On-demand flat-top wideband OAM mode converter based on a cladding-etched helical fiber grating.

A new method enabling to provide an on-demand flat-top wideband orbital angular momentum (OAM) mode converter is proposed and experimentally demonstrated, which is based on utilization of a cladding-etched helical long-period fiber grating (CEHLPG). By appropriately selecting the grating period and precisely controlling the diameter of the CEHLPG in-situ, both the radial order and central wavelength of the flat-top band for the generated OAM mode can be flexibly tailored according to specific requirements. As typical examples, the first azimuthal order OAM modes with a flat-top bandwidth of 95 nm at -20 dB, a central operating wavelength of ∼1500 nm, and the radial-orders of 9, 8, 5, and 2, respectively, have been demonstrated consecutively. The proposed method provides an excellent flexibility and robustness in controlling both the radial order and the central wavelength of the resulting flat-top wideband OAM mode conversion, which may support a variety of practical optical vortex applications.

Ultra-broad edge filter based on a periodically twisted graded-index fiber and its application to a power-interrogated temperature sensor.

A novel and reliable method enabling to produce an ultra-broad edge-filter (UBEF) is firstly proposed and demonstrated both theoretically and experimentally, which is realized by using a periodically-twisted graded-index few-mode fiber (GI-FMF). By using the proposed method, an UBEF with a dynamic wavelength-range up to ∼380 nm is numerically obtained. Furthermore, an UBEF with a linear dynamic range larger than ∼300 nm in wavelength and ∼12.7 dB in power was successfully demonstrated in experiment, which represent the highest performances among all those achieved from the fiber-based optical edge-filters (OEFs) reported to date. The proposed UBEF can be used as an ultra-broadband power interrogation component to well demodulate the wavelength-dependent signal, meanwhile it can be used as a highly-sensitive power-interrogated sensor as well. As typical application example of the proposed UBEF, a power-interrogated temperature sensor has been successfully demonstrated. The temperature responsivities with respect to the power change and the spectral shift are 0.0179 dB/°C and ∼0.49 nm/°C, respectively. The UBEF-based power-interrogated sensing system has the advantages of fast response, low cost, small size and high reliability.