TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: PMS 435 - Submarine Electromagnetic Systems

OBJECTIVE: Develop high performance ultra-narrow band tunable filters for Radio Frequency (RF) photonic systems that will be utilized by the submarine electronic warfare next generation architecture.

DESCRIPTION: The Navy seeks development of ultra-narrow optical band pass filters that would enable the utilization of RF photonic signal distribution systems for next generation electronic warfare (EW) platforms. A narrow band optical filter featuring ultra-steep roll off, size (150mm x 30mm x 15mm), weight (< 16oz), and power (< 3W) comparable to commercially available technology, and wide tunability is desired to advance the current technology and improve performance metrics for military RF photonic signal distribution systems. The filters should operate with center wavelength in the c-band (1525-1565nm) as a first step, but should have a means to scale to other wavelength regimes. Tuning range should exceed 40GHz with tuning speed less than 25ms, and tuning resolution less than 0.10GHz. The rejection at 4GHz from the 3dB point should be greater than 45dB, with bandwidth scalable from 1-10GHz, and insertion loss less than 3dB. These narrow band optical filters should be compatible with standard single mode optical fiber including polarization maintaining single mode fiber. State of the art commercial off the shelf (COTS) filters utilize thermally tuned fiber Bragg grating (FBG) filter solutions, but improvement is required for faster tuning and higher spectral rejection of signals located just GHz from the passband.

Improved RF signal distribution performance enhances tactical EW, situational awareness, and electronic maneuver warfare capabilities for the Navy. The submarine EW next generation architecture is considering Radio Frequency over Fiber (RFoF) technology to improve its signal distribution architecture to transport high fidelity RF signals inboard and distribute them to the appropriate receivers. The benefits of intensity modulated direct detection (IMDD) RFoF links are well documented, as are their deficiencies. However, there have been substantial improvements in areas traditionally detrimental to the proliferation of RFoF technology in the EW/Intelligence, Surveillance, and Reconnaissance (ISR)/Signals Intelligence (SIGINT) applications. Recent improvements in size, weight, and power (SWaP), manufacturability, and RF performance (Noise Figure, Gain, and Spur-free Dynamic Range) is beginning to better align RFoF technology with these mission sets.

Beyond general IMDD links, there is potential to realize performance improvement through use of optical signal distribution that may utilize optical heterodyne systems to achieve RF block down conversion or an RF tuning capability. The submarine community believes that if these systems can be enabled, they will realize significant improvements in situational awareness through opening the door for improved directional and tethered antennas. This topic addresses the optical filters necessary to enable such systems.

PHASE I: Develop a concept to fabricate an ultra-narrow tunable optical band pass filters prototype. Include modeling, analysis, and experimental laboratory verification where achievable. Demonstrate concept feasibility through modeling, experiment, or other means of an optical filter capable of meeting the requirements outlined in the description of the topic.� Key technological aspects should be demonstrated theoretically and include simulations and experimental evidence where applicable. The Phase I option, if awarded, would include the initial layout and process development necessary to fabricate prototypes in Phase II. Develop a Phase II plan.

PHASE II: Based on the results of the Phase I effort and the Phase II Statement of Work (SOW), fabricate and deliver a prototype consisting of fiber coupled, packaged optical filters in a form factor consistent with commercial technology in an effort to demonstrate performance metrics outlined in the topic description. Refine the fabrication process and filter design with a focus on creating a consistent product towards aiding transition in Phase III. The company will prepare a Phase III development plan to transition the technology for Navy and potential commercial use.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the optical filters to a larger optical RF signal distribution system for eventual insertion into the AN/BLQ-10B (V) program of record through PMS 435 Submarine Electromagnetic Systems Program Office.

Optical band-pass filters are used to isolate signals falling within a defined spectral range from a broader spectrum signal. Tunable band pass filters are used for dynamically selecting this spectral range allowing for channelization of the spectrum. This technology is applicable toward RF Photonic signal distribution systems associated with 5G cellular technologies.� Next generation cellular architectures are investigating RF photonic solutions for long-haul signal transport.

REFERENCES:

1. Sadot, D. and Boimovich, E. �Tunable Optical Filters for dense WDM networks.� IEEE Comm. Mag. Vol.36 Issue12, pp 50-55 1998. http://ieeexplore.ieee.org/document/735877/?reload=true

2. Poulin, M., Painchaud, Y., Ayotte, S., Latrasse, C. Broucu, G., Pelletier, F., Morin, M., Guy, M. and Cliche, J-F. �Ultra-narrowband fiber Bragg gratings for laser linewidth reduction and RF filtering.� Proc. SPIE 7579, Laser Resonators and Beam Control XII, 75791C, February 17, 2010. http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=781672

KEYWORDS: Optical Filter; Tunable Filter; Band Pass Filter; Optical Heterodyne; Fiber Bragg Grating Filter; Optical RF Down Conversion