Dual-wavelength Mode-locked Operation Research Articles

Tunable and dual-wavelength mode-locked Yb-doped fiber laser based on graded-index multimode fiber device

We have implemented wavelength-tunable and dual-wavelength in an ytterbium-doped passively mode-locked fiber laser using a single mode-graded index multimode-single mode fiber (SMF-GIMF-SMF) device as the saturable absorber (SA) without additional components. Such an all-fiber SA device exhibits fantastic properties with a large modulation depth of 22.9%, a small saturation fluence of 8.3 μJ/cm2, and the transmission curve with a capacity of gain-flattening, which are suitable for the tunable mode-locking generation. Benefiting from the intracavity birefringence-induced filtering effect of the laser cavity, tuning and dual-wavelength operations are obtained. For the tuning operation, the central wavelength of the dissipative solitons (DSs) can be tuned from 1028.5 to 1074.4 nm, with the pulse duration of tens of picoseconds. For the dual-wavelength mode-locking operation, the central wavelengths of dual-wavelength can be switched from 1032.3/1054.1 nm to 1049.3/1072.6 nm. Our results indicate that the SMF-GIMF-SMF device provides a novel platform for wavelength-tunable and dual-wavelength mode-locking in Yb-doped fiber lasers.

Generation of wavelength-tunable and coherent dual-wavelength solitons in the C + L band by controlling the intracavity loss

A wavelength-tunable and dual-wavelength mode-locking operation is achieved in an Er-doped fiber laser using a hybrid no-core fiber graded index multimode fiber as the saturable absorber. In the tuning operation, continuously wavelength-tunable pulses with a tuning range of 46.7 nm, stable 3-dB bandwidth of around 5 nm, and pulse duration of ∼850 fs are obtained by increasing the intracavity loss of a variable optical attenuator. In the dual-wavelength operation, the two solitons at different wavelengths demonstrate the characteristics of mutual coherence. By increasing the intracavity loss, the spectral spacing can be tuned from 11 to 33.01 nm while maintaining the coherence of the solitons. Such coherent solitons have high potential for applications in dual-comb frequency and multicolor pulses in nonlinear microscopy.

Single-wavelength-tunable and dual-wavelength-switchable Tm-doped fiber soliton laser based on single-walled carbon nanotubes

We propose a single-wavelength-tunable and dual-wavelength-switchable Tm-doped fiber soliton laser with single-walled carbon nanotubes. The laser can deliver single-wavelength mode-locked pulse tunable from 1892 nm to 1924 nm. Dual-wavelength mode-locking operation can also be achieved by increasing pump power and rotating the polarization controller (PC), meanwhile the wavelength can be switched between 1883/1894 nm and 1905/1910 nm. Both the tunable and switchable operations are realized with great ease by solely adjusting the parameters of PC. The proposed Tm-doped fiber laser can operate in two mode-locking states, which is helpful for further understanding of the mode-locking mechanism and useful for practical applications.

L-Band Tunable and Dual-Wavelength Mode-Locked Fiber Laser With NCF-GIMF-Based SA

A hybrid structure of no-core fiber and graded-index multimode fiber (NCF-GIMF) is demonstrated, which can be used as both the saturable absorber (SA) and the wavelength selective element. By employing such a device, an L-band wavelength tunable Er-doped mode-locked laser is realized and stable single solitons of ~1.7 ps, with continuously tunable wavelengths from 1574 to 1601.1 nm, are generated. Moreover, dual-wavelength mode-locked laser operation at 1575.4 and 1603 nm is achieved, with a pulse duration of 1.2 and 1.7 ps, respectively. The proposed device is simple and compact and represents an effective approach for tunable and dual-wavelength mode-locked fiber laser operation.

All-polarization-maintaining dual-wavelength mode-locked fiber laser based on Sagnac loop filter.

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.

Dual-wavelength quasi-mode-locked regimes of an Er-doped fiber ring laser

We demonstrate the dual-wavelength quasi mode-locked operation of a passively mode-locked Er-doped fiber ring laser with twisted fiber in the cavity and a double-pass amplifier with a Faraday mirror. The configuration allows very strict control of the polarization. We observed synchronous dual-wavelength generation of noise-like pulses (NLP) with spectra centered at 1534 nm and 1562 nm. Rotation of the azimuth of the radiation propagating in the cavity caused a switching between the generation of NLPs and packets of pulses with typical solitons spectrum. In the latter regime, we observed partially synchronous sub-pulses at two different wavelengths.

Multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror.

In this paper, a multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror is reported. An ultra-high numerical aperture fiber is employed to compensate the cavity abnormal dispersion, and the net cavity dispersion value is fixed at -0.046 ps2. By changing the pump power, three different mode-locked regions, namely Q-switched mode-locking operation, mode-locking operation, and dual-wavelength mode-locking operation, are observed sequentially. When the pump power is raised to the threshold of 1.60W, the transition state of the Q-switched mode locking begins to be observed. When the pump power increases from 2.88W to 8.75W, stable single-wavelength mode-locking operation is obtained. And the center wavelength is 1988.73nm corresponding to the 3dB spectral bandwidth of 11.21nm. As the pump power is raised beyond 8.75W, dual-wavelength mode-locking operation is developed, where the dual wavelengths are 1969.70nm and 1984.12nm with the 3dB spectral bandwidth of ∼4.11 nm and ∼6.14 nm, respectively.

Self-starting simple structured dual-wavelength mode-locked erbium-doped fiber laser using a transmission-type semiconductor saturable absorber

A self-starting simple structured dual-wavelength passively mode-locked (ML) erbium-doped fiber (EDF) laser is proposed in this Letter. An all-fiber ring cavity is adopted and a transmission-type semiconductor saturable absorber is used as modelocker. In this laser, there are two gain humps located at the 1530 nm region and the 1550 nm region, respectively. Along with the length of EDF increasing, the intensity of the hump at 1530 nm region is gradually suppressed because of the re-absorption of emission by the ground state. With the proper length of EDF, the gain intensities of two regions are very close. When the pump power is above the ML threshold, the self-starting dual-wavelength ML operation is achieved easily without manual adjustment. The two spectral peaks with close intensities are located at 1532 and 1552 nm, respectively. The effect of intracavity dispersion on the output spectrum is also experimentally demonstrated.

Dual-wavelength mode-locked fiber laser based on tungsten disulfide saturable absorber

We report on the generation of dual-wavelength mode-locked laser pulse in an Er-doped ring-shaped fiber cavity with WS2 nanosheets based saturable absorber (SA), emitting at wavelength of 1531.8 nm and 1556.7 nm. The WS2 nanosheets were precipitated on the head face of fiber patch cord via light precipitation method. By adjusting the polarization of lasing mode, the gain of the Er-doped fiber laser was effectively controlled and the stable dual-wavelength mode-locking operation was achieved. Our investigation revealed WS2’s extraordinary nonlinear properties, which make it an excellent material for saturable absorber for passively mode-locked fiber lasers.

Dual-wavelength mode-locked Er-doped fiber laser based on optimizing gain fiber length

Recently,multi-wavelength pulsed lasers have become a research hotspot due to their versatile applications,such as precision spectroscopy,microwave/terahertz photonics,optical signal processing,and wavelength division multiplexed optical fiber communication systems.As a promising candidate,passively mode-locked fiber laser has the advantages of ultrashort pulse,ultrahigh peak power,compact structure and low-cost.In the existing multi-wavelength passively mode-locked fiber lasers,multi-wavelength mode-locked operation is achieved by adjusting the intracavity modulators to a proper state after laser has worked.It is inconvenient for practical use,so,its application scope is restricted.In this paper,a new method to achieve dual-wavelength mode-locked operation in an erbium-doped fiber laser is proposed. For an erbium-doped fiber,the peaks of both absorption and emission spectra overlap in the 1530 nm-region.So the emission light in the 1530 nm-region will be re-absorbed by the erbium-doped fiber with low pump power or long gain fiber.Utilizing the emission re-absorption effect,the gain spectrum can be modified by different lengths of gain fiber. In the experiment,an all-fiber ring cavity is adopted and a transmission-type semiconductor saturable absorber is used as a modelocker.The cavity consists of ～3.2-m-long single mode fiber and an erbium-doped fiber.Gain fibers with different lengths are used in the cavity to reveal the dependence of emission re-absorption on both gain spectrum and mode-locked output spectrum.According to the experimental results,there are two humps in the amplified spontaneous emission spectrum located in the 1530 nm-region and 1560 nm-region,respectively.With the gain fiber length increasing, gain spectrum in the 1530 nm-region is suppressed,and gain intensity in the 1560 nm-region gradually surpasses that in the 1530 nm-region.Based on the experimental results,self-starting dual-wavelength mode-locked operation is achieved with a 31-cm-long gain fiber.The two spectral peaks with close intensity are located at 1532.4 nm and 1552.3 nm, respectively.The maximum output power is 4.8 mW at a repetition rate of 58.01 MHz and a signal-to-noise ratio of 58.2 dB.This self-starting dual-wavelength mode-locked erbium-doped fiber laser is convenient for practical use and can meet the requirements for many potential applications.

