Whispering-gallery-mode full-color laser textiles and their anticounterfeiting applications

Integrating light into textiles enables new wearable technologies spanning displays, safety, fashion, and therapy. While luminescent and electronic textiles are advancing, there remains no facile approach to fabricate large-area, flexible lasing textiles. Whispering-gallery-mode (WGM) microcavities offer high Q factors and small mode volumes and can be fabricated by diverse techniques, making them promising for integration. Polymer microfibers are attractive due to mechanical flexibility and biocompatibility and can serve both as resonant cavities and flexible textile elements. The research question addressed here is how to mass-produce flexible, multicolor WGM lasing microfibers that can be woven into large-area textiles with wide color gamut, and how to encode them for anticounterfeiting. The purpose is to develop a scalable fabrication method, demonstrate full-color lasing textiles with tunable emission, and showcase practical encryption by nanoparticle patterning. This is important for enabling flexible laser displays and wearable photonic devices.

Prior work has demonstrated light-emitting fabrics and smart textiles capable of communication, sensing, and energy functions. Microlaser arrays have expanded optoelectronic capabilities, with WGM microcavities used in full-color imaging, sensing, on-chip communication, and encryption. WGM resonators have been made from glass, semiconductors, and polymers; polymer-based WGM cavities are especially compelling for flexibility and biocompatibility. Polymer microfibers provide both resonant cavities and flexible substrates for wearables. Despite advances in WGM devices and fabrication (microfabrication, self-assembly, inkjet printing, electrospinning), large-area lasing textiles composed of woven WGM microfibers had not been reported, and scalable, controllable microfiber fabrication remained a challenge.

Fabrication strategy: A gravity-assisted rotatory drawing method produces flexible polymer microfibers that act as WGM cavities. A syringe dispenses a viscous PVA/SDS/dye solution at a controlled, slow flow rate onto a rotating drum collector. Gravity sustains an elongating liquid filament that is uniformly collected between drum fins. The syringe position is motorized to translate, yielding evenly arranged microfiber films over tens of centimeters. Solvent evaporation forms free-standing microfibers that can be detached and woven into textiles. Materials and ink formulations: Polyvinyl alcohol (PVA, Mw 198,000 g/mol) at 176 mg mL⁻¹ in deionized water serves as the polymer matrix. Sodium dodecyl sulfate (SDS) adjusts solution viscosity and surface tension; concentrations ranged from 10–50 mg mL⁻¹. Laser dyes as gain media: disodium 4,4'-bis(2-sulfonatostyryl) biphenyl (S420, blue), fluorescein disodium salt (Uranin, green; high concentration enabling yellow by reabsorption), rhodamine 6G (R6G, orange), and rhodamine B (RhB, red). Dye concentrations used: S420 12 mg mL⁻¹, R6G 3 mg mL⁻¹, RhB 6 mg mL⁻¹; Uranin 1 and 10 mg mL⁻¹ to tune emission. Solutions were magnetically stirred at 60 °C for 6 h and loaded into 2.5 mL syringes. Process parameters: Microsyringe pump flow rate 1 mL h⁻¹; drum rotation 3 rpm; syringe translation 3 mm s⁻¹; tip-to-collector distance 17 cm; ambient environment. Viscosity modulation via SDS controlled microfiber diameter. Without SDS (low viscosity), capillary retraction yields fibers too thin for lasing. Post-processing for waterproofing: Because PVA is water-soluble, formed microfibers were treated with glutaraldehyde vapor to crosslink PVA via acetal bridges between hydroxyl groups and difunctional aldehyde groups, rendering fibers waterproof with minimal impact on lasing properties. Textile weaving and patterning: Multicolor microfibers doped with different dyes were woven into patterns (e.g., radial/orthogonal, triangles, pentangles, and a “BJUT” motif) on fabric meshes. The number of microfibers and pumping positions/spots were adjusted to tune perceived colors and color temperature. Anticounterfeiting encoding: TiO₂ nanoparticles (100 nm, high refractive index) dispersed in ethanol were inkjet-printed in patterns onto lasing textiles. Printed NPs introduce scattering loss at the microfiber surface and absorb some UV light, creating optical leakage channels that suppress lasing locally. This enables binary encoding over m×n cells: lasing = “1”, fluorescence-only = “0”. Standard printers and phone-generated QR codes can program patterns for authentication labels. Optical characterization: Microfibers were optically pumped by a 343 nm nanosecond laser (third harmonic of 1030 nm Yb:YAG), 200 Hz repetition rate, 1 ns pulse width. Emissions were collected via a microscope and analyzed with a PI spectrometer. Mode properties including free spectral range (FSR) versus diameter and polarization modes (TE/TM) were examined. Refractive index of mixed PVA–SDS–dye films was measured by ellipsometry.

