24 October 2013
I work in the area of optical signal processing in which the signal is processed in the optical domain such that the processing speed is very fast and the processing bandwidth is broad. The electronic bottleneck can thus be avoided by utilising all-optical signal processing. I am also working on fibre optical sensing, which utilises optical fibre as the sensor head. Optical fibre sensors are superior due to their high sensitivity, improved compactness, advanced reliability, unique capability for distributed sensing and so on.
We have demonstrated an advanced method for obtaining ultra-highly sensitive strain sensing. We utilised all-optical signal processing technology based on an optical nonlinear process in a highly nonlinear fibre to realise all-optical frequency chirp magnification such that the strain induced resonant-wavelength drifting can be magnified. The all-optical signal processing is simply an optical magnifier and thus a very small amount of strain can be observed without processing the sensor head.
This method is a post-processing method and it does not require pre-processing of the sensor head for obtaining a high sensitivity, which is totally different to the conventional solutions. Up to now, this is the only post-processing method for enhancing the sensitivity of a fibre Bragg grating (FBG) strain sensor. The post-processing only deals with the optical sensing signal and thus it can be applied to a wide range of optical sensors to enhance the sensitivity. The enhancement is significant because the sensitivity increases along with the four wave mixing (FWM) idler order.
Optical fibre sensors’ superior performance of sensitivity is one of its key advantages. Higher sensitivity is always a highly desired quality for a fibre sensor. Ultra-high sensitivity is desired for some particular applications like crustal deformation detection, in which strain sensitivity at the scale of 10-9 unit-strain is needed. By utilising our proposed method, the difficulty for obtaining high strain sensitivity for applications like crustal deformation detection can be reduced.
In the next steps we need to improve the post-processing efficiency, namely the FWM efficiency, so that higher order FWM idlers can be obtained and higher sensitivity measurement can be realised. Also, we need to extend this method to other sensors to investigate the effectiveness of the sensitivity enhancement.
The realisation of FWM is costly at this stage and the FWM efficiency needs to be improved. Those are the biggest challenges for bringing this method into wide-spread real-world use. On the other hand, I think it is also at an acceptable level to be implemented in a real-world system for some particular applications at this stage.
Our proposed method applies all-optical signal processing technology to FBG sensing for obtaining high sensitivity strain measurement. The idea of using all-optical signal processing to enhance the sensitivity of an optical fibre sensor can be extended to other sensors, which should be useful to pioneers in this field. In the next few years, I think there will be some quite high sensitivity optical fibre sensors developed based all-optical post processing. Issues like efficiency, cost and system stability will be addressed in follow-up works in this field. And along with the reduction of the cost and the improvement of the post-processing efficiency, real-world applications can be realised in some particular scenarios. I hope we can push the record performance in sensitivity to a higher level based on the all-optical post-processing method in this field.
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