Scaling the Sensitivity of Integrated Plasmo-Photonic Interferometric Sensors

Abstract

We present a new optical biosensing integration approach with multifunctional capabilities using plasmonic and photonic components on the same chip and a new methodology to design interferometric biosensors exhibiting record high sensitivity and enhanced resolution relying on a planar surface plasmon polariton (SPP) waveguide. First, we use this approach to demonstrate a proof of concept integrated plasmo-photonic liquid refractive index sensor based on a silicon nitride (Si 3 N 4 ) Mach− Zehnder Interferometer (MZI). A 70 μm long, gold metal stripe is incorporated in the sensing arm serving as the transducer element. A variable optical attenuator and a thermo-optic phase shifter are deployed in the Si 3 N 4 reference arm for performance optimization. The variable optical attenuator stage targets high extinction ratio of the resonance at the interferometer output by balancing the power between the two arms whereas the phase shifter is used to tune the MZI at the desired spectral window. Experimental results matched well with numerical simulations showing bulk sensitivity up to 1930 nm/RIU and a resonance extinction ratio of 37 dB. We also provide a theoretical analysis for correlating the sensitivity performance of the sensor with its free spectral range (FSR). Based on this analysis, we propose optimized sensor designs and show that, by engineering the free spectral range of the sensor in the range of 600 nm, sensitivity may be boosted up to 60000 nm/RIU.

Silicon‐Based Integrated Label‐Free Optofluidic Biosensors: Latest Advances and Roadmap

“…Reproduced with permission. [ 221 ] Copyright 2019, American Chemical Society. h) Sketch of the two types of reactions between ligand and metal nanorod decorated on a microsphere.…”

“…Chatzianagnostou et al developed an integrated optical sensor consisting of a silicon nitride MZI and a gold stripe as a plasmonic waveguide with a butt‐coupled interface (see Figure 13f). [ 221 ] Besides, active thermal tuning elements including a variable optical attenuator (VOA) and a phase shifter were deployed for spectrally tuning to the desired spectral window with a maximized extinction ratio and optimizing the LOD. Proof‐of‐concept refractive index sensing experiments in Figure 13g suggest a bulk sensitivity up to 1930 nm per RIU.…”

Critical assessment of relevant methods in the field of biosensors with direct optical detection based on fibers and waveguides using plasmonic, resonance, and interference effects

“…Another interesting approach for an optical microfiber reader based on a Mach-Zehnder interferometer has been published [313]. Some novel integrated plasmo-photonic Mach-Zehnder interferometer structures have been designed and experimentally evaluated recently [314]. The different possible limiting factors for the limit of detection of such devices are examined and discussed [315].…”

Design Rule of Mach-Zehnder Interferometer Sensors for Ultra-High Sensitivity

“…The other popular type of integrated optical waveguide sensors is based on two-beam interference, such as Mach-Zehnder interferometers (MZI), featuring a broad dynamic range and long interaction length [22][23][24][25][26][27]. Usually, an MZI sensor is used by measuring the output power change for a given single wavelength.…”

“…The achieved sensitivity is up to 21,500 nm/RIU [24], which is much higher than the sensitivity of 2870 nm/RIU for a regular MZI sensor. More recently, 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. In addition, they also show the sensitivity may be up to 60,000 nm/RIU by engineering the free spectral range to be 600 nm.…”