An effective nonreciprocal circuit for semiconductor laser-to-optical-fiber coupling using a YIG sphere

A practical nonreciprocal optical circuit for laser-diode (LD)-to-optical-fiber coupling in the 1.3-μm wavelength region is described. It consists of a yttrium iron garnet- (YIG) sphere graded-index (GRIN) rod lens and a polarizer. The YIG sphere can function not only as a Faraday rotator but also as an effective coupling lens. High coupling efficiency of more than -5 dB for a single-mode fiber, and more than -2 dB for a multimode fiber, is easily achievable. Alignment sensitivities and coupling characteristics of the proposed circuit are also discussed theoretically and experimentally. The increase in LD relative intensity noise (RIN), caused by light injected into the LD, is estimated using the reciprocal characteristics of LD-to-single-mode-fiber coupling. By comparing the LD-RIN increase in the proposed non-reciprocal circuit with that of the reciprocal, high isolation of about 32 dB is confirmed. The fact that reflected light from the proposed circuit has little influence on LD characteristics is also clarified.     

Optical circulator consisting of a YIG spherical lens, PANDA-fibre polarisers and a fibre-optic polarising beam splitter

A novel optical circulator is reported which employs an yttrium-iron-garnet (YIG) sphere, PANDA-fibre polarisers and a fibre-optic polarising beam splitter. The splitting ratios of the fibre-optic polarising beam splitter were 1.0:99.0 for x-polarisation and 97.5:2.5 for y-polarisation, with an excess loss of 0.5 dB at 1.30 ?m wavelength. The backward isolation of the optical circulator was 30 dB with the total insertion loss of 4.5 dB.     

A compact optical isolator with a plano-convex YIG lens forlaser-to-fiber coupling

An optical isolator for laser-to-single-mode fiber coupling is discussed. The coupling unit consists of a confocal two-lens system with a spherical glass lens and a planoconvex lens which is made of yttrium iron garnet (YIG). To minimize the number of elements, the YIG lens is used as a Faraday rotator as well as a coupling lens. Nevertheless, the planoconvex YIG lens satisfies the requirements of high coupling efficiency, high isolation, and low optical feedback from the Faraday rotator. The arrangement is theoretically and experimentally investigated. At a coupling efficiency of 34%, the total optical feedback into the laser diode was measured to be about -60 dB     

Some Design Considerations and Realizations of Iris-Coupled YIG-Tuned Filters in the 12-40 GHz Region

YIG filters covering the frequency ranges 12 to 18, 18 to 26, and 26 to 40 GHz have been designed and developed. The filters in the 18- to 40-GHz range were of three sections and achieved 80-MHz bandwidth and greater than 40 dB of higher order mode rejection. The filter in the 12- to 18-GHz region was of four sections utilizing staggered spheres in order to achieve a larger bandwidth filter with a minimum magnet gap. The bandwidth of this filter was 50 to 60 MHz with greater than 55 dB of higher order mode rejection. Useful information for the design of these filters was obtained with a special test fixture built to measure mutual coupling between spheres as a function of the angle between the line joining the sphere centers and the dc magnetic field. This data is reported for various iris sizes, shapes, and sphere spacings and indicates large differences in mutual coupling as the angle is varied from 0 to 90/spl deg/. The effect of various types of discontinuities and iris sizes and shapes on higher order mode excitation and coupling are discussed as well as constructional problems and the design of high field magnets from vanadium permendur.     

YIG Oscillators: Is a Planar Geometry Better? (Short Papers)

Two yttrium-iron-garnet (YIG) oscillator technologies are compared: the more mature YIG sphere oscillator technology which is based on the uniform (resonant) precession of the electron spins in a small sphere of YIG, and the new planar YIG technology which utilizes the propagation of magnetostatic waves in an epitaxial film of YIG. The YIG sphere technology has been used for microwave oscillators for more than 25 years, but has two significant areas of difficulty in applications the alignment of the YIG sphere in the magnetic bias field coupling cavity requires great precision and the gain element requires a negative resistance element to sustain oscillation. The MSW technology is much newer and less well understood, but the resonator elements are fabricated using a 50- µm line width planar technology making it an appealing candidate. Both technologies are reviewed herein with regard to resonant element theory, temperature, and noise characteristics. New data and theory are presented on MSW resonator optimization.     

