Hollow Optical Fiber Based Microring Optofluidic Laser For Concentration Detection And Array Application

Optofluidic laser integrates microfluidic,optical microcavity and laser gain media.It has significant advantages in biochemical sensing such as high sensitivity,low detection limit,and wide detection range.Due to the enhanced light-mater interaction,optofluidic laser is sensitive to tiny changes in the both structure and concentration of biomolecules.Detection of protein in single molecular layer can also be realized.Disposable sensors have been widely used in bio-diagnostics due to their intrinsic safety,ease of use,and low cost.However,massively produce optical microcavities with high repeatability in geometric structure and optical quality remains a big challenge.Therefore,the disposable sensors based on optofluidic laser remains to be explored.In this paper,we proposed a fiber optofluidic laser based on specifically designed hollow optical fiber.The fiber serves as both microcavity and liquid channel.The fiber optofluidic laser is promising in bioassay due to its low cast,small sample consumption,easy to integrate and real time monitoring.Moreover,the fiber optofluidic lasers can be used in disposable and arrayed sensing due to the high repeatability and symmetry in geometry.This article focuses on the laser characteristics of hollow optical fiber,concentration sensing and arrayed fiber optofluidic laser.The contributions of this paper is three folds:?1?The finite element analysis?FEA?used to model the light distribution.For thick-wall single-hole fiber?thickness from tens of micrometers to hundreds of micrometers?,the laser emission appears when the fiber is filled with high refractive index gain medium solution.For thin-wall fiber?4?m and below?,both high refractive index solutions and low refraction index solution enables lasing emission.Laser emission from the single-hole fiber with 8?m wall has been demonstrated with both low and high refractive index.?2?A hollow optical fiber?n₁=1.44?with an outer diameter of 132?m and a wall thickness of 8?m was used in the experiment.2 mM Rhodamine in quinoline?n₂=1.63?was used as gain medium.Laser emission was observed when the fiber optofluidic laser was pumped with a pulsed laser??=532 nm?.The threshold of the laser is only 0.9?J/mm².The laser emission was collected from different angles,indicating a uniform distribution in the angular direction?standard deviation is only 0.6%?.Furthermore,spectra of ten different single-hole fibers were collected under the same pump conditions.The result shows that the fiber optofluidic laser based on hollow optical fiber is highly reproducible?standard deviation is 7.4%?.These excellent characteristics of hollow optical fiber microring laser lays the foundation for one-time sensing and array applications.?3?The hollow optical fiber microring laser array was studied by imaging techniques to synchronously process and monitor the output of the micro-flow laser array.Compared with the spectrometer,the camera is cheap and most importantly,signals from multiple channels can be recorded and analyzed simultaneously.The images collected in the experiment were processed with imaging technology.The thresholds?0.8?J/mm²?of the ten single-hole fibers in the array were obtained,and the consistency was demonstrated?standard deviation was 3.9%?.Finally,gain medium concentration sensing with a dynamic range from 0.125 mM to 4 mM was experimentally demonstrated.