Song Cui

Linearity Indices and Linearity Improvement of 2-D Tetralateral Position-Sensitive Detector

A 2-D tetralateral position-sensitive detector (PSD) is able to provide continuous position measurements with high position resolution, fast response, and low cost. However, it suffers from the nonlinearity problem, which leads to inaccurate measurements. In this paper, two linearity indices are proposed as measures of linearity for its position measurement. Then, a systematic procedure is developed to design new formulas to achieve any degree of linearity through the use of the linearity indices. As an example, a simple estimation formula for the 2-D tetralateral PSD has been derived based on the procedure. Compared to the conventional formula, the linearity of the measurement is greatly improved when the new formula is used. To verify its effectiveness, the new formula is implemented in analog circuits and tested in our experiment. Similar linearity improvement for other 2-D PSDs can also be achieved by following the same design procedure.

Improved measurement accuracy of the quadrant detector through improvement of linearity index

This paper presents a set of formulae for estimating the beam position projected on a quadrant detector (QD). Our new formulae are designed through a systematic procedure to improve the measurement accuracy of the QD. It can be applied to different beam profiles. It is shown in simulations that our new formulae have achieved a much better measurement accuracy. It is also shown through experimental study that our approach is robust and able to achieve very good performance in practice.

An Accurate Separation Estimation Algorithm for the Casimir Oscillator

A novel algorithm is proposed for estimating the separation gap in the Casimir oscillator. The Casimir oscillator is a nanoelectromechanical system actuated by the Casimir force that exists between two conductive metals. The Casimir oscillator has a great potential for use as a separation sensor at the nanometer scale. However, the complex nonlinear behavior of the Casimir oscillator makes it difficult to achieve an accurate separation estimation. The novel estimation algorithm proposed here is able to give an accurate separation estimate even when the nonlinearity is severe. Theoretical analysis and extensive simulations have been conducted to prove its effectiveness and robustness. In addition, this algorithm is also applicable to other estimation problems like the gap separation estimation in electrostatically actuated microelectromechanical systems (MEMS).

Analysis and improvement of Laguerre-Gaussian beam position estimation using quadrant detectors.

Laguerre-Gaussian beams have become increasingly important in areas like optical manipulation and quantum communications. A good understanding of the accuracy and sensitivity of their displacement measurements are required for these applications. In this Letter, we present a method to analyze and compare the performance of these measurements, and an estimation technique is proposed to improve their measurement accuracies. The effectiveness of our methods is verified by simulation studies.

The effect of spot size on linearity improvement of tetra-lateral position sensitive detector

Linearity improvement of tetra-lateral position sensitive detector (PSD) is highly desired in many applications where accurate measurements of the PSD are required. The effect of beam size on our newly proposed linearity improvement scheme is discussed in this paper. Theoretical studies are presented to simplify the numerical calculation when the beam size is considered. Simulation results show that our new formula can still give a nearly perfect linearity and measurement accuracy even if the spot has a considerable beam size.

Separation Gap Estimation in Dynamic Systems Actuated by Casimir Force

In this paper, a new estimation method is proposed to estimate the separation gap and other unknown parameters in Casimir force actuated systems. Real experimental conditions like the finite conductivity and surface roughness are considered as well. Simulation study shows that the method is accurate even when the system has severe nonlinearity.

A novel probe–sample separation estimation scheme for atomic force microscopy

This paper presents a novel estimation scheme to calculate the probe-sample separation in atomic force microscopy (AFM). The AFM is capable of measuring the sample topography by using a probe to interact with the sample. The interaction is dominated by the atomic force which is dependent on the probe-sample separation and sample properties. The key to successful AFM applications is accurate sensing and regulation of the probe-sample separation in nanometer scale. Our proposed scheme provides an accurate estimate of the probe-sample separation based on the information of the main sinusoidal and its harmonics. The estimation is shown to have a good performance even when noise is present.

Linearity improvement of lateral effect position sensitive devices

In this paper, a linearity index is proposed to assess the performance of the position measurement of using position sensitive devices (PSDs). Using the index, a set of position measurement formulae is proposed for PSD with tetra-lateral structures. Compared to the conventional results, the proposed measurement formulae have improved the area with distortion less than 1% from the currently best result of 13% to 25%. Simulation results are reported to verify the theoretical analysis.