Multiwavelength Mode-locked Fiber Research Articles

Tunable and switchable multi-wavelength mode-locked fiber lasers induced by an optimized hybrid mode-locked composite filtering effect

A multi-wavelength mode-locked fiber laser can generate different wavelengths from a single laser cavity, offering potential as a dual-frequency comb and serving as an ideal light source for terahertz wave generation. We present an optimized hybrid mode-locked Er-doped fiber laser with flexible outputs: switchable and tunable dual-wavelength mode-locking, along with stable tri-wavelength mode-locking, which is achieved by introducing 0.69 m polarization-maintaining fiber and bent 200 m single-mode fiber to enhance intra-cavity birefringence and nonlinear effect to optimize the hybrid mode-locking effect, that is, build the composite filter effect. The dual-wavelength mode-locking not only covers a tunable wavelength range of 5 nm but also provides tunable wavelength intervals of 4-26 nm due to the composite filter effect. The formation dynamics of the tri-wavelength mode-locking can be switched either pair-by-pair or one-by-one. This approach enables the realization of wavelength interval tunable dual-wavelength mode-locking in mode-locked fiber lasers simply by introducing fiber without additional actions. Such a simple, compact fiber laser with tunable wavelength capabilities holds significant potential for diverse applications.

L-band of ∼ 1.6 μm tunable multi-wavelength mode-locked Er-doped fiber laser with an MMF- FMF based structure

1.6 μm tunable mode-locked fiber laser are mainly used in the biomedical field, laser processing, and other aspects, have excellent application prospects. We propose a novel MMF-FMF-based device, which acts both as a saturable absorber and a wavelength selection filter. The reduction of insertion loss caused by FMF affects the laser gain competition process, leading to changes in gain allocation and bandwidth allocation. The laser generated stable mode-locked pulses with a repetition frequency of 23.23 MHz at pump powers exceeding 51 mW. By adjusting the angle of the fiber optic squeezer with the PC, successfully achieved switchable single-, dual-, and triple-wavelength lasing outputs, as well as tunable single- and dual-wavelength lasing outputs. The wavelength-tuning ranges for the single- and dual-wavelength lasing outputs were 31 nm (1570 nm-1601 nm) and 24 nm, respectively. The accurately adjustable L-band novel mode-locked fiber laser exhibits enormous potential for application.

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

Tunable Single and Multi-Wavelength Er-Doped Mode-Locked Fiber Laser Based on GIMF-PCF-GIMF

Thulium-doped multi-wavelength and mode-locked fiber laser based on multimode interference

We demonstrate a thulium-doped multi-wavelength mode-locked fiber laser with a single-mode-gradient refractive index multimode-single-mode fiber (SMF-GIMF-SMF) structure which acts as both a filter and a saturable absorber. Based on the multimode interference effect (MMI) filtering, wavelength-tunable operation with a tunable range of up to 15.69 nm can be obtained in the fiber laser. Moreover, tunable multi-wavelength continuous wave (CW) laser output of up to four wavelengths can be obtained by properly adjusting the pump power and polarization controller. Owing to mode interference and phase modulation, the SMS structure also plays a role as a saturable absorber (SA), which leads to the multi-wavelength output of the fiber laser accompanied by mode-locking. The state of dual-wavelength mode locking and the state of coexistence of continuous wave and mode-locking pulses at different wavelengths were observed in the laser. These results suggest that the all-fiber SMF-GIMF-SMF structure is a key device for fiber lasers to achieve multi-wavelength and mode-locked pulse output, which may find potential applications in nonlinear microscopy, biodegradable material processing, and terahertz spectroscopy.

A switchable multi-wavelength mode-locked fiber laser based on a multi-mode interference device

A switchable multi-wavelength, passively mode-locked fiber laser in the 1 μm regime is demonstrated in this paper. The key principles of working include the nonlinear polarization rotation (NPR) mechanism for the mode-locked pulse generation and a single mode-multimode-single mode (SMS) structure as the spectral filter. The SMS structure is coiled on the paddles of a polarization controller (PC). Stable mode-locking operation is achieved at the fundamental repetition rate of 7.97 MHz. The pulse duration is 429 ps at the pump level of 216 mW, with the dual-wavelength laser emitting at 1037.86 nm and 1045.72 nm. By properly tuning the paddles of PCs, multi-wavelength mode-locked laser spectra can be observed switching from triple- to sextuple-wavelength, with the emission bandwidth of 27.6 nm from 1035.6 nm to 1063.2 nm.

