We propose an equivalent circuit model for the coplanar waveguide (CPW) which serves as the traveling wave electrode to drive carrier-depletion-based silicon modulators. Conformal mapping and partial capacitance techniques are employed to calculate each element of the circuit. The validity of the model is confirmed by the comparison with both finite-element simulation and experimental result. With the model, we calculate the modulation bandwidth for different CPW dimensions and termination impedances. A 3 dB modulation bandwidth of 15 GHz is demonstrated with a traveling wave electrode of 3 mm. The calculation indicates that, by utilizing a traveling wave electrode of 2 mm, we can obtain a 3 dB modulation bandwidth of 28 GHz.

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An Equivalent Circuit Model of the Traveling Wave Electrode for Carrier-Depletion-Based Silicon Optical Modulators

Traveling wave GaAs electrooptic waveguide modulators at a wavelength of 1.3 mu m with bandwidth in excess of 20 GHz have been developed and characterized. The design and characteristics of both p-i-n modulators in microstrip configuration and Schottky barrier on n/sup -/-GaAs/semi-insulating (SI) GaAs in the coplanar strip configuration modulators are discussed. It is shown that microwave loss and slowing on n/sup +/ GaAs substrates will limit the bandwidth of the microstrip modulator to less than 10 GHz for a device 8 mm in length. Modulators with bandwidths in excess of 10 GHz are fabricated on SI GaAs substrates. >

High speed III-V electrooptic waveguide modulators at lambda -1.3 mu m

We report a 13‐μm GaAs traveling‐wave electro‐optic waveguide modulator with a 3‐dB optical bandwidth in excess of 20 GHz The bandwidth was determined by directly detecting the modulated optical signal with a high‐speed InP/GaInAs photodiode The modulator has a coplanar strip electrode configuration with a double heterojunction Al0032Ga0968As/GaAs/Al0032Ga0968As optical guide grown by low‐pressure organometallic vapor phase epitaxy

GaAs traveling‐wave polarization electro‐optic waveguide modulator with bandwidth in excess of 20 GHz at 1.3 μm

We demonstrate a fully independent differential-drive capable of traveling-wave modulator in silicon using slow-wave transmission line electrode. The reported 3.5-mm device achieves a bandwidth of 27 GHz at $-$ 1 V bias with 7.8-V small signal $V_\pi$ and 50- $\Omega$ impedance. Raising the impedance to this extent requires effectively expanding the RF mode size and radically changes the RF phase velocity, but we show that this can be done with minimal crosstalk effects between the two arms and overall velocity mismatch, and thus, with a high EO bandwidth achieved. 40-Gb/s operation is demonstrated with 1.6-Vpp differential-drive, and performance comparisons to Lithium Niobate modulators are made.

High-Speed Silicon Modulator With Slow-Wave Electrodes and Fully Independent Differential Drive

High-speed silicon depletion-mode Mach-Zehnder modulators are demonstrated and characterized in this paper. Based on the structural dimensions and material parameters, transmission-line parameters and frequency response performances of the modulators are calculated and predicted by a proposed distributed circuit model. Parasitic coupled-slotline mode excited by the modulator is analyzed and suppressed by gold-wire bridges. Using a spectrum analysis method, the effect of this modification on the modulated optical signal is simulated. Over a broad frequency range from 10 MHz to 40 GHz, silicon depletion-mode Mach-Zehnder modulators with flat electro-optic modulation responses and broad bandwidths have been experimentally demonstrated.

Demonstration and Characterization of High-Speed Silicon Depletion-Mode Mach–Zehnder Modulators

GaAs PIN traveling-wave modulators with terminating resistors of various resistances operated at 1.3 microm have been fabricated from material grown by organometallic vapor phase epitaxy (OMVPE) on n(+) (100) GaAs substrates. It was found that modulators with positive reflection coefficients at the load exhibted initial rolloff in the frequency response. However, modulators with negative reflection coefficients at the load exhibited some peaking behavior at low frequencies at the expense of lower detected microwave powers. Based on this observation, a compromised PIN traveling-wave modulator was designed and measured to have a 3-dB bandwidth of 9.6 GHz.

S. H. Lin

Papers

High-throughput GaAs PIN electrooptic modulator with a 3-dB bandwidth of 9.6 GHz at 1.3 microm.