A micro-structured optical waveguides was fabricated in a single-crystal by femtosecond laser inscribing and acid etching, which can realize midinfrared waveguiding with a low loss 28. Based on laser-induced structural changes, many photonic crystal structures can be fabricated in transparent dielectrics such as glass, sapphire, and Lithium niobite 25, 26, 27. After laser processing, post-treatment like chemical etching 23 and annealing 24 can help to form hollow structures in laser-affected areas. Ultralow-loss geometric phase optical elements like prism, lens, and vector beam convertors can be fabricated through a new type of laser modification inside silica glass 22. Femtosecond laser can induce physical and chemical changes in focus region due to well confinement of energy, which originated from the ultrafast properties 19, 20, 21. Recently, femtosecond laser is employed to fabricate photonic crystals because of its processing ability for micro-nanostructures 16, 17, especially three-dimensional fabrication in transparent materials 18. The ultrashort pulse duration also makes ultrafast laser lithography a non-thermal processing method, which can be used in many applications like aerospace, energy 14, and optoelectronics 15. Due to the ultrahigh intensity, ultrafast laser can overcome bandgap of crystals and realize direct micromachining 13. It is known that ultrafast laser is a versatile tool used for marking, cutting, patterning, and structuring. Laser lithography is one of potential techniques for 3D structure fabrication in crystals. Different from the 1D and 2D cases, the fabrication of 3D structure is rather difficult because the refractive index should be varied at three spatial directions 11, 12. Photonic crystal structures in these optical devices are characterized as one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) according to lattice arrangements. Due to unique optical properties of photonic crystals, photonics devices can be constructed including light emitting devices, optical receivers, switchers, modulators, and resonators 8, 9, 10. Due to the periodical arrangement of different refractive index structures, photonic crystals behave a considerable manipulation ability for light and photonics since its discovery 6, 7. The uniform dielectric “atoms” can be air-filled holes, channels, dielectric rods, and other structures which have different refractive index with original materials. Photonic crystals are a kind of structure consisting of a periodic array of uniform dielectric “atoms”. As one of basic components of integrated photonics, photonic crystals play an important part in the transmission and regulation of light 3, 4, 5. Manipulation of light propagation is an interesting field in optics and optoelectronics 1, 2. This approach can efficiently manufacture nanostructures with controllable gap, and offer an alternative to the fabrication of complex photonic crystal for integrated photonics applications. Optical gratings of different periods are fabricated, which can diffract incident light in particular ways. With the superimposed phase hologram designing, functional structures of complicated channel arrays distribution can be created in crystal. ![]() Combining optical simulation based on Debye diffraction, we experimentally show the gap width of parallel channels can be controlled at nanoscale by changing phase holograms. ![]() Using multi-beam ultrafast laser processing and etching, parallel channels with subwavelength gap are obtained in yttrium aluminum garnet crystal. ![]() Herein, we propose a novel multi beam lithography method to fabricate photonic crystal with nanoscale structure without cracking. Photonic crystal with nanoscale structure is important for the manipulation of light propagation in visible and near-infrared range. ![]() Photonic crystals are utilized in many noteworthy applications like optical communications, light flow control, and quantum optics.
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