Self-starting Mode-locking Research Articles

Effect of gain media characteristics on the formation of soliton molecules in fiber laser

Erbium doped fiber and Er3+/Yb3+ codoped phosphate glass fiber are used as the laser media, respectively, to achieve self-started mode-locking based on nonlinear polarization rotation. It is found that the formation of the soliton molecule is the popular phenomenon in fiber laser. The laser media with high gain coefficient and short length is benefit of the formation of the soliton molecule at fundamental repetition rate and will generate evident soliton molecule pulse profile with strong accompanied structures. The achievement of soliton molecule owes to the partial operation of polarization filter effect in laser cavity due to the weak nonlinear polarization rotation in gain media with high gain coefficient and short length.

All-fiber ultrashort Yb3+ doped fiber laser self-started by spectral filter

Theory of the passively mode-locked Yb3+ doped fiber ring laser self-starting through spectral filter is presented. The all-fiber Yb3+ doped fiber ring laser generating ultrashort pulses are designed and fabricated. High concentration Yb3+ doped fiber was employed as gain medium, which was pumped by a 980 nm diode laser. In the all-normal-dispersion cavity, a spectral filter was spliced to reduce the large emission peak at 1030 nm of Yb3+ ion and to generate an additional pulse shaping through spectral filtering of chirped pulse. Self-starting and stable mode-locking centered at 1053 nm was achieved by nonlinear polarization evolution along with spectral filtering from the filter. The mode-locking threshold was 300 mW, with the slope efficiency of 18.3%, the maximum output power was 53.07 mW, corresponding to the maximum pulse energy of 3.2 nJ. The center wavelength of the mode-locked pulse was 1053.6 nm, with 3 dB bandwidth of 10.84 nm at the repetition rate of 16.45 MHz. The picosecond mode-locked pulse can be dechirped to 188 fs using grating pair outside the cavity.

Mode locked multi-core photonic crystal fiber laser

A mode locked fiber laser based on Yb-doped large mode area photonic crystal fiber operating in the all-normal dispersion regime is experimentally studied. The eighteen cores of the gain fiber are arranged in array-type geometry with an equivalent mode diameter of about 52 μm. A sigma laser cavity is used without using any elements for dispersion compensation. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser directly produces 4.92 ps chirped pulses at a 44.68 MHz repetition rate for an average power of 3.3 W corresponding to a pulse energy of 74 nJ. The pulses are compressed to 780 fs with a grating pair outside the cavity.

Mode-Locking Using $\chi ^{(2)}$ Waveguide Arrays

It is demonstrated theoretically that the use of a χ(2) waveguide array in conjunction with a fiber laser cavity is capable of producing self-starting, robust, and stable mode-locking. The χ(2) waveguide array takes advantage of several key effects to enhance the mode-locking stability and effective saturable absorption, including the nonlinear mode-coupling in the waveguide array and the phase-sensitivity of the amplifier. Specifically, the mode-locked pulse phase is locked and stabilized by the pump field upon successive cavity round-trips. The combined advantages of these mode-locking conditions make the χ(2) waveguide-array-based mode-locked laser a technologically attractive photonic device warranting further experimental and theoretical invesgation.

Passive mode-locking of a diode-pumped Nd:YVO_4 laser by intracavity SHG in PPKTP

Experimental results on passive mode-locking of a Nd:YVO(4) laser using intracavity frequency doubling in periodically poled KTP (PPKTP) crystal are reported. Both, negative cascaded chi((2)) lensing and frequency doubling nonlinear mirror (FDNLM) are exploited for the laser mode-locking. The FDNLM based on intensity dependent reflection in the laser cavity ensures self-starting and self-sustaining mode-locking while the cascaded chi((2)) lens process contributes to substantial pulse shortening. This hybrid technique enables generation of stable trains of pulses at high-average output power with several picoseconds pulse width. The pulse repetition rate of the laser is 117 MHz with average output power ranging from 0.5 to 3.1 W and pulse duration from 2.9 to 5.2 ps.

Experimental research on high-energy dissipative solitons in an erbium-doped fiber laser

We have employed a nonlinear polarization rotation technique to realize the self-starting passive mode-locking in an erbium-doped fiber laser with positive dispersion. The laser can emit high-energy dissipative solitons without wave-breaking. The pulse-shaping mechanism, which is qualitatively distinct from the conservative solitons in negative dispersion cavity, may originate from the laser gain, loss, NPR, cavity dispersion, or other fiber nonlinearity effects. To our best knowledge, it is the first report on the experimental observations for high-energy wave-breaking-free dissipative solitons forming in a fiber laser with ultra-large net-normal cavity dispersion. The spectrum of these strongly chirped pulses covers the wavelength range from 1530 to 1660 nm. The FWHM width of the spectrum can be as large as 42 nm, and the maximal total energy of a single-pulse is estimated to be ~34.4 nJ.

