Sidelobe suppression of s.a.w. resonant filter using twin-turn reflectors

Sidelobe suppression of twin-turn reflector filters is accomplished using longitudinal deformations of i.d.t.s. 41° Y-X LiNbO3 substrate is used, and in experiment the Japanese t.v.i.f. specification is nearly satisfied.     

嵌埋材料对分布式布拉格反射镜腔共振模式的影响

低维材料嵌入微腔已经广泛应用于纳米激光器和探测器等。为了实现增益材料和光学微腔之间的有效耦合,需要深入研究嵌埋材料对腔共振模式的影响。本文主要讨论了嵌埋材料的厚度、位置、腔层厚度以及分布式布拉格反射镜的对数对腔供着模式的影响。结果表明,腔共振模式随嵌埋材料位置的不同呈现周期性变化并且在λ/2光程周期内存在最大峰位移。最大峰位移随腔层厚度增加而减小,但与嵌埋材料的厚度成正比。分布式布拉格反射镜的对数不影响腔共振模式。这些结果为光学器件的设计和实验现象的分析提供了指导,并且可以应用于不同波长分布式布拉格反射腔结构。     

Compact lowpass filter using spiral compact microstrip resonant cells

A novel lowpass filter using spiral compact microstrip resonant cells (SCMRCs) for size reduction is presented. Four SCMRC resonators as open stub lines are connected at both sides of an SCMRC resonator so that the port impedance at the lowpass band is matched to 50 /spl Omega/. The proposed lowpass filter has compact circuit size and wide stop-band. A demonstration lowpass filter is designed, fabricated and measured. It shows low insertion loss, flat response in the lowpass band and wide stop-band.     

An adaptive resonant filter

A solid-state adaptive (analog storage) device with stable electrical characteristics is described and demonstrated. The device is a resonant bandpass electronic filter with adaptable voltage gain; that is, the voltage gain-frequency transfer characteristic can be "set" to different values of attenuation by the application of an adapt signal and will retain that "setting" after the adapt signal has been removed. Ferroelectric materials are used as the dielectric in a filter structure composed of two capacitors bonded together so that resonant mechanical vibrations established in one (the input resonator) are coupled to the other (the output resonator). Converse and direct piezoelectric effects generate the mechanical vibrations and the output voltages, respectively. Ferroelectric effects in either capacitor provide the analog storage capabilities. The acoustical coupling mechanism employed in the device design results in electrically stable device characteristics. Previous ferroelectric adaptive devices used unstable field effect coupling mechanisms which led to unacceptable device performance. Experimental adaptive resonant filters fabricated with ceramic lead zirconate-lead titanate material compositions are discussed. These filters have electronic Q values near 100 at resonant frequencies in the range 10²to 10⁷Hz. The voltage gain-frequency characteristic has a maximum value at resonance of about 0 to +10 dB. Application of a voltage adapt pulse (100 to 300 volts) of low energy (mJ) to either side of the filter can adapt the entire gain characteristic by any value between 0 and about -60 dB within an arbitrary switching time (limited to a practical range of roughly 10⁺³to 10^-4seconds) as determined by the pulse amplitude. Voltage gain settings are electrically stable and can be reproduced by the same or an equivalent sequence of adapting pulses.     

光纤激光器共腔法纵模选择技术

复合腔法光纤激光器谐振腔结构灵活,可以根据需要构成各种结构实现纵模选择.但稳定性差是制约其应用的主要原因,为提高光纤激光器纵模选择的稳定性及抗干扰能力,在复合腔基础上提出“共腔结构”光纤激光器这一概念.分别采用传输矩阵和自由光谱范围(FSR)两种方法详细分析了“共腔结构”光纤激光器的特性,理论分析证明:共腔结构可有效增...     

Current mode multifunction filter using two CDBAs

This paper presents a cascadable current-mode (CM) multifunction biquadratic filter. The proposed circuit realizes all five different filter transfer functions employing only two current differencing buffered amplifiers (CDBAs), while previously reported CM multifunction filters require more CDBAs and more passive component count for the same number of filter transfer function realizations. Examples for different filter transfer functions are given along with the results of circuit simulations. It is shown that theoretical and simulation results are in good agreement.     

Nth order current mode universal filter using MOCCCIIs

This article presents a new current mode single-input-multiple-output nth order universal filter. The proposed circuit employs (n + 1) number multiple output second generation current conveyors and n number grounded capacitors only. Presented circuits can realize current mode low pass, high pass, band pass, notch and all pass responses simultaneously at different high output impedance terminals. The current mode filter circuit provides low input impedance by selecting the proper value of bias current and also has high output impedance, which is suitable for cascading. The circuit offers some important features such as resistor less realization, no passive component matching constraints, low sensitivity, electronic tunability and active-C realization. The functionality of the proposed filter circuit is tested with the PSPICE simulation, which is found to agree well with the proposed theory.     

Compact wideband bandpass filter using quad mode resonator

This paper presents a compact wideband bandpass filter for TETRA band applications. The proposed filter design is based on a quad mode resonator designed using small rectangular loop loaded with four Stepped Impedance Stubs (SISs) and a short circuit stub. The four modes of the resonator help in generating a wide passband. The use of SISs makes the filter compact. In addition to four transmission poles, the resonator inherently generates a transmission zero above the higher end of passband. Two transmission zeros are generated by the input/output coupling which helps in increasing the selectivity and also for achieving wide stopband. This filter provides a 3 dB fractional bandwidth of 30.33% and maximum insertion loss of 1.3 dB at the center frequency 0.36 GHz with a compact size of 0.125 λ_g × 0.085 λg (4.1 × 2.78 cm²).     

