Songtao Li

Plasmonic random laser on the fiber facet

A random laser on the optical fiber facet is constructed by dipping an optical fiber end face into the solution of polydimethylsiloxane doped with rhodamine 6G organic dye and silver nanowires. The PDMS film doped with rhodamine 6G acts as the active waveguide layer, and the silver nanowires provide a three-dimensional plasmonic feedback. The plasmon resonance of silver nanowires significantly improves the pump efficiency of the random laser. The most output energy of random laser concentrates in a small angle range along the axis of the optical fiber. This fabrication technique provides a simple and efficient way for the fabrication of random lasers on the optical fiber facet with low cost.

Plasmonic random lasing in polymer fiber.

A random fiber laser is achieved based on the plasmonic feedback mechanism, which is constructed by first siphoning the polymer solution doped with silver nanoparticles into a 300-μm capillary tube and then evaporating the solvent. Strong amplification of the radiation can be obtained by employing the variable gain region, the fiber waveguide scheme and three-dimensional plasmonic feedback provided by the silver nanoparticles. Low-threshold directional random lasing is observed in the polymer fiber. This simple and straightforward approach facilitates the investigation of plasmonic random fiber lasers.

Red-green-blue plasmonic random laser

A red-green-blue plasmonic random laser is achieved in a multilayer structure, which is fabricated by spin-coating three polymer solutions successively on a silica substrate. Under optical pumping, strong amplification of the polymer radiation can be observed due to the localized surface plasmon resonance of silver nanoparticles embedded in the multilayer structure. Red-green-blue random lasing is simultaneously obtained from the sample based on the enhanced scattering strength of silver nanoparticles. These results are useful for designing compact integrated random laser sources.

Dual-wavelength polymer laser based on an active/inactive/active sandwich-like structure

Dual-wavelength laser emission is achieved by using an active/inactive/active sandwich-like structure, which can be conveniently fabricated using spin coating technique. Poly [(9, 9-dioctylfluorenyl-2, 7-diyl)-alt-co-(1, 4-benzo-(2, 1′, 3) -thiadiazole)] and polyvinyl alcohol are employed as the active and the inactive materials, respectively. Two laser wavelengths are simultaneously observed, which are attributed to the difference of the surrounding refractive index of two active waveguides in the sandwich-like structure. Each wavelength is controlled by the respective waveguide structure, meaning that multi-wavelength laser can be designed by stacking the active/inactive layer pair. These results provide more flexibility to design compact laser sources.

Free-standing membrane polymer laser on the end of an optical fiber

One- and two-dimensional distributed feedback cavities were constructed on free-standing polymer membranes using spin-coating and lift-off techniques. Low threshold lasing was generated through feedback amplification when the 290-nm membrane device was optically pumped, which was attributed to the strong confinement mechanism provided by the active waveguide layer without a substrate. The free-standing membrane polymer laser is flexible and can be transplanted. Single- and dual-wavelength fiber lasers were achieved by directly attaching the membrane polymer laser on the optical fiber end face. This technique provides potential to fabricate polymer lasers on surfaces with arbitrary shapes.

Multi-wavelength lasing in a beat structure

Multi-wavelength polymer lasers are produced with one-dimensional beat structures fabricated with multiple gratings at the same substrate location using interference lithography. As a distributed feedback cavity, the beat structure is equivalent to a linear superposition of multiple grating cavities. Each emission wavelength is determined by the corresponding grating cavity, which implies that interaction between different cavities is very weak. For a beat structure consisting of three gratings, emission peaks at 558 nm, 565 nm, and 569 nm originate from 350-nm, 362-nm, and 374-nm cavities, with thresholds of 14.5 μJ/cm2, 15.0 μJ/cm2, and 13.5 μJ/cm2, respectively. This technique provides an alternative way to design compact polymer lasers.

Polymer lasers assembled by suspending membranes on a distributed feedback grating

Polymer lasers are fabricated by an assembly method. A polymer membrane is directly attached on the one- or two- dimensional grating. The suspended membrane acts as an active waveguide, which is supported by the grating ridge, leaving air gaps in the grating valley. Most of the radiation is effectively confined within the active waveguide due to the strong reflection at the membrane/air interfaces. So, low threshold lasing can be achieved when the sample is optically pumped. This fabrication method provides an alternative to investigate low-threshold polymer lasers.

Investigation of bimetallic nanoparticles with broad plasmon response

Abstract. Gold–silver bimetallic nanoparticles with broad plasmon response were fabricated on soft substrates using a laser-induced transfer technique. The bimetallic nanostructures were fabricated with centimeter scale. By careful design, an approximately 200-nm broad plasmon response can be obtained by gold–silver alloy nanoparticles, which can be attributed to the electromagnetic interaction between gold and silver nanoparticles. This nanofabrication technique provides an annealing-free approach for the fabrication of flexible bimetallic nanostructures with a broad plasmon response with low cost.

Polymer Lasing in a Periodic-RandomCompound Cavity

Simultaneous distributed feedback (DFB) lasing and linear polarized random lasing are observed in a compound cavity, which consists of a grating cavity and a random cavity. The grating cavity is fabricated by interference lithography. A light-emitting polymer doped with silver nanoparticles is spin-coated on the grating, forming a random cavity. DFB lasing and random lasing occur when the periodic-random compound cavity is optically pumped. The directionality and polarization of the random laser are modified by the grating structure. These results can potentially be used to design integrated laser sources.

Distributed feedback lasing in a metallic cavity

Distributed feedback (DFB) lasing is observed in a metallic cavity, which consists of a gold grating and a polymer membrane. The gold grating is prepared by evaporating a 25 nm thin film of gold on the photoresist grating fabricated by interference lithography. A 150 nm thick polymer membrane is directly attached on the gold grating, forming a suspended membrane supported by the grating ridge. The assembly method decreases the metallic contact area, which makes the mode more photonic and thereby reduces the ohmic loss of the metal. Low threshold DFB lasing can be achieved when the sample is optically pumped. The fabrication technique provides a facile way to realize plasmonic DFB polymer lasers.