Rugged, Sensitive Optical Fiber sensors for military sonars and monitoring military assets and earthquakes

The fiber optic sensors also called as optical fiber sensors use optical fiber or sensing element.  These Sensors can measure a large variety of parameters, such as temperature, pressure, strain, refractive index, vibrations, displacements, bending, loading, and liquid level or concentration of chemical species. Fiber optic sensors have become a focus in the field of sensing technologies by right of their many advantages such as compact, light-weighted, high sensitivity, high multiplexing, anti-electromagnetic interference and easy to be embedded into material. Following the development of optical fiber communication industry, the optical fiber sensing technologies become another major industry of optoelectronic technologies

Fiber-optic sensor  consists of optical source (Light Emitting Diode, LASER, and Laser diode), optical fiber, sensing element, optical detector and end-processing devices (optical-spectrum analyzer, oscilloscope). The optical fiber consists of the core and the cladding, which have different refractive indexes. The light beam travels through the core by repeatedly bouncing off the wall of the cladding. The light beam, having passed through the fiber without any loss in light quantity, is dispersed at an angle of approximately 60° and emitted to the target.

Fundamentally, fibre-optic sensors make use of optical fibre as an essential element to transfer and amplify the quantity to be measured. An optical-fibre cable receives light beam as input, which is nothing but the quantity to be measured, as sensed by input of the sensor. Input for the cable is provided by a broadband light source such as LED, or narrow-band light source such as laser diode.

 

The fiber laser acts as the optical light source within a sensing element, and can achieve high signal-to-noise ratio, high sensitivity, long distance sensing, and multi-parameter sensing. The wavelength shift can be calculated using a device, optical frequency-domain reflectrometry. The time-delay of the fiber optic sensors can be decided using a device such as an optical time-domain Reflectometer.

 

Fiber optic sensors are supreme for insensitive conditions, including noise, high vibration, extreme heat, wet and unstable environments.  The optical fiber sensors have advantages like  immunity to electromagnetic interference, lightweight, small size, high sensitivity, large bandwidth, and ease in implementing multiplexed or distributed sensors. The fiber optic sensor  allow for detection in tight spaces or where a small profile is beneficial. They are resistant to high temperature and explosive environment. No possibility of spark, so are safe to be used in hazardous sensing environments, such as oil refineries, grain bins, mining operations, pharmaceutical manufacturing and chemical processing

 

Over the past decade, optical fiber sensors have gained widespread acceptance within the oil and gas industry due to their reliability, flexibility and low operating costs, as well as the benefits brought by their multipoint and distributed sensing capabilities. More recently, extensive interest has been shown in the development and commercialization of fiber optic seismic and acoustic sensing arrays – land and underwater – for oil and gas exploration, pipeline surveillance, geophysical monitoring, reservoir monitoring and management, geothermal monitoring, and structural monitoring of offshore platforms and oil tankers.  Distributed acoustic sensing (DAS) enables detection, discrimination and location of acoustic events on an optical fiber over tens of kilometers.

 

Hydrophones are used for seismic and sonar applications. Hydrophones with more than 100 sensors per fibre cable have been developed. Hydrophone sensor systems are used by oil industries and in the navies of some countries.

 

Fiber-optic gyroscopes and fiber-optic current sensors are good examples of rather mature and commercialized optical fiber sensor technologies. Fiber optic gyroscopes (FOGs) are critical tools in many different platforms; aircrafts, missiles, unmanned aerial vehicles (UAVs), and ground vehicles all require advanced optical fiber navigation technology to ensure reliability and safety.