Multi-wavelength Mode-locked Fiber Laser 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.

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.

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.

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.

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.

Tunable multiwavelength mode-locked fiber laser using intra-cavity polarization and wavelength dependent loss

We report a tunable multiwavelength mode-locked fiber ring laser in C-band. Multiwavelength characteristic and tuning of laser wavelengths is achieved by inducing polarization and wavelength dependent loss in the cavity by using a combination of two polarization controllers (PCs) and an intensity modulator, inserted between the two PCs. With this technique we obtained pulses of 14ps (FWHM) at a repetition rate of 10GHz by actively mode-locking the laser. We obtained simultaneous lasing of 5 wavelengths with 3-dB spectral width of 0.2nm for each lasing wavelength. We measured short-term stability of the pulses and corresponding spectra by continuously collecting time and spectral domain data for 600s, sampled at an interval of 20s. The pulsewidth was measured to be stable to within ±732fs and peak power fluctuations were within ±0.16mW. For simultaneous lasing of two wavelengths, the linewidth was found to be stable within ±0.07nm with a peak power fluctuation of ±1dB.

Tunable multiwavelength mode-locked Tm/Ho-doped fiber laser based on a nonlinear amplified loop mirror.

We propose and demonstrate a tunable multiwavelength mode-locked Tm/Ho-doped fiber laser based on a nonlinear amplified loop mirror (NALM). Without using polarization-maintaining fiber, only passive fibers with low birefringence were inserted into the NALM to help overcome mode competition and realize mode-locking. The spacing between adjacent channels was measured to be ∼6 nm. By adjusting the polarization controllers (PCs) to an appropriate position, self-started mode-locking was achieved, which further overcame the mode competition in the fiber laser. A multiwavelength mode-locked fiber laser with at least three available channels were tunable in the widest range of 30 nm (from 1935 to 1965 nm) with a 3 dB channel bandwidth of ∼1.6 nm. This multiwavelength mode-locked fiber laser is quite stable with the maximum peak fluctuation within 0.47 dB in long-term observations.

Tunable 19 × 10 GHz L-band FP-SOA based multi-wavelength mode-locked fiber laser

We present a multi-wavelength mode-locked fiber ring laser incorporating a semiconductor optical amplifier (SOA) and a Fabry–Perot semiconductor optical amplifier (FP-SOA). Because the gain of the SOA is depleted by an external injection optical signal, the SOA acts as a loss modulator. The FP-SOA serves as a tunable comb filter. The presented laser source can generate 19 synchronized wavelength channels with the extinction ratio of about 21 dB, each mode-locked at 10 GHz, and mode-locked pulse width is about 40 ps. Oscillation wavelengths band can be tuned by adjusting the bias current of the SOA, and wavelength spacing also can be changed by using a tunable optical delay line (ODL) or a temperature controller. The polarization-insensitive devices ensure that the output power is rather stable. This fiber laser has potential applications in longer waveband (L-band) within the low-attenuation window.

Numerical and theoretical analysis of an alternate multiwavelength mode-locked fiber laser

The generation of alternate multiwavelength pulse trains in an actively mode-locked erbium-doped fiber laser containing an unbalanced Mach-Zehnder interferometer is analyzed using numerical simulations and a theoretical Gaussian pulse analysis. The results obtained allow the interpretation of recent experimental results reporting multiwavelength pulse laser operation and provide a clear physical description of the operation of the multiwavelength laser. Furthermore, the analysis and modeling also provide guidelines for experimental design.