the concentrationfurther increases. Quantum efficiency of this transition is;65%620%. The concentration quenching mechanismsacting on the (3F3 ,3F4) manifolds are probably cross-relaxation processes corresponding to either(3F3 ,3F4): 3H5→(3F2 ,3H6): (3F2 ,3H6) or (3F3 ,3F4):3H4→(3F2 ,3H6): 3H5 .17 Therefore, the Pr31 concentrationshould be kept lower than 0.05 mol % (;900 ppm wt) tominimize the concentration quenching.

We added Er31 into the Pr31-doped glasses as a sensi-tizer to enhance the excitation efficiency of the 1480 nm

pumping. Figure 2~b! shows a typical emission spectrum ofPr31/Er31-codoped glasses. The emission intensity increasedwhen Er31 was introduced. Arrangement of the spectral mea-surement setup as well as dimension of the samples wasidentical when comparing the 1.6mm emission intensitieseach other. It was verified that the experimental uncertaintiesinvolved in the measurements were small suffient to comparethe emission intensities directly. To confirm an energy trans-fer from Er31 to Pr31, lifetimes of the codoped samples weremeasured at 1650 nm for the (3F3 ,3F4) level and at 1535nm for the Er31: 4I 13/2 level. Figure 4 shows the measuredduration times of the two levels under pumping at 1480 nm.Lifetime of the Er31: 4I 13/2 level decreases as the Er31 con-centration increases in the codoped samples, while the appar-ent duration time of the Pr31: (3F3 ,3F4) level increases.Lifetimes of the 4I 13/2 level in Er31-single-doped andPr31/Er31-codoped glasses where Er31 concentration is 0.1mol %, are;3.26 and;0.75 ms, respectively. This confirmsthat a fast energy transfer between the Er31: 4I 13/2 andPr31: (3F3 ,3F4) levels takes place. On the other hand, thelifetime increase of the (3F3 ,3F4) level is dedicated to theprolonged population feeding from the Er31: 4I 13/2 even afterstop of the excitation. The maximum Er31 concentration canbe determined in consideration of magnitude of the4I 15/2

→4I 13/2 ground state absorption at the 1.6mm band and REsolubility of the host. Shown in Fig. 5 are detailed absorption

FIG. 1. Absorption spectrum of a 1.0 mol % Pr31-doped selenide glass.

FIG. 2. Emission spectra of 0.05 mol % Pr31-doped glasses. Codoped Er31

concentrations were~a! 0 and~b! 0.2 mol %. Note that the optical excitationwas performed with a conventional 1480 nm laser diode for both cases.

FIG. 3. Measured lifetimes of the (3F3 ,3F4) manifold against Pr31 concen-trations.

FIG. 4. Measured duration times of~a! Pr31: (3F3 ,3F4) and~b! Er31: 4I 13/2

levels in Pr31/Er31-codoped glasses. Pr31 concentration was fixed at 0.05mol %.

1250 Appl. Phys. Lett., Vol. 78, No. 9, 26 February 2001 Choi et al.

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cross-section spectra of the two RE-single-doped samples.Magnitude of the absorption cross section of Er31 is aboutten times smaller than that of Pr31 at near 1480 nm, but it isquite comparable with that of Pr31 absorption at;1536 nmwhere the absorption cross section of Er31 peaks. In thisregard, if excited with a 1.5mm pump source instead of the1480 nm one, Pr31/Er31-codoped glasses may emit the 1.6mm luminescence with a greater intensity.

In the case of Pr31-single-doped glasses, a direct excita-tion to the upper Stark components of the (3F3 ,3F4) multip-let is preferred to make an efficient emission at 1.6mm be-cause the UV-side absorption of the host starts at around 800nm as shown in Fig. 1.

Since a good core/clad structured selenide optical fiber isreadily available,18 the 1.6mm emission from the Pr31- and

Pr31/Er31-doped selenide glasses is useful for potential fiberamplifiers in a transmission window of 1600–1700 nm.

1G. A. Thomas, B. I. Shraiman, P. F. Glodis, and M. J. Stephen, Nature~London! 404, 262 ~2000!.

2See, for example, papers inOptical Amplifiers and Their Applications,OSA Trends in Optics and Photonics Series~TOPS!, Vol. 16, edited by M.N. Zerras, A. E. Miller, and S. Sasaki~OSA, Washington DC, 1997!, pp.2–12.

3R. J. Mears, L. Reekie, I. M. Jauncey, and D. N. Payne, Electron. Lett.23,1026 ~1987!.

4Y. Ohishi, A. Mori, M. Yamada, H. Ono, Y. Nishida, and K. Oikawa, Opt.Lett. 23, 274 ~1998!.

5H. Tawarayama, E. Ishikawa, K. Yamanaka, K. Itoh, K. Okada, H. Aoki,H. Yanagita, Y. Matsuoka, and H. Toratani, J. Am. Ceram. Soc.83, 792~2000!.

6D. T. Schaafsma, L. B. Shaw, B. Cole, J. S. Sanghera, and I. D. Aggarwal,IEEE Photonics Technol. Lett.10, 1548~1998!.

7T. Kasamatsu, Y. Yano, and H. Sekita, Opt. Lett.24, 1684~1999!.8T. Sakamoto, M. Shimizu, M. Yamada, T. Kanamori, Y. Ohishi, Y. Ter-unuma, and S. Sudo, IEEE Photonics Technol. Lett.8, 349 ~1996!.

9S. R. Bowman, J. Ganem, B. J. Feldman, and A. W. Kueny, IEEE J.Quantum Electron.30, 2925~1994!.

10L. B. Shaw, B. B. Harbison, B. Cole, J. S. Sanghera, and I. D. Aggarwal,Opt. Express1, 87 ~1997!.

11T. Kanamori, Y. Terunuma, and T. Miyashita, Rev. Electr. Commun. Lab.32, 469 ~1984!.

12P. Nemec, B. Frumarova, and M. Frumar, J. Non-Cryst. Solids270, 137~2000!.

13Y. G. Choi, K. H. Kim, S. H. Park, and J. Heo, J. Appl. Phys.88, 3832~2000!.

14Y. G. Choi, K. H. Kim, B. J. Lee, Y. B. Shin, Y. S. Kim, and J. Heo, J.Non-Cryst. Solids278, 137 ~2000!.

15L. B. Shaw, S. R. Bowman, B. J. Feldman, and J. Ganem, IEEE J. Quan-tum Electron.32, 2166~1996!.

16Y. G. Choi, K. H. Kim, and J. Heo, J. Am. Ceram. Soc.82, 2762~1999!.17S. M. Kirkpatrick, S. R. Bowman, L. B. Shaw, and J. Ganem, J. Appl.

Phys.82, 2759~1997!.18J. S. Sanghera and I. D. Aggarwal, J. Non-Cryst. Solids256&257, 6

~1999!.

FIG. 5. Absorption cross-section spectra of~a! the Pr31: 3H4→(3F3 ,3F4)and~b! Er31: 4I 15/2→4I 13/2 transitions in the selenide glass host used in thisstudy.

1251Appl. Phys. Lett., Vol. 78, No. 9, 26 February 2001 Choi et al.

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