The Fabrication And Structural Analysis Of Photonic Lattice In Photorefractive Crystals

Photonic crystal is a kind of artificial structure with periodic dielectric coefficient in space, and its biggest feature is that it contains photonic band gap. Photonic band gap offers a new idea for people to control photons, thus it has gained extensive attention for several years. The existence of photonic band gap makes light with some certain wavelengths unable to propagate in the photonic crystal, which can be used for the inhibition of spontaneous radiation effect. It also suggests that Bragg diffraction has occurred at some certain angles, which can be used to test the structure of photonic crystal and to fabricate wavelength division demultiplexers based on photonic crystal diffraction grating.The shortcomings of traditional fabrication (like precise processing method, inverse opal method, electron-beam lithography etc.) of photonic crystals include device complexity, process difficulties, high costs, low efficiency, etc. As a new way of manufacturing photonic crystals, optical induction method utilizes photorefractive effect to change the spatial distribution of the materials’refractive indices, which then induces the periodic distribution of the materials’refractive indices. Optical induction method has the advantages as simplicity, high efficiency and low costs. The study of the structure of photonic crystal is another focus of attention. Some research on one-dimensional photonic microstructure fabricated by optical induction method has been carried out previously, Patrick Rose and others discussed the structure of one-dimensional photonic lattices in detail by the experiments of Bragg diffraction. By contrast, the structure of two-dimensional photonic lattices is more complicated, which changes the propagation of light within. Therefore, the research and discussion on the structure features of two-dimensional photonic lattices is a very meaningful subject.This paper adopts a method to fabricate two-dimensional photonic lattices with a large area in photorefractive materials using optical induction method. The key of this method is the application of a triangle wedge-shaped prism, which is used to implement multiple beam interference. This method requires simple devices instead of aseismatic equipment or complicated optical adjustion system; besides, it’s not only available for photorefractive materials but also available for other light-sensitive materials. Based on this, we continue to analyze the band gap distribution of two-dimensional photonic lattices and measure its lattice constant by the experiments of Bragg diffraction, which quantitatively studies the structure features of two-dimensional photonic lattice in a simple and reliable way. Finally, infrared and ultraviolet spectrometers are applied for spectral analyses of two-dimensional photonic lattice, which help us to understand its concrete frequency band gap distribution in another way.The innovations of this paper include:(1) two-dimensional photonic lattices with a large area are fabricated successfully in LiNbO3:Fe crystal using a triangle wedge-shaped prism; (2) the spatial band gap structure of two-dimensional photonic lattices is systematically analyzed via the experiments of Bragg diffraction; (3) the frequency band gap structure of two-dimensional photonic lattices with a large area is particularly studied via the infrared and ultraviolet spectral tests combined with theoretical simulations.