Photo-bleaching induced electro-optic polymer modulators with dual driving electrodes operating at 1.55 /spl mu/m wavelength

Electro-optic (EO) polymeric Mach-Zehnder (MZ) modulators with photo-bleaching (PB) induced waveguides and dual driving electrodes operating at 1.55 /spl mu/m wavelength have been demonstrated. The half-wave voltage of the integrated polymeric modulator was 4.5 V in a push-pull configuration with a 1.5 cm interaction length. The extinction ratio was greater than 20 dB, and the fibre-to-fibre insertion loss was 8 dB for the TM polarisation. The achieved fibre-to-fibre insertion loss and driving voltage are the best, to the authors knowledge, in the reported PB induced MZ EO polymeric modulators.     

High-performance optical modulator with a wide center electrode and thin x-cut LiNbO/sub 3/ substrate

We propose an excellent large-bandwidth back-slot lithium niobate (LN) modulator with a wide center electrode of typically 50 /spl mu/m or wider and relatively thin electrodes. From the calculation, a modulator with a 3-dBe bandwidth of 34 GHz and a half-wave voltage of 2.0 V for a 50-/spl Omega/ characteristic impedance system was realized theoretically. This means when their half-wave voltages are identical, by applying a wider electrode, the modulator bandwidth becomes 2.6 times larger than that of a conventional one. We also confirmed experimentally that the wide center electrode structure is effective for back-slot LN modulators.     

Numerical simulation of ultra-compact electro-optic modulator based on nanoscale plasmon metal gap waveguides

An ultra-compact Mach-Zehnder (MZ) electro-optic (EO) modulator composed of nanoscale metal gap waveguides is numerically demonstrated. Propagation of surface plasmon polaritons in nano-size channels and their EO modulations is investigated by the finite-difference time-domain method considering the Lorentz-Drude model. The half-wave voltage (V _pi) of the resulting MZ modulator for push-pull operation is 1.73 V using the interference arm with a sub-micron length (500-nm).     

Design and Modeling of Traveling-Wave Electro-Optic Polymer Modulator for Ultrahigh Speed Applications

We present a complete model and design approach for high speed electro-optic (EO) polymer modulators. A general numerical model for arbitrary travelling-wave EO modulators is built, and the dispersion characteristic of each polymer layer in the device stack is carefully considered and integrated into the model. A velocity compensation layer is added to allow more room for increasing the waveguide core index to optimize half-wave voltage of the device. Microstrip mode analysis is also included to estimate the influence of different polymer stack to the E filed distribution inside the waveguide core. The device has been successfully designed and achieves more than 45 GHz EO bandwidth with a half-wave voltage of 3.2 V. A 100 Gbps EO modulator is under development.     

A 40-gb/s InGaAlAs-InAlAs MQW n-i-n Mach-Zehnder Modulator with a drive Voltage of 2.3 V

We have developed a traveling-wave Mach-Zehnder modulator using an n-i-n heterostructure fabricated on an InP substrate. We obtained an extremely small /spl pi/ voltage (V/spl pi/) of 2.2 V, even for a short signal-electrode length of 3 mm. We confirmed that the device has an impedance-matched electrode and operates at 40 Gb/s with a single-ended drive voltage of 2.3 V.     

Optical intensity modulator based on a novel electrooptic polymerincorporating high μβ chromophore

We have synthesized a novel electrooptic (EO) polymer based on a high μβ chromophore incorporating tricyanobutadiene acceptors. A crosslinked polyurethane network was also adopted to enhance its thermal stability. In order to find the optimum poling condition for the polymer, the influence of the electric poling profile on optical characteristics such as the EO effect, thermal stability, and damage was investigated. Then a high-speed intensity modulator using the EO polymer was designed and fabricated. The measured half-wave voltage V_π was 4.5 V at the wavelength of 1.31 μm. Accordingly, the achieved EO coefficient r₃₃ was as high as 25 pm/V, and the thermal stability of the poled polymer was as high as 95°C. Finally, the modulator was successfully operated up to 40 GHz     

Millimeter-wave Ti:LiNbO3 optical modulators

The design, fabrication, and characteristics of ridged Ti:LiNbO ₃ optical modulators that work in the millimeter-wave region are presented. A new concept of design under velocity matching is demonstrated for the proposed modulator. It has been shown by calculation that impedance matching is achieved and conductor loss is greatly reduced under velocity matching with wider gaps and a thicker coplanar waveguide electrode in conjunction with a ridge structure. Two types of Mach-Zehnder optical intensity modulators for the wavelength of 1.5 μm are developed. A fully packaged module for 40 Gb/s transmission with a half-wave voltage of 3.5 V and a broadband modulator responsible up to 100 GHz with a half-wave voltage of 5.1 V     

Low-loss electrooptic BaTiO/sub 3/ thin film waveguide modulator

A strip-loaded electrooptic waveguide modulator based on an epitaxial BaTiO/sub 3/ thin film was fabricated and characterized for the first time. The strip-loaded waveguide structure greatly improves waveguide propagation and polarization-dependent loss performance. A propagation loss of 1.1 dB/cm and polarization dependent loss of 0.1 dB/cm were measured. The electrooptic waveguide modulator exhibited a half-wave voltage-interaction length product of 4.5 V /spl middot/ cm at a wavelength of 1542 nm. The measured effective electrooptic coefficient of the as-grown BaTiO/sub 3/ waveguide modulator was 38 pm/V. The experimental results indicate that a strip-loaded thin film waveguide modulator is suitable for photonic applications.     

