TE-TM Mode Conversion Research Articles

Gyrotropy and magnetic fluid dependences of magneto-optical properties in YIG-magnetic photonic crystal fiber

In this work, a kind of magnetic photonic crystal fiber (MPCF) design based on yttrium iron garnet (YIG) structure filled with magnetic fluid (MF) is presented. In order to improve the magneto-optical (MO) properties of isolator devices, a numerical study has been developed to investigate the non-reciprocal TE-TM mode conversion. This technique consists in producing, under the influence of a magnetic field parallel to the direction of propagation, a coupling between the modes. The influence of gyrotropy and MF infiltration at different magnetic nanoparticle volume fraction concentrations is investigated. The results revealed that the mode conversion efficiency (Rm) increases with the increase of the MF concentration, while modal birefringence (∆n) is inversely proportional to its increase. Thus, the higher concentration provides the best results. For MF concentration and gyrotropy equal respectively to 1.75% and 0.0125, Rm is improved to over 93%, and ∆n is reduced to close to 10–6. Whereas, Rm decreases to 89.59 and ∆n increases to 6 × 10–6 for MF concentration equal to 0.25%. From these results, it can be seen that this MPCF filled with MF concentration equal to 1.75% is well suited to the design of MO isolators.

Design of non-reciprocal device based on magnetic photonic crystal fiber with enhanced birefringence

In this paper, a non-reciprocal device based on magnetic photonic crystal fiber of Yttrium iron garnet (YIG) is proposed. The unique magneto-optical (MO) properties of YIG are used to produce under the influence of a magnetic field parallel to the direction of propagation, a TE-TM mode conversion. The influence of gyrotropy on this latter, which depends on Faraday rotation, is analyzed. The structure parameters are simulated and the optimum efficiency of 93.57% is obtained. Faraday rotation and modal birefringence have been calculated by varying gyrotropy from 0.01 to 0.04. Compared to similar devices, the numerical results reveal an improvement of the MO properties, with an enhanced modal birefringence, which make it suitable for the design of MO isolators.

Acousto-optic frequency shift modulators with acoustic and optic waveguides on X-cut lithium niobate substrates

An optimal configuration of the waveguide acousto-optic frequency shift modulators on the X-cut lithium niobate substrates was analyzed. The conditions for efficient excitation of surface acoustic waves (SAW) and their interaction with the guided light in integrated optical structures were found. The influence of acoustic waveguide presence and interdigital transducer (IDT) geometry and material on the SAW resonance excitation was investigated. An acoustic waveguide configuration was proposed for increasing the TE-TM optical mode conversion efficiency. A low power (about 15 dBm) high frequency modulation signal was required for full TE-TM mode conversion in the proposed modulator configuration.

Simulation of magneto-optical properties of magnetic photonic crystal waveguides

We propose a kind of magnetic photonic crystal (MPC) slab waveguide made from magneto-optical material, namely bismuth iron garnet. The finite difference beam propagation method is employed for numerical calculations, which is the most widely used propagation technique for modeling integrated and photonic devices. The mode conversion and the influence of corresponding parameters are studied theoretically. As a numerical example, a TE-TM mode conversion waveguide-type optical isolator based on this designed MPC is described. An effective away to enhance the Faraday rotation at the 1.55-μm telecommunication wavelength is shown.

Efficient magneto-optical TE/TM mode converter in a hybrid structure made with a SiO2/ZrO2 layer coated on an ion-exchanged glass waveguide

The TE-TM mode conversion is an important requirement for magneto-optical waveguide devices. In this work, we report on the theoretical study of magneto-optical waveguides on an ion-exchanged glass waveguide. This study explores the possibility to realize a mode converter TE-TM on a hybrid structure. This hybrid device is made by coating a SiO2/ZrO2 layer doped with magnetic nanoparticles on an ion-exchanged glass waveguide. It has been analyzed by means of a beam propagation method for numerical solution of the full-vectorial wave equation. We have also used the transparent boundary condition. The mode converters TE-TM based on the Faraday rotation and modal birefringence are then numerically simulated. Depending on the increasing of nanoparticles volume fraction in the SiO2/ZrO2 layer and on decreasing the modal birefringence of the hybrid structure, the TE-TM conversion efficiency varies from several percent to several tens of percent.

Magneto-optical properties of magnetic photonic crystal fiber of terbium gallium garnet filled with magnetic fluid

We present in this work, magneto-optical (MO) properties of a magnetophotonic crystal fiber (MPCF) based on terbium gallium garnet Tb3Ga5O12 or TGG. The air holes of a periodic triangular lattice are filled with magnetic fluid (MF). With a light which can be confined in the core area of this MF filled MPCF we obtain a confinement corresponding to the propagation of the single mode by assuming an effective index (neff). The variations of neff as a function of the gyrotropy parameter (g) and magnetic nanoparticle volume fraction concentrations are well established at the telecommunication wavelength λ=1.55μm. The TE-TM mode conversion based on the Faraday rotation and modal birefringence are then numerically simulated. Faraday rotation exhibits largest value of 8700.08°/cm at MF concentration of 0.25% and g=0.0144, whereas the modal birefringence is reduced to 0.00177 at the same conditions. These results could be helpful for experimentally designing and realizing isolators with these filled MF-MPCFs based on this TGG material. They appear to possess significant potential for the practical applications due to their unique MO properties.

