Design equations for the reflectivity of deep-etch distributedBragg reflector gratings

This paper reports a computationally efficient, grid-independent method for calculating the reflectivity of deep-etch distributed Bragg reflector (DBR) gratings. The method employs Gaussian beam propagation in conjunction with a Fabry-Perot model that includes the effects of multiple reflections in multiple cavities. We include both, grating pitch and number of Bragg pairs in our analysis. We obtain very good agreement with results generated by a Helmholtz equation solver     

100% reflectivity Bragg reflectors produced in optical fibres by single excimer laser pulses

It is shown for the first time that fibre gratings with reflectivities in excess of 99.8% and fractional bandwidths of 0.005 (7.5 nm or 970 GHz at 1550 nm) can be written by interferometric side exposure of a fibre core to a single 40 mJ UV pulse of 20 ns duration at 248 nm. These highly efficient reflectors are formed by a new mechanism in which the core glass fuses, resulting in a very large periodic modulation of the refractive index. They are stable at temperatures as high as 800 degrees C.<>     

一种高选择性的宽带滤波功分器

为了实现无线通信系统的小型化,设计了一种同时具有滤波和功分功能的器件.将传统Wilkinson功分器中的两个四分之一波长传输线替换为两个具有带通响应的滤波器.同时,为了实现两个端口之间良好的隔离,将一个电阻安放在两个输出端口之间.利用奇偶模的分析方法,推导出了该滤波功分器的设计公式.实验结果表明,该器件的3 dB带宽达到了62%,在低频段和高频段的抑制度分别达到了38.4 dB和31.4 dB（2.67f₀）,该器件非常适用于小型化无线通信系统.     

Large reflectivity modulation using InGaAs-GaAs

The first reflection modulator using electroabsorption in strained InGaAs-GaAs quantum wells is reported. With an insertion loss of 1.9 dB and a reflectivity change of 42% at room temperature, the modulator is comparable to the best devices reported in GaAs-Al-GaAs system. A framework is presented for examining the tradeoff between insertion loss and modulation ratio from a theoretical perspective and compare the predicted limits to reported devices     

Synthetic aperture radar calibration using reference reflectors

A simple expression for the terrain backscatter coefficient is derived in terms of the integrated power of an adjacent known radar reflector in a synthetic aperture radar (SAR) image. It is shown that this technique for SAR image calibration is independent of the radar system focus or partial coherence and thereby possesses an important advantage over the usual technique, which relies on an estimate of the peak of the reflector impulse response. Results from airborne SAR overflights of corner reflectors and active radar calibrators are used to demonstrate the validity and consistency of the method and to show that the method is robust under defocus caused by an incorrect FM rate or inadequate motion compensation of data collected during turbulence. It is also shown that the fading errors associated with the integral method are comparable to or slightly worse than those associated with the peak estimation method. However, this small disadvantage is outweighed by the fact that the integral method is independent of actual resolution     

一种利用反射电极偏压的半反半透LCD

介绍了一种VA模式反射电极偏压的常黑单盒厚半反半透LCD.在透射区,形成连续且均匀的贯穿液晶层的电场;而在反射区,电场则主要由电极表面形状控制.由此,可使透射区的位相延迟约是反射区的2倍.这样一种半反半透LCD不论透射区还是反射区都有很高的光透过率(＞90%),同时二者灰阶特性重合度也很好.     

Analysis of blended rolled edge reflectors using numerical UTD

The uniform geometrical theory of diffraction (UTD) concept is used to predict the scattered fields in the target zones of compact-range reflectors. Since the necessary diffraction coefficients are not known in a closed form, a numerical method to calculate the diffraction coefficients is described. In the numerical method, the problem is reduced to two dimensions, and physical optics line integration is used to compute the diffraction coefficients. Thus, the method is computationally efficient. The method is used to analyze two compact-range reflectors. The results obtained using the numerical UTD show good agreement with the scattered fields obtained using a corrected physical optics surface integration     

Electrical and optical characteristics of n-type-doped distributedBragg mirrors on InP

