Optical-to-Millimeter-Wave Carrier Frequency Down-Conversion by UTC-PD-Integrated HEMT

To realize future ultra-broadband ubiquitous, resilient communication networks, the seamless convergence of optical and wireless networks (full-coherent networks) is required. For this purpose, a carrier frequency downconverter from optical data signals to wireless data signals with the preservation of their data modulation format is needed. For this purpose, we have studied the so-called photonic double-mixing functionality of transistors, where the photomixing of an optical carrier signal and an optical subcarrier signal in the channel and the RF mixing of the beat-note signal and an RF signal impinged into the gate are performed simultaneously and an IF signal is generated. In this paper, we examine the integration of a uni-traveling-carrier photodiode (UTC-PD) structure in an InGaAs-channel high-electron-mobility transistor (InGaAs-HEMT) for the enhancement of the double-mixing efficiency. We measured the output intensity of the device for the input 1.55-um optical signals with the difference frequency of 112.5 GHz and the input RF signal into the gate at 90 GHz, and we demonstrated a significant enhancement of the output intensity at 22.5 GHz, by 34 dB, in comparison with the output intensity of a standard HEMT.