Broadband Circulator Research Articles

Analysis and modeling of magnetic-free broadband circulator based on three switched reflection delay lines

Magnetic-free broadband circulator structure based on three switched reflection type delay lines with a total electrical length of 180-degree at the switching frequency is investigated. The nonreciprocal transmission property is modeled and simulated, the impedance mismatching property and reconfigurable direction are studied. A prototype magnetic-free circulator circuit is designed and fabricated using coaxial cables and switches driving by switching frequency of 7.94 MHz with tolerance of ±10%. The nonreciprocal scatter parameters are measured in 300kHz ∼ 100 MHz. It shows that the circulator direction can be reconfigured by changing the switching frequency, and the maximum operating bandwidth equals 1.5f s which is limited by clock feedthrough and spectrum aliasing.

Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding

Optical isolators and circulators are fundamental building block in photonic integrated circuits to block undesired reflections and routing light according to a prescribed direction. In silicon photonics, heterogeneous integration of magneto-optic garnet bonded on a pre-patterned silicon layer has been demonstrated to be an effective solution for manufacturing optical isolators and circulators for TM polarized light. However, most integrated semiconductor lasers emit TE polarized light, which indicates the need to find a reliable solution for this polarization. In this paper, we demonstrated broadband optical isolators and circulators for TE polarized light based on heterogeneous bonding on the silicon photonics platform. To achieve this goal, an integrated adiabatic coupler and a broadband polarization rotator are designed and optimized. The nonreciprocal behavior is induced through an energy-efficient integrated electromagnet with a minimum power consumption of 3 mW. Two isolators/circulators are fabricated with small and large free spectral range, respectively. In the former case, an optical isolation ratio as large as 30 dB is measured at 1555 nm with an insertion loss of 18 dB, while for the broadband circulator, an optical isolation larger than 15 dB is guaranteed over more than 14 nm (1.75 THz) for all port combinations with an insertion loss between 14 and 18 dB at 1560 nm. Finally, it has been theoretically shown that the insertion loss can be reduced below 6 dB with design and fabrication improvements. To the best of the authors’ knowledge, the proposed integrated TE optical circulator is the first experimental demonstration of this device in silicon photonics.

Circulation of spoof surface plasmon polaritons: Implementation and verification

In this letter, we are dedicated to implementation and experimental verification of broadband circulator for spoof surface plasmon polaritons (SSPPs). For the ease of fabrication, a circulator operating in X band was firstly designed. The comb-like transmission lines (CL-TLs), a typical SSPP structure, are adopted as the three branches of the Y-junction. To enable broadband coupling of SSPP, a transition section is added on each end of the CL-TLs. Through such a design, the circulator can operate under the sub-wavelength SSPP mode in a broad band. The simulation results show that the insertion loss is less than 0.5dB while the isolation and return loss are higher than 20dB in 9.4-12.0GHz. A prototype was fabricated and measured. The experimental results are consistent with the simulation results and verify the broadband circulation performance in X band.

Circulator Based on Spoof Surface Plasmon Polaritons

In the letter, we propose the design of circulators based on spoof surface plasmon polaritons (SSPP). Rather than striplines, the center conductor is replaced with a blade structure that supports the SSPP mode and exhibits a shorter wavelength and larger wave vector. To enhance the efficiency, a matching transition is employed between the coplanar waveguide and the blade structure. With biased ferrites attached on both the top and bottom sides, the blade structure shows good nonreciprocal properties. The simulation results indicate that in the 5.0-6.6 GHz frequency range, the isolation and return loss reaches 15 dB and the insertion loss is less than 0.5 dB. Since the circulator utilizes the SSPP mode, which exhibits a shorter wavelength than its analogous stripline mode, the size of ferrites, and thus the size of the circulator, can be reduced. Our work provides an effective route to the design of compact, broadband circulators.

Compact, low-loss and broadband photonic crystal circulator based on a star-type ferrite rod

Abstract We propose and investigate a compact, low-loss and broadband circulator based on a star-type ferrite rod in two-dimensional square-lattice photonic crystals. Only one ferrite rod is required to be inserted in our structure. Firstly, the performances of circulator based on the star-type, circle, and square ferrite rod are compared, showing that the circulator with the star-type ferrite rod performs better than the other two ones. And then, based on the star-type ferrite rod circulator, four cases of improvement, in which the background rods around the center ferrite rod are replaced respectively by the backward-triangle, forward-triangle, backward-semicircle, and forward-semicircle rods, are investigated to modulate the coupling between the center magneto-optical micro-cavity and the corresponding waveguides. The results show that, with proper parameters, all the four cases can greatly improve the output properties of the circulator, and different cases have its own advantages. The mechanism behind these improvements is also discussed. Finite-element method is used to calculate the characteristics of the circulator and Nelder-Mead optimization method is employed to obtain the optimized parameters. The ideas presented here are useful for designing broadband, low insertion loss, and high-isolation circulators which have potential application in integrated photonic crystal devices.

