High-frequency signal generators are required in such applications as telecommunications, radar, medical equipment, remote control, probing, radio astronomy, and spectroscopy. One can use an optoelectronic oscillator on a photonic integrated circuit in these applications due to its ease of implementation and low phase noise level. This article considers an optoelectronic oscillator with a phase shifter as a phase modulator implemented in a photonic integrated circuit to simplify the photonic integrated circuit design. The simulation results show that this system can generate microwave signals with a high signal-to-noise ratio (at least 35.27 dB). The side mode suppression ratio was up to 5.94 dB lower than the Mach-Zehnder modulator scheme. This proposed scheme can be used for microwave signal generation in various telecommunication applications and in interrogation tasks.
The article describes an approach to simulating a microring resonator structure on the silicon nitride integrated photonics platform when exposed to various hazardous to human health gases. We simulated various gases by changing the refractive index of the medium surrounding the resonator from 1 (vacuum) to 1.001768 (CCl4). The microring structure resonant wavelengths varied for various gases, and the quality factor, sensitivity, and intrinsic detection limit were determined. The simulation results show that it is possible to detect a wide range of gases hazardous to human health, including carbon tetrachloride, mercury vapor, carbon monoxide, and nitrogen monoxide, using the developed sensor. However, it is impossible to distinguish the last two gases based on the results of the current work using the SiN platform. Coatings are one of the potential ways to improve the designed sensor for detecting these gases.
The paper proposes a photonic integrated circuit (PIC) design for multi-channel swept-source optical coherence tomography (SS-OCT) with a high-scale elements integration on the chip. The PIC contains a tunable reference arm, four spaced apart sample arms, a k-clock based on an unbalanced Mach-Zehnder interferometer, an OCT interferometer, and balanced photodiodes. The PIC is developed for a silicon nitride manufacturing platform, providing minimum losses. The simulation results demonstrate the possibility of simultaneous reception of OCT data from four different points of the studied tissue sample, which can significantly increase the scanning speed.
Intelligent automatic diagnosis of diseases, which acts as a recommendation system for diagnosticians, reduces the burden on medical personnel and potentially reduces the impact of the human factor. This circumstance is especially true against the background of rejuvenation of retinal diseases, in particular age-related macular degeneration. In this article, we analysed how neural network models and dataset dimensionality affect the effectiveness of an intelligent diagnostic algorithm for three stages of age-related macular degeneration based on optical coherence tomography images. We identified the advantages and disadvantages of convolutional and recurrent neural networks when dealing with each stage of the disease, as well as different dataset sizes. Based on the obtained information, we concluded the most effective neural network architecture in terms of achievable specificity and sensitivity values, as well as the impact of augmentation for increasing the original dataset on the overall generalization ability of the algorithm.
In this paper we propose a design of an integrated wavelength-tunable vortex beam emitter based on the silicon photonics platform. The proposed device utilizes the free-plasma dispersion effect in order to change the effective index of the ring waveguide, which leads to displacement of the resonant wavelengths. This scheme allows to bypass the dependence of the emitter resonant characteristics from the fabrication errors. Our simulations also show that for the micro-ring resonators with a small free spectral range it becomes possible to switch the emitted vortex order keeping the same wavelength. Such capabilities make the proposed emitter useful in a wide applications range from communication systems to sensors.
In this article we present the brief review of different scenarios of using the photonic integrated circuits (PIC) in the swept-source optical coherence tomography (SS-OCT) with different degree of integration and propose implementation of PICs on the Si/Ge manufacturing technology with integrated analogous balanced photodetectors. The first PIC implementation contains two arms for processing backscattered light and light reflected in “off-axis” mode on the same chip. We present results of simulation of such PIC that demonstrate its functionality. The second PIC implementation provides functionality for the optical processing of the backscattered signals and includes integrated narrow-band filter based on the adjustable unbalanced Mach-Zehnder interferometer for reseting the digital signal processor in the beginning of the every period of the frequency sweep. Implementing the SS-OCT functionality on the PIC will make possible to reduce the cost of the final device, as well as significantly reduce its geometric size, which is an important factor that provides portable use.
