The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

Control over the dispersion of the refractive index is essential to the performance of most modern optical systems. These range from laboratory microscopes to optical fibres and even consumer products, such as photography cameras. Conventional methods of engineering optical dispersion are based on altering material composition, but this process is time-consuming and difficult, and the resulting optical performance is often limited to a certain bandwidth. Recent advances in nanofabrication have led to high-quality metasurfaces with the potential to perform at a level comparable to their state-of-the-art refractive counterparts. In this Review, we introduce the underlying physical principles of metasurface optical elements (with a focus on metalenses) and, drawing on various works in the literature, discuss how their constituent nanostructures can be designed with a highly customizable effective index of refraction that incorporates both phase and dispersion engineering. These metasurfaces can serve as an essential component for achromatic optics with unprecedented levels of performance across a broad bandwidth or provide highly customized, engineered chromatic behaviour in instruments such as miniature aberration-corrected spectrometers. We identify some key areas in which these achromatic or dispersion-engineered metasurface optical elements could be useful and highlight some future challenges, as well as promising ways to overcome them. Flat metasurface optics provides an emerging platform for combining semiconductor foundry methods of manufacturing and assembling with nanophotonics to produce high-end and multifunctional optical elements. This Review highlights the design of metasurfaces, recent advances in the field and initial promising applications.

Flat optics with dispersion-engineered metasurfaces

Based on transformation optics, we introduce another set of generalized laws of reflection and refraction (differs from that of [Science 334, 333 (2011)]), through which a transformation media slab is derived as a meta-surface, producing anomalous reflection and refraction for all polarizations of incident light.

Generalized laws of reflection and refraction from transformation optics

Quantum cascade lasers are unipolar semiconductor lasers covering a wide range of the infrared and terahertz spectrum. Lasing action is achieved by using optical intersubband transitions between quantized states in specifically designed multiple-quantum-well heterostructures. A systematic improvement of quantum cascade lasers with respect to operating temperature, efficiency, and spectral range requires detailed modeling of the underlying physical processes in these structures. Moreover, the quantum cascade laser constitutes a versatile model device for the development and improvement of simulation techniques in nano- and optoelectronics. This review provides a comprehensive survey and discussion of the modeling techniques used for the simulation of quantum cascade lasers. The main focus is on the modeling of carrier transport in the nanostructured gain medium, while the simulation of the optical cavity is covered at a more basic level. Specifically, the transfer matrix and finite difference methods for solving the one-dimensional Schrodinger equation and Schrodinger-Poisson system are discussed, providing the quantized states in the multiple-quantum-well active region. The modeling of the optical cavity is covered with a focus on basic waveguide resonator structures. Furthermore, various carrier transport simulation methods are discussed, ranging from basic empirical approaches to advanced self-consistent techniques. The methods include empirical rate equation and related Maxwell-Bloch equation approaches, self-consistent rate equation and ensemble Monte Carlo methods, as well as quantum transport approaches, in particular the density matrix and non-equilibrium Green's function formalism. The derived scattering rates and self-energies are generally valid for n-type devices based on one-dimensional quantum confinement, such as quantum well structures.

Modeling techniques for quantum cascade lasers

With the rapid development of analytical techniques, it has become much easier to detect chemical and biological analytes, even at very low detection limits. In recent years, techniques based on vibrational spectroscopy, such as surface enhanced Raman spectroscopy (SERS), have been developed for non-destructive detection of pathogenic microorganisms. SERS is a highly sensitive analytical tool that can be used to characterize chemical and biological analytes interacting with SERS-active substrates. However, it has always been a challenge to obtain consistent and reproducible SERS spectroscopic results at complicated experimental conditions. Microfluidics, a tool for highly precise manipulation of small volume liquid samples, can be used to overcome the major drawbacks of SERS-based techniques. High reproducibility of SERS measurement could be obtained in continuous flow generated inside microfluidic devices. This article provides a thorough review of the principles, concepts and methods of SERS-microfluidic platforms, and the applications of such platforms in trace analysis of chemical and biological analytes.

https://iopscience.iop.org/article/10.1088/0957-4484/26/9/092001/pdf

Analytical characterization using surface-enhanced Raman scattering (SERS) and microfluidic sampling

Automated recognition of spectral signal is an importance part of spectral analysis, which involves comparing spectral signals under the same conditions and obtaining relation of chemistry constitution according to similarity by pattern recognition method and computer technique, and is useful to determine the nature of spectral signal and validate spectral signal. This paper takes spectral signal according with Lambert-beer′law as object, introduces basic theory and method of recognition of spectral signal in brief, normalizes spectral signal to decrease difficulty, introduces wavelet analysis theory, puts forward the method of wavelet packet analysis to gain (features) of spectral signal, obtains formula to compute feature vector and error vector by statistics method, then makes use of binary tree′ mode distinguishing step by step for quick recognition, and finally gives an example to explain.

