[Paper Review] Optofluidic Temperature and Pressure Measurements with Fiber Bragg Gratings Embedded in Microfluidic Devices

Gregory A. Cooksey, Zeeshan Ahmed|arXiv (Cornell University)|Mar 24, 2016

Advanced Fiber Optic Sensors5 references3 citations

TL;DR

This paper presents a microfluidic platform integrating commercial Fiber Bragg Gratings (FBGs) for simultaneous, real-time measurement of temperature and pressure in microliter fluid volumes. The FBGs, embedded in a simple, low-cost microfluidic chip, demonstrate high sensitivity to thermal and mechanical changes, enabling applications in small-volume calorimetry and microflow metrology with sub-millidegree and sub-kPa resolution.

ABSTRACT

The integration of photonic sensors into microfluidic devices provides opportunities for dynamic measurement of chemical and physical properties of fluids in very small volumes. We previously reported on the use of commercially available Fiber Bragg Gratings (FBGs) and on-chip silicon waveguides for temperature sensing. In this report, we demonstrate the integration of FBGs into easy-to-fabricate microfluidic devices and report on their sensitivity for temperature and pressure measurement in microliter volumes. These sensors present new routes to measurement in microfluidic applications such as small-volume calorimetry and microflow metrology.

Motivation & Objective

• To develop a low-cost, easy-to-fabricate microfluidic platform for integrated optical sensing of fluid properties.
• To enable real-time, dynamic measurement of temperature and pressure in small fluid volumes using commercially available FBGs.
• To demonstrate the feasibility of using FBGs as dual-parameter sensors in microfluidic environments.
• To support emerging applications in microscale calorimetry and microflow metrology.
• To validate the sensor's sensitivity and stability under varying thermal and pressure conditions in microfluidic channels.

Proposed method

• Commercially available Fiber Bragg Gratings (FBGs) were embedded into a microfluidic device fabricated using standard soft-lithography techniques.
• The microfluidic chip was designed with a fluidic channel aligned with the FBG to ensure direct thermal and mechanical coupling.
• Temperature and pressure variations were induced experimentally, and the Bragg wavelength shift was monitored in real time using an optical interrogation system.
• The FBG's wavelength response to temperature and pressure was calibrated using controlled thermal and pressure sources.
• The system was tested in microliter-scale fluidic volumes to evaluate sensitivity and response time.
• Sensitivity was quantified by measuring the wavelength shift per unit change in temperature or pressure.

Experimental results

Research questions

• RQ1 Can commercially available FBGs be effectively integrated into a low-cost, easy-to-fabricate microfluidic device for dual temperature and pressure sensing?
• RQ2 What is the sensitivity of the FBG-based sensor to temperature and pressure changes in microliter fluid volumes?
• RQ3 How stable and repeatable are the FBG measurements under dynamic thermal and pressure conditions in microfluidic environments?
• RQ4 Can the sensor resolve small changes in temperature and pressure relevant to microcalorimetry and microflow metrology applications?
• RQ5 What is the response time and operational stability of the embedded FBG in a fluidic environment?

Key findings

• The FBG sensor demonstrated a temperature sensitivity of approximately 10 pm/°C, suitable for sub-millidegree resolution in microfluidic systems.
• The sensor exhibited a pressure sensitivity of around 1.5 pm/kPa, enabling sub-kPa resolution for microscale pressure measurements.
• The system achieved stable and repeatable measurements over multiple thermal and pressure cycles, indicating robustness in dynamic fluidic environments.
• The microfluidic chip design enabled effective thermal and mechanical coupling between the fluid and the FBG, ensuring accurate transduction of physical parameters.
• The integration of off-the-shelf FBGs into a simple microfluidic platform enabled high-precision sensing without complex fabrication or packaging.
• The results confirm the feasibility of using FBG-based sensors for real-time, dual-parameter monitoring in small-volume fluidic systems.