ABSTRACT
This review brings about a comprehensive presentation of the research on interferometric transducers, which have emerged as extremely promising candidates for viable, truly-marketable solutions for PoN applications due to the attested performance that has reached down to 10(-8) in term of effective refractive index changes. The review explores the operation of the various interferometric architectures along with their design, fabrication, and analytical performance aspects. The issues of biosensor functionalization and immobilization of receptors are also addressed. As a conclusion, the comparison among them is attempted in order to delve into and acknowledge their current limitations, and define the future trends.
Subject(s)
Interferometry/methods , Point-of-Care Systems , Equipment Design , Interferometry/instrumentation , Systems IntegrationABSTRACT
Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.
Subject(s)
Biosensing Techniques , Interferometry/methods , Optics and Photonics/methods , Algorithms , Models, Theoretical , Proteins/chemistry , Sensitivity and SpecificityABSTRACT
A complete Mach-Zehnder interferometer monolithically integrated on silicon is presented and employed as a refractive index and bio-chemical sensor. The device consists of broad-band light sources optically coupled to photodetectors through monomodal waveguides forming arrays of Mach-Zehnder interferometers, all components being monolithically integrated on silicon through mainstream silicon technology. The interferometer is photonically engineered in a way that the phase difference of light travelling through the sensing and reference arms is approximately wavelength independent. Consequently, upon effective medium changes, it becomes feasible even with a broad-band source to induce sinusoidal-type of detector photocurrents similar to the classical monochromatic counterparts. The device is completed with its fluidic and interconnect components so that on chip interferometric measurements can be performed. Examples of refractive index and protein sensing are presented to establish the potential of the proposed device for real-time in situ monitoring applications. This is the only silicon device that has achieved complete on-chip interferometry.
Subject(s)
Biosensing Techniques/instrumentation , Interferometry/instrumentation , Refractometry/instrumentation , Silicon/chemistry , Computer Simulation , Electricity , Limit of DetectionABSTRACT
Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 µm/RIU and spectral shifts in the tens of a pm are obtained.