Spectral Signal Recognition Based on Wavelet Packet Analysis

This paper advances a kind of micro-spectrometer based on Fabry-Perot cavity's character of filtering the waves. The basic structure of the micro-spectrometer is the array of Fabry-Perot cavity which contains many different lengths of cavity on the substrate of silicon, consequently the authors can achieve the detection at several wavelengths simultaneously. The unit of probing is a Fabry-Perot cavity made up of the substrate of silicon-metal film-silicon dioxide layer-metal film. The authors carried out the corresponding simulation. In the basic structure of aluminum film(14 nm)-silicon dioxide layer-silver film(39 nm), the resolution can reach 15 nm. When the area of a unit of probing is 0.14 mm x 0.14 mm only, it can reach the luminous flux of miniature grating spectrum instrument (the minimum volume in the order of cm), but the volume of the part of spectrum detection is only of the order of mm. The design size of the micro-spectrometer is a few millimeters. Furthermore it has no movable parts and could detect several wavelengths at the same time. It is possible to fabricate such micro-spectrometer through existing processing methods of IC technology.

[The project and simulation of a compositive miniature spectrum instrument based on the array of Fabry-Perot cavity].

The invention discloses a tunnel type MEMS (Micro-electromechanical Systems) gyroscope and belongs to the technical field of micro-electromechanical systems. The tunnel type MEMS gyroscope provided by the invention comprises a thin plate with a normal hexadecagon shape; the thin plate is used as a sensitive mass block to be bonded on a glass substrate; each edge of the normal hexadecagon shape corresponds to one electrode; the sixteen electrodes are divided into four sets and are respectively used as driving electrodes, adjusting electrodes, feedback electrodes and wedged conical tip electrodes for generating tunneling current; the conical tip electrodes are arranged on a movable comb. The invention provides a brand-new structure and adopts the symmetrical polygonal mass block; the feedback electrodes and the adjusting electrodes are good for realizing the match of a driving modal frequency and a detection modal frequency, and the high sensitivity is realized; meanwhile, the movable comb is used for controlling the distance between the conical tip electrodes and the mass block; the two transverse conical tip electrodes are used for detecting the difference tunnel current so as to be good for reducing the drifting and further improve the detection sensitivity.

Tunnel type MEMS (Micro-electromechanical Systems) gyroscope

The invention provides a reflecting-type super diffraction line focusing device based on a metal strip-shaped antenna array. The device sequentially comprises the metal strip-shaped antenna array, a dielectric layer, a metal membrane layer and a substrate layer. Each metal strip-shaped antenna array unit is of a Y-direction array structure formed by arranging metal strip-shaped antennas in the Y direction by taking Ty as a cycle, and the metal strip-shaped antenna array units are arranged in the X direction by taking Tx as a cycle to form the metal strip-shaped antenna array. For the given incident light wavelength gamma, regulation and control over the amplitude and the phase of reflected light in the space plane are achieved by selecting a metal material, a material of the dielectric layer and the thickness of the metal strip-shaped antennas and changing the length L and the width W of metal strips, the length Li and the width Wi of the i metal-shaped antenna of which the center is located at xi are obtained according to amplitude space distribution A(xi) and phase space distribution P(xi), and then a far-field super diffraction line focusing function on the reflected light is achieved. According to device, the diffraction limit can be broken through, the focal spot size smaller than the diffraction limit is achieved, the sidelobe peak ratio is low, and the peak strength is high.

Reflecting-type super diffraction line focusing device based on metal strip-shaped antenna array

We demonstrate a silicon cone array substrate coated with gold nanoparticles and which was highly sensitive, homogeneous, and provided a large area for surface-enhanced Raman spectroscopy (SERS). A deep reactive ion-etching process was used to fabricate the high-density silicon cone array, and gold nanoparticles were formed on the silicon cone surface by magnetron sputtering. The substrate was tested with 10−6 M rhodamine 6 G solution. Enhancement of the substrate was about 60-fold greater than that of flat substrate. Moreover, SERS signals obtained from 24 random areas on the substrate showed good homogeneity with an average standard deviation of 3.9%.

Gang Chen

Papers

Spectral Signal Recognition Based on Wavelet Packet Analysis

[The project and simulation of a compositive miniature spectrum instrument based on the array of Fabry-Perot cavity].

Tunnel type MEMS (Micro-electromechanical Systems) gyroscope

Reflecting-type super diffraction line focusing device based on metal strip-shaped antenna array

Gold nanoparticle-coated silicon cone array for surface-enhanced Raman spectroscopy