Femtosecond Laser Direct Writing Research Articles

Femtosecond Laser Direct-writing Tilted Fiber Bragg Gratings in Multi-core Fiber

Femtosecond Laser Direct-writing Tilted Fiber Bragg Gratings in Multi-core Fiber

Eight-wavelength-switchable single-frequency fiber laser with scattering-enhanced fiber-based wavelength self-adaptive linewidth compression

We demonstrate an eight-wavelength-switchable single-frequency (SF) ultra-narrow linewidth erbium-doped fiber laser (EDFL). A switchable polarization-dependent eight-channel filter (S-PDECF), fabricated using femtosecond laser direct-writing technology, determines the eight wavelengths of the laser output, with four channels concentrated near 1530 nm and the other four near 1550 nm. A dual-coupler ring-based compound-cavity filter is utilized to achieve single-longitudinal-mode selection for the EDFL. The introduction of a femtosecond laser direct-written scattering-enhanced fiber (SEF) effectively narrows the laser linewidth, enabling ultra-narrow linewidth outputs lasing at all eight wavelengths, and the wavelength self-adaptive linewidth compression of the SEF is verified for the first time. Furthermore, the incorporation of SEF significantly enhances the overall performance of the EDFL. The eight switchable single-wavelength laser outputs all exhibit exceptional characteristics, including spectral wavelength fluctuations of ≤0.011 nm, spectral peak power fluctuations of ≤0.54 dB, optical signal-to-noise ratios of ≥71 dB, linewidths of ≤248 Hz, output power fluctuations of ≤0.252 dB over a 10-min measurement period, and relative intensity noise of ≤−150.17 dB/Hz @≥ 3 MHz.

Study on the Thermal Radiation Characteristics of Tungsten Surface Grating Structures Prepared by Femtosecond Laser Direct Writing

Study on the Thermal Radiation Characteristics of Tungsten Surface Grating Structures Prepared by Femtosecond Laser Direct Writing

Short-length nanosecond pulsed 1.653-μm DBR fiber Raman laser oscillator fabricated by femtosecond laser direct-writing

We demonstrate a nanosecond pulsed 1.653-μm fiber Raman laser (FRL) oscillator in a short-length distributed Bragg reflector (DBR) cavity made by femtosecond laser direct-writing technique. The DBR FRL cavity is composed of commercial ultrahigh NA germanium-doped silica fiber with a short length of 10 m and a pair of fiber Bragg gratings (FBGs). The FBGs were directly inscribed on the ends of the Raman gain fiber, using femtosecond-laser point-by-point (PbP) writing method. A home-made 1.55-μm nanosecond fiber laser source was used as the pump of the FRL. 1.653-μm nanosecond pulsed laser oscillation with maximum average output power of 125 mW (corresponding to peak power of 6.6 W), 3 dB linewidth of ≤ 0.15 nm, and slope efficiency of 48 % was obtained under 1.55-μm pump with optimized repetition rate of 10 MHz. The optical signal-to-noise-ratio (OSNR) of the 1.653-μm narrow-linewidth Raman lasing is above 70 dB. The short-length DBR FRL output exhibits decently high degree of polarization (DOP) and high degree of linear polarization (DOLP) above 80 % in 3-hour period, benefitted from the birefringent FBGs made by femtosecond laser direct-writing method. It is expected that by further reducing the cavity length to < 1 m, the 1.653-μm DBR FRL oscillator made by femtosecond laser direct-writing method is promising as single-frequency narrow-linewidth, highly linearly polarized, high-OSNR laser sources for high-sensitivity CH4 gas detection.

