Effects Of The Linear Birefringence In ZF-7 Glass Upon The Output Performance Of Optical Current Sensors

Linear birefringence is one of the prominent parameters limiting the practical applications of optical current sensors(OCSs).Although compared with the fiber OCSs,harmful effect of the linear birefringence upon bulk glass optical current sensors(BGOCSs) output is reduced to a great degree,it still exist and can not be eliminated thoroughly.Considering that sensing heads of most BGOCSs are made by ZF-7 glass,this dissertation analyzes the effect of the linear birefringence in ZF-7 glass upon the output performance of BGOCSs.Different formulae and simulating curves describing the relation between the linear birefringence and the output of the single loop BGOCS,of the Faraday mirror-typed return-back optical-pathed BGOCS,of the direct reflection-typed return-back optical-pathed BGOCS and of the roof-prism reflection-typed return-back optical-pathed BGOCS are derived,respectively.Furthermore,the formulae are compared with each other.The results show that,when the polarizing angle of the input light beam is 0°,45°,90°…,compared with the single loop BGOCS on hand,the return-back optical-pathed sensing plan of the Faraday mirror-typed BGOCS will rise the system sensitivity with respect to 2 times,in the premise of not increasing the effects of the linear birefringence;the return-back optical-pathed sensing plan of the reflection-typed BGOCS will increase the effects of the linear birefringence along with the rising of the system sensitivity;while for the roof-prism reflection-typed return-back optical-pathed BGOCS,the system sensitivity will depend on the linear birefringence inside the sensing head.These conclusions indicate that the return-back optical-pathed current sensing designs with conventional signal processing scheme of '+/-' can improve the system sensitivity to different degree but can not eliminate the harmful effects of the linear birefringence thoroughly,furthermore,disconfirm the thesis proposed by Laming et al that "effect of the linear birefringence could be eliminated and the Faraday effect would be double for fiber OCSs or BGOCSs by using a return-back optical-path design".Based on those facts,a novel sensing design of orthoconjugate typed OCS formed by employing the Faraday Mirror as the sensing element and abandoning the original optical glass sensing head is proposed.A formula and corresponding simulating curves describing the relation between the linear birefringence and the output of this novel design are derived.The results show that,when the polarizing angle of the input light beam is 0°,45°,90°…,output of the orthoconjugate typed OCS is affected by both the linear birefringence and the polarizing angle induced by the Faraday Mirror,both of which can affect the slope and the intercept of the characteristic curve of the system to different degree.Hopefully,these results can provide a theoretical guide to those who contribute themselves to improve the sensing head to restrain the effect of the linear birefringence upon the system.