Fiber Lasers: Fundamentals and Applications

Transcription

1 Fiber Lasers: Fundamentals and Applications Lecture 4 V R Supradeepa Center for Nano Science and Engineering (CeNSE) Indian Institute of Science Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 1

2 Source Material New review paper: V R Supradeepa, Yan Feng, Jeffrey W. Nicholson, Raman Fiber Lasers, IOP Journal of Optics (2017). Please refer to the paper for exact references to material shown in this lecture Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 2

3 Technology The rare-earth doped core absorbs and reemits the pump light into a high brightness beam (multimode to single mode conversion) Highly multimode pump light Single mode laser light From encyclopedia of laser physics and technology Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 3

4 Current Technology of High Power Fiber Lasers Raman fiber lasers Power availability: Limited primarily to Ytterbium doped lasers Wide white-spaces: No laser technology available Wide variety of technologies: Every wavelength needs a different laser Raman laser only scalable technology Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 4

5 1.5micron band lasers Eye Safety Atmospheric Transparency From wikipedia Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 5

6 High power 1.5micron lasers Cladding pumped Er:Yb doped fiber lasers Pumped using 975nm diodes Spurious lasing by Yb ions Low efficiency < 25% Resonantly Cladding pumped Yb free Er doped fiber using 15xx pump diodes Expensive Long wavelength operation Reduced Beam quality Raman lasers offer a more efficient, cost-effective and scalable solution.

7 Technology of (Cascaded) Raman Fiber Lasers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

8 Raman gain coeff (W -1 km -1 ) Principle of Raman Lasers 3 Raman gain for cascaded Raman resonator fiber (CRRF) 2 1 Accessible high power lasers frequency shift (THz) Inaccessible wavelengths Raman shifting Wavelength (micron) Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 8

9 Conventional implementation of Cascaded Raman Fiber Lasers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

10 Raman Laser with one wavelength shift Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 10

11 Light at 1117nm Cascaded Raman laser (more than one wavelength shift) Light at 1480nm v Raman conversion achieved with nested cavities spaced at the Stokes shifts Salient Points First Proposed in 1993 (1 W level), scaled to 40W in 2007 Efficiency (best efficiencies achieved for a 5 th order cascaded system - ~30% (1117 to 1480, Quantum limited efficiency ~75%) Further Scattering of Signal Unstable at higher powers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc 11

12 Systems and components of Raman Lasers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

13 High Power Rare-earth doped fiber laser Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

14 Raman Wavelength conversion Fibers for Raman Wavelength conversion Fiber Bragg gratings for wavelength conversion Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

15 Raman Wavelength conversion Fibers for Raman Wavelength conversion Fiber Bragg gratings for wavelength conversion Components for isolation of Raman cavity from rare-earth doped fiber laser Long period gratings Tilted fiber Bragg gratings Wavelength division multiplexers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

16 Design of Raman Fiber Lasers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

17 Numerical Modeling of Raman Fiber Lasers dp k b,f dz = ±α k P b,f g R j, k k P f j j + P b j P b,f υ k g R k, j k ± P f j j + P b b,f j P k A j<k eff υ j>k j A eff g R j, k hυ j k Δυ(j) P f j + P b υ k g R k, j b,f j ± hυ j j Δυ(j)P j A eff υ j A eff j<k j>k P k f 0 = R k f P k b 0, P k b L = R k b P k f L R 1 f = 0, R n b = R oc P out = (1 R oc )P f n (L) η = P out = (1 R oc)p f n (L) P in P f 1 (0) Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc

18 Optimization of Resonator Components Fiber Length Grating reflectivities Grating Bandwidths Splice losses between various fibers Nonlinear Photonics and High Power Lasers Laboratory, CeNSE, IISc