Six-wavelength-switchable narrow-linewidth thulium-doped fiber laser with polarization-maintaining sampled fiber Bragg grating

Twelve-Wavelength-Switchable Thulium-Doped Fiber Laser With a Multimode Fiber Bragg Grating

“…The proposed fiber laser is compared with some of the previously reported TDFLs with switchable single wavelength output using FBG, as shown in Table . 1. The number of lasing lines in the TDFL proposed in this article is 12, which is more than in those reported [14,[26][27][28], and the maximum OSNR is obtained. The fluctuation of the output wavelength is higher than that in the previous reports [14,26,28], and a moderate fluctuation of output power is obtained.…”

“…The MMFBG was fabricated using the phase mask method [14] with a 248-nm KrF excimer laser. Different from the previous work [14], the grating was inscribed on a section of commercial graded-index multimode fiber (Nufern GI-62.5/125-S; Nufern Inc., Granby, CT, USA) with numerical aperture of 0.275, which was hydrogen-loaded for 14 days before the grating was inscribed, and the core/cladding diameter was 62.5/125 μm. The period and length of the uniform phase mask was 1347.3 nm and 2 cm, respectively.…”

“…To date, various TDFLs have been proposed, including the TDFL with switchable output [12], [13], TDFL with single-longitudinal-mode operation [14], [15], mode-locked TDFL [16], [17] and high power TDFL [18]. The TDFL with switchable output is extensively used in optical fiber sensing and wavelength routing networks due to its flexible lasing performance.…”

“…S. Liu et al built a TDFL with a two switchable single-wavelength output by combining a PM-FBG and a PM F-P filter, in which the optical signal-to-noise ratio (OSNR) of the single-wavelength operation can reach 60 dB [28]. More recently, based on a PM sampled fiber Bragg grating, a six-wavelength switchable output was obtained [14]. Importantly, the number of switchable output was less than six in the previous reports.…”

“…The mechanism to obtain the switchable output is mainly based on adjusting the manually controlled polarization controller (PC) [14], [26], [28], which is always random and cannot be accurately controlled, or based on balancing the gain and loss in the cavity by multi-tubular mounts [27], which complicates the structure of the fiber laser. With an MMFBG, the reflection spectrum varies with the mode excitation conditions, which may result in more accurate and simpler output control.…”