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Packaging High Power Photodetectors for 100 MHz to 100 GHz RF Photonic Applications


OBJECTIVE: Develop optical pigtailing and packaging for newly developed high RF output power photodetectors (PDs); e.g. normal incidence, single ended, balanced and arrayed, modified uni-traveling-carrier, normal incidence PDs operating from DC up to 100 GHz. DESCRIPTION: High frequency analog RF photonic links are desired to improve size, weight and power efficiencies for military RF antenna transmit and receive applications. State-of-the-art intrinsic RF performance and large dynamic range require fast, high-power photodiodes (PDs). In these systems PDs must be able to provide very high photocurrent level and thus, high output RF power to increase signal-to-noise-ratio while maintaining high linearity for large spurious-free dynamic range. However, there are two primary effects that impact high-power capability in PDs, which are space-charge screening [1], and thermal [2] effects. Recently, a charge-compensated modified uni-traveling-carrier (CC-MUTC) PDs with cliff layer [3] was demonstrated with record high output RF power up to 0.75 W at 15 GHz [4]. On-going developments have shown that improved and repeatable flip-chip processing leading to better thermal management and RF interconnects has increased the 3-dB bandwidth to 30 GHz. One way to overcome the trade-off between high speed and large saturation current, as an example, is to distribute symmetrically the optical signal to several PDs and combine their photocurrents by means of a transmission line. In this configuration, the optical signal is split by a power divider and fed into several discrete PDs, which are connected by an output transmission line. Due to the uniform optical power distribution, the photocurrent flowing through each PD scales inversely with the number of PDs. By embedding the discrete PDs within a transmission line, a traveling wave PD array can be formed [5]. PHASE I: Develop and provide packaging, with single-ended fiber optic pigtails and balanced pigtails, for government furnished normal incidence DC to 60 GHz MUTC PDs flip-chipped onto aluminum nitride (AlN) sub-mounts. The objective is to concurrently optimize frequency AND power handling capability. Investigate arrayed fiber optic pigtails designs. PHASE II: Develop and provide packaging for government furnished photodetectors with single-ended and arrayed fiber optic pigtails for the DC to 100 GHz MUTC waveguide photodetectors flip-chipped onto synthetic diamond sub-mounts. Collaboration with existing AFRL partners is anticipated. The offeror may choose to provide their own photodetectors in addition to those furnished for packaging. PHASE III: Ruggedize PD packaging and function over the full avionics operational environment. Ruggedized packaging is needed for military and commercial applications where extreme vibration and temperature exists. Conventional packaging would be useful for other applications, for example in an RF laboratory. REFERENCES: 1. K.J. Williams, R.D. Esman,"Design considerations for high-current photodetectors,"J. Lightw. Technol., vol. 17, no. 8, pp. 1443-1454, 1999. 2. H. Chen, A. Beling, H. Pan, J. C. Campbell,"A Method to Estimate the Junction Temperatures of Photodetectors Operating at High Photocurrent,"IEEE J. Quant. Electron., vol. 45, no. 12, 2009. 3. Z. Li, H. Pan, H. Chen, A. Beling, J. C. Campbell,"High Saturation Current Modified Uni-Traveling-Carrier Photodiode with cliff layer,"IEEE J. Quantum Electronics, vol. 46, no. 5, 2010. 4. Beling, Li, Fu, Pan, and Campbell,"High-Power and High-Linearity Photodiodes,"2011 IEEE Photonics Conference, pg. 19-20, October 2011. 5. Beling, Chen, Pan, and Campbell,"High-Power Monolithically Integrated Traveling Wave Photodiode Array,"IEEE Photonic Technology Letters, Vol. 21, No. 24, 2009.
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