Optofluidic Dye Laser Research Articles

Highly Accurate Pneumatically Tunable Optofluidic Distributed Feedback Dye Lasers.

Optofluidic dye lasers integrated into microfluidic chips are promising miniature coherent light sources for biosensing. However, achieving the accurate and efficient tuning of lasers remains challenging. This study introduces a novel pneumatically tunable optofluidic distributed feedback (DFB) dye laser in a multilayer microfluidic chip. The dye laser device integrates microfluidic channels, grating structures, and vacuum chambers. A second-order DFB grating configuration is utilized to ensure single-mode lasing. The application of vacuum pressure to the chambers stretches the soft grating layer, enabling the sensitive tuning of the lasing wavelength at a high resolution of 0.25 nm within a 7.84 nm range. The precise control of pressure and laser tuning is achieved through an electronic regulator. Additionally, the integrated microfluidic channels and optimized waveguide structure facilitate efficient dye excitation, resulting in a low pump threshold of 164 nJ/pulse. This pneumatically tunable optofluidic DFB laser, with its high-resolution wavelength tuning range, offers new possibilities for the development of integrated portable devices for biosensing and spectroscopy.

All-in-One Optofluidic Chip for Molecular Biosensing Assays.

Integrated biosensor platforms have become subjects of high interest for consolidated assay preparation and analysis to reduce sample-to-answer response times. By compactly combining as many biosensor processes and functions as possible into a single lab-on-chip device, all-in-one point-of-care devices can aid in the accessibility and speed of deployment due to their compact size and portability. Biomarker assay preparation and sensing are functionalities that are often carried out on separate devices, thus increasing opportunity of contamination, loss of sample volume, and other forms of error. Here, we demonstrate a complete lab-on-chip system combining sample preparation, on-chip optofluidic dye laser, and optical detection. We first show the integration of an on-chip distributed feedback dye laser for alignment-free optical excitation of particles moving through a fluidic channel. This capability is demonstrated by using Rhodamine 6G as the gain medium to excite single fluorescent microspheres at 575 nm. Next, we present an optofluidic PDMS platform combining a microvalve network (automaton) for sample preparation of nanoliter volumes, on-chip distributed feedback dye laser for target excitation, and optical detection. We conduct concurrent capture and fluorescence tagging of Zika virus nucleic acid on magnetic beads in 30 min. Target-carrying beads are then optically excited using the on-chip laser as they flow through an analysis channel, followed by highly specific fluorescence detection. This demonstration of a complete all-in-one biosensor is a tangible step in the development of a rapid, point-of-care device that can assist in limiting the severity of future outbreaks.

Optical fiber optofluidic laser based on surfactant solubilization of rhodamine B gain in an aqueous solution.

We report a whispering gallery mode (WGM)-based fiber optofluidic laser (FOFL), in which rhodamine B (RhB) in an aqueous surfactant solution of sodium dodecylbenzene sulfonate (SDBS) is used as the laser gain medium. Here, the role of SDBS is to scatter the RhB dye molecules to effectively prevent its self-association in the aqueous solution. Therefore, the fluorescence quantum yield of the used RhB dye is improved due to the enhanced solubilization, which results in a low lasing threshold of ∼2.2 µJ/mm2 when the concentration of SDBS aqueous solution reaches up to 20 mM, on par with or even better than most of the optofluidic dye lasers using RhB as the gain medium in an organic solution. We then establish a model of solubilization capacity of SDBS micelles, which successfully addresses the mechanisms of dye-surfactant interactions in the proposed FOFL system. We further apply this FOFL platform to the case of concentration sensing of the used SDBS, which exhibits a 2-order-of-magnitude improvement in sensitivity compared to the fluorescence measurement due to the signal amplification inherent to the lasing process. The proposed FOFL platform in combination with surfactant solubilization gain medium in an aqueous solution promises to enable chip-scale coherent light sources for various environmental and bio-chemical sensing applications.

Pneumatically tunable optofluidic DFB dye laser using corrugated sidewalls.

Polydimethylsiloxane-based optofluidics provides a powerful platform for a complete analytical lab-on-chip. Here, we report on a novel on-chip laser source that can be integrated with sample preparation and analysis functions. A corrugated sidewall structure is integrated into a microfluidic channel to form a distributed feedback (DFB) laser using rhodamine 6G dissolved in an ethylene glycol and water solution. Lasing is demonstrated with a threshold pump power of 87.9 µW, corresponding to a pump intensity of 52.7mW/cm2. Laser threshold and output power are optimized with respect to rhodamine 6G concentration and core index and found to be in good agreement with a rate equation model. Additionally, the laser can be switched on and off mechanically using a pneumatic cell inducing positive pressure on the grating.

