Wavelength-Tunable, Ultra-Broadband, Biconical, Long-Period Fiber Grating Mode Converter Based on the Dual-Resonance Effect

Abstract

We demonstrated a wavelength-tunable, ultra-wideband, biconical, long-period fiber grating (BLPFG) mode converter in a two-mode fiber based on fusion taper technology and CO2 laser writing technology. Theoretical and experimental results show that after changing the diameter of the two-mode fiber by fusing and tapering, the dispersion turning point of the fiber is adjusted and wavelength-tunable broadband mode conversion is achieved efficiently. Theoretical simulation shows that the mode conversion bandwidth can cover the O + E + S + C band. In the experiment, we fabricated adiabatic tapers with cladding diameters of 113 μm and 121 μm and wrote gratings on these tapers to achieve dual-resonance coupling, thus realizing mode conversion from LP01 to LP11, with a 15 dB bandwidth of 148.8 nm from 1229.0 nm to 1377.8 nm and of 168.5 nm from 1319.7 nm to 1488.2 nm, respectively. As far as we know, this is the first time that fusion taper technology has been used to adjust the window of the dual-resonant coupling of an optical fiber. This work broadens the scope of application of the dual-resonance effect and proposes a general method for widening the bandwidth of a fiber grating with tunable wavelength.

Design of a Broadband Integrated Mode Converter Based on Non-Uniform Binary Long-Period Grating by Direct Multiparameter Optimization

“…purposes, depending on the coupling type [1,2]. In particular, LPGs can be used as mode converters [3][4][5][6][7][8][9][10][11][12][13][14] when coupling occurs between different copropagating core modes. Due to the resonant nature of the couplings, LPGs typically have a narrow spectral bandwidth, which is an important limitation in many practical applications.…”

“…Due to the resonant nature of the couplings, LPGs typically have a narrow spectral bandwidth, which is an important limitation in many practical applications. To overcome this problem, several methods for broadening and shaping the spectral characteristics of LPGs have been proposed, including chirping the grating period [4,15,16], shifting the phase of different grating sections [5,6,17], fabricating multisection phase-shifted gratings with proper period variation within each section [6,18], apodized phase-shifted gratings [19], and exploiting a dual resonance coupling effect [7,8,20]. Using such solutions, a significant broadening of the spectral bandwidth of LPG-based devices has already been experimentally and theoretically demonstrated.…”

“…Using such solutions, a significant broadening of the spectral bandwidth of LPG-based devices has already been experimentally and theoretically demonstrated. For example, in the optical fiber LPGs, the following conversion bandwidth was obtained between LP01 and LP11 modes: 105 nm for -10 dB crosstalk (CT) level for phase-shifted LPGs [5], 145 nm (-13 dB CT) for phase-shifted chirped LPG composed of 4 segments [4], 182 nm (-10 dB CT) for cascaded lengthapodized phase shifted LPGs [6], 130 nm (-15 dB CT) for tapered dual-resonance LPG [7], and 118 nm (-15 dB CT) for dual-resonance LPG [8].…”

Experimental Dataset of Tunable Mode Converter Based on Long-Period Fiber Gratings Written in Few-Mode Fiber: Impacts of Thermal, Wavelength, and Polarization Variations

“…Furthermore, they provided evidence that the OAM vortex phase of the produced modes remained unchanged as the temperature rose from 23 °C to 50 °C. In 2021, Zheng et al demonstrated a wavelength-tunable mode converter based on an LPFG [30]. To do this, they first created adiabatic tapers with cladding diameters of 113 µm and 121 µm, then the LPFGs were written in the optical fiber taper in such a way that modal conversion between LP 01 and LP 11 modes was generated.…”