提高光学隔离器／环行器的反向隔离比方法

理论和实验研究了干涉效应对光学隔离器／环行器反向隔离比的影响，结果表明可大幅度提高反向隔离比。     

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     

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     

Fibre-embedded optical isolator

A fibre-embedded optical isolator without a lens element is proposed and fabricated. The isolator consists of beam-expanding fibres, laminated polarisers and a Faraday rotation garnet. Backward and forward losses at 1.3 mu m wavelength are 36.9 and 1.6 dB, respectively.<>     

偏振无关型光环行器的研究

本文报导一种新型偏振无关光环行器的设计及实验结果。器件由偏振分离器、偏振组合器、法拉弟旋转器及半波片组成。对1.37微米不同偏振方向入射光,器件的插入损耗为2.8分贝,隔离为18～35分贝。     

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     

Simple polarisation-independent optical circulator for optical transmission systems

A simple polarisation-independent optical circulator has been developed. The circulator consists of a 45°Y3Fe5O12 rotator and a quartz rotator and two polarising beam-splitting cubes. Measured insertion loss was about 1.3 dB at 1.32 ?m wavelength. The circulator was connected to graded-index multimode fibres using rod lenses.     

Proposed interferometric optical isolator

This correspondence describes the concept of a non-reciprocal transmission isolator or four-port circulator consisting of an anisotropic index of refraction element inside the perimeter of a traveling-wave (ring) interferometer. The potential advantages of this device with regard to feedback power rejection capability and rejection ratio are discussed.     

Compact optical circulator for near-infrared region

A compact Faraday-rotation 4-port circulator was developed for the near-infrared region. This circulator consists of an yttrium-iron-garnet Faraday rotator, biased by two permanent magnets, and two Glan-Taylor prisms. Insertion losses of 2.7?3.2 dB and isolation ratios of 13?28 dB among non-reciprocal ports were obtained at 1.15?m wavelength.     

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.     

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     

一种光环行器优化设计方法

针对光纤通信系统中最常用的晶体型三端口光环形器,详细论述了器件的工作原理,分析了现有方案中存在的光路不对称问题,提出了一种优化设计方法,通过引入位移型的Wollaston棱镜和改进型的位移晶体,设计出一种光路完全对称的器件结构,提高了光路调试和器件封装的效率.     

Polarisation-independent optical circulator coupled with multimode fibres

An experiment on a polarisation-independent optical circulator coupled with graded-index fibres was performed. Insertion losses of 2.5?2.9 dB and isolation ratios of 15?34 dB among nonreciprocal ports were measured, at 1.27 ?m wavelength.     

Compact optical isolator for near-infrared radiation

Compact Faraday rotation isolators have been developed for near-infrared radiation. Two types of Faraday rotators were used: one was composed of two permanent magnets, the other of a closed magnetic circuit with a permanent magnet. 2.0 dB insertion loss and 30 dB isolation ratio at 1.15 ?m wavelength have been obtained.     

Polarization-independent in-line optical isolator with lens-freeconfiguration

A fiber-embedded polarization-independent optical isolator that consists of an isolator chip, and thermally expanded core (TEC) fibers, and that has no lens elements was developed. The chip was made of birefringent crystal plates, rutile polarization-splitters, a quartz half-wave plate, and a Faraday rotation garnet, with the chip embedded into a TEC fiber. By utilizing the proper orientation flat formed on the edge of each plate, alignment of these plates was simplified. Measured backward and forward losses at a wavelength of 1.55 μm are >40 dB and ~2.5 dB, respectively, which agree with predicted values. It is also shown that the characteristics would be dramatically improved by utilizing new polarization splitters instead of rutile plates. Experimental results support the promise of constructing fiber-integrated isolators which then enable the mass-production of inline isolators     

光纤传输用的磁光隔离器

本文报导了光纤通信用光隔离器的研究工作.隔离器由稀土铁石榴石法拉第旋转器及两只方解石棱镜组成.在波长为1.15微米时,器件插入损耗为2.4分贝,隔离比为34.8分贝.讨论了使用不同的复合稀土铁石榴石材料及采用不依赖偏振光技术对器件性能的改进.     

A phototransistor optical isolator noise model

A noise model for the phototransistor optical isolator is presented and used to predict optical isolator noise performance. Results are shown to agree with existing experimental data on phototransistor optical isolator noise. The model presented includes burst noise, flicker noise and shot noise.     

Polarisation-insensitive high-isolation nonreciprocal device for optical circulator application

A novel high-isolation structure for a polarisation-insensitive nonreciprocal device intended for optical circulator application is proposed. It consists of birefringent crystals and polarisation rotators. Experimental demonstration shows an isolation of over 42 dB and an insertion loss of under 1.5 dB.<>     

Design feasibility of a single-mode optical isolator

Isolator conditions are derived by a perturbation method for optical slab isolators in which magnetooptical crystal and anisotropic dielectric crystal films are integrated for reciprocal and non-reciprocal TE-TM mode conversion functions. The general expressions show that isolator conditions can be satisfied for any combination of wavelength, normalized frequency, waveguide thickness, and gyrotropic constant of the magnetooptical crystal by appropriate choice of the magnitude of the birefringence of the top layer film and its crystal orientation angle. Design examples of single-mode isolators with waveguide thicknesses of 4, 4.5, and 5 μm are given at 1.55 μm wavelength. It is also pointed out that isolators of the above design can be fabricated with Y3Fe5O12, Y1.5Gd1.5Fe3O12, and Tm3Fe5O12crystal films as magnetooptical materials and a solid solution of LiNbO3and LiTaO3as an anisotropic film. Tolerance in the required film thickness becomes less stringent with this design. Isolation of more than 20 dB with an insertion loss of less than 0.12 dB is feasible without any parameter adjustment, even when there is as much as a ten percent deviation in the film thickness.     

Analysis and design of semileaky-type thin-film optical waveguide isolator

This paper describes an optical waveguide isolator that utilizes the unidirectional guided-radiation mode coupling in a magnetooptic/anisotropic slab guide. The basic structure is the semileaky-type waveguide that has been previously used as a polarization mode filter. Specific features of the proposed device are its compact one-section form resulting from the inherent polarization-discrimination property and the relaxed dimensional tolerance due to the automatic phase-matching of coupled modes. Design data and a related discussion are given for the example of LiNbO3/YIG/GGG layered structure operating in the 1.15-μm-wavelength region.