Slide 1: Rare Earth Doped Fibers for Use in Fiber Lasers and Amplifiers
Photonics Media Webinar: 4th Nov 2013 Rare Earth Doped Fibers for Use in Fiber Lasers and Amplifiers George Oulundsen, Fiber Product Line Manager Bryce Samson, VP Business Development 1
Slide 2: Outline
Outline • Introduction • Part I: Fiber basics • Part II: Rare earth doped double-clad fibers • Part III: Example fiber laser and amplifier platforms • Part IV: Conclusion • Q&A 2
Slide 3: Introduction
Introduction • Overall the laser market was worth >$2B/year in 2012 • Fiber lasers have ~25% of the market • In 2012 fiber lasers had the highest growth (16%) of all categories • Fiber lasers will continue to grow in 2013 with expectation of 7% growth (vs. 2% for lasers overall) Source: David Belfor
Slide 4: Introduction
Introduction • In some markets fiber lasers are the dominant laser technology, one example is the marking and engraving segment (~$360M in 2012) • Overall market share for fiber lasers was ~75% • This is primarily pulsed fiber lasers competing Total: $359 million against DPSSL and CO2 lasers Source:
Slide 5: Introduction
Introduction • This $570M market for fiber lasers covers a wide range of suppliers and fiber laser technologies including: – kW CW fiber lasers – nsec pulsed fiber lasers – ps & fs ultra-fast fiber lasers • Few things are in common between the companies making and selling this wide range of fiber la
Slide 6: Introduction
Introduction • Some intrinsic advantages of fiber lasers are also common across these multiple markets • Fiber laser efficiency is very high, requiring less diode pump power than most other solid state lasers – Less diode power means lower cooling requirements and lower cost – The thermal load is di
Slide 7: Introduction
Introduction • Technologically there has been a revolution in power scaling from CW fiber lasers, partly enabled by the high efficiency of the fiber – Output power from a near single mode fiber “laser” increased from ~100W to >10kW in ~10 years • Output power at “eye-safer” wavelengths has started t
Slide 8: Part I: Fiber Basics
Part I: Fiber Basics • Guiding light in optical fibers • Some important properties of optical fibers • Types of optical fibers • Examples of fiber laser results 8
Slide 9: Part I: Fiber Basics
Part I: Fiber Basics • Core = Glass, carries light/signal, typical size: 10-200 m • Cladding = Glass, helps define optical characteristics, makes fiber bigger & stronger for handling, typical size: 80-400 m (~diameter of human hair) • Coating = Plastic / Acrylate, for protection & handling, typical
Slide 10: Part I: Fiber Basics
Part I: Fiber Basics • Total internal reflection driven by refractive index difference between the core glass and the cladding glass • Light gets trapped in core is reflected at the core/clad boundary and exits at the other end • Because the fiber is ultrapure the loss of light as it propagates is e
Slide 11: Part I: Fiber Basics
Part I: Fiber Basics The difference in the optical property called refractive index is what confines the light in the core and prevents it from leaking into the cladding. coating • Index difference between core & cladding is important design parameter: • Typical number is 0.0055 • Range from 0.001 t
Slide 12: Part I: Fiber Basics
Part I: Fiber Basics • Fibers with different core sizes and NA Singlemode Multimode Large Mode Area “SM” “MM” “LMA” # of Modes 1 ~ 1000 2 to 5 Core Size (microns) 3 – 10 50 – 150 15 - 50 NA 0.12 – 0.20 0.20 – 0.35 0.05 – 0.10 % of Fiber 90% 9% <1% Worldwide Used in Fiber Lasers Yes, low power Yes, u
Slide 13: Part I: Fiber Basics
Part I: Fiber Basics • Attenuation limits the operating wavelength for silica optical fiber between ~350nm and ~2100nm – 350-1500nm loss dominated by Rayleigh scattering – >1600nm loss dominated by IR absorption of silica • At shorter wavelength glass composition can affect the attenuation 13
Slide 14: Part I: Fiber Basics
Part I: Fiber Basics • The core is physically & optically different Core than the cladding, because it is made of a Diameter different type of glass. • However, the light does not exactly fit the core, it travels slightly outside. The effective area in which it travels is called the Mode Field Diame
Slide 15: Part I: Fiber Basics
Part I: Fiber Basics • MFD determined by index profile & NA • Higher NA = smaller MFD, light tightly confined in core • Lower NA = larger MFD, light spreads outs beyond the core • MFD varies with wavelength – shorter wavelengths behave more like a stream of photons and longer wavelengths have more w
Slide 16: Part I: Fiber Basics
