Waveguide polarization-independent optical circulator

We fabricated a new type of waveguide polarization-independent optical circulator which does not need a polarization-beam splitter. The circulator is based on a non-reciprocal Mach-Zehnder interferometer which consists of two waveguide Faraday rotators, two thin-film half-waveplates and two planar lightwave circuit-type 3-dB couplers. The fabricated circulator provides a 14.0-23.7-dB isolation and a 3.0-3.3 dB insertion loss at λ=1.55 μm. This circulator presents a new possibility for developing non-reciprocal devices in the field of integrated optics     

A Latching Ring-And-Post Ferrite Waveguide Circulator

This paper presents the performance and normalized design parameters for a latching ring-and-post ferrite circulator in waveguide. A C-band circulator has provided an insertion loss of 0.35 dB and a 20-dB isolation bandwidth of 17 percent. When the circulator was matched for higher maximum isolation (50 dB) but narrower bandwidth (10 percent) at room temperature, the 20-dB isolation bandwidth was 7.8 percent across the -40/spl deg/ to +75/spl deg/C temperature range. Low-loss operation was obtained at pulsed powers up to 7.5 kilowatts, and at least 20 dB of isolation was maintained up to 100 kilowatts. This performance, in conjunction with a switching speed of a fraction of a microsecond, permits the use of these circulators for transmitting-receiving functions in high-reliability RADARs.     

A Proposal of Zero Leakage-Loss Passive Optical Combiner Based on Nonreciprocal Waveguide

In this letter, a zero-leakage-loss passive optical combiner based on nonreciprocal waveguides is proposed to remove the inherent 3-dB leakage loss in the conventional ones, which consists of a nonreciprocal waveguide grating-type isolator and circulator. The device concept is given, and the dispersion relation analysis and 3-D magnetooptical beam propagation method are employed to validate the feasibility and the device performance.     

High-isolation polarization-independent optical circulator

A high-isolation polarization-independent optical circulator is reported. The circulator structure can sharply reduce isolation dependency on both the rotation error of a rotator and on extinction ratio of a polarizing beam splitter. As a result, the circulator has high isolation over a wide wavelength and temperature range. A 4-port circulator coupled with single-mode fibers was fabricated. Its measured insertion loss and isolation were <1.8 and >31.5 dB, respectively. Consequently, a loss ratio of over 29.7 dB has been realized. The isolation (which is free from reflections) was measured to be >45.1 dB. It is confirmed that the wavelength range for this kind of isolation over 40-dB is very wide. The measured range was wider than the measurement system limit of 90 nm     

The Design of Planar Circulators for Wide-Band Operation

The stripline circulator used in microwave integrated circuits (MIC) is considered one of ferrite planar circuits (two-dimesional circuits). We investigated the optimum shape of a planar circulator for wide-band operation, perceiving the wider freedom of the planar structure in circuit design. The wide-band planar circulator, designed using the powerful contour-integral method is triangular shaped with slightly concave sides. The 20-dB isolation fractional bandwidth of the designed circulator is about 52 percent.     

Lumped Element Y Circulator

A lumped element Y circulator using ferrite, having a mesh mechanism in place of the center conductor of an ordinary Y strip line circulator, is proposed. A theory is developed relating to bandwidth, insertion loss, and temperature dependence of the reactive energy and the tensor permeability of ferrite, and the bandwidth enlargement is discussed on the basis of the equivalent network. The size of the circulator is approximately 1~2 cm in diameter for VHF and UHF bands and the characteristics are, for example, about 50 percent bandwidth for 20-dB isolation, 2-dB insertion loss at 600-Mc/s center frequency. It is also shown that the insertion loss has its minimum value at a definite bandwidth and, as a practical example, a circulator is described with 0.25 dB of insertion loss and 6.5 percent bandwidth at 700 Mc/s.     