All-fiber dual-wavelength Q-switched and mode-locked EDFL by SMF-THDF-SMF structure as a saturable absorber

We demonstrate all-fiber dual-wavelength Q-switched and mode-locked erbium-doped fiber laser (EDFL) by utilizing the thulium-holmium-doped fiber (THDF) as a fiber saturable absorber (SA) and also a Mach-Zehnder interferometer (MZI) element. The 19cm long THDF has a core diameter of 11.5µm, refractive index difference of 0.005, and cutoff wavelength of 1810nm. Stable dual-wavelength Q-switching operation was generated at 1555.14nm and 1557.64nm with free spectral range (FSR) of 2.5nm. The repetition rate of 14.45–78.49kHz was obtained between 12 and 100mW pump power. At maximum pump power, the maximum output power and pulse energy were 2.58mW and 32.87 nJ, respectively. By adding 195cm long SMF in the same cavity, the stable dual-wavelength mode-locking operation was started at 166mW and continue stable to 201mW pump power. This mode-locking operation produced stable dual-wavelength pulses at 1530.34nm and 1532.84nm with a repetition rate of 1MHz with a pulse duration of 128ns and signal-to-noise ratio (SNR) of 62dB. It shares the same value of FSR in Q-switching operation. The highest output power of 1.57 nJ corresponds to the maximum output power of 1.57mW was obtained. Our results validate the linear absorption characteristic at C-band region and multimode fiber effect of THDF can be utilized as SA to generate stable all-fiber dual-wavelength pulsed lasers. Remarkably, these findings expand a fiber gain medium application in short pulse generation.

Tunable dual-wavelength passively mode-locked thulium-doped fiber laser using carbon nanotube

A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single-and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single-and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Orthogonally polarized bright–dark pulse pair generation in mode-locked fiber laser with a large-angle tilted fiber grating

We report on the generation of orthogonally polarized bright–dark pulse pair in a passively mode-locked fiber laser with a large-angle tilted fiber grating (LA-TFG). The unique polarization properties of the LA-TFG, i.e., polarization-dependent loss and polarization-mode splitting, enable dual-wavelength mode-locking operation. Besides dual-wavelength bright pulses with uniform polarization at two different wavelengths, the bright–dark pulse pair has also been achieved. It is found that the bright–dark pulse pair is formed due to the nonlinear couplings between lights with two orthogonal polarizations and two different wavelengths. Furthermore, harmonic mode-locking of bright–dark pulse pair has been observed. The obtained bright–dark pulse pair could find potential use in secure communication system. It also paves the way to manipulate the generation of dark pulse in terms of wavelength and polarization, using specially designed fiber grating for mode-locking.

Dual-wavelength mode-locked operation on a novel Nd^3+,Gd^3+:SrF_2 crystal laser

We report on efficient continuous-wave (CW) and dual-wavelength mode-locked operations on a novel Nd3+,Gd3+:SrF2 crystal laser for the first time. Codping Gd3+ in the Nd3+:SrF2 crystal significantly increased the fluorescence intensity and aroused and inhomogeneously broadened the emission spectrum. A CW operation with an output power of 992 mW and corresponding slope efficiency as high as 42.7% was obtained. We also obtained dual-wavelength synchronously mode-locked operation, with pulse duration of 1.9 ps. The mode-locked spectrum separated distinctly at 1052.2 nm and 1059.4 nm. Autocorrelation trace clearly showed a 417 fs beating period, and 1.94 THz repetition rate.

