Non-photorefractive CW Tm-indiffused Ti:LiNbO/sub 3/ waveguide laser operating at room temperature

We report laser operation at 1.81 /spl mu/m and 1.85 /spl mu/m in a Tm/sup 3+/:LiNbO/sub 3/ Ti-diffused waveguide doped by thermal indiffusion at high temperature. We believe this is the first time lasing has been seen in Tm:LiNbO/sub 3/ at room temperature. Continuous-wave operation was achieved at room temperature with a threshold of 42 mW launched pump power. The output power was observed to be stable, without any sign of photorefractive damage.     

KNbO_3电光偏转器

分析了ＫＮｂＯ３晶体的电光性质，利用电光张量系数γ３３加工成电光偏转器，偏转梯度电场由四个柱面电极产生。实验结果表明，在结构参数、通光口径及其它条件均等同的情况下，该器件的基本品质因子约是ＬｉＮｂＯ３电光偏转器的２倍。     

Proton Isolation for GaAs Integrated Circuits

Significant improvement in the electrical isolation of closely spaced GaAs integrated circuit (IC) devices has been achieved with proton implantation. Isolation voltages have been increased by a factor of four in comparison to a selective implant process. In addition, the tendency of negatively based ohmic contacts to reduce the current flow in neighboring MESFET's (backgating) has been reduced by at least a factor of three. The GaAs IC compatible process includes implantation of protons through the SiO/sub 2/ field oxide layer and a three-layered dielectric- Au mask which is definable to 3-µm linewidths and is easily removed. High temperature storage tests have demonstrated that proton isolation, with lifetimes on the order of 10/sup 5/ h at 290° C, is not a lifetime limiting component in a GaAs IC process.     

Measurement of reduction in SHG coefficient of LiNbO/sub 3/ by proton exchanging

The SHG coefficient of a proton-exchanged layer of LiNbO/sub 3/, relative to the bulk value, has been measured for the first time by non-phase-matched SHG using a grating sample. It was found that the d/sub 33/ coefficient is reduced to approximately 0.5 of the bulk value by proton exchanging in pure benzoic acid.<>     

Blue light generation by frequency doubling CW diode laser radiation in KNbO/sub 3/ channel waveguides

Blue light at 430 nm is generated by frequency doubling CW AlGaAs diode lasers in ion-implanted KNbO/sub 3/ channel waveguides. Stable Cerenkov-type second harmonic generation is demonstrated at room temperature without the the need for precise temperature control. With 97 mW of fundamental power in a channel guide of 5.6 mm length a blue light output power of 1.1 mW is achieved. Efficiencies of more than 40%/W cm are obtained by adding up the contributions from several modes of the multimode waveguide.<>     

KNbO_3:Fe自泵相位共轭

本文提出KNbO_3:Fe光折变晶体的异形切割和最佳实验配置,首次在室温下获得内环腔自泵相位共轭,反射率高达～60％。     

Modulation bandwidth enhancement of all-optical modulators based on photo-induced intersub-band absorption in GaAs/AlGaAs quantum wells by proton bombardment

All-optical modulators at 10 mu m based on photo-induced intersub-band absorption in multiquantum wells can exhibit very large extinction ratios. However, the frequency response of such modulators is imposed by the electronic band-to-band recombination processes which usually limit the bandwidth to a few tens of megahertz. The authors show that the modulation bandwidth can be substantially improved by proton bombardment of the multiquantum wells. The results of experiments on a 250 period GaAs/Al/sub 0.25/Ga/sub 0.75/As quantum well structure agree closely with calculations. Modulation bandwidths larger than 200 MHz appear feasible with implantation doses less than 10/sup 13/cm/sup -2/.<>     

Broad-band distributed Bragg reflectors with photorefractive Ti : Cu : LiNbO/sub 3/ waveguide gratings

We have realized broad-band distributed Bragg reflectors with photorefractive gratings recorded at 441.6 nm in channel Ti : Cu : LiNbO/sub 3/ waveguides. Proton-assisted copper exchange is used to enable a high level of copper doping and, thereby, achieve an extremely large modulation of refractive index (/spl ges/ 5/sup */10/sup -4/) within a photorefractive grating. Experimental structures demonstrate reflectivities up to 17% with full-width at half-maximum bandwidths in excess of 1.2 nm at center wavelengths around 1.55 /spl mu/m.     

