Erbium-doped fiber amplifiers Joonas Leppänen Emma Kiljo Jussi Taskinen Niklas Heikkilä Alexander Permogorov Group 3 EDFA Photonics School of Electrical Engineering

Content 1.Introduction 2.Theoretical Background 3.Manufacturing 4.Applications 5.Current Trends and Future Perspectives 6.Conclusions Photonics Group 3: EDFA

Introduction Invented in the 90's The most important optical amplifiers in long-distance fiber communications, up to 800km Operates in wavelenghts of ca. 1.5 µm Coincidently the wavelength minimum of tradtitional optical fibers Used to amplify the optical signal directly –No need for optical-electrical-optical conversions! Photonics Group 3: EDFA

Theoretical Background Signal input and laser diode output are multiplexed into fiber doped with trivalent erbium Er 3+ Laser signal is used to pump the active media in order to amplify signal via stimulated emission at around 1.55 µm for optical telecomms systems operating at C band Glass compositions can affect the gain spectrum R. Paschotta, Photonics, Encyclopedia of Laser Physics and Technology. Photonics Group 3: EDFA Image: RP Photonics, Encyclopedia of Laser Physics and Technology

Theoretical Background Commonly via higher absorption cross-section, shorter lifetime upper state (less noise but more stabilized source required) or broader absorption band lower state transition (more noise but higher power efficiency) Fibers often also doped with Ytterbium Yb 3+ at 980 nm for more effective transition by increasing pumping efficiency via larger absorption cross-section of Ytterbium around 980 nm Higher concentration of Yb 3+ than Er 3+ is used [Honkanen1997] S. Honkanen, High Er concentration phosphate glasses for planar waveguide amplifiers, Proc. SPIE 2996, Rare-Earth-Doped Devices, 32, 1997 [Paschotta] R. Paschotta, Photonics, Encyclopedia of Laser Physics and Technology. [Ron2011] I. Ron, Neodymium, erbium, and ytterbium co-doped fiber amplifier, Opt. Eng, 2011 Photonics Group 3: EDFA

Manufacturing Vapour Phase Fabrication Methods Low vapour pressure problem with Er-halides  Variety of inside deposition (ID) 1.Dopant chamber –Some control of concentration by adj. temp. 2.Impregnation of silica sponge with Er-salt –Reproducible results for very low concentration –Uniform for long lengths 3.Introducing Al 2 Cl 6 causes incorporation of Al 2 O 3 deposition –Utilizes seed fiber inserted into center  High quality outside vapor deposition (OVD) methods speculated –Organo metallic method on Nd [Ainslie1991] B. J. Ainslie, A review of the fabrication and properties of erbium-doped fibers for optical amplifiers, Journal of Lightwave Technology, 9(2), 220–227, 1991 [Mori1997] A. Mori, Erbium-doped tellurite glass fibre laser and amplifier, Electronics Letters, 33(10), 863, 1997 Photonics Group 3: EDFA Dopant chamber Fused Er-halide ~1000 °C Stationary burner Cladding layer Core with Er dopant Impregnated silica sponge Deposition tube Er-halide Core with Er dopant + Al 2 O 3 Heated lines Porous boule Burner

Manufacturing Liquid Phase method 1.Deposition of porous core 2.Soaking the porous layer in Er salt solution 3.Drying the impregnated porous layer 4.Fusing the porous layer + collapsing into solid rod Well known and simple Difficult to maintain high concentration in the middle  Possibility to increase efficiency of pump power usage via composite core structures [Ainslie1991] B. J. Ainslie, A review of the fabrication and properties of erbium-doped fibers for optical amplifiers, Journal of Lightwave Technology, 9(2), 220–227, 1991 [Mori1997] A. Mori, Erbium-doped tellurite glass fibre laser and amplifier, Electronics Letters, 33(10), 863, 1997 Photonics Group 3: EDFA Porous core Deposited cladding Burner Er solution Silica from deposit. tube Deposited cladding Core

Applications Splitting of same signal between lines Used in Cable TV Amplify input to give sufficient output to all branches Photonics Group 3: EDFA Amplification before splitting

Applications Maintain SNR Smaller gain, but more frequent Highly robust Photonics Group 3: EDFA Amplification between long spans of fiber

Wideband EDFA ● Basic EDFAs have only 12 nm bandwidth, which can be doubled by adding gain equalization filters ● Combining separate amplifiers of different gain spectrum can yield a wider gain for the whole system ● Amplification rate is not affected by the data rate, which makes it easier to make upgrades to the system

Current Trends and Future Perspectives L. Bigot, "Few-Mode Erbium-Doped Fiber Amplifiers: A Review," in Journal of Lightwave Technology, vol. 33, no. 3, pp , Feb.1, Photonics Group 3: EDFA ● Gain higher power output ● Achieve accurate control over the bandwidth ● Tailor the Er doping and pump beam profiles to enhance effectiveness

Conclusions Photonics Group 3: EDFA

Thanks! Photonics Group 3: EDFA