All-fiber Laser Cavity Research Articles

Transient light shift register mechanism of bi-chromatic pulse generation

Primary methods for generating short pulses in lasers require intracavity elements or physical mechanisms for modulation or the saturable absorption of radiation. This often complicates laser design and limits capabilities, particularly beyond single-wavelength operation. We propose and explore a method for the synchronous generation of bicolor, high-repetition-rate pulses that combines stimulated emission from Yb rare-earth ions and Raman scattering in a shared all-fiber laser cavity, without employing saturable absorbers or modulators. The proposed mechanism for pulsed lasing is analogous to an optical shift register, with two pulse trains shifting relative to each other by one period after every round trip. This naturally solves the critical problem of compensating for the dispersion-induced differential delay of bi-chromatic pulses during an intracavity round trip. The shift register inherently enables stationary generation of bi-chromatic pulses with a common relatively high repetition rate that is inversely proportional to the differential delay. We have demonstrated the feasibility of the proposed technique through the stable generation of sub-nanosecond bi-chromatic (1066 and 1241 nm) pulses with a repetition rate exceeding 166 MHz. The proposed approach is rather general, and we anticipate that it can facilitate more affordable bi-chromatic pulse generation in a variety of laser systems.

Tunable optical nonlinearities and surface plasmon resonance in Fe3O4 nanoparticles-decorated Ti3C2 MXene composite for ultrafast fiber lasers

In this work, the Ti3C2 MXene was modified with Fe3O4 nanoparticles to obtain a composite with in-plane optical anisotropy and surface plasmon properties. Based on a side-polished D-shaped fiber (DSF), this Fe3O4/Ti3C2 MXene (F/M) composite exhibits a tunable nonlinear optical (NLO) absorption response under 1.5 μm laser excitation with different polarization states. The modulation depths can be obtained from 0.9% to 12.1%. As an application, the ultrafast erbium-doped fiber laser (EDFL) with multiple pulsed laser operations was demonstrated using the F/M-DSF device as a saturable absorber (SA). Both stable Q-switching and mode-locking operations were demonstrated in the same all-fiber laser cavity, which generated pulsed laser with microsecond and sub-picosecond durations respectively. In addition, the bound state (BS) of solitons in harmonic mode-locked lasers with the pulse time interval of 3 ps and the highest order of 30th was also realized. This versatile and simple-structured all-fiber laser has great potential in various applications, such as optical communication. With the numerical simulations, the dynamic of F/M composite-based soliton mode-locking was also explored, illustrating the mechanism of soliton formation and propagation. This work not only expands the advanced applications of F/M composite in ultrafast photonics but also provides a new perspective for designing and optimizing its ultrafast modulating performance.

Fiber optical parametric oscillator made of soft glass

Fiber optical parametric oscillators (FOPOs) are compact optical sources of coherent and broadly tunable light compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band, but the strong material absorption of silica glass at wavelengths >2 µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two proof-of-concept FOPOs are presented, one driven by pure parametric gain leading to wavelength-tunable Stokes emission within the range 2.088-2.139 µm, and the other driven by Raman-assisted parametric gain leading to Stokes emission within the range 2.023-2.048 µm. This demonstration is a promising first step toward the development of fully fiberized MIR light sources.

Nanostructured Large Mode Area Fiber for Laser Applications

We developed a passive silica based large mode area fiber with the nanostructured core with a diameter of 30 m devoted to fiber Bragg grating inscription for application in an all-fiber laser cavity. The fiber is perfectly matched to the commercial active fiber with NA=0.06 and core/cladding diameters 30/250 m. Measured modal characteristics and bending loss of the fiber confirm single-mode operation for bending diameter of 8 cm with bending losses as low as 0.15 dB/m. Although the nanostructured fiber core is low germanium doped, we fabricated high reflectivity (98.5%) UV induced fiber Bragg grating (FBG) and verified its performance in fiber laser setup. The laser cavity formed with highly reflective FBG inscribed in the fiber and Fresnel reflection on the free end of active fiber results in lasing efficiency of 65.5%. The flexibility of the nanostructuring approach gives prospects for the development of free-form large mode area fibers for passive fiber components and matched with any type of active fibers.

Ultrafast Photonics of Ternary RexNb(1-x)S2 in Fiber Lasers.