A novel wet-etching method using electric-field-assisted proton exchange in LiNbO/sub 3/

This paper presents a novel wet etching method for LiNbO/sub 3/ using electric-field-assisted proton exchange. By applying voltage with appropriate polarity on designed electrodes placed on both sides of substrate, the induced electric-field distribution can effectively suppress or enhance proton diffusion in the lateral and depth directions. Thus, the proton-exchanged range in LiNbO/sub 3/ can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO/sub 3/ acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO/sub 3/ substrate. Under appropriate electrode and proton-exchange parameters, a vertical sidewall with smooth surface is successfully produced, which makes fabricating reflection mirrors and T-junctions in LiNbO/sub 3/ possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO/sub 3/.     

Temperature and substrate-impedance dependence of noise figure of monolithic RF inductors on silicon

In this letter, we analyze the effects of temperature (from -50/spl deg/C to 200/spl deg/C) and substrate impedance on the noise figure (NF) and quality factor (Q-factor) performances of monolithic RF inductors on silicon. The results show a 0.75 dB (from 0.98 to 0.23 dB) reduction in minimum NF (NF/sub min/) at 8 GHz, an 86.1% (from 15.1 to 28.1) increase in maximum Q-factor (Q/sub max/), and a 4.8% (from 16.5 to 17.3 GHz) improvement in self-resonant frequency (f/sub SR/) were obtained if post-process of proton implantation had been done. This means the post-process of proton implantation is effective in improving the NF and Q-factor performances of inductors on silicon mainly due to the reduction of eddy current loss in the silicon substrate. In addition, it was found that NF increases with increasing temperature but show a reverse behavior within a higher frequency range. This phenomenon can be explained by the positive temperature coefficients of the series metal resistance (R/sub s/), the parallel substrate resistances (R/sub sub1/ and R/sub sub2/), and the resistance R/sub s1/ of the substrate transformer loop. The present analyzes are helpful for RF designers to design less temperature-sensitive high-performance fully on-chip low-noise-amplifiers (LNAs) and voltage-controlled-oscillators (VCOs) for single-chip receiver front-end applications.     

Internal fluorescence induced refreshment of thermally fixed photorefractive grating in Ti:Fe:Er:LiNbO/sub 3/ for stable laser emission

It is shown that thermally fixed photorefractive gratings fabricated for waveguide lasers in Ti:Fe:Er:LiNbO/sub 3/ can be refreshed and stabilised by the upconverted green fluorescence from Er/sup 3+/ ions. Spectral properties of such refreshed gratings are found to be superior and are excellent for a single-frequency laser emission.     

A highly damage-resistant Zn:LiNbO/sub 3/ ridge waveguide and its application to a polarization-independent wavelength converter

We have fabricated a periodically poled ridge waveguide using a liquid phase epitaxy (LPE)-grown Zn:LiNbO/sub 3/ substrate. The waveguide can confine both the transverse electric and transverse magnetic mode. Its strong resistance to photorefractive damage enables stable parametric amplification. We demonstrate polarization-independent wavelength conversion using polarization diversity in a single waveguide.     

