Faraday Rotator Research Articles

Single-longitudinal-mode operation of a 2.09 μm holmium laser with anti-misalignment corner cube ring cavity

A single-longitudinal-mode (SLM) 2.09 μm Ho:YAG laser with anti-misalignment corner cube ring cavity was demonstrated. Unidirectional components composed of a faraday rotator and half-wave plate were used to organize the travelling wave beam propagation and to eliminate the spatial hole-burning effect. The maximum SLM power was 728 mW. The corresponding slope efficiency achieved 23.42% and the optical conversion efficiency was 7.16%. Widely tunable wavelength outputs from 2090.43 nm to 2098.37 nm have been achieved by employing a Fabry–Perot etalon. With the advantage of long cavity length and small volume, this structure of the Ho:YAG SLM laser with corner cube ring cavity is a potentially useful way to ensure narrow linewidth output and strong anti-misalignment stability.

Model of the spectral dependence of changes in the polarization state of laser radiation in magneto-optical crystal in the presence of multiple reflections from its faces

In this work we investigated the phenomena in the Faraday rotator that can affect the polarization state of transmitting laser radiation. We have found that multiple reflections of radiation from the faces of the terbium gallium garnet (TGG) crystal can cause deterioration of radiation extinction ratio and, therefore, isolation properties of Faraday cell. We were able to calculate the impact of this factor on polarization extinction ratio of monochromatic and quasimonochromatic laser radiation transmitting through the crystal.

Development of Large Diameter Faraday Rotator Using TGG Ceramic for High-Average-Power Laser System

Development of Large Diameter Faraday Rotator Using TGG Ceramic for High-Average-Power Laser System

Fabrication and Magneto-Optical Property of (Dy0.7Y0.25La0.05)2O3 Transparent Ceramics by PLSH Technology

(Dy0.7Y0.25La0.05)2O3 magneto-optical transparent ceramics were successfully fabricated by pressureless sintering in reductive H2 atmosphere (PLSH). The raw powder of (Dy0.7Y0.25La0.05)2O3 was synthesized by a modified self-propagating high-temperature synthesis (SHS) and sintered to transparent ceramics at 1400–1600 °C in a flowing H2 atmosphere, showing good sinterability of the as-synthesized raw powder. The magneto-optical Verdet constant of (Dy0.7Y0.25La0.05)2O3 transparent ceramics was measured to be −191.57 rad/(T·m) at a wavelength of 632.8 nm. In this magneto-optical material of (Dy0.7Y0.25La0.05)2O3, relative cheaper Dy and Y were used to replace Tb, and the low cost and good magneto-optical property showed the advantage of application on Faraday isolators (FIs) and Faraday rotators (FRs).

Phase-only modulation of light.

We disclose the method to obtain polarization insensitive phase-only modulation that preserves both the state and the degree of polarization of light modulated using a medium with controlled birefringence. We find that, in the double-pass configuration involving reflection from the Faraday rotator mirror, such a medium acts as the phase-only modulator. The experimental data measured in the Michelson-interferometer-based setup for deformed-helix ferroelectric liquid crystal cells are found to be in good agreement with the theoretical results. For such cells, we experimentally demonstrate high-frequency (4 kHz modulation rate) 2π phase-only light modulation governed by the average phase shift and solve the problem of optical axes switching.

Squeezed-Light Interferometry on a Cryogenically Cooled Micromechanical Membrane.

Squeezed states of light reduce the signal-normalized photon counting noise of measurements without increasing the light power and enable fundamental research on quantum entanglement in hybrid systems of light and matter. Squeezed states of light have high potential to complement cryogenically cooled sensors, whose thermal noise is suppressed below the quantum noise of light by operation at low temperature. They allow us to reduce the optical heat load on cooled devices by lowering the light power without losing measurement precision. Here, we demonstrate the squeezed-light position sensing of a cryo-cooled micromechanical membrane. The sensing precision is improved by up to 4.8dB below photon counting noise, limited by optical loss, at a membrane temperature of about 20K. We prove that realizing a high interference contrast in a cryogenic Michelson interferometer is feasible. Our setup is the first conceptual demonstration towards the envisioned European gravitational-wave detector, the "Einstein telescope," which is planned to use squeezed states of light together with cryo-cooled mirror test masses.

