We experimentally demonstrate the operation of a stable harmonically mode-locked Raman fiber laser based on the nonlinear polarization rotation technique. A maximum average output power of up to 235 mW is achieved at the repetition rate of 466.2 MHz, corresponding to the 1665th order harmonic mode-locking. The temporal width of the mode-locked pulse train is 450 ps. The experimental results should shed some light on the design of wavelength versatile ultrashort lasers with high repetition rate and average output power.
We have investigated the broadband saturable absorption property of graphene–Bi2Te3 heterostructures and demonstrated their applications for stable harmonic mode-locking operation in a Yb-doped fiber laser and wavelength-tunable Q-switching operation in an Er-doped fiber laser. The modulation depth of a graphene–Bi2Te3 heterostructure saturable absorber (G-Bi2Te3-SA) is dependent on the coverage of Bi2Te3 on the graphene. By using 15%-Bi2Te3-covered G-Bi2Te3-SA with a modulation depth of 23.28% and saturable intensity of 3.32 MW/cm2, the harmonic mode-locked Yb-doped fiber laser outputs the mode-locked pulses with a pulse duration down to 189.94 ps, spectral bandwidth of 3.5 nm, and repetition rate of 79.13 MHz (21st order of the fundamental frequency). After inserting the G-Bi2Te3-SA with 85% coverage of Bi2Te3 on graphene into Er-doped fiber laser cavity, whose modulation depth and saturable intensity are about 40.79% and 12.48 MW/cm2, respectively, the wavelength-tunable Q-switched pulse with tunable wavelength range over 13.2 nm has been obtained by adjusting the intracavity fiber filter. These results suggest that the graphene–Bi2Te3 heterostructure could serve as a high nonlinear photonic device for practical applications.
We demonstrate an erbium-doped fiber laser passively mode-locked by few layers of graphene prepared by the mechanical exfoliation of the high oriented pyrolytic graphite through the Scotch-tape method. This all-fiber ring cavity delivered a pulse train with a repetition rate of 1.646 MHz and pulse duration of 1.656 ps. By continuously adjusting the laser cavity parameters, one can observe various soliton patterns, such as ordered-, chaotic-, bunched-, and harmonic-multisoliton state. This evidenced that a mode-locked fiber laser based on graphene saturable absorber indeed provided a well-controlled nonlinear optics platform for soliton dynamics study.
Based on the exact solution of the Maxwell’s equations, the group velocity dispersion characteristics of micro/nano optical fibers near 2-μm wavelength have been studied numerically. The results show that the micro/nano optical fiber has large normal dispersion near 2-μm wavelength by carefully choosing the core size. For air-clad micro/nano optical fiber with core size 900 nm, the group velocity dispersion can be up to 3318.78 ps 2 /km . By introducing a thin dielectric layer, the maximum dispersion can be adjusted by varying the thickness and refractive index of the dielectric layer.
Graphene, due to its linear energy band structure and the Pauli blocking principle, exhibits broadband optical saturable
absorption. We experimentally demonstrated the saturable absorption in graphene with different layers at 800 nm. By
performing the balanced twin-detector method, we are able to characterize the nonlinear optical property of the
as-fabricated different layer graphene samples. Under strong illumination, we find that absorption of graphene decreases
with the increase of incident power, and by fitting the experiment data with theoretical model, the saturable intensity and
the normalized modulation depth is measured to be 7.911 GW/cm2 and 10.6% in 3 layers sample and 2.77 GW/cm2 and
73.6% in monolayer sample, respectively. The experimental result shows that graphene may be a promising saturable
absorber, with the potential laser photonics applications, such as laser mode locker or Q-switcher, at 800 nm band.
We propose a simple method to fabricate graphene saturable absorber (GSA) through drop casting the graphene dispersion prepared by liquid-phase exfoliation of graphite onto quartz plate and realize the passively mode-locked of an Erbium-doped fiber laser by this saturable absorber (SA). In contrast with previous GSAs, due to the incorporation of additional free space alignment from the SA component, we are able to deliberately control the laser radiation spot size and location on GSA, leading to flexibility in mode-locked performance. Finally, we can obtain stable soliton pulse emission with central wavelength at 1564.42 nm, 3 dB bandwidth of 1.02 nm, and pulse duration of 2.89 ps, and also note that soliton parameters (pulse energy, central wavelength, and pulse duration) sensitively depend on the position of GSA, which could be traced back to nonuniformity of saturable absorption from the nonhomogeneous morphology of the as-prepared graphene sample.
In order to obtain high slope efficiency of 2 μm laser output, it is essential to design operating parameters of fiber laser
prior to the experiment. Based on the rate equations, the pump and signal power equations of thulium doped fiber laser
have been built. The effects of the cross relaxation coefficient K3101, the pump power filling factor Γp, the laser
reflectivity of input mirror R3, the laser reflectivity of output mirror R4, and the Tm3+ concentration N of kilowatt level
thulium doped fiber laser on the slope efficiency have been theoretically analyzed by an improved shooting algorithm.
The results indicate that the slope efficiency decreases with the increasing laser reflectivity of output mirror, the pump
power filling factor. Meanwhile, the slope efficiency increases with the increasing laser reflectivity of input mirror, the
doping concentration and the cross relaxation coefficient, but the doping concentration and the cross relaxation
coefficient have more obvious influence on the slope efficiency compared with the laser reflectivity of input mirror.
We have investigated the dispersion and the nonlinearity properties of the subwavelength-diameter optical fiber (SDOF)
with high-index-contrast dielectric thin films. The dispersion length and the nonlinearity length have been calculated to
discuss the propagation properties of pulse in SDOF. The waveguide dispersion and nonlinearity analysis is used to
guide the waveguide dimension design for possible applications. The high nonlinearity of SDOF makes it especially
suitable for nonlinearity devices.
Pulse compression of initial negative frequency chirp pulses in silicon photonic nanowire has been analyzed numerically.
The effects of the initial negative frequency chirp and core diameter variation on pulse compression have been
numerically investigated. By analyzing the interaction of SPM, positive group-velocity dispersion and the initial negative
frequency chirp, we find that the compression factor increases but the quality factor and the optimum fiber length
decrease with the increasing initial negative chirp when the core diameter is specified. A compression factor of 8.02 can
be achieved by a pulse with initial negative frequency chirp of -20 and initial FWHM duration of 30 fs in a 4.35 μm long
silicon nanowire.
We have developed an analytical model to calculate the EL profile at high electric field in single layer structure, taking into account the charge injection process at each electrode, fission and recombination of polaron-excitons. By simulation, the influences of injection barriers on EL efficiency and fission distance on recombination efficiency are thoroughly studied. Using either both ohmic contacts or using an ohmic contact to inject the low mobility carrier and a contact limited contact to inject the high mobility carrier can obtain efficient devices. By comparison of the theoretical results with the experimental data reported in the literature, we found this model can reasonably elucidates the influences of some factors on injection and recombination.
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