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. 10512-47 Conference 10512: Fiber Lasers XV: Technology and Systems Session: Mode-locked Fiber Oscillators
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
All-normal Dispersion Fiber Ring Laser total cavity fiber length approx. 39.5 m CONS not long term stable alignment of three waveplates not trivial PRO operational parameter can be varied experimentally
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
Data Evaluation detector [V] 1.2 1.0 0.8 0.6 0.4 0.2 oscilloscope trace optical spectrum radio-frequency spectrum 0.0 0.5 1.0 time [µs] number of pulses in cavity: harmonic mode-locking? T 1.5 intensity [db] -20-30 -40-50 -60 1000 1020 FWHM FW20dB λ max λ c 1040 1060 wavelength [nm] 0dB -3dB -20dB 1080 1100 by inverse fourier transform estimate of transform limited pulse duration ττ pppppppppp amplitude [dbm] -20-40 -60-80 0 P A 20 pulse energy jitter f 1 f 2 f 3 f 4 f 5 P B 40 1/T 60 80 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, 201-217 (1986)
Data Evaluation detector [V] 1.2 1.0 0.8 0.6 0.4 0.2 oscilloscope trace optical spectrum radio-frequency spectrum 0.0 T 0.5 1.0 time [µs] 1.5 intensity [db] -20-30 -40-50 -60 1000 1020 FWHM FW20dB λ max λ c 1040 1060 wavelength [nm] 0dB -3dB -20dB 1080 1100 amplitude [dbm] -20-40 -60-80 0 P A f 1 f 2 f 3 f 4 f 5 P B 20 40 1/T 60 80 RF frequency [MHz] P C 100 detector [V] 1.0 0.8 0.6 0.4 0.2 0.0 0.5 T 1.0 time [µs] 1.5 intensity [db] 2.0-20 -30-40 -50 1020 FWHM FW20dB λ c λ max 1030 1040 wavelength [nm] 0dB -3dB -20dB 1050 amplitude [dbm] -20-40 -60-80 0 P A 1/T f 1 f 2 f 3 f 4 f 5 P C 20 40 60 80 100 RF frequency [MHz]
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).
Histogram of pulse energy jitter - operation modes double line CW 13.5 THz 1.4 THz mode-locked RAMAN single line CW
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
map of continuous-wave operation mode EE EE = 0.1 0.11 color coded with wavelength band-like structure each band covers approx. 20 nm wavelength tunable with waveplates overall tunability approx. 55 nm
Self-optimization with genetic algorithm
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%)
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
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