Dye-doped Waveguide Research Articles

Fano resonant behaviour of waveguide mode in all-dielectric multilayer structure directly monitored by fluorescence of embedded dye molecules

A method that allows direct monitoring of Fano resonant behaviours of local electric fields inside a waveguide layer in multilayer structures was developed. All-dielectric multilayer structures consisting of two polystyrene waveguide layers separated by a polyvinyl alcohol spacer layer were prepared. One of the waveguide layers was doped with fluorescent dye molecules. The fluorescence spectra of the sample were measured in a Kretschmann attenuated-total-reflection geometry as a function of the angle of incidence of the excitation light. The angle-scan fluorescence excitation spectra exhibited a sharp Fano line shape superposed on a broad band. Results of electromagnetic calculations of the electric field distribution inside the multilayer structure revealed that the local electric fields inside the dye-doped waveguide layer exhibit Fano resonant behaviours due to the near-field coupling to the waveguide mode supported by another waveguide layer. Using the calculated local electric fields, theoretical fluorescence spectra were calculated based on a point dipole model. The theoretical fluorescence spectra were found to reproduce the experimental ones very well, confirming that the observed Fano line shapes in the fluorescence spectra are the manifestation of the Fano resonant behaviours of the local electric fields inside the dye-doped layer.

Systematic study of the hybrid plasmonic-photonic band structure underlying lasing action of diffractive plasmon particle lattices

We study lasing in distributed feedback lasers made from square lattices of silver particles in a dye-doped waveguide. We present a systematic analysis and experimental study of the band structure underlying the lasing process as a function of the detuning between the particle plasmon resonance and the lattice Bragg diffraction condition. To this end, as gain medium we use either a polymer doped with Rh6G only, or polymer doped with a pair of dyes (Rh6G and Rh700) that act as a F\orster energy transfer (FRET) pair. This allows for gain, respectively, at 590 or 700 nm when pumped at 532 nm, compatible with the achievable size tunability of silver particles embedded in the polymer. By polarization-resolved spectroscopic Fourier microscopy, we are able to observe the plasmonic/photonic band structure of the array, unraveling both the stop gap width, as well as the loss properties of the four involved bands at fixed lattice Bragg diffraction condition and as a function of detuning of the plasmon resonance. To explain the measurements we derive an analytical model that sheds insights on the lasing process in plasmonic lattices, highlighting the interaction between two competing resonant processes, one localized at the particle level around the plasmon resonance, and one distributed across the lattice. Both are shown to contribute to the lasing threshold and the overall emission properties of the array.

Experimental demonstration of PT‐symmetric stripe lasers (Laser Photonics Rev. 10(4)/2016)

A PT-symmetric configuration is applied by Gu et al. on a dye-doped waveguide, i. e., half gain and half loss. With the increase of pumping power, two adjacent modes merge and thus the mode spacing is doubled after the exceptional point. The laser and absorber are obtained simultaneously in this PT-symmetric system. This research provides a new platform to study the applications of unconventional lasers such as optical switches and direct modulated microlasers. (Picture: Zhiyuan Gu et al., 10.1002/lpor.201500114 pp. 588–594, in this issue)

Statistics of Randomized Plasmonic Lattice Lasers

We study lasing in randomized lattices of silver particles in a dye-doped waveguide. We set out to answer a basic question, triggered by earlier observations of distributed feedback lasing in 2D periodic plasmonic particle lattices: how much order do you need to obtain lasing? We start from a diffractive 2D square lattice of silver nanoparticles with a pitch that satisfies the second-order Bragg diffraction condition at the emission wavelength of the dye. By randomly removing particles and by displacing particles we increase disorder. We observe that lasing at the second-order Bragg diffraction condition is very robust, with lasing even persisting when 99% of particles are removed. Above a certain amount of disorder new features appear in the spectrum as well as in the Fourier image that are due to random lasing. We classify Fourier space output on the basis of structure factor calculations. In addition we apply speckle intensity statistics analysis to real-space fluorescence images and introduce a new me...

Optically pumped distributed feedback thin film waveguide lasers with multiwavelength and polarized emissions

Zirconia titania organically modified silicate (ZrO2-TiO2-ORMOSIL) thin film waveguides of thickness from 0.4 to 7.0 μm were synthesized using low temperature sol–gel method. Narrow linewidth distributed feedback (DFB) lasing was demonstrated in rhodamine 6G-doped ZrO2-TiO2-ORMOSIL waveguides. Simultaneous tuning of multiple-output wavelengths was achieved in the dye-doped waveguides by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. As many as eight separate output wavelengths were observed for a planar ZrO2-TiO2-ORMOSIL waveguide of thickness 7.0-μm. The output polarizations of the DFB waveguide lasers can be tuned by varying the polarization of the crossing pump beams. TE and TM optical waves belonging to the same propagation mode were generated by crossing two polarized pump beams, resulting in an effective double of the number of output wavelengths. Continuous tuning of the polarized laser outputs was also achieved by varying the crossing angle.