• Scalable microfiber production: Gravity-assisted rotatory drawing yields smooth, cylindrical polymer microfibers that can be woven into large-area textiles with uniform arrangement.
• Diameter control via viscosity: Increasing SDS concentration from 10 to 50 mg mL⁻¹ increases bulk solution viscosity from ~25 to ~175 Pa·s at 30 °C and enlarges microfiber diameters from 4.8 to 65.3 µm.
• WGM confirmation: FSR decreases with increasing microfiber diameter; λ²/FSR vs diameter shows a linear relation with slope corresponding to πn_cav ≈ 5.00, giving n_cav ≈ 1.59, consistent with ellipsometry (n ≈ 1.55). TE and TM modes and mode numbers were identified.
• Lasing performance: Clear thresholds observed for S420-, Uranin-, and RhB-doped microfibers at ~11.5, 10.5, and 28.1 µJ cm⁻², respectively. Above threshold, spectra show sharp peaks with FWHM as low as 0.03 nm (Lorentz fit), yielding Q ≈ 18,000. RhB exhibits higher threshold due to smaller UV absorption cross-section.
• Full-color display and color gamut: RGB microfibers woven into a triangular pattern produce tunable multicolor lasing (B, G, R, C, M, Y, and white) by selective pumping. The mixed white’s chromaticity is close to ideal white. The achievable color gamut is approximately 79.1% larger than standard sRGB space.
• Mechanical and environmental stability: Microfibers are flexible and bendable; bent fibers retain lasing with slightly higher threshold. Glutaraldehyde crosslinking renders fibers waterproof with almost no change in lasing properties; morphology and lasing persist after 24 h water immersion.
• Anticounterfeiting encoding: Inkjet-printed TiO₂ NP patterns are invisible under natural/UV light but selectively suppress lasing under above-threshold pumping, enabling binary encoding (lasing=1, fluorescence=0) for information storage (e.g., QR codes) using commercial printers.

The study addresses the gap in scalable fabrication of large-area, flexible lasing textiles by introducing a gravity-assisted rotatory drawing method that mass-produces smooth polymer WGM microfibers. By tuning solution viscosity (via SDS) and gain media (dye type and concentration), fiber diameter and lasing characteristics are controlled, enabling robust WGM operation with high Q and low thresholds. Weaving multicolor microfibers into programmable patterns and controlling pumping positions realize full-color lasing with a wide color gamut surpassing standard sRGB, demonstrating suitability for flexible laser displays. Post-fabrication crosslinking ensures environmental resilience (waterproofing) without compromising lasing, crucial for wearable applications. The inkjet-printed TiO₂ NP approach provides a simple, scalable route to encode textiles with spatially programmable lasing/fluorescence responses, enabling practical anticounterfeiting labels readable under laser excitation. Collectively, the findings validate that polymer microfibers can unify function as both flexible substrates and high-quality WGM cavities for advanced wearable photonics.

A facile, scalable method to mass-produce flexible, multicolor WGM lasing microfibers was demonstrated. By regulating dye composition and solution viscosity, high-Q lasing with low thresholds was achieved, and microfibers were woven into full-color textiles exhibiting a color gamut about 79.1% larger than standard RGB. Posttreatment with glutaraldehyde produced waterproof fibers with stable lasing even after prolonged water exposure and mechanical bending. Inkjet printing of TiO₂ nanoparticles enabled programmable suppression of lasing for binary encoding, providing an effective anticounterfeiting label. This work unifies fabrication and application of lasing textiles and provides a pathway toward novel wearable lasing devices.

• Material sensitivity to water necessitated posttreatment; untreated PVA microfibers are water-soluble and unsuitable for wet environments.
• Fiber formation without adequate SDS (low viscosity) yields filaments too thin to support lasing, indicating a limited processing window for viscosity.
• RhB-doped microfibers exhibited higher lasing thresholds due to weaker UV absorption, suggesting dye-dependent performance variations.
• Bending introduces a slight increase in lasing threshold, indicating some sensitivity to mechanical deformation.
• Demonstrations used UV pumping (343 nm), which may limit practical deployment without suitable excitation sources.