Hu Cui

Wavelength switchable flat-top all-fiber comb filter based on a double-loop Mach-Zehnder interferometer

A wavelength switchable all-fiber comb filter with flat-top spectral response based on a double-loop Mach-Zehnder (M-Z) interferometer is proposed and demonstrated. The proposed flat-top filter consists of a rotatable polarizer and a double-loop M-Z interferometer composed of two fiber couplers with a polarization controller (PC) in the first loop. In the theoretical analysis, when the second coupler of the M-Z interferometer is a non-3dB one, with proper settings of the polarization state of the input light and the PC, the wavelength switchable comb filter with flat-top passband can be obtained. Theoretical prediction was verified by experimental demonstration. The measured 1 dB bandwidth was 0.51 nm with a channel spacing of 0.98 nm, indicating that the flat-top passband of 1 dB bandwidth extends to about 50% of the comb spacing.

Vector dissipative soliton resonance in a fiber laser

We report on the vector nature of rectangular pulse operating in dissipative soliton resonance (DSR) region in a passively mode-locked fiber laser. Apart from the typical signatures of DSR, the rectangular pulse trapping of two polarization components centered at different wavelengths was observed and they propagated as a group-velocity locked vector soliton. Moreover, the polarization resolved soliton spectra show different spectral distributions. The observed results will enhance the understanding of fundamental physics of DSR phenomenon.

Graphene-deposited microfiber photonic device for ultrahigh-repetition rate pulse generation in a fiber laser.

We report on the generation of a high-repetition-rate pulse in a fiber laser using a graphene-deposited microfiber photonic device (GMPD) and a Fabry-Perot filter. Taking advantage of the unique nonlinear optical properties of the GMPD, dissipative four-wave mixing effect (DFWM) could be induced at low pump power. Based on DFWM mode-locking mechanism, the fiber laser delivers a 100 GHz repetition rate pulse train. The results indicate that the small sized GMPD offers an alternative candidate of highly nonlinear optical component to achieve high-repetition rate pulses, and also opens up possibilities for the investigation of other abundant nonlinear effects or related fields of photonics.

Coexistence of harmonic soliton molecules and rectangular noise-like pulses in a figure-eight fiber laser

We report the coexistence of high-order harmonic soliton molecules and rectangular noise-like pulses (NLP) in a figure-eight fiber laser mode-locked by a nonlinear amplifying loop mirror. The harmonic soliton molecule has a repetition rate of 936.6 MHz, corresponding to the 466th harmonics of the fundamental cavity repetition rate, with soliton separation of 16.5 ps. Meanwhile, the rectangular NLP operates at the fundamental repetition rate. In addition, these two types of pulses could be generated independently by manipulating the polarization controllers. The experimental results demonstrate an interesting operation regime of the fiber laser and contribute to enriching the dynamics of mode-locked pulses in fiber lasers.

Photonic crystal fiber for supporting 26 orbital angular momentum modes.

We propose and numerically investigate a photonic crystal fiber (PCF) based on As2S3 for supporting the orbital angular momentum (OAM) modes up to 26. The designed PCF is composed of four well-ordered air hole rings in the cladding and an air hole at the center. The OAM modes can be well separated due to the large effective index difference of above 10-4 between the eigenmodes and maintain single-mode condition radially. In addition, the dispersions of the modes increase slowly with wavelengths, while the confinement loss keeps as low as 10-9 dB/m. The proposed PCF increases the supported OAM modes which could have some potential applications in short-distance, high-capacity transmission.

Enhanced pulse adaptive to PMD by modulating breath-depth

The enhancement of adaptive abilities of nonlinear optical pulses to polarization mode dispersion (PMD) is obtained by modulating breath-depth of two polarization states of the pulses. The breath-depth modulation is realized based on the interaction among self-phase modulation, cross phase modulation, group velocity dispersion and degenerate four-wave mixing, which results in making two polarization states of the pulses into a tighter state when nonlinear pulses propagate in optical fibers with high birefringence. Numerical results show that the transmission stabilities of modulated breath-depth optical pulses are improved in conventional fibers with random birefringence. The pulse broadening trend of the modulated breath-depth pulses induced by PMD is effectively suppressed by our proposed method. The symmetric output pulse shape is also reshaped in conventional fibers.

ENHANCED POLARIZATION SOLITON'S ROBUSTNESS TO POLARIZATION MODE DISPERSION IN FIBER SYSTEMS WITH FREQUENCY-DEPENDENT LOSS

We propose a new method to strengthen the nonlinear pulses robustness to polarization mode dispersion in the conventional lossy fiber systems. The method is based on the generation of the stable trapped state of polarization solitons in an initial optical fiber with high birefringence. It is proven that the obtained bound state of nonlinear pulses have stronger adaptive abilities to polarization mode dispersion than common solitons when they propagate in conventional fibers with random birefringence.

Dissipative soliton resonance in Bismuth-doped fiber laser

We experimentally demonstrate the generation of dissipative soliton resonance (DSR) in a passively mode-locked Bi-doped fiber ring laser based on nonlinear polarization rotation (NPR) technique. The DSR with the central wavelength of 1169.5 nm has a repetition rate of 343.7 kHz. By purely increasing the pump power, the DSR evolves from Gaussian shape to rectangular shape with the duration extending from 2.1 ns to 13.1 ns, while keeping the pulse amplitude and the 3-dB spectrum bandwidth almost constant. The single-pulse energy reaches 24.82 nJ. Furthermore, we construct a lumped model to reproduce the mode-locking process and the traits of the DSR pulse. The obtained results indicate that it could achieve higher pulse energy in mode-locked Bi-doped fiber laser by generating DSR.

Tunable and switchable dual-waveband ultrafast fiber laser with 100 GHz repetition-rate

We demonstrate a tunable and switchable dual-waveband 100 GHz high-repetition-rate (HRR) ultrafast fiber laser based on dissipative four-wave-mixing (DFWM) mode-locked technique. Each waveband maintains HRR operation. The DFWM effect was realized by combining a Fabry-Perot (F-P) filter and a piece of highly nonlinear fiber (HNLF). The tunable and switchable operations were achieved by nonlinear polarization rotation (NPR) technique. Through appropriately controlling the filtering effect induced by NPR, the laser could operate at two kinds of tunable regimes. One is that the spacing between these two wavebands could be tuned while keeping their center at 1559 nm. The other is that the central position of the entire dual-waveband is tunable while with the same separation between these two wavebands of 13.2 nm. Moreover, the laser could switch between these two wavebands. Correspondingly, the center of the single-waveband has a tuning range of 15.2 nm. This versatile ultrafast fiber laser may find applications in fields of optical frequency combs, high speed optical communications, where HRR pulses are necessary.

Wiggling and bending-free spatial solitons at the interface between photovoltaic photorefractive crystals with opposite diffusion effects

In this paper, we used numerical simulations to investigate the propagation behavior of (1+1)-dimensional bright spatial solitons at the interface formed by two photovoltaic (PV) photorefractive (PR) crystals with opposite diffusion effects. When the incident direction of the soliton beam is parallel to the interface with an appropriate structure, the soliton beam follows a wiggling trajectory and passes periodically through the interface under the co-influence of two opposite diffusion effects. Moreover, the intensity of the soliton beam slightly oscillates during propagation at a composite frequency containing a low-frequency component and a high-frequency component. Furthermore, when the incident direction of the soliton beam coincides with the interface, the soliton beam moves along a straight line, and the self-deflection that arises from the diffusion effect is suppressed. These results provide what we believe is a feasible method to control the propagation trajectory of soliton beams in PV PR crystals.