A tunable dual-frequency optoelectronic oscillator (OEO) based on a tunable dual-passband microwave photonic filter (DPMPF) is proposed and demonstrated. The DPMPF is based on phase-to-intensity modulation (PM-IM) conversion and stimulated Brillouin scattering (SBS). Two pump lightwaves are generated through carrier-suppression doublesideband modulation (CS-DSB) in a Mach-Zehnder modulator (MZM) to generate two SBS gain regions in a single mode fiber. Two SBS gain regions act on the phase modulation signal to achieve a dual-passband filter. Through simply varying the frequency of the radio frequency (RF) signal used for CS-DSB, the two central frequencies of the OEO can be tuned with the frequency interval kept constant. In addition, adjusting the frequency of tunable optical source launched to the MZM, the frequency interval of the OEO can be tuned. In the experiment, the dual-frequency OEOs with frequency intervals of 0.2 GHz and 1.2 GHz are achieved, respectively. The frequency tuning range from 3 to 8 GHz is demonstrated. The dual-frequency OEO with the frequency interval tuned is also achieved.
A microwave mixer based on a tunable microwave photonic filter is presented and experimentally demonstrated. The tunable microwave photonic filter consists of a broadband optical source and a dual-parallel Mach–Zehnder modulator employing a variable optical carrier time-shift method. The central frequency of the tunable single-passband filter can be tuned by adjusting an optical variable delay line. The filter can select the wanted mixing components and suppress the other mixing spurs. Experiments are performed and the results show that the out-of-band rejection ratio of the filter is over 45 dB. The up-converted and down-converted signals are successfully selected, and the unwanted mixing spurs are effectively suppressed.
We propose and demonstrate a multiwavelength mode-locked fiber laser with cylindrical vector beam generation for the first time, to the best of our knowledge. The mode-locking mechanism is nonlinear polarization rotation, and the multiwavelength operation is contributed to the in-line birefringence fiber filter with periodic multiple passbands formed by incorporating a section of polarization maintaining fiber into the laser cavity with a polarizer. Furthermore, using the mode selective coupler, which acts as mode converter from fundamental mode to higher-order mode, multiwavelength mode-locked cylindrical vector beams have been obtained, which may have potential applications in mode-division multiplexing optical fiber communication and material processing.
A coherence-free and reconfigurable filter based on semiconductor optical amplifier (SOA) is proposed and experimentally demonstrated. A high coherent RF-modulated light source is converted to an incoherent light source by employing the cross-gain modulation of amplified spontaneous emission (ASE) of the SOA. The inversely modulated ASE is sliced by an optical wavelength demultiplexer to realize a stable transversal microwave filter. Reconfigurability of the filter can be achieved by controlling the number and apodization of the taps. The filters with two, three and four taps are experimentally demonstrated.
This paper investigates optical properties of few-mode fiber with non-uniform refractive index, namely: the few mode fiber with U-shape refractive index and the two-mode and four-mode few-mode fiber with bent radius. Finite element method is used to analyze the mode distributions based on their non-uniform refractive index. Effective mode control can be achieved through these few mode fibers to achieve vector beam generation. Finally, reflection spectra of a few-mode fiber Bragg grating are calculated theoretically and then measured under different bending conditions. Experimental results are in good accordance with the theoretical ones. These few mode fibers show potential applications in generation of cylindrical vector beam both for optical lasing and sensing systems.
An all-fiber ytterbium-doped laser based on nonlinear polarization rotation (NPR)
without dispersion compensation and additional filter has been demonstrated. The
formation of the dissipative soliton pulse is a self-consistent result of various effects
in the laser cavity. Stable mode-locked pulses with pulse energy of 1.1 nJ have been
achieved.
Passive harmonically mode-locked erbium-doped fiber ring laser with scalable
repetition rates up to 1.2 gigahertz is experimentally demonstrated, to our best
knowledge, which is hitherto maximum repetition rate from only-erbium-doped fiber
laser. Owing to the acousto-optic effect, stable passive harmonically mode-locking
can only occur at some certain discrete repetition rates corresponding to resonant
frequencies of transversal acoustic wave induced by propagating optical pulses in
fibers.
Passive harmonically mode-locked fiber ring laser with long single-mode fiber (SMF) has been demonstrated. With the increase of nonlinearity due to the incorporation of a long SMF, it is found that the laser can operate in harmonic mode-locking states with various repetition rates. Furthermore, based on the passively mode-locked fiber ring laser, a novel and simple technique for fiber length measurement with resolution on the order of centimeters has been proposed. The fiber length can be easily obtained from the fundamental cavity frequency of the mode-locked fiber laser because the transit time in a laser cavity is exactly proportional to the cavity length.
Fiber laser with two polarization-dependent output states is demonstrated.
On one hand, nonlinear polarization rotation induced intensity-dependent loss of
nonlinear optical loop mirror can balance mode competition of homogenous
broadening gain medium, and thus allows for stable room-temperature
multiwavelength generation. On the other hand, intensity-dependent transmission can
act as an equivalent saturable absorber, which results in passively mode-locking of
fiber laser. It may be a potential multifunction fiber laser.
A fiber laser with two different polarization-dependent output states is demonstrated. On the one hand, intensity-dependent loss in a nonlinear optical loop mirror, induced by nonlinear polarization rotation, can balance mode competition of a homogeneous broadening gain medium, and thus allows for stable room-temperature multiwavelength generation. On the other hand, intensity-dependent transmission can act as an equivalent saturable absorber, which results in passive mode locking of the fiber laser. It may thus serve two functions: passive mode locking and multiwavelength emission.
The operation of a passively mode-locked erbium-doped fiber ring laser in two-color pulse mode has been experimentally observed. The experiments demonstrate that the wavelengths of two-color pulses can be switched among three wavelength bands. Through carefully controlling the polarization states of the laser cavity, various modulation patterns of the two-color pulses are obtained, which are due to the interaction of two different-wavelength pulses. Single- and three-color pulses are also observed. Multiwavelength oscillation is ascribed to the wavelength-dependent transmission induced by birefringence, and can synchronously mode-lock through nonlinear polarization rotation.
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