Abstract
A continuous wave, switchable multi-wavelength, thulium-doped fiber laser (TDFL) with a polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated for the first time. A length of 150 m highly-nonlinear fiber (HNLF) was used to introduce the four-wave mixing effect for the efficient suppression of the wavelength competition existing in the gain medium of thulium-doped fiber. By adjusting the state of polarization (SOP) of light in the laser cavity, two six-wavelength operations at two orthogonal SOPs and a ten-wavelength operation were obtained. When the TDFL ran at the six-wavelength operation mode with a pump power of 4.11 W, there were at least four lasing wavelengths with an optical signal-to-noise ratio (OSNR) higher than 30 dB, and when it ran at the ten-wavelength operation mode with a pump power of 4.60 W, there were nine lasing wavelengths with an OSNR higher than 30 dB. Regardless of the operation mode, the TDFL exhibited high stability.
Highlights
Thulium-doped fiber lasers (TDFLs), especially narrowlinewidth and wavelength-tunable thulium-doped fiber laser (TDFL), have recently become a research focus because they work at the eye-safe 2 μm band in which an atmospheric window exists, and they can be applied in free-space optical communication (FSOC), fiber optical sensors, optical measurement, and medical treatment [1]–[6]
We have proposed dual-wavelength TDFLs using a high-birefringence Fiber Bragg grating (FBG)-based filter and a polarizationmaintaining, chirped-moiré FBG-based filter, respectively [14], [15]
First, the TDFL without the highly-nonlinear fiber (HNLF) or the PC2 was investigated at room temperature (24 ◦C), and this TDFL, with a threshold of 2.34 W, could be switched between singlewavelength and dual-wavelength operations
Summary
Thulium-doped fiber lasers (TDFLs), especially narrowlinewidth and wavelength-tunable TDFLs, have recently become a research focus because they work at the eye-safe 2 μm band in which an atmospheric window exists, and they can be applied in free-space optical communication (FSOC), fiber optical sensors, optical measurement, and medical treatment [1]–[6]. Among the different kinds of reported TDFLs, the multi-wavelength TDFL can stably and simultaneously output numerous wavelengths, and because of its merits of high beam quality, low cost and compact structure, it can be widely used in wavelength-division-multiplexing FSOC [7]. It meets the requirements of reducing the cost and improving the communication capacity of FSOC networks, and has attracted increasingly more and more attention. Fiber Bragg grating (FBG) has been used as a filter in fiber laser systems due to its simple structure, small size, and flexible tunability.
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