TECHNOLOGY AREA(S): Air Platform, Electronics, Weapons

ACQUISITION PROGRAM: PMA-234 Airborne Electronic Attack Systems

OBJECTIVE: Develop two-core, single-mode, multicore fiber optic package optical subassemblies for wideband digital and analog photonic integrated circuit components.

DESCRIPTION: Complex military communications, sensing, and surveillance systems require distribution of high fidelity analog and digital signals. Due to their wide bandwidth, low weight, and immunity against electromagnetic interference, analog and digital fiber optic links have attracted ample attention. For analog links, meeting the dynamic range requirements of communication and radar systems has proven to be challenging. In particular, nonlinearities of the electro-optic modulator, photodetectors, and electronic amplifiers have prevented the true potential of analog photonic links to be realized. In addition to dynamic range, link noise figure poses another bottleneck for some wideband applications. For digital links, while significant research has been conducted on improving the wavelength division multiplexing avionics network components including tunable lasers, wavelength converters and filters, and on avionics local area network topology and node definition, wavelength division multiplexing technology has had difficulty penetrating the avionics, sensor and electronic warfare aircraft application markets. In summary, analog optical links and wavelength division multiplexed network links that meet the stringent performance metrics of a military airborne platform system has remained elusive.

In recent years, there has been significant progress in linearization of wideband high-power photodetectors for analog radio frequency over fiber (RFoF) links. For digital photonic components, the advent of embedded optical engine and 100 gigabit per second non-return to zero technology is providing components for commercial sector hyperscale data center and computer network roadmap implementations. The objectives of this SBIR topic are: (1) to leverage the progress in wideband high-power photodetectors to improve the dynamic range of analog optical links via the use of multicore fiber; and (2) to leverage the hyperscale growth of data center fiber optic technology to improve multicore processor to level 2 (L2) cache memory data transmission and retrieval.

The envisioned RFoF link would utilize a wideband photodetector pair to receive wideband optical signals emitted from a remote modulator. Interfacing two-core, multicore, single-mode fiber to dual-output modulators and balanced photodetectors for link distances no less than 100 meters for use in the harsh avionics, sensor and electronic warfare environment is a primary subject of interest. It is envisioned that the multicore fiber will have two single-mode cores separated by a distance that enables low, 0.75 dB, optical loss, low, 30 dB return loss, and low, -40 dB optical crosstalk. 38-micrometer core-to-core spacing and splicing capability has been reported in the literature, and U.S.-based specialty fiber manufacturers have demonstrated the capability to produce multicore fiber [Ref 3]. This SBIR topic is focused on multicore fiber optical subassembly development for two-core-, multicore-, single mode, fiber optic-based analog and digital links whereby the two cores are �weakly coupled� per the discussion of multicore fiber in Reference 4. The desired electro-optic modulators used in analog fiber optic links must be compatible with distributed feedback (DFB) lasers with greater than 200 mWatts of single-mode fiber coupled optical power. The modulator must have dual outputs for use with balanced photo detector receivers to enable a higher link gain, a lower noise figure, and a higher spur free dynamic range [Ref 8]. A bandwidth of up to 45 GHz, with a minimum bandwidth of 10MHz, is required and it must be compatible with emerging systems out to 100 GHz. In addition to the RFoF analog link application, the envisioned digital link would utilize 10 to 100 gigabit per second transmitter and receiver technology for links that interface L2 cache memory to multicore processors.

This SBIR topic is focused on optical subassembly development for two-core-, multicore-, single mode fiber optic-based links. Development of new photonic or electro-optic devices are not contemplated under this project. It is anticipated that the optical subassemblies contemplated under this SBIR topic will be integrated in next-generation analog and digital link components installed onboard avionics, sensor, and electronic warfare platforms.

PHASE I: Develop an optical subassembly design concept that addresses the goals stated above. Detail approaches to RFoF modulator, RFoF photodetector, and digital transmitter/receiver optical subassembly integration. Develop detailed optical subassembly designs to provide low optical loss interfaces to two-core-, multicore-, single mode optical fiber. Perform modeling and simulation of the RFoF optical subassembly optical characteristics and links as well as of the digital optical subassembly optical characteristics and links to demonstrate feasibility. Develop a Phase II plan.

