Compact Fiber Laser Research Articles

Dissipative soliton resonance Ytterbium-doped fiber laser with cylindrical vector beam generation

We experimentally demonstrate a dissipative soliton resonance (DSR) Ytterbium-doped fiber laser with high-purity cylindrical vector beam (CVB) generation, using a mode-selective coupler (MSC) as transverse mode converter and splitter. The all-normal-dispersion mode-locked Ytterbium-doped fiber laser operating at DSR regime without spectral filter can deliver CVB pulses with a pulse duration of ∼733 ps and a pulse energy as high as ∼0.439 nJ. The radially and azimuthally polarized beams can be switched by adjusting the polarization controller, with a high mode purity measured to be >94.5%. This compact DSR fiber laser could find potential applications in the field of material processing, nonlinear optics and so on.

结构紧凑的双波长连续波掺铒光纤激光器

Multiwavelength erbium-doped fiber lasers can be applied to many fields, such as wavelength division multiplexing optical communication and others attracting considerable attention. To meet the requirements of different applications, we propose a compact dual-wavelength continuous-wave erbium-doped fiber laser based on nonlinear amplifying loop mirror. An all-polarization-maintaining fiber cavity is adopted in which there are only three intracavity devices besides fiber itself:a wavelength division multiplexer, a 2×2 fiber coupler and a fiber reflector. The intensity-dependent loss effect induced by the nonlinear amplifying loop mirror is used to equalize the intensity in the cavity. The input laser with higher power suffers a higher loss than the one with lower power. This feature can be used to suppress mode competition and achieve stable multiwavelength oscillation. With a pump power of 260 mW, dual-wavelength erbium-doped fiber laser can be achieved, with wavelengths of 1 560.5 nm and 1 563.2 nm, respectively. The side-mode suppression ratio is 46.8 dB. As pump power increases, the laser can operate in single-, dual-and triple-wavelength regions in proper order. As the multi-wavelength lasing oscillation is a balance between intensity-dependent loss and mode competition, the intensity change breaks the original balance state, resulting in the change in number and wavelength of lasing lines. This laser is simply structured and easy to operate. It can have applications in many fields.

Passively Q-switched and mode-locked Erbium-doped fiber laser with topological insulator Bismuth Selenide (Bi2Se3) as saturable absorber at C-band region

We experimentally demonstrate Q-switched and mode-locked Erbium-doped fiber laser (EDFL) by using topological insulator (TI) Bismuth Selenide (Bi2Se3) as saturable absorber (SA). The fabricated Bi2Se3 SA exhibits modulation depth and saturation intensity at 39.8% and 90.2 MW/cm2, respectively. By incorporating the fabricated Bi2Se3 SA into the laser cavity, Q-switching operation is generated with repetition rate ranging from 23.5 kHz to 68.2 kHz, pulse width ranging from 2.4 μs to 8.6 μs and maximum peak power is calculated at 19.9 mW. Our cavity can also generate soliton mode-locked pulse with repetition rate of 23.3 MHz and pulse width of 0.63 ps by inserting an additional 5 m long single mode fiber (SMF) into the existing laser cavity. Spectral peaks due to Kelly side-bands and four wave mixing (FWM) were observed on the soliton spectrum. Both Q-switching and mode-locking pulses are stable in the laboratory environment, allowing the realization of compact and low cost pulsed fiber laser with Bi2Se3 SA for various photonics applications.

Bend resistant large mode area fiber with step-index core and single trench

Abstract A novel bend resistant large mode area fiber with step-index core and single trench in the cladding is proposed. Numerical results demonstrate that the largest effective mode area reaches up to 2460 μm2 at the wavelength of 2 μm when the bend radius is only 10 cm. To achieve the better performance of single mode, the loss ratio of the lowest loss of higher order mode to the highest loss of fundamental mode can reach up to 886 with a fundamental mode bend loss lower than 0.0083 dB/m through optimizing structure parameters. The circular symmetry of fiber structure makes it insensitive to the bending direction. Furthermore, this fiber structure can be also used to develop bend resistant large mode area fiber with high performance at the wavelengths of 1.06 μm and 1.55 μm. Due to large mode area, good single mode properties, small bend radius and insensitivity to bend direction, this fiber has the potential application for compact high power fiber lasers.

