The formation of submicrometer voids within Ce(DBM)3Phen doped poly(methyl methacrylate)(PMMA) was reported under multiphoton absorption excited by an infrared laser beam. The absorption spectra, photoluminescence and electron spin resonance (ESR) spectra before and after femtosecond laser irradiation were discussed. An ultrashort-pulsed laser beam with a pulse width of 200 femtosecond at a wavelength of 800 nm was focused into doped PMMA. The large changes in refractive index and the fluorescence associated with a void allowed conventional optical microscopy and reflection-type confocal microscopy to be used as detection methods. Voids could be arranged in a three-dimensional multilayered structure for high-density optical data storage. The separation of adjacent bits and layers were 4 and 16 μm, respectively.