Switchable Multi-Wavelength Thulium-Doped Fiber Laser Using Four-Mode Fiber Based Sagnac Loop Filter

Abstract

A switchable multi-wavelength thulium-doped fiber laser (TDFL) using a fourmode fiber based Sagnac loop filter was proposed and demonstrated. The Sagnac loop, incorporating a 4.8 m long four-mode step-index fiber, acting as a comb filter was analyzed theoretically and experimentally. By adjusting two polarization controllers, eight stable single-wavelength operations and five stable dual-wavelength operations were obtained with easy switching between the different operation modes. The wavelength range covered during the single-wavelength switchable operation with a signal-to-noise ratio of up to 55 dB was ∼28.51 nm. In dual-wavelength switchable operation, the maximum and minimum wavelength spacings were ∼21.78 nm and ∼1.50 nm, respectively. Due to the abundant wavelength resources, the proposed TDFL has great potential in wavelength division multiplexing free-space optical communications, optical fiber sensing, and photonic generation of microwave signals.

Thulium-doped fiber laser with switchable single-wavelength output using polarization-dependent loss

“…However, PDL can be easily induced by inserting a polarization controller and an in-line polarizer that are compatible with the fiber structure of the laser cavity. In fact, however, using PDL to realize switchable output in TDFL has rarely been reported [33][34][35].…”

Stable Multi-Wavelength Thulium-Doped Fiber Laser With Two Cascaded Single-Mode-Four-Mode-Single-Mode Fiber Interferometers

“…As a result, the filtering period cannot be tuned freely, and subsequently only uneven dual-wavelength lasing can be achieved. Those problems are expected to be solved by using a few-mode fiber, such as the two-mode fiber (TMF) [22] or the four-mode fiber (FMF) [23], in the interferometer instead of the multimode fiber. We have reported [22] a MWTDFL using a TMF-based interferometer filter.…”

“…1, a segment of step-index FMF (YOFC: ULL SI-4) with a core diameter of 19 μm is sandwiched between two SMFs in an axial-aligned single-mode-fourmode-single-mode (SFS) structure, and the fibers are fusion spliced with each other. The LP01 and LP02 modes are circumferentially symmetric distributions, which can be stimulated at the input splicing point between the SMF and FMF [23,29]. As the LP01 and LP02 modes have different effective refractive indices (n1 = 1.44548 and n2 = 1.44425, respectively) in the 2-µm band, a Mach-Zehnder interferometer (MZI) forms at the output splicing point between the FMF and the SMF [30].…”

Wavelength-Switchable Single-Longitudinal- Mode Thulium-Doped Fiber Laser With Sampled Fiber Bragg Grating

“…To switch the wavelength, wavelength-selection and competitioninhibition mechanisms are needed. The wavelength can be selected with filters, such as the Mach-Zehnder interferometer [17] , cascaded Sagnac loop [18] , fiber-based Lyot filter [19] , micro fiber-optic Fabry-Perot interferometer [20] , few-mode fiber-based interferometer [21][22][23] and fiber Bragg grating (FBG) filters [7,24] . In particular, the FBG filter has been a good choice due to its simple structure, small size, and flexible tunability [25][26][27] .…”