Stability Compensation Design and Analysis of a Piezoelectric Ceramic Driver with an Emitter Follower Stage.

Piezoelectric ceramic has been widely applied in many fields because of its characteristics, and the performance of piezoelectric ceramic is determined strongly by its driver. In this study, an approach to analyzing the stability of a piezoelectric ceramic driver with an emitter follower stage was presented, and a compensation was proposed. First of all, using the method of modified nodal analysis and loop gain analysis, the transfer function for the feedback network was analytically deduced, and the cause of the instability of the driver was found to be the pole composed of the effective capacitance from the piezoelectric ceramic and the transconductance from the emitter follower. Then, a compensation involving a novel delta topology composed of an isolation resistor and a second feedback path was proposed, and its function principle was discussed. Simulations showed a correspondence between the analysis and the effectiveness of the compensation. Finally, an experiment was set up with two prototypes, one with compensation, and the other without compensation. Measurements showed the elimination of oscillation in the compensated driver.

Apparatus and its principle for thermal aberration compensation.

Thermal aberrations caused by absorption of laser beams degrade the image quality of exposure tools during the working process. Many compensators, such as lens movement or lens deformation, are used to compensate for low-order thermal aberrations of optical systems. In this paper, an apparatus with higher-order aberration correction capability is presented. The main principle of the apparatus is to actively heat and cool the lens near the pupil to generate a desired temperature profile to compensate for thermal aberrations. We first introduce the basic concept of the apparatus. Then we establish an analytical model to describe the lens temperature of the apparatus based on its working principle and demonstrate its compensation capability. Finally, an algorithm for dynamic thermal aberrations compensation is proposed to overcome the time lag effects of a thermally controlled lens.

Constrained pupil balance compensation for specific lithographic illuminator settings.

Pupil energy balances have always been considered significant elements for emersion lithography generally due to the large angle of incidence and offset imaging field. Those imbalances impact on exposure uniformity and decay pattern resolution. To overcome such shortcomings, a study on pupil compensation is discussed in this manuscript. A computational method based on a constrained optimization solution is proposed. By using a self-designed optical model of a zoomed system incorporating axicon lenses, a series of computations are developed and discussed. Also, the validity of our compensation method has been fully verified by simulations under multiple illumination settings.

Design and engineering verification of an ultrashort throw ratio projection system with a freeform mirror.

A refractive-reflective combined ultrashort throw ratio projection optical system is designed. We use a freeform mirror to shorten the projection distance and correct distortion, and a plane mirror to turn back the optical path and reduce system volume. The projection system design method combines refractive lens group design and freeform surface mirror design with integrated optimization. The system's throw ratio is 0.11 with a projection distance of 320 mm and a 130 in. (1 in.=25.4 mm) screen size, which illustrates the advantages of the low throw ratio. The system's maximum distortion is 0.07%. To demonstrate the proposed system's performance, a prototype is developed. Experimental results confirm that the system performs excellently while meeting the design requirements. The system's advantages include low throw ratio, excellent imaging quality, miniaturization, and engineering feasibility.

Adaptive Spiral Tool Path Generation for Diamond Turning of Large Aperture Freeform Optics.

Slow tool servo (STS) diamond turning is a well-developed technique for freeform optics machining. Due to low machining efficiency, fluctuations in side-feeding motion and redundant control points for large aperture optics, this paper reports a novel adaptive tool path generation (ATPG) for STS diamond turning. In ATPG, the sampling intervals both in feeding and cutting direction are independently controlled according to interpolation error and cutting residual tolerance. A smooth curve is approximated to the side-feeding motion for reducing the fluctuations in feeding direction. Comparison of surface generation of typical freeform surfaces with ATPG and commercial software DiffSys is conducted both theoretically and experimentally. The result demonstrates that the ATPG can effectively reduce the volume of control points, decrease the vibration of side-feeding motion and improve machining efficiency while surface quality is well maintained for large aperture freeform optics.

High-performance laser projection display illumination system based on a diffractive optical element.

Lasers have been regarded as the potential illumination source for next generation projectors. With the additional feature of coherency, diffractive optical elements (DOEs) become available in the illumination light path. DOEs in laser projection display systems add strong beam-shaping ability, good uniform performance and small size, which makes it is possible to realize efficient and uniform illumination on a spatial light modulator (SLM). Moreover, it is helpful for the simplification and compactness of illumination optics. This paper proposed what we believe is a novel RGB laser projection display illumination system based on a DOE, which used the DOE and optical path compensation system (OPCS) as the beam-shaping and relay system (BSRS), instead of a light pipe and relay lens group in the conventional laser projection display illumination system. We designed the DOE and established the simulation model of the illumination system. The simulation results show that the new illumination system is simple and compact, the illumination uniformity is more than 90%, the illumination efficiency of RGB illumination in BSRS is more than 75%, and the numerical aperture (NA) of the illumination beam is about 0.01.

