Design of Microdisk-Shaped Ge on Si Photodetector with Recess Structure for Refractive-Index Sensing

In this paper, we introduce a disk-shaped Ge-on-Si photodetector for refractive-index difference sensing at an operating wavelength of 1550 nm. For the implementation of a small-scale sensor, a Ge layer was formed on top of a Si layer to increase the absorption coefficient at the expense of the light-detection area. Additionally, the sensor had a ring waveguide structure along the edge of the disk formed by a recess into the inner part of the disk. This increased the interaction between the dominant optical mode traveling along the edge waveguide and the refractive index of the cladding material to be sensed, and conclusively increased detection sensitivity. The simulation results show that the proposed sensor exhibited a detection sensitivity of >50 nm/RIU (Refractive Index Unit), a quality factor of approximately 3000, and a minimum detectable refractive index change of 0.95 × 10−2 RIU with a small disk radius of 3 μm. This corresponds to 1.67 times the sensitivity without a recess (>30 nm/RIU).

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Speckle Noise Removal in Image-based Detection of Refractive Index Changes in Porous Silicon Microarrays

Scientific Reports ◽

10.1038/s41598-019-51435-y ◽

2019 ◽

Vol 9 (1) ◽

Author(s):

Ruyong Ren ◽

Zhiqing Guo ◽

Zhenhong Jia ◽

Jie Yang ◽

Nikola K. Kasabov ◽

...

Keyword(s):

Refractive Index ◽

Porous Silicon ◽

Refractive Index Change ◽

Speckle Noise ◽

Noise Removal ◽

Detection Sensitivity ◽

Gray Level ◽

Denoising Method ◽

Index Changes ◽

Gray Values

Abstract Based on porous silicon (PSi) microarray images, we propose a new method called the phagocytosis algorithm (PGY) for removing the influence of speckle noise on image gray values. In a theoretical analysis, speckle noise of different intensities is added to images, and a suitable denoising method is developed to restore the image gray level. This method can be used to reduce the influence of speckle noise on the gray values of PSi microarray images to improve the accuracy of detection and increase detection sensitivity. In experiments, the method is applied to detect refractive index changes in PSi microcavity images, and a good linear relationship between the gray level change and the refractive index change is obtained. In addition, the algorithm is applied to a PSi microarray image, and good results are obtained.

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Ultrasensitive Surface Plasmon Resonance Biosensor Using Blue Phosphorus–Graphene Architecture

Sensors ◽

10.3390/s20113326 ◽

2020 ◽

Vol 20 (11) ◽

pp. 3326

Author(s):

Keyi Li ◽

Lintong Li ◽

Nanlin Xu ◽

Xiao Peng ◽

Yingxin Zhou ◽

...

Keyword(s):

Refractive Index ◽

Surface Plasmon Resonance ◽

Surface Plasmon ◽

Plasmon Resonance ◽

Gold Film ◽

Detection Sensitivity ◽

Graphene Layers ◽

Surface Plasmon Resonance Biosensor ◽

Magnitude Sensitivity ◽

Index Unit

This study theoretically proposed a novel surface plasmon resonance biosensor by incorporating emerging two dimensional material blue phosphorus and graphene layers with plasmonic gold film. The excellent performances employed for biosensing can be realized by accurately tuning the thickness of gold film and the number of blue phosphorus interlayer. Our proposed plasmonic biosensor architecture designed by phase modulation is much superior to angular modulation, providing 4 orders of magnitude sensitivity enhancement. In addition, the optimized stacked configuration is 42 nm Au film/2-layer blue phosphorus /4-layer graphene, which can produce the sharpest differential phase of 176.7661 degrees and darkest minimum reflectivity as low as 5.3787 × 10−6. For a tiny variation in local refractive index of 0.0012 RIU (RIU, refractive index unit) due to the binding interactions of aromatic biomolecules, our proposed biosensor can provide an ultrahigh detection sensitivity up to 1.4731 × 105 °/RIU, highly promising for performing ultrasensitive biosensing application.

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Theoretical study of photoconductivity and refractive index change in LiNbO3:Fe

Journal de Physique IV (Proceedings) ◽

10.1051/jp4:2005123067 ◽

2005 ◽

Vol 123 ◽

pp. 365-369

Author(s):

M. A. Ouabbou ◽

D. Khatib

Keyword(s):

Refractive Index ◽

Theoretical Study ◽

Refractive Index Change ◽

Index Change

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Femtosecond laser direct writing of Nd:YAG waveguide with Type I modification: Positive refractive index change in track

Optical Materials ◽

10.1016/j.optmat.2021.110844 ◽

2021 ◽

Vol 113 ◽

pp. 110844

Author(s):

Yuying Zhang ◽

Jiaming Wu ◽

Lei Wang ◽

Feng Chen

Keyword(s):

Refractive Index ◽

Femtosecond Laser ◽

Refractive Index Change ◽

Type I ◽

Direct Writing ◽

Laser Direct Writing ◽

Index Change

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Critical angle reflection imaging for quantification of molecular interactions on glass surface

Nature Communications ◽

10.1038/s41467-021-23730-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Guangzhong Ma ◽

Runli Liang ◽

Zijian Wan ◽

Shaopeng Wang

Keyword(s):

Refractive Index ◽

Small Molecule ◽

Molecular Interactions ◽

Glass Surface ◽

Critical Angle ◽

Dynamic Range ◽

Refractive Index Change ◽

Label Free ◽

Index Change ◽

Sensing Range

AbstractQuantification of molecular interactions on a surface is typically achieved via label-free techniques such as surface plasmon resonance (SPR). The sensitivity of SPR originates from the characteristic that the SPR angle is sensitive to the surface refractive index change. Analogously, in another interfacial optical phenomenon, total internal reflection, the critical angle is also refractive index dependent. Therefore, surface refractive index change can also be quantified by measuring the reflectivity near the critical angle. Based on this concept, we develop a method called critical angle reflection (CAR) imaging to quantify molecular interactions on glass surface. CAR imaging can be performed on SPR imaging setups. Through a side-by-side comparison, we show that CAR is capable of most molecular interaction measurements that SPR performs, including proteins, nucleic acids and cell-based detections. In addition, we show that CAR can detect small molecule bindings and intracellular signals beyond SPR sensing range. CAR exhibits several distinct characteristics, including tunable sensitivity and dynamic range, deeper vertical sensing range, fluorescence compatibility, broader wavelength and polarization of light selection, and glass surface chemistry. We anticipate CAR can expand SPR′s capability in small molecule detection, whole cell-based detection, simultaneous fluorescence imaging, and broader conjugation chemistry.

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