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     

High-isolation polarization-independent optical circulator coupledwith single-mode fibers

A high-isolation polarization-independent optical circulator is reported. The goal is to provide a simple structure that sharply diminishes the degradation on the isolation caused by imperfection of polarization separation in the polarizing beam splitters. The circulator structure is almost the same as that of a conventional circulator except that a birefringent plate is added to each port to achieve high isolation. The effectiveness of the added birefringent plate has been confirmed by calculation and experiment. Insertion loss and isolation of the fabricated circulator coupled with single-mode fibers have been measured to be <1.0 dB and >29.9 dB, respectively, for 1.299 μm wavelength light. A loss ratio over 28.9 dB has been realized     

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 mm-wave four-port quasi-optical circulator

A four-port quasi-optical circulator has been designed, built and tested for operation in the millimetre wave band. The specific circulator reported here was investigated over a 20 GHz bandwidth, centred on 94 GHz. Good performance characteristics were obtained over this bandwidth. Isolations of better than 30 dB and insertion losses of around 0.5 dB were achieved. The input vswr was found to be less than 1.35 over the whole bandwidth investigated and vswr's of less than 1.1 were achieved for narrower bandwidths. It is possible of course to configure the 4-port circulator as a 3-port circulator or indeed as 2-port isolator. Further optimization and consequent improvements in performance are almost certainly obtainable.     

High-isolation polarization-insensitive optical circulator foradvanced optical communication systems

An optical circulator configuration that does not use polarization beam-splitters (PBSs) is described. Birefringent crystals (BCs) are used instead of PBSs to achieve a high-isolation polarization-insensitive optical circulator. The use of BCs simplifies fabrication. A conceptual configuration and two concrete structures are proposed. The prototype optical circulator was tested and exhibited over 60 dB of isolation in the wavelength range of 70 nm around 1550 nm. The insertion loss is under 1.5 dB and fluctuates only 0.2 dB with changes in the polarization state     

Proposal for a polarization-independent integrated optical circulator

A polarization-independent waveguide circulator design is proposed which is well suited for monolithic integration. The circulator consists of multimode interferometers, half-wave plates, and Faraday rotators all in waveguide form. The length of the circulator is 712 /spl mu/m. Simulations show the circulator to have 25 dB of isolation and 1.3 dB of insertion loss at a wavelength of 1.55 /spl mu/m.     

A polarization-independent optical circulator for 1.3 µm

A compact polarization-independent optical circulator for 1.3μm is described. The device utilizes birefringent plates (rutile) for beam splitting, YIG plus a single-order quartz half-wave plate for polarization rotation, and a slotted 45° glass prism for beam steering. The fiber-to-fiber insertion loss is 2.0 or 2.5 dB and the isolation is 25 or 35 dB, depending upon the ports in question. The use of birefringent plates for beam splitting and combining eliminates the need for multiple dielectric coatings for polarization beam splitting, requires only optical plate processing, virtually eliminates sensitivity to translational misalignment of individual beam-splitting/combining components, and reduces the required number of optical-quality surfaces.     

A quasi-optical polarization-independent diplexer for use in the beam feed system of millimeter-wave antennas

The theory and performance of a quasi-optical Fabry-Perot diplexer employing two rectangular meshes and capable of polarization-independent operation at large angles of incidence are presented. The diplexer is suitable for use in a dual-polarization dual-frequency beam feed system for millimeter-wave antennas. An experimental diplexer operating at an angle of incidence of56.5deg pm 1degwas found to separate two 1.1-GHz bands centered at 21 and 31.5 GHz with a loss of less than 0.3 dB in either band and a cross-polarization discrimination of more than 40 dB in the higher band and 30 dB in the lower band.     

High-isolation demultiplexing in bend-tuned twin-core fiber

By applying a cantilever bend to a twin-core optical fiber wavelength division demultiplexer, isolations of >30 dB have been achieved between channels at 1.33-1.54 μm. These bend-tuned TCF's exhibit ⩾20 dB isolation over a bandwidth of 32 and 21 nm in the two wavelength windows, respectively. This is significantly better than that typically offered by commercially available, single-stage, tapered coupler demultiplexers. The bend-tuning mechanism is demonstrated experimentally and described theoretically using a coupled local-mode analysis     

高隔离度S波段MEMS膜桥开关

常规的 MEMS膜桥开关在 1 0 GHz以上频段才具有低插损、高隔离度 (>2 0 d B)的优点。文中介绍了一种应用于微波低频段—— S波段的高隔离 MEMS膜桥开关 ,给出了开关的设计与优化方法 ,建立了开关的等效电路模型。通过双膜桥结构、选择高介电常数的介质膜、微电感结构膜桥这些措施 ,达到提高开关隔离度的目的。利用 HFSS软件仿真的结果表明 ,该开关在微波低频段 (3～ 6GHz)有着很好的隔离性能。开关样品在片测试的电性能指标 :插损 <0 .3 d B,隔离度 >40 d B,驱动电压 <2 0 V     

A polarization-independent grating resonator

A polarization-independent optical resonator based on a novel phase-shifted grating structure is proposed and analyzed. Its application as a polarization-independent optical wavelength filter with ultranarrow bandwidth and fine tunability is described     

High-isolation single-mode wavelength-division multiplexer/demultiplexer

A single-mode fibre-optic wavelength-division multiplexer/demultiplexer with excellent isolation is reported. The device utilises a fused biconical structure similar to that of 3 dB couplers and exhibits an insertion loss of 0.04 dB and a wavelength isolation of 43 dB at 1.300 ?m and 30 dB at 1.523 ?m.     

