Intelligent Laser System for CBM+ of Naval Platforms

Navy SBIR 20.2 - Topic N202-131

Office of Naval Research (ONR) - Ms. Lore-Anne Ponirakis [email protected]

Opens: June 3, 2020 - Closes: July 2, 2020 (12:00 pm ET)



N202-131       TITLE: Intelligent Laser System for CBM+ of Naval Platforms


RT&L FOCUS AREA(S): Microelectronics

TECHNOLOGY AREA(S): Air Platform, Ground Sea, Materials


OBJECTIVE: Develop an intelligent laser-based system for powering, sensing, and communicating between a centralized health management unit and all the different nodes, sensors, and actuators of a platform-wide distributed fiber optic network for Condition Based Maintenance Plus (CBM+) of Naval platforms.


DESCRIPTION: For predictive maintenance of Naval platforms (ships, aircraft, submarines, UXVs), the primary degradation modes (fatigue, micro-cracking, vibration, impact damage, delaminations, heat damage, etc.) of systems aboard platforms (Hull, Structural, Mechanical, Electrical, Propulsion, Drive, etc.) need to be detected, classified and monitored as early as possible within their life cycle (incubation, nucleation, coalescence, propagation, steady growth, unstable growth) to help plan appropriate maintenance action in a safe and cost-effective manner. To accomplish this in a reliable manner, these systems need to be monitored continuously during operations and/or while at rest to the finest resolution possible (from micro to macro scales). Until now such a feat would require a large number of electrical-based sensors of different types (thermocouples, strain gauges, accelerometers, acoustic emission sensors, ultrasonic transducers, etc.) - each one with its own power and shielded cables, signal conditioning boxes in close proximity, data loggers, and signal processors. A system of this type is not practical, with too many parts, too many cables, with requirements for electromagnetic (EMI) shielding, adding significant weight to the platform, and possible requiring more maintenance (sensor recalibration, re-soldering, prone to corrosion) than avoiding it.


Fiber optic technology offers the possibility of performing all those monitoring activities simultaneously with a single optical fiber in a distributed fashion without corrosion or EMI issues and in a safe and cost-effective manner. For this purpose, different types of Bragg grating (BG)-like sensors would be engraved in a single fiber and interrogated from one end with a multi-laser-based interrogation unit. Cost-competitive approaches already exist in the market and new ones are being developed that can monitor temperature and strain at frequencies of up a 100 Hz or impact events and vibration in the 100 Hz to 10 kHz range with BG grating sensors engraved in a single optical fiber of up to a kilometer and interrogated continuously with a single or multiple laser based system. The challenge is expanding the range of applicability to reliably detect small amplitude, high frequency (10kHz - 1MHz) acoustic emission events from growing cracks, spoliation, fretting from faying surfaces or other damaging mechanisms at many points in the same fiber in a cost-effective manner. A possible solution would be to engrave a large number (around 100 or as many as technically feasible) of very sensitive sensors in an optical fiber with very narrow spectral features (less than 10 picometer spectral width) such as BG Fabry-Perot, pi-BG, or other BG-like sensors.� These sensors could then be interrogated with a small number (between 4 - 8 or the fewest possible consistent with reliability of detection) of low noise, high sensitivity (able to achieve a strain sensitivity of 100 femto-strain/sqrt(Hz) or better in the frequency range from 10 kHz � 1 MHz), tunable lasers (over an entire band or more) managed by an intelligent system (machine learning, neural network or neuromorphic processor) that is informed by all the sensors (low, mid and high frequency) in the network and that can position the tunable lasers dynamically on sensors near hot spots as they develop on the system being monitored. Neither the intelligent neural processor nor cost-effective (around $1,000/laser module or less), small footprint (4 sq. inches), low noise, high sensitivity, tunable lasers exist today. Most multichannel telecommunication lasers have poor frequency noise performance in the region of interest (10kHz - 1 MHz). Also, these lasers are only available in the C-band and L-band for long distance communications (100s of kilometers) but for CBM+ applications one typically only monitors distances of less than a few 100 meters where other bands could be used.


