arXiv subjects

Chengkuo Lee

Publications and source records attributed to Chengkuo Lee.

7 recordsLinked to original sources

arXiv2023

Capping Layer Effects on $Sb_{2}S_{3}$-based Reconfigurable Photonic Devices

Capping layers are essential for protecting phase change materials (PCMs) used in non-volatile photonics technologies. This work demonstrates how $(ZnS)_{0.8}-(SiO_2)_{0.2}$ caps radically influence the performance of $Sb_{2}S_{3}$ and Ag-doped $Sb_{2}S_{3}$ integrated photonic devices. We found that at least 30 nm of capping material is necessary to protect the material from Sulfur loss. However, adding this cap affects the crystallization temperatures of the two PCMs in different ways. The crystallization temperature of $Sb_{2}S_{3}$ and Ag-doped $Sb_{2}S_{3}$ increased and decreased respectively, which is attributed to interfacial energy differences. Capped and uncapped Ag-doped $Sb_{2}S_{3}$ microring resonator (MRR) devices were fabricated and measured to understand how the cap affects the device performance. Surprisingly, the resonant frequency of the MRR exhibited a larger red-shift upon crystallization for the capped PCMs. This effect was due to the cap increasing the modal overlap with the PCM layer. Caps can, therefore, be used to provide a greater optical phase shift per unit length, thus reducing the overall footprint of these programmable devices. Overall, we conclude that caps on PCMs are not just useful for stabilizing the PCM layer, but can also be used to tune the PCM crystallization temperature and reduce device footprint. Moreover, the capping layer can be exploited to enhance light-matter interactions with the PCM element.

physics.optics↗

arXiv2023

Thin-film PMUTs: A Review of 40 Years of Research

A concise review on the thin-film PMUTs, which has been one of the rather important research topics amongst microultrasound experts is being reported. It has been rigorously surveyed, scrutinized, and perceived that the work in this direction began nearly 44 years ago, with the primitive development of functional piezoelectric thin-film material, and now there are already three major companies commercializing them on a bulk scale. This fascinating fact illustrates the enormous contribution made by more than 70 different centers, research institutes, and agencies spread across 4 different continents to develop the vast know-how of these devices design, make, and function. This review covers such important contributions in a short but comprehensive fashion and in particular, intends to educate the readers about the global scenario of PMUTs, the principles governing their design, the ways following their make, all non-conventional useful PMUT designs, and lastly, category wise applications. Crucial comparison charts in terms of thin-film piezoelectric material used in PMUTs, and in terms of targeted applications are also depicted and discussed, which is believed to enlighten any MEMS designer planning to begin working with PMUTs. Moreover, each relevant section is provided with a crisp future forecast, from the authors past knowledge and expertise in this very field of research along with the elements of a careful literature survey. In short, this review can be considered a one-stop time-efficient guide for whoever is interested in knowing about these small devices.

physics.ins-det↗

arXiv2022

Geometric Filterless Photodetectors for Mid-infrared Spin Light

Free-space circularly polarized light (CPL) detection, requiring polarizers and waveplates, has been well established, while such spatial degree of freedom is unfortunately absent in integrated on-chip optoelectronics. So far, those reported filterless CPL photodetectors suffer from the intrinsic small discrimination ratio, vulnerability to the non-CPL field components, and low responsivity. Here, we report a distinct paradigm of geometric photodetectors in mid-infrared exhibiting colossal discrimination ratio, close-to-perfect CPL-specific response, a zero-bias responsivity of 392 V/W at room temperature, and a detectivity of ellipticity down to 0.03$^o$ Hz$^{-1/2}$. Our approach employs plasmonic nanostructures array with judiciously designed symmetry, assisted by graphene ribbons to electrically read their near-field optical information. This geometry-empowered recipe for infrared photodetectors provides a robust, direct, strict, and high-quality solution to on-chip filterless CPL detection and unlocks new opportunities for integrated functional optoelectronic devices.

physics.optics↗

arXiv2018

A quantized physical framework for understanding the working mechanism of ion channels

A quantized physical framework, called the five-anchor model, is developed for a general understanding of the working mechanism of ion channels. According to the hypotheses of this model, the following two basic physical principles are assigned to each anchor: the polarity change induced by an electron transition and the mutual repulsion and attraction induced by an electrostatic force. Consequently, many unique phenomena, such as fast and slow inactivation, the stochastic gating pattern and constant conductance of a single ion channel, the difference between electrical and optical stimulation (optogenetics), nerve conduction block and the generation of an action potential, become intrinsic features of this physical model. Moreover, this model also provides a foundation for the probability equation used to calculate the results of electrical stimulation in our previous C-P theory.

q-bio.NC↗

arXiv2018

Unveiling Stimulation Secrets of Electrical Excitation of Neural Tissue Using a Circuit Probability Theory

A new theory, named the Circuit-Probability theory, is proposed to unveil the secret of electrical nerve stimulation, essentially explain the nonlinear and resonant phenomena observed when neural and non-neural tissues are electrically stimulated. For the explanation of frequency dependent response, an inductor is involved in the neural circuit model. Furthermore, predicted response to varied stimulation strength is calculated stochastically. Based on this theory, many empirical models, such as strength-duration relationship and LNP model, can be theoretically explained, derived, and amended. This theory can explain the complex nonlinear interactions in electrical stimulation and fit in vivo experiment data on stimulation-responses of many experiments. As such, the C-P theory should be able to guide novel experiments and more importantly, offer an in-depth physical understanding of the neural tissue. As a promising neural model, we can even further explore the more accurate circuit configuration and probability equation to better describe the electrical stimulation of neural tissues in the future.

q-bio.NC↗

arXiv2018

The first principle of neural circuit and the general Circuit-Probability theory

A new neural circuit is proposed by considering the myelin as an inductor. This new neural circuit can explain why the lump-parameter circuit used in previous C-P theory is valid. Meanwhile, it provides a new explanation of the biological function of myelin for neural signal propagation. Furthermore, a new model for magnetic nerve stimulation is built and all phenomena in magnetic nerve stimulation can be well explained. Based on this model, the coil structure can be optimized.

q-bio.NC↗

arXiv2018

"Exclusive-OR" operation with Fano resonant MEMS Metamaterial

In recent years, a range of reconfigurable metamaterials controlled with thermal, electric, magnetic and optical signals have been developed for dynamically manipulating the intensity, phase and wave-front of electromagnetic radiation across the broad electromagnetic spectrum ranging from microwave to optics. Here for the first time, we demonstrate a reconfigurable metasurface performing exclusive OR (XOR) logical operation using two independent control electrical inputs and an optical read-out in the form of far-field Fano intensity states at terahertz wavelengths. At the same time, the near field resonant confinement enables a universal NAND logical operation. Further, by using a single electrical input control and an optical readout, a logical NOT operation is achieved at the far-field intensity states of the Fano resonance. The proposed reconfigurable microcantilever based Fano design that exhibits multiple logical operations can create a versatile platform for realization of programmable and randomly accessible metamaterials with enhanced electro-optical performance, multichannel data processing and encryption techniques for high speed wireless networks which are now being pushed towards terahertz wavelengths.

physics.app-ph↗