Mode conversion in magneto photonic crystal fibre

The first concept of an integrated isolator was based on nonreciprocal TE–TM mode conversion, the nonreciprocal coupling between these modes is caused by the Faraday rotation if the magnetization is aligned along the z–axis, parallel to mode propagation.We propose to study this magneto-optical phenomenon, by the simulation of magneto photonic crystal fibre (MPCF), it consists of a periodic triangular lattice of air-holes filled with magnetic fluid which consists of magnetic nanoparticles into a BIG (Bismuth Iron Garnet) fibre. We simulated the influence of gyrotropy and the wavelength, and calculated Faraday rotation and modal birefringence. In this fibre the light is guided by internal total reflection, like classical fibres. However it was shown that they could function on a mode conversion much stronger than conventional fibres.

Mode conversion in magneto-optic rib waveguide made by silica matrix doped with magnetic nanoparticles

The TE-TM mode conversion is an important requirement for magneto-optical waveguide devices. It has been analyzed by means of a full-vectorial beam propagation method. The present work is based on the study of the influence of diagonal and off-diagonal elements of the complex dielectric tensor on the conversion efficiency in magneto-optical rib waveguide. We have found that in the presence of the absorption (taking into account the imaginary part of diagonal tensor) the conversion efficiency is affected by the absorption and these latter increases as the volume fraction of nanoparticles increases.

Nonreciprocal TE–TM Mode Conversion Based on Photonic Crystal Fiber of Air Holes Filled With Magnetic Fluid Into a Terbium Gallium Garnet Fiber

The nonreciprocal optical effect of Faraday rotation (FR) is widely exploited in optical isolators to suppress back-reflections to protect optical sources and other devices from injection noise, or in optical circulators to route counter-propagating signals in a single physical channel to different ports [1]. The first concept of an integrated isolator was based on nonreciprocal TE-TM mode conversion. However, most proposals of the waveguide type isolators are based on nonreciprocal TE-TM mode conversion [2], the nonreciprocal coupling between these modes is caused by the FR if the magnetization is aligned along the z-axis, parallel to mode propagation. FR effect can be used for magnet sensors, because the Verdet constant of silica fibre is small (∼1.1 rad/(T.m) at 1064 nm) [3]. In this work, we propose to study the nonreciprocal TE-TM mode conversion phenomenon, by the simulation of magneto photonic crystal fibre (MPCF). It consists of a periodic triangular lattice of air-holes filled with magnetic fluids (Fe 3 O 4 ) into a Terbium Gallium Garnet (TGG) fibre which is a kind of synthetic garnet with chemical composition Tb 3 Ga 5 O 12 . This garnet was chosen as a Faraday rotator material which has excellent transparency properties and is very resistant to laser damage. TGG has also a high Verdet constant which results in the FR effect. We simulated the influence of gyrotropy and the wavelength, and calculated the FR and modal birefringence. In this MPCF fibre, the light is guided by internal total reflection, like classical fibres. However, it was shown that they could function on a mode conversion much stronger than conventional fibres.

Design of polarization rotators in TE–TM mode conversion optical isolator with Ce:YIG guiding layer

An optical isolator with a (CeY)3Fe5O12 guiding layer employing TE–TM mode conversion was investigated. The optical isolator consisted of a nonreciprocal polarization rotator and a reciprocal polarization rotator. The reciprocal polarization rotator was realized by inserting a polyimide half-wave plate into a groove in the magnetooptic waveguide. Propagation distances required for the nonreciprocal polarization rotator were calculated at a wavelength of 1.55 µm. Diffraction loss due to the insertion of the half-wave plate was also calculated. The reciprocal polarization rotator integrated with a spot-size converter was proposed for suppressing the diffraction loss. By introducing the spot-size converter for an input facet and an output facet of the half-wave plate, a calculated total insertion loss was reduced to 0.22 dB.

A novel mode converter based on a 2D dielectrically chiral photonic structure

Abstract We designed a novel two-dimensional periodic chiral waveguide structure, which can achieve complete TE-TM mode conversion. We study the effect of the relevant parameters of structure on the conversion efficiency and confirm that in a certain range, the mode conversion has a rather high efficiency.

Mode conversion in a magnetic photonic crystal waveguide

In this work, we have reported a theoretical study of a magnetic photonic crystal waveguide (also called a magneto photonic crystal waveguide). This structure is formed by a triangular lattice of air holes in a bismuth iron garnet (BIG) film, grown on gallium gadolinium garnet substrates. Nonreciprocal TE–TM mode conversion is caused by the Faraday rotation if the magnetization is aligned along the z-axis, parallel to mode of propagation. The properties of this phenomenon are simulated using the beam propagation method. The conversion output has been simulated, and the Faraday rotation and modal birefringence have been calculated by varying the gyrotropy and the thickness of the BIG film. This magnetic photonic crystal waveguide has the advantage of enhancing Faraday rotation in optical isolators.