This topic seeks innovative approaches to develop and commercialize a cost-effective, intelligent, multi-laser based system for CBM applications. The intelligent laser based fiber optic (FO) CBM system will have high strain sensitivity to detect low amplitude, high frequency and short duration ultrasonic bursts of energy generated by growing cracks or other sources. The system should operate in one of the standard communication bands and monitor close to one hundred sensors in a long optical fiber. When designing a system, the team should be aware that the background temperature around the sensors can vary by 10�s of degrees Fahrenheit in a few minutes thereby requiring feedback control to compensate for thermal drifts. Since the number of hot spots will increase over the operational life of the component/vehicle, it is desirable that the system is designed so that it can easily expand to incorporate and manage more intelligent lasers.� Ultimately (not in this SBIR topic), the intelligent system should be able to learn and reconfigure itself not just based on the data from all the sensors in the fiber optic network, but also from the other sources of information such as platform operations, environmental conditions, maintenance actions, structural drawings, system changes and others.


PHASE I: Define and develop a concept for a cost-effective, intelligent, multi-laser based system operating in one of the standard communication bands for monitoring close to one hundred (or as many as technical feasible) fiber optic sensors in a single long optical fiber.� These sensors will have high strain sensitivity to detect low amplitude, high frequency, low duration, ultrasonic bursts of energy generated by growing defects. For validation purposes, and to help with the down selection for the Phase II effort, the team will conduct a laboratory demonstration of a bench top system. (Note: Due to the cost restrictions of a Phase I effort, the laser system will have a minimum of one benchtop, narrow band, high sensitivity (able to achieve a strain sensitivity of 100 femto-strain/sqrt(Hz) or better in the frequency range between 100 kHz-1MHz), tunable (over an entire band), low-cost laser.� The intelligent aspects of the system will also be kept to a minimum during the Phase I to maximize resources for the laser development.)� Ensure that a minimum of three fiber optic sensors (more if the budget allows) are engraved in a long optical fiber (with the sensors effectively spatially and spectrally spaced to demonstrate performance). Prove that the three sensors can detect acoustic emissions (AE) events when coupled to a 3' x 3' x 1/8" square aluminum plate (more plates and sensors are desirable if the budget allows).� Use pencil lead break tests (ASTM E976010 Standard) to simulate acoustic emissions from growing cracks. If the budget allows, perform multiple tests that demonstrate the intelligence of the system such as by showing how it can classify different sources of AE signals in real-time or by showing how it can preposition the laser or lasers among the sensors based on knowledge gained from previous measurements. The system that demonstrates the best performance and the capability to cost effectively expand further will be selected for Phase II.


PHASE II: Produce an integrated, ruggedized, cost-effective, intelligent, multi-laser based system prototype operating in one of the standard communication bands for monitoring close to one hundred (or as many as technically feasible) fiber optic sensors along a single long fiber to detect low amplitude, high frequency, low duration, ultrasonic burst of energy generated by growing defects. The final prototype will include a minimum of 8 tunable lasers.� For validation purposes, a long optical fiber with a minimum of 24 fiber optic AE sensors will be attached to the perimeters of a minimum of three 3' x 3' x 1/8" square aluminum plates (more plates and sensors are desirable if the budget allows).� If the budget allows it is desirable that other fiber optic sensors are engraved in the same optical fiber that simultaneously monitor parameter such for temperature, strain, vibration or others. The team will perform multiple experiments to demonstrate the sensitivity, adaptability and intelligent characteristics of the system.


PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for fleet use through test and validation to qualify and certify the system. Further refine the prototype for production and determine its effectiveness in an operationally relevant environment. A system of this nature could have a large number of commercial applications such as for structural health monitoring of civil aviation aircraft, oil tankers, bridges, and oil and gas pipelines for both integrity and security-related needs.



1. Zhang, Qi, et al. "Acoustic emission sensor system using a chirped fiber-Bragg-grating Fabry�Perot interferometer and smart feedback control." Optics letters, Vol. 42, Issue 3, 2017, pp. 631-634.


2. Rosenthal, Amir, Daniel Razansky, and Ntziachristos, Vasilis. "High-sensitivity compact ultrasonic detector based on a pi-phase-shifted fiber Bragg grating." Optics letters, Vol. 36, Issue10, 2011, pp. 1833-1835.


3. Hu, Lingling and Han, Ming. "Reduction of laser frequency noise and intensity noise in phase-shifted fiber Bragg grating acoustic-emission sensor system." IEEE Sensors Journal, Vol. 17, Issue15, 2017, pp. 4820-4825.


KEYWORDS: Condition Based Management Plus, Continuous Based Monitoring, Artificial Intelligence, Neuromorphic Processing, Structural Health Monitoring, Optical Fibers, Bragg Gratings, Acoustic Emission, Ultrasound Generation, Sensors and Actuators, Crack Detection



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