Ultrashort pulses supported by SESAM absorber

We have developed a mode-locked diode-pumped Yb:KYW laser generating nearly band-width limited pulses as short as 101 fs. At 1.1 W absorbed power and 3% transmission output coupler, the laser delivers 150 mW for pulse duration of 110 fs, what corresponds to an efficiency of 14%. It was achieved using semiconductor saturable absorber mirror (SESAM) grown by molecular beam epitaxy. SESAM contains a distributed Bragg reflector (DBR) completed by single quantum well (SQW) playing role of an absorbing layer. The absorbers were crystallized in accordance with the predicted structure parameters under optimised growth conditions. The resonant-like type of structures ensured relatively high enhancement factor due to antireflective properties of SiO2 capping material and a wavelength independence of a group delay dispersion. The optimisation of the growth conditions of both an absorbing layer and DBR structure were widely carried out. Optical reflectance and high resolution X-ray diffraction have been used for characterization and verification of DBR structures. It results in reduction of the nonsaturable absorption in SESAM and self-starting mode-locking of the ultrashort pulses.

LT-InGaAs Layer Grown for Near Surface SESAM Application

We have developed a mode-locked diode-pumped Yb:KYW laser generating nearly band-width limited pulses as short as 101 fs using semiconductor saturable absorber mirror (SESAM). With the nonsaturable losses of 1.94% and the modulation depth of 1.48% the self-starting and stable mode-locking was observed. The nonsaturable losses are mainly related to AsGa-CB transitions in InGaAs QW absorbing layer and low temperature defects. Low temperature defects are eliminated by using higher growth temperature and lower ratio of group V to group III beam equivalent pressure than typically used. The InGaAs layer was grown by molecular beam epitaxy at the temperature as high as 420 ◦C, under the V/III ratio as low as 10. No annealing was performed.

High-energy femtosecond pulses from a dissipative soliton fiber laser

We report the generation of sub-150 fs pulses from a passively mode-locked laser featuring a large-mode-area microstructure fiber. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser generates 63 nJ chirped pulses at 22 MHz repetition rate for an average power of 1.4 W. The 2.2 ps output pulses are compressed outside the cavity to 150 fs.

Mode-locked Yb-doped Bragg fiber laser

We report on a mode-locked fiber laser featuring an Yb-doped large-mode-area Bragg fiber and exploiting dissipative-soliton pulse shaping. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser generates 30 nJ chirped pulses at 17 MHz repetition rate for an average power of 510 mW. The 3.2 ps output pulses are compressed outside the cavity to 440 fs.

Femtosecond Er doped fiber laser using high modulation depth SESAM based on metal/dielectric hybrid mirror

We proposed and fabricated a metal/dielectric mirror based high modulation depth semiconductor saturable absorber mirror (SESAM), for ease of the growth restrictions. Using such a SESAM, we obtained self-starting mode-locking in a ring cavity fiber laser, which produced 102 fs pulses at a repetition rate of 36.2 MHz.

Passive mode-locking of a Tm-doped bulk laser near 2 μm using a carbon nanotube saturable absorber

Stable and self-starting mode-locking of a Tm:KLu(WO(4))(2) crystal laser is demonstrated using a transmission-type single-walled carbon nanotube (SWCNT) based saturable absorber (SA). These experiments in the 2 microm regime utilize the E11 transition of the SWCNTs for nonlinear saturable absorption. The recovery time of the SWCNT-SA is measured by pump-probe measurements as approximately 1.2 ps. The mode-locked laser delivers approximately 10 ps pulses near 1.95 microm with a maximum output power of up to 240 mW at 126 MHz repetition rate.

Mode-Locked Bi-Doped All-Fiber Laser With Chirped Fiber Bragg Grating

We demonstrate a bi-doped fiber laser with dispersion compensation provided by a linearly chirped fiber Bragg grating. Reliable self-starting mode-locking was achieved by using an InGaAsN semiconductor saturable absorber mirror. The all-fiber laser generated short optical pulses with a duration of 1.9 ps at ~ 1165 nm. The large anomalous dispersion of the fiber grating ensured operation in the soliton pulse regime. This in turn enabled us to increase the repetition rate of the output pulse train up to 100.6 MHz via harmonic mode-locking.

