Comparing different nonlinearities in readout systems for optical neuromorphic computing networks

Nonlinear activation is a crucial building block of most machine-learning systems. However, unlike in the digital electrical domain, applying a saturating nonlinear function in a neural network in the analog optical domain is not as easy, especially in integrated systems. In this paper, we first investigate in detail the photodetector nonlinearity in two main readout schemes: electrical readout and optical readout. On a 3-bit-delayed XOR task, we show that optical readout trained with backpropagation gives the best performance. Furthermore, we propose an additional saturating nonlinearity coming from a deliberately non-ideal voltage amplifier after the detector. Compared to an all-optical nonlinearity, these two kinds of nonlinearities are extremely easy to obtain at no additional cost, since photodiodes and voltage amplifiers are present in any system. Moreover, not having to design ideal linear amplifiers could relax their design requirements. We show through simulation that for long-distance nonlinear fiber distortion compensation, using only the photodiode nonlinearity in an optical readout delivers BER improvements over three orders of magnitude. Combined with the amplifier saturation nonlinearity, we obtain another three orders of magnitude improvement of the BER.

Computer Image Recognition and Recovery Method for Distorted Underwater Images by Structural Light

When imaging through water surface, the random fluctuation of sea surface will cause the distortion of the target scene image, so the distorted image needs to be corrected and reconstructed. At present, distortion compensation mainly adopts iterative registration strategy based on image sequences which is difficult to satisfy the real-time observation. This paper presents a correction method based on active imaging of structured light for underwater image. Experimental results show that compared with the traditional iterative algorithm, the proposed algorithm cannot only improve the restoration accuracy, but also greatly shorten the processing time. Experimental test results demonstrate that the proposed algorithm has good recovery results.

ALGORITHMS FOR THE FORMATION OF NARROW-BAND SPECTRAL-EFFICIENT RADIO SIGNALS OUTSIDE THE RING OF PULSE-PHASE AUTOMATIC FREQUENCY TUNING OF THE FREQUENCY SYNTHESIZER

Рассмотрен процесс формирования радиосигнала с помощью квадратурного модулятора. Точность осуществления переноса на несущую является критически важным фактором. При передаче информационного сообщения значения сигнала несущей частоты должны принимать соответствующие дискретные значения, согласно закону изменения информационной последовательности, таким образом, формирование неискажённого радиосигнала является одним из основных требований, предъявляемых к работе квадратурного модулятора. При реализации сигналов с угловой модуляцией, как правило, используют генератор, управляемый напряжением. Проанализирована работа квадратурного модулятора и квадратурного фазового модулятора, основанного на формирователях функциональных составляющих модулирующего сигнала. Предложен метод компенсации искажений, возникающих в балансных смесителях и фазовращателе за счет быстроизменяющихся помех, приходящих с выхода высокочастотного генератора или с выхода усилителя мощности по цепи обратной связи, а также медленных отклонений фазы и амплитуды сигнала. Проведено моделирование работы схемы, осуществляющей компенсацию амплитудно-фазовых искажений квадратурного модулятора сигналов угловой модуляции за счёт генерирования компенсационных сигналов. Предложена структурная схема синтеза неискаженного сигнала амплитудно-фазовой модуляции с компенсацией амплитудно-фазовой нестабильности квадратурного формирователя, позволяющая осуществлять нелинейное усиление радиосигнала The paper considers the process of data transmission over a radio channel by modulating the parameters of the carrier wave with an information signal. When transmitting an information signal, the carrier frequency values must take discrete values in one-to-one correspondence with the information sequence, thus the formation of an undistorted radio signal is one of the main requirements for the operation of a quadrature modulator. The article analyzes the operation of a quadrature modulator and a quadrature phase modulator based on the shapers of the functional components of the modulating signal. We propose a distortion compensation method using synthesized compensation signals, which makes it possible to effectively compensate, firstly, rapidly changing noise inside balanced modulators and phase shifters, and secondly, noise coming along with an input high-frequency signal, for example, from the output of a power amplifier through circuits feedback and, third, slow deviations of amplitudes and phases. We carried out the modeling of the distortion compensation method using synthesized compensation signals

Study on Distortion Compensation of Underwater Archaeological Images Acquired through a Fisheye Lens and Practical Suggestions for Underwater Photography - A Case of Taean Mado Shipwreck No. 1 and No. 2 -

Underwater archaeology relies heavily on photography and video image recording during surveillances and excavations like ordinary archaeological studies on land. All underwater images suffer poor image quality and distortions due to poor visibility, low contrast and blur, caused by differences in refractive indices of water and air, properties of selected lenses and shapes of viewports. In the Yellow Sea (between mainland China and the Korean peninsula), the visibility underwater is far less than 1 m, typically in the range of 30 cm to 50 cm, on even a clear day, due to very high turbidity. For photographing 1 m x 1 m grids underwater, a very wide view angle (180o) fisheye lens with an 8 mm focal length is intentionally used despite unwanted severe barrel-shaped image distortion, even with a dome port camera housing. It is very difficult to map wide underwater archaeological excavation sites by combining severely distorted images. Development of practical compensation methods for distorted underwater images acquired through the fisheye lens is strongly desired. In this study, the source of image distortion in underwater photography is investigated. We have identified the source of image distortion as the mismatching, in optical axis and focal points, between dome port housing and fisheye lens. A practical image distortion compensation method, using customized image processing software, was explored and verified using archived underwater excavation images for effectiveness in underwater archaeological applications. To minimize unusable area due to severe distortion after distortion compensation, practical underwater photography guidelines are suggested.

Algorithm of phase-frequency distortion adaptive compensation for broadband signals during propagation through transionospheric channels.

The models of distortions of digital broadband signals during their propagation through transionospheric channels which are equivalent to a linear filter with an impulse response determined by a number of parameters, in particular, the central frequency of the signals, are presented. Distortions of the phase-frequency characteristics of digital broadband signals due to the dispersion properties of the ionosphere causes time scattering and the appearance of interference noise which reduces the reliability of information systems and with certain characteristics of the radiochannel destroys their operation. This determines the relevance of developing computational procedures for processing digital signals that reduce the effectiveness of this type of interference, a characteristic property of which is the linear dependence of their power on the power of information signals. The description of the algorithm for adaptive compensation of these distortions based on the use of information signals and the formation of an inverse filter is given, which corresponds to the general concept of "blind" processing. The possibility of the considered distortion compensation for digital wideband signals with phase shift keying and achievement of probabilistic characteristics of erroneous reception providing an acceptable quality of a radiochannels for information systems has been shown by means of computer simulations.