Xuemin Cheng

An image stabilization optical system using deformable freeform mirrors.

An image stabilization optical system using deformable freeform mirrors is proposed that enables the ray sets to couple dynamically in the object and image space. It aims to correct image blurring and degradation when there is relative movement between the imaging optical axis and the object. In this method, Fermats principle and matrix methods are used to describe the optical path of the entire optical system with a shift object plane and a fixed corresponding image plane in the carrier coordinate system. A constant optical path length is determined for each ray set, so the correspondence between the object and the shift free image point is used to calculate the solution to the points on the surface profile of the deformable mirrors (DMs). Off-axis three-mirror anastigmats are used to demonstrate the benefits of optical image stabilization with one- and two-deformable mirrors.

Four-group stabilized zoom lens design of two focal-length-variable elements

We present a theoretical method for analyzing the first-order optics of stabilized zoom lenses with two focal-length-variable elements. The zoom equations are established through the use of the Gaussian brackets method. This is done because the optical power of the focal-length-variable elements varies during the zooming process. The first and second derivatives and the Hessian matrix of the zoom equations with respect to the Gaussian parameters are determined using the equations. These parameters could represent the sensitivity of the zoom ratio of the system to changes in the corresponding system variables. We select the initial values of these system variables, i.e. the magnification of the focal-length-variable element and the structure parameters of the fixed lens group, to be close to the steepest gradient direction. Here the sensitivity of the system focal length is high with respect to variations in the zoom variables. This process leads to an increase in the zoom ratio of the zoom system. The results show successful four-group stabilized zoom lens designs with 2:1 and 5:1 zoom ratios, using two deformable mirrors as focal-length-variable elements. This system, with the inherent characteristics of a steepest gradient, could miniaturize zoom systems.

An Electrically Tunable Zoom System Using Liquid Lenses

A four-group stabilized zoom system using two liquid lenses and two fixed lens groups is proposed. We describe the design principle, realization, and the testing of a 5.06:1 zoom system. The realized effective focal length (EFL) range is 6.93 mm to 35.06 mm, and the field of view (FOV) range is 8° to 40°. The system can zoom fast when liquid lens 1’s (L1’s) optical power take the value from 0.0087 mm−1 to 0.0192 mm−1 and liquid lens 2’s (L2’s) optical power take the value from 0.0185 mm−1 to −0.01 mm−1. Response time of the realized zoom system was less than 2.5 ms, and the settling time was less than 15 ms.The analysis of elements’ parameters and the measurement of lens performance not only verify the design principle further, but also show the zooming process by the use of two liquid lenses. The system is useful for motion carriers e.g., robot, ground vehicle, and unmanned aerial vehicles considering that it is fast, reliable, and miniature.

Research on the design of an optical information storage sensing system using a diffractive optical element.

This paper introduces a compact optical information storage sensing system. Applications of this system include longitudinal surface plasmon resonance detection of gold nanorods with a single femtosecond laser in three-dimensional space as well as data storage. A diffractive optical element (DOE) is applied in the system to separate the recording-reading beam from the servo beam. This allows us to apply a single laser and one objective lens in a single optical path for the servo beam and the recording-reading beam. The optical system has a linear region of 8 λ, which is compatible with current DVD servo modules. The wavefront error of the optical system is below 0.03 λrms. The minimum grating period of the DOE is 13.4 μm, and the depth of the DOE is 1.2 μm, which makes fabrication of it possible. The DOE is also designed to conveniently control the layer-selection process, as there is a linear correlation between the displacement of the DOE and the layer-selection distance. The displacement of DOE is in the range of 0–6.045 mm when the thickness of the layer-selection is 0.3 mm. Experiments were performed and the results have been verified.

