All-normal Dispersion Cavity Research Articles

All-polarization-maintaining, all-normal-dispersion mode-locked fiber laser with spectral filtering in a nonlinear optical loop mirror.

The spectral filtering effect is essential to dissipative dynamics in an all-normal-dispersion (ANDi) mode-locked fiber laser. In this study, we numerically and experimentally demonstrate the spectral filtering process of a nonlinear optical loop mirror (NOLM). Taking advantage of the 40/60 NOLM's spectral filtering ability, we designed a novel all-polarization-maintaining ANDi mode-locked fiber laser without using a separate spectral filter. The NOLM functions as an artificial saturable absorber and a spectral filter in an ANDi cavity. During mode locking, we observed that the NOLM decreased the spectral width of the pulse from 5.46 to 4.38 nm. The fiber laser generated 509-fs compressed pulses at the repetition rate of 13.4 MHz. Our work provides a promising novel and compact ANDi fiber laser for ultrafast photonic applications.

Generation of noise-like pulse and dissipative soliton pair in actively mode-locked fiber laser

This paper reports on the experimental observation of a stable single dissipative soliton, a noise-like pulse, and a dissipative soliton pair in an actively mode-locked fiber laser within an all-normal dispersion cavity. The laser consists of fully polarization-maintaining fibers and components, providing a linear output polarization state. The full width at half maximum of the pulse is measured to be 25.3 ps and the output pulse energy after the gain fiber can reach 1.07 nJ. By shifting the direct current (DC) bias voltage of the modulator to Vπ, the spectral width increased from 6.3 nm to 7.7 nm. Under the same pumping power of 246 mW, the single dissipative soliton and the pair can exchange with each other by adjusting the DC voltage of the Mach–Zehnder intensity modulator.

Discrete Similariton and Dissipative Soliton Modelocking for Energy Scaling Ultrafast Thin-Disk Laser Oscillators

Since their first demonstration, modelocked thin-disk lasers have consistently surpassed other modelocked oscillator technologies in terms of achievable pulse energy and average power by several orders of magnitude. Surprisingly, state-of-the-art results using this technology have so far only been achieved in modelocking regimes where soliton pulse shaping is dominant (i.e., soliton modelocking with semiconductor saturable absorber mirrors or Kerr lens modelocking), in which only small nonlinear phase shifts are tolerable, ultimately limiting pulse energy scaling. Inspired by the staggering success of novel modelocking regimes applied to overcome these limitations in modelocked fiber lasers, namely the similariton (self-similarly evolving pulses) and dissipative soliton regimes, here, we explore these nonlinearity-resistant regimes for the next generation of high-energy modelocked thin-disk lasers, whereby millijoule pulse energies appear to be realistic targets. In this goal, we propose two possible implementations. The first is based on a passive multipass cell and designed to support dissipative solitons in an all-normal dispersion cavity. The second incorporates an active multipass cell and is designed to support similaritons. Our numerical investigations indicate that this is a very promising path to increase the pulse energy achievable directly from modelocked oscillators toward the millijoule level while additionally simplifying their implementation by eliminating the need for operation in cumbersome vacuum chambers.

Dissipative soliton and synchronously dual-wavelength mode-locking Yb:YSO lasers.

We experimentally demonstrate the dissipative soliton mode-locking operation of a Yb:YSO laser by using an all-normal dispersion cavity. Strongly chirped pulses are obtained with pulse duration of 9.3 ps at a repetition rate of 113.4 MHz. The central wavelength is 1082 nm with 3.1 nm FWHM bandwidth. A dual-wavelength synchronously mode-locking operation at central wavelengths of 1059.2 nm and 1082.2 nm is also reported. Stable mode-locked pulses are achieved with pulse duration of 10 ps and total average output power of 164 mW. Periodic ultrashort beat pulses with pulse duration of 169 fs at an ultrahigh repetition rate of 1.4 THz can be distinctly observed from the measured autocorrelation trace. To our knowledge, this is the first demonstration of dual-wavelength synchronously mode-locking operation from a Yb:YSO laser.