Two-dimensional (2D) transition metal chalcogenides (TMCs) become more attractive upon addition of a third element owing to their unique structure and remarkable physical and chemical properties, which endow these materials with considerable potential for applications in nanoscale devices. In this work, a RexNb(1-x)S2-based saturable absorber (SA) device for ultrafast photonics applications is studied. The device is assembled by placing RexNb(1-x)S2 nanosheets with a thickness of 1-3 nm onto a microfiber to increase their compatibility with an all-fiber laser cavity. The prepared RexNb(1-x)S2-based device exhibits a modulation depth of 24.3%, a saturation intensity of 10.1 MW/cm2, and a nonsaturable loss of 28.5%. Furthermore, the RexNb(1-x)S2-based device is used to generate ultrashort pulses in an erbium-doped fiber (EDF) laser cavity. At a pump power of 260 mW, the EDF laser operates in a conventional soliton mode-locked region. The pulse width is 285 fs, and the repetition frequency is 61.993 MHz. In particular, the bound-state soliton mode-locking operation is successfully obtained in a pump power range of 300-900 mW. The bound-state pulses are formed by doubling identical solitons with a temporal interval of 0.8 ps. The output power is as high as 47.9 mW, and the repetition frequency is 123.61 MHz. These results indicate that the proposed RexNb(1-x)S2-based SAs have comparable properties to currently used 2D SAs and provide a basis for their application in the field of ultrafast photonics.

Study of asymmetric biconical fiber tapers for in-fiber Mach-Zehnder interferometers and applications in single-frequency fiber lasers.

In this paper, asymmetric biconical fiber tapers (ABFTs) for in-fiber Mach-Zehnder interferometers (IFMZIs) are proposed and analyzed to enhance the interference effect. The proposed ABFT-IFMZIs are fabricated, tested, and demonstrated in applications of single-frequency (SF) emissions when incorporated into an all-fiber laser cavity as the frequency selecting component. In comparison with the traditional IFMZIs composed of all symmetric biconical fiber tapers (SBFTs), higher average transmittance and fringe contrast have been demonstrated with the ABFT-based IFMZIs. When applied to the SF fiber laser emission, lower pump threshold and higher slope efficiency have also been confirmed with the ABFT-IFMZI device. The theoretical and experimental results have indicated that the interference effect of IFMZIs can indeed be improved by the designated asymmetry of conical taper angles in ABFTs that can offer an extra flexibility in fiber taper design, fabrication, and applications.

Layered structured binary alkaline metal phosphide of KP15 as saturable absorbers for ultrashort pulsed laser generation

We demonstrated an all-fiber passively mode-locked 980 nm picosecond laser using KP15 materials as saturable absorbers (SAs). The micron-sized wire-like KP15 crystals were prepared using a vapor-phase transfer method. The material not only shows excellent optoelectronic properties, such as optical anisotropic and large binding energy, but also long-term stability. By inserting the KP15 crystals into the ytterbium-doped all-fiber laser cavity, a mode-locked 980 nm laser with a pulse duration of 30 ps, a repetition rate of 15.65 MHz and spectral width of 5.6 nm was achieved for the first time, to the best of our knowledge. In addition, we investigated the long-term stability of the KP15-based mode-locked 980 nm laser, and the root-mean-square of the output power of the picosecond pulse was only 1.03% when operating for 4 h. The results indicated that the KP15 material prepared using a chemical vapor transport method was a promising SA for ultrafast fiber laser generation.

Pump-controlled flexible generation between dissipative soliton and noise-like pulses from a mode-locked Er-doped fiber laser.

We experimentally investigate the alternative generation of dissipative solitons (DSs) or noise-like pulses (NLPs) from a passively mode-locked Er-doped all-fiber laser with a 45° tilted fiber grating (45° TFG). The 45° TFG serves as an in-fiber polarizer for mode locking in the all-fiber laser cavity. Under the fixed orientations of the polarization controllers, flexible generation between DSs and NLPs can be precisely controlled by adjusting the pump power only. To the best of our knowledge, the total cavity length 4.92 m of our fiber laser is the shortest one among all NLP fiber lasers. We obtain the DS with 3 dB bandwidth of 20.4 nm centered at 1577 nm and the NLP with 3 dB bandwidth of 25.2 nm centered at 1574 nm. The fundamental repetition rate of the mode-locked pulses is 42.3 MHz. This DS-NLP switchable Er-doped fiber laser can be regarded as a multifunctional optical source for diverse practical and potential applications.

