Two 2nd order PQ:PMMA reflecting VBGs with Bragg wavelengths of 488.8 nm and 525.6 nm were recorded using 532 nm as the recording wavelength. The formation of 2nd order PQ:PMMA VBG is explained and simulated based on the diffusion model of the PQ molecules in the PMMA matrix. The 525.6 nm VBG successfully served as the ECDL cavity mirror of a 522 nm diode laser and achieved more than 10000-fold output spectrum narrowing.