Optical activity induced in Bi/sub 4/Ge/sub 3/O/sub 12/ waveguides by ion implantation

The authors report data for ion implanted Bi/sub 4/Ge/sub 3/O/sub 12/ in which the modified material becomes optically active. The optical rotary power, after implantation and annealing, increases from zero to some 90 degrees /mm. The effect is attributed to an ion beam induced relaxation to a modified BiGeO phase.<>     

Proton-implanted shallow-ridge quantum-cascade laser

We demonstrate a shallow-ridge quantum-cascade laser (QCL) with performance comparable or better than that of deep-ridge QCLs fabricated from the same wafer. The shallow-ridge QCL emits at /spl ap/4 /spl mu/m with a 4.6-4.8 kA/cm/sup 2/ threshold current density at room temperature which is similar to the deep-ridge QCL. At the same time the shallow-ridge QCL shows a better temperature stability, T/sub 0/=160 K, than the deep-ridge QCL, with T/sub 0/=120 K. The increase in the characteristic temperature of the shallow-ridge laser compared to the deep-ridge laser results from the improved heat dissipation out of the laser ridge through the lateral heat flow. Lateral spreading of the injection current-usually a drawback of shallow-ridge lasers-is suppressed by proton implantation into the strain-compensated InGaAs-AlAs active region layers on either side of the ridge. In contrast to the case of In/sub 0.53/Ga/sub 0.47/As layers and of In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As heterostructures lattice matched to InP, the proton implantation of strain-compensated In/sub 0.73/Ga/sub 0.27/As-AlAs heterostructure on InP creates deep (180 meV) carrier traps, resulting in this material being electrically insulating even at room temperature.     

KNbO_3:Fe在632.8nm处的自泵相位共轭

本文报道在He-Ne激光的632.8nm实现KNbO_3:Fe自泵相位共轭。虽然光折变材料的耦合系数随工作波长的增加而减少,但通过晶体材料的特殊切割,充分利用了最大电光系数:r_42=380pm/V和内表面的全反射,获得的自泵相位共轭反射率可达40％。     

KNbO_3∶Fe自感相干光振荡

本文报道光折变晶体KNbO_3∶Fe线型腔中自感相干光振荡的实验观察研究,在线型腔透过率P=0.28时,分别测量了振荡光I_A~′,相位共轭光I_(PC),相位共轭反射率R_c,振荡光建立时间常数τ_(ob)相位共轭光建立时间常数τ_c与入射光I_P的依赖关系。当I_P=7.8W/cm~2时,测得最大的反射率R_c=1.6％和振荡光I_A=2I′_A=1.0W/cm~2。     

Subpicometer accuracy laser wavelength sensor using multiplexed Bragg gratings

Wavelength- and angle-multiplexed holographic Bragg gratings are used as a highly sensitive wavelength sensor. An absolute wavelength accuracy as high as 0.3 pm has been demonstrated with gratings recorded in an Fe-doped LiNbO/sub 3/ photorefractive crystals of dimension of 5/spl times/5/spl times/4 (mm/sup 3/). This technique provides a simple and accurate solution to laser wavelength measurement in applications such as wavelength division multiplexed (WDM) fiber-optic networks, precision interferometry, Doppler spectroscopy, and others.     

1710-V 2.77-m/spl Omega/cm/sup 2/ 4H-SiC trenched and implanted vertical junction field-effect transistors

This letter reports the demonstration of a 4H-SiC trenched and implanted vertical-junction field-effect transistor (TI-VJFET). The p/sup +/n junction gates are created on the sidewalls of deep trenches by angled Al implantation, which eliminates the need for epitaxial regrowth during the JFET fabrication. Blocking voltages up to 1710 V has been achieved with a voltage supporting drift layer of only 9.5 /spl mu/m by using a two-step junction termination extension. The TI-VJFET shows a low specific on-resistance R/sub ON-sp/ of 2.77m/spl Omega/cm/sup 2/, corresponding to a record high value of V/sub B//R/sub ON-sp/ equal to 1056 MW/cm/sup 2/.     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.     

Nd:MgO:LiNbO/sub 3/ self-frequency-doubled laser pumped by a flashlamp at room temperature

A small Xe flashlamp-pumped Nd:MgO:LiNbO/sub 3/ self-frequency-doubled laser at room temperature is described. The laser device could be operated with 400 mu J/shot output of pure green light at 26 degrees C. The threshold is smaller than 4.8 J. The optimum phase-matching could be achieved over 15 degrees C to 45 degrees C, if the crystal was aligned and no photorefractive damage was observed.<>