Abstract

High-power sources¹ and optical amplifiers improve the performance of wideband fiber-optic systems by increasing the received optical power; more than 100 mW is currently possible. However, to avoid deleterious effects of high powers (>1 mW) exhibited by surface-illuminated high-frequency photodetectors (PDs),² the PD optical power must be limited. Edge-illuminated waveguide PDs³ extend, but do not eliminate, the PD power limit. Additionally, large half-wave voltages (V_π = 5-15 V) of external optical modulators (EOMs) result in low modulation efficiencies. The resultant large unmodulated carrier either forces the use of a pre-detection attenuator or limits the usefulness of an optical preamplifier. Efficiency improvements have been proposed by biasing the EOM below quadrature,⁴ however, the technique requires EOM access and is limited by second harmonic generation.

© 1994 Optical Society of America