Single Trench SiON Waveguide TE-TM Mode Converter

A TE-TM mode converter fabricated in a single trench SiON waveguide is described. The device has the advantage that only single masking and etching process is needed to fabricate it. We discuss the design of the mode converter from the view point of fabrication tolerance. The single trench structure is fabricated using the reactive ion-etch lag phenomenon. A 97% TE-TM mode conversion (extinction ratio=15 dB) is demonstrated at a wavelength of 1.27μm . An excess loss is measured to be 0.8 dB.

Operation principle of optical waveguide isolator based on TE-TM mode conversion

According to the perturbation theory, the theory of self-phase compensation is developed for the optical waveguide isolator based on the TE-TM mode conversion. The operation principle of such a device is explained in terms of synchronization of phase and power conversion. The effect of balancing phase mismatches of the two convertors on achieving a proper percentage of mode conversion is revealed. The simulation results confirm the self-phase compensation theory.

Hybrid magneto-optical mode converter made with a magnetic nanoparticles-doped SiO2/ZrO2 layer coated on an ion-exchanged glass waveguide

This paper describes the possibility to achieve a TE-TM mode conversion in a magneto-optical hybrid waveguide operating at λ = 1550 nm. This hybrid device is made by coating a SiO2/ZrO2 layer doped with magnetic nanoparticles on an ion-exchanged glass waveguide. Soft annealing (90 °C) and UV treatment, both compatible with the ion exchange process, have been implemented to finalize the magneto-optical film. Optical characterizations that have been carried out demonstrated the efficiency of these hybrid structures in terms of lateral confinement and mode conversion. Indeed, TE to TM mode conversion has been observed when a longitudinal magnetic field is applied to the device. The amount of this conversion is discussed taking into account the distribution of light between the layer and the guide, and the modal birefringence of the structure.

Waveguide Isolator With Phase Mismatch

A novel optical waveguide isolator constructed from mode convertors with unsuppressed phase mismatch is proposed. The troublesome requirement of phase matching for transverse electric (TE)-transverse magnetic (TM) mode conversion is eliminated without degradation on the performances. It is found that a kind of self-phase compensation phenomenon occurs during TE-TM mode conversion that facilitates the operation of the isolator. An isolator based on this mechanism is designed and simulated. An isolation of -24.4 dB is obtained.

Elimination of phase-matching requirement for optical waveguide isolator

A novel optical waveguide isolator based on self-phase compensated TE–TM mode conversion was proposed. In this work, the troublesome phase-match condition for the TE–TM mode conversion is eliminated without degradation on the performances. An isolator based on this mechanism is designed and simulated. An insertion loss of −0.1 dB and an isolation of −25 dB was obtained. The tolerance of fabrication and bandwidth of the isolator was also discussed.

Single-trench waveguide TE-TM mode converter

A TE-TM mode converter is proposed in a single trench GaInAsP/InP waveguide, which is fabricated by a single masking and etching process. Use of single-trench structure makes the design and the fabrication much simpler. The design of single-trench mode converter is described together with its fabrication in this article. We investigated the dependence of conversion efficiency on the waveguide width, trench depth, and trench position. Also, the wavelength dependence of mode conversion efficiency was calculated in a wavelength range between 1.5 microm to 1.58 microm. 95% TE-TM mode conversion was measured at a wavelength of 1.55 microm in a fabricated device with a 210-microm half-beat length.

Low birefringent magneto-optical waveguides fabricated via organic-inorganic sol-gel process

This paper is devoted to the study and the characterization of novel magneto-optical waveguides prepared via organic-inorganic sol-gel process. Thin silica/zirconia films doped with magnetic nanoparticles were coated on glass substrate using dip-coating technique. After annealing, samples were UV-treated. Two different techniques were used to measure their properties: m-lines spectroscopy and free space ellipsometry. Results evidence low refractive index waveguides that combine a low modal birefringence (2×10−4) with a Faraday rotation around 15 °/cm (ϕ = 0.1%). The low birefringence is obtained with a soft UV treatment and a graded intrinsic anisotropy is evidenced for films thicker than 5 μm. Therefore, we prove that the organic-inorganic sol-gel approach is very promising to realize magneto-optical waveguides with a non-reciprocal functionality such as TE-TM mode conversion.

A novel phase self-compensation isolator based on TE-TM mode conversion

The intrinsic factors of magneto-optical waveguide isolator based on 45° nonreciprocal mode conversion and 45° reciprocal mode conversion are introduced. A novel phase self-compensation isolator is designed and simulated by the full-vectorial FD-BPM. The insertion loss of this isolator is -12dB and the isolation is-34dB.