Faraday Element Research Articles

Enhancement of Faraday effect of transparent ferromagnetic Co‐MgF2 granular film by introducing Fabry–Pérot resonant structure

AbstractTo detect the magnetic field using polarization of a light, transparent magnetic material having a Faraday effect is required. The Co‐MgF2 granular film is promising as a candidate of the Faraday element for the magnetic field sensing. In this study, Fabry–Pérot resonant structure was introduced into the Co‐MgF2 granular film to enhance the Faraday effect. It was found that the Faraday effect per unit film thickness [deg/μm] was enhanced due to a light localized in the Co‐MgF2 granular layer sandwiched by Bragg mirror of the insulator multilayer. The maximum Faraday effect of the proposed structure was −1.24°/μm, which was about 3.4 times enhancement compared with a single Co‐MgF2 film, when the number of layer period x in Fabry–Pérot resonant multilayer was 5, where the structure was substrate/(Ta2O5/SiO2)x/Co‐MgF2/(SiO2/Ta2O5)2/Air. Furthermore, the multicavity structure, consisting of the Fabry–Pérot resonant multilayer film continuously placed, exhibited a 50% increase of figure of merit (FOM) defined as Faraday rotation angle per transmission loss [deg/dB].

Experimental study of the mutual influence of fibre Faraday elements in a spun-fibre interferometer

An all-spun-fibre linear reflective interferometer with two linked Faraday fibre coils is studied. It is found experimentally that there is mutual influence of Faraday fibre coils in this interferometer. It manifests itself as an additional phase shift of the interferometer response, which depends on the circular birefringence induced by the Faraday effect in both coils. In addition, the interferometer contrast and magneto-optical sensitivity of one of the coils change. A probable physical mechanism of the discovered effect is the distributed coupling of orthogonal polarised waves in the fibre medium, which is caused by fibre bend in the coil.

Application for Power Equipment of Optical Fiber Current Sensors

The size of optical fi ber current sensors with a Faraday effect can be small with greater weight savings compared with electromagnetic induction type CTs. We advanced such utilizations for power equipment, especially for optical fi ber current sensors that use fl int glass fi ber for the Faraday element. This paper outlines the principle, the composition of optical CTs, and fault point location systems to which an optical fi ber current sensor is applied as well as the practical use situations and the development status of 500-kV independence type optical CTs that are aimed at applications in all digital substations.

Ring Interferometric Magnetic Field Optical Sensor Using a Garnet Single Crystal

A magnetic-field sensor based on reflection-ring interferometry is proposed to achieve a probing scheme with a polarization maintaining fiber (PMF). We used Tb0.19Y0.81Fe5O12 ((TbY)IG) crystals with a striped magnetic domain structure as a Faraday element to enable both parallel and perpendicular fields to the propagating direction of the optical wave to be measured. A linear magnetization curve without hysteresis and a linear Faraday effect were expected to be obtained as the magnetization process of rotation occurred in each striped magnetic domain. This assumption was confirmed in an experiment. Experimental results such as sensitivity and SNR were well explained by this model. The obtained sensor sensitivity was 1.08 × 10-3 %/(A/m), and good linearity of sensor output was obtained over a wide dynamic range between 1 A/m to 104 A/m.

Magnetic Field Optical Sensor with a Laser-Diode-Pumped Microchip Solid-State Laser

A new type of magnetic field optical sensor with a diode-pumped solid-state microchip laser was studied. It was found that use of the self-mixing laser intensity modulation method combined with an acousto-optic frequency shift enabled the detection of Faraday signals in an extremely weak feedback field. Through experiments using an Nd:YVO4 microchip laser and a YIG crystal as a Faraday element, modulation signals proportional to the applied magnetic field were obtained in the very weak amplitude feedback region of 10-6.

Self-mixing laser Doppler velocimetry with a dual-polarization Yb:Er glass laser

Self-mixing laser Doppler velocimetry using a dual-polarization Yb:Er-doped phosphate glass laser is investigated. The two orthogonally polarized eigenstates emitted simultaneously by the laser oscillator are employed to perform a heterodyne detection, allowing a complete characterization of the lateral sidebands generated via the optical feedback around the beating peak. Two different experimental set-ups have been implemented: (i) direct feedback on one of the two modes or (ii) crosstalk between the two modes via a non-reciprocal Faraday element. The results are analysed and applications to velocity measurements are discussed. Finally, some considerations of the noise correlated in phase and in opposite phase on the two polarization states are also discussed.

