Photonic sensor opportunities for distributed and wireless systems in security applications

A broad range of homeland security sensing applications can benefit from using distributed fiber-optic sensors and photonics integrated wireless systems.¹ These applications include the protection of ‘smart structures’ such as bridges, tunnels, and dams, power line and pipeline monitoring, chemical/biological detection, and wide-area surveillance, which encompasses perimeter, border, and port security (cargo containers). Many vital assets that span wide geographic areas, such as pipelines and borders, are under constant threat of being attacked or breached. Basic civilian infrastructure such as water supply, power utilities, communications, and transportation systems is also under similar threat. Hence the urgency in developing a coordinated and integrated solution for threat detection.

In this context, fiber-optic sensor technology can address a broad range of needs provided that it be made compatible with other surveillance technologies to facilitate integration. In addition, the multifunctionality of these sensors must be expanded to include biochemical detection.

To date, a number of barriers have hindered their acceptance and widespread use. Compared with telecommunications, their usage volume is low. Proprietary and custom specifications have also kept their price high. Additionally, the technology suffers from a general lack of manufacturing infrastructure and poor packaging and reliability standards. Finally, several other technologies, either photonics-based or more conventional, remain strong competitors.

It is estimated that the market potential for distributed fiber- optic sensing systems (not including installation) could exceed $500 million by 2010. However, these markets are in the early development stage, and hence fragmented and difficult to forecast accurately. Key drivers identified by available market analysis include pipeline monitoring and security, wide-area surveillance for perimeters and borders, and smart structures. While most fiber-optic sensor technologies are currently used to detect strain, temperature, or vibration, the addition of a photonic biochemical sensing capacity coupled to wireless architectures would greatly expand the marketplace.

Cargo container security provides a good example. At this time, major ports cannot monitor all transit cargo containers due to prohibitive costs. Point inspections, as used, for example, in Container Security Initiative (CSI) ports such as Hong Kong, do not provide high-level security since containers are moved to other destinations. If we consider that less than 5% of the cargo containers entering the United States are effectively monitored, we understand that port security is in dire need of improvement. Continuous monitoring with embedded integrated sensing systems could provide a much higher level of security. Assuming that a cost-effective approach could be implemented, the market potential for both shipboard and truck cargo container security could exceed $1.4 billion in 2010.

As for expanding the technology to include biochemical sensing and wireless architectures, fiber-optic distributed sensors such as interferometric, Bragg grating, and evanescent wave sensors can all support biochemical detection. Intrinsic biophotonic sensors are also promising candidates. In these devices, the modulation of light by an embedded biomolecular element provides the sensing function. The sensor has a recognition layer consisting of chemical or biological receptors that react with the target analyte, modifying fluorescence, scattering, or absorption properties. Biophotonic sensors can detect bacteria, spores, viruses, and toxins and have the potential to be developed for the simultaneous monitoring of multiple target analytes. Additionally, they are insensitive to dirty environments, which allows them to function with low false alarm rates.

Motes represent an emerging wireless technology of high interest to the Department of Defense. They were originally developed as tiny, self-contained, battery-powered computers with radio links, capable of communicating and exchanging data with one another, and of self-organizing into ad hoc networks. In telecommunications, motes form the building blocks of cost-effective wireless sensor networks.³ They are sometimes referred to as ‘smart dust’ because their size is relatively small. Each sensor node in the network (star or mesh) consists of a low-power transceiver, sensor, sensor processor, power source, antenna, and GPS device.

Mote technology has many advantages in wide-area surveillance applications.⁴ It is easy to install and can be integrated with a wide variety of sensor technologies, including photonics. It also has a high cost-effectiveness potential. However, the technology is still in a relatively early development stage, and issues of reliability, ultra-low-power operation for long lifetime, integration of multifunctional sensors, and cost remain to be addressed.

It is nevertheless anticipated that photonic sensor capability will evolve to multifunctional sensing applicable to biochemical detection. The use of wireless and distributed fiber solutions is also expected to become application-specific and integrated. At first, most sensor applications will be designed for alarm systems (and not for quantitative analysis). The homeland security market has the potential of reaching $1.9 billion in 2010, but many barriers must be overcome, such as standards and the design of full engineering solutions. Cost will also be a factor in the widespread application of this technology. The goal of the OIDA Fiber Optic (Photonic) Sensor Consortium is to address these challenges and contribute to the development of a robust sensor marketplace.