Fiber Optic Intrusion Detection System

The two Key words are Time of Flight and Rayleigh Backscattering,

i. Backscattering is the return light from minute imperfections in the fibre, as physical changes such as temperature, strain and vibration act of the fibre the spectrum of this return light is altered. Rayleigh Backscattering is the part of this spectrum that responds to vibration which allows vibration in the field to be taken out of the return light.

ii. Time of Flight is like a sonar, laser or radar, in that the time the pulse is traveling relates to a distance, in Fibre optic sensing this is a not just taken at the reflection point but for every bit of the fibre the pulse travels though.

No, it can be undetected underground around the border as well.

Time of flight. Locations of intrusions are able to be accurately determined by a method called time of flight. The amount of time from sending the

laser pulse to receiving a return signal is recorded. Due to the internal properties of a fibre optic core, the speed of light through a fibre is consistent at approximately two thirds of the speed of light through a vacuum (around 400μs for a 40km round trip). As this is consistent, the return time can be used to calculate a distance on the fibre.

Detection of vibration is Praetorian’s primary sensing method and uses on the amount of vibration energy created by a disturbance to the perimeter (fences, walls, Covert underground fibre etc) at the disturbance’s location.

In Praetorian, an optical effect called Rayleigh backscatter is used to observe vibrational effects on a fibre. In a fibre optic core, backscatter is the light that reflects off natural imperfections and polarizations within the fibre and returns to the light source. The return light gets diffracted into different frequencies similar to light moving through a prism and Rayleigh backscatter is one of these diffracted frequencies. The amount of compression that vibration from an intrusion causes on the core determines the strength of the Rayleigh component of the backscatter. In this way the intensity and frequency of the vibration is measurable by recording the behaviors of the Rayleigh backscatter component. This change in intensity and frequency is used to determine the presence and position of an intruder to within on meter.

To being classified as an alarm the amount of time, the dominant frequencies and the relative intensity all need to be present within pre-determined thresholds. This reduces the amount of false signals that make it to alarm state.

Praetorian has a number of unique features which make it a market leading technology. Unlike other fibre sensing technologies the field programmable gate array allows for ultra fast parallel processing of the returned signals. Praetorian does not have to time splice or “skip” sections of time to keep up, potentially allowing a chance for an intruder to go unnoticed.

One distinct advantage with the Praetorian system is that it is able to work such that it is immune to the effects of a broken or cut fibre. The unit is able to be attached as a loop to both channels on independent fibres and in the event of a cut will report the damage but continue to monitor the fibre on both sides up to the cut.

In all distributed acoustic fibre sensors, the detected signal level has certain variations depending on the polarization state of the received signal which produces scattering of the signal. This scattering can be constructive interference or deconstructive interference and to date there has been no method to control this scattering which is commonly referred to as signal fading. HAWK has patented an effective solution to overcome signal fading where small signals can be detected without fading.

Yes, we encourage it in fact! We have specially made systems that are shipped all over the world specifically for technology trials.