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

The invention discloses an MEMS current vortex accelerometer and a preparation method. The MEMS current vortex accelerometer comprises a metal substrate, a metal structure, electrodes and inductance coils. The metal structure comprises a mass block and a rectangular support framework. The support framework is arranged on the metal substrate. The mass block is arranged in the support framework. The left side and the right side of the mass block are respectively provided with one elastic beam connected with the support framework. The metal substrate is successively provided with a first silicon nitride film and a second silicon nitride film from up to down. The electrodes comprises two first electrodes and two second electrodes which are respectively arranged on the first silicon nitride film and the second silicon nitride film. The two inductance coils are arranged below the mass block and are connected with the first electrodes and the second electrodes. The MEMS current vortex accelerometer is relatively small in size, simple in structure, good in stability and high in measuring precision; in addition, a surface machining technology is adopted, the introduction of interference stress is avoided, the mass production of the MEMS current vortex accelerometers can be realized by a normal technology device, and the cost is relatively low.

MEMS current vortex accelerometer and preparation method

All-optical modulation in a quantum cascade laser (QCL) can be rapidly evaluated using a photoluminescence (PL) spectrum. The PL spectrum reflects the electron transition rate of the sub-bands of the active region of a QCL. The peak position, amplitude, and displacement of the PL spectrum can be used to determine the optimal wavelength, spot position, the laser incident angle, optical power, and displacement in the electric field of the near-infrared laser. This PL spectrum approach is rapid, accurate, and simple. Furthermore, it can be used to optimize high-speed all-optical modulation of QCLs for use in free-space optical communication and molecular-detection applications.

/pdf/rapid-evaluation-of-all-optical-modulation-in-quantum-3f5u5z8d5x.pdf

Rapid Evaluation of All-Optical Modulation in Quantum Cascade Laser Using Photoluminescence Spectrum

In some implanted and distributed system, the power consume of these devices is tiny (generally just at uW level), and effective, long term, power supplier are lacking. For this need, several forms of vibration-driven MEMS micro generator are possible and are reported in the literature, with potential application areas including distributed sensing and ubiquitous. Our goal is to develop a micro power source translating the ambient vibration energy into the electric power which can offer 30uW power to some sensors. In our work, we designed the power generator based on a charge induced by a electret transported between two parallel capacitors. It consists of combed in-plane capacitor, electret and selenium rectifier. The combed in-plane capacitor is the key part of the generator; it will fulfill the charge transportation and translation of the energy. We design the structure of the capacitor and simulate the amplitude-frequency characteristic and phase-frequency characteristic. And then the electric-mechanic coupling is simulated, and we know the relationship between output voltage, power density and frequency. Finally a micro power generator is designed and its dimension is 8000*3000um.When the exterior oscillation is 10um and the load is 1e-6ohm, the output power is 30uW and the voltage is 4.1V.

Design of a micropower generator

Superoscillation metalenses have demonstrated promising prospects in breaking the theoretical diffraction limitations on the resolution of optical devices and systems. However, most reported superoscillation metalenses have a very small field of view of several tenths of a degree, which greatly limits their applications in imaging and microscopy. Therefore, it is of critical importance to achieve absolute high resolution by increasing the numerical apertures (NAs) of optical devices and systems. Unfortunately, similar to the case in traditional optics, it is challenging to realize a large field of view at high NA, especially in the superoscillation regime. To date, no attempt has been made to achieve flat-field focusing in the superoscillation regime, to our knowledge. Here, we demonstrate a high-NA superoscillation metalens with an entrance aperture stop, which is optimized for superoscillation performance with a comparatively large field of view. The proposed flat-field superoscillation metalens has an effective NA as large as 0.89 and achieves superoscillation focusing within a field of view of 9°. Such a superoscillation metalens may offer a promising way toward superoscillation imaging and fast-scanning label-free far-field superoscillation microscopy. 

Flat-field Superoscillation Metalens

We demonstrated the all-optical modulation in the optical emission power of a standard middle infrared quantum cascade laser by optically illuminating its front facet with femtosecond near infrared pulse train The modulation frequency is found up to 1035 GHz, much faster than the observed laser current response, only 3 GHz

Gang Chen

Papers

MEMS current vortex accelerometer and preparation method

Rapid Evaluation of All-Optical Modulation in Quantum Cascade Laser Using Photoluminescence Spectrum

Design of a micropower generator

Flat-field Superoscillation Metalens

All-optical amplitude modulation of a middle-infrared quantum cascade laser