Dielectric waveguide circulator

The design and development of a millimeter wave Y-junction ferrite circulator operating in the dielectric waveguide medium is described. This device utilizes NiZn ferrite as the gyromagnetic junction material and magnesium titinate as the dielectric waveguide; the entire structure being mounted on and supported by a low permittivity dielectric substrate.     

Mirror-folded polarization-independent wavelength filter

A 1.55- mu m polarization-independent optical bandpass filter with a 3-dB bandwidth of 6 AA and a tuning range of at least 100 AA is demonstrated. The photonic circuit of the filter consists of a waveguide TE-TM mode splitter, two parallel electrooptic TE-to-TM, TM-to-TE mode converters as the wavelength selective element, and a reflective mirror at the far end of the crystal. The circuit can be viewed as a mirror-folded version of the polarization-independent filter. It is shown that by passing the light two times through the narrowband mode converters, the filter bandwidth can be reduced by about a factor of two compared to a conventional single-pass filter of the same length. A novel tunable mode converter structure is also demonstrated that allows coherent in-phase mode conversion during the two passes through the mirror-folded filter.<>     

Wide-band polarization-independent tensile-strained InGaAs MQW-SOAgate

A high-performance tensile-strained InGaAs multi-quantum-well semiconductor optical amplifier (MQW-SOA) gate developed for wavelength-division-multiplexing (WDM) applications is reported. The -0.47% InGaAs-strained SOA gate has a very low polarization dependence of 0.3 dB over a driving current between 30 and 60 mA and a wide-input signal wavelength range from 1530 to 1580 nm. The fabrication tolerance of the mesa stripe width is very large, ranging from 1.0 to 1.75 μm. The MQW-SOA gate has an extinction ratio of more than 40 dB. The fiber-to-fiber lossless operation current is less than 50 mA over the fiber-amplifier gain band. The gating speed is less than 1 ns     

Quasi-optical ferrite reflection circulator

A quasi-optical Faraday rotation ferrite circulator for microwave or millimeter radiation is analyzed by a matrix formalism. Both reflection and transmission configurations at oblique incidence are examined. Numerical results are presented for the band centered at 35 GHz. Theory and experiment are compared over a 10%-20% band. Notwithstanding the complexities of oblique incidence, the reflection-type device promises favorable bandwidth, low loss, and isolation comparable to those of the transmission version now in system deployment, and offers the potential for much higher heat-dissipation capability     

Bidirectional thin-film lumped-element circulator

The possibility of making a `bidirectional? thin-film ferrite lumped-element circulator (l.e.c.) has been deduced after a detailed analysis of the scattering-matrix eigenvalues' frequency dependence has been made. The bidirectional effect is obtained for two different frequencies that are not simply related.     

Millimeter wave microstrip circulator

A new and unique microstrip “drop-in” type Y-junction circulator has been designed and developed for operation in the millimeter wave frequency region. This device utilizes NiZn ferrite as the gyromagnetic material which is mounted on a duroid substrate.     

内置驱动器的砷化镓高隔离开关芯片

采用增强/耗尽型(E/D)结构的赝配高电子迁移率晶体管(PHEMT)技术,研制开发的射频开关,具有插损低、隔离度高、承受功率大、线性度高等特点.产品采用0.5μm栅长的砷化镓PHEMT E/D标准工艺加工,将开关电路和驱动电路集成在一颗芯片上,并做了相应的静电防护设计.测试结果表明,在0.01～5.o GHz带内,插入损耗≤1.2 dB@3 GHz、≤1.6 dB@5 GHz,带内输入输出驻波比≤1.5,隔离度≥60 dB@3 GHz、≥52 dB@5 GHz,1dB压缩功率点达到了30 dBm,IP3超过了+-52 dBm.     

Efficiency of quasi-optical couplers

Millimeter-wave devices are often coupled to radiation by means of a feed antenna placed at the focus of a primary lens or mirror, a technique known as “quasioptical coupling”. A general expression for the efficiency of such a coupler is derived. The efficiency of such a coupler depends on the relationship of the feed antenna pattern to the numerical aperture of the primary lens. An approximate general rule for coupler design is obtained. This rule is as follows. Let θ_o be the angle between the direction in which the feed pattern is maximum and the direction in which the pattern intensity has one-half its maximum value. Then the optimum numerical aperture of the primary lens is approximately sin (1.67 θ_o). The effects of focussing errors and lens aberrations can also be calculated by this technique.