Arbitrary polarization control by magnetic field variation.

We propose a universal scheme for the construction of a device for arbitrary-to-arbitrary polarization transformation, which consists of two quarter-wave plates and two Faraday rotators. Using this device, one can continuously change the retardance and the rotation angle simply by changing the magnetic fields in each Faraday rotator.

Determination of single crystal elastic moduli of KTb3F10 by resonant ultrasound spectroscopy

KTb3F10 (KTF) has been developed in recent years as a candidate Faraday rotator material because of its cubic symmetry, high figures of merit, and low absorption coefficient. While considerable efforts have focused on crystal growth and optical properties, investigations of fundamental thermodynamic behavior of KTF have been limited. Here, we report elastic moduli C11, C12, and C44 of single crystalline KTF measured by resonant ultrasound spectroscopy from 280 K up to 300 K and the obtained temperature derivatives of each modulus. We additionally report the single crystal elastic moduli of the rare-earth garnet Y3Al5O12 (YAG), yielding results that agree well with the prior literature. We found C11=135.62 GPa, C12=58.11 GPa, and C44=44.81 GPa for KTF and C11=332.43 GPa, C12=109.58 GPa, and C44=114.81 GPa for YAG at room temperature. The present results have been compared with previous experimental and theoretical results and with common oxide and fluoride optical materials, revealing the relative softness of KTF. The low elastic moduli of KTF are, in turn, responsible for its low thermal conductivity and low Debye frequency compared to other laser host materials.

A proposal for a multi-functional tunable dual-band plasmonic absorber consisting of a periodic array of elliptical grooves

In this paper, a tunable plasmonic absorber composed of an elliptically grooved metallic film sandwiched between two dielectric layers is presented. To understand the optical response of the structure, its absorption spectrum and resonance modes profiles are numerically calculated using computer simulation technology microwave studio. It is shown that the proposed device can provide two absorption peaks, in the near-infrared region, with absorption coefficients dependent upon the polarization angle of the incident light. Therefore, using a Faraday rotator and applying a variable external magnetic field, the device can be converted into a tunable magneto-optic modulator. From a different point of view, the proposed device is applicable as a sensor to measure mechanical rotations from 0 to 90 degrees. Besides, it is discussed that by adding a graphene layer to the structure, a tunable dual band modulator is realized, by which two absorption bands can be adjusted independently. Simulation results show that modulations of absorption per graphene Fermi energy, about 73.33% eV−1 and 69.54% eV−1 are achieved for the first and the second peaks, respectively. Taking advantage of the above mentioned effects, the proposed device can be used in several applications including magneto-optic modulation, rotation detection, electro-optic modulation and spectral selective tunable absorption.

Excess Relative-Intensity-Noise Reduction in a Fiber Optic Gyroscope Using a Faraday Rotator Mirror

The fiber optic gyroscope (FOG) suffers from the excess relative intensity noise (RIN) caused by the broadband light source, which significantly impacts the angular random walk (ARW) of the FOG. The existing suppression methods for the excess RIN usually require complex configuration or devices with big volume, and thus are not suitable for practical applications especially in small-sized FOGs. What is more, as the key parameters or components, that determine the practical suppression effects of the excess RIN, and the corresponding impacting mechanisms are not clarified, there is no efficient way in evaluating or optimizing the excess-RIN reduction configuration in practice. In this work, we propose a simple but effective method to achieve the reduction of the excess RIN at the demodulation frequency, in which a Faraday rotator mirror is inserted to the dead arm of the source coupler to realize the delay line filter for the excess RIN. Experimental results show that the ARW is improved from 1.70 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> to 0.58 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> for a navigation-grade FOG. More importantly, this work provides a comprehensive understanding on how the main defects in the excess-RIN reduction scheme impact the practical excess-RIN suppression effects both theoretically and experimentally, which demonstrates the inherent robustness of the proposed scheme against internal and external influencing factors. This method is especially suitable for realizing the excess-RIN reduction in small-sized FOGs and upgrading the existing FOG products with minimal modifications, and is also potentially referable in evaluating and optimizing other similar excess-RIN reduction schemes.

