Narrow bandwidth electrooptic polarization modulator using GaAs quantum-well waveguides

An electrooptic TE-TM polarization converter using a strip-loaded GaAs-AlGaAs multiple quantum well waveguide is discussed. At a wavelength of 870.5 nm, or an energy of approximately 50 meV below the heavy hole exciton resonance, a polarization conversion efficiency of 0.6 degrees /V-mm has been achieved. In addition, a spectral bandwidth of approximately 0.6 nm has been measured for a 3.8-mm-long device. Results indicate that modal birefringence and electroabsorption, due to exciton broadening in the presence of a lateral field, has a significant effect on device efficiency and spectral bandwidth. The mode converter described should be well-suited for use with semiconductor laser diodes in optical signal processing and computing applications.<>     

Vector beam propagation analysis of polarization conversion in periodically loaded waveguides

An improved design of a short and low-loss polarization converter is proposed. It consists of an asymmetrically periodic loaded rib waveguides. At a wavelength of 1.5 /spl mu/m, 98% polarization conversion ratio is obtained with a relatively short 0.74-mm device length and an extremely low 0.13-dB total insertion loss. The simulation results are obtained using a full vector beam propagation method based on the finite element method.     

A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 μm. This modulator is fabricated as a traveling wave modulator incorporating 50 Ω, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth     

Coupled GaAs multiple-quantum-well channel waveguides includingquadratic electrooptic effect

Two coupled channel waveguides using GaAs multiple quantum wells are investigated using an improved coupled-mode theory for anisotropic waveguides and the effective index method. The quadratic electrooptic effect in the multiquantum-well structures is taken into consideration. It is shown that only a moderate electric field for multiquantum-well waveguides is necessary to achieve the optical power switching compared with that required for a bulk GaAs waveguide     

AlGaAs-GaAs polarization converter with electrooptic phase mismatchcontrol

We designed and fabricated an electrooptic transverse magnetic-transverse electric mode converter with phase mismatch control integrated in AlGaAs-GaAs. The electrode scheme, which is reported for the first time in such a device, insures a high polarization conversion efficiency with low-driving voltages     

Efficient electrooptic modulator in InGaAlAs/InP optical waveguides

A single heterostructure InGaAlAs/InP phase modulator utilizing the quadratic electrooptic effect (QEO) is reported for the first time. The calculated value of the QEO coefficient from the measurements is 3.7×10^-19 m²/V² at 80 meV below the band edge. In addition, the linear electrooptic effect (LEO) coefficient is estimated to be 1.2×10^-12 m/V, which is comparable to that of GaAs. The propagation loss of a single mode ridge waveguide is in the range of 1.5-1.7 dB/cm, which is better than the previously reported value in this material system. The measured single mode phase shifts are 5.5 and 2.8°/V mm for TE and TM polarizations, respectively. These values are the largest reported so far in an InGaAlAs system     

Photobleached refractive index tapers in electrooptic polymer rib waveguides

Photobleached refractive index tapers in electrooptic polymer rib waveguides, which act as two-dimensional optical mode transformers, are investigated. One taper method involves a discrete step mask-shifting scheme with a fixed intensity UV light source. A second method utilizes a gray-scale mask to precisely control the intensity of UV light reaching each portion of the taper. Using a gray-scale mask, adiabatic refractive index tapers can be inscribed into electrooptic polymer waveguides in a single fabrication step with no scanning parts. Optimized taper profiles are derived and applications for their incorporation into passive-to-active waveguide transitions are described.     

High-speed electrooptic phase modulators using InGaAs/InAlAsmultiple quantum well waveguides

High-speed phase modulation of waveguided InGaAs/InAlAs multiple-quantum-well optical modulators operating at 1.55 μm is described. The modulator requires a low voltage for π-phase-shift ( V_π=2.5 V) as well as a small intensity modulation depth of 1 dB. The measured electrical 3-dB bandwidth is 10 GHz, giving a bandwidth-to-voltage ratio of 4 GHz/V     

A polarization independent guided-wave LiNbO/sub 3/ electrooptic switch employing polarization diversity

A 2*2 lithium niobate optical switch is demonstrated which uses polarization diversity to obtain polarization-independent operations with good crosstalk, a simple electrical drive configuration, and low drive voltage. The switch, on Z-cut LiNbO/sub 3/, is suitable for operation at 1.3 mu m with standard single-mode fibers. Resonant metal-loaded directional coupler mode-splitters enable the processing of each polarization component to be separately optimized. Switching voltages of 7 V for transverse magnetic and 24 V for transverse electric components have been achieved using a single substrate.<>     

Efficient modulation and coupling of CW junction laser light using electrooptic waveguides

The use of an electrooptical-waveguide modulator to achieve over 80-percent modulation of 7980-Å light from a room temperature laser diode operating at 10 mW CW is reported. The insertion loss of the modulator including couplers is 8.5 dB, and the output beam has high coherence.     

Mode conversion in planar-dielectric separating waveguides

The mode-conversion behavior of branching or separating planar-dielectric waveguides is studied theoretically as a function of branch asymmetry and taper slope. When the taper slope is large in a near-symmetric structure, considerable mode conversion will occur and the structure will act as a power divider. In an asymmetric structure with small taper slope, mode conversion is negligible and the structure will act as a mode splitter. A quantitative formula is presented which can be used to determine the behavior of a given separating structure.     

