Optical Waveguide Theory

2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

Demand for accessible and affordable healthcare for infectious and chronic diseases present significant challenges for providing high-value and effective healthcare. Traditional approaches are expanding to include point-of-care (POC) diagnostics, bedside testing, and community-based approaches to respond to these challenges.1 Innovative solutions utilizing recent advances in mobile technologies, nanotechnology, imaging systems, and microfluidic technologies are envisioned to assist this transformation.

Infectious diseases have considerable economic and societal impact on developing settings. For instance, malaria is observed more commonly in sub-Saharan Africa and India.2 The societal impact of acquired immune deficiency syndrome (AIDS) and tuberculosis is high, through targeting adults in villages and leaving behind declining populations.3 In resource-constrained settings, it is estimated that about 32% of the disease burden is from communicable diseases such as respiratory infections, AIDS, and malaria, while 43% of the burden is from noncommunicable diseases, such as cardiovascular diseases, neuropsychiatric conditions, and cancer.4 Developing diagnostic platforms that are affordable, robust, and rapid-targeting infectious diseases is one of the top priorities for improving healthcare delivery in the developing world.5 The early detection and monitoring of infectious diseases and cancer through affordable and accessible healthcare will significantly reduce the disease burden and help preserve the social fabric of these communities. Further, improved diagnostics and disease monitoring technologies have potential to enhance foreign investment, trade, and mobility in the developing countries.6

Highly sensitive and specific lab assays such as cell culture methods, polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) are available for diagnosis of infectious diseases in the developed world. They require sample transportation, manual preparation steps, and skilled and well-trained technicians. These clinical conventional methods provide results in several hours to days, precluding rapid detection and response at the primary care settings. Another diagnostic challenge is identifying multiple pathogens. Since common symptoms like sore throat and fever can be caused by multiple infectious agents (e.g., bacteria and viruses), it is important to accurately identify the responsible agent for targeted treatment. Therefore, high-throughput sensors for multiplexed identification would help improve patient care.7

Medical instruments in centrally located institutions in the developed world rely on uninterrupted electricity and running water and require controlled environmental conditions. It may not be viable to satisfy some of these criteria in some POC settings, where well-trained healthcare personnel are not available and clean water access is unreliable.7,8 Further, in remote settings without infrastructure, rain and dust can act as contaminants.7 Diagnostic devices for POC testing in these settings are identified by the World Health Organization to be affordable, sensitive, user-friendly, specific to biological agents, and providing rapid response to small sample volumes.9 Optical biosensor devices are emerging as powerful biologic agent detection platforms satisfying these considerations.10

Optical sensing platforms employ various methods, including refractive index change monitoring, absorption, and spectroscopic-based measurements.11 Optical sensors that are based on refractive index monitoring cover a range of technologies, including photonic crystal fibers, nano/microring resonator structures, interferometric devices, plasmonic nano/micro arrays, and surface plasmon resonance (SPR)-based platforms.11,12 The latter two are plasmonic-based technologies. Plasmonics is an enabling optical technology with applications in disease monitoring, diagnostics, homeland security, food safety, and biological imaging applications. The plasmonic-based biosensor platforms along with the underlying technologies are illustrated in the Figure ​Figure1.1. Here, we reviewed SPR, localized surface plasmon resonance (LSPR), and large-scale plasmonic arrays (e.g., nanohole arrays).



Figure 1

Plasmonic-based technologies for versatile biosensor applications. SPR stands for surface plasmon resonance, LSPR for localized surface plasmon resonance, SPRi for surface plasmon resonance imaging, and SERS for surface-enhanced Raman scattering.

https://canarycenter.stanford.edu/content/dam/sm/canarycenter/documents/research/bamm-lab/ChemicalReview.pdf

Advances in Plasmonic Technologies for Point of Care Applications

We present and numerically characterize a closed-form multi-core holey fiber based plasmonic sensor. The coupling properties of the specific modes are investigated comprehensively by the finite element method. It is found that not only phase matching but also loss matching plays a key role in the coupling process between the fundamental mode and plasmonic mode. The coupling transforms from incomplete coupling to complete coupling with increasing analyte RI. An average sensitivity of 2929.39nm/RIU in the sensing range 1.33-1.42, and 9231.27nm/RIU in 1.43-1.53 with high linearity is obtained. The dynamic sensing range is the largest among the reported holey fiber based plasmonic sensors, to the best of our knowledge.

