Refractive-index-sensing fiber comb using intracavity multi-mode interference fiber sensor

Ryo Oe, Takeo Minamikawa, Shuji Taue, Hideki Fukano, Yoshiaki Nakajima, Kaoru Minoshima, Takeshi Yasui

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Refractive index measurement is important for evaluation of liquid materials, optical components, and bio sensing. One promising approach for such measurement is use of optical fiber sensors such as surface plasmonic resonance or multi-mode interference (MMI), which measure the change of optical spectrum resulting from the refractive index change. However, the precision of refractive index measurement is limited by the performance of optical spectrum analyzer. If such the refractive index measurement can be performed in radio frequency (RF) region in place of optical region, the measurement precision will be further improved by the frequency-standard-based RF measurement. To this end, we focus on the disturbance-to-RF conversion in a fiber optical frequency comb (OFC) cavity. Since frequency spacing frep of OFC depends on an optical cavity length nL, frep sensitively reflects the external disturbance interacted with nL. Although we previously demonstrated the precise strain measurement based on the frep measurement, the measurable physical quantity is limited to strain or temperature, which directly interacts with the fiber cavity itself. If a functional fiber sensor can be installed into the fiber OFC cavity, the measurable physical quantity will be largely expanded. In this paper, we introduce a MMI fiber sensor into a ring-type fiber OFC cavity for refractive index measurement. We confirmed the refractive-index-dependent frep shift.

Original languageEnglish
Title of host publicationOptical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII
EditorsIsrael Gannot, Israel Gannot
ISBN (Electronic)9781510614611
Publication statusPublished - 2018
EventOptical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII 2018 - San Francisco, United States
Duration: Jan 27 2018Jan 28 2018

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


OtherOptical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII 2018
Country/TerritoryUnited States
CitySan Francisco


  • fiber sensor
  • multi-mode interference
  • optical frequency comb
  • radio frequency
  • refractive index

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Atomic and Molecular Physics, and Optics
  • Radiology Nuclear Medicine and imaging


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