We demonstrate a new concept for analog-to-digital (A/D) conversion based on photonic time stretch. The analog electrical signal is intensity modulated on a chirp optical waveform generated by dispersing an ultrashort pulse. The modulated chirped waveform is dispersed in an optical fiber, leading to the stretching of its envelope. We have derived analytical expressions for the stretch factor and the resolution of the system. An analogto-digital converter (ADC) consisting of the photonic time-stretch preprocessor and a 1-Gsample/s electronic ADC is demonstrated. This technique is promising for A/D conversion of ultrafast signals and, hence, for realization of the digital receiver.

Recent developments in silicon based optoelectronics relevant to fiber optical communication are reviewed. Siliconon-insulator photonic integrated circuits represent a powerful platform that is truly compatible with standard CMOS processing. Progress in epitaxial growth of silicon alloys has created the potential for silicon based devices with tailored optical response in the near infrared. The deep submicrometer CMOS process can produce gigabits-per-second low-noise lightwave electronics. These trends combined with economical incentives will ensure that silicon-based optoelectronics will be a player in future fiber optical networks and systems.

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was recorded over 180" using a hemicylindrical screen of photosensitive paper (Kodak Panalure) with the capillary at the centre. (i) and (ii) in Fig. 3 show the response of a water-filled, uncoated capillary under TE and TM illumination, adjusted to strike a broad range of angles and to highhght the region of the capillary response corresponding to reflections from the internal surface