Tunable all fiber multi-wavelength mode-locked laser with a large dynamic range using polarization controller coiled SMF-GIMF-SMF structure as both saturable absorber and comb filter

We have demonstrated a tunable, multi-wavelength mode-locked fiber laser with a large dynamic range based on polarization controller (PC) coiled graded index multimode fiber (GIMF) as a saturable absorber (SA) and comb filter for the first time. The SA device that consists of a section of GIMF coiled into a polarization controller and two sections of single mode fibers aim to mitigate the technical difficulty of multimode fiber (MMF) in the length accuracy requirements and tune multi-wavelength operation in an Yb-doped fiber laser. Nonlinear multimode interference and transverse light field evolution in multimode fiber are simulated. Experimentally, we achieved the stable continuous-wave mode-locked (CWML), pulse bunches, and high-harmonic mode-locked (HML) operation. Furthermore, the PC-based GIMF structure can also be used as a filter to tune the laser line numbers. Continuously tunable multi-wavelength mode-locked operation with a large dynamic range was demonstrated by varying the polarization orientation of MMF. The range of six-wavelength spectrum is up to 28 nm. Our results indicate that the PC coiled GIMF could serve as an SA and a filter, which makes it beneficial to realize tunable, multi-wavelength mode-locked laser with a large dynamic range.

Conserved spacing multi-wavelength mode-locked erbium-doped fiber laser based on barium titanate saturable absorber

A compact multi-wavelength harmonic passive mode-locked (MWHML) erbium-doped fiber laser (EDFL) has been demonstrated by integrating a Barium Titanate (BaTiO3) in the ring cavity configuration. The BaTiO3 with 9.5% modulation depth serves as a saturable absorber (SA) and is optically deposited by the Top-Down method to form an end face fiber integrated saturable absorber. Both the saturable absorption property and the large third-order nonlinearity of BaTiO3 assisted in generating a second-order harmonic pulse beside the fundamental frequency. Moreover, in real-time, eight wavelengths around 1560 nm with 0.7 nm wavelength spacing were produced with a maximum output power of 2.7 mW pulse duration of 5.2 ps. These results further suggest that BaTiO3 could be a good candidate for the saturable absorber and high nonlinear photonic device for related applications.

Switchable multi-wavelength mode-locked linear-cavity fiber laser of cylindrical vector beam

We have proposed and demonstrated a switchable multi-wavelength passively mode-locked linear-cavity fiber laser to generate cylindrical vector beam (CVB) pulses by using a semiconductor saturable absorption mirror (SESAM). A home-made broadband long-period fiber grating (LPFG) and two cascaded polarization-maintaining fiber Bragg gratings (PMFBGs) are used as mode converter and wavelength selectors, respectively. This fiber laser can be switched among four different single-wavelength and two different dual-wavelength lasing oscillations with CVB output. The laser has a mode-locking threshold value of 33.55 mW and delivers CVB pulses with duration of hundreds of picoseconds. The purity of the CVB is measured to be 94.1%. This laser can have some important applications in mode division multiplexed (MDM) systems and wavelength division multiplexed (WDM) systems in the future.

Fe2O3-SiO2 nanocomposite film-induced high nonlinear effect for multiwavelength mode-locked generation in ytterbium-doped fiber laser

In this work, the possibility of a multiwavelength mode-locked fiber laser generation based on Four-Wave Mixing (FWM) induced by Fe2O3-SiO2 nanocomposite material is investigated for the first time. A multiwavelength mode-locked pulses fiber laser are generated from Ytterbium–doped fiber laser (YDFL) due to the combined action of high nonlinear absorption and high refractive coefficients of Fe2O3-SiO2 nanocomposite incorporated inside YDFL ring cavity. Up to more than 20 lasing lines in the 1040–1070 nm band with an equally lines separation of ~0.6 nm have been observed by just simple variation of passive modulation of the state of the polarization and the pump power altogether. Moreover, a passively mode-locked operation of YDFL laser has been realized with repetition rate of 18.75 MHz and pulse width of 10 ps. The proposed laser offers excellent long-standing stability with the average amount of optical signal/noise ratio of more than 41 dBm. Our study may pave a novel technique to generate multiwavelength lasing from fiber laser with the assistance by nanocomposite disordered media at low threshold pumping.