Reduction of thermal-stress-induced birefringence in a Faraday rotator based on a crystal with a negative optical anisotropy parameter

Thermally induced polarization distortions in a Faraday rotator based on a crystal with a negative value of the optical anisotropy parameter was investigated in experiments. A terbium-containing cubic zirconia crystal was taken as a magneto-active medium. A crystal was cut in the orientation in which the axes of thermal-stress-induced birefringence are oriented in one direction. It was demonstrated that the distortions in such a Faraday rotator were reduced by an order of magnitude compared to the minimum possible depolarization arising with the use of a magneto-optical element with the standard [001] orientation, but were still higher than the calculated values. It was shown that for successful development of Faraday isolators based on crystals with a negative optical anisotropy parameter, the theoretical model describing thermal-stress-induced birefringence needs improvement.

Application of a novel spatial non-reciprocal phase modulator in fiber optic gyroscope

Abstract Based on the primary electro-optic effect of lithium niobate crystal and combined with a polarizer and a Faraday rotator, a novel spatial non-reciprocal phase modulator design scheme suitable for Sagnac loop structure is proposed. On the one hand, this structure fundamentally eliminates the influence of eigenfrequency on the modulation mode of the system, and improves the sensitivity and accuracy of the system. On the other hand, experiments show that this phase modulator has good modulation characteristics and temperature stability. Applying this phase modulator to a fiber optic gyroscope (FOG), the experimental results are in good agreement with the theoretical analysis, which proves the correctness and feasibility of the structure. It provides new options for the use of phase modulators for test instrument such as fiber-optic gyroscopes and current transformers, and provides a way of thinking to promote the development of fiber-optic gyroscopes to high precision.

High thermal-stability Er-doped superfluorescent fiber source with a vertical cleaved fiber tail

Abstract Mean wavelength stability, a key indicator for evaluating the dynamic performance of Er-doped superfluorescent fiber source (ED-SFS) and high-precision fiber optic gyroscope (FOG), shows high sensitivity to environmental temperature fluctuations. In this paper, a thermally-stable ED-SFS in a one-stage backward configuration is proposed by incorporating a vertical cleaved fiber tail which acts as a Fresnel reflector. Our proposed method demonstrates a mean wavelength stability of 150 ppm and a scale factor error of 702 ppm. Comparing with alternative techniques such as Faraday rotator mirror (FRM) or fiber mirror (FM) over a 100 °C range (−40 °C to +60 °C), the wavelength stability and scale factor error are 105~120 ppm and 230~400 ppm less, respectively. The proposed ED-SFS has a spectral width (FWHM) of 37.682 nm and 10.42 mW output power, which satisfies the requirements of high-precision FOG.

편광유지 광자결정 광섬유 기반 투과형 격자 및 Faraday 회전 반사체를 이용한 스트레인과 온도의 분리 측정

In this paper, we performed separate measurement of strain and temperature using a fiber transmission grating (FTG) inscribed on polarization-maintaining photonic crystal fiber (PMPCF) by a CO₂ laser and a Faraday rotator reflector (FRR). The FTG fabricated on PMPCF (referred to as a PMPC-FTG), connected in series with the FRR, has two resonance dips with different cladding-mode orders in its reflection spectrum. The wavelengths λ₁ and λ₂ of the two resonance dips (referred to as D₁ and D₂) were 1471 and 1495 nm, respectively, and D₁ and D₂ were utilized as sensor indicators for the separate measurement of strain and temperature. Strain and temperature responses were independently investigated for the two sensor indicators in a strain range of 0∼2548 με and a temperature range of 30∼90℃, respectively. Both D₁ and D₂ showed linear and uncorrelated responses to strain and temperature. Based on the previously obtained strain and temperature sensitivities, any strain and temperature changes applied to the PMPC-FTG can be estimated by measuring the wavelength shifts of D₁ and D₂.