The development of high reflectivity and low electrical resistivity Bragg mirrors is crucial for the emergence of 1.55-μm vertical-cavity surface-emitting lasers (VCSEL's). Here, we report on three different n-type-doped semiconductor Bragg mirrors which are all lattice-matched to InP. The material systems are InGaAsP-InP, AlGaInAs-AlInAs, and AlGaAsSb-AlAsSb and the layers are designed for 1.55-μm operation. The influence of the structural and intrinsic properties of the different heterostructures on the electrical resistivity and optical reflectivity is analyzed for the three samples     

Optimisation of SIW bandpass filter with wide and sharp stopband using space mapping

This work presents a substrate integrated waveguide (SIW) bandpass filter with wide and precipitous stopband, which is different from filters with a direct input/output coupling structure. Higher modes in the SIW cavities are used to generate the finite transmission zeros for improved stopband performance. The design of SIW filters requires full wave electromagnetic simulation and extensive optimisation. If a full wave solver is used for optimisation, the design process is very time consuming. The space mapping (SM) approach has been called upon to alleviate this problem. In this case, the coarse model is optimised using an equivalent circuit model-based representation of the structure for fast computations. On the other hand, the verification of the design is completed with an accurate fine model full wave simulation. A fourth-order filter with a passband of 12.0–12.5 GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return loss is better than 17.4 dB in the passband and the rejection is more than 40 dB in the stopband. The stopband is from 2 to 11 GHz and 13.5 to 17.3 GHz, demonstrating a wide bandwidth performance.     

Offset dual-reflector multiple-beam antennas using circularly symmetric main reflectors

An investigation into the multiple-beam capability of offset antennas using circularly symmetric main reflectors is described. The efficiency and sidelobe performance of systems designed to produce beams up to 4.6° either side of boresight with reflector diameters ranging from 100 to 300 wavelengths are shown to make the antennas suitable for multiple-satellite-access earth stations. Comparison is made with a nonsymmetrical main-reflector antenna designed for the same requirements.     

Characterisation of a fibre Raman oscillator using fibre grating reflectors

We have constructed a completely integrated fibre Raman oscillator using two fibre grating reflectors. This was synchronously mode-locked using a CW mode-locked Nd:YAG laser operating at 1.06?m. Spectral and temporal characteristics of the Raman oscillator are presented.     

Feedforward pulse width modulators for switching power converters

This paper describes pulse width modulators (PWMs) that employ feedforward compensation to improve the steady-state and dynamic responses of power converters. It is shown how ideal feedforward PWMs (FF-PWMs) can be constructed for all duty-ratio controlled switch-mode power converters operating in the continuous conduction mode. A power converter with FF-PWM behaves at low frequencies as a linear power amplifier with constant gain independent of operating conditions. The proposed FF-PWM can be easily implemented using the same building blocks found in conventional PWM controllers. Experimental and simulation examples are included to illustrate applications of the FF-PWM     

Voltage-controlled distributed Bragg reflectors for modulation andintegrated power monitoring of vertical-cavity surface-emitting lasers

The authors demonstrate a voltage-controlled distributed Bragg reflector with a very high off-state reflectivity and low-voltage operation suitable for use within a vertical-cavity surface-emitting laser. The unbiased peak reflectivity approaches 99.8% at 980 nm, which may be modulated through the quantum-confined Stark effect by 1%. The mirror allows measurement of photocurrent to monitor VCSEL output power     

高精度测量高功率光纤激光器低反光纤光栅反射率的方法

作为高功率光纤激光器谐振腔的输出端,低反光纤光栅（Output Coupler,OC）的反射率值较小,采用基于透射谱的方法测量OC反射率时,光源功率不稳定或光谱仪测量的误差,会使得OC反射率的测量结果产生较大误差。因此提出一种基于菲涅耳反射原理,获得反射谱测量OC反射率的方法。通过实验对该方法进行了验证,结果表明该方法的测量精度和稳定性有了显著提高。同时分析了该方法带来的带宽测量不准确的问题,提出了使用折射率匹配液的方法解决了该问题。     

