Integrated 1.55 ?m photomixer local oscillator sources for heterodyne receivers from 70 GHz to beyond 250 GHz</title>

Photomixing is a flexible and efficient method of providing both local oscillator signals for heterodyne receivers and high frequency phase reference signals. Ultrafast, 70 GHz bandwidth, ? = 1.55 ?m, photodiodes from u2t Photonics AG have been incorporated into three designs of mm-wave waveguide mounts. The photomixers utilise a thin freestanding gold foil, or a gold on dielectric, probe to couple power into the waveguide and to deliver the photodiode bias. The frequency coverage of the designs is from 70 GHz to 300 GHz. A method of rapidly characterizing the frequency response of these photomixers using spontaneous-spontaneous beating of light from an EDFA is described. Recent work has been directed at increasing the degree of integration of the photodiode with the waveguide probe and choke filter to reduce the frequency dependence of the output power. A simplified photomixer block manufacturing process has also been introduced. A combined probe and filter structure, impedance matched to both the coplanar output line on the photodiode chip and to 0.4 height milled waveguide, is presented. This matching is achieved over the W-band with a fixed waveguide backshort. We present modelled and experimental results showing the increased efficiency and smoother tuning. The design and frequency response of such a probe is reported. We also present the performance of a simpler mount, operating in the frequency range from 160 GHz to 300 GHz, which generates powers of around 10 ?W up to 250 GHz.