Measurement Of Micro Nano Fiber Diameter And Application Of Micro Nano Fiber In Entangled Photon Source

Because of its excellent optical and mechanical properties,optical fiber has always been a very important optical structure in optical applications.In recent years,micro nano optical fiber has been prepared by means of fused taper,electrospun,polymer solution drawing and so on,which provides an excellent platform for modern optical applications in the current trend of integration.Due to its high refractive index and air cladding,micro nano fiber has the advantages of low optical loss,strong light field binding,high evanescent field occupation ratio,good toughness,strong mechanical properties and so on.It has many applications in the field of modern optics,such as biosensing,integrated interconnection(optical coupling),nonlinear frequency conversion,optical fiber coupled quantum light source and cold atom capture.In order to realize the application of micro nano fiber in these fields,such as the generation of second harmonics with phase matching,it requires the precise engineering of the size and continuity of the micro nano fiber diameter.Under such circumstances,the measurement of the diameter of micro/nano fiber is particularly important.At present,the measurement methods of micro nano fiber diameter mainly include optical measurement and SEM electron scanning microscope measurement,in which the optical measurement methods include whispering gallery modes measurement,inter-modal beating measurement and photonic crystal cavity measurement.SEM and other electron microscopy methods have high accuracy and good visibility,but these methods are destructive measurements and are not real time measurements.The fiber cannot be used after the measurement,therefore the electron microscopy is not applicable in many practical cases.Compared with other measurement methods,optical measurement can achieve real-time non-destructive measurement,and the fiber can still be used after the measurement.Whispering gallery modes measurement is based on the whispering gallery modes in optical fiber to calculate the perimeter of optical fiber.Although this method relies on WGM resonance with high Q value,it can only be applied to tens of micron scale optical fiber,and it is invalid for micro nano fiber with smaller diameter.Inter mode beat frequency measurement uses transmission light power and inter-mode interference to deduce fiber diameter.This method requires complex data processing and is easily affected by uneven optical fiber surface.The measurement method of photonic crystal can achieve real-time nondestructive measurement at the same time with high precision,but this method needs to rely on expensive nano manufacturing technology,which makes the economy and repeatability of the method lower,so it is difficult to popularize.In this paper,a nondistructive micro nano fiber diameter measurement method based on the high order Prague reflection is introduced.This method uses the blazed grating to contact the micro nano fiber to form the Prague reflection grating.This method is economical,efficient and repeatable,and its measurement range ranges from 600nm to lum with accuracy of about 15nm.On the other hand,quantum optics has attracted much attention this year.The demand of highly efficient entangled photon sources is a problem facing the development of quantum optics.The entangled photon source based on spontaneous parametric down conversion is an effective way.Driven by the development of integrated optics,how to design and manufacture entangled photon sources based on waveguide structure has become an important research direction.As a low loss waveguide structure,micro/nano fiber can be used as an entangled photon source to achieve efficient convergence between photon source and other optical fiber systems.Lithium niobate is a negative uniaxial crystal.It has three rotational pairs relative to the crystal Z axis.It belongs to the three square crystal system and has excellent nonlinear optical properties.It is a important material in nonlinear optics.Using the principle of pattern hybrids,a micro efficient SPDC prediction entangled photon source is prepared by combining PE(Proton-Exchange)with lithium niobate nanoscale waveguide and micro nano silica fiber.In this paper,an efficient and economical method for measuring the diameter of micro nano fiber is introduced.Based on the high order Prague reflection resonance peak,a commercial flashing grating is used to measure the diameter and continuity of the micro optical fiber in real time.And hybrid microfiber-lithium niobite nanowaveguide structures is also introduced as heralded photon source.