Showing papers by "Gang Chen published in 2014"

Super-oscillation focusing lens based on continuous amplitude and binary phase modulation.

Abstract: In this paper, we numerically demonstrate the advantage of utilizing continuous amplitude and phase modulation in super-oscillation focusing lens design. Numerical results show that compared with simple binary amplitude modulation, continuous amplitude and phase modulation can greatly improve the super-oscillation focusing performance by increasing the central lobe intensity and the ratio of its energy to the total energy, reducing the sidelobe intensity, and substantially extending the field of view. Our study also reveals the role of phase distribution in reducing the spatial frequency bandwidth of the super-oscillation optical field on the focal plane. Based on continuous amplitude and binary phase modulation, a lens was designed with double layer metal slit array for wavelength of 4.6 µm. COMSOL is used to carry out the 2D simulation. The lens focal length is 40.18λ and the focal spot FWHM is 0.308λ. Two largest sidelobes are located right next to the central lobe with intensity about 40% of the central lobe intensity. Except for the two sidelobes, other sidelobes have intensity less than 25% of the central lobe intensity, which leads to a clear field of view on the whole focal plane.

Double-Layer Metallic Holes Lens Based on Continuous Modulation of Phase and Amplitude

Abstract: We have demonstrated numerically a lens design based on continuous modulation of both phase and amplitude utilizing array of double-layer metallic aluminum holes filled with silicon dioxide. The tuning range is 0-π and 0-0.3 for phase and amplitude, respectively, at wavelength 365 nm, allowing flexible lens design. Two lenses are designed and compared. At wavelength 365 nm, the lens based on pure phase modulation generates a 600-nm hot spot at a distance of 6.5 μm, while the phase-amplitude-modulation-based lens leads to an improved focusing spot size of 450 nm, which is beyond the diffraction limit 608 nm and the superoscillation criterion 462 nm. An example of subwavelength superoscillation focusing (0.32λ) is also demonstrated with a continuous amplitude modulated lens, which shows small sidelobe and broad view field. Our approach shows great potential in superoscillation lens design and can be applied to other optical spectrum ranges as well.

Microchannel-based surface-enhanced Raman spectroscopy for integrated microfluidic analysis.

Abstract: We have demonstrated a microchannel-based, surface-enhanced Raman spectroscopy (SERS) sensing approach for integrated microfluidic analysis developed using standard micro-fabrication technology. Our approach allows high-sensitivity SERS sensing with a comparatively low-excitation optical power intensity and large cross-sectional microchannel for biological cell analysis. Utilizing a microchannel with a cross section of 100 × 70 μm2, we achieved a detection limit smaller than 10 nM for rhodamine 6G at an excitation power intensity of 132 W/cm2, avoiding any possible heating effects on the sample under investigation. There is great potential for further improvement in the sensitivity of this microchannel-based SERS detection.

Continuous amplitude regulation and control ultra oscillation focusing lens based on single layer metal slit structure array

Abstract: A continuous amplitude regulation and control ultra oscillation focusing lens based on a single layer metal slit structure array comprises a substrate, a metal film and slit structure units. Each slit structure unit is a slit carved on the metal film, wherein the length of the metal film is L, the width of the metal film is a, the length of the slit is l, the width of the slit is w, and the depth of the slit is the same as the thickness t2 of the metal film. The slit structure array is composed of the series of slit structure units which are parallel to one another, wherein the width of the ith slit structure unit is ai, and the width of the ith slit structure unit is wi. For the given lens amplitude spatial distribution A(xi), the width wi of the slit at the spatial position xi is determined through the relation A(w) between the width of the slit and the amplitude transmittance, and therefore planar amplitude spatial distribution A(xi) is achieved by the adoption of the corresponding slit structure array, and the ultra oscillation focusing function of the lens is achieved. The focusing performance of the ultra oscillation focusing lens can be improved, fox example, the focusing energy is improved, sidelobes of a focusing light field are reduced, and the field range of the focusing light field is enlarged.

Non-resonant optical modulation of quantum cascade laser and its application potential in infrared spectroscopy

Abstract: Based on the nature of ultra-fast carrier life time in semiconductor quantum well, optical modulation of quantum cascade laser offers an unique way to control intersubband transition through interband transition. This method circumvents the problem of parasitic effects associated with electrical modulation, resulting in a high modulation bandwidth. In addition it allows for fast wavelength modulation on standard type quantum cascade lasers by directly injecting charge carriers to laser active region with near-infrared optical excitation. Here, we demonstrate the first infrared spectroscopic measurement conducted with this all-optical modulation approach. Using wavelength modulation spectroscopy, a 1st order derivative spectrum of methanol vapor gas is observed. Optically based wavelength modulation up to 200 MHz is purely induced by pumping the front facet of quantum cascade laser with an intensity-modulated 1550 nm DFB laser. Compared with conventional direct absorption approach, the noise equivalent sensitivity is improved by a factor of 10 by adding optical modulation in a non-optimized system.

Tunnel type MEMS (Micro-electromechanical Systems) gyroscope

Abstract: 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.

Sub-wavelength pore structure array with continuous amplitude and phase regulation function

Abstract: The invention relates to a sub-wavelength pore structure array with a continuous amplitude and phase regulation function. The sub-wavelength pore structure array is composed of a metal material film and a plurality of double-layer pore structure units which are located in the metal material film, wherein each double-layer pore structure unit is composed of upper-layer pores and lower-layer pores which are produced in the metal film, and the upper-layer pores and the lower-layer pores are coaxial through holes; the upper end surfaces of the upper-layer pores are superposed with the upper surface of the metal film layer, and the lower end surfaces of the lower-layer pores are superposed with the lower surface of the metal film layer; for an electromagnetic wave with a given wavelength, the effective refractive index of the double-layer pore structure unit can be adjusted by changing the diameters and depths of the upper-layer pores, and the diameters and depths of the lower-layer pores; and then continuous regulation for an amplitude and a phase in a certain range is realized. The plurality of double-layer pore structure units (that is, double-layer pore structure arrays) can be adopted on a plane as needed to realize continuous regulation for amplitude and phase distributions in the plane space. Meanwhile, the vibration and phase regulation function for the double-layer pore structure units can be further improved by filling a medium material in the double-layer pore structures.