Noise-like pulses generated from a passively mode-locked fiber laser with a WS2 saturable absorber on microfiber

We report on a noise-like pulse (NLP) generation in a mode-locked erbium-doped all-fiber laser using a WS2-deposited microfiber saturable absorber (SA). The prepared WS2 SA can serve as an excellent mode-locked and highly nonlinear device in the all-fiber laser cavity. At proper pump power and polarization states, typical NLPs can be generated. Adjusting the polarization also yields special NLPs with second-order harmonic mode-locking. For typical NLPs, 37 mW maximum output power and 8.8 nJ pulse energy are achieved at 334 mW pump power. The microfiber-based WS2 component could be a potential device for exploring nonlinear dynamics, such as NLPs.

Wavelength tunable L Band polarization-locked vector soliton fiber laser based on SWCNT-SA and CFBG

Wavelength tunable L-Band polarization-locked vector soliton fiber laser based on single-walled carbon nanotube saturable absorber (SWCNT-SA) and chirped fiber Bragg grating (CFBG) is presented for the first time. By inserting the SWCNT-SA into an all-fiber laser cavity, polarization-locked vector solitons (PLVS) are obtained. The CFBG glued on a plastic cantilever is used for wavelength tuning. By mechanically bending the cantilever, the center wavelength of the PLVS pulses can be continuously tuned from 1606.8 nm to 1614 nm, while the polarization-locked state is kept stable. The properties and dynamics of PLVSs are experimentally investigated and stable PLVS operation including high-order PLVSs is demonstrated. The pulse width and repetition rate are 7.06 ps and 11.9 MHz at a wavelength of 1611 nm, respectively. This work demonstrates the feasibility of using polarization-insensitive CFBG to realize wavelength tuning in PLVS fiber laser.

Compact Two-Color Pr3+-Doped ZBLAN Fiber Lasers

ABSTRACTTwo-color laser simultaneous oscillation in compact trivalent praseodymium ion (Pr3+)-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber lasers is investigated. Fiber pigtails by coating high-reflective visible dielectric films are utilized as fiber mirrors (FMs) to construct compact all-fiber laser cavity. Reflectance/transmittance of FMs is intentionally designed to balance net gains and reduce gain competition of different lasable wavelengths in the constructed fiber lasers. By using two selected FMs with high reflectivity at green-light and low reflectivity at red-light, simultaneous green and red laser emission in all-fiber Pr3+-doped ZBLAN fiber laser is obtained. Moreover, simultaneous orange and red laser emission is also achieved with another selected FM of high reflectivity at orange-light and low reflectivity at red-light. Our work will provide an effective and easy method to construct compact special fiber (e.g.,ZBLAN fiber, chalcogenide fiber) lasers.

30 W fluoride glass all-fiber laser at 2.94 μm.

We report the demonstration of a 2938 nm erbium-doped fluoride glass fiber laser delivering a record output power of 30.5 W in continuous wave operation. The passively cooled all-fiber laser cavity based on intracore fiber Bragg gratings has an overall laser efficiency of 16% as a function of the launched pump power at 980 nm and a single-mode output beam quality of M2<1.2. This power scaling demonstration of a fiber laser operating near the vibrational resonance of water is likely to have a significant impact on several biomedical applications.

Mode-locking of Er-doped fiber laser using a multilayer MoS2 thin film as a saturable absorber in both anomalous and normal dispersion regimes.

Application of a multilayer Molybdenum Disulfide (MoS2) thin film as a saturable absorber was experimentally demonstrated by realizing a stable and robust passive mode-locked fiber laser via the evanescent field interaction between the light and the film. The MoS2 film was grown by chemical vapor deposition, and was then transferred to a side polished fiber by a lift-off method. Intensity-dependent optical transmission through the MoS2 thin film on side polished fiber was experimentally observed showing efficient saturable absorption characteristics. Using erbium doped fiber as an optical gain medium, we built an all-fiber ring cavity, where the MoS2 film on the side polished fiber was inserted as a saturable absorber. Stable dissipative soliton pulse trains were successfully generated in the normal dispersion regime with a spectral bandwidth of 23.2 nm and the pulse width of 4.98 ps. By adjusting the total dispersion in the cavity, we also obtained soliton pulses with a width of 637 fs in the anomalous dispersion regime near the lasing wavelength λ = 1.55 μm. Detailed and systematic experimental comparisons were made for stable mode locking of an all-fiber laser cavity in both the normal and anomalous regimes.