In this Letter, we report a tailored 532/1064-nm demultiplexer based on a multimode interference (MMI) coupler with an efficiency of 100%. The device structure is designed according to the self-imaging principle, and the propagation and the wavelength division performance are simulated by the beam propagation method. The demultiplexer is fabricated in a y-cut LiNbO3 crystal by femtosecond laser direct writing (FLDW) combined with the ion implantation technique. The end-face coupling system is used to measure the near field intensity distribution, and the spectra collected from the output ports are obtained by spectrometers. The simulated and the experimental results indicate that the customized demultiplexer in the LiNbO3 crystal presents excellent wavelength division performance operating at 532 nm and 1064 nm. This work demonstrates the application potential of FLDW technology for developing miniaturized photonic components and provides a new strategy for fabricating high-efficiency integrated wavelength division devices on an optical monocrystalline platform.

Wavelength division multiplexing is a widely used monolithic device with modulating light sources at different wavelengths based on a designed configuration. In this paper, we report an in-chip demultiplexer with a simple design operating at 532/1064 nm in pure YAG crystal. The device is fabricated by femtosecond laser direct writing inside the transparent substrate with just a width of 36 µm. The compact structure is designed based on the principle of self-imaging, and the propagation features have been simulated by utilizing the beam propagation method. The performance of this wavelength demultiplexer has been investigated through an end-face coupling system, which proves the device can separate 532 nm and 1064 nm light into two discrete waveguides polarization-insensitively with an extinction ratio as high as 13 dB. These superior performances manifest this exquisite device can emerge into kinds of photonic applications in the future. Also, this work further proves that femtosecond laser direct writing technology has irreplaceable advantages in processing micro-nano devices in transparent materials for in-chip integration.