Wide-wavelength polarization-independent optical modulator based on tensile-strained quantum well with mass-dependent width

We have fabricated a multiple-quantum-well (MQW) waveguide optical modulator incorporating tensile strain and quantum well with mass-dependent width (QWMDW) for the first time. The structure was built on a strain relief InAlGaAs buffer layer grown on a GaAs substrate. Polarization-independent modulation with more than -10 dB extinction (at 8 V reverse voltage) was achieved over a very wide operating range, from 858 to 886 nm wavelength.     

Polarization-independent field-induced absorption-coefficientvariation spectrum in an InGaAs/InP tensile-strained quantum well

The authors report the absorption-coefficient variation of a tensile-strained InGaAs/InP quantum well measured throughout the spectral range near and away from the bandgap. They discuss the spectral absorption-coefficient variation spectra of an unstrained, a 0.15%, a 0.30%, and a 0.45% tensile-strained quantum well and show that the difference between the wavelengths of absorption-coefficient variation peaks for TE and TM modes becomes zero with 0.3% tensile strain. It is shown that this wavelength difference varies linearly with the magnitude of the strain     

Zero-bias modulation of tensile-strained InGaAs/InGaAsP quantum well lasers with wide phase margins

1 Gbit/s, zero-bias modulation with wide phase margins was achieved over a 20-100 degrees C temperature range with a tensile-strained InGaAs/InGaAsP quantum well laser emitting at a wavelength of 1.5 mu m.<>     

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     

Uniaxial, tensile-strained Si devices

Uniaxial, in-plane, tensile straining of silicon devices is reported. Strain is applied via mechanical techniques and then fixed by bonding to an appropriate substrate. Results are reported for diffused resistors and for some metal-oxide semiconductor field effect transistor (MOSFET) devices. Strain is introduced after device processing is complete, which enables full advantage to be taken of mainstream silicon processing technology. This macroscopic method is effective regardless of device size but has particular benefit in the deep submicron region. Mobility conductivity enhancement factors >2 for an applied strain of 0.05% are reported.     

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     

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.<>     

High-isolation polarization-independent quasi-optical circulator

A polarization-independent quasi-optical circulator having high isolation over a wide wavelength range is reported. The proposed quasi-circulator is composed of two polarization beam splitters, two pentagonal prisms, two nonreciprocal rotators, and two walkoff polarizing beam splitters. Its structure is very simple. A three-port quasi-circulator has been fabricated with single-mode fibers. Its insertion loss and isolation have been measured to be ⩽1.7 and ⩾48.6 dB, respectively, at the nominal wavelength of 1.3 μm. A loss ratio of over 47.0 dB has been realized. The wavelength range over a 50-dB isolation between two fibers was measured to be about 50 nm     

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     

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-performance 770-nm AlGaAs-GaAsP tensile-strained quantum-welllaser diodes

Experimental results on tensile-strained Al_0.3Ga_0.66As-GaAs_0.78P_0.22 separate-confinement-heterostructure single-quantum-well (SCH-SQW) laser diodes are reported. Threshold current density as low as 260 A/cm² for broad-stripe lasers with a cavity length of 1500 μm has been observed. Broad-stripe devices have operated cw at room temperature with output power as high as 620 mW/facet. Ridge-waveguide lasers have exhibited cw threshold currents as low as 13.5 mA and output power of 90 mW. The output of the tensile-strained lasers is TM polarized     

A tunable polarization-independent liquid-crystal Fabry-Perotinterferometer filter

The authors propose a simple structure for a tunable polarization-independent wavelength-selective filter. This successfully fabricated filter consists of a liquid crystal Fabry-Perot interferometer, a γ/4 plate, and a mirror. The input light is divided into a transmitted light and a reflected light. The polarization of this reflected light is rotated 90° by the γ/4 plate and the mirror and then this light is input again into the filter. The bandwidth is 0.48 nm and the tuning range is 50 nm. Fiber-to-fiber loss is approximately 3.9 dB and polarization dependence of the loss is approximately 0.3 dB     

Low-threshold tensile-strained InGaAs-InGaAsP quantum-well laserswith single-step separate-confinement heterostructures

The authors studied tensile-strained InGaAs-InGaAsP quantum-well lasers with single-step separate-confinement heterostructures (SCH). They obtained threshold currents below 2 mA at 20°C and below 10 mA at 100°C with indium mole fractions of 0.3 and 0.35 in the active layers. They found that the poorer carrier confinement of the longer wavelength SCH layer lowered the characteristic temperature at high temperatures. A laser with two In_0.35Ga_0.65As wells and a 1.1-μm composition InGaAsP SCH layer produced a 1.6-mA CW threshold current at 20°C and lasing at 120°C. Using this laser, very short lasing delays under zero-bias current over a wide temperature range and 2 Gb/s modulation under zero-bias current at 70°C were achieved     