Green smart multifunctional wooden roofs enabled by single-step hydrophobic laser-induced graphene fabrication

Global warming, contributing to the worsening climate crisis, has led to more frequent heavy snowfall and rainfall. This causes corrosion, mold, and structural damage to roofs, which shortens the roofs' lifespan and potentially creates safety hazards. Addressing these challenges, we propose an approach to develop a multifunctional roof crucial for proactive adaptation to extreme weather. In this article, we present hydrophobic laser-induced graphene (LIG) onto wood in a single-step process using femtosecond-laser-direct-writing (FsLDW) technology in ambient air without additional chemical treatment. This hydrophobic LIG, showcasing a high electrical conductivity of 10.0 Ω·sq⁻1 and a high contact angle of 148.8°, seamlessly integrates onto roofs, creating cost-effective, fast, eco-friendly, and smart roofing solutions. The hydrophobic surface of these LIG electrodes incorporates a heating function of LIG showcasing their versatility in providing waterproofing, drying wood, and facilitating de-icing functions. This eco-friendly invention, reliant solely on laser patterning on wood, not only extends roof lifespan but also relieves concerns about electronic waste and recycling, promising the integration of green, smart, and sustainable roofing solutions.

3D Directional Assembly of Liquid Crystal Molecules.

The precise construction of hierarchically long-range ordered structures using molecules as fundamental building blocks can fully harness their anisotropy and potential. However, the 3D, high-precision, and single-step directional assembly of molecules is a long-pending challenge. Here, a 3D directional molecular assembly strategy via femtosecond laser direct writing (FsLDW) is proposed and the feasibility of this approach using liquid crystal (LC) molecules as an illustrative example is demonstrated. The physical mechanism for femtosecond (fs) laser-induced assembly of LC molecules is investigated, and precise 3D arbitrary assembly of LC molecules is achieved by defining the discretized laser scanning pathway. Additionally, an LC-based Fresnel zone plate array with polarization selection and colorization imaging functions is fabricated to further illustrate the potential of this method. This study not only introduces a 3D high-resolution alignment method for LC-based functional devices but also establishes a universal protocol for the precise 3D directional assembly of anisotropic molecules.

Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties.

Luminescent carbon dots (CDs) were locally synthesized in the core of CYTOP fibers using IR femtosecond laser direct writing (FLDW), a one-step simple method serving as a post-treatment of the pristine fiber. This approach enables the creation of several types of modifications such as ellipsoid voids. The CDs and photoluminescence (PL) distribute at the periphery of the voids. The PL spectral properties were studied through the excitation/emission matrix in the visible range and excitation/emission spectra in the UV/visible range. Our findings reveal the presence of at least three distinct luminescent species, facilitating a broad excitation range extending from UV to green, and light emission spanning from blue to red. The average laser power and dose influence the quantity and ratio of these luminescent CD species. Additionally, we measured the spatially resolved lifetime of the luminescence during and after the irradiation. We found longer lifetimes at the periphery of the laser-induced modified regions and shorter ones closer to the center, with a dominant lifetime ~2 ns. Notably, unlike many other luminophores, these laser-induced CDs are insensitive to oxygen, enhancing their potential for display or data storage applications.

1.94 & 2.04 µm dual-band four-wavelength-switchable single-frequency narrow linewidth fiber laser using a novel fs-laser direct-written polarization-dependent four-channel filter

We present a dual-band four-wavelength-switchable single-frequency thulium-holmium co-doped fiber laser (THDFL) utilizing a novel band-switchable polarization-dependent four-channel filter (BS-PDFCF). The filter incorporates two high-birefringence fiber Bragg gratings (HB-FBGs) and an electrical-controlled optical switch (EC-OS). Specifically designed for operation in the 1.94 μm and 2.04 μm bands, two HB-FBGs are fabricated using femtosecond (fs) laser direct-writing technology in two segments of polarization-maintaining fibers via a point-by-point method. Each HB-FBG features two narrow-band reflection channels with perpendicular polarization directions. The EC-OS switches the operation band of the BS-PDFCF. A 1.2 m long dynamic ultra-narrow-band filter is employed in the THDFL to achieve single-longitudinal-mode oscillation. The THDFL achieves exceptional output performance, including four single-wavelength and two dual-wavelength operations, spectral wavelength and power fluctuations of ≤0.012 nm and ≤0.386 dB, respectively, OSNRs of >76 dB, RINs of ≤−142.48 dB/Hz@≥5 MHz, linewidths of ≤3.59 kHz@1.94 μm band and ≤5.46 kHz@2.04 μm band, and output power fluctuations of ≤0.109 dB in a measurement time span of 30 min.