High-power dissipative soliton resonance fiber laser with compact linear-cavity configuration

An ultra-compact mode-locked Yb-doped fiber laser under the operation regime of dissipative soliton resonance (DSR) has been demonstrated, which exports sub-nanoscond pulses with a maximum output average power of 2.4 W. The linear-cavity configuration of the proposed fiber laser is formed by a highly reflective fiber Bragg grating at 1066 nm and a nonlinear optical loop mirror (NOLM) consisting of a 5/95 optical coupler. As a result, DSR pulses with maximum average power of 2.4 W and repetition rate of 10.119 MHz have been obtained, when pump power is 10 W. The compact DSR Yb-doped fiber laser with high output power have great potential applications in material processing, optical communications, and so on.

Efficient Terahertz Generation Using Fe/Pt Spintronic Emitters Pumped at Different Wavelengths

Recent studies in spintronics have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz radiation sources. Such spintronic multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect, a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800-nm excitation wavelength using femtosecond Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 {\mu}m MgO substrate is just as effective as a THz radiation source when excited either at {\lambda} = 800 nm or at {\lambda} = 1550 nm by ultrafast laser pulses from a fs fiber laser (pulse width close to 100 fs, repetition rate around 100 MHz). Even with low incident power levels, the Fe/Pt spintronic emitter exhibits efficient generation of THz radiation at both excitation wavelengths. The efficient THz emitter operation at 1550 nm facilitates the integration of such spintronic emitters in THz systems driven by relatively low cost and compact fs fiber lasers without the need for frequency conversion.

PbS Nanoparticles for Ultrashort Pulse Generation in Optical Communication Region

AbstractLead sulfide (PbS) has attracted great attention due to its unique electronic, optical, and chemical properties. In particular, the narrow bandgap of PbS (≈0.37 eV) makes it very suitable for the ultrafast application in optical communication or even longer wavelength region. In this work, PbS nanoparticles' (NPs) dispersion without any polymer is utilized as saturable absorber (SA) to generate ultrafast pulse in a fiber ring laser for the first time. The characterization and nonlinear properties of PbS NPs are investigated experimentally. PbS NPs are deposited on a flange to compose a nonlinear device. The nonlinear absorption is measured by a power‐dependent method with a modulation depth of 12.2%. Most importantly, PbS NPs can be applied for the ultrafast photonics applications. A compact mode‐locked fiber laser with 1.01 ps pulse duration, 2.93 nm spectral width, and 3.97 MHz repetition rate at 1533 nm is successfully achieved with long time stability. The output laser is detected with a good stability for more than 1 month without any degradation. This work can demonstrate that the PbS NPs' dispersion is indeed a new and excellent photonics material for SA photonics, photoconductive detection, and optical modulator, etc.

Multi‐component yttrium aluminosilicate (YAS) fiber prepared by melt‐in‐tube method for stable single‐frequency laser

AbstractThe multi‐component glass fibers have demonstrated their unique advantages in the application of single‐frequency lasers due to their higher solubility of rare‐earth ions and thus a higher gain per unit length in a compact fiber laser cavity. In this study, multi‐component yttrium aluminosilicate (YAS) fiber with high doping concentration of Yb3+ was prepared by the “melt‐in‐tube” (MIT) method. A unit‐length gain of 3 dB/cm was obtained in a 4.4 cm‐long YAS fiber, the laser output slope efficiency reached 23.8% in a 10 cm‐long Yb:YAS fiber. Single‐frequency laser operation was achieved in a 1.7‐cm‐long Yb:YAS active fiber. To the best of our knowledge, this is the first demonstration of single‐frequency laser with this YAS glass fiber as gain medium. The novel multi‐component YAS fiber can be applied as a new gain material to realize single‐frequency fiber laser.

