A Photonic Nanojet Device Based On Optical Fiber

Photonic nanojet（PNJ）,a kind of optical field features narrow waist,high intensity and non-evanescent.It can travel several wavelengths with low divergence and can have a sub-wavelength transverse width.It has a rapid development since it was found.However,most photonic nanojet device is based on simulation,and the realization of photonic nanojet device have difficults in manufacturing or controlling.In this work,we combine optical fiber with PNJ,and propose two types of fiber-based PNJ generation device.On the one hand,the suspended optical fiber（SOF）itself is used to generate PNJ,which has advantages in simple structure,high stability and easy to be integrated,and on the other hand,the mode source is chosen to be the incident light,combine the diversity and controllability of the mode source,the single or dual PNJ is realized.The main work of this particle is as follows:1.First,we simulate the PNJ generated from SOF through FDTD Solutions,and investigate the influence of the outside parameter such as wavelength,waist,polarization and the off-axis incident on the generated PNJ.Then,the influence of the SOF is further simulated,we mainly focus on the influence of the insert depth,the outer radius and the inner radius on the generation of PNJ,when the fiber core is immersed in water,the influence of immerse depth is also investigated.Finally,we measure the PNJ generated from the SOF under three wavelength:980 nm,1310 nm and 1550 nm.Results show that the parameters FWHM and attenuation length is coincident with the simulation.2.Combine with the diversity of mode source in dual mode optical fiber,the sphere illuminate from different mode source is investigate.Define the axis of symmetrical of two mode pattern spot as the baseline,when the polarization direction LP₁₁ mode perpendicular to the baseline,the single PNJ with a big sidelobe is generated,and when the polarization direction LP₁₁mode parallel to the baseline,the dual-PNJ is generated.Results show that for different polarization of the mode source inspired in the fiber,the generated single or dual PNJ can be generated selectively.Last,we further investigate the influence of different parameters,such as the size,index of the sphere,and the medium of the surrounding on the generation of PNJ.