High-Performance WR-4.3 Optically Controlled Variable Attenuator With 60-dB Range

We report the design, fabrication, and characterization of a high-performance optically controlled WR-4.3 variable attenuator. The attenuation is based on the interaction between the incident waves and photogenerated free carriers inside an E-plane micromachined silicon absorber. Tuning is realized by illuminating the silicon with different light intensities using three 808-nm infrared laser diodes. Measurement results show that an average attenuation range of 60 dB, a 0.7-dB insertion loss, and a greater than 15-dB return loss have been achieved over the entire WR-4.3 band. In addition, a 3-dB modulation bandwidth of 350 kHz has been obtained experimentally. Initial thermal stability test of the device has also been performed, with less than 0.4-dB amplitude drift and 2° drift in phase over 30-min demonstration.