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This paper reports a study of the effect of wafer tilt during dopant implantation on the performance of silicon PN phase shifter and traveling-wave Mach-Zehnder modulator. The PN phase shifter is designed and process simulated to include the effects of different fabrication processes in the device performance. The wafer tilt during implantation is varied from 0° to 3°, 5°, and 7°. The resulting crystal damage during dopant implantation to form the PN junction and the active concentration profile upon annealing, along with the formation of dopant–defect clusters, are discussed. Compared to 0° tilt, 7° tilt results in $1.58\times $ higher phase shift and better modulation efficiency. The overall phase shifter performance is improved using 5° wafer tilt for implantation resulting in $1.23\times $ lower absorption, $1.45\times $ better modulation efficiency, and $3.14\times $ higher 3 dB $RC$ modulation bandwidth for lumped-driven phase shifter. A traveling-wave electrode to enhance the modulation bandwidth is used, and the modulator performance for non-return-to-zero on-off-keying modulation with–2.5 V bias and 2.5 $\text{V}_{pp}$ drive signal across each arm is evaluated using a dual-arm push-pull drive. The sample with 5° tilt shows better traveling-wave and modulator high-speed characteristics compared to the other samples. Among the four samples with different wafer tilts, the sample with 0° tilt shows the worst phase shifter performance, and the sample with 3° tilt shows the worst modulator characteristics. The best overall performance is obtained for the sample with 5° tilt. Compared to the modulator with implantation at 0° tilt, the 5° tilted sample shows $2.3\times $ higher 6.4 dB electrical bandwidth and $1.36\times $ higher 3 dB electro-optic bandwidth at–2.5 V using a traveling-wave electrode with $1.48\times $ lower energy-per-bit for 5 km transmission at the KP4-forward-error-correction bit-error-rate threshold. The comparison of the effect of wafer tilt angles on various device metrics is presented and discussed.

In this paper, we present the design, fabrication, and characterization of a traveling-wave directional coupler modulator based on electro-optic polymer, which is able to provide both high linearity and broad bandwidth. The high linearity is realized by introducing Δβ -reversal technique in the two-domain directional coupler. A traveling-wave electrode is designed to function with bandwidth-length product of 302 GHz·cm , by achieving low microwave loss, excellent impedance matching, and velocity matching, as well as smooth electric-field profile transformation. The 3-dB bandwidth of the device is measured to be 10 GHz. The spurious-free dynamic range of 110 dB ±3 Hz2/3 is measured over the modulation frequency range of 2-8 GHz. To the best of our knowledge, such high linearity is first measured at the frequency up to 8 GHz. In addition, a 1 × 2 multimode interference 3-dB splitter, a photobleached refractive index taper, and a quasi-vertical taper are used to reduce the optical insertion loss of the device.

Comparing with a lumped electroabsorption modulator (EAM), we show the merits of a long EAM with traveling-wave electrode with high radio-frequency (RF) gain that could be used in high-frequency analog application. By terminating the RF output port with the characteristic impedance of 30 Ω, the device exhibited a large enhancement of 6 dB above 10 GHz in the electrical-to-optical response and a wide fractional bandwidth as estimated from simulation. In addition, an input impedance matching circuit of stub embedded on the device chip was found to be very effective for improving RF characteristics in the narrow band of frequency. [ABSTRACT FROM PUBLISHER]

LiNbO3 Mach-Zehnder optical modulators, which are expected to be used for multi-Gbit/s optical transmission scheme, have one problem which is a dc drift phenomenon. In order to operate this modulator for a long time, a control unit to adjust a bias voltage for such dc drift is therefore necessary. So far, a method to superimpose a control signal with a main signal has been commonly used. However, the control signal may influence the output signal in this method. A novel automatic bias voltage control scheme utilizing the feature of Mach-Zehnder modulator with traveling-wave electrodes is proposed in this paper. A dc drift can be detected with a probe light propagating along a direction opposite to that of a modulated voltage waveform, and therefore very little influence of the probe signal on the output signal would be expected. A theoretical discussion on a dc drift detection and control method is described. This method has been successfully demonstrated to work for a mark density of 1/4, 1/2, and 3/4. [ABSTRACT FROM AUTHOR]

This paper describes a shielded-velocity-matched Ti:LiNbO3 optical modulator which realizes a wide band- width with the velocity matching between the optical wave and the modulation microwave by placing a shielding conductor close to the coplanar waveguide traveling electrode through an air overlay. In the design of the traveling-wave electrode, a quasi-TEM approximation and a spectral domain approach with hybrid mode are used. From numerical analysis it has been found that the effective refractive indices of the microwave and the light wave can be matched by optimally setting the overlay thickness. It has also been found that the increase in the microwave propagation loss or decrease in the characteristic impedance can be suppressed by increasing the thickness of the SiO2 buffer layer. As for the optical waveguide, the design parameters have been clarified by using a newly developed modified step segment method. Based on these examinations, a Mach-Zehnder intensity modulator and a phase modulator for the 1.5-μm wavelength band have been designed and fabricated. As a result of measurement, the optical modulation bandwidth has been improved greatly to 20 GHz. As for the drive voltage, the intensity modulator uses 4.7 V and the phase modulator uses 6 V. The total insertion loss including the connector loss is 2.2 dB for the intensity modulator and 2 dB for the phase modulator. It has also been verified that the modulators have superior ambient stability. [ABSTRACT FROM AUTHOR]

We analyze ring resonator-based traveling-wave modulators that show high modulation efficiency at frequencies around multiples of the free spectral range. The modulators have better tolerance for the optical/microwave velocity mismatch and the loss of the microwave transmission line than traveling-wave Mach-Zehnder modulators. [ABSTRACT FROM PUBLISHER]