# Small and Robust All-Polymer Fiber Bragg Grating based pH Sensor

Research output: Contribution to journalJournal articleResearchpeer-review

### Abstract

The smallest all-polymer optical fiber Bragg grating based transducer element for pH sensing is presented. We show that, considering it's size and robustness, it out-performs similar state-of-the-art fiber Bragg grating based pH sensors regarding both sensitivity and response time. A 5 μm - 10 μm thick pH sensitive hydrogel coating is placed on a PMMA based microstructured Polymer Optical Fiber Bragg Grating (mPOFBG). The hydrogel expands or contracts depending on the pH and thus changes in pH are monitored by following the fiber strain induced changes in the reflected Bragg wavelength $\lambda_B$ . Prior to applying the hydrogel coating the mPOF is etched from 150 μm to 80 μm to enhance sensitivity and surface crazing is introduced with a 50/50 vol% solution of acetone and methanol to enhance spreading of the hydrogel during the application and adhesion after cure. With this design we achieved a sensitivity of $\Delat\lambda_B = 73 {\rm pm/pH}$ ±2 pm/pH and response times below 4.5 mins. for pH 5 - 7 and 4 - 7 respectively and a thermal cross sensitivity of 31.4 pm/°C ± 0.4 pm/°C.
Original language English Journal of Lightwave Technology 37 18 4480 - 4486 0733-8724 https://doi.org/10.1109/JLT.2019.2902638 Published - 2019

### Keywords

• Fiber optics
• Fiber Bragg gratings
• Etching
• Chemical sensors
• Optical polymers
• Polymer gels
• pH measurement

### Cite this

title = "Small and Robust All-Polymer Fiber Bragg Grating based pH Sensor",
abstract = "The smallest all-polymer optical fiber Bragg grating based transducer element for pH sensing is presented. We show that, considering it's size and robustness, it out-performs similar state-of-the-art fiber Bragg grating based pH sensors regarding both sensitivity and response time. A 5 μm - 10 μm thick pH sensitive hydrogel coating is placed on a PMMA based microstructured Polymer Optical Fiber Bragg Grating (mPOFBG). The hydrogel expands or contracts depending on the pH and thus changes in pH are monitored by following the fiber strain induced changes in the reflected Bragg wavelength $\lambda_B$ . Prior to applying the hydrogel coating the mPOF is etched from 150 μm to 80 μm to enhance sensitivity and surface crazing is introduced with a 50/50 vol{\%} solution of acetone and methanol to enhance spreading of the hydrogel during the application and adhesion after cure. With this design we achieved a sensitivity of $\Delat\lambda_B = 73 {\rm pm/pH}$ ±2 pm/pH and response times below 4.5 mins. for pH 5 - 7 and 4 - 7 respectively and a thermal cross sensitivity of 31.4 pm/°C ± 0.4 pm/°C.",
keywords = "Fiber optics, Fiber Bragg gratings, Etching, Chemical sensors, Optical polymers, Polymer gels, pH measurement",
author = "Jakob Janting and Jens Pedersen and Getinet Woyessa and Kristian Nielsen and Ole Bang",
year = "2019",
doi = "10.1109/JLT.2019.2902638",
language = "English",
volume = "37",
pages = "4480 -- 4486",
journal = "Journal of Lightwave Technology",
issn = "0733-8724",
publisher = "Institute of Electrical and Electronics Engineers",
number = "18",

}

In: Journal of Lightwave Technology, Vol. 37, No. 18, 2019, p. 4480 - 4486.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Small and Robust All-Polymer Fiber Bragg Grating based pH Sensor

AU - Janting, Jakob

AU - Pedersen, Jens

AU - Woyessa, Getinet

AU - Nielsen, Kristian

AU - Bang, Ole

PY - 2019

Y1 - 2019

N2 - The smallest all-polymer optical fiber Bragg grating based transducer element for pH sensing is presented. We show that, considering it's size and robustness, it out-performs similar state-of-the-art fiber Bragg grating based pH sensors regarding both sensitivity and response time. A 5 μm - 10 μm thick pH sensitive hydrogel coating is placed on a PMMA based microstructured Polymer Optical Fiber Bragg Grating (mPOFBG). The hydrogel expands or contracts depending on the pH and thus changes in pH are monitored by following the fiber strain induced changes in the reflected Bragg wavelength $\lambda_B$ . Prior to applying the hydrogel coating the mPOF is etched from 150 μm to 80 μm to enhance sensitivity and surface crazing is introduced with a 50/50 vol% solution of acetone and methanol to enhance spreading of the hydrogel during the application and adhesion after cure. With this design we achieved a sensitivity of $\Delat\lambda_B = 73 {\rm pm/pH}$ ±2 pm/pH and response times below 4.5 mins. for pH 5 - 7 and 4 - 7 respectively and a thermal cross sensitivity of 31.4 pm/°C ± 0.4 pm/°C.

AB - The smallest all-polymer optical fiber Bragg grating based transducer element for pH sensing is presented. We show that, considering it's size and robustness, it out-performs similar state-of-the-art fiber Bragg grating based pH sensors regarding both sensitivity and response time. A 5 μm - 10 μm thick pH sensitive hydrogel coating is placed on a PMMA based microstructured Polymer Optical Fiber Bragg Grating (mPOFBG). The hydrogel expands or contracts depending on the pH and thus changes in pH are monitored by following the fiber strain induced changes in the reflected Bragg wavelength $\lambda_B$ . Prior to applying the hydrogel coating the mPOF is etched from 150 μm to 80 μm to enhance sensitivity and surface crazing is introduced with a 50/50 vol% solution of acetone and methanol to enhance spreading of the hydrogel during the application and adhesion after cure. With this design we achieved a sensitivity of $\Delat\lambda_B = 73 {\rm pm/pH}$ ±2 pm/pH and response times below 4.5 mins. for pH 5 - 7 and 4 - 7 respectively and a thermal cross sensitivity of 31.4 pm/°C ± 0.4 pm/°C.

KW - Fiber optics

KW - Fiber Bragg gratings

KW - Etching

KW - Chemical sensors

KW - Optical polymers

KW - Polymer gels

KW - pH measurement

U2 - 10.1109/JLT.2019.2902638

DO - 10.1109/JLT.2019.2902638

M3 - Journal article

VL - 37

SP - 4480

EP - 4486

JO - Journal of Lightwave Technology

JF - Journal of Lightwave Technology

SN - 0733-8724

IS - 18

ER -