Switchable dual-wavelength fiber laser mode-locked by monolayer graphene on D-shaped fiber

A switchable mode-locking fiber laser is demonstrated by means of a monolayer graphene saturable absorber (SA) based on a D-shaped fiber. The monolayer graphene, which is grown by chemical vapor deposition, is transferred onto the D-shaped fiber and then the light–graphene interaction via the evanescent field of the fiber is enhanced greatly. Using such a graphene-based SA, the single-wavelength mode locking can be switched from 1531.5 to 1559.1 nm by appropriately adjusting the polarization controller (PC). In addition, the stable dual-wavelength mode-locking operation is also observed at the proper state of PC.

Mode-locking of 2 μm Tm,Ho:YAG laser with GaInAs and GaSb-based SESAMs

We have investigated passive mode-locking of Tm,Ho:YAG lasers with GaInAs- and GaSb-based semiconductor saturable absorber mirrors (SESAMs). With a GaInAs-based SESAM, stable dual-wavelength mode-locking operation was achieved at 2091 nm and 2097 nm, generating pulses with duration of 56.9 ps and a maximum output power of 285 mW. By using the GaSb-based SESAMs, we could generate mode-locked pulses as short as 21.3 ps at 2091 nm with a maximum output power of 63 mW. We attribute the shorter pulse duration obtained with the GaSb SESAMs to the ultrafast recovery time of the absorption and higher nonlinearity compared to standard GaInAs SESAMs.

Switchable mode-locking fiber laser with fiber Bragg gratings

A switchable mode-locking fiber laser is proposed by means of fiber Bragg grating (FBG). The FBG plays two key roles, the switchable wavelength operation and the spectral filtering effect, on the proposed laser. The switchable single-wavelength mode-locking operation, lasing at either 1545.25 or 1548.34 nm, corresponding to the central wavelengths of the FBGs, is obtained by appropriately rotating the polarization controllers (PC). In addition, the dual-wavelength mode-locking operation is observed with proper PC state. The switchable mode-locking operation attributes to the wavelength-dependent loss mechanism and the spectral filter formed by PCs and FBGs.

Formation and evolution of passively mode-locked fiber soliton lasers operating in a dual-wavelength regime

The formation and evolution of dual-wavelength solitons in passively mode-locked fiber soliton lasers are investigated both numerically and experimentally. By solving the Ginzburg–Landau equation and taking the gain profile into account, mode-locked soliton emissions at 1532 and 1555 nm are achieved simultaneously. Numerical results show that the two solitons exhibit the same intensity and duration, indicating that the dual-wavelength pulses possess the soliton energy quantization effect. In the process of pulse–pulse collisions, two solitons pass through each other and maintain their properties, qualitatively distinct from single-wavelength solitons that never overlap each other. The dual-wavelength mode-locked operation evolves into single-wavelength mode locking with the decrease of the pumping strength. The dual-peak gain spectrum of erbium-doped fiber and the birefringence-induced cavity filtering effect play crucial roles in the formation of dual-wavelength solitons. Numerical results agree well with analytical solutions and experimental observations. Our study provides an optional method of measuring the fiber dispersion by means of the dual-wavelength solitons.

Switchable Dual-Wavelength and Passively Mode-Locked All-Normal-Dispersion Yb-Doped Fiber Lasers

A switchable dual-wavelength and passively mode- locked ytterbium-doped fiber laser (YDFL) in the all-normal-dispersion (ANDi) regime is reported and demonstrated for the first time. Using a phase-shifted long-period fiber grating (PS-LPFG) as an all-fiber format spectral filter in the laser cavity, a stable and switchable dual-wavelength mode-locked operation is achieved by nonlinear polarization evolution (NPE). The maximum output energy of the dual-wavelength pulse is 25.76 nJ at a repetition rate of 2.499 MHz. It opens a new possibility to achieve switchable multiwavelength and mode-locked laser output in the ANDi cavity in an all-fiber format.

Dual-wavelength mode-locked quantum-dot laser, via ground and excited state transitions: experimental and theoretical investigation

We report a dual-wavelength passive mode locking regime where picosecond pulses are generated from both ground (lambda = 1263 nm) and excited state transitions (lambda = 1180 nm), in a GaAs-based monolithic two-section quantum-dot laser. Moreover, these results are reproduced by numerical simulations which provide a better insight on the dual-wavelength mode-locked operation.