We present design of photonic integrated orbital angular momentum (OAM) emitters consisting of access waveguides and ring resonator with top grating made from holes. Access waveguides are coupled to the resonator using “pulleycoupler” scheme. The device is designed for silicon-on-insulator (SOI) manufacturing platform. We simulated singlemode resonator with one access waveguide and shown that it emits two OAM modes in out-of-plane regime. Than we simulated multimode resonator with two access waveguides and shown that it emits up to four OAM modes. The implementation of OAM emitter based on the ring resonator has specific resonance spectrum therefore such devices are WDM compatible. Compactness of such device allows using it in photonic integrated circuits.
In this paper we propose design of the mode converter for implementing in photonic integrated circuits. Mode converter consists of single-mode ring resonator, single-mode access waveguide and multimode access waveguide, and we propose using of vertical coupling, i.e. locating waveguides under the ring with little gap. Using finite difference time domain simulation we showed high efficiency of proposed device design. We showed dependence of the device performance on the shape of multimode waveguide coupler: straight waveguide provide low level of mode crosstalk, “pulley coupling” scheme with small arc angle (about 13 degrees) provide strong wavelength selectivity. Devices with proposed design is suitable for SDM-WDM systems.
In this paper we propose to evaluate the possibility of applying the method known as differential transformation of signals to reduce the dynamic range of optical signals for mitigation of impairments caused by Kerr-nonlinearities. The essence of this method is as follows. The channel signal is the difference between the original signal and its extrapolated values. We have simulated nonlinear propagation of proposed signal and original signal to define nonlinear impairments reduction due to signal compression. Presented results show that differential transformation of signal allows to sufficiently mitigate envelope distortions caused by self-phase modulation and cross-phase modulation.
In this paper we study statistical properties of nonlinear impairments enhancement due to linear mode coupling in few mode optical fibers. Previously we have shown that strong linear mode coupling leads to the enlargement of nonlinear distortions, but in the case of the weak linear mode coupling this phenomenon shows itself in the stochastic manner. Therefore we use simulations based on numerical solving of the generalized coupled nonlinear Schrödinger equations to plot distribution histograms of the difference between rms of nonlinear impairments in the case of presence and in the case of absence of the weak linear mode coupling for different mean lengths of coupling fiber sections, different values of signal power, and modulation formats. Presented results show that distribution plotted for the fundamental mode has higher dispersion than the same one for the first- or second-order modes. In mode division multiplexed systems it means that channel using fundamental mode as a carrier is more affected to nonlinear impairments enhancement than mode channels of higher orders. Nonlinear impairments may sufficiently decrease the effectiveness of linear coupling compensation for all the mode channels.
In this paper we consider nonlinear impairments of mode division multiplexed signals with QAM modulation in optical fibers with linear mode coupling of spatial modes. We simulate simultaneous propagation of fundamental mode and two first-order vortex modes in standard single mode fiber at 850 nm and propagation of fundamental mode and first- and second-order vortices in step-index fiber with enlarged core at 1550 nm. Simulation results shows that in strong coupling regime linear coupling lead to sufficient increasing of nonlinear impairments, but QAM-modulated signal is more robust to this effect than OOK modulated signal.
We considered interaction of PMD and Kerr-nonlinearities in the two-channel WDM system to derive conditions of signal improvement due to such interaction. We presented statistics of eye-diagram opening and investigated properties of fiber links providing this kind of signal improvement.
This paper presents results of investigation on interaction of PMD and Kerr-nonlinearities in long-haul fiber links. It is shown that PMD may significantly reduce impairments caused by nonlinear effects. There are shown dependences on the input polarization, peak pulse power, PMD coefficient and used line codes.
This paper presents results of investigation on cross-phase modulation effect and influence of polarization effects on it. It
is shown that fast polarization scrambling can effectively reduce impairments caused by cross-phase modulation in the
case of NRZ signal.
This paper presents results of numerically solved model of fiber link including Kerr-nonlinearities,
dispersive effects and polarization-mode dispersion. Different types of Gaussian pulses are modeled
at step-index and non-zero dispersion shifted fibers.
We present a solution of the synthesis for reflective optical filters designed for WDM-systems. Filter is based on multilayer dielectric structures with apodized (modulated) refractive index profile. The method of synthesis provides calculation of the uniform quarter-wave filter-prototype. The calculation of the prototype is executed with relation, which join given spectrum characteristics with constructive parameters of the filter. On the base of calculated filterprototype
the filter with bilateral Gaussian apodization of a refractive index profile, possessing given spectral properties is formed.
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