Simulated and experimental study of laser-beam-induced thermal aberrations in precision optical systems.

Precision optical systems that utilize laser beams as working media usually suffer from thermal aberrations caused by absorbed energy. Based on a specially designed three-lens system, the causes and contributions of mechanical structures to the system's thermal aberrations are studied. The contribution of three thermal effects, surface deformation, change of refractive index, and stress birefringence on the system's thermal aberrations, is analyzed respectively through an integrated optomechanical simulation method. The impact of the structure's thermal dissipating capability and structure configuration on the system's thermal aberrations is analyzed, too. Experiments have been carried out to validate the correctness and accuracy of the simulation method. Both the simulated and tested results can provide a reference for structure design and thermal aberration analysis of the similar optical systems.

Absolute surface figure testing by shift-rotation method using Zernike polynomials.

In surface figure testing, most of them are relative tests, and the reference surface usually limits the accuracy of test results. Absolute calibration is one of the most important and efficient techniques to reach subnanometer accuracy in surface figure testing. An absolute testing method, a shift-rotation method using Zernike polynomials, is presented, which can be used to calibrate both flat and spherical surfaces (concave or convex). Calibration contains at least three position measurements: one basic position, one rotation, and one lateral shift of the test surface. Experiments show that the repeatability of this method is 0.13 nm RMS, and pixel-to-pixel comparison with the two-sphere method is 0.2 nm RMS.

Mathematical construction and perturbation analysis of Zernike discrete orthogonal points.

Zernike functions are orthogonal within the unit circle, but they are not over the discrete points such as CCD arrays or finite element grids. This will result in reconstruction errors for loss of orthogonality. By using roots of Legendre polynomials, a set of points within the unit circle can be constructed so that Zernike functions over the set are discretely orthogonal. Besides that, the location tolerances of the points are studied by perturbation analysis, and the requirements of the positioning precision are not very strict. Computer simulations show that this approach provides a very accurate wavefront reconstruction with the proposed sampling set.

A high-accuracy and convenient figure measurement system for large convex lens.

We present a novel optical configuration of a phase-shifting interferometer for high-accuracy figure metrology of large dioptric convex spherical surfaces. The conformation and design considerations according to measurement accuracy, practicability, and system errors analysis are described. More in detail, we show the design principle and methods for the crucial parts. Some are expounded upon with examples for thorough understanding. The measurement procedures and the alignment approaches are also described. Finally, a verification experiment is further presented to verify our theoretical design. This system gives full-aperture and high-precision surface testing while maintaining relatively low cost and convenient operation.

Design of algorithms for phase shifting interferometry using self-convolution of the rectangle window.

The objective of this paper is to design phase shifting algorithms error-resistant to the nonlinearity of phase-shift error and photoelectric detector simultaneously. An effective construction approach is proposed based on self-convolution of the rectangle window to design algorithms with perfect zero point distribution, according to the fact that the error-resistant capability is entirely determined by the number and order of zero points of Fourier transform of the related window function. Theoretical analysis and numerical simulations compared to the commercial 13-frame algorithm demonstrate the validity of the approach to design algorithms with enhanced error-resistant capability not only to CCD-caused harmonics but also to PZT ramping nonlinearity.

[Measurement technology for relative spectral responsivity of the ultraviolet ICCD].

The spectral responsivity is one of the important parameters of detector. With the development of ultraviolet detect technique accurate measure for the spectral responsivity of ultraviolet detector becomes more and more important. A measure principle which is based on the direct comparison measuring method for relative spectral response measurement of the ultraviolet ICCD is introduced. Based on the scientific-grade spectrometer with ultraviolet responsivity, a measurement facility was built. The relative spectral responsivity curve of the ultraviolet ICCD was obtained. The curve indicates that the spectral-response of UV-ICCD is from 220 to 300 nm and the peak response is near 270 nm, which indicates that the UV-ICCD is solar blind. The analysis of the uncertainty shows that the most largest uncertainty of measurement for relative spectral responsivity of the UV-ICCD is 7.79% and meets the requirement.