Dark pulses and harmonic mode locking in graphene-based passively mode-locked Yb3+-doped fiber laser with all-normal dispersion cavity

Graphene has recently been proposed as an attractive material in saturable absorption (SA) applications due to its broad operation range, low saturation power, easy fabrication, high reliability, and quick recovery time. In this paper, we use laser-induced deposition to prepare graphene saturable absorber, and apply it in a mode-locked all-normal-dispersion (ANDi) Yb-doped fiber laser to experimentally investigate different operational states. By adjusting a polarization controller (PC) and the pump power, bright pulses, dark-bright pulse pairs and their second-harmonic pulses, as well as dark pulses and their second, third-harmonic pulses can all be obeserved. In particular, it is the first time to our knowledge to report on the formation of dark-bright pulse pairs, dark pulses and their harmonic mode locking (HML) counterparts in graphene-based passively mode-locked Yb-doped fiber laser with ANDi cavity. Accoding to simulation, the main causes of these pulses are different cavity nonlinear effects which result from the fiber mode-lock members including graphene. Bright pulses, dark pulses and dark-bright pulse pairs are determined both by the laser structure and their own initial signals. Bright pulse harmonic generation is ascribed to the noise gains which form new components. However, it is found that the multiple-time repetition rate of dark pulses is a result of square pulse splitting of each component. This consequence may be of potential application in new type mode-locked fiber lasers.

Dark soliton fiber lasers.

Dark soliton formation and soliton dynamics in all-normal dispersion cavity fiber ring lasers without an anti-saturable absorber in cavity is studied both theoretically and numerically. It is shown that under suitable conditions the dark solitons formed could be described by the nonlinear Schrödinger equation. The dark soliton formation in an all-normal-dispersion cavity erbium-doped fiber ring laser without an anti-saturable absorber in cavity is first experimentally demonstrated. Individual dark solitons are experimentally identified. Excellent agreement between theory and experiment is observed.

Tunable Active Harmonic Mode-Locking Yb-Doped Fiber Laser With All-Normal Dispersion

We report tunable active harmonic mode-locking of a dissipative soliton ytterbium-doped fiber laser based on a high-speed intensity modulator with all-normal-dispersion (ANDi) cavity. Adjusting the working frequency and the data length of radio driving signals for the dissipative soliton pulses shaping, the repetition rates can be facilely and accurately scalable from 20.33 to 609.84 MHz corresponding to the harmonic order from the fundamental rate to 30th, which is higher than the passive harmonic mode-locking (HML) fiber laser in an all-fiber and ANDi cavity. The cavity supermode-suppression ratio is suppressed up to 50 dB, and the signal-to-noise ratio is better than 57 dB at the 30th HML.

Characteristics of a low repetition rate passively mode-locked Yb-doped fiber laser in an all-normal dispersion cavity

The lasing characteristics of a 365 kHz low repetition rate Yb-doped fiber laser operated in an all-normal dispersion cavity and mode-locked by the nonlinear polarization rotation mechanism are investigated in detail. As the pump power increases, the laser exhibits two transition routes when evolved from the continuous-wave (CW) state to the mode-locked (ML) state. In one evolution route the Q-switched mode-locked (QML) state is sandwiched between the CW and ML states, whereas in the other more interesting evolution route the hysteresis transition between the CW and ML states is found for the first time. Under the mode-locking operation, the laser generates sub-nanosecond pulses with linear dependence of pulsewidth on bandwidth under different pump powers, indicating the presence of giant linear chirps on the laser output pulses.

Switchable Dual-Wavelength and Passively Mode-Locked All-Normal-Dispersion Yb-Doped Fiber Lasers

A switchable dual-wavelength and passively mode- locked ytterbium-doped fiber laser (YDFL) in the all-normal-dispersion (ANDi) regime is reported and demonstrated for the first time. Using a phase-shifted long-period fiber grating (PS-LPFG) as an all-fiber format spectral filter in the laser cavity, a stable and switchable dual-wavelength mode-locked operation is achieved by nonlinear polarization evolution (NPE). The maximum output energy of the dual-wavelength pulse is 25.76 nJ at a repetition rate of 2.499 MHz. It opens a new possibility to achieve switchable multiwavelength and mode-locked laser output in the ANDi cavity in an all-fiber format.