On-Chip Single-Mode Optofluidic Microresonator Dye Laser Sensor

Optofluidic dye laser devices have great potential as coherent light sources for lab-on-a-chip applications such as sensing and spectroscopy applications, owing to their promising properties such as wide wavelength-tunability, proper microfluidic integration, and an extremely miniaturized footprint. The wide emission spectrum of dye molecules and narrow free spectral range of ring resonators, make these lasers inherently multi-mode. In this article, two polydimethylsiloxane-based miniaturized optofluidic ring resonator dye lasers are numerically designed and investigated. First, multi-mode lasing from a single optofluidic ring resonator with a spectral linewidth of 10 nm and a threshold energy density of $2.2~{\mu }\text{j}$ /mm2 is demonstrated. Then, by exploiting two coupled optofluidic ring resonators and Vernier effect, single-mode lasing at a center wavelength of 566 nm with a spectral linewidth as small as ${5.36}\times {10}^{-{4}}$ nm is achieved. Moreover, simulations demonstrate the sensitivity of 500 nm/RIU for the proposed dye laser sensor.

Single mode operation and ultrawide tuning of on-chip optofluidic dye lasers.

Single transverse mode lasers that can be continuously tuned over ultrawide wavelength ranges with a narrow linewidth are very important components for lab-on-a-chip systems. Such lasers that can be tuned over the whole visible spectrum or even beyond have not been demonstrated hitherto regardless of many years of research in this area. This article presents an on-chip optofluidic distributed Bragg reflector (DBR) dye laser constituted by a combination of a T-shaped optofluidic waveguide (T waveguide) and two ridge-waveguide-based fluidic DBR gratings, in which the T waveguide provides gain for lasing and the DBR gratings select the lasing wavelength. This configuration guarantees that the fundamental mode has a much lower loss (consequently much lower lasing threshold) than all the higher order modes. By fabricating PDMS devices of such structure and changing the fluid in DBR gratings as well as the gain fluid in the T waveguide, we demonstrate a single mode optofluidic dye laser that can be continuously tuned over a wavelength range of more than 450 nm with a linewidth less than 0.1 nm. Mode patterns obtained when using different laser dyes in the T waveguide verify fundamental mode operation over the wide wavelength range.

Optofluidic laser explosive sensor with ultralow detection limit and large dynamic range using donor-acceptor-donor organic dye

Due to the significance of explosive detection for homeland security and environmental protection, the research of new materials and new methodologies for sensing electron-deficient explosive nitryl aromatics is urgently imperative. In this paper we demonstrate an optofluidic laser sensor for explosive detection by using a highly electron-rich dye (dye-1) with donor-acceptor-donor conjugated structure. The design and facile synthesis process of dye-1 are described. Theoretical calculations, UV–vis absorption and fluorescence spectra are investigated to understand the structure-property relations. Exceptionally high quantum yield of emission in solution is achieved. As a proof of concept, electron-deficient explosive molecule 2, 4-dinitrotoluene (DNT) is used as a model analyte to evaluate the performance of the optofluidic laser sensor. Experimental results indicate that the optofluidic dye laser sensor achieves a large dynamic range with 4 orders of magnitude and an ultralow limit of detection (10 nM), much better than fluorescent sensor. This work provides a route to expand the applications of optofluidic laser for sensitive biochemical detection through specific luminescent materials.

Reconfigurable RGB dye lasers based on the laminar flow control in an optofluidic chip.

The optofluidic dye laser serves as an important on-chip optical source in microfluidic technology for a breadth of applications. One of the ultimate goals of such a light source is an optofluidic white dye laser. However, realizing such a device has been challenging, because it is difficult to achieve simultaneous multi-wavelength lasers that span the most visible spectrum, especially on an integrated system. Here, we demonstrate white lasing in an optofluidic chip that simultaneously lases in red, green, and blue (RGB) colors inside a microfluidic channel. A Fabry-Perot cavity formed by two end-coated fibers provides the optical feedback of the laser. Easy reconfigurable emission can be obtained based on the laminar flow control. Eventually, white lasing at a low threshold was obtained when the pumping energy density is in excess of 26.1 μJ/mm2.

Optofluidic Dye Lasers Based on Holey Fibers: Modeling and Performance Analysis

Holey optical fibers with air-filled openings can be turned into unconventional optofluidic components by selectively introducing a suitable liquid into their internal holes. Enhanced interaction between the light guided by the fiber and molecular species suspended in the confined liquid then forms the basis for designing unique optofluidic devices—filters, sensors, or lasers—whose operating characteristics are extremely sensitive to minute changes in the liquid composition. We present a comprehensive mathematical analysis of dye lasers based on suspended-core and hollow-core fibers, with aqueous solution of Rhodamine B dye injected into the internal holes of the fibers acting as the gain medium. Our model consists of coupled first-order differential equations that characterize the population of lasing levels and the variation of pump and signal laser powers along the fiber length in the steady state. We obtain optimum operating conditions of the proposed holey fiber dye lasers, such as the optimum fiber length and dye concentration, and compare their performance to conventional dye jet lasers. We conclude that the fiber variant of dye laser using the hollow-core fiber is superior in terms of low lasing threshold and high slope efficiency. The presented theoretical framework can find applications in designing practical holey fiber dye lasers serving as fiber-based alternatives of conventional dye jet lasers as well as novel biological/chemical sensors and bio-lasers.