Environmentally Stable, High Pulse Energy Yb-Doped Large-Mode-Area Photonic Crystal Fiber Laser Operating in the Soliton-Like Regime

A high pulse energy passively mode-locking fiber laser operating in the soliton-like regime is demonstrated. The laser is based on a linear cavity design. A segment of Yb-doped single-polarization large-mode-area photonic crystal fiber serves as the gain medium, and the self-starting mode-locking is achieved by a high contrast semiconductor saturable absorber mirror. The laser directly generates 600-fs pulses with 900 mW of average power at a repetition rate of 47.3 MHz, corresponding to a single pulse energy of 19 nJ. Furthermore, this fiber laser is directly used for pumping ZnTe to generate broadband terahertz radiation, resulting in a compact terahertz source.

High precision optical characterization of semiconductor saturable absorber mirrors

Semiconductor saturable absorber mirrors (SESAMs) have become a key element of many ultrafast laser sources, enabling passively modelocked lasers with >100 GHz repetition rate or with >10 microJ pulse energy. Precise knowledge of the nonlinear optical reflectivity is required to optimize the SESAMs for self-starting passive modelocking at record high repetition rates or pulse energies. In this article, we discuss a new method for wide dynamic range nonlinear reflectivity measurements. We achieve a higher accuracy (<0.05%) with a simpler and more cost-efficient measurement scheme compared with previous measurement systems. The method can easily be implemented for arbitrary wavelength regions and fluence ranges.

Experimental investigation of self-starting operation in a F8L based on a symmetrical NOLM

We experimentally analyze the self-starting operation of a figure-eight mode-locked fiber laser. The design is based on a power-balanced nonlinear optical loop mirror (NOLM) with highly twisted low-birefringence fiber and a quarter-wave (QW) retarder in the loop. The NOLM operates by nonlinear polarization rotation. Self-starting mode-locking requires a careful adjustment of the NOLM low-power transmission, which is easily realized with our setup by adjusting the angle of the QW retarder. The laser is capable of generating ∼20ps pulses at the fundamental repetition frequency of 0.78MHz.

High-power self-mode-locked Yb:Y_2O_3 ceramic laser

We have experimentally demonstrated a high-power self-mode-locked Yb:Y(2)O(3) ceramic laser. Without any additional active or passive element in the cavity, self-started cw mode-locking was achieved. The maximum output power was as high as 2.7 W with a pulse duration of 1.1 ps. Numerical studies show that the diffraction loss induced by thermal lens aberration, in combination with the Kerr self-focusing effect in the gain medium, results in the mode locking of the laser. To our knowledge, this is the first self-mode-locked ceramic laser.

Self-started unidirectional operation of a fibre ring soliton laser without an isolator

We demonstrate self-started mode-locking in an erbium-doped fibre ring laser by using the nonlinear polarization rotation mode-locking technique but without an isolator in cavity. We show that, due to the intrinsic effective nonlinearity discrimination of the mode-locked pulse propagating along different cavity directions, the soliton operation of the laser is always unidirectional, and its features have no difference to that of unidirectional lasers with an isolator in cavity.

Fiber laser mode-locked with a semiconductor saturable absorber etalon operating in transmission

We demonstrate a ring cavity ytterbium fiber laser mode-locked with a semiconductor saturable absorber used in transmission. The resonant cavity-enhanced nonlinear response corresponding to the low-loss transmission state enables a robust self-starting mode-locking. Such a transfer function is opposite to that of the resonant absorber operating in the reflection mode, where the highest modulation depth matches the high-loss state. The device ensures ultrashort pulse operation with the wavelength self-adjusted to the optimal value corresponding to the low-loss state of the laser cavity. When using a saturable absorber etalon in transmission mode, the mode-locking mechanism is also highly tolerant to the total cavity dispersion

Wavelength tunable stretched-pulse mode-locked all-fiber erbium ring laser with single polarization fiber

A wavelength tunable stretched-pulse mode-locked all-fiber ring laser using single polarization fiber (SPF) was demonstrated. In this laser, a segment of SPF was used simultaneously as a polarizer and a tunable filter in the laser cavity. Self-starting mode-locking with femtosecond output pulses was demonstrated. A wavelength tuning of ~20nm was achieved by bending the SPF with different radii.