Complex soliton patterns formation in a multi-wavelength Er-doped fiber laser

We report on the emission of complex soliton patterns from a multi-wavelength mode-locked Er-doped fiber laser through nonlinear polarization rotation (NPR). The optical spectrum exhibits three distinct well-separated spectral peaks centred at 1567 nm, 1585 nm, and 1616 nm. It is mainly attributed to the linear losses and the nonlinear birefringence filtering inside the cavity. Each wavelength in the spectrum contributes by its own soliton dynamics to a composite-state soliton regime. This is verified by using an external optical tunable filter with 0.5 nm filter bandwidth to filter out the lasing at each wavelength. By controlling the cavity parameters, this regime still can be operated in harmonic states.

Self-mode-locking and self-phase modulation in Tm3+-doped double clad fiber laser for pulse peak power enhancement and multi-wavelength generation

A dual frequency mode-locked Tm3+-doped double clad fiber laser (TDCFL) is proposed by combining self-mode-locking with self-phase modulation (SPM) effect. The SPM effect stimulates the 24th harmonic mode-locking operation. The unpumped gain fiber-based self-mode-locking effect initiates the fundamental mode-locked operation. This fundamental mode-locked pulse acts as a modulation envelope of the 24th harmonic one. In this situation, the maximum pulse peak power and the largest pulse energy improve greatly. Its maximum pulse peak power is at least 311 times higher than the fundamental mode-locked one. And the difference of pulse energy is ~7.8 times. Furthermore, this dual frequency mode-locked TDCFL generates multi-wavelength light under high pump power. These results could offer an exciting new prospect for obtaining simple, compact and high performance multi-wavelength mode-locked fiber lasers.

(INVITED)Switchable multi-wavelength mode-locked Yb-doped fiber laser using a polarization maintaining 45°-tilted fiber gratings based Lyot filter

We demonstrate a multi-wavelength mode-locked Yb-doped fiber laser by incorporating a pair of polarization maintaining 45° tilted fiber gratings (PM-45°TFG) based Lyot filter. Thanks to the functions of the polarizer and the comb filtering introduced by the Lyot filter, dissipative soliton (DS) pulses centered at 1035.26 nm, 1044.93 nm, 1055.62 nm, 1066.11 nm and 1076.63 nm can be generated respectively by finely tuning the intracavity polarization controllers (PCs). Moreover, the laser also can operate in a multi-wavelength regime via appropriately adjusting the pump power and polarization orientation. The high nonlinearity induced by the long cavity length leads to the generation of h-shaped mode-locked pulse with a repetition rate of 566.27 kHz. In the absence of any disturbance, the laser can operate steadily, that can potentially be used in various fields including wavelength division multiplexing systems etc.

Ultra-long-period grating-based multi-wavelength ultrafast fiber laser [Invited

We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period gratings (ULPGs) for the first time, to the best of our knowledge. Study found that the ULPG can be used as both a mode-locker for pulse shaping and a comb filter for multi-wavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six-, and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength soliton pulses, their pulse width is about 7.8 ps. The maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of a four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multi-wavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application.

基于非线性放大环镜和Lyot滤波器的多波长与耗散孤子锁模态开关型掺铥光纤激光器

基于非线性放大环镜和Lyot滤波器的多波长与耗散孤子锁模态开关型掺铥光纤激光器

All-Fiber Dual-Wavelength Mode-Locked Laser Using a Bend-Induced-Birefringence Lyot-Filter as Gain-Tilt Equalizer

Multi-wavelength fiber lasers have emerged as a promising light source for the application in wavelength division multiplexing communication, terahertz wave generation and optical sensing due to high efficiency and robustness. Lyot-filter emerges as a potential device for multi-wavelength generation application. However, because of the high birefringence of polarization maintaining fiber in Lyot-filter, it is difficult to generate broadband dual-wavelength or multi-wavelength mode-locked fiber laser by using common Lyot-filter. In this paper, for the first time, we propose an idea of using the low birefringence induced by bending the single-mode fiber to form a Lyot-filter for dual-wavelength mode-locked fiber laser generation. The dual-wavelength output centers at 1532 and 1556 nm and it may simplify the set-up for dual-wavelength mode-locked laser.