Part I: Fiber Basics • Cutoff defines where the single mode operating window starts • Bend-edge defines where operating bandwidth ends. 5 4.5 Bend Loss occurs Cutoff due to light leaking 4 Peak from core when 3.5 ~1220 fiber tightly bent 3 ~1620 2.5 Fiber Is Multimode Fiber is Singlemode 2 1.5 1 0.5
Slide 17: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Doping the optical fiber with rare earth ions such as: – Ytterbium (Yb3+) – Erbium (Er3+) – Thulium (Tm3+) – Holmium (Ho3+) • The fiber becomes an active medium with gain rather than passive transmission medium. • In order for the gain to be efficient and deliver h
Slide 18: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Rare earth is doped into the core of the optical fiber along with the modifier element (Al, Ge, P, etc) • Create two waveguide regions: the core and the inner cladding – both guide light. • Inner cladding waveguide created by making lower index region outside of in
Slide 19: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Double-clad fibers increase the ability of the core to absorb light by allowing higher input pump powers enhancing interaction between active ions in the core and the pump light. Shaped cladding used to increase light-ion interaction. Standard Fiber Double-Clad Fib
Slide 20: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Each active fiber works within a specific wavelength range determined by the RE ion and the pump light is a shorter wavelength than the lasing wavelength Ho - Output Er - Output Ho - Pump 140 Er - Pump 120 Attenuation (dB/km) 100 80 Tm - Output Yb - Output Tm - Pum
Slide 21: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Unlike in crystals, the absorption and emission spectrum are very broad in Absorption, g* For a Typical doped silica fibers Nufern EDFC-980-HP Fiber • Compared with many crystal 7.0 hosts, the rare earth doping 6.0 Absorption g* Absorption, g* (dB/m) levels in fibe
Slide 22: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • The detailed pump absorption cross section and emission cross section also depend on the details of the glass composition. • Solubility of the rare earths is not high in silica and can be different for each rare earth – To increase solubility in the silica glass a
Slide 23: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • In many applications it is desirable to use a few-moded fiber with larger core diameter – Has an increased mode field for LP01 mode – Also reduces the fiber length (large core to clad ratio) – Increases energy storage in the fiber • Lower limit of RE doped, step-in
Slide 24: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Typical fiber lengths assuming 13dB pump absorption (95%) for standard Yb- doped fibers pumped at 915nm • For 975nm pumping use 3x short lengths Core/Clad 5 m 10 m 15 m 20 m 25 m 30 m diameter 130 m 24m 10m 7m 4.5m N/A N/A 0.55dB/m 1.3dB/m 1.8dB/m 2.8 dB/m 250 m N/
Slide 25: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • In order to operate these LMA fiber based lasers at >1kW, careful optimization of the different fibers along the amplifier chain is necessary – The splice loss between the active and passive fibers, can lead to failure of splices at high power and deterioration of
Slide 26: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • 1.5µm and 2µm have become important wavelengths of operation because of the need for eye-safer operating wavelengths in some cases (>1400nm) • 2µm fiber lasers based on Tm-doped Typical lasing wavelengths for Tm-fiber laser fibers are seeing significant growth 25 T
Slide 27: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Current generation of Tm-doped fibers is pumped at 790nm • Cross relaxation of excited Tm-ions in highly doped fibers leads to increased slope efficiency for ~790nm pumping compared with the quantum limit (~40%) 3H 4 Cross relaxation of adjacent Tm-ions Increasing
Slide 28: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • By optimizing the fiber composition, efficiencies of 790nm pumped Tm-fibers have steadily improved over the last 10 years • Efficiency for 790nm pumping of Tm-doped silica is now typically around 60% 28
Slide 29: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • A range of standard Tm-doped LMA fibers (10-25 m core) are available from suppliers using a pedestal core design (-P) 29
Slide 30: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • Recently interest has grown in the properties of Holmium doped silica fibers • Tuning results for Holmium doped silica shows better operation at longer wavelengths >2.1 m than Tm-fibers (A. Hemming et al, CLEO 2013) 30
Slide 31: Part II: Rare Earth Doped Fibers
Part II: Rare Earth Doped Fibers • In addition, the resonant pumping of Ho-doped fibers shows promise for power scaling to very high power levels (A. Hemming et al, CLEO 2013) 31