Route towards extreme optical pulsation in linear cavity ultrafast fibre lasers

Pathways towards the generation of extreme optical pulsation in a chaotic transition regime in a linear fibre laser cavity configuration are presented. In a thulium mode-locked fibre laser, extreme events that can be controllably induced by manipulating the cavity birefringence for pulse energies exceeding the single soliton pulse operating regime are studied in detail for the first time. While a solitonic pulsation structure at the fundamental repetition rate is maintained, additional energy is shed in a chaotic manner, leading to broader spectral generation and shorter pulse durations whose behaviour deviates significantly from a classical statistical distribution. These pulses display markedly different characteristics from any previously reported extreme events in fibre lasers associated with multiple solitons and pulse bunching, thus presenting a novel observation of extreme pulsation. Detailed noise studies indicate that significant enhancement of relaxation oscillations, modulation instability and the interplay with reabsorption mechanisms contribute in this transient chaotic regime. The extreme pulsation generated in a compact fibre laser without any additional nonlinear attractors can provide an attractive platform to accelerate the exploration of the underlying physics of the chaos observed in mode-locked laser systems and can lead to novel fibre laser cavity designs.

Ultralong \u03c0-phase shift fiber Bragg grating empowered single-longitudinal mode DFB phosphate fiber laser with low-threshold and high-efficiency

Phosphate glass fiber is one of the candidates for building compact fiber lasers because of its capability of high-concentration of rare-earth ions doping in fiber core. Nevertheless, it is challenging for the integration of UV-written intra-core fiber Bragg gratings into the fiber laser cavity due to the low photosensitivity of phosphate glass fiber. The research presented in this paper will focus on demonstration of UV-written Bragg gratings in phosphate glass fiber and its application in direct-written short monolithic single-frequency fiber lasers. A 5-cm-long strong π-phase shift Bragg grating structure is direct-inscribed into the Er/Yb co-doped gain fiber using an excimer laser. The fiber laser device emits output power of 10.44 mW with a slope efficiency of 21.5% and the threshold power is about 42.8 mW. Single-longitudinal mode operation is validated by radio frequency spectrum measurement. Moreover, the output spectrum at the highest power shows an excellent optical signal to noise ratio of about 70 dB. These results, to the best of our knowledge, show the lowest power threshold and highest efficiency among the reports that using the same structure to achieve single-longitudinal mode laser output.

Coherent Perfect Absorption in a Weakly Absorbing Fiber

Coherent perfect absorption refers to the interferometric enhancement of absorption in a partially lossy medium upto 100%. This can be achieved without modifying the absorbing medium itself, instead of engineering its photonic environment. Ion-doped fibers are one of the most technologically relevant absorbing materials in optics, which are widely employed in fiber amplifiers and lasers. Realizing complete optical absorption of an incident field in short-length moderately-doped fibers remains a challenge for the cost-effective design of compact fiber lasers. Here, we exploit the concept of coherent perfect absorption to overcome this challenge, whereby two appropriately designed fiber Bragg gratings define a short-length erbium-doped-fiber cavity that enforces complete absorption of an incident field on resonance--independently of the doped-fiber intrinsic absorption. This approach applies to any spectral window and guarantees the efficient utilization of the fiber dopants along its length, thus, suggesting the possibility of next-generation efficient single-longitudinal-mode fiber lasers for applications in optical communication, sensing, and metrology.

Self Q-switched mode-locking in compact red Pr3+-doped ZBLAN fiber laser

The self Q-switching mode-locking effect in compact red fiber laser has been investigated. The Q-switched mode-locking state can keep operating with a pump power ranging from 120.5 mW to 564.8 mW. The maximum average output power of this self Q-switched mode-locking laser is 22.5 mW, and the central wavelength of the output optical spectrum is 635.9 nm with a 3 dB bandwidth of 2.4 nm, as well as the fundamental repetition rate of mode-locking pulse trains being 25.8 MHz. This work can provide an attractive method for Q-switched mode-locking pulse generation in visible fiber lasers.