A multi-core holey fiber based plasmonic sensor with large detection range and high linearity

An optical fiber bend sensor assisted with a photonic crystal fiber(PCF) has been fabricated by splicing a section of photonic crystal fiber between two single mode fibers. Such a structure could be developed a Mach-Zehnder interferometer (MZI). The PCF-based MZI is sensitive to structure bending with a sensitivity of 6dB/m_1 and is independent on temperature only with a sensitivity of 0.01 dB/°C. Such a bend sensor can effectively reduce the cross-sensitivity between bend and temperature.

High-sensitivity bend sensor based on Mach-Zehnder interferometer using photonic crystal fiber

This paper investigates optical properties of few-mode fiber with non-uniform refractive index, namely: the few mode fiber with U-shape refractive index and the two-mode and four-mode few-mode fiber with bent radius. Finite element method is used to analyze the mode distributions based on their non-uniform refractive index. Effective mode control can be achieved through these few mode fibers to achieve vector beam generation. Finally, reflection spectra of a few-mode fiber Bragg grating are calculated theoretically and then measured under different bending conditions. Experimental results are in good accordance with the theoretical ones. These few mode fibers show potential applications in generation of cylindrical vector beam both for optical lasing and sensing systems.

/pdf/optical-property-of-few-mode-fiber-with-non-uniform-3d1wco1ayc.pdf

Optical property of few-mode fiber with non-uniform refractive index for cylindrical vector beam generation

Multispectral stealth technology including terahertz (THz) band will play an increasingly important role in modern military and civil applications. Here, based on the concept of modularization design, two kinds of flexible and transparent metadevices were fabricated for multispectral stealth, covering the visible, infrared (IR), THz, and microwave bands. First, three basic functional blocks for IR, THz, and microwave stealth are designed and fabricated by using flexible and transparent films. And then, via modular assembling, that is, by adding or removing some stealth functional blocks or constituent layers, two multispectral stealth metadevices are readily achieved. Metadevice 1 exhibits THz-microwave dual-band broadband absorption, with average measured absorptivity of 85% in 0.3-1.2 THz and higher than 90% in 9.1-25.1 GHz, suitable for THz-microwave bi-stealth. Metadevice 2 is for IR and microwave bi-stealth, with measured absorptivity higher than 90% in 9.7-27.3 GHz and low emissivity around 0.31 in 8-14 µm. Both metadevices are optically transparent and able to maintain good stealth ability under curved and conformal conditions. Our work offers an alternative approach for designing and fabricating flexible transparent metadevices for multispectral stealth, especially for applications in nonplanar surfaces.

Flexible and transparent metadevices for terahertz, microwave, and infrared multispectral stealth based on modularization design.

In this paper, a novel microfiber refractive index sensor prepared with tapering-twisting-tapering technique has been proposed and demonstrated for the first time. Experimental results show that the interference intensity of the novel microfiber increases with the increment of pre-tapered length and the intervening twist number. Furthermore, the refractive index sensitivity of this microfiber sensor can reach to ∼809 nm/refractive index unit (RIU) in the refractive index ranging from 1.30 to 1.33. Taking advantages of its tiny size, easy preparation and flexible design, the novel microfiber has great potential application in refractive index sensing.

A novel microfiber refractometric sensor fabricated with tapering-twisting-tapering technique

In this paper we propose and demonstrate a novel all-fiber fused-type mode selective coupler (MSC) that capable of converting LP01 mode to LP11 mode with high efficiency and purity. Unlike other coupler fabrication techniques for which single mode fiber (or few mode fiber) must be pre-tapered, the advantage of our proposed coupler is that pre-tapering is not required. Two different fibers of the MSC have the same diameter. We achieve LP11 mode with a high modal purity of > 90% and a coupling efficiency of >20%, with a low insertion loss of about 0.3 dB at the wavelength of 1064 nm.

/pdf/all-fiber-fused-type-mode-selective-coupler-with-high-10cr86aeux.pdf

Bing Sun

Papers

High-sensitivity bend sensor based on Mach-Zehnder interferometer using photonic crystal fiber

Optical property of few-mode fiber with non-uniform refractive index for cylindrical vector beam generation

Flexible and transparent metadevices for terahertz, microwave, and infrared multispectral stealth based on modularization design.

A novel microfiber refractometric sensor fabricated with tapering-twisting-tapering technique

All-fiber fused-type mode selective coupler with high performance and free of pre-tapering