Elektrik Elektronik Mühendisliği Bölümü

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Citation Count: Baykal, Y. (2022). "Adaptive optics correction of beam spread in biological tissues", Journal of Quantitative Spectroscopy and Radiative Transfer, Vol.283.
Adaptive optics correction of beam spread in biological tissues
(2022) Baykal, Yahya
Beam spread in turbulent biological tissues is examined when the tissue is excited with a collimated Gaussian laser beam. Adaptive optics correction is applied to the beam spread in the form of piston only (P Only), tilt only (T Only), piston+tilt (P+T), and the reduction in the beam spread is evaluated as compared to the no adaptive optics (No AO) corrected beam spread. No AO and adaptive optics corrected beam spread are expressed for various biological tissue types, against the variations in the strength coefficient of the refractive-index fluctuations, source size, small length-scale factor of turbulence, tissue length, fractal dimension, characteristic lengths of heterogeneity and the wavelength. For the examined tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human) and deep dermis (mouse), No AO beam spread and the adaptive optics corrected beam spread are found to increase as the strength coefficient of the refractive-index fluctuations, tissue length, fractal dimension, the characteristic lengths of heterogeneity increase, and to decrease as the source size, small length-scale factor, wavelength increase. Reduction ratio of P+T correction is almost the same for all the evaluated cases which is 74%.
Adaptive optics effect on performance of BPSK-SIM oceanic optical wireless communication systems with aperture averaging in weak turbulence
(2020) Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın; 7812
Turbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.
Citation Count: Baykal, Yahya; Gökçe, Muhsin Caner; Ata, Yalçın (2020). "Application of adaptive optics on bit error rate of M-ary pulse-position-modulated oceanic optical wireless communication systems", Laser Physics, Vol. 30, No. 7.
Application of adaptive optics on bit error rate of M-ary pulse-position-modulated oceanic optical wireless communication systems
(2020) Baykal, Yahya; Gökçe, Muhsin Caner; Ata, Yalçın; 7812
An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.
Citation Count: Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın (2021). "Effects of adaptive optics on bit error rate of M-ary PPM oceanic optical wireless communication systems with aperture averaging in strong turbulence", Laser Physics, Vol. 31, No. 11.
Effects of adaptive optics on bit error rate of M-ary PPM oceanic optical wireless communication systems with aperture averaging in strong turbulence
(2021) Gökçe, Muhsin Caner; Baykal, Yahya; Ata, Yalçın; 7812
Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma-gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens-Fresnel technique is used to obtain the average received signal power.
Citation Count: Ata, Yalçın; Gökçe, Muhsin Caner; Baykal, Yahya (2020). "M-ary pulse position modulation performance with adaptive optics corrections in atmospheric turbulence", Journal of Modern Optics, Vol. 67, No. 6, pp. 563-568.
M-ary pulse position modulation performance with adaptive optics corrections in atmospheric turbulence
(2020) Ata, Yalçın; Gökçe, Muhsin Caner; Baykal, Yahya; 7812
The performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.
Citation Count: Yalçın, Ata; Gökçe, Muhsin Caner; Baykal, Yahya. (2022). "Mitigation of atmospheric turbulence on up and downlink optical communication systems using receiver diversity and adaptive optics", Optical and Quantum Electronics, Vol.54, No.10.
Mitigation of atmospheric turbulence on up and downlink optical communication systems using receiver diversity and adaptive optics
(2022) Yalçın, Ata; Gökçe, Muhsin Caner; Baykal, Yahya; 7812
Improvement in the performance of uplink and downlink optical communication systems by means of receive diversity and adaptive optics correction is investigated. We develop a communication system model using adaptive optics correction in the transmitter and maximum ratio combining diversity technique in the receiver. The effect of adaptive optics correction modes, receive diversity, zenith angle, link length, wind speed and the height of transmitter/receiver on the ground are evaluated. Performance improvement is observed with both adaptive optics correction and the receive diversity. It is aimed to provide researchers an option to determine the method they will use to reduce the effect of turbulence. As the numerical values of the main results, we report that adaptive optics correction with 5 mode Zernike removal reduces BER from 1 0 - 8 to 1 0 - 10 for one receiver. When the number of receivers is 6, BER is found to reduce from 1 0 - 6 to 1 0 - 12. The results obtained in this study can be beneficial to optimize the design of the slant path uplink and downlink optical communication links between the ground and low-orbit satellites that are exposed to atmospheric turbulence.
Citation Count: Gökçe, Muhsin Caner; Yalçın, Ata; Baykal, Yahya Kemal. (2022). "Performance evaluation of aeronautical uplink/downlink free-space optical communication system with adaptive optics over gamma-gamma turbulence channel", Journal of Optics (United Kingdom), Vol.24, No.10.
Performance evaluation of aeronautical uplink/downlink free-space optical communication system with adaptive optics over gamma-gamma turbulence channel
(2022) Gökçe, Muhsin Caner; Ata, Yalçın; Baykal, Yahya Kemal; 7812
In this study, we analyze the effect of adaptive optics corrections on the performance of an aeronautical free-space optical (FSO) system with bidirectional slant path uplink and downlink communication channels. The aeronautical FSO communication (FSOC) system operates in a gamma-gamma atmospheric turbulence channel and employs adaptive optics corrections for the distorted wave front of the Gaussian beam wave. The modulation type of the aeronautical FSOC system is chosen to be M-ary phase-shift-keying-subcarrier intensity modulation and the type of the employed photodetector is positive-intrinsic-negative. In analysis, the effect of system parameters such as zenith angle, the height of transmitter/receiver on the ground, M-ary level, filter bandwidth, link distance, and the adaptive optics correction modes on bit-error-rate are demonstrated.
Citation Count: Ata, Yalçın; Baykal, Yahya; Gökçe, Muhsin Caner (2021). "Signal-to-noise ratio with adaptive optics compensation in non-Kolmogorov weak turbulent atmosphere", Waves in Random and Complex Media.
Signal-to-noise ratio with adaptive optics compensation in non-Kolmogorov weak turbulent atmosphere
(2021) Ata, Yalçın; Baykal, Yahya; Gökçe, Muhsin Caner; 7812
This study investigates the average signal-to-noise ratio (Formula presented.) at the shot-noise limited receiver of an optical wireless communication system (OWC) that uses collimated Gaussian beam with adaptive optics correction in non-Kolmogorov weak turbulent atmosphere. (Formula presented.) and the variation in the percentage (Formula presented.) are calculated and the results are presented against various adaptive optics correction modes, non-Kolmogorov power-law exponent, receiver aperture size, Gaussian beam source size, photodetector quantum efficiency, electronic bandwidth, link length, and turbulence strength. Adaptive optics correction is analyzed for tilt, defocus, astigmatism, coma and trefoil modes and their variations. The effects of adaptive optics compensation are examined that cause an increase in SNR, hence improve the performance of an OWC system using collimated Gaussian beam and operating in the non-Kolmogorov weak turbulent atmosphere.

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