Preparation of ultrathin graphitic carbon nitride nanosheet and its application to a tunable multi-wavelength mode-locked fiber laser

Tunable multi-wavelength mode-locked ytterbium-doped fiber laser is realized by using ultrathin graphitic carbon nitride (g-C3N4) nanosheets as saturable absorber. g-C3N4 nanosheets with an average thickness of 3.5 nm are obtained through liquid-phase ultrasonic exfoliation of g-C3N4 powder prepared by high temperature sintering. Passively mode-locked ytterbium-doped fiber laser was obtained by using the g-C3N4 nanosheets coated D-shaped fiber as saturable absorber. It is interesting that tunable dual-, triple- and quadruple-wavelength mode-locked lasers were obtained by adjusting the pump power and polarization controller. And the maximum average output power of the mode-locked laser can reach 10.32 mW. The pulse width of the quadruple-wavelength mode-locked laser is 1.9 ns, with a working repetition of 11.2 MHz. To our best knowledge, this is the first time reporting this tunable multi-wavelength mode-locking phenomenon based on g-C3N4.

A Microfiber Knot Incorporating a Tungsten Disulfide Saturable Absorber Based Multi-Wavelength Mode-Locked Erbium-Doped Fiber Laser

A novel multi-wavelength mode-locked Erbium-doped fiber laser with tungsten disulfide (WS2) combined with a microfiber knot is described. This hybrid fiber structure facilitates strong light matter interaction between the saturated absorption of the WS2 material and high optical non-linearity of the microfiber knot. It is demonstrated experimentally that the novel fiber laser works stably in the absence of an external comb filter, with the generation of stable multi-wavelength picosecond pulses. In the multi-wavelength lasing regime, up to seven-wavelength stable mode-locked pulses are obtained using a polarization controller with the pump power at ∼250 mW. The pulse period and the pulsewidth are 188.7 ns and 16.3 ps, respectively. In addition, the number of multi-wavelength lasing channels can be changed by simply adjusting the microfiber knot size. Experimental results show the laser to have a stable output over 12-h recording period. The results of this investigation demonstrate that the optical microfiber knot with a WS2 overlay based fiber laser device can operate as a highly nonlinear optical component and a saturable absorber. The proposed multi-wavelength lasing device can therefore be widely used for non-linear and ultrafast photonics and has a number of advantages compared to similar devices using more conventional technologies, including low cost and good stability.

Multi-wavelength mode-locked thulium-doped fiber laser based on a fiber-optic Fabry–Perot interferometer and a nonlinear optical loop mirror

An all-fiberized multi-wavelength mode-locked thulium-doped fiber laser (TDFL) based on fiber-optic Fabry–Perot interferometer (FPI) and nonlinear optical loop mirror (NOLM) has been presented. The fiber-optic FPI played the roles of wavelength selective filter and output mirror, which constructs by a single mode-hollow core-single mode fiber structure (SMF-HCF-SMF). A NOLM with wavelength-dependent cavity loss was employed to alleviate the mode competition in thulium-doped fiber and enabled the multi-wavelength mode-locking. With proper manipulation of the polarization controller and the pump power, besides the single-wavelength (~1948 nm) fundamental and high orders harmonic mode-locked operations, switchable dual-wavelength (1924.67/1949.16 nm and 1949.64/1972.68 nm) and stable three-wavelength (1924.80/1951.42/1972.14 nm) mode-locked operations are obtained. The multi-wavelength mode-locked TDFL exhibits a good stability with maximum peak power fluctuations of less than 0.5 dB in 2 h.

Multiwavelength mode-locked cylindrical vector beam fiber laser based on mode selective coupler

We propose and demonstrate a multiwavelength mode-locked fiber laser with cylindrical vector beam generation for the first time, to the best of our knowledge. The mode-locking mechanism is based on a nonlinear polarization rotation effect in fiber, and the multiwavelength operation is contributed to by an in-line birefringence fiber filter with periodic multiple passbands, formed by incorporating a section of polarization maintaining fiber into the laser cavity with a fiber polarizer. Furthermore, by using a home-made mode selective coupler, which acts as both a mode converter from fundamental mode to higher-order mode and an output coupler, multiwavelength mode-locked cylindrical vector beams have been obtained. This may have potential applications in mode-division multiplexing optical fiber communication and material processing.

Triwavelength synchronously mode-locked fiber laser based on few-layered black phosphorus

A triwavelength synchronously mode-locked erbium-doped fiber laser with black phosphorus (BP) was demonstrated. The BP was proved to be not only an excellent saturable absorber (SA) but also a strong nonlinear material benefiting the stabilization of a multiwavelength fiber laser. The laser worked for a long time at three synchronous wavelengths of 1557.2, 1557.7, and 1558.2 nm. The autocorrelation trace of 9.41 ps pulses showed an interference beating of 0.06 THz, corresponding to a beating period of 16.37 ps. To the best of our knowledge, this is the first report on the usage of BP as an SA for building a multiwavelength synchronous mode-locked fiber laser.