A two-stage optical parametric amplifier for femtosecond fiber laser generation at 920 nm

We demonstrate a cascaded, two-stage, fiber-based optical parametric amplifier (OPA) in which the signal pulses are generated in the first stage via spontaneous degenerate four-wave mixing (DFWM) mechanism and subsequently are used as the seed pulse for the stimulated DFWM in the second stage. A compact femtosecond fiber laser provides the pump pulse with 220-fs duration at 20-MHz repetition rate. Large-mode area (LMA) photonic crystal fibers (PCFs) with zero dispersion wavelength at 1054 nm and a dispersion slope of 0.20 ps/km/nm2 provide the parametric gain. Pulses with 2-mW average power in spectral range from 850 to 1000 nm are obtained from the first-stage OPA, and they are further amplified to 23.4 mW in the second stage OPA, corresponding to 10.7-dB parametric gain. The output pulse duration and spectral bandwidth are closely related to the temporal delay between the signal and pump pulses in the second stage. With an optimized time delay, pulses with >1 nJ energy and <200 fs duration are obtained at the spectral range from 850 to 1000 nm.

Dead-band-free, high-resolution microwave frequency measurement using a free-running triple-comb fiber laser

Microwave photonic solutions of frequency measurement have advantages in broad frequency coverage, but achieving high-resolution measurement remains a challenge. Those schemes based on optical frequency combs could achieve high-resolution measurement over a broad frequency range. Here, a dead-band-free, high-resolution microwave frequency measurement scheme based on undersampling the microwave signal by three pulse sequences generated from a triple-wavelength mode-locked fiber laser is proposed and demonstrated. The triple-wavelength ultrashort pulses generated in one laser cavity have slightly different repetition rates due to chromatic dispersion. This eliminates the needs of multiple mode-locked lasers and frequency control between them and drastically reduces the system complexity. The absolute frequency of the microwave signal can be determined based on three down-converted low-frequency beat notes of the microwave signal with the nearest comb lines without ambiguity. A 10–10 relative measurement precision at a sampling speed of 100 Hz is demonstrated from 1 to 20 GHz, and the measurement accuracy remains within 0.3 Hz. Microwave signal with an RF power as low as −75 dBm can be measured with a 10 Hz precision at 10 GHz by using RF frontend amplifiers. The simple and compact triple-comb fiber laser would enable the development of low-complexity, high-performance microwave characterization instrument.

Bending-Resistant Design of a Large Mode Area Segmented Cladding Fiber With Resonant Ring

A novel design of segmented cladding fiber (SCF) with resonant ring is proposed in this paper. A high leakage loss ratio (>100) between the high-order modes (HOMs) and the fundamental mode can be achieved at wavelength 1.064 μm. The HOMs suppression is better than the traditional SCF. The numerical results show that the effectively single-mode operation with a mode area of 790 μm2 can be achieved at a bend radius of 15 cm. Besides, the fiber performance is insensitive to the bending orientation at the ranging of [−180°, 180°]. This fiber design shows great potential in developing compact high-power fiber lasers and amplifiers.

2 µm high-power dissipative soliton resonance in a compact σ-shaped Tm-doped double-clad fiber laser

We report direct generation of a high-power, large-energy dissipative soliton resonance (DSR) in a 2 µm Tm-doped double-clad fiber laser. A compact σ-shaped cavity is formed by a fiber Bragg grating and a 10/90 fiber loop mirror (FLM). The 10/90 FLM is not only used as an output mirror, but also acts as a nonlinear optical loop mirror for initiating mode locking. The mode-locked laser can deliver high-power, nanosecond DSR pulses at 2005.9 nm. We further perform a comparison study of the effect of the FLM’s loop length on the mode-locking threshold, peak power, pulse energy, and optical spectrum of the DSR pulses. We achieve a maximum average output power as high as 1.4 W, a maximum pulse energy of 353 nJ, and a maximum peak power of 84 W. This is, to the best of our knowledge, the highest power for 2 µm DSR pulses obtained in a mode-locked fiber laser.

Cascaded Brillouin, Raman, and Four-Wave-Mixing Generation in a 1.06-μm Microsphere-Feedback Yb-Fiber Laser

