Abstract
We report an experimental observation of wavelength tuning and bound states in fiber lasers. A Mach-Zehnder interferometer (MZI) is adopted as an intra-cavity tunable filter to realize large-scale wavelength tuning and bandwidth controlling. By finely manipulating the MZI and intra-cavity polarization state, continuous wavelength-tunable operation from 1550.7 nm to 1580.8 nm is achieved. Meanwhile, the spectral bandwidth varying from 1.85 nm to 3.41 nm is also controlled by broadening the free spectrum range (FSR) of the MZI. Additionally, with modest polarization adjustment, both tightly and loosely bound states are experimentally observed, which can be validated by the numerical simulations. The results indicate that the proposed fiber laser is attractive for telecommunication systems, on account that the tuning feature can be applied to wavelength-division multiplexer (WDM) and the various soliton bound states could contribute to the high-level modulation format.
Highlights
Due to the advantages of high repetition rate or pulse energy[1,2], the dissipative solitons (DSs) mode-locked fiber lasers have been widely studied for improving ultrashort pulsed light sources
Mach-Zehnder interferometer (MZI) has been applied in fiber laser for generating high repetition rate pulses based on the filter-driven four-wave mixing effect[17] or providing flexibly tunable filtering function[18], whose flexible wavelength control paves another way to implement the wavelength-tunable operation of fiber lasers and match the wavelength-division multiplexer (WDM) technique
Continuous wavelength-tuning can be achieved through finely adjusting the MZI; the spectral bandwidth is controllable by changing the free spectrum range (FSR) of MZI
Summary
We report an experimental observation of wavelength tuning and bound states in fiber lasers. Some approaches have been proposed and demonstrated to achieve the wavelength-tuning of mode-locked fiber lasers, such as exploiting cascaded fiber grating cavities[3,4] or various fixed comb filter structures[5,6,7,8]. The modified tunable fiber lasers are studied based on fiber birefringence induced invisible filter[9,10,11,12,13,14,15] or space optical coupling structure[16] In these ways, more flexible wavelength tuning and wider adjustable range around 20 nm are achieved. Numerical simulations are conducted to confirm the specific parameters of the soliton molecules including phase difference and pulse separations
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