Abstract
We report a method for compensation of errors caused by temperature fluctuations in refractive index measurements using Silicon photonic microring sensors. The method involves determination of resonance wavelength shifts caused by thermal fluctuations using real-time measurement of on-chip temperature variations and thermo-optic coefficient (TOC) of analyte liquids. Resistive metal lines patterned around Silicon microrings are used to track temperature variations and TOC of analyte is calculated by measuring wavelength shifts caused by controlled increments in device temperature. The TOC of de-ionized water is determined to be -1.12 × 10-4/°C, with an accuracy of ±8.26 × 10-6/°C. In our system, chip-surface temperature variations were measured with an instrument limited precision of 0.004 °C yielding a factor of 16 enhancement in tracking accuracy compared to conventional, bottom-of-chip temperature measurement. We show that refractive index detection limit of the microring sensor is also improved by the same factor.
Highlights
Silicon photonic sensors have been studied extensively for measurement of refractive index shift in liquids
An important figure-of-merit of the Silicon photonic sensor is its detection limit, or the smallest change of refractive index that can be reliably measured by the system
We propose and demonstrate the use of analyte thermo-optic coefficient (TOC) for compensating errors in RI measurements caused by variations in ambient temperature
Summary
Silicon photonic sensors have been studied extensively for measurement of refractive index shift in liquids. An important factor that influences the detection limit of the Silicon microring sensor is the variation in operating temperature of the device This has several causes such as fluctuations in the ambient temperature, differences in the temperatures of sensor chip and the external analyte reservoir and local heating caused by viscous dissipation [7]. The spatial separation between the reference and sensor microrings can result in differences of temperature variation profiles resulting in imperfect compensation of errors in wavelength shifts To overcome these drawbacks, we propose and demonstrate the use of analyte TOCs for compensating errors in RI measurements caused by variations in ambient temperature. Metal rings patterned around Silicon microrings are used to monitor fluctuations of ambient temperature through measurement of variations in electrical resistance Using this method, thermo-optic coefficients of three standard liquids; De-ionized water, Ethanol and Isopropanol were measured and are shown to be in good agreement with literature reports. We discuss sensing schemes that eliminate the requirement of TEC based temperature controllers for RI shift measurements in specific cases where TOCs of analytes are known beforehand as standard values
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