Application of Electric Bias to Enhance the Sensitivity of Graphene-Based Surface Plasmon Resonance Sensors

Surface plasmon resonance sensors that incorporate graphene as one of the layers in the sensor structure have been proven to provide higher sensitivity in the detection of biomolecules, compared to sensors without graphene. Graphene an allotrope of carbon facilitates better adsorption to biomolecule samples due to the carbon-hydrocarbon affinity to biomolecules, thereby resulting in higher sensitive biosensors. Recently, a revolutionary method has been presented, at least in theory for now, that there is still a possibility to increase the sensitivity of the SPR sensors by the application of electric bias across the metal-graphene sensor system. A mathematical treatment to understand the physics of how the electrical bias contributes to an increase in sensitivity is presented in this chapter, using a sensor surface structure comprising of Au-MoS2-Gr. The results indicate that the application of electrical bias across the sensor surface consisting of Gr and other materials provides a method to increase the sensitivity of these biosensors. The scope and impact of this research can be felt in many industries that need sensors either in the food industry for food contamination check, harmful gas detection for environmental monitoring or safety measures, medical diagnostics etc

Enhanced sensitivity in graphene-based SPR biosensors using electrical bias

© 2020 Optical Society of America A theoretical framework to increase the sensitivity of graphene-based surface plasmon resonance (SPR) biosensors by the application of electrical bias voltage across the sensor surface is presented. Graphene layers deposited on thin gold film (50 nm) form the sensor surface system where the surface plasmon is excited. The real and imaginary parts of the refractive index of this gold–graphene system can be controlled by tuning its chemical potential using electrical modulation. Numerical calculations show a promising method to enhance the sensitivity of graphene-based SPR biosensors

Delivery of optical frequency references through atmosphere using a frequency comb

Optical frequency references are transferred in the atmosphere over a 60-m round-trip propagation distance. Fractional instability ~10-14-10-13 at 1s is observed and large phase modulation caused by air fluctuation leads to sizeable linewidth broadening. © 2010 Optical Society of America

Atmospheric delivery of a microwave clock using an optical frequency comb

Atmospheric delivery of a microwave clock using an optical frequency comb is tested over 60 m. Phase noise measurement shows a picosecond-scale rms timing jitter under various weather conditions. A strong amplitude-phase correlation is observed. © 2010 Optical Society of America

A numerical study on instantaneous-phase evolution of femtosecond pulses in an erbium-doped fiber amplifier

Femtosecond pulse amplification using erbium-doped fiber amplifiers (EDFAs) is a critical technique for fiber-optic communications, supercontinuum generation as well as optical frequency comb technology. When designing an ultrafast fiber amplifier, it is necessary to understand the evolution of pulse properties, such as temporal intensity and phase and frequency chirp, during pulse propagation in the gain fiber. While a lot of previous numerical research has carefully studied various pulse property variations of femtosecond pulses inside EDFAs, little work has been seen to map out the instantaneous phase evolution throughout the amplification process with all the relevant dispersion and nonlinear effects considered. Here we present our numerical results on this topic

Multiheterodyne characterization of excess phase noise in atmospheric transfer of a femtosecond-laser frequency comb

We report an experimental investigation on remote transfer of a femtosecond-laser frequency comb through an open atmospheric link. Optical multiheterodyne is used to measure the excess phase noise and the frequency stability of the transferred comb. The dispersion of air is found to have a minimal impact on the multiheterodyne signal, and the effectiveness of the technique to characterize the behaviors of comb lines under the influence of turbulence is theoretically analyzed. Large phase modulation due to the index fluctuation of the air over a 60-m transmission link is found to cause a significant linewidth broadening. Under low-wind conditions, a fractional frequency stability in the order of 10-14 has been achieved over several minutes with a 1-s averaging time. A comparison of this work with previous tests based on continuous wave (CW) lasers indicates that pulsed lasers can work as well as CW lasers for remote transfer of optical frequency references through the atmosphere. © 2006 IEEE

Atmospheric timing transfer using a femtosecond frequency comb

We have experimentally demonstrated atmospheric transfer of microwave timing references using a femtosecond frequency comb. The excess timing jitter induced by the atmospheric propagation has been characterized, and evidence is provided to show that such characterization is not compromised by the parasitic effect of power-to-phase coupling in the photodetector. The fractional frequency stability for a 60-m total transmission distance is on the order of 10 -12 with a 1-s averaging time. The Allan deviation shows a τ-1 dependence up to 500 s. Scale estimate confirms that the measured excess timing noise is caused by clear-air turbulence. Comparisons with previous works show that our results offer a more precise characterization of atmospheric timing transfer. The work may potentially help the development of high-fidelity synchronization for future free-space optical communications. © 2010 IEEE

Atmospheric delivery of a microwave clock using an optical frequency comb

Atmospheric delivery of a microwave clock using an optical frequency comb is tested over 60 m. Phase noise measurement shows a picosecond-scale rms timing jitter under various weather conditions. A strong amplitude-phase correlation is observed. © 2010 Optical Society of America

Ultrasensitive Surface Plasmon Resonance Sensor with a Feature of Dynamically Tunable Sensitivity and High Figure of Merit for Cancer Detection

Cancer is one of the leading causes of death worldwide, and it is well known that an early detection of cancer in a human body will provide an opportunity to cure the cancer. Early detection of cancer depends on the sensitivity of the measuring device and method, where the lowest detectable concentration of the cancerous cell in a test sample becomes a matter of high importance. Recently, Surface Plasmon Resonance (SPR) has proven to be a promising method to detect cancerous cells. The SPR method is based on the detection of changes in refractive indices of samples under testing and the sensitivity of such a SPR based sensor is related to the smallest detectable change in the refractive index of the sample. There exist many techniques where different combinations of metals, metal alloys and different configurations have been shown to lead to high sensitivities of the SPR sensors. Based on the difference in the refractive index between a normal healthy cell and a cancerous cell, recently, SPR method has been shown to be applicable to detect different types of cancers. In this work, we propose a new sensor surface configuration that comprises of gold-silver-graphene-black phosphorus to detect different cancerous cells based on the SPR method. Additionally, recently we proposed that the application of electric field across gold-graphene layers that form the SPR sensor surface can provide enhanced sensitivity than that is possible without the application of electrical bias. We utilized the same concept and numerically studied the impact of electrical bias across the gold-graphene layers combined with silver and black Phosphorus layers which forms the SPR sensor surface. Our numerical results have shown that electrical bias across the sensor surface in this new heterostructure can provide enhanced sensitivity compared to the original unbiased sensor surface. Not only that, our results have shown that as the electrical bias increases, the sensitivity increases up to a certain value and stabilizes at a still improved sensitivity value. Such dependence of sensitivity on the applied bias provides a dynamic tunability of the sensitivity and figure-of-merit (FOM) of the sensor to detect different types of cancer. In this work, we used the proposed heterostructure to detect six different types of cancers: Basal, Hela, Jurkat, PC12, MDA-MB-231, and MCF-7. Comparing our results to work published recently, we were able to achieve an enhanced sensitivity ranging from 97.2 to 1851.4 (deg/RIU) and FOM values ranging from 62.13 to 89.81 far above the values presented recently by other researchers