Yongchao Zou

Approaches to tilted magnetic recording for extremely high areal density

In this paper, we systematically present our fundamental understanding of the advantages of tilted magnetic recording. We investigate the various configurations of tilted magnetic recording including tilted longitudinal recording, tilted perpendicular recording with tilted media and normal single pole head, and tilted perpendicular recording with perpendicular media and tilted writing head. Tilted media with easy axis along the down-track and cross-track directions and tilted media with varied in-plane orientation ratios have been investigated and compared in detail. One important finding is that slightly oriented (in-plane) tilted media show a tremendous improvement in recording performance, which may release the pressure on the fabrication of perfect tilted hard disk magnetic media. Various fabrication methods for tilted media have also been discussed.

Miniature adjustable-focus endoscope with a solid electrically tunable lens.

The design, fabrication and characterization of a miniature adjustable-focus endoscope are reported. Such an endoscope consists of a solid tunable lens for optical power tuning, two slender piezoelectric benders for laterally moving the lens elements perpendicular to the optical axis, and an image fiber bundle for image transmission. Both optical and mechanical designs are presented in this paper. Dynamic tuning of optical powers from about 135 diopters to about 205 diopters is experimentally achieved from the solid tunable lens, which contains two freeform surfaces governed by 6-degree polynomials and optimized by ray tracing studies. Results show that there is no obvious distortion or blurring in the images obtained, and the recorded resolution of the lens reaches about 30 line pairs per mm. Three test targets located at various object distances of 20 mm, 50 mm and 150 mm are focused individually by the endoscope by applying different driving DC voltages to demonstrate its adjustable-focus capability.

Alignment tolerances and optimal design of MEMS-driven Alvarez lenses

The Alvarez lens offers variable focal lengths through lateral shifting of two lens elements. Imaging characteristics and alignment tolerances of the Alvarez lens are studied, and one analytic method for optimal coefficient selection is proposed. Results show that the performance of the Alvarez lens decays with increasing element displacements, and dominant optical aberrations are spherical aberrations, defocus and coma. The lens performance is most sensitive to misalignments in the y direction. If the tolerance is defined as a 10% rise of normalized RMS spot radius, the misalignment should be smaller than 0.01 mm and the tilt angle about any axis can never exceed 1°. By adopting the new coefficient-selection method, lens performance is improved evidently and the degrading trend with increasing displacements is mitigated markedly. In addition, alignment tolerance is increased as well.

Development of Miniature Tunable Multi-Element Alvarez Lenses

The design, fabrication, and characterization of miniature tunable multi-element Alvarez lenses are reported in this paper. Optical design including optimal lens configuration and surface coefficient selection, together with the effects of assembly errors on lens performances, is numerically studied using the ray-tracing method. To demonstrate the working principle, a four-element Alvarez lens is experimentally demonstrated in comparison with a conventional two-element lens. Lens elements are fabricated by a diamond turning and replication molding process and are driven by two piezo actuators integrated with displacement amplification mechanisms. Dynamic tuning of optical power is experimentally determined to be around 43.2 diopters (from 50.9 to 94.1 diopters) for the four-element lens and 21.1 diopters (from 25.3 to 46.4 diopters) for the two-element lens. Lens imaging performance is also characterized comparatively, indicated by images of the 1951 USAF resolution test chart through the lens and Modulation Transfer Function curves calculated accordingly.

Out-of-plane nano-electro-mechanical tuning of the Fano resonance in photonic crystal split-beam nanocavity

We propose and experimentally demonstrate the use of Fano resonance as a means to improve the Quality factor of photonic crystal split-beam nanocavities. The Fano resonance is triggered by the interference between the second-order quasi-transverse electric resonant mode and the leaky high-order quasi-transverse electric propagation mode of the optimized photonic crystal split-beam nanocavity. Compared with a similar photonic crystal split-beam nanocavity without asymmetric Fano lineshape, the Q-factor is increased up to 3-fold: from 1.99×104 to  5.95×104. Additionally, out-of-plane tuning of the Fano resonance is investigated by means of a Nano-Electro-Mechanical Systems based actuator. The maximum centre wavelength shift of the Fano resonance reached 116.69 pm, which is more than 4.5 times the original quasi-Full Width at Half Magnitude.

Solid electrically tunable dual-focus lens using freeform surfaces and microelectro-mechanical-systems actuator

Entangled systems with large quantum Fisher information (QFI) can be used to outperform the standard quantum limit of the separable systems in quantum metrology. However, the interaction between the system and the environments inevitably leads to decoherence and decrease of the QFI, and it is not clear whether the entanglement systems can be better resource than separable systems in the realistic physical condition. In this work, we study the steady QFI of two driven and collectively damped qubits with homodyne-mediated feedback. We show that the steady QFI can be significantly enhanced both in the cases of symmetric feedback and nonsymmetric feedback, and the shot-noise limit of separable states can be surpassed in both cases. The QFI can even achieve the Heisenberg limit for appropriate feedback parameters and initial conditions in the case of symmetric feedback. We also show that an initial-condition-independent steady QFI can be obtained by using nonsymmetric feedback.

Development of Miniature Camera Module Integrated With Solid Tunable Lens Driven by MEMS-Thermal Actuator

The design, fabrication, assembly, and characterization of a miniature adjustable-focus camera module driven by MEMS-thermal actuators are presented. The camera module consists of one solid tunable lens for optical power variation, two identical MEMS-thermal actuators integrated with displacement amplifiers for lens element driving, a CMOS image sensor for recording, and necessary CNC fabricated components for supporting and housing. Fully 3D-multiphysics simulations with valid material properties are performed to explore the design and, hence, optimize the performance of the system. In this paper, the fabricated MEMS-devices are clearly demonstrated, and followed by the detailed characterization of the camera module. Static characterizations of the system, including the temperature distribution on actuators, electric resistance change with temperature increase, displacement-voltage curve of actuator, and the focal length tuning capability, are tested. Dynamic response speed and imaging performance of the camera module are also covered. Results show that the designed MEMS actuator is able to provide a maximum output displacement of 135

Novel one-dimensional photonic crystal air-slotted nanobeam cavity for gas sensing

\mu \text{m}

Mode competition and hopping in optomechanical nano-oscillators

when a 10 V driving voltage is applied. Driven by the thermal actuator, the solid tunable lens presents a repeatable focal length tuning from 9.2 to 7.9 mm with precise focus control. The adjustable-focus capability of the miniature camera module is experimentally demonstrated by clearly focusing targets placed at different object distances. [2016-0072]

Endoscope zoom optics using Alvarez lenses

We have designed a novel photonic crystal air-slotted nanobeam cavity featuring high quality factor and small mode volume. The calculated high sensitivity and response factor pave the way for precise ambient gas sensing.