Integration of magnetooptical waveguides onto a III-V semiconductorsurface

Optical waveguides fabricated on a yttrium iron garnet (YIG) substrate are integrated onto a semiconductor surface by using ridge waveguides patterned onto a prefabricated recess in the YIG surface. The recess separates the waveguides from the semiconductor substrate with an air-gap. This structure makes it possible to avoid coupling light within the YIG waveguides into the semiconductor substrate which has a higher refractive index. The excess optical loss due to the coupling can be as low as ⩽0.1 dB/cm with a 1-μm-wide air-gap. The calculated coupling loss is confirmed by comparing the guided TE and TM modes     

YIG Resonator Circuit with Isolator Property and its Application to a Gunn Diode Oscillator

This paper presents the analysis and experiment of a newly developed YIG resonator circuit with isolator property, which is constructed with a YIG sphere, three coupling loops, and a 3-dB stripline directional coupler. This YIG circuit can be used advantageously as the toning element of a magnetically tunable oscillator. The circuit has an advantage in preventing frequency pulling and the variation of output power level of the oscillator due to a change in load condition because of the resonator circuit having isolator property at the same time. The design procedure and experiment of a magnetically tunable Gunn diode oscillator with the YIG circuit is also shown. It has been confirmed that the YIG circuit when applied to a tunable oscillator is quite useful.     

Low-Temperature Microwave Power Limiter (Correspondence)

A passive microwave power limiter, using the nonlinear properties of ferromagnetic resonance in yttrium-iron-garnet (YIG) has been evaluated at 4.2° K, 77° K, and 297° K. The limiter, of the DeGrasse type, consists of two decoupled, half-wavelength coaxial cavities as shown schematically in Fig. 1. Input and output coupling is made through the use of quarter-wavelength matching transformers. An optically polished sphere of single crystal YIG is placed in the position of maximum RF magnetic fields common to both cavities.     

微波场效应管YIG振荡器的实验研究

本文扼要叙述了单YIG小球双调谐场效应管振荡器的设计及其优点。在2.2～4.8GHz的振荡频率范围内,输出功率大于10mW。在2.2～4.4GHz的倍频程带宽内,输出功率大于20mW,功率起伏小于3dB。     

Polarisation-independent optical circulator consisting of two fibre-optic polarising beam splitters and two YIG spherical lenses

A novel polarisation-independent optical circulator, which employs two fibre-optic polarising beam splitters and two yttrium-iron-garnet (YIG) spherical lenses, is reported. The present structure has the advantage of low-loss splicing with other single-mode fibres. The insertion loss was 2.5 dB at 1.30 ?m wavelength, and was almost independent of the incident polarisation angle. The backward attenuation was more than 18 dB.     

Analysis and design of a novel leaky YIG film guided wave opticalisolator

A guided wave optical isolator using a four layered leaky yttrium iron garnet (YIG) waveguide with a YIG guiding layer is proposed and analyzed through a transfer matrix formulation. The dependence of isolation characteristics on different waveguide parameters are discussed. It is shown that for four layered structures an isolation ratio of about 24 dB can be achieved with YIG films having large gyrotropy. It is also shown that by replacing the single guiding YIG film with multilayers of YIG with compensated walls and proper permittivity, high isolation ratio can be achieved even with currently available YIG films having low gyrotropy     

Magnetostatic surface wave straight-edge resonators

The performance of the magnetostatic surface wave straight-edge resonator (MSSW-SER) is presented. The resonator uses a rectangular YIG film to propagate MSSWs where the straight edge serves as a reflector. Problems arising from coupling to width mode resonances and their effect on the main resonance are investigated. Through a careful choice of YIG and transducer parameters, the interference effects of the width mode resonances with the main resonance are minimized. As a result, highQ tunable microwave resonators with a tuning range from 2–20 GHz, insertion loss less than 10 dB, and spurious rejection better than 10 dB could be designed and fabricated. This MSSW resonator could be used to construct a tunable low-phase-noise feedback oscillator. However, the tuning range of this MSW feedback oscillator is limited by the phase change of the external amplifier circuit.     

