High Verdet Constant Materials for Magneto-Optical Faraday Rotation: A Review

Abstract

The Faraday effect is a magneto-optical (MO) phenomenon by which the polarization direction of linearly polarized light is rotated when passing through a transparent material with the application of a magnetic field along the direction of light propagation. The magnitude of the angle by which light is rotated at specific wavelengths, temperatures, and applied magnetic fields is directly proportional to the Verdet constant, which is an intrinsic bulk property of an optically transparent material. A high Verdet constant is desired for MO applications such as optical isolators, sensors, or modulators to reduce the path length required to obtain large optical rotation with modest magnetic fields to enable device miniaturization and overall cost reduction. MO material development has been ongoing for nearly the past two centuries, from which a wide range of materials have emerged. Herein, we review the development of high Verdet constant MO materials across many material classes, with an emphasis on recent developments of higher Verdet constant polymeric and polymer-nanocomposite materials. Inorganic materials have primarily been used for Faraday rotation systems which initially focused on the use of amorphous glasses and has since expanded into MO active crystals, ceramics, ferrofluids, organic small molecules, synthetic polymers, and polymer–nanoparticle nanocomposites. Although the most widely used materials for MO applications, hard matter based on inorganic materials typically possess Verdet constants on the order of 103–104 °/T·m at room temperature when measured in the visible and NIR ranges. More recent work has focused on using soft matter alternatives composed of organic small molecules, polymers, and polymer–nanoparticle nanocomposites which afford higher Verdet constants ranging from 104 to 106 °/T·m at room temperature. The current Review aims to discuss inorganic, organic, and hybrid high Verdet constant materials, which has been previously complicated by nonuniformity in the units and sampling conditions used for these MO measurements.

Tb3Al3Ga2O12: A Novel Visible–Infrared Faraday Crystal Exhibiting a Superior Magneto-Optical Performance

“…19 Therefore, Faraday materials with high Verdet constants are in high demand to meet the continuous development of advanced high-quality lasers. 4 It is well-known that Tb transparency. 20 However, until now, only small-size TAG single crystals have been harvested through the edge-defined film-fed technique and hybrid laser floating zone method; 21 an industrially practicable TAG crystal cannot be obtained due to its incongruent melting nature.…”

“…Recently, Faraday isolators (FIs) have attracted a lot of attention because of the rapid development of advanced optical communication, smart grids, lasers, and so forth. − FIs are magneto-optical devices that can nonreciprocally rotate the polarization plane of the laser beam, thus enabling reduction of unwanted light feedback and prevent instabilities of the laser source . Obtaining an optical polarization rotation is often required for a Faraday crystal, which fundamentally determines the performance of FIs. , So far, Y 3 Fe 5 O 12 (YIG) is one of the most well-known magneto-optical crystals. , It has been widely used in commercial infrared (IR) FIs due to its large specific Faraday rotation, high transparency, and low saturation magnetization.…”

“…Over the past decades, considerable interest has focused on VIS–NIR magneto-optical crystals, especially the Tb 3+ -based crystals with a garnet structure. ,, They are optically isotropic and possess a very large Faraday rotation. Among them, the Tb 3 Ga 5 O 12 (TGG) crystal has been market-dominating for FIs because of its excellent properties and favorable growth characteristics. − A commercial large-size TGG crystal can be obtained through the Czochralski (Cz) method because of its congruent melting nature.…”

Terbium (III) Oxide (Tb2O3) Transparent Ceramics by Two-Step Sintering from Precipitated Powder

“…After the discovery of the Faraday effect in 1845, magneto-optical effects such as the Kerr effect in 1876, Zeeman effect in 1896 and Cotton-Mouton effect in 1907 have been discovered in succession [1][2][3]. As a result, a variety of magneto-optical materials, which own the magneto-optical properties, have emerged and developed subsequently, and these are applied universally in optical communication, optical fiber current sensor [4], optical isolator [5][6][7][8] and other magneto-optical devices. As one of the magneto-optical effects, the Faraday effect, which can make the polarization plane of the transmitted light nonreciprocally deflect, is widely applied in the optical isolator of lasers to ensure laser unidirectional passing and block the reverse light effectively.…”

Synthesis of Tb2O3 nanoparticles by laser ablation in Ar gas flow

“…In recent years, high Verdet constant materials based on terbium sesquioxide (Tb 2 O 3 ) have attracted considerable interest as promising magnetoactive media for Faraday isolators used in high-power near-IR laser sources [1][2][3]. The intensity of research and development in this direction has risen significantly since Veber et al demonstrated the first growth of millimeter-sized cubic Tb 2 O 3 single crystals using a controlled atmosphere flux method in 2015 [4].…”