1. Double-Clad Erbium-Ytterbium Co-Doped Fiber Laser Colin Diehl & Connor Pogue

2. 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

3. Single-Mode Fiber 6 µm core / 125 µm cladding + High Beam Quality + Low Propagation Loss - Lower Power Pumping - Expensive Pumping Multimode Fiber 50 µm core / 125 µm cladding + Higher Power Pumping + Inexpensive Pumping - Poor Beam Quality - High Propagation Loss

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

5. Erbium-Ytterbium Co-Doped Fiber

7. Output Power

8. 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

9. RP Fiber Power: Output Power

10. RP: Power vs. Position

11. RP: Active Fiber Length

12. RP: Power vs. Position

13. RP: Output Power with 975 nm Pump

14. RP: Power vs. Position with 975 nm Pump

15. RP: Active Fiber Length with 975 nm Pump

16. 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

17. 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

18. Determining Single Longitudinal Mode Fabry-Perot Cavity Periodic single peak signal Self-Heterodyne Linewidth Measurement Narrow linewidth

19. Self-Heterodyne Linewidth Measurement

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

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

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

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

25. Multi-Ring Cavity Power

26. Linewidth

27. 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