Novel Fiber Optic Current Transformer With New Phase Modulation Method

Based on the transverse electro-optic effect of lithium niobate crystal, combined with polarizers and Faraday rotator, this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method, and the feasibility of the scheme is verified by both the theoretical and experimental evidences. The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency, improves the sensitivity and stability of the system, and reduces the volume and cost of fiber optic current transformer. The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect, which enhances the signal to noise ratio and simplifies demodulation mode. The experimental results show that the current ratio errors measured at room temperature range from 1% to 120% of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S. The temperature stability of the current transformer is also tested, and the ratio error measured at the rated current does not exceed ±0.2% in the range of -30 °C to 50 °C.

XANES/EXAFS study of the Lu and Y incorporation in the single crystal Tb3Sc2Al3O12 Faraday rotator

Tb3Sc2Al3O12 (TSAG) is a paramagnetic insulator which, in spite of its congruent nature and excellent magneto-optical properties as Faraday rotators for optical isolators (OIs), cannot be industrially produced. The reason is that its lattice structure is so stressed that single crystals easily crack upon cooling after growth or during the cutting process. By the incorporation of a small amount of Lu, it has been demonstrated that the stress in the structure can be effectively released, and, therefore, the crystal cracking can be avoided. This has enabled the substitution of standard Tb3Ga5O12 (TGG), achieving better high-power performance and compacter OIs. In this study, the charge state and the lattice site location of Lu as well as Y dopants in TSAG are investigated by X-ray Absorption Near Edge Structure and Extended X-ray Absorption Fine Structure Analysis. Measurements on single crystal and powdered samples indicate that both dopants are incorporated in the 3+ charge state and substitute predominantly in the dodecahedral Tb-site (&amp;gt;87.5%), while a minor fraction is found in the octahedral Sc-site.

Trace Hydrogen Sulphide Gas Sensor Based on Cu/rGO Membrane-Coated Photonic Crystal Fibre Michelson Interferometer

Abstract A novel Michelson interferometric hydrogen sulphide sensor coated with copper/reduced graphene oxide (Cu/rGO) composite membrane is proposed and fabricated. A section of endlessly photonic crystal fibre (EPCF) was sandwiched in two single-mode fibres (SMFs). One SMF was spliced and tapered with EPCF; the other SMF was connected with the Faraday rotator mirror to construct the Michelson structure. The cladding of the EPCF was coated by the Cu/rGO-sensing membrane, which was prepared by the dip-coating method. The obtained Cu/rGO-sensing film has a length of 25.0 mm. The fabricated sensing membrane is characterised by the scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and so on. Experimental results demonstrated that the Cu/rGO-sensing film has a 24.56-nm thickness with a compact and uniform appearance. The XPS and Raman spectra indicate that there are three elements (C, O, and Cu), which are consistent with the expected compositions of the Cu/rGO membrane. With the increase of concentration of hydrogen sulphide, the interference spectra appear red-shifted. The linearity of 0.97662 and the sensitivity of 13.23 pm/ppm are achieved. In addition, the dynamic response and recovery time of the sensor are approximately 70 and 88 s, respectively. The surface adsorption energies of the film are calculated by the density functional theory. The theoretical results are in good agreement with the experimental findings. This sensor has some key advantages of small size, simple structure, easy fabrication, and great applicability for detecting the trace hydrogen sulphide.

