Abstract
A design rule for a Mach-Zehnder interferometer (MZI) sensor is presented, allowing tunable sensitivity by appropriately choosing the MZI arm lengths according to the formula given in this paper. The present MZI sensor designed by this method can achieve an ultra-high sensitivity, which is much higher than any other traditional MZI sensors. An example is given with silicon-on-insulator (SOI) nanowires and the device sensitivity is as high as 106 nm/refractive-index -unit (or even higher), by choosing the MZI arms appropriately. This makes it possible for one to realize a low-cost optical sensing system with a detection limit as high as 10−6 refractive-index-unit, even when a cheap optical spectrum analyzer with low-resolution (e.g., 1 nm) is used for the wavelength-shift measurement.
Highlights
The demand for label-free, low-cost, highly-sensitive and compact optical sensors keeps increasing rapidly in many areas, such as biological, environmental and chemical detections [1,2,3,4,5,6,7,8,9,10]
In this paper, According to Equation (4), it can be seen that an ultrahigh sensitivity S2 can be achieved by we focus on improving device sensitivity, S2, by optimizing Mach-Zehnder interferometer (MZI) design
TM mode is considered to achieve higher waveguide which can be realized by choosing the MZI arm lengths according to Equation (7)–(8)
Summary
The demand for label-free, low-cost, highly-sensitive and compact optical sensors keeps increasing rapidly in many areas, such as biological, environmental and chemical detections [1,2,3,4,5,6,7,8,9,10]. In [25], an integrated plasmo-photonic liquid refractive index sensor based on an MZI with amplitude and phase tuning elements has been realized, with a bulk sensitivity of 1930 nm/RIU experimentally. They show the sensitivity may be up to 60,000 nm/RIU by engineering the free spectral range to be. An example is given with SOI nanowires, and the sensitivity is as high as 106 nm/RIU (or even higher) Such ultra-high sensitivity makes it possible to realize a low-cost optical sensing system with a detection limit as high as 10−6 RIU, even when using a cheap optical spectrum analyzer with a low high-resolution (e.g., 1 nm)
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