Electroabsorption and electrooptic modulation in single crystalZnSe-ZnSSe waveguides grown by OMVPE on GaAs

Electroabsorption and the electrooptical effect were used to modulate argon laser light in ZnSe single crystal waveguides. The electrical contacts were Schottky barriers that created a nonuniform electric field in the samples. The nonuniform electric fields are modeled, and the experimental results are matched to this model. The electroabsorption experiments showed a modulation depth of 9.2 dB at an applied voltage of 255 V and a wavelength of 476 nm. With the same applied voltage at λ=488 nm the modulation depth was only 0.53 dB. Electrooptic phase modulation was also investigated. A phase shift of π was found at 60 V for a sample of 3 mm length. The half wave voltage was independent of wavelength for wavelengths from 488 to 515 nm     

Simulation of polarization converter formed by poling-inducedpolymer waveguides

A polarization converter using electrooptic (EO) polymer waveguides is proposed and it is simulated by a full vectorial beam propagation method (VBPM) for anisotropic medium. First, an efficient structure of poling electrodes is proposed for the fabrication of TE-mode poling-induced waveguides in EO polymer. For given electrode structures of both TE-mode and TM-mode waveguides, poling-induced dielectric tensors are calculated by the finite-element method to provide refractive index distribution, data for VBPM simulation. It is shown numerically that the poled TE and TM mode waveguides work efficiently as the corresponding polarization filters. Then, new poling electrodes are suggested to fabricate a waveguide device formed by connecting the TE and TM mode waveguides adiabatically with a slowly varying structure. This waveguide device has the optic axis slowly rotating as one moves along the propagation direction, so that it will act as polarization converter. VBPM simulation shows that the polarization of the guided mode rotates following the optic axis distribution. Polarization conversion is demonstrated successfully with high conversion efficiency and low excess loss     

Optical pulse generation using guided-wave electrooptic modulator with resonant electrodes and polarization reversal

This paper reports on optical pulse generation using a new guided-wave electrooptic (EO) phase modulator with long resonant electrodes and polarization reversal. Adopting polarization-reversal structure to a guided-wave EO modulator with long standing-wave resonant electrodes, high-efficiency optical modulation is obtained by the compensation of the transit-time effect. By operating a fabricated EO phase modulator with a large amplitude modulation signal, optical sidebands over 100 GHz were obtained. Furthermore, optical pulse trains of an /spl sim/ 25-ps pulsewidth and a 15.28-GHz repetition frequency were successfully obtained by controlling the generated optical sidebands by use of an optical synthesizer.     

Parametric Raman wavelength conversion in scaled silicon waveguides

The benefits of using submicrometer modal-dimension silicon waveguides in realizing high-efficiency parametric Raman wavelength conversion are demonstrated theoretically and experimentally. The combined effects of Raman nonlinearities and free-carrier losses induced by two-photon absorption (TPA) are analyzed using the coupled-mode theory. The analysis indicates that scaling down the lateral dimensions increases the conversion efficiency of the Raman process and reduces the effective lifetime of free carriers and hence ameliorates the free-carrier losses. The feasibility of data conversion is demonstrated by coherent transfer of the analog radio-frequency (RF) signal from Stokes to anti-Stokes channels. The conversion efficiency, and hence signal-to-noise ratio (SNR), and bandwidth of the conversion process are found to be limited by the phase mismatch between the pump, Stokes, and anti-Stokes fields. The dispersion properties of submicrometer waveguides are also studied from the point of view of achieving phase matching and enhancing the conversion efficiency.     

Electric field, permittivity, and strain distributions induced by interdigitated electrodes on electrooptic waveguides

Integrated optical interdigitated-electrode devices are used to diffract light and to launch acoustic waves. The electric field and the permittivity and strain tensors induced by a voltage applied to periodic interdigitated electrodes of finite thickness on the surface of an anisotropic electrooptic crystalline waveguide are calculated rigorously. A buffer layer between the electrodes and the waveguide is included in the analysis.     

基于铌酸锂光波导的全光波长转换

研究了双脉冲泵浦情况下,在准相位匹配(QPM)的周期性极化反转的铌酸锂光波导(PPLN)中,基于级联二阶非线性效应--和频与差频效应(SFG DFG)的全光波长转换.推导了描述SFG DFG波长转换的理论模型.通过数值模拟,研究了波长转换过程,观察到脉冲传播过程中出现了走离效应与脉冲展宽.研究了器件长度、信号波长、脉宽等参数对波长转换效率的影响.     

Non reciprocal single mode conversion in multilayer magnetooptical waveguides

Multilayer structures are of great interest in the fabrication of single mode devices for Integrated Optics. this work it is shown that a multilayer structure allows not only single-mode behaviour but it enhaces the non-reci procity of the quide.     

Polarization conversion in the reflectivity properties of photoniccrystal waveguides

Strong resonant polarization conversion is observed in the reflectivity properties of one-dimensional (1-D) lattices of air trenches deeply etched in AlGaAs surface waveguides. The symmetry properties and the magnitudes of the observed effects are found to be in good agreement with the results of scattering matrix calculations     

Strong polarization conversion in periodically loaded stripwaveguides

We give a comprehensive explanation for an unexpected strong polarization conversion effect in periodically loaded strip waveguides, which was detected experimentally some years ago. The effect can be put down to the occurrence of hybrid supermodes. Based on this knowledge, design proposals for new, highly efficient polarization converters can be given