A dumbbell-shaped fiber laser with dual-functional pulsed outputs is demonstrated using a filmy polyvinyl alcohol-based gold nanorods (GNRs) saturable absorber (SA), which can deliver mode-locked soliton and multiwavelength Q-switched pulse. The GNRs-SA is fabricated by seed-mediated method with a modulation depth of 4.1% and nonsaturable loss of 32.9%. When the fiber laser operates in mode-locked regime, stable fundamental solitons with a temporal width of 910 fs and repetition rate of 2.88 MHz are directly generated from the laser cavity. The corresponding spectrum is located at 1560.1 nm with a 3-dB bandwidth of 3.08 nm. When the laser operates in Q-switched regime, more than 5-wavelength oscillation is achieved. The repetition rate of Q-switched monotonically increases from 13.4 to 31.7 kHz and the pulse duration can be significantly narrowed from 6.07 to 3.12 μs by varying the pump power from 128 to 154 mW. The results further expand the applications of GNRs-SA to obtain versatile pulse sources in ultrafast laser field.
A novel all-fiber flat-top comb filter is proposed based on Sagnac loop interferometer of photonic crystal fiber
(PCF). The transmission function of the proposed Sagnac loop filter is expressed theoretically by Jones transmit-matrix.
The influences of birefringence of PCF, the lengths of two sections of PCFs and the rotatable angle of polarization
controllers on its output spectra are numerically studied. On the basis of theoretical analysis, a wavelength switchable
comb filter with flat-top spectral response is realized. This kind of filter can be expected to be used widely in DWDM
systems in the future.
The depressed-index dual core PCF-based broadband directional coupler is designed by using semivectorial finite
difference method. We study the influence of the structural parameters on the coupling characteristics in the dual core
PCF. The results show that once the structural parameter of the cladding of the dual core PCF and the doping degree in
the dual core region are optimised, the broadband coupling can be realised: in the wavelength range of 1.22~1.65μm, the value of the coupling length is stabilized at 26637nm±235nm and when the couplers are designed as two kinds
of couple with coupling ratio of 50% and 10%, the coupling ratios of (50±0.702)% and (10±0.664)% are realized,
respectively.
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