Self-optimizing additive pulse mode-locked fiber laser: wavelength tuning and selective operation in continuous-wave or mode-locked regime

Transcription

1 Self-optimizing additive pulse mode-locked fiber laser: wavelength tuning and selective operation in continuous-wave or mode-locked regime Manuel Ryser, Christoph Bacher, Christoph Lätt, Alexander Heidt, Philippe Raisin, Thomas Feurer, Valerio Romano Institute of Applied Physics, University of Bern, Switzerland January 31, 2018 Paper No Conference 10512: Fiber Lasers XV: Technology and Systems Session: Mode-locked Fiber Oscillators

2 Motivation and Vision From todays femtosecond fiber-laser systems... mode-locking regime often lost due to temperature drift or mechanical disturbance no tuning or critical parameters possible long term stable operation only in lab-like conditions...towards self-optimizing fiber laser systems. online-monitoring (optical spectrum, RF spectrum etc.) electronic tuning of fiber-optic components (filters, couplers, polarization controllers) global opimization algorithms for efficient self-optimization continuous supervision and fine adjustments

3 All-normal Dispersion Fiber Ring Laser total cavity fiber length approx m CONS not long term stable alignment of three waveplates not trivial PRO operational parameter can be varied experimentally

4 high-resolution mapping procedure servo: 180 travel range, 8bit resolution 180 /256 steps = 0.7 stepsize; 256^3 = 16'777'216 servo positions 180 /64 steps = 2.8 stepsize; 64^3 = 262'144 servo positions

5 Data Evaluation detector [V] oscilloscope trace optical spectrum radio-frequency spectrum time [µs] number of pulses in cavity: harmonic mode-locking? T 1.5 intensity [db] FWHM FW20dB λ max λ c wavelength [nm] 0dB -3dB -20dB by inverse fourier transform estimate of transform limited pulse duration ττ pppppppppp amplitude [dbm] P A 20 pulse energy jitter f 1 f 2 f 3 f 4 f 5 P B 40 1/T RF frequency [MHz] EE EE P C 100 PP CC PP AA 1 temporal pulse jitter tt TT PP BB PPAA nn nn D. Von der Linde, Appl. Phys. B 39, (1986)

6 Data Evaluation detector [V] oscilloscope trace optical spectrum radio-frequency spectrum 0.0 T time [µs] 1.5 intensity [db] FWHM FW20dB λ max λ c wavelength [nm] 0dB -3dB -20dB amplitude [dbm] P A f 1 f 2 f 3 f 4 f 5 P B /T RF frequency [MHz] P C 100 detector [V] T 1.0 time [µs] 1.5 intensity [db] FWHM FW20dB λ c λ max wavelength [nm] 0dB -3dB -20dB 1050 amplitude [dbm] P A 1/T f 1 f 2 f 3 f 4 f 5 P C RF frequency [MHz]

7 High-resolution maps map of wavelength λλ cc tunable briefringent filter [1] map of pulse energy jitter log EE EE log PP CC PP AA 1 tunable saturable absorber [2] [1] Humphrey, P. and Bowers, J. (1993). [2] Haus, H., Ippen, E., and Tamura, K. (1994).

8 Histogram of pulse energy jitter - operation modes double line CW 13.5 THz 1.4 THz mode-locked RAMAN single line CW

9 map of mode-locked operation mode EE EE < 0.01 color coded with wavelength clusters with mode-locked areas at different wavelengths each cluster covers approx. 20 nm wavelength tunable with waveplates overall tunability approx. 55 nm

10 map of continuous-wave operation mode EE EE = color coded with wavelength band-like structure each band covers approx. 20 nm wavelength tunable with waveplates overall tunability approx. 55 nm

11 Self-optimization with genetic algorithm

12 Single objective genetic algorithm objective: pulse energy jitter operation mode at "best" setting: optical spectrum RF spectrum population size of 50 individuals algorithm converges after approx. 35 generations 50*35 = 1'750 servo positions to be evaluated until convergence (16'777'216 servo positions for full 3D scan --> 0.01%)

13 Multi-objective genetic algorithm optical spectrum RF spectrum population size optical of 50 spectrum individuals optical spectrum algorithm converges after approx. 284 generations 50*284 = 14'200 servo positions to be evaluated until convergence (16'777'216 servo positions for full 3D scan --> 0.08%) RF spectrum RF spectrum

14 Summary & Outlook Experimental Setup: automated all-normal dispersion additive pulse mode-locked fiber laser High-resolution three dimensional maps: pulse-energy jitter: allows to discriminate between different operating regimes lasing wavelength: tunable over more than 55nm for CW and mode-locked operation Self-optimization by genetic-algorithm towards desired operating state: single-objective: mode-locked multi-objective: mode-locked at desired wavelength Outlook map of further parameters: pulse duration, timing jitter, harmonic mode-locking include these parameters into multi-objective optimization by genetic algorithm include pump power into optimization