Synthesis and characterization of a titanium phosphate‐tellurite glass for Faraday rotators

AbstractThis work is focused on investigation of thermal, structural, optical, magnetic, and magneto‐optical properties of novel titanium phosphate‐tellurite glass applied as Faraday rotators. The glass belonging to the system 35Li2O–10Al2O3–5TiO2–45P2O5–5TeO2 was prepared by a nonconventional wet route of raw materials processing, followed by melting‐quenching‐annealing steps. Some important physical properties of the investigated glass have been measured and calculated, providing knowledge related to glass compactness, electronic structure, glass forming capability, etc. XRD analysis evidenced an amorphous network structure of the investigated glass. The optical absorption in the Vis domain is mainly due to Ti3+ ions and Te2 clusters formed during the glass melting process. A relatively low optical absorption is noticed over 600 nm that activates a significant Faraday magneto‐optical effect. Photoluminescence bands in the blue, red, and infrared domains are observed, caused by Te2 clusters formed during the glass melting process. The magnetization in dependency on applied magnetic field reveals a complex behavior of the glass, depending on temperature. Thus, it is found a ferromagnetic behavior up to 2000 Oe, a paramagnetic component up to 40 000 Oe, followed by a diamagnetic one over 40 000 Oe. Faraday rotation angle and Verdet constant values in the visible domain are correlated with the reduced TeO2 content of the glass.

편광상이 고리 기반 광섬유 다파장 필터의 입력 편광으로 제어되는 채널 간격 스위칭에 대한 연구

In this paper, we propose an optical fiber multiwavelength filter based on a polarization-diversified loop (PDL), whose channel spacings (CSs) can be controlled by its input state of polarization (SOP). The PDL-based filter consists of a polarization beam splitter, three half-wave plates (HWPs), a Faraday rotator (FR), and two polarization-maintaining fiber (PMF) segments with equal birefringence and different lengths. At proper orientation angle sets (θ<SUB>h1</SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>) of the three HWPs, the proposed filter can have its polarization-dependent transmittance, offering the CS-switchable operation realized by switching between two orthogonal input SOPs of linear horizontal polarization (LHP) and linear vertical polarization (LVP). In particular, at a fixed input SOP, a half-period wavelength switching operation, i.e., an interleaving operation, can also be implemented by controlling only one HWP angle (θ<SUB>h1</SUB> or θ<SUB>h3</SUB>). Theoretical prediction was verified by experiments. For orthogonal input SOPs of LHP and LVP, the fabricated PDL-based filter could provide transmission spectra with CSs of ∼0.9 and ∼0.3nm or vice versa at appropriate sets of (θ<SUB>h1</SUB><SUB></SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>), respectively, and each of the transmission spectra could be interleaved by adjusting only θ<SUB>h1</SUB> or θ<SUB>h3</SUB>.

Solution-Processed Faraday Rotators Using Single Crystal Lead Halide Perovskites.

Lead halide perovskites (LHPs) have become a promising alternative for a wide range of optoelectronic devices, thanks to their solution‐processability and impressive optical and electrical properties. More recently, LHPs have been investigated in magneto‐optic studies and have exhibited spin‐polarized emission, photoinduced magnetization, and long spin lifetimes. Here, the viability of methylammonium lead bromide (MAPbBr3) single crystals as solution‐processed Faraday rotators is demonstrated. Compared to terbium gallium garnet, the industry standard in the visible, it is found that MAPbBr3 exhibits Verdet constants (i.e., strength of Faraday effect) of similar or greater magnitude (up to 2.5x higher), with lower temperature dependence. Due to its low trap absorption, it is calculated that an optical isolator made from MAPbBr3, with appropriate antireflection coatings, should reach ≈95% transmission and achieve 40 dB isolation for incoming powers of over 2 W. It is also shown that the Verdet constant of MAPbBr3 can be calculated accurately from its dispersion in refractive index, allowing the possibility to predict similar effects in other perovskite materials.