Magnetic field optical sensors using (TbY)IG crystals with stripe magnetic domain structure

In this paper, a new type of magnetic field optical sensor based on Faraday effect created by the magnetization rotation process in each stripe magnetic domain is proposed. For these sensors, (Tb/sub 0.19/Y/sub 0.81/)/sub 3/Fe/sub 5/O/sub 12/ ((TbY)IG) crystals were used as Faraday element. At the wavelength of 1.3 /spl mu/m, the obtained sensitivity is 4.7/spl times/10/sup -3/ %/A/m. The small linearity error of the sensor output is also obtained in a wide dynamic range between 1 A/m and 10/sup 4/ A/m. When the magnetic field is applied perpendicularly to the easy axis, we consider that a linear magnetization curve without hysterisis is obtained by a rotation of domain magnetization. This assumption is confirmed by experiment. The experimental results such as the sensitivity, the linearity error and the signal-to-noise ratio were explained well by the proposed model.

Magnetic field optical sensors using Ce:YIG single crystals as a Faraday element

In this paper, a new type of magnetic field optical sensor based on creation of the Faraday effect by rotation magnetization of Ce:YIG single crystals was studied. A large linear magnetic birefringence (LMB, the Cotton–Mouton effect) of Δ n = −1.7 × 10 −4 was observed in Ce:YIG crystal at the wavelength of 1.3 μm, and it was found that this effect is the main origin of the reduction of the sensitivity and its large temperature dependence. The validity of the method of utilizing a pair of Ce:YIG crystals with an azimuth angle of 90° in the optical axis is demonstrated as a method of improving these phenomena

Unidirectional single-frequency operation of a Nd:YVO4 ring laser with and without a Faraday element.

We demonstrate high-performance unidirectional and single-frequency ring-laser operation based on a diode-side-pumped Nd:YVO4 bounce amplifier, obtained in a ring system both with and without a Faraday rotating element. Ring-laser operation with intracavity Faraday unidirectional element produces 15-W cw output in a TEM00 and single-longitudinal mode with beam propagation parameter M2 < 1.1 with 35-W diode pumping. A novel non-Faraday-based ring laser uses a polarization-dependent output coupler and asymmetric polarization state in the birefringent Nd:YVO4 gain medium and is demonstrated to produce highly unidirectional (1200:1) single-frequency output of 14 W in a TEM00 mode with beam propagation factor M2 < 1.2 at 30 W of diode pumping.

Nonlinear dynamics of lasers with intracavity modulation of ellipticity

In this work we consider polarization dynamics of a class A vector laser subject to new kind of vector modulation which drives the eigenmode ellipticity. Such a modulation can be accomplished by an intracavity device consisting of two crossed quarterwave plates with Faraday element between them. It is found that sinusoidal modulation of the eigenmode ellipticity is directly transferred to the polarization parameters of the emitted field only at small amplitude of modulation. Among interesting features in the laser dynamic behaviour we report on resonant and quasiperiodic behaviours in the vicinity of the polarization relaxation frequency.

A compact polarimetric glucose sensor using a high-performance fibre-optic Faradayrotator

A compact high-efficiency Faraday rotator is constructed which uses a single-mode flint glassfibre as the Faraday element and a small-diameter toroidal electric coil as the magnetic system.Using a fibre Faraday rotator as the polarization modulator and/or the polarization compensator,glucose solution in the 10 mm long fused silica cell is detected with a high resolution of0.01 g dl−1 in the widemeasurement range of 0–25 g dl−1.

Magnetic field rotating-type Faraday polarization controller

We developed a new polarization controller based on the Faraday effect. The transmittance fluctuation was suppressed to less than 0.03 dB by controlling the direction of a magnetic field with a magnitude exceeding the saturation field of Faraday elements. Because it has no mechanical parts, the new polarization controller can perform polarization control with high reproducibility and high-speed polarization control of better than 10/sup 3/ turns/s on a Poincare sphere. The new polarization controller has a rotatory polarization angle setting accuracy of /spl plusmn/5/spl deg/ and a reproducibility of /spl plusmn/0.3/spl deg/ on the Poincare sphere.

Magnetic field sensors using Ce:YIG single crystals as a Faraday element

Magnetic field sensors based on creation of the Faraday effect by rotation magnetization in Ce:YIG crystals are studied. The large linear magnetic birefringence (LMB) of /spl Delta/n=-1.7/spl times/10/sup -4/ was observed in the Ce/sub 0.18/Y/sub 2.82/Fe/sub 5/O/sub 12/ crystal and it was found from both the calculation and experimental investigations that the LMB affects the linearity of the sensor output. The validity of the method of utilizing a pair of Ce:YIG crystals with an azimuthal angle of 90 deg in the optical axis is demonstrated as a method of improving these phenomena.

Magnetic field sensors based on a ring interferometry

In this paper, magnetic field sensors based on ring interferometry are studied to enable the measurement of direct (DC) magnetic field as well as alternating (AC) magnetic field. By experiments using (CdMn)Te crystals as a Faraday element, the relative error within /spl plusmn/1% was obtained for AC magnetic field of up to 15 kA/m. Then, by introducing a phase modulation technique to this interferometry, DC magnetic field measurement with high sensitivity of 0.5/spl times/10/sup -2/%/A/m is realized.

