Double-Clad Erbium-Ytterbium Co-Doped Fiber Laser

Colin Diehl & Connor Pogue

Fiber Lasers

Advantages• Compact• Reliable• High optical quality• High output power• Convenient

Applications• Telecommunications• Materials Processing• Medicine• Directed Energy Weapons

Active fiber doped with rare-earth elements pumped by a laser diode

Single-Mode Fiber6 µm core / 125 µm cladding

+ High Beam Quality+ Low Propagation Loss- Lower Power Pumping- Expensive Pumping

Multimode Fiber50 µm core / 125 µm cladding

+ Higher Power Pumping+ Inexpensive Pumping- Poor Beam Quality- High Propagation Loss

Double-Clad Fiber Laser light propagates in single-mode core Pump light propagates in inner cladding

Erbium-Ytterbium Co-Doped Fiber

Output Power

RP Fiber Power Simulated fiber ring laser using SM-EYDF-6/125-HE

fiber to optimize active fiber length Simulated with uniform pump intensity profile

RP Fiber Power: Output Power

RP: Power vs. Position

RP: Active Fiber Length

RP: Power vs. Position

RP: Output Power with 975 nm Pump

RP: Power vs. Position with 975 nm Pump

RP: Active Fiber Length with 975 nm Pump

Implementing Single Longitudinal Mode

Multiple longitudinal modes due to long cavity • ~ 270,000 modes without FBG• ~ 430 modes with FBG

Applied 10 mm Fabry-Perot etalon into cavity• Aligned for 75% transmission• Limited to a few cavity modes • Reduced output power from 1.1 W to 250 mW

Multi-Ring Cavity

Small ring cavities within larger ring cavity Effective FSR equal to least common multiple of

FSR of each cavity Polarization must match when cavities combine Free space polarizer with λ/2 plate in fiber bench

• Power reduced from 800 mW to 250 mW In-fiber polarizer with polarization controller

Determining Single Longitudinal Mode

Fabry-Perot Cavity• Periodic single peak signal

Self-Heterodyne Linewidth Measurement• Narrow linewidth

Self-Heterodyne Linewidth Measurement

Single Cavity Laser 900 mW output FWHM = 0.1 nm = 12.5 GHz 7.63 mm coherence length

With One Internal Cavity 351 mW output FWHM = 1.92 fm = 240 kHz 398 m coherence length

With Two Internal Cavities 383 mW output FWHM = 385 am = 48 kHz 1.99 km coherence length

With Three Internal Cavities 302 mW output FWHM = 88.2 am = 11 kHz 8.68 km coherence length

Multi-Ring Cavity Power

Linewidth

Conclusion

Implemented single longitudinal mode operation through multi-ring cavity design

Constructed self-heterodyne interferometer to measure linewidth with resolution of ~10 kHz

Constructed single-mode fiber laser delivering 302 mW at 1550 nm with linewidth of 88.2 am