Broadband circulator based on spoof surface plasmon polaritons

In this paper, we proposed a method to design broadband circulators with a compact size. We show that spoof surface plasmon polaritons (SSPPs), which are mediated by metallic blade structures, can be used for the design. The SSPPs wave on metallic blade structures and the transverse electromagnetic (TEM) wave on strip lines are combined to realize wideband circulation performance. A broadband characteristic, which is different from a traditional one, with a compact size can be achieved by combining the SSPPs wave and the TEM wave, which propagates simultaneously in the circulator. The simulation results indicate that from 4.5 GHz to 14 GHz, the return loss and isolation degree basically reaches up to 12 dB and 15 dB, respectively. The mechanism of the broadband transmission characteristic is analyzed using field distributions obtained in simulation. Moreover, the insertion loss is less than 1 dB. This method is helpful to reduce the size of the device and the bulk of ferrite.

Broadband Unidirectional Electromagnetic Mode along an Arbitrary Surface

Based on coordinate transformation, we extend the theory of unidirectional surface mode at a plane interface to a more general case of arbitrary boundary. We provide direct simulations to prove the validity of extension. Because it depends only on the signs of off-diagonal elements in the tensor of permittivity (for TM mode) or permeability (for TE mode), the unidirectionality is robust in a wide range of frequency. Moreover, this kind of surface mode is fairly robust with smoothly changing surface. These properties are very useful to design compact nonreciprocal component with wide range of operating frequency in various cases, such as broadband isolators and circulators.

Broadband circulators based on directional coupling of one-way waveguides

Resonator-based optical circulators are fundamentally bandwidth-limited by their quality factors. We propose a new type of circulator based on directional coupling between one-way photonic chiral edge states and conventional two-way waveguides. The operational bandwidth of such circulators is tied to the bandwidth of the directional waveguide coupler and has the potential for simultaneous broadband operation and small device footprint.

Ferrite-Coupled Line Circulator Simulations For Application at X-Band Frequency

We have designed and simulated a circulator circuit in which the magnetization aligns along the plane of an yttrium iron garnet (YIG) film. For an X-band frequency (8-12 GHz) circulator we have utilized a YIG slab (~200 mum thick) with saturation magnetization (4piMS ) and ferrimagnetic resonance (FMR) linewidth (DeltaH) of ~139.26 kA/m and 10 Oe, respectively. Broadband circulator operation was realized for frequencies above FMR, f=5 GHz. The applied FMR field was 79.58 kA/m. The Ansoft HFSS software suite was used to simulate the circulator response. The insertion loss S21 and the isolation S12 were calculated to be ~0.9 dB and ~-52 dB, respectively, with ~15% bandwidth at the center frequency of 10.1 GHz. We believe that this in-plane circulator design may enable high performance with significant volume and weight reduction

Theoretical design for 120 GHz semiconductor junction circulators: effects of different numbers of terms in the Green's function

A theoretical analysis of the predicted performance and field distributions for semiconductor junction circulators is based on Bosma's Green's function approach which involves a summation of infinite series in the mathematical derivation. The effects are considered of taking a different number of terms in the series, looking at three different circulators centred at 120 GHz. The narrowband semiconductor circulators show a similar effect to the ferrite junction circulator because the field distributions inside the semiconductor discs can be approximated by only considering the dominant modes. However, there is no dominant mode in the broadband circulator and the higher order modes play an important role in the operation of this circulator. In order to obtain a precise representation of the circulation effects inside both narrowband and broadband circulators, at least up to the 6th term, or 18 terms in all, are required to be added in the summation of Green's functions.

A method for investigating a class of inhomogeneous stripline circulators

Broad-band stripline circulators are studied by means of a mixed numerical technique which employs both boundary integral and segmentation methods; this technique allows the analysis of planar circuits where the substrate is constituted by several regions with arbitrary shapes and different electrical properties. It is known that tracking circulators require matching structures because they present a low-gyrator impedance (real and almost constant in an octave frequency band). The matching structures (generally tapers or multisection's transmission line transformers) must be realized on a reciprocal substrate. The overall device (circular disk on ferrite substrate and matching structure on dielectric substrate) constitutes a planar circuit with an inhomogeneous medium. The method of study presented here allows the determination of the overall impedance matrix of the planar circuit constituted by the nonreciprocal disk with sections of striplines connected to each port; in this way, the discontinuities between reciprocal and nonreciprocal medium are included in characterization of the overall device. Moreover the accuracy of the representation is increased, In fact, the coupling ports of the overall device may be located at a suitable distance from the disk boundary where higher-order modes excited by the discontinuities have been sufficiently attenuated and only the TEM mode is present on the striplines (which is the only one considered in the design of the matching structures).