Compact microstrip lowpass filter with wide stopband and sharp roll-off using tapered resonator

In this article, a novel microstrip lowpass filter (LPF) with specifications such as sharp cut-off, wide stopband, low insertion loss and high return loss using tapered resonator is presented. The LPF has cut-off frequency of 1.11 GHz, where unwanted harmonics are suppressed by novel tapered cells. The bandwidth is enhanced, and the size is reduced as compared to the conventional tapered filter. The transition band is approximately 0.29 GHz from 1.11 to 1.4 GHz with corresponding attenuation levels of –3 and –20 dB, respectively. The stopband with greater than –20 dB rejection is from 1.4 to 8.9 GHz, insertion loss in the passband is less than 0.1 dB, return loss is less than –18 dB and the overall size of the filter is 0.12 × 0.073 λ_g. The proposed filter is fabricated and measured. The simulation and measurement results are in good agreement. This LPF is designed for microwave communication applications, especially wireless video transmitters.     

Determination of wavelength dependence of the reflectivity at ARcoated diode facets

Wavelength dependence of the reflectivity at an antireflection (AR) coated diode facet has been determined by comparing the spontaneous emission spectra obtained under the same bias condition before and after this facet is AR coated. Reliable measurements can be achieved by proper choice of the bias current     

Class of transfer functions with finite stopband attenuation with both passband and stopband exhibiting equiripple behaviour

A new family of transfer functions is derived in which three parameters, passband ripple, stopband attenuation and stop-band ripple, are assignable. The method uses standard elliptic transfer functions, which are transformed. Formulas relating the desired response to the prototype elliptic-transfer-function characteristics are given.     

Compact wide stopband lowpass filter using spiral loaded tapered compact microstrip resonator cell

A new spiral loaded tapered compact microstrip resonator cell (SPLT-CMRC) is presented. The addition of spiral stubs to the CMRC creates transmission zeroes in the stopband which extended the stopband of the ?lter. The proposed resonator is used to design a compact lowpass ?lter (LPF) with wide and high rejection in stopband. The fabricated ?lter has a 3 dB cutoff frequency at 8 GHz. The insertion loss in the passband is less than 0.2 dB from DC to 7.2 GHz. The proposed ?lter has wide stopband from 9.47 to 40 GHz with attenuation level of ?20 dB. The demonstrated filter is designed and fabricated. There is a good agreement between the measured and simulated S-parameters.     

A novel microstrip lowpass filter with sharp roll-off and ultra-wide stopband using SICMRC

This paper presents a novel microstrip lowpass filter with sharp roll-off and ultra-wide stopband using stepped-impedance resonator and bended transmission line structure. The filter includes stepped-impedance prototype filter and stepped-impedance compact microstrip resonator cells that are combined in one structure. The proposed filter has good specifications such as sharp roll-off, ultra-wide stopband and low insertion loss. The transition band is approximately 0.25 GHz from 1.75 to 2 GHz with corresponding attenuation levels of ?3 and ?40 dB. The attenuation level in the stopband is better than ?20 dB that is achieved from 1.94 to 23 GHz, and the insertion loss in the passband is less than 0.4 dB. The proposed filter is fabricated and measured, and the simulation and measurement results are found to be in good agreement with each other.     

Measurement of facet reflectivity of antireflection-coatedelectroabsorption modulator using induced photocurrent

A new method to measure the facet reflectivity of an antireflection (AR)-coated electroabsorption (EA) modulator in the region of operating wavelengths is proposed. First, by measuring the induced photocurrent and reflectance simultaneously at the front facet of an EA waveguide, the cleaved facet reflectivity and propagation loss are determined. After coating the facet with AR, the residual reflectivity of AR-coated facet is obtained from the measured photocurrent spectra and the predetermined facet reflectivity. We demonstrate the reflectivity of a double-layer AR-coated EA modulator can be measured to be ~4×10^-4 at 1.55 μm for TE polarization by using the proposed technique