Light-Triggered Transmittance Control in Thermoresponsive Hydrogels by Femtosecond Laser Direct Writing

Light-Triggered Transmittance Control in Thermoresponsive Hydrogels by Femtosecond Laser Direct Writing

Surface-Enhanced Raman Scattering Based on Sb2S3 Microstructures via Femtosecond Laser Direct Writing.

The noble-metal-free surface-enhanced Raman scattering (SERS) substrates have gained significant attention due to their abundant sources, signal uniformity, biocompatibility, and chemical stability. However, the lack of controllable synthesis and fabrication methods for high-SERS-activity noble-metal-free substrates hinders their practical applications. In this study, we demonstrate the use of a femtosecond laser direct writing technique to precisely manipulate and modify microstructures, resulting in enhanced SERS signals from Sb2S3 nonmetal-oxide semiconductor materials. Compared with unpatterned Sb2S3 samples, the Sb2S3 microstructures exhibited up to a 16-fold increase in Raman scattering intensity. Interestingly, our results indicate that the femtosecond laser can induce a transformation in the crystalline state of Sb2S3 and significantly enhance the Raman spectrum signal within the Sb2S3 microstructures. This enhancement is also highly dependent on the period and depth of the microstructures, possibly due to the cavity effects, resulting in a stronger local field enhancement.

Second harmonic generation of visible vortex laser based on a waveguide-grating emitter in LBO.

In this work, we propose a practical solution to visible vortex laser emission at 532 nm based on second harmonic generation (SHG) in a well-designed waveguide-grating structure. Such an integrated structure is fabricated by femtosecond laser direct writing (FsLDW) in an LBO crystal. Confocal micro-Raman spectroscopy is employed for detailed analysis of FsLDW-induced localized crystalline damage. By optical excitation at 1064 nm, the guiding properties, SHG performance, as well as vortex laser generation of the waveguide-grating hybrid structure are systematically studied. Our results indicate that FsLDW waveguide-grating emitter is a reliable design holding great promise for nonlinear vortex beam generation in integrated optics.

Printing 3D Metallic Structures in Porous Matrix.

The fabrication of metallic micro/nanostructures has great potential for advancing optoelectronic microdevices. Over the past decade, femtosecond laser direct writing (FsLDW) technology has played a crucial role in driving progress in this field. In this study, silica gel glass is used as a supporting medium, and FsLDW is employed to reduce gold and palladium ions using 7-Diethylamino-3-thenoylcoumarin (DETC) as a two-photon sensitizer, enabling the printing of conductive multilayered and 3D metallic structures. How the pore size of the silica gel glass affects the electrical conductivity of printed metal wires is systematically examined. This 3D printing method is versatile and offers expanded opportunities for applying metallic micro/nanostructures in optoelectronic devices.

Femtosecond laser one-step direct-writing high quality volume Bragg grating.

Volume Bragg grating is one-step fabricated with femtosecond laser direct-writing technology inside a high nonlinearity chalcogenide glass of As2S3. As the generated femtosecond laser filamentation effect could combined with the cylindrical lens focusing method, a two-dimensional refractive index change interface could spontaneously grow along the incident direction with either the laser pulse energy or number increasing. A number of two-dimensional refractive index change interfaces are periodically arranged to stack into a volume Bragg grating. Through periodically moving the sample stage, a grating of 2 mm × 2 mm × 1.7 mm can be fabricated in 15 minutes. And the maximum diffraction efficiency of grating reached 95.49% under the optimal parameters. This study provides a new processing strategy for femtosecond laser direct-writing volume Bragg grating with high processing efficiency and excellent structural performance.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review.