偏振无关的电光多波长滤波器设计

基于双折射铌酸锂（LiNbO3）晶体的电光效应,设计了一种偏振无关的二端口波导型多波长可调谐滤波器。在非对称干涉仪的上下分支波导上,耦合电极与相移电极周期性交叉级联实现模式的偏振转换。利用琼斯矩阵的Z 域分析,求解驱动电压模拟实现多个波长的同时选择。仿真实现了自由光谱范围（FSR）内分布任意的窄带多波长输出。波长中心处传输率为100%;旁瓣大小受到所选波长个数的影响,三个波长同时滤波的旁瓣可达12 dB。同时得到了梳状滤波输出谱,其通带顶部平坦,旁瓣可达20 dB 以上。     

消偏振二维二元闪耀光栅设计

为减小成像光谱仪的偏振敏感度并提高其定量化探测精度,提出一种透射式消偏振二维二元闪耀光栅。它在两个正交方向上都具有周期性槽形单元,每个槽形单元包含7个子周期。每个子周期的介质占空比在两个方向上是独立的,可同时调制TE和TM偏振态的等效折射率,以此优化光栅偏振特性。本文将等效介质理论拓展到二维情况,设计了以熔石英为基底,工作波段为0.6~0.8μm的高衍射效率消偏振二维二元闪耀光栅。光栅两正交方向周期分别为3.31μm和0.473μm。仿真结果表明,在参考波长0.7μm处TE和TM偏振态衍射效率分别为79.5%和79.6%,0.6~0.8μm波段范围内TE和TM偏振态衍射效率均高于70%,偏振敏感度低于2.6%。与一维二元闪耀光栅相比,二维二元闪耀光栅具有高衍射效率、低偏振敏感度和易制作的优势。所得结论可用于指导实际应用中透射式二元闪耀光栅的设计,可望在光栅型高光谱成像仪中得到应用。     

Wide-band orthomode transducers

A summary of the results of a mainly experimental investigation into the development of wideband orthomode transducers (OMTs) is presented. It is shown that satisfactory performance for many applications is possible over bandwidths in excess of 2:1. The wideband return loss and cross-polarization behavior are given where the OMT used is measured in conjunction with a wideband corrugated horn. Two types of OMT are considered: one based on a finline technique and the other on a quad-ridged waveguide geometry. Overall, the latter design gives superior performance     

Wide-band superconductive chirp filters

Chirp filters are described that consist of a miniature tapped superconductive stripline. The stripline consists of 40-μm-wide niobium thin films in a spiral pattern on 125-μm-thick silicon wafers, and tapping is effected by backward-wave couplers between neighboring lines. Sophisticated fabrication and packaging techniques have led to a now mature technology. Devices with 2.6-GHz bandwidths and time-bandwidth products of 98 are routinely fabricated that exhibit amplitude errors within a few tenths of a decibel and phase errors within a fraction of a degree of theoretical. In pulse-compression tests, matched amplitude-weighted devices yield peak relative side-lobe levels of -32 dB     

Wide-band planar monopole antennas

The circular disc monopole (CDM) antenna has been reported to yield wide-impedance bandwidth. Experiments have been carried out on a CDM that has twice the diameter of the reported disc with similar results. New configurations are proposed such as elliptical (with different ellipticity ratios), square, rectangular, and hexagonal disc monopole antennas. A simple formula is proposed to predict the frequency corresponding to the lower edge of the bandwidth for each of these configurations. The elliptical disc monopole (EDM) with ellipticity ratio of 1.1 yields the maximum bandwidth from 1.21 GHz to more than 13 GHz for voltage standing wave ratio (VSWR)<2     

Low-threshold 833-nm GaAsP-AlGaAs tensile-strained quantum-well laser diodes

We report the demonstration of TM polarized laser emission at 833 nm from GaAsP-AlGaAs quantum well laser structures grown on GaAs substrates by low-pressure organometallic vapor phase epitaxy for the first time. This is the longest wavelength near infrared TM polarized laser ever reported. Broad area laser diodes containing single GaAs/sub 0.95/P/sub 0.05/ quantum well lased at a low threshold current density of 280 A/cm/sup 2/ for a cavity length of 1 mm and with a high differential quantum efficiency of 32%/facet for cavity length less than 500 /spl mu/m.