Ultrafast lasers are enabling precision machining of a wide variety of materials. However, the optimal laser parameters for proper material processing can differ greatly from one material to another. In order to cut high aspect-ratio features at high processing speeds the laser parameters such as pulse energy, repetition rate, and cutting speed need to be optimized. In particular, a shorter pulse duration plays an important role in reducing the thermal damage in the Heat-Affected Zones. In this paper we present a novel ps fiber laser whose electronically tunable parameters aim to facilitate the search for optimal processing parameters. The 20W 1064nm Yb fiber laser is based on a Master Oscillator Power Amplifier (MOPA) architecture with a repetition rate that can be tuned continuously from 120kHz to 120MHz. More importantly, the integration of three different pulse generators enables the pulse duration to be switched from 25ps to 50ps, or to any value within the 55ps to 2000ps range. By reducing the pulse duration from the ns-regime down to 25ps, the laser approaches the transition from the thermal processing regime to the ablation regime of most materials. Moreover, in this paper we demonstrate the synchronization of the pulses from two such MOPA lasers. This enables more elaborate multipulse processing schemes where the pulses of each laser can be set to different parameter values, such as an initial etching pulse followed by a thermal annealing pulse. It should be noted that all the laser parameters are controlled electronically with no moving parts, including the synchronization.
Mid-infrared lasers find interesting applications in laser-based countermeasure technologies, remote sensing,
maritime/terrestrial awareness and so on. However, the development of laser sources in this spectral region is limited.
We present here an alternative solution to the mid-infrared laser which is based on difference-frequency generation
(DFG) in a nonlinear crystal pumped by synchronized and tunable near-infrared fiber lasers that are commercially
available. This idea is not new and has been explored by other groups, but the latest innovations in near-infrared fiber
lasers have enabled the creation of fast-scanning picosecond fiber lasers. One such picosecond system is the
synchronized programmable laser from Genia Photonics that can combine two picosecond fiber laser systems in which
both output pulses are synchronized at the DFG crystal. The first laser was continuously tunable from 1525 nm to 1600
nm and one million different wavelengths can be scanned within one second. For the second fiber laser, its wavelength
was fixed at 1080 nm. In principle, the DFG in a PPLN crystal could produce a tunable mid-infrared source spanning
from 3.32 μm up to 3.7 μm. Other and wider tuning ranges are possible with different choices of pump wavelengths. For
the PPLN crystal used in this work, the DFG phase-matching window for a fixed temperature was 2.6 nm wide and was
broad enough for our 25 ps pulse train having a spectral width of 0.25 nm. The quantum efficiency achieved for the DFG
was 44% at the maximum power available.
We report here the successful realization of 25 millions wavelengths per second using an SOA based PL around 1565
nm at a 75 MHz repetition rate. The laser is simply composed of an SOA, a CFBG (10 ps/nm) with a 100 nm bandwidth,
an optical circulator, an EOM (intensity modulator), and an output coupler (20%). Pulse duration is around 45 ps and
OSNR of the pulse is around 35 dB at 1565 nm without sweeping. Tunable dispersion compensating module (TDCM)
was used to compress the chirped pulse output and 10 ps pulse duration was obtained at 1548 nm. Finally 25 megawavelengths
per second was realized with under 3 pulses per wavelength and 1024 discrete wavelengths. Linear k-space
sweeping function was enabled in the swept-source OCT (SS-OCT) system through graphical user interface (GUI).
This paper presents a unique and novel picosecond laser source that offers complete tailoring of the wavelength sweep
and that benefits swept-source optical coherence tomography (SS-OCT) applications. Along with the advantages of a
fiber-based architecture, the source is a fully programmable, electronically controlled actively mode-locked laser capable
of rapidly tuning the wavelength and pulse characteristics. Furthermore, several sweep modes and configurations are
available which can be defined by range, with linear sweeps in wavelength or k-space, or by arbitrary wavelengths. The
source design is discussed and its use in SS-OCT with a prototype using a semiconductor optical amplifier as a gain
medium is illustrated.
We present a programmable picosecond fiber laser delivering a single pulse at two wavelengths, one in the C band, the
other in the L band. The difference between those wavelengths is tunable over 75 nm or up to 9.4THz. The laser thus
yield tunable synchronized wavelength ideal for the nonlinear generation of frequencies in the THz or pump-probe
experiments such as CARS/SRS in the fingerprint spectral region.
