Dynamic population gratings in highly doped erbium fibers

Transcription

1 Dynamic population gratings in highly doped erbium fibers Sonia Melle, Oscar G. Calderón, Z. C. Zhuo, M. A. Antón, F. Carreño Lasers, Quantum Optics and Non-linear Optics Group Complutense University of Madrid, Spain

2 Previous works Dynamic gratings recorded in Er-doped fiber amplifiers Frisken, Opt. Lett. 17, 1776 (1992) TRANSENT TUNABLE BRAGG REFLECTON GRATNG N AN EDF Long: Efficient thickness given by fiber length Narrow-band filter ~ 16 MHz Tunable: Grating wavelength controlled by the recording wavelength Transient: Grating disappear after removal of the recording waves ncident Reflected λ λ GRATNG clading core λ nduced-shift SENSORS λ Transmitted Fundamental works: Nonlinear optical properties, wave mixing (Review Stepanov, 2008) Applications: Single frequency fiber lasers (Horowitz et al. 1994, Cheng et al 1995) Tunable narrow-band filters (Frisken 1992, Feuer 1998, Havstad et al 1999) Fiber sensors, adaptive interferometers (Stepanov et al. 2004, Fan et al. 2005)

3 How to generate a dynamic population grating? Forward in Backward out Forward out Backward in Recording wavelength λ = 1536 nm 0 Λ = nterference pattern = F + B + 2 F B cos( Kz) Absorption Grating K = 2π Λ α = 1+ α 0 sat Linear absorp. coeff. Absorp. saturation SATURABLE ABSORBER

4 Motivation: Generate dynamic gratings in shorter devices by increasing ion concentration Objective Optimize the efficiency of the dynamic gratings recorded in highly doped Er fibers Fiber code Peak absorption (db/m) ons density (m -3 ) α 0 (m -1 ) Er20 20 ± x Er30 30 ± x HGHLY DOPED FBERS Er40 40 ± x Er80 80 ± x ULTRA-HGHLY DOPED FBER Manufactured by Liekki 1550nm = 6.5 ± 0.5 μm Cladding = 125 ± 2 μm Coating = 245 ± 15 μm NA =0.2 ± 0.02

5 How to characterize the dynamic grating? ncoherent waves: NO GRATNG E F ( z = 0) E B ( z = L) Coherent waves: GRATNG E F ( z = 0) E B ( z = L) The diffracted waves add in phase to the transmitted waves The grating increase the transmitted signals

6 How to characterize the dynamic grating? Coherent waves: GRATNG E F ( z = 0) E B ( z = L) Grating formation time τ g <10 ms with grating without grating Square phase modulation

7 Experimental setup: transient TWM FORWARD 1536 nm BACKWARD with grating Relative amplitude = ΔV V 0 V 0 ΔV without grating

8 Experimental results: transient TWM

9 Experimental results: transient TWM

10 Experimental results: transient TWM

11 Simulations: nterference pattern = + + m cos( ) α Kz Optical absorption 0 α = α α δα cos( Kz) sat av E F ( z = 0) E B ( z = L) δα α av Nonlinear coupled wave equations E z E z F B α av δα = EF + E 2 4 α av δα = EB EF 2 4 B Numerically solved Stepanov, J. Phys. D: Appl. Phys. 41 (2008)

12 Simulations: Quenching in the fluorescence for the more highly doped fiber Er80 nhomogeneous cooperative upconversion PAR-NDUCED QUENCHNG (PQ) Li et al, J. Mod. Opt (2008)

13 Simulations: PQ effect at high ion concentration Li et al, J. Mod. Opt (2008) Excited ion (DONOR) Excited ion (ACCEPTOR) 4 9/2 4 13/2 fast decay μs 1536 nm 4 15/2 PQ One excited ion is lost N = N + 2N T i Number of isolated ions p Number of ion pairs κ = N N p T α = α 0 (1 2κ ) 1+ sat solated ions α 0 2κ sat sat Paired ions FRACTON OF ON PARS

14 Simulations: PQ effect at high ion concentration Li et al, J. Mod. Opt (2008) Estimation of the number of ion pairs κ = 0.25

15 Conclusions Grating efficiency increases with optical density At very high ion densities (~ 6 x ions /m 3 ), cooperative upconversion processes (PQ) that occurs between closely locate erbium ions decrease the grating efficiency. Thank you for your attention!!