PHASE II: Build and test prototype packaged modulator, photodetector, and digital components based on two-core-, multicore-, single mode fiber optical subassemblies. Demonstrate multicore fiber enhanced analog optical links with 100-meter multicore fiber lengths. Demonstrate multicore fiber enhanced with 10 and 100 gigabit per second digital embedded optical links to replace address and data lines of a multicore processor with multicore fiber between each processor core and the L2 cache memory. Also demonstrate the communication between the multiple processor cores and the L2 cache. Perform thermal shock and temperature cycling [Ref. 9] to verify optical subassembly performance.

PHASE III DUAL USE APPLICATIONS: Perform extensive modulator and balanced photodetector optical subassembly reliability and durability testing. Transition the demonstrated technology to Naval aviation platforms and interested commercial applications.

The technology would find application in commercial systems such as fiber optic networks and telecommunications.

REFERENCES:

1. Urick, V.J., Williams, K.J., & McKinney, J.D. �Fundamentals of Microwave Photonics�. Wiley Series in Microwave and Optical Engineering, Kai Chang, Editor, 2015. ISBN: 978-1-118-29320-1

2. Hutchinson, M., Estrella, S. & Mashanovich, M. �Packaged wideband MUTC photodetectors for high SFDR applications�. Proceedings of the IEEE Avionics, Fiber Optics and Vehicle Conference 2016.� http://ieeexplore.ieee.org/document/7789931/

3. Zhu, B., Taunay, T.F., Fini, M.F., Fishteyn, M., Monberg, E.M., & Dimarcello, F.V. �Seven-core multicore fiber transmissions for passive optical network.�� Optics Express, vol. 18, no. 11, pp. 11117-11122, 24 May 2010. https://doi.org/10.1364/OE.18.011117

4. Saitoh, K. & Matsuo, S. �Multicore fiber technology�. Journal of Lightwave Technology, vol 34, no. 1, pp. 55-66, 1 January 2016. http://ieeexplore.ieee.org/document/7214203/

5. Struszewski, P., Bieler, M., Humphreys, D., Bao, H., Peccianti, M. & Pasquazi, A. �Characterization of high speed balanced photodetectors�. IEEE Transactions on Instrumentation and Measurement, vol. 66, issue 6, pp. 1613-1620, June 2017. http://ieeexplore.ieee.org/document/7835183/

6. Runge, P., Zhou, G., Beckerwerth, T., Ganzer, F., S., Seifert, S., Ebert, W., Mutschall, S., Seeger, A. and Schell, M. "Waveguide integrated balanced photodetectors for coherent receivers." IEEE Journal of Selected Topics in Quantum Electronics, vol. 24, issue 2, March-April, 2018. http://ieeexplore.ieee.org/document/7968460/?reload=true

7. MIL-PRF-38534J, Performance Specification: Hybrid Microcircuits, General Specification For Defense Logistics Agency, Columbus, Ohio.� http://everyspec.com/MIL-PRF/MIL-PRF-030000-79999/MIL-PRF-38534J_52190/

8. Beling, A., Xie, X., and Campbell, J.C., �High-power, high-linearity photodiodes� Optica, vol. 3, no. 3, pp. 328-338, March, 2016 https://www.osapublishing.org/DirectPDFAccess/E56B6A83-A926-DB5B-3097EAA531FFD58B_338262/optica-3-3-328.pdf?da=1&id=338262&seq=0&mobile=no

9. MIL-STD-883J (METHODS 1000 - 1034), DEPARTMENT OF DEFENSE TEST METHOD STANDARD - MICROCIRCUITS: 1000 TO 1034.1 SERIES TEST METHODS (07-JUN-2013]. http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-883J__METHOD_1000-SERIES_47064/

KEYWORDS: Multicore Fiber; Radio-frequency Over Fiber; Balanced Photodetector; Dual-output Modulator; Microprocessor; Cache Memory