We describe theoretical and experimental investigations on the spectral and temporal control of an actively
mode-locked erbium-doped fiber laser equipped with a highly dispersive cavity. The laser design is based on a
unidirectional ring cavity in which a pair of diffraction gratings is inserted. A direct outcome of the dispersion
due to the diffraction gratings resides in the fact that the duration of a complete roundtrip in the laser cavity
becomes sensitively dependent upon laser wavelength. Tuning of laser emission is then achieved by controlling
the modulation frequency of the waveform applied to the loss modulator that produces mode-locked operation.
Such a fiber laser enables the generation of picosecond pulses with a rapid tuning over a large bandwidth. We also
incorporated a Gires-Tournois interferometer (GTI) in the laser setup in order to investigate how perturbations
such as group delay ripple affect the temporal shape of the laser pulses and their spectral content, as well as
the stability of the selected laser wavelength. Variation of pulse duration between 40 to100 picoseconds and
continuous tuning of laser wavelength will be described.
A rapidly tunable, electronically controlled, pulse duration adjustable, arbitrarily programmable wavelength, picosecond
mode-locked fiber laser is presented. The laser is tunable over 80 nm with sweeping frequency over 10 million
wavelengths per second. The user can select from a preset linear sweep in either wavelength or optical frequency (kspace)
or a custom (user-defined) sweep. Pulse duration is adjustable over tens of picoseconds with nearly Fourier
limited linewidth. The laser can be harmonically mode-locked over 1 GHz. The average power is again fully
programmable and is at least 50 mW, Watt level is possible with a high power amplifier. The output is a single mode
polarization maintaining fiber. The laser possesses several external triggers, such as one trigger per optical pulse, one
delayed trigger per optical pulse to synchronize with the experiments, one at the beginning when the laser is ready to
sweep to start the data acquisition and one for each consecutive sweep, and finally one trigger for each wavelength
change. Such a laser is so versatile that it can be used for medical imaging, material machining and nonlinear optics. It
proves also a valuable research tool since all the parameters are adjustable.
We report theoretical and experimental investigations on the spectral and temporal control of a mode-locked
fiber laser using a chirped fiber Bragg grating and a loss modulator in either a undirectionnal ring cavity or a
standing-wave cavity. The fiber laser generates picosecond pulses with a rapid tuning over a large bandwidth.
Tuning is achieved by controlling the frequency of the applied modulation waveform. The adjustement of pulse
duration between 40 - 500 ps and the rapid tuning from 1513 nm to 1588 nm are described.
We use the method of moments to calculate the propagation of an arbitrarily shaped pulse in a nonlinear
dispersive fiber. By assuming that the pulse is linearly chirped, we are able to determine analytically the
evolution of the second order moments (representing the duration, bandwidth and chirp of the pulse) along
propagation regardless of the initial pulse shape. The evolution of the moments is given by an implicit equation
and several invariants. These invariants allow an easy estimation of the different pulse parameters. The linear
chirp approximation implies that the arbitrary pulse shape remains invariant along propagation but allows to
calculate the propagation in both dispersion regimes from the same solution. The solution show an oscillatory
behavior in the anomalous dispersion regime and a monotonic behavior in the normal dispersion regime. In both
regimes the calculations are compared to numerical split-step simulations and are shown to agree for propagation
over many dispersion and nonlinear lengths.
While this method describes well the evolution of the pulse duration, bandwidth and chirp, we need to proceed
differently to find the evolution of the pulse shape. From these propagation equations for the moments, we
derive an approximate implicit solution describing the propagation of a Gaussian pulse in the normal dispersion
regime. This approximate solution describes the pulse shaping toward a parabola that the pulse undergoes
along propagation. A good agreement is found between the pulse obtained from numerically solving the implicit
equation and the split-step propagation of the same pulse. Numerically solving the implicit analytical function
describing the pulse is much faster than using purely numerical simulations, which becomes time consuming for
highly chirped pulses with large bandwidths over long propagation distances. These and other results suggest
that pulse shaping along propagation is only adequately modeled by implicit functions.