Large-signal phase retardation with a poled electrooptic fiber

A linear electrooptic coefficient of 0.3 pm/V is induced in a germanosilicate fiber by thermal/electric-field poling. Reducing the fiber thickness by simple mechanical polishing following the poling, leads to a half-wave drive voltage of only 75 V for a 12-cm active length with no measurable linear optical loss in the fiber. The induced linear electrooptic coefficient shows no decay at room temperature for over four months, and only a 10% decay after heating to 90/spl deg/C for 1000 h.     

Analysis and design optimization of electrooptic interferometric modulators for microphotonics applications

Scaling the electrode layout (electrode gap, electrode length) down to microscale dimensions extends the application of electrooptic (EO) modulators to microphotonics. In this paper, design criteria are set up to minimize the switching voltage of microscale EO Mach-Zehnder interferometric modulators. Mach-Zehnder interferometric modulators under different directions of electric field with respect to the optic axis are analyzed. Three expressions of the intensity output characteristics are presented for various crystal classes and compared in terms of conditions of validity and design applications. The analysis in this paper suggests that the switching voltage is strongly related with the direction of the electric field relative to the optic axis. For the 4-mm BaTiO/sub 3/ (r/sub 33/=28 pm/V,r/sub 51/=820 pm/V) Mach-Zehnder modulators, r/sub 51/ is utilized when the electric field is applied normal to the optic axis. In this configuration, the thermal stability and polarization insensitivity improve but the extinction ratio becomes a function of the electrode length. The phase-retardation expression is useful to find a suitable modulator length and maximize the extinction ratio. Some of the discussions also apply to Fabry-Pe/spl acute/rot interferometric modulators.     

1064nm低电压薄膜铌酸锂电光调制器

低半波电压电光调制器是实现大规模光电集成的关键。文章提出了一种半波电压低于1.5 V的薄膜铌酸锂马赫-曾德尔(Mach-Zehnder, MZ)电光调制器，选用绝缘体上单晶薄膜铌酸锂材料作为设计基础，分析了直波导、多模干涉耦合器、弯曲波导和调制臂等结构对电光调制器的影响。结果表明，当调制臂长为3 mm时，该薄膜铌酸锂电光调制器具有1.05 V的低半波电压、0.319 dB的低损耗和27 dB的高消光比。同时，该调制器半波电压长度积为0.315 V·cm,调制效率高，具有与CMOS技术兼容的半波电压，有利于大规模光电集成。     

Optimization of the optical properties of a deeply etched semiconductor electrooptic modulator

A rigorous numerical study of a deeply etched semiconductor electrooptic modulator is presented. A Laplace equation solver followed by a full-vectorial modal solution technique for general anisotropic optical waveguides, all based on the versatile finite-element method, is used to find the potential distribution, the modulating electric fields, the changes in the permittivity tensor associated with the electrooptic effect, and the different modes of propagation. In particular, the optimization of the optical properties of the modulator structure such as the half-wave voltage length product V/sub /spl pi//L and the optical losses due to the imperfectly conducting electrodes has been carefully carried out and results reported. In addition, the effect of the waveguide parameters on the microwave properties such as the microwave index n/sub m/ and characteristic impedance Z/sub c/ is explained.     

A 0.7-V MOSFET-only switched-opamp /spl Sigma//spl Delta/ modulator in standard digital CMOS technology

A 0.7-V MOSFET-only /spl Sigma//spl Delta/ modulator for voice band applications is presented. The second-order modulator is realized using a switched-opamp technique. All capacitors are realized using compensated MOS devices operated in the depletion region. A combination of parallel and series compensated depletion-mode MOSCAPs is used to obtain high area efficiency. The circuit is fabricated in a 0.18-/spl mu/m CMOS process. The only components used are standard n-MOS and p-MOS transistors with threshold voltages of approximately 400 mV. All transistors are operated within the supply voltage window of 0.7 V; voltage boosting techniques are not used. The active area is 0.082 mm/sup 2/. The modulator achieves 67-dB signal-to-noise-and-distortion ratio, 70-dB signal-to-noise ratio, and 75-dB dynamic range at 8-kHz signal bandwidth and consumes 80 /spl mu/W of power.     

16-arrayed electrooptic polymer modulator

A 16-arrayed polymeric optical modulator is fabricated using an electrooptic (EO) polymer with a large EO coefficient and good thermal stability. The 16-arrayed modulator has lumped-type electrodes with a response time of less than 1 ns. The 16-arrayed modulator has good uniform modulation characteristics between the individual modulators. The deviation of half-wave voltages is 0.2 V and that of insertion losses about 1 dB. Crosstalks range from -28 to -36 dB and extinction ratios are more than 21 dB.     

