Ultra-sensitive chip-based photonic temperature sensor using ring resonator structures

Abstract

Resistance thermometry provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches has produced considerable interest in developing photonic temperature sensors to leverage advances in frequency metrology and to achieve greater mechanical and environmental stability. Here we show that silicon-based optical ring resonator devices can resolve temperature differences of 1 mK using the traditional wavelength scanning methodology.An even lower noise floor of 80 μK for measuring temperature difference is achieved in the side-of-fringe, constant power mode measurement.Temperature measurements play a central role in modern life ranging from process control in manufacturing 1 , physiological monitoring 2 and tissue ablation 3 in 2 medicine, and environmental control and monitoring in buildings 4 and automobiles 5 .Despite the ubiquity of thermometers, the underlying technology has been slow to advance over the last century. 6 The standard bearer for accurate temperature measurement, the standard platinum resistance thermometer (SPRT) was initially developed over a century ago. 6,7 Furthermore, many modern temperature sensors still rely on resistance measurements of a thin metal film or wire whose resistance varies with temperature. 6 Though resistance thermometers can routinely measure temperature with uncertainties of 10 mK, they are sensitive to mechanical shock which causes the resistance to drift over time requiring frequent off-line, expensive, and time consuming calibrations. 7In recent years there has been considerable interest in developing photonic devices as an alternative to resistance thermometers 8-10 as they have the potential to provide greater temperature sensitivity while being robust against mechanical shock and electromagnetic interference. Furthermore, the low weight, small form factor photonic devices might be multiplexed to provide a low-cost sensing solutions.Photonic temperature sensors exploit temperature dependent changes in a material's properties -typically, a combination of thermo-optic effect and thermal expansion. The temperature dependence of the ring resonator arises from temperatureinduced changes in refractive index (n) and in the physical dimensions of the ring. A qualitative analysis of a ring resonator yields a resonance wavelength for a single ring resonator of:where m is the vacuum wavelength, n eff is the effective refractive index, m is the mode number, L is the ring perimeter, and T is the temperature. Thus, the temperature-induced shift in wavelength is given by:Where the group index is n g = [ ( ) . The variation in the refractive index due to the thermal expansion coefficient for silicon (3.57 x 10 -6 /K) is a factor of 100 smaller 4 than that of the estimated thermo-optic effect (2 x 10 -4 /K) of the silicon waveguide and thus not included in our analysis of the performance of ring resonator devices. wafer with a 220 nm thick layer of silicon on top of a 2 μm thick buried oxide layer that isolates the ...

Thermomechanical MEMS membranes for fiber optic temperature sensing

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Optical temperature sensor with enhanced sensitivity by employing hybrid waveguides in a silicon Mach-Zehnder interferometer

“…So far, the most accessible method for measuring the temperature is still resistance thermometry, in which a metal's resistance varies with the temperature. However, given its problem of being sensitive to electromagnetic interference (EMI), humidity, and mechanical shocks, resistance thermometers' territory is being seized by sensors utilizing other methods, among which optical temperature sensors are attracting substantial interests [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Optical temperature sensors have been demonstrated in fibers inscribed with Bragg gratings [6,7] and in configurations of Mach-Zehnder Interferometers (MZIs) [8,9], or e.g.…”

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“…Diverse silicon photonic structures have been utilized to achieve temperature sensors, including ring resonators [11][12][13][14][15], Bragg reflectors [16,17], Fabry-Perrot (FP) cavities [18], and interferometers [19][20][21]. However, the temperature sensitivity of above demonstrated sensors are typically limited to ~80 pm/°C.…”

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