偏心铁氧体圆柱加载波导Y结环行器的分析

采用点匹配法结合坐标变换分析了偏心全高铁氧体圆柱加载波导Ｙ结环行器的特性，讨论了铁氧体圆柱相对于结中心的偏移对环行器性能产生的影响．由数值计算结果可见：（１）偏心铁氧体柱加载波导Ｙ结环行器可被用作具有低插入损耗、小驻波和高隔离的高性能Ｙ结隔离器；（２）非对称波导Ｙ结环行器性能的非对称性可以通过偏移铁氧体柱加以校正．     

Design and fabrication of a nonradiative dielectric waveguidecirculator

A technique is described for constructing a high-performance nonradiative dielectric waveguide (NRD guide) circulator for use at 50 GHz. A mode suppressor, which serves to reduce unwanted modes to a negligible level, was devised and used to improve circulator performance significantly. A half-wavelength step transformer was installed at each port of the circulator to increase the operational bandwidth. The insertion loss of this circulator is less than 0.3 dB, and the 20-dB isolation bandwidth is about 2.6 GHz. Characteristics of the NRD guide circulator are analyzed based on an equivalent circuit representation. This analysis considerably facilitates the design procedure of the circulator     

Improved Microwave Noise Measurements Using Ferrites

The ferrite isolator and the ferrite circulator have been applied separately to improve the accuracy of measuring small microwave noise powers or small power differences. Either the isolator or the circulator effectively isolated the input circuit of a microwave receiver from the impedance of the source. As a result, the measurement errors introduced by mismatched source impedances were reduced by as much as 98 per cent. The added input circuit losses of the ferrite components reduced the receiver sensitivity by only about 10 per cent. Since the accuracy of measuring small noise power differences was limited principally by impedance errors, the addition of ferrite isolation to the receiver input circuit increased the sensitivity of measurement to near the theoretical limit. The ferrite isolator was used as a passive transmission element in these experiments. The ferrite circulator, however, was used as an electrically-operated, microwave switch. This switch was used to replace the mechanical chopper in a Dicke-type radiometer. In addition to impedance isolation, the ferrite switch makes possible rapid comparison measurements of the microwave noise powers from any two sources, or of the noise powers from the same source in two different polarizations.     

Distributed amplifiers as duplexer/low crosstalk bidirectionalelements in S-band

Research into a novel class of distributed amplifiers which have a high isolation bandstop response in the reverse gain direction is described. These devices may be used as duplexer/circulator or bidirectional amplifier elements which, for many applications, can perform the function of ferrite isolator and circulator elements. The authors detail the design of such an amplifier, working in the S-band, and gives measured test data     

Low-Loss Cryogenic L-Band Circulator (Correspondence)

It is shown that a three-port stripline circulator can be constructed to operate in Z-band at 15/spl deg/K with 0.5 dB insertion loss and up to 20-percent bandwidth for the 20-dB isolation.     

An Accurate Junction Circulator Design Procedure (Correspondence)

A two-step design procedure for the accurate synthesis of a junction circulator is given. The procedure is accurate to within a few decibels for isolation in the 20- to 40-dB range.     

High-Power Ferrite Load Isolators

The principles of ferromagnetic resonance have been well described in literature. It is the purpose of this paper to point out the application of these principles to the design of practical microwave components, especially for high power. The various types of ferrite microwave circuits that can be used in the design of a load isolator are presented. The advantages and disadvantages of each of these circuits are discussed in regard to the electrical, mechanical, thermal, and magnetic field requirements. Experimental data are given for the optimum design of nonreciprocal ferrite absorbers for rectangular guide. Finally, practical design information for a power circulator in rectangular waveguide is presented which has been modified for use as a load isolator. This device has extremely high isolations (50 db) and low insertion loss (.5 db), and has maintained an isolation in excess of 30 db over a 25 per cent bandwidth with a permanent magnet field. Power handling ability of 250 kw peak with a .001 duty cycle is easily accomplished without external cooling. This isolator requires quite small magnetic fields for proper operations and hence packaged isolator is quite lightweight. Use of this power circulator for high-power modulators and duplexers is discussed.     

