![]() In this work, we demonstrate that asymmetrical transmission for light of arbitrary polarization may be obtained in a grating-free multilayer planar structure based on non-magnetic linear materials, which provides means for diversion of backward propagation without use of external magnetic field. It has been demonstrated that asymmetrical transmission of TM-polarized light can be achieved through fabrication of nanopatterned asymmetric metallic grating or magnetization. Recently, hyperbolic metamaterials (HMM) have emerged as a promising class of structures that may be employed to obtain optical-diode behavior. What is more, it has been shown that appropriate nanopatterning or presence of magneto-optical response may also lead to broadband asymmetric light transport in a metasurface. Until now, it has been demonstrated that a complex triple-helix metamaterial structure may provide magnetic-free optical isolation within a broad spectral range. Most recent scientific efforts in this field have been oriented towards exploitation of artificially-created structures, the so-called metamaterials. Moreover, there have been few successful attempts to obtain asymmetrical transmission based on a coupled multiple-microcavity system with balanced gain and loss, i.e., parity-time symmetry. Recent advances in nanofabrication allowed to achieve new means for non-reciprocity via use of novel photonic components, such as magneto-optical photonic crystals or a two-cavity optomechanical system. However, optical isolators based on non-linear materials are applicable only to high intensity signals, which often does not eliminate unwanted feedback to a sufficient degree. Over the last two decades, non-linear optical effects have been considered as promising means for optical isolation in integrated systems. With the development of integrated optics, there exists an ever-growing demand for compatible solutions for optical isolation. However, systems utilizing magneto-optic effect are typically characterized by a large size and cannot be easily implemented in on-chip optical systems. Since the first successful realization of optical isolation, the most common approach to induce non-reciprocity in an optical system is to employ Faraday effect. In addition, an optical diode may be employed to suppress unwanted interference and interaction between different optical components, as well as to eliminate parasitic light routing in waveguiding systems. This type of device is often used to prevent undesired back propagation that may be harmful to optical instruments and components. Single polarization fiber optic isolators are also used with laser diodes, gyroscopic systems, optical modular interfaces, and a variety of other mechanical control and testing applications.By definition, a “true” optical isolator (optical diode) is a device equivalent, in terms of functionality, to an electronic diode, which blocks or diverts all possible states of radiation for backward propagation. They are reliable devices when used in conjunction with fiber optic amplifiers, fiber optic ring lasers, fiber optic links in CATV applications, and high-speed and coherent fiber optic communication systems. Optical isolators are used in many optical applications in corporate, industrial, and laboratory settings. Polarization dependant loss is the attenuation caused by polarization. Insertion loss is the attenuation caused by the insertion of an optical component. Isolation, generally measure in decibels (db), is a measure of how effectively back reflections are prevented and the degree to which the isolator can transmit. This characteristic is usually measured in nm. Center wavelength is the center of the wavelength range in which the isolator is designed to function optimally. Important specifications for optical isolators include center wavelength, isolation, insertion loss, and polarization dependant loss. They must be directly mounted to the object that needs isolation. Free space isolators, by contrast, do not have an integral connection system. That is to say that they come with built-in fiber optic cable and connectors so that they may be integrated directly into a fiber optic system. Inline fiber optical isolators are designed in pigtail fashion. There are two major classifications of optical isolators: inline isolators (fiber optic isolators) and free space isolators. Ideally an isolator would pass all light in one direction and block all light in the reverse direction. ![]() Optical feedback degrades signal-to-noise ratio and consequently bit-error rate. They are most often used to prevent any light from reflecting back down the fiber, as this light would enter the source and cause backscattering and feedback problems. Optical isolators are passive optical devices that allow light to be transmitted in only one direction. ![]()
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