ALL-SILICON INTEGRATED OPTICAL MODULATOR

We describe the operating principle, design, and performance of an all-silicon light modulator at 1.3-mu-m wavelength. The modulator is based on the plasma effect in silicon and the mode selectivity of single-mode optical fibers, resulting in low polarization dependence and the capability of handling high light intensities. Standard silicon IC technology is used in the fabrication process and the modulator has a vertical structure that takes up a small surface area (the active area matches the single-mode fiber core of 9-mu-m diameter), simplifying integration with other circuitry on the same chip. The modulator can be directly coupled to a single-mode optical fiber, without using lenses or other bulk optical components. Typical performance of the fabricated modulators is 6 dB insertion loss, 24% modulation depth, and 60 MHz bandwidth with a current drive of 22 mA rms. Higher modulation depth is projected for later generation modulators. The main advantages of this modulator are the compatibility with silicon IC technology and easy coupling to optical fibers. The most likely applications are in medical instrumentation and data acquisition from silicon sensors and in communication systems where functionality and ease of integration is more important than bandwidth.