Optical circular-polarization modulator employing tilt-poled electrooptic polymers

A polymer-based integrated circular-polarization modulator (CPM) is demonstrated in this paper. Tilted poling is adopted to achieve polarization conversion in the electrooptic (EO) polymeric waveguide and then realize the power balance between transverse electric and transverse magnetic modes. Detailed analysis and experiments on polarization conversion are presented. The tensor nature of poled polymeric materials is used to generate the phase difference. Contact poling is applied to perform tilted poling and activate the EO effect of polymeric materials. With appropriate voltage control, the polarization state of the output from the CPM can alternate between the left and right-hand-circular states. The extinction ratios at the 45/spl deg/- and -45/spl deg/-tilted linearly polarized states are larger than 25 dB.     

Spread spectrum frequency response of coded phase reversal traveling wave modulators

Application of aperiodic phase reversals to the electrode pattern of a Mach-Zehnder traveling wave modulator according to suitable pseudorandom sequences considerably improves the high-frequency response for fixed drive voltage. Simulations for a family of devices based on the Barker codes are presented, in the presence of frequency dependent microwave losses and impedance mismatch, using a new theorem relating the modulation transfer function to the Laplace transform of the electrode pattern evaluated on a parabolic contour in thes-plane. Projecting from our recent experimental results on 4 and 5 bit Barker codes, at 1.3-μm wavelengths, a 2-cm-long 13-bit Barker code device fabricated in LiNbO3will exhibit 5-dB optical modulation bandwidth in excess of 50 GHz with a half-wave voltage less than 8 V.     

Low-voltage high-contrast n-i-p-i-based waveguide modulators with alloyed selective contacts

We investigated an electroabsorptive n-i-p-i waveguide modulator based on the Franz-Keldysh effect (FKE), which is especially designed to operate with very low voltage swings over a broad wavelength range. In order to contact the n-i-p-i structure, the layer sequence and annealing conditions of Au-Zn-Au and Ni-Ge-Au contacts were optimized with respect to good selectivity and low contact resistance. The transmission measurements yield a contrast ratio of 30 dB, achieved with a voltage swing less than 1.5 V at a wavelength of 910 /spl mu/m with a 900-/spl mu/m-long waveguide modulator. Contrast ratios of /spl ges/20 dB have been obtained within the whole spectral range from 910 nm to 940 mm with a voltage swing less than 2 V. The absorption loss due to the FKE is below 3 dB.     

Ridged LiNbO/sub 3/ modulators fabricated by a novel oxygen-ion implant/wet-etch technique

This paper demonstrates a new ion implantation and wet-etch technique for fabricating high-quality ridged optical waveguides for high-speed LiNbO/sub 3/-based optical modulators. In addition, the paper demonstrates the fabrication of optical waveguide ridges >3 /spl mu/m in height with 90/spl deg/, and even re-entrant sidewall angles for the first time. The modeling used indicates that 90/spl deg/ (and re-entrant) sidewall ridges can reduce the required modulator drive voltage by 10-20% over modulators with conventional trapezoidal ridge profiles fabricated with reactive ion etching. A 40-Gb/s modulator with a 30-GHz bandwidth, 5.1-V switching voltage at 1 GHz, and a 4.8-dB optical insertion loss is fabricated using the ion implantation/wet-etch process. Fabricated devices showed good stability against accelerated aging, indicating that this process could be used for commercial purposes.     

高效微带线聚合物电光调制器的研制

设计、制作并测试了1.55 m 光波长的微带线行波电极电光调制器。如果聚合物材料的电光系数33=30 pm/V,中心电极L 为20 mm,设计的调制器性能参数半波电压为6.70 V。用自主合成的发色团分子组成二阶非线性光学聚合物材料做为芯层制作的聚合物调制器,对调制器的各项性能参数进行了直流、低频和微波性能的测试,采用不同极化方法,在1.55 m 波长上测得低频半波电压分别为10.5 V(电晕极化)和4.9 V(接触极化),折算得芯层材料的电光系数分别为21 pm/V 和45 pm/V。测得消光比为24 dB。用矢量网络分析仪测试电极系统的微波性能,S 参数反映了此电极系统具有低的微波传输损耗和反射损耗。     

Design of an opto-electronic modulator driver amplifier for 40-Gb/s data rate systems

This paper describes the design and performance of a broad-band driver amplifier for 40-Gb/s noreturn-to-zero system applications. The function of the amplifier is to raise the output from a multiplexer (nominally 0.4 V peak to peak) to a level of /spl sim/5 Vp-p, which is suitable to drive a GaAs-based Mach-Zehnder optoelectronic modulator. The amplifier module contains two GaAs pseudomorphic high-electron mobility transistor traveling-wave MMICs fabricated on a 0.2-/spl mu/m gate process. The design issues relating to the specific requirements of a modulator driver amplifier and the techniques to resolve them are described.