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Three‐Dimensional Waveguide Topological Photonic Structures in Glass Fabricated by Femtosecond Laser Direct Writing (Invited)

Three‐Dimensional Waveguide Topological Photonic Structures in Glass Fabricated by Femtosecond Laser Direct Writing (Invited)

Femtosecond Laser Direct Writing of On-Chip Tilted Waveguide Bragg Gratings With Controllable Cladding Modes for Refractive Index Sensing

Femtosecond Laser Direct Writing of On-Chip Tilted Waveguide Bragg Gratings With Controllable Cladding Modes for Refractive Index Sensing

Femtosecond Laser Direct Writing of Polarization-Controllable DBR Fiber Lasers for Harsh Environmental Vibration/Acoustic Sensing

Femtosecond Laser Direct Writing of Polarization-Controllable DBR Fiber Lasers for Harsh Environmental Vibration/Acoustic Sensing

Femtosecond Laser Direct-Writing Optical Waveguide Amplifiers and Lasers (Invited)

Femtosecond Laser Direct-Writing Optical Waveguide Amplifiers and Lasers (Invited)

Monolithic ultrashort-cavity DBR gain-switched thulium doped fiber laser made by high-precision femtosecond laser direct-writing

We demonstrate a novel monolithic ultrashort-cavity distributed Bragg reflector (DBR) gain-switched thulium doped silica fiber laser. Commercial heavily thulium doped non-polarization-maintaining silica fiber was selected as the gain medium. Monolithic linear laser resonator, which includes a pair of uniform fiber Bragg gratings (FBGs) with a space of 1.0-mm inbetween, was inscribed in the thulium fiber by femtosecond-laser point-by-point (PbP) writing method. The reflectivity of either FBG is close to 100 % and the effective cavity length is calculated to be 3.5 mm. Such an ultrashort-DBR-cavity fiber laser exhibited high Q factor and low cavity loss, allowing the efficient utilization of pump power within the millimeter-long cavity. Single-longitudinal, linearly polarized, gain-switched TDFL at 2003 nm, with a recorded shortest pulse duration of 4.3 ns, a repetition rate of 50 kHz, a maximum peak power of 500 W, and single pulse energy of 2.14 μJ, has been realized, benefitted from the ultrashort cavity length.

Bragg gratings with novel waveguide models fabricated in bulk glass via fs-laser writing and their slow-light effects.

We present the experimental realization of an innovative parallel partially overlapping waveguides (PO-WGs) model grounded in the thermal accumulated regime and fabricated using femtosecond (fs) laser direct-writing within low-iron bulk glass. The 75mm long novel PO-WGs model was made by partially overlapping the shell parts of two core-shell types of waveguides via a back-and-forth single pass fs-laser inscription. The detailed evolution of the PO-WGs model from inception to completion was offered, accompanying by a thorough characterization, which unveils a substantial refractive index (RI) change, on the order of 10-3, alongside low propagation loss (0.2 dB/cm) and distinctive features associated with the single mode and shell-guided light. Notably, the unsaturated performance of PO-WGs model after the primary inscription paves the way for potential applications in the successful creation of two distinctive types of Bragg gratings: first-order dot-Bragg grating and second-order line-Bragg grating. The 75 mm long dot-Bragg grating was written by a periodic dot array with a height of 6 µm atop the PO-WGs, and the birefringence was measured of 1.5 × 10-5 with a 16 pm birefringence-induced wavelength difference. The line-Bragg grating, which was inscribed with dual PO-WGs extending the line grating part to 40 mm in length along its period for increasing the transmission dip, exhibits a pronounced polarization dependence showcasing an effective birefringence of 4.2 × 10-4 at the birefringence-induced wavelength difference of 0.45 nm. We delved into the slow-light effects of the two Bragg gratings thoroughly, which the theoretical analysis revealed an effective group delay of 0.58 ns (group index 2.3) for the dot-Bragg grating. Similarly, the line-Bragg grating exhibited an effective group delay of 0.3 ns (group index 2.3), in good agreement with experimental measurements. These findings underscore the exciting potential of our gratings for creating optical slow-wave structures, particularly for future on-chip applications.