A 300 GHz quasioptical faraday rotation isolator

A quasioptical isolator has been developed at 285 GHz with insertion loss≤2 dB and isolation≥ 18 dB over a 1% bandwidth. By improving matching techniques, the device should perform as well over bandwidths up to 5%. This design can be easily modified to make a circulator.     

Room temperature solid-state plasma nonreciprocal microwave devices

Nonreciprocal microwave propagation at room temperature in a waveguide which contains of a thin slab n-InSb has been demonstrated by the construction of an isolator, a three-port circulator, and a variable power divider, all operating at K-band frequencies. A forward loss and an isolation of 3 and 15 dB, respectively, was observed for the isolator; the forward and backward losses between adjacent ports of the circulator were 3 and 20 dB, respectively, and the power ratio of the divider could be varied from 1 to 10 for a given direction of the magnetic field. Transmission losses of about 3 dB were present in the forward direction and in each case, all but 1 dB of these were shown to be due to reflections resulting from impedance mismatch.     

Design of a New Broad-Band Isolator

The design theory and experimental results of a proposed broad-band technique of an isolator are presented. The isolator not only has a broad-band backward loss but also a low broad-band insertion loss. The network constants and the performance are obtained in connection with the magnetic loss of ferrite, and they are confirmed by experimental data. The trial ultrawide-band isolator the performance of 20-dB isolation over the frequency band from 70 MHz to 800 MHz.     

Ferrite Elements for Hybrid Microwave Integrated Systems

Complete realization of the potentialities of hybrid microwave integrated circuits will require both semiconductor and ferrite elements. This paper presents performance data for several microstrip ferrite devices that can play an important role in the exploitation of microwave integrated circuits. Data on both fixed-field and latched microstrip junction circulators are given including a fixed-field circulator with less than 0.4-dB loss and greater than 20-dB isolation over the 6.5- to 9.3-GHz band. The characteristics of microstrip meander-line phasers are discussed, and a simple, rugged technique for fabricating single-crystal YIG devices by embedding the YIG element in the substrate is presented.     

Ferrite Elements for Hybrid Microwave Integrated Systems

Complete realization of the potentialities of hybrid microwave integrated circuits will require both semiconductor and ferrite elements. This paper presents performance data for several microstrip ferrite devices that can play an important role in the exploitation of microwave integrated circuits. Data on both fixed-field and latched microstrip junction circulators are given including a fixed-field circulator with less than 0.4-dB loss and greater than 20-dB isolation over the 6.5- to 9.3-GHz band. The characteristics of microstrip meander-line phasers are discussed, and a simple, rugged technique for fabricating single-crystal YIG devices by embedding the YIG element in the substrate is presented.     

Isolators, polarizers, and other optical waveguide devices using a resonant-layer effect

This paper investigates the effect of a high-refractive-index layer added onto the clad layer of an optical waveguide. With proper design, the value of the fundamental mode's confinement factor in the added layer can exhibit a resonance. This resonance depends on the added layer's location, thickness, complex index, and wavelength of operation. If loss is incorporated into this added layer, relatively small changes in waveguide properties can result in large changes in loss. This phenomenon is referred to in this paper as the resonant-layer effect (RLE). A number of devices, including isolators, polarizers, and modulators, can be made and/or improved by using the RLE. As examples, this paper describes an integratable isolator giving 240-dB/cm isolation and 13-dB/cm insertion loss, an integratable polarizer with 90-dB/cm rejection and about 0.8-dB/cm insertion loss, and a 300-/spl mu/m-long modulator requiring electric fields of /spl plusmn/5 V//spl mu/m for /spl sim/45% intensity modulation. In general, the resonant layer need not be epitaxial with the waveguide, allowing for integration with a variety of material systems.     

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.