Broadband theoretical gyroelectric junction circulator tracking behavior at 77 K

The perfect circulation conditions for the gyroelectric circulator are given for a gyroelectric ratio with magnitude in the range zero to two. Values of this ratio above unity given in this paper correspond to the frequency regions where the effective permittivity is negative. The subsequent Green's function analysis employs the modified Bessel function. In accordance with the Drude model of semiconductors, a theoretical low-loss GaAs design is presented with a 20 dB isolation bandwidth of approximately 90% at an operating temperature of 77 K. The theoretical broadband circulation tracking behavior of this design is demonstrated for gyroelectric ratios which may exceed a magnitude of unity. The operating frequency range for this particular circulator design is below the extraordinary wave resonance frequency. In order to measure the microwave properties of the magnetised semiconductor disk, a two port analysis is performed based upon the Drude model of semiconductors.

Low-field loss in ferrites-relevance to broadband circulator design

The criteria for selecting ferrite materials for broadband circulator applications are discussed. Transmission measurements in a circulator-like microstrip fixture are used to select materials for applications in a given frequency band. Data concerning the frequency dependence of transmission loss in the partially magnetized state at various values of bias field are presented. >

Theory of low-field loss in partially magnetized ferrites

Low-field loss in partially magnetized ferrites has important implications for the design of broadband circulators and other microwave devices. A quantitative theory of this effect has been developed that takes the inhomogeneity of the DC bias field into account. The theory is specifically applied to a calculation of the transmission loss for a microstrip line on a rectangular ferrite platelet. >

Design and Performance of Broadband Circulator

Broadband miniaturized stripline junction circulator (operating in a below resonance mode) using lithium ferrite is discussed. The design criteria and the advantages of this device over the other type namely EGW circulator are outlined. The device operates over a bandwidth of 8 to 18 GHz with 15 dB (min) isolation, insertion loss of than 0.6 dB and return loss 15 dB minimum.

Broad-band circulator models for active microwave circuit analysis

A general method is presented for determining a broad-band equivalent circuit of a lossy, nonideal circulator from the scattering parameters over the frequency range of interest. The equivalent circuit has application to the design and analysis of circulator-coupled circuits such as amplifiers and oscillators. The method is applied to two different circulator forms, in coaxial line and waveguide, to show the close agreement to measured performance that can be attained by the method in practice.

An equivalent circuit for narrow-band nonideal circulators

The scattering parameters of a simple equivalent circuit based upon modification of an earlier circuit of Bosma [1] are derived and compared with previously published experimental results to demonstrate the suitability of the equivalent circuit for use in the analysis of microwave circuits such as circulator-coupled single-stage and multi-stage negative-resistance amplifiers. The approach followed here can be generalized to obtain circuit models for broad-band circulators.

Temperature-Stabilized 1.7-GHz Broad-Band Lumped-Element Circulator

A new construction technique for broad-banding and temperature stabilization of a lumped-element circulator is presented to obtain a compact circulator for practical usage. By using a new integrated wide-banding network consisting of three series resonant circuits on the back of the junction substrate, 1.7-GHz double-tuned and triple-tuned broad-band circulators have been successfully developed. Fundamental junction parameters, such as an in-phase eigeninductance, parasitic capacitance, and nonreciprocal filling factor, have been investigated experimentally. A design theory for temperature compensation of a lumped-element circulator is also presented, and temperature compensation with bias magnetic field of postitive temperature coefficient has been applied to the 1.7-GHz broad-band circulators. As a result, 20-dB isolation bandwidths of more than 600 MHz (double-tuned type) and 950 MHz (triple-tuned type) have been obtained throughout the temperature range of -10 ~ +60/spl deg/C.

The Edge-Guided-Wave Circulator (Short Papers)

A complete study is presented on "edge-guided-wave" circulators (EGC). The fundamental physical principles which underlie EGC's operation are established and exploited to construct a broad-band circulator in the 8-12-GHz band. The performance data are compared to those of a "continuous tracking" circulator (CTC) and a traditional Y-junction circulator.

A Temperature-Stabilized Broad-Band Lumped-Element Circulator

An equivalent circuit including the stray reactance of a microstrip-type lumped-element circulator is derived to establish the design procedure, and it is shown theoretically that a broad-band circulator with a 30-percent bandwidth can be reafized. Additionally, to obtain the broad-band characteristics over a wide range of temperatures, the necessary temperature coefficients of ferrite materials and magnets are calculated. A new ferrite material with a low temperature coefficient as well as a new fabrication process for thin-film crossovers have been developed. The experiments indicate that a radial magnetizing field improves the circulator characteristics in both bandwidth and loss. An experimental circulator exhibits the following characteristics over a wide temperature range from -10 to 60/spl deg/C: VSWR 20 dB over a bandwidth of 450 MHz centered at 1.7 GHz.