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

A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873–1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.

We experimentally demonstrate a switchable multiwavelength thulium-doped fiber laser with cylindrical vector beam (CVB) emission, which is the first report, to our best knowledge, on the generation of CVBs in a 2 µm wavelength band. The Sagnac loop filter, made up of a 50:50 coupler, a section of polarization-maintaining fiber and a polarization controller, serves as a periodical filter and accounts for the excitation of multiwavelength channels. The mode-selective coupler consisting of both tapered single-mode and four-mode fibers has been designed and fabricated as a mode converter from LP01 to LP11 mode with a purity of >80%. By adjusting the polarization controllers, laser outputs with 1–3 switchable wavelengths have been realized in the spectrum ranging from 1988–1998 nm. The laser could find miscellaneous applications in wavelength/mode-division multiplexing system, etc.

We propose and demonstrate an efficiently switchable dual-wavelength passively mode-locked fiber laser incorporating a semiconductor saturable absorber mirror (SESAM) and a comb filter. The onset of passive mode-locking is assisted with the SESAM. By properly rotating the polarization controllers (PCs), the switchable dual-wavelength mode-locked operation are efficiently obtained.

This research proposes and experimentally demonstrates a highly stable, precisely controlled, tunable, and switchable multi-wavelength thulium-doped fiber laser (TDFL), utilizing a high-curvature-sensitivity interferometer. The curvature sensor was fabricated by splicing two identical sections of no-core fiber (NCF) between three sections of single-mode fiber (SMF), and the structural order was SMF-NCF-SMF-NCF-SMF (SNSNS). Using the beam propagation method to analyze the sensor's self-imaging distance, a curvature sensitivity of 13.43 nm/m-1 can be obtained experimentally, demonstrating its functionality as a novel bending-actuated tuning element for the 2-μm-band. By bending the SNSNS with a step of 10 µm, precise and continuous tuning of seventeen distinct lasing channels with a uniform 0.33 nm interval can be obtained. The stability was monitored over 50 minutes without temperature control or vibration isolation, wavelength shifts and power fluctuations remained below 0.02 nm and 0.36 dB, respectively. Furthermore, as the pump power increased, adjusting the polarization controller enabled versatile switching among eighty-five single-wavelength, five dual-wavelength, and two three-wavelength operational states. Statistical analysis was conducted on the output wavelengths of TDFL and the peak wavelengths of the transmission spectrum of SNSNS, with the standard deviation below 0.12 nm, confirming the excellent tuning accuracy of the laser. These results demonstrate a robust, flexible, and high-precision multi-wavelength TDFL.

A novel concept of individually switchable and widely tunable erbium-doped multiwavelength fiber laser (MWFL) is proposed and experimentally demonstrated. The key component of the laser is a channel transmissivity individually variable comb filter composed of two cascaded different-length long-period fiber gratings (LPFGs), named cascaded mismatching LPFGs. When inserted into the laser cavity, this polarization-dependent comb filter functions as the wavelength selector and switching filter simultaneously. By properly adjusting the polarization controllers (PCs) in the laser cavity and in the high birefringence Sagnac loop mirror (HiBi-SLM), eleven individually switchable wavelengths with different flexible lasing states, including successively tunable adjacent single-, dual- and triple-wavelength outputs, nonadjacent dual- and triple-wavelength outputs, as well as quadruple- and quintuple-wavelength outputs, have been achieved. This MWFL may be useful in optical fiber sensing or other fields desiring very flexible optical source.

Switchable multiwavelength erbium-doped fiber laser employing wavelength-dependent loss

A simple scheme of a switchable multi-wavelength and dual-scale soliton fiber laser is proposed by cascading three chirped fiber Bragg gratings (CFBGs). By managing the cavity dispersion and controlling the losses of attenuators, quadruple-wavelength switchable pulses are generated, including one dissipative soliton (DS) and three conventional solitons (CSs). The central wavelength of the DS is 1565 nm with a pulse duration of 12.5 ps which can be compressed to ~571 fs after a 70 m single mode fiber external to cavity. Three CSs are achieved at 1539.5, 1544.5, and 1549.5 nm with pulse durations of 9.6, 8.7, and 8.8 ps, corresponding to the CFBG-based comb spectral filtering. These results demonstrate that the proposed method offers potential opportunities to exploit the flexibly switchable multi-wavelength CS/DS-pulse sources at picosecond and femtosecond scales.

