A Robust Continuous-Time Multi-Dithering Technique for Laser Communications using Adaptive Optics

Abstract

Abstract-A robust system architecture to achieve optical coherency free optimization. Several methods that had been proposed in the in multiple-beam free-space laser communication links with adaptive past, such as multi-dithering [4] and sequential perturbations [8], optics is introduced. It is based on deterministic multi-dithering and as well as the recently proposed stochastic parallel gradient descent gradient descent flows and accounts for phase delays in the dither signal, during propagation in the atmosphere, as well as saturation of the optical [5] [10]), however the one proposed communications has always been one of their major advantages over here features several properties that make it attractive for use in conventional RF communications, as it provides a larger modulation modem laser communications. First, it is meant for implementation bandwidth and therefore higher data rates, and less interference in a VLSI circuit, combining low-power consumption, compact size, between optical systems. The reason that laser communications have faster computation, higher perturbation frequencies and control of not expanded as expected, so far, has been the difficulty to compen-multiple channels. Second, it compensates for possible phase shifts sate for atmospheric turbulence. Turbulence causes random optical of the dither signal in the case of long-distance communications. inhomogeneities in the atmosphere that result in beam spreading, Finally, it accounts for saturation of the phase controllers when the beam wander and scintillation (intensity fluctuation), and therefore multi-dither algorithm dictates continuous increase or decrease in the distort the transmitted data [1].controlling phase. Over the last few decades, significant work has been done in the field of adaptive optics in order to alleviate or at least mitigate wave-II. THE MULTI-DITHER ALGORITHM front distortion and therefore enhance the use of laser communicationThe purpose of the multi-dither algorithm is to maximize the value systems. The techniques that have been so far proposed can be divided of a performance metric of the optical system, usually the waveinto two main categories [2]: wave-front conjugation and model-free front's intensity. This is done by calculating the gradient of the optimization. Wave-front conjugation requires the reconstruction of metric and then, using the gradient descent method, find its maximum the wave-front at the receiver and provides information for both phase value. First, a brief overview of the gradient descent method is given (2) of strong intensity modulation used in several laser communication dt dt schemes, the wave-front can be difficultly reproduced, imposing indicating that J(u(t)) is a strictly decreasing function of time unless constraints in the use of the wave-front conjugation technique [5]. u has reached an equilibrium point of (1). The factors discussed above, as well as the emergence of highAssuming that J does not have saddle points, (2) implies that the bandwidth phase controllers (e.g. [7]...

Adaptive delay compensation in multi-dithering adaptive control

“…The considered system architecture for which the algorithm is developed was introduced in [13], is based on sinusoidal multi-dithering and is shown in Fig. 1.…”

“…Delay compensation leads to continuous-time high-speed adaptation as demonstrated in [13], [1], where the need for a real-time phase selection process for the dithers in synchronous detection had been stressed. Recognizing this need, the work presented here proposes an adaptive algorithm for phase (and therefore time) delay compensation nested to, and one level higher than, that of the adaptive control of the plant.…”

Multi-Channel Coherent Detection for Delay-Insensitive Model-Free Adaptive Control

“…In the case of sinusoidal perturbations, as shown in [9], a propagation delay scales the estimate of the partial derivative of J with respect to u i by a factor cos(ϕ i ), namely…”

“…IMPLEMENTATION The design of the implemented VLSI circuit is based on the architecture described in [9]. A brief review is given and further insight on the actual implementation of the main building blocks is provided.…”

7-decades tunable translinear SiGe BiCMOS 3-phase sinusoidal oscillator

“…Oscillators covering a broad range of frequencies can be useful for built-in self test of analog and mixed-signal integrated circuits [2], [3]. Incorporation of wide range oscillators in synchronous detection schemes for characterizing and controlling linear and nonlinear systems has been demonstrated [4]. Applications in biology have been also reported, such as e.g.…”