High-Power Photodiodes With Optimized Electrode Design

we demonstrate a back-illuminated flip-chip bonded modified uni-traveling carrier photodiodes by optimizing coplanar waveguide on AlN to improve the bandwidth and output power of the photodiode. The 3-dB bandwidth of the optimized devices increased from 56 GHz to 67 GHz for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14~\mu $ </tex-math></inline-formula>m diameter photodiode, and from 39 GHz to 46 GHz for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu $ </tex-math></inline-formula>m diameter device, representing an approximate 20% improvement in both cases. Thanks to the improved high-frequency performance of the devices, the photodiodes with diameters of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14~\mu $ </tex-math></inline-formula>m exhibit high RF output powers of 23.8 dBm at 30 GHz and 17 dBm at 65 GHz, respectively. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14~\mu $ </tex-math></inline-formula>m diameter PD exhibits low phase noise, with the maximum phase variation of the RF signal remaining within 10 degrees across the photocurrent range of 5 mA to 50 mA. The phase noise of optically generated RF signals, exacerbated by coupling amplitude noise on an optical pulse train to phase noise (AM-PM), exhibits a null at 17 mA. Additionally, the fully packaged module with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22~\mu $ </tex-math></inline-formula>m diameter photodiode exhibits a 3-dB bandwidth of 40 GHz and a high RF output power of 16.6 dBm at 40 GHz. This study lays the groundwork for the development of high-performance microwave photonics system and the generation of ultra-low noise microwave signals.