Optical current transducers using flint glass fiber as the faraday sensor element

This paper describes development of the optical current transducers using flint glass fiber as the Faraday effect sensing element. Excellent polarization properties of the fiber with low birefringence are described, and the design and test data of a current transducer using the fiber manufactured for use in electric power facilities are reviewed. Experimental results on flexible characteristics of a scheme with round trip light transmission in the fiber is also reported.

Development of optical ZCT and its application to fault section detection for 66‐kV underground branch transmission lines

AbstractThe optical ZCT (Zero‐phase Current Transformer) which combines an optical magnetic field sensor with a magnetic ring core of silicon steel plates has been developed. Bi‐doped YIG [Yttrium Iron Garnet, (BiYbGd)3Fe5o12] having a large Verdet constant is used as a Faraday element. The optical ZCT detects the conductor current of 0 to 2000 A at high resolution and has been applied to the fault section detection system for 66‐kV underground branch transmission lines which monitors a multiterminal line having Y‐branch joint box in on‐line state. Optical ZCTs and a section detector/indicator are connected with optical fibers which are capable of nonrepeatedly transmitting signals over 6 km, and allow monitoring long‐distance underground power transmission lines. A developed system is now operating on the JR Kasai line (Shinkawa pump line) of Tokyo Electric Power Company.

光ZCTの開発と66kV地中分岐送電線路事故区間判別への応用

The optical ZCT (Zero-phase Current Transformer) which combines an optical magnetic field sensor with a magnetic ring core of silicon steel plates has been developed. Bi-doped YIG [Yttrium Iron Garnet, (BiYbGd)3Fe5o12] having a large Verdet constant is used as a Faraday element. The optical ZCT detects the conductor current of 0 to 2000 A at high resolution and has been applied to the fault section detection system for 66-kV underground branch transmission lines which monitors a multiterminal line having Y-branch joint box in on-line state. Optical ZCTs and a section detector/indicator are connected with optical fibers which are capable of nonrepeatedly transmitting signals over 6 km, and allow monitoring long-distance underground power transmission lines. A developed system is now operating on the JR Kasai line (Shinkawa pump line) of Tokyo Electric Power Company.

Magnetooptic Current Field Sensor with Sensitivity Independent of Verdet Constant and Light Intensity

A new type of ac current sensor utilizing the Faraday effect is proposed. A stabilized dc bias magnetic field H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sup> is applied to a Faraday element placed between a crossed Nicols pair of polarizers. The amplitudes of the fundamental signal I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ω</sub> and second harmonic signal I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2ω</sub> induced by the ac field H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sup> in the intensity of light emerging from the analyzer are phase-detected. The ratio R=I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2ω</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ω</sub> gives the output signal. When the Faraday rotation angles a (∝H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sup> ) and θ (∝H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sup> are so small that such higher terms as a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and θ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be neglected, we obtain R=H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sup> /4H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sup> , which is independent not only of the light intensity, but of the Verdet constant of the Faraday element as well. Experiments performed at 20 to 100°C on FR-5 glass and Bi-substituted YIG Faraday elements corroborated this prediction. The effect due to the nonlinear terms a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and θ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is calculated, and found to agree with our experimental results.

New optical magnetic field sensor with optional white light source (abstract)

A new type of magnetic field sensor which measures ac electric current utilizing Faraday rotation is proposed. On a Faraday element a stabilized dc bias magnetic field Hb is applied. Output signal is given by the ratio R = I2ω/Iω, where Iω and I2ω are fundamental and second harmonic signals generated by the field Hx which the ac current induces. Since R is calculated as R = Hx/4Hb, we can measure Hx independent not only of light intensity but also of the Verdet constant (and therefore its temperature dependence) of the Faraday element. This was supported by experiments performed at 20–100 °C for HeNe laser (λ=0.633 and 1.15 μm) light on Faraday elements of FR-5 paramagnetic glass and Bi-substituted YIG crystal. The bias field Hb was generated by a stabilized dc current in a coil and using a SmGdCo plastic magnet with very weak temperature dependence of remanent magnetization (&amp;lt;1% at T=20–120 °C). According to theory the equation holds even when broad spectrum polychromatic light is used. This was confirmed by experiments performed with a halogen-lamp white light transmitted through an optical fiber. Calculated signal-to-noise ratio of the sensor with a polychromatic light agreed with experiments.

Visibility limits in fibre-optic michelson interferometer with birefringence compensation

The operation of a polarisation-insensitive fibre optic Michelson interferometer is further analysed. In particular, details are reported of an investigation of the limits in interference fringe visibility of the system due to offsets in the rotation angle of the Faraday elements used to effect the birefringence compensation.