Recent developments in two-port YIG delay lines

A new type of two-port YIG delay line has been designed and realized which makes use of the YIG acoustic birefringence in order to obtain the smallest level of losses for the transmitted signal through the YIG bar. A minimum value of 26 dB was measured at 2.5 GHz for a 3.5-µs delay and a 3-dB bandwidth of 160 MHz.     

Distributed feedback laser diode (DFB-LD) to single-mode fiber coupling module with optical isolator for high bit rate modulation

A distributed feedback laser diode (DFB-LD) module for single-mode fiber coupling is described in the 1.5-μm wavelength region. An optical isolator is constructed in the two lens coupling circuit to stabilize the DFB-LD characteristics. It consists of a DFB-LD as a polarizer, a yttrium iron garnet (YIG) plate and an analyzer. Coupling characteristics and attainable isolation of the proposed circuit have been studied theoretically and experimentally. The effect of reflected light on the DFB-LD characteristics such as relative intensity noise (RIN) and oscillation spectrum has been experimentally investigated taking into account the polarization of the reflected light. It has been clarified that the DFB-LD can function as an effective polarizer with an extinction ratio of more than 20 dB. The DFB-LD module was successfully fabricated to have stable spectrum characteristics and to sufficiently suppress the noise caused by reflections. It has been confirmed by a long haul transmission experiment that this module is applicable to large capacity optical fiber transmission systems.     

Low-loss GaAs/GaAlAs strip-loaded waveguides with high coupling efficiency to single-mode fibres

We report measurements of low-loss MOVPE-grown GaAlAs/GaAs strip-loaded waveguides with high coupling efficiency to single-mode fibres. A propagation loss of 2 dB/cm and a coupling efficiency of 70% has been achieved for a p+-i-n+-structure waveguide. A propagation loss of 0.7 dB/cm and a coupling efficiency of 61% has also been achieved for an n?-i-n?-structure waveguide.     

YIG tuning of a stripline Gunn oscillator

A YIG sphere is used to provide frequency tuning in an X-band Gunn-effect stripline oscillator circuit. A tuning range of 1 GHz with a power output variation of 7.4-9 mW is achieved. It is suggested that the technique has application in microwave integrated circuits, particularly where FM noise reduction is important.     

Frequency selective limiters for high dynamic range microwavereceivers

A broadband frequency selective limiter (FSL) which provides over 14 dB of limiting across more than an octave bandwidth is described. The limiter is fabricated with epitaxially grown YIG (yttrium iron garnet) films in a stripline configuration and has a threshold power level of below 0 dBm. Individual limiter strips limit microwave signals in the 1-100-mW range across more than an octave of bandwidth. Multiple FSLs have been cascaded with amplifiers to allow compression of microwave signals with a power range of 60 dB into a range of less than 5 dB     

YIG magnetoelastic two-ports for microwave pulse compression

By coupling to the magnetoelastic spin-wave mode in YIG crystals with microwave acoustic transducers, dispersive two-port components can be realized. Preliminary characteristics of such a device employing a CdS shear transducer are reported in the UHF range. Elastic coupling losses, spin-wave limiting characteristics, dynamic range, and delay dispersion linearity of YIG devices are discussed for microwave pulse compression applications.     

Robust Two‐Phase Clock Oxide TFT Shift Register over Threshold Voltage Variation and Clock Coupling Noises

This letter describes a two‐phase clock oxide thin‐film transistor shift register that executes a robust operation over a wide threshold voltage range and clock coupling noises. The proposed circuit employs an additional Q generation block to avoid the clock coupling noise effects. A SMART‐SPICE simulation shows that the stable shift register operation is established for the clock coupling noises and the threshold voltage variation from ?4 V to 5 V at a line time of 5 μs. The magnitude of coupling noises on the Q(15) node and Qb(15) node of the 15th stage is respectively ?12.6 dB and ?26.1 dB at 100 kHz in the proposed circuit, compared to 6.8 dB and 10.9 dB in a conventional one. In addition, the estimated power consumption is 1.74 mW for the proposed 16‐stage shift registers at , compared to 11.5 mW for the conventional circuits.