0.77-V drive voltage electro-optic modulator with bandwidth exceeding 67 GHz.

A 0.77-V drive voltage (V(π)) electro-optic modulator with bandwidth exceeding 67 GHz is described. Modulator is a compound semiconductor device fabricated using substrate removal technology. This allows placement of metal electrodes on both sides of an optical waveguide containing a p-i-n diode. Hence ohmic losses are reduced significantly. Electrode gap is essentially the same as i layer thickness, which can be kept very uniform and small. Waveguide core also contains a MQW, which improves electro-optic efficiency. Lack of p doping in the waveguide and large detuning between MQW absorption peak and operating wavelength keep the propagation loss low. Large size of the waveguide also helps to keep coupling loss low. Modulator is designed as a traveling wave device using the loaded line approach, which is used for velocity matching. Combination of these approaches yields a device with the lowest V(π) and widest bandwidth.

Electrodes for wide-bandwidth substrate-removed electro-optic modulators.

This Letter is on wide-bandwidth electrodes suitable for ultralow voltage substrate-removed compound semiconductor electro-optic modulators. Using a loaded line approach, traveling wave electrodes suitable for wide-bandwidth and low-voltage operation were studied theoretically and experimentally up to 35 GHz. Using staircase waveguides and n-i-p-i-n epilayer designs, electrode capacitance and resistance were reduced significantly. Experimental and modeling results are found to agree very well. Theoretical and experimental results indicate that subvolt modulators with electrical to optical bandwidths in excess of 30 GHz are possible.

A photonic analog-to-digital converter based on an unbalanced Mach-Zehnder quantizer.

A Mach-Zehnder modulator (MZM) based analog to digital converter (ADC) is described. The signal to be digitized is applied to a single electrode of a high speed unbalanced modulator that acts as a quantizer. The rest of the system consists of commercially available wavelength division multiplexing (WDM) components. Analysis indicates that 6 bit operation at 40 Giga Samples per second (GS/s) is possible with moderate optical carrier power.

Propagation loss study of very compact GaAs/AlGaAs substrate removed waveguides.

Very compact GaAs/AlGaAs optical waveguides with propagation loss as low as 0.9 dB/cm at lambda=1.55 microm were demonstrated using substrate removal and evaporated Si for index loading. Loss components were identified and minimized through process and waveguide design. Process induced roughness contributed significantly to overall propagation loss. Therefore a low damage process in addition to proper waveguide design is needed for loss minimization.

Electro-optic and electro-absorption characterization of InAs quantum dot waveguides.

Optical properties of multilayer InAs quantum dot waveguides, grown by molecular beam epitaxy, have been studied under applied electric field. Fabry-Perot measurements at 1515 nm on InAs/GaAs quantum dot structures yield a significantly enhanced linear electro-optic efficiency compared to bulk GaAs. Electro-absorption measurements at 1300 nm showed increased absorption with applied field accompanied with red shift of the spectra. Spectral shifts of up to 21% under 18 Volt bias was observed at 1320 nm.

Extremely small multimode-interference coupled triangular resonator with sharp angle of incidence.

Novel triangular ring resonators combining extremely small multimode-interference (MMI) coupler, low loss total internal reflection (TIR) mirrors, and semiconductor optical amplifiers are reported for the first time. The MMI length of 90 microm is among the shortest reported. The incidence angle of the TIR mirror inside the resonator is 22 degrees. A free-spectral range of approximately 2 nm is observed near 1550 nm along with an on-off ratio of 17 dB. The triangular resonators with a sharp angle are very attractive components due to their promise of compact size and high levels of integration. Therefore, large numbers of resonators can be integrated on a chip to increase functionality in future optical wavelength division multiplexing system.

High-Q silicon-on-insulator optical rib waveguide racetrack resonators.

In this work, detailed design and realization of high quality factor (Q) racetrack resonators based on silicon-on-insulator rib waveguides are presented. Aiming to achieve critical coupling, suitable waveguide geometry is determined after extensive numerical studies of bending loss. The final design is obtained after coupling factor calculations and estimation of propagation loss. Resonators with quality factors (Q) as high as 119000 has been achieved, the highest Q value for resonators based on silicon-on-insulator rib waveguides to date with extinction ratios as large as 12 dB.