Research Project: Milk Contamination Sensor Based On Optical Fiber Cavity Ring Down Spectroscopy
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Contributors
Funders
ID
TB.00327
Authors
Kiraz, Alper
Faculty Member
Publications
Linear cavity tapered fiber sensor using amplified phase-shift cavity ring-down spectroscopy
(Optica Publishing Group, 2021) Ayaz, Rana Muhammed Armaghan; Kiraz, Alper; Morova, Berna; Uysallı, Yiğit; Department of Physics; Graduate School of Sciences and Engineering; Department of Electrical and Electronics Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Engineering
Phase-shift cavity ring-down spectroscopy (PS-CRDS) enables the measurement of minute fluctuations in optical loss encountered by an intensity modulated laser beam via lock-in demodulation of the accumulated signal phase as the laser beam propagates through the cavity. A linear fiber cavity containing two highly reflective fiber Bragg gratings (FBGs) and a tapered fiber is a favorable cavity geometry for sensor applications due to its compact nature and wide availability of its components at telecom wavelengths. However, due to the optical absorption of water, usage of telecom wavelengths for sensing of aqueous solutions degrades the sensitivity. This problem can be worked around via an optical amplifier placed inside the fiber cavity, compensating for intrinsic cavity losses. In this work, we demonstrate amplified PS-CRDS using such a linear cavity tapered fiber sensor utilizing an optical amplifier that enables the use of thinner tapered fibers, thus achieving higher sensitivities. We also employ continuous laser wavelength sweeps and analyze peak-to-peak PSs of individual cavity modes instead of using laser-cavity mode locking with the Pound-Drever-Hall technique. This enables further simplification of the experimental arrangement without compromising sensor performance. To test the performance of the reported sensor, solutions of varying sucrose concentrations in deionized water were measured systematically by tracking the average peak-to-peak PS of the cavity modes. Tapered fibers with waist diameters (D-taper) around 2.2 mu m were used during the experiment and limit of detection (LOD) values were measured down to 2.7 mu M, corresponding to 1.01 x 10(-7) RIU. The reported LOD values can be further improved by mechanical stabilization and thermal control of the device by the use of FBGs with higher reflectivity, by applying automatic optical gain control, and by spectral filtering to remove errors caused by amplified spontaneous emission. The presented concentration sensing device can be suitable for developing compact and highly sensitive, label-free optofluidic sensors.
Linear cavity tapered fiber sensor using mode-tracking phase-shift cavity ring-down spectroscopy
(Optica Publishing Group, 2020) Ayaz, Rana Muhammed Armaghan; Bavili, Nima; Kiraz, Alper; Morova, Berna; Uysallı, Yiğit; Ullah, Ubaid; Ghauri, M. Daniyal; Cheema, M. Imran; Department of Physics; Graduate School of Sciences and Engineering; Department of Electrical and Electronics Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; College of Engineering
Phase-shift cavity ring-down spectroscopy (PS-CRDS) is an alternative CRDS approach that allows the detection of minute changes in cavity losses by measurement of the phase shift experienced by a modulated laser as it propagates through a high-quality factor cavity. Fiber loop resonators and microresonators have been employed in previous PS-CRDS demonstrations for liquid phase applications. Here we employ a tapered fiber-based linear fiber cavity for the demonstration of a highly sensitive sensor for sucrose concentration in water using PS-CRDS. Our linear fiber cavity has a small cavity length (similar to 1.25 m) that enables the observation and tracking of individual cavity modes in transmission and phase spectra recorded during laser sweeps. Hence, we eliminate the need for Pound-Drever-Hall locking of the laser source to the cavity resonance and thus provide a simpler experimental scheme. We analyze the recorded data sets to track the changes in phase shifts observed only when the laser wavelength is in resonance with the cavity modes. Such a mode-tracking PS-CRDS approach reveals limit of detection values less than around 400 mu M better than the performance of previously demonstrated PS-CRDS sucrose concentration sensors employing fiber loop resonators. The sensitivity of our sensor critically depends on the fiber taper diameter and can reach up to around 6 degrees/1 mM Suc. for 3.2 mu m taper diameter at 6 MHz modulation frequency using fiber Bragg gratings (FBGs) with reflectivities around 86%. This value can be further increased by employing FBGs with higher reflectivities or fiber tapers with smaller diameters provided that the cavity loss due to water absorption is compensated with an amplifier.