Third order voltage mode universal filter using CCCII

This paper brings a multi input single output third order universal filter using second generation current controlled current conveyor (CCCII). The proposed structure consists of three CCCIIs and three capacitors for all filter responses. The universal filter offers all five sections of filter responses, namely: low-pass, high-pass, band-pass, notch filter and all-pass. The topology can provide all filter responses by the proper selection of input. The proposed universal filter offers some important features like no external resistor, minimum number of CCCIIs, no component matching constraint for filter response, electronically adjustable filter response using bias current of CCCIIs and many more. The workability of the proposed structure is well verified with PSPICE in which simulation results follow the theoretical one.     

Current mode allpass/notch and bandpass filter using single CCII

A current mode second-order allpass notch and bandpass filter using a single CCII, two grounded capacitors and four resistors is proposed. The allpass and notch output current signals, taken out through port z of a CCII and having high output impedance, can be obtained by tuning a resistor in the proposed network. The resonance angular frequency and quality factor of the new network have the advantages of low passive sensitivities and are insensitive to the current tracking error of the nonideal CCII.<>     

Broadband source tracking using adaptive directional filter withmaximally flat responses at null directions

A new algorithm for the tracking of broadband sources in linear arrays employing tapped delay line processing is presented and investigated. Using this technique, each broadband source is individually tracked in a time-multiplexed manner by steering a broadband null formed from the use of a tapped delay line filter whose weights are constrained to have a maximally flat frequency response at the nulling direction. To ensure that the other nulls are not changed while a particular null is being adjusted, a beamformer is employed to preprocess the element signals before adaptive processing. Since the new algorithm updates only one tapped delay line filter at any instant, the overall implementation complexity of the proposed algorithm is comparable with using the LMS algorithm directly on a broadband array. However, unlike the latter algorithm, the convergence behavior of the new algorithm is significantly faster and is almost independent of the external noise environment     

Self resonant IDT as a grating reflector of surface acoustic waves

An IDT, when resonantly loaded by a pure inductance, behaves as a perfect reflector of SAWs. It is shown that this ideal condition can be approached by using the self resonance of an IDT. The reflection coefficient of the self resonant IDT is calculated to be about 0.96 and is observed to be in the range 0.93 to 0.95. It is demonstrated that the frequency of self resonance at which the reflection peak and hence the transmission null occurs can be shifted by an external capacitor connected across the self resonant reflector IDT.     

A new electronically tunable current mode universal filter using MO-CCCII

A new electronically tunable universal current mode biquad filter structure employing three multiple output current controlled conveyors (MOCCCII) and two grounded capacitors is presented. The proposed filter offers the following advantageous features: low input impedance and high output impedance—a desirable property of current mode filters; realization of low pass, band pass, high pass, notch, and all pass; no matching constraint; low sensitivity performance and use of grounded capacitors suitable for integration. The practical design problems due to nonlinearities of MOCCCIIs have also been addressed. The feasibility of the design is confirmed via SPICE simulations.     

Compact and selective lowpass filter with very wide stopband using tapered compact microstrip resonant cells

A novel microstrip lowpass filter is proposed. It consists of a simple tapered structure using periodical compact microstrip resonant cells. Owing to the introduction of the tapered structure, the proposed lowpass filter has successfully addressed simultaneously the problems of compactness, matching, selectivity, insertion loss and the suppression of spurious frequency bands. A demonstration filter has been designed, fabricated and tested to show the validity of the proposed structure.     

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.     

Trapped-energy flexural mode filter

An electromechanical filter using trapped-energy flexural modes in a rectangular plate is proposed. The filter is amenable to fabrication by planar techniques and it can operate in the l.f. range, including the voice band. Bandwidth is easily controllable. A considerable gain in size can be obtained with respect to flexural bar filters.     

Compact mode expanders using resonant coupling between a taperedactive region and an underlying coupling waveguide

A novel technique for enhanced laser-fiber coupling, based on resonant power coupling between a tapered active waveguide and an underlying coupling waveguide, is presented. Spot-sizes are transformed from 2.0×1.1 μm in the active region to 6.0×3.1 μm in the coupling waveguide, over a length of 200 μm, with a mode transformation loss of only 0.36 dB. Butt-coupling efficiencies of 55% (2.6 dB loss) are estimated to standard cleaved single-mode fibers at 1.55 μm. The proposed device requires a single epitaxial growth and conventional processing techniques, making it amenable for low-cost manufacturing     

Compact resonant bandpass filter based on PBG structure

A new resonant bandpass filter based on a photonic band gap (PBG) structure is designed and optimised. The finite-difference time-domain method is applied to characterise the proposed filter. The filter is much easier to fabricate, more compact and simpler to design than the conventional parallel-coupled line filter, has wide stopband and steep and deep upper bandstop. The filter length is about one guiding wavelength (/spl lambda/e). A semiconductor-based structure is realised using microelectronics technology and good agreement between the experimental and simulation results has been achieved.     

Broadband configurable bandstop filter with composite tuning mechanism

The design and experimental performance of a bandstop filter which combines both continuous and discrete tuning using varactor and PIN diodes to achieve a two-octave tuning range is reported. The topology allows independent control of the passband and stopband frequencies.     

Above-threshold mode discrimination in external reflector andphase-shifted DFB lasers

The longitudinal mode discrimination above threshold in both distributed feedback lasers with one external reflector and those with phase-shifted grating structures is studied. By numerically solving a pair of coupled mode equations, it is shown that when these types of lasers have nonsaturable index coupling, they lose their mode discrimination at powers only a few times the saturation power of the medium due to the effects of spatial hole burning