We propose and experimentally demonstrate a compact microresonator-feedback single-frequency fiber laser at 1.06 μm, and further initiating different-type nonlinear lasing based on stimulated Brilliouin scattering, stimulated Raman scattering, and four-wave mixing (FWM). A silica microsphere with an ultrahigh Q-factor is employed in our experiment as a narrow bandwidth cavity mirror around 1.06 μm, and a generator of nonlinear optical effects subsequently. With the help of mode selection both from the silica microsphere and a fiber Bragg grating, single-frequency lasing with a linewidth as narrow as 281 kHz is obtained at 1.06 μm by employing 974-nm laser diode pumped Ytterbium-doped fiber as a gain medium. By optimizing the polarization states, controlling the coupling position between the fiber taper and microsphere as well as the pump power, three-order cascaded Brilliouin Stokes lasings at 1.06 μm, and cascaded Raman lasing at 1.12, 1.18 and 1.23 μm are realized, respectively. An FWM-based optical frequency comb (OFC) with a bandwidth ∼31 nm is further realized with center wavelength of ∼1.06 μm. Interestingly, a 1.18-μm-centered OFC with ∼37-nm bandwidth is also generated assisted by the second-order Raman-gain.

An actively Q-switched fiber laser with cylindrical vector beam generation

We demonstrate an actively Q-switched fiber laser with cylindrical vector beam (CVB) emission using a few-mode fiber Bragg grating as the mode selection component and an acousto-optic modulator to achieve Q-switching. To the best of our knowledge, this is the first such demonstration. Using a linear cavity configuration, an actively Q-switched CVB with a pulse width of about 64 ns, a pulse energy of 4.25 µJ and a repetition rate of 20 kHz has been obtained. Moreover, by tuning the polarization controllers radially and azimuthally, polarized Q-switched beams can be excited separately with a polarization purity of >94.5%. This compact Q-switched fiber laser with ns CVB pulse output could find potential applications in the field of material processing, nonlinear optics and so on.

Mid-infrared Fe2+:ZnSe semiconductor saturable absorber mirror for passively Q-switched Er3+-doped ZBLAN fiber laser

A mid-infrared (mid-IR) semiconductor saturable absorber mirror (SESAM) based on Fe2+:ZnSe for passively Q-switched Er3+-doped ZBLAN fiber laser has been demonstrated. Fe2+:ZnSe SESAM was fabricated by electron beam evaporation method. Fe2+ was innovatively doped into the reflective Bragg stack, in which ZnSe layer served as both doped matrix and high refractive layer during the fabricating process. By using the Fe2+:ZnSe SESAM, stable passively Q-switched pulses with the minimum pulse width of 0.43 μs under a repetition rate of 160.82 kHz were obtained. The recorded maximum average output power of 873 mW with a peak power of 12.59 W and pulse energy of 5.43 μJ were achieved. The results demonstrated a new method for fabricating Fe2+:ZnSe SESAM, which can be used in compact mid-IR Q-switched fiber laser.

Rapid virtual hematoxylin and eosin histology of breast tissue specimens using a compact fluorescence nonlinear microscope

Up to 40% of patients undergoing breast conserving surgery for breast cancer require repeat surgeries due to close to or positive margins. The lengthy processing required for evaluating surgical margins by standard paraffin-embedded histology precludes its use during surgery and therefore, technologies for rapid evaluation of surgical pathology could improve the treatment of breast cancer by reducing the number of surgeries required. We demonstrate real-time histological evaluation of breast cancer surgical specimens by staining specimens with acridine orange (AO) and sulforhodamine 101 (SR101) analogously to hematoxylin and eosin (H&E) and then imaging the specimens with fluorescence nonlinear microscopy (NLM) using a compact femtosecond fiber laser. A video-rate computational light absorption model was used to produce realistic virtual H&E images of tissue in real time and in three dimensions. NLM imaging could be performed to depths of 100 μm below the tissue surface, which is important since many surgical specimens require subsurface evaluation due to contamination artifacts on the tissue surface from electrocautery, surgical ink, or debris from specimen handling. We validate this method by expert review of NLM images compared to formalin-fixed, paraffin-embedded (FFPE) H&E histology. Diagnostically important features such as normal terminal ductal lobular units, fibrous and adipose stromal parenchyma, inflammation, invasive carcinoma, and in situ lobular and ductal carcinoma were present in NLM images associated with pathologies identified on standard FFPE H&E histology. We demonstrate that AO and SR101 were extracted to undetectable levels after FFPE processing and fluorescence in situ hybridization (FISH) HER2 amplification status was unaffected by the NLM imaging protocol. This method potentially enables cost-effective, real-time histological guidance of surgical resections.