Observation of Lasing Emission Based on a Hexagonal Cavity Embedded in a Kagome PCF

A versatile optofluidic dye laser based on the sub-micron thickness resonator embedded in the Kagome photonic crystal fiber is demonstrated. The hexagonal hollow core supported by the cladding scaffolds serves as the microcavity and microfluidic channel for gain medium in the meantime, offering good compactness and robustness. Lasing emission could be achieved by employing dyes with refractive index either lower or higher than silica background. The lasing thresholds for dye LDS751 dissolved in methanol or DMSO at 0.2 mM are 0.43 and $0.51~\mu \text{J}$ , respectively. In addition, the lasing peaks exhibit obvious redshift as the refractive index of the gain medium increases, which is in agreement with our theoretical expectation.

Optofluidic laser based on a hollow-core negative-curvature fiber

Abstract An optofluidic laser based on a hollow-core negative-curvature fiber (HC-NCF) is proposed and demonstrated. The submicron-thick circular capillary tubes embedded in the cladding of the HC-NCF act as antiresonant elements and are used as both a resonator and dye microfluidic channels. A stable optofluidic dye laser with a low threshold of 15.14 nJ/mm2 is achieved. The laser is compact and robust and exhibits directional output.

Optofluidic droplet dye laser generated by microfluidic nozzles.

We present an optofluidic droplet dye laser that is generated by an array of microfluidic nozzles fabricated on a polycarbonate chip. A droplet resonator forms upon pressurizing the nozzle backside microfluidic channel. Multimode low-threshold lasing is observed from individual microdroplets doped with dye. Additionally, droplets can be conveniently released from the nozzle by water rinsing from the top microfluidic channel and subsequently regenerated, and thus achieve optofluidic lasers on-demand. Our work demonstrates a new approach to generating on-chip laser source and laser arrays in a simple, reproducible, reconfigurable, and low-cost fashion.

On-chip tunable optofluidic dye laser

We demonstrate a chip-scale tunable optofluidic dye laser with Au-coated fibers as microcavity. The chip is fabricated by soft lithography. When the active region is pumped, a relatively low threshold of 6.7 μJ/mm2 is realized with multimode emission due to good confinement of the cavity mirrors, long active region, as well as total reflectivity. It is easy to tune the lasing emission wavelength by changing the solvent of laser dye. In addition, the various intensity ratios of multicolor lasing can be achieved by controlling flow rates of two fluid streams carried with different dye molecules. Furthermore, the convenience in fabrication and directional lasing emission outcoupled by the fiber make the tunable optofluidic dye laser a promising underlying coherent light source in the integrated optofluidic systems.

Tunable optofluidic microring laser based on a tapered hollow core microstructured optical fiber.

A tunable optofluidic microring dye laser within a tapered hollow core microstructured optical fiber was demonstrated. The fiber core was filled with a microfluidic gain medium plug and axially pumped by a nanosecond pulse laser at 532 nm. Strong radial emission and low-threshold lasing (16 nJ/pulse) were achieved. Lasing was achieved around the surface of the microfluidic plug. Laser emission was tuned by changing the liquid surface location along the tapered fiber. The possibility of developing a tunable laser within the tapered simplified hollow core microstructured optical fiber presents opportunities for developing liquid surface position sensors and biomedical analysis.

All-fiber high repetition rate microfluidic dye laser

Optofluidic dye lasers may play a significant role in future laser applications in numerous areas, combining wavelength flexibility with integration and ease of operation. Nevertheless, no all-fiber integrated dye lasers have been demonstrated so far. In this paper, we report on a series of optofluidic all-fiber Rhodamine optical sources operating at a repetition rate as high as 1 kHz. Dye bleaching is avoided by circulating the Rhodamine dye during optical excitation. The laser radiation is extracted via conventional fibers that are spliced to the dye-filled capillary active medium. A tuneable amplified spontaneous emission source, a multimode laser, and a few transverse-mode laser are demonstrated by adjusting the setup. Threshold pump energies as low as ∼1 μJ and slope efficiencies of up to ∼9% were obtained, indicating the potential for real-world applications in areas such as spectroscopy and biomedicine.

