Optical image transformations for fully parallel optical analog-to-digital conversion

An optical method for a fully parallel analog-to-digital conversion is proposed. The proposed method is carried out by means of intensity transformations of an analog input image and the thresholding for the transformed images and is suitable for two-dimensional implementation based on spatial light modulators. The intensity transformations are implemented by a liquid-crystal spatial light modulator, and thresholding is simulated by computer in consideration of the optical realization.     

Stochastic-flash analog-to-digital conversion

Flash-type analog-to-digital converters (ADC's) presenting a nonlinear behavior, i.e., having nonequally spaced threshold levels, may introduce harmonic distortion that can be reduced by employing large-amplitude dither-based conversion techniques. However, large-scale dithering is difficult to implement and, in addition, severely reduces the ADC input dynamic range. In this paper, a new ADC architecture is presented based on ordinary flash conversion and dynamic element matching, that strongly reduces nonlinear distortion. It eliminates the need for large-scale dither signals by randomizing the resistor positions in the resistor string used to generate the voltage references. Some properties of this architecture are analyzed and simulation results that validate the theoretical assumptions are presented     

Computer simulation of the analog-to-digital conversion of magnetic quantities

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 54–56, December, 1991.     

All-optical analog-to-digital conversion scheme based on Sagnac loop and balanced receivers

An all-optical analog-to-digital conversion scheme based on a Sagnac loop and balanced receivers is proposed and experimentally demonstrated. Adjustable phase shift about the transfer function of the Sagnac loop is obtained by using the multiwavelength optical pulses to realize the phase-shift optical quantization. Benefit from the complementary outputs at the transmitted and reflected ports of the Sagnac loop and balanced receiver can be used to obtain the quantized output binary signal for the encoding operation. A proof-of-concept experiment is implemented using a wavelength tunable continuous-wave laser diode. Using 16 different wavelengths, the 16 quantization levels are demonstrated and an effective number of bits (ENOB) of 4?bits is obtained.     

Study of an ultrafast analog-to-digital conversion scheme based on diffractive optics

A potentially ultrafast optical analog-to-digital (A/D) converter scheme is proposed and was partly studied experimentally. In the A/D converter scheme the input signal controls the wavelength of a diode laser, whose output beam is incident on a grating. The beam from the grating hits a diffractive optical element in an array. The wavelength determines which element is illuminated. Each element fans out a unique spot-pattern bit code to be read out in parallel by individual detectors. In the experiment all patterns but one from 64 array elements were read out correctly.     

Error margin and constraint on the quantization interval of analog-to-digital conversion in systems for analytic research

Fundamental computational formulas are obtained. When a signal and its relative measurement error are given in a specified form, these formulas make it possible to determine the frequency sampling frequency by means of the Kotel 'nikov theorem. A program package by means of which the parameters of an analog-to-digital converter for a standard analytic signal may be quickly found is proposed.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 20–22, May, 1994.     

Fiber-optic microphones for battlefield acoustics

We describe recent work to evaluate the potential performance of an interferometric fiber-optic microphone for battlefield acoustics. The microphone design has high sensitivity and flat response at low frequency and is readily multiplexed. The design is simple and could be manufactured at low cost, which is desirable since in operation the sensors may need to be disposable. Field trial results from an array of microphones are discussed.     

Testing methodologies for analog-to-digital converters

A theoretical approach and an experimental test system devoted to introducing a set of parameters based on Walsh functions and conformed to characterize the transfer function of analog-to-digital converters are presented. Building on the previous work, the authors propose an enhanced system that provides better accuracy in the evaluation of the performance of conversion devices under dynamic conditions. The theory covers an introductive approach to generalize the conversion processes and employs a powerful purpose-oriented tool to understand their in-depth operativity. The error parameters are defined by mathematical algorithms based on Walsh functions and related transform, while their properties are correlated to a standard reference input, a triangular waveform provided by the system. This methodology opens the wave towards the introduction of standard techniques in testing conversion devices     

Optical screen for direct projection of integral imaging

We describe a way to display three-dimensional images by integral imaging using an ordinary projector. We first explain a method that uses a large-aperture converging lens, then we explain the proposed method that uses two sets of lens array. Based on the principle of this new approach, front projection as well as rear projection is possible. Only a proper viewing area can be formed on the optical screen by this method, which improves the brightness of images on the screen. The projector itself does not need an additional optical system. We report on the results of an experiment carried out to confirm the validity of the proposed method.     

Logarithmic analog-to-digital converter

Translated from Izmeritel'naya Tekhnika, No. 5, pp. 4–6, May, 1989.     

Evaluation of organic perovskite photoconductors for direct conversion X-ray imaging detectors

Enhancing the sensitivity of a direct conversion flat panel X-ray imaging detector with minimum manufacturing cost has been a major dream for long decades. This criterion has been recently addressed by the usage of MAPbX₃ (MA is CH₃NH₃ and X is a halogen atom such as Cl, I, or Br) perovskite in X-ray imaging detectors. Though MAPbI₃ has shown large area deposition capability and good X-ray sensitivity, it has to fulfil other criteria such as low dark current, high spatial resolution and high signal to noise transfer capabilities. This paper evaluates the imaging performances such as X-ray sensitivity, detective quantum efficiency (DQE) and modulation transfer function (MTF) of organic perovskites (e.g., MAPbI₃ and MAPbBr₃) with comparison to amorphous selenium (a-Se). These perovskite materials have slightly higher linear attenuation coefficients than a-Se and the expected X-ray sensitivity of these two perovskite photoconductors are higher than a-Se. The mechanisms of the dark current and photocurrent gain in MAPbI₃ detector are also investigated. The MAPbI₃ detector shows some photocurrent gain, which is due to the enhanced electron injection under X-ray illumination. The expected theoretical zero spatial frequency DQE of the MAPbI₃ detectors is similar to that of a-Se while the MAPbBr₃ detector establishes a better DQE than a-Se. The expected MTF of the MAPbBr₃ detectors is similar to that of a-Se while the MAPbI₃ shows worse resolution than a-Se. Based upon our theoretical investigation, we believe that the organic perovskite can find its state of the art in near future if rigorous research for improving the charge carrier transport properties and optimizing its detector structure for low dark current were to be made.