Effects Of Fabrication Errors Research Articles

Algorithm for the real-structure design of neutron supermirrors

The effect of structure imperfections of neutron supermirrors on their performance is well known. Nevertheless, supermirrors are designed with the algorithms based on the theories of reflection from perfect layered structures. In the present paper an approach is suggested, in which the design of a supermirror is made on the basis of its real-structure model (the RSD algorithm) with the use of exact numerical methods. It allows taking the growth laws and the reflectance of real structures into account. The new algorithm was compared with the Gukasov–Ruban–Bedrizova (GRB) algorithm and with the most frequently used algorithm of Hayter and Mook (HM). Calculations showed that, when the parameters of the algorithms are chosen so that the supermirrors designed for a given angular acceptance m have the same number of bilayers, (a) for perfect layers the GRB, HM and RSD algorithms generate sequences of practically the same reflectance; (b) for real structures with rough interfaces and interdiffusion the GRB and HM algorithms generate sequences with insufficient number of thinner layers and the RSD algorithm turns out to be more responsive and efficient. The efficiency of the RSD algorithm increases for larger m. In addition, calculations have been carried out to demonstrate the effect of fabrication errors and absorption on the reflectance of Ni/Ti supermirrors.

Diffractive elements for high-power fibre coupling applications

Optical fibre delivery systems using multiple fibres can increase the amount of light delivered to a manufacturing process. By using diffractive optical elements to optimize the launch conditions, it is possible to remove any ‘hot spots’ from the input beam, maximizing the power-handling capabilities of the delivery system. We present diffractive elements to optimize the launch conditions when coupling to a fibre bundle or more than one individually mounted fibres. The maximum efficiency of these elements approaches 80% with uniformity errors of less than 10%. The effect of fabrication errors on the performance of the diffractive elements is discussed.

Femtosecond pulse shaping by a reflection grating in the resonance domain

Femtosecond pulse shaping by temporal superresolution with a single metallic diffraction grating in the resonance domain has been numerically investigated. It is predicted that a femtosecond pulse can be compressed by more than 20%. Comparing with the previously reported pulse compression with a transmission grating, a metallic reflection grating can avoid several problems associated with a grating substrate of a transmission one. Therefore, the proposed pulse compression scheme is highly feasible in practical experiments. Effects of fabrication errors on the performances and applicable pulse width range are discussed. In addition, potential problems of analysis and design in using a multilevel grating for pulsed light are discussed.

Effect of fabrication errors in channel waveguide Bragg gratings

The spectral performances of nonideal rectangular Bragg gratings, integrated in a rib waveguide, are analyzed by a multilayer approach based on the effective-index method. The effects of errors on the photolithographic definition of the grating, that is, period and shape, and of errors on the control of etching depth are investigated. Also the influence of the stitching error, which is unavoidable when the grating is realized by means of electron-beam photolithography, is addressed. A novel analytical approach that extends coupled-mode theory to the analysis of real gratings is also presented.

Effects of fabrication errors on the performance of cylindrical diffractive lenses: rigorous boundary-element method and scalar approximation

The effects of fabrication errors on the performance of collimating finite-thickness cylindrical diffractive lenses with eight discrete levels are investigated with a rigorous boundary-element method and a scalar approach. The photolithographic fabrication errors considered are mask alignment errors, exposure errors (that result in linewidth errors), and etch-depth errors. A cylindrical Gaussian beam of TE or TM polarization is incident upon the resulting lenses. Lenses of F/4, F/2, and F/1.4 are examined. The diffraction efficiencies of the lenses with fabrication errors are generally lower than the error-free lenses with the most severe performance degradation occurring for mask misalignment and exposure errors.

Effects of process errors on the diffraction characteristics of binary dielectric gratings

The effects of fabrication errors on the predicted performance of surface-relief phase gratings are analyzed with a rigorous vector diffraction technique. For binary elements, errors in the dimensions of the profile [depth, linewidth (fill factor), and grating period], as well as errors in the shape of the profile, are investigated. It is shown that the dimension errors do not have a significant effect on grating performance when the grating is designed for either maximum or minimum diffraction efficiency. A trapezoid is used to model the shape error of the profile. For the first time, design rules that significantly reduce the effects of any shape error are presented.

Double-ion-exchange process in glass for the fabrication of computer-generated waveguide holograms

We experimentally optimize double-ion-exchange process parameters to achieve a designed phase modulation for a wave front passing through a computer-generated waveguide hologram and numerically analyze the effects of fabrication errors. We also demonstrate a gradient-thickness waveguide hologram for ? beam splitting.

Effect of fabrication errors on multilevel Fresnel zone lenses

Blazed Fresnel zone lenses for the 1.5-μm wavelength were fabricated in quartz glass by means of microstructuring technology. The blazed profile in each zone of the lenses was approximated by two, four, and eight discrete levels. The effects of fabrication errors, such as depth and alignment errors, on the diffraction efficiency of the different Fresnel zone lenses were investigated. Further the location and intensity of the parasitic foci appearing due to the discrete level approximation are calculated. Theoretical results along with experimental measurements are presented.

Analysis of effect of fabrication errors on performance of surface-acoustic-wave m-sequence correlators

The paper describes in detail the statistical analysis used in a study of the degradation produced by imperfections in surface-acoustic-wave correlators. We consider the effect of errors in either one or both of the generator/detector pair when the input signal is either a single or a periodic m-sequence. A theoretical model, which incorporates taper, band limitation, random amplitude variations and spurious signal level, accounts for a large measure of the experimentally observed degradation of performance.