Plasmonic Sensor Integrated in Optical Resonator for Refractive Index
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Solution Overview
Problem
Current surface plasmon resonance (SPR) sensors face limitations in detecting low-molecular weight analytes and larger molecules at low concentrations due to intrinsic instabilities and noise in the opto-electronic system, and are often large, costly, and inefficient in compact form factors.
Innovation Solution
A method utilizing a plasmonic sensor integrated within an optical resonator, where TE and TM polarized fields at different frequencies co-propagate, allowing for simultaneous interrogation and noise cancellation, enabling direct frequency measurement of refractive index changes independent of amplitude or phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SPR sensors are used, then refractive index measurement is possible, but sensitivity is insufficient for low-molecular weight analytes and larger molecules at very low concentration
Solution Approach 1:
The patent combines two independent SPR sensing channels (one for reference, one for measurement) into a single integrated sensor platform. Both channels share common components including the prism, metal layer, and optical path, while maintaining separate detection of s-polarized and p-polarized light. This merging approach enables differential measurement that cancels common-mode noise and drift, significantly improving measurement precision and reliability for detecting low-molecular weight analytes and larger molecules at very low concentrations.
2Ease of operation
If discrete components such as micro-objective lenses, lasers and photodetectors are used, then SPR sensing is achieved, but the system is sensitive to vibrations and requires complex alignment
Solution Approach 1:
The patent merges the reference and measurement optical paths into a common configuration where both s-polarized and p-polarized light traverse the same physical components (prism, metal layer, sample chamber). This common-path design eliminates differential alignment requirements and makes the system inherently robust against vibrations, as any environmental disturbance affects both channels equally and is cancelled in the differential measurement.
Solution Approach 2:
The patent creates an equipotential optical environment by ensuring that the reference and measurement beams experience identical optical path conditions, including the same prism, metal layer, and sample interface. By equalizing the environmental exposure of both channels, the system eliminates differential sensitivity to external disturbances such as vibrations and temperature fluctuations.
3Volume of moving object
If wavelength spectroscopy SPR is used, then sensor size is reduced and made more compact, but performance is limited by amplitude noise requiring deep noise filtering and offline averaging
Solution Approach 1:
The patent implements equipotential noise rejection by ensuring that both the reference and measurement channels experience identical amplitude noise and environmental conditions. The differential measurement approach subtracts common-mode noise components, eliminating the need for deep noise filtering and offline averaging while maintaining high signal-to-noise ratio in a compact sensor configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances sensitivity and compactness by canceling common mode noise and allowing real-time readout, improving the detection of refractive index changes and chemical bond formations, particularly for low-molecular weight analytes and larger molecules.
Implementation Method 1
An optical resonator is provided having a output channel, the plasmonic sensor being integrated in the optical resonator as a reflecting surface of the same
Implementation Method 2
Surface Plasmon Polaritons (SPP) or Surface Plasmons are electromagnetic waves that can propagate along the interface between two media, such as at the interface between a metal and a dielectric material. They correspond to oscillations of electrons at the interface between the materials
Implementation Method 3
providing a second input field of electromagnetic radiation as a secondary carrier having a second frequency different from the first frequency and defined as follow: where Δv is the frequency difference between the first frequency and the second frequency
Data Source
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AI summary
The invention relates to a method to measure the refractive index of a sample (24), the method including: •providing a plasmonic sensor (3) capable to allow, upon illumination with electromagnetic radiation, a surface plasmon resonance condition, the plasmonic sensor (3) including a sensing surface (32) in contact with the sample (24) to be measured; •providing an optical resonator (10) having a output channel, the plasmonic sensor (3) being integrated in the optical resonator as a reflecting surface (13) of the same; •providing a first input field (4') of electromagnetic radiation as a primary carrier having a first frequency and having a TE and/or a TM polarized component with respect to the sensing surface (32); • providing a second input field (4') of electromagnetic radiation as a secondary carrier having a second frequency different from the first frequency and defined as: second frequency = first frequency + Δν and having a TE and/or a TM polarized component, the first and second input field being part of the same beam and travelling along the same optical path; • impinging simultaneously with the first and second input field (4, 4') the plasmonic sensor (3) integrated in the optical resonator (10) so as to excite two orthogonal modes of the optical resonator to produce a first and second intra-cavity field in the optical resonator corresponding to the TE or TM component of the first input field (4) and to the TM or TE component of the second input field (4'); tuning the frequency of the first field (4) and/or the value of Δν till the value of the first frequency and the value of the second frequency are such that the first intra-cavity field corresponding to the TE field or TM field component of the first input field (4) is resonating in the optical resonator (10) and the second frequency (v 2) at which the second intra-cavity field corresponding to the TM field or TE field component of the second input field (4') is resonant in the optical resonator (10) simultaneously, obtaining a first resonating frequency and a second resonating frequency; detecting a resonator output power (6) corresponding to the first and second intra-cavity fields resonating in the optical resonator (10); determining a difference between the first resonating frequency (v 1) and the second resonating frequency (v 2); and calculating the refractive index of the sample (24) from the difference between the first and second frequency.