Demonstration of a refractometric sensor based on optical microfiber coil resonator

Abstract

We experimentally demonstrated a refractometric sensor based on a coated optical microfiber coil resonator. It is robust, compact, and comprises an intrinsic fluidic channel. A sensitivity of about 40 nm/RIU ͑refractive index unit͒ has been measured, in agreement with predictions. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2898211͔ Evanescent-field-based optical resonators in the form of microspheres, photonic crystals, microdisks, microtoroids, and microrings have been under intensive investigation for deployment as biological and/or chemical sensors. [1][2][3][4][5][6][7][8][9] Resonating structures can provide a simple, inexpensive, highthroughput technology for label-free real-time measurements and are attracting increasing interest. Subwavelengthdiameter optical microfibers are ideal sensor elements because of their low cost, low loss, and very large evanescent fields. [10][11][12][13] Microfiber resonators, in the form of loop and multicoils, have the advantage of a launching/collection efficiency close to unity thanks to their extremities fiber pigtails. Thus, microfiber resonators do not suffer the onerous input/ output coupling problems experienced by other high-Q ͑quality factor͒ resonators. The remaining dominating problem, associated with devices based on microfiber resonators, is the temporal degradation of their optical and mechanical properties when manufactured in air. 13 This issue was resolved by embedding the devices and this has led to the proposal to develop several high sensitivity sensors 14,15 based on microfiber coil resonators. [16][17][18] Although they are protected by a layer of coating, they still have a large evanescent field. Three-dimensional ͑3D͒ microfiber microcoil resonators have been experimentally demonstrated by wrapping microfibers on a rod 19 and coating them with Teflon 20 or immersing them in a low refractive index liquid. 21 The optical microfiber coil refractometric sensor ͑OMCRS͒ has been obtained from an embedded 3D microfiber microcoil resonator by removing its supporting rod. The proposed OMCRS has a microfluidic channel for the analyte delivery and has small size, high sensitivity, high selectivity, and low detection limits. It is also strong and portable because it is coated and embedded in a polymeric host.In this letter, we experimentally demonstrate an OMCRS based on a Teflon-coated 3D microfiber coil resonator.The OMCRS was fabricated as follows. First, a microfiber was fabricated with the so-called modified flamebrushing technology using the setup presented in Ref. 22 with a microheater ͑NTT-AT, Japan͒. The length and diameter of the uniform waist region of the fabricated microfiber were 50 mm and ϳ2.5 m, respectively. The microfiber was then wrapped on a 1 mm diameter polymethylmethacrylate ͑PMMA͒ rod. PMMA is a polymer with an amorphous structure which is soluble in acetone, has a density of 1.19 g / cm 3 , very low water absorption, and a refractive index in the range of 1.49-1.51. The whole structure was repeatedly coated by the Teflon solut...

High Sensitivity Fiber Refractometer Based on an Optical Microfiber Coupler

“…Examples include microfiber loop resonators [3], microsphere resonators [4], and microfiber coil resonators [5]. However they have either relatively low sensitivity, typically 40-800 nm/RIU, or they need complex manipulation of the microfibers to form the sensing structure.…”

Tapered fiber Mach–Zehnder interferometer for simultaneous measurement of refractive index and temperature

“…Though LPGs have been revealed to possess a high sensitivity to the refractive index of the ambient medium, the typical full width at half maximum of the resonance peak of a LPG is about tens of nanometers, which limits the measurement accuracy and its multiplexing capability. Most recently, optical refractive index sensors or refractometers based on all-fiber interferometers 16,17 or resonators 18 have received considerable attention for their high sensitivity, absolute detection with wavelength codified information, broad measurement range, and compact size. These fiber interferometric techniques are cumbersome systems with high cost and simultaneous sensing of refractive index and temperature is missing.…”

Optical microfibers and nanofibers

“…Around the same time, Xu et al reported a loop resonator refractometric sensor embedded in polymer and studied the dependency of sensitivity on the MNF diameter and coating thickness [86]. Later, the same group demonstrated a refractometric sensor based on optical microfiber coil resonator and achieved a sensitivity of about 40 nm/ RIU by using a 2.5-μm-diameter MNF wrapping around a 1-mm-diameter rod with a total sensing length of about 50 mm [159]. In 2009, Scheuer proposed an optical rotation sensor based on a fiber microcoil resonator.…”