In this paper, a tunable and switchable erbium-doped fiber laser (EDFL) based on parallel dual Lyot filters cascaded with a Sagnac loop is proposed. The filter can be regarded as a composite filter, whose structure is composed of cascaded different filters to ensure the presented tuning range and flexibility of parameter configuration. The wavelength resolution and polarization stability of the filter are enhanced by the synergistic effect of the multistage polarization-maintaining fibers (PMFs) and polarization controllers (PCs). The experimental results show that when the pump power is 250 mW and the lengths of the PMFs used are 4 m, 4 m, and 8 m respectively, the wavelength spacing can be adjusted by tuning the three PCs in the filter, allowing the laser to be reconfigured to alter the polarization state, thereby achieving continuous excitation of 1 to 7 wavelengths in the range from 1530.52 nm to 1568.04 nm. In addition, the output wavelength is adjustable over a range of ∼37.52 nm. The side-mode suppression ratios for the output wavelengths of this laser all exceed ∼41.60 dB. The proposed EDFL has good tunability, switchability, and stability.

In this study, a copper-based metal–organic framework (Cu-MOF) was synthesized using terephthalic acid (TPA, H2L), 1,2-bis(4-pyridyl)ethene (bpe) as organic binders, and Cu2+ ions, to act as a saturable absorber (SA) material. The SA was fabricated by depositing Cu-MOF on an arc-shaped fiber, and was then incorporated into a thulium-doped fiber laser (TDFL) and a holmium-doped fiber laser (HDFL), with both achieving stable mode-locking operation. The SA exhibited a modulation depth of 5.7% and a saturation intensity of 13.8 MW/cm2, respectively. The maximum average output power of the TDFL was 6.82 mW, while that of the HDFL was 2.64 mW. Pulse widths were measured at 1.08 ps for the TDFL and 1.75 ps for the HDFL respectively. The TDFL achieved a pulse energy of 464 pJ and a peak power of 430 W. The output of the HDFL had a pulse energy of 180 pJ and a peak power of 94.9 W, respectively. Both lasers were monitored for 4 h to ensure their stability.

Tunable and switchable multiwavelength fiber laser incorporating tapered few-mode fiber Bragg gratings

Multiwavelength fiber laser in four mode fiber

A picosecond pulse multi-wavelength erbium-doped fiber ring laser based on an optically switchable/tunable Mach-Zehnder interferometer (MZI) filter is proposed and experimentally demonstrated. The MZI configuration is constructed with two 3 dB couplers and two short pieces of endlessly single-mode photonic crystal fiber with different lengths in each arm. The combination of the MZI and a polarization controller (PC) acts as a selective comb filter and a mode-locking device. By adjusting the pump power or the first PC (PC1) state, the laser can emit up to 10 channels with a 20 nm tuning range (1530 to 1550 nm). Furthermore, by changing the PC1 condition, stable picosecond mode-locking generation with a repetition rate of 13.5 MHz is realized. To achieve wavelength spacing tunable multiple-channel laser emissions, the MZI is configured by incorporating a second PC (PC2) in one arm of the conventional MZI. Four channels of picosecond mode-locking pulses with a repetition rate of 11.6 MHz in the range of 1530-1550 nm are realized by carefully controlling the pump power and/or PC2 state. With the manipulation of intracavity birefringence through PCs with comb filtering via MZI, the proposed structure may be a potential tool in various photonics applications.

A multiwavelength erbium-doped fiber laser with linear cavity configuration is proposed and demonstrated. A power-symmetric nonlinear optical loop mirror (NOLM) serves as the laser’s output coupler and has an intensity-induced increase in transmission (IIT) that leads to higher cavity loss for oscillating wavelengths with higher power. The IIT feature of the NOLM suppresses the mode competition in the erbium-doped fiber and ensures stable multiwavelength operation at room temperature. Both the wavelength number and the output power of the laser can be flexibly controlled by adjusting the work state of the NOLM via a quarter wave plate and/or a polarization controller.

Single- and multi-wavelength laser operation of a diode-pumped ND:GGG single crystal around 1.33 µm

We propose and experimentally demonstrate a tunable and switchable multi-wavelength erbium-doped fiber ring pulsed laser based on a nonlinear optical loop mirror (NOLM) and an improved Sagnac filter. To achieve multi-wavelength pulsed laser output, we adopt a NOLM as a quasi-saturable absorber and an improved Sagnac loop as a wavelength selected filter. The constructed laser has a maximum output wavelength number of five with a pulse repetition frequency of 40.45kHz and pulse duration of 108ns. The laser can output single-wavelength and dual-wavelength pulsed lasers within a certain wavelength tuning range and a five-wavelength pulsed laser with a constant wavelength interval of 3nm by adjusting the polarization controller. Dual-wavelength, three-wavelength, and four-wavelength pulsed lasers with various wavelength intervals are also obtained. The output performance of the constructed laser is tested with a maximum average output power of 127.45µW and minimum pulse duration of 52ns, and the stability of the laser output is also tested with a maximum power fluctuation of 0.62dB and minimum wavelength drift of 0.51nm with pump power of 350mW.