Agazzi, L.

Aravazhi, S.

Bernhardi, Edward

García Blanco, Sonia Maria

Geskus, D.

Pollnau, Markus

Yong, Yean Sheng

English

Gain around 981 nm in Yb-doped potassium-double-tungstate channel waveguides increases linearly with dopant concentration up to ~50% Yb. A 55-nm gain bandwidth obtains in all waveguides, with at least 150 dB/cm for 47.5% Yb concentration

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   Concentration Dependence of Optical Gain in  Yb3+-doped Potassium Double Tungstate Channel Waveguides  D. Geskus1, Y. S. Yong2,3, E. H. Bernhardi2, L. Agazzi2, S. M. García-Blanco2,3, S. Aravazhi2, and M. Pollnau1,2 1.  Department of Materials and Nano Physics, KTH - Royal Institute of Technology, Isafjordsgatan 22, 16440 Kista, Sweden 2.  Integrated Optical MicroSystems Group and 3.  Optical Sciences Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands  Yb3+-doped potassium double tungstates exhibit an excellent gain performance [1]. Liquid-phase epitaxy of KGdxLuyYb1-x-y(WO4)2 layers onto undoped KY(WO4)2 substrates allows one to independently design active doping level and refractive index [2,3]. The highest Yb3+ concentration enabling lattice matching between layer and substrate leads to the composition KGd0.465Lu0.000Yb0.535(WO4)2. In Fig. 1(a), lifetime measurements (red) and correction [4] of radiation reabsorption (blue) show that energy migration among Yb3+ ions and subsequent energy transfer to impurities or cooperative upconversion diminishes the lifetime from ~270 µs to slightly less than 200 µs at 47.5% Yb3+ concentration. This small amount of quenching does not affect the gain significantly. We fabricated channel waveguides with Yb3+ concentrations of 15%, 20%, and 47.5%, and pump-probe measurements provided a gain of 280 dB/cm, 430 dB/cm, and 935 dB/cm, respectively, at the peak wavelength of 980.6 nm, see Fig. 1(b). Besides, we grew thin films with 47.5% and 57.5%, beyond the lattice-matching limit of 53.5%, and perpendicular gain measurements indicate a gain of 1028 dB/cm [1] and 1050 dB/cm [5], respectively. In all waveguides, a gain bandwidth of 55 nm from 977–1032 nm was measured, see Fig. 1(c), equaling 16.3 THz spectral bandwidth, providing 150 dB/cm gain for 47.5% Yb3+ concentration (red arrow). (a)0 10 20 30 40 50050100150200250300350400450500Data: Data1_TauModel: reabsorptionWeighting: y No weighting  Chi^2/DoF = 5.43344R^2 =  0.99912  Tw 263.58362 ±1.53909A 0.0296 ±0.0008N0 84.09354 ±1.89803Lifetime (s)Yb conc. (mol%)deconvolution (b)    Fig. 1. (a) 2F5/2 lifetime as a function of Yb3+ concentration. Red line: fit [4]. Blue line: deconvolution showing the self-quenching. (b) Peak gain at 980.6 nm as a function of Yb3+ concentration. Red squares: waveguides. Red line: linear fit. Blue triangles: thin films. Black line: concentration limit for lattice matching.  (c) Obtained modal gain of three waveguide amplifiers with Yb3+ concentrations of 15%, 20%, and 47.5%. Symbols: measured gain. Lines: calculated gain. Arrow: gain exceeding 150 dB/cm over a bandwidth of 55 nm.           (c)  References 1  D. Geskus, S. Aravazhi, S. M. García-Blanco, and M. Pollnau, “Giant optical gain in a rare-earth-ion-doped microstructure,” Adv. Mater. 24, OP19-OP22 (2012) [2] F. Gardillou, Y. E. Romanyuk, C. N. Borca, R. P. Salathé, and M. Pollnau, “Lu, Gd codoped KY(WO4)2:Yb epitaxial layers: towards integrated optics based on KY(WO4)2,” Opt. Lett. 32, 488-490 (2007) [3] S. Aravazhi, D. Geskus, K. van Dalfsen, S. A. Vázquez-Córdova, C. Grivas, U. Griebner, S. M. García-Blanco, and M. Pollnau, “Engineering lattice matching, doping level, and optical properties of KY(WO4)2:Gd, Lu, Yb layers for a cladding-side-pumped channel waveguide laser,” Appl. Phys. B 111, 433-446 (2013) [4] F. Auzel, G. Baldacchini, L. Laversenne, and G. Boulon, "Radiation trapping and self-quenching analysis in Yb3+, Er3+, and Ho3+ doped Y2O3," Opt. Mater. 24, 103-109 (2003) [5] Y. S. Yong, S. Aravazhi, S. A. Vázquez-Córdova, S. M. García-Blanco, and M. Pollnau, “Highly Yb-doped KGd(WO4)2 thin-film amplifier,” submitted (2015) 0200400600800100012000 10 20 30 40 50 60Gain [dB/cm]Yb Concentration [at.%]-1200-1000-800-600-400-20002004006008001000960 970 980 990 1000 1010 1020 1030 1040Gain (dB/cm)Wavelength (nm)P = 60 mWP = 30 mWP = 18 mWP = 12 mWP = 9 mWP = 6 mWP = 3 mWP = 0 mWP = 60 mWP = 48 mWP = 36 mWP = 24 mWP = 19.2 mWP = 14.4 mWP = 12 mWP = 9.6 mWP = 7.2 mWP = 2.4 mWP = 0 mWExperimentaldataModeled data-600-400-2000200400600960 970 980 990 1000 1010 1020 1030 1040Gain (dB/cm)Wavelength (nm)P = 60 mWP = 30 mWP = 18 mWP = 12 mWP = 9 mWP = 6 mWP = 3 mWP = 0 mWP = 60 mWP = 48 mWP = 36 mWP = 24 mWP = 19.2 mWP = 14.4 mWP = 12 mWP = 9.6 mWP = 7.2 mWP = 2.4 mWP = 0 mWExperimentaldataModeled data-400-2000200400960 970 980 990 1000 1010 1020 1030 1040Gain (dB/cm)Wavelength (nm)P = 60 mWP = 30 mWP = 18 mWP = 12 mWP = 9 mWP = 6 mWP = 3 mWP = 0 mWP = 60 mWP = 48 mWP = 36 mWP = 24 mWP = 19.2 mWP = 14.4 mWP = 12 mWP = 9.6 mWP = 7.2 mWP = 2.4 mWP = 0 mWExperimentaldataModeled data978-1-4673-7475-0/15/$31.00 ©2015 IEEE

Concentration dependence of optical gain in Yb<sup>3+</sup>-doped potassium double tungstate channel waveguides

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Concentration dependence of optical gain in Yb<sup>3+</sup>-doped potassium double tungstate channel waveguides

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