Dynamic focus control of the Blu-ray optical pickup unit

The collimator in BD/DVD/CD compatible optical pickup unit has been designed to motivate and translate along the optical axis by the motor, for multi kinds of disc compatibilities of spherical aberration compensation incurred when reading and writing. The driving motor is huge and not easy to activate. Another technical obstacle to be handled is the alignment so that the reflective mirror should be adjusted and rotated along two axes. In this paper, this kind of optical pickup unit might be minimized, and realize dynamic focus control by micro machined deformable mirror. The optimal sensitivity should be achieved when the focusing spot size is equal to the diffraction limited diameter of the focal spot of the reflected beam.

Measurement and comparison of one- and two-dimensional modulation transfer function of optical imaging systems based on the random target method

Abstract. One-dimensional modulation transfer function (1-D MTF) has been generally calculated to evaluate the image quality of optical imaging systems, such as the horizontal MTF and vertical MTF. These MTFs can be measured by the use of some mature ways. However, the information of 1-D MTF for performance evaluation may not enough for the systems handling two-dimensional (2-D) targets of high resolution, thus discussing 2-D MTF will be necessary. We investigate the measurement method for the 1-D and 2-D MTF of optical imaging systems based on the random target method, and the characteristics of 2-D MTF and 1-D MTF in terms of MTF values and cutoff frequency are also noted.

Wavefront Aberration Detection: A New Perspective

A variety of specialized wavefront detection technologies have been widely used, generally need specialized sensor or device. In this contribution, we proposed an algorithm to calculate the wavefront aberration with two-dimensional modulation transfer function data. The relationship between the wavefront aberration and the modulation transfer function is built based on the optical transfer function and simplified by applying the Newton-cotes quadrature. Thus the wavefront aberration can be numerically calculated by use of the results of the system performance in frequency domain. Numerical calculation result is provided for validating the proposed algorithm.

Design and Implementation of Optical Eccentric Detect System Based on S3C6410 and WinCE6.0

This paper introduces a control system based on ARM and WINCE for optical eccentric detector. The system adopts S3C6410 based on ARM11 architecture as the core chip controls the four-phase stepping motor to drive the rotation of mirror being tested, captured by the image sensor OV9650.It can capture the brightest point in each image, and fits multiple points from many images by least square circle fitting to get the optical eccentric value. Test results show that the system works well and gives stable data, with good real-time performance.

Servo Lens Design for NVD Optical Pick-Up

The NVD(Next generation Versatile Disc) OPU(Optical Pick-Up),based on general red light, is able to read a new type of disk which has 15 GB capacity with 2 layers on one side. The linear span of the focus error signal of original NVD OPU light path is shorter than the requirement proposed by the electron servo system. Increasing the thickness of the tilted-parallel-plate to broaden the linear span will increase the coma aberration which will deteriorate the servo accuracy. Furthermore, the thickness of the tilted-parallel-plate is related to the coexistence of DVD and CD servo signal. Therefore, an aberration-compensated and multi-freedom servo lens for NVD OPU is necessary. The servo lens proposed in this paper is a single lens, which the first surface is a combination of cylindrical surface and tilted surface, and the rear surface is a common spherical surface. According to the conversion of Zernike-to-Seidel wavefront aberration, a given amount of astigmatism will be achieved by bending the curvature of the cylindrical surface to broaden the linear span, and the coma will be corrected by the tilted surface. The function of the spherical surface is guaranteeing the coexistence of DVD and CD servo signal. Finally, the specification of the servo lens and simulation result of the whole system will be addressed.

Quality optimization and control technology for a full field-of-view imaging surface using a stationary phase method and an ambiguity function method

Abstract. A stationary phase method and ambiguity function (AF) method were used to conduct an analytical study of a modulation transfer function (MTF). From the perspective of mathematic models, there was a double integral relationship between the MTF and system wave aberrations. Based on the stationary phase and AF methods, the wave aberration term in the MTF expression was analytically discussed to achieve an aberration function derivation and extreme point analysis, thereby obtaining the analytical expressions of an every field-of-view (FOV) MTF and defocusing distance (i.e., the deviation of an MTF optimal imaging plane from an axial imaging plane) in the full FOV of an optical system. From the obtained image quality evaluation function, the defocusing distance and system image quality could be effectively controlled in a full FOV, which was verified using the examples.