Slide 32: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Monolithic fiber lasers • FBGs for making lasers • Pump laser diodes • Combiners for pumping fibers • High power MOPA systems • Tm-doped fiber lasers 32
Slide 33: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • The first 1kW near single mode (M2 ~3.4) fiber laser was demonstrated in 2004 (ORC, University of Southampton) using free space laser cavity • HR mirror and 4% Fresnel reflection from the fiber endface formed the cavity Y. Jeong et al, Electron
Slide 34: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • However the use of free space optics within the laser cavity has proved unreliable at the high power levels fiber lasers now operate • Monolithic designs are now preferred using fiber Bragg gratings to form the laser cavity • Writing the gratin
Slide 35: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Photosensitive (PS) fibers were developed and optimized for the telecom industry during the 1990’s (key component in WDM systems) • Modification of these “telecom” fibers has enabled high power FBG’s for the fiber laser industry • LMA versions
Slide 36: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Typically this fiber is a different composition from the RE doped fiber (Ge doped fiber) for enhanced photosensitivity • Most common method for writing FBG is UV exposure through the side of the fiber using a phase mask • Requires stripping of
Slide 37: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Complete monolithic fiber lasers now routinely operate at >1kW output power based on LMA Yb-doped fiber and LMA FBGs spliced together • High slope efficiency and good beam quality at high power level Y. Xiao et al, Optics Express, Jan 2012 37
Slide 38: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Diode options for pumping Yb-fibers depend on the application and may be split into different categories by technology and wavelength • Single emitter based pump diodes • Typically coupled into 105/125 fiber (10-12W) • Multi-emitter packages •
Slide 39: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Pump combiner is a component that combines multiple fibers from the pump laser diodes into one output fiber (7x1 combiner for example) • The number of input fibers depends on the diameter and NA of the output fiber Typical delivery fibers for s
Slide 40: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • In order to handle kW of pump light these combiners need to be low loss • Versions carrying signal fiber are also needed for amplifiers (6+1 to 1) Co-Pump Counter- P Total 2.81 kW 2.2 kW H. Yu et al, Pump 2.8 kW 1.1 kW Photonics West 2012 Signa
Slide 41: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • These combiners are commercially available from multiple suppliers in various standard configurations • Cladding light strippers & end cap terminations are also commercially available to match the various standard LMA fibers ITF Labs Part No. F
Slide 42: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • For some applications a MOPA system (master oscillator, power amplifier) is preferred and can contain multiple amplifier stages with inter-stage isolation • Can use PM fiber for a linear polarized output and deliver narrow linewidth output bett
Slide 43: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Co-pumped MOPA operating at ~1.5kW using LMA-YDF fiber and delivering single mode output with no sign of multimode instability (MMI) Co-Pumped MOPA 20 FUD-9049/Lot#: 10-A1501-10-3B-09-01 10m/1st ~4.5m in 100mm Coil Abs Length ~17dB MMC: PC-022
Slide 44: Part III: Example fiber laser and amplifier platforms
Part III: Example fiber laser and amplifier platforms • Tm-doped fibers have operated at 1kW output power, pumped at 790nm • Delivering good beam quality from standard LMA Tm- doped fiber in 2-stage MOPA system 6- Pumps 790nm 6-Pumps 790nm Active Fiber-Tm Active Fiber-Tm doped doped 1200 1000 Signal
Slide 45: Part IV: Future Trends and Conclusion
Part IV: Future Trends and Conclusion • Further improvements in Yb-doped LMA fibers for higher output power without multimode instability (MMI) & maintaining beam quality • New fiber technologies continue to be developed with advances in fibers aimed at higher performance lasers • In general the goa
Slide 46: Part IV: Future Trends and Conclusion
Part IV: Future Trends and Conclusion • Fiber laser industry has benefited from standardization of Yb-doped fibers and associated components over the last 10 years – This has helped drive down the costs of the technology – Made it easier for new entrants into the fiber laser market without the need
Slide 47: Part IV: Conclusion and Q&A
Part IV: Conclusion and Q&A • Thank you for your attention • Any questions? 47