Optical encoders are commonly used for high accuracy position measurement, both linear and angular. In order to determine the position, the optical encoder generates two electrical signals that are combined using the arctangent algorithm. There are a number of situations, optical, mechanical and electronic, that affect these signals and produce an error in the position measurement. In this work, we analyze the error produced in optical encoders when the electrical signals vary from their nominal values. By using a linear expansion, simple expressions for the error estimation are obtained which can be used to improve the design of the optical encoders. In addition, an experimental verification of the theoretical results is performed.

https://iopscience.iop.org/article/10.1088/0957-0233/19/11/115104/pdf

Metrological errors in optical encoders

An apparatus for producing structured light comprises a first optical arrangement which comprises a microlens array comprising a multitude of transmissive or reflective microlenses which are regularly arranged at a lens pitch P and an illumination unit for illuminating the microlens array. The illumination unit comprises an array of light sources for emitting light of a wavelength L each and having an aperture each, wherein the apertures are located in a common emission plane which is located at a distance D from the microlens array. For the lens pitch P, the distance D and the wavelength L, the following equation applies P 2=2LD/N, wherein N is an integer with N≧1. High-contrast high-intensity light patterns can be produced.

Apparatus for producing patterned illumination including at least one array of light sources and at least one array of microlenses

We introduce a modulation mechanism for negative index materials (NIM) in the GHz frequency range by means of photoconductive coupling. This leads the way to a monolithically integrated modulable NIM achieved by conventional microfabrication techniques. The photosensitive material is deposited in the gap of the split ring resonator (SRR) structure and the response in terms of S-parameters is simulated using a high frequency structure simulator (HFSSTM) program. Only a single SRR particle is simulated to demonstrate total suppression of resonance amplitude and without any loss of generality the concept is applicable to a NIM comprising of both negative permeability and negative permittivity. This simple modulation of refractive indices can lead to novel optical device developments with the potential to dramatically improve the performance of existing phased array antennas, optical beam-forming networks, antenna remoting and transportation of RF power through fiber.

Switching between positive and negative permeability by photoconductive coupling for modulation of electromagnetic radiation

Holography offers unique advantages over conventional photography or traditional photogrammetric techniques in the recording of three-dimensional objects over a large depth of field. However, there are several fundamental problems in recording and replay that must be understood and overcome. The authors discuss the techniques of in-line and off-axis holography, and the problems that are encountered in practice. They present a review of several applications in particulate recording, bubble chamber holography, fuel-rod 'hologrammetry', endoscopy etc. The emphasis is on precision three-dimensional coordinate measurements from holographic images.

Precision coordinate measurements using holographic recording

Under certain circumstances, Voigt waves can propagate in a biaxial composite medium even though the component material phases individually do not support Voigt wave propagation. This phenomenon is considered within the context of the strong-permittivity-fluctuation theory. A generalized implementation of the theory is developed in order to explore the propagation of Voigt waves in any direction. It is shown that the correlation length—a parameter characterizing the distributional statistics of the component material phases—plays a crucial role in facilitating the propagation of Voigt waves in the homogenized composite medium. (Some figures in this article are in colour only in the electronic version)

Correlation length facilitates Voigt wave propagation

It has been shown that the process of coded imaging of incoherently illuminated extended objects by self-imaging structures (SIS) naturally leads to the formation of Lau-type fringes at finite conjugates. The object grating and the grating representing the SIS need not be of the same period. The generalised Lau fringes are obtained under a conjugate relation characteristic of the SIS imaging and a general matching condition involving the periods and frequencies of the two periodic structures. The classical Lau fringes and the so-called finite conjugate classical Lau fringes are formed under special imaging conditions. Useful applications have been mentioned.

The Generalised Lau Effect

The process of speckle averaging in the imaging step in Sub-channel holography has been studied experimentally. First order statistics of the recorded speckle patterns have also been considered and the calculated probability density functions and the values of speckle contrast have been presented. Good agreement between the experimental speckle patterns and the first order statistics is found to exist. A model analysis of the integrated speckle pattern is given in which the randomness introduced by the photographic recording has been considered ia terms of a ‘screen’ function.

Speckle Averaging in the Imaging Step in Sub-Channel Holography

The phenomenon of the shift of the far field diffraction pattern when a small aperature is half-covered with a transparent or partly transmitting film, which has been called the “Talbot effect”, has been studied in detail for dielectric and metallic films. The physical shifts of the central maximum and the first minimum, as well as the variation of relative irradiances at fixed points in the far field have been specifically investigated. Experimental results have been presented to confirm this phenomenon and to illustrate the application of the effect to the measurement of thickness of thin barium stearate and aluminium films. The results show that the effect can be used for the determination of thickness of thin films of known optical constants.

The Talbot Effect and its Use in the Diffractometry of Thin Films

A novel technique of noise reduction in holographic microscopy has been experimentally studied. It has been shown that significant improvement in the holomicroscopic images of actual low-contrast continuous tone biological objects can be achieved without trade off in image resolution. The technique makes use of holographically produced multidirectional phase gratings used as diffusers and the continuous addition of subchannel holograms. It has been shown that the self-imaging property of this type of diffuser makes the use of these diffusers ideal for microscopic objects. Experimental results have also been presented to demonstrate real-time image processing capability of this technique.

Improvement of image quality in holographic microscopy.

The properties of inhomogeneous diffusing media are discussed by use of the matrix treatment as developed in Part I. For this purpose, the elements of the characteristic matrices for a few representative media have been explicity determined in terms of the exact solutions of the appropriate differential equations. Explicit expressions are given for a few useful quantities related to the properties of inhomogeneous media. The similarities in behaviour between a few specific inhomogeneous media and homogeneous media are pointed out.

Matrix Formulation of the Schuster-Kubelka-Munk Theory of Diffuse Scattering. II. Evaluation of Characteristic Matrices For Inhomogeneous Diffusing Layers and Related Properties

S. C. Som

Papers

The Generalised Lau Effect

Speckle Averaging in the Imaging Step in Sub-Channel Holography

The Talbot Effect and its Use in the Diffractometry of Thin Films

Improvement of image quality in holographic microscopy.

Matrix Formulation of the Schuster-Kubelka-Munk Theory of Diffuse Scattering. II. Evaluation of Characteristic Matrices For Inhomogeneous Diffusing Layers and Related Properties