Integrated wavelength-selective optical waveguides for microfluidic-based laser-induced fluorescence detection

We demonstrate the fabrication and characterization of a novel, inexpensive microchip capable of laser induced fluorescence (LIF) detection using integrated waveguides with built-in optical filters. Integrated wavelength-selective optical waveguides are fabricated by doping poly(dimethysiloxane) (PDMS) with dye molecules. Liquid-core waveguides are created within dye-doped PDMS microfluidic chips by filling channels with high refractive index liquids. Dye molecules are allowed to diffuse into the liquid core from the surrounding dye-doped PDMS. The amount of diffusion is controlled by choosing either polar (low diffusion) or apolar (high diffusion) liquid waveguide cores. The doping dye is chosen to absorb excitation light and to transmit fluorescence emitted by the sample under test. After 24 h, apolar waveguides demonstrate propagation losses of 120 dB cm(-1) (532 nm) and 4.4 dB cm(-1) (633 nm) while polar waveguides experience losses of 8.2 dB cm(-1) (532 nm) and 1.1 dB cm(-1) (633 nm) where 532 and 633 nm light represent the excitation and fluorescence wavelengths, respectively. We demonstrate the separation and detection of end-labelled DNA fragments using polar waveguides for excitation light delivery and apolar waveguides for fluorescence collection. We demonstrate that the dye-doped waveguides can provide performance comparable to a commercial dielectric filter; however, for the present choice of dye, their ultimate performance is limited by autofluorescence from the dye. Through the detection of a BK virus polymerase chain reaction (PCR) product, we demonstrate that the dye-doped PDMS system is an order of magnitude more sensitive than a similar undoped system (SNR: 138 vs. 9) without the use of any external optical filters at the detector.

Long lifetime and high repetition rate operation from distributed feedback plastic waveguided dye lasers

Abstract Long lifetime and high repetition rate laser operation was demonstrated from laser-dye-doped waveguides with distributed feedback (DFB) structures. The waveguides were fabricated with a spin-coating and lithography techniques, and DFB structure was written by an ultraviolet holography technique. A compact frequency-doubled Nd:YAG microchip laser was used as a pumping source, and the laser output wavelength range of 575–945 nm was obtained from 10 different kinds of laser-dye-doped plastic film and the laser performance was evaluated about 5 of them. Very low pumping energy requirement of around several μJ could extend the durabilities of the DFB dye-doped waveguides, and the lifetime of more than one million shots was obtained. Further a high repetition laser operation up to 1000 pps was demonstrated with an output energy stability of less than ±0.5%. A palm-top size tunable laser is realized by this configuration.

PHOTOSTABILITY STUDIES ON HIGH DIPOLE NONLINEAR OPTICAL ADDUCTS OF TCNQ IN POLYMER OPTICAL WAVEGUIDES

The photostabilities of nonlinear optical organic dyes doped as guests into Poly(methyl mathacrylate), (PMMA), waveguide films have been investigated using measurements of planner waveguide transmission over time. Direct photodecomposition of the dyes is observed when the doped films are exposed to wavelengths lying within the main absorption bands. The dyes exhibit a rapid photochemical degradation that is enhanced when the experiments are repeated in an air environment at the irradiation between 450 nm and 515 nm. Excitation of the zeroth-order transverse magnetic mode (TM0) by prism couplers produced complete degradation within 30 minutes. The dye photostabilities are compared to that of a commonly studied laser dye, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran, DCM, which exhibits a photo-oxidation mechanism. The experiments in air lead to comparable degradation after 3 to 4 hours but the dye proves to be exceptionally photostable in vacuum. Further interesting results are reported on the formation of crystallites in the films when irradiated at 632.8 nm where linear absorption in the films is low. Microscopic examination of the waveguide films at the input coupling position confirms the formation of crystallites for all the films studied. Cross coupling to higher order modes from the light scattering of crystallites is revealed by scanning m-line images of the waveguides. This is associated with a marked refractive index decrease in the films. An air and humidity environment is found to favor the crystallite formation in the dye-doped waveguides.