Ultra-low loss electro-optical polymer modulator based on D-shaped few-mode fiber using improved M-Z structure

•The LP01 and LP02 mode in the FMF form the two optical paths of MZI.•Its simple cascade and axial alignment design enhances the stability of modulators.•Using improved M-Z structure, the modulator achieves insertion loss of less than 2 dB.•The length of modulator is only 25.69 mm. An electro-optical polymer optical fiber modulator based on D-shaped few-mode fiber is proposed and optimized. In the D-shaped few-mode fiber, the electro-optic polymer coated on the few-mode fiber influences the refractive index of LP01 mode and LP02 mode, while LP01 mode is more sensitive. According to that, the mode field distribution has been analyzed and the varying properties of D-shaped FMF covered with electro-optic polymer has been discussed. Its simple cascade and axial alignment design enhances the stability of all-fiber modulators. Using improved M-Z structure with advanced operating point, the electro-optic modulator achieves an insertion loss of less than 2 dB with a modulation depth of 22 dB at 1550 nm. And the length of modulator is 25.69 mm. Moreover, the Vpi is 2.7 V and the optical bandwidth is 6.9 nm, which make the modulator have low power consumption and can be used in next-generation all-optical communication networks.