Time- and Frequency-Domain Characteristics of Direct-Detection Acousto-Optic Delay Lines

Hasanov

Rustamov

et al. 2022

TAPR

The object of research is a mathematical model of the photoelastic interaction in an acousto-optic delay line (AODL). Two possible cases are discussed as applied to the ratio of the input pulse duration to the time of crossing the optical beam by an elastic wave packet. It is shown that in both cases the voltage at the output of the device is found as the sum of three components, which are formed by different mechanisms. If the duration of the input pulse is longer than the time of crossing the optical beam by an elastic wave packet, then the first component is determined by the process of entry of the leading edge of the elastic wave packet into the optical beam, the second – by the process of complete interaction of the optical beam with the elastic wave packet, and the third – by the process of exit of the trailing edge of the elastic wave packet from the optical beam. In the second case, i. e. when the duration of the input pulse is less than the time of crossing the optical beam by an elastic wave packet, the first term is determined by the process of entry of the elastic wave packet into the optical beam, the second – by the process of advancing the elastic wave packet in the aperture of the optical beam, and the third – by the process of exit of the elastic wave packet from the aperture of the optical beam. The corresponding equations for calculating the parameters of the output pulse were obtained by applying a rectangular pulse to the AODL input. It is proved that if the pulse duration at the AODL input is longer than the time of intersection of the optical beam by an elastic wave packet, then the pulse duration at its output will be equal to the duration of the input pulse. In the case when the duration of the input pulse is less than the time of crossing the optical beam by an elastic wave packet, the duration of the output pulse will be determined by the time of propagation of the elastic wave packet in the aperture of the optical beam. The obtained equations are confirmed by numerical calculations. The results of the numerical analysis were tested experimentally, which confirms the unequivocal adequacy of the proposed model of photoelastic interaction in an AODL.

Section: Methodsmentioning

confidence: 99%

Development of an axonometric model of photoelastic interaction in an acousto-optic delay line and its approbation

Hasanov

Rustamov

et al. 2022

TAPR

Acousto-optic Light Pulse Shaper for Measuring the Parameters of Photo-detectors

Hasanov

Rustamov

et al. 2021

jour

The paper emphasizes that intensive utilization of the optical range increases the need for the development of new optoelectronic devices. Accordingly, there is a growth in the need for effective methods and tools to study photoelectric properties of semiconductor materials, including photo-detectors.In the paper we have analyzed the well-known methods and tools for measuring the photo-detector parameters, defined the restrictions in their applications, and proved that it is relevant to create a measuring system, the parameters of which are easily adapted to the study of photoelectric characteristics of a wide range of semiconductor materials, including photo-detectors.The scheme and principle of operation of the acousto-optic processor and the features of the photo-elastic effect are discussed, and it is proved that they can be used to form a light pulse of required duration and power. The expressions obtained for calculating the response at the acousto-optic processor output enable us to estimate separately the effects of time of crossing the optical beam by the elastic wave packet and the photo-detector inertia.The capability to determine the time of crossing the optical beam by the elastic wave packet and taking it into account as a device error has been substantiated. The proposed formulas have been tested and by numerical analysis based on the datasheet specifications of the FD-24K photodiode, the effectiveness of the obtained expressions has been convincingly proven.The inertia parameters of a particular sample of the FD-24K photodiode are experimentally studied. The emphasis is upon measuring the rise time of the transient response of the object under study. The exact rise time value of the transient response of the experimental FD-24K sample was approximately 7 μs, which is less than that indicated (≤10 μs) in the product certificate. In real life, such a measurement is necessary when selecting the photodiode pairs with identical parameters.By comparing the results of numerical analysis and experimental studies, it has been convincingly proven that the features of the photo-elastic effect can be used to construct a light pulse shaper with the required parameters.

Photo-elastic Effect Features Used for Measuring Laser Radiation Parameters

Gasanov

Guseinov

et al. 2020

jour

Self Cite

The article discusses the photo-elastic effect features in acousto-optic processors for processing pulse signals on the time axis. The photo-elastic interaction in these devices is divided into two areas. In the first area, the input pulse duration is longer than the time of intersecting the optical beam by the elastic wave packet. This particular area is widely used in the practical applications of these processors, where it is a priori assumed that the input pulse duration is longer than the time for the elastic wave packet to intersect the optical beam.In the second area, the input pulse duration is less than the time for the optical beam to be intersected by the elastic wave packet. The objective of this work is to study the photo-elastic effect features in this area. It was established that in this area the pulse duration at the processor output is equal to the time for the optical beam to be intersected by the elastic wave packet and does not depend on the input pulse duration, which is permissible in some cases (for example, in radar pulse existence rather than its duration is recorded). It is shown that in the second area, the output pulse is formed as the sum of three terms. The first term corresponds to the elastic wave packet entering the optical beam. The second term corresponds to the elastic wave packet advancement in the optical beam aperture, and the third one keeps with the elastic wave packet leaving the aperture of the optical beam. The corresponding equations for calculating the pulse at the device output are obtained. The numerical calculations have proved the provisions and patterns established. The numerical modeling results were tested experimentally using a prototype of an acousto-optic processor with direct detection. The analysed results of theoretical and experimental studies unequivocally confirmed that the obtained formulas, formulated statements, and established provisions can be used to expand the functionality of acousto-optic processors, both with direct detection and of heterodyne type. It is shown that with a significant decrease in the input pulse duration relative to the time during which the optical beam is intersected by the elastic wave packet, the latter is converted into a scanning line and can be used to measure the geometric and energy characteristics of the quasi-coherent light.