Fabrication and Testing of Photonic Thermometers

Summary

We describe the process of fabrication and testing of photonic thermometers.

Abstract

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

Introduction

The gold standard for temperature metrology, the platinum resistance thermometer, was first proposed by Sir Siemens in 1871 with Callender¹ developing the first device in 1890. Since that time incremental progress in the design and manufacturing of thermometers has delivered a wide range of temperature measurement solutions. The standard platinum resistance thermometer (SPRT) is the interpolating instrument for realizing International Temperature Scale (ITS-90) and its dissemination using resistance thermometry. Today, more than a century after its invention, resistance thermometry plays a crucial role in various aspects of industry and everyda....

Protocol

1. Device Fabrication

Note: Silicon photonic devices can be fabricated using silicon-on-insulator (SOI) wafers applying conventional CMOS-technology via photo- or electron beam lithography followed by inductive plasma reactive ion etch (ICP RIE) of 220 nm-thick topmost silicon layer. After ICP RIE etch the devices can be top-cladded with a thin polymer film or SiO₂ protective layer. Below are the main steps of in fabrication of SOI photonic devices.

1. Clean an SOI wafer in a piranha solution for 10 min, a mixture 4:1 of sulfuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂), follo....

Results

As shown in Figure 2, the ring resonator transmission spectra shows a narrow dip in transmission corresponding to the resonance condition. The resonance fringe shifts to longer wavelengths as temperature is increased from 20 °C to 105 °C in 5 °C increments. The transmission spectrum is fitted to a polynomial function from which the peak center is extracted. The polynomial fit was found to give the most consistent results in the presence of a sloping baseline .......

Discussion

The objective of this experiment was to quantify the temperature dependent response of a photonic thermometer. For quantitative measurements of temperature, it is prudent to utilize a stable heat source such as a metrology grade deep dry well, small volume sensors, ensure good thermal contact between the well and the sensor, and minimize heat loses to the environment. These requirements are easily met by bonding optical fibers to the chip, effectively creating a packaged device that can be lowered deep into the metrology.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Packaging process
6-axis stage	PI instruments
video cameras
epoxy dispensation system
Fiber array
Temperature Measurement
Metrology Well	Fluke	9170	Dry well stable to better than .01 K
Laser	Newport	TLB6700	1520-1570 nm tunable laser
Wavemeter	HighFinesse	WS/7	100 Hz wavemeter
Power meter	Newport	1936-R	power meter with broad range