Random lasing action in a polydimethylsiloxane wrinkle induced disordered structure

This paper presents a chip-scale random lasing action utilizing polydimethylsiloxane (PDMS) wrinkles with random periods as disordered medium. Nanoscale wrinkles with long range disorder structures are formed on the oxidized surface of a PDMS slab and confirmed by atomic force microscopy. Light multiply scattered at each PDMS wrinkle-dye interfaces is optically amplified in the presence of pump gain. The shift of laser emission wavelength when pumping at different regions indicates the randomness of the winkle period. In addition, a relatively low threshold of about 27 μJ/mm2 is realized, which is comparable with traditional optofluidic dye laser. This is due to the unique sinusoidal Bragg-grating-like random structure. Contrast to conventional microfluidic dye laser that inevitably requires the accurate design and implementation of microcavity to provide optical feedback, the convenience in both fabrication and operation makes PDMS wrinkle based random laser a promising underlying element in lab-on-a-chip systems and integrated microfluidic networks.

Optofluidic microring dye laser embedded in polydimenthylsiloxane with reduced threshold

We demonstrate an integrated optofluidic microring dye laser with a relatively low threshold on a polydimenthylsiloxane (PDMS) chip. The chip was fabricated through conventional soft lithography. It consists of a liquid waveguide with microring structure providing the feedback. A reduced threshold is realized due to the unique design of the bus waveguide across the center of the microring structure, which results in a great reduction in the cavity losses. Laser dye rhodamine 6G (R6G) dissolved in benzyl alcohol was injected into the microfluidic channel as the gain medium. When the dye laser was pumped with a pulsed laser at 532 nm, the dye laser oscillation was achieved with a threshold of only 4–5 μJ mm−2. The convenience in fabrication and operation makes the optofluidic microring dye laser a promising underlying photonic component in the integrated optofluidic systems.

Ultraviolet single-frequency coupled optofluidic ring resonator dye laser

Ultraviolet single-frequency lasing is realized in a coupled optofluidic ring resonator (COFRR) dye laser that consists of a thin-walled capillary microfluidic ring resonator and a cylindrical resonator. The whispering gallery modes (WGMs) in each resonator couple to each other and generate single-frequency laser emission. Single-frequency lasing occurs at 386.75 nm with a pump threshold of 5.9 μJ/mm. The side-mode-suppression ratio (SMSR) is about 20 dB. Moreover, the laser emits mainly in two directions, and each of them has a divergence of only 10.5°.

Diffusion driven optofluidic dye lasers encapsulated into polymer chips

Lab-on-a-chip systems made of polymers are promising for the integration of active optical elements, enabling e.g. on-chip excitation of fluorescent markers or spectroscopy. In this work we present diffusion operation of tunable optofluidic dye lasers in a polymer foil. We demonstrate that these first order distributed feedback lasers can be operated for more than 90 min at a pulse repetition rate of 2 Hz without fluidic pumping. Ultra-high output pulse energies of more than 10 μJ and laser thresholds of 2 μJ are achieved for resonator lengths of 3 mm. By introducing comparatively large on-chip dye solution reservoirs, the required exchange of dye molecules is accomplished solely by diffusion. Polymer chips the size of a microscope cover slip (18 × 18 mm(2)) were fabricated in batches on a wafer using a commercially available polymer (TOPAS(®) Cyclic Olefin Copolymer). Thermal imprinting of micro- and nanoscale structures into 100 μm foils simultaneously defines photonic resonators, liquid-core waveguides, and fluidic reservoirs. Subsequently, the fluidic structures are sealed with another 220 μm foil by thermal bonding. Tunability of laser output wavelengths over a spectral range of 24 nm on a single chip is accomplished by varying the laser grating period in steps of 2 nm. Low-cost manufacturing suitable for mass production, wide laser tunability, ultra-high output pulse energies, and long operation times without external fluidic pumping make these on-chip lasers suitable for a wide range of lab-on-a-chip applications, e.g. on-chip spectroscopy, biosensing, excitation of fluorescent markers, or surface enhanced Raman spectroscopy (SERS).

A tunable 3D optofluidic waveguide dye laser via two centrifugal Dean flow streams

This paper presents a tunable optofluidic waveguide dye laser utilizing two centrifugal Dean flows. The centrifugal Dean flow increases the light confinement of the dye laser by shaping a three-dimensional (3D) liquid waveguide from curved microchannels. The active medium with the laser dye is dissolved in the liquid core and pumped with an external pump laser to produce stimulated emission. The laser's Fabry-Pérot microcavity is formed with a pair of aligned gold-coated fiber facets to amplify the fluorescent emission. The advantage of the 3D optofluidic waveguide dye laser is its higher efficiency, thus to obtain lasing at a reduced threshold (60%) with higher output energy. The demonstrated slope efficiency is at least 3-fold higher than its traditional two-dimensional equivalent. In addition, the laser output energy can be varied on demand by tuning the flow rates of the two flows. This technique provides a versatile platform for high potential applications microfluidic biosensor and bioanalysis.