High-power photodiodes in millimeter-wave photonic systems
Date
2022
Authors
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Publisher
University of Delaware
Abstract
Wireless links prioritize wide information bandwidths, carrier flexibility, and low size, weight, and power (SWaP). Demand for these characteristics is driven by the desire to deploy transmit and receive architectures almost anywhere that can adapt to user functions and maintain reliable data transfer. The latter has motivated development of systems that operate across millimeter wave frequencies (30—300 GHz) where a vast spectrum is available. To access this spectrum, wireless links require ultrawideband (UWB) phased arrays and widely-tunable millimeter wave sources that are difficult to realize in traditional all-electronic systems. This work proposes radiofrequency (RF) photonics to fulfill these system needs. ☐ Although electronic systems are a mature technology, millimeter waves present fundamental design challenges, such as banded signal generation components, prohibitive conductor losses, and bulky cabling. For wireless links, these design challenges are amplified by the densely populated phased arrays that are required for high power millimeter wave transmission. Recent work has shown that RF photonics is a viable alternative. In contrast to electronic feeding, RF photonics uses a low loss, light weight optical fiber feed to drive photonic antennas. Using high power charge-compensated modified uni-traveling carrier (CC-MUTC) photodiodes, these photonic antennas have achieved effective isotropic radiated power (EIRP) exceeding 1 W, and RF power conversion efficiency (PCE) approaching 50 %. However, much like their electronic counterparts, they had not yet demonstrated millimeter wave phased array operation. ☐ In this work, the design methodology developed for UWB photonic antennas is extended to millimeter wave frequencies to demonstrate the first steerable phased array that operates across 13—60 GHz. The fabricated 1 x 3 array achieved radiated power near 1 mW across the full designed bandwidth and an EIRP of 87 mW at 40 GHz. Although the array exhibited efficient millimeter wave radiation, RF power was limited by the decreased power handling observed in photodiodes with increased bandwidth. To improve thermal management and increase power output, pulsed-wave (PW) operation is proposed and achieves a record-high peak power exceeding 500 mW at 77 GHz. In addition to RF power, the scalability of the photonic array was limited. Since photonic antennas are still an emerging technology, the processes used for fabrication are not ideal. For example, the current optical integration methods used for photodiode integration rely on labor-intensive sequential alignments, which are prohibitive on a large scale. These current methods are presented, and proposed methods using grating couplers achieve promising results.
Description
Keywords
Millimeter-